JP6440239B2 - Wavelength conversion device and wavelength conversion method - Google Patents
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本発明は、基本波光となるレーザー光の波長を所望の大きさに変換する波長変換装置、及び波長変換方法に関する。 The present invention relates to a wavelength conversion device and a wavelength conversion method for converting the wavelength of laser light serving as fundamental wave light into a desired size.
レーザー光は、金属の切断や加工、半導体製造のためのフォトリソグラフィ装置用光源、レーザーディスプレイ用光源、外科や眼科、歯科等の医療用手術装置、各種の測定装置等の幅広い技術分野に応用されている。また、レーザー光をこれらの用途で使用するために、ニオブ酸リチウムＬｉＮｂＯ３（ＰＰＬＮ：periodically poled lithium niobate ）等の周期分極反転型の非線形光学結晶からなる波長変換素子を用いて、レーザー光の波長を当該用途に適合した所望の大きさに変換する波長変換技術が開発されている。 Laser light is applied to a wide range of technical fields such as metal cutting and processing, light source for photolithography equipment for semiconductor manufacturing, light source for laser display, surgical operation equipment for surgery, ophthalmology, dentistry, etc., various measuring equipment, etc. ing. Further, in order to use laser light in these applications, a wavelength conversion element made of a periodically poled nonlinear optical crystal such as lithium niobate LiNbO 3 (PPLN: periodic poled lithium niobate) is used. A wavelength conversion technique has been developed for converting the light into a desired size suitable for the application.
特許文献１には、半導体レーザーとバルク型波長変換結晶からなる波長変換素子との間に、狭域体バンドパスフィルター等の波長選択光学素子を設けた波長変換モジュールが開示されている。当該波長変換モジュールでは、波長選択光学素子によって光波長変換素子の端面で反射して半導体レーザーにフィードバックするレーザービームの波長を選択することによって、半導体レーザーの発振波長を正確にロックして、波長変換後の光を安定して発振させている。 Patent Document 1 discloses a wavelength conversion module in which a wavelength selection optical element such as a narrow bandpass filter is provided between a semiconductor laser and a wavelength conversion element made of a bulk wavelength conversion crystal. In this wavelength conversion module, the wavelength of the semiconductor laser is accurately locked by selecting the wavelength of the laser beam that is reflected from the end face of the optical wavelength conversion element by the wavelength selection optical element and fed back to the semiconductor laser, thereby converting the wavelength. The later light is oscillated stably.
波長変換装置に備わる波長変換素子として主に用いられる非線形光学結晶は、角度依存性を有しており、高い効率で波長変換を行なうためには、この波長変換素子に入射するレーザー光の入射角を厳密に調節して位相整合をとる必要がある。このため、高効率な波長変換を実現するためには、一般的に単一周波数のレーザー光が用いられている。また、超短パルスレーザーのように、波長の範囲が広くても出力光が短パルス列となって実効的な強度が桁違いに上がっている場合には、その強い光電場で高効率な波長変換が行われている。 The nonlinear optical crystal mainly used as the wavelength conversion element provided in the wavelength conversion device has angle dependency, and in order to perform wavelength conversion with high efficiency, the incident angle of the laser light incident on the wavelength conversion element Must be adjusted precisely to achieve phase matching. For this reason, in order to realize highly efficient wavelength conversion, a single-frequency laser beam is generally used. Also, if the output light becomes a short pulse train and the effective intensity increases by orders of magnitude, even with a wide wavelength range, such as an ultrashort pulse laser, high-efficiency wavelength conversion is achieved with the strong photoelectric field. Has been done.
しかしながら、高出力な連続発振ファイバーレーザー等のような簡便で光子コストに優れたレーザーでは、発振スペクトルが狭窄化されていることが少なく、このように複数の波長、色を有し、波長方向に単一でないレーザー光の波長変換をする際に、その高効率化が望めなかった。特許文献１には、半導体レーザーの発振波長を正確にロックして、波長変換後のレーザー光の発振の安定化については、言及しているものの、発振スペクトルが狭窄化されていないレーザー光を効率よく波長変換することには、言及していない。 However, a simple laser with excellent photon cost, such as a high-power continuous-wave fiber laser, is rarely narrowed in the oscillation spectrum, and thus has multiple wavelengths and colors in the wavelength direction. When converting the wavelength of a non-single laser beam, high efficiency could not be expected. Patent Document 1 mentions that the oscillation wavelength of a semiconductor laser is accurately locked to stabilize the oscillation of the laser beam after wavelength conversion, but the laser beam whose oscillation spectrum is not narrowed is efficiently used. There is no mention of wavelength conversion well.
本発明は、上記課題に鑑みてなされたものであり、発振スペクトルが狭窄化されていないレーザー光でも効率的に波長変換することの可能な、新規かつ改良された波長変換装置、及び波長変換方法を提供することを目的とする。 The present invention has been made in view of the above problems, and a novel and improved wavelength conversion apparatus and wavelength conversion method capable of efficiently performing wavelength conversion even with laser light whose oscillation spectrum is not narrowed. The purpose is to provide.
本発明の一態様は、基本波光を波長変換素子によって波長変換する波長変換装置であって、前記基本波光としてファイバーレーザーによって発振スペクトルが非狭窄化されたレーザー光を連続的に発振するレーザー発振部と、前記レーザー発振部で発振された前記基本波光のビーム径を拡大する拡大光学系部と、前記拡大光学系部で前記ビーム径が拡大された拡大基本波光を透過させて該拡大基本波光の波長を分散させる回折格子が設けられる波長分散部と、前記波長分散部から所定の大きさの光学的距離を介して設けられ、前記波長が分散された拡大基本波光を集光レンズで集光して前記波長変換素子に導く波長・角度分散部と、を備え、前記波長分散部は、前記回折格子として設けられる少なくとも一の透過型回折格子と複数の反射ミラーが環状に配置されて構成され、前記透過型回折格子によって前記拡大基本波光を回折させて、該拡大基本波光の前記波長が分散させられ、前記反射ミラーによって反射後の前記拡大基本波光を前記透過型回折格子に戻し、再度回折させ、前記反射ミラーは、前記透過型回折格子で回折後の前記拡大基本反射光を反射させて、前記透過型回折格子の最大分散効率が得られる入射角度で該透過型回折格子に戻せるように、設置角度が調整可能に構成されていることを特徴とする。 One aspect of the present invention is a wavelength conversion device that converts the wavelength of fundamental wave light using a wavelength conversion element, and continuously oscillates laser light whose oscillation spectrum is not narrowed by a fiber laser as the fundamental wave light. And an magnifying optical system unit that expands the beam diameter of the fundamental wave light oscillated by the laser oscillation unit; and the magnifying fundamental wave light whose beam diameter is expanded by the magnifying optical system unit is transmitted to transmit the expanded fundamental wave light. A wavelength dispersion unit provided with a diffraction grating for dispersing the wavelength, and an extended fundamental wave light, which is provided through an optical distance of a predetermined size from the wavelength dispersion unit, is condensed by a condenser lens. And a wavelength / angle dispersion part guided to the wavelength conversion element, wherein the wavelength dispersion part comprises at least one transmission diffraction grating provided as the diffraction grating and a plurality of reflection mirrors. Are arranged in an annular shape, the diffracted fundamental wave light is diffracted by the transmissive diffraction grating, the wavelength of the magnified fundamental wave light is dispersed, and the reflected reflected reflected fundamental light is transmitted by the reflection mirror. The reflection mirror reflects the enlarged fundamental reflected light after being diffracted by the transmission diffraction grating at an incident angle at which the maximum dispersion efficiency of the transmission diffraction grating is obtained. The installation angle can be adjusted so that it can be returned to the transmission type diffraction grating.
