JP2010177328A

JP2010177328A - Wavelength swept light source

Info

Publication number: JP2010177328A
Application number: JP2009016414A
Authority: JP
Inventors: Kenichi Nakamura; 賢一中村; Takashi Nakayama; 貴司中山; Shintaro Morimoto; 慎太郎森本
Original assignee: Anritsu Corp
Current assignee: Anritsu Corp
Priority date: 2009-01-28
Filing date: 2009-01-28
Publication date: 2010-08-12
Anticipated expiration: 2029-01-28
Also published as: JP5103412B2

Abstract

<P>PROBLEM TO BE SOLVED: To continuously sweep over a predetermined wavelength band, in a state without mode hopping. <P>SOLUTION: Relating to a wavelength sweep-over light source of external resonator type in the Littman method, a rotating mirror is connected to a frame 31 with a pair of twist-deformable connecting parts 33 and 34, along with a reflecting plate 32 arranged inside the frame, and a force is periodically applied to an end of the reflecting plate 32 so that the reflecting plate 32 is reciprocatively turned about the connection parts 33 and 34. The wavelength swept light source includes a light-receiving unit 60 for receiving zeroth-order diffraction for the light incident on the diffraction plane of a diffraction grating 25 from a semiconductor laser 22; a mode-hop detecting means 61 for detecting a discontinuous change in the output signal of the light receiver 60 that occurs due to mode hopping, while the outgoing optical wavelength of the semiconductor laser 22 is swept by the reciprocative turning of the reflecting plate 32; and an injection current control means 65 for changing the injection current of the semiconductor laser 22 so that the discontinuous change in the output signal of the light receiving unit 60 due to mode hopping disappears. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

本発明は、リトマン方式のシングルモードの波長掃引光源において、波長掃引時に生じうるモードホップを抑制するための技術に関する。 The present invention relates to a technique for suppressing a mode hop that may occur during wavelength sweeping in a Litman single-mode wavelength sweeping light source.

光波長は光の基本特性の１つであり、光通信、分光分析、表面形状測定や光センシングなど様々な分野で、それを利用したシステムや測定器が開発されてきた。特に、単色性が高く、コヒーレントな高品質の光は、高度なシステム、高精度な測定を可能とするためその利用価値は極めて高い。 Light wavelength is one of the basic characteristics of light, and systems and measuring instruments using it have been developed in various fields such as optical communication, spectroscopic analysis, surface shape measurement and optical sensing. In particular, high-monochromatic and coherent high-quality light is extremely useful because it enables advanced systems and high-precision measurements.

そのため、高品質な光を出力できる波長掃引光源が例えば特許文献１に提案されている。図１５に示す光源１はその基本構成を示すものであり、半導体レーザ２から出射されコリメートレンズ３を経た光を回折格子４の回折面４ａに所定角度で入射し、回折光のうち回折格子４に対向する位置に支持されたミラー５の反射面５ａに直交する方向に出射された光を逆光路で回折格子４に戻して、その戻した光に対する回折光を半導体レーザ２に逆光路で戻すとともに、回折格子４に対して特定位置Ｏを中心にミラー５を回動させる構造を有しており、半導体レーザ２の実効共振端面２ａから回折格子４を経てミラー５の反射面５ａに至る光路長で決まる共振器長を、ミラー５の反射面５ａの回動により変化させて、半導体レーザの出射光の波長を所定範囲連続的に掃引する外部共振型の波長掃引光源である。ここで特定位置Ｏは、回折格子４の回折面４ａの延長面Ｈ１と、半導体レーザ２の実効共振端面２ａの延長面Ｈ２と交わる位置にあり、ミラー５はその反射面５ａの延長面Ｈ３が特定位置Ｏに交わるように規定される。 Therefore, for example, Patent Document 1 proposes a wavelength swept light source that can output high-quality light. The light source 1 shown in FIG. 15 shows the basic configuration, and light emitted from the semiconductor laser 2 and passed through the collimating lens 3 is incident on the diffraction surface 4a of the diffraction grating 4 at a predetermined angle. The light emitted in the direction orthogonal to the reflecting surface 5a of the mirror 5 supported at the position opposite to is returned to the diffraction grating 4 by the reverse optical path, and the diffracted light for the returned light is returned to the semiconductor laser 2 by the reverse optical path. In addition, it has a structure in which the mirror 5 is rotated around the specific position O with respect to the diffraction grating 4, and the optical path from the effective resonance end face 2 a of the semiconductor laser 2 to the reflection surface 5 a of the mirror 5 through the diffraction grating 4. This is an external resonance type wavelength sweeping light source that sweeps the wavelength of the emitted light of the semiconductor laser continuously within a predetermined range by changing the resonator length determined by the length by the rotation of the reflecting surface 5a of the mirror 5. Here, the specific position O is at a position where the extended surface H1 of the diffraction surface 4a of the diffraction grating 4 and the extended surface H2 of the effective resonance end surface 2a of the semiconductor laser 2 intersect, and the mirror 5 has an extended surface H3 of the reflecting surface 5a. It is defined to cross a specific position O.

この光源は一般的にリトマン方式と呼ばれており、原理的にはシングルモード発振するレーザ光を、モードホップさせることなく所定の波長範囲で連続的に掃引させることが可能である。 This light source is generally called a Litman method, and in principle, laser light that oscillates in a single mode can be continuously swept in a predetermined wavelength range without mode hopping.

しかしながら、この特許文献１に示された実際の波長掃引光源は、大型かつ重量のある金属ブロックに設置されたミラーをモータとベアリングで回転させることで波長掃引を行うので、原理的に高速な波長掃引を行えない。 However, the actual wavelength sweeping light source disclosed in Patent Document 1 performs wavelength sweeping by rotating a mirror installed on a large and heavy metal block with a motor and a bearing. The sweep cannot be performed.

また、その回転機構の精度の低さゆえにモードホップが発生し、しかも、波長掃引のたびにモードホップが生じる波長が変わってしまうという極めて再現性の悪いものであった。このようなモードホップは、たとえ光源の温度や半導体レーザへの注入電流が一定になるよう制御されていたとしても避けられない。 In addition, mode hops occur due to the low accuracy of the rotation mechanism, and the wavelength at which the mode hops change every time the wavelength is swept is extremely poorly reproducible. Such mode hops are inevitable even if the temperature of the light source and the injection current to the semiconductor laser are controlled to be constant.

また上記の基本的な配置の場合には、ミラーあるいはそれを支持して一体的に回動する支持部材と、光軸とが交差するので、ミラーあるいはその支持部材に光を通過させるための穴や切欠等を設ける必要があり、それによる剛性低下で変形しやすくモードホップを招く場合もある。 Further, in the case of the above basic arrangement, the mirror or the support member that supports the mirror and rotates integrally with the optical axis intersects the mirror or the hole for passing light through the support member. It is necessary to provide a notch or the like, and there is a case where mode hops are easily caused due to a reduction in rigidity caused by the deformation.

これを制御するには、コリメートレンズや回折格子の配置を微調整することで光軸を調整するといった非常に複雑な制御が必要となり、波長の高速掃引を困難にする原因にもなっている。 In order to control this, very complicated control such as adjusting the optical axis by finely adjusting the arrangement of the collimating lens and the diffraction grating is necessary, which makes it difficult to sweep the wavelength at high speed.

そこで、より安定した回転機構を利用して小型かつ高速な波長掃引を可能とする波長掃引光源が例えば特許文献２で提案されている。この光源で用いられる波長掃引機構は、半導体基板に対するエッチング処理等で精度よく且つ小型に形成された所謂ＭＥＭＳ構造を有しており、矩形のフレームの内側に矩形の反射板が同心に配置され、フレーム上部内縁の中間部から反射板の上辺縁の中間部との間と、フレーム下部内縁の中間部から反射板の下辺縁の中間部との間が、それぞれ捩れ変形可能な連結部によって連結された構造を有し、この反射板の一端あるいは両端に静電的あるいは磁気による力を周期的に付与することで、反射板を連結部の捩れ変形により往復回動させることができる。 Therefore, for example, Patent Document 2 proposes a wavelength swept light source that enables a small and fast wavelength sweep using a more stable rotation mechanism. The wavelength sweeping mechanism used in this light source has a so-called MEMS structure that is accurately and compactly formed by etching processing on a semiconductor substrate, etc., and a rectangular reflector is concentrically arranged inside a rectangular frame, Between the middle part of the upper inner edge of the frame and the middle part of the upper edge of the reflector, and between the middle part of the lower edge of the frame and the middle part of the lower edge of the reflector, the torsionally deformable coupling parts are connected. By periodically applying an electrostatic or magnetic force to one or both ends of the reflecting plate, the reflecting plate can be reciprocated by torsional deformation of the connecting portion.

この機構の場合、波長掃引のために回転される反射板の運動は極めて安定しているため、この機構をミラー部として用いたリトマン方式外部共振器型の波長掃引光源は、従来にはなく小型で、シングルモードかつモードホップなしの安定した高速波長掃引を可能にしている。 In the case of this mechanism, the movement of the reflecting plate rotated for the wavelength sweep is extremely stable. Therefore, a Litman-type external resonator type wavelength sweep light source using this mechanism as a mirror part is smaller than before. Thus, a stable high-speed wavelength sweep without single mode and mode hop is enabled.

