JP2008020340A - Interference light measuring device - Google Patents

Interference light measuring device Download PDF

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JP2008020340A
JP2008020340A JP2006192805A JP2006192805A JP2008020340A JP 2008020340 A JP2008020340 A JP 2008020340A JP 2006192805 A JP2006192805 A JP 2006192805A JP 2006192805 A JP2006192805 A JP 2006192805A JP 2008020340 A JP2008020340 A JP 2008020340A
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light
light receiving
interference
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phase
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Hiromi Saito
裕己 齊藤
Minoru Maeda
稔 前田
Takaaki Hirata
隆昭 平田
Tetsuo Yano
哲夫 矢野
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Yokogawa Electric Corp
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<P>PROBLEM TO BE SOLVED: To provide an interference light measuring device with wide measurement wavelength range and measurement dynamic range capable of measuring coherent light efficiently with high accuracy. <P>SOLUTION: This interference light measuring device 10 comprises a device 12 which generates signal light L2 and reference light L1 and generates interference light L3 by making both light interfering each other, and a light receiving device 13 which has a plurality of light receiving elements arranged to the interference fringes of the interference light L3 with a predetermined relation on a light receiving surface and receives the interference light L3 emitted on the light receiving surface. The beam widths of the signal light L2 and the reference light L2 emitted onto the light receiving surface of the light receiving device 13 is set smaller than the size of the light receiving surface of the light receiving elements 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、信号光と参照光とを干渉させた干渉光を測定する干渉光測定装置に関する。   The present invention relates to an interference light measuring apparatus that measures interference light obtained by causing signal light and reference light to interfere with each other.

干渉光測定装置は、一般的に信号光と参照光とを生成してこれらを別々の光路を通過させた後で重ね合わせ、信号光と参照光との干渉光を受光する装置である。この干渉光測定装置は、例えば波長測定、距離の測定、光学部品・モジュール等の被測定デバイス（ＤＵＴ：Device Under Test）の表面形状又は透過特性・反射特性の測定等に用いられる。この干渉光測定装置の一種に、例えばＤＦＢレーザ（Distributed Feedback−Laser Diode）光源、ＤＢＲレーザ（Distributed Bragg Reflector−Laser Diode）光源、回折格子を使用した外部共振器型の波長可変光源等の各種レーザ光源から射出されるレーザ光の波長を測定する波長モニタ装置、又はレーザ測長器等がある。   The interference light measuring device is a device that generally generates signal light and reference light, superimposes them after passing through separate optical paths, and receives interference light between the signal light and the reference light. This interference light measuring apparatus is used for wavelength measurement, distance measurement, measurement of the surface shape or transmission / reflection characteristics of a device under test (DUT) such as an optical component / module. Various kinds of lasers such as a DFB laser (Distributed Feedback-Laser Diode) light source, a DBR laser (Distributed Bragg Reflector-Laser Diode) light source, and an external resonator type wavelength tunable light source using a diffraction grating are included in one type of the interference light measuring apparatus. There is a wavelength monitor device for measuring the wavelength of laser light emitted from a light source, a laser length measuring device, or the like.

図９は、従来のレーザ測長器の構成の一例を示す図である。尚、このレーザ測長器は、例えば以下の非特許文献１に開示されている。図９に示す従来のレーザ測長器１００は、レーザ光源１０１、レンズ１０２、ハーフミラー１０３、固定反射ミラー１０４、可動反射ミラー１０５、フォトダイオードアレイ１０６、演算増幅器１０７、及びカウンタ１０８を備えている。   FIG. 9 is a diagram showing an example of the configuration of a conventional laser length measuring device. In addition, this laser length measuring device is disclosed by the following nonpatent literature 1, for example. A conventional laser length measuring device 100 shown in FIG. 9 includes a laser light source 101, a lens 102, a half mirror 103, a fixed reflection mirror 104, a movable reflection mirror 105, a photodiode array 106, an operational amplifier 107, and a counter 108. .

レーザ光源１０１は例えばＤＢＲレーザであり、測定光としてのレーザ光を射出する。レンズ１０２は、レーザ光源１０１から射出されたレーザ光を平行光に変換する。ハーフミラー１０３、固定反射ミラー１０４、及び可動反射ミラー１０５は、マイケルソン型の干渉計を構成している。ハーフミラー１０３はレンズ１０２を介したレーザ光を参照光Ｌ１と信号光Ｌ２とに分岐するとともに、固定反射ミラー１０４で反射された参照光Ｌ１と可動反射ミラー１０５で反射された信号光Ｌ２とを合波する。尚、参照光Ｌ１及び信号光Ｌ２は、干渉光Ｌ３に干渉縞を生じさせるために、その光軸が僅かに傾けられている。   The laser light source 101 is a DBR laser, for example, and emits laser light as measurement light. The lens 102 converts the laser light emitted from the laser light source 101 into parallel light. The half mirror 103, the fixed reflection mirror 104, and the movable reflection mirror 105 constitute a Michelson interferometer. The half mirror 103 branches the laser light that has passed through the lens 102 into the reference light L1 and the signal light L2, and the reference light L1 reflected by the fixed reflection mirror 104 and the signal light L2 reflected by the movable reflection mirror 105. Combine. Note that the optical axes of the reference light L1 and the signal light L2 are slightly inclined in order to generate interference fringes in the interference light L3.

固定反射ミラー１０４はハーフミラー１０３に対して位置が固定された反射ミラーであり、ハーフミラー１０３で分岐された参照光Ｌ１をハーフミラー１０３に向けて反射する。可動反射ミラー１０５はハーフミラー１０３に対して、信号光Ｌ２の進行方向に沿う方向に位置が可変な反射ミラーであり、ハーフミラー１０３で分岐された信号光Ｌ２をハーフミラー１０３に向けて反射する。尚、可動反射ミラー１０５がレーザ光の波長の半波長分だけ移動すると干渉光Ｌ３の干渉縞の位置がフォトダイオードアレイ１０６の受光面に沿う方向に１周期分だけずれる。また、そのずれの方向は可動反射ミラー１０５の移動方向に対応している。   The fixed reflection mirror 104 is a reflection mirror whose position is fixed with respect to the half mirror 103, and reflects the reference light L <b> 1 branched by the half mirror 103 toward the half mirror 103. The movable reflecting mirror 105 is a reflecting mirror whose position is variable in the direction along the traveling direction of the signal light L <b> 2 with respect to the half mirror 103, and reflects the signal light L <b> 2 branched by the half mirror 103 toward the half mirror 103. . When the movable reflecting mirror 105 moves by a half wavelength of the wavelength of the laser light, the position of the interference fringe of the interference light L3 is shifted by one period in the direction along the light receiving surface of the photodiode array 106. Further, the direction of the shift corresponds to the moving direction of the movable reflecting mirror 105.

フォトダイオードアレイ１０６は、複数の受光素子（フォトダイオード）を備えており、参照光Ｌ１と信号光Ｌ２とがハーフミラー１０３で合波さることにより得られる干渉光Ｌ３を受光する。尚、フォトダイオードアレイ１０６の受光素子は、４素子が干渉光Ｌ３の干渉縞の１周期に相当するようにその間隔が設定されている。演算増幅器１０７はフォトダイオードアレイ１０６から出力される受光信号を演算増幅するとともに、所定の演算を行ってパルス信号を生成する。具体的には、フォトダイオードアレイ１０６から出力される受光信号のうち、互いに位相が反転している受光信号を減算して直流成分（ＤＣ成分）を除去することによりパルス信号を生成する。カウンタ１０８は、演算増幅器１０７で生成されるパルス信号を計数する。   The photodiode array 106 includes a plurality of light receiving elements (photodiodes), and receives interference light L3 obtained by combining the reference light L1 and the signal light L2 by the half mirror 103. The intervals of the light receiving elements of the photodiode array 106 are set so that four elements correspond to one cycle of the interference fringes of the interference light L3. The operational amplifier 107 computes and amplifies the received light signal output from the photodiode array 106 and performs a predetermined computation to generate a pulse signal. Specifically, a pulse signal is generated by subtracting the light receiving signals whose phases are inverted from each other from the light receiving signals output from the photodiode array 106 to remove a direct current component (DC component). The counter 108 counts pulse signals generated by the operational amplifier 107.

上記構成において、レーザ光源１０１から射出されたレーザ光は、レンズ１０２に入射して平行光に変換された後でハーフミラー１０３に入射し、参照光Ｌ１と信号光Ｌ２とに分岐される。そして、参照光Ｌ１は固定反射ミラー１０４で反射され、信号光Ｌ２は可動反射ミラー１０５で反射され、反射されたこれらの参照光Ｌ１及び信号光Ｌ２は再びハーフミラー１０３に入射して合波される。これにより、フォトダイオードアレイ１０６の受光面には、参照光Ｌ１と信号光Ｌ２とが干渉した干渉光Ｌ３が入射する。この干渉光Ｌ３が、フォトダイオードアレイ１０６で受光されることにより演算増幅器１０７からはパルス信号が出力される。そして、このパルス信号がカウンタ１０８で計数され、可動反射ミラー１０５の移動量とその移動方向が求められる。
平田隆昭、他２名（T. Hirata et al.）, 「レーザ干渉計測位システムのための波長安定化レーザダイオード及びフォトダイオードアレイ（Wavelength-stable Laser Diode and Photodiode Array for Laser Interferometer Positioning Systems）」，横河技報（Yokogawa Technical Report）, ２００１年，Ｎｏ．３２，ｐ．１−４ In the above configuration, the laser light emitted from the laser light source 101 enters the lens 102 and is converted into parallel light, then enters the half mirror 103, and is branched into the reference light L1 and the signal light L2. The reference light L1 is reflected by the fixed reflecting mirror 104, the signal light L2 is reflected by the movable reflecting mirror 105, and the reflected reference light L1 and signal light L2 enter the half mirror 103 again and are combined. The Thereby, the interference light L3 obtained by the interference between the reference light L1 and the signal light L2 is incident on the light receiving surface of the photodiode array 106. When this interference light L3 is received by the photodiode array 106, a pulse signal is output from the operational amplifier 107. Then, this pulse signal is counted by the counter 108, and the moving amount and moving direction of the movable reflecting mirror 105 are obtained.
Takaaki Hirata and two others (T. Hirata et al.), “Wavelength-stable Laser Diode and Photodiode Array for Laser Interferometer Positioning Systems”, Yokogawa Technical Report, 2001, no. 32, p. 1-4

ところで、上述した通り、図９に示す従来のレーザ測長器１００は、レーザ光源１０１から射出される波長が一定のレーザ光を用いて可動反射ミラー１０５の移動量とその移動方向とを求める装置であるが、近年においては、図９に示す従来のレーザ測長器１００を、広い波長範囲を測定可能な波長モニタ装置に適用することが試みられている。しかしながら、上述した構成のレーザ測長器１００を波長モニタ装置に適用した場合に、測定可能な波長範囲を広げるのは困難である。なぜならば、図９に示す従来のレーザ測長器１００では、フォトダイオードアレイ１０６の受光素子の間隔が干渉光Ｌ３の干渉縞の周期に相当するように設定されてるが、測定光の波長が大きく変化するとフォトダイオードアレイ１０６の受光素子の間隔と干渉光Ｌ３の干渉縞の周期との関係が大きくずれるため、測定誤差が大きくなるからである。   By the way, as described above, the conventional laser length measuring device 100 shown in FIG. 9 is a device for obtaining the moving amount and moving direction of the movable reflecting mirror 105 using laser light having a constant wavelength emitted from the laser light source 101. However, in recent years, it has been attempted to apply the conventional laser length measuring device 100 shown in FIG. 9 to a wavelength monitor device capable of measuring a wide wavelength range. However, when the laser length measuring device 100 configured as described above is applied to a wavelength monitor device, it is difficult to widen the measurable wavelength range. This is because, in the conventional laser length measuring device 100 shown in FIG. 9, the interval between the light receiving elements of the photodiode array 106 is set to correspond to the period of the interference fringes of the interference light L3, but the wavelength of the measurement light is large. This is because the measurement error increases because the relationship between the interval between the light receiving elements of the photodiode array 106 and the period of the interference fringes of the interference light L3 greatly deviates.