本発明の一態様によれば、拡大光学系部でビーム径が拡大された基本波光を回折格子に透過させることによって、その波長を分散させた拡大基本波光を所定の光学的距離を経由させてから集光レンズで集光する。このため、発振スペクトル幅がこの設計値内で変化した場合でも、波長変換素子により確実に導けるので、効率的に波長変換できるようになる。また、波長により最適角度になるようにビーム径を拡大した基本波光で波長変換素子に導入するので、基本波光による波長変換素子の加熱が空間的に分散されて、波長変換効率の低下を軽減できる。さらに、透過型回折格子の最大分散効率が得られる入射角度、ビーム径で数回、透過型回折格子を利用して回折できるので、回折格子の最大限の波長分散を利用しながら、基本波光の波長が分散された状態で波長変換素子に導入できる。特に、基本波光としてファイバーレーザーの出力光を使用することによって、そのレーザー光の空間モードの安定性が高められ、固体レーザーの励起において高精度な励起が可能になる。 According to one aspect of the present invention, the fundamental wave light whose beam diameter is enlarged by the magnification optical system unit is transmitted through the diffraction grating, so that the magnified fundamental wave light whose wavelength is dispersed is passed through a predetermined optical distance. Condensed with a condenser lens. For this reason, even when the oscillation spectrum width changes within this design value, it can be reliably guided by the wavelength conversion element, so that wavelength conversion can be performed efficiently. In addition, since the fundamental wave light whose beam diameter is expanded so as to have an optimum angle depending on the wavelength is introduced into the wavelength conversion element, the heating of the wavelength conversion element by the fundamental wave light is spatially dispersed, thereby reducing the decrease in wavelength conversion efficiency. . Furthermore, the diffraction angle can be diffracted several times at the incident angle and beam diameter at which the maximum dispersion efficiency of the transmissive diffraction grating can be obtained. It can be introduced into the wavelength conversion element in a state where the wavelengths are dispersed. In particular, by using the output light of the fiber laser as the fundamental wave light, the stability of the spatial mode of the laser light is enhanced, and high-precision excitation is possible in the excitation of the solid-state laser.
また、本発明の一態様では、前記波長・角度分散部は、前記光学的距離が下記の条件式を満たすように設定されることとしてもよい。
Ｌ／ｆ＝１．２６×δｃｏｓβ
Ｌ：回折格子と集光レンズとの距離
ｆ：集光レンズの焦点距離
δ：回折格子の溝の間隔
β：回折格子による回折角
In the aspect of the invention, the wavelength / angle dispersion unit may be set so that the optical distance satisfies the following conditional expression.
L / f = 1.26 × δcosβ
L: Distance between the diffraction grating and the condensing lens f: Focal length of the condensing lens δ: Distance between the grooves of the diffraction grating β: Diffraction angle by the diffraction grating
このように、波長分散部から距離を置いて波長・角度分散部を設けることによって、横方向に位置ずれした各波長のレーザー光を単一の集光レンズで集光して、波長変換素子に導くことができる。 In this way, by providing the wavelength / angle dispersion portion at a distance from the wavelength dispersion portion, the laser light of each wavelength shifted in the lateral direction is condensed by a single condensing lens to be a wavelength conversion element. Can lead.
また、本発明の一態様では、前記拡大光学系部は、入力段側に設けられる第１レンズと出力段側に設けられる第２レンズが所定の距離を介して対向するように構成され、前記第１レンズと前記第２レンズとの距離を変更することによって、前記基本波光の前記ビーム径を調整することとしてもよい。 In the aspect of the invention, the magnifying optical system unit is configured such that a first lens provided on the input stage side and a second lens provided on the output stage side are opposed to each other with a predetermined distance, The beam diameter of the fundamental wave light may be adjusted by changing the distance between the first lens and the second lens.
このように、第１レンズと第２レンズとの距離を変更して基本波光のビーム径を調整することによって、波長・角度分散部での分解能を高めることができる。 In this way, by changing the distance between the first lens and the second lens and adjusting the beam diameter of the fundamental wave light, the resolution at the wavelength / angle dispersion unit can be increased.
また、本発明の他の態様は、基本波光を波長変換素子によって波長変換する波長変換方法であって、ファイバーレーザーによって発振スペクトルが非狭窄化されたレーザー光を前記基本波光として連続的に発振するレーザー光発振工程と、前記基本波光のビーム径を拡大するビーム径拡大工程と、前記ビーム径が拡大された拡大基本波光を回折格子に透過させて該拡大基本波光の波長を分散させる波長分散工程と、前記波長が分散された拡大基本波光を前記回折格子から所定の大きさの光学的距離を介して設けられた集光レンズによって前記波長変換素子に導く波長・角度分散工程と、を含み、前記波長分散工程では、前記回折格子として設けられる透過型回折格子によって回折させてから分散された前記拡大基本波光が反射ミラーによって反射してから前記透過型回折格子の最大分散効率が得られる入射角度で前記透過型回折格子に戻されて、該透過型回折格子で再度回折させられることを特徴とする。 Another aspect of the present invention is a wavelength conversion method for converting the wavelength of fundamental wave light by a wavelength conversion element, and continuously oscillates laser light whose oscillation spectrum is not narrowed by a fiber laser as the fundamental wave light. Laser light oscillation step, beam diameter expanding step for expanding the beam diameter of the fundamental wave light, and wavelength dispersion step for dispersing the wavelength of the expanded fundamental wave light by transmitting the expanded fundamental wave light with the expanded beam diameter through a diffraction grating And a wavelength / angle dispersion step for guiding the expanded fundamental wave light in which the wavelength is dispersed to the wavelength conversion element by a condensing lens provided from the diffraction grating via an optical distance of a predetermined size, and In the wavelength dispersion step, the expanded fundamental wave light that has been diffracted by a transmission type diffraction grating provided as the diffraction grating and then dispersed is reflected by a reflection mirror. Shines at an angle of incidence which the maximum dispersion efficiency of the transmissive diffraction grating is obtained from and returned to the transmission diffraction grating, characterized in that it is is diffracted again by said transmission diffraction grating.
本発明の他の態様によれば、基本波光のビーム径を拡大されてから、かかる拡大基本波光を回折格子に透過させて波長分散させるので、回折格子の最大限の波長分散を利用できる。また、この拡大光学系のレンズ間隔を調整することで、集光レンズ位置で波長分散させた拡大基本波光を低損失で集光レンズに集光できる。このため、発振スペクトルがこの設計値内で変化した場合でも、拡大基本波光を波長変換素子により確実に導けるので、効率的に波長変換できるようになる。 According to another aspect of the present invention, since the expanded fundamental wave light is transmitted through the diffraction grating and wavelength-dispersed after the beam diameter of the fundamental wave light is enlarged, the maximum wavelength dispersion of the diffraction grating can be used. Further, by adjusting the lens interval of the magnifying optical system, the magnifying fundamental wave light wavelength-dispersed at the condenser lens position can be condensed on the condenser lens with low loss. For this reason, even when the oscillation spectrum changes within this design value, the expanded fundamental wave light can be reliably guided by the wavelength conversion element, so that wavelength conversion can be performed efficiently.
以上説明したように本発明によれば、発振スペクトルが狭窄化されていないレーザー光を波長変換素子に確実に導けるので、効率的な波長変換が実現される。 As described above, according to the present invention, laser light whose oscillation spectrum is not narrowed can be reliably guided to the wavelength conversion element, so that efficient wavelength conversion is realized.
以下、本発明の好適な実施の形態について詳細に説明する。なお、以下に説明する本実施形態は、特許請求の範囲に記載された本発明の内容を不当に限定するものではなく、本実施形態で説明される構成の全てが本発明の解決手段として必須であるとは限らない。 Hereinafter, preferred embodiments of the present invention will be described in detail. The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and all the configurations described in the present embodiment are essential as means for solving the present invention. Not necessarily.
まず、本発明の一実施形態に係る波長変換装置の概略構成について、図面を使用しながら説明する。図１は、本発明の一実施形態に係る波長変換装置の概略構成図である。 First, a schematic configuration of a wavelength conversion device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a wavelength conversion device according to an embodiment of the present invention.
