JP2006266796A - Apparatus for optical heterodyne interference - Google Patents

Apparatus for optical heterodyne interference Download PDF

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JP2006266796A
JP2006266796A JP2005083692A JP2005083692A JP2006266796A JP 2006266796 A JP2006266796 A JP 2006266796A JP 2005083692 A JP2005083692 A JP 2005083692A JP 2005083692 A JP2005083692 A JP 2005083692A JP 2006266796 A JP2006266796 A JP 2006266796A
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optical
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Koji Kawakita
浩二 川北
Hiroshi Shimotahira
寛 下田平
Takao Tanimoto
隆生 谷本
Akihito Otani
昭仁 大谷
Kensuke Ogawa
憲介 小川
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Anritsu Corp
Bussan Nanotech Research Institute Inc
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Bussan Nanotech Research Institute Inc
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Abstract

<P>PROBLEM TO BE SOLVED: To improve sensitivity of phase detection and make an apparatus economical. <P>SOLUTION: This apparatus for optical heterodyne interference is provided with a Mach-Zehnder interferometer 30 having both a light branching means 14 for branching incident light into two and emitting two beams of light having different frequencies and an optical coupler 6 for emitting interference light by combining the two beams of light entering through different optical paths; a light receiver 8 for performing heterodyne detection on interference light; and a synchronous detector 15 for detecting the phase of its detection signals. The light branching means 14 comprises an ultrasonic generator 14b for generating ultrasonic waves of a frequency f<SB>1</SB>; an ultrasonic generator 14c for generating ultrasonic waves of a frequency f<SB>2</SB>; an acoustooptic frequency shifter (AOFS) 14d driven by the ultrasonic waves of the frequency f<SB>1</SB>; and an AOFS 14e driven by the ultrasonic waves of the frequency f<SB>2</SB>. A frequency difference between the emergent two beams of light is made equal to a frequency difference between the two ultrasonic waves, and the synchronous detector 15 is constituted of a lock-in amplifier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、干渉計から出射される干渉光の位相から例えば被測定物の位相特性を測定する光ヘテロダイン干渉装置に関し、特にマッハツェンダ型干渉計内に音響光学周波数シフタ（ＡＯＦＳ： Acousto-Optic Frequency Shifter ）を配置して、分岐した２つの光にヘテロダイン検波のための周波数差を与えるようにした光ヘテロダイン干渉装置に関する。   The present invention relates to an optical heterodyne interferometer that measures, for example, the phase characteristics of an object to be measured from the phase of interference light emitted from an interferometer, and more particularly to an acousto-optic frequency shifter (AOFS) in a Mach-Zehnder interferometer. ) To provide a frequency difference for heterodyne detection between the two branched lights.

従来、マッハツェンダ型干渉計内にＡＯＦＳを配置して、分岐した２つの光にヘテロダイン検波のための周波数差を与えるようにした光ヘテロダイン干渉装置として、マッハツェンダ型干渉計がその光路に光ファイバを用いて構成される光ファイバ干渉計で、被測定物の位相特性から波長分散を測定するものがあった。（例えば、非特許文献1参照）   Conventionally, as an optical heterodyne interferometer in which an AOFS is arranged in a Mach-Zehnder interferometer and a frequency difference for heterodyne detection is given to two branched lights, the Mach-Zehnder interferometer uses an optical fiber in its optical path. There are some optical fiber interferometers configured to measure the chromatic dispersion from the phase characteristics of the object to be measured. (For example, see Non-Patent Document 1)

この種の光ヘテロダイン干渉装置の概略構成を図４に示す。波長可変光源１は、例えば波長可変レーザであり、制御手段１３から出力される制御信号ａに基づいて所定の周波数範囲の測定光を順次発振して光カプラ３へ出射する。また、光源２は、例えばレーザであり、波長可変光源１の発振周波数とは異なる固定周波数の参照光を発振して光カプラ３へ出射する。光カプラ３は、上記測定光及び参照光を合波して波長多重し、その波長多重光をＡＯＦＳ４ｂへ出射する。   A schematic configuration of this type of optical heterodyne interferometer is shown in FIG. The wavelength tunable light source 1 is, for example, a wavelength tunable laser, and sequentially oscillates measurement light in a predetermined frequency range based on a control signal a output from the control unit 13 and emits the measurement light to the optical coupler 3. The light source 2 is a laser, for example, and oscillates reference light having a fixed frequency different from the oscillation frequency of the wavelength variable light source 1 and emits it to the optical coupler 3. The optical coupler 3 combines the measurement light and the reference light and multiplexes them, and emits the WDM light to the AOFS 4b.

ＡＯＦＳ４ｂは、超音波発生器４ａから入力される周波数ｆ１の超音波によって駆動され、光カプラ３から入射される波長多重光を２つの光に分岐するとともに、その分岐した２つの光にヘテロダイン検波のための周波数差（ビート信号の周波数となる）を与えて出射する。すなわち、ＡＯＦＳ４ｂは、光カプラ３からの波長多重光を２つの光に分岐して、一方は０次の回折に基づく第１経路の光として被測定物１０を介して光カプラ６へ出射し、また他方は超音波の周波数ｆ１分だけ周波数シフトした＋１次の回折に基づく第２経路の光として遅延器５へ出射する。周波数関係を具体的に示すと、入射される波長多重光の周波数をν（波長可変光源１の発振周波数）及びν０（参照光の固定周波数）とすると、第１経路の光の周波数はν及びν０、第２経路の光の周波数はν＋ｆ１及びν０＋ｆ１となる。そして、それらが光カプラ６で合波された後にヘテロダイン検波されるとビート信号の周波数ｆ１の電気信号が出力される。 AOFS4b is driven by the ultrasonic frequency f 1 input from the ultrasonic generator 4a, with branches the wavelength-multiplexed light incident from the optical coupler 3 into two light, heterodyne detection to the branched two optical A frequency difference (becomes the frequency of the beat signal) is given and emitted. That is, the AOFS 4b splits the wavelength multiplexed light from the optical coupler 3 into two lights, one of which is emitted to the optical coupler 6 through the device under test 10 as the light of the first path based on the 0th order diffraction, The other is emitted to the delay device 5 as light of the second path based on the + 1st order diffraction shifted by the frequency f1 of the ultrasonic wave. Specifically, when the frequency relationship of incident wavelength multiplexed light is ν (the oscillation frequency of the wavelength tunable light source 1) and ν 0 (the fixed frequency of the reference light), the frequency of the light in the first path is ν. And ν 0 , the frequencies of light in the second path are ν + f 1 and ν 0 + f 1 . When they are combined by the optical coupler 6 and then subjected to heterodyne detection, an electrical signal having the frequency f 1 of the beat signal is output.

遅延器５は、例えば光ファイバ遅延線で構成され、マッハツェンダ型干渉計の２つのアームで光路長をできる限り合わせるために、第２経路の光を、第１経路の光が被測定物１０によって遅延される時間にほぼ等しい時間分遅延させて光カプラ６へ出射する。光カプラ６は、被測定物１０を介して入射される第１経路の光と遅延器５を介して入射される第２経路の光とを合波して、測定光に基づく干渉光と参照光に基づく干渉光とを光分波器７へ出射する。   The delay device 5 is constituted by, for example, an optical fiber delay line, and in order to match the optical path length as much as possible with the two arms of the Mach-Zehnder interferometer, the light of the second path is changed by the object 10 to be measured. The light is output to the optical coupler 6 with a delay approximately equal to the delay time. The optical coupler 6 multiplexes the light of the first path incident through the device under test 10 and the light of the second path incident through the delay device 5 to reference the interference light based on the measurement light and the reference light. The interference light based on the light is emitted to the optical demultiplexer 7.

なお、超音波発生器４ａ及びＡＯＦＳ４ｂは光分岐手段４を構成し、そしてこの光分岐手段４、被測定物１０、遅延器５及び光カプラ６はマッハツェンダ型干渉計２０を構成している。したがって、光分岐手段４は、入射光を２つに分岐して別々の光路を通してから結合（干渉）させるマッハツェンダ型干渉計における、入射光を２つに分岐する手段であり、また光カプラ６は、別々の光路を通してから結合（干渉）させる手段である。マッハツェンダ型干渉計２０は、自身がその光路に光ファイバを含んで構成される光ファイバ干渉計であったり、又はその光路長を合わせる遅延器５が光ファイバ遅延線であったりする場合、温度変化や振動などに起因した光ファイバの揺らぎによる位相変動を生じやすい。それを改善するために、測定光と参照光とを波長多重して同時にマッハツェンダ型干渉計２０へ入射して、測定光における位相変動を参照光における位相変動で相殺している。   The ultrasonic generator 4a and the AOFS 4b constitute the optical branching means 4, and the optical branching means 4, the DUT 10, the delay device 5 and the optical coupler 6 constitute a Mach-Zehnder interferometer 20. Therefore, the light branching means 4 is a means for branching the incident light into two in a Mach-Zehnder interferometer for branching the incident light into two and coupling (interfering) after passing through separate optical paths. , Means for coupling (interference) through separate optical paths. When the Mach-Zehnder interferometer 20 is an optical fiber interferometer that includes an optical fiber in its optical path, or when the delay unit 5 that matches the optical path length is an optical fiber delay line, the temperature changes. It is likely to cause phase fluctuations due to fluctuations in the optical fiber due to vibration and vibration. In order to improve this, the measurement light and the reference light are wavelength-multiplexed and simultaneously incident on the Mach-Zehnder interferometer 20, and the phase fluctuation in the measurement light is canceled by the phase fluctuation in the reference light.

光分波器７は、光カプラ６から入射される測定光と参照光とが波長多重してなる波長多重光の干渉光を受けて、それぞれの周波数（波長）に分波し、測定光の干渉光を受光器（ＰＤ）８に、参照光の干渉光を受光器（ＰＤ）９に出射する。受光器８は、光分波器７から入射される測定光の干渉光を受けてヘテロダイン検波し上述の第１経路の光のうちの周波数νの光及び第２経路の光のうちの周波数ν＋ｆ１の光との周波数差（ｆ１）のビート信号を第１の電気信号に変換する。また、受光器９は、光分波器７から入射される参照光の干渉光を受けてヘテロダイン検波し上述の第１経路の光のうちの周波数ν０の光及び第２経路の光のうちの周波数ν０＋ｆ１の光の周波数差（ｆ１）のビート信号を第２の電気信号に変換する。同期検波器であるＲＦロックインアンプ１１は、上記第２の電気信号を同期信号ｂとして受け、この同期信号ｂに基づいて上記第１の電気信号の位相検出を行う。処理手段１２は、制御手段１３から入力される制御信号ａをトリガにして、ＲＦロックインアンプ１１から入力される位相信号のデータ処理を行い被測定物の位相特性から波長分散を求める。制御手段１３は、測定光の周波数を可変制御するための制御信号ａを発生して波長可変光源１及び処理手段１２に出力する。 The optical demultiplexer 7 receives the interference light of the wavelength multiplexed light formed by wavelength multiplexing the measurement light and the reference light incident from the optical coupler 6, demultiplexes them to the respective frequencies (wavelengths), and The interference light is emitted to the light receiver (PD) 8 and the interference light of the reference light is emitted to the light receiver (PD) 9. The light receiver 8 receives the interference light of the measurement light incident from the optical demultiplexer 7 and performs heterodyne detection, and performs the light of the frequency ν in the light of the first path and the frequency ν + f of the light of the second path. converting the frequency difference between the first optical beat signals of (f 1) to a first electrical signal. Further, the light receiver 9 receives the interference light of the reference light incident from the optical demultiplexer 7 and performs heterodyne detection, and among the light of the frequency ν 0 and the light of the second path among the light of the first path described above. A beat signal having a frequency difference (f 1 ) of light having a frequency ν 0 + f 1 is converted into a second electric signal. The RF lock-in amplifier 11, which is a synchronous detector, receives the second electric signal as a synchronizing signal b, and detects the phase of the first electric signal based on the synchronizing signal b. The processing means 12 uses the control signal a input from the control means 13 as a trigger to perform data processing of the phase signal input from the RF lock-in amplifier 11, and obtains chromatic dispersion from the phase characteristics of the device under test. The control means 13 generates a control signal a for variably controlling the frequency of the measurement light and outputs it to the wavelength variable light source 1 and the processing means 12.

