JP2006065089A - Optical directional coupler and wavelength-independent coupler - Google Patents

Optical directional coupler and wavelength-independent coupler Download PDF

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JP2006065089A
JP2006065089A JP2004248810A JP2004248810A JP2006065089A JP 2006065089 A JP2006065089 A JP 2006065089A JP 2004248810 A JP2004248810 A JP 2004248810A JP 2004248810 A JP2004248810 A JP 2004248810A JP 2006065089 A JP2006065089 A JP 2006065089A
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optical
wavelength
waveguide
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directional coupler
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Masaya Suzuki
賢哉 鈴木
Toshimi Kominato
俊海 小湊
Yasuyuki Inoue
靖之 井上
Akio Sugita
彰夫 杉田
Yoshinori Hibino
善典 日比野
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Nippon Telegraph and Telephone Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical directional coupler and a wavelength-independent coupler having a large allowable range for manufacture errors including changes in the optical waveguide width as a main cause of decrease in yield and changes in the relative refractive index in the optical waveguide. <P>SOLUTION: The wavelength-independent coupler is composed of a Mach-Zehnder interferometer comprising two optical directional couplers each having two optical waveguides and two optical waveguides of different lengths connecting the above two optical directional couplers. Each of the two optical directional couplers has zero length of a straight portion in the optical coupling region to induce optical coupling, and the width of the optical waveguide and the gap between the optical waveguides in the optical coupling region are determined so as to obtain the intensity of exiting light independent from the wavelength of incident light. The two optical waveguides are formed as tapered to be thinner from the input end to the optical coupling region where optical coupling is induced, and tapered to be wider from the optical coupling region to the output end. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、光方向性結合器および波長無依存カプラに関し、より詳細には、光ファイバ通信において用いられる光方向性結合器および波長無依存カプラに関する。   The present invention relates to an optical directional coupler and a wavelength-independent coupler, and more particularly to an optical directional coupler and a wavelength-independent coupler used in optical fiber communication.

通信の高速化、大容量化において光通信は最も期待される技術であることから、光通信技術は急速な発達を続けている。このような文脈の中で、今日の光通信技術の発達を支える各種光部品の研究開発は行われているが、中でも平面基板上の光導波路を基本とした光導波路型光部品が最も重要な位置を占めている。これは、光導波路型光部品がフォトリソグラフィ技術および微細加工技術により光波長以下の精度で再現性良く量産可能という特徴を有するからである。特に、石英系光導波路により構成される波長無依存カプラは、容易にアレイ化が実現でき、経時変化に対する安定性、制御性の点において優れており、ＦＴＴＨ応用を念頭に精力的に研究開発が進められている。   Since optical communication is the most promising technology for increasing communication speed and capacity, optical communication technology continues to develop rapidly. In this context, research and development of various optical components that support the development of today's optical communication technology is underway, but optical waveguide type optical components based on optical waveguides on flat substrates are the most important. Occupies a position. This is because the optical waveguide type optical component has the feature that it can be mass-produced with good reproducibility with accuracy below the optical wavelength by photolithography technology and microfabrication technology. In particular, wavelength-independent couplers composed of silica-based optical waveguides can be easily arrayed, and are excellent in terms of stability and controllability over time, and research and development with FTTH applied in mind. It is being advanced.

波長無依存カプラとは、前段光方向性結合器、後段光方向性結合器およびそれらを接続する２本の光路長差を与える光導波路からなるマッハツェンダ干渉計により構成さる光カプラである。この波長無依存カプラは、波長無依存性を有し、後述のように前段および後段の光方向性結合器の結合角が適切に設定されることにより、射出される光の強度が入射された光の波長に依存しない。   The wavelength-independent coupler is an optical coupler configured by a Mach-Zehnder interferometer including a front-stage optical directional coupler, a rear-stage optical directional coupler, and an optical waveguide that connects two optical path lengths connecting them. This wavelength-independent coupler has wavelength independence, and the intensity of the emitted light is made incident by appropriately setting the coupling angles of the front and rear optical directional couplers as will be described later. It does not depend on the wavelength of light.

光方向性結合器とは、入力端に入射した光を分岐し、または結合して出力端に射出する機能を有する光カプラであって、特に第１および第２の光導波路からなる２入力２出力の光カプラである。また、マッハツェンダ干渉計とは、入射光を２つの光路に分岐して再び結合することにより、その光路長差による干渉縞を定量的に測定することができる干渉計である。   The optical directional coupler is an optical coupler having a function of branching or coupling light incident on the input end and emitting it to the output end, and in particular, a two-input two composed of first and second optical waveguides. Output optical coupler. The Mach-Zehnder interferometer is an interferometer that can quantitatively measure interference fringes due to the optical path length difference by splitting incident light into two optical paths and recombining them.

