JP6028530B2 - Optical receiver - Google Patents

Optical receiver Download PDF

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JP6028530B2
JP6028530B2 JP2012246669A JP2012246669A JP6028530B2 JP 6028530 B2 JP6028530 B2 JP 6028530B2 JP 2012246669 A JP2012246669 A JP 2012246669A JP 2012246669 A JP2012246669 A JP 2012246669A JP 6028530 B2 JP6028530 B2 JP 6028530B2
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light
polarization
diffraction grating
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polarized light
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JP2013128272A (en
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大井　好晴
好晴 大井
浩司 宮坂
浩司 宮坂
村川　真弘
真弘 村川
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AGC Inc
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  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
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Description

本発明は、光受信装置に関する。   The present invention relates to an optical receiver.

光ファイバーを用いた大容量・長距離伝送を実現する波長多重光通信装置などの基幹部品として光送受信モジュールが用いられる。近年、通信トラフィックの増加に伴い、高速・大容量伝送化に有効なデジタルコヒーレント光伝送技術が注目されている。この技術は、伝送情報容量を増加させるため、伝送光の強度変調信号に位相変調信号を付加して送受信する光伝送方式である。このような位相変調方式による通信方法では、光の位相検出が必要となるため、光伝送後に受信した信号光と周波数の等しい別途用意された局部発振光源の参照光とを干渉させ、このビート信号から信号光の強度変調情報と位相変調情報を検知するホモダイン検出法が用いられる。デジタルコヒーレント光受信装置では、位相ダイバーシティ・ホモダイン光受信器と高速デジタル信号処理との組み合わせにより安定性の高い光受信が構築されている。デジタルコヒーレント光伝送技術およびデジタルコヒーレント光受信装置に関しては、例えば、特許文献１及び非特許文献１に記載されている。   An optical transmission / reception module is used as a key component of a wavelength division multiplexing optical communication device or the like that realizes large-capacity and long-distance transmission using an optical fiber. In recent years, with the increase in communication traffic, digital coherent optical transmission technology effective for high-speed and large-capacity transmission has attracted attention. This technique is an optical transmission method in which a phase modulation signal is added to an intensity modulation signal of transmission light to transmit / receive in order to increase transmission information capacity. In such a communication method using the phase modulation method, it is necessary to detect the phase of the light, so that the signal light received after optical transmission interferes with the reference light of a separately prepared local oscillation light source having the same frequency, and this beat signal A homodyne detection method for detecting intensity modulation information and phase modulation information of the signal light is used. In a digital coherent optical receiver, highly stable optical reception is constructed by a combination of a phase diversity homodyne optical receiver and high-speed digital signal processing. The digital coherent optical transmission technology and the digital coherent optical receiver are described in, for example, Patent Document 1 and Non-Patent Document 1.

図１には、非特許文献１に記載された位相ダイバーシティ・ホモダイン光受信器の光回路部の原理的構成を示す。光ファイバー伝送後に受信した信号光と同一光周波数である局部発振光源の出射光である参照光ＬＯの偏光は同じであると仮定する。参照光ＬＯはＬＯ１とＬＯ２に２分岐され、ＬＯ１とＬＯ２には９０°光ハイブリッドにより９０°（即ち、π／２）の位相差が与えられる。２分岐された信号光をそれぞれＬＯ１およびＬＯ２に合波し、信号光と参照光の干渉によりビート信号となる。参照光ＬＯの位相を基準として、信号光とＬＯ１との干渉光ビート信号の直交偏光成分であるＩ１とＩ２を光検出することにより信号光のコサイン成分ＩＩが抽出され、信号光とＬＯ２との干渉光ビート信号の直交偏光成分であるＩ３とＩ４を光検出することにより信号光のサイン成分ＩＱが抽出される。アナログ電気信号ＩＩおよびＩＱをデジタル信号変換し、デジタル信号処理により光複素振幅が得られる。 FIG. 1 shows the basic configuration of the optical circuit unit of the phase diversity homodyne optical receiver described in Non-Patent Document 1. It is assumed that the polarization of the reference light LO that is the outgoing light of the local oscillation light source having the same optical frequency as the signal light received after the optical fiber transmission is the same. The reference light LO is bifurcated into LO1 and LO2, and a phase difference of 90 ° (ie, π / 2) is given to LO1 and LO2 by a 90 ° optical hybrid. The two branched signal lights are multiplexed into LO1 and LO2, respectively, and become beat signals due to interference between the signal light and the reference light. The cosine component I I of the signal light is extracted by optically detecting the orthogonally polarized components I1 and I2 of the interference light beat signal between the signal light and the LO1 based on the phase of the reference light LO, and the signal light and the LO2 sine component I Q of the signal light is extracted by detecting an orthogonal polarization components of the interference light beat signal I3 and I4 light. The analog electric signals I I and I Q are converted into digital signals, and optical complex amplitude is obtained by digital signal processing.

尚、９０°光ハイブリッド位相ダイバーシティ・ホモダイン光受信器の具体的な光学素子及び光学系については、例えば、特許文献２に複数の構成例が記載されている。   For example, Patent Document 2 describes a plurality of configuration examples of specific optical elements and optical systems of a 90 ° optical hybrid phase diversity homodyne optical receiver.

特開２００７−６４８６０号公報JP 2007-64860 A 特開２０１１−１２００３０号公報JP 2011-120030 A

応用物理、第７８巻、第９号（２００９）、ＰＰ．８５６−８６１Applied Physics, Vol. 78, No. 9 (2009), PP. 856-861

特許文献１に開示されているホモダイン検出を用いた光電界波形観測装置においては、位相検出の際に偏光ビームスプリッタを複数用いる必要があり部品点数が増加してしまう。また、光合分波用素子として光カプラが用いられているが、この際、光ファイバーと光カプラとの結合に伴う光損失や大型化を招いてしまう。更に、特許文献２に開示されている９０°光ハイブリッドにおいては、複数の波長板および複数の偏光分離素子が分離配置された構成からなり、部品点数が多くなる。その結果、光受信装置の小型化が困難となり、光受信装置の製造の際の組立工程が複雑になるという問題点を有していた。   In the optical electric field waveform observation apparatus using homodyne detection disclosed in Patent Document 1, it is necessary to use a plurality of polarization beam splitters at the time of phase detection, which increases the number of components. In addition, an optical coupler is used as the optical multiplexing / demultiplexing element. At this time, however, an optical loss and an increase in size due to the coupling between the optical fiber and the optical coupler are caused. Furthermore, the 90 ° optical hybrid disclosed in Patent Document 2 has a configuration in which a plurality of wave plates and a plurality of polarization separation elements are separately arranged, and the number of parts increases. As a result, it is difficult to reduce the size of the optical receiver, and there is a problem in that the assembly process at the time of manufacturing the optical receiver is complicated.

よって、組立工程が簡略化できるとともに小型化されたデジタルコヒーレント光伝送に用いられる９０°光ハイブリッド位相ダイバーシティ・ホモダイン光受信に適した光受信装置が望まれていた。   Therefore, there has been a demand for an optical receiver suitable for 90 ° optical hybrid phase diversity homodyne optical reception that can be used for digital coherent optical transmission that can simplify the assembly process and is miniaturized.

本発明は、直線偏光の光であるｓ偏光の光と、前記ｓ偏光の光と直交するｐ偏光の光とが含まれる入射光を、２つの進行方向に分岐する無偏光分岐部と、前記無偏光分岐部により分岐された２つの光のうち、一方の光に対して位相差を与えず、他方の光に対してのみ、前記ｓ偏光の光と前記ｐ偏光の光との間で、９０°の奇数倍に略等しい位相差を与えるように、厚さ方向に光学軸が揃った複屈折性材料を有する波長板と、９０°の奇数倍に略等しい位相差を与えられた光を含む２つの光が入射し、互いに直交する、第１の直線偏光の光と第２の直線偏光の光毎、２つの進行方向に分岐する偏光性分岐部と、前記無偏光分岐部及び前記偏光性分岐部により４つに分岐された光の各々を受光する４つの光検出器と、を備え、前記無偏光分岐部は無偏光回折格子であって、入射光の＋１次回折光と−１次回折光を２つの進行方向に分岐された光とすることを特徴とする光受信装置。 The present invention provides an unpolarized light branching unit that branches incident light including s-polarized light, which is linearly polarized light, and p-polarized light orthogonal to the s-polarized light, into two traveling directions; Of the two lights branched by the non-polarization branching section, no phase difference is given to one light, and only the other light is between the s-polarized light and the p-polarized light, A wave plate having a birefringent material having optical axes aligned in the thickness direction so as to give a phase difference substantially equal to an odd multiple of 90 °, and light given a phase difference substantially equal to an odd multiple of 90 °. The first and second linearly polarized light beams that are incident and orthogonal to each other, a polarization branching unit that branches in two traveling directions, the non-polarization branching unit, and the polarization Four photodetectors for receiving each of the light branched into four by the sex branching unit , the non-polarization branching unit being An optical receiver , which is a polarization diffraction grating, wherein incident light is divided into + 1st order diffracted light and −1st order diffracted light in two traveling directions .

また、本発明は、前記入射光は、同じ波長の信号光と参照光を含むものであって、前記無偏光分岐部と、波長板と、偏光性分岐部とにより形成される偏光位相分離素子により前記入射光が分岐されるものであることを特徴とする光受信装置。   In the invention, it is preferable that the incident light includes signal light and reference light having the same wavelength, and the polarization phase separation element is formed by the non-polarization branching unit, the wavelength plate, and the polarization branching unit. An optical receiver characterized in that the incident light is branched.

また、本発明は、前記無偏光分岐部により分岐された２つの光の分岐方向と前記偏光性分岐部により分岐された光の分岐方向とが所定の角度を成すように構成されていることを特徴とする光受信装置。   Further, the present invention is configured such that the branch direction of the two lights branched by the non-polarization branch part and the branch direction of the light branched by the polarizing branch part form a predetermined angle. An optical receiver characterized.

また、本発明は、前記無偏光分岐部は無偏光回折格子であって、入射光の＋１次回折光と−１次回折光を２つの進行方向に分岐された光とすることを特徴とする光受信装置。   According to the present invention, the non-polarization branching unit is a non-polarization diffraction grating, and the + 1st order diffracted light and the −1st order diffracted light of the incident light are branched into two traveling directions. apparatus.

また、本発明は、前記偏光性分岐部は偏光性回折格子であって、入射光の常光偏光成分を回折せず透過するとともに異常光偏光成分を回折する、または、入射光の異常光偏光成分を回折せず透過するとともに常光偏光成分を回折することを特徴とする光受信装置。   Further, in the present invention, the polarizing branching portion is a polarizing diffraction grating and transmits the ordinary light polarization component of the incident light without diffracting it, and diffracts the extraordinary light polarization component, or the extraordinary light polarization component of the incident light. Is transmitted without diffracting the light and diffracts the ordinary polarized light component.

また、本発明は、前記偏光性回折格子は、光学軸が厚さ方向に揃い、常光屈折率ｎｏと異常光屈折率ｎｅ（ｎｏ≠ｎｅ）を有する複屈折性材料からなる複屈折性材料層および、屈折率がｎｓとなる等方性材料からなる等方性材料層によって周期的凹凸が形成され、前記屈折率ｎｓは、前記常光屈折率ｎｏまたは前記異常光屈折率ｎｅと略等しく、前記複屈折性材料層の光学軸の方向と、前記波長板の光学軸の方向とが、略４５°の角度をなすことを特徴とする光受信装置。

Further, the present invention, the polarizing diffraction grating, double that aligned in the thickness direction optical axis, consisting of birefringent material having a ordinary refractive index n o and extraordinary refractive index n e (n o ≠ n e ) refractive material layer and the periodic unevenness is formed by isotropic material layer made of an isotropic material having a refractive index becomes n s, a refractive index n s is the ordinary refractive index n o or the extraordinary refractive substantially equal to the rate n e, the direction of the optical axis of the birefringent material layer, and the direction of the optical axis of the wavelength plate, an optical receiving apparatus, characterized in that an angle of approximately 45 °.

また、本発明は、前記無偏光回折格子の格子長手方向と前記偏光性回折格子の格子長手方向とが所定の角度をなすことを特徴とする光受信装置。   In the optical receiver according to the present invention, the longitudinal direction of the non-polarized diffraction grating and the longitudinal direction of the polarizing diffraction grating form a predetermined angle.

また、本発明は、前記波長板は、前記ｓ偏光の光と前記ｐ偏光の光との間で、位相差を与えない第１の領域と、前記ｓ偏光の光と前記ｐ偏光の光との間で、９０°の奇数倍に略等しい位相差を与える第２の領域を有し、前記第２の領域にのみ、高分子液晶を有することを特徴とする光受信装置。   In the present invention, the wave plate may include a first region that does not give a phase difference between the s-polarized light and the p-polarized light, the s-polarized light, and the p-polarized light. An optical receiver having a second region that gives a phase difference substantially equal to an odd multiple of 90 ° between them, and a polymer liquid crystal only in the second region.

また、本発明は、前記波長板は、前記ｓ偏光の光と前記ｐ偏光の光との間で、位相差を与えない第１の領域と、前記ｓ偏光の光と前記ｐ偏光の光との間で、９０°の奇数倍に略等しい位相差を与える第２の領域を有し、前記第１の領域および前記第２の領域は、いずれも高分子液晶を有し、前記第１の領域における高分子液晶は厚さ方向に略平行に配向されることを特徴とする光受信装置。   In the present invention, the wave plate may include a first region that does not give a phase difference between the s-polarized light and the p-polarized light, the s-polarized light, and the p-polarized light. Between the first region and the second region, the first region and the second region both have a polymer liquid crystal, and the second region gives a phase difference substantially equal to an odd multiple of 90 °. An optical receiver characterized in that the polymer liquid crystal in the region is aligned substantially parallel to the thickness direction.

また、本発明は、互いに直交するｓ偏光の光とｐ偏光の光を合波させる偏光ビームスプリッタを備え、異なる方向から入射する前記信号光と参照光を偏光ビームスプリッタにより合波することにより前記偏光位相分離素子への入射光を生成することを特徴とする光受信装置。   The present invention also includes a polarizing beam splitter that combines s-polarized light and p-polarized light that are orthogonal to each other, and combines the signal light and the reference light incident from different directions by the polarizing beam splitter. An optical receiver that generates incident light to a polarization phase separation element.