第51回応物連合会「二波長ヘテロダインファイバー干渉計による波長分散評価」28p-R-12（2004.3）：小川憲介、ティ ティ レイ（DNRI）51th Japan Federation of Reciprocal Products “Evaluation of Chromatic Dispersion Using a Two-Wavelength Heterodyne Fiber Interferometer” 28p-R-12 (2004.3): Kensuke Ogawa, Titi Ray (DNRI)

しかしながら、このような従来の光ヘテロダイン干渉装置では、マッハツェンダ型干渉計２０の光分岐手段４を、超音波発生器４ａからＡＯＦＳ４ｂに入力される超音波の周波数ｆ１がヘテロダイン検波される周波数（ビート信号の周波数）と等しくなるように構成しているために、ヘテロダイン検波される周波数を超音波の周波数より低くすることができない。その結果、ヘテロダイン検波されたビート信号の電気信号から位相検出を行う同期検波器として、超音波の周波数とほぼ同じ周波数帯域（数１０〜数１００ＭＨｚ）のＲＦロックインアンプを用いざるを得ず、ＲＦロックインアンプに比べ感度が約６０ｄＢ良く、かつ経済的な、約１００ＫＨｚ以下で動作する通常のロックインアンプが使用できないという問題があった。換言すると、ビート信号の周波数を通常のロックインアンプが使用できる約１００ＫＨｚ以下にすることができれば、同期検波器にＲＦロックインアンプを用いずに済むために、同期検波器での位相検出の感度を約６０ｄＢ改善でき、また同期検波器の経済化が図れるともに、ビート信号の周波数が低いために受光器等の経済化も図れることとなる。また、位相検出に位相敏感検出器（ＰＳＤ：Phase Sensitive Detector）を用いた場合においても、周波数が２ＭＨｚ以下であれば小型のものが使用できる。 However, in such a conventional optical heterodyne interferometer, the optical branching means 4 of the Mach-Zehnder interferometer 20 is subjected to the frequency (beat) at which the ultrasonic frequency f 1 input from the ultrasonic generator 4a to the AOFS 4b is heterodyne-detected. The frequency of the heterodyne detection cannot be made lower than the frequency of the ultrasonic wave. As a result, an RF lock-in amplifier having almost the same frequency band as the ultrasonic frequency (several tens to several hundreds of MHz) must be used as a synchronous detector that performs phase detection from the electrical signal of the beat signal subjected to heterodyne detection. There is a problem that a normal lock-in amplifier operating at about 100 KHz or less cannot be used because the sensitivity is about 60 dB better than the RF lock-in amplifier and economical. In other words, if the frequency of the beat signal can be reduced to about 100 KHz or less at which a normal lock-in amplifier can be used, it is not necessary to use an RF lock-in amplifier for the synchronous detector. The synchronous detector can be made more economical, and the frequency of the beat signal is low, so that the light receiving device and the like can be made more economical. In addition, even when a phase sensitive detector (PSD) is used for phase detection, a small detector can be used if the frequency is 2 MHz or less.

本発明は、これらの課題を解決し、位相検出の感度を改善するとともに、装置の経済化を図った光ヘテロダイン干渉装置を提供することを目的としている。   It is an object of the present invention to provide an optical heterodyne interferometer that solves these problems, improves the sensitivity of phase detection, and achieves an economical device.

上記課題を解決するために、本発明の請求項１の光ヘテロダイン干渉装置では、入射光である周波数可変の測定光を受けて、２つに分岐するとともに互いに周波数の異なる第１経路の光及び第２経路の光として出射する光分岐手段（１４）並びに被測定物を介して入射される前記第１経路の光と前記被測定物を介さないで入射される前記第２経路の光とを合波して干渉光を出射する光結合手段（６）を有するマッハツェンダ型干渉計（３０）と、
前記干渉光を受けてヘテロダイン検波し前記第１経路の光と前記第２経路の光の周波数差のビート信号を電気信号に変換する受光器（８）と、前記ビート信号の周波数とほぼ同じ周波数の同期信号に基づいて前記電気信号の位相検出を行う同期検波器（１５）と、前記測定光の瞬時周波数に対応する、前記同期検波器から出力される位相信号のデータ処理を行って前記被測定物の光周波数−位相特性を求める処理手段（１２）とを備えた光ヘテロダイン干渉装置において、前記光分岐手段は、周波数ｆ１の第1の超音波を発生させる第１の超音波発生器（１４ｂ）と、周波数ｆ２の第２の超音波を発生させる第２の超音波発生器（１４ｃ）と、前記第1の超音波で駆動される第1の音響光学周波数シフタ（１４ｄ）と、前記第２の超音波で駆動される第２の音響光学周波数シフタ（１４ｅ）とを有し、前記第１経路の光と前記第２経路の光との周波数差が前記第1の超音波と前記第２の超音波との周波数差と同一になるようにし、かつ、前記同期検波器がロックインアンプで構成されている。 In order to solve the above-described problems, in the optical heterodyne interferometer according to claim 1 of the present invention, receiving the frequency-variable measurement light that is incident light, the light is split into two and the lights of the first path having different frequencies from each other and The light branching means (14) that emits light as the second path light and the light of the first path incident through the object to be measured and the light of the second path incident without passing through the object to be measured. A Mach-Zehnder interferometer (30) having optical coupling means (6) for combining and emitting interference light;
A receiver (8) that receives the interference light and performs heterodyne detection to convert a beat signal having a frequency difference between the light of the first path and the light of the second path into an electric signal; and a frequency substantially the same as the frequency of the beat signal A synchronous detector (15) for detecting the phase of the electrical signal based on the synchronous signal of the signal, and data processing of the phase signal output from the synchronous detector corresponding to the instantaneous frequency of the measurement light. In the optical heterodyne interferometer having processing means (12) for obtaining the optical frequency-phase characteristic of the measurement object, the optical branching means is a first ultrasonic generator for generating a first ultrasonic wave of frequency f 1 . (14b), a second ultrasonic generator (14c) for generating a second ultrasonic wave of frequency f2, and a first acoustooptic frequency shifter (14d) driven by the first ultrasonic wave , Driven by the second ultrasonic wave A second acousto-optic frequency shifter (14e), and a frequency difference between the light of the first path and the light of the second path is a frequency between the first ultrasonic wave and the second ultrasonic wave. The synchronous detector is configured by a lock-in amplifier so that the difference is the same.

また、本発明の請求項２の光ヘテロダイン干渉装置では、入射光である周波数可変の測定光を受けて、２つに分岐するとともに互いに周波数の異なる第１経路の光及び第２経路の光として出射する光分岐手段（１４）並びに被測定物を介して入射される前記第１経路の光と前記被測定物を介さないで入射される前記第２経路の光とを合波して干渉光を出射する光結合手段（６）を有するマッハツェンダ型干渉計（３０）と、前記干渉光を受けてヘテロダイン検波し前記第１経路の光と前記第２経路の光の周波数差のビート信号を電気信号に変換する受光器（８）と、前記ビート信号の周波数とほぼ同じ周波数の同期信号に基づいて前記電気信号の位相検出を行う同期検波器（１５）と、前記測定光の瞬時周波数に対応する、前記同期検波器から出力される位相信号のデータ処理を行って前記被測定物の光周波数−位相特性を求める処理手段（１２）とを備えた光ヘテロダイン干渉装置において、前記光分岐手段は、高周波交流信号と低周波交流信号との間で振幅変調を行うことにより、前記高周波交流信号の周波数を中心周波数とし、前記低周波交流信号の周波数分シフトしたサイドバンド周波数成分でなる第１の超音波と第２の超音波を発生させる第３の超音波発生器（１４ｇ）と、前記第１の超音波と前記第２の超音波で駆動される第３の音響光学周波数シフタ（１４ｆ）とを有し、前記第１経路の光と前記第２経路の光との周波数差が前記第１の超音波と前記第２の超音波との周波数差と同一になるようにし、かつ、前記同期検波器がロックインアンプで構成されている。   Further, in the optical heterodyne interferometer according to claim 2 of the present invention, as the light of the first path and the light of the second path which receive the frequency variable measurement light which is the incident light, split into two and have different frequencies. The light splitting means (14) that emits light and the light of the first path incident through the object to be measured and the light of the second path incident without passing through the object to be measured are combined to produce interference light. A Mach-Zehnder interferometer (30) having an optical coupling means (6) that emits light, and heterodyne detection in response to the interference light to generate a beat signal of a frequency difference between the light of the first path and the light of the second path A receiver (8) for converting into a signal, a synchronous detector (15) for detecting the phase of the electrical signal based on a synchronous signal having the same frequency as the beat signal, and the instantaneous frequency of the measuring light The synchronous detector In the optical heterodyne interferometer, comprising processing means (12) for processing the data of the output phase signal to obtain the optical frequency-phase characteristic of the device under test, the optical branching means includes a high-frequency AC signal and a low-frequency signal. By performing amplitude modulation with the alternating current signal, the first ultrasonic wave and the second ultrasonic wave composed of sideband frequency components shifted by the frequency of the low frequency alternating current signal with the frequency of the high frequency alternating current signal as the center frequency. A third ultrasonic generator (14g) for generating a sound wave; a third acoustooptic frequency shifter (14f) driven by the first ultrasonic wave and the second ultrasonic wave; The frequency difference between the light of one path and the light of the second path is the same as the frequency difference between the first ultrasonic wave and the second ultrasonic wave, and the synchronous detector is a lock-in amplifier. It consists of

また、本発明の請求項３の光ヘテロダイン干渉装置では、上述した請求項１の光ヘテロダイン干渉装置において、前記光分岐手段は、更に、前記入射光である前記測定光を受けて２つに分岐し、一方の光を前記第１の音響光学周波数シフタに、他方の光を前記第２の音響光学周波数シフタにそれぞれ出射する第１の光カプラ（１４ａ）を有し、前記第１の音響光学周波数シフタは、前記第１の光カプラから入射される一方の光の周波数を前記第1の超音波の周波数ｆ１分周波数シフトして前記第１経路の光として出射し、かつ、前記第２の音響光学周波数シフタは、前記第１の光カプラから入射される他方の光の周波数を前記第２の超音波の周波数ｆ２分周波数シフトして前記第２経路の光として出射している。 In the optical heterodyne interference device according to claim 3 of the present invention, in the optical heterodyne interference device according to claim 1, the optical branching unit further receives the measurement light as the incident light and branches it into two. A first optical coupler (14a) that emits one light to the first acousto-optic frequency shifter and the other light to the second acousto-optic frequency shifter. The frequency shifter shifts the frequency of one light incident from the first optical coupler by a frequency f 1 of the first ultrasonic wave and emits it as the light of the first path, and the second The acousto-optic frequency shifter shifts the frequency of the other light incident from the first optical coupler by a frequency f 2 of the second ultrasonic wave and emits the light as the second path light.

また、本発明の請求項４の光ヘテロダイン干渉装置では、上述した請求項１〜３のいずれかの光ヘテロダイン干渉装置において、前記マッハツェンダ型干渉計は、更に、前記光分岐手段と前記光結合手段との間に設けられ、該光分岐手段から出射された前記第２経路の光が前記光結合手段に到達するまでの時間と、前記第１経路の光が前記被測定物を介して前記光結合手段に到達するまでの時間とがほぼ等しくなるように、前記第１経路の光又は前記第２経路の光を遅延させる遅延器（５）を備えている。   The optical heterodyne interferometer according to claim 4 of the present invention is the optical heterodyne interferometer according to any one of claims 1 to 3, wherein the Mach-Zehnder interferometer further includes the optical branching unit and the optical coupling unit. And the time until the light of the second path emitted from the light branching means reaches the optical coupling means, and the light of the first path passes through the object to be measured A delay device (5) for delaying the light of the first path or the light of the second path is provided so that the time until reaching the coupling means becomes substantially equal.