本発明の一実施形態に係る波長変換装置１は、基本波光Ｌ１となるレーザー光の波長をニオブ酸リチウムＬｉＮｂＯ３（ＰＰＬＮ：periodically poled lithium niobate ）の周期分極反転型の非線形光学結晶からなる波長変換素子５０で変換する装置である。波長変換装置１は、図１に示すように、レーザー発振部１０と、拡大光学系部２０と、波長分散部３０と、波長・角度分散部４０と、波長変換素子５０とを備える。なお、本実施形態では、波長変換素子５０として、ＰＰＬＮ結晶を用いているが、周期分極反転型の非線形光学結晶であれば、ＫＴＰ結晶、ＬＴ結晶、ＬＢＯ結晶、ＢＢＯ結晶等を用いてもよい。 Wavelength conversion apparatus 1 according to an embodiment of the present invention, the fundamental wave light L1 to become a laser beam having a wavelength of lithium niobate LiNbO 3 and the wavelength conversion consisting of (PPLN periodically poled lithium niobate) periodic polarization inversion type of the nonlinear optical crystal of This is a device for conversion by the element 50. As shown in FIG. 1, the wavelength conversion device 1 includes a laser oscillation unit 10, an expansion optical system unit 20, a wavelength dispersion unit 30, a wavelength / angle dispersion unit 40, and a wavelength conversion element 50. In this embodiment, a PPLN crystal is used as the wavelength conversion element 50. However, a KTP crystal, an LT crystal, an LBO crystal, a BBO crystal, or the like may be used as long as it is a periodically poled nonlinear optical crystal. .
レーザー発振部１０は、基本波光Ｌ１となるレーザー光を高出力で連続的に発振する機能を有する。レーザー発振部１０は、ファイバーレーザー１２と、ファラデーアイソレーター１４と、λ／２波長板１６とを備える。 The laser oscillating unit 10 has a function of continuously oscillating a laser beam as the fundamental wave light L1 at a high output. The laser oscillation unit 10 includes a fiber laser 12, a Faraday isolator 14, and a λ / 2 wavelength plate 16.
本実施形態では、レーザー光の発振源として、イッテルビウムＹｂやネオジムＮｄ等の希土類イオン固体赤外レーザーからなるファイバーレーザー１２が使用され、例えば、中心波長１０６４ｎｍのＣＷレーザー光が連続発振される。このように、基本波光Ｌ１としてファイバーレーザー１２の出力光を使用することによって、そのレーザー光の空間モードの安定性が高められ、固体レーザーの励起において高精度な励起が可能になる。ファイバーレーザー１２から発振されたレーザー光は、かかるレーザー光を一方向に伝搬するために設けられるファラデーアイソレーター１４と、当該レーザー光の偏光を調整するために設けられるλ／２波長板１６を経て、基本波光Ｌ１として発振される。 In the present embodiment, a fiber laser 12 made of a rare earth ion solid-state infrared laser such as ytterbium Yb or neodymium Nd is used as a laser light oscillation source. For example, CW laser light having a center wavelength of 1064 nm is continuously oscillated. Thus, by using the output light of the fiber laser 12 as the fundamental wave light L1, the stability of the spatial mode of the laser light is enhanced, and high-precision excitation is possible in the excitation of the solid-state laser. Laser light oscillated from the fiber laser 12 passes through a Faraday isolator 14 provided for propagating the laser light in one direction, and a λ / 2 wavelength plate 16 provided for adjusting the polarization of the laser light. Oscillated as fundamental wave light L1.
また、本実施形態では、レーザー発振部１０は、レーザー光の発振源がファイバーレーザー１２であり、基本波光Ｌ１として発振スペクトルが非狭窄化されたレーザー光を連続的に発振することを特徴とする。すなわち、レーザー発振部１０は、基本波光として、複数の異なる波長、色を含んで、波長方向に単一でないレーザー光、換言すると発振スペクトルが狭窄化されていないレーザー光を高出力に連続発振する。 In the present embodiment, the laser oscillation unit 10 is characterized in that the laser light oscillation source is the fiber laser 12 and continuously oscillates the laser light whose oscillation spectrum is not narrowed as the fundamental light L1. . That is, the laser oscillating unit 10 continuously oscillates with high output a laser beam that includes a plurality of different wavelengths and colors as a fundamental wave light and that is not single in the wavelength direction, in other words, a laser beam whose oscillation spectrum is not narrowed. .
本実施形態の波長変換装置１は、このように狭窄化されていない連続発振レーザーを波長変換素子５０で波長変換する際に問題となる位相不整合を補償するために、波長角度分散型光学系を導入して、高効率に波長を変換可能としたことを特徴とする。波長変換装置１は、９０％以上の高い回折効率を有する回折格子を用いて角度分散型波長変換を実現させる波長角度分散型光学系として、拡大光学系部２０と、波長分散部３０と、波長・角度分散部４０と、を備える。 The wavelength conversion device 1 of the present embodiment includes a wavelength-angle-dispersion optical system in order to compensate for phase mismatch that becomes a problem when the wavelength conversion element 50 converts the wavelength of a continuous wave laser that is not narrowed in this way. Is introduced to enable wavelength conversion with high efficiency. The wavelength conversion device 1 is a wavelength angle dispersion type optical system that realizes angle dispersion type wavelength conversion using a diffraction grating having a high diffraction efficiency of 90% or more. An angle dispersion unit 40 is provided.
拡大光学系部２０は、レーザー発振部１０で発振された基本波光のビーム径を拡大する機能を有する。本実施形態では、拡大光学系部２０は、入力段側に設けられる第１レンズ２２と出力段側に設けられ、第１レンズ２２より焦点距離の大きい第２レンズ２４が所定の距離を介して対向するように構成されている。そして、第１レンズ２２と第２レンズ２４との距離を変更することによって、基本波光Ｌ１のビーム径を調整する。 The expansion optical system unit 20 has a function of expanding the beam diameter of the fundamental light oscillated by the laser oscillation unit 10. In the present embodiment, the magnifying optical system unit 20 is provided on the input stage side with the first lens 22 provided on the input stage side, and the second lens 24 having a larger focal length than the first lens 22 via a predetermined distance. It is comprised so that it may oppose. Then, by changing the distance between the first lens 22 and the second lens 24, the beam diameter of the fundamental wave light L1 is adjusted.
このように、第１レンズ２２と第２レンズ２４との距離を変更して基本波光Ｌ１のビーム発散角を調整することによって、基本波光Ｌ１の集光レンズ４２の位置でのビーム径を最適化できる。このため、後段側に有する波長変換部３０の回折格子３２によって、異なる複数の発振スペクトルを有する狭窄化されていないレーザー光の波長を、それぞれの発振スペクトルごとに分散させられる。それによって、波長変換装置１の最終段側に有する波長・角度分散部４０での分解能を高めることができる。 Thus, by adjusting the beam divergence angle of the fundamental light L1 by changing the distance between the first lens 22 and the second lens 24, the beam diameter of the fundamental light L1 at the position of the condenser lens 42 is optimized. it can. For this reason, the wavelength of the non-narrowed laser beam having a plurality of different oscillation spectra can be dispersed for each oscillation spectrum by the diffraction grating 32 of the wavelength conversion unit 30 provided on the rear stage side. Thereby, the resolution in the wavelength / angle dispersion unit 40 on the final stage side of the wavelength converter 1 can be increased.
波長分散部３０は、拡大光学系部２０でビーム径が拡大された拡大基本波光Ｌ２を透過させて、当該拡大基本波光Ｌ２の波長を分散させる回折格子３２が設けられる。本実施形態では、波長分散部３０は、所定間隔の溝３２ａ（図６参照）が設けられるガラス等から形成される９０％以上の高い回折効率を有する透過型回折格子３２から構成され、拡大基本波光Ｌ２を回折させて、かかる拡大基本波光Ｌ２の波長を分散させる。 The wavelength dispersion unit 30 is provided with a diffraction grating 32 that transmits the extended fundamental wave light L2 whose beam diameter is enlarged by the enlargement optical system unit 20 and disperses the wavelength of the extended fundamental wave light L2. In the present embodiment, the wavelength dispersion unit 30 is composed of a transmission type diffraction grating 32 having a high diffraction efficiency of 90% or more, which is formed of glass or the like provided with grooves 32a (see FIG. 6) having a predetermined interval. The wave light L2 is diffracted to disperse the wavelength of the expanded fundamental wave light L2.