本発明によれば、複数の機能が集積化された空間結合型の小型光学部品を用いることにより、部品点数が少ない、小型・軽量の９０°光ハイブリッド位相ダイバーシティ・ホモダイン光受信装置を得ることができる。また、光受信装置を構成する偏光位相分離素子において、無偏光分岐部と波長板と偏光性分岐部を一体形成することにより、光受信装置の製造の際の組立工程が簡略化できる。また、偏光位相分離素子における波長板の入射角度依存性が小さなため、入射光が光検出器の受光面に集光される集束光の光路中に配置できる。その結果、光受信装置の小型化につながる。また、光受信装置を構成する偏光位相分離素子において、無偏光回折格子からなる無偏光分岐部により生成される分岐光の内の不要光、および、偏光性回折格子からなる偏光性分岐部で生成される分岐光の内の不要光が光検出器の受光面に混入しないため、ＳＮ比の高い光信号を検出できる。   According to the present invention, it is possible to obtain a compact and lightweight 90 ° optical hybrid phase diversity homodyne optical receiver with a small number of parts by using a spatially coupled small optical component in which a plurality of functions are integrated. it can. In addition, in the polarization phase separation element constituting the optical receiver, the assembly process at the time of manufacturing the optical receiver can be simplified by integrally forming the non-polarization branching part, the wave plate, and the polarizing branching part. Further, since the incident angle dependency of the wave plate in the polarization phase separation element is small, the incident light can be arranged in the optical path of the focused light that is collected on the light receiving surface of the photodetector. As a result, the optical receiving apparatus can be downsized. Also, in the polarization phase separation element that constitutes the optical receiver, unnecessary light out of the branched light generated by the non-polarized light splitting part made of the non-polarized diffraction grating and generated by the polarizing branch part made of the polarizing diffraction grating Since unnecessary light in the branched light does not enter the light receiving surface of the photodetector, an optical signal with a high S / N ratio can be detected.

位相ダイバーシティ・ホモダイン光受信器の光回路部の原理的な構成図Principle configuration diagram of optical circuit section of phase diversity homodyne optical receiver 第１の実施の形態における光受信装置の構成図Configuration diagram of optical receiver in first embodiment 第１の実施の形態における光受信装置に用いられる偏光位相分離素子の構成図Configuration diagram of a polarization phase separation element used in the optical receiver in the first embodiment 第１の実施の形態における光受信装置の偏光位相分離素子に用いられる波長板の構成図Configuration diagram of wave plate used for polarization phase separation element of optical receiver in first embodiment 第１の実施の形態における光受信装置の偏光位相分離素子に用いられる偏光性回折格子の構成図1 is a configuration diagram of a polarizing diffraction grating used in a polarization phase separation element of an optical receiver according to a first embodiment. 第１の実施の形態における光受信装置に用いられる偏光分離機能素子の説明図（１）Explanatory drawing (1) of the polarization separation functional element used for the optical receiver in the first embodiment 第１の実施の形態における光受信装置に用いられる偏光分離機能素子の説明図（２）Explanatory drawing (2) of the polarization separation functional element used for the optical receiver in 1st Embodiment 第１の実施の形態における光受信装置に用いられる偏光分離機能素子の説明図（３）Explanatory drawing (3) of the polarization separation functional element used for the optical receiver in 1st Embodiment 第１の実施の形態における光受信装置に用いられる偏光位相分離素子の入射角度と位相差の相関図Correlation diagram between incident angle and phase difference of polarization phase separation element used in optical receiver in first embodiment 第１の実施の形態における光受信装置に用いられる偏光位相分離素子の他の構成図Another configuration diagram of the polarization phase separation element used in the optical receiver in the first embodiment 第２の実施の形態における光受信装置の構成図The block diagram of the optical receiver in 2nd Embodiment

本発明を実施するための形態について、以下に説明する。尚、同じ部材等については、同一の符号を付して説明を省略する。   The form for implementing this invention is demonstrated below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

〔第１の実施の形態〕
（光受信装置）
第１の実施の形態における光受信装置について説明する。図２は、本実施の形態における光受信装置の構成図である。本実施の形態における光受信装置１００は、Ｘ軸方向の直線偏光の信号光ＳとＹ軸方向の直線偏光の参照光Ｒを含む伝送光を出射する光ファイバーや光導波路など光伝送部７０と、光伝送部７０からの出射光を光検出器６０へ集光する集光レンズ８０と、集光レンズ８０と光検出器６０の光路中に配置する偏光位相分離素子１０から構成されている。偏光位相分離素子１０は、無偏光分岐部となる無偏光回折格子２０と波長板３０と偏光性分岐部となる偏光性回折格子４０からなり、この順番に配置された偏光位相分離素子１０に入射する収束光である入射光５０が、４つ光束である光５３ａ、５３ｂ、５３ｃ、５３ｄに分岐される。この４つ光束はそれぞれ光検出器６０の分割された光検出器の受光面６０ａ、６０ｂ、６０ｃ、６０ｄに集光される。偏光位相分離素子１０の機能は後述する。 [First Embodiment]
(Optical receiver)
The optical receiver in the first embodiment will be described. FIG. 2 is a configuration diagram of the optical receiving apparatus according to the present embodiment. The optical receiving apparatus 100 according to the present embodiment includes an optical transmission unit 70 such as an optical fiber or an optical waveguide that emits transmission light including linearly polarized signal light S in the X-axis direction and linearly polarized reference light R in the Y-axis direction, The condenser lens 80 condenses the light emitted from the light transmission unit 70 onto the photodetector 60, and the polarization phase separation element 10 disposed in the optical path of the condenser lens 80 and the photodetector 60. The polarization phase separation element 10 includes a non-polarization diffraction grating 20 serving as a non-polarization branch part, a wave plate 30, and a polarization diffraction grating 40 serving as a polarization branch part, and is incident on the polarization phase separation element 10 arranged in this order. The incident light 50 that is convergent light is branched into four light beams 53a, 53b, 53c, and 53d. These four light beams are condensed on the light receiving surfaces 60a, 60b, 60c, and 60d of the divided photodetectors of the photodetector 60, respectively. The function of the polarization phase separation element 10 will be described later.

光伝送部７０の出射光である信号光Ｓと参照光Ｒは、ホモダイン検出に適合するように同一波長で、信号光Ｓは強度変調および位相変調された光情報を含み、参照光Ｒは一定強度で位相がそろっている。   The signal light S and the reference light R that are emitted from the optical transmission unit 70 have the same wavelength so as to be suitable for homodyne detection, the signal light S includes optical information that is intensity-modulated and phase-modulated, and the reference light R is constant. Intensity and phase are aligned.

本実施の形態における光受信装置に適合する波長の制約は無いが、デジタルコヒーレント光受信装置のホモダイン検出に適合する可干渉長を有する波長幅の充分狭い伝送光であって、例えば、長距離伝送のＷＤＭ（Wavelength Division Multiplexing）波長多重光通信に用いられるＳバンド（１４６０〜１５３０ｎｍ）、Ｃバンド（１５３０〜１５６５ｎｍ）、Ｌバンド（１５６５〜１６２５ｎｍ）の各波長チャネルに対応した波長である。   Although there is no restriction on the wavelength suitable for the optical receiver in the present embodiment, the transmission light has a sufficiently narrow wavelength width and has a coherence length suitable for homodyne detection of the digital coherent optical receiver, for example, long-distance transmission It is a wavelength corresponding to each wavelength channel of S band (1460-1530 nm), C band (1530-1565 nm), and L band (1565-1625 nm) used for WDM (Wavelength Division Multiplexing) wavelength division multiplexing optical communication.

尚、光検出器６０（６０ａ、６０ｂ、６０ｃ、６０ｄ）で電気信号に変換された光強度信号は、電子信号処理回路（図示せず）を用いてＡＤ変換後にデジタル信号処理され、信号光Ｓに含まれる強度変調信号および位相変調信号として検出される。   The light intensity signal converted into an electrical signal by the photodetector 60 (60a, 60b, 60c, 60d) is subjected to digital signal processing after AD conversion using an electronic signal processing circuit (not shown), and the signal light S Are detected as an intensity modulation signal and a phase modulation signal.

ＷＤＭ光通信において光ファイバー中を長距離伝送された信号光の偏光は揃っていないため、光ファイバーの出射光を偏光ビームスプリッタＰＢＳ(Polarization Beam Splitter)を用いてｓ偏光とｐ偏光に分離し、ｓ偏光の信号光とｐ偏光の信号光に対して図２の光受信装置を適用すればよい。この場合、参照光は信号光の直線偏光と直交するように、ｓ偏光の信号光に対してはｐ偏光とし、ｐ偏光の信号光に対してはｓ偏光とする。   Since the polarization of the signal light transmitted over a long distance in the optical fiber in WDM optical communication is not uniform, the outgoing light of the optical fiber is separated into s-polarized light and p-polarized light using a polarization beam splitter PBS (Polarization Beam Splitter), and s-polarized light 2 may be applied to the signal light of p and the signal light of p polarization. In this case, the reference light is p-polarized for the s-polarized signal light and s-polarized for the p-polarized signal light so as to be orthogonal to the linearly polarized light of the signal light.

尚、信号光に対し直交する直線偏光の参照光は、ＰＢＳを用いて同一の光軸に効率よく合波できる。また、参照光は、信号光と同一波長で、可干渉長が長い狭い発振波長幅の局部発振光源であるレーザを別途準備して発生させる。具体的には、１０Ｈｚ以下の発振波長幅が好ましい。   Note that linearly polarized reference light orthogonal to the signal light can be efficiently combined on the same optical axis using PBS. The reference light is generated by separately preparing a laser that is a local oscillation light source having the same wavelength as that of the signal light and a long oscillation wavelength and a narrow oscillation wavelength width. Specifically, an oscillation wavelength width of 10 Hz or less is preferable.

光検出器６０は、外部からのノイズを低減するために大きさを小さくする場合があるが、このような光検出器６０に対して光を十分小さく集光するために、集光レンズ８０の像側開口数は大きくすることが好ましい。例えば、波長１．５μｍの光に対して３０μｍ以下に集光する場合、回折限界の式から開口数は０．０３以上である必要がある。開口数が大きいレンズの場合、偏光位相分離素子１０には入射角度の大きい光線が入射する。開口数が０．０３である場合、入射角度は１．７°以下となる。開口数が大きい場合、偏光位相分離素子１０への入射角度は大きくなるので偏光位相分離素子１０への入射角度は１．７°以上となりうる。   The photodetector 60 may be reduced in size in order to reduce noise from the outside, but in order to condense light to such a photodetector 60 sufficiently small, It is preferable to increase the image-side numerical aperture. For example, when condensing light having a wavelength of 1.5 μm to 30 μm or less, the numerical aperture needs to be 0.03 or more from the diffraction limit equation. In the case of a lens having a large numerical aperture, a light beam having a large incident angle enters the polarization phase separation element 10. When the numerical aperture is 0.03, the incident angle is 1.7 ° or less. When the numerical aperture is large, the incident angle to the polarization phase separation element 10 becomes large, so the incidence angle to the polarization phase separation element 10 can be 1.7 ° or more.

（偏光位相分離素子）
本実施の形態における光受信装置において用いられる偏光位相分離素子の実施の形態について説明する。図３は、本実施の形態における偏光位相分離素子の構成図である。本実施の形態における偏光位相分離素子１０は、無偏光分岐部である無偏光回折格子２０、波長板３０および偏光性分岐部である偏光性回折格子４０を有し、図３に示すように、この順に光が入射するように構成されている。 (Polarization phase separation element)
An embodiment of a polarization phase separation element used in the optical receiver according to the present embodiment will be described. FIG. 3 is a configuration diagram of the polarization phase separation element in the present embodiment. The polarization phase separation element 10 in the present embodiment has a non-polarization diffraction grating 20, which is a non-polarization branching part, a wave plate 30, and a polarization diffraction grating 40, which is a polarization branching part, as shown in FIG. The light is incident in this order.

無偏光回折格子２０は、例えば、光学的に等方性の屈折率を示す等方性材料からなる透明基板の表面に周期的な凹凸が形成されたものであったり、透明基板の表面に、他の等方性材料が凹凸状に形成されたものであったりしてもよい。回折格子の断面が矩形状の凹凸である場合、±１次回折光の回折効率が最大になるように設定すると、＋１次回折光と−１次回折光の光量をそれぞれ大きくすることができ、直進透過する０次回折光（直進透過光）を小さくすることができるので、効率よく２つの光に分岐することができる。   The non-polarized diffraction grating 20 is, for example, one in which periodic irregularities are formed on the surface of a transparent substrate made of an isotropic material exhibiting an optically isotropic refractive index, or on the surface of the transparent substrate, Other isotropic materials may be formed in an uneven shape. When the cross section of the diffraction grating is a rectangular unevenness, if the diffraction efficiency of the ± first-order diffracted light is set to be maximum, the light amounts of the + 1st-order diffracted light and the −1st-order diffracted light can be increased, and the light passes through straight. Since the 0th-order diffracted light (straight forward transmitted light) can be reduced, the light can be efficiently branched into two lights.

この場合、矩形状の回折格子によって分岐された＋１次回折光と−１次回折光の光量は等しくなるので波長などの変動がある場合でも＋１次回折光と−１次回折光の光量比を一定に保つことができ、後述する位相差検出処理が容易になる。また、回折格子の断面がブレーズ形状の凹凸またはブレーズ状を階段状に近似した擬似ブレーズ形状の凹凸である場合、０次回折光と例えば＋１次回折光の光量をそれぞれ大きくすることができ、−１次回折光を小さくすることができるので、効率よく２つの光に分岐することができる。尚、回折角度は、入射する光の波長と回折格子の周期の幅（格子ピッチ）によって決定する。例えば、回折角度を大きくして光を分岐させる場合は、格子ピッチを狭く設計するとよい。   In this case, since the light amounts of the + 1st order diffracted light and the −1st order diffracted light branched by the rectangular diffraction grating are equal, the light quantity ratio between the + 1st order diffracted light and the −1st order diffracted light is kept constant even when there is a variation in wavelength. Therefore, the phase difference detection process described later is facilitated. Further, when the cross section of the diffraction grating is a blazed concavo-convex shape or a quasi-blazed concavo-convex shape approximating a blazed shape like a staircase, the light amounts of the 0th-order diffracted light and, for example, the + 1st-order diffracted light can be increased. Since the folding light can be reduced, the light can be efficiently branched into two lights. The diffraction angle is determined by the wavelength of incident light and the period width (grating pitch) of the diffraction grating. For example, when the light is branched by increasing the diffraction angle, the grating pitch may be designed to be narrow.