また、図９に示すレーザ測長器１００を、ＤＵＴの透過特性等を測定する干渉光測定装置に適用することも試みられている。。つまり、図９に示す信号光Ｌ２の光路上にＤＵＴを配置し、ＤＵＴを介した信号光Ｌ２と参照光Ｌ１とを干渉させた干渉光Ｌ３をフォトダイオードアレイ１０６で受光することにより、ＤＵＴの特定を測定することができる。しかしながら、かかる干渉光測定装置では、ＤＵＴによって信号光が減衰するために信号光の光強度が変動し、フォトダイオードアレイ１０６から出力される受光信号のうち、互いに位相が反転している受光信号を演算増幅器１０７で減算した後の直流成分（ＤＣ成分）が変動し、この結果として精度の高い測定を行うことができないという問題がある。   Further, an attempt has been made to apply the laser length measuring device 100 shown in FIG. 9 to an interference light measurement device that measures the transmission characteristics of the DUT. . That is, the DUT is arranged on the optical path of the signal light L2 shown in FIG. 9, and the photodiode array 106 receives the interference light L3 obtained by causing the signal light L2 and the reference light L1 through the DUT to interfere with each other. Specificity can be measured. However, in the interference light measuring apparatus, since the signal light is attenuated by the DUT, the light intensity of the signal light fluctuates, and among the received light signals output from the photodiode array 106, the received light signals whose phases are inverted with respect to each other. The DC component (DC component) after subtraction by the operational amplifier 107 fluctuates, and as a result, there is a problem that high-precision measurement cannot be performed.

更に、図９に示すレーザ測長器１００、及びこれを用いた干渉光測定装置においては、フォトダイオードアレイ１０６の受光面に入射する参照光Ｌ１又は信号光Ｌ２が強度分布を有している場合にも演算増幅器１０７で直流成分が除去されず、精度の高い測定を行うことはできない。このため、従来は、フォトダイオードアレイ１０６の受光面に対して参照光Ｌ１又は信号光Ｌ２のビーム幅をできる限り大きくしている。これにより、レーザ光源１０１から射出されるレーザ光は強度分布を有しているが、フォトダイオードアレイ１０６の受光面に照射される参照光Ｌ１及び信号光Ｌ２はほぼ均一な強度分布となる。しかしながら、レーザ光源１０１から射出されたレーザ光のうち、フォトダイオードアレイ１０６で受光されるものは僅かであるため、極めて効率が悪いという問題がある。   Furthermore, in the laser length measuring device 100 shown in FIG. 9 and the interference light measuring device using the same, the reference light L1 or the signal light L2 incident on the light receiving surface of the photodiode array 106 has an intensity distribution. In addition, the operational amplifier 107 does not remove the direct current component, so that highly accurate measurement cannot be performed. For this reason, conventionally, the beam width of the reference light L1 or the signal light L2 is made as large as possible with respect to the light receiving surface of the photodiode array 106. As a result, the laser light emitted from the laser light source 101 has an intensity distribution, but the reference light L1 and the signal light L2 irradiated on the light receiving surface of the photodiode array 106 have a substantially uniform intensity distribution. However, since only a small amount of laser light emitted from the laser light source 101 is received by the photodiode array 106, there is a problem that the efficiency is extremely low.

本発明は上記事情に鑑みてなされたものであり、測定波長範囲と測定ダイナミックレンジが広く、且つ高い精度で効率良く干渉光の測定を行うことができる干渉光測定装置を提供することを目的とする。   The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an interference light measurement device that can measure interference light efficiently with high accuracy, with a wide measurement wavelength range and measurement dynamic range. To do.

上記課題を解決するために、本発明の干渉光測定装置は、入射光から信号光（Ｌ２）と参照光（Ｌ１）とを生成するとともに、当該信号光と参照光とを干渉させて干渉光（Ｌ３）を生成する干渉装置（１２）と、当該干渉装置で生成される干渉光の干渉縞に対して所定の関係をもって配列された複数の受光素子（Ｅ１〜ＥＮ）を受光面（１３ａ）に有し、当該受光面に照射される前記干渉光を前記複数の受光素子の各々で受光する受光装置（１３）とを備える干渉光測定装置（１０）において、前記受光装置の前記受光面に照射される前記信号光及び前記参照光のビーム幅が、前記受光素子の前記受光面の大きさ以下に設定されていることを特徴としている。
この発明によると、干渉光測定装置に入射光が入射すると、干渉装置で参照光と信号光とが生成されるとともにこれらを干渉させた干渉光が生成される。ここで、信号光及び参照光のビーム幅が受光素子の受光面の大きさ以下に設定されているため、生成された干渉光のビーム幅は受光素子の受光面の大きさ以下で受光面に照射される。
また、本発明の干渉光測定装置は、前記複数の受光素子が、前記信号光及び前記参照光の波長が所定の基準波長である場合に、前記受光面に照射される前記干渉光の干渉縞の１周期毎に４個の受光素子が配置されるように配列されていることを特徴としている。
また、本発明の干渉光測定装置は、前記受光装置が備える前記受光素子の各々で受光された受光信号に対して所定の演算を行い、前記信号光及び前記参照光の波長が所定の基準波長である場合に、位相が互いに９０度だけ異なるＡ相信号とＢ相信号とを生成する演算装置（２１、２２）を備えることを特徴としている。
また、本発明の干渉光測定装置は、前記信号光及び前記参照光のビーム幅が、前記受光素子の前記受光面の大きさ以下であって、前記Ａ相信号及び前記Ｂ相信号のオフセット値が所定値以下となるように設定されていることが望ましい。
或いは、前記信号光及び前記参照光のビーム幅は、前記受光素子の前記受光面の大きさ以下であって、前記Ａ相信号及び前記Ｂ相信号から計算される位相の真値からのずれが所定値以下となるように設定されていることが望ましい。
更に、本発明の干渉光測定装置は、前記演算装置によって生成される前記Ａ相信号と前記Ｂ相信号とに対して所定の信号処理を行って、前記入射光の波長を測定する波長測定装置（２３）を備えることを特徴としている。
或いは、本発明の干渉光測定装置は、前記演算装置によって生成される前記Ａ相信号と前記Ｂ相信号とに対して所定の信号処理を行って、前記信号光の光路に配置される被測定デバイスの特性を測定する光学特性測定装置（２３）を備えることを特徴としている。 In order to solve the above-described problem, the interference light measurement device of the present invention generates the signal light (L2) and the reference light (L1) from the incident light, and causes the signal light and the reference light to interfere with each other to cause interference light. The light receiving surface (13a) includes an interference device (12) that generates (L3) and a plurality of light receiving elements (E1 to EN) arranged with a predetermined relationship with respect to interference fringes of interference light generated by the interference device. And an interference light measuring device (10) comprising: a light receiving device (13) for receiving the interference light irradiated on the light receiving surface by each of the plurality of light receiving elements; The beam widths of the signal light and the reference light to be irradiated are set to be equal to or smaller than the size of the light receiving surface of the light receiving element.
According to the present invention, when incident light is incident on the interference light measurement device, the interference light generates reference light and signal light, and interference light is generated by causing the interference light to interfere therewith. Here, since the beam widths of the signal light and the reference light are set to be equal to or smaller than the size of the light receiving surface of the light receiving element, the beam width of the generated interference light is equal to or smaller than the size of the light receiving surface of the light receiving element. Irradiated.
In the interference light measuring apparatus according to the present invention, the plurality of light receiving elements may have interference fringes of the interference light irradiated on the light receiving surface when the signal light and the reference light have a predetermined reference wavelength. It is characterized in that four light receiving elements are arranged every one cycle.
Further, the interference light measurement apparatus of the present invention performs a predetermined calculation on the received light signal received by each of the light receiving elements included in the light receiving device, and the wavelength of the signal light and the reference light is a predetermined reference wavelength. In this case, it is characterized by comprising arithmetic units (21, 22) for generating an A-phase signal and a B-phase signal whose phases are different from each other by 90 degrees.
In the interference light measurement apparatus of the present invention, the signal light and the reference light have beam widths equal to or smaller than the size of the light receiving surface of the light receiving element, and the offset values of the A phase signal and the B phase signal Is preferably set to be equal to or less than a predetermined value.
Alternatively, the beam widths of the signal light and the reference light are equal to or smaller than the size of the light receiving surface of the light receiving element, and there is a deviation from the true value of the phase calculated from the A phase signal and the B phase signal. It is desirable that the value is set to be equal to or less than a predetermined value.
Furthermore, the interference light measurement apparatus of the present invention performs a predetermined signal processing on the A-phase signal and the B-phase signal generated by the arithmetic device, and measures the wavelength of the incident light. (23).
Alternatively, the interference light measurement apparatus of the present invention performs predetermined signal processing on the A-phase signal and the B-phase signal generated by the arithmetic device, and is measured in the optical path of the signal light. An optical characteristic measuring device (23) for measuring the characteristics of the device is provided.

本発明によれば、Ａ相信号及びＢ相信号のオフセット値及びＡ相信号及びＢ相信号から計算される位相の真値からのずれの少なくとも一方が所定値以下となるよう信号光及び参照光のビーム幅を設定しているため、測定波長範囲が広く且つ高い精度で干渉光を測定することができるという効果がある。
また、受光装置の受光面に照射される信号光及び参照光のビーム幅が、受光装置の受光面の大きさ以下に設定されており、信号光及び参照光のパワーの大部分が受光装置の受光面に照射されるため、従来に比べて測定ダイナミックレンジを広げることができ、効率良く干渉光の測定を行うことができるという効果がある。 According to the present invention, the signal light and the reference light are such that at least one of the offset value of the A phase signal and the B phase signal and the deviation from the true value of the phase calculated from the A phase signal and the B phase signal is equal to or less than a predetermined value. Therefore, the interference wavelength can be measured with a wide measurement wavelength range and high accuracy.
The beam widths of the signal light and the reference light applied to the light receiving surface of the light receiving device are set to be equal to or smaller than the size of the light receiving surface of the light receiving device, and most of the power of the signal light and the reference light is that of the light receiving device. Since the light receiving surface is irradiated, the measurement dynamic range can be expanded as compared with the conventional case, and the interference light can be efficiently measured.

以下、図面を参照して本発明の一実施形態による干渉光測定装置について詳細に説明する。図１は、本発明の一実施形態による干渉光測定装置の概略構成を示すブロック図である。図１に示す通り、本実施形態の干渉光測定装置１０は、レーザ光源１１、干渉装置１２、受光装置１３、及び信号処理装置１４を備えている。レーザ光源１１は、例えば外部共振器型波長可変光源であって、レーザ光を射出する。このレーザ光の波長は、例えば１５５０ｎｍである。   Hereinafter, an interference light measurement apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an interference light measurement apparatus according to an embodiment of the present invention. As shown in FIG. 1, the interference light measurement device 10 of this embodiment includes a laser light source 11, an interference device 12, a light receiving device 13, and a signal processing device 14. The laser light source 11 is an external resonator type wavelength variable light source, for example, and emits laser light. The wavelength of this laser beam is 1550 nm, for example.