具体的には、本実施形態の波長分散部３０は、図１に示すように、透過型回折格子３２が三角形の一の頂点上に有するような配置となるように設けられ、反射ミラー３４、３６が当該三角形の他の頂点上にそれぞれ有するような配置となるように設けられている。これらの反射ミラー３４、３６は、入射する回折後の拡大基本反射Ｌ３−１（Ｌ３）を反射させて、透過型回折格子３２の最大分散効率が得られる入射角度で当該透過型回折格子３２に戻せるように、適宜、設置角度が調整可能な構成となっている。 Specifically, as shown in FIG. 1, the wavelength dispersion unit 30 of the present embodiment is provided so as to have a transmission diffraction grating 32 on one vertex of a triangle, and a reflection mirror 34, 36 are arranged so as to have each on the other vertex of the triangle. These reflection mirrors 34 and 36 reflect the incident diffracted magnified basic reflection L3-1 (L3) to the transmission diffraction grating 32 at an incident angle at which the maximum dispersion efficiency of the transmission diffraction grating 32 is obtained. The installation angle can be adjusted as appropriate so that it can be returned.
波長分散部３０をかかる構成とすることによって、拡大光学系部２０から導入された拡大基本波光Ｌ２は、まず、透過型回折格子３２で回折する。次に、当該透過型回折格子３２で回折した拡大基本波光Ｌ３−１（Ｌ３）は、２つの反射ミラー３４、３６でそれぞれ反射されてから、再び透過型回折格子３２の最大分散効率が得られる入射角度で戻って回折する。そして、その回折後の拡大基本波光Ｌ３−２（Ｌ３）が後段側に設けられる反射ミラー３８で反射してから、その反射光となる拡大基本波光Ｌ３−３（Ｌ３）が波長・角度分散部４０に導かれるようになっている。なお、本実施形態では、波長分散部３０の後段側に反射ミラー３８が設けられているが、反射ミラー３８を設けずに、波長分散部３０で波長分散された拡大基本波光Ｌ３−２（Ｌ３）が直接、波長・角度分散部４０に導入される構成としてもよい。 By configuring the wavelength dispersion unit 30 as described above, the expanded fundamental wave light L2 introduced from the expanding optical system unit 20 is first diffracted by the transmissive diffraction grating 32. Next, the expanded fundamental wave light L3-1 (L3) diffracted by the transmission diffraction grating 32 is reflected by the two reflection mirrors 34 and 36, respectively, and then the maximum dispersion efficiency of the transmission diffraction grating 32 is obtained again. Diffracts back at the incident angle. Then, after the diffracted fundamental wave light L3-2 (L3) is reflected by the reflection mirror 38 provided on the rear stage side, the magnified fundamental wave light L3-3 (L3) that becomes the reflected light is reflected by the wavelength / angle dispersion unit. 40 is led. In the present embodiment, the reflection mirror 38 is provided on the rear stage side of the wavelength dispersion unit 30, but the extended fundamental wave light L3-2 (L3) wavelength-dispersed by the wavelength dispersion unit 30 without providing the reflection mirror 38. ) May be directly introduced into the wavelength / angle dispersion unit 40.
このように、本実施形態では、波長分散部３０が透過型回折格子３２と反射ミラー３４、３６を備える構成としたので、波長により最適な角度になるように基本波光Ｌ３の光路を確保してから、波長・角度分散部４０を介して波長変換素子５０に導入できる。このため、基本波光Ｌ１で結晶内に生じてしまう加熱分布が分散されるように、波長変換素子５０に導入されるようになる。従って、熱の影響を受けやすい波長変換素子５０が、基本波光Ｌ１の熱によって波長変換効率を低下するリスクを軽減できる。 As described above, in this embodiment, the wavelength dispersion unit 30 includes the transmission type diffraction grating 32 and the reflection mirrors 34 and 36. Therefore, the optical path of the fundamental light L3 is secured so as to have an optimum angle depending on the wavelength. To the wavelength conversion element 50 via the wavelength / angle dispersion unit 40. For this reason, it introduce | transduces into the wavelength conversion element 50 so that the heating distribution which arises in a crystal | crystallization by the fundamental wave light L1 may be disperse | distributed. Therefore, it is possible to reduce the risk that the wavelength conversion element 50 that is easily affected by heat decreases the wavelength conversion efficiency due to the heat of the fundamental light L1.
また、本実施形態では、波長分散部３０は、反射ミラー３４、３６を設けることによって、ビーム径を拡大した基本波光Ｌ３−１（Ｌ３）の光路を確保しながら、透過型回折格子３２の最大分散効率が得られる入射角度で反射後の拡大基本波光Ｌ３−１（Ｌ３）を透過型回折格子３２に戻せる。このように、反射ミラー３４、３６を設けることによって、透過型回折格子３２の最大分散効率が得られる入射角度で反射後の拡大基本波光Ｌ３−１（Ｌ３）を戻してから回折するので、透過型回折格子３２で最大限に回析後の拡大基本波光Ｌ３−２、Ｌ３−３（Ｌ３）の波長を分散させられる。 Further, in the present embodiment, the wavelength dispersion unit 30 is provided with the reflection mirrors 34 and 36 to secure the optical path of the fundamental wave light L3-1 (L3) whose beam diameter is enlarged, while the maximum of the transmission type diffraction grating 32 is secured. The expanded fundamental wave light L3-1 (L3) after reflection can be returned to the transmissive diffraction grating 32 at an incident angle at which dispersion efficiency is obtained. Thus, by providing the reflection mirrors 34 and 36, the reflected fundamental wave light L3-1 (L3) after reflection is diffracted after being reflected at an incident angle at which the maximum dispersion efficiency of the transmission diffraction grating 32 is obtained. The wavelength of the extended fundamental wave light L3-2 and L3-3 (L3) after diffraction is maximally dispersed by the diffraction grating 32.
このため、拡大基本波光Ｌ３に含まれる各波長のレーザー光をそれぞれ波長ごとに効率的に分散させて、後段側に設けられた波長・角度分散部４０に導入できる。また、波長分散部３０に反射ミラー３４、３６を設けることによって、限られたスペース内で拡大基本波光Ｌ３−１の光路を確保できるようになるので、波長変換装置１のコンパクト化も図れるようになる。 For this reason, laser light of each wavelength included in the extended fundamental wave light L3 can be efficiently dispersed for each wavelength and introduced into the wavelength / angle dispersion unit 40 provided on the rear stage side. Further, by providing the reflection mirrors 34 and 36 in the wavelength dispersion unit 30, the optical path of the extended fundamental wave light L3-1 can be secured in a limited space, so that the wavelength conversion device 1 can be made compact. Become.
なお、本実施形態では、波長分散部３０は、１つの透過型回折格子３２が設けられているが、回折格子の数は、１つに限定されず、例えば、回折格子を２つ以上から構成されるようにしてもよい。また、本実施形態では、波長分散部３０に２つの反射ミラー３４、３６が設けられているが、その設置数は、２つに限定されず、反射光を再び透過型回折格子３２の最大分散効率が得られる入射角度で戻して、再度回折させる構成となっていれば、１つでも、３つ以上としてもよい。ただし、反射光を再び透過型回折格子３２の最大分散効率が得られる入射角度で確実に戻して、再度回折させるためには、反射ミラーの設置数は、２枚、４枚等の偶数枚が好ましい。 In the present embodiment, the wavelength dispersion unit 30 is provided with one transmissive diffraction grating 32, but the number of diffraction gratings is not limited to one, and includes, for example, two or more diffraction gratings. You may be made to do. In the present embodiment, the two reflection mirrors 34 and 36 are provided in the wavelength dispersion unit 30, but the number of the reflection mirrors 34 and 36 is not limited to two, and the reflected light is again dispersed to the maximum extent of the transmission diffraction grating 32. If it is the structure which returns by the incident angle which can obtain efficiency, and is made to diffract again, it is good also as one or three or more. However, in order to reliably return the reflected light again at the incident angle at which the maximum dispersion efficiency of the transmissive diffraction grating 32 is obtained and diffract it again, the number of reflection mirrors installed is an even number such as two or four. preferable.