回折角度と格子ピッチはグレーティング方程式に従うので、格子ピッチをＰｇの無偏光回折格子２０に波長λの光が入射した場合、屈折率ｎｇを有する媒質に出射されるｍ次の回折光の回折角度θｇ（ｍ）は、下記の式を満たす。 Since the diffraction angle and the grating pitch follows the grating equation, when the light of wavelength λ is incident on the non-polarization grating 20 of the grating pitch P g, the diffraction of the emitted m order diffracted light to the medium having a refractive index n g The angle θ g (m) satisfies the following formula.

ｎｇｓｉｎθｇ（ｍ）＝ｍＰｇ／λ
また、波長板３０までの距離をＬｇｗとし波長板３０の位置における光の径をφｗとすると分岐される光を＋１次回折光と−１次回折光とした場合、下記の式を満たしていると、
Ｌｇｗ｛ｔａｎθｇ（＋１）−ｔａｎθｇ（−１）｝＞φｗ
波長板３０上で分岐された光を分離することができ、ノイズの原因となる迷光の発生を低減することができるので好ましい。分岐される光を＋１次回折光と０次回折光とした場合、下記の式を満たしていると、
Ｌｇｗｔａｎθｇ（＋１）＞φｗ
波長板３０上で分岐された光を分離でき、ノイズの原因となる２つの分岐された光間のクロストークを低減できるので好ましい。 ng sin θ g (m) = mP g / λ
Also, if the distance to the wave plate 30 was light +1 order diffracted light and -1 order diffracted light branched with the diameter of the light and phi w at the position of the wave plate 30 and L gw, satisfies the following formula When,
L gw {tanθ g (+1) -tanθ g (-1)}> φ w
It is preferable because the light branched on the wave plate 30 can be separated and the generation of stray light causing noise can be reduced. When the branched light is + 1st order diffracted light and 0th order diffracted light,
L gw tan θ g (+1)> φ w
It is preferable because the light branched on the wave plate 30 can be separated and the crosstalk between the two branched lights causing noise can be reduced.

また、光が出射される側の媒質の平均的な屈折率ｎｇが大きい場合、回折角度が小さくなるため２つの分岐される光の間のクロストークを低減するために素子の厚みが大きくなってしまう。したがって、無偏光回折格子２０と波長板３０の間の媒質の平均的な屈折率は小さい方が好ましく、平均的な屈折率として１．６以下であることが好ましく、１．４５以下であるとより好ましく、１．４以下であるとさらに好ましい。１．６以下の屈折率の材料としてＢＫ７などのホウケイ酸ガラスを用いることができ、１．４５以下の屈折率の材料として石英ガラスやホタル石などの材料を用いることができ、１．４下の屈折率の材料としてフッ素樹脂や空気などの材料を用いることができる。無偏光回折格子２０の格子ピッチとして５μｍであると好ましく、２μｍ以下であるとより好ましい。 In addition, when the average refractive index ng of the medium on which light is emitted is large, the diffraction angle is small, so that the thickness of the element is increased to reduce crosstalk between the two branched lights. End up. Accordingly, the average refractive index of the medium between the non-polarized diffraction grating 20 and the wave plate 30 is preferably small, and the average refractive index is preferably 1.6 or less, and is 1.45 or less. More preferably, it is further preferably 1.4 or less. A borosilicate glass such as BK7 can be used as a material having a refractive index of 1.6 or less, and a material such as quartz glass or fluorite can be used as a material having a refractive index of 1.45 or less. A material such as a fluororesin or air can be used as a material having a refractive index of 10%. The grating pitch of the non-polarized diffraction grating 20 is preferably 5 μm, and more preferably 2 μm or less.

無偏光回折格子２０の回折光は、格子断面の凹凸部長手方向と入射光の成す平面に対し垂直でかつ０次回折光の進行方向を含む面内の方向に進行する。即ち、０次回折光または±１次回折光の分岐方向は格子凹凸部長手方向と直交する。図３において、入射光５０は無偏光回折格子２０により±１次回折光がＹ軸方向に発生するように、回折格子の長手方向が直線でＸ軸方向となるように設計されている。   The diffracted light of the non-polarized diffraction grating 20 travels in a direction perpendicular to the longitudinal direction of the concavo-convex portion of the grating cross section and the plane formed by the incident light and in the plane including the traveling direction of the 0th-order diffracted light. That is, the branching direction of the 0th order diffracted light or ± 1st order diffracted light is orthogonal to the longitudinal direction of the grating irregularities. In FIG. 3, the incident light 50 is designed such that the longitudinal direction of the diffraction grating is a straight line and the X-axis direction so that ± first-order diffracted light is generated in the Y-axis direction by the non-polarization diffraction grating 20.

波長板３０は、無偏光回折格子２０で分岐された２つの光それぞれに対応した、第１の領域３１と第２の領域３２を有しており、第１の領域３１または第２の領域３２のいずれかは、信号光と参照光との間に９０°の位相差が与えられるように設定されていればよい。例えば、第１の領域３１は等方性材料から構成され、第２の領域３２は複屈折性材料から構成され、第２の領域３２の厚さを調整することで所望の位相差を与えることができる。また、第１の領域３１または第２の領域３２のいずれか一方は、透明な等方性材料から構成されているものに限らず、空気であってもよい。一方が空気である場合、他方の領域にのみ所望の位相差を与えられるように設計された複屈折性材料が備えられていればよい。詳細の構成については後述する。   The wave plate 30 has a first region 31 and a second region 32 corresponding to the two lights branched by the non-polarized diffraction grating 20, and the first region 31 or the second region 32. Any of these may be set so that a phase difference of 90 ° is given between the signal light and the reference light. For example, the first region 31 is made of an isotropic material, the second region 32 is made of a birefringent material, and a desired phase difference is given by adjusting the thickness of the second region 32. Can do. In addition, one of the first region 31 and the second region 32 is not limited to one made of a transparent isotropic material, and may be air. When one is air, it is only necessary to provide a birefringent material designed to give a desired phase difference only to the other region. A detailed configuration will be described later.

偏光性回折格子４０は、入射する光のうち互いに直交する偏光状態の光毎、透過または回折させて進行する方向が互いに異なるように作用する。例えば、入射する光のうち、第１の直線偏光の光は直進透過させ、第１の直線偏光の光と直交する第２の直線偏光の光を回折させる機能を有する。偏光性回折格子４０は、例えば、光学的に複屈折性を示す複屈折性材料と等方性材料とが、断面が周期的な凹凸を形成するように構成される。そして、複屈折性材料の常光屈折率ｎｏまたは異常光屈折率ｎｅ（ｎｏ≠ｎｅ）と、等方性材料の屈折率ｎｓとが略一致する材料を組み合わせることによって、上記の作用を得ることができる。 The polarizing diffraction grating 40 acts so that the light traveling in the polarization state orthogonal to each other among the incident light is transmitted or diffracted and the traveling directions are different from each other. For example, of the incident light, the first linearly polarized light has a function of allowing the first linearly polarized light to pass straight through and diffracting the second linearly polarized light orthogonal to the first linearly polarized light. The polarizing diffraction grating 40 is configured, for example, such that an optically birefringent birefringent material and an isotropic material form irregularities with a periodic cross section. Then, by combining a material in which the ordinary refractive index n o or extraordinary refractive index n e (n o ≠ n e ) of the birefringent material and the refractive index n s of the isotropic material substantially match, The effect can be obtained.

偏光性回折格子４０の回折効率は（ｎｅ−ｎｏ）と複屈折材料の厚みの積を光の波長λによって除算した因子に依存するため、（ｎｅ−ｎｏ）が小さい場合には複屈折材料の厚みの影響が大きくなる。複屈折材料の厚みが大きくなると光の入射角度の変化に応じて光路長の変化が大きくなるため、光の入射角度に対する回折効率の変動が大きくなる。したがって、（ｎｅ−ｎｏ）＞０．０１となる複屈折材料を用いることが好ましく、（ｎｅ−ｎｏ）＞０．０４となる複屈折材料を用いるとより好ましく、（ｎｅ−ｎｏ）＞０．０５となる複屈折材料を用いるとより好ましく、（ｎｅ−ｎｏ）＞０．０６５となる複屈折材料を用いるとさらに好ましい。 Since the diffraction efficiency of the polarizing diffraction grating 40 depends on a factor obtained by dividing the product of (n e −n o ) and the thickness of the birefringent material by the wavelength λ of light, when (n e −n o ) is small, The influence of the thickness of the birefringent material is increased. When the thickness of the birefringent material is increased, the change in the optical path length is increased in accordance with the change in the incident angle of light, so that the variation in diffraction efficiency with respect to the incident angle of light is increased. Thus, (n e -n o)> It is preferable to use a birefringent material of 0.01, more preferably the use of birefringent material comprising a (n e -n o)> 0.04 , (n e - n o)> more preferably the use of birefringent material of 0.05, further preferable to use a birefringent material as the (n e -n o)> 0.065 .

尚、回折角度は、無偏光回折格子２０と同様に、回折角度を大きくして光を分岐させる場合、格子ピッチを狭く設計するとよい。偏光性回折格子４０の回折光は、格子断面の凹凸部長手方向と入射光の成す平面に対し垂直でかつ０次回折光の進行方向を含む面内の方向に進行する。即ち、０次回折光または±１次回折光の分岐方向は格子凹凸部長手方向と直交する。図３に示す例では、Ｚ軸方向に進行する入射光５０に対して、無偏光回折格子２０により回折光がＹ軸方向に発生するように格子の長手方向が直線でＸ軸方向となるように設計され、偏光性回折格子４０により回折光がＹ軸方向に発生するように格子の長手方向が直線でＸ軸方向となるように設計されている。   As in the case of the non-polarized diffraction grating 20, the diffraction angle may be designed to be narrow when the diffraction angle is increased and light is branched. The diffracted light of the polarizing diffraction grating 40 travels in a direction perpendicular to the longitudinal direction of the concavo-convex portion of the grating cross section and the plane formed by the incident light and in the plane including the traveling direction of the 0th-order diffracted light. That is, the branching direction of the 0th order diffracted light or ± 1st order diffracted light is orthogonal to the longitudinal direction of the grating irregularities. In the example shown in FIG. 3, with respect to incident light 50 traveling in the Z-axis direction, the longitudinal direction of the grating is linear and the X-axis direction so that diffracted light is generated in the Y-axis direction by the non-polarized diffraction grating 20. Designed so that the longitudinal direction of the grating is a straight line and the X-axis direction so that diffracted light is generated by the polarizing diffraction grating 40 in the Y-axis direction.

図３に示すような配置とする場合、無偏光回折格子３０によって発生する不要な回折光が偏光性回折格子４０を透過することで、所望の光と同一の地点に到達しないように各回折素子の格子ピッチおよび素子の厚さを設計することが好ましい。これは所望の光と不要な回折光が同一地点に到達すると光の干渉が生じて検出する光の光量が変動するためである。このような設計はグレーティング方程式と光線追跡法を用いることで可能である。このような設計の一例として無偏光回折格子３０の格子ピッチと偏光性回折格子４０の格子ピッチを互いに整数倍としないようにすることができる。   In the case of the arrangement as shown in FIG. 3, each diffraction element prevents unwanted diffracted light generated by the non-polarized diffraction grating 30 from passing through the polarizing diffraction grating 40 so as to reach the same point as the desired light. It is preferable to design the lattice pitch and the element thickness. This is because when desired light and unnecessary diffracted light reach the same point, light interference occurs and the amount of light to be detected varies. Such a design is possible by using a grating equation and a ray tracing method. As an example of such a design, the grating pitch of the non-polarized diffraction grating 30 and the grating pitch of the polarizing diffraction grating 40 can be made not to be an integral multiple of each other.

入射する光のうち互いに直交する偏光状態の光の進行方向を互いに異ならせるものであれば偏光性回折格子４０の位置に偏光性回折格子４０の代わりに偏光分離機能を有する素子を配置してもよい。偏光分離機能として複屈折を有する材料のウォークオフを利用することができる。また、複屈折材料の厚みに傾斜を持たせ２つの異なる光学軸方向の屈折率の違いによって異なる方向に屈折させるものを用いてもよい。   An element having a polarization separation function may be arranged in place of the polarizing diffraction grating 40 at the position of the polarizing diffraction grating 40 as long as the traveling directions of the polarized light beams orthogonal to each other are different from each other. Good. A walk-off of a material having birefringence can be used as the polarization separation function. Alternatively, a birefringent material having an inclined thickness and refracting in different directions depending on a difference in refractive index between two different optical axis directions may be used.

次に、偏光位相分離素子１０の作用について説明する。本実施の形態における偏光位相分離素子１０に入射した入射光５０は、無偏光回折格子２０により透過および／または回折によって、互いに分離した２つの光５１ａと５１ｂとに分岐される。尚、入射光５０は信号光と参照光とが合波された光であり、図３において偏光位相分離素子１０にはＺ軸方向に入射する。矢印Ｓは信号光の偏光方向を示すものであり、矢印Ｒは参照光の偏光方向を示すものである。図３では、矢印Ｓに示される信号光の偏光方向はＸ軸方向であり、矢印Ｒに示される参照光の偏光方向はＹ軸方向とし、信号光Ｓの偏光方向と参照光Ｒの偏光方向とは、略直交して入射する。   Next, the operation of the polarization phase separation element 10 will be described. Incident light 50 incident on polarization phase separation element 10 in the present embodiment is split into two light beams 51 a and 51 b separated from each other by transmission and / or diffraction by non-polarization diffraction grating 20. The incident light 50 is a light obtained by combining the signal light and the reference light, and is incident on the polarization phase separation element 10 in the Z-axis direction in FIG. An arrow S indicates the polarization direction of the signal light, and an arrow R indicates the polarization direction of the reference light. In FIG. 3, the polarization direction of the signal light indicated by the arrow S is the X-axis direction, the polarization direction of the reference light indicated by the arrow R is the Y-axis direction, and the polarization direction of the signal light S and the polarization direction of the reference light R Is incident substantially orthogonally.

分岐された光５１ａは、波長板３０における第１の領域３１に入射し、分岐された光５１ｂは、波長板３０における第２の領域３２に入射する。波長板３０における第１の領域３１に入射した光５１ａは、信号光と参照光、つまり、Ｘ軸方向の光成分とＹ軸方向の光成分とにおいて位相差が付加されることなく光５２ａとして出射される。一方、波長板３０における第２の領域３２に入射した光５１ｂは、信号光と参照光との間で９０°の位相差が付加され光５２ｂとして出射される。尚、位相差は９０°に限らず、９０°の奇数倍となるようにすれば同様の効果を得ることができるが、波長板の厚さを薄くできることを考えると位相差が９０°とすることが好ましい。   The branched light 51 a is incident on the first region 31 of the wave plate 30, and the branched light 51 b is incident on the second region 32 of the wave plate 30. The light 51a incident on the first region 31 of the wave plate 30 is the light 52a without adding a phase difference between the signal light and the reference light, that is, the light component in the X-axis direction and the light component in the Y-axis direction. Emitted. On the other hand, the light 51b incident on the second region 32 of the wave plate 30 is emitted as light 52b with a 90 ° phase difference added between the signal light and the reference light. The phase difference is not limited to 90 °, but the same effect can be obtained by setting it to an odd multiple of 90 °. However, considering that the thickness of the wave plate can be reduced, the phase difference is 90 °. It is preferable.