干渉装置１２は、ハーフミラー１５、第１反射ミラー１６、及び第２反射ミラー１７を含んで構成されるマイケルソン型の干渉計である。尚、ここでは、干渉装置１２がマイケルソン型の干渉計である場合を例に挙げて説明するが、他の方式の干渉計を用いることもできる。ハーフミラー１５はレーザ光源１１から射出されたレーザ光を分岐して参照光Ｌ１と信号光Ｌ２とを生成するとともに、第１反射ミラー１６で反射された参照光Ｌ１と第２反射ミラー１７で反射された信号光Ｌ２とを合波して（干渉させて）干渉光Ｌ３を生成する。尚、図１に示す例では、信号光Ｌ２の光路上（ハーフミラー１５と第２反射ミラー１７との間の光路上）に、光学部品・モジュール等の被測定デバイス（ＤＵＴ）２０が配置されている。   The interference device 12 is a Michelson interferometer that includes a half mirror 15, a first reflection mirror 16, and a second reflection mirror 17. Here, the case where the interferometer 12 is a Michelson interferometer will be described as an example, but other types of interferometers may be used. The half mirror 15 splits the laser light emitted from the laser light source 11 to generate the reference light L1 and the signal light L2, and reflects the reference light L1 reflected by the first reflecting mirror 16 and the second reflecting mirror 17. The signal light L2 thus combined is combined (interfered) to generate interference light L3. In the example shown in FIG. 1, a device under test (DUT) 20 such as an optical component / module is disposed on the optical path of the signal light L2 (on the optical path between the half mirror 15 and the second reflecting mirror 17). ing.

第１反射ミラー１６は、ハーフミラー１５で分岐された参照光Ｌ１をハーフミラー１５に向けて反射する。また、第２反射ミラー１７は、ハーフミラー１５で分岐された信号光Ｌ２をハーフミラー１５に向けて反射する。ここで、第１反射ミラー１６及び第２反射ミラー１７は、参照光Ｌ１及び信号光Ｌ２が、受光装置１３の受光面１３ａに対して所定の角度を持って入射するように僅かに傾けられている。   The first reflection mirror 16 reflects the reference light L <b> 1 branched by the half mirror 15 toward the half mirror 15. The second reflection mirror 17 reflects the signal light L <b> 2 branched by the half mirror 15 toward the half mirror 15. Here, the first reflecting mirror 16 and the second reflecting mirror 17 are slightly tilted so that the reference light L1 and the signal light L2 are incident on the light receiving surface 13a of the light receiving device 13 with a predetermined angle. Yes.

受光装置１３は、例えば受光面１３ａに沿って配列された複数の受光素子（フォトダイオード）を備えたフォトダイオードアレイである。尚、ここでは、受光素子の配列方向は紙面に沿う方向であるとする。尚、以下の説明では、受光素子の配列方向を「素子配列方向」という。受光装置１３の受光面１３ａには参照光Ｌ１と信号光Ｌ２とをハーフミラー１５で合波して得られる干渉光Ｌ３が照射され、受光装置１３はこの干渉光Ｌ３を複数の受光素子で受光する。尚、干渉光Ｌ３の干渉縞が現れる方向は素子配列方向と同じ方向（紙面に沿う方向）であるとする。   The light receiving device 13 is, for example, a photodiode array including a plurality of light receiving elements (photodiodes) arranged along the light receiving surface 13a. Here, it is assumed that the arrangement direction of the light receiving elements is a direction along the paper surface. In the following description, the arrangement direction of the light receiving elements is referred to as “element arrangement direction”. The light receiving surface 13a of the light receiving device 13 is irradiated with interference light L3 obtained by combining the reference light L1 and the signal light L2 with the half mirror 15, and the light receiving device 13 receives the interference light L3 with a plurality of light receiving elements. To do. It is assumed that the interference fringes of the interference light L3 appear in the same direction as the element arrangement direction (the direction along the paper surface).

信号処理装置１４は、受光装置１３から出力される受光信号に基づいて所定の信号処理を行ってＤＵＴ２０の光学特性（例えば、透過特性）を求める。尚、図１に示す干渉光測定装置１０は、信号光Ｌ２の光路上にＤＵＴ２０が配置されていなければ、レーザ光源１１から射出されるレーザ光の波長を測定する波長モニタ装置として用いることもできる。波長モニタ装置として用いる場合には、信号処理装置１４は受光装置１３から出力される受光信号に基づいて所定の信号処理を行ってレーザ光源１１から射出されるレーザ光の波長を求める。   The signal processing device 14 performs predetermined signal processing based on the light reception signal output from the light receiving device 13 to obtain the optical characteristics (for example, transmission characteristics) of the DUT 20. The interference light measurement device 10 shown in FIG. 1 can also be used as a wavelength monitoring device that measures the wavelength of the laser light emitted from the laser light source 11 if the DUT 20 is not disposed on the optical path of the signal light L2. . When used as a wavelength monitoring device, the signal processing device 14 performs predetermined signal processing based on the received light signal output from the light receiving device 13 to obtain the wavelength of the laser light emitted from the laser light source 11.

次に、受光装置１３の受光面１３ａに照射される干渉光Ｌ３について説明する。図２は、干渉光Ｌ３と受光装置１３との関係を説明するための図である。図２に示す通り、受光装置１３の受光面１３ａに沿って複数の受光素子Ｅ１，Ｅ２，…，ＥＮ（Ｎは２以上の整数）が配列されている。受光装置１３の受光面１３ａに照射される干渉光１３ａは参照光Ｌ１と信号光Ｌ２とを干渉させたものであるが、これら参照光Ｌ１と信号光Ｌ２とを干渉させずに個別に受光装置１３の受光面１３ａに照射した場合には、受光面１３ａ上における参照光Ｌ１及び信号光Ｌ２の光強度分布は図２（ａ）に示す分布となる。   Next, the interference light L3 irradiated on the light receiving surface 13a of the light receiving device 13 will be described. FIG. 2 is a diagram for explaining the relationship between the interference light L <b> 3 and the light receiving device 13. As shown in FIG. 2, a plurality of light receiving elements E1, E2,..., EN (N is an integer of 2 or more) are arranged along the light receiving surface 13a of the light receiving device 13. The interference light 13a applied to the light receiving surface 13a of the light receiving device 13 is obtained by causing the reference light L1 and the signal light L2 to interfere with each other. The light receiving device is individually received without causing the reference light L1 and the signal light L2 to interfere with each other. When the 13 light receiving surfaces 13a are irradiated, the light intensity distributions of the reference light L1 and the signal light L2 on the light receiving surface 13a are as shown in FIG.

つまり、参照光Ｌ１及び信号光Ｌ２は、素子配列方向については、受光面１３ａの中心（受光面１３ａの中心（Ｌ＝０））に関して対称な分布（例えば、ガウス分布）となる。尚、Ｌは素子配列方向における受光面１３ａの中心からの距離である。ここで、信号光Ｌ２の強度の最大値（ピーク強度）Ｐ２が参照光Ｌ１のピーク強度Ｐ１よりも低くなっているのは、信号光Ｐ２がＤＵＴ２０を通過して減衰するためである。   That is, the reference light L1 and the signal light L2 have a symmetrical distribution (for example, a Gaussian distribution) with respect to the center of the light receiving surface 13a (the center of the light receiving surface 13a (L = 0)) in the element arrangement direction. Note that L is a distance from the center of the light receiving surface 13a in the element arrangement direction. Here, the reason why the maximum value (peak intensity) P2 of the intensity of the signal light L2 is lower than the peak intensity P1 of the reference light L1 is that the signal light P2 passes through the DUT 20 and is attenuated.

また、参照光Ｌ１及び信号光Ｌ２は、素子配列方向におけるビーム幅が受光面１３ａの大きさ以下に設定されている。これは、測定に用いられる参照光Ｌ１及び信号光Ｌ２（受光面１３ａに照射される参照光Ｌ１及び信号光Ｌ２）の光量を増やすことで、効率を向上させるためである。つまり、従来は、参照光Ｌ１及び信号光Ｌ２のビーム幅を受光面１３ａの大きさに比べて大きくし、これにより受光面１３ａに照射される参照光Ｌ１及び信号光Ｌ２の強度をほぼ均一としていた。しかしながら、これによると参照光Ｌ１及び信号光Ｌ２の多くが測定に使用されず無駄に消費されていた。   Further, the reference light L1 and the signal light L2 have a beam width in the element arrangement direction set to be equal to or smaller than the size of the light receiving surface 13a. This is for improving the efficiency by increasing the amount of the reference light L1 and the signal light L2 (reference light L1 and signal light L2 irradiated on the light receiving surface 13a) used for the measurement. That is, conventionally, the beam widths of the reference light L1 and the signal light L2 are made larger than the size of the light receiving surface 13a, whereby the intensities of the reference light L1 and the signal light L2 irradiated on the light receiving surface 13a are made substantially uniform. It was. However, according to this, most of the reference light L1 and the signal light L2 are not used for measurement and are wasted.

本実施形態では素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅を受光面１３ａの大きさ以下にすることで、より多くの参照光Ｌ１及び信号光Ｌ２を受光面１３ａに照射し、これにより測定に用いられる参照光Ｌ１及び信号光Ｌ２の光量を増やして効率を向上させることができる。ここで、素子配列方向におけるビーム幅は、強度がピーク強度の１／ｅ２となる幅である。つまり、参照光Ｌ１については強度がＰ１／ｅ２以上である部分の幅であり、信号光Ｌ２については強度がＰ２／ｅ２以上である部分の幅である。 In the present embodiment, by making the beam widths of the reference light L1 and the signal light L2 in the element arrangement direction equal to or smaller than the size of the light receiving surface 13a, more reference light L1 and signal light L2 are irradiated onto the light receiving surface 13a. Thus, it is possible to improve the efficiency by increasing the light amounts of the reference light L1 and the signal light L2 used for measurement. Here, the beam width in the element arrangement direction is a width at which the intensity is 1 / e 2 of the peak intensity. That is, the reference light L1 is the width of the portion where the intensity is P1 / e 2 or more, and the signal light L2 is the width of the portion where the intensity is P2 / e 2 or more.

尚、素子配列方向に交差する方向（図１の紙面に交差する方法）については、干渉光Ｌ３（参照光Ｌ１，信号光Ｌ２）は広がりが僅かであり、そのビーム幅は受光面１３ａの大きさ以下にされている。また、素子配列方向に交差する方向については、例えば図１に示す干渉装置１２と受光装置１３との間にシリンドリカルレンズ等を配置して積極的に集光し、干渉光Ｌ３（参照光Ｌ１，信号光Ｌ２）のビーム幅を受光面１３の大きさ以下にしても良い。   In the direction intersecting the element arrangement direction (the method intersecting the paper surface of FIG. 1), the interference light L3 (reference light L1, signal light L2) is slightly spread, and its beam width is the size of the light receiving surface 13a. Has been below. For the direction intersecting the element arrangement direction, for example, a cylindrical lens is disposed between the interference device 12 and the light receiving device 13 shown in FIG. The beam width of the signal light L2) may be made smaller than the size of the light receiving surface 13.

図２（ｂ）は、受光面１３ａ上での素子配列方向における干渉光Ｌ３の強度分布の一例を示す図である。尚、図２（ｂ）に破線で示す曲線はレーザ光源１１から射出されるレーザ光の波長が基準波長（例えば、１５５０ｎｍ）のときに得られる干渉光Ｌ３１の分布を示しており、実線で示す曲線はレーザ光の波長が基準波長から所定量だけずれているときに干渉光Ｌ３２の分布を示している。   FIG. 2B is a diagram illustrating an example of the intensity distribution of the interference light L3 in the element arrangement direction on the light receiving surface 13a. 2B shows the distribution of the interference light L31 obtained when the wavelength of the laser light emitted from the laser light source 11 is a reference wavelength (for example, 1550 nm), and is indicated by a solid line. The curve shows the distribution of the interference light L32 when the wavelength of the laser light is deviated by a predetermined amount from the reference wavelength.