また、本発明の請求項５の光ヘテロダイン干渉装置では、上述した請求項１〜４のいずれかの光ヘテロダイン干渉装置において、更に、前記第１の超音波発生器から出力される前記第１の超音波と前記第２の超音波発生器から出力される前記第２の超音波とを受けて混合し、又は前記第３の超音波発生器から出力される前記第１の超音波と前記第２の超音波とを受けて混合し、該第１の超音波と該第２の超音波との差周波数の信号を発生して前記同期検波器に前記同期信号として出力するミキサ（１６）を備えている。   Moreover, in the optical heterodyne interference device according to claim 5 of the present invention, in the optical heterodyne interference device according to any one of claims 1 to 4 described above, the first output from the first ultrasonic generator is further performed. The ultrasonic wave and the second ultrasonic wave output from the second ultrasonic wave generator are received and mixed, or the first ultrasonic wave output from the third ultrasonic wave generator and the first ultrasonic wave are mixed. A mixer (16) that receives and mixes the two ultrasonic waves, generates a signal having a difference frequency between the first ultrasonic wave and the second ultrasonic wave, and outputs the signal to the synchronous detector as the synchronous signal; I have.

また、本発明の請求項６の光ヘテロダイン干渉装置では、周波数可変の測定光と当該測定光の出力周波数と異なる固定周波数の参照光とを波長多重してなる波長多重光を受けて、当該波長多重光を分岐するとともに、第１経路の光と第２経路の光とを出力する光分岐手段（１４）であって、当該第１経路の光及び当該第２経路の光はそれぞれ測定光に基づく測定光成分と参照光に基づく参照光成分とからなり、前記第１経路の光に含まれる測定光成分の周波数と前記第２経路の光に含まれる測定光成分の周波数とが異なるとともに、前記第１経路の光に含まれる参照光成分の周波数と前記第２経路の光に含まれる参照光成分の周波数とが同じだけ異なる光分岐手段（１４）並びに被測定物を経由する前記第１経路の光と前記被測定物を経由しない前記第２経路の光とを合波する光結合手段（６）を有するマッハツェンダ型干渉計（３０）と、前記測定光成分と前記参照光成分とを周波数分波する光分波器（７）と、該光分波器で分波された、前記第１経路の光の測定光成分と前記第２経路の光の測定光成分とからなる第１の干渉光を第１の電気信号に変換する第１の受光器（８）と、前記光分波器で分波された、前記第１経路の光の参照光成分と前記第２経路の光の参照光成分とからなる第２の干渉光を第２の電気信号に変換する第２の受光器（９）と、前記第２の電気信号を同期信号として前記第１の電気信号の位相検出を行う同期検波器（１５）と、前記測定光の出力周波数に対応した、前記同期検波器から出力される位相信号をデータ処理して、前記被測定物の光周波数−位相特性を求める処理手段（１２）とを備えた光ヘテロダイン干渉装置において、前記光分岐手段は、周波数ｆ１の第１の超音波を発生させる第１の超音波発生器（１４ｂ）と、周波数ｆ２の第２の超音波を発生させる第２の超音波発生器（１４ｃ）と、前記第１の超音波で駆動される第１の音響光学周波数シフタ（１４ｄ）と、前記第２の超音波で駆動される第２の音響光学周波数シフタ（１４ｅ）とを有し、前記第１経路の光の測定光成分と前記第２経路の光の測定光成分との周波数差、及び前記第１経路の光の参照光成分と前記第２経路の光の参照光成分との周波数差が、前記第１の超音波と前記第２の超音波との周波数差と同一になるようにし、かつ、前記同期検波器がロックインアンプで構成されている。 In the optical heterodyne interferometer according to claim 6 of the present invention, the wavelength-multiplexed light obtained by wavelength-multiplexing the frequency-variable measurement light and the reference light having a fixed frequency different from the output frequency of the measurement light is received, and the wavelength An optical branching means (14) for branching the multiplexed light and outputting the light of the first path and the light of the second path, wherein the light of the first path and the light of the second path are respectively converted into measurement light. A measurement light component based on the reference path and a reference light component based on the reference light, the frequency of the measurement light component included in the light of the first path is different from the frequency of the measurement light component included in the light of the second path, The frequency of the reference light component contained in the light of the first path and the frequency of the reference light component contained in the light of the second path are different from each other by the same amount as the optical branching means (14) and the first object passing through the object to be measured. Via the light of the path and the measured object A Mach-Zehnder interferometer (30) having optical coupling means (6) for multiplexing the light of the second path, and an optical demultiplexer (7) for demultiplexing the measurement light component and the reference light component. ), And the first interference light that is demultiplexed by the optical demultiplexer and includes the measurement light component of the light of the first path and the measurement light component of the light of the second path, as the first electric signal A first light receiver (8) for conversion, and a second light comprising a reference light component of the light of the first path and a reference light component of the light of the second path, which is demultiplexed by the optical demultiplexer A second light receiver (9) for converting the interference light into a second electric signal; a synchronous detector (15) for detecting the phase of the first electric signal using the second electric signal as a synchronizing signal; Data processing is performed on the phase signal output from the synchronous detector corresponding to the output frequency of the measurement light, and the optical frequency-position of the device under test is measured. In the optical heterodyne interference apparatus having processing means (12) for determining the characteristics, the light branching means, a first ultrasonic generator for generating a first ultrasonic frequency f 1 and (14b), the frequency f A second ultrasonic generator (14c) for generating two second ultrasonic waves, a first acoustooptic frequency shifter (14d) driven by the first ultrasonic wave, and the second ultrasonic wave And a second acousto-optic frequency shifter (14e) driven by the frequency difference between the measurement light component of the light of the first path and the measurement light component of the light of the second path, and the first path The frequency difference between the reference light component of the first light and the reference light component of the second path light is the same as the frequency difference between the first ultrasonic wave and the second ultrasonic wave, and The synchronous detector is composed of a lock-in amplifier.

また、本発明の請求項７の光ヘテロダイン干渉装置では、上述した請求項６の光ヘテロダイン干渉装置において、前記マッハツェンダ型干渉計は、更に、前記光分岐手段と前記光結合手段との間に設けられ、該光分岐手段から出射された前記第２経路の光が前記光結合手段に到達するまでの各時間と、前記第１経路の光が前記被測定物を介して前記光結合手段に到達するまでの各時間とがほぼ等しくなるように、前記第１経路の光又は前記第２経路の光を遅延させる遅延器（５）を備えている。   The optical heterodyne interferometer according to claim 7 of the present invention is the optical heterodyne interferometer according to claim 6, wherein the Mach-Zehnder interferometer is further provided between the optical branching means and the optical coupling means. Each time until the light of the second path emitted from the light branching means reaches the optical coupling means, and the light of the first path reaches the optical coupling means via the object to be measured. A delay device (5) for delaying the light of the first path or the light of the second path is provided so that each time until the time becomes approximately equal.

また、本発明の請求項８の光ヘテロダイン干渉装置では、上述した請求項６又は７の光ヘテロダイン干渉装置において、前記マッハツェンダ型干渉計は、その光路中に光ファイバを含んで構成される光ファイバ干渉計であるようにしている。   The optical heterodyne interferometer according to claim 8 of the present invention is the optical heterodyne interferometer according to claim 6 or 7, wherein the Mach-Zehnder interferometer includes an optical fiber in its optical path. It is an interferometer.

また、本発明の請求項９の光ヘテロダイン干渉装置では、上述した請求項１〜５のいずれかの光ヘテロダイン干渉装置において、更に、所定の周波数範囲内で周波数可変の前記測定光を順次発振させ、前記光分岐手段へ前記入射光として出射する波長可変光源（１）と、該波長可変光源からの測定光の周波数を可変するための制御信号を当該波長可変光源に出力する制御手段（１３）とを備えている。   In the optical heterodyne interference device according to claim 9 of the present invention, in the optical heterodyne interference device according to any one of claims 1 to 5, the measurement light having a variable frequency within a predetermined frequency range is sequentially oscillated. The wavelength tunable light source (1) emitted as the incident light to the light branching means, and the control means (13) for outputting a control signal for varying the frequency of the measurement light from the wavelength tunable light source to the wavelength tunable light source And.

また、本発明の請求項１０の光ヘテロダイン干渉装置では、上述した請求項６〜８のいずれかの光ヘテロダイン干渉装置において、更に、所定の周波数範囲内で周波数可変の前記測定光を順次発振させる波長可変光源（１）と、該波長可変光源からの測定光の周波数を可変するための制御信号を当該波長可変光源に出力する制御手段（１３）と、前記測定光の周波数とは異なる固定周波数の前記参照光を発振させる光源（２）と、前記波長可変光源から出射される前記測定光と前記光源から出射される前記参照光とを受け合波することによって波長多重し、得られた前記波長多重光を前記光分岐手段へ前記入射光として出射する第２の光カプラ（３）とを備えている。   Moreover, in the optical heterodyne interference device according to claim 10 of the present invention, in the optical heterodyne interference device according to any of claims 6 to 8, the measurement light having a variable frequency within a predetermined frequency range is sequentially oscillated. A variable wavelength light source (1), a control means (13) for outputting a control signal for varying the frequency of the measurement light from the variable wavelength light source to the variable wavelength light source, and a fixed frequency different from the frequency of the measurement light The light source (2) that oscillates the reference light, the measurement light emitted from the wavelength tunable light source, and the reference light emitted from the light source are combined and wavelength-multiplexed to obtain the obtained A second optical coupler (3) for emitting wavelength-multiplexed light to the optical branching means as the incident light.