図１に、従来の光導波路による波長無依存カプラの一実施形態の構成図を示す。従来の波長無依存カプラでは、入力導波路１より入射した光信号は、波長依存性を有する前段光方向性結合器２を介して、波長ごとに異なる分岐比にて分岐された後、適切な光路長差Ｌを有するアーム導波路３および４を経由して、後段光方向性結合器５にて再び結合される。後段光方向性結合器５では干渉光は出力導波路６および７へと出力されるが、光強度は前段光方向性結合器２、後段光方向性結合器５の波長特性および光路長差Ｌを有するアーム導波路３，４間の位相差の波長特性を考慮した比率で出力される。出力導波路６からの光強度すなわちメインポートの光量Ｉ１、出力導波路７からの光強度すなわちタップポートの光量Ｉ２の比率は FIG. 1 shows a configuration diagram of an embodiment of a wavelength-independent coupler using a conventional optical waveguide. In the conventional wavelength-independent coupler, an optical signal incident from the input waveguide 1 is branched at a different branching ratio for each wavelength via the upstream optical directional coupler 2 having wavelength dependency, The light beams are coupled again by the post-stage optical directional coupler 5 via the arm waveguides 3 and 4 having the optical path length difference L. The interference light is output to the output waveguides 6 and 7 in the post-stage optical directional coupler 5, but the light intensity is the wavelength characteristics of the pre-stage optical directional coupler 2 and the post-stage optical directional coupler 5 and the optical path length difference L. Are output at a ratio that takes into account the wavelength characteristics of the phase difference between the arm waveguides 3 and 4. The ratio of the light intensity from the output waveguide 6, that is, the light amount I 1 of the main port, and the light intensity from the output waveguide 7, that is, the light amount I 2 of the tap port is

Figure 2006065089
Figure 2006065089

で表される。ここで、β（λ）は光導波路の伝搬定数、Φ１（λ）、Φ２（λ）はそれぞれ、前段光方向性結合器２および後段光方向性結合器５での結合角である。このことから、伝搬定数および方向性結合器の結合角に波長依存性が存在し、これらを適切に設定することで波長無依存カプラが実現されることが知られている（非特許文献１参照）。 It is represented by Here, β (λ) is a propagation constant of the optical waveguide, and Φ1 (λ) and Φ2 (λ) are coupling angles in the front-stage optical directional coupler 2 and the rear-stage optical directional coupler 5, respectively. From this, it is known that there is a wavelength dependency in the propagation constant and the coupling angle of the directional coupler, and a wavelength-independent coupler is realized by appropriately setting these (see Non-Patent Document 1). ).

適切な結合角を実現するため、従来の波長無依存カプラでは図２に示す方式で、前段光方向性結合器２および後段光方向性結合器５の波長特性を調整していた。すなわち、前段光方向性結合器２および後段光方向性結合器５は、それぞれ同じ幅の光導波路１０，１１を平行に延在させ、一定のギャップＧを設定するとともに、平行に延在させる長さＬを調節することで波長無依存カプラの波長無依存性を実現していた。特に、光導波路幅ＷおよびギャップＧ（図２）を前段および後段光方向性結合器で同じ値に設定し、前段光方向性結合器の直線部長Ｌ１と後段光方向性結合器の直線部長Ｌ２を異なる値に設定することで、光方向性結合器の直線部中心間距離の変化をもたらす製造誤差のひとつであるコア中心間距離の変動に対するトレランスを向上させることができることが知られている（非特許文献２参照）。 In order to achieve an appropriate coupling angle, the conventional wavelength-independent coupler adjusts the wavelength characteristics of the front-stage optical directional coupler 2 and the rear-stage optical directional coupler 5 by the method shown in FIG. That is, the front-stage optical directional coupler 2 and the rear-stage optical directional coupler 5 extend the optical waveguides 10 and 11 having the same width in parallel, set a certain gap G, and extend in parallel. By adjusting the length L, the wavelength independence of the wavelength independent coupler has been realized. In particular, to set the optical waveguide width W and the gap G (FIG. 2) to the same value in the front-stage and rear-stage optical directional coupler straight director linear director L 1 and the back optical directional coupler front optical directional coupler L 2 and by setting to a different value, it is known that it is possible to improve the tolerance to variations in the core center distance which is one of the manufacturing error resulting in a change in the linear portion the distance between the centers of the optical directional coupler (See Non-Patent Document 2).

K.Jinguji, N.Takato, A.Sugita, M.Kawachi, “Mech-Zehnder interferometer type optical waveguide coupler with wavelength-flattened ratio," Electron.Lett,Vol.26, No.17, pp.1326-1327, 1990.K. Jinguji, N. Takato, A. Sugita, M. Kawachi, “Mech-Zehnder interferometer type optical waveguide coupler with wavelength-flattened ratio,” Electron. Lett, Vol. 26, No. 17, pp. 1326-1327, 1990. Q.Chen, T.Tsuda, T.Ono, H.Urabe, H.Kawashima, K.Nare, “Stable high yield manufacturing of WINC with same core gap in directional couplers," 信学全国大会C-3-148, p.322, 2004年３月，東京Q.Chen, T.Tsuda, T.Ono, H.Urabe, H.Kawashima, K.Nare, “Stable high yield manufacturing of WINC with same core gap in directional couplers,” National Congress C-3-148, p.322, March 2004, Tokyo