図２（ｂ）に示す通り、参照光Ｌ１と信号光Ｌ２とが干渉した干渉光Ｌ３（干渉光Ｌ３１，Ｌ３２）は、受光面１３ａ上においてある分布を有する。ここで、受光面１３ａに照射される参照光Ｌ１及び信号光Ｌ２の強度が均一であれば干渉光Ｌ３（干渉光Ｌ３１，Ｌ３２）の強度分布は正弦波状に変化するものとなる。しかしながら、図２（ａ）に示す通り、参照光Ｌ１及び信号光Ｌ２はある分布を有しているため、干渉光Ｌ３（干渉光Ｌ３１，Ｌ３２）は受光面１３ａの中心（距離Ｌ＝０）付近で極めて大きくなるが、受光面１３ａの両端部では極大値が小さくなる分布となる。   As shown in FIG. 2B, the interference light L3 (interference light L31, L32) in which the reference light L1 and the signal light L2 interfere has a certain distribution on the light receiving surface 13a. Here, if the intensities of the reference light L1 and the signal light L2 irradiated on the light receiving surface 13a are uniform, the intensity distribution of the interference light L3 (interference light L31, L32) changes in a sine wave shape. However, as shown in FIG. 2A, since the reference light L1 and the signal light L2 have a certain distribution, the interference light L3 (interference light L31, L32) is the center of the light receiving surface 13a (distance L = 0). Although it becomes extremely large in the vicinity, the maximum value is distributed at both ends of the light receiving surface 13a.

図３は、干渉光Ｌ３と受光装置１３に設けられる受光素子との関係を示す図である。尚、図３においては受光素子Ｅ１〜ＥＮのうちの隣接する４つの受光素子（例えば、受光面１３ａの中心から順に４つ配列された受光素子）について符号ｅ１〜ｅ４を付して示している。受光装置１３の受光素子Ｅ１〜ＥＮは、図３に示す通り、レーザ光源１１から射出されるレーザ光の波長が基準波長（例えば、１５５０ｎｍ）のときに得られる干渉光Ｌ３１の干渉縞の１周期毎に４つの受光素子ｅ１〜ｅ４が配置されるよう配列されている。言い換えると、干渉光Ｌ３１の干渉縞の１周期の長さが４つの受光素子ｅ１〜ｅ４が占める長さになるよう、受光装置１３の受光面１３ａに対する参照光Ｌ１及び信号光Ｌ２の入射角度が設定されている。   FIG. 3 is a diagram showing the relationship between the interference light L3 and the light receiving element provided in the light receiving device 13. As shown in FIG. In FIG. 3, four adjacent light receiving elements (for example, four light receiving elements arranged in order from the center of the light receiving surface 13a) among the light receiving elements E1 to EN are denoted by reference numerals e1 to e4. . As shown in FIG. 3, the light receiving elements E1 to EN of the light receiving device 13 have one cycle of interference fringes of the interference light L31 obtained when the wavelength of the laser light emitted from the laser light source 11 is a reference wavelength (for example, 1550 nm). It arranges so that four light receiving elements e1-e4 may be arranged for every. In other words, the incident angles of the reference light L1 and the signal light L2 with respect to the light receiving surface 13a of the light receiving device 13 are set so that the length of one period of the interference fringes of the interference light L31 is the length occupied by the four light receiving elements e1 to e4. Is set.

これにより、図３に示す例では、位相が０度である干渉光Ｌ３１が受光素子ｅ１で受光され、位相が９０度である干渉光Ｌ３１が受光素子ｅ２で受光される。また、位相が１８０度である干渉光Ｌ３１が受光素子ｅ３で受光され、位相が２７０度である干渉光Ｌ３１が受光素子ｅ４で受光される。尚、ここでいう「干渉光の位相」は、厳密な位相の意味ではなく、ある程度の幅を持っている点に注意されたい。例えば、受光素子ｅ１は位相が０〜９０度の範囲内の干渉光Ｌ３１を受光する。   Accordingly, in the example illustrated in FIG. 3, the interference light L31 having a phase of 0 degrees is received by the light receiving element e1, and the interference light L31 having a phase of 90 degrees is received by the light receiving element e2. The interference light L31 having a phase of 180 degrees is received by the light receiving element e3, and the interference light L31 having a phase of 270 degrees is received by the light receiving element e4. It should be noted that the “phase of interference light” here does not mean a strict phase but has a certain width. For example, the light receiving element e1 receives the interference light L31 having a phase in the range of 0 to 90 degrees.

尚、図３に示す通り、レーザ光源１１から射出されるレーザ光の波長が基準波長からずれているときに得られる干渉光Ｌ３２の干渉縞の周期は、レーザ光の波長が基準波長であるときに得られる干渉光Ｌ３１の干渉縞の周期からずれる（図３に示す例で長くなっている）。このため、干渉光Ｌ３２と受光装置１３に設けられる受光素子との関係が崩れてしまう。   As shown in FIG. 3, the period of the interference fringes of the interference light L32 obtained when the wavelength of the laser light emitted from the laser light source 11 deviates from the reference wavelength is obtained when the wavelength of the laser light is the reference wavelength. Is deviated from the period of the interference fringes of the interference light L31 obtained (lengthened in the example shown in FIG. 3). For this reason, the relationship between the interference light L32 and the light receiving element provided in the light receiving device 13 is broken.

図４は、干渉光Ｌ３と受光装置１３に設けられる受光素子との関係に加えて、信号処理装置１４の内部構成を示す図である。図４に示す通り、信号処理装置１４は、差動増幅器２１，２２（演算装置）及び処理装置２３（波長測定装置、光学特性測定装置）を備える。差動増幅器２１の正相入力端には受光素子ｅ１から出力される受光信号（位相が０度の干渉光Ｌ３を受光した受光信号）が入力され、逆相入力端には受光素子ｅ３から出力される受光信号（位相が１８０度の干渉光Ｌ３を受光した受光信号）が入力される。また、差動増幅器２２の正相入力端には受光素子ｅ２から出力される受光信号（位相が９０度の干渉光Ｌ３を受光した受光信号）が入力され、逆相入力端には受光素子ｅ４から出力される受光信号（位相が２７０度の干渉光Ｌ３を受光した受光信号）が入力される。   FIG. 4 is a diagram showing an internal configuration of the signal processing device 14 in addition to the relationship between the interference light L3 and the light receiving element provided in the light receiving device 13. As shown in FIG. 4, the signal processing device 14 includes differential amplifiers 21 and 22 (arithmetic device) and a processing device 23 (a wavelength measuring device and an optical characteristic measuring device). A light receiving signal output from the light receiving element e1 (light receiving signal receiving the interference light L3 having a phase of 0 degree) is input to the positive phase input terminal of the differential amplifier 21, and output from the light receiving element e3 to the negative phase input terminal. Received light signal (light reception signal that received interference light L3 having a phase of 180 degrees) is input. In addition, a light receiving signal output from the light receiving element e2 (light receiving signal receiving the interference light L3 having a phase of 90 degrees) is input to the positive phase input terminal of the differential amplifier 22, and the light receiving element e4 is input to the negative phase input terminal. The light reception signal (the light reception signal that received the interference light L3 having a phase of 270 degrees) is input.

尚、前述した通り、受光装置１はＮ個の受光素子Ｅ１〜ＥＮを備えているが、差動増幅器２１，２２の正相入力端及び逆相入力端には、それぞれ４つおきの受光素子から出力される受光信号が入力される。例えば、差動増幅器２１の正相入力端には受光素子Ｅ１，Ｅ５，Ｅ９，Ｅ１３，…から出力される受光信号が入力され、差動増幅器２１の逆相入力端には受光素子Ｅ３，Ｅ７，Ｅ１１，Ｅ１５，…から出力される受光信号が入力される。また、差動増幅器２２の正相入力端には受光素子Ｅ２，Ｅ６，Ｅ１０，Ｅ１４，…から出力される受光信号が入力され、差動増幅器２２の逆相入力端には受光素子Ｅ４，Ｅ８，Ｅ１２，Ｅ１６，…から出力される受光信号が入力される。   As described above, the light receiving device 1 includes the N light receiving elements E1 to EN. However, every four light receiving elements at the positive phase input terminal and the negative phase input terminal of the differential amplifiers 21 and 22, respectively. The light reception signal output from is input. For example, the light receiving signal output from the light receiving elements E1, E5, E9, E13,... Is input to the positive phase input terminal of the differential amplifier 21, and the light receiving elements E3, E7 are input to the negative phase input terminal of the differential amplifier 21. , E11, E15,... The light receiving signals output from the light receiving elements E2, E6, E10, E14,... Are input to the positive phase input terminals of the differential amplifier 22, and the light receiving elements E4, E8 are input to the negative phase input terminals of the differential amplifier 22. , E12, E16,...

差動増幅器２１は、位相が０度の干渉光の受光信号と、位相が１８０度の干渉光の受光信号との差動増幅を行い、図４中に示すＡ相信号を処理装置２３に出力する。また、差動増幅器２２は、位相が９０度の干渉光の受光信号と、位相が２７０度の干渉光の受光信号との差動増幅を行い、図４中に示すＢ相信号を処理装置２３に出力する。受光装置１３の受光面１３ａに照射される干渉光Ｌ３（参照光Ｌ１、信号光Ｌ２）の波長が基準波長である場合には、差動増幅器２１，２２からそれぞれ出力されるＡ相信号とＢ相信号とは位相が９０°ずれた信号となる。   The differential amplifier 21 differentially amplifies the received light signal of interference light having a phase of 0 degrees and the received light signal of interference light having a phase of 180 degrees, and outputs the A-phase signal shown in FIG. To do. Further, the differential amplifier 22 performs differential amplification of the received light signal of the interference light having a phase of 90 degrees and the received light signal of the interference light having a phase of 270 degrees, and the B phase signal shown in FIG. Output to. When the wavelength of the interference light L3 (reference light L1, signal light L2) applied to the light receiving surface 13a of the light receiving device 13 is the reference wavelength, the A phase signal and B output from the differential amplifiers 21 and 22, respectively. The phase signal is a signal whose phase is shifted by 90 °.

尚、本実施形態では、受光面１３ａ上の素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅が受光面１３ａの大きさ以下であるため、通常は差動増幅器２１，２２で作動増幅しても直流成分（ＤＣ成分）が完全に除去されない。このため、図４に示す通り、Ａ相信号及びＢ相信号は共にオフセットを有する場合がある。処理装置２３は、差動増幅器２１，２２から出力されるＡ相信号及びＢ相信号に対して所定の信号処理を行って、レーザ光源１１から射出されるレーザ光の波長を測定し、又は、ＤＵＴ２０の光学特性（例えば、透過特性）を測定する。   In the present embodiment, since the beam widths of the reference light L1 and the signal light L2 in the element arrangement direction on the light receiving surface 13a are equal to or smaller than the size of the light receiving surface 13a, the differential amplifiers 21 and 22 normally perform operational amplification. However, the direct current component (DC component) is not completely removed. For this reason, as shown in FIG. 4, both the A phase signal and the B phase signal may have an offset. The processing device 23 performs predetermined signal processing on the A phase signal and the B phase signal output from the differential amplifiers 21 and 22, and measures the wavelength of the laser light emitted from the laser light source 11, or The optical characteristics (for example, transmission characteristics) of the DUT 20 are measured.