米国特許第５３１９６６８号明細書US Pat. No. 5,319,668

特開２００５−２８４１２５号公報JP 2005-284125 A

しかしながら、このようなＭＥＭＳ構造の回動ミラーを用いた波長掃引光源であっても光源の組み立て精度が悪い場合や、温度変化による光部品の光軸ずれなどの原因によりモードホップが発生してしまう。 However, even a wavelength swept light source using such a MEMS-structured rotating mirror may cause mode hops due to poor assembly accuracy of the light source or due to optical axis misalignment of the optical component due to temperature changes. .

また、光源からの出力光のパワーを変化させるために注入電流や半導体レーザの温度を調整すると、必然的にモードホップが生じてしまうという問題もあった。 Further, when the injection current or the temperature of the semiconductor laser is adjusted to change the power of the output light from the light source, there is a problem that mode hops are inevitably caused.

本発明は、これらの問題を解決して、小型で、モードホップなしの状態で所定の波長範囲を連続的に且つ高速に掃引することのできるリトマン方式外部共振器型の波長掃引光源を提供することを目的としている。 The present invention solves these problems, and provides a wavelength-swept light source of a Littman-type external resonator type that can be swept continuously and at high speed in a small size and without mode hopping. The purpose is that.

前記目的を達成するために、本発明の請求項１の波長掃引光源は、
基台（２１）と、
前記基台上に固定され、少なくとも一方の光出射用の端面が低反射率面で、注入電流により光を出射する半導体レーザ（２２）と、
前記基台上に固定され、前記半導体レーザの前記低反射率面からの出射光を平行光に変換するコリメートレンズ（２３）と、
光を回折するための溝が平行に形成されている回折面（２５ｂ）を有し、前記コリメートレンズから出射された光が、前記溝と直交し且つ前記回折面に対して非直交となる所定入射角で所定入射位置に入射される状態で前記基台上に固定された回折格子（２５）と、
前記回折格子の回折面と対向する反射面を有し、前記回折格子の溝と平行で特定位置の軸を中心にして前記回折面と直交する平面内で回動可能に形成され、前記コリメートレンズから出射されて前記回折格子の回折面に入射した光に対する回折光のうち前記反射面に直交する光軸に沿った光を反射して逆光路で前記回折格子に戻し、該戻した光を入射光路と同じ光軸で前記コリメートレンズを介して前記半導体レーザへ戻させる回動ミラー（３０）と有し、
前記回動ミラーの回動中心から前記回折格子の前記所定入射位置までの距離ｒ、前記回動中心から前記反射面を延長した平面までの距離Ｌ２、前記半導体レーザの実効共振端面から前記回折格子の所定入射位置に至る光路長Ｌ１および前記回折格子の回折面への光入射角αとの間に、
ｒ＝（Ｌ１−Ｌ２）／sin α
の関係を成立させて、
前記回動ミラーの反射面の角度変化に応じて、前記半導体レーザから前記コリメートレンズおよび前記回折格子の回折面を経て前記回動ミラーの反射面に至る共振器長を変化させ、前記半導体レーザが出射する光の波長を所定範囲内で連続的に変化させるリトマン方式外部共振器型の波長掃引光源において、
前記回動ミラーは、前記基台に固定されたフレーム（３１）と、該フレームの内側に配置され一面側に前記反射面が形成された反射板（３２）と、該反射板の外縁と前記フレームの内縁との間を連結する捩れ変形可能で前記回折格子の溝と平行な一直線上に並ぶ一対の連結部（３３、３４）とで一体的に形成され、前記反射板の端に力を周期的に付与する回動駆動手段（３５、３６、４０）により、前記連結部を中心に前記反射板を往復回動させる構造を有しており、
さらに、
前記基台上に固定され、前記半導体レーザの前記一方の端面と反対の端面から出射される光、または前記半導体レーザから前記回折格子の回折面に入射された光に対する０次回折光のいずれかを受け、該受けた光の強度に応じた電気の信号を出力する受光器（６０）と、
前記回動ミラーの反射板の往復回動により前記半導体レーザの出射光波長が掃引されている間、前記受光器の出力を監視し、モードホップによって生じる前記受光器の出力信号の不連続変化を検出するモードホップ検出手段（６１）と、
前記モードホップ検出手段によって検出された前記受光器の出力信号の不連続変化が無くなるように前記半導体レーザの注入電流を変化させる注入電流制御手段（６５）とを設けたことを特徴とする。 In order to achieve the above object, the wavelength swept light source according to claim 1 of the present invention comprises:
A base (21);
A semiconductor laser (22) fixed on the base, wherein at least one end surface for light emission is a low reflectivity surface, and emits light by injection current;
A collimator lens (23) fixed on the base and converting the light emitted from the low reflectance surface of the semiconductor laser into parallel light;
A predetermined diffraction surface (25b) in which grooves for diffracting light are formed in parallel, and light emitted from the collimating lens is orthogonal to the grooves and non-orthogonal to the diffraction surface A diffraction grating (25) fixed on the base in a state of being incident at a predetermined incident position at an incident angle;
The collimating lens has a reflecting surface facing the diffraction surface of the diffraction grating, and is rotatable in a plane that is parallel to the groove of the diffraction grating and that is orthogonal to the diffraction surface about an axis at a specific position. Of the diffracted light with respect to the light emitted from and incident on the diffraction surface of the diffraction grating, the light along the optical axis perpendicular to the reflection surface is reflected and returned to the diffraction grating by a reverse optical path, and the returned light is incident A rotating mirror (30) for returning to the semiconductor laser via the collimating lens with the same optical axis as the optical path;
A distance r from the rotation center of the rotation mirror to the predetermined incident position of the diffraction grating, a distance L2 from the rotation center to a plane obtained by extending the reflection surface, and the diffraction grating from the effective resonance end surface of the semiconductor laser Between the optical path length L1 to the predetermined incident position and the light incident angle α to the diffraction surface of the diffraction grating,
r = (L1-L2) / sin α
Establishing the relationship
In response to a change in the angle of the reflecting surface of the rotating mirror, the resonator length from the semiconductor laser to the reflecting surface of the rotating mirror via the collimating lens and the diffraction surface of the diffraction grating is changed. In the wavelength sweep light source of the Litman method external resonator type that continuously changes the wavelength of the emitted light within a predetermined range,
The rotating mirror includes a frame (31) fixed to the base, a reflecting plate (32) disposed inside the frame and having the reflecting surface formed on one side thereof, an outer edge of the reflecting plate, and the It is integrally formed with a pair of connecting portions (33, 34) that can be torsionally deformed to connect between the inner edges of the frame and are aligned in a straight line parallel to the grooves of the diffraction grating, and applies a force to the end of the reflecting plate. It has a structure in which the reflection plate is reciprocally rotated around the connecting portion by a rotation driving means (35, 36, 40) that is periodically applied.
further,
Either a light fixed on the base and emitted from an end surface opposite to the one end surface of the semiconductor laser, or a zero-order diffracted light with respect to light incident on the diffraction surface of the diffraction grating from the semiconductor laser A light receiver (60) for receiving and outputting an electrical signal corresponding to the intensity of the received light;
While the output wavelength of the semiconductor laser is swept by the reciprocating rotation of the reflecting plate of the rotating mirror, the output of the light receiver is monitored, and a discontinuous change in the output signal of the light receiver caused by a mode hop is observed. Mode hop detection means (61) for detecting;
Injection current control means (65) for changing the injection current of the semiconductor laser so as to eliminate the discontinuous change in the output signal of the light receiver detected by the mode hop detection means is provided.

また、本発明の請求項２の波長掃引光源は、請求項１記載の波長掃引光源において、
前記注入電流制御手段は、前記反射板の往復回動と同期させて半導体レーザへの注入電流を可変制御することを特徴する。 Moreover, the wavelength sweep light source of Claim 2 of this invention is the wavelength sweep light source of Claim 1,
The injection current control means variably controls the injection current to the semiconductor laser in synchronization with the reciprocating rotation of the reflector.

また、本発明の請求項３の波長掃引光源は、請求項２記載の波長掃引光源において、
前記注入電流制御手段は、波長掃引中における前記受光器の出力信号の不連続変化がなく且つ波長掃引範囲における光出力がほぼ一定となるように注入電流を可変制御することを特徴とする。 Moreover, the wavelength sweep light source of Claim 3 of this invention is the wavelength sweep light source of Claim 2,
The injection current control means variably controls the injection current so that there is no discontinuous change in the output signal of the light receiver during the wavelength sweep and the optical output in the wavelength sweep range is substantially constant.

また、本発明の請求項４の波長掃引光源は、請求項１〜３のいずれかに記載の波長掃引光源において、
前記半導体レーザまたはその周囲の温度を検出する温度センサ（７０）と、
少なくとも前記半導体レーザの温度を可変するためのペルチェ素子（７１）と、
前記温度センサの出力と前記受光器の出力とに基づいて前記ペルチェ素子への供給電流を制御することで、前記半導体レーザの出射光の波長掃引範囲における平均出力が所望値となるようする温度制御手段（７５）とを備えていることを特徴とする。 Moreover, the wavelength sweep light source of Claim 4 of this invention is the wavelength sweep light source in any one of Claims 1-3,
A temperature sensor (70) for detecting the temperature of the semiconductor laser or its surroundings;
A Peltier element (71) for varying the temperature of at least the semiconductor laser;
Temperature control for controlling the supply current to the Peltier element based on the output of the temperature sensor and the output of the light receiver so that the average output in the wavelength sweep range of the emitted light of the semiconductor laser becomes a desired value Means (75).