しかしながら、上記の方法では、コア中心間距離の変動が歩留まり低下の主要因ではない場合、たとえば光導波路幅の変動や光導波路比屈折率差の製造誤差に対しては、プロセス変動に対する耐性が必ずしも十分ではなかった。特に平均的な石英系光導波路の製造過程では、コア中心間距離の変動はほとんど無視できる程度であり、むしろ光導波路比屈折率の変動やフォトリソグラフィや反応性イオンエッチングの工程における光導波路幅の変動が大きな誤差要因である。たとえば、典型的な石英系光導波路の作製においては、コア中心間距離は０．０１μｍ以下の精度で安定であるが、光導波路比屈折率差に関しては０．００５％程度、光導波路幅の変動に関しては０．０７μｍ程度の変動がある。   However, in the above method, when the variation in the center-to-core distance is not the main factor of the yield reduction, for example, the tolerance to the process variation is not necessarily against the variation in the optical waveguide width and the manufacturing error of the optical waveguide relative refractive index difference. It was not enough. In particular, in the manufacturing process of an average silica-based optical waveguide, the variation in the distance between the core centers is almost negligible. Rather, the variation in the relative refractive index of the optical waveguide and the width of the optical waveguide in the photolithography and reactive ion etching processes. Variation is a major error factor. For example, in the manufacture of a typical silica-based optical waveguide, the core center distance is stable with an accuracy of 0.01 μm or less, but the optical waveguide relative refractive index difference is about 0.005%, and the optical waveguide width varies. There is a fluctuation of about 0.07 μm.

図３に、非特許文献２のレイアウトに対してビーム伝搬法により計算した波長無依存カプラのプロセス誤差に対するメインポートの光量変化率を示す。特に、図３では製造誤差要因として、非特許文献２で改善されることが示されている光方向性結合器のコア中心間距離（Ｃ２Ｃ）、および光導波路比屈折率差（Ｄｅｌｔａ）ならびに光導波路幅の変化量（Ｓｈｉｆｔ）に関して、その製造誤差トレランスを計算した。図３のグラフにおいて、横軸は波長であり、縦軸は各誤差要因が単位量変化した場合の波長無依存カプラのメインポートの光量の変化率（Ｉ１）である。各誤差要因の単位量は、Ｃ２ＣおよびＳｈｉｆｔに関してはμｍ、Ｄｅｌｔａに関しては０．１％である。言い換えると、コア中心間距離、光導波路幅の変化量に関しては１μｍ変化したときのメインポートの光量の変化、光導波路比屈折率差に関しては、その値が０．１％変化した場合のメインポートの光量の変化である。上述の製造誤差の典型値を当てはめると、１．２−１．７μｍの光波長範囲で、コア中心間距離の変動による影響は最大で０．０４ｄＢ程度、光導波路幅の変化に対しては０．１ｄＢ程度、光導波路比屈折率差の変動に対しても０．１ｄＢ程度のメインポートの光量変化を与える。このように、従来の波長無依存カプラにおいては、光導波路幅および光導波路比屈折率の製造誤差によりその光量特性が大きく変動するという問題を生じていた。 FIG. 3 shows the light amount change rate of the main port with respect to the process error of the wavelength-independent coupler calculated by the beam propagation method for the layout of Non-Patent Document 2. In particular, in FIG. 3, as the cause of manufacturing errors, the distance between the core centers of optical directional couplers (C2C), optical waveguide relative refractive index difference (Delta), and optical The manufacturing error tolerance was calculated with respect to the change amount (Shift) of the waveguide width. In the graph of FIG. 3, the horizontal axis represents the wavelength, and the vertical axis represents the change rate (I 1 ) of the light amount of the main port of the wavelength-independent coupler when each error factor changes by a unit amount. The unit amount of each error factor is μm for C2C and Shift, and 0.1% for Delta. In other words, regarding the change in the distance between the core centers and the width of the optical waveguide, the change in the light amount of the main port when the optical waveguide changes by 1 μm, and the optical port relative refractive index difference when the value changes by 0.1%. Change in the amount of light. When the typical value of the manufacturing error described above is applied, in the optical wavelength range of 1.2 to 1.7 μm, the influence due to the fluctuation of the core center distance is about 0.04 dB at the maximum, and 0 for the change of the optical waveguide width. A change in the light amount of the main port of about 0.1 dB is given to a fluctuation of the optical waveguide relative refractive index difference of about 0.1 dB. As described above, the conventional wavelength-independent coupler has a problem that the light quantity characteristic fluctuates greatly due to the manufacturing error of the optical waveguide width and the optical waveguide relative refractive index.

本発明の目的は、歩留まり低下の主要因である光導波路幅の変動および光導波路比屈折率の変動を含む製造誤差に対する許容範囲の大きな光方向性結合器および波長無依存カプラを提供することにある。   An object of the present invention is to provide an optical directional coupler and a wavelength-independent coupler that have a large tolerance for manufacturing errors including fluctuations in optical waveguide width and fluctuations in optical waveguide relative refractive index, which are main causes of yield reduction. is there.

本発明は、このような目的を達成するために、請求項１に記載の発明は、基板と、該基板上に構成された２本の光導波路とを備えた光方向性結合器において、前記２本の光導波路は、光結合を生じる光結合領域における直線部分の長さがゼロであることを特徴とする。   In order to achieve the above object, the present invention provides an optical directional coupler comprising a substrate and two optical waveguides formed on the substrate. The two optical waveguides are characterized in that the length of the straight line portion in the optical coupling region where optical coupling occurs is zero.

