JP2004241659A - Two-wavelength semiconductor laser device, two-wavelength interference measurement device, two-wavelength semiconductor laser oscillation method, and two-wavelength interference measurement method - Google Patents

Abstract

A two-wavelength semiconductor laser light source that generates two wavelengths with one semiconductor laser, has a wide measurement range, and has a simple configuration.
A semiconductor laser has a property that the wavelength of output light changes according to changes in injection current and temperature, and that a mode hop occurs in which the wavelength of output light changes stepwise at a certain current and temperature. The temperature controller 2 controls the temperature of the semiconductor laser 1 to a temperature at which a mode hop occurs, so that the semiconductor laser 1 outputs light including two different wavelengths before and after the mode hop. In this state, the current controller 3 controls the injection current or the voltage supplied to the semiconductor laser 1 and causes the semiconductor laser 1 to selectively output one of two different wavelengths.
[Selection diagram] Fig. 1

Description

【００４８】
ここで、Ｌは、光路差の半分である。また、位相差△αは、整理すると次式で表される。
【００４９】
【数２】

【００５０】
ここで、Λを等価波長という。等価波長は光源の発振波長より長いため、干渉計の測定範囲を１波長型の干渉計に比べて拡大することができる。本実施の形態では、２つの異なる波長を１つの光源により発生させることが可能であり、２つの光源を有する干渉計に対して、光源数が減少できる、光軸あわせのための光学系が不要となる等、装置の構成を簡単化することが可能である。
【００５１】
光検出器１４は、干渉した光を受光し干渉信号を生成する。例えば、光検出器１４は、ＣＣＤ等のイメージセンサを用いることができる。測定部１５は、光検出器１４から干渉信号を入力し、干渉信号を処理することにより測定物体２０の段差、形状等を求める。
【００５２】
なお、スペクトラムアナライザ４を用いる場合は、光学系にビームスプリッタ等の適宜の分岐器を挿入し、半導体レーザ１からの出力光をスペクトラムアナライザ４に導くようにする構成をとればよい。
【００５３】
４−２ 動作例−１
まず、測定部１５は、例えば、外部から入力した波長又は予め定められた初期値に基づいて、測定に用いる波長（測定波長）又は波長差を決定する。次に、測定部１５は、２波長型半導体レーザ装置１０に対して、測定波長の光を出力させる指示を出力する。例えば、測定部１５は、２波長型半導体レーザ装置１０の発振制御部５に対して指示を出力する。また、測定部１５は、発振制御部５の機能をさらに有し、測定波長を出力させるための温度及び波長選択信号を温度コントローラ２及び電流コントローラ３に出力してもよい。２波長型半導体レーザ装置１０は、温度及び電流を制御し、測定部１５が出力した指示に応じた光を半導体レーザ１から出力させる。
【００５４】
半導体レーザ１から発した光は、ビームスプリッタ１２で分岐され、参照鏡１３及び測定物体２０で反射してビームスプリッタ１２上で干渉する。光検出器１４は、干渉した光を受光して干渉信号を生成する。測定部１５は、光検出器１４から干渉信号を入力し、測定波長と対応させて記憶部１５１に記憶する。
【００５５】
次に、測定部１５は、２波長型半導体レーザ装置１０に対し、先とは異なる波長の光を出力させる指示を出力する。上述と同様に、２波長型半導体レーザ装置１０は、指示に応じた光を半導体レーザ１から出力させ、その光に対する干渉信号は、測定波長に対応して測定部１５の記憶部１５１に記憶される。
【００５６】
測定部１５は、記憶部１５１に記憶された２つの干渉信号及び測定波長を読み出し、干渉信号にフーリエ変換等の信号処理を行って、位相分布を求め、位相差を算出する。例えば、測定部１５は、読み出した干渉信号をフーリエ変換し、スペクトルの一番大きい空間周波数付近の周波数成分を取り出し、その周波数成分を０にシフトして逆フーリエ変換することで位相分布、位相差を求める。
【００５７】
さらに、測定部１５は、位相差及び測定波長に基づき、数式２を用いて光路差Ｌを算出し、測定物体２０の段差及び形状等を求める。なお、測定部１５は、干渉信号及び測定波長に基づき適宜の処理を実行し、測定物体２０の平面度や球面形状等を求めてもよい。また、測定部１５は、求めた測定結果を適宜のタイミングで記憶部１５１に記憶し、表示部１５２に表示してもよい。
【００５８】
４−３ 動作例−２
上述の動作例−１では、２つの異なる波長の光をそれぞれ出力、受光して測定物体２０の段差及び形状を求めているが、２波長（λ_１、λ_２）を含む光を同時（又は略同時）に出力し、２つの干渉光を受光して測定することも可能である。２波長を同時に発振すると、各波長に対応して縞の間隔が異なる２つの干渉縞が発生し、光検出器１４では、これらが重なった状態の干渉信号が生成される。この２つの干渉縞を含む干渉信号に基づき位相差を求めることにより、測定物体２０の段差及び形状等を求めることができる。
【００５９】
まず、測定部１５は、測定に用いる波長（測定波長）又は波長差を決定し、２波長型半導体レーザ装置１０に対して、決定した測定波長と、光を同時に出力させる指示とを出力する。２波長型半導体レーザ装置１０は、温度及び電流を制御し、測定部１５が出力した指示に応じた２つの波長を含む光を同時（又は略同時）に半導体レーザ１から出力させる。
【００６０】
半導体レーザ１から発した光は、ビームスプリッタ１２で分岐され、参照鏡１３及び測定物体２０で反射してビームスプリッタ上で干渉する。この時の干渉光は、２つの波長に対応する干渉光を含んでいる。光検出器１４は、干渉した光を受光して干渉信号を生成する。測定部１５は、光検出器１４から干渉信号を入力し、入力した干渉信号に基づき位相差を求め、上述と同様に測定物体２０の段差及び形状等を求める。位相差を求める方法については後述する。
【００６１】
なお、測定部１５は、干渉信号及び測定波長に基づき適宜の処理を実行し、測定物体２０の平面度や球面形状等を求めてもよい。また、測定部１５は、分離した干渉信号及び求めた測定結果を適宜のタイミングで記憶部１５１に記憶し、表示部１５２に表示してもよい。
【００６２】
次に、２つの干渉縞を含む干渉信号から位相差を求める方法について述べる。（空間周波数の差を利用した測定）
図１３は、空間周波数により２つの干渉縞を分離する説明図である。図１３に示すように、参照鏡１３を光路差Ｌ_ｒが生じるようにわずかに傾けた干渉計に、λ_１及びλ_２の波長の光を同時に入射して干渉縞を観測すると、周期のわずかに異なる２つの干渉縞が発生する。この縞は、光検出器１４上で重なって観測されるが、等価波長Λを小さくすると縞の周期の差も大きくなり、空間周波数に差ができる。例えば、等価波長Λ＝Ｌ_ｒ／２のときは、図１３に示すように、ちょうど１周期だけ縞の数に差が生じる。この空間周波数の差を利用して２つの縞を分離することにより、２波長の同時出力による測定が可能である。
【００６３】
なお、本測定の場合、参照鏡１３は、位置により光路差が生じるように傾けて配置する。また、参照鏡１３の傾きを変化させる駆動部をさらに備えてもよい。
【００６４】
測定部１５は、等価波長Λを小さくし，空間周波数に差ができるように発振波長を決定する。また、測定部１５は、光検出器１４から入力した干渉信号に対してフーリエ変換等の信号処理を行い、周波数軸上で２つの縞を分離する。この時、２つの縞の空間周波数に対応したスペクトルが得られる。測定部１５は、各縞に対応した空間周波数の周りの周波数成分に基づき位相及び位相差を求め、位相差及び測定波長に基づき段差、表面形状等を求める。
【００６５】
（干渉縞の位相差を利用した測定）
また、空間周波数の差を利用する以外にも、重なった干渉縞から２つの波長に対応する干渉光の位相差を求めることもできる。干渉縞は、一般に次式で表すことができる。
【００６６】
【数３】

