JP3805555B2 - Laser frequency measurement method, laser frequency control method, laser frequency measurement device, and laser light generator - Google Patents

Laser frequency measurement method, laser frequency control method, laser frequency measurement device, and laser light generator Download PDF

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JP3805555B2
JP3805555B2 JP08478999A JP8478999A JP3805555B2 JP 3805555 B2 JP3805555 B2 JP 3805555B2 JP 08478999 A JP08478999 A JP 08478999A JP 8478999 A JP8478999 A JP 8478999A JP 3805555 B2 JP3805555 B2 JP 3805555B2
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optical
frequency comb
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laser light
optical frequency
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JP2000275107A5 (en
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元伸 興梠
元一 大津
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Kanagawa Academy of Science and Technology
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Kanagawa Academy of Science and Technology
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Description

【０００１】
【発明の属する技術分野】
本発明は、周波数間隔一定の側帯波をもつレーザ光からなる光周波数コムを利用したレーザ周波数測定方法、レーザ周波数制御方法、レーザ周波数測定装置及びレーザ光発生装置に関する。
【０００２】
【従来の技術】
従来より、２つのレーザ光をヘテロダイン検波してその差周波数を測定あるいは制御する場合、その帯域は受光素子の帯域で制限され、おおむね数十ＧＨｚ程度であるので、光周波数コム発生器を用いて広帯域なヘテロダイン検波系を構築するようにしている。光周波数コム発生器は、入射したレーザ光の側帯波を等周波数間隔毎に数百本発生させるもので、発生される側帯波の周波数安定度はもとのレーザ光のそれとほぼ同等である。そこで、この側帯波と被測定レーザ光をヘテロダイン検波することにより、数ＴＨｚに亘る広帯域なヘテロダイン検波系を構築することができる。
【０００３】
【発明が解決しようとする課題】
ところで、従来、光周波数コムと被測定レーザ光をヘテロダイン検波してその差周波数を測定あるいは制御する場合、コムの１つのモード（サイドバンド）と被測定レーザ光とで直接ビート発生を行いビート測定していたために、コムのサイドバンドパワーでＳＮ比が決定していた。サイドバンドパワーはコムの中心周波数から離れるに従って減少する傾向にあるので、コムのパワーが小さい場合にＳＮ比が低くなり十分な測定精度を確保することができなくなってしまうという問題点があった。
【０００４】
本発明の目的は、このような従来の問題点に鑑み、光周波数コムと被測定レーザ光をヘテロダイン検波してその差周波数を測定あるいは制御するに当たり、ＳＮ比を改善して十分な測定精度を確保し、広範囲に亘ってレーザ周波数を測定あるいは制御することができるようにしたレーザ周波数測定方法、レーザ周波数制御方法、レーザ周波数測定装置及びレーザ光発生装置を提供することにある。
【０００５】
【課題を解決するための手段】
本発明に係るレーザ周波数測定方法は、第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コムと第２のレーザ光とを混合し、その混合光から１つの非線形光学結晶素子を介して、上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と上記光周波数コムの光第２高調波成分を得て、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分のヘテロダイン成分を検出し、上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を測定することを特徴とする。
また、本発明に係るレーザ周波数測定方法は、第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コムと第２のレーザ光とを混合し、その混合光から第１の非線形光学結晶素子を介して上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分を得るとともに、上記光周波数コムから第２の非線形光学結晶素子を介して光第２高調波発生により光第２高調波成分を得て、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とを混合し、その混合光から上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分を検出し、上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を測定することを特徴とする。
本発明に係るレーザ周波数測定方法において、上記第２の光周波数コム成分は、例えば、上記光周波数コムと上記第２のレーザ光の和周波数成分である。
また、本発明に係るレーザ周波数測定方法では、例えば、上記第１のレーザ光又は第２のレーザ光の一方のレーザ光を基準として、検出された上記ヘテロダイン成分に基づいて、他方のレーザ光の周波数を測定する。
【０００６】
本発明に係るレーザ周波数制御方法は、第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コムと第２のレーザ光とを混合し、その混合光から１つの非線形光学結晶素子を介して上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、上記光周波数コムの光第２高調波成分を得て、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分のヘテロダイン成分を検出し、上記ヘテロダイン成分の検出出力に基づいて上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように帰還制御することを特徴とする。
また、本発明に係るレーザ周波数制御方法は、第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コムと第２のレーザ光とを混合し、その混合光から第１の非線形光学結晶素子を介して上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分を得るとともに、第２の非線形光学結晶素子を介して光第２高調波発生による上記光周波数コムの光第２高調波成分を得て、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とを混合し、その混合光から上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分を検出し、上記ヘテロダイン成分の検出出力に基づいて上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように帰還制御することを特徴とする。
本発明に係るレーザ周波数制御方法において、上記第２の光周波数コム成分は、例えば、上記光周波数コムと上記第２のレーザ光の和周波数成分である。
【０００７】
本発明に係るレーザ周波数測定装置は、第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを発生する光周波数コム発生手段と、上記光周波数コム発生手段により生成された光周波数コムと第２のレーザ光とを混合する光学系と、上記光学系により混合された上記光周波数コムと第２のレーザ光の混合光が入射される非線形光学結晶素子と、上記非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、光第２高調波発生による上記光周波数コムの光第２高調波成分のヘテロダイン成分を検出するヘテロダイン検波手段とを備え、上記ヘテロダイン検波手段による上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を測定することを特徴とする。