この構成によれば、コア中心間距離の変動に加え、光導波路幅の変動および光導波路比屈折率の変動を含むプロセス変動に対し、結合率の変動量を低減することが可能となる。   According to this configuration, it is possible to reduce the fluctuation amount of the coupling ratio with respect to the process fluctuation including the fluctuation of the optical waveguide width and the fluctuation of the optical waveguide relative refractive index in addition to the fluctuation of the core center distance.

請求項３に記載の発明は、基板と、該基板上に構成された２本の光導波路をそれぞれが有する２つの光方向性結合器と、前記２つの光方向性結合器を接続する長さの異なる２本の光導波路とを備えるマッハツェンダ干渉計により構成された波長無依存カプラにおいて、前記２つの光方向性結合器の各々は、請求項１または２に記載の光方向性結合器であり、射出される光の強度が入射される光の波長に依存しないように前記光結合領域の光導波路幅および光導波路間ギャップが設定されていることを特徴とする。   According to a third aspect of the present invention, there is provided a substrate, two optical directional couplers each having two optical waveguides formed on the substrate, and a length connecting the two optical directional couplers. A wavelength-independent coupler configured by a Mach-Zehnder interferometer having two different optical waveguides, wherein each of the two optical directional couplers is the optical directional coupler according to claim 1 or 2. The optical waveguide width of the optical coupling region and the gap between the optical waveguides are set so that the intensity of the emitted light does not depend on the wavelength of the incident light.

この構成によれば、コア中心間距離の変動に加え、歩留まりの主要因である光導波路幅の変動および光導波路比屈折率の変動を含む光導波路の製造誤差に対し安定した光量特性を有することが可能となる。   According to this configuration, in addition to fluctuations in the distance between core centers, the light quantity characteristics are stable against optical waveguide manufacturing errors including fluctuations in optical waveguide width and optical waveguide relative refractive index, which are the main factors of yield. Is possible.

本発明によれば、光導波路を利用した光方向性結合器に対して、コア中心間距離の変動に加え、歩留まりの主要因である光導波路幅の変動および光導波路比屈折率の変動を含む製造誤差に対する耐性の強い光方向性結合器を与えることが可能である。また、本発明によれば、この光方向性結合器を波長無依存カプラに適用することにより、同様にコア中心間距離の変動に加え、光導波路幅の変動および光導波路比屈折率の変動を含む製造誤差に対する耐性の強い波長無依存カプラを実現することが可能となる。   According to the present invention, for an optical directional coupler using an optical waveguide, in addition to the variation in the distance between core centers, the variation in the optical waveguide width and the variation in the relative refractive index of the optical waveguide, which are the main factors of the yield, are included. It is possible to provide an optical directional coupler that is highly resistant to manufacturing errors. In addition, according to the present invention, by applying this optical directional coupler to a wavelength-independent coupler, in addition to the variation in the distance between the core centers, the variation in the optical waveguide width and the variation in the relative refractive index of the optical waveguide are also achieved. It becomes possible to realize a wavelength-independent coupler that is highly resistant to manufacturing errors.

以下、図面を参照しながら本発明の実施形態について詳細に説明する。   Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

〔実施形態１〕
図４に、本発明の一実施形態にかかる光方向性結合器の構成図を示す。図４において、光方向性結合器は、シリコン基板、該シリコン基板上に形成された２本の光導波路からなり、該光導波路は、２本の入力曲げテーパ導波路３１および入力曲げテーパ導波路３２、ならびに２本の出力曲げテーパ導波路３３および出力曲げテーパ導波路３４から構成される。入力曲げテーパ導波路は、その入力端すなわち入力曲げテーパ導波路の光結合が生じない部分において幅Ｗｗを有し、光方向性結合器の中心部すなわち入力曲げテーパ導波路と出力曲げテーパ導波路とが接する光結合を生じる領域（以下「光結合領域」という）において幅Ｗｎを有する。同様に、出力曲げテーパ導波路は、光方向性結合器の中心部すなわち出力曲げテーパ導波路と入力曲げテーパ導波路との接する光結合領域において幅Ｗｎを有し、その出力端すなわち出力曲げテーパ導波路の光結合を生じない部分において幅Ｗｗを有する。ここで、各入力曲げテーパ導波路３１，３２の光導波路幅のＷｗからＷｎまでの変化、各出力曲げテーパ導波路３３，３４の光導波路幅のＷｎからＷｗまでの幅の変化、および各入出力曲げテーパ導波路の湾曲は、回路全体の損失や偏波依存性を低く抑えるために断熱的になされる。従って、各入出力曲げテーパ導波路は、急激な曲げ半径を与えず、ある一定値以上の曲げ半径において湾曲する。このため、光結合領域においても光導波路が湾曲しており、直線部分の長さが略ゼロになっている。加えて、入力曲げテーパ導波路３１，３２および出力曲げテーパ導波路３３，３４は、その幅がＷｎとなるときに、その間隔がギャップＧｉとなる位置まで最近接する。 Embodiment 1
FIG. 4 is a configuration diagram of an optical directional coupler according to an embodiment of the present invention. In FIG. 4, the optical directional coupler includes a silicon substrate and two optical waveguides formed on the silicon substrate. The optical waveguide includes two input bending taper waveguides 31 and an input bending taper waveguide. 32, and two output bending taper waveguides 33 and 34. The input bending taper waveguide has a width Ww at the input end thereof, that is, the portion where the optical coupling of the input bending taper waveguide does not occur, and the central portion of the optical directional coupler, that is, the input bending taper waveguide and the output bending taper waveguide. A region where optical coupling occurs in contact with (hereinafter referred to as “optical coupling region”) has a width Wn. Similarly, the output bend taper waveguide has a width Wn at the center of the optical directional coupler, that is, the optical coupling region where the output bend taper waveguide and the input bend taper waveguide are in contact with each other. The portion of the waveguide that does not cause optical coupling has a width Ww. Here, the change of the optical waveguide width of each input bending taper waveguide 31, 32 from Ww to Wn, the change of the optical waveguide width of each output bending taper waveguide 33, 34 from Wn to Ww, and each input The bending of the output bending taper waveguide is adiabatic in order to suppress the loss and polarization dependency of the entire circuit. Therefore, each input / output bending taper waveguide does not give an abrupt bending radius and curves at a bending radius of a certain value or more. For this reason, the optical waveguide is also curved in the optical coupling region, and the length of the straight portion is substantially zero. In addition, the input bending taper waveguides 31 and 32 and the output bending taper waveguides 33 and 34 are closest to the position where the gap becomes the gap Gi when the width is Wn.