また、本発明の請求項１１の光ヘテロダイン干渉装置では、周波数可変の測定光と当該測定光の出力周波数と異なる固定周波数の参照光とを波長多重してなる波長多重光を受けて、当該波長多重光を分岐するとともに、第１経路の光と第２経路の光とを出力する光分岐手段（１４）であって、当該第１経路の光及び当該第２経路の光はそれぞれ測定光に基づく測定光成分と参照光に基づく参照光成分とからなり、前記第１経路の光に含まれる測定光成分の周波数と前記第２経路の光に含まれる測定光成分の周波数とが異なるとともに、前記第１経路の光に含まれる参照光成分の周波数と前記第２経路の光に含まれる参照光成分の周波数とが同じだけ異なる光分岐手段（１４）並びに被測定物を経由する前記第１経路の光と前記被測定物を経由しない前記第２経路の光とを合波する光結合手段（６）を有するマッハツェンダ型干渉計（３０）と、前記測定光成分と前記参照光成分とを周波数分波する光分波器（７）と、該光分波器で分波された、前記第１経路の光の測定光成分と前記第２経路の光の測定光成分とからなる第１の干渉光を第１の電気信号に変換する第１の受光器（８）と、前記光分波器で分波された前記第１経路の光の参照光成分と前記第２経路の光の参照光成分とからなる第２の干渉光を、前記測定光の出力周波数に対応した前記第１の電気信号の位相量を検出するための同期信号となる第２の電気信号に変換する第２の受光器（９）とを備えた光ヘテロダイン干渉装置において、前記光分岐手段は、周波数ｆ１の第１の超音波を発生させる第１の超音波発生器（１４ｂ）と、周波数ｆ２の第２の超音波を発生させる第２の超音波発生器（１４ｃ）と、前記第１の超音波で駆動される第１の音響光学周波数シフタ（１４ｄ）と、前記第２の超音波で駆動される第２の音響光学周波数シフタ（１４ｅ）とを有し、前記第１経路の光の測定光成分と前記第２経路の光の測定光成分との周波数差、及び前記第１経路の光の参照光成分と前記第２経路の光の参照光成分との周波数差が、前記第１の超音波と前記第２の超音波との周波数差と同一になるようにし、かつ、当該第１の超音波と第２の超音波との周波数差が２ＭＨｚ以下であるようにしている。 In the optical heterodyne interference device according to claim 11 of the present invention, the wavelength-multiplexed light obtained by wavelength-multiplexing the frequency-variable measurement light and the reference light having a fixed frequency different from the output frequency of the measurement light is received, and the wavelength An optical branching means (14) for branching the multiplexed light and outputting the light of the first path and the light of the second path, wherein the light of the first path and the light of the second path are respectively converted into measurement light. A measurement light component based on the reference path and a reference light component based on the reference light, the frequency of the measurement light component included in the light of the first path is different from the frequency of the measurement light component included in the light of the second path, The frequency of the reference light component contained in the light of the first path and the frequency of the reference light component contained in the light of the second path are different from each other by the same amount as the optical branching means (14) and the first object passing through the object to be measured. Via the light of the path and the measured object A Mach-Zehnder interferometer (30) having an optical coupling means (6) for multiplexing the light of the second path not present, and an optical demultiplexer (7) for frequency-demultiplexing the measurement light component and the reference light component ), And the first interference light that is demultiplexed by the optical demultiplexer and includes the measurement light component of the light of the first path and the measurement light component of the light of the second path, as the first electric signal Second interference comprising a first light receiver (8) to be converted, and a reference light component of the light of the first path and a reference light component of the light of the second path, which are demultiplexed by the optical demultiplexer. A second light receiver (9) that converts light into a second electric signal that is a synchronization signal for detecting a phase amount of the first electric signal corresponding to the output frequency of the measurement light; in the optical heterodyne interference apparatus, the light branching means, a first ultrasonic generator for generating a first ultrasonic frequency f 1 (1 and b), the second ultrasonic generator for generating a second ultrasound frequency f 2 and (14c), and said first first acousto-optic frequency shifter which is driven by the ultrasonic (14d), A second acoustooptic frequency shifter (14e) driven by the second ultrasonic wave, and a frequency difference between the measurement light component of the light of the first path and the measurement light component of the light of the second path And the frequency difference between the reference light component of the light of the first path and the reference light component of the light of the second path is the same as the frequency difference between the first ultrasonic wave and the second ultrasonic wave. In addition, the frequency difference between the first ultrasonic wave and the second ultrasonic wave is 2 MHz or less.

また、本発明の請求項１２の光ヘテロダイン干渉装置では、入射光である周波数可変の測定光を受けて、２つに分岐するとともに互いに周波数の異なる第１経路の光及び第２経路の光として出射する光分岐手段（１４）並びに被測定物を介して入射される前記第１経路の光と前記被測定物を介さないで入射される前記第２経路の光とを合波して干渉光を出射する光結合手段（６）を含むマッハツェンダ型干渉計（３０）と、前記干渉光を受けて、前記第１経路の光と前記第２経路の光との周波数差のビート信号とほぼ同じ周波数の同期信号に基づいて、前記測定光の出力周波数に対応する位相変化量が検出されるべき電気信号を出力する受光器（８）とを備えた光ヘテロダイン干渉装置において、前記光分岐手段は、周波数ｆ１の第１の超音波を発生させる第１の超音波発生器（１４ｂ）と、周波数ｆ２の第２の超音波を発生させる第２の超音波発生器（１４ｃ）と、前記第１の超音波で駆動される第１の音響光学周波数シフタ（１４ｄ）と、前記第２の超音波で駆動される第２の音響光学周波数シフタ（１４ｅ）とを有し、前記第１経路の光と前記第２経路の光との周波数差が、前記第１の超音波と前記第２の超音波との周波数差と同一になるようにし、かつ、当該第１の超音波と第２の超音波との周波数差が２ＭＨｚ以下であるようにしている。 In the optical heterodyne interferometer according to claim 12 of the present invention, as the light of the first path and the light of the second path, which receives the variable frequency measurement light which is the incident light, branches into two and has different frequencies. The light splitting means (14) that emits light and the light of the first path incident through the object to be measured and the light of the second path incident without passing through the object to be measured are combined to produce interference light. A Mach-Zehnder interferometer (30) including an optical coupling means (6) that emits light, and the beat signal of the frequency difference between the light of the first path and the light of the second path in response to the interference light In the optical heterodyne interferometer, comprising: a light receiver (8) that outputs an electrical signal whose phase change amount corresponding to the output frequency of the measurement light is to be detected based on a frequency synchronization signal; , First supersonic of frequency f 1 First ultrasonic generator for generating a wave and (14b), a second ultrasonic generator for generating a second ultrasound frequency f 2 and (14c), is driven by the first ultrasonic A first acousto-optic frequency shifter (14d) and a second acousto-optic frequency shifter (14e) driven by the second ultrasonic wave, the light of the first path and the light of the second path; Is equal to the frequency difference between the first ultrasonic wave and the second ultrasonic wave, and the frequency difference between the first ultrasonic wave and the second ultrasonic wave is 2 MHz. The following is set.

本発明の請求項１及び２の光ヘテロダイン干渉装置では、光分岐手段はヘテロダイン検波される周波数を超音波の周波数より低くすることができる構成とし、かつ、同期検波器は約１００ＫＨｚ以下で動作する通常のロックインアンプを使用するようにしたので、従来の同期検波器にＲＦロックインアンプを用いなければならない場合に比べ、位相検出の感度を約６０ｄＢ改善でき、また同期検波器の経済化が図れるともに、ビート信号の周波数が低いために受光器等の経済化も図れる。   In the optical heterodyne interference apparatus according to claims 1 and 2 of the present invention, the optical branching means is configured to be able to make the frequency of heterodyne detection lower than the frequency of the ultrasonic wave, and the synchronous detector operates at about 100 KHz or less. Since a normal lock-in amplifier is used, the sensitivity of phase detection can be improved by about 60 dB compared to the case where an RF lock-in amplifier must be used for a conventional synchronous detector, and the synchronous detector can be made more economical. In addition to the fact that the frequency of the beat signal is low, the cost of the photoreceiver can be improved.

本発明の請求項３の光ヘテロダイン干渉装置では、光分岐手段は第１の音響光学周波数シフタと第２の音響光学周波数シフタとを並列に配置するようにしたので、この２つの音響光学周波数シフタで生じる位相特性（波長分散）をキャンセルすることができる。   In the optical heterodyne interferometer according to claim 3 of the present invention, the optical branching means is arranged such that the first acoustooptic frequency shifter and the second acoustooptic frequency shifter are arranged in parallel. It is possible to cancel the phase characteristics (wavelength dispersion) generated in step (1).

本発明の請求項４及び７の光ヘテロダイン干渉装置では、遅延器によってマッハツェンダ型干渉計の２つの光路長を合わせるようにしたので、位相測定精度を上げることができる。   In the optical heterodyne interferometers according to claims 4 and 7 of the present invention, the two optical path lengths of the Mach-Zehnder interferometer are matched by the delay unit, so that the phase measurement accuracy can be improved.

本発明の請求項６の光ヘテロダイン干渉装置では、光分岐手段はヘテロダイン検波される周波数を超音波の周波数より低くすることができる構成とし、かつ、同期検波器は約１００ＫＨｚ以下で動作する通常のロックインアンプを使用するようにしたので、従来の同期検波器にＲＦロックインアンプを用いなければならない場合に比べ、位相検出の感度を約６０ｄＢ改善でき、また同期検波器の経済化が図れるともに、ビート信号の周波数が低いために受光器等の経済化も図れる。また、測定光と参照光とを波長多重して同時にマッハツェンダ型干渉計へ入射して、干渉計の不安定性により生じる測定光における位相変動を参照光における位相変動で相殺するようにしたので、例えマッハツェンダ型干渉計がその光路中に光ファイバを含んで構成される光ファイバ干渉計であったとしても、その光ファイバの温度変化や振動などに起因して生じる揺らぎによる位相変動を改善することができる。   In the optical heterodyne interference device according to claim 6 of the present invention, the optical branching means is configured to be able to make the frequency of heterodyne detection lower than the frequency of the ultrasonic wave, and the synchronous detector operates at a normal frequency of about 100 KHz or less. Since a lock-in amplifier is used, the phase detection sensitivity can be improved by about 60 dB compared to the case where an RF lock-in amplifier must be used for a conventional synchronous detector, and the synchronous detector can be made more economical. Moreover, since the frequency of the beat signal is low, the cost of the photoreceiver can be improved. In addition, the measurement light and the reference light are wavelength-multiplexed and simultaneously incident on the Mach-Zehnder interferometer so that the phase fluctuation in the measurement light caused by the instability of the interferometer is canceled by the phase fluctuation in the reference light. Even if the Mach-Zehnder interferometer is an optical fiber interferometer configured to include an optical fiber in its optical path, it is possible to improve phase fluctuation due to fluctuations caused by temperature change or vibration of the optical fiber. it can.

本発明の請求項８の光ヘテロダイン干渉装置では、マッハツェンダ型干渉計をその光路中に光ファイバを含んで構成される光ファイバ干渉計とするようにしたので、光路が空間で構成される干渉計を用いる場合に比べ装置の小型化、経済化が可能となる。   In the optical heterodyne interferometer according to the eighth aspect of the present invention, the Mach-Zehnder interferometer is an optical fiber interferometer that includes an optical fiber in its optical path. Compared to the case of using the device, the apparatus can be made smaller and more economical.

本発明の請求項１１及び１２の光ヘテロダイン干渉装置では、光分岐手段はヘテロダイン検波される周波数を超音波の周波数より低くすることができる構成とし、かつ、そのヘテロダイン検波される周波数を２ＭＨｚ以下であるようにしたので、同期検波器に位相敏感検出器（ＰＳＤ：Phase Sensitive Detector）を用いる場合においても小型のものが使用できる。   In the optical heterodyne interference apparatus according to claims 11 and 12 of the present invention, the optical branching means is configured to be able to make the frequency of heterodyne detection lower than the frequency of the ultrasonic wave, and the frequency of heterodyne detection is 2 MHz or less. Since it was made to exist, even when using a phase sensitive detector (PSD) for a synchronous detector, a small thing can be used.

以下に本発明の実施形態を記載する。   Embodiments of the present invention will be described below.

［第１実施形態］
本発明の第１実施形態の光ヘテロダイン干渉装置の構成を図１に示す。従来の光ヘテロダイン干渉装置と同一要素には同一符号を付し詳細説明は省略する。波長可変光源１は、例えば波長可変レーザであり、制御手段１３から出力される制御信号ａに基づいて所定の周波数範囲（例えば波長で１５２５〜１６２０ｎｍ）の測定光（周波数ν）を順次発振して光カプラ３へ出射する。また、光源２は、例えばレーザであり、波長可変光源１の発振周波数とは異なる固定周波数（例えば波長で１６２５ｎｍ）の参照光（周波数ν０）を発振して光カプラ３へ出射する。光カプラ３は、上記測定光及び参照光を合波して波長多重し、その波長多重光をマッハツェンダ型干渉計３０の光分岐手段１４へ出射する。 [First Embodiment]
The configuration of the optical heterodyne interference apparatus according to the first embodiment of the present invention is shown in FIG. The same elements as those of the conventional optical heterodyne interference device are denoted by the same reference numerals, and detailed description thereof is omitted. The wavelength variable light source 1 is, for example, a wavelength variable laser, and sequentially oscillates measurement light (frequency ν) in a predetermined frequency range (for example, 1525 to 1620 nm in wavelength) based on a control signal a output from the control unit 13. The light is emitted to the optical coupler 3. The light source 2 is, for example, a laser, and oscillates reference light (frequency ν 0 ) having a fixed frequency (for example, 1625 nm in wavelength) different from the oscillation frequency of the wavelength tunable light source 1 and emits it to the optical coupler 3. The optical coupler 3 combines the measurement light and the reference light and wavelength-multiplexes them, and emits the wavelength-multiplexed light to the optical branching means 14 of the Mach-Zehnder interferometer 30.