波長・角度分散部４０は、波長分散部３０から所定の大きさの光学的距離を介して設けられ、波長が分散された拡大基本波光Ｌ３（Ｌ３−３）を集光レンズ４２で集光して波長変換素子５０に導く機能を有する。本実施形態では、波長・角度分散部４０は、波長分散部３０から所定の大きさの光学的距離を介して設けられるので、横方向に位置ずれした各波長を単一の集光レンズ４２で集光することで、波長変換素子５０となるＰＰＬＮ結晶の持つ角度・波長・温度の位相整合条件の最適条件を達成させられる。なお、波長・角度分散部４０の設置条件となる波長分散部３０からの光学的距離の詳細については、後述する。 The wavelength / angle dispersion unit 40 is provided via an optical distance having a predetermined size from the wavelength dispersion unit 30, and condenses the expanded fundamental wave light L <b> 3 (L <b> 3-3) with the wavelength dispersed by the condenser lens 42. And has a function of leading to the wavelength conversion element 50. In the present embodiment, the wavelength / angle dispersion unit 40 is provided via an optical distance having a predetermined size from the wavelength dispersion unit 30, so that each wavelength shifted in the lateral direction is converted by a single condenser lens 42. By focusing the light, it is possible to achieve the optimum condition of the phase matching condition of the angle, wavelength, and temperature of the PPLN crystal serving as the wavelength conversion element 50. The details of the optical distance from the wavelength dispersion unit 30 that is the installation condition of the wavelength / angle dispersion unit 40 will be described later.
一般的に、ＣＷ単一モード発振の高出力ファイバーレーザーでは、中心波長１０６４ｎｍに対するスペクトル幅が０．１ｎｍ程度であり、Δλ／λが１０−４以上の波長分解能が必要になる。その際におけるこの波長幅に対する分散角が０．１ｍｒａｄ程度にしかならないので、ＰＰＬＮ等の波長変換素子５０の波長・角度分散補償の要求値と比較すると桁違いに小さい。 In general, a CW single-mode oscillation high-power fiber laser has a spectral width of about 0.1 nm with respect to the center wavelength of 1064 nm, and requires a wavelength resolution of Δλ / λ of 10 −4 or more. In this case, since the dispersion angle with respect to this wavelength width is only about 0.1 mrad, it is much smaller than the required value of wavelength / angle dispersion compensation of the wavelength conversion element 50 such as PPLN.
そこで、本実施形態では、波長分散部３０から集光レンズ４２まで、所定の大きさの光学的距離として数ｍ程度の光路長を持たせるようにしているので、図２に示すように、基本波光Ｌ１に含まれる各波長ごとに集光レンズ４２の幅方向における位置を分散させることができる。すなわち、波長分散部３０から距離を挟んで波長・角度分散部４０を設けることによって、ＰＰＬＮ結晶５０の前段側に設けられる集光レンズ４２の位置において、基本波光Ｌ１に含まれる各波長に応じた入射横方向位置を取らせることができる。このため、波長・角度分散部４０の集光レンズ４２によって、拡大基本波光Ｌ３が基本波光Ｌ１に含まれる各波長に応じた最適な入射角度で波長変換素子５０に導かれるようになる。 Therefore, in this embodiment, an optical path length of about several meters is provided as an optical distance of a predetermined size from the wavelength dispersion unit 30 to the condensing lens 42. Therefore, as shown in FIG. The position of the condenser lens 42 in the width direction can be dispersed for each wavelength included in the wave light L1. That is, by providing the wavelength / angle dispersion unit 40 with the distance from the wavelength dispersion unit 30, depending on each wavelength included in the fundamental light L <b> 1 at the position of the condenser lens 42 provided on the front stage side of the PPLN crystal 50. The incident lateral direction position can be taken. For this reason, the expanded fundamental wave light L3 is guided to the wavelength conversion element 50 at an optimum incident angle corresponding to each wavelength included in the fundamental wave light L1 by the condenser lens 42 of the wavelength / angle dispersion unit 40.
前述したように、ＰＰＬＮ等の非線形光学結晶からなる波長変換素子５０は、角度依存性を有しており、高い効率で波長変換を行なうためには、この波長変換素子５０に入射するレーザー光の入射角を厳密に調節して位相整合をとる必要がある。このため、従来では、高効率な波長変換を実現するために、単一周波数のレーザー光が用いられていた。 As described above, the wavelength conversion element 50 made of a nonlinear optical crystal such as PPLN has angle dependency, and in order to perform wavelength conversion with high efficiency, the laser beam incident on the wavelength conversion element 50 is not affected. It is necessary to precisely adjust the incident angle to achieve phase matching. For this reason, conventionally, a single-frequency laser beam has been used to realize highly efficient wavelength conversion.
これに対して、本実施形態では、拡大光学系部１０でビーム径が拡大された基本波光Ｌ２を回折格子３２に透過させることによって、その波長を分散させた拡大基本波光Ｌ３を所定の光学的距離を経由させてから集光レンズ４２で集光する。このため、発振スペクトルが狭窄化されていないレーザー光でも、当該レーザー光に含まれる各波長ごとに最適な入射角で波長変換素子５０に導くことができるので、効率的な波長変換が実現される。具体的には、図３に示すように、従来の波長変換装置による非波長・角度分散に比べて、本実施形態の波長変換装置１による波長・角度分散の場合では、１０Ｗ以上の入力で５０％以上の変換効率の改善が見られた。 On the other hand, in the present embodiment, the fundamental wave light L2 whose beam diameter has been enlarged by the magnification optical system unit 10 is transmitted through the diffraction grating 32, whereby the enlarged fundamental wave light L3 having its wavelength dispersed is transmitted to a predetermined optical wavelength. The light is collected by the condenser lens 42 after passing through the distance. For this reason, even laser light whose oscillation spectrum is not narrowed can be guided to the wavelength conversion element 50 at an optimum incident angle for each wavelength included in the laser light, so that efficient wavelength conversion is realized. . Specifically, as shown in FIG. 3, in the case of the wavelength / angle dispersion by the wavelength conversion device 1 of the present embodiment, compared with the non-wavelength / angle dispersion by the conventional wavelength conversion device, the input is 50 W or more. % Conversion efficiency was improved.
なお、実際の波長角度分散型光学系の設計では、拡大基本波光Ｌ３の集光レンズ４２への入射角を固定した状態で、当該入射光の波長に対する最適結晶温度を測定し（λopt＝ｆ（Ｔopt））、次に、入射光の波長を固定して、それぞれの入射角での最適温度依存性を測定する（θopt =ｇ（Ｔopt））。そして、これらの２つの関数から、入射角と波長との関係を示す関数θopt =ｈ（λopt）を導出する。すなわち、拡大基本波光Ｌ３の集光レンズ４２への入射角度を固定して波長と温度との関係と、波長を固定して角度と温度との関係と、温度を固定したときの角度と波長との関係を調べることを行って、その中で一番いい関係のものを選び出す。本実施形態では、一例として、結晶長３０ｍｍのＭｇＯ・ＰＰＬＮ結晶では、０．１ｎｍ のバンド幅で１２６ｍｒａｄの角度分散が必要になる。 In the actual design of the wavelength angle dispersion optical system, the optimum crystal temperature for the wavelength of the incident light is measured (λopt = f () while the incident angle of the expanded fundamental wave light L3 to the condenser lens 42 is fixed. Next, the wavelength of the incident light is fixed, and the optimum temperature dependence at each incident angle is measured (θopt = g (Topt)). Then, from these two functions, a function θopt = h (λopt) indicating the relationship between the incident angle and the wavelength is derived. That is, the incident angle of the expanded fundamental wave light L3 to the condenser lens 42 is fixed, the relationship between the wavelength and the temperature, the relationship between the angle and the temperature when the wavelength is fixed, and the angle and the wavelength when the temperature is fixed. To find out the best relationship among them. In the present embodiment, as an example, an MgO · PPLN crystal having a crystal length of 30 mm requires an angular dispersion of 126 mrad with a bandwidth of 0.1 nm.