以上、干渉光測定装置１０の構成について説明したが、次に参照光Ｌ１及び信号光Ｌ２のビーム幅と、Ａ相信号及びＢ相信号のオフセット及び位相ずれとの関係について考察する。いま、受光装置１３の受光面１３ａに照射される参照光Ｌ１及び信号光Ｌ２の素子配列方向における強度分布がガウス分布を有していると仮定し、参照光Ｌ１のピーク強度をＰ１、素子配列方向における参照光Ｌ１のビーム幅をＷ、素子配列方向における受光面１３ａの中心からの距離をＬ、ＤＵＴ２０の減衰量をαとすると、受光装置１３の受光面１３ａに照射される参照光Ｌ１及び信号光Ｌ２の素子配列方向における強度分布Ｉ１（Ｌ）,Ｉ２（Ｌ）は以下の（１）式で表される。

Figure 2008020340
The configuration of the interference light measurement apparatus 10 has been described above. Next, the relationship between the beam widths of the reference light L1 and the signal light L2 and the offsets and phase shifts of the A phase signal and the B phase signal will be considered. Now, assuming that the intensity distribution in the element arrangement direction of the reference light L1 and the signal light L2 irradiated to the light receiving surface 13a of the light receiving device 13 has a Gaussian distribution, the peak intensity of the reference light L1 is P1, and the element arrangement When the beam width of the reference light L1 in the direction is W, the distance from the center of the light receiving surface 13a in the element arrangement direction is L, and the attenuation amount of the DUT 20 is α, the reference light L1 irradiated on the light receiving surface 13a of the light receiving device 13 and The intensity distributions I 1 (L) and I 2 (L) in the element array direction of the signal light L2 are expressed by the following equation (1).
Figure 2008020340

また、参照光Ｌ１の全パワーはパワービーム幅によらず一定であるため、参照光Ｌ１のピーク強度Ｐ１を参照光Ｌ１の全パワーで正規化すると、以下の（２）式で表される。

Figure 2008020340
Further, since the total power of the reference light L1 is constant regardless of the power beam width, when the peak intensity P1 of the reference light L1 is normalized by the total power of the reference light L1, it is expressed by the following equation (2).
Figure 2008020340

ここで、図３を用いて説明した通り、受光装置１３の受光面１３ａに照射される干渉光Ｌ３（参照光Ｌ１、信号光Ｌ２）の波長が基準波長からずれているときに得られる干渉光Ｌ３２の干渉縞の周期は、レーザ光の波長が基準波長であるときに得られる干渉光Ｌ３１の干渉縞の周期からずれる。いま、基準波長をλ０、基準波長からずれた波長をλｍとし、干渉光Ｌ３の波長が基準波長λ０のときの干渉縞の周期をｌ０、干渉光Ｌ３の波長が波長λｍのときの干渉縞の周期をｌｍとすると、以下の（３）式が成り立つ。

Figure 2008020340
Here, as described with reference to FIG. 3, the interference light obtained when the wavelength of the interference light L <b> 3 (reference light L <b> 1, signal light L <b> 2) irradiated on the light receiving surface 13 a of the light receiving device 13 is deviated from the reference wavelength. The period of the interference fringes of L32 deviates from the period of the interference fringes of the interference light L31 obtained when the wavelength of the laser light is the reference wavelength. Now, the reference wavelength lambda 0, the wavelength deviated from the reference wavelength is lambda m, the period of the interference fringes when the wavelength of the interference light L3 is the reference wavelength lambda 0 l 0, the wavelength of the interference light L3 having a wavelength lambda m when the period of the interference fringes and l m of time, holds the following equation (3).
Figure 2008020340

また、干渉光Ｌ３の波長が基準波長λ０のときには、受光装置１３の受光素子Ｅ１〜ＥＮの各々で受光される干渉光Ｌ３（干渉光Ｌ３１）の位相は９０度の倍数となるが、干渉光Ｌ３の波長が基準波長λ０のときには、各受光素子Ｅ１〜ＥＮの各々で受光される干渉光Ｌ３（干渉光Ｌ３２）の位相θｍは以下の（４）式で表される

Figure 2008020340
Further, when the wavelength of the interference light L3 is the reference wavelength lambda 0, the phase of the interference light L3 (interference light L31) received by the respective light receiving elements E1~EN of the light receiving device 13 is a multiple of 90 degrees, interference when the wavelength of the light L3 of the reference wavelength lambda 0, the phase theta m of the interference light L3 (interference light L32) received by the respective light receiving elements E1~EN is expressed by the following equation (4)
Figure 2008020340

以上を踏まえて、受光装置１３に設けられた受光素子Ｅ１〜ＥＮの各々で受光される干渉光Ｌ３のパワー変動を求める。各受光素子Ｅ１〜ＥＮで受光される干渉光Ｌ３の強度は、干渉装置１２の光路長差（参照光Ｌ１の光路長と信号光Ｌ２の光路長との差）ΔＬで定まる波長変動を１周期として変動することになる。いま、図２（ｂ）に示す通り、素子配列方向における受光装置１３の受光面１３ａの中心（Ｌ＝０）を基準として干渉縞の周期が広がった場合には、受光素子Ｅ１〜ＥＮの素子間隔をＬｇ、波長変動に対応する位相変動をφとすると、受光面１３ａ上における干渉光Ｌ３の強度ｉ（Ｌ）は以下の（５）式で表される。

Figure 2008020340
Based on the above, the power fluctuation of the interference light L3 received by each of the light receiving elements E1 to EN provided in the light receiving device 13 is obtained. The intensity of the interference light L3 received by each of the light receiving elements E1 to EN is a period of wavelength fluctuation determined by ΔL of the optical path length difference of the interference device 12 (difference between the optical path length of the reference light L1 and the optical path length of the signal light L2). Will fluctuate as. Now, as shown in FIG. 2B, when the period of the interference fringes spreads with reference to the center (L = 0) of the light receiving surface 13a of the light receiving device 13 in the element arrangement direction, the elements of the light receiving elements E1 to EN. When the interval is L g and the phase variation corresponding to the wavelength variation is φ, the intensity i (L) of the interference light L3 on the light receiving surface 13a is expressed by the following equation (5).
Figure 2008020340

上記の（５）式で示される干渉光Ｌ３が受光装置１３の受光面１３ａに照射された場合に、受光装置１３が備える受光素子Ｅ１〜ＥＮの各々に入射されるパワーＩ（ｎ）は、上記の（５）式を各受光素子Ｅ１〜ＥＮの大きさ（素子配列方向の大きさ）で定積分することにより得られ、以下の（６）式で表される。

Figure 2008020340
When the interference light L3 expressed by the above equation (5) is irradiated onto the light receiving surface 13a of the light receiving device 13, the power I (n) incident on each of the light receiving elements E1 to EN included in the light receiving device 13 is: The above equation (5) is obtained by definite integration with the size of each of the light receiving elements E1 to EN (size in the element array direction), and is expressed by the following equation (6).
Figure 2008020340

尚、上記（６）式中の変数ｎは、受光素子Ｅ１〜ＥＮの素子番号を示すものであり、受光素子Ｅ１の素子番号は「１」、受光素子Ｅ２の素子番号は「２」であり、受光素子ＥＮの素子番号は「Ｎ」である。また、上記（６）式中の変数Ｌｒは、受光素子Ｅ１〜ＥＮの各々が実際に照射される光を受光することができる素子配列方向の長さ（有効受光長）である。図５は、有効受光長Ｌｒを説明するための受光装置１３の拡大図である。尚、図５では、受光装置１３の受光素子Ｅ１〜Ｅ４のみを図示している。図５に示す通り、各受光素子Ｅ１〜ＥＮは、その内部に入射する光を受光する領域Ｒを有する。この領域Ｒの素子配列方向の長さが有効受光長Ｌｒであり、有効受光長Ｌｒ＜素子間隔Ｌｇなる関係がある。 The variable n in the above equation (6) indicates the element numbers of the light receiving elements E1 to EN, the element number of the light receiving element E1 is “1”, and the element number of the light receiving element E2 is “2”. The element number of the light receiving element EN is “N”. In addition, the variable L r in the above equation (6) is the length (effective light receiving length) in the element array direction in which each of the light receiving elements E1 to EN can receive the light actually irradiated. Figure 5 is an enlarged view of the light receiving device 13 for explaining an effective light receiving length L r. In FIG. 5, only the light receiving elements E1 to E4 of the light receiving device 13 are illustrated. As shown in FIG. 5, each of the light receiving elements E <b> 1 to EN has a region R that receives light incident on the light receiving elements E <b> 1 to EN. Element length of the array direction of the region R is the effective light-receiving length L r, the effective light-receiving length L r <element spacing L g becomes relevant.

受光装置１３が備える受光素子Ｅ１〜ＥＮの各々から出力される受光信号は、受光素子Ｅ１〜ＥＮの各々で受光される干渉光Ｌ３のパワーに比例する。このため、差動増幅器２１から出力されるＡ相信号ｉＡ及び差動増幅器２２から出力されるＢ相信号ｉＢは、以下の（７）式で表される。但し、以下の（７）式中の変数ｑは、受光素子Ｅ１〜ＥＮの総数Ｎを４で除算して得られる商（即ち、ｑ＝Ｎ％４）である。

Figure 2008020340
The light reception signal output from each of the light receiving elements E1 to EN included in the light receiving device 13 is proportional to the power of the interference light L3 received by each of the light receiving elements E1 to EN. Therefore, the A-phase signal i A output from the differential amplifier 21 and the B-phase signal i B output from the differential amplifier 22 are expressed by the following equation (7). However, the variable q in the following equation (7) is a quotient obtained by dividing the total number N of the light receiving elements E1 to EN by 4 (that is, q = N% 4).
Figure 2008020340

例えば、受光装置１３が計１６個の受光素子Ｅ１〜Ｅ１６を備えるものとすると、上記（７）式は、以下の（８）式のように書き下せる。

Figure 2008020340
For example, when the light receiving device 13 includes a total of 16 light receiving elements E1 to E16, the above equation (7) can be written as the following equation (8).
Figure 2008020340

よって、Ａ相信号とＢ相信号とを合成した信号（リサージュ信号）の振幅Ｉｒ、及びＡ相信号とＢ相信号との位相差θｒは以下の（９）式で表される。

Figure 2008020340
Therefore, the amplitude I r of the signal (Lissajous signal) obtained by combining the A-phase signal and the B-phase signal and the phase difference θ r between the A-phase signal and the B-phase signal are expressed by the following equation (9).
Figure 2008020340

上記の（７）式又は（８）式で示されるＡ相信号ｉＡの平均値、又はＢ相信号ｉＢの平均値を算出すれば、各々のオフセットを求めることができる。尚、Ａ相信号ｉＡのオフセットとＢ相信号ｉＢのオフセットとは、絶対値が同じ値をとり、符号が逆になる。また、Ａ相信号ｉＡとＢ相信号ｉＢの位相差θｒは上記（９）式で求められる。 By calculating an average value of the equation (7) or (8) the average value of the A-phase signal i A of formula, or B-phase signal i B, can be obtained each offset. Note that the offset of the offset and the B-phase signal i B of the A-phase signal i A, the absolute value takes the same value, the sign is reversed. Further, the phase difference θ r between the A-phase signal i A and the B-phase signal i B is obtained by the above equation (9).

ここで、受光面１３ａに照射される干渉光Ｌ３の強度ｉ（Ｌ）を示す上記（５）式を参照すると、右辺第１項は参照光Ｌ１の強度分布Ｉ１（Ｌ）を示す式であり、右辺第２項は信号光Ｌ２の強度分布Ｉ２（Ｌ）を示す式である。また、右辺第３項は参照光Ｌ１の強度分布Ｉ１（Ｌ）と信号光Ｌ２の強度分布Ｉ２（Ｌ）との積の平方根に余弦関数（コサイン）が掛けられた式である。このため、干渉光Ｌ３の強度ｉ（Ｌ）は、素子配列方向における参照光Ｌ１及び信号光Ｌ２の強度分布Ｉ１（Ｌ）,Ｉ２（Ｌ）に応じて変化することが分かる。また、（５）式の右辺第３項中の余弦関数（コサイン）には、波長λｍ及び波長変動に対応する位相変動φが含まれているため、参照光Ｌ１及び信号光Ｌ２の波長が基準波長λ０からずれると素子配列方向における参照光Ｌ３の干渉縞の周期が変化することが分かる。 Here, referring to the above equation (5) indicating the intensity i (L) of the interference light L3 irradiated to the light receiving surface 13a, the first term on the right side is an equation indicating the intensity distribution I 1 (L) of the reference light L1. Yes, the second term on the right side is an expression indicating the intensity distribution I 2 (L) of the signal light L2. The third term on the right side is an expression cosine function (cosine) is applied to the square root of the product of the intensity distribution I 2 of the intensity of the reference light L1 distribution I 1 (L) and signal light L2 (L). For this reason, it can be seen that the intensity i (L) of the interference light L3 changes according to the intensity distributions I 1 (L) and I 2 (L) of the reference light L1 and the signal light L2 in the element arrangement direction. Further, since the cosine function (cosine) in the third term on the right side of the equation (5) includes the wavelength λ m and the phase variation φ corresponding to the wavelength variation, the wavelengths of the reference light L1 and the signal light L2 are determined. period of the interference fringes of the reference light L3 in shifts the element array direction from the reference wavelength lambda 0 can be seen to vary.