また、本発明の請求項５の波長掃引光源は、請求項１〜４のいずれかに記載の波長掃引光源において、
前記コリメートレンズから出射された光を前記基台上に固定された固定ミラー（２４）を介して前記回折格子へ入射させる構造で且つ前記半導体レーザ、前記コリメートレンズ、前記固定ミラーおよび前記回折格子が前記回動ミラーの前記反射板の一面側に配置されるようにし、前記半導体レーザから前記固定ミラーを介して前記回折格子に至る光軸が、前記回動ミラーの前記反射板と非交差状態となるようにしたことを特徴とする。 Moreover, the wavelength sweep light source of Claim 5 of this invention is the wavelength sweep light source in any one of Claims 1-4,
The semiconductor laser, the collimating lens, the fixed mirror, and the diffraction grating have a structure in which light emitted from the collimating lens is incident on the diffraction grating via a fixed mirror (24) fixed on the base. The optical axis extending from the semiconductor laser to the diffraction grating via the fixed mirror is arranged in a non-crossing state with the reflector of the pivot mirror so that it is disposed on one surface side of the reflector of the pivot mirror. It was made to become.

このように本発明の波長掃引光源では、その回動ミラーの動作が極めて安定しているために従来の光源に比べて不規則なモードホップの発生が格段に少なくなる。そして、定常的な光軸ずれ等に起因して規則的にモードホップが生じる場合であっても、波長掃引中におけるモードホップによる受光器の出力の不連続変化を検出するモードホップ検出手段を有しているので、その不連続変化がなくなるように半導体レーザへの注入電流を規則的に制御することにより、簡単にモードホップのない状態を実現し、保持できる。 As described above, in the wavelength swept light source of the present invention, the operation of the rotating mirror is extremely stable, so that the generation of irregular mode hops is remarkably reduced as compared with the conventional light source. Even if mode hops occur regularly due to steady optical axis misalignment, etc., there is a mode hop detection means that detects discontinuous changes in the output of the optical receiver due to mode hops during wavelength sweeping. Therefore, a mode-hop-free state can be easily realized and maintained by regularly controlling the current injected into the semiconductor laser so that the discontinuous change is eliminated.

また、モードホップなしの状態を保持できる注入電流に幅があるので、その範囲内で半導体レーザへの注入電流を変化させることで光源の出力光パワーを変化させることもできる。例えば、モードホップなしの状態を保持できる注入電流の幅の範囲内で波長掃引に同期させて半導体レーザの注入電流を可変制御すれば、掃引波長範囲内の光出力を平坦化することができる。 In addition, since there is a range of injection current that can maintain the state without mode hop, the output light power of the light source can be changed by changing the injection current to the semiconductor laser within the range. For example, if the injection current of the semiconductor laser is variably controlled in synchronization with the wavelength sweep within the range of the injection current that can maintain the state without mode hop, the optical output within the sweep wavelength range can be flattened.

さらに、温度センサとペルチェ素子と温度制御部を備えた波長掃引光源では、半導体レーザの温度制御により、モードホップ無しの状態で光出力を広範囲に可変することができる。 Furthermore, in a wavelength swept light source including a temperature sensor, a Peltier element, and a temperature controller, the optical output can be varied over a wide range without mode hops by controlling the temperature of the semiconductor laser.

また、半導体レーザから出射された光を、固定ミラーを介して回折格子へ入射させる構造で且つ半導体レーザ、固定ミラーおよび回折格子が回動ミラーの反射板の一面側に配置されるようにし、半導体レーザから固定ミラーを介して回折格子に至る光軸が、回動ミラーの反射板と非交差状態となるようにしたので、ミラーの剛性低下がなく、より安定な波長掃引が可能となり、注入電流による制御および温度制御をより再現性高く行うことができる。 The semiconductor laser has a structure in which light emitted from the semiconductor laser is incident on the diffraction grating via the fixed mirror, and the semiconductor laser, the fixed mirror, and the diffraction grating are arranged on one surface side of the reflecting plate of the rotating mirror, The optical axis from the laser to the diffraction grating via the fixed mirror is not crossed with the reflector of the rotating mirror, so the mirror does not lose its rigidity and more stable wavelength sweeping is possible. And temperature control can be performed with higher reproducibility.

本発明の実施形態の全体構成図Overall configuration diagram of an embodiment of the present invention 実施形態の光学部の平面図Plan view of optical unit of embodiment 実施形態の要部の分解斜視図The exploded perspective view of the principal part of an embodiment 実施形態の駆動信号と波長変化との関係を示す図The figure which shows the relationship between the drive signal and wavelength change of embodiment 波長を連続的に掃引するための条件を説明するための図Diagram for explaining conditions for continuous wavelength sweeping モードホップがないあるいは抑制された場合と、モードホップがある場合の波長対光出力の特性をおよびその時間変化の絶対値を示す図Figure showing the wavelength vs. optical output characteristics when there is no mode hopping or when there is mode hopping and when there is mode hopping, and the absolute value of the time change 縦モードと共振器の選択特性との関係を示す図Diagram showing the relationship between longitudinal mode and resonator selection characteristics モードホップがある場合にそれを注入電流のダイナミック制御により抑制する場合の注入電流の変化パターンの例を示す図The figure which shows the example of the change pattern of the injection current when it suppresses it by the dynamic control of the injection current when there is a mode hop モードホップが抑制された状態において注入電流を半固定的に変化させたときの波長対光出力の特性を示す図Diagram showing wavelength vs. optical output characteristics when injection current is changed semi-fixed with mode hop suppressed モードホップが抑制された状態において、注入電流のダイナミック制御により光出力を平坦化させたときの波長対光出力の特性を示す図Figure showing the characteristics of wavelength versus optical output when the optical output is flattened by dynamic control of the injection current in a state where mode hops are suppressed 要部の変形例を示す図The figure which shows the modification of the principal part 要部の変形例を示す図The figure which shows the modification of the principal part 光学部の配置の変形例を示す図The figure which shows the modification of arrangement | positioning of an optical part. 光学部の配置の変形例を示す図The figure which shows the modification of arrangement | positioning of an optical part. リトマン方式外部共振器型の波長掃引光源の基本構成図Basic configuration diagram of wavelength-swept light source of Litman external resonator type

以下、図面に基づいて本発明の実施の形態を説明する。
図１は、本発明の実施形態の波長掃引光源２０の全体構成図、図２は光学部の平面図、図３は光学部の要部の構造を示している。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of a wavelength swept light source 20 according to an embodiment of the present invention, FIG. 2 is a plan view of an optical unit, and FIG. 3 shows a structure of a main part of the optical unit.

図１、図２に示しているように、この波長掃引光源２０は、上面が互いに平行な高段部２１ａ、２１ａ′と低段部２１ｂとを有する基台２１上に構成され、その高段部２１ａには、低段部２１ｂの上面に平行な光を低反射率の端面（低反射率面）から出射する半導体レーザ２２と、半導体レーザ２２から出射された光を平行光に変換するコリメートレンズ２３と、コリメートレンズ２３から出射された平行光を高段部２１ａの上面に垂直な反射面２４ａで受け、後述する回折格子２５の回折面２５ａに向けて反射する固定ミラー２４とが固定されている。なお、基台２１の上面側は、外部からノイズ光、熱、空気の流れを遮断するとともに、波長掃引光を出射させ、電気信号を通過させるケース８０に覆われている。 As shown in FIG. 1 and FIG. 2, the wavelength swept light source 20 is configured on a base 21 having high steps 21a, 21a ′ and low steps 21b whose upper surfaces are parallel to each other. The part 21a includes a semiconductor laser 22 that emits light parallel to the upper surface of the low step part 21b from an end face (low reflectance surface) with low reflectivity, and a collimator that converts the light emitted from the semiconductor laser 22 into parallel light. The lens 23 and the fixed mirror 24 that receives the parallel light emitted from the collimator lens 23 at the reflecting surface 24a perpendicular to the upper surface of the high step portion 21a and reflects it toward the diffraction surface 25a of the diffraction grating 25 described later are fixed. ing. The upper surface side of the base 21 is covered with a case 80 that blocks the flow of noise light, heat, and air from the outside, and emits wavelength-swept light to pass an electrical signal.

固定ミラー２４の反射光は、基台２１の低段部２１ｂに垂直に立てられた回折格子２５の回折面２５ａの所定入射位置に非直交で所定の入射角αで入射される。回折格子２５の回折面２５ａには、光を回折するための回折溝２５ｂが低段部２１ｂに垂直な向きで平行に設けられており、固定ミラー２４で反射された回折溝２５ｂに対して直交し且つ回折面２５ａに対して入射角αで入射される平行光は、回折溝２５ｂにより波長に応じた方向に回折される。なお、光軸や各部材の向きに関して、基台２１の上面を基準として説明するが、各部の位置は相対的に規定されるものであり、この実施形態の配置に限定されるものではない。 The reflected light of the fixed mirror 24 is incident at a predetermined incident angle α in a non-orthogonal direction at a predetermined incident position of the diffraction surface 25a of the diffraction grating 25 standing vertically to the lower step portion 21b of the base 21. A diffraction groove 25b for diffracting light is provided on the diffraction surface 25a of the diffraction grating 25 in parallel with the direction perpendicular to the low step portion 21b, and is orthogonal to the diffraction groove 25b reflected by the fixed mirror 24. In addition, the parallel light incident on the diffractive surface 25a at an incident angle α is diffracted in a direction corresponding to the wavelength by the diffraction groove 25b. In addition, although it demonstrates on the basis of the upper surface of the base 21 regarding the direction of an optical axis or each member, the position of each part is prescribed | regulated relatively and is not limited to arrangement | positioning of this embodiment.