次に、光５２ａ及び光５２ｂは、偏光性回折格子４０に入射する。偏光性回折格子４０に用いる複屈折性材料の光学軸４０ａは、直行する信号光Ｓの偏光方向と参照光Ｒの偏光方向の中間で、略４５°の角度をなすことが好ましい。よって、偏光性回折格子４０に入射した光５２ａ及び光５２ｂはそれぞれ、光学軸４０ａの方向の直線偏光の光と光学軸４０ａと直交する方向の直線偏光の光とに分岐される。即ち、偏光性回折格子４０に入射した光５２ａは、光学軸４０ａに直交する偏光方向の光５３ａと光学軸４０ａと平行な偏光方向の光５３ｂとに分岐され出射される。尚、光学軸は、遅相軸または進相軸のいずれかである。例えば、光学軸４０ａが遅相軸であって、複屈折性材料の異常光屈折率ｎｅとなる方向とし、複屈折性材料の常光屈折率ｎｏと等方性材料の屈折率ｎｓと略一致（ｎｏ≒ｎｓ、ｎｅ≠ｎｓ）している場合を考える。このとき、光５３ａは、光学軸４０ａに直交する直線偏光の光であるため、偏光性回折格子４０において回折されることなくそのまま直進して出射され、光５３ｂは、光学軸４０ａに平行な直線偏光の光であるため、偏光性回折格子４０において回折されて出射される。 Next, the light 52 a and the light 52 b enter the polarizing diffraction grating 40. The optical axis 40a of the birefringent material used for the polarizing diffraction grating 40 preferably forms an angle of approximately 45 ° between the orthogonal polarization direction of the signal light S and the polarization direction of the reference light R. Accordingly, the light 52a and the light 52b incident on the polarizing diffraction grating 40 are branched into linearly polarized light in the direction of the optical axis 40a and linearly polarized light in a direction orthogonal to the optical axis 40a, respectively. That is, the light 52a incident on the polarizing diffraction grating 40 is branched and emitted into light 53a having a polarization direction orthogonal to the optical axis 40a and light 53b having a polarization direction parallel to the optical axis 40a. The optical axis is either a slow axis or a fast axis. For example, a slow axis optical axis 40a, a direction in which the extraordinary refractive index n e of the birefringent material, the refractive index n s of the ordinary refractive index n o and an isotropic material of the birefringent material Consider a case where there is a substantial match (n o ≈n s , n e ≠ n s ). At this time, since the light 53a is linearly polarized light orthogonal to the optical axis 40a, the light 53a travels straight without being diffracted by the polarizing diffraction grating 40, and the light 53b is a straight line parallel to the optical axis 40a. Since it is polarized light, it is diffracted and emitted by the polarizing diffraction grating 40.

このため、偏光位相分離素子１０に入射した入射光５０は、進行方向が異なる４つの光５３ａ、５３ｂ、５３ｃ及び５３ｄとして出射され、４つの光５３ａ、５３ｂ、５３ｃ及び５３ｄは、入射光５０の位相差を基準にしたとき、信号光Ｓと参照光Ｒとの位相差が、各々１８０°、０°、２７０°、９０°となる。   Therefore, the incident light 50 incident on the polarization phase separation element 10 is emitted as four lights 53a, 53b, 53c, and 53d having different traveling directions, and the four lights 53a, 53b, 53c, and 53d are emitted from the incident light 50. When the phase difference is used as a reference, the phase differences between the signal light S and the reference light R are 180 °, 0 °, 270 °, and 90 °, respectively.

次に、本実施の形態における偏光位相分離素子１０の機能について、ジョーンズベクトルを用いて説明する。信号光Ｓの電場強度（＝１）に対して電場強度がＡ倍となるような参照光Ｒを入射させるとすると、入射する入射光５０における電場Ｅ１は、数１に示す式で表される。ここで、△φは参照光Ｒの位相を基準にした信号光Ｓの位相差であり、信号光Ｓに位相変調された位相情報が含まれる場合、位相差△φを検出できればよい。 Next, the function of the polarization phase separation element 10 in the present embodiment will be described using Jones vectors. Assuming that the reference light R having an electric field strength A times the electric field strength (= 1) of the signal light S is incident, the electric field E 1 in the incident light 50 is expressed by the equation shown in Equation 1. The Here, Δφ is a phase difference of the signal light S based on the phase of the reference light R, and when the phase information modulated by the phase is included in the signal light S, it is only necessary to detect the phase difference Δφ.

Figure 0006028530
この後、無偏光回折格子２０によって２つの光５１ａ及び光５１ｂに分岐され、更に、波長板３０を透過した、光５２ａにおける電場Ｅ２、光５２ｂにおける電場Ｅ３は、数２、数３に示す式で表される。
Figure 0006028530
 After that, the electric field E 2 in the light 52 a and the electric field E 3 in the light 52 b that are branched into the two light 51 a and the light 51 b by the non-polarized diffraction grating 20 and transmitted through the wave plate 30 are expressed by Equations 2 and 3. It is represented by the formula

Figure 0006028530
Figure 0006028530

Figure 0006028530
尚、数２におけるα、数３におけるβは、光を分岐した際における強度の係数である。また、数３におけるＭは、ｓ偏光とｐ偏光との間において、９０°の位相差を与えるジョーンズ行列であり、例えば、数４に示されるものである。
Figure 0006028530
 Note that α in Equation 2 and β in Equation 3 are coefficients of intensity when light is branched. M in Equation 3 is a Jones matrix that gives a phase difference of 90 ° between s-polarized light and p-polarized light. For example, M is shown in Equation 4.

Figure 0006028530
更に、偏光性回折格子４０によって、光５２ａは光５３ａと光５３ｂとに分岐され、光５３ａにおける電場Ｅ４、光５３ｂにおける電場Ｅ５は、数５、数６に示す式で表される。同様に、偏光性回折格子４０によって、光５２ｂは光５３ｃと光５３ｄとに分岐され、光５３ｃにおける電場Ｅ６、光５３ｄにおける電場Ｅ７は、数７、数８に示す式で表される。
Figure 0006028530
 Furthermore, the light 52a is branched into light 53a and light 53b by the polarizing diffraction grating 40, and the electric field E 4 in the light 53a and the electric field E 5 in the light 53b are expressed by the equations shown in Equations 5 and 6. Similarly, the light 52b is branched into light 53c and light 53d by the polarizing diffraction grating 40, and the electric field E 6 in the light 53c and the electric field E 7 in the light 53d are expressed by the equations shown in Equations 7 and 8. .

Figure 0006028530
Figure 0006028530

Figure 0006028530
Figure 0006028530

Figure 0006028530
Figure 0006028530

Figure 0006028530
ここで、数５におけるＰ１、数６におけるＰ２は、偏光子を表すジョーンズ行列であり、例えば、数９、数１０に示す式で表される。尚、γ、δは強度の係数を示す。
Figure 0006028530
 Here, P 1 in Equation 5 and P 2 in Equation 6 are Jones matrices representing the polarizer, and are represented by, for example, the equations shown in Equations 9 and 10. Note that γ and δ indicate strength coefficients.

Figure 0006028530
Figure 0006028530

Figure 0006028530
ここで、数９及び数１０に示す式を用い、α、β、γ、δを１とした場合、電場Ｅ４、Ｅ５、Ｅ６及びＥ７により得られる光信号強度Ｉ４、Ｉ５、Ｉ６及びＩ７は、以下のように、表すことができる。
Figure 0006028530
 Here, the optical signal intensities I 4 and I 5 obtained by the electric fields E 4 , E 5 , E 6, and E 7 when α, β, γ, and δ are set to 1 using the equations shown in Equations 9 and 10. , I 6 and I 7 can be expressed as follows:

Ｉ４＝（１＋Ａ２−２ＡｃｏｓΔφ）／４、
Ｉ５＝（１＋Ａ２＋２ＡｃｏｓΔφ）／４、
Ｉ６＝（１＋Ａ２＋２ＡｓｉｎΔφ）／４、
Ｉ７＝（１＋Ａ２−２ＡｓｉｎΔφ）／４、
上記光信号強度Ｉ４、Ｉ５、Ｉ６及びＩ７に基づき、下記の演算を行うことにより、Ａ倍に増強された光強度信号Ｓｉｇを検出することができる。 I 4 = (1 + A 2 −2A cos Δφ) / 4,
I 5 = (1 + A 2 + 2A cos Δφ) / 4,
I 6 = (1 + A 2 + 2AsinΔφ) / 4,
I 7 = (1 + A 2 −2 Asin Δφ) / 4,
Based on the optical signal intensities I 4 , I 5 , I 6 and I 7 , the optical intensity signal Sig enhanced by A times can be detected by performing the following calculation.

Ｓｉｇ＝｛（Ｉ４−Ｉ５）２＋（Ｉ６＋Ｉ７）２｝１／２
＝｛（ＡｃｏｓΔφ）２＋（ＡｓｉｎΔφ）２｝１／２
＝Ａ
これより、偏光位相分離素子を透過した４つの光それぞれを検出し、更に、演算機能を有する光検出器を備えることで、光強度信号Ｓｉｇを高い感度で検出することができる。従って、この光受信装置を用い、信号光Ｓに含まれる強度変調された光情報の検出において、高いＳ／Ｎ比を得ることができる。 Sig = {(I 4 −I 5 ) 2 + (I 6 + I 7 ) 2 } 1/2
= {(AcosΔφ) 2 + (AsinΔφ) 2 } 1/2
= A
Accordingly, by detecting each of the four lights transmitted through the polarization phase separation element and further including a photodetector having a calculation function, the light intensity signal Sig can be detected with high sensitivity. Therefore, a high S / N ratio can be obtained in the detection of intensity-modulated optical information contained in the signal light S using this optical receiver.

さらに、下記の演算を行うことにより、参照光Ｒと信号光Ｓの位相差△φを検出することができる。   Furthermore, the phase difference Δφ between the reference light R and the signal light S can be detected by performing the following calculation.

（Ｉ６―Ｉ７）／（Ｉ５―Ｉ４）＝｛（ＡｓｉｎΔφ）／（ＡｃｏｓΔφ）｝
＝ｔａｎΔφ
従って、
Δφ＝ｔａｎ−１｛（Ｉ６―Ｉ７）／（Ｉ５―Ｉ４）｝
その結果、参照光Ｒは位相が一定のため、信号光Ｓに含まれる位相変調された情報を高いＳ／Ｎ比で検知できる。 (I 6 -I 7 ) / (I 5 -I 4 ) = {(Asin Δφ) / (Acos Δφ)}
= TanΔφ
Therefore,
Δφ = tan −1 {(I 6 −I 7 ) / (I 5 −I 4 )}
As a result, since the phase of the reference light R is constant, the phase-modulated information included in the signal light S can be detected with a high S / N ratio.

例えば、Δφの値が、０°、９０°、１８０°、２７０°の４値である場合、光検出器６０が、Ｉ４−Ｉ５の演算、Ｉ７−Ｉ６の演算を行う機能を有するとすると、Ｓｉｇ１＝Ｉ４−Ｉ５＝ＡｃｏｓΔφ、Ｓｉｇ２＝Ｉ７−Ｉ６＝ＡｓｉｎΔφより、下記に基づき、Δφの値を知ることができる。 For example, when the value of Δφ is four values of 0 °, 90 °, 180 °, and 270 °, the photodetector 60 has a function of calculating I 4 -I 5 and calculating I 7 -I 6. Assuming that Sig1 = I 4 −I 5 = AcosΔφ and Sig2 = I 7 −I 6 = AsinΔφ, the value of Δφ can be known based on the following.

Δφ＝０°の場合、（Ｓｉｇ１、Ｓｉｇ２）＝Ａ（１、０）、
Δφ＝９０°の場合、（Ｓｉｇ１、Ｓｉｇ２）＝Ａ（０、１）、
Δφ＝１８０°の場合、（Ｓｉｇ１、Ｓｉｇ２）＝Ａ（−１、０）、
Δφ＝２７０°の場合、（Ｓｉｇ１、Ｓｉｇ２）＝Ａ（０、−１）、
即ち、位相情報を検知することが可能な小型で組立等の製造が容易な光受信装置１００を得ることができる。 When Δφ = 0 °, (Sig1, Sig2) = A (1, 0),
When Δφ = 90 °, (Sig1, Sig2) = A (0, 1),
When Δφ = 180 °, (Sig1, Sig2) = A (−1, 0),
When Δφ = 270 °, (Sig1, Sig2) = A (0, −1),
That is, it is possible to obtain a small-sized optical receiver 100 that can detect phase information and that can be easily assembled and manufactured.

（波長板）
次に、本実施の形態における偏光位相分離素子１０に用いられる波長板３０について説明する。波長板３０としては、様々な構成のものが考えられる。尚、図３に示すように、第１の領域３１と第２の領域３２は、無偏光回折格子２０で分岐した２つの光５１ａ、５１ｂがそれぞれ入射するように配置されていればよく、第１の領域３１と第２の領域３２の形状やこれらの領域の境界線がどのようなものでもよい。 (Wavelength plate)
Next, the wave plate 30 used for the polarization phase separation element 10 in the present embodiment will be described. The wave plate 30 may have various configurations. As shown in FIG. 3, the first region 31 and the second region 32 may be arranged so that the two lights 51a and 51b branched by the non-polarized diffraction grating 20 are incident on the first region 31 and the second region 32, respectively. The shape of the first region 31 and the second region 32 and the boundary line between these regions may be arbitrary.