次に、本発明の一実施形態に係る波長変換装置における波長・角度分散部４０の設置条件となる波長分散部３０からの光学的距離の詳細について、図面を使用しながら説明する。図４は、本発明の一実施形態に係る波長変換装置の概略構成を説明する模式図であり、図５及び図６は、本発明の一実施形態に係る波長変換装置の要部の詳細説明図である。なお、図４では、説明の便宜上、波長分散部３０を１つの回折格子３２のみで構成される場合を示し、また、波長分散部３０から回析後の拡大基本波光Ｌ３が直接、波長・角度分散部４０に導かれる場合を示している。また、図５は、波長変換装置１の要部として、主に波長分散部３０と波長・角度分散部４０との光学的距離、図６は、波長変換装置１の要部として、波長分散部３０における入射角と回折角との関係を示す。 Next, details of the optical distance from the wavelength dispersion unit 30 which is the installation condition of the wavelength / angle dispersion unit 40 in the wavelength conversion device according to the embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a schematic diagram illustrating a schematic configuration of a wavelength conversion device according to an embodiment of the present invention, and FIGS. 5 and 6 are detailed descriptions of the main parts of the wavelength conversion device according to an embodiment of the present invention. FIG. 4 shows a case where the wavelength dispersion unit 30 is configured by only one diffraction grating 32 for convenience of explanation, and the expanded fundamental wave light L3 after diffraction from the wavelength dispersion unit 30 is directly wavelength / angle. The case where it is guided to the dispersion unit 40 is shown. 5 is mainly an optical distance between the wavelength dispersion unit 30 and the wavelength / angle dispersion unit 40 as a main part of the wavelength conversion device 1, and FIG. 6 is a wavelength dispersion unit as a main part of the wavelength conversion device 1. The relationship between the incident angle and the diffraction angle at 30 is shown.
本実施形態では、狭窄化されていないレーザー光を効率よく波長変換するために、波長・角度分散部４０の集光レンズ４２を、波長分散部３０の回折格子３２から所定の大きさの光学的距離を介して設置する必要がある。すなわち、横方向に位置ずれした各波長のレーザー光を集光レンズ４２で集光して波長変換素子５０に導くために、波長・角度分散部４０は、波長分散部３０から所定の大きさの距離を置いて設けられる。 In the present embodiment, in order to efficiently convert the wavelength of the laser beam that is not narrowed, the condenser lens 42 of the wavelength / angle dispersion unit 40 is optically connected to the diffraction grating 32 of the wavelength dispersion unit 30 with a predetermined size. It is necessary to install through the distance. That is, the wavelength / angle dispersion unit 40 has a predetermined size from the wavelength dispersion unit 30 in order to condense the laser light of each wavelength displaced in the lateral direction by the condenser lens 42 and guide it to the wavelength conversion element 50. Provided at a distance.
具体的には、波長・角度分散部４０は、波長分散部３０との間に有する所定の大きさの光学的距離として、下記の条件式（１）を満たすように設定される。
Ｌ／ｆ＝１．２６×δｃｏｓβ・・・（１）
Ｌ：回折格子と集光レンズとの距離
ｆ：集光レンズの焦点距離
δ：回折格子の溝の間隔
β：回折格子による回折角
Specifically, the wavelength / angle dispersion unit 40 is set to satisfy the following conditional expression (1) as an optical distance having a predetermined size with the wavelength dispersion unit 30.
L / f = 1.26 × δcosβ (1)
L: Distance between the diffraction grating and the condensing lens f: Focal length of the condensing lens δ: Distance between the grooves of the diffraction grating β: Diffraction angle by the diffraction grating
上記の条件式（１）を算出する過程を以下で説明する。図５に示すように、波長分散部３０と波長・角度分散部４０との間に有する光学的距離となる回折格子３２から集光レンズ４２までの距離をＬ、集光レンズ４２の位置での拡大基本波光Ｌ３の波長差による横方向の広がりの大きさをΔｘ、集光レンズ４２の焦点距離をｆ、回折格子３２による回折角の広がりをΔβ、集光レンズ４２による集光角度をΔθとすると、これらは、下記の条件式（２）及び（３）を満たす。
Δｘ＝ＬΔβ ・・・（２）
Δθ＝Δｘ／ｆ・・・（３）
The process of calculating the conditional expression (1) will be described below. As shown in FIG. 5, the distance from the diffraction grating 32 to the condensing lens 42, which is an optical distance between the wavelength dispersion unit 30 and the wavelength / angle dispersion unit 40, is L, and the position of the condensing lens 42 is as follows. The magnitude of the lateral spread due to the wavelength difference of the expanded fundamental wave light L3 is Δx, the focal length of the condenser lens 42 is f, the spread of the diffraction angle by the diffraction grating 32 is Δβ, and the light collection angle by the condenser lens 42 is Δθ. Then, these satisfy the following conditional expressions (2) and (3).
Δx = LΔβ (2)
Δθ = Δx / f (3)
一方、図６に示すように、波長分散部３０における拡大基本波光Ｌ２の入射角をα、回折格子による回折角をβ、回折格子３２の溝３２ａの間隔をδとすると、当該回折格子３２における回折格子方程式は、以下の式（４）で表される。
δ（ｓｉｎα＋ｓｉｎβ）＝ｍλ・・・（４）（ｍ：回折次数、λ：波長）
On the other hand, as shown in FIG. 6, when the incident angle of the expanded fundamental wave light L2 in the wavelength dispersion unit 30 is α, the diffraction angle by the diffraction grating is β, and the interval between the grooves 32a of the diffraction grating 32 is δ, The diffraction grating equation is expressed by the following equation (4).
δ (sin α + sin β) = mλ (4) (m: diffraction order, λ: wavelength)
上記の式（４）に示すシステムにおいて、ｍ＝１であり、使用する回折格子３２によって、最適入射角αと溝間隔δが決定済みの定数となることから、上記の式（４）を微分すると、下記の式（５）が得られる。 In the system shown in the above equation (4), m = 1, and the optimum incident angle α and groove interval δ are determined constants depending on the diffraction grating 32 to be used. Then, the following formula (5) is obtained.
上記の式（５）に前述した条件式（２）及び（３）を代入して整理すると、下記の関係式（６）が得られる。 When the conditional expressions (2) and (3) described above are substituted into the above expression (5) and rearranged, the following relational expression (6) is obtained.
上記の式（６）の左辺の値は、波長変換素子５０となるＰＰＬＮの長さと分極周期で決定される。本実施形態では、Δθ／Δλの値が例えば、１．２６（ｒａｄ／ｎｍ）となる。従って、上記の式（６）にΔθ／Δλの値として１．２６を代入すると、前述した関係式（１）が得られる。 The value on the left side of the above equation (6) is determined by the length of PPLN that becomes the wavelength conversion element 50 and the polarization period. In the present embodiment, the value of Δθ / Δλ is, for example, 1.26 (rad / nm). Therefore, when 1.26 is substituted as the value of Δθ / Δλ in the above equation (6), the above-described relational equation (1) is obtained.
このように、本実施形態では、前述した関係式（１）を満たすように、回折格子３２と集光レンズ４２との距離Ｌと集光レンズ４２の焦点距離ｆの組み合わせを決定する。すなわち、本実施形態では、横方向に位置ずれした各波長のレーザー光を集光レンズ４２で集光して波長変換素子５０に導くことによって、狭窄化されていないレーザー光を効率よく波長変換するために、集光レンズ４２と波長分散部３０の回折格子３２との設置条件となる光学的距離、すなわち回折格子３２と集光レンズ４２との距離Ｌを設定する。 Thus, in the present embodiment, the combination of the distance L between the diffraction grating 32 and the condenser lens 42 and the focal length f of the condenser lens 42 is determined so as to satisfy the relational expression (1) described above. In other words, in this embodiment, laser light of each wavelength shifted in the horizontal direction is condensed by the condensing lens 42 and guided to the wavelength conversion element 50, thereby efficiently converting the wavelength of the laser light that is not narrowed. For this purpose, an optical distance as an installation condition between the condenser lens 42 and the diffraction grating 32 of the wavelength dispersion unit 30, that is, a distance L between the diffraction grating 32 and the condenser lens 42 is set.