回折格子２５で回折された光は回動ミラー３０に入射される。回動ミラー３０は、固定ミラー２４から入射される平行光に対して回折格子２５が出射する回折光を、垂直に入力された波長成分の光を逆光路で回折格子２５の回折面２５ａへ反射して半導体レーザ２２へ戻すための反射面３２ａを有している。 The light diffracted by the diffraction grating 25 enters the rotating mirror 30. The rotating mirror 30 reflects the diffracted light emitted from the diffraction grating 25 with respect to the parallel light incident from the fixed mirror 24, and the light of the wavelength component input vertically to the diffraction surface 25a of the diffraction grating 25 through the reverse optical path. Thus, a reflecting surface 32 a for returning to the semiconductor laser 22 is provided.

この回折格子２５の回折面２５ａに対する反射面３２ａの角度を所定角度範囲で周期的に変化させることで、回動ミラー３０の反射面３２ａにより半導体レーザ２２に逆光路で戻される光の波長が連続的に且つ周期的に変化し、これによって波長掃引光源２０から出射される光の波長も連続的に且つ周期的に変化する。 By periodically changing the angle of the reflecting surface 32a with respect to the diffractive surface 25a of the diffraction grating 25 within a predetermined angle range, the wavelength of light returned to the semiconductor laser 22 by the reflecting surface 32a of the rotating mirror 30 in the reverse optical path is continuous. Change periodically and periodically, whereby the wavelength of the light emitted from the wavelength sweep light source 20 also changes continuously and periodically.

この回動ミラー３０は、図１〜図３に示しているように、導電性を有する基板（例えばシリコン基板）に対するエッチング処理等によって形成され、例えば図示しているように上板３１ａ、下板３１ｂ、横板３１ｃ、３１ｄで横長矩形枠状に形成されたフレーム３１と、フレーム３１の内側に同心状に配置され、少なくとも一面側に光を反射するための反射面３２ａが形成された横長矩形の反射板３２と、フレーム３１の上板３１ａ、下板３１ｂの互いに対向する内縁中央から反射板３２の上縁中央および下縁中央まで上下に一直線上に並ぶようにそれぞれ延びてフレーム３１の上板３１ａ、下板３１ｂと反射板３２との間を連結し、捩れ変形して反射板３２を回動させる一対の連結部３３、３４とを有している。 As shown in FIGS. 1 to 3, the rotating mirror 30 is formed by etching or the like on a conductive substrate (for example, a silicon substrate). For example, the upper plate 31a and the lower plate are illustrated. A frame 31 formed in a horizontally long rectangular frame shape by 31b and horizontal plates 31c and 31d, and a horizontally long rectangle formed concentrically on the inner side of the frame 31 and having a reflecting surface 32a for reflecting light on at least one surface side The upper plate 31a and the lower plate 31b of the frame 31 extend from the center of the inner edge facing each other to the center of the upper and lower edges of the reflector 32 so as to be aligned in a straight line. The plate 31a, the lower plate 31b, and the reflecting plate 32 are connected to each other, and a pair of connecting portions 33 and 34 for rotating the reflecting plate 32 by twisting deformation are provided.

反射板３２の反射面３２ａとしては、例えば素材表面に対する鏡面仕上げ、高い反射率を示す金属膜の蒸着、あるいは誘電体多層膜で形成することができる。また、回動ミラー３０がレーザ光に対して高い反射率を示す材質である場合には、反射膜や反射シートを設けなくても、その素材表面を反射面とすることができる。 The reflecting surface 32a of the reflecting plate 32 can be formed of, for example, a mirror finish on the material surface, vapor deposition of a metal film exhibiting high reflectivity, or a dielectric multilayer film. Further, when the rotating mirror 30 is made of a material exhibiting a high reflectance with respect to the laser light, the surface of the material can be used as a reflecting surface without providing a reflecting film or a reflecting sheet.

ただし、回動ミラー３０が導電性を持たない場合には、後述する静電駆動力確保のため、ミラー材として導電性の金属膜を蒸着する必要がある。 However, when the rotating mirror 30 does not have conductivity, it is necessary to deposit a conductive metal film as a mirror material in order to secure an electrostatic driving force described later.

連結部３３、３４の幅および長さは、連結部３３、３４自体がその長方向に沿って捩じれ変形でき、その変形に対して自ら元の状態に戻るための復帰力を生じるように設定されている。 The widths and lengths of the connecting portions 33 and 34 are set so that the connecting portions 33 and 34 themselves can be twisted and deformed along the longitudinal direction, and a restoring force is generated to return to the original state by the deformation. ing.

また、この回動ミラー３０のフレーム３１の横板３１ｃ、３１ｄの一方（ここでは横板３１ｃ）の両面には、反射板３２に静電的に外力を与えるための電極板３５、３６がそれぞれ絶縁性を有するスペーサ３７を介して取り付けられている。電極板３５、３６は、反射板３２の一端側（ここでは左端側）の両面にスペーサ３７の厚み分の隙間を開けた状態でオーバラップしている。なお、ここではスペーサ３７を縦長矩形状にしているが、フレーム３１全体の補強のために、スペーサ３７をフレーム３１と重なり合う矩形枠状に形成してもよい。 In addition, on both surfaces of one of the horizontal plates 31c and 31d (here, the horizontal plate 31c) of the frame 31 of the rotating mirror 30, electrode plates 35 and 36 for applying external force to the reflecting plate 32 are provided. It is attached via an insulating spacer 37. The electrode plates 35 and 36 are overlapped with a gap corresponding to the thickness of the spacer 37 formed on both surfaces of one end side (here, the left end side) of the reflection plate 32. Here, the spacer 37 has a vertically long rectangular shape, but the spacer 37 may be formed in a rectangular frame shape that overlaps the frame 31 in order to reinforce the entire frame 31.

この回動ミラー３０は、反射板３２の回動中心（連結部３３、３４の中心を結ぶ線）が、回折格子２５の回折面２５ａを延長した面上で且つ回折溝２５ｂと平行となる状態で、基台２１上に固定されている。 In the rotating mirror 30, the rotation center of the reflecting plate 32 (the line connecting the centers of the coupling portions 33 and 34) is in a state where the diffraction surface 25a of the diffraction grating 25 is extended and parallel to the diffraction groove 25b. Thus, it is fixed on the base 21.

なお、回動ミラー３０は、電極板３５、３６およびスペーサ３７を含めて前記したようにシリコン基板のエッチング処理等で形成されるが、その製造方法は任意である。 The rotating mirror 30 includes the electrode plates 35 and 36 and the spacers 37 and is formed by etching the silicon substrate as described above, but the manufacturing method is arbitrary.

例えば、単層基板で回動ミラー３０のフレーム３１、反射板３２および連結部３３、３４をエッチング形成し、別の基板でスペーサ３７、３７と、電極板３５、３６を形成して、これらを貼り合わせて構成する方法、あるいは、ＳＯＩ基板等の３層基板を用い、その上層基板に、回動ミラー３０のフレーム３１、反射板３２、連結部３３、３４をエッチング形成し、その下層基板にスペーサ３７をエッチング形成し、別の工程で製造された電極板３５を貼付けて一方の電極を形成する等、種々の方法で製造可能である。 For example, the frame 31, the reflecting plate 32, and the connecting portions 33 and 34 of the rotating mirror 30 are formed by etching with a single layer substrate, and the spacers 37 and 37 and the electrode plates 35 and 36 are formed with another substrate. A method of bonding and using a three-layer substrate such as an SOI substrate, the frame 31, the reflector 32, and the connecting portions 33 and 34 of the rotating mirror 30 are etched on the upper substrate, and the lower substrate is formed on the lower substrate. It can be manufactured by various methods such as etching the spacer 37 and attaching the electrode plate 35 manufactured in another process to form one electrode.

図１に示しているミラー駆動装置４０は、図２のように、回動ミラー３０のフレーム３１を基準電位として２つの電極板３５、３６に対して例えば図４の（ａ）、（ｂ）のように位相が１８０度ずれた信号Ｖ１、Ｖ２を印加して、電極板３５、３６と反射板３２の端部との間に静電的な吸引力を交互に生じさせ、反射板３２を往復回動させる。 As shown in FIG. 2, the mirror driving device 40 shown in FIG. 1 has, for example, (a) and (b) in FIG. 4 with respect to two electrode plates 35 and 36 with the frame 31 of the rotating mirror 30 as a reference potential. The signals V1 and V2 that are 180 degrees out of phase as shown in FIG. 6 are applied to alternately generate an electrostatic attractive force between the electrode plates 35 and 36 and the end of the reflecting plate 32. Turn back and forth.

この信号Ｖ１、Ｖ２の周波数は、回動ミラー３０の反射板３２の形状、重さおよび連結部３３、３４の捩れバネ定数等によって決まる反射板３２の固有振動数に等しくなるように設定されているので、少ない駆動電力で反射板３２を大きな角度で往復回動させることができる。 The frequency of the signals V1 and V2 is set to be equal to the natural frequency of the reflector 32 determined by the shape and weight of the reflector 32 of the rotating mirror 30 and the torsion spring constant of the coupling portions 33 and 34. Therefore, the reflecting plate 32 can be reciprocated at a large angle with a small driving power.

この反射板３２の往復回動により、外部共振器の共振器長および回折面２５ａに対する反射面３２ａの角度が変化して、半導体レーザ２２から出射されるレーザ光の波長が図４の（ｃ）のように、連続的に且つ周期的に変化する。 The reciprocating rotation of the reflecting plate 32 changes the resonator length of the external resonator and the angle of the reflecting surface 32a with respect to the diffractive surface 25a, and the wavelength of the laser light emitted from the semiconductor laser 22 is as shown in FIG. It changes continuously and periodically.