図４は、波長板３０の具体的な構成として、波長板３０ａ、波長板３０ｂ及び波長板３０ｃの断面模式図を例示したものである。これらの波長板３０ａ、波長板３０ｂ及び波長板３０ｃは、いずれも図２及び図３に示される波長板３０として用いることができるものである。具体的には、図４（ａ）に示されるように、波長板３０ａは、第１の領域３１ａにおいて、等方性材料３３ａが透明基板３５ａ及び３６ａに挟持され、第２の領域３２ａにおいて、複屈折性材料となる高分子液晶３４ａと等方性材料３３ａとが透明基板３５ａ及び３６ａに挟持される構造を有する。図４（ａ）においては、高分子液晶３４ａは、Ｙ軸方向に平行に配向される。波長板３０ａは、透明基板３６ａ上に一様に高分子液晶膜を成膜した後、フォトリソグラフィ及びエッチング加工により第１の領域３１ａにおける高分子液晶膜を除去し、第２の領域３２ａにのみ高分子液晶３４ａを形成し、この後、充填剤となる等方性材料３３ａを透明基板３５ａと透明基板３６ａとの間に、充填させることにより形成することができる。尚、第２の領域３２ａには等方性材料３３ａが備えられていない（空気）構造であってもよい。   FIG. 4 illustrates a schematic cross-sectional view of the wave plate 30 a, the wave plate 30 b, and the wave plate 30 c as a specific configuration of the wave plate 30. These wave plate 30a, wave plate 30b and wave plate 30c can all be used as the wave plate 30 shown in FIGS. Specifically, as shown in FIG. 4A, the wave plate 30a includes an isotropic material 33a sandwiched between the transparent substrates 35a and 36a in the first region 31a, and in the second region 32a. A polymer liquid crystal 34a serving as a birefringent material and an isotropic material 33a are sandwiched between transparent substrates 35a and 36a. In FIG. 4A, the polymer liquid crystal 34a is aligned parallel to the Y-axis direction. The wave plate 30a is formed by uniformly forming a polymer liquid crystal film on the transparent substrate 36a, and then removing the polymer liquid crystal film in the first region 31a by photolithography and etching, so that only in the second region 32a. It can be formed by forming the polymer liquid crystal 34a and then filling an isotropic material 33a serving as a filler between the transparent substrate 35a and the transparent substrate 36a. The second region 32a may have an (air) structure in which the isotropic material 33a is not provided.

また、図４（ｂ）に示されるように、波長板３０ｂは、第１の領域３１ｂが、透明基板面に垂直方向（Ｚ軸方向）に配向された垂直配向液晶３３ｂを有し、第２の領域３２ｂが、透明基板面に水平方向に配向された水平配向液晶３４ｂを有する。図４（ｂ）においては、水平配向液晶３４ｂは、Ｙ軸方向に平行に配向される。このような波長板３０ｂの形成方法は、透明基板３５ｂ及び３６ｂにおいて、第１の領域３１ｂでは液晶が垂直配向するように、第２の領域３２ｂでは液晶が水平配向するように、配向処理を行い、配向処理の行われた面を対向させて液晶を封入して製造することができる。尚、配向処理の方法としては、配向膜のラビング、光配向処理、イオンビーム照射、配向させるための溝形成等の方法を用いることができる。   As shown in FIG. 4B, the wave plate 30b includes a first region 31b having a vertically aligned liquid crystal 33b aligned in a direction perpendicular to the transparent substrate surface (Z-axis direction). The region 32b has horizontal alignment liquid crystal 34b aligned in the horizontal direction on the transparent substrate surface. In FIG. 4B, the horizontal alignment liquid crystal 34b is aligned parallel to the Y-axis direction. Such a wave plate 30b is formed by performing an alignment process on the transparent substrates 35b and 36b so that the liquid crystal is vertically aligned in the first region 31b and the liquid crystal is horizontally aligned in the second region 32b. The liquid crystal can be encapsulated with the surfaces subjected to the alignment treatment facing each other. In addition, as a method of alignment treatment, methods such as rubbing of an alignment film, photo-alignment treatment, ion beam irradiation, and groove formation for alignment can be used.

また、図４（ｃ）に示されるように、波長板３０ｃは、透明基板３３ｃ上の第１の領域３１ｃには何も形成せず、基板３３ｃ上の第２の領域３２ｃ上にのみ複屈折層３４ｃとして構造複屈折を有する材料やフォトニック結晶を形成することにより発生する位相差を調整するものである。この他、複屈折層３４ｃとして延伸した高分子フィルムを形成したものでもよい。また、第１の領域または第２の領域を透過する光に対して、位相差を与えないものとして、媒質が空気であってもよく、その場合、波長板は、実質的に第１の領域または第２の領域のいずれかに配置するものであって、入射する波長λの光に対して９０°の奇数倍の位相差を与える複屈折性材料を形成すればよい。   Further, as shown in FIG. 4C, the wave plate 30c does not form anything in the first region 31c on the transparent substrate 33c, but birefringence only on the second region 32c on the substrate 33c. A phase difference generated by forming a material having a structural birefringence or a photonic crystal as the layer 34c is adjusted. In addition, a stretched polymer film may be formed as the birefringent layer 34c. In addition, the medium may be air assuming that no phase difference is given to the light transmitted through the first region or the second region. In this case, the wave plate is substantially the first region. Alternatively, a birefringent material that is disposed in any one of the second regions and that gives a phase difference of an odd multiple of 90 ° with respect to the incident light having the wavelength λ may be formed.

また、常光屈折率ｎｗｏと異常光屈折率ｎｗｅ（ｎｗｏ≠ｎｗｅ）との関係においては、（ｎｗｅ−ｎｗｏ）＞０．０１となる複屈折材料を用いることが好ましく、（ｎｗｅ−ｎｗｏ）＞０．０４となる複屈折材料を用いるとより好ましく、（ｎｗｅ−ｎｗｏ）＞０．０５となる複屈折材料を用いるとさらに好ましく、（ｎｗｅ−ｎｗｏ）＞０．０６５となる複屈折材料を用いるとより好ましい。また、用いることのできる複屈折材料の観点より、０．３＞（ｎｗｅ−ｎｗｏ）となるものが好ましい。 In addition, in the relationship between the ordinary light refractive index n wo and the extraordinary light refractive index n we (n wo ≠ n we ), it is preferable to use a birefringent material satisfying (n we −n wo )> 0.01, n we -n wo)> more preferably the use of birefringent material serving as 0.04, (n we -n wo) > more preferably the use of birefringent material serving as 0.05, (n we -n wo) It is more preferable to use a birefringent material with> 0.065. Further, from the viewpoint of a birefringent material that can be used, those satisfying 0.3> (n we −n wo ) are preferable.

（偏光性回折格子）
次に、偏光性回折格子４０について説明する。本実施の形態における偏光位相分離素子１０に用いられる偏光性回折格子４０は、図５に示すように、断面がブレーズ形状または、ブレーズ形状を階段状に近似した擬似ブレーズ形状を有し、高分子液晶からなる複屈折性材料層４４と、等方性材料が、複屈折性材料層４４の凹凸を平坦化するように配置されてなる等方性材料層４５とが、透明基板４２及び４３に挟持される構造を有する。尚、複屈折性材料層４４は、凸状となる部分が＋Ｙ方向に厚くなるような（擬似）ブレーズ形状の傾きを有するが、逆の傾きを有するものでもよく、さらに、光学軸の方向が４５°方向であれば、Ｘ−Ｙ平面において複屈折性材料層４４の長手方向が任意の方向に揃うものでもよい。 (Polarizing diffraction grating)
Next, the polarizing diffraction grating 40 will be described. As shown in FIG. 5, the polarizing diffraction grating 40 used in the polarization phase separation element 10 in the present embodiment has a blazed shape or a pseudo blazed shape in which the blazed shape approximates a step shape, and is a polymer. A birefringent material layer 44 made of liquid crystal and an isotropic material layer 45 in which an isotropic material is arranged so as to flatten the unevenness of the birefringent material layer 44 are formed on the transparent substrates 42 and 43. It has a sandwiched structure. The birefringent material layer 44 has a (pseudo) blazed inclination such that the convex portion becomes thick in the + Y direction. However, the birefringent material layer 44 may have a reverse inclination, and further, the direction of the optical axis is If the direction is 45 °, the longitudinal direction of the birefringent material layer 44 may be aligned in an arbitrary direction on the XY plane.

また、複屈折性材料層４４の配向方向（例えば遅相軸）は、図５のＸ−Ｙ平面において、Ｘ軸より４５°の角度をなす方向とする。尚、等方性材料の屈折率をｎｓとするとき、等方性材料は、高分子液晶の常光屈折率ｎｏまたは異常光屈折率ｎｅ（ｎｏ≠ｎｅ）のいずれか一方に略一致する材料によって構成されている。尚、偏光性回折格子として、断面が（擬似）ブレーズ形状とすると、透過または回折して分岐する光の利用効率を高くできる点で好ましいが、これに限らず矩形状の周期的凹凸を有するものでもよい。 In addition, the orientation direction (for example, the slow axis) of the birefringent material layer 44 is a direction that forms an angle of 45 ° with respect to the X axis in the XY plane of FIG. Incidentally, the refractive index of the isotropic material when the n s, isotropic material, in one of the polymer liquid crystal ordinary refractive index n o or the extraordinary refractive index n e (n o ≠ n e ) It is made of a substantially matching material. It is preferable that the polarizing diffraction grating has a (pseudo) blazed cross section because it can increase the utilization efficiency of light that is transmitted or diffracted and branched, but is not limited to this, and has a rectangular periodic unevenness. But you can.

ここで、屈折率の関係をｎｓ≒ｎｏ、ｎｓ≠ｎｅとするとき、高分子液晶の遅相軸方向となる異常光屈折率の方向の偏光成分の光は回折され、高分子液晶の進相軸方向となる常光屈折率の方向の偏光成分の光は回折されることなく直進透過する。このような偏光性回折格子４０は、透明基板４２上に高分子液晶膜を形成した後、フォトリソグラフィとエッチングを繰り返し行うことにより擬似ブレーズ形状となる高分子液晶からなる複屈折性材料層４４を形成し、この後、透明基板４２と透明基板４３との間に、充填剤として等方性材料を充填した等方性材料層４５を形成して作製することができる。また、複屈折性材料層４４の形成方法としては、構造複屈折又はフォトニック結晶を格子状に形成する方法により作製することも可能である。 Here, when the relationship between the refractive index n s ≒ n o, and n s ≠ n e, the light of the polarization component in the direction of the extraordinary refractive index of the slow axis direction of the polymer liquid crystal is diffracted, polymer The light of the polarization component in the direction of the ordinary refractive index that is the fast axis direction of the liquid crystal passes straight through without being diffracted. Such a polarizing diffraction grating 40 is formed by forming a polymer liquid crystal film on a transparent substrate 42 and then repeating photolithography and etching to form a birefringent material layer 44 made of polymer liquid crystal having a pseudo-blazed shape. After forming, an isotropic material layer 45 filled with an isotropic material as a filler can be formed between the transparent substrate 42 and the transparent substrate 43 to be manufactured. Further, as a method of forming the birefringent material layer 44, it is also possible to produce the birefringent material layer 44 by a method of forming a structural birefringence or a photonic crystal in a lattice shape.

波長板３０の第１の領域３１と第２の領域３２を透過する無偏光回折格子２０で分岐された２つの光に対して、偏光性回折格子４０における複屈折性材料層４４の凸状の格子パターン（格子ピッチおよび格子長手方向）が異なるように形成してもよい。ここで、無偏光回折格子２０および偏光性回折格子４０の格子パターンに応じて発生する４つの分岐光が集光する位置に光検出器６０の受光面を配置する。   With respect to two lights branched by the non-polarization diffraction grating 20 that transmits the first region 31 and the second region 32 of the wave plate 30, the convex shape of the birefringent material layer 44 in the polarization diffraction grating 40 You may form so that a grating | lattice pattern (grating pitch and a grating | lattice longitudinal direction) may differ. Here, the light receiving surface of the photodetector 60 is arranged at a position where four branched lights generated according to the grating patterns of the non-polarization diffraction grating 20 and the polarization diffraction grating 40 are condensed.

入射する光のうち互いに直交する偏光状態の光の進行方向を互いに異ならせるものであれば、偏光性回折格子４０の位置に偏光性回折格子４０の代わりに、偏光分離機能を有する素子を配置してもよい。   If the traveling directions of the polarized light beams that are orthogonal to each other are made different from each other in the incident light, an element having a polarization separation function is arranged in place of the polarizing diffraction grating 40 at the position of the polarizing diffraction grating 40. May be.

このような偏光分離機能素子の例として、複屈折材料のウォークオフを用いる偏光分離機能素子９０ａを図６に示す。図６においてＸ'軸は図３における４０ａ方向と直交した方向であり、Ｙ'軸は４０ａと同じ方向となっている。偏光分離機能素子９０ａは複屈折材料９１を用いており、その光学軸はＹ'軸からＹ'Ｚ面内で所定の角度となる方向を向いている。このような複屈折材料９１に対して光を入射すると、Ｘ'偏光方向の光とＹ'偏光方向の光でポインティングベクトルの方向が異なるいわゆるウォークオフが生じる。ウォークオフが生じることで、Ｘ'偏光方向の光とＹ'偏光方向の光を分離することができる。   As an example of such a polarization separation functional element, a polarization separation functional element 90a using a birefringent material walk-off is shown in FIG. In FIG. 6, the X ′ axis is a direction orthogonal to the 40a direction in FIG. 3, and the Y ′ axis is the same direction as 40a. The polarization separation functional element 90a uses a birefringent material 91, and its optical axis is oriented from the Y ′ axis in a direction that forms a predetermined angle in the Y′Z plane. When light is incident on such a birefringent material 91, a so-called walk-off occurs in which the pointing vector direction differs between light in the X ′ polarization direction and light in the Y ′ polarization direction. When the walk-off occurs, the light in the X ′ polarization direction and the light in the Y ′ polarization direction can be separated.

また、このような偏光分離機能素子の他の例として、複屈折材料の厚みに傾斜を持たせた偏光分離機能素子９０ｂを図７に示す。図７においてＸ'軸は、図３における４０ａ方向と直交した方向であり、Ｙ'軸は４０ａと同じ方向となっている。偏光分離機能素子９０ｂは複屈折材料９２を用いており、その光学軸はＸ'軸方向を向いている。また、複屈折材料９２はＹ'軸方向に厚みが傾斜している。このような複屈折材料９２に対して、光を入射すると複屈折材料９２の出射側の界面においてＸ'偏光方向の屈折率とＹ'偏光方向の屈折率が異なることで屈折角が変化し、Ｘ'偏光方向の光とＹ'偏光方向の光が異なる方向へ出射される。このようにしてＸ'偏光方向の光とＹ'偏光方向の光を分離することができる。   Further, as another example of such a polarization separation functional element, FIG. 7 shows a polarization separation functional element 90b in which the thickness of the birefringent material is inclined. In FIG. 7, the X ′ axis is a direction orthogonal to the 40a direction in FIG. 3, and the Y ′ axis is the same direction as 40a. The polarization separation functional element 90b uses a birefringent material 92, and its optical axis is in the X′-axis direction. The birefringent material 92 is inclined in the Y′-axis direction. When light is incident on such a birefringent material 92, the refractive angle changes due to the difference in the refractive index in the X ′ polarization direction and the refractive index in the Y ′ polarization direction at the output-side interface of the birefringent material 92. The light in the X ′ polarization direction and the light in the Y ′ polarization direction are emitted in different directions. In this way, light in the X ′ polarization direction and light in the Y ′ polarization direction can be separated.