次に、本発明の一実施形態に係る波長変換装置による波長変換方法について、図面を使用しながら説明する。図７は、本発明の一実施形態に係る波長変換方法の概略を示すフロー図である。 Next, a wavelength conversion method by the wavelength conversion device according to the embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a flowchart showing an outline of the wavelength conversion method according to the embodiment of the present invention.
本発明の一実施形態に係る波長変換方法は、基本波光の波長を波長変換素子によって変換する。本実施形態では、まず、発振スペクトルが狭窄化されていないレーザー光、すなわち、発振スペクトルが非狭窄化されたレーザー光を基本波光として連続的に発振する（レーザー光発振工程Ｓ１１）。 In the wavelength conversion method according to an embodiment of the present invention, the wavelength of the fundamental light is converted by the wavelength conversion element. In this embodiment, first, laser light whose oscillation spectrum is not narrowed, that is, laser light whose oscillation spectrum is not narrowed is continuously oscillated as fundamental light (laser light oscillation step S11).
次に、拡大光学系部２０の第１レンズ２２と第２レンズ２４との距離を調整しながら、基本波光Ｌ１のビーム径を拡大する（ビーム径拡大工程Ｓ１２）。本実施形態では、後段側に設けられる波長分散部３０によって、狭窄化されていないレーザー光の波長を分散させ易くするために、基本波光Ｌ１のビーム径を拡大する。また、波長分散部３０の回折格子３２で回折後の拡大基本波光Ｌ３を集光レンズ４２で集光して波長変換素子５０に導く際に、拡大基本波光Ｌ３が集光レンズ４２で各波長ごとに明確に色分けされるようにするために、基本波光Ｌ１のビーム径を所望の大きさとなるように調整する。 Next, the beam diameter of the fundamental light L1 is expanded while adjusting the distance between the first lens 22 and the second lens 24 of the magnifying optical system unit 20 (beam diameter expanding step S12). In the present embodiment, the beam diameter of the fundamental wave light L1 is expanded in order to facilitate the dispersion of the wavelength of the laser light that is not narrowed by the wavelength dispersion unit 30 provided on the rear stage side. Further, when the expanded fundamental wave light L3 diffracted by the diffraction grating 32 of the wavelength dispersion unit 30 is collected by the condenser lens 42 and guided to the wavelength conversion element 50, the expanded fundamental wave light L3 is collected by the condenser lens 42 for each wavelength. Therefore, the beam diameter of the fundamental wave light L1 is adjusted so as to be a desired size.
その後、ビーム径が拡大された拡大基本波光Ｌ２を波長分散部３０の回折格子３２に透過させて、当該拡大基本波光の波長を分散させる（波長分散工程Ｓ１３）。本実施形態では、波長分散部３０は、９０％以上の高い回折効率を有する透過型回折格子３２から構成されるので、この透過型回折格子３２によって拡大基本波光Ｌ２を回折させて、かかる拡大基本波光Ｌ３の波長を分散させる。 Thereafter, the expanded fundamental wave light L2 having an enlarged beam diameter is transmitted through the diffraction grating 32 of the wavelength dispersion unit 30 to disperse the wavelength of the expanded fundamental wave light (wavelength dispersion step S13). In the present embodiment, the wavelength dispersion unit 30 is composed of a transmissive diffraction grating 32 having a high diffraction efficiency of 90% or more. Therefore, the diffractive fundamental wave light L2 is diffracted by the transmissive diffraction grating 32, and the enlarged fundamental light is transmitted. The wavelength of the wave light L3 is dispersed.
次に、波長が分散された拡大基本波光Ｌ３を回折格子３２から所定の大きさの光学的距離を介して設けられた波長・角度分散部４０の集光レンズ４２によって、波長変換素子５０に導く（波長・角度分散工程Ｓ１４）。本実施形態では、波長・角度分散部４０は、波長分散部３０から所定の大きさの光学的距離を介して設けられるので、横方向に位置ずれした各波長を単一の集光レンズ４２で集光することで、波長変換素子５０の持つ角度・波長・温度の位相整合条件の最適条件を達成させられる。 Next, the expanded fundamental wave light L3 in which the wavelength is dispersed is guided to the wavelength conversion element 50 by the condenser lens 42 of the wavelength / angle dispersion unit 40 provided from the diffraction grating 32 through an optical distance having a predetermined size. (Wavelength / angle dispersion step S14). In the present embodiment, the wavelength / angle dispersion unit 40 is provided via an optical distance having a predetermined size from the wavelength dispersion unit 30, so that each wavelength shifted in the lateral direction is converted by a single condenser lens 42. By condensing, the optimum condition of the phase matching condition of the angle, wavelength, and temperature of the wavelength conversion element 50 can be achieved.
このようにして、本実施形態では、基本波光Ｌ１のビーム径を拡大されてから、かかる拡大基本波光Ｌ２を回折格子３２に透過させて波長分散させる。そして、その波長を分散させた拡大基本波光Ｌ３が、所定の光学的距離を経由して集光レンズ４２で集光させてから、波長変換素子５０に導かれる。このため、発振スペクトルが狭窄化されていないレーザー光でも、波長が異なることによる位相不整合を解消して、当該レーザー光に含まれる各波長ごとに好適な入射角で波長変換素子５０に導けるので、効率的に波長変換できるようになる。 In this manner, in the present embodiment, after the beam diameter of the fundamental wave light L1 is enlarged, the enlarged fundamental wave light L2 is transmitted through the diffraction grating 32 to be wavelength-dispersed. Then, the expanded fundamental wave light L3 in which the wavelength is dispersed is condensed by the condenser lens 42 via a predetermined optical distance and then guided to the wavelength conversion element 50. For this reason, even with laser light whose oscillation spectrum is not narrowed, phase mismatch due to different wavelengths can be eliminated and guided to the wavelength conversion element 50 at a suitable incident angle for each wavelength included in the laser light. The wavelength can be converted efficiently.
また、本実施形態の波長変換装置１及び波長変換方法では、単一周波数レーザー光や超短パルスレーザーと異なり、高出力な連続発振ファイバーレーザー等の簡便で光子コストに優れ、発振スペクトルが狭窄化されていない質の良くないレーザー光でも、その波長を変換することによって、所望の用途に適用可能な高調波光に変換することができる。このため、発振スペクトルが狭窄化されていないレーザー光でも波長変換することによって、波長変換後の高調波光の適用範囲を広げられ、その光源のコスト削減も実現されるようになる。 Also, in the wavelength conversion device 1 and the wavelength conversion method of the present embodiment, unlike a single frequency laser beam or an ultrashort pulse laser, a simple and excellent photon cost such as a high-power continuous wave fiber laser is provided, and the oscillation spectrum is narrowed. Even laser light of poor quality that has not been converted can be converted to harmonic light applicable to a desired application by converting its wavelength. Therefore, by converting the wavelength of the laser light whose oscillation spectrum is not narrowed, the application range of the harmonic light after wavelength conversion can be expanded, and the cost of the light source can be reduced.
例えば、金属の切断や加工等において、加工用の数百Ｗ以上のＣＷファイバーレーザーでも、波長を１／２の大きさ等に高効率で波長変換することによって得られる波長変換後の高調波光でその加工精度を向上させられる。また、高出力連続ＣＷレーザーを波長変換することによって、その波長変換後の高調波光をレーザーディスプレイにおけるＲＧＢの緑色光源として、より廉価に適用することも可能である。さらに、波長変換後の高調波光による緑色光によって、チタンサファイヤを励起してフェムト秒レーザーの発振に適用することもできる。 For example, in the cutting and processing of metals, even with a CW fiber laser of several hundred W or more for processing, it is a harmonic light after wavelength conversion obtained by converting the wavelength to a size of 1/2 or the like with high efficiency. The processing accuracy can be improved. Further, by converting the wavelength of a high-power continuous CW laser, the harmonic light after the wavelength conversion can be applied at a lower cost as an RGB green light source in a laser display. Furthermore, the titanium sapphire can be excited by green light generated by harmonic light after wavelength conversion, and applied to oscillation of a femtosecond laser.