光分岐手段１４は、光カプラ１４ａ、周波数ｆ１の超音波を発生する超音波発生器１４ｂ、この周波数ｆ１の超音波によって駆動されるＡＯＦＳ１４ｄ、周波数ｆ２の超音波を発生する超音波発生器１４ｃ、及びこの周波数ｆ２の超音波によって駆動されるＡＯＦＳ１４ｅで構成されており、光カプラ３から入射される波長多重光を２つの光に分岐するとともに、その分岐した２つの光にヘテロダイン検波のための周波数差（ビート信号の周波数となる）を与えて、それぞれ第１経路の光、第２経路の光として出射する。すなわち、光カプラ１４ａは、光カプラ３からの波長多重光を２つの光に分岐して、一方をＡＯＦＳ１４ｄに、他方をＡＯＦＳ１４ｅにそれぞれ出射する。ＡＯＦＳ１４ｄは、上記一方を超音波の周波数ｆ１分周波数シフトさせてなる第１経路の光を、被測定物１０を介して光カプラ６へ出射する。また、ＡＯＦＳ１４ｅは、上記他方を超音波の周波数ｆ２分周波数シフトさせてなる第２経路の光を遅延器５へ出射する。なお、第１経路の光及び第２経路の光は、それぞれ測定光からなる成分(測定光成分)と参照光からなる成分(参照光成分)とからなる。この第１実施形態では、第１経路の光のうちの測定光成分、参照光成分の周波数は、それぞれν＋ｆ１、ν０＋ｆ１であり、第２経路の光のうちの測定光成分、参照光成分の周波数は、それぞれν＋ｆ２、ν０＋ｆ２である。このように構成された光分岐手段１４は、ＡＯＦＳ１４ｄ及びＡＯＦＳ１４ｅを並列に配列しているので、この２つのＡＯＦＳ１４ｄ、１４ｅで生じる位相特性（波長分散）をキャンセルすることができる。 Light branching means 14, an optical coupler 14a, an ultrasonic generator 14b for generating an ultrasonic wave of frequency f 1, the frequency f 1 of AOFS14d driven by ultrasound, ultrasonic generator for generating ultrasonic waves of a frequency f 2 vessels 14c, and is composed of AOFS14e driven by ultrasound of the frequency f 2, as well as branching the wavelength division multiplexed light incident from the optical coupler 3 into two light, heterodyne detection to the branched two optical Is given as a frequency difference (becomes the frequency of the beat signal) and emitted as light on the first path and light on the second path, respectively. That is, the optical coupler 14a splits the wavelength multiplexed light from the optical coupler 3 into two lights, and outputs one to the AOFS 14d and the other to the AOFS 14e. The AOFS 14d emits light of the first path obtained by shifting one of the above frequencies by an ultrasonic frequency f 1 to the optical coupler 6 via the device under test 10. Further, the AOFS 14 e emits light of a second path obtained by shifting the other side by the frequency of the ultrasonic wave f 2 to the delay unit 5. The light of the first path and the light of the second path are each composed of a component (measurement light component) composed of measurement light and a component (reference light component) composed of reference light. In the first embodiment, the frequencies of the measurement light component and the reference light component in the light of the first path are ν + f 1 and ν 0 + f 1 , respectively, and the measurement light component and the reference in the light of the second path The frequencies of the light components are ν + f 2 and ν 0 + f 2 , respectively. Since the optical branching unit 14 configured as described above has the AOFS 14d and the AOFS 14e arranged in parallel, the phase characteristics (wavelength dispersion) generated by the two AOFSs 14d and 14e can be canceled.

具体的な超音波の周波数の例としては、超音波の周波数ｆ１は８０．０５ＭＨｚ、超音波の周波数ｆ２は８０ＭＨｚである。そして、これらの超音波の周波数に基づく第１経路の光及び第２経路の光が光カプラ６で合波された後にヘテロダイン検波されると、周波数ｆ１−ｆ２（＝０．０５ＭＨｚ）の第１の電気信号（測定光成分の場合）が出力される。すなわち、第１経路の光及び第２経路の光の測定光成分同士の周波数差［（ν＋ｆ１）−（ν＋ｆ２）］は、２つの超音波の周波数差（ｆ１−ｆ２）と同一の０．０５ＭＨｚとなる。これは、後述する同期検波器として、約１００ｋＨｚ以下で動作する通常のロックインアンプ１５が使用できる周波数である。 As a specific example of the ultrasonic frequency, the ultrasonic frequency f 1 is 80.05 MHz, and the ultrasonic frequency f 2 is 80 MHz. When the light of the first path and the light of the second path based on these ultrasonic frequencies are combined by the optical coupler 6 and then heterodyne detection is performed, the frequency f 1 −f 2 (= 0.05 MHz) is obtained. A first electrical signal (in the case of a measurement light component) is output. That is, the frequency difference [(ν + f 1 ) − (ν + f 2 )] between the measurement light components of the light of the first path and the light of the second path is the same as the frequency difference (f 1 −f 2 ) of the two ultrasonic waves. 0.05 MHz. This is a frequency at which a normal lock-in amplifier 15 operating at about 100 kHz or less can be used as a synchronous detector described later.

遅延器５は、例えば光ファイバ遅延線で構成され、マッハツェンダ型干渉計の光路長を合わせるために、第２経路の光を、第１経路の光が被測定物１０によって遅延される時間に対応する時間分遅延させて光カプラ６へ出射する。なお、遅延器５は可変できるものであってもよいし、また第１経路に設けてもよい。ただし、この遅延器５は、干渉計の光路長を合わせて位相測定精度をあげるのに有効であるが、必ずしも必須ではない。光カプラ６は、被測定物１０を介して入射される第１経路の光（波長多重光をそれぞれｆ１だけ周波数シフトした光）と遅延器５を介して入射される第２経路の光（波長多重光をそれぞれｆ２だけ周波数シフトした光）とを合波して波長多重光の干渉光を光分波器７へ出射する。 The delay unit 5 is configured by, for example, an optical fiber delay line, and corresponds to the time when the light of the first path is delayed by the DUT 10 in order to match the optical path length of the Mach-Zehnder interferometer. The light is delayed by the time to be output to the optical coupler 6. The delay unit 5 may be variable or may be provided in the first path. However, the delay unit 5 is effective in increasing the phase measurement accuracy by matching the optical path length of the interferometer, but is not necessarily essential. The optical coupler 6 receives the first path light incident on the device under test 10 (the wavelength-shifted light having a frequency shifted by f 1 ) and the second path light incident on the delayer 5 ( The wavelength-multiplexed light is combined with the light whose frequency is shifted by f 2 ), and the interference light of the wavelength-multiplexed light is emitted to the optical demultiplexer 7.

なお、光分岐手段１４、被測定物１０、遅延器５及び光カプラ６はマッハツェンダ型干渉計３０を構成している。したがって、光分岐手段１４は、入射光を２つに分岐して別々の光路を通してから結合（干渉）させるマッハツェンダ型干渉計における、入射光を２つに分岐する手段であり、また光カプラ６は、別々の光路を通してから結合（干渉）させる手段である。マッハツェンダ型干渉計３０は、自身がその光路に光ファイバを含んで構成される光ファイバ干渉計であったり、又はその光路長を合わせる遅延器５が光ファイバ遅延線であったりする場合、温度変化や振動などに起因した光ファイバの揺らぎによる位相変動を生じやすい。それを改善するために、測定光と参照光とを波長多重して同時にマッハツェンダ型干渉計３０へ入射して、位相検出時に干渉計の不安定性により生じる測定光における位相変動を参照光における位相変動で相殺している。なお、被測定物１０としては、光ファイバ、ＦＧＢセンサ等の光部品が対象である。   The optical branching means 14, the DUT 10, the delay device 5, and the optical coupler 6 constitute a Mach-Zehnder interferometer 30. Therefore, the optical branching means 14 is a means for splitting the incident light into two in a Mach-Zehnder interferometer that splits the incident light into two and couples (interferes) after passing through separate optical paths. , Means for coupling (interference) after passing through separate optical paths. When the Mach-Zehnder interferometer 30 is an optical fiber interferometer that includes an optical fiber in its optical path, or the delay device 5 that matches the optical path length is an optical fiber delay line, the temperature change It is likely to cause phase fluctuations due to fluctuations in the optical fiber caused by vibration and vibration. In order to improve this, the measurement light and the reference light are wavelength-multiplexed and simultaneously incident on the Mach-Zehnder interferometer 30, and the phase fluctuation in the measurement light caused by the instability of the interferometer during phase detection is detected. Is offset by The object to be measured 10 is an optical component such as an optical fiber or an FGB sensor.

光分波器７は、光カプラ６から入射される測定光成分同士の第１の干渉光と参照光成分同士の第２の干渉光とを受けて、それぞれの周波数（波長）、例えば１５２５〜１６２０ｎｍの波長帯域と１６２５ｎｍの波長とに分波し、測定光成分同士の干渉光を受光器（ＰＤ）８に、参照光成分同士の干渉光を受光器（ＰＤ）９に出射する。受光器８は、光分波器７から入射される測定光成分同士の干渉光を受けてヘテロダイン検波し周波数ν＋８０．０５ＭＨｚの光及び周波数ν＋８０ＭＨｚの光の周波数差０．０５ＭＨｚのビート信号を第１の電気信号に変換する。また、受光器９も、同様に、光分波器７から入射される参照光成分同士の干渉光を受けてヘテロダイン検波し周波数差０．０５ＭＨｚのビート信号を第２の電気信号に変換する。   The optical demultiplexer 7 receives the first interference light of the measurement light components incident from the optical coupler 6 and the second interference light of the reference light components, and receives respective frequencies (wavelengths), for example, 1525 to 2525. The light is split into a wavelength band of 1620 nm and a wavelength of 1625 nm, and interference light between the measurement light components is emitted to the light receiver (PD) 8, and interference light between the reference light components is emitted to the light receiver (PD) 9. The light receiver 8 receives the interference light between the measurement light components incident from the optical demultiplexer 7 and performs heterodyne detection to generate a beat signal having a frequency difference of 0.05 MHz between the light having the frequency ν + 80.05 MHz and the light having the frequency ν + 80 MHz. Convert to electrical signal. Similarly, the light receiver 9 receives the interference light between the reference light components incident from the optical demultiplexer 7 and performs heterodyne detection to convert a beat signal having a frequency difference of 0.05 MHz into a second electric signal.

ロックインアンプ１５は、同期検波器であり、上記第２の電気信号を同期信号ｂとして受け、この同期信号ｂに基づいて上記第１の電気信号の位相検出を行う。このロックインアンプ１５は、約１００ＫＨｚ以下で動作する通常のロックインアンプであり、従来例の数１０〜数１００ＭＨｚで動作するＲＦロックインアンプ１１とは当業者間で区別されている。通常のロックインアンプは、ＲＦロックインアンプに比べて、位相検出の感度が約６０ｄＢ良く、また経済的である点で優っている。処理手段１２は、制御手段１３から入力される制御信号ａをトリガにして、ロックインアンプ１５から入力される位相信号のデータ処理を行い被測定物の位相特性から伝播遅延時間、波長分散、温度などの物理量等を求める。制御手段１３は、測定光の周波数を可変制御するための制御信号ａを発生して波長可変光源１及び処理手段１２に出力する。   The lock-in amplifier 15 is a synchronous detector, receives the second electric signal as the synchronous signal b, and detects the phase of the first electric signal based on the synchronous signal b. The lock-in amplifier 15 is a normal lock-in amplifier that operates at about 100 KHz or less, and is distinguished from those of ordinary skill in the art by the RF lock-in amplifier 11 that operates at several tens to several hundreds of MHz in the conventional example. Ordinary lock-in amplifiers are superior to RF lock-in amplifiers in that the phase detection sensitivity is about 60 dB better and economical. The processing means 12 uses the control signal a input from the control means 13 as a trigger to perform data processing on the phase signal input from the lock-in amplifier 15, and from the phase characteristics of the device under test to propagation delay time, chromatic dispersion, temperature Obtain physical quantities such as The control means 13 generates a control signal a for variably controlling the frequency of the measurement light and outputs it to the wavelength variable light source 1 and the processing means 12.