また、このような偏光分離機能素子の他の例として、複屈折材料の厚みに傾斜を持たせた偏光分離機能素子９０ｃを図８に示す。図８において、Ｘ'軸は図３における４０ａ方向と直交した方向であり、Ｙ'軸は４０ａと同じ方向となっている。偏光分離機能素子９０ｃは複屈折材料９３を用いており、その光学軸はＸ'軸方向を向いている。また、複屈折材料９３はＹ'軸方向に厚みが傾斜しており、偏光分離機能素子９０ｃは等方性材料９４によって平坦化されている。このような偏光分離機能素子９０ｃに対して光を入射すると、複屈折材料９３と等方性材料９４の界面においてＸ'偏光方向の屈折率とＹ'偏光方向の屈折率が異なることで屈折角が変化し、Ｘ'偏光方向の光とＹ'偏光方向の光が異なる方向へ出射される。このようにしてＸ'偏光方向の光とＹ'偏光方向の光を分離することができる。   As another example of such a polarization separation functional element, FIG. 8 shows a polarization separation functional element 90c in which the thickness of the birefringent material is inclined. In FIG. 8, the X ′ axis is a direction orthogonal to the 40a direction in FIG. 3, and the Y ′ axis is the same direction as 40a. The polarization separation functional element 90c uses a birefringent material 93, and its optical axis faces the X′-axis direction. The birefringent material 93 is inclined in the Y′-axis direction, and the polarization separation functional element 90 c is flattened by the isotropic material 94. When light is incident on such a polarization separation functional element 90c, the refractive angle in the X ′ polarization direction is different from the refractive index in the Y ′ polarization direction at the interface between the birefringent material 93 and the isotropic material 94. Changes, and light in the X ′ polarization direction and light in the Y ′ polarization direction are emitted in different directions. In this way, light in the X ′ polarization direction and light in the Y ′ polarization direction can be separated.

図８では等方性材料９４と複屈折材料９３の光学軸方向の屈折率が一致した例を示しているが、このような場合に限らず等方性材料９４と複屈折材料９３の光学軸方向の屈折率が一致していない場合にも、等方性材料９４と複屈折材料９３の界面で２つの偏光方向の光が異なる方向に屈折させることが可能である。また、図８では、単一の鋸刃状の複屈折材料の形状としているが、これに限らず複数の鋸刃状の凹凸を有する複屈折材料の形状としてもよい。このようにすることで複屈折材料の厚みを小さくすることができる。   FIG. 8 shows an example in which the refractive indexes in the optical axis direction of the isotropic material 94 and the birefringent material 93 coincide with each other. However, the optical axis of the isotropic material 94 and the birefringent material 93 is not limited to this case. Even when the refractive indexes of the directions do not match, it is possible to refract light in two polarization directions in different directions at the interface between the isotropic material 94 and the birefringent material 93. Further, in FIG. 8, the shape of a single saw blade-shaped birefringent material is used, but the shape is not limited to this, and the shape of a birefringent material having a plurality of saw blade-shaped irregularities may be used. By doing so, the thickness of the birefringent material can be reduced.

複屈折材料９１、９２、９３として複屈折性を有する結晶を用いてもよい。また、有機材料を用いてもよく、フィルム材料や液晶材料を用いることができる。液晶材料を用いる場合、高分子液晶を用いると温度特性が安定化されるため好ましい。また、液晶材料を用いる場合、ガラスなど材料で作られたセルの内に液晶を封じたものであってもよい。このような場合、液晶材料の厚みや光学軸が図６から図８に示すようにすればよい。   As the birefringent materials 91, 92, 93, crystals having birefringence may be used. An organic material may be used, and a film material or a liquid crystal material can be used. When a liquid crystal material is used, it is preferable to use a polymer liquid crystal because temperature characteristics are stabilized. In the case where a liquid crystal material is used, the liquid crystal may be sealed in a cell made of a material such as glass. In such a case, the thickness of the liquid crystal material and the optical axis may be as shown in FIGS.

（偏光位相分離素子の入射角依存性）
次に、本実施の形態における偏光位相分離素子１０の入射角度依存性について説明する。図９は、本実施の形態における偏光位相分離素子１０の波長板３０の第２の領域３２において生じるｐ偏光とｓ偏光の位相差と、従来の偏光位相変換分離素子、即ち、特許文献１に記載されている偏光位相変換分離素子となる角度選択性偏光変換素子において生じるｐ偏光とｓ偏光の位相差とについて、入射角度依存性を計算した結果である。尚、計算方法は、４×４行列法を用い、入射角度は空気中からの入射を想定した角度を示している。 (Dependence on incident angle of polarization phase separation element)
Next, the incident angle dependency of the polarization phase separation element 10 in the present embodiment will be described. FIG. 9 shows the phase difference between p-polarized light and s-polarized light generated in the second region 32 of the wave plate 30 of the polarization phase separation element 10 according to the present embodiment, and the conventional polarization phase conversion separation element, that is, Patent Document 1. It is the result of having calculated the incident angle dependence about the phase difference of the p polarized light and s polarized light which arise in the angle selective polarization conversion element used as the polarization | polarized-light phase conversion separation element described. The calculation method uses a 4 × 4 matrix method, and the incident angle indicates an angle assuming incidence from the air.

従来の角度選択性偏光変換素子については、光学軸を光軸と一致させた水晶において計算を行ったものであり、水晶における常光屈折率を１．５５７、異常光屈折率を１．５６７とし、入射角度１０°で生じる位相差が、９０°となるように、厚さを０．８６ｍｍとして行った。一方、本実施の形態における波長板３０については、第２の領域３２に、水平配向している高分子液晶膜を形成した場合について、入射角度依存性の計算を行ったものであり、高分子液晶における常光屈折率を１．５１０、異常光屈折率を１．５５２とし、厚さを２．４μｍとして行った。   For a conventional angle selective polarization conversion element, the calculation was performed on a crystal whose optical axis coincided with the optical axis, and the ordinary light refractive index in the crystal was 1.557, the extraordinary light refractive index was 1.567, The thickness was 0.86 mm so that the phase difference generated at an incident angle of 10 ° was 90 °. On the other hand, with respect to the wave plate 30 in the present embodiment, the calculation of the incident angle dependence is performed for the case where a horizontally aligned polymer liquid crystal film is formed in the second region 32. The normal light refractive index in the liquid crystal was 1.510, the extraordinary light refractive index was 1.552, and the thickness was 2.4 μm.

図９に示されるように、本実施の形態における偏光位相分離素子１０の波長板３０では、入射角度が変化しても、出射される光のｓ偏光とｐ偏光との間に生じる位相差は略９０°で、殆ど変化しないのに対し、従来の偏光位相変換分離素子に用いられる角度選択性偏光変換素子では、入射角度が変化すると、出射される光の位相差も変化してしまう。   As shown in FIG. 9, in the wave plate 30 of the polarization phase separation element 10 in the present embodiment, even if the incident angle changes, the phase difference generated between the s-polarized light and the p-polarized light is In contrast to the angle selective polarization conversion element used in the conventional polarization phase conversion separation element, when the incident angle changes, the phase difference of the emitted light also changes.

このような入射角度に対する依存性の違いは、複屈折材料の光学軸の方向に依存している。波長板の光学軸が光軸と一致した方向を向いている場合、角度が変化することによって、屈折率楕円体の断面の形が変化し各偏光における屈折率が変化することにより、角度依存性を生じる。これに対して、本実施の形態における波長板の光学軸は、波長板面内を向いており、特に、入射光の入射方向のベクトルを波長板面内へ投影した場合に、投影されたベクトルの方向が光学軸と直交する方向になるようにしている。このように配置することで入射角度が変化した際にも屈折率楕円体の断面の形が変化しないため波長板によって生じる位相差の良好な角度依存性を得ることができる。   Such a difference in dependence on the incident angle depends on the direction of the optical axis of the birefringent material. When the optical axis of the wave plate is in the direction that coincides with the optical axis, the angle changes by changing the angle and changing the shape of the cross section of the refractive index ellipsoid. Produce. On the other hand, the optical axis of the wave plate in the present embodiment is oriented in the wave plate surface, and in particular, when the vector of the incident direction of incident light is projected into the wave plate surface, the projected vector Is set to be a direction orthogonal to the optical axis. By arranging in this way, the cross-sectional shape of the refractive index ellipsoid does not change even when the incident angle changes, so that it is possible to obtain good angular dependence of the phase difference caused by the wave plate.

このように、本実施の形態において用いられる波長板３０は、従来の角度選択性偏光変換素子に比べ、光の入射角度依存性が極めて低く、光学設計の自由度が大きく、製造のバラツキにより光学特性が大きく変化することも少ない。   As described above, the wave plate 30 used in the present embodiment has extremely low dependency on the incident angle of light compared to the conventional angle-selective polarization conversion element, has a large degree of freedom in optical design, and is optical due to manufacturing variations. The characteristics do not change significantly.

次に、無偏光回折格子２０の回折光の進行方向と偏光性回折格子４０の回折光の進行方向とが同一方向とならないように、偏光位相分離素子における偏光性回折格子の複屈折性材料層４４からなる凸状部分の長手方向が、無偏光回折格子２０の格子長手方向であるＸ軸方向と角度をなすように形成された偏光位相分離素子について、図１０に示す偏光位相分離素子１１の構成図を用いて説明する。   Next, the birefringent material layer of the polarizing diffraction grating in the polarization phase separation element is set so that the traveling direction of the diffracted light of the non-polarizing diffraction grating 20 and the traveling direction of the diffracted light of the polarizing diffraction grating 40 are not the same direction. For the polarization phase separation element formed so that the longitudinal direction of the convex portion made of 44 forms an angle with the X-axis direction that is the grating longitudinal direction of the non-polarization diffraction grating 20, the polarization phase separation element 11 shown in FIG. This will be described with reference to the configuration diagram.

偏光位相分離素子１０と偏光位相分離素子１１の相違点は、偏光性回折格子４１の複屈折性材料層４４からなる凸状部分の長手方向のみで、他の構成は同じである。その結果、入射光５０が無偏光回折格子２０により回折され、２つの光５１ａ及び５１ｂとなって進行し、偏光性回折格子４１により回折されないで直進透過する偏光成分の透過光である光５３ａ及び５３ｃに対し、偏光性回折格子４１により回折される偏光成分の＋１次回折光である光５３ｂ及び５３ｄの光軸は、光５３ａ及び５３ｃの分岐光の光軸で規定される平面内には存在しない。   The difference between the polarization phase separation element 10 and the polarization phase separation element 11 is only in the longitudinal direction of the convex portion made of the birefringent material layer 44 of the polarizing diffraction grating 41, and the other configurations are the same. As a result, the incident light 50 is diffracted by the non-polarization diffraction grating 20, travels as two lights 51a and 51b, and is transmitted through a polarized light component 53a and 51a and 51b that is not diffracted by the polarizing diffraction grating 41 and passes straight. With respect to 53c, the optical axes of the light components 53b and 53d, which are the + 1st order diffracted light components of the polarization component diffracted by the polarizing diffraction grating 41, do not exist in the plane defined by the optical axes of the branched light beams 53a and 53c. .

理想的ブレーズ形状に作製された場合を除き、回折素子の入射光は複数の回折次数に対応する回折角度に回折光が発生する。無偏光回折格子２０では、信号検出目的の±１次回折光以外の回折光が発生する。また、偏光性回折格子４１では、信号検出目的の光は複屈折性材料層４４の光学軸４０ａに平行な直線偏光で発生する＋１次回折光と、光学軸４０ａに直交する直線偏光の０次回折光だが、それぞれの＋１次回折光および０次回折光以外の回折光が製造ばらつきなどに起因して発生する。このような不要な回折光が光検出器の受光面に入射すると信号のＳ／Ｎ比低下となる。特に、無偏光回折格子の透過・回折光と偏光性回折格子の透過・回折光の多重透過・回折光が多数発生するため、迷光化しやすい。   Except for the case where it is fabricated in an ideal blazed shape, the incident light of the diffractive element generates diffracted light at diffraction angles corresponding to a plurality of diffraction orders. The non-polarized diffraction grating 20 generates diffracted light other than ± first-order diffracted light for signal detection purposes. In the polarizing diffraction grating 41, the light for signal detection is + 1st order diffracted light generated by linearly polarized light parallel to the optical axis 40a of the birefringent material layer 44, and 0th order diffracted light of linearly polarized light orthogonal to the optical axis 40a. However, diffracted lights other than the + 1st order diffracted light and the 0th order diffracted light are generated due to manufacturing variations. When such unnecessary diffracted light is incident on the light receiving surface of the photodetector, the S / N ratio of the signal is lowered. In particular, a large number of multiple transmitted / diffracted light beams are generated, that is, transmitted / diffracted light of the non-polarized diffraction grating and transmitted / diffracted light of the polarizing diffraction grating, and therefore, stray light is easily generated.

しかし、偏光位相分離素子１１では、無偏光回折格子２０の透過・回折光の方向と偏光性回折格子４１の透過・回折光の方向が異なるため、４つの分岐された信号光である光５３ａ、５３ｂ、５３ｃ、５３ｄの集光位置にそれぞれ配置された光検出器６０ａ、６０ｂ、６０ｃ、６０ｄの受光面には発生した迷光が混入しない。その結果、光信号情報を高いＳ／Ｎ比を維持して電気信号情報に変換され、高精度の強度変調情報および位相変調情報が検知できる。尚、偏光位相分離素子１１は、図２及び図３において、偏光位相分離素子１０に代えて用いることができる。   However, in the polarization phase separation element 11, since the direction of the transmitted / diffracted light of the non-polarized diffraction grating 20 and the direction of the transmitted / diffracted light of the polarizing diffraction grating 41 are different, the light 53a that is four branched signal lights, The generated stray light is not mixed in the light receiving surfaces of the photodetectors 60a, 60b, 60c, and 60d arranged at the condensing positions of 53b, 53c, and 53d, respectively. As a result, optical signal information is converted to electrical signal information while maintaining a high S / N ratio, and highly accurate intensity modulation information and phase modulation information can be detected. The polarization phase separation element 11 can be used in place of the polarization phase separation element 10 in FIGS.