図５に、比屈折率差０．４％の石英系光導波路において、従来の構成の光方向性結合器と本実施形態１における光方向性結合器の製造誤差耐性をビーム伝搬法により計算した結果を示す。従来の光方向性結合器は、その光結合領域での光導波路ギャップが３μｍ、光導波路幅は全領域で８μｍとし、光結合領域における直線長を５００μｍとした。また、本実施形態１の光方向性結合器としてＷｗ＝８μｍ、Ｗｎ＝５μｍ、Ｇｉ＝１．２μｍ、入力端側から光導波路ギャップがＧｉに達する点までの長さを７５０μｍ、最小曲げ半径を１５ｍｍとした。従来の構成、本実施形態１の構成ともに、光方向性結合器の結合率は光波長が１．５５μｍのときおよそ５０％となる。また、ここでは製造誤差要因として光導波路比屈折率差のみを考慮した。すなわち、図５は、光導波路比屈折率差が０．１％変化したときの結合率の変化量を示している。図５によれば、従来の光方向性結合器に比べて、その光導波路比屈折率差依存性は半分以下に低減されていることがわかる。   FIG. 5 shows the manufacturing error tolerance of the optical directional coupler having the conventional configuration and the optical directional coupler in the first embodiment calculated in the quartz optical waveguide having a relative refractive index difference of 0.4% by the beam propagation method. Results are shown. The conventional optical directional coupler has an optical waveguide gap of 3 μm in the optical coupling region, an optical waveguide width of 8 μm in the entire region, and a linear length in the optical coupling region of 500 μm. Further, as the optical directional coupler of Embodiment 1, Ww = 8 μm, Wn = 5 μm, Gi = 1.2 μm, the length from the input end side to the point where the optical waveguide gap reaches Gi is 750 μm, and the minimum bending radius is It was 15 mm. In both the conventional configuration and the configuration of the first embodiment, the coupling rate of the optical directional coupler is approximately 50% when the light wavelength is 1.55 μm. Here, only the relative refractive index difference of the optical waveguide is considered as a factor of manufacturing errors. That is, FIG. 5 shows the amount of change in the coupling rate when the optical waveguide relative refractive index difference changes by 0.1%. According to FIG. 5, it can be seen that the optical waveguide relative refractive index difference dependency is reduced to less than half compared to the conventional optical directional coupler.

このように、本発明の光方向性結合器は、コア中心間距離の変動に加え、光導波路幅の変動および光導波路比屈折率の変動を含む製造誤差に対して許容範囲の大きな光方向性結合器を与えるものである。   As described above, the optical directional coupler according to the present invention has an optical directional property having a large allowable range with respect to manufacturing errors including fluctuations in the optical waveguide width and optical waveguide relative refractive index in addition to fluctuations in the distance between core centers. A combiner is provided.

〔実施形態２〕
図６に、本発明の一実施形態にかかる波長無依存カプラの構成図を示す。図６において、波長無依存カプラは、シリコン基板、該シリコン基板上に形成された２本の光導波路からなり、該光導波路は、入力導波路１１および１８、波長依存性を有する前段光方向性結合器１２、波長依存性を有する後段光方向性結合器１５、前記前段光方向性結合器１２と前記後段光方向性結合器１５を接続し、適切な光路長差Ｌを有するアーム導波路１３および１４、ならびに出力導波路１６および１７からなる。図６において、入力導波路１１から入射した光信号は、波長依存性を有する前段光方向性結合器１２を経由して、波長ごとに異なる分岐比にて分岐された後、適切な光路長差Ｌを有するアーム導波路１３および１４を介して、おなじく波長依存性を有する後段光方向性結合器１５へと伝搬する。後段光方向性結合器１５にて結合された干渉光は出力導波路１６および１７へと出力されるが、光強度は前段光方向性結合器１２、後段光方向性結合器１５の波長特性および光路長差Ｌを有するアーム導波路１３，１４間の位相差の波長特性を考慮した比率で出力される。 [Embodiment 2]
FIG. 6 shows a configuration diagram of a wavelength-independent coupler according to an embodiment of the present invention. In FIG. 6, the wavelength-independent coupler includes a silicon substrate and two optical waveguides formed on the silicon substrate. The optical waveguides are input waveguides 11 and 18, and the upstream optical directionality having wavelength dependency. A coupler 12, a post-stage optical directional coupler 15 having wavelength dependency, an arm waveguide 13 that connects the front-stage optical directional coupler 12 and the rear-stage optical directional coupler 15 and has an appropriate optical path length difference L And 14 and output waveguides 16 and 17. In FIG. 6, an optical signal incident from the input waveguide 11 is branched at a different branching ratio for each wavelength via the upstream optical directional coupler 12 having wavelength dependency, and then an appropriate optical path length difference is obtained. The light propagates through the arm waveguides 13 and 14 having L to the latter optical directional coupler 15 having the same wavelength dependency. The interference light coupled by the rear-stage optical directional coupler 15 is output to the output waveguides 16 and 17, and the light intensity is determined based on the wavelength characteristics of the front-stage optical directional coupler 12 and the rear-stage optical directional coupler 15, and It is output at a ratio that takes into account the wavelength characteristics of the phase difference between the arm waveguides 13 and 14 having the optical path length difference L.