なお、上記のように本発明の各実施形態について詳細に説明したが、本発明の新規事項及び効果から実体的に逸脱しない多くの変形が可能であることは、当業者には、容易に理解できるであろう。従って、このような変形例は、全て本発明の範囲に含まれるものとする。 Although each embodiment of the present invention has been described in detail as described above, it is easily understood by those skilled in the art that many modifications can be made without departing from the novel matters and effects of the present invention. It will be possible. Therefore, all such modifications are included in the scope of the present invention.
例えば、明細書又は図面において、少なくとも一度、より広義又は同義な異なる用語と共に記載された用語は、明細書又は図面のいかなる箇所においても、その異なる用語に置き換えることができる。また、波長変換装置の構成、動作も本発明の各実施形態で説明したものに限定されず、種々の変形実施が可能である。 For example, a term described with a different term having a broader meaning or the same meaning at least once in the specification or the drawings can be replaced with the different term in any part of the specification or the drawings. The configuration and operation of the wavelength converter are not limited to those described in the embodiments of the present invention, and various modifications can be made.
１ 波長変換装置、１０ レーザー発振部、１２ ファイバーレーザー、１４ ファラデーアイソレーター、１６ λ／２波長板、２０ 拡大光学系部、２２ 第１レンズ、２４ 第２レンズ、３０ 波長分散部、３２、透過型回折格子（回折格子）、３４、３６、３８ 反射ミラー、４０ 波長・角度分散部、４２ 集光レンズ、５０ 波長変換素子、ｆ 焦点距離、Ｌ 光学的距離、Ｌ１ 基本波光、Ｌ２、Ｌ３ 拡大基本波光、Ｓ１１ レーザー光発振工程、Ｓ１２ ビーム径拡大工程、Ｓ１３ 波長分散工程、Ｓ１４ 波長・角度分散工程 DESCRIPTION OF SYMBOLS 1 Wavelength converter, 10 Laser oscillation part, 12 Fiber laser, 14 Faraday isolator, 16 (lambda) / 2 wavelength plate, 20 Magnification optical system part, 22 1st lens, 24 2nd lens, 30 Wavelength dispersion part, 32, Transmission type Diffraction grating (Diffraction grating), 34, 36, 38 Reflection mirror, 40 Wavelength / angle dispersion part, 42 Condensing lens, 50 Wavelength conversion element, f Focal length, L Optical distance, L1 fundamental wave light, L2, L3 Expansion basic Wave light, S11 laser light oscillation process, S12 beam diameter expansion process, S13 wavelength dispersion process, S14 wavelength / angle dispersion process
Claims (4)
前記基本波光としてファイバーレーザーによって発振スペクトルが非狭窄化されたレーザー光を連続的に発振するレーザー発振部と、
前記レーザー発振部で発振された前記基本波光のビーム径を拡大する拡大光学系部と、
前記拡大光学系部で前記ビーム径が拡大された拡大基本波光を透過させて該拡大基本波光の波長を分散させる回折格子が設けられる波長分散部と、
前記波長分散部から所定の大きさの光学的距離を介して設けられ、前記波長が分散された拡大基本波光を集光レンズで集光して前記波長変換素子に導く波長・角度分散部と、を備え、
前記波長分散部は、前記回折格子として設けられる少なくとも一の透過型回折格子と複数の反射ミラーが環状に配置されて構成され、前記透過型回折格子によって前記拡大基本波光を回折させて、該拡大基本波光の前記波長が分散させられ、前記反射ミラーによって反射後の前記拡大基本波光を前記透過型回折格子に戻し、再度回折させ、
前記反射ミラーは、前記透過型回折格子で回折後の前記拡大基本反射光を反射させて、前記透過型回折格子の最大分散効率が得られる入射角度で該透過型回折格子に戻せるように、設置角度が調整可能に構成されることを特徴とする波長変換装置。 A wavelength conversion device that converts wavelength of fundamental wave light using a wavelength conversion element,
A laser oscillation unit that continuously oscillates laser light whose oscillation spectrum is not narrowed by a fiber laser as the fundamental wave light;
A magnifying optical system for enlarging a beam diameter of the fundamental light oscillated by the laser oscillation unit;
A wavelength dispersion unit provided with a diffraction grating that transmits the expanded fundamental wave light with the beam diameter expanded by the expanded optical system unit and disperses the wavelength of the expanded fundamental wave light;
A wavelength / angle dispersion unit that is provided through an optical distance of a predetermined size from the wavelength dispersion unit, condenses the expanded fundamental wave light in which the wavelength is dispersed with a condenser lens, and guides it to the wavelength conversion element; With
The wavelength dispersion unit is configured by arranging at least one transmission type diffraction grating provided as the diffraction grating and a plurality of reflection mirrors in an annular shape, and diffracts the expanded fundamental wave light by the transmission type diffraction grating, and the expansion The wavelength of the fundamental wave light is dispersed, and the expanded fundamental wave light after being reflected by the reflection mirror is returned to the transmissive diffraction grating, and diffracted again.
The reflecting mirror is installed so that the enlarged fundamental reflected light after being diffracted by the transmissive diffraction grating can be reflected and returned to the transmissive diffraction grating at an incident angle at which the maximum dispersion efficiency of the transmissive diffraction grating can be obtained. A wavelength converter configured to be adjustable in angle.
Ｌ／ｆ＝１．２６×δｃｏｓβ
Ｌ：回折格子と集光レンズとの距離
ｆ：集光レンズの焦点距離
δ：回折格子の溝の間隔
β：回折格子による回折角 The wavelength conversion device according to claim 1, wherein the wavelength / angle dispersion unit is set so that the optical distance satisfies the following conditional expression.
L / f = 1.26 × δcosβ
L: Distance between the diffraction grating and the condensing lens f: Focal length of the condensing lens δ: Distance between the grooves of the diffraction grating β: Diffraction angle by the diffraction grating
ファイバーレーザーによって発振スペクトルが非狭窄化されたレーザー光を前記基本波光として連続的に発振するレーザー光発振工程と、
前記基本波光のビーム径を拡大するビーム径拡大工程と、
前記ビーム径が拡大された拡大基本波光を回折格子に透過させて該拡大基本波光の波長を分散させる波長分散工程と、
前記波長が分散された拡大基本波光を前記回折格子から所定の大きさの光学的距離を介して設けられた集光レンズによって前記波長変換素子に導く波長・角度分散工程と、を含み、
前記波長分散工程では、前記回折格子として設けられる透過型回折格子によって回折させてから分散された前記拡大基本波光が反射ミラーによって反射してから前記透過型回折格子の最大分散効率が得られる入射角度で前記透過型回折格子に戻されて、該透過型回折格子で再度回折させられることを特徴とする波長変換方法。 A wavelength conversion method for converting wavelength of fundamental wave light by a wavelength conversion element,
A laser beam oscillation step of continuously oscillating a laser beam whose oscillation spectrum is not narrowed by a fiber laser as the fundamental wave beam;
A beam diameter expanding step for expanding the beam diameter of the fundamental light;
A wavelength dispersion step of dispersing the wavelength of the expanded fundamental wave light by transmitting the expanded fundamental wave light having an enlarged beam diameter through a diffraction grating;
A wavelength / angle dispersion step of guiding the extended fundamental wave light in which the wavelength is dispersed to the wavelength conversion element by a condensing lens provided from the diffraction grating through an optical distance of a predetermined size, and
In the wavelength dispersion step, an incident angle at which the maximum dispersion efficiency of the transmission type diffraction grating is obtained after the expanded fundamental wave light that has been diffracted by the transmission type diffraction grating provided as the diffraction grating and then reflected by a reflection mirror Returning to the transmissive diffraction grating and re-diffracting with the transmissive diffraction grating.
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