次に、素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅、ＤＵＴ２０における減衰量、及びレーザ光源１１から射出されるレーザ光の波長を変化させたときのＡ相信号ｉＡ及びＢ相信号ｉＢのオフセット並びに位相差θｒの変化を示すシミュレーション結果について説明する。尚、以下に示すシミュレーションでは、受光装置１３に設けられる受光素子Ｅ１〜ＥＮの素子間隔Ｌｇが０．１ｍｍであり、各受光素子Ｅ１〜ＥＮの有効受光長Ｌｒが０．０８ｍｍであるとしている。また、基準波長λ０を１５５０μｍとしている Next, the A phase signal i A and the B phase signal when the beam widths of the reference light L1 and the signal light L2 in the element arrangement direction, the attenuation in the DUT 20 and the wavelength of the laser light emitted from the laser light source 11 are changed. A simulation result showing changes in the offset of i B and the phase difference θ r will be described. In the simulation described below, element spacing L g of the light-receiving element E1~EN provided in the light receiving device 13 is 0.1 mm, as the effective light-receiving length L r of the light receiving elements E1~EN is 0.08mm Yes. The reference wavelength λ 0 is 1550 μm.

図６は、素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅とＤＵＴ２０の減衰量とを変化させたときのＡ相信号又はＢ相信号のオフセットの変化を示すシミュレーション結果である。尚、かかるシミュレーションでは、レーザ光源１１から射出されるレーザ光の波長を基準波長λ０に固定している。図６（ａ）は受光装置１３の受光素子数が「８」であり、図６（ｂ）は受光装置１３の受光素子数が「１６」であり、図６（ｃ）は受光装置１３の受光素子数が「２４」であるときのシミュレーション結果をそれぞれ示している。また、図６（ａ）〜図６（ｃ）では横軸に参照光Ｌ１及び信号光Ｌ２のビーム幅をとり、縦軸に原点ずれ率をとっている。ここで、原点ずれ率とは、Ａ相信号又はＢ相信号の振幅（最大値と最小値との差）に対するオフセットの大きさの比率を示す図である。 FIG. 6 is a simulation result showing a change in the offset of the A-phase signal or the B-phase signal when the beam widths of the reference light L1 and the signal light L2 and the attenuation amount of the DUT 20 are changed in the element arrangement direction. In such a simulation, securing the wavelength of the laser light emitted from the laser light source 11 to the reference wavelength lambda 0. 6A, the number of light receiving elements of the light receiving device 13 is “8”, FIG. 6B is the number of light receiving elements of the light receiving device 13, and FIG. The simulation results when the number of light receiving elements is “24” are shown. 6A to 6C, the horizontal axis represents the beam widths of the reference light L1 and the signal light L2, and the vertical axis represents the origin deviation rate. Here, the origin deviation rate is a diagram showing a ratio of the magnitude of the offset to the amplitude (difference between the maximum value and the minimum value) of the A phase signal or the B phase signal.

図６（ａ）〜図６（ｃ）に示す通り、ＤＵＴ２０の減衰量を０〜３０ｄＢまで５ｄＢ刻みで変化させている。これらの図を参照すると、素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅が変化すると原点ずれ率が大きく変化することが分かる。また、ＤＵＴ２０の減衰量が大きくなるにつれてビーム幅の変化に対する原点ずれ率の変化量が大きくなることも分かる。   As shown in FIGS. 6A to 6C, the attenuation of the DUT 20 is changed from 0 to 30 dB in increments of 5 dB. Referring to these figures, it can be seen that the origin deviation rate changes greatly when the beam widths of the reference light L1 and the signal light L2 in the element arrangement direction change. It can also be seen that the amount of change in the origin deviation rate with respect to the change in the beam width increases as the attenuation of the DUT 20 increases.

図１に示す干渉光測定装置１０を用いてＤＵＴ２０の光学特性を測定する場合には、減衰量が未知のＤＵＴ２０が信号光Ｌ２の光路上に配置されるため、原点ずれ率はＤＵＴ２０の減衰量に拘わらず「０」になることが理想的である。このため、図６（ａ）のシミュレーション結果から、受光装置１３の受光素子数が「８」であるとき（即ち、素子配列方向における受光面１３ａの大きさが０．８ｍｍのとき）には、参照光Ｌ１及び信号光Ｌ２のビーム幅を０．７５ｍｍ程度に設定するのが望ましい。また、受光装置１３の受光素子数が「１６」であるとき（即ち、素子配列方向における受光面１３ａの大きさが１．６ｍｍのとき）には、参照光Ｌ１及び信号光Ｌ２のビーム幅を０．９９ｍｍ程度に設定するのが望ましい。   When the optical characteristics of the DUT 20 are measured using the interference light measurement apparatus 10 shown in FIG. 1, the DUT 20 whose attenuation is unknown is arranged on the optical path of the signal light L2, so that the origin deviation rate is the attenuation of the DUT 20. Regardless of the case, it is ideal to be “0”. Therefore, from the simulation result of FIG. 6A, when the number of light receiving elements of the light receiving device 13 is “8” (that is, when the size of the light receiving surface 13a in the element arrangement direction is 0.8 mm), It is desirable to set the beam widths of the reference light L1 and the signal light L2 to about 0.75 mm. When the number of light receiving elements of the light receiving device 13 is “16” (that is, when the size of the light receiving surface 13a in the element arrangement direction is 1.6 mm), the beam widths of the reference light L1 and the signal light L2 are set. It is desirable to set it to about 0.99 mm.

同様に、受光装置１３の受光素子数が「２４」であるとき（即ち、素子配列方向における受光面１３ａの大きさが２．４ｍｍのとき）には、参照光Ｌ１及び信号光Ｌ２のビーム幅を１．１８ｍｍ程度に設定するのが望ましい。以上の通り、受光装置１３が備える受光素子の数に拘わらず、素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅を受光面１３ａの大きさ以下に設定すれば、ＤＵＴ２０の減衰量が変化しても原点ずれ率を小さくすることができる。   Similarly, when the number of light receiving elements of the light receiving device 13 is “24” (that is, when the size of the light receiving surface 13a in the element arrangement direction is 2.4 mm), the beam widths of the reference light L1 and the signal light L2 Is preferably set to about 1.18 mm. As described above, regardless of the number of light receiving elements included in the light receiving device 13, if the beam widths of the reference light L1 and the signal light L2 in the element arrangement direction are set to be equal to or smaller than the size of the light receiving surface 13a, the attenuation amount of the DUT 20 changes. Even so, the origin deviation rate can be reduced.

以上の通り、ＤＵＴ２０の減衰量に拘わらず原点ずれ率が「０」になるよう参照光Ｌ１及び信号光Ｌ２のビーム幅を設定するのが理想的であるが、干渉光測定装置１０に必要とされる精度に応じて原点ずれ率はある程度許容される。このため、例えばＤＵＴ２０の最大の減衰量が３０ｄＢのときに、干渉光測定装置１０に原点ずれ率が±５％許容される場合について考える。かかる場合において、受光素子数が「８」であると（図６（ａ）参照）、ビーム幅の僅かな変化に対して原点ずれ率が大きく変化するため、許容されるビーム幅のずれは小さい。しかしながら、素子数が増えるに従って許容されるビーム幅のずれの許容度も大きくなる。例えば、受光素子数が「１６」の場合には、図６（ｂ）に示す通り、０．９〜１．２ｍｍ程度の範囲で許容され、受光素子数が「２４」の場合には、図６（ｃ）に示す通り、０．９〜２．３ｍｍ程度の範囲で許容される。   As described above, although it is ideal to set the beam widths of the reference light L1 and the signal light L2 so that the origin deviation rate becomes “0” regardless of the attenuation amount of the DUT 20, it is necessary for the interference light measurement apparatus 10. The origin deviation rate is allowed to some extent according to the accuracy to be performed. For this reason, for example, a case is considered where the origin deviation rate is allowed to be ± 5% in the interference light measurement apparatus 10 when the maximum attenuation of the DUT 20 is 30 dB. In such a case, if the number of light receiving elements is “8” (see FIG. 6A), the deviation of the origin is greatly changed with respect to a slight change in the beam width, so that the allowable deviation of the beam width is small. . However, as the number of elements increases, the allowable deviation of the beam width increases. For example, when the number of light receiving elements is “16”, as shown in FIG. 6B, the allowable range is about 0.9 to 1.2 mm, and when the number of light receiving elements is “24”, As shown in FIG. 6 (c), it is allowed in the range of about 0.9 to 2.3 mm.

このため、素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅は、受光面の大きさ以下であって、干渉光測定装置１０に必要とされる精度に応じて適宜設定することができる。尚、実際上の原点ずれ率は、経年変化等を考慮すると、干渉光測定装置１０の精度上許容される原点ずれ率の１０分の１程度であるのが望ましい。このため、例えば干渉光測定装置１０の原点ずれ率が±５％許容される場合には、原点ずれ率が±０．５％以内に収まるよう参照光Ｌ１及び信号光Ｌ２のビーム幅を設定するのが好ましい。   For this reason, the beam widths of the reference light L1 and the signal light L2 in the element arrangement direction are equal to or smaller than the size of the light receiving surface, and can be appropriately set according to the accuracy required for the interference light measurement device 10. It should be noted that the actual origin deviation rate is preferably about one-tenth of the origin deviation rate allowed for the accuracy of the interference light measurement apparatus 10 in consideration of changes over time. For this reason, for example, when the origin deviation rate of the interference light measurement apparatus 10 is allowed to be ± 5%, the beam widths of the reference light L1 and the signal light L2 are set so that the origin deviation rate is within ± 0.5%. Is preferred.

図７は、素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅とレーザ光源１１から射出されるレーザ光の波長を変化させたときのＡ相信号及びＢ相信号から（９）式で計算される位相の変化を示すシミュレーション結果である。尚、かかるシミュレーションでは、ＤＵＴ２０での減衰量を０ｄＢに固定している。図７（ａ）は受光装置１３の受光素子数が「８」であり、図７（ｂ）は受光装置１３の受光素子数が「１６」であり、図７（ｃ）は受光装置１３の受光素子数が「２４」であるときのシミュレーション結果をそれぞれ図示している。また、図７（ａ）〜図７（ｃ）では横軸に参照光Ｌ１及び信号光Ｌ２のビーム幅をとり、縦軸にＡ相信号及びＢ相信号から計算される位相の真値からのずれをとっている。   FIG. 7 is calculated by the equation (9) from the A phase signal and the B phase signal when the beam width of the reference light L1 and the signal light L2 in the element arrangement direction and the wavelength of the laser light emitted from the laser light source 11 are changed. It is a simulation result which shows the change of the phase to be performed. In this simulation, the attenuation at the DUT 20 is fixed to 0 dB. FIG. 7A shows that the number of light receiving elements of the light receiving device 13 is “8”, FIG. 7B shows that the number of light receiving elements of the light receiving device 13 is “16”, and FIG. The simulation results when the number of light receiving elements is “24” are illustrated. 7A to 7C, the horizontal axis represents the beam widths of the reference light L1 and the signal light L2, and the vertical axis represents the phase calculated from the true value of the phase calculated from the A phase signal and the B phase signal. I'm taking a gap.

図７（ａ）〜図７（ｃ）に示す通り、レーザ光源１１から射出されるレーザ光の波長を１３５０〜１７５０μｍまで１００ｎｍ刻みで変化させている。これらの図を参照すると、レーザ光の波長が基準波長λ０である場合には、素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅が変化しても位相ずれが全く生じないことが分かる。これは、図３を用いて説明した通り、干渉光Ｌ３と受光装置１３の受光素子との関係が、干渉光Ｌ３（干渉光Ｌ３１）の干渉縞の１周期毎に４つの受光素子が配置された関係にあるからである。 As shown in FIGS. 7A to 7C, the wavelength of the laser light emitted from the laser light source 11 is changed in increments of 100 nm from 1350 to 1750 μm. Referring to these figures, it can be seen that when the wavelength of the laser light is the reference wavelength λ 0 , no phase shift occurs even if the beam widths of the reference light L1 and the signal light L2 in the element arrangement direction change. . As described with reference to FIG. 3, the relationship between the interference light L3 and the light receiving element of the light receiving device 13 is such that four light receiving elements are arranged for each period of the interference fringe of the interference light L3 (interference light L31). Because there is a relationship.