また、本発明に係るレーザ周波数測定装置は、第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを発生する光周波数コム発生手段と、上記光周波数コム発生手段により発生された光周波数コムと第２のレーザ光とを混合する第１の光学系と、上記第１の光学系により混合された上記光周波数コムと第２のレーザ光の混合光が入射される第１の非線形光学結晶素子と、上記光周波数コム発生手段により発生された光周波数コムが入射される第２の非線形光学結晶素子と、上記第１の非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、上記第２の非線形光学結晶素子を介して得られる光第２高調波発生による上記光周波数コムの光第２高調波成分とを混合する第２の光学系と、上記第２の光学系により混合された上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分の混合光から、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分を検出するヘテロダイン検波手段と、上記ヘテロダイン検波手段による上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を測定することを特徴とする。
本発明に係るレーザ周波数測定装置において、上記第２の光周波数コム成分は、例えば、上記光周波数コムと上記第２のレーザ光の和周波数成分である。
また、本発明に係るレーザ周波数測定装置では、例えば、上記第１のレーザ光又は第２のレーザ光の一方のレーザ光を基準として、上記ヘテロダイン検波手段により検出された上記ヘテロダイン成分に基づいて、他方のレーザ光の周波数を測定する。
【０００８】
本発明に係るレーザ光発生装置は、第１のレーザ光を出射する第１のレーザ光源と、上記第１のレーザ光源から出射された第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを発生する光周波数コム発生手段と、第２のレーザ光を出射する第２のレーザ光源と、上記光周波数コム発生手段により生成された光周波数コムと上記第２のレーザ光源から出射された第２のレーザ光とを混合する光学系と、上記光学系により混合された上記光周波数コムと第２のレーザ光の混合光が入射される非線形光学結晶素子と、上記非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、光第２高調波発生による上記光周波数コムの光第２高調波成分のヘテロダイン成分を検出するヘテロダイン検波手段と、上記ヘテロダイン検波手段による上記ヘテロダイン成分の検出出力に基づいて上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように上記第１のレーザ光源と第２のレーザ光源の一方を帰還制御する制御手段とを備えることを特徴とする。
また、本発明に係るレーザ光発生装置は、第１のレーザ光を出射する第１のレーザ光源と、上記第１のレーザ光源から出射された第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを発生する光周波数コム発生手段と、第２のレーザ光を出射する第２のレーザ光源と、上記光周波数コム発生手段により発生された光周波数コムと第２のレーザ光とを混合する第１の光学系と、上記第１の光学系により混合された上記光周波数コムと上記第２のレーザ光源から出射された第２のレーザ光の混合光が入射される第１の非線形光学結晶素子と、上記光周波数コム発生手段により発生された光周波数コムが入射される第２の非線形光学結晶素子と、上記第１の非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、上記第２の非線形光学結晶素子を介して得られる光第２高調波発生による上記光周波数コムの光第２高調波成分とを混合する第２の光学系と、上記第２の光学系により混合された上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分の混合光から、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分を検出するヘテロダイン検波手段と、上記ヘテロダイン検波手段による上記ヘテロダイン成分の検出出力に基づいて上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように上記第１のレーザ光源と第２のレーザ光源の一方を帰還制御する制御手段とを備えることを特徴とする。
本発明に係るレーザ光発生装置において、上記第２の光周波数コム成分は、例えば、上記光周波数コムと上記第２のレーザ光の和周波数成分である。
【０００９】
【発明の実施の形態】
以下、本発明の実施の形態について、図面を参照しながら詳細に説明する。
【００１０】
本発明は、例えば図１に示すような構成のレーザ周波数測定システム１００に適用される。
【００１１】
この図１に示したレーザ周波数測定システム１００は、基準レーザ光を出射する第１のレーザ光源１１０と、この第１のレーザ光源１１０から出射された基準レーザ光が入射される光周波数コム発生器１２０と、被測定レーザ光を出射する第２のレーザ光源１３０と、上記光周波数コム発生器１２０により発生された光周波数コムと上記第２のレーザ光源１３０から出射された被測定レーザ光とを混合する光学系１４０と、この光学系１４０により混合されたレーザ光が入射される非線形光学結晶素子１５０と、この非線形光学結晶素子５０から出射されたレーザ光を受光する光検出器１６０と、この光検出器１６０による検出出力が供給される周波数測定器１７０とからなる。
【００１２】
このレーザ周波数測定システム１００において、上記光学系１４０により混合されたレーザ光が入射される非線形光学結晶素子１５０から出射されるレーザ光には、上記光学系１４０により混合されたレーザ光すなわち光周波数コムと被測定レーザ光との和周波数成分と、光第２高調波発生（ＳＨＧ）による光第２高調波成分が含まれる。
【００１３】
そして、上記周波数測定器１７０では、上記非線形光学結晶素子１５０から出射されたレーザ光を受光する光検出器１６０による検出出力に基づいて、上記被測定レーザ光と光周波数コムの和周波数成分と光第２高調波発生（ＳＨＧ）による光第２高調波成分のヘテロダイン成分を検出することにより、上記被測定レーザ光の周波数を測定する。
【００１４】
このレーザ周波数測定システム１００において、上記第１のレーザ光源１１０には、例えば波長が１．５４８μｍの基準レーザ光を出射するレーザダイオードを用いた。上記光周波数コム発生器１２０は、上記第１のレーザ光源１１０から出射された基準レーザ光の周波数を中心に低周波数側と高周波数側に周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを発生する。上記光周波数コム発生器１２０としては、結合空洞共振器型光周波数コム発生器（CC_OFCG: Coupled Cavity Optical Frequency Comb Generator）や例えば特開平７−５８３８６号公報に記載されているような導波路型光位相変調器を用いた光周波数コム発生器を使用することができる。
【００１５】
このレーザ周波数測定システム１００では、上記光周波数コム発生器１２０により発生された帯域１０ＴＨｚ、平均パワー０．４ｍＷ、パルス幅１ｐｓの光周波数コムを帯域幅が４．５ＴＨｚのファイバー増幅器２１により平均パワー１８０ｍＷまで増幅して光学系１４０に入射するようにしてある。
【００１６】
また、上記第２のレーザ光源１３０が出射する被測定レーザ光は波長が１．５２８μｍで平均パワー１５ｍＷとした。したがって、基準レーザ光と被測定レーザ光の間の差周波数（δν）は２．４ＴＨｚとなっている。
【００１７】
また、このレーザ周波数測定システム１００では、上記非線形光学結晶素子１５０として周期的に分極反転されたニオブ酸リチウムＰＰＬＮ(periodically poled lithium niobate)結晶が用いられており、１．５５２μｍ付近の波長に対する光第２高調波に位相整合させている。ここで、上記非線形光学結晶素子１５０によるＳＨＧの中心周波数に対応する波長０．７７６μｍは、１．５２８μｍの被測定レーザ光と光周波数コムの１．５７６μｍ付近の成分の和周波数成分の波長にも対応している。
【００１８】