【００６７】
ここで、Ｓ_ａは干渉光の直流成分、Ｓ_ｂは交流成分の振幅、ｆは空間周波数、αは位相である。また、交流成分の振幅Ｓ_ｂと直流成分Ｓ_ａとの比をビジビリティ（又はコントラスト）といい、次式で計算される。
Ｖ＝Ｓ_ｂ／Ｓ_ａ
例えば、干渉光に基づく干渉信号をフーリエ変換して得た直流成分と交流成分を用いて、ビジビリティＶを得るとこができる。上述の空間周波数の差を利用した測定では、数式３のカッコ内第１項目に注目しているが、ここでは第２項目に注目する。
【００６８】
波長がλ_１、λ_２の２波長で測定した場合、各波長に対する干渉縞はそれぞれ、以下の式で表される。
【００６９】
【数４】

【００７０】
ただし、
α_１（ｘ）＝（２π／λ_１）ｄ
α_２（ｘ）＝（２π／λ_２）ｄ （ｄ：光路差）
である。例えば、ｄ＝ｎΛ＋Λ／４の場合には、位相差は、
α_１（ｘ）−α_２（ｘ）＝π／２
となり、２つの縞は９０度位相がずれる。
【００７１】
ここで、干渉光の直流成分Ｓ_ａ、交流成分の振幅Ｓ_ｂ、空間周波数ｆを、
Ｓ_ａ１＝Ｓ_ａ２＝Ｓ_ａ
Ｓ_ｂ１＝Ｓ_ｂ２＝Ｓ_ｂ
ｆ_１＝ｆ_２＝ｆ
とおく。なお、直流成分Ｓ_ａと交流成分の振幅Ｓ_ｂについては、２波長の光が同じ半導体レーザ１から出射されていることからＳ_ａ１＝Ｓ_ａ２、Ｓ_ｂ１＝Ｓ_ｂ２が成立する。
【００７２】
空間周波数ｆ_１＝ｆ_２について、以下に説明する。光検出器１４で取得する各波長λ_１、λ_２に対応する干渉縞の周期Ｎ_１、Ｎ_２は、
Ｎ_１＝ｄ／λ_１
Ｎ_２＝ｄ／λ_２
である。この式から、周期Ｎ_１とＮ_２の関係は、次式で表せる。
Ｎ_２＝（λ_１／λ_２）Ｎ_１
ここで、２波長型半導体レーザ装置１０から出力される波長λ_１、λ_２の波長差を、各波長に対して小さく設定すれば、Ｎ_２＝Ｎ_１とみなすことができる。例えば、２波長型半導体レーザ装置１０から出力される波長の差が０．６ｎｍ、中心波長が６８５ｎｍとし（λ_１＝６８５ｎｍ、λ_２＝６８５．６ｎｍ）、光検出器１４で取得する画像内に波長λ_１の光により発生した縞をＮ_１＝３０周期入れるとする。この時、波長λ_２で発生した縞の周期数は、上述の関係式によりＮ_２＝２９．９７となり、ほぼ３０である。したがって、空間周波数は周期の逆数であるので、ｆ１＝ｆ２とみなすことができる。
【００７３】
干渉光の直流成分Ｓ_ａ、交流成分の振幅Ｓ_ｂ、空間周波数ｆを上述のようにおくと、重なった２つの縞画像を表す式は、次式で表すことができる。
【００７４】
【数５】

【００７５】
また、数式５より、重なった２つの縞画像のビジビリティＶは、次式で表すことができる。
【００７６】
【数６】

【００７７】
数式６より、ビジビリティＶは、位相差α_１（ｘ）−α_２（ｘ）に応じて変化することがわかる。また、数式６のＳ_ｂ／Ｓ_ａは一定値である。例えば、Ｓ_ｂ／Ｓ_ａは、予め１つの波長のみを使って取得した縞画像から求めたビジビリティＶであり、予め記憶部１５１等に記憶しておく。
【００７８】
測定部１５は、光検出器１４から入力した干渉信号に基づきビジビリティＶを求め、数式６を用いて位相差を求める。具体的には、まず、測定部１５は、光検出器１４から入力した信号を、フーリエ変換等の信号処理を行い、周波数軸上で直流成分と交流成分に分離する。このとき、交流成分のスペクトルは周波数ｆの場所に現れ、その大きさは
【００７９】
【数７】