ただし、この波長掃引光源２０のように、一面側に反射面３２ａが形成されている反射板３２自体を回動させるという単純化された構造の場合、その回動中心は、連結部３３、３４の中心を結ぶ線上、即ち、反射板３２の内部にあって反射面３２ａを延長した面上にはなく、前記した従来のリトマン方式の条件を満たさない。 However, in the case of a simplified structure in which the reflecting plate 32 itself having the reflecting surface 32a formed on one surface side is rotated like the wavelength swept light source 20, the rotation center is the connecting portions 33, 34. Is not on the line connecting the centers of the two, i.e., on the inside of the reflecting plate 32 and extending the reflecting surface 32a, and does not satisfy the conditions of the conventional Litman method.

そこで、この実施形態の波長掃引光源２０では、次の特許文献３に開示された技術を適用して波長を連続的に可変している。 Therefore, in the wavelength swept light source 20 of this embodiment, the wavelength is continuously varied by applying the technique disclosed in the following Patent Document 3.

特許第３０６９６４３号公報Japanese Patent No. 3069643

即ち、上記特許文献３は、図５の点線で示すように固定ミラー２４を用いずにレーザ光が反射板３２を透過するとした仮想的な配置において、回折格子２５の回折面２５ａを延長した平面をＨ１、半導体レーザ２２の内部の屈折率を考慮した実効共振端面２２ａを延長した平面をＨ２、反射板３２の反射面３２ａを延長した平面をＨ３とし、反射面３２ａの回動中心と回折格子との間の位置で平面Ｈ１と平面Ｈ３とが交わる場合、回動中心Ｏから回折格子２５の所定入射位置Ｇまでの距離をｒ、所定入射位置Ｇから半導体レーザ２２の実効共振端面２２ａまでの実効光路長をＬ１、回動中心Ｏから平面Ｈ３までの距離をＬ２、回折格子２５に対する光の入射角αとすると、
ｒ＝（Ｌ１−Ｌ２）／sin α
が成り立つようにすることで、モードホップを発生することなく、波長を連続的に可変できるというものである。 That is, in Patent Document 3, a plane in which the diffraction surface 25a of the diffraction grating 25 is extended in a virtual arrangement in which laser light is transmitted through the reflection plate 32 without using the fixed mirror 24 as indicated by the dotted line in FIG. H1 is a plane obtained by extending the effective resonance end face 22a in consideration of the refractive index inside the semiconductor laser 22, and H3 is a plane obtained by extending the reflection surface 32a of the reflection plate 32. The rotation center of the reflection surface 32a and the diffraction grating When the plane H1 and the plane H3 intersect with each other, the distance from the rotation center O to the predetermined incident position G of the diffraction grating 25 is r, and the distance from the predetermined incident position G to the effective resonance end face 22a of the semiconductor laser 22 is When the effective optical path length is L1, the distance from the rotation center O to the plane H3 is L2, and the incident angle α of light with respect to the diffraction grating 25,
r = (L1-L2) / sin α
Thus, the wavelength can be continuously varied without generating a mode hop.

ただし、この実施形態のように半導体レーザ２２から回折格子２５に至る光路を固定ミラー２４を介して折り曲げた場合、所定入射位置点Ｇから半導体レーザ２２の実効共振端面２２ａまでの実効光路長Ｌ１は、半導体レーザ２２の実効共振端面２２ａと固定ミラー２４までの光路長Ｌ３と、固定ミラー２４から所定入射位置Ｇまでの光路長Ｌ４との和で表される（Ｌ１＝Ｌ３＋Ｌ４）。 However, when the optical path from the semiconductor laser 22 to the diffraction grating 25 is bent via the fixed mirror 24 as in this embodiment, the effective optical path length L1 from the predetermined incident position point G to the effective resonance end face 22a of the semiconductor laser 22 is The optical path length L3 from the effective resonance end face 22a of the semiconductor laser 22 to the fixed mirror 24 and the optical path length L4 from the fixed mirror 24 to the predetermined incident position G are expressed as L1 = L3 + L4.

よって、次の式が成り立つように各部を配置することで、図４の（ｃ）に示しているように、モードホップのない連続波長掃引が可能となる。 Therefore, by arranging each part so that the following equation is established, continuous wavelength sweep without mode hopping is possible as shown in FIG.

ｒ＝（Ｌ３＋Ｌ４−Ｌ２）／sin α r = (L3 + L4-L2) / sin α

また、固定ミラー２４を介して回折格子２５に光を入射して、半導体レーザ２２、コリメートレンズ２３、固定ミラー２４および回折格子２５を反射板３２の一面側に配置させ、反射板３２と光路とを交差させない構造であるので、反射板３２自体に光通過用の穴などを設ける必要がなく、その剛性低下による変形が起こらず、薄い板でも安定で再現性の高い高速な波長掃引が行える。 Further, light is incident on the diffraction grating 25 through the fixed mirror 24, and the semiconductor laser 22, the collimating lens 23, the fixed mirror 24, and the diffraction grating 25 are arranged on one surface side of the reflection plate 32, and the reflection plate 32 and the optical path are arranged. Therefore, it is not necessary to provide a hole for passing light through the reflecting plate 32, and deformation due to a decrease in rigidity does not occur, and even a thin plate can perform high-speed wavelength sweeping that is stable and highly reproducible.

このように実施形態の波長掃引光源２０では、反射板３２の反射面３２ａを延長した平面と回折面２５ａを回動中心方向に延長した面ではさまれた空間内で、且つ回動中心と回折面２５ａの所定入射位置との間に固定ミラー２４を配置し、回動ミラー３０の反射板３２の反射面３２ａを延長した面で区切られてなる２つの空間のうち、回折格子２５が含まれる方の空間に半導体レーザ２２とコリメートレンズ２３を配置し、その半導体レーザ２２からコリメートレンズ２３を介して固定ミラー２４に光を入射し、その反射光を回折格子２５の回折面２５ａの所定入射位置に入射している。 As described above, in the wavelength swept light source 20 of the embodiment, the reflection plate 32 is extended in the space between the plane extending the reflection surface 32a and the plane extending the diffraction surface 25a in the direction of the rotation center, and the rotation center and diffraction. The fixed mirror 24 is arranged between the surface 25a and a predetermined incident position, and the diffraction grating 25 is included in two spaces separated by a surface obtained by extending the reflecting surface 32a of the reflecting plate 32 of the rotating mirror 30. A semiconductor laser 22 and a collimator lens 23 are arranged in the opposite space, light enters the fixed mirror 24 from the semiconductor laser 22 via the collimator lens 23, and the reflected light is incident on a predetermined incident position of the diffraction surface 25a of the diffraction grating 25. Is incident.

このため、光路とは無関係に、反射面３２ａを有する反射板３２自体を往復回動させるという極めて単純な構造で回動ミラーを構成することができ、高速で精度の高い波長可変が行える。 Therefore, regardless of the optical path, the rotating mirror can be configured with a very simple structure in which the reflecting plate 32 itself having the reflecting surface 32a is reciprocally rotated, and the wavelength can be tuned at high speed and with high accuracy.

ただし、前記したように、ＭＥＭＳ構造の回動ミラー３０を用いた波長掃引光源２０であっても、各部の組み立て精度が悪い場合や、温度変化による光部品の光軸ずれなどの原因によりモードホップが発生してしまう。 However, as described above, even in the case of the wavelength swept light source 20 using the rotating mirror 30 having the MEMS structure, the mode hop is caused by the reason that the assembly accuracy of each part is bad or the optical axis shift of the optical component due to the temperature change. Will occur.

また、出力光のパワーを変化させるために半導体レーザの注入電流や温度を調整すると、必然的にモードホップが生じてしまうという問題もあった。 Further, when the injection current and temperature of the semiconductor laser are adjusted in order to change the power of the output light, there is a problem that mode hops inevitably occur.

そこで、この実施形態では、図１、図２に示しているように、回折格子２５への入射光に対してその入射角αと対称な方向に出射される０次回折光を受けてその光の強度に応じた大きさの電気の信号を出力する受光器６０を高段部２１ａ′上に固定しており、制御部１００内には、前記したミラー駆動装置４０の他に、モードホップ検出手段６１と注入電流制御手段６５が設けられている。 Therefore, in this embodiment, as shown in FIGS. 1 and 2, the zero-order diffracted light emitted in a direction symmetrical to the incident angle α with respect to the light incident on the diffraction grating 25 is received and the light A light receiver 60 that outputs an electrical signal having a magnitude corresponding to the intensity is fixed on the high stage portion 21a '. In addition to the mirror driving device 40 described above, mode hop detection means is included in the control unit 100. 61 and injection current control means 65 are provided.

なお、この実施形態では、光源としての出力光である波長掃引光を半導体レーザ２２の他端面側（コリメートレンズ２３に対向する端面と反対側の面）から出射することを考慮して回折格子２５の０次回折光を受光器６０で受けているが、この０次回折光の代わりに半導体レーザ２２の他端面から出射される光を受光器６０で受け、０次回折光を光源としての出力光である波長掃引光として出射する場合もある。 In this embodiment, the diffraction grating 25 is considered in consideration that the wavelength swept light, which is output light as a light source, is emitted from the other end surface side of the semiconductor laser 22 (surface opposite to the end surface facing the collimator lens 23). The 0th-order diffracted light is received by the light receiver 60, but instead of the 0th-order diffracted light, the light emitted from the other end surface of the semiconductor laser 22 is received by the light receiver 60, and the 0th-order diffracted light is output light as a light source. In some cases, it is emitted as a wavelength-swept light.