ここで、上記光学系１４０により被測定レーザ光と光周波数コムを混合したレーザ光を分解能が０．１ｎｍの光スペクトラムアナライザにより観測した結果を図２に示してある。この図２から明らかなように、上記ファイバー増幅器１２１により増幅された光周波数コムは、上記ファイバー増幅器１２１のカットオフにより帯域制限され、１．５２８μｍ帯域では減衰してしまっている。
【００１９】
また、上記非線形光学結晶素子１５０から出射されたレーザ光を分解能が０．１ｎｍの光スペクトラムアナライザにより観測した結果を図３に示してある。
【００２０】
図３において、（Ａ）は上記第２のレーザ光源１３０をオフにしたときに上記非線形光学結晶素子１５０から出射されたＳＨＧ光周波数コムのスペクトラムを示し、（Ｂ）は、上記第２のレーザ光源１３０をオンにしたときに上記非線形光学結晶素子１５０から出射されたＳＨＧ光周波数コムのスペクトラムを示している。
【００２１】
この図３から明らかなように、（Ａ）は上記第２のレーザ光源１３０をオフにしたときに上記非線形光学結晶素子１５０から出射されたＳＨＧ光周波数コムのスペクトラム（Ａ）よりも、上記第２のレーザ光源１３０をオンにしたときに上記非線形光学結晶素子１５０から出射されたＳＨＧ光周波数コムのスペクトラム（Ｂ）の方が、範囲が広いとともにパワーが大きい。
【００２２】
このように、ＳＨＧの中心周波数を１．５５２μｍ付近の波長に設定したＰＰＬＮ結晶を上記非線形光学結晶素子１５０として用いることにより、光周波数コムの１．５７６μｍ付近の成分と１．５２８μｍの被測定レーザ光の和周波数と光周波数コムの１．５５２μｍ付近の成分のＳＨＧを１つのの結晶で行うことができる。そして、上記光周波数コムの１．５７６μｍ付近の成分と１．５２８μｍの被測定レーザ光の和周波数と光周波数コムの１．５５２μｍ付近の成分のＳＨＧ成分は共に０．７７６μｍの波長帯域で重なるために、その両者のヘテロダイン（ビート）成分を上記光検出器１６０による検出出力に基づいて検出することができる。
【００２３】
ここで、被測定レーザ光と光周波数コムのヘテロダイン（ビート）成分を分解能１ＭＨｚ、スパン１００ＭＨｚの無線周波数スペクトラムアナライザにより観測した結果を図４に示してある。
【００２４】
図４において、（Ａ）は上記光学系１４０により光周波数コムと被測定レーザ光を混合したレーザ光をゲルマニウムピン（Ｇｅ−ＰＩＮ）フォトダイオードで検出し、その検出出力に基づいて観測した被測定レーザ光と光周波数コムのヘテロダイン（ビート）成分のスペクトラムを示し、（Ｂ）は上記非線形光学結晶素子１５０からの出射光をシリコンアバランシェフォトダイオード（Ｓｉ−ＡＰＤ）で検出し、その検出出力に基づいて観測した上記被測定レーザ光と光周波数コムを混合した和周波数の光周波数コムとＳＨＧ光周波数コムのヘテロダイン（ビート）成分のスペクトラムを示している。
【００２５】
この図４から明らかなように、上記光検出器１６０による検出出力に基づいて上記被測定レーザ光と光周波数コムを混合した和周波数の光周波数コムとＳＨＧ光周波数コムのヘテロダイン（ビート）成分を検出することにより、ＳＮ比を５ｄＢ程度改善することができた。
【００２６】
すなわち、上記被測定レーザ光と光周波数コムを混合した和周波数の光周波数コムとＳＨＧ光周波数コムのヘテロダイン（ビート）成分は、位相が揃っているので、高いＳＮ比で検出することができる。なお、このレーザ周波数測定システム１００では、上記非線形光学結晶素子１５０として用いる非線形光学結晶を選択したり、レーザパワーを上げることによりさらに高いＳＮ比で検出することが可能となる。
【００２７】
このレーザ周波数測定システム１００のように、基準レーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コムと被測定レーザ光との光混合により得られる上記光周波数コムと被測定レーザ光の和周波数成分と、上記光周波数コムから光第２高調波発生により得られる光第２高調波成分とのヘテロダイン成分を検出することにより、高いＳＮ比でヘテロダイン成分を検出することができ、上記ヘテロダイン成分の検出出力に基づいて上記被測定レーザ光の周波数を高い測定精度を確保して広範囲に亘って測定することができる。
【００２８】
ここで、上記レーザ周波数測定システム１００では、第１のレーザ光源１１０から出射される基準レーザ光に基づいて光周波数コム発生１２０により光周波数コムを発生し、第２のレーザ光源１３０から出射される被測定レーザ光の周波数を測定するようにしたが、ヘテロダイン成分の検出による周波数測定は相対的な周波数測定であるから、第１のレーザ光源１１０と第２のレーザ光源１３０を置き換えて、被測定レーザ光に基づいて光周波数コム発生１２０により光周波数コムを発生するようにしてもよい。
【００２９】
また、上記レーザ周波数測定システム１００では、第１のレーザ光源１１０と第２のレーザ光源１３０を用いてヘテロダイン成分の検出による周波数測定を行ったが、３個のレーザ光源を用い、そのうちの１つから出射される基準レーザ光に基づいて他の２個のレーザ光源から出射されるレーザ光の差周波数を測定する等の変形も可能である。
【００３０】
また、上記レーザ周波数測定システム１００では、上記光学系１４０を介して光周波数コムと被測定レーザ光を混合したレーザ光が入射される上記非線形光学結晶素子１５０により、上記光周波数コムと被測定レーザ光の和周波数成分と、上記光周波数コムの光第２高調波成分を得るようにしたが、図５に示すレーザ周波数測定システム１００Ａのように、上記光周波数コムと被測定レーザ光の和周波数成分と、上記光周波数コムの光第２高調波成分を個別の非線形光学結晶素子１５０Ａ，１５０Ｂにより得るようにすることもできる。
【００３１】
すなわち、図５に示すレーザ周波数測定システム１００Ａでは、第１のレーザ光源１１０から出射された基準レーザ光に基づいて光周波数コム発生器１２０により周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コム発生器１２０により発生された光周波数コムと第２のレーザ光源１３０から出射された被測定レーザ光を第１の光学系１４０Ａを混合し、この第１の光学系１４０Ａにより混合されたレーザ光から第１の非線形光学結晶素子１５０Ａにより上記光周波数コムと被測定レーザ光の和周波数成分を得るとともに、第２の非線形光学結晶素子１５０Ｂにより上記光周波数コムの光第２高調波成分を得て、上記光周波数コムと被測定レーザ光の和周波数成分と上記光周波数コムの光第２高調波成分を第２の光学系１４０Ｂにより混合するようになっている。そして、周波数測定器１７０は、上記第２の光学系１４０Ｂから出射される混合光を受光する光検出器１６０による検出出力に基づいて、上記被測定レーザ光と光周波数コムの和周波数成分と、光周波数コムの光第２高調波成分とのヘテロダイン成分を検出することにより、上記被測定レーザ光の周波数を測定する。
【００３２】
このレーザ周波数測定システム１００Ａでは、上記光周波数コムと被測定レーザ光の和周波数成分を得るため第１の非線形光学結晶素子１５０Ａと、上記光周波数コムの光第２高調波成分を得るため第２の非線形光学結晶素子１５０Ｂの特性を個別に最適化することができるので、ヘテロダイン成分のＳＮ比をさらに高くすることができる。
【００３３】
また、本発明は、例えば図６に示すような構成のレーザ光発生装置２００に適用される。
【００３４】
この図６に示したレーザ光発生装置２００は、基準レーザ光を出射する第１のレーザ光源２１０と、この第１のレーザ光源２１０から出射された基準レーザ光が入射される光周波数コム発生器２２０と、被制御レーザ光を出射する第２のレーザ光源２３０と、上記光周波数コム発生器２２０により発生された光周波数コムと上記第２のレーザ光源２３０から出射された被制御レーザ光とを混合する光学系２４０と、この光学系２４０により混合されたレーザ光が入射される非線形光学結晶素子２５０と、この非線形光学結晶素子２５０から出射されたレーザ光を受光する光検出器２６０と、この光検出器２６０による検出出力に基づいて上記第２のレーザ光源２３０を制御する制御装置２７０とからなる。
【００３５】
このレーザ光発生装置２００において、光周波数コム発生器２２０は、第１のレーザ光源２１０から出射された基準レーザ光の周波数を中心に低周波数側と高周波数側に周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを発生する。また、光学系２４０は、上記光周波数コム発生器２２０により発生された光周波数コムと上記第２のレーザ光源２３０から出射された被制御レーザ光とを混合し、その混合光を光第２高調波発生（ＳＨＧ）用の非線形光学結晶素子２５０に供給する。また、上記非線形光学結晶素子２５０は、上記光学系２４０を介して供給される光周波数コムと被制御レーザ光の混合光を入射光とし、基準レーザ光と被制御レーザ光の波長の中間の周波数に中心周波数を設定した光第２高調波発生（ＳＨＧ）を行う。そして、制御装置２７０は、この非線形光学結晶素子２５０から出射されたレーザ光を受光する光検出器２６０による検出出力に基づいて、上記レーザ光に含まれる上記光周波数コムと被測定レーザ光の和周波数成分と上記非線形光学結晶素子２５０による光第２高調波発生により得られる光第２高調波成分のヘテロダイン（ビート）成分を検出し、その検出出力を上記第２のレーザ光源２３０に帰還することにより、上記第２のレーザ光源２３０が出射する被制御レーザ光の周波数を上記光周波数コムにより与えられる目的の周波数にロックする制御を行う。