【００８０】
である。また、直流成分のスペクトルは２Ｓ_ａである。
【００８１】
次に、測定部１５は、直流成分と交流成分の振幅の比をとり、ビジビリティＶを求める。また、測定部１５は、求めたビジビリティＶと、予め記憶部１５１に記憶されているＳ_ｂ／Ｓ_ａの値を用いて、数式６により位相差を求める。
【００８２】
測定部１５は、求めた位相差により測定物体２０の段差及び形状等を求めることができる。なお、上述の数式及び説明は、ｘを変数とする一次元で示しているが、二次元とすることもできる。
【００８３】
【発明の効果】
本発明によると、１つの半導体レーザで２つの波長を発生させる２波長型半導体レーザ装置を提供することができる。また、本発明によると、レーザ光の強度を大きく変化させることなく、できるだけ波長差の大きい２つの波長を選択的に発生させることができる。また、本発明によると、注入電流の増減により出力光の選択を行うため、時定数が大きい温度の増減を行うよりも高速で効率的に２波長の切り替えが可能である。さらに、本発明によると、注入電流制御のみによる装置よりも波長差の大きい２波長の光を１つの半導体レーザで得ることができ、特に、干渉計測装置の分解能向上に大きく寄与する。本発明によると、２波長型半導体レーザ装置を用いて、シンプルで、より安価な２波長型干渉計測装置を提供することができる。
【図面の簡単な説明】
【図１】第１の実施の形態における２波長型半導体レーザ装置の構成図。
【図２】半導体レーザの発振波長の注入電流依存性及び温度依存性を模式的に表す図。
【図３】２波長型半導体レーザ装置の動作説明図。
【図４】モードホップする温度付近におけるレーザスペクトルを示す図。
【図５】異なる波長の光を選択的に出力させた時のレーザスペクトルを示す図。
【図６】発振波長の温度依存性の実験結果を示す図。
【図７】温度制御及び注入電流制御による２波長出力の実験結果を示す図。
【図８】温度制御による波長選択の説明図。
【図９】任意の電流においてモードホップを生じさせる説明図。
【図１０】第２の実施の形態における２波長型半導体レーザ装置の構成図。
【図１１】出力波長テーブルのデータフォーマット。
【図１２】２波長型干渉計測装置の構成図。
【図１３】空間周波数により２つの干渉縞を分離する説明図。
【符号の説明】
１ 半導体レーザ
２ 温度コントローラ
３ 電流コントローラ
３１ 発振器
３２ 可変バイアス源
４ スペクトラムアナライザ
５ 発振制御部
６ レンズ
１０ ２波長型半導体レーザ装置
１１ レンズ
１２ ビームスプリッタ
１３ 参照鏡
１４ 光検出器
１５ 測定部
１５１ 記憶部
１５２ 表示部
２０ 測定物体[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a two-wavelength semiconductor laser device, a two-wavelength interference measurement device, a two-wavelength semiconductor laser oscillation method, and a two-wavelength interference measurement method, and more particularly to a two-wavelength type capable of selectively outputting two wavelengths. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-wavelength interference measurement device and a measurement method using a two-wavelength semiconductor laser device as a light source.
[0002]
[Prior art]
As a method for measuring the shape of an object with high accuracy, an interferometric measurement method using a semiconductor laser has been conventionally proposed. Generally, it is impossible to measure a step larger than half a wavelength with an interferometer, and it is difficult to measure a large step with a one-wavelength interferometer. As means for solving this problem, a two-wavelength interferometer using two semiconductor lasers as light sources and using lights having different wavelengths has been proposed.
[0003]
As a method of obtaining two or more wavelengths, for example, an apparatus that generates light of different wavelengths by two or more light sources and combines and combines laser beams on the same optical axis using a beam splitter or the like is available. It is disclosed (for example, see Patent Document 1).
[0004]
In addition, a diffraction grating is provided for each of two or more semiconductor lasers, and a heater for controlling the temperature of each diffraction grating is disposed. Each of the heaters outputs the maximum optical power at a desired wavelength light. A multi-wavelength light source device that controls the temperature of a diffraction grating has been disclosed (for example, see Patent Document 2). Further, a light source has been proposed in which a large number of diffraction gratings are formed in one element to simultaneously generate multiple wavelengths (for example, see Patent Document 3).
[0005]
On the other hand, a semiconductor laser has a property that the oscillation wavelength changes with an injection current, and it is known that light of different wavelengths can be generated by controlling the injection current (for example, see Non-Patent Document 1). .
[0006]
[Patent Document 1]
JP 2001-284740 A
[Patent Document 2]
JP 2000-174397 A
[Patent Document 3]
JP-A-9-270568
[Non-patent document 1]
T. Suzuki, O .; Sasaki, and T.S. Maruyama, "Absolute Distance Measurement Using Wavelength-Multiplexed Phase-Locked Laser Diode Interferometry", Optical Engineering, Vol. 35, no. 2 492-497 (1996)
[0007]
[Problems to be solved by the invention]
The light sources using two or more semiconductor lasers as in the conventional devices described in Patent Documents 1 and 2 can obtain a plurality of wavelengths at the same time, but the optical axis alignment is complicated and the optical system becomes complicated. There is a problem that. Further, the light source described in Patent Literature 3 requires a special structure such as forming many diffraction gratings in one element. Further, it is assumed that an optical system having such a complicated configuration or a device having a special structure will be expensive. Dye lasers and YAG lasers are known as two-wavelength light sources. However, Dye lasers are large and YAG lasers are hardly visible to human eyes, so they are not suitable as light sources for interferometers.
[0008]
The wavelength difference of the light output from the semiconductor laser by controlling the injection current described in Non-Patent Document 1 is extremely small. In addition, since it is necessary to greatly change the injection current, there is a problem that the intensity of the laser light also greatly changes. For example, the wavelength change rate in current modulation is about 5 × 10^-3nm / mA, and the current change must be 1-2 mA in order to suppress the change in light intensity within a negligible range. The wavelength change obtained by this current change is 5-10 × 10^-3nm.
[0009]
In view of the above, an object of the present invention is to provide a two-wavelength semiconductor laser device that generates two wavelengths with one semiconductor laser. Another object of the present invention is to selectively generate two wavelengths having the largest possible wavelength difference without greatly changing the intensity of the laser beam. It is another object of the present invention to provide a simpler and less expensive two-wavelength interferometer using a two-wavelength semiconductor laser device.
[0010]
[Means for Solving the Problems]
According to a first solution of the present invention,
A semiconductor laser in which the wavelength of the output light changes in response to a change in injection current and / or temperature, and a mode hop in which the wavelength of the output light changes stepwise in response to the change in injection current and / or temperature;
A current controller for controlling an injection current or voltage to the semiconductor laser,
A temperature controller for changing the temperature of the semiconductor laser;
Equipped
One of the temperature controller or the current controller controls the semiconductor laser to output a light including two different wavelengths before and after mode hop,
There is provided a two-wavelength semiconductor laser device that controls the other of the temperature controller and the current controller to selectively output one of wavelengths before and after a mode hop from the semiconductor laser in the state.
[0011]
According to a second solution of the present invention,
The two-wavelength semiconductor laser device;
A reference mirror that reflects a part of output light from the two-wavelength semiconductor laser device;
Interfering means for branching output light from the two-wavelength type semiconductor laser device to the reference mirror and the measurement object, and forming interference light by reflected light or transmitted light from the reference mirror and the measurement object. ,
A photodetector that receives the interference light from the interference means, generates and outputs an interference signal,
A measuring unit for determining a step and / or a shape of a measurement object based on an interference signal from the photodetector and an output wavelength of the two-wavelength semiconductor laser device;
Is provided.
[0012]
According to a third solution of the present invention,
2. A semiconductor laser using a mode laser in which the wavelength of the output light changes according to the change in the injection current and / or the temperature, and the wavelength of the output light changes stepwise in response to the change in the injection current and / or the temperature. A wavelength type semiconductor laser oscillation method,
Controlling the temperature or injection current or voltage of the semiconductor laser so that the semiconductor laser outputs light including two different wavelengths before and after mode hopping,
In this state, there is provided the two-wavelength type semiconductor laser oscillation method for controlling an injection current or a voltage or a temperature to the semiconductor laser so as to selectively output one of wavelengths before and after a mode hop from the semiconductor laser. .
[0013]
According to a fourth solution of the present invention,
2. A semiconductor laser using a mode laser in which the wavelength of the output light changes according to the change in the injection current and / or the temperature, and the wavelength of the output light changes stepwise in response to the change in the injection current and / or the temperature. A wavelength-type interference measurement method,
Controlling the temperature or injection current or voltage of the semiconductor laser so that the semiconductor laser outputs light including two different wavelengths before and after mode hopping,
In this state, controlling the injection current or the voltage or the temperature to the semiconductor laser so as to output the first wavelength and / or the second wavelength light before and after the mode hop from the semiconductor laser,
Generating an interference signal by receiving interference light formed by reflected light or transmitted light from the reference mirror and the measurement object of the light of the first and second wavelengths;
A two-wavelength interference measurement method for determining a step and / or a shape of a measurement object based on the interference signal and the first and second wavelengths is provided.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
1. First Embodiment of Two-Wavelength Semiconductor Laser Device
1-1 Device configuration
FIG. 1 is a configuration diagram of a two-wavelength semiconductor laser device according to the first embodiment. The two-wavelength semiconductor laser device includes a semiconductor laser 1, a temperature controller 2, and a current controller 3. The current controller 3 has an oscillator 31 and a variable bias source 32.
[0015]
The semiconductor laser 1 oscillates with an injection current from the oscillator 31 and the variable bias source 32, and emits laser light having an intensity corresponding to the injection current. Further, the semiconductor laser 1 has an injection current dependency in which the oscillation wavelength changes in accordance with a change in the injection current, and a temperature dependency in which the oscillation wavelength changes with a change in temperature.
[0016]
FIG. 2 is a diagram illustrating the dependence of the oscillation wavelength of the semiconductor laser 1 on the injection current and the temperature. FIG. 2A shows the injection current dependency of the oscillation wavelength when the temperature T of the semiconductor laser 1 is constant (for example, T = c). The oscillation wavelength of the semiconductor laser 1 changes with an increase in injection current, but shows a large stepwise change near a certain current (hereinafter, referred to as mode hop). Generally, in the current modulation, a continuous portion indicated by “b” in FIG. 2A is used. However, if the change is used in a range where the change in the intensity of the laser beam can be ignored (for example, a current of 1 to 2 mA), the wavelength difference Is 5-10 × 10^-3nm. Even if the current is changed from end to end of the continuous portion without considering the intensity change of the laser beam, the change in the current is about 10 mA, and the obtained wavelength difference is 5 × 10^-2nm.