本実施形態の波長無依存カプラでは、前段光方向性結合器１２および後段光方向性結合器１５として、以下に説明する構造をとることで、その製造誤差による影響を低減する。図７に、本発明の一実施形態にかかる波長無依存カプラにおける前段光方向性結合器１２および後段光方向性結合器１５の構成図を示す。前段光方向性結合器１２および後段光方向性結合器１５は、２本の入力曲げテーパ導波路２１および２２と２本の出力曲げテーパ導波路２３および２４からなる。入力曲げテーパ導波路は、その入力端すなわち入力曲げテーパ導波路の光結合が生じない部分において幅Ｗｗを有し、その光方向性結合器の中心部すなわち入力曲げテーパ導波路と出力曲げテーパ導波路とが接する光結合領域において幅Ｗｎを有する。同様に、出力曲げテーパ導波路は、光方向性結合器の中心部すなわち出力曲げテーパ導波路と入力曲げテーパ導波路が接する光結合領域において幅Ｗｎを有し、その出力端すなわち出力曲げテーパ導波路の光結合を生じない部分において幅Ｗｗを有する。ここで、各入力曲げテーパ導波路２１，２２の光導波路幅のＷｗからＷｎまでの変化、各出力曲げテーパ導波路２３，２４の光導波路幅のＷｎからＷｗまでの幅の変化、ならびに各入出力曲げテーパ導波路の湾曲は、回路全体の損失や偏波依存性を低く抑えるために断熱的になされる。従って、各入出力曲げテーパ導波路は、急激な曲げ半径を与えず、ある一定値以上の曲げ半径において湾曲する。加えて、入力曲げテーパ導波路２１，２２および出力曲げテーパ導波路２３，２４は、その幅がＷｎとなるときに、その間隔がギャップＧｉとなる位置まで最近接する。ここで、Ｇｉは前段光方向性結合器１２および後段光方向性結合器１５で異なる値に設定する。   In the wavelength-independent coupler of this embodiment, the front-stage optical directional coupler 12 and the rear-stage optical directional coupler 15 have the structure described below, thereby reducing the influence of manufacturing errors. FIG. 7 shows a configuration diagram of the front-stage optical directional coupler 12 and the rear-stage optical directional coupler 15 in the wavelength-independent coupler according to the embodiment of the present invention. The front optical directional coupler 12 and the rear optical directional coupler 15 are composed of two input bending tapered waveguides 21 and 22 and two output bending tapered waveguides 23 and 24. The input bending taper waveguide has a width Ww at the input end thereof, that is, the portion where the optical coupling of the input bending taper waveguide does not occur, and the central portion of the optical directional coupler, that is, the input bending taper waveguide and the output bending taper waveguide. A width Wn is provided in the optical coupling region in contact with the waveguide. Similarly, the output bending taper waveguide has a width Wn at the center of the optical directional coupler, that is, the optical coupling region where the output bending taper waveguide contacts the input bending taper waveguide, and its output end, ie, output bending taper guide. A width Ww is provided at a portion of the waveguide where no optical coupling occurs. Here, the change of the optical waveguide width of each of the input bending taper waveguides 21 and 22 from Ww to Wn, the change of the optical waveguide width of each of the output bending taper waveguides 23 and 24 from Wn to Ww, and each input The bending of the output bending taper waveguide is adiabatic in order to suppress the loss and polarization dependency of the entire circuit. Therefore, each input / output bending taper waveguide does not give an abrupt bending radius and curves at a bending radius of a certain value or more. In addition, the input bending taper waveguides 21 and 22 and the output bending taper waveguides 23 and 24 are closest to the position where the gap becomes the gap Gi when the width is Wn. Here, Gi is set to a different value in the front-stage optical directional coupler 12 and the rear-stage optical directional coupler 15.