【００３６】
このレーザ光発生装置２００のように、基準レーザ光の周波数を中心に低周波数側と高周波数側に周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムと被制御レーザ光とを混合し、上記光周波数コムと被制御レーザ光との混合光から光第２高調波発生により得られる光第２高調波成分と、上記混合光に含まれる上記光周波数コムと被制御レーザ光の和周波数成分とのヘテロダイン成分を検出し、高いＳＮ比でヘテロダイン成分を検出することができ、上記ヘテロダイン成分の検出出力を帰還して被制御レーザ光の周波数を制御することにより、被制御レーザ光の周波数を広範囲に亘って高精度に制御することができる。したがって、このレーザ光発生装置２００では、広い周波数範囲に亘って極めて安定した被制御レーザ光を発生することができる。
【００３７】
ここで、上記レーザ光発生装置２００では、第１のレーザ光源２１０から出射される基準レーザ光に基づいて光周波数コム発生２２０により光周波数コムを発生し、第２のレーザ光源２３０から出射される被制御レーザ光の周波数を制御するようにしたが、ヘテロダイン成分の検出による周波数制御は相対的制御であるから、第１のレーザ光源２１０と第２のレーザ光源２３０を置き換えて、被測定レーザ光に基づいて光周波数コム発生２２０により光周波数コムを発生するようにしてもよい。
【００３８】
また、上記レーザ光発生装置２００では、上記光学系２４０を介して光周波数コムと被制御レーザ光を混合したレーザ光が入射される上記非線形光学結晶素子２５０により、上記光周波数コムと被測定レーザ光の和周波数成分と、上記光周波数コムの光第２高調波成分を得るようにしたが、上記光周波数コムと被測定レーザ光の和周波数成分と、上記光周波数コムの光第２高調波成分を個別の非線形光学結晶素子により得るようにしてもよい。各非線形光学結晶素子を個別に最適化することにより、ヘテロダイン成分のＳＮ比をさらに高くすることができる。
【００３９】
【発明の効果】
本発明に係るレーザ周波数測定方法では、第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コムと第２のレーザ光の混合光から１つの非線形光学結晶素子を介して、上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と上記光周波数コムの光第２高調波成分を得て、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分のヘテロダイン成分を検出するので、高いＳＮ比で上記ヘテロダイン成分を検出することができ、上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を広範囲に亘って高い測定精度を確保して測定することができる。
また、本発明に係るレーザ周波数測定方法では、第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コムと第２のレーザ光の混合光から第１の非線形光学結晶素子を介して上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分を得るとともに、上記光周波数コムから第２の非線形光学結晶素子を介して光第２高調波発生により光第２高調波成分を得て、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分の混合光から上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分を検出するので、高いＳＮ比で上記ヘテロダイン成分を検出することができ、上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を広範囲に亘って高い測定精度を確保して測定することができる。そして、このレーザ周波数測定方法では、上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分を得るため第１の非線形光学結晶素子と、上記光周波数コムの光第２高調波成分を得るため第２の非線形光学結晶素子の特性を個別に最適化することができるので、ヘテロダイン成分のＳＮ比をさらに高くすることができる。
そして、本発明に係るレーザ周波数測定方法では、例えば、上記第１のレーザ光又は第２のレーザ光の一方のレーザ光を基準として、上記ヘテロダイン検波手段により検出された上記ヘテロダイン成分に基づいて、高い測定精度を確保して他方のレーザ光の周波数を広範囲に亘って測定することができる。
【００４０】
本発明に係るレーザ周波数制御方法では、第１のレーザ光から生成した光周波数コムと第２のレーザ光の混合光から１つの非線形光学結晶素子を介して上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、上記光周波数コムの光第２高調波成分を得て、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分のヘテロダイン成分を検出するので、高いＳＮ比で上記ヘテロダイン成分を検出することができ、上記ヘテロダイン成分の検出出力に基づいて、上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように帰還制御することにより、上記差周波数を広範囲に亘って高精度に制御することができる。
また、本発明に係るレーザ周波数制御方法では、第１のレーザ光から生成した光周波数コムと第２のレーザ光の混合光から第１の非線形光学結晶素子を介して上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分を得るとともに、第２の非線形光学結晶素子を介して光第２高調波発生による上記光周波数コムの光第２高調波成分を得て、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分の混合光から上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分を検出するので、高いＳＮ比でヘテロダイン成分を検出することができ、上記ヘテロダイン成分の検出出力に基づいて、上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように帰還制御することにより、上記差周波数を広範囲に亘って高精度に制御することができる。さらに、このレーザ周波数制御方法では、上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分を得るため第１の非線形光学結晶素子と、上記光周波数コムの光第２高調波成分を得るため第２の非線形光学結晶素子の特性を個別に最適化することができるので、ヘテロダイン成分のＳＮ比をさらに高くすることができる。
【００４１】
本発明に係るレーザ周波数測定装置では、光周波数コム発生手段により第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コムと第２のレーザ光との混合光から１つの非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、光第２高調波発生による上記光周波数コムの光第２高調波成分のヘテロダイン成分をヘテロダイン検波手段により検出するので、高いＳＮ比で上記ヘテロダイン成分を検出することができ、上記ヘテロダイン検波手段による上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を広範囲に亘って高い測定精度を確保して測定することができる。
また、本発明に係るレーザ周波数測定装置では、光周波数コム発生手段により第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コムと第２のレーザ光の混合光から第１の非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、第２の非線形光学結晶素子を介して得られる光第２高調波発生による上記光周波数コムの光第２高調波成分の混合光から、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分をヘテロダイン検波手段により検出するので、高いＳＮ比で上記ヘテロダイン成分を検出することができ、上記ヘテロダイン成分の検出出力に基づいて上記差周波数を広範囲に亘って高い測定精度を確保して測定することができる。さらに、このレーザ周波数測定方法では、上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分を得るため第１の非線形光学結晶素子と、上記光周波数コムの光第２高調波成分を得るため第２の非線形光学結晶素子の特性を個別に最適化することができるので、ヘテロダイン成分のＳＮ比をさらに高くすることができる。