モードホップ検出手段６１は、回動ミラー３０の反射板３２の往復回動により半導体レーザ２２の出射光波長が掃引されている間、受光器６０の出力を監視し、モードホップによって生じる受光器６０の出力信号の不連続変化を検出する。 The mode hop detection means 61 monitors the output of the light receiver 60 while the wavelength of the emitted light of the semiconductor laser 22 is swept by the reciprocating rotation of the reflecting plate 32 of the rotating mirror 30, and the light receiver 60 generated by the mode hop. Detects discontinuous changes in the output signal.

ここで、例えば光波長が１５００ｎｍから１６００ｎｍの間で掃引される場合を考える。モードホップが生じていない場合、受光器６０で検出される回折格子２５からの０次光のパワーＰの波長依存性（掃引時の経時変化）は図６の（ａ）のように、連続で滑らかになり、受光器６０の出力信号の時間に対する微分の絶対値｜dP/dt｜も緩やかな変化となる。ここで、波長掃引時に光のパワーＰが変化しているのは、各光部品の特性に波長依存性があるためである。 Here, for example, consider a case where the light wavelength is swept between 1500 nm and 1600 nm. When no mode hop occurs, the wavelength dependence of the power P of the zero-order light from the diffraction grating 25 detected by the light receiver 60 (change over time at the time of sweep) is continuous as shown in FIG. As a result, the absolute value | dP / dt | of the derivative with respect to time of the output signal of the light receiver 60 also changes gradually. Here, the power P of the light changes during the wavelength sweep because the characteristics of each optical component have wavelength dependency.

これに対して、例えば波長λhpにてモードホップが生じた場合、同パワーＰの波長依存性は図６（ｂ）のように波長λhpにおいて不連続に変化し、受光器６０の出力信号そのものの急激な変化｜ΔＰ｜もしくはその時間に対する微分の絶対値｜dP/dt｜は急峻に且つ大きな値に変化する。ただし、いずれの例においても、光源の温度は一定とする。 On the other hand, for example, when a mode hop occurs at the wavelength λhp, the wavelength dependency of the power P changes discontinuously at the wavelength λhp as shown in FIG. The abrupt change | ΔP | or the absolute value | dP / dt | of the derivative with respect to the time changes sharply and to a large value. However, in any example, the temperature of the light source is constant.

したがって、受光器６０の出力信号そのものの急激な変化｜ΔＰ｜もしくはその時間に対する微分の絶対値｜dP/dt｜を計算すれば、モードホップの有無が判る。 Therefore, the presence or absence of a mode hop can be determined by calculating the abrupt change | ΔP | of the output signal itself of the light receiver 60 or the absolute value | dP / dt |

前記したモードホップ検出手段６１は受光器６０の出力信号に対して上記演算を行い、得られた｜ΔＰ｜もしくは｜dP/dt｜の値と予め設定したそれぞれのしきい値との比較によりモードホップの発生の有無と、その発生タイミングを検出する。この発生タイミングは、掃引のための駆動信号の立ち上がりや立ち下がり等を基準として計測する。 The mode hop detection means 61 performs the above calculation on the output signal of the light receiver 60, and compares the obtained | ΔP | or | dP / dt | with the respective threshold values set in advance. The presence / absence of a hop and its occurrence timing are detected. This generation timing is measured with reference to the rise and fall of the drive signal for sweeping.

ここで、モードホップの発生原理について簡単に説明する。モードホップが生じないときは、図７の（ａ）のように、半導体レーザ２２で発振しうる縦モードのうち特定の１つの縦モード（実線）の波長変化に対して、外部共振器による選択特性Ｆの中心波長が追従変化することで、その特定の縦モードが選択され続けている。 Here, the principle of mode hop generation will be briefly described. When the mode hop does not occur, as shown in FIG. 7A, the external resonator selects the wavelength change of one specific longitudinal mode (solid line) among the longitudinal modes that can be oscillated by the semiconductor laser 22. As the center wavelength of the characteristic F changes, the specific longitudinal mode continues to be selected.

これに対して、モードホップが生じるときは、縦モードと外部共振器による選択特性Ｆの中心波長がずれてしまい、図７の（ｂ）のように、ある波長λｈｐにおいて、選択特性Ｆによって選択される縦モードが所望のもの（実線）から１つ隣のモード（破線）に飛んでしまう。 On the other hand, when a mode hop occurs, the center wavelength of the selection characteristic F by the longitudinal mode and the external resonator is shifted, and the selection characteristic F is selected at a certain wavelength λhp as shown in FIG. The vertical mode is jumped from the desired mode (solid line) to the next mode (dashed line).

ここで、半導体レーザ２２への注入電流を変化させると、縦モードの発振波長を連続的に変化させることができ、共振器の選択特性Ｆの中心波長から大きく外れないように縦モードの発振波長を変化させることで隣の縦モードへの飛び、即ちモードホップを抑制できる。 Here, if the injection current to the semiconductor laser 22 is changed, the oscillation wavelength of the longitudinal mode can be continuously changed, and the oscillation wavelength of the longitudinal mode is not greatly deviated from the center wavelength of the selection characteristic F of the resonator. By changing, it is possible to suppress jumping to the adjacent vertical mode, that is, mode hopping.

ただし、モードホップが高い再現性を持って同一波長で生じる状況下でなければ、この注入電流による制御は行えないが、本発明では、前記したように回動ミラー３０が安定な動作をしているので、半導体レーザ２２に対する注入電流の調整あるいは可変制御により、図６の（ａ）に示したように出力光パワーに飛びのないのない、モードホップフリーの波長掃引を容易に実現することができる。 However, the control by the injection current cannot be performed unless the mode hops are generated at the same wavelength with high reproducibility. However, in the present invention, the rotating mirror 30 operates stably as described above. Therefore, by adjusting or variably controlling the injection current to the semiconductor laser 22, it is possible to easily realize a mode hop-free wavelength sweep without a jump in the output optical power as shown in FIG. it can.

ここで、半導体レーザ２２に対する注入電流の制御としては、前の波長掃引でモードホップが検出された場合に、注入電流を所定量変化させて、次の波長掃引を行いモードホップを検出するという処理を繰り返し、モードホップが発生しない一定の注入電流を見付ける半固定制御モードと、波長掃引でモードホップが検出された場合、そのモードホップ発生タイミングにおける注入電流がモードホップを抑制する電流となるように変化させる掃引中に変化させるダイナミック制御とが考えられる。 Here, as control of the injection current for the semiconductor laser 22, when a mode hop is detected in the previous wavelength sweep, the injection current is changed by a predetermined amount, and the next wavelength sweep is performed to detect the mode hop. When the mode hop is detected by the wavelength sweep and the semi-fixed control mode that finds a constant injection current that does not generate a mode hop, the injection current at the mode hop generation timing becomes a current that suppresses the mode hop. A dynamic control that is changed during a changing sweep can be considered.

ダイナミック制御の場合、注入電流の変化パターンは任意であるが、例えば図８の注入電流ａのように、モードホップ発生タイミングｔ１、ｔ２の少し手前のタイミング毎に段階的に変化するパターンや、注入電流ｂのように、傾きをもつ直線（あるいは曲線的）で連続的に変化するパターンでもよい。 In the case of dynamic control, the change pattern of the injection current is arbitrary, but for example, a pattern that changes step by step at timings slightly before the mode hop generation timings t1 and t2, such as injection current a in FIG. A pattern that continuously changes in a straight line (or curvilinear) having a slope like the current b may be used.

また、一つの制御例としては、始めに半固定制御モードによりモードホップが発生しない一定の注入電流を見付ける処理を行い、その処理で全てのモードホップが無くなった場合には処理を終了し、この処理でモードホップが完全になくならない場合に、最もモードホップ発生が少なくなる注入電流に設定してから、ダイナミック制御モードによりモードホップ毎に注入電流を変化させてその発生を抑制する。このような制御により、容易にモードホップをなくすことができる。 In addition, as one control example, first, a process for finding a constant injection current in which no mode hops are generated in the semi-fixed control mode is performed, and when all the mode hops are lost in the process, the process is terminated. When the mode hops are not completely eliminated by the processing, the injection current is set so as to minimize the generation of the mode hops, and then the injection current is changed for each mode hop by the dynamic control mode to suppress the generation. By such control, mode hops can be easily eliminated.

なお、前述のようにこの実施形態の回動ミラー３０の回動は安定しているため、掃引波長範囲でモードホップを生じさせない注入電流にある程度の幅があり、その範囲内で注入電流を変化（半固定制御モード）させることで、図９に示すようにモードホップのない状態で光出力の平均値を変化させることができる。 Since the rotation of the rotating mirror 30 of this embodiment is stable as described above, there is a certain range in the injection current that does not cause mode hops in the sweep wavelength range, and the injection current is changed within the range. By performing (semi-fixed control mode), the average value of the light output can be changed without a mode hop as shown in FIG.

さらに、また、このモードホップフリーの範囲を積極的に利用し、ダイナミック制御モードを用い、図１０に示すように、制御前の元の出力が所望値より大きい波長範囲では元の出力と所望値との差分に応じて注入電流を減らし、元の出力が所望値より小さい波長範囲では元の出力と所望値との差分に応じて注入電流を増加させ、掃引波長範囲における光出力をほぼ一定（波長対出力の平坦化）にすることが可能となる。 Further, the mode hop-free range is actively used, and the dynamic control mode is used. As shown in FIG. 10, the original output and the desired value are in a wavelength range where the original output before control is larger than the desired value. The injection current is reduced according to the difference between the original output, and in the wavelength range where the original output is smaller than the desired value, the injection current is increased according to the difference between the original output and the desired value, and the optical output in the sweep wavelength range is substantially constant ( Wavelength vs. output flattening).