本実施形態２では、比屈折率差が０．４％の石英系光導波路にて製造した波長無依存カプラを仮定し、ビーム伝搬法による計算を用いて本発明の効果を検証した。波長無依存カプラの上述の値として、Ｗｗ＝８μｍ、Ｗｎ＝５μｍ、Ｌ＝０．６μｍとし、ギャップＧｉは前段光方向性結合器に対して２．１μｍ、後段光方向性結合器に対して３．５μｍ、入力端側から最初に光導波路ギャップがＧｉに達する点までの長さを７５０μｍ、最小曲げ半径を１５ｍｍとした。図８に、本実施形態２の波長無依存カプラのタップポート光出力の各種プロセス誤差に対する変化率を示す。上述のように、製造誤差要因として、光方向性結合器のコア中心間距離（Ｃ２Ｃ）、および光導波路比屈折率差（Ｄｅｌｔａ）ならびに光導波路幅の変化量（Ｓｈｉｆｔ）に関して、その製造誤差トレランスを計算した。図８のグラフにおいて、横軸は波長であり、縦軸は各誤差要因が単位量変化した場合の波長無依存カプラのタップポートの光量の変化率（Ｉ２）である。各誤差要因の単位量は、Ｃ２ＣおよびＳｈｉｆｔに関してμｍ、Ｄｅｌｔａに関しては０．１％である。言い換えると、コア中心間距離、光導波路の幅の変化量に対しては１μｍ変化したときのタップポートの光量の変化、光導波路比屈折率差に関しては、その値が０．１％変化したときのタップポートの光量の変化である。 In the second embodiment, a wavelength-independent coupler manufactured with a silica-based optical waveguide having a relative refractive index difference of 0.4% is assumed, and the effect of the present invention is verified using calculation by a beam propagation method. As the above-mentioned values of the wavelength-independent coupler, Ww = 8 μm, Wn = 5 μm, L = 0.6 μm, the gap Gi is 2.1 μm for the front-stage optical directional coupler, and for the rear-stage optical directional coupler. The length from the input end side to the point where the optical waveguide gap first reaches Gi is 750 μm, and the minimum bending radius is 15 mm. FIG. 8 shows the rate of change of the tap port optical output of the wavelength-independent coupler of Embodiment 2 with respect to various process errors. As described above, as a manufacturing error factor, the manufacturing error tolerance with respect to the core center distance (C2C) of the optical directional coupler, the optical waveguide relative refractive index difference (Delta), and the change amount of the optical waveguide width (Shift). Was calculated. In the graph of FIG. 8, the horizontal axis represents the wavelength, and the vertical axis represents the change rate (I 2 ) of the light amount of the tap port of the wavelength-independent coupler when each error factor changes by a unit amount. The unit amount of each error factor is μm for C2C and Shift, and 0.1% for Delta. In other words, with respect to the change in the light amount of the tap port when the distance between the core centers and the width of the optical waveguide is changed by 1 μm, and the relative refractive index difference of the optical waveguide is changed by 0.1%. This is a change in the light amount of the tap port.

製造誤差の典型値として、コア中心間距離の誤差０．０１μｍ、光導波路幅の誤差０．０７μｍ、光導波路比屈折率差の誤差０．００５％を当てはめると、１．２−１．７μｍの波長域の最悪値で、コア中心間距離の変動に対して０．０５ｄＢ程度、光導波路幅の変動に対して０．０５ｄＢ、光導波路比屈折率差の変動に対して０．０５ｄＢが得られた。すなわち、コア中心間距離に関しては、従来の波長無依存カプラと同程度の誤差誘起にとどめることができる上、光導波路幅の変動および光導波路比屈折率差の変動に対しては、劇的にその影響を低減することができる。   As typical values of manufacturing errors, an error of 0.01 μm in the distance between core centers, an error of optical waveguide width of 0.07 μm, and an error of relative refractive index difference of optical waveguide of 0.005% are applied. The worst value in the wavelength range is about 0.05 dB for fluctuations in the distance between core centers, 0.05 dB for fluctuations in the optical waveguide width, and 0.05 dB for fluctuations in the optical waveguide relative refractive index difference. It was. In other words, the distance between the core centers can be limited to the same level of error induction as that of conventional wavelength-independent couplers. In addition, the optical waveguide width variation and the optical waveguide relative refractive index difference variation are dramatically reduced. The influence can be reduced.

すなわち、本発明では、波長無依存カプラを構成する前段・後段光方向性結合器として、光結合を誘起する部分の直線長をゼロとし、前段・後段光方向性結合器の光結合を誘起する部分の光導波路幅および光導波路間ギャップを適切に設定することで波長無依存特性を実現する。本発明の結合長ゼロの光方向性結合器においては、これまでの結合領域の直線長が有限の値を有する光方向性結合器に比べて、光導波路幅および光導波路比屈折率差の製造誤差依存性を低減する。平均的な石英系光導波路の製造プロセスにおいては、上述の光導波路幅および光導波路比屈折率差の変動が大きく、本発明の光方向性結合器を適用することで、光方向性結合器の製造誤差による結合率特性の変動は最小限に抑えられるため、結果として波長無依存カプラの製造誤差による光量特性劣化も低減される。   That is, in the present invention, as the front-stage and rear-stage optical directional couplers constituting the wavelength-independent coupler, the linear length of the portion that induces optical coupling is set to zero, and the optical coupling of the front-stage and rear-stage optical directional couplers is induced. Wavelength-independent characteristics are realized by appropriately setting the width of the optical waveguide and the gap between the optical waveguides. In the optical directional coupler with zero coupling length according to the present invention, the optical waveguide width and the optical waveguide relative refractive index difference are manufactured as compared with the conventional optical directional coupler in which the linear length of the coupling region has a finite value. Reduce error dependency. In the average silica-based optical waveguide manufacturing process, the above-mentioned optical waveguide width and optical waveguide relative refractive index difference greatly vary. By applying the optical directional coupler of the present invention, the optical directional coupler Since the fluctuation of the coupling rate characteristic due to the manufacturing error is minimized, as a result, the deterioration of the light amount characteristic due to the manufacturing error of the wavelength-independent coupler is also reduced.