[0017]
FIG. 2B shows the temperature dependence of the oscillation wavelength when the injection current I of the semiconductor laser 1 is constant (for example, I = a). The oscillation wavelength of the semiconductor laser 1 changes as the temperature rises, and a mode hop occurs near a certain temperature as in the case of injection current dependency. In the portions (a) and (b) of FIG. 2B (adjacent modes), there is a wavelength difference of, for example, about 1 nm, and a wavelength difference of about 100 to 200 times compared to the current modulation is obtained.
[0018]
Generally, in a two-wavelength interferometer, the larger the wavelength difference, the greater the resolution of measurement. Therefore, when used in a two-wavelength interferometer, a light source that obtains a large wavelength difference is effective. In the present embodiment, by using the temperature dependency and the injection current dependency of the semiconductor laser 1 at the same time, light of two different wavelengths is selectively output.
[0019]
The temperature controller 2 has a heat generating and / or heat radiating / absorbing means for changing the temperature of the semiconductor laser 1 and a temperature detecting means for detecting the temperature of the semiconductor laser 1. As the heat generation and / or heat radiation / heat absorption means, for example, a Peltier element can be used. The Peltier element generates heat by passing a current, and absorbs heat by reversing the direction of the current. In addition to the Peltier element, appropriate heat generation and / or heat radiation / heat absorption means may be used. Further, the heat generating means and the heat absorbing means may have different configurations. As the heat absorbing means, a means for promoting heat radiation of the semiconductor laser 1 using a heat radiation fan or the like may be used. The temperature detecting means is, for example, an appropriate temperature sensor such as a semiconductor temperature sensor, and detects the temperature of the semiconductor laser 1.
[0020]
The temperature controller 2 generates a control signal for setting the temperature of the semiconductor laser 1 to a temperature at which a mode hop occurs (for example, the temperature c or d in FIG. 2B) based on the output of the temperature detecting means, for example. Output to heat generation and / or heat radiation / heat absorption means. The temperature at which the mode hop occurs may be set in advance or may be input from outside. For example, the temperature controller 2 may input the temperature from a control unit that stores the temperature at which the mode hop occurs, an external device such as a PC, or an appropriate input unit. Further, the light output from the semiconductor laser 1 may be measured using, for example, a spectrum analyzer, and the temperature controller 2 may control the temperature so that the measured light includes spectra of different wavelengths.
[0021]
The current controller 3 controls a bias current or a voltage from the variable bias source 32, and controls an injection current supplied to the semiconductor laser 1. The current controller 3 increases or decreases the current from the variable bias source 32 based on the wavelength selection signal input from the outside in a state where the temperature is controlled near the temperature at which the mode hop occurs by the temperature controller 2. Current control is performed so as to stably oscillate the selected wavelength. The wavelength selection signal is an appropriate signal for instructing which of the two output wavelengths is to be output. For example, it may be an instruction or a value for increasing or decreasing the injection current, or a current value or a wavelength. The current controller 3 can also control the injection current supplied to the semiconductor laser 1 by changing the amplitude of the alternating current or the voltage supplied from the oscillator 31.
[0022]
The oscillator 31 of the current controller 3 generates an alternating current or a voltage for causing the semiconductor laser 1 to oscillate. The variable bias source 32 generates, for example, a DC bias current or a voltage to be supplied to the semiconductor laser 1. The variable bias source 32 may be a variable current source or a voltage source that can vary the current by varying the voltage. The current from the oscillator 31 and the variable bias source 32 is supplied to the semiconductor laser 1 as an injection current. The change in the bias current from the variable bias source 32 changes the wavelength and intensity of the laser light output from the semiconductor laser 1.
[0023]
1-2 Operation example
FIG. 3 is a diagram illustrating the operation of the two-wavelength semiconductor laser device. FIG. 3 shows the injection current dependency and the temperature dependency shown in FIG. 2 three-dimensionally in one diagram. 2A and 2B, the semiconductor laser 1 mode-hops at the current a and the temperature c. That is, the mode hop at the current a in FIG. 2A and the mode hop at the temperature c in FIG. 2B have the same characteristics, and this portion overlaps in FIG. For example, the current controller 3 and the temperature controller 2 control the injection current to a and the temperature to c so that a mode hop occurs. In this state, the current controller 3 increases or decreases the injection current or the temperature controller 2 increases or decreases the temperature. Thus, the wavelength in the mode “a” or the mode “b” in FIG. 3 can be selectively output. The injection current and the temperature may be other currents and temperatures at which mode hops occur (for example, the current b or the temperature f in FIG. 3) other than the current a and the temperature c in FIG. It is also possible to cause a mode hop between the currents a and b by appropriately changing the temperature. The details will be described later.
[0024]
FIGS. 4 and 5 are diagrams showing spectra of laser light emitted from the semiconductor laser 1. FIG. Hereinafter, the operation of the two-wavelength semiconductor laser device will be described with reference to FIGS. First, the current controller 3 and the temperature controller 2 control the current and the temperature so that a mode hop occurs. For example, the current controller 3 fixes the injection current to the current a in FIG. 3, and the temperature controller 2 controls the temperature of the semiconductor laser 1 to the temperature c in FIG. The information of the current a and the temperature c may be set in the respective controllers in advance, or may be input from outside. FIG. 4 shows the spectrum of the laser light emitted from the semiconductor laser 1 in a state where the current and the temperature are controlled so that a mode hop occurs. As for the spectrum of the laser beam output from the semiconductor laser 1, two spectra having different wavelengths appear simultaneously (or almost simultaneously).
[0025]
Next, the current controller 3 slightly changes (for example, 1 mA) the injection current supplied from the variable bias source 32. For example, the current controller 3 inputs a wavelength selection signal from the outside, and increases or decreases the injection current based on the wavelength selection signal. FIG. 5A shows a spectrum of laser light emitted from the semiconductor laser 1 when the injection current is slightly reduced (for example, 1 mA). The spectrum on the short wavelength side of the two wavelength spectra in FIG. 4 stably stands. On the other hand, FIG. 5B shows the spectrum of the laser light emitted from the semiconductor laser 1 when the injection current is slightly increased (for example, 1 mA). In this case, the spectrum on the long wavelength side of the two wavelength spectra in FIG. 4 stably stands. That is, in a state where light having two spectra is output, if the injection current is slightly decreased or increased, only one of the spectra appears to be dominant. At this time, the required change in the injection current is extremely small, and the intensity of the laser beam does not change significantly. For this reason, when used for an interferometer, even if a large change in wavelength occurs in the light source, a measurement error due to a change in the intensity of the laser beam hardly occurs.
[0026]
These output wavelengths are not temporary, and the semiconductor laser 1 can stably output the spectra shown in FIGS. 4 and 5 even after several hours. It should be noted that the temperature controller 2 only needs to control the temperature at which the semiconductor laser 1 outputs light including two different wavelengths, and does not necessarily need to accurately control the temperature at which mode hops occur.
[0027]
1-3 Operation check by experiment
6 and 7 are diagrams showing the results of an oscillation experiment of the semiconductor laser 1. FIG. 6 and 7 show that the semiconductor laser 1 has an optical output of 30 mW and an oscillation wavelength of 686 nm, and a temperature controller 2 having a Peltier element and a semiconductor temperature sensor (temperature error 0.5 ° C., temperature coefficient +10.0 mV / ° C.). Are the results of an experiment of two-wavelength output by controlling the temperature dependence of the oscillation wavelength, the temperature, and the injection current. These configurations and experimental results are examples of a two-wavelength semiconductor laser device, and do not limit the configuration, numerical values, and the like.
[0028]
FIG. 6 is a diagram showing an experimental result of the temperature dependence of the oscillation wavelength. At the injection current I = 80 mA determined by the current controller 3, the temperature of the semiconductor laser 1 is changed by changing the current flowing through the Peltier element in the temperature controller 2, and the oscillation wavelength at each temperature is measured by a spectrum analyzer. . It can be confirmed that the oscillation wavelength of the semiconductor laser 1 changes stepwise while repeating mode hops. It should be noted that the temperature at which the semiconductor laser 1 mode-hops can be known from the experimental results.
[0029]
FIG. 7 is a diagram showing experimental results of two-wavelength output by temperature control and injection current control. First, the injection current was set to I = 80 mA, and the temperature of the semiconductor laser 1 was controlled by the temperature controller 2 to a temperature at which mode hop occurs (here, 22.8 ° C.). FIG. 7A shows the spectrum distribution of the output light from the semiconductor laser 1 at that time. Two spectra having different wavelengths stand out, and it can be confirmed that the semiconductor laser 1 outputs laser light including two wavelengths. The difference between the two wavelengths is about 0.6 nm.
[0030]
Next, as shown in FIG. 7A, in a state where the semiconductor laser 1 outputs light including a spectrum of two wavelengths, only the injection current was increased or decreased by 1 mA. FIGS. 7B and 7C show the spectral distribution of the output light from the semiconductor laser 1 when the injection current is increased or decreased. It can be confirmed that when the injection current is increased, the spectrum on the long wavelength side stably stands, whereas when the injection current is decreased, the spectrum on the short wavelength side stably stands. The three states shown in FIGS. 7A to 7C are stable even after 6 hours.