また、図９のように半導体レーザ２２への注入電流の調整だけでは、モードホップなしのまま出力を変化させることのできる範囲は限定されるが、半導体レーザ２２の温度を変化させる（一般的にその温度を下げると光出力は増大する）ことでより広い出力範囲においてモードホップなしの波長掃引を実現できる。 Further, as shown in FIG. 9, the range in which the output can be changed without any mode hops is limited only by adjusting the injection current to the semiconductor laser 22, but the temperature of the semiconductor laser 22 is changed (generally). When the temperature is lowered, the light output increases), and a wavelength sweep without a mode hop can be realized in a wider output range.

そのために、この実施形態の波長掃引光源２０では、図１、図２に示しているように半導体レーザ２２の外周部に半導体レーザ２２の温度を検出するための温度センサ７０を設けるとともに、基板２１の下面側にペルチェ素子７１を設け、温度制御手段７５が、温度センサ７０の出力と受光器６０の出力とに基づいてペルチェ素子７１への供給電流を制御し、ペルチェ素子７１による加熱・冷却作用により半導体レーザ２２の温度を変化させ、半導体レーザ２２の出射光の波長掃引範囲における平均出力が所望値（外部から指定されたパワー）となるようにしている。そして、温度の可変制御により波長掃引光の平均出力が変更される場合には、モードホップが発生することが考えられるが、平均出力を決めて温度を固定してしまえば、モードホップの発生は、前記同様に注入電流の制御により、抑制（消失）させることができ、所望出力でモードホップのない波長掃引が可能となる。 Therefore, in the wavelength swept light source 20 of this embodiment, as shown in FIGS. 1 and 2, a temperature sensor 70 for detecting the temperature of the semiconductor laser 22 is provided on the outer periphery of the semiconductor laser 22, and the substrate 21. A Peltier element 71 is provided on the lower surface side of the Peltier element, and the temperature control means 75 controls the supply current to the Peltier element 71 based on the output of the temperature sensor 70 and the output of the light receiver 60, and the heating / cooling action by the Peltier element 71 Thus, the temperature of the semiconductor laser 22 is changed so that the average output in the wavelength sweep range of the emitted light of the semiconductor laser 22 becomes a desired value (power designated from the outside). And when the average output of the swept wavelength light is changed by variable temperature control, mode hops may occur, but if the average output is fixed and the temperature is fixed, the mode hops will be generated. In the same manner as described above, the injection current can be suppressed (disappeared) by controlling the injection current, and a wavelength sweep without a mode hop with a desired output becomes possible.

なお、モードホップが発生している期間は、外部に文字やランプあるいは音などによってこれを報知する手段を設けてもよい。 It should be noted that means for notifying the outside by letters, lamps or sounds may be provided during the period when the mode hop is occurring.

また、ここでは温度センサ７０が半導体レーザ２２の温度を検出しているが、ケース８０内の温度を検出する温度センサおよびその温度を可変できるペルチェ素子等を別途設けて、光源内部の平均的な温度を安定化（恒温槽化）して、外部の温度変化の影響を受けにくくし、半導体レーザ２２の温度を単独に可変制御できる構成としてもよい。 Here, the temperature sensor 70 detects the temperature of the semiconductor laser 22. However, a temperature sensor for detecting the temperature in the case 80 and a Peltier element that can change the temperature are separately provided, so that the average inside the light source can be obtained. It may be configured such that the temperature is stabilized (constant temperature chamber) so that it is not easily affected by external temperature changes, and the temperature of the semiconductor laser 22 can be variably controlled independently.

このように簡単な制御方法を用いるだけでモードホップを抑制できるのは、ＭＥＭＳ構造の回動ミラー３０による波長掃引方式が非常に安定しているためである。たとえモードホップが起きたとしても極めて再現性がよいため、これを注入電流の制御により抑制することはたやすく、モードホップなしの状態での高速な波長掃引を容易に実現できる。 The reason why the mode hop can be suppressed only by using such a simple control method is that the wavelength sweeping method using the rotating mirror 30 having the MEMS structure is very stable. Even if a mode hop occurs, the reproducibility is very good. Therefore, it is easy to suppress this by controlling the injection current, and a high-speed wavelength sweep without a mode hop can be easily realized.

上記実施形態では、反射板３２を連結部３３、３４に対して左右対称に形成し、その一端側を光反射部として用い、他端側で外力を受けるようにしていたが、反射板の形状、外力の付与形態は、上記実施形態に限定されるものではない。 In the above embodiment, the reflecting plate 32 is formed symmetrically with respect to the connecting portions 33 and 34, and one end side thereof is used as a light reflecting portion, and an external force is received at the other end side. The form of external force application is not limited to the above embodiment.

例えば、図１１に示す回動ミラー３０の反射板３２のように、外力を受けるための他端側の横方向の長さを一端側より短くし、その幅（縦方向の長さ）を広くして、左右の回転モーメントをつりあわせてもよい。この場合、回動ミラー３０全体の横幅を小さくすることができる。 For example, like the reflecting plate 32 of the rotating mirror 30 shown in FIG. 11, the lateral length on the other end side for receiving external force is made shorter than the one end side, and the width (length in the vertical direction) is widened. Thus, the left and right rotational moments may be balanced. In this case, the horizontal width of the entire rotating mirror 30 can be reduced.

また、上記実施形態では、反射板３２の一端側に外力を周期的に与えて往復回動させる場合について説明したが、外力を付与する位置は任意であり、例えば、図１２のように、反射板３２の背面側の両端に電極板３５、３６を配置し、前記信号Ｖ１、Ｖ２をそれぞれ印加することで、前記同様に反射板３２を往復回動できる。 Moreover, although the said embodiment demonstrated the case where an external force was periodically given to the one end side of the reflecting plate 32, and the reciprocating rotation was carried out, the position which provides an external force is arbitrary, for example, as shown in FIG. By arranging the electrode plates 35 and 36 at both ends on the back side of the plate 32 and applying the signals V1 and V2, respectively, the reflection plate 32 can be reciprocally rotated as described above.

また、電極板３５、３６の形状などについても任意であり、前記実施例のような平板状のもの以外に、櫛歯状のものを用いてもよい。 The shape of the electrode plates 35 and 36 is also arbitrary, and a comb-like shape may be used in addition to the flat shape as in the above embodiment.

また、外力として前記した静電的な力以外に、電磁石（またはコイル）と磁性板の組合せ、永久磁石と電磁石（またはコイル）の組合せ等により、電磁的に外力を与えることも可能であり、さらには、超音波振動器により、反射板３２の固有振動数に等しい周波数の超音波振動を基台２１に与えて、反射板３２を固有振動数で往復回動させることもできる。なお、このように静電的以外の外力を与える場合、回動ミラー３０の材料が導電性を有している必要はない。 In addition to the electrostatic force described above as an external force, an external force can be applied electromagnetically by a combination of an electromagnet (or coil) and a magnetic plate, a combination of a permanent magnet and an electromagnet (or coil), etc. Furthermore, the ultrasonic vibrator having a frequency equal to the natural frequency of the reflecting plate 32 can be applied to the base 21 and the reflecting plate 32 can be rotated back and forth at the natural frequency. In addition, when giving external force other than electrostatic in this way, the material of the rotation mirror 30 does not need to have electroconductivity.

また、上記実施形態では、固定ミラー２４の反射面２４ａが回折格子２５の回折溝２５ｂと平行で、半導体レーザ２２から、コリメートレンズ２３、固定ミラー２４、回折格子２５を経て反射板３２に至る光路が同一平面上となるように構成されていたが、これは本発明を限定するものではなく、半導体レーザ２２とコリメートレンズ２３は、反射板３２の反射面３２ａを延長した平面で隔成される２つの空間のうち回折格子２５が含まれる方の空間であれば任意の位置に配置することができ、その位置に合わせて固定ミラー２４の反射面２４ａの向きを設定すればよい。 In the above embodiment, the reflecting surface 24 a of the fixed mirror 24 is parallel to the diffraction groove 25 b of the diffraction grating 25, and the optical path from the semiconductor laser 22 to the reflection plate 32 through the collimator lens 23, the fixed mirror 24, and the diffraction grating 25. However, this does not limit the present invention, and the semiconductor laser 22 and the collimating lens 23 are separated by a plane obtained by extending the reflecting surface 32a of the reflecting plate 32. Any one of the two spaces including the diffraction grating 25 can be arranged at any position, and the direction of the reflecting surface 24a of the fixed mirror 24 may be set in accordance with the position.

例えば、図１３のように、半導体レーザ２２とコリメートレンズ２３を、その光軸が回折格子２５の回折溝２５ａと平行となるよう基台２１に対して上下に並ぶように配置し、コリメートレンズ２３からの光を、基台２１の上面に対して４５度の角度をなす反射面２４ａの固定ミラー２４で受けて、回折格子２５の回折面２５ａに入射してもよい。なお、半導体レーザ２２、コリメートレンズ２３および固定ミラー２４は支持部材４１に支持されている。 For example, as shown in FIG. 13, the semiconductor laser 22 and the collimating lens 23 are arranged so as to be aligned vertically with respect to the base 21 so that the optical axis thereof is parallel to the diffraction grooves 25 a of the diffraction grating 25. May be received by the fixed mirror 24 of the reflecting surface 24 a that forms an angle of 45 degrees with respect to the upper surface of the base 21 and may enter the diffraction surface 25 a of the diffraction grating 25. The semiconductor laser 22, the collimating lens 23, and the fixed mirror 24 are supported by the support member 41.