そして、本発明に係るレーザ周波数測定装置では、例えば、上記第１のレーザ光又は第２のレーザ光の一方のレーザ光を基準として、上記ヘテロダイン検波手段により検出された上記ヘテロダイン成分に基づいて、高い測定精度を確保して他方のレーザ光の周波数を広範囲に亘って測定することができる。
【００４２】
本発明に係るレーザ光発生装置では、光周波数コム発生手段により第１のレーザ光源から出射された第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コム発生手段により生成された光周波数コムと上記第２のレーザ光源から出射された第２のレーザ光の混合光から、１つの非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、光第２高調波発生による上記光周波数コムの光第２高調波成分のヘテロダイン成分をヘテロダイン検波手段により検出するので、高いＳＮ比でヘテロダイン成分を検出することができ、上記ヘテロダイン成分の検出出力に基づいて、制御手段により上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように広い周波数範囲に亘って極めて安定に帰還制御することができる。
また、本発明に係るレーザ光発生装置では、光周波数コム発生手段により第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、上記光周波数コムと第２のレーザ光の混合光から第１の非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、第２の非線形光学結晶素子を介して得られる光第２高調波発生による上記光周波数コムの光第２高調波成分の混合光から、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分をヘテロダイン検波手段により検出するので、高いＳＮ比で上記ヘテロダイン成分を検出することができ、上記ヘテロダイン成分の検出出力に基づいて、制御手段により上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように広い周波数範囲に亘って極めて安定に帰還制御することができる。さらにこのレーザ光発生装置では、上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分を得るため第１の非線形光学結晶素子と、上記光周波数コムの光第２高調波成分を得るため第２の非線形光学結晶素子の特性を個別に最適化することができるので、ヘテロダイン成分のＳＮ比をさらに高くすることができる。
【図面の簡単な説明】
【図１】本発明を適用したレーザ周波数測定システムの構成を示すブロック図である。
【図２】上記レーザ周波数測定システムおいて被測定レーザ光と光周波数コムを混合したレーザ光を分解能が０．１ｎｍの光スペクトラムアナライザにより観測した結果を示す図である。
【図３】上記レーザ周波数測定システムおいて、非線形光学結晶素子から出射されたレーザ光を分解能が０．１ｎｍの光スペクトラムアナライザにより観測した結果を示す図であり、（Ａ）は第２のレーザ光源をオフにしたときに上記非線形光学結晶素子から出射されたＳＨＧ光周波数コムのスペクトラムを示し、（Ｂ）は、上記第２のレーザ光源をオンにしたときに上記非線形光学結晶素子から出射されたＳＨＧ光周波数コムのスペクトラムを示している。
【図４】上記レーザ周波数測定システムおいて、被測定レーザ光と光周波数コムのヘテロダイン（ビート）成分を分解能１ＭＨｚ、スパン１００ＭＨｚの無線周波数スペクトラムアナライザにより観測した結果を示す図であり、（Ａ）は被測定レーザ光と光周波数コムを混合したレーザ光に含まれる被制御レーザ光と光周波数コムのヘテロダイン（ビート）成分のスペクトラムを示し、（Ｂ）は非線形光学結晶素子から出射されたレーザ光に含まれる上記被測定レーザ光と光周波数コムを混合した和周波数の光周波数コムとＳＨＧ光周波数コムのヘテロダイン（ビート）成分のスペクトラムを示している。
【図５】本発明を適用したレーザ周波数測定システムの他の構成例を示すブロック図である。
【図６】本発明を適用したレーザ光発生装置の構成を示すブロック図である。
【符号の説明】
１００，１００Ａ レーザ周波数測定システム、１１０ 第１のレーザ光源、１２０ 光周波数コム発生器、１２１ ファイバー増幅器、１３０ 第２のレーザ光源、１４０，１４０Ａ，１４０Ｂ 光学系、１５０，１５０Ａ，１５０Ｂ 非線形光学結晶素子、１６０ 光検出器、１７０ 周波数測定器、 ２００ レーザ光発生装置、２１０ 第１のレーザ光源、２２０ 光周波数コム発生器、２３０ 第２のレーザ光源、２４０ 光学系、２５０ 非線形光学結晶素子と２６０ 光検出器、２７０ 制御装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser frequency measurement method, a laser frequency control method, a laser frequency measurement device, and a laser light generation device using an optical frequency comb composed of laser light having sidebands with a constant frequency interval.
[0002]
[Prior art]
Conventionally, when heterodyne detection is performed on two laser beams and the difference frequency is measured or controlled, the band is limited by the band of the light receiving element and is generally about several tens of GHz. Therefore, an optical frequency comb generator is used. A wideband heterodyne detection system is constructed. The optical frequency comb generator generates several hundred sidebands of incident laser light at equal frequency intervals, and the frequency stability of the generated sideband is almost the same as that of the original laser light. Therefore, by performing heterodyne detection on the sideband and laser light to be measured, a wideband heterodyne detection system extending over several THz can be constructed.
[0003]
[Problems to be solved by the invention]
By the way, conventionally, when heterodyne detection of the optical frequency comb and the laser beam to be measured is performed to measure or control the difference frequency, beat measurement is performed by directly generating a beat with one mode (sideband) of the comb and the laser beam to be measured. Therefore, the signal-to-noise ratio was determined by the sideband power of Com. Since the sideband power tends to decrease with increasing distance from the center frequency of the comb, there has been a problem that when the power of the comb is small, the SN ratio becomes low and sufficient measurement accuracy cannot be secured.