なお、上記第１実施形態では、波長可変光源１から出射される測定光と光源２から出射される参照光とを合波して波長多重する光カプラ３と、この光カプラ３から入射される波長多重光を２つの光に分岐する光カプラ１４ａとを、機能的に区別してそれぞれを別の光カプラで構成しているが、１つの光カプラでも構成できることは自明である。   In the first embodiment, the optical coupler 3 that combines the measurement light emitted from the wavelength tunable light source 1 and the reference light emitted from the light source 2 and multiplexes the light is incident on the optical coupler 3. The optical coupler 14a that branches the wavelength-multiplexed light into two lights is functionally distinguished from each other and is constituted by different optical couplers. However, it is obvious that the optical coupler 14a can also be constituted by one optical coupler.

［第２実施形態］
本発明の第２実施形態の光ヘテロダイン干渉装置の構成を図２に示す。第２実施形態は、マッハツェンダ型干渉計が光ファイバ干渉計ではなく、また例え光ファイバ干渉計であったとしても光ファイバの揺らぎによる位相変動が無視でき、参照光を用いて測定光に基づくビート信号の位相変動を相殺しなくてもよい場合の構成である。第１実施形態の図１とは、下記の(１)、（２）のみ異なり他は同一である。したがって詳細説明は省略する。（１）参照光の発振、合波、分波及びヘテロダイン検波に係わる要素、つまり光源２、光カプラ３、光分波器７及び受光器９を備えていない。（２）超音波発生器１４ｂから出力される周波数ｆ１の超音波と超音波発生器１４ｃから出力される周波数ｆ２の超音波とを受けて混合し、これら２つの超音波の差周波数信号を発生して同期検波器としてのロックインアンプ１５に同期信号ｂとして出力するミキサ（ＭＩＸ）１６を備えている。 [Second Embodiment]
The configuration of the optical heterodyne interference apparatus according to the second embodiment of the present invention is shown in FIG. In the second embodiment, even if the Mach-Zehnder interferometer is not an optical fiber interferometer, and even if it is an optical fiber interferometer, phase fluctuations due to fluctuations in the optical fiber can be ignored, and the beat based on the measurement light using the reference light In this configuration, it is not necessary to cancel the signal phase fluctuation. It differs from FIG. 1 of the first embodiment only in the following (1) and (2), and the others are the same. Therefore, detailed description is omitted. (1) Elements related to oscillation, multiplexing, demultiplexing, and heterodyne detection of the reference light, that is, the light source 2, the optical coupler 3, the optical demultiplexer 7, and the light receiver 9 are not provided. (2) The ultrasonic wave having the frequency f 1 output from the ultrasonic generator 14b and the ultrasonic wave having the frequency f 2 output from the ultrasonic generator 14c are received and mixed, and a difference frequency signal between these two ultrasonic waves. And a mixer (MIX) 16 that outputs the signal as a synchronization signal b to a lock-in amplifier 15 as a synchronous detector.

なお、上述の第１実施形態、第２実施形態の光分岐手段１４としては、図１、図２に示したものの他に、図３（ａ）、（ｂ）、（ｃ）に示すものでもよい。すなわち、図３（ａ）においては、ＡＯＦＳ１４ｄ及びＡＯＦＳ１４ｅが直列に配列されている。先ず、ＡＯＦＳ１４ｄは、入射光（周波数ν）を２つの光に分岐して、一方は０次の回折光を第１経路の光（周波数ν）として出射し、他方は超音波発生器１４ｂから入力される超音波の周波数ｆ１分だけ周波数シフトした＋１次の回折光（周波数ν＋ｆ１）をＡＯＦＳ１４ｅへ出射する。次に、ＡＯＦＳ１４ｅは、ＡＯＦＳ１４ｄからの＋１次の回折光を超音波発生器１４ｃから入力される超音波の周波数ｆ２分だけさらに周波数シフトした−１次の回折光（周波数ν＋ｆ１−ｆ２）を第２経路の光として出射する。これにより、第１経路の光と第２経路の光の周波数差はｆ１−ｆ２となる。 The optical branching means 14 of the first and second embodiments described above may be those shown in FIGS. 3A, 3B, and 3C in addition to those shown in FIGS. Good. That is, in FIG. 3A, the AOFS 14d and the AOFS 14e are arranged in series. First, the AOFS 14d splits incident light (frequency ν) into two lights, one of which emits 0th-order diffracted light as light of the first path (frequency ν), and the other is input from the ultrasonic generator 14b. + 1st order diffracted light (frequency ν + f 1 ) shifted by the frequency f 1 of the ultrasonic wave to be emitted is emitted to the AOFS 14e. Then, AOFS14e the + 1st order diffracted light ultrasonic generator 14c -1-order diffracted light further frequency shifted frequency f 2 minutes of ultrasonic waves to be inputted from the AOFS14d (frequency ν + f 1 -f 2) Is emitted as light of the second path. As a result, the frequency difference between the light of the first path and the light of the second path is f 1 −f 2 .

また、図３（ｂ）においては、図３（ａ）と同様に、ＡＯＦＳ１４ｄ及びＡＯＦＳ１４ｅが直列に配列されている。先ず、ＡＯＦＳ１４ｄは、入射光（周波数ν）を２つの光に分岐して、一方は０次の回折光（周波数ν）をＡＯＦＳ１４ｅへ出射する。他方は超音波発生器１４ｂから入力される超音波の周波数ｆ１分だけ周波数シフトした＋１次の回折光（周波数ν＋ｆ１）を第１経路の光として出射する。次に、ＡＯＦＳ１４ｅは、ＡＯＦＳ１４ｄからの０次の回折光を超音波発生器１４ｃから入力される超音波の周波数ｆ２分だけ周波数シフトした＋１次の回折光（周波数ν＋ｆ２）を第２経路の光として出射する。これにより、第１経路の光と第２経路の光の周波数差はｆ１−ｆ２となる。 Further, in FIG. 3B, similarly to FIG. 3A, the AOFS 14d and the AOFS 14e are arranged in series. First, the AOFS 14d splits the incident light (frequency ν) into two lights, one of which emits 0th-order diffracted light (frequency ν) to the AOFS 14e. On the other hand, + 1st order diffracted light (frequency ν + f 1 ) shifted by the frequency f 1 of the ultrasonic wave input from the ultrasonic generator 14b is emitted as light of the first path. Then, AOFS14e is the zero-order diffracted light ultrasonic generator 14c +1 order diffracted light frequency shifted by a frequency f 2 minutes of ultrasonic input from (frequency [nu + f 2) a second path from AOFS14d Emits as light. As a result, the frequency difference between the light of the first path and the light of the second path is f 1 −f 2 .

また、図３（ｃ）においては、超音波発生器１４ｇは、周波数（ｆ１＋ｆ２）／２の高周波信号と周波数（ｆ２−ｆ１）／２の低周波信号との間で振幅変調を行い、中心周波数が（ｆ１＋ｆ２）／２で（ｆ１＋ｆ２）／２±（ｆ２−ｆ１）／２＝ｆ１，ｆ２のサイドバンド周波数でなる２周波数成分の信号、すなわち周波数ｆ１の第１の超音波と周波数ｆ２の第２の超音波とを発生してＡＯＦＳ１４ｆに出力する。ＡＯＦＳ１４ｆは、入射光（周波数ν）を周波数ｆ１分だけ周波数シフトした回折光（周波数ν＋ｆ１）を第１経路の光として出射するとともに、周波数ｆ２分だけ周波数シフトした回折光（周波数ν＋ｆ２）を第２経路の光として出射する。これにより、第１経路の光と第２経路の光の周波数差はｆ１−ｆ２となる。 In FIG. 3C, the ultrasonic generator 14g performs amplitude modulation between a high-frequency signal having a frequency (f 1 + f 2 ) / 2 and a low-frequency signal having a frequency (f 2 −f 1 ) / 2. And the center frequency is (f 1 + f 2 ) / 2, and (f 1 + f 2 ) / 2 ± (f 2 −f 1 ) / 2 = a signal of two frequency components consisting of side bands of f 1 and f 2 , that is, outputs the AOFS14f generated the first second ultrasound ultrasound frequency f 2 of the frequency f 1. AOFS14f is configured to emit incident light (frequency [nu) only 1 minute frequency f frequency-shifted diffracted light (frequency [nu + f 1) as the light of the first path, the frequency f 2 minutes by the frequency-shifted diffracted light (frequency [nu + f 2 ) As the light of the second path. As a result, the frequency difference between the light of the first path and the light of the second path is f 1 −f 2 .

本発明の第１実施形態の構成を示す図The figure which shows the structure of 1st Embodiment of this invention. 本発明の第２実施形態の構成を示す図The figure which shows the structure of 2nd Embodiment of this invention. 本発明の第１実施形態及び第２実施形態の光分岐手段１４の別の構成を示す図The figure which shows another structure of the optical branching means 14 of 1st Embodiment and 2nd Embodiment of this invention. 従来例の概略構成を示す図The figure which shows schematic structure of a prior art example

符号の説明Explanation of symbols

１・・・波長可変光源、２・・・光源、３，６，１４ａ・・・光カプラ、４，１４・・・光分岐手段、４ａ，１４ｂ，１４ｃ，１４ｇ・・・超音波発生器、４ｂ，１４ｄ，１４ｅ，１４ｆ・・・音響光学周波数シフタ（ＡＯＦＳ）、５・・・遅延器、７・・・光分波器、８，９・・・受光器（ＰＤ）、１０・・・被測定物、１１・・・ＲＦロックインアンプ、１２・・・処理手段、１３・・・制御手段、１６・・・ミキサ（ＭＩＸ）、１５・・・ロックインアンプ、２０，３０・・・マッハツェンダ型干渉計。 DESCRIPTION OF SYMBOLS 1 ... Variable wavelength light source, 2 ... Light source, 3, 6, 14a ... Optical coupler, 4, 14 ... Optical branching means, 4a, 14b, 14c, 14g ... Ultrasonic generator, 4b, 14d, 14e, 14f ... Acousto-optic frequency shifter (AOFS), 5 ... Delay device, 7 ... Optical demultiplexer, 8, 9 ... Light receiver (PD), 10 ... DUT, 11 ... RF lock-in amplifier, 12 ... processing means, 13 ... control means, 16 ... mixer (MIX), 15 ... lock-in amplifier, 20, 30 ... Mach-Zehnder interferometer.