また、上記実施形態では、各部の配置を理解しやすいように、基台２１上に、回折格子２５と回動ミラー３０を立てた構造で示しているが、半導体レーザ２２、コリメートレンズ２３、固定ミラー２４を含め、これら各部の支持形態は任意である。 Moreover, in the said embodiment, although it has shown with the structure which stood the diffraction grating 25 and the rotation mirror 30 on the base 21, so that arrangement | positioning of each part can be understood easily, the semiconductor laser 22, the collimating lens 23, fixed The support form of each part including the mirror 24 is arbitrary.

例えば、図１４のように、平坦な基台５０の上部両端に立設した支持部材５１、５２で回動ミラー３０のフレーム３１を支持し、基台５０の上部に立設した支持部材５３で回折格子２５を支持し、さらに、支持部材５３の近傍に立設した支持部材５４で、半導体レーザ２２、コリメートレンズ２３および固定ミラー２４を支持し、受光器６０を支持部材５５で支持する構造でもよい。なお、支持部材５３〜５５は一体化してもよい。 For example, as shown in FIG. 14, the frame 31 of the rotating mirror 30 is supported by support members 51 and 52 erected on both upper ends of the flat base 50, and the support member 53 erected on the upper part of the base 50. A structure in which the diffraction grating 25 is supported, and the semiconductor laser 22, the collimating lens 23, and the fixed mirror 24 are supported by the support member 54 erected in the vicinity of the support member 53, and the light receiver 60 is supported by the support member 55. Good. The support members 53 to 55 may be integrated.

また、図１４の点線で示すように、反射板３２の他端側にも、半導体レーザ２２、コリメートレンズ２３、固定ミラー２４および受光器６０を支持部材５３〜５５で支持して、波長可変光を２系統出射できるように構成することも可能である。この場合、２系統の波長可変範囲を同一にすれば、２チャネルの波長掃引光源が実現でき、また、２系統の波長可変範囲を変えておけば、より広帯域な波長掃引光源を実現できる。 Further, as shown by a dotted line in FIG. 14, the semiconductor laser 22, the collimating lens 23, the fixed mirror 24, and the light receiver 60 are also supported by the support members 53 to 55 on the other end side of the reflector 32, so It is also possible to configure so that two systems can be emitted. In this case, if the two wavelength variable ranges are the same, a two-channel wavelength swept light source can be realized, and if the two wavelength variable ranges are changed, a broader wavelength swept light source can be realized.

また、図示しないが、反射板３２の反対面側にも半導体レーザ２２、コリメートレンズ２３、固定ミラー２４および受光器６０を１組あるいは２組配置して、さらに出射光の系統数を増加させ、多チャネル化、広帯域化されたモードホップのない波長掃引光源を構成することもできる。 Although not shown, one or two sets of the semiconductor laser 22, the collimator lens 23, the fixed mirror 24, and the light receiver 60 are arranged on the opposite side of the reflector 32, and the number of outgoing light systems is further increased. It is also possible to construct a wavelength-swept light source having no multi-channel and broadband mode hops.

上記した波長掃引光源の多チャネル化あるいは広帯域化は、光路が回動ミラー３０に交差しないで構造であって、反射板３２の反射面の一面側に、回折格子２５だけでなく、半導体レーザ２２、コリメートレンズ２３、固定ミラー２４および受光器６０をまとめて配置したことによってもたらされる効果である。 The above-described wavelength swept light source has a multi-channel structure or a broadband structure in which the optical path does not intersect the rotating mirror 30, and the semiconductor laser 22 as well as the diffraction grating 25 is provided on one surface of the reflecting surface of the reflecting plate 32. This is an effect brought about by arranging the collimating lens 23, the fixed mirror 24 and the light receiver 60 together.

２０……波長掃引光源、２１……基台、２２……半導体レーザ、２３……コリメートレンズ、２４……固定ミラー、２５……回折格子、３０……回動ミラー、３１……フレーム、３２……反射板、３２ａ……反射面、３３、３４……連結部、３５、３６……電極板、３７……スペーサ、４０……ミラー駆動装置、５０……基台、５１〜５５……支持部材、６０……受光器、６１……モードホップ検出手段、６５……注入電流制御手段、７０……温度センサ、７１……ペルチェ素子、７５……温度制御手段、８０……ケース 20... Wavelength swept light source, 21... Base, 22... Semiconductor laser, 23... Collimating lens, 24... Fixed mirror, 25 .. diffraction grating, 30. …… Reflecting plate, 32a …… Reflecting surface, 33, 34 …… Connecting portion, 35, 36 …… Electrode plate, 37 …… Spacer, 40 …… Mirror driving device, 50 …… Base, 51 to 55 …… Support member, 60... Receiver, 61... Mode hop detection means, 65... Injection current control means, 70... Temperature sensor, 71.

Claims

A base (21);
A semiconductor laser (22) fixed on the base, wherein at least one end surface for light emission is a low reflectivity surface, and emits light by injection current;
A collimator lens (23) fixed on the base and converting the light emitted from the low reflectance surface of the semiconductor laser into parallel light;
A predetermined diffraction surface (25b) in which grooves for diffracting light are formed in parallel, and light emitted from the collimating lens is orthogonal to the grooves and non-orthogonal to the diffraction surface A diffraction grating (25) fixed on the base in a state of being incident at a predetermined incident position at an incident angle;
The collimating lens has a reflecting surface facing the diffraction surface of the diffraction grating, and is rotatable in a plane that is parallel to the groove of the diffraction grating and that is orthogonal to the diffraction surface about an axis at a specific position. Of the diffracted light with respect to the light emitted from and incident on the diffraction surface of the diffraction grating, the light along the optical axis perpendicular to the reflection surface is reflected and returned to the diffraction grating by a reverse optical path, and the returned light is incident A rotating mirror (30) for returning to the semiconductor laser via the collimating lens with the same optical axis as the optical path;
A distance r from the rotation center of the rotation mirror to the predetermined incident position of the diffraction grating, a distance L2 from the rotation center to a plane obtained by extending the reflection surface, and the diffraction grating from the effective resonance end surface of the semiconductor laser Between the optical path length L1 to the predetermined incident position and the light incident angle α to the diffraction surface of the diffraction grating,
r = (L1-L2) / sin α
Establishing the relationship
In response to a change in the angle of the reflecting surface of the rotating mirror, the resonator length from the semiconductor laser to the reflecting surface of the rotating mirror via the collimating lens and the diffraction surface of the diffraction grating is changed. In the wavelength sweep light source of the Litman method external resonator type that continuously changes the wavelength of the emitted light within a predetermined range,
The rotating mirror includes a frame (31) fixed to the base, a reflecting plate (32) disposed inside the frame and having the reflecting surface formed on one side thereof, an outer edge of the reflecting plate, and the It is integrally formed with a pair of connecting portions (33, 34) that can be torsionally deformed to connect between the inner edges of the frame and are aligned in a straight line parallel to the grooves of the diffraction grating, and applies a force to the end of the reflecting plate. It has a structure in which the reflection plate is reciprocally rotated around the connecting portion by a rotation driving means (35, 36, 40) that is periodically applied.
further,
Either a light fixed on the base and emitted from an end surface opposite to the one end surface of the semiconductor laser, or a zero-order diffracted light with respect to light incident on the diffraction surface of the diffraction grating from the semiconductor laser A light receiver (60) for receiving and outputting an electrical signal corresponding to the intensity of the received light;
While the output wavelength of the semiconductor laser is swept by the reciprocating rotation of the reflecting plate of the rotating mirror, the output of the light receiver is monitored, and a discontinuous change in the output signal of the light receiver caused by a mode hop is observed. Mode hop detection means (61) for detecting;
Wavelength sweep characterized by comprising injection current control means (65) for changing the injection current of the semiconductor laser so as to eliminate the discontinuous change in the output signal of the light receiver detected by the mode hop detection means. light source.

2. The wavelength swept light source according to claim 1, wherein the injection current control means variably controls the injection current to the semiconductor laser in synchronization with the reciprocating rotation of the reflecting plate.

The injection current control means variably controls the injection current so that there is no discontinuous change in the output signal of the light receiver during the wavelength sweep and the optical output in the wavelength sweep range is substantially constant. 2. The wavelength swept light source according to 2.

A temperature sensor (70) for detecting the temperature of the semiconductor laser or its surroundings;
A Peltier element (71) for varying the temperature of at least the semiconductor laser;
Temperature control for controlling the supply current to the Peltier element based on the output of the temperature sensor and the output of the light receiver so that the average output in the wavelength sweep range of the emitted light of the semiconductor laser becomes a desired value The wavelength swept light source according to any one of claims 1 to 3, further comprising means (75).

The semiconductor laser, the collimating lens, the fixed mirror, and the diffraction grating have a structure in which light emitted from the collimating lens is incident on the diffraction grating via a fixed mirror (24) fixed on the base. The optical axis extending from the semiconductor laser to the diffraction grating via the fixed mirror is arranged in a non-crossing state with the reflector of the pivot mirror so that it is disposed on one surface side of the reflector of the pivot mirror. The wavelength swept light source according to any one of claims 1 to 4, wherein