〔第２の実施の形態〕
次に、第２の実施の形態における光受信装置について説明する。図１１は、本実施の形態における光受信装置の構成図である。本実施の形態における光受信装置２００において、光受信部１００ａと光受信部１００ｂの部分は図２に示す第１の実施の形態の光受信装置１００とほぼ同じ構成であるため説明を省略する。 [Second Embodiment]
Next, an optical receiver in the second embodiment will be described. FIG. 11 is a configuration diagram of the optical receiver in this embodiment. In the optical receiver 200 according to the present embodiment, the optical receiver 100a and the optical receiver 100b have substantially the same configuration as the optical receiver 100 according to the first embodiment shown in FIG.

光ファイバー等の光伝送部２７１より強度変調および位相変調された光情報を含む信号光Ｓが発散光２５２となって出射し、集光レンズ２８３により平行光となる。この信号光Ｓは、光ファイバー伝送中に偏光状態が変化し、図１１においてＹ軸方向の直線偏光であるｐ偏光成分とＸ軸方向の直線偏光であるｓ偏光成分が位相差を有して合成された楕円偏光となっている。   The signal light S including the optical information subjected to intensity modulation and phase modulation is emitted as divergent light 252 from the optical transmission unit 271 such as an optical fiber, and becomes parallel light by the condenser lens 283. The polarization state of the signal light S changes during optical fiber transmission. In FIG. 11, the p-polarized component that is linearly polarized in the Y-axis direction and the s-polarized component that is linearly polarized in the X-axis direction have a phase difference. It becomes the elliptically polarized light.

信号光Ｓのｐ偏光成分Ｓｂは、ＰＢＳ２９３を透過し、ホモダイン検出部である光受信部１００ｂに入射する。一方、信号光Ｓのｓ偏光成分Ｓａは、ＰＢＳ２９３およびＰＢＳ２９２で反射された後、ホモダイン検出部である光受信部１００ａに入射する。   The p-polarized component Sb of the signal light S passes through the PBS 293 and enters the light receiving unit 100b that is a homodyne detection unit. On the other hand, the s-polarized component Sa of the signal light S is reflected by the PBS 293 and the PBS 292 and then enters the optical receiving unit 100a which is a homodyne detection unit.

信号光Ｓと同一波長で直線偏光の参照光Ｒは、可干渉長が長く狭い発振波長幅の局部発振光源であるレーザ光源２７２を用いて生成され、図１１のＸ−Ｙ平面内でＸ軸方向に対して４５°傾斜した直線偏光の発散光２５１となって出射する。集光レンズ２８１により平行光となった参照光Ｒは同じ振幅比率のＸ軸およびＹ軸方向の偏光成分を有し、Ｙ軸方向の直線偏光であるｐ偏光成分Ｒａは、ＰＢＳ２９１およびＰＢＳ２９２を透過し、ホモダイン検出部である光受信部１００ａに入射する。一方、Ｘ軸方向の直線偏光であるｓ偏光成分Ｒｂは、ＰＢＳ２９１および１８０°光路を切り替える全反射プリズム２９４で全反射され、ＰＢＳ２９３で反射された後、ホモダイン検出部である光受信部１００ｂに入射する。   The reference light R having the same wavelength as that of the signal light S and linearly polarized light is generated by using a laser light source 272 that is a local oscillation light source having a long coherence length and a narrow oscillation wavelength width, and the X axis in the XY plane of FIG. The light is emitted as linearly polarized divergent light 251 inclined by 45 ° with respect to the direction. The reference light R converted into parallel light by the condenser lens 281 has a polarization component in the X-axis and Y-axis directions having the same amplitude ratio, and the p-polarization component Ra that is linearly polarized light in the Y-axis direction passes through the PBS 291 and the PBS 292 Then, the light is incident on the optical receiver 100a which is a homodyne detector. On the other hand, the s-polarized component Rb, which is linearly polarized light in the X-axis direction, is totally reflected by the PBS 291 and the total reflection prism 294 that switches the optical path of 180 °, is reflected by the PBS 293, and then enters the light receiving unit 100b that is a homodyne detection unit. To do.

尚、光受信部１００ａに入射した光は複数の光受光面を有する光検出器２６１ａにより検出され、光受信部１００ｂに入射した光は複数の光受光面を有する光検出器２６１ｂにより検出される。   The light incident on the light receiving unit 100a is detected by a photodetector 261a having a plurality of light receiving surfaces, and the light incident on the light receiving unit 100b is detected by a light detector 261b having a plurality of light receiving surfaces. .

図２に示した第１の実施の形態に比べ、光受信装置内にホモダイン検出に必用な参照光を生成するレーザ光源２７２を備え、外部からの信号光入力のみで、部品点数が少なく小型・軽量の９０°光ハイブリッド位相ダイバーシティ・ホモダイン光受信装置を実現できる。また、信号光の偏光状態が伝送中に変化し、光検出器２６１ａ及び２６１ｂで検知される信号光強度が変化しても、合算信号強度の変動は無いため、偏波ダイバーシティ検出となっている。尚、上記以外の内容については、第１の実施の形態と同様である。   Compared to the first embodiment shown in FIG. 2, a laser light source 272 that generates reference light necessary for homodyne detection is provided in the optical receiver, and the number of components is small with only signal light input from the outside. A lightweight 90 ° optical hybrid phase diversity homodyne optical receiver can be realized. In addition, even if the polarization state of the signal light changes during transmission and the signal light intensity detected by the photodetectors 261a and 261b changes, there is no fluctuation in the combined signal intensity, so polarization diversity detection is performed. . The contents other than the above are the same as in the first embodiment.

（実施例１）
実施例として、第１の実施の形態における光受信装置について説明する。本実施例における光受信装置は、図２に示されるようにＷＤＭ光通信におけるＣバンド波長帯の９０°光ハイブリッド位相ダイバーシティ・ホモダイン光受信装置となる光受信装置１００である。 Example 1
As an example, the optical receiver in the first embodiment will be described. The optical receiver in the present embodiment is an optical receiver 100 serving as a 90 ° optical hybrid phase diversity homodyne optical receiver in the C-band wavelength band in WDM optical communication as shown in FIG.

信号光Ｓおよび参照光Ｒの波長を１５４５ｎｍ、入射側および出射側ＮＡが約０．１２で有効径が約１ｍｍの集光レンズ８０、偏光位相分離素子１１、光検出器６０をこの順番に配置する。集光レンズ８０と偏光位相分離素子１１および光検出器６０との間隔は、それぞれ約０．５ｍｍと４．５ｍｍとする。偏光位相分離素子１１は図１０に示す構成および機能を有する。   The condensing lens 80, the polarization phase separation element 11, and the photodetector 60 having a wavelength of the signal light S and the reference light R of 1545 nm, an incident side and an output side NA of about 0.12, and an effective diameter of about 1 mm are arranged in this order. To do. The intervals between the condenser lens 80, the polarization phase separation element 11, and the photodetector 60 are about 0.5 mm and 4.5 mm, respectively. The polarization phase separation element 11 has the configuration and function shown in FIG.

無偏光回折格子２０は、厚さ２ｍｍの石英ガラス基板の平面上に、Ｘ軸方向が長手方向でＹ軸方向に周期的な凹凸加工を行った回折格子であり、周期的な凹凸構造のピッチが３μｍ、凹凸の深さが約１.７６μｍとなるように加工する。石英ガラスの屈折率を１．４４とすると、波長１５４５ｎｍの光に対して、Ｙ軸方向に±１次回折光が発生しその効率は約４０％、０次回折効率は約０％となる。±１次回折光の光線を追跡すると、厚さ２ｍｍの石英ガラス基板を通過後、＋１次回折光と−１次回折光は空間的に重ならない。   The non-polarized diffraction grating 20 is a diffraction grating obtained by performing periodic uneven processing on the plane of a quartz glass substrate having a thickness of 2 mm and having a longitudinal direction in the X-axis direction and a periodic direction in the Y-axis direction. Is processed to be 3 μm and the depth of the unevenness is about 1.76 μm. When the refractive index of quartz glass is 1.44, ± 1st order diffracted light is generated in the Y-axis direction with respect to light having a wavelength of 1545 nm, and its efficiency is about 40%, and the 0th order diffraction efficiency is about 0%. When the light beam of ± first-order diffracted light is traced, the + 1st-order diffracted light and the −1st-order diffracted light do not overlap spatially after passing through a quartz glass substrate having a thickness of 2 mm.

波長板３０は図４（ｂ）の波長板３０ｂと同様の構造を有しており、厚さ０．３ｍｍの一対の石英ガラス基板で高分子液晶を挟持した構造となっている。一対の石英ガラス基板は第１の領域３１ｂ、第２の領域３２ｂに対してそれぞれ垂直配向処理、Ｘ方向が異常光方向となるような水平配向処理がなされ、配向処理を施した平面を対向させるように重ね、その空隙を液晶で満たすようにする。高分子液晶の異常光屈折率を１．６５、常光屈折率を１．５３とし、高分子液晶の厚さを約３．２２μｍとする。このとき垂直配向をした第１の領域３１ｂではＸ軸方向とＹ軸方向の直線偏光に対して位相差が発生せずに、第２の領域３２ｂではＸ軸方向とＹ軸方向の直線偏光に対して約１８０°の位相差が発生する。第１の領域３１ｂには無偏光回折格子による＋１次回折光が入射し、第２の領域３２ｂには−１次回折光が入射するので、−１次回折光はＸ軸方向とＹ軸方向の直線偏光に対して約１８０°の位相差が与えられる。   The wave plate 30 has the same structure as the wave plate 30b of FIG. 4B, and has a structure in which a polymer liquid crystal is sandwiched between a pair of quartz glass substrates having a thickness of 0.3 mm. The pair of quartz glass substrates are subjected to a vertical alignment process for the first region 31b and the second region 32b, respectively, and a horizontal alignment process in which the X direction becomes the extraordinary light direction, and the planes subjected to the alignment process are opposed to each other. So that the gap is filled with liquid crystal. The extraordinary refractive index of the polymer liquid crystal is 1.65, the ordinary light refractive index is 1.53, and the thickness of the polymer liquid crystal is about 3.22 μm. At this time, in the first region 31b which is vertically aligned, no phase difference is generated with respect to the linearly polarized light in the X-axis direction and the Y-axis direction, and in the second region 32b, the linearly polarized light in the X-axis direction and the Y-axis direction On the other hand, a phase difference of about 180 ° is generated. Since the + 1st order diffracted light from the non-polarized diffraction grating is incident on the first region 31b and the -1st order diffracted light is incident on the second region 32b, the -1st order diffracted light is linearly polarized in the X-axis direction and the Y-axis direction. Is given a phase difference of about 180 °.

偏光性回折格子４０は厚さ０．３ｍｍの石英ガラス基板のＸ−Ｙ平面上でＸ軸方向から４５度方向に配向した高分子液晶を１６段の擬似ブレーズ形状とし、充填材によって厚さ０．３ｍｍの石英ガラス基板と貼り合わせる。高分子液晶の異常光屈折率を１．６５、常光屈折率を１．５３、充填材の屈折率を１．５３とする。ブレーズ形状は長手方向がＹ軸方向で、Ｘ軸方向に対して周期的に配置され、回折格子ピッチは１０μｍ、ブレーズの各段の高さは約０．８μｍである。ＲＣＷＡ（Rigorous Coupled Wave Analysis）法によって回折効率を計算すると、常光屈折率となる方向の直線偏光が入射した場合には回折せずに直進透過し、異常光屈折率となる方向の直線偏光が入射した場合にはＸ軸方向に＋１次回折光が発生しその効率が約９２％となる。   The polarizing diffraction grating 40 is a 16-stage quasi-blazed polymer liquid crystal oriented in the 45-degree direction from the X-axis direction on the XY plane of a quartz glass substrate having a thickness of 0.3 mm. . Laminated with a 3 mm quartz glass substrate. The extraordinary light refractive index of the polymer liquid crystal is 1.65, the ordinary light refractive index is 1.53, and the refractive index of the filler is 1.53. The blaze shape has a longitudinal direction in the Y-axis direction and is periodically arranged with respect to the X-axis direction, the diffraction grating pitch is 10 μm, and the height of each stage of the blaze is about 0.8 μm. When the diffraction efficiency is calculated by the RCWA (Rigorous Coupled Wave Analysis) method, when linearly polarized light in the direction of ordinary light refractive index is incident, it is transmitted straight without being diffracted, and linearly polarized light in the direction of abnormal light refractive index is incident. In this case, + 1st order diffracted light is generated in the X-axis direction, and the efficiency is about 92%.

無偏光回折格子２０、波長板３０および偏光性回折格子４０を光入射側よりこの順番で一体化し、素子厚約３．２ｍｍの偏光位相分離素子１１を作製する。   The non-polarization diffraction grating 20, the wave plate 30, and the polarization diffraction grating 40 are integrated in this order from the light incident side, and the polarization phase separation element 11 having an element thickness of about 3.2 mm is manufactured.

以上のように偏光位相分離素子１１に入射した入射光５０は４つの光束となる光５３ａ、５３ｂ、５３ｃ、５３ｄに分岐され、光検出器６０（６０ａ、６０ｂ、６０ｃ、６０ｄ）の各受光面に集光される。無偏光回折格子２０の他の回折光、偏光性回折格子４０の他の回折光およびそれらの多重回折光は、光検出器６０の受光面と異なる位置に集光されるため、信号検出目的の光のＳ／Ｎ比低下につながる迷光とはならない。   As described above, the incident light 50 incident on the polarization phase separation element 11 is branched into four light beams 53a, 53b, 53c, and 53d, and each light receiving surface of the photodetector 60 (60a, 60b, 60c, 60d). It is focused on. Since the other diffracted light of the non-polarized diffraction grating 20, the other diffracted light of the polarizing diffraction grating 40 and the multiple diffracted lights thereof are condensed at a position different from the light receiving surface of the photodetector 60, It is not stray light that leads to a decrease in the S / N ratio of light.