[0031]
2. Another operation example of a two-wavelength semiconductor laser device
2-1 Wavelength selection by temperature control
FIG. 8 is an explanatory diagram of wavelength selection by temperature control. FIGS. 8A and 8B show an injection current dependency and a temperature dependency of the semiconductor laser 1 shown in FIG. As shown in FIG. 8B, for example, the semiconductor laser 1 mode-hops between the modes “a” and “b” at the current a and the temperature c, and “d” at the current a and the temperature f. Mode hop between the mode of "C" and "C". FIG. 8C is a diagram showing this in a graph of injection current dependency. Although FIG. 8C shows the temperatures c and f, the injection current dependence at the temperatures d and e in FIG. 8B is the same. By controlling the temperature to a specific temperature by the temperature controller 2, the output wavelength or the wavelength difference can be selected.
[0032]
2-2 Mode hop at arbitrary current
FIG. 9 is an explanatory diagram for causing a mode hop at an arbitrary current. For example, in FIG. 2, the semiconductor laser 1 generates a mode hop at the currents a and b, but can generate a mode hop at the current g between the currents a and b.
[0033]
FIG. 9B shows the temperature dependence of the injection current g. As shown in FIG. 9B, when the injection current is g, the semiconductor laser 1 causes a mode hop between the modes (1) and (2) when the temperature is h. When the temperature of the semiconductor laser 1 is controlled to the temperature h by the temperature controller 2, the injection current dependency becomes as shown in FIG. 9A, and the output wavelength of the semiconductor laser 1 is mode-hopped by the current g. As described above, mode hop can be generated at an arbitrary current, and two different wavelengths can be selectively output. For example, this is effective when it is desired to use an injection current near g due to restrictions on the intensity of laser light.
[0034]
3. Second Embodiment of Two-Wavelength Semiconductor Laser Device
FIG. 10 is a configuration diagram of a two-wavelength semiconductor laser device according to the second embodiment. The two-wavelength type semiconductor laser device includes a semiconductor laser 1, a temperature controller 2, a current controller 3, and an oscillation control unit 5. The oscillation controller 5 instructs the temperature controller 2 and the current controller 3 to control the temperature and the current, and controls the oscillation of the semiconductor laser 1. Further, a memory may be provided which stores an output wavelength table in which the temperature, the wavelength before and after the mode hop, and the wavelength difference correspond to each injection current.
[0035]
FIG. 11 shows a data format of the output wavelength table stored in the memory of the oscillation control unit 5. The output wavelength table stores, for each injection current, the output wavelengths before and after the mode hop (two wavelengths that can be selectively output) and / or the wavelength difference before and after the mode hop, corresponding to the temperature at which the mode hop occurs.
[0036]
Further, the two-wavelength type semiconductor laser device may include a spectrum analyzer 4 and a lens 6 for converting light output from the semiconductor laser 1 into, for example, parallel light. The spectrum analyzer 4 receives the light output from the semiconductor laser 1 via the lens 6, obtains a wavelength spectrum of the received light, and outputs the wavelength spectrum to the oscillation control unit 5. The wavelength spectrum data to be output may be the wavelength and intensity of two spectra having large spectral intensities. By comparing these two intensities, it can be determined whether the semiconductor laser 1 is outputting light containing two wavelengths or outputting one wavelength dominantly. Further, the wavelength and intensity of the spectrum may be larger than a predetermined threshold.
[0037]
The operation will be described below.
First, the oscillation controller 5 sets a bias current. Further, the oscillation controller 5 sets the wavelength or the wavelength difference of the output light. For example, the oscillation control unit 5 may read data stored in a memory in advance, or may input data from outside.
[0038]
Next, based on the set current and wavelength or wavelength difference, the oscillation control unit 5 refers to the output wavelength table stored in the memory and obtains a control target temperature (control temperature). When the set wavelength and wavelength difference are not in the output wavelength table, the control temperature may be obtained based on the wavelength and the wavelength difference within a predetermined range.
[0039]
The oscillation controller 5 instructs the temperature controller 2 to control the temperature of the semiconductor laser 1 to the obtained control temperature. The temperature controller 2 controls the temperature of the semiconductor laser 1 according to an instruction from the oscillation control unit 5. When the temperature of the semiconductor laser 1 reaches the specified control temperature, the temperature controller 2 outputs a signal indicating completion of temperature setting to the oscillation control unit 5.
[0040]
When the spectrum analyzer 4 is provided, the oscillation control unit 5 that has received the temperature setting completion signal receives the wavelength spectrum data from the spectrum analyzer 4 and checks whether the semiconductor laser 1 is outputting light including two wavelengths. Judge. For example, the oscillation control unit 5 compares two spectra having large intensities among the input wavelength spectrum data and outputs light including two wavelengths if the difference in intensity is within a predetermined allowable value. Can be determined to be. The oscillation controller 5 outputs an instruction to adjust the temperature of the semiconductor laser 1 to the temperature controller 2 when the oscillation controller 5 determines that the semiconductor laser 1 is outputting light including two wavelengths or has not reached a predetermined temperature. I do. Note that the data input and the temperature adjustment instruction from the spectrum analyzer 4 may be omitted. Further, instead of controlling the temperature based on the output of the temperature detecting means, the temperature controller 2 inputs the wavelength spectrum data from the spectrum analyzer 4, and the semiconductor laser 1 emits light including two wavelengths based on the wavelength spectrum data. The temperature may be controlled so as to be in a state of emitting light.
[0041]
On the other hand, when the oscillation control unit 5 determines that the semiconductor laser 1 is in a state of outputting light including two wavelengths (or receives a temperature setting completion signal), it determines which of the two wavelengths that can be output. It decides whether to dominantly output, and generates a wavelength selection signal. For example, the output wavelength may be determined based on the set wavelength, or the output may be performed from a low wavelength or a high wavelength. Further, the wavelength selection signal may be a value or instruction for increasing or decreasing the current, or may be a current value. The oscillation control unit 5 outputs a wavelength selection signal to the current controller 3 according to an instruction from an operator or an external device. The current controller 3 controls the injection current supplied from the variable bias source 32 according to the wavelength selection signal from the oscillation control unit 5 to generate light of the wavelength before or after the mode hop from the semiconductor laser 1.
[0042]
The oscillation control unit 5 can change the wavelength selection signal output to the current controller 3 according to an instruction from an operator or an external device or at an appropriate timing, and cause the semiconductor laser 1 to output light of a different wavelength. In the above-described embodiment, the temperature controller 2 and the current controller 3 control the temperature and the current in response to the instruction from the oscillation control unit 5, but the oscillation control unit 5 controls the temperature and the current. It may be. Further, in each of the above-described embodiments, one of the two wavelengths is selected by increasing or decreasing the current while fixing the temperature. Conversely, the temperature may be changed while fixing the current.
[0043]
4. Two-wavelength interferometer
4-1 Hardware configuration
FIG. 12 is a configuration diagram of a two-wavelength interference measurement device. The two-wavelength interference measurement device includes a two-wavelength semiconductor laser device 10, a lens 11, a beam splitter (interference means) 12, a reference mirror 13, a photodetector 14, and a measurement unit 15. The measurement unit 15 can include a storage unit 151 that stores the input signal and the measurement result, and a display unit 152 that displays the measurement result. The two-wavelength semiconductor laser device 10 includes a semiconductor laser 1, a temperature controller 2, and a current controller 3. The two-wavelength semiconductor laser device 10 may further include the spectrum analyzer 4 and the oscillation control unit 5, as in the above-described second embodiment. The details of the two-wavelength semiconductor laser device 10 are the same as those described above, and a description thereof will be omitted.
[0044]
The lens 11 converts the light output from the semiconductor laser device 10 into parallel light, and guides the light to the beam splitter 12. The beam splitter 12 splits the laser light, which has become parallel light by the lens 11, and transmits the split laser light to the reference mirror 13 and the measurement object 20. The split light is reflected by the reference mirror 13 and the measurement object 20 and returns to the beam splitter 12 again. The beam splitter 12 superimposes the reflected light to cause interference, and transmits the interference light to the photodetector 14.
[0045]
The interference light can be made bright and dark due to the optical path difference between the light reflected by the reference mirror 13 (reference light) and the light reflected from the measurement object 20 (measurement light). If the optical path difference between the reference light and the measurement light is an integer multiple of the wavelength, the brightness of the interference light is maximum, while if the optical path difference is shifted by half a wavelength from the integer multiple of the wavelength, the brightness of the interference light is minimum. It becomes. When the optical path difference is not constant, bright and dark interference fringes are formed. By receiving and processing the interference light, the step, shape, and the like of the measurement object 20 can be measured. The intensity of the interference is related to the wavelength of the light from the light source, and an interferometer cannot measure a step larger than a half wavelength. The two-wavelength interferometer uses two different wavelengths of light to extend the measurement range more than the one-wavelength interferometer.
[0046]
Two wavelengths λ₁, Λ₂When there is a light source that can use the light of₁, Α₂Is obtained by the following equation.
[0047]
(Equation 1)