Claims (12)

入射光である周波数可変の測定光を受けて、２つに分岐するとともに互いに周波数の異なる第１経路の光及び第２経路の光として出射する光分岐手段（１４）並びに被測定物を介して入射される前記第１経路の光と前記被測定物を介さないで入射される前記第２経路の光とを合波して干渉光を出射する光結合手段（６）を有するマッハツェンダ型干渉計（３０）と、
前記干渉光を受けてヘテロダイン検波し前記第１経路の光と前記第２経路の光の周波数差のビート信号を電気信号に変換する受光器（８）と、
前記ビート信号の周波数とほぼ同じ周波数の同期信号に基づいて前記電気信号の位相検出を行う同期検波器（１５）と、
前記測定光の瞬時周波数に対応する、前記同期検波器から出力される位相信号のデータ処理を行って前記被測定物の光周波数−位相特性を求める処理手段（１２）とを備えた光ヘテロダイン干渉装置において、
前記光分岐手段は、周波数ｆ１の第1の超音波を発生させる第１の超音波発生器（１４ｂ）と、周波数ｆ２の第２の超音波を発生させる第２の超音波発生器（１４ｃ）と、前記第1の超音波で駆動される第1の音響光学周波数シフタ（１４ｄ）と、前記第２の超音波で駆動される第２の音響光学周波数シフタ（１４ｅ）とを有し、前記第１経路の光と前記第２経路の光との周波数差が前記第1の超音波と前記第２の超音波との周波数差と同一になるようにし、かつ、
前記同期検波器がロックインアンプで構成されたことを特徴とする光ヘテロダイン干渉装置。 Upon receiving the frequency-variable measurement light that is incident light, the light is branched into two and is emitted as the light of the first path and the light of the second path having different frequencies from each other, and the measured object. A Mach-Zehnder interferometer having optical coupling means (6) for combining the incident light of the first path and the incident light of the second path without passing through the device under test to emit interference light. (30),
A light receiver (8) that receives the interference light and performs heterodyne detection to convert a beat signal of a frequency difference between the light of the first path and the light of the second path into an electrical signal;
A synchronous detector (15) for detecting the phase of the electrical signal based on a synchronous signal having substantially the same frequency as the frequency of the beat signal;
Optical heterodyne interference comprising processing means (12) for processing data of a phase signal output from the synchronous detector corresponding to the instantaneous frequency of the measurement light to obtain an optical frequency-phase characteristic of the object to be measured In the device
The optical branching means includes a first ultrasonic generator (14b) for generating a first ultrasonic wave having a frequency f1, and a second ultrasonic generator (for generating a second ultrasonic wave having a frequency f2. 14c), a first acoustooptic frequency shifter (14d) driven by the first ultrasonic wave, and a second acoustooptic frequency shifter (14e) driven by the second ultrasonic wave. The frequency difference between the light of the first path and the light of the second path is the same as the frequency difference between the first ultrasonic wave and the second ultrasonic wave, and
An optical heterodyne interferometer, wherein the synchronous detector comprises a lock-in amplifier. 入射光である周波数可変の測定光を受けて、２つに分岐するとともに互いに周波数の異なる第１経路の光及び第２経路の光として出射する光分岐手段（１４）並びに被測定物を介して入射される前記第１経路の光と前記被測定物を介さないで入射される前記第２経路の光とを合波して干渉光を出射する光結合手段（６）を有するマッハツェンダ型干渉計（３０）と、
前記干渉光を受けてヘテロダイン検波し前記第１経路の光と前記第２経路の光の周波数差のビート信号を電気信号に変換する受光器（８）と、
前記ビート信号の周波数とほぼ同じ周波数の同期信号に基づいて前記電気信号の位相検出を行う同期検波器（１５）と、
前記測定光の瞬時周波数に対応する、前記同期検波器から出力される位相信号のデータ処理を行って前記被測定物の光周波数−位相特性を求める処理手段（１２）とを備えた光ヘテロダイン干渉装置において、
前記光分岐手段は、高周波交流信号と低周波交流信号との間で振幅変調を行うことにより、前記高周波交流信号の周波数を中心周波数とし、前記低周波交流信号の周波数分シフトしたサイドバンド周波数成分でなる第１の超音波と第２の超音波を発生させる第３の超音波発生器（１４ｇ）と、前記第１の超音波と前記第２の超音波で駆動される第３の音響光学周波数シフタ（１４ｆ）とを有し、前記第１経路の光と前記第２経路の光との周波数差が前記第１の超音波と前記第２の超音波との周波数差と同一になるようにし、かつ、
前記同期検波器がロックインアンプで構成されたことを特徴とする光ヘテロダイン干渉装置。 Upon receiving the frequency-variable measurement light that is incident light, the light is branched into two and is emitted as the light of the first path and the light of the second path having different frequencies from each other, and the measured object. A Mach-Zehnder interferometer having optical coupling means (6) for combining the incident light of the first path and the incident light of the second path without passing through the device under test to emit interference light. (30),
A light receiver (8) that receives the interference light and performs heterodyne detection to convert a beat signal of a frequency difference between the light of the first path and the light of the second path into an electrical signal;
A synchronous detector (15) for detecting the phase of the electrical signal based on a synchronous signal having substantially the same frequency as the frequency of the beat signal;
Optical heterodyne interference comprising processing means (12) for processing data of a phase signal output from the synchronous detector corresponding to the instantaneous frequency of the measurement light to obtain an optical frequency-phase characteristic of the object to be measured In the device
The optical branching means performs amplitude modulation between the high-frequency AC signal and the low-frequency AC signal, thereby setting the frequency of the high-frequency AC signal as a center frequency and shifting the sideband frequency component by the frequency of the low-frequency AC signal. A third ultrasonic generator (14g) for generating a first ultrasonic wave and a second ultrasonic wave, and a third acoustooptic device driven by the first ultrasonic wave and the second ultrasonic wave. A frequency shifter (14f), and the frequency difference between the light of the first path and the light of the second path is the same as the frequency difference between the first ultrasonic wave and the second ultrasonic wave. And
An optical heterodyne interferometer, wherein the synchronous detector comprises a lock-in amplifier. 前記光分岐手段は、更に、前記入射光である前記測定光を受けて２つに分岐し、一方の光を前記第１の音響光学周波数シフタに、他方の光を前記第２の音響光学周波数シフタにそれぞれ出射する第１の光カプラ（１４ａ）を有し、
前記第１の音響光学周波数シフタは、前記第１の光カプラから入射される一方の光の周波数を前記第1の超音波の周波数ｆ１分周波数シフトして前記第１経路の光として出射し、かつ、前記第２の音響光学周波数シフタは、前記第１の光カプラから入射される他方の光の周波数を前記第２の超音波の周波数ｆ２分周波数シフトして前記第２経路の光として出射することを特徴とする請求項１に記載の光ヘテロダイン干渉装置。 The light branching means further receives the measurement light, which is the incident light, and branches the light into two, with one light being sent to the first acoustooptic frequency shifter and the other light being sent to the second acoustooptic frequency. A first optical coupler (14a) that respectively emits to the shifter;
The first acousto-optic frequency shifter shifts the frequency of one light incident from the first optical coupler by a frequency f 1 of the first ultrasonic wave and emits it as light of the first path. And the second acousto-optic frequency shifter shifts the frequency of the other light incident from the first optical coupler by a frequency f 2 of the second ultrasonic wave to light the second path. The optical heterodyne interference device according to claim 1, wherein 前記マッハツェンダ型干渉計は、更に、前記光分岐手段と前記光結合手段との間に設けられ、該光分岐手段から出射された前記第２経路の光が前記光結合手段に到達するまでの時間と、前記第１経路の光が前記被測定物を介して前記光結合手段に到達するまでの時間とがほぼ等しくなるように、前記第１経路の光又は前記第２経路の光を遅延させる遅延器（５）を備えたことを特徴とする請求項１〜３のいずれかに記載の光ヘテロダイン干渉装置。   The Mach-Zehnder interferometer is further provided between the optical branching unit and the optical coupling unit, and a time until the light of the second path emitted from the optical branching unit reaches the optical coupling unit And the light of the first path or the light of the second path are delayed so that the time until the light of the first path reaches the optical coupling means via the object to be measured is substantially equal. The optical heterodyne interference device according to any one of claims 1 to 3, further comprising a delay device (5). 前記第１の超音波発生器から出力される前記第１の超音波と前記第２の超音波発生器から出力される前記第２の超音波とを受けて混合し、又は前記第３の超音波発生器から出力される前記第１の超音波と前記第２の超音波とを受けて混合し、該第１の超音波と該第２の超音波との差周波数の信号を発生して前記同期検波器に前記同期信号として出力するミキサ（１６）を備えたことを特徴とする請求項１〜４のいずれかに記載の光ヘテロダイン干渉装置。   Receiving and mixing the first ultrasonic wave output from the first ultrasonic generator and the second ultrasonic wave output from the second ultrasonic generator, or the third ultrasonic wave Receiving and mixing the first ultrasonic wave and the second ultrasonic wave output from the sound wave generator, and generating a signal having a difference frequency between the first ultrasonic wave and the second ultrasonic wave; The optical heterodyne interferometer according to any one of claims 1 to 4, further comprising a mixer (16) for outputting the synchronous detector as the synchronous signal. 周波数可変の測定光と当該測定光の出力周波数と異なる固定周波数の参照光とを波長多重してなる波長多重光を受けて、当該波長多重光を分岐するとともに、第１経路の光と第２経路の光とを出力する光分岐手段（１４）であって、当該第１経路の光及び当該第２経路の光はそれぞれ測定光に基づく測定光成分と参照光に基づく参照光成分とからなり、前記第１経路の光に含まれる測定光成分の周波数と前記第２経路の光に含まれる測定光成分の周波数とが異なるとともに、前記第１経路の光に含まれる参照光成分の周波数と前記第２経路の光に含まれる参照光成分の周波数とが同じだけ異なる光分岐手段（１４）並びに被測定物を経由する前記第１経路の光と前記被測定物を経由しない前記第２経路の光とを合波する光結合手段（６）を有するマッハツェンダ型干渉計（３０）と、
前記測定光成分と前記参照光成分とを周波数分波する光分波器（７）と、
該光分波器で分波された、前記第１経路の光の測定光成分と前記第２経路の光の測定光成分とからなる第１の干渉光を第１の電気信号に変換する第１の受光器（８）と、
前記光分波器で分波された、前記第１経路の光の参照光成分と前記第２経路の光の参照光成分とからなる第２の干渉光を第２の電気信号に変換する第２の受光器（９）と、
前記第２の電気信号を同期信号として前記第１の電気信号の位相検出を行う同期検波器（１５）と、
前記測定光の出力周波数に対応した、前記同期検波器から出力される位相信号をデータ処理して、前記被測定物の光周波数−位相特性を求める処理手段（１２）とを備えた光ヘテロダイン干渉装置において、
前記光分岐手段は、周波数ｆ１の第１の超音波を発生させる第１の超音波発生器（１４ｂ）と、周波数ｆ２の第２の超音波を発生させる第２の超音波発生器（１４ｃ）と、前記第１の超音波で駆動される第１の音響光学周波数シフタ（１４ｄ）と、前記第２の超音波で駆動される第２の音響光学周波数シフタ（１４ｅ）とを有し、前記第１経路の光の測定光成分と前記第２経路の光の測定光成分との周波数差、及び前記第１経路の光の参照光成分と前記第２経路の光の参照光成分との周波数差が、前記第１の超音波と前記第２の超音波との周波数差と同一になるようにし、かつ、
前記同期検波器がロックインアンプで構成されたことを特徴とする光ヘテロダイン干渉装置。 The wavelength-multiplexed light obtained by wavelength-multiplexing the frequency-variable measurement light and the reference light having a fixed frequency different from the output frequency of the measurement light is received, and the wavelength-multiplexed light is branched. An optical branching means (14) for outputting the light of the path, wherein the light of the first path and the light of the second path are respectively composed of a measurement light component based on the measurement light and a reference light component based on the reference light. The frequency of the measurement light component included in the light of the first path is different from the frequency of the measurement light component included in the light of the second path, and the frequency of the reference light component included in the light of the first path The light branching means (14) having the same frequency as the frequency of the reference light component contained in the light of the second path and the light of the first path passing through the device under test and the second path not passing through the device under test Has optical coupling means (6) to multiplex That the Mach-Zehnder interferometer (30),
An optical demultiplexer (7) for demultiplexing the measurement light component and the reference light component;
A first interference light that is demultiplexed by the optical demultiplexer and composed of the measurement light component of the light of the first path and the measurement light component of the light of the second path is converted into a first electric signal. 1 receiver (8),
A second interference light that is demultiplexed by the optical demultiplexer and composed of the reference light component of the light of the first path and the reference light component of the light of the second path is converted into a second electrical signal. Two receivers (9);