また、これらの図から、ビーム幅がある範囲に収まっている場合には、レーザ光の波長が基準波長λ０からずれても位相ずれは殆ど生じないが、その範囲から外れるとレーザ光の波長が基準波長λ０からずれるにつれて位相ずれが大きくなることが分かる。具体的には、図７（ａ）を参照すると、ビーム幅が０．４９ｍｍのときにはレーザ光の波長が基準波長λ０からずれても位相ずれは殆ど生じないが、ビーム幅が０．４９ｍｍ以外のときにはレーザ光の波長が基準波長λ０からずれると位相ずれが大きく変化する。 Further, from these figures, if they fall within a certain range the beam width, the phase shift is hardly be shifted wavelength of the laser light from the reference wavelength lambda 0, the wavelength of the laser beam deviates from its scope It can be seen that the phase shift increases with the shift from the reference wavelength λ 0 . Specifically, referring to FIG. 7 (a), but when the beam width is 0.49mm phase shift hardly be shifted wavelength of the laser light from the reference wavelength lambda 0, the beam width is other than 0.49mm In this case, when the wavelength of the laser beam deviates from the reference wavelength λ 0 , the phase deviation greatly changes.

また、図７（ｂ）を参照すると、ビーム幅が０．６〜０．８ｍｍ程度の範囲内であるときにはレーザ光の波長が基準波長λ０からずれても位相ずれは殆ど生じない。更に、図７（ｃ）を参照すると、ビーム幅が０．６〜１．２５ｍｍ程度の範囲内であるときにはレーザ光の波長が基準波長λ０からずれても位相ずれは殆ど生じない。つまり、受光装置１３が備える受光素子の数が増えるに従って、位相ずれが殆ど生じないビーム幅の範囲が拡大することが分かる。 Referring also to FIG. 7 (b), when the beam width is within a range of about 0.6~0.8mm phase shift hardly be shifted wavelength of the laser light from the reference wavelength lambda 0. Furthermore, referring to FIG. 7C, when the beam width is in the range of about 0.6 to 1.25 mm, even if the wavelength of the laser beam is deviated from the reference wavelength λ 0 , there is almost no phase deviation. That is, it can be seen that as the number of light receiving elements included in the light receiving device 13 increases, the range of the beam width in which the phase shift hardly occurs increases.

尚、レーザ光源１１から射出されるレーザ光の波長変動を測定する場合には、波長変動があってもＡ相信号及びＢ相信号から計算される位相の位相ずれが「０」になることが理想的である。このため、図７（ａ）〜図７（ｃ）に示すシミュレーション結果から、受光装置１３の受光素子数が「８」であるとき（即ち、素子配列方向における受光面の大きさが０．８ｍｍのとき）には、参照光Ｌ１及び信号光Ｌ２のビーム幅を０．５ｍｍ程度に設定するのが望ましい。また、受光装置１３の受光素子数が「１６」であるとき（即ち、素子配列方向における受光面の大きさが１．６ｍｍのとき）には、参照光Ｌ１及び信号光Ｌ２のビーム幅を０．６〜０．８ｍｍ程度の範囲内に設定するのが望ましい。   When measuring the wavelength variation of the laser light emitted from the laser light source 11, the phase shift of the phase calculated from the A phase signal and the B phase signal may be “0” even if there is a wavelength variation. Ideal. Therefore, from the simulation results shown in FIGS. 7A to 7C, when the number of light receiving elements of the light receiving device 13 is “8” (that is, the size of the light receiving surface in the element arrangement direction is 0.8 mm). In this case, it is desirable to set the beam widths of the reference light L1 and the signal light L2 to about 0.5 mm. When the number of light receiving elements of the light receiving device 13 is “16” (that is, when the size of the light receiving surface in the element arrangement direction is 1.6 mm), the beam widths of the reference light L1 and the signal light L2 are set to 0. It is desirable to set within a range of about 6 to 0.8 mm.

同様に、受光装置１３の受光素子数が「２４」であるとき（即ち、素子配列方向における受光面の大きさが２．４ｍｍのとき）には、参照光Ｌ１及び信号光Ｌ２のビーム幅を０．６〜１．２５ｍｍ程度の範囲内に設定するのが望ましい。このように、受光装置１３が備える受光素子の数に拘わらず、素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅が受光面の大きさ以下に設定していれば、レーザ光の波長が変化しても位相ずれを小さくすることができる。   Similarly, when the number of light receiving elements of the light receiving device 13 is “24” (that is, when the size of the light receiving surface in the element arrangement direction is 2.4 mm), the beam widths of the reference light L1 and the signal light L2 are set. It is desirable to set within a range of about 0.6 to 1.25 mm. Thus, regardless of the number of light receiving elements provided in the light receiving device 13, if the beam widths of the reference light L1 and the signal light L2 in the element arrangement direction are set to be equal to or smaller than the size of the light receiving surface, the wavelength of the laser light is Even if it changes, the phase shift can be reduced.

尚、波長ずれに起因するＡ相信号及びＢ相信号から計算される位相の位相ずれは、原点ずれ率と同様に、干渉光測定装置１０に必要とされる精度に応じてある程度許容される。このため、素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅は、受光面の大きさ以下であって、干渉光測定装置１０に必要とされる精度に応じて適宜設定することができる。このとき、経年変化等を考慮して干渉光測定装置１０の精度上許容される位相ずれの１０分の１程度であるのが望ましい。このため、例えば干渉光測定装置１０の位相ずれが±２．５度許容される場合には、原点ずれ率が±０．２５度以内に収まるよう参照光Ｌ１及び信号光Ｌ２のビーム幅を設定するのが好ましい。   In addition, the phase shift of the phase calculated from the A phase signal and the B phase signal due to the wavelength shift is allowed to some extent according to the accuracy required for the interference light measurement apparatus 10 as with the origin shift rate. For this reason, the beam widths of the reference light L1 and the signal light L2 in the element arrangement direction are equal to or smaller than the size of the light receiving surface, and can be appropriately set according to the accuracy required for the interference light measurement device 10. At this time, it is desirable that the phase shift is about one-tenth of the allowable phase shift in terms of accuracy of the interference light measurement device 10 in consideration of aging and the like. Therefore, for example, when the phase shift of the interference light measurement apparatus 10 is allowed to be ± 2.5 degrees, the beam widths of the reference light L1 and the signal light L2 are set so that the origin shift rate is within ± 0.25 degrees. It is preferable to do this.

以上、Ａ相信号及びＢ相信号の原点ずれ及び位相ずれのシミュレーション結果について説明したが、参照光Ｌ１及び信号光Ｌ２のビーム幅は、原点ずれにのみ着目して原点ずれが極力小さくなるように設定しても良く、位相ずれのみに着目して位相ずれが極力小さくなるよう設定しても良い。例えば、干渉光測定装置１０をＤＵＴ２０の光学特性に用いる場合には原点ずれに着目して参照光Ｌ１及び信号光Ｌ２のビーム幅を設定するのが望ましく、干渉光測定装置１０をレーザ光の波長変動の測定に用いる場合には位相ずれに着目して参照光Ｌ１及び信号光Ｌ２のビーム幅を設定するのが望ましい。勿論、原点ずれと位相ずれとの双方に着目して参照光Ｌ１及び信号光Ｌ２のビーム幅を設定しても良い。   The simulation results of the origin deviation and the phase deviation of the A-phase signal and the B-phase signal have been described above. The beam widths of the reference light L1 and the signal light L2 are focused only on the origin deviation so that the origin deviation is minimized. It may be set, or the phase shift may be set as small as possible by paying attention only to the phase shift. For example, when the interference light measurement device 10 is used for the optical characteristics of the DUT 20, it is desirable to set the beam widths of the reference light L1 and the signal light L2 while paying attention to the origin deviation. When used for measurement of fluctuation, it is desirable to set the beam widths of the reference light L1 and the signal light L2 while paying attention to the phase shift. Of course, the beam widths of the reference light L1 and the signal light L2 may be set by paying attention to both the origin deviation and the phase deviation.

図８は、受光素子の素子数と最適ビーム幅との関係を示す図である。尚、図８では、横軸に受光素子数をとり、縦軸にビーム幅をとっている。図中符号Ｄ１を付した直線は原点ずれ率が最小となる最適ビーム幅を示す直線であり、符号Ｄ２を付した直線は位相ずれが最小となる最適ビーム幅を示す直線である。尚、図７を用いて説明した通り、位相ずれが殆ど生じなくなるビーム幅にはある程度の範囲があるため、この範囲をエラーバーで示している。   FIG. 8 is a diagram showing the relationship between the number of light receiving elements and the optimum beam width. In FIG. 8, the horizontal axis represents the number of light receiving elements, and the vertical axis represents the beam width. In the figure, a straight line denoted by reference sign D1 is a straight line indicating the optimum beam width at which the origin deviation rate is minimized, and a straight line denoted by reference sign D2 is a straight line indicating the optimum beam width at which phase shift is minimized. As described with reference to FIG. 7, there is a certain range in the beam width at which almost no phase shift occurs, and this range is indicated by error bars.

図８を参照すると、原点ずれ率に対する最適ビーム幅と位相ずれに対する最適ビーム幅とは一致しないため、原点ずれ率と位相ずれを共に最小にするビーム幅を設定することはできない。しかしながら、例えば素子数が「２４」であるときには、位相ずれが殆ど生じなくなるビーム幅の範囲に原点ずれ率を最小にするビーム幅が含まれている。このため、原点ずれ率を最小とするビーム幅に設定すれば、原点ずれ率と位相ずれとを共に小さくすることができる。   Referring to FIG. 8, since the optimum beam width for the origin deviation rate and the optimum beam width for the phase deviation do not coincide with each other, the beam width that minimizes both the origin deviation rate and the phase deviation cannot be set. However, for example, when the number of elements is “24”, the beam width that minimizes the origin deviation rate is included in the range of the beam width where the phase deviation hardly occurs. For this reason, if the beam width that minimizes the origin deviation rate is set, both the origin deviation rate and the phase deviation can be reduced.

これに対し、素子数が「８」又は「１６」の場合には、位相ずれが殆ど生じなくなるビーム幅の範囲に原点ずれ率を最小にするビーム幅が含まれることはない。このような場合には、例えば原点ずれ率を最小にするビーム幅と位相ずれを最小にするビーム幅との中間のビーム幅に設定することができる。或いは、図６及び図７を参照すると、原点ずれが殆ど生じなくなるビーム幅の範囲は、位相ずれが殆ど生じなくなるビーム幅の範囲よりも狭い傾向がある。このため、原点ずれ率が極力小さくなるようにビーム幅を設定するのが望ましい。   On the other hand, when the number of elements is “8” or “16”, the beam width that minimizes the origin deviation rate is not included in the range of the beam width where the phase deviation hardly occurs. In such a case, for example, the beam width can be set to an intermediate value between the beam width that minimizes the origin deviation rate and the beam width that minimizes the phase deviation. Alternatively, referring to FIGS. 6 and 7, the beam width range in which the origin deviation hardly occurs tends to be narrower than the beam width range in which the phase deviation hardly occurs. For this reason, it is desirable to set the beam width so that the origin deviation rate is minimized.