[0048]
Here, L is half of the optical path difference. The phase difference Δα can be expressed by the following equation.
[0049]
(Equation 2)

[0050]
Here, Λ is called an equivalent wavelength. Since the equivalent wavelength is longer than the oscillation wavelength of the light source, the measurement range of the interferometer can be expanded as compared with a single-wavelength interferometer. In the present embodiment, two different wavelengths can be generated by one light source, and an interferometer having two light sources can reduce the number of light sources and does not require an optical system for optical axis alignment. For example, the configuration of the device can be simplified.
[0051]
The photodetector 14 receives the interfering light and generates an interference signal. For example, as the photodetector 14, an image sensor such as a CCD can be used. The measurement unit 15 receives an interference signal from the photodetector 14 and processes the interference signal to determine a step, a shape, and the like of the measurement object 20.
[0052]
When the spectrum analyzer 4 is used, a configuration may be adopted in which an appropriate branching device such as a beam splitter is inserted into the optical system to guide the output light from the semiconductor laser 1 to the spectrum analyzer 4.
[0053]
4-2 Operation example-1
First, the measurement unit 15 determines a wavelength (measurement wavelength) or a wavelength difference to be used for measurement based on, for example, a wavelength input from the outside or a predetermined initial value. Next, the measurement unit 15 outputs an instruction to the two-wavelength semiconductor laser device 10 to output light of the measurement wavelength. For example, the measurement unit 15 outputs an instruction to the oscillation control unit 5 of the two-wavelength type semiconductor laser device 10. Further, the measurement unit 15 may further have a function of the oscillation control unit 5, and may output a temperature and wavelength selection signal for outputting a measurement wavelength to the temperature controller 2 and the current controller 3. The two-wavelength semiconductor laser device 10 controls the temperature and the current, and causes the semiconductor laser 1 to output light corresponding to the instruction output by the measurement unit 15.
[0054]
Light emitted from the semiconductor laser 1 is split by the beam splitter 12, reflected by the reference mirror 13 and the measurement object 20, and interferes on the beam splitter 12. The photodetector 14 receives the interfering light and generates an interference signal. The measurement unit 15 receives the interference signal from the photodetector 14 and stores the interference signal in the storage unit 151 in association with the measurement wavelength.
[0055]
Next, the measuring unit 15 outputs an instruction to the two-wavelength semiconductor laser device 10 to output light having a different wavelength from the previous wavelength. As described above, the two-wavelength type semiconductor laser device 10 causes the semiconductor laser 1 to output light corresponding to the instruction, and an interference signal corresponding to the light is stored in the storage unit 151 of the measurement unit 15 corresponding to the measurement wavelength. You.
[0056]
The measurement unit 15 reads out the two interference signals and the measurement wavelength stored in the storage unit 151, performs signal processing such as Fourier transform on the interference signals, obtains a phase distribution, and calculates a phase difference. For example, the measuring unit 15 performs a Fourier transform on the read interference signal, extracts a frequency component near the largest spatial frequency of the spectrum, shifts the frequency component to 0, and performs an inverse Fourier transform to obtain a phase distribution and a phase difference. Ask for.
[0057]
Further, the measurement unit 15 calculates the optical path difference L using Expression 2 based on the phase difference and the measurement wavelength, and obtains the step, the shape, and the like of the measurement object 20. Note that the measurement unit 15 may execute appropriate processing based on the interference signal and the measurement wavelength to obtain the flatness, the spherical shape, and the like of the measurement object 20. The measuring unit 15 may store the obtained measurement result in the storage unit 151 at an appropriate timing and display the result on the display unit 152.
[0058]
4-3 Operation example-2
In the above-described operation example-1, two different wavelengths of light are output and received, and the step and the shape of the measurement object 20 are obtained.₁, Λ₂) Can be simultaneously (or substantially simultaneously) output, and two interference lights can be received and measured. When two wavelengths are oscillated at the same time, two interference fringes having different fringe intervals corresponding to the respective wavelengths are generated, and the photodetector 14 generates an interference signal in which these are superposed. By calculating the phase difference based on the interference signal including the two interference fringes, the step, the shape, and the like of the measurement object 20 can be determined.
[0059]
First, the measurement unit 15 determines a wavelength (measurement wavelength) or a wavelength difference to be used for measurement, and outputs to the two-wavelength semiconductor laser device 10 the determined measurement wavelength and an instruction to output light simultaneously. The two-wavelength type semiconductor laser device 10 controls the temperature and the current, and causes the semiconductor laser 1 to simultaneously (or substantially simultaneously) output light including two wavelengths according to the instruction output by the measurement unit 15.
[0060]
Light emitted from the semiconductor laser 1 is split by the beam splitter 12, reflected by the reference mirror 13 and the measurement object 20, and interferes on the beam splitter. The interference light at this time includes the interference light corresponding to the two wavelengths. The photodetector 14 receives the interfering light and generates an interference signal. The measurement unit 15 receives an interference signal from the photodetector 14, determines a phase difference based on the input interference signal, and determines a step, a shape, and the like of the measurement object 20 in the same manner as described above. A method for obtaining the phase difference will be described later.
[0061]
Note that the measurement unit 15 may execute appropriate processing based on the interference signal and the measurement wavelength to obtain the flatness, the spherical shape, and the like of the measurement object 20. Further, the measurement unit 15 may store the separated interference signal and the obtained measurement result in the storage unit 151 at an appropriate timing and display the same on the display unit 152.
[0062]
Next, a method for obtaining a phase difference from an interference signal including two interference fringes will be described. (Measurement using spatial frequency difference)
FIG. 13 is an explanatory diagram for separating two interference fringes by a spatial frequency. As shown in FIG. 13, the reference mirror 13 is moved to the optical path difference L._rThe interferometer tilted slightly so that₁And λ₂When the interference fringes are observed by simultaneously inputting light having the wavelengths of two, two interference fringes having slightly different periods are generated. These fringes are observed overlapping on the photodetector 14, but when the equivalent wavelength Λ is reduced, the difference in the period of the fringes increases, resulting in a difference in the spatial frequency. For example, equivalent wavelength Λ = L_rIn the case of / 2, as shown in FIG. 13, there is a difference in the number of stripes for exactly one period. By separating the two fringes using the difference between the spatial frequencies, it is possible to perform measurement by simultaneous output of two wavelengths.
[0063]
In the case of this measurement, the reference mirror 13 is arranged at an angle so that an optical path difference occurs depending on the position. Further, a drive unit for changing the inclination of the reference mirror 13 may be further provided.
[0064]
The measuring unit 15 determines the oscillation wavelength such that the equivalent wavelength Λ is reduced and the spatial frequency is different. The measuring unit 15 performs signal processing such as Fourier transform on the interference signal input from the photodetector 14 to separate two fringes on the frequency axis. At this time, a spectrum corresponding to the spatial frequency of the two stripes is obtained. The measuring unit 15 obtains a phase and a phase difference based on frequency components around a spatial frequency corresponding to each stripe, and obtains a step, a surface shape, and the like based on the phase difference and the measured wavelength.
[0065]
(Measurement using phase difference of interference fringes)
In addition to using the difference between the spatial frequencies, the phase difference between the interference lights corresponding to the two wavelengths can be obtained from the overlapped interference fringes. The interference fringes can be generally expressed by the following equation.
[0066]
(Equation 3)