[0004]
In view of such conventional problems, the object of the present invention is to improve the S / N ratio and provide sufficient measurement accuracy in heterodyne detection of the optical frequency comb and the measured laser beam and measuring or controlling the difference frequency. It is an object of the present invention to provide a laser frequency measurement method, a laser frequency control method, a laser frequency measurement device, and a laser light generation device that are secured and capable of measuring or controlling a laser frequency over a wide range.
[0005]
[Means for Solving the Problems]
The laser frequency measurement method according to the present invention generates an optical frequency comb composed of laser light having sidebands having a constant frequency interval based on the first laser light, and mixes the optical frequency comb with the second laser light. Then, a second optical frequency comb component having the same frequency interval as the optical frequency comb and an optical second harmonic component of the optical frequency comb are obtained from the mixed light through one nonlinear optical crystal element, And detecting the heterodyne component of the second optical frequency comb component and the optical second harmonic component of the optical frequency comb, and detecting the light of the second optical frequency comb component and the optical frequency comb based on the detection output of the heterodyne component. A difference frequency from the second harmonic component is measured.
The laser frequency measurement method according to the present invention generates an optical frequency comb composed of laser light having a sideband with a constant frequency interval based on the first laser light, and the optical frequency comb, the second laser light, And a second optical frequency comb component having the same frequency interval as the optical frequency comb is obtained from the mixed light through the first nonlinear optical crystal element, and the second nonlinear optical crystal element is obtained from the optical frequency comb. To obtain an optical second harmonic component by optical second harmonic generation, and mix the second optical frequency comb component and the optical second harmonic component of the optical frequency comb from the mixed light. A heterodyne component between the second optical frequency comb component and the optical second harmonic component of the optical frequency comb is detected, and the second optical frequency comb component and the optical frequency comb are detected based on the detection output of the heterodyne component. of And measuring the difference frequency between the second harmonic component.
In the laser frequency measurement method according to the present invention, the second optical frequency comb component is, for example, a sum frequency component of the optical frequency comb and the second laser light.
In the laser frequency measurement method according to the present invention, for example, based on one of the first laser light and the second laser light as a reference, the other laser light is detected based on the detected heterodyne component. Measure the frequency.
[0006]
The laser frequency control method according to the present invention generates an optical frequency comb composed of laser light having sidebands having a constant frequency interval based on the first laser light, and mixes the optical frequency comb and the second laser light. Then, a second optical frequency comb component having the same frequency interval as the optical frequency comb and an optical second harmonic component of the optical frequency comb are obtained from the mixed light through one nonlinear optical crystal element, And detecting a heterodyne component of the second optical frequency comb component and an optical second harmonic component of the optical frequency comb, and calculating a difference frequency between the first laser beam and the second laser beam based on the detection output of the heterodyne component. The feedback control is performed so as to be constant.
The laser frequency control method according to the present invention generates an optical frequency comb composed of laser light having a sideband with a constant frequency interval based on the first laser light, and the optical frequency comb and the second laser light And a second optical frequency comb component having the same frequency interval as that of the optical frequency comb is obtained from the mixed light via the first nonlinear optical crystal element, and the second optical frequency comb component is obtained via the second nonlinear optical crystal element. An optical second harmonic component of the optical frequency comb due to second harmonic generation is obtained, the second optical frequency comb component and the optical second harmonic component of the optical frequency comb are mixed, and the mixed light A heterodyne component between a second optical frequency comb component and an optical second harmonic component of the optical frequency comb is detected, and a difference between the first laser beam and the second laser beam based on a detection output of the heterodyne component Constant frequency Characterized by a feedback control such that.
In the laser frequency control method according to the present invention, the second optical frequency comb component is, for example, a sum frequency component of the optical frequency comb and the second laser light.
[0007]
The laser frequency measuring device according to the present invention includes an optical frequency comb generating means for generating an optical frequency comb composed of laser light having a sideband with a constant frequency interval based on the first laser light, and the optical frequency comb generating means. An optical system for mixing the generated optical frequency comb and the second laser light, a nonlinear optical crystal element on which the mixed light of the optical frequency comb and the second laser light mixed by the optical system is incident, A second optical frequency comb component having the same frequency interval as that of the optical frequency comb obtained through the nonlinear optical crystal element, and a heterodyne component of the optical second harmonic component of the optical frequency comb due to optical second harmonic generation are obtained. Heterodyne detection means for detecting, based on the detection output of the heterodyne component by the heterodyne detection means, the second optical frequency comb component and the optical frequency And measuring the difference frequency between the number comb of optical second harmonic component.
The laser frequency measuring apparatus according to the present invention includes an optical frequency comb generating means for generating an optical frequency comb composed of laser light having a sideband with a constant frequency interval based on the first laser light, and the optical frequency comb generation described above. The first optical system for mixing the optical frequency comb generated by the means and the second laser light, and the mixed light of the optical frequency comb and the second laser light mixed by the first optical system are incident Obtained through the first nonlinear optical crystal element, the second nonlinear optical crystal element to which the optical frequency comb generated by the optical frequency comb generating means is incident, and the first nonlinear optical crystal element. A second optical frequency comb component having the same frequency interval as the optical frequency comb, and an optical second harmonic component of the optical frequency comb generated by optical second harmonic generation obtained through the second nonlinear optical crystal element From the mixed light of the second optical system that mixes the second optical frequency comb component and the optical second harmonic component of the optical frequency comb mixed by the second optical system. Heterodyne detection means for detecting a heterodyne component of a frequency comb component and an optical second harmonic component of the optical frequency comb, and the second optical frequency comb component based on the detection output of the heterodyne component by the heterodyne detection means And measuring the difference frequency between the optical second harmonic component of the optical frequency comb.
In the laser frequency measurement device according to the present invention, the second optical frequency comb component is, for example, a sum frequency component of the optical frequency comb and the second laser light.
Further, in the laser frequency measuring device according to the present invention, for example, based on the heterodyne component detected by the heterodyne detection means with reference to one of the first laser beam or the second laser beam, The frequency of the other laser beam is measured.
[0008]
A laser beam generator according to the present invention includes a first laser light source that emits a first laser beam, and a sideband having a constant frequency interval based on the first laser beam emitted from the first laser light source. An optical frequency comb generating means for generating an optical frequency comb composed of a laser beam, a second laser light source for emitting a second laser light, an optical frequency comb generated by the optical frequency comb generating means, and the second An optical system for mixing the second laser light emitted from the laser light source, a nonlinear optical crystal element on which the mixed light of the optical frequency comb mixed by the optical system and the second laser light is incident, A heterodyne of a second optical frequency comb component having the same frequency interval as that of the optical frequency comb obtained through the nonlinear optical crystal element, and an optical second harmonic component of the optical frequency comb by optical second harmonic generation. Heterodyne detection means for detecting the minute, and the first laser light source so as to make the difference frequency between the first laser light and the second laser light constant based on the detection output of the heterodyne component by the heterodyne detection means And control means for performing feedback control of one of the second laser light sources.