以上説明した通り、本実施形態による干渉光測定装置１０においては、Ａ相信号及びＢ相信号の原点ずれ率及びＡ相信号及びＢ相信号から計算される位相の真値からのずれの少なくとも一方が所定値以下となるよう信号光Ｌ１及び参照光Ｌ２のビーム幅を設定しているため、波長可変範囲が広く且つ高い精度で干渉光を測定することができる。また、受光装置１３の受光面１３ａに照射される信号光Ｌ１及び参照光Ｌ２のビーム幅が、受光面１３ａの大きさ以下に設定されており、信号光Ｌ１及び参照光Ｌ２のパワーの大部分が受光面１３ａに照射されるため、従来に比べて測定ダイナミックレンジを広げることができ、効率良く干渉光の測定を行うことができる。   As described above, in the interference light measurement apparatus 10 according to the present embodiment, at least one of the origin deviation rate of the A phase signal and the B phase signal and the deviation from the true value of the phase calculated from the A phase signal and the B phase signal. Since the beam widths of the signal light L1 and the reference light L2 are set so as to be equal to or less than a predetermined value, interference light can be measured with a wide wavelength variable range and high accuracy. Further, the beam widths of the signal light L1 and the reference light L2 applied to the light receiving surface 13a of the light receiving device 13 are set to be equal to or smaller than the size of the light receiving surface 13a, and most of the powers of the signal light L1 and the reference light L2 are set. Is irradiated on the light receiving surface 13a, the measurement dynamic range can be expanded compared to the conventional case, and interference light can be measured efficiently.

以上、本発明の一実施形態による干渉光測定装置について説明したが、本発明は上記実施形態に制限される訳ではなく、本発明の範囲内で自由に変更が可能である。例えば、上記実施形態では、レーザ光の波長が基準波長λ０であるときに、干渉光Ｌ３の干渉縞の１周期毎に４個の受光素子が配列されている場合を例に挙げたが、干渉縞の１周期毎の受光素子数は任意に設定することができる。また、上記実施形態では、受光装置１３が備える受光素子数が「８」，「１６」，「２４」である場合のシミュレーション結果についてのみ説明したが、受光装置１３が備える受光素子数はこれらに限定されることはない。 The interference light measuring apparatus according to the embodiment of the present invention has been described above. However, the present invention is not limited to the above embodiment, and can be freely changed within the scope of the present invention. For example, in the above embodiment, when the wavelength of the laser light is the reference wavelength λ 0 , an example in which four light receiving elements are arranged for each period of the interference fringe of the interference light L3 is described as an example. The number of light receiving elements per cycle of the interference fringes can be set arbitrarily. In the above embodiment, only the simulation results when the number of light receiving elements included in the light receiving device 13 is “8”, “16”, and “24” have been described. However, the number of light receiving elements included in the light receiving device 13 is not limited thereto. There is no limit.

更に、上記実施形態では、マイケルソン型の干渉装置１２を備える干渉光測定装置１０について説明したが、干渉光を生成する干渉装置はこれに限られることはない。例えば、基板上に形成された複数本の光路差を利用した干渉装置を備える干渉光測定装置にも本発明を適用することができる。尚、本発明の干渉光測定装置は、被測定光の波長をモニタする波長モニタ装置、ＤＵＴ２０の光学特性を測定する装置以外に、例えば測長装置にも応用することができる。   Furthermore, in the above-described embodiment, the interference light measurement device 10 including the Michelson-type interference device 12 has been described. However, the interference device that generates interference light is not limited thereto. For example, the present invention can also be applied to an interference light measuring device including an interference device using a plurality of optical path differences formed on a substrate. The interference light measuring device of the present invention can be applied to, for example, a length measuring device in addition to a wavelength monitoring device that monitors the wavelength of light to be measured and a device that measures the optical characteristics of the DUT 20.

本発明の一実施形態による干渉光測定装置の概略構成を示すブロック図である。1 is a block diagram illustrating a schematic configuration of an interference light measurement apparatus according to an embodiment of the present invention. 干渉光Ｌ３と受光装置１３との関係を説明するための図である。It is a figure for demonstrating the relationship between the interference light L3 and the light-receiving device. 干渉光Ｌ３と受光装置１３に設けられる受光素子との関係を示す図である。It is a figure which shows the relationship between the interference light L3 and the light receiving element provided in the light-receiving device. 干渉光Ｌ３と受光装置１３に設けられる受光素子との関係に加えて、信号処理装置１４の内部構成を示す図である。4 is a diagram showing an internal configuration of a signal processing device 14 in addition to the relationship between interference light L3 and a light receiving element provided in the light receiving device 13. FIG. 有効受光長Ｌｒを説明するための受光装置１３の拡大図である。It is an enlarged view of the light-receiving device 13 for demonstrating the effective light reception length Lr. 素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅とＤＵＴ２０の減衰量とを変化させたときのＡ相信号又はＢ相信号のオフセットの変化を示すシミュレーション結果である。It is a simulation result which shows the change of the offset of the A phase signal or B phase signal when the beam width of the reference light L1 and the signal light L2 in the element arrangement direction and the attenuation amount of the DUT 20 are changed. 素子配列方向における参照光Ｌ１及び信号光Ｌ２のビーム幅とレーザ光源１１から射出されるレーザ光の波長を変化させたときのＡ相信号及びＢ相信号から計算される位相の変化を示すシミュレーション結果である。A simulation result showing a change in phase calculated from the A phase signal and the B phase signal when the beam width of the reference light L1 and the signal light L2 in the element arrangement direction and the wavelength of the laser light emitted from the laser light source 11 are changed. It is. 受光素子の素子数と最適ビーム幅との関係を示す図である。It is a figure which shows the relationship between the element number of a light receiving element, and the optimal beam width. 従来のレーザ測長器の構成の一例を示す図である。It is a figure which shows an example of a structure of the conventional laser length measuring device.

符号の説明Explanation of symbols

１０ 干渉光測定装置
１２ 干渉装置
１３ 受光装置
１３ａ 受光面
２１，２２ 差動増幅器
２３ 処理装置
Ｅ１〜ＥＮ 受光素子
Ｌ１ 参照光
Ｌ２ 信号光
Ｌ３ 干渉光
DESCRIPTION OF SYMBOLS 10 Interfering light measuring device 12 Interfering device 13 Light receiving device 13a Light receiving surface 21, 22 Differential amplifier 23 Processing device E1-EN Light receiving element L1 Reference light L2 Signal light L3 Interference light

Claims (7)

入射光から信号光と参照光とを生成するとともに、当該信号光と参照光とを干渉させて干渉光を生成する干渉装置と、当該干渉装置で生成される干渉光の干渉縞に対して所定の関係をもって配列された複数の受光素子を受光面に有し、当該受光面に照射される前記干渉光を前記複数の受光素子の各々で受光する受光装置とを備える干渉光測定装置において、
前記受光装置の前記受光面に照射される前記信号光及び前記参照光のビーム幅が、前記受光素子の前記受光面の大きさ以下に設定されていることを特徴とする干渉光測定装置。 An interference device that generates signal light and reference light from incident light, generates interference light by causing interference between the signal light and reference light, and predetermined interference fringes of interference light generated by the interference device In the interference light measuring device comprising: a plurality of light receiving elements arranged in a relationship with each other on a light receiving surface; and a light receiving device that receives the interference light irradiated on the light receiving surface by each of the plurality of light receiving elements.
The interference light measurement device, wherein beam widths of the signal light and the reference light irradiated on the light receiving surface of the light receiving device are set to be equal to or smaller than a size of the light receiving surface of the light receiving element. 前記複数の受光素子は、前記信号光及び前記参照光の波長が所定の基準波長である場合に、前記受光面に照射される前記干渉光の干渉縞の１周期毎に４個の受光素子が配置されるように配列されていることを特徴とする請求項１記載の干渉光測定装置。   When the wavelength of the signal light and the reference light is a predetermined reference wavelength, the plurality of light receiving elements includes four light receiving elements for each period of the interference fringes of the interference light irradiated on the light receiving surface. The interference light measuring device according to claim 1, wherein the interference light measuring device is arranged so as to be arranged. 前記受光装置が備える前記受光素子の各々で受光された受光信号に対して所定の演算を行い、前記信号光及び前記参照光の波長が所定の基準波長である場合に、位相が互いに９０度だけ異なるＡ相信号とＢ相信号とを生成する演算装置を備えることを特徴とする請求項２記載の干渉光測定装置。   When a predetermined calculation is performed on the received light signal received by each of the light receiving elements included in the light receiving device, and the wavelengths of the signal light and the reference light are a predetermined reference wavelength, the phases are only 90 degrees from each other. The interference light measuring apparatus according to claim 2, further comprising an arithmetic unit that generates different A-phase signals and B-phase signals. 前記信号光及び前記参照光のビーム幅は、前記受光素子の前記受光面の大きさ以下であって、前記Ａ相信号及び前記Ｂ相信号のオフセット値が所定値以下となるように設定されていることを特徴とする請求項３記載の干渉光測定装置。   Beam widths of the signal light and the reference light are set to be equal to or smaller than the size of the light receiving surface of the light receiving element, and offset values of the A phase signal and the B phase signal are equal to or smaller than a predetermined value. The interference light measuring apparatus according to claim 3, wherein 前記信号光及び前記参照光のビーム幅は、前記受光素子の前記受光面の大きさ以下であって、前記Ａ相信号及び前記Ｂ相信号から計算される位相の真値からのずれが所定値以下となるように設定されていることを特徴とする請求項３又は請求項４記載の干渉光測定装置。   Beam widths of the signal light and the reference light are equal to or smaller than the size of the light receiving surface of the light receiving element, and a deviation from a true value of a phase calculated from the A phase signal and the B phase signal is a predetermined value. 5. The interference light measurement apparatus according to claim 3, wherein the interference light measurement apparatus is set to satisfy the following conditions. 前記演算装置によって生成される前記Ａ相信号と前記Ｂ相信号とに対して所定の信号処理を行って、前記入射光の波長を測定する波長測定装置を備えることを特徴とする請求項１から請求項５の何れか一項に記載の干渉光測定装置。   2. The apparatus according to claim 1, further comprising a wavelength measuring device that performs predetermined signal processing on the A-phase signal and the B-phase signal generated by the arithmetic device to measure the wavelength of the incident light. The interference light measuring apparatus according to claim 5. 前記演算装置によって生成される前記Ａ相信号と前記Ｂ相信号とに対して所定の信号処理を行って、前記信号光の光路に配置される被測定デバイスの特性を測定する光学特性測定装置を備えることを特徴とする請求項１から請求項５の何れか一項に記載の干渉光測定装置。
An optical characteristic measuring apparatus that performs predetermined signal processing on the A-phase signal and the B-phase signal generated by the arithmetic unit and measures characteristics of a device under measurement arranged in the optical path of the signal light. The interference light measuring apparatus according to any one of claims 1 to 5, further comprising:
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JP2009186191A (en) * 2008-02-01 2009-08-20 National Institute Of Advanced Industrial & Technology Dimension measuring device and method
JP2014035216A (en) * 2012-08-07 2014-02-24 Fujitsu Ltd Optical rotary encoder and correction method thereof

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JPH01187406A (en) * 1988-01-22 1989-07-26 Rikagaku Kenkyusho Method and device for detecting position of equal-interval interference fringe
JPH028703A (en) * 1988-06-27 1990-01-12 Fujitsu Ltd Phase detection of interference fringe
JP2002071518A (en) * 2000-08-28 2002-03-08 Ando Electric Co Ltd Wavelength dispersion measuring device

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Publication number Priority date Publication date Assignee Title
JPH01187406A (en) * 1988-01-22 1989-07-26 Rikagaku Kenkyusho Method and device for detecting position of equal-interval interference fringe
JPH028703A (en) * 1988-06-27 1990-01-12 Fujitsu Ltd Phase detection of interference fringe
JP2002071518A (en) * 2000-08-28 2002-03-08 Ando Electric Co Ltd Wavelength dispersion measuring device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009186191A (en) * 2008-02-01 2009-08-20 National Institute Of Advanced Industrial & Technology Dimension measuring device and method
JP2014035216A (en) * 2012-08-07 2014-02-24 Fujitsu Ltd Optical rotary encoder and correction method thereof

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