[0067]
Where S_aIs the DC component of the interference light, S_bIs the amplitude of the AC component, f is the spatial frequency, and α is the phase. Also, the amplitude S of the AC component_bAnd DC component S_aIs called visibility (or contrast) and is calculated by the following equation.
V = S_b/ S_a
For example, visibility V can be obtained using a DC component and an AC component obtained by performing Fourier transform on an interference signal based on interference light. In the above-described measurement using the difference between the spatial frequencies, the first item in parentheses in Expression 3 is focused, but the second item is focused here.
[0068]
Wavelength is λ₁, Λ₂When measured at two wavelengths, the interference fringes for each wavelength are represented by the following equations.
[0069]
(Equation 4)

[0070]
However,
α₁(X) = (2π / λ)₁) D
α₂(X) = (2π / λ)₂) D (d: optical path difference)
It is. For example, when d = nΛ + Λ / 4, the phase difference is
α₁(X) -α₂(X) = π / 2
And the two fringes are 90 degrees out of phase.
[0071]
Here, the DC component S of the interference light_a, The amplitude S of the AC component_b, The spatial frequency f,
S_a1= S_a2= S_a
S_b1= S_b2= S_b
f₁= F₂= F
far. The DC component S_aAnd the amplitude S of the AC component_bIn the case of S, since light of two wavelengths is emitted from the same semiconductor laser 1, S_a1= S_a2, S_b1= S_b2Holds.
[0072]
Spatial frequency f₁= F₂Will be described below. Each wavelength λ acquired by the photodetector 14₁, Λ₂Period N of the interference fringes corresponding to₁, N₂Is
N₁= D / λ₁
N₂= D / λ₂
It is. From this equation, the period N₁And N₂Can be expressed by the following equation.
N₂= (Λ₁/ Λ₂) N₁
Here, the wavelength λ output from the two-wavelength type semiconductor laser device 10₁, Λ₂If the wavelength difference is set small for each wavelength, N₂= N₁Can be considered. For example, the difference between the wavelengths output from the two-wavelength semiconductor laser device 10 is 0.6 nm, and the center wavelength is 685 nm (λ₁= 685 nm, λ₂= 685.6 nm) and the wavelength λ in the image acquired by the photodetector 14.₁The fringes generated by the light₁= 30 periods. At this time, the wavelength λ₂The number of periods of the fringes generated in the above equation is N₂= 29.97, which is almost 30. Therefore, since the spatial frequency is the reciprocal of the period, it can be considered that f1 = f2.
[0073]
DC component S of interference light_a, The amplitude S of the AC component_b, And the spatial frequency f is set as described above, the expression representing the two overlapping fringe images can be expressed by the following expression.
[0074]
(Equation 5)

[0075]
From Equation 5, the visibility V of two overlapping fringe images can be expressed by the following equation.
[0076]
(Equation 6)

[0077]
From Equation 6, the visibility V is represented by the phase difference α₁(X) -α₂It turns out that it changes according to (x). Also, S in Equation 6_b/ S_aIs a constant value. For example, S_b/ S_aIs a visibility V previously obtained from a stripe image obtained using only one wavelength, and is stored in the storage unit 151 or the like in advance.
[0078]
The measurement unit 15 obtains the visibility V based on the interference signal input from the photodetector 14, and obtains the phase difference using Expression 6. Specifically, first, the measurement unit 15 performs signal processing such as Fourier transform on the signal input from the photodetector 14 and separates the signal into a DC component and an AC component on a frequency axis. At this time, the spectrum of the AC component appears at the frequency f, and its magnitude is
[0079]
(Equation 7)

[0080]
It is. The spectrum of the DC component is 2S_aIt is.
[0081]
Next, the measuring unit 15 obtains the visibility V by taking the ratio of the amplitude of the DC component to the amplitude of the AC component. Further, the measuring unit 15 determines the determined visibility V and the S stored in the storage unit 151 in advance._b/ S_aThe phase difference is obtained by Expression 6 using the value of.
[0082]
The measurement unit 15 can obtain the step, the shape, and the like of the measurement object 20 based on the obtained phase difference. Although the above formulas and explanations are shown in one dimension with x as a variable, they may be two dimensional.
[0083]
【The invention's effect】
According to the present invention, it is possible to provide a two-wavelength semiconductor laser device that generates two wavelengths with one semiconductor laser. Further, according to the present invention, two wavelengths having as large a wavelength difference as possible can be selectively generated without largely changing the intensity of the laser beam. Further, according to the present invention, since the output light is selected by increasing or decreasing the injection current, it is possible to switch between the two wavelengths at higher speed and more efficiently than by increasing or decreasing the temperature having a large time constant. Furthermore, according to the present invention, light of two wavelengths having a larger wavelength difference than that of a device using only injection current control can be obtained by one semiconductor laser, which greatly contributes to improvement in resolution of an interference measurement device. According to the present invention, it is possible to provide a simpler and less expensive two-wavelength interferometer using a two-wavelength semiconductor laser device.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a two-wavelength semiconductor laser device according to a first embodiment.
FIG. 2 is a diagram schematically showing an injection current dependency and a temperature dependency of an oscillation wavelength of a semiconductor laser.
FIG. 3 is a diagram illustrating the operation of a two-wavelength semiconductor laser device.
FIG. 4 is a diagram showing a laser spectrum around a mode-hopping temperature.
FIG. 5 is a diagram showing a laser spectrum when light of different wavelengths is selectively output.
FIG. 6 is a diagram showing an experimental result of temperature dependence of an oscillation wavelength.
FIG. 7 is a diagram showing experimental results of two-wavelength output by temperature control and injection current control.
FIG. 8 is an explanatory diagram of wavelength selection by temperature control.
FIG. 9 is an explanatory diagram for generating a mode hop at an arbitrary current.
FIG. 10 is a configuration diagram of a two-wavelength semiconductor laser device according to a second embodiment.
FIG. 11 is a data format of an output wavelength table.
FIG. 12 is a configuration diagram of a two-wavelength interference measurement device.
FIG. 13 is an explanatory diagram for separating two interference fringes by a spatial frequency.
[Explanation of symbols]
1 Semiconductor laser
2 Temperature controller
3 Current controller
31 oscillator
32 Variable bias source
4 Spectrum analyzer
5 Oscillation control unit
6 lenses
10 Two-wavelength semiconductor laser device
11 lenses
12 Beam splitter
13 Reference mirror
14 Photodetector
15 Measurement section
151 storage unit
152 Display
20 Measurement object

Claims (19)