The laser light generator according to the present invention includes a first laser light source that emits the first laser light, and a side having a constant frequency interval based on the first laser light emitted from the first laser light source. An optical frequency comb generating means for generating an optical frequency comb composed of a laser beam having a band; a second laser light source for emitting a second laser light; an optical frequency comb generated by the optical frequency comb generating means; The first optical system that mixes the two laser beams, the optical frequency comb mixed by the first optical system, and the mixed light of the second laser beam emitted from the second laser light source. Obtained through the first nonlinear optical crystal element, the second nonlinear optical crystal element to which the optical frequency comb generated by the optical frequency comb generating means is incident, and the first nonlinear optical crystal element. Above The second optical frequency comb component having the same frequency interval as several combs and the optical second harmonic component of the optical frequency comb obtained by the optical second harmonic generation obtained through the second nonlinear optical crystal element are mixed. The second optical frequency comb, and the second optical frequency comb from the mixed light of the second optical frequency comb component mixed by the second optical system and the optical second harmonic component of the optical frequency comb. Heterodyne detection means for detecting a heterodyne component of the component and the optical second harmonic component of the optical frequency comb, and the first laser light and the second laser based on the detection output of the heterodyne component by the heterodyne detection means Control means for feedback-controlling one of the first laser light source and the second laser light source so as to make the difference frequency of light constant.
In the laser beam generator according to the present invention, the second optical frequency comb component is, for example, a sum frequency component of the optical frequency comb and the second laser beam.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0010]
The present invention is applied to, for example, a laser frequency measurement system 100 configured as shown in FIG.
[0011]
A laser frequency measurement system 100 shown in FIG. 1 includes a first laser light source 110 that emits a reference laser beam, and an optical frequency comb generator that receives the reference laser beam emitted from the first laser light source 110. 120, a second laser light source 130 that emits laser light to be measured, an optical frequency comb generated by the optical frequency comb generator 120, and a laser light to be measured emitted from the second laser light source 130. An optical system 140 to be mixed, a nonlinear optical crystal element 150 to which the laser light mixed by the optical system 140 is incident, a photodetector 160 that receives the laser light emitted from the nonlinear optical crystal element 50, and The frequency measuring device 170 is supplied with a detection output from the photodetector 160.
[0012]
In this laser frequency measurement system 100, the laser light emitted from the nonlinear optical crystal element 150 on which the laser light mixed by the optical system 140 is incident is included in the laser light mixed by the optical system 140, that is, an optical frequency comb. And a sum frequency component of the laser light to be measured and an optical second harmonic component by optical second harmonic generation (SHG).
[0013]
Then, in the frequency measuring device 170, based on the detection output by the photodetector 160 that receives the laser light emitted from the nonlinear optical crystal element 150, the sum frequency component of the measured laser light and the optical frequency comb and the light The frequency of the laser beam to be measured is measured by detecting the heterodyne component of the optical second harmonic component caused by second harmonic generation (SHG).
[0014]
In the laser frequency measurement system 100, the first laser light source 110 is a laser diode that emits a reference laser beam having a wavelength of 1.548 μm, for example. The optical frequency comb generator 120 is an optical frequency composed of laser light having sidebands having a constant frequency interval on the low frequency side and the high frequency side around the frequency of the reference laser light emitted from the first laser light source 110. Generate a com. Examples of the optical frequency comb generator 120 include a coupled cavity resonator type optical frequency comb generator (CC_OFCG) and a waveguide type light described in, for example, Japanese Patent Laid-Open No. 7-58386. An optical frequency comb generator using a phase modulator can be used.
[0015]
In this laser frequency measurement system 100, an optical frequency comb having a bandwidth of 10 THz, an average power of 0.4 mW and a pulse width of 1 ps generated by the optical frequency comb generator 120 is averaged by a fiber amplifier 21 having a bandwidth of 4.5 THz and an average power of 180 mW. So as to be incident on the optical system 140.
[0016]
The laser beam to be measured emitted from the second laser light source 130 has a wavelength of 1.528 μm and an average power of 15 mW. Therefore, the difference frequency (δν) between the reference laser beam and the laser beam to be measured is 2.4 THz.
[0017]
Further, in the laser frequency measurement system 100, a periodically poled lithium niobate PPLN (periodically poled lithium niobate) crystal is used as the nonlinear optical crystal element 150, and the optical frequency for a wavelength near 1.552 μm is used. Phase matched to the second harmonic. Here, the wavelength of 0.776 μm corresponding to the center frequency of SHG by the nonlinear optical crystal element 150 is the wavelength of the sum frequency component of the laser light to be measured of 1.528 μm and the component near 1.576 μm of the optical frequency comb. It corresponds.
[0018]
Here, FIG. 2 shows a result obtained by observing the laser beam obtained by mixing the laser beam to be measured and the optical frequency comb by the optical system 140 with an optical spectrum analyzer having a resolution of 0.1 nm. As apparent from FIG. 2, the optical frequency comb amplified by the fiber amplifier 121 is band-limited by the cut-off of the fiber amplifier 121 and attenuated in the 1.528 μm band.
[0019]
FIG. 3 shows the result of observation of the laser light emitted from the nonlinear optical crystal element 150 with an optical spectrum analyzer having a resolution of 0.1 nm.
[0020]
3A shows the spectrum of the SHG optical frequency comb emitted from the nonlinear optical crystal element 150 when the second laser light source 130 is turned off, and FIG. 3B shows the second laser. The spectrum of the SHG optical frequency comb emitted from the nonlinear optical crystal element 150 when the light source 130 is turned on is shown.
[0021]
As is apparent from FIG. 3, (A) is more than the spectrum (A) of the SHG optical frequency comb emitted from the nonlinear optical crystal element 150 when the second laser light source 130 is turned off. The spectrum (B) of the SHG optical frequency comb emitted from the nonlinear optical crystal element 150 when the second laser light source 130 is turned on has a wider range and higher power.
[0022]
In this way, by using a PPLN crystal in which the center frequency of SHG is set to a wavelength near 1.552 μm as the nonlinear optical crystal element 150, a component near 1.576 μm of the optical frequency comb and a laser to be measured of 1.528 μm are used. SHG with a component near 1.552 μm of the sum frequency of light and the optical frequency comb can be performed with one crystal. Since the sum frequency of the component near 1.576 μm of the optical frequency comb and the laser light under measurement of 1.528 μm and the SHG component of the component near 1.552 μm of the optical frequency comb overlap in the wavelength band of 0.776 μm. In addition, both heterodyne (beat) components can be detected based on the detection output of the photodetector 160.