光検出器６０により電気信号に変換された光信号強度Ｉ４、Ｉ５、Ｉ６及びＩ７を実施の形態で説明した方法で、Ｉ４−Ｉ５及びＩ７−Ｉ６の演算を行うことにより、Ｓｉｇ１＝Ｉ４−Ｉ５＝ＡｃｏｓΔφ、Ｓｉｇ２＝Ｉ７−Ｉ６＝ＡｓｉｎΔφとなる。その結果、信号光Ｓの信号強度が参照光ＲによりＡ倍に増幅され、参照光Ｒに対する信号光Ｓの位相差△φの値を検知できる。即ち、デジタルコヒーレント光伝送で有効な９０°光ハイブリッド位相ダイバーシティ・ホモダイン光受信装置において、高いＳ／Ｎ比で光強度情報と位相情報を検知できる小型で組立等の製造が容易な光受信装置となる。 The optical signal intensities I 4 , I 5 , I 6 and I 7 converted into electric signals by the photodetector 60 are calculated using the method described in the embodiment, and I 4 -I 5 and I 7 -I 6 are calculated. Thus, Sig1 = I 4 −I 5 = AcosΔφ and Sig2 = I 7 −I 6 = AsinΔφ. As a result, the signal intensity of the signal light S is amplified A times by the reference light R, and the value of the phase difference Δφ of the signal light S with respect to the reference light R can be detected. That is, in a 90 ° optical hybrid phase diversity homodyne optical receiver that is effective in digital coherent optical transmission, an optical receiver that can detect light intensity information and phase information with a high S / N ratio and is easy to manufacture. Become.

本実施の形態における光受信装置に用いられる偏光位相分離素子として、無偏光分岐部が無偏光回折格子からなり、偏光性分岐部が偏光性回折格子からなる構成例について説明したが、他の光学素子を用いてもよい。例えば、無偏光回折格子の代わりに入射面で空間２分割された断面が二等辺三角形の三角柱プリズムを用い、入射角の異なるプリズム斜面の屈折を利用して入射光を２方向に分岐してもよい。また、偏光性回折格子の代わりにウオラストンプリズム、グラントムソンプリズムなどの複屈折結晶を用いて入射直交偏光を分岐してもよい。   As the polarization phase separation element used in the optical receiver according to the present embodiment, the configuration example in which the non-polarization branch portion is made of a non-polarization diffraction grating and the polarization branch portion is made of a polarization diffraction grating has been described. An element may be used. For example, instead of a non-polarized diffraction grating, a triangular prism having a section of isosceles triangle divided into two spaces on the incident surface may be used, and incident light may be branched in two directions using refraction of prism slopes having different incident angles. Good. Further, the incident orthogonal polarization may be branched using a birefringent crystal such as a Wollaston prism or a Glan-Thompson prism instead of the polarizing diffraction grating.

（実施例２）
実施例２の光受信装置は実施例１の無偏光回折格子２０のみを変更したものであり、その他の構成については実施例１と同じものである。 (Example 2)
The optical receiver according to the second embodiment is obtained by changing only the non-polarized diffraction grating 20 according to the first embodiment, and the other configurations are the same as those of the first embodiment.

無偏光回折格子２０は、厚さ０．５ｍｍの石英ガラス基板の平面上に、Ｘ軸方向が長手方向でＹ軸方向に周期的な凹凸加工を行った回折格子であり、周期的な凹凸構造のピッチが１．９μｍ、凹凸の深さが約１.７６μｍとなるように加工する。石英ガラスの屈折率を１．４４とすると、波長１５４５ｎｍの光に対して、Ｙ軸方向に±１次回折光が発生しその効率は約４０％、０次回折効率は約０％となる。無偏光回折格子２０と波長板３０の間が空気となるように１．５ｍｍの間隔となるように設置する。このようにすることで無偏光回折格子２０の回折部と波長板３０の波長板部の平均的な屈折率を（０．５×１．４４＋１．５×１＋０．３×１．４４）／２．３＝１．１５と小さくすることができる。±１次回折光の光線を追跡すると、厚さ２ｍｍの石英ガラス基板を通過後、＋１次回折光と−１次回折光は空間的に重ならない。   The non-polarized diffraction grating 20 is a diffraction grating obtained by performing periodic uneven processing on the plane of a quartz glass substrate having a thickness of 0.5 mm and having a longitudinal direction in the X-axis direction and a periodic direction in the Y-axis direction. Is processed so that the pitch of 1.9 is 1.9 μm and the depth of the unevenness is about 1.76 μm. When the refractive index of quartz glass is 1.44, ± 1st order diffracted light is generated in the Y-axis direction with respect to light having a wavelength of 1545 nm, and its efficiency is about 40%, and the 0th order diffraction efficiency is about 0%. The non-polarized diffraction grating 20 and the wave plate 30 are installed so as to have an interval of 1.5 mm so as to be air. In this way, the average refractive index of the diffraction part of the non-polarization diffraction grating 20 and the wave plate part of the wave plate 30 is (0.5 × 1.44 + 1.5 × 1 + 0.3 × 1.44) / 2. .3 = 1.15. When the light beam of ± first-order diffracted light is traced, the + 1st-order diffracted light and the −1st-order diffracted light do not overlap spatially after passing through a quartz glass substrate having a thickness of 2 mm.

以上、本発明の実施に係る形態について説明したが、上記内容は、発明の内容を限定するものではない。   As mentioned above, although the form which concerns on implementation of this invention was demonstrated, the said content does not limit the content of invention.

１０、１０ａ、１０ｂ、１１ 偏光位相分離素子
２０ 無偏光回折格子
３０、３０ａ、３０ｂ、３０ｃ 波長板
３１、３１ａ、３１ｂ、３１ｃ 第１の領域
３２、３２ａ、３２ｂ、３２ｃ 第２の領域
３３ａ 等方性材料
３３ｂ 高分子液晶（垂直配向）
３４ａ、３４ｂ 高分子液晶
４０、４１ 偏光性回折格子
４０ａ 光学軸
４２、４３ 透明基板
４４ 複屈折性材料層
４５ 等方性材料層
５０ 入射光
５１ａ、５１ｂ、５２ａ、５２ｂ、５３ａ、５３ｂ、５３ｃ、５３ｄ 光
６０、６０ａ、６０ｂ、６０ｃ、６０ｄ、２６１ａ、２６１ｂ 光検出器
７０、２７１ 光伝送部
８０、２８１、２８２、２８３、２８４ 集光レンズ
９０ａ、９０ｂ、９０ｃ 偏光分離機能素子
９１、９２、９３ 複屈折材料
９４ 等方性材料
１００、２００ 光受信装置
２５１、２５２ 発散光
２７２ レーザ光源
２９１、２９２、２９３ 偏光ビームスプリッタ（ＰＢＳ）
２９４ 全反射プリズム
Ｓ、Ｓａ、Ｓｂ 信号光
Ｒ、Ｒａ、Ｒｂ 参照光 10, 10a, 10b, 11 Polarization phase separation element 20 Non-polarization diffraction grating 30, 30a, 30b, 30c Wave plate 31, 31a, 31b, 31c First region 32, 32a, 32b, 32c Second region 33a Material 33b Polymer liquid crystal (vertical alignment)
34a, 34b Polymer liquid crystals 40, 41 Polarizing diffraction grating 40a Optical axes 42, 43 Transparent substrate 44 Birefringent material layer 45 Isotropic material layer 50 Incident light 51a, 51b, 52a, 52b, 53a, 53b, 53c, 53d Light 60, 60a, 60b, 60c, 60d, 261a, 261b Photodetector 70, 271 Optical transmission unit 80, 281, 282, 283, 284 Condensing lenses 90a, 90b, 90c Polarization separation functional elements 91, 92, 93 Birefringent material 94 Isotropic material 100, 200 Optical receiver 251 252 Diverging light 272 Laser light source 291 292 293 Polarized beam splitter (PBS)
294 Total reflection prism S, Sa, Sb Signal light R, Ra, Rb Reference light

Claims (9)

直線偏光の光であるｓ偏光の光と、前記ｓ偏光の光と直交するｐ偏光の光とが含まれる入射光を、２つの進行方向に分岐する無偏光分岐部と、
前記無偏光分岐部により分岐された２つの光のうち、一方の光に対して位相差を与えず、他方の光に対してのみ、前記ｓ偏光の光と前記ｐ偏光の光との間で、９０°の奇数倍に略等しい位相差を与えるように、厚さ方向に光学軸が揃った複屈折性材料を有する波長板と、
９０°の奇数倍に略等しい位相差を与えられた光を含む２つの光が入射し、互いに直交する、第１の直線偏光の光と第２の直線偏光の光毎、２つの進行方向に分岐する偏光性分岐部と、
前記無偏光分岐部及び前記偏光性分岐部により４つに分岐された光の各々を受光する４つの光検出器と、
を備え、
前記無偏光分岐部は無偏光回折格子であって、入射光の＋１次回折光と−１次回折光を２つの進行方向に分岐された光とすることを特徴とする光受信装置。 A non-polarization branching unit that branches incident light including s-polarized light that is linearly polarized light and p-polarized light orthogonal to the s-polarized light in two traveling directions;
Of the two lights branched by the non-polarization branching section, no phase difference is given to one light, and only the other light is between the s-polarized light and the p-polarized light. A wave plate having a birefringent material with optical axes aligned in the thickness direction so as to give a phase difference substantially equal to an odd multiple of 90 °,
Two light beams including light having a phase difference substantially equal to an odd multiple of 90 ° are incident and are orthogonal to each other, in each of the first linearly polarized light and the second linearly polarized light, in two traveling directions. A polarizing branch that branches;
Four photodetectors for receiving each of the light branched into four by the non-polarization branching unit and the polarizing branching unit;
Equipped with a,
The non-polarization branching unit is a non-polarization diffraction grating, and is a light receiving device characterized in that the + 1st order diffracted light and the −1st order diffracted light of the incident light are branched into two traveling directions . 前記入射光は、同じ波長の信号光と参照光を含むものであって、前記無偏光分岐部と、波長板と、偏光性分岐部とにより形成される偏光位相分離素子により前記入射光が分岐されるものであることを特徴とする請求項１に記載の光受信装置。   The incident light includes signal light and reference light having the same wavelength, and the incident light is branched by a polarization phase separation element formed by the non-polarization branching unit, the wave plate, and the polarizing branching unit. The optical receiver according to claim 1, wherein 互いに直交するｓ偏光の光とｐ偏光の光を合波させる偏光ビームスプリッタを備え、異なる方向から入射する前記信号光と参照光を偏光ビームスプリッタにより合波することにより前記偏光位相分離素子への入射光を生成することを特徴とする請求項２に記載の光受信装置。 A polarization beam splitter that combines s-polarized light and p-polarized light that are orthogonal to each other, and combines the signal light and the reference light incident from different directions by the polarization beam splitter, to the polarization phase separation element. The optical receiver according to claim 2 , wherein incident light is generated. 前記無偏光分岐部により分岐された２つの光の分岐方向と前記偏光性分岐部により分岐された光の分岐方向とが所定の角度を成すように構成されていることを特徴とする請求項１から３のいずれかに記載の光受信装置。 2. The branching direction of the two lights branched by the non-polarization branching part and the branching direction of the light branched by the polarizing branching part are configured to form a predetermined angle. 4. The optical receiver according to any one of items 1 to 3 . 前記偏光性分岐部は偏光性回折格子であって、入射光の常光偏光成分を回折せず透過するとともに異常光偏光成分を回折する、または、入射光の異常光偏光成分を回折せず透過するとともに常光偏光成分を回折することを特徴とする請求項１から４のいずれかに記載の光受信装置。   The polarizing branch is a polarizing diffraction grating, which transmits the ordinary light polarization component of incident light without diffracting and diffracts the extraordinary light polarization component, or transmits the extraordinary light polarization component of incident light without diffracting it. The optical receiver according to any one of claims 1 to 4, wherein the optically polarized component is diffracted together. 前記偏光性回折格子は、光学軸が厚さ方向に揃い、常光屈折率ｎｏと異常光屈折率ｎｅ（ｎｏ≠ｎｅ）を有する複屈折性材料からなる複屈折性材料層および、屈折率がｎｓとなる等方性材料からなる等方性材料層によって周期的凹凸が形成され、前記屈折率ｎｓは、前記常光屈折率ｎｏまたは前記異常光屈折率ｎｅと略等しく、前記複屈折性材料層の光学軸の方向と、前記波長板の光学軸の方向とが、略４５°の角度をなすことを特徴とする請求項５に記載の光受信装置。 The polarizing diffraction grating, aligned in the thickness direction is the optical axis, the ordinary refractive index n o and the birefringent material layer made of a birefringent material having an extraordinary refractive index n e (n o ≠ n e ) and, periodic unevenness is formed by isotropic material layer having a refractive index consisting of isotropic material as a n s, a refractive index n s is substantially equal to the ordinary refractive index n o or the extraordinary refractive index n e 6. The optical receiver according to claim 5, wherein an optical axis direction of the birefringent material layer and an optical axis direction of the wave plate form an angle of about 45 degrees. 前記無偏光回折格子の格子長手方向と前記偏光性回折格子の格子長手方向とが所定の角度をなすことを特徴とする請求項５または６に記載の光受信装置。   7. The optical receiver according to claim 5, wherein the longitudinal direction of the non-polarized diffraction grating and the longitudinal direction of the polarizing diffraction grating form a predetermined angle. 前記波長板は、前記ｓ偏光の光と前記ｐ偏光の光との間で、位相差を与えない第１の領域と、前記ｓ偏光の光と前記ｐ偏光の光との間で、９０°の奇数倍に略等しい位相差を与える第２の領域を有し、前記第２の領域にのみ、高分子液晶を有することを特徴とする請求項１から７のいずれかに記載の光受信装置。   The wave plate is 90 ° between the first region that does not give a phase difference between the s-polarized light and the p-polarized light, and between the s-polarized light and the p-polarized light. The optical receiver according to claim 1, further comprising: a second region that gives a phase difference that is substantially equal to an odd multiple of, and a polymer liquid crystal only in the second region. . 前記波長板は、前記ｓ偏光の光と前記ｐ偏光の光との間で、位相差を与えない第１の領域と、前記ｓ偏光の光と前記ｐ偏光の光との間で、９０°の奇数倍に略等しい位相差を与える第２の領域を有し、前記第１の領域および前記第２の領域は、いずれも高分子液晶を有し、前記第１の領域における高分子液晶は厚さ方向に略平行に配向されることを特徴とする請求項１から７のいずれかに記載の光受信装置。   The wave plate is 90 ° between the first region that does not give a phase difference between the s-polarized light and the p-polarized light, and between the s-polarized light and the p-polarized light. A second region that gives a phase difference substantially equal to an odd multiple of the first region, the first region and the second region both have a polymer liquid crystal, and the polymer liquid crystal in the first region is The optical receiver according to any one of claims 1 to 7, wherein the optical receiver is oriented substantially parallel to the thickness direction.
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