従来の波長無依存カプラの構成図である。It is a block diagram of the conventional wavelength independent coupler. 従来の波長無依存カプラを構成する光方向性結合器の構成図である。It is a block diagram of the optical directional coupler which comprises the conventional wavelength independent coupler. 従来の波長無依存カプラの製造誤差依存性を示すグラフである。It is a graph which shows the manufacturing error dependence of the conventional wavelength independent coupler. 本発明の実施形態１における光方向性結合器の構成図である。It is a block diagram of the optical directional coupler in Embodiment 1 of this invention. 本発明の実施形態１における従来の光方向性結合器特性の光導波路比屈折率差依存性を示すグラフである。It is a graph which shows the optical waveguide specific refractive index difference dependence of the conventional optical directional coupler characteristic in Embodiment 1 of this invention. 本発明の実施形態２における波長無依存カプラの構成図である。It is a block diagram of the wavelength independent coupler in Embodiment 2 of this invention. 本発明の実施形態２における波長無依存カプラを構成する光方向性結合器の構成図である。It is a block diagram of the optical directional coupler which comprises the wavelength independent coupler in Embodiment 2 of this invention. 本発明の実施形態２における波長無依存カプラの製造誤差依存性を示すグラフである。It is a graph which shows the manufacturing error dependence of the wavelength independent coupler in Embodiment 2 of this invention.

符号の説明Explanation of symbols

１ 入力曲げ導波路
２ 前段光方向性結合器
３ アーム導波路
４ アーム導波路
５ 後段光方向性結合器
６ 出力曲げ導波路
７ 出力曲げ導波路
８ 入力曲げ導波路
１１ 入力曲げ導波路
１２ 前段光方向性結合器
１３ アーム導波路
１４ アーム導波路
１５ 後段光方向性結合器
１６ 出力曲げ導波路
１７ 出力曲げ導波路
１８ 入力曲げ導波路
２１ 入力曲げ導波路
２２ 入力曲げ導波路
２３ 出力曲げ導波路
２４ 出力曲げ導波路
３１ 入力曲げ導波路
３２ 入力曲げ導波路
３３ 出力曲げ導波路
３４ 出力曲げ導波路
Ｗ 光導波路幅
Ｇ ギャップ DESCRIPTION OF SYMBOLS 1 Input bending waveguide 2 Front | former stage optical directional coupler 3 Arm waveguide 4 Arm waveguide 5 Back | latter stage optical directional coupler 6 Output bending waveguide 7 Output bending waveguide 8 Input bending waveguide 11 Input bending waveguide 12 Previous stage light Directional coupler 13 Arm waveguide 14 Arm waveguide 15 Rear optical directional coupler 16 Output bending waveguide 17 Output bending waveguide 18 Input bending waveguide 21 Input bending waveguide 22 Input bending waveguide 23 Output bending waveguide 24 Output bending waveguide 31 Input bending waveguide 32 Input bending waveguide 33 Output bending waveguide 34 Output bending waveguide W Optical waveguide width G Gap

Claims (3)

基板と、該基板上に構成された２本の光導波路とを備えた光方向性結合器において、
前記２本の光導波路は、光結合を生じる光結合領域における直線部分の長さがゼロであることを特徴とする光方向性結合器。 In an optical directional coupler comprising a substrate and two optical waveguides configured on the substrate,
In the optical directional coupler, the two optical waveguides have a length of a straight line portion in an optical coupling region that generates optical coupling is zero. 前記２本の光導波路は、入力端から光結合を生じる光結合領域へ向かってテーパ状に細くなり、前記光結合領域から出力端へ向かってテーパ状に広くなるように形成されていることを特徴とする請求項１に記載の光方向性結合器。   The two optical waveguides are formed so as to taper from the input end toward the optical coupling region where optical coupling occurs, and to increase from the optical coupling region toward the output end. The optical directional coupler according to claim 1. 基板と、該基板上に構成された２本の光導波路をそれぞれが有する２つの光方向性結合器と、前記２つの光方向性結合器を接続する長さの異なる２本の光導波路とを備えるマッハツェンダ干渉計により構成された波長無依存カプラにおいて、
前記２つの光方向性結合器の各々は、請求項１または２に記載の光方向性結合器であり、射出される光の強度が入射される光の波長に依存しないように前記光結合領域の光導波路幅および光導波路間ギャップが設定されていることを特徴とする波長無依存カプラ。
A substrate, two optical directional couplers each having two optical waveguides formed on the substrate, and two optical waveguides having different lengths connecting the two optical directional couplers In a wavelength-independent coupler composed of a Mach-Zehnder interferometer with
Each of the two optical directional couplers is the optical directional coupler according to claim 1 or 2, wherein the optical coupling region is configured such that the intensity of emitted light does not depend on the wavelength of incident light. An optical waveguide width and a gap between the optical waveguides are set.
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