A semiconductor laser in which the wavelength of the output light changes in response to a change in injection current and / or temperature, and a mode hop in which the wavelength of the output light changes stepwise in response to the change in injection current and / or temperature;
A current controller for controlling an injection current or voltage to the semiconductor laser,
A temperature controller that changes the temperature of the semiconductor laser,
One of the temperature controller or the current controller controls the semiconductor laser to output a light including two different wavelengths before and after mode hop,
A two-wavelength semiconductor laser device that controls the other of the temperature controller and the current controller to selectively output one of wavelengths before and after a mode hop from the semiconductor laser in the state. The temperature controller controls the temperature of the semiconductor laser to a temperature externally input, or to a temperature at which a preset mode hop occurs, so that the semiconductor laser emits two different wavelengths before and after the mode hop. And output light including
2. The two-wavelength semiconductor laser device according to claim 1, wherein the current controller controls an injection current or a voltage in the state and selectively outputs one of wavelengths before and after a mode hop from the semiconductor laser. The current controller controls the injection current or voltage to the semiconductor laser to a current or voltage input from the outside, or to a current or voltage at which a preset mode hop occurs. A state in which light including two different wavelengths before and after the mode hop is output,
2. The two-wavelength semiconductor laser device according to claim 1, wherein the temperature controller controls the temperature of the semiconductor laser in the state and selectively outputs one of wavelengths before and after a mode hop from the semiconductor laser. 4. An oscillation controller for instructing the current controller and / or the temperature controller with a current or a voltage and / or a temperature to be a control target according to an external instruction or a preset value. The two-wavelength semiconductor laser device according to any one of the above. The oscillation control unit has an output wavelength table in which output wavelengths and / or wavelength differences before and after the mode hop are stored in correspondence with the injection current and the temperature at which the mode hop occurs, and is input from the outside or predetermined. 5. The temperature according to claim 4, wherein a temperature at which a mode hop occurs is obtained by referring to the output wavelength table based on the injection current and the output wavelength and / or the wavelength difference, and the obtained temperature is output as a control temperature to the temperature controller. Two-wavelength semiconductor laser device. Further comprising a spectrum analyzer to receive the output light from the semiconductor laser to determine the wavelength spectrum,
The said oscillation control part makes the said semiconductor laser output the light containing two different wavelengths before and after a mode hop by the said temperature controller or the said current controller based on the output from the said spectrum analyzer. 2. The two-wavelength semiconductor laser device according to item 1. A two-wavelength semiconductor laser device according to any one of claims 1 to 6,
A reference mirror that reflects a part of output light from the two-wavelength semiconductor laser device;
Interfering means for branching output light from the two-wavelength type semiconductor laser device to the reference mirror and the measurement object, and forming interference light by reflected light or transmitted light from the reference mirror and the measurement object. ,
A photodetector that receives the interference light from the interference means, generates and outputs an interference signal,
A two-wavelength interference measurement device, comprising: a measurement unit that obtains a step and / or a shape of a measurement object based on an interference signal from the photodetector and an output wavelength of the two-wavelength semiconductor laser device. The measurement unit outputs an externally input or predetermined measurement wavelength signal to the two-wavelength semiconductor laser device,
The two-wavelength type semiconductor laser device controls a temperature and a current or a voltage, and outputs light of first and second wavelengths according to a measurement wavelength signal from the measurement unit, respectively.
The measurement unit inputs interference signals due to the light of the first and second wavelengths from the photodetector, respectively, and obtains a step and / or a shape of a measurement object based on the interference signals and the first and second wavelengths. The two-wavelength interference measurement device according to claim 7. The measurement unit outputs, to the two-wavelength semiconductor laser device, an instruction to output a light having two wavelengths and a measurement wavelength signal input or predetermined from the outside,
The two-wavelength semiconductor laser device controls temperature and current or voltage, and simultaneously outputs light including both the first and second wavelengths according to the measurement wavelength signal from the measurement unit,
The measurement unit inputs an interference signal based on two interference lights corresponding to the first and second wavelengths from the photodetector, and determines a step and a step of a measurement object based on the interference signal and the first and second wavelengths. The two-wavelength interference measuring apparatus according to claim 7, wherein the shape is obtained. The reference mirror is arranged to be inclined at a predetermined angle so that an optical path difference occurs depending on the position,
The measurement unit is based on the difference in the spatial frequency of the input interference signal, separates into interference signals corresponding to each wavelength, obtains each phase and phase difference based on the separated interference signal, and determines the measurement object by the obtained phase difference. The two-wavelength interferometer according to claim 9, wherein a step and / or a shape is obtained. The measurement unit calculates a phase difference of the interference light based on visibility or contrast which is a ratio of a DC component and an AC component of the input interference signal, and calculates a step and / or a shape of the measurement object based on the obtained phase difference. Item 10. A two-wavelength interference measurement device according to item 9. 2. A semiconductor laser using a mode laser in which the wavelength of the output light changes according to the change in the injection current and / or the temperature, and the wavelength of the output light changes stepwise with the change in the injection current and / or the temperature. A wavelength type semiconductor laser oscillation method,
Controlling the temperature or injection current or voltage of the semiconductor laser so that the semiconductor laser outputs light including two different wavelengths before and after mode hopping,
In this state, the two-wavelength type semiconductor laser oscillation method controls an injection current, a voltage, or a temperature to the semiconductor laser so as to selectively output one of wavelengths before and after a mode hop from the semiconductor laser. By controlling the temperature of the semiconductor laser to a temperature input from the outside or a temperature at which a preset mode hop occurs, the semiconductor laser outputs light including two different wavelengths before and after the mode hop. ,
13. The two-wavelength semiconductor laser oscillation method according to claim 12, wherein in this state, the injection current or the voltage is controlled to selectively output one of the wavelengths before and after the mode hop from the semiconductor laser. By controlling the injection current or voltage to the semiconductor laser to a current or voltage input from the outside, or to a current or voltage at which a preset mode hop occurs, the semiconductor laser can be used for two before and after the mode hop. Output light containing different wavelengths,
13. The two-wavelength semiconductor laser oscillation method according to claim 12, wherein in this state, the temperature of the semiconductor laser is controlled to selectively output one of wavelengths before and after a mode hop from the semiconductor laser. 2. A semiconductor laser using a mode laser in which the wavelength of the output light changes according to the change in the injection current and / or the temperature, and the wavelength of the output light changes stepwise with the change in the injection current and / or the temperature. A wavelength-type interference measurement method,
Controlling the temperature or injection current or voltage of the semiconductor laser so that the semiconductor laser outputs light including two different wavelengths before and after mode hopping,
In this state, controlling the injection current or the voltage or the temperature to the semiconductor laser so as to output the first wavelength and / or the second wavelength light before and after the mode hop from the semiconductor laser,
Receiving interference light formed by reflected light or transmitted light from the reference mirror and the measurement object of the first and / or second wavelength light to generate an interference signal;
A two-wavelength interference measurement method for determining a step and / or a shape of a measurement object based on the interference signal and the first and second wavelengths. Controlling the injection current or voltage or temperature to the semiconductor laser so that the semiconductor laser outputs light of the first and second wavelengths,
Generating interference signals by receiving interference light beams of the first and second wavelengths, respectively;
The two-wavelength interference measurement method according to claim 15, wherein a step and / or a shape of the measurement object is obtained based on the interference signal. Controlling the injection current or voltage or temperature to the semiconductor laser so that the semiconductor laser simultaneously outputs light including first and second wavelengths,
Receiving two interference lights corresponding to the first and second wavelengths to generate an interference signal;
The two-wavelength interference measurement method according to claim 15, wherein a step and / or a shape of the measurement object is obtained based on the interference signal. Tilt the reference mirror at a predetermined angle so that an optical path difference occurs depending on the position,
Based on the difference in the spatial frequency of the interference signal, the signal is separated into interference signals corresponding to the first and second wavelengths, each phase and phase difference are determined based on the separated interference signal, and the step of the measurement object is determined based on the determined phase difference. 18. The two-wavelength interference measurement method according to claim 17, wherein a shape is obtained. 18. The step according to claim 17, wherein a phase difference of the interference light is obtained based on visibility or contrast which is a ratio of a DC component and an AC component of the interference signal, and a step and / or a shape of the measurement object is obtained based on the obtained phase difference. Wavelength interference measurement method.

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