A synchronous detector (15) for performing phase detection of the first electrical signal using the second electrical signal as a synchronization signal;
Optical heterodyne interference comprising processing means (12) for processing the phase signal output from the synchronous detector corresponding to the output frequency of the measurement light to obtain the optical frequency-phase characteristic of the object to be measured In the device
The optical branching means includes a first ultrasonic generator (14b) that generates a first ultrasonic wave having a frequency f1, and a second ultrasonic generator (14b) that generates a second ultrasonic wave having a frequency f2. 14c), a first acoustooptic frequency shifter (14d) driven by the first ultrasonic wave, and a second acoustooptic frequency shifter (14e) driven by the second ultrasonic wave. A frequency difference between the measurement light component of the light of the first path and the measurement light component of the light of the second path, and a reference light component of the light of the first path and a reference light component of the light of the second path The frequency difference between the first ultrasonic wave and the second ultrasonic wave is the same, and
An optical heterodyne interferometer, wherein the synchronous detector comprises a lock-in amplifier. 前記マッハツェンダ型干渉計は、更に、前記光分岐手段と前記光結合手段との間に設けられ、該光分岐手段から出射された前記第２経路の光が前記光結合手段に到達するまでの各時間と、前記第１経路の光が前記被測定物を介して前記光結合手段に到達するまでの各時間とがほぼ等しくなるように、前記第１経路の光又は前記第２経路の光を遅延させる遅延器（５）を備えたことを特徴とする請求項６に記載の光ヘテロダイン干渉装置。   The Mach-Zehnder interferometer is further provided between the optical branching unit and the optical coupling unit, and each of the light until the light of the second path emitted from the optical branching unit reaches the optical coupling unit. The light of the first path or the light of the second path is set so that the time and the time until the light of the first path reaches the optical coupling means via the object to be measured are substantially equal. 7. The optical heterodyne interference device according to claim 6, further comprising a delay device (5) for delaying. 前記マッハツェンダ型干渉計は、その光路中に光ファイバを含んで構成される光ファイバ干渉計であることを特徴とする請求項６又は７に記載の光ヘテロダイン干渉装置。   The optical heterodyne interferometer according to claim 6 or 7, wherein the Mach-Zehnder interferometer is an optical fiber interferometer configured to include an optical fiber in an optical path thereof. 所定の周波数範囲内で周波数可変の前記測定光を順次発振させ、前記光分岐手段へ前記入射光として出射する波長可変光源（１）と、
該波長可変光源からの測定光の周波数を可変するための制御信号を当該波長可変光源に出力する制御手段（１３）とを備えたことを特徴とする請求項１〜５のいずれかに記載の光ヘテロダイン干渉装置。 A wavelength tunable light source (1) that sequentially oscillates the measurement light having a variable frequency within a predetermined frequency range and emits the incident light as the incident light to the optical branching unit;
The control means (13) for outputting a control signal for changing the frequency of the measurement light from the wavelength tunable light source to the wavelength tunable light source, according to any one of claims 1 to 5, Optical heterodyne interferometer. 所定の周波数範囲内で周波数可変の前記測定光を順次発振させる波長可変光源（１）と、
該波長可変光源からの測定光の周波数を可変するための制御信号を当該波長可変光源に出力する制御手段（１３）と、
前記測定光の周波数とは異なる固定周波数の前記参照光を発振させる光源（２）と、
前記波長可変光源から出射される前記測定光と前記光源から出射される前記参照光とを受け合波することによって波長多重し、得られた前記波長多重光を前記光分岐手段へ前記入射光として出射する第２の光カプラ（３）とを備えたことを特徴とする請求項６〜８のいずれかに記載の光ヘテロダイン干渉装置。 A wavelength tunable light source (1) for sequentially oscillating the measurement light having a variable frequency within a predetermined frequency range;
Control means (13) for outputting a control signal for varying the frequency of the measurement light from the wavelength tunable light source to the wavelength tunable light source;
A light source (2) for oscillating the reference light having a fixed frequency different from the frequency of the measurement light;
The measurement light emitted from the wavelength tunable light source and the reference light emitted from the light source are combined and wavelength multiplexed to obtain the wavelength multiplexed light as the incident light to the optical branching unit. 9. The optical heterodyne interference device according to claim 6, further comprising a second optical coupler (3) that emits light. 周波数可変の測定光と当該測定光の出力周波数と異なる固定周波数の参照光とを波長多重してなる波長多重光を受けて、当該波長多重光を分岐するとともに、第１経路の光と第２経路の光とを出力する光分岐手段（１４）であって、当該第１経路の光及び当該第２経路の光はそれぞれ測定光に基づく測定光成分と参照光に基づく参照光成分とからなり、前記第１経路の光に含まれる測定光成分の周波数と前記第２経路の光に含まれる測定光成分の周波数とが異なるとともに、前記第１経路の光に含まれる参照光成分の周波数と前記第２経路の光に含まれる参照光成分の周波数とが同じだけ異なる光分岐手段（１４）並びに被測定物を経由する前記第１経路の光と前記被測定物を経由しない前記第２経路の光とを合波する光結合手段（６）を有するマッハツェンダ型干渉計（３０）と、
前記測定光成分と前記参照光成分とを周波数分波する光分波器（７）と、
該光分波器で分波された、前記第１経路の光の測定光成分と前記第２経路の光の測定光成分とからなる第１の干渉光を第１の電気信号に変換する第１の受光器（８）と、
前記光分波器で分波された前記第１経路の光の参照光成分と前記第２経路の光の参照光成分とからなる第２の干渉光を、前記測定光の出力周波数に対応した前記第１の電気信号の位相量を検出するための同期信号となる第２の電気信号に変換する第２の受光器（９）とを備えた光ヘテロダイン干渉装置において、
前記光分岐手段は、周波数ｆ１の第１の超音波を発生させる第１の超音波発生器（１４ｂ）と、周波数ｆ２の第２の超音波を発生させる第２の超音波発生器（１４ｃ）と、前記第１の超音波で駆動される第１の音響光学周波数シフタ（１４ｄ）と、前記第２の超音波で駆動される第２の音響光学周波数シフタ（１４ｅ）とを有し、前記第１経路の光の測定光成分と前記第２経路の光の測定光成分との周波数差、及び前記第１経路の光の参照光成分と前記第２経路の光の参照光成分との周波数差が、前記第１の超音波と前記第２の超音波との周波数差と同一になるようにし、かつ、当該第１の超音波と第２の超音波との周波数差が２ＭＨｚ以下であることを特徴とする光ヘテロダイン干渉装置。 The wavelength-multiplexed light obtained by wavelength-multiplexing the frequency-variable measurement light and the reference light having a fixed frequency different from the output frequency of the measurement light is received, and the wavelength-multiplexed light is branched. An optical branching means (14) for outputting the light of the path, wherein the light of the first path and the light of the second path are respectively composed of a measurement light component based on the measurement light and a reference light component based on the reference light. The frequency of the measurement light component included in the light of the first path is different from the frequency of the measurement light component included in the light of the second path, and the frequency of the reference light component included in the light of the first path The light branching means (14) having the same frequency as the frequency of the reference light component contained in the light of the second path and the light of the first path passing through the device under test and the second path not passing through the device under test Has optical coupling means (6) to multiplex That the Mach-Zehnder interferometer (30),
An optical demultiplexer (7) for demultiplexing the measurement light component and the reference light component;
A first interference light that is demultiplexed by the optical demultiplexer and composed of the measurement light component of the light of the first path and the measurement light component of the light of the second path is converted into a first electric signal. 1 receiver (8),
The second interference light composed of the reference light component of the light of the first path and the reference light component of the light of the second path demultiplexed by the optical demultiplexer corresponds to the output frequency of the measurement light. In an optical heterodyne interferometer comprising a second light receiver (9) for converting into a second electrical signal that becomes a synchronization signal for detecting the phase amount of the first electrical signal,
The optical branching means includes a first ultrasonic generator (14b) that generates a first ultrasonic wave having a frequency f1, and a second ultrasonic generator (14b) that generates a second ultrasonic wave having a frequency f2. 14c), a first acoustooptic frequency shifter (14d) driven by the first ultrasonic wave, and a second acoustooptic frequency shifter (14e) driven by the second ultrasonic wave. A frequency difference between the measurement light component of the light of the first path and the measurement light component of the light of the second path, and a reference light component of the light of the first path and a reference light component of the light of the second path Is equal to the frequency difference between the first ultrasonic wave and the second ultrasonic wave, and the frequency difference between the first ultrasonic wave and the second ultrasonic wave is 2 MHz or less. An optical heterodyne interferometer characterized by 入射光である周波数可変の測定光を受けて、２つに分岐するとともに互いに周波数の異なる第１経路の光及び第２経路の光として出射する光分岐手段（１４）並びに被測定物を介して入射される前記第１経路の光と前記被測定物を介さないで入射される前記第２経路の光とを合波して干渉光を出射する光結合手段（６）を含むマッハツェンダ型干渉計（３０）と、
前記干渉光を受けて、前記第１経路の光と前記第２経路の光との周波数差のビート信号とほぼ同じ周波数の同期信号に基づいて、前記測定光の出力周波数に対応する位相変化量が検出されるべき電気信号を出力する受光器（８）とを備えた光ヘテロダイン干渉装置において、
前記光分岐手段は、周波数ｆ１の第１の超音波を発生させる第１の超音波発生器（１４ｂ）と、周波数ｆ２の第２の超音波を発生させる第２の超音波発生器（１４ｃ）と、前記第１の超音波で駆動される第１の音響光学周波数シフタ（１４ｄ）と、前記第２の超音波で駆動される第２の音響光学周波数シフタ（１４ｅ）とを有し、前記第１経路の光と前記第２経路の光との周波数差が、前記第１の超音波と前記第２の超音波との周波数差と同一になるようにし、かつ、当該第１の超音波と第２の超音波との周波数差が２ＭＨｚ以下であることを特徴とする光ヘテロダイン干渉装置。 Upon receiving the frequency-variable measurement light that is incident light, the light is branched into two and is emitted as the light of the first path and the light of the second path having different frequencies from each other, and the measured object. A Mach-Zehnder interferometer including optical coupling means (6) for combining the incident light of the first path and the incident light of the second path without passing through the object to be measured to emit interference light. (30),
In response to the interference light, a phase change amount corresponding to the output frequency of the measurement light based on a synchronization signal having substantially the same frequency as the beat signal of the frequency difference between the light of the first path and the light of the second path An optical heterodyne interferometer comprising an optical receiver (8) for outputting an electrical signal to be detected,
The optical branching means includes a first ultrasonic generator (14b) that generates a first ultrasonic wave having a frequency f1, and a second ultrasonic generator (14b) that generates a second ultrasonic wave having a frequency f2. 14c), a first acoustooptic frequency shifter (14d) driven by the first ultrasonic wave, and a second acoustooptic frequency shifter (14e) driven by the second ultrasonic wave. The frequency difference between the light of the first path and the light of the second path is made equal to the frequency difference between the first ultrasonic wave and the second ultrasonic wave, and the first An optical heterodyne interference device, wherein a frequency difference between the ultrasonic wave and the second ultrasonic wave is 2 MHz or less.
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JP2011529180A (en) * 2008-07-25 2011-12-01 サントル ナシオナル ドゥ ラ ルシェルシェサイアンティフィク（セエヌエールエス） Synchronous interferometer with frequency comb
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