[0023]
Here, FIG. 4 shows the result of observing the heterodyne (beat) component of the laser light to be measured and the optical frequency comb with a radio frequency spectrum analyzer having a resolution of 1 MHz and a span of 100 MHz.
[0024]
In FIG. 4, (A) shows a laser beam obtained by mixing an optical frequency comb and a laser beam to be measured by the optical system 140 with a germanium pin (Ge-PIN) photodiode and observing it based on the detected output. The spectrum of the heterodyne (beat) component of the laser beam and the optical frequency comb is shown, and (B) shows the output light from the nonlinear optical crystal element 150 detected by a silicon avalanche photodiode (Si-APD) and based on the detected output. The spectrum of the heterodyne (beat) component of the optical frequency comb of the sum frequency which mixed the said to-be-measured laser beam and optical frequency comb observed in this way, and the SHG optical frequency comb is shown.
[0025]
As apparent from FIG. 4, the heterodyne (beat) component of the sum frequency optical frequency comb and the SHG optical frequency comb, which is a mixture of the laser light to be measured and the optical frequency comb, based on the detection output from the optical detector 160 is obtained. By detecting, the SN ratio could be improved by about 5 dB.
[0026]
That is, the optical frequency comb of the sum frequency obtained by mixing the laser light to be measured and the optical frequency comb and the heterodyne (beat) component of the SHG optical frequency comb have the same phase, and can be detected with a high S / N ratio. In this laser frequency measurement system 100, it is possible to detect a higher S / N ratio by selecting a nonlinear optical crystal used as the nonlinear optical crystal element 150 or increasing the laser power.
[0027]
Like this laser frequency measurement system 100, an optical frequency comb composed of laser light having sidebands with a constant frequency interval is generated based on the reference laser light, and obtained by optical mixing of the optical frequency comb and the measured laser light. By detecting the heterodyne component of the sum frequency component of the optical frequency comb and the laser beam to be measured and the optical second harmonic component obtained from the optical frequency comb by optical second harmonic generation, a high SN ratio is obtained. The heterodyne component can be detected, and the frequency of the laser beam to be measured can be measured over a wide range while ensuring high measurement accuracy based on the detection output of the heterodyne component.
[0028]
Here, in the laser frequency measurement system 100, an optical frequency comb is generated by the optical frequency comb generation 120 based on the reference laser light emitted from the first laser light source 110 and is emitted from the second laser light source 130. The frequency of the laser beam to be measured is measured. Since the frequency measurement by detecting the heterodyne component is a relative frequency measurement, the first laser light source 110 and the second laser light source 130 are replaced to measure the frequency to be measured. An optical frequency comb may be generated by the optical frequency comb generation 120 based on the laser light.
[0029]
In the laser frequency measurement system 100, frequency measurement is performed by detecting the heterodyne component using the first laser light source 110 and the second laser light source 130. Three laser light sources are used, one of which is used. Modifications such as measuring the difference frequency between the laser beams emitted from the other two laser light sources based on the reference laser beam emitted from the laser beam are possible.
[0030]
In the laser frequency measurement system 100, the optical frequency comb and the laser to be measured are received by the nonlinear optical crystal element 150 to which a laser beam obtained by mixing the optical frequency comb and the laser beam to be measured is incident via the optical system 140. Although the sum frequency component of light and the optical second harmonic component of the optical frequency comb are obtained, the sum frequency of the optical frequency comb and the laser light to be measured is obtained as in the laser frequency measurement system 100A shown in FIG. The component and the optical second harmonic component of the optical frequency comb can be obtained by the individual nonlinear optical crystal elements 150A and 150B.
[0031]
That is, in the laser frequency measurement system 100A shown in FIG. 5, an optical frequency composed of laser light having sidebands with a constant frequency interval by the optical frequency comb generator 120 based on the reference laser light emitted from the first laser light source 110. A comb is generated, and the optical frequency comb generated by the optical frequency comb generator 120 and the measured laser light emitted from the second laser light source 130 are mixed with the first optical system 140A, and the first optical system is mixed. A sum frequency component of the optical frequency comb and the laser light to be measured is obtained from the laser light mixed by the system 140A by the first nonlinear optical crystal element 150A, and light of the optical frequency comb is obtained by the second nonlinear optical crystal element 150B. A second harmonic component is obtained, and the sum frequency component of the optical frequency comb and laser light to be measured and the optical second harmonic of the optical frequency comb. The component is adapted to mix the second optical system 140B. And the frequency measuring device 170 is based on the detection output by the photodetector 160 that receives the mixed light emitted from the second optical system 140B, and the sum frequency component of the laser light to be measured and the optical frequency comb, The frequency of the laser beam to be measured is measured by detecting a heterodyne component with the optical second harmonic component of the optical frequency comb.
[0032]
In this laser frequency measurement system 100A, a first nonlinear optical crystal element 150A is obtained to obtain the sum frequency component of the optical frequency comb and the laser light to be measured, and a second second harmonic component is obtained to obtain the optical second harmonic component of the optical frequency comb. Since the characteristics of the non-linear optical crystal element 150B can be individually optimized, the SN ratio of the heterodyne component can be further increased.
[0033]
Further, the present invention is applied to a laser beam generator 200 having a configuration as shown in FIG. 6, for example.
[0034]
The laser light generator 200 shown in FIG. 6 includes a first laser light source 210 that emits a reference laser light, and an optical frequency comb generator that receives the reference laser light emitted from the first laser light source 210. 220, a second laser light source 230 that emits controlled laser light, an optical frequency comb generated by the optical frequency comb generator 220, and a controlled laser light emitted from the second laser light source 230. An optical system 240 to be mixed, a nonlinear optical crystal element 250 to which the laser light mixed by the optical system 240 is incident, a photodetector 260 for receiving the laser light emitted from the nonlinear optical crystal element 250, and And a control device 270 for controlling the second laser light source 230 based on the detection output from the photodetector 260.
[0035]
In this laser light generator 200, the optical frequency comb generator 220 has sidebands with a constant frequency interval on the low frequency side and the high frequency side centered on the frequency of the reference laser light emitted from the first laser light source 210. An optical frequency comb composed of laser light is generated. Further, the optical system 240 mixes the optical frequency comb generated by the optical frequency comb generator 220 and the controlled laser light emitted from the second laser light source 230, and uses the mixed light as an optical second harmonic. A non-linear optical crystal element 250 for wave generation (SHG) is supplied. Further, the nonlinear optical crystal element 250 uses the mixed light of the optical frequency comb and the controlled laser light supplied via the optical system 240 as incident light, and has an intermediate frequency between the reference laser light and the controlled laser light. Optical second harmonic generation (SHG) in which the center frequency is set to is performed. The control device 270 then sums the optical frequency comb included in the laser light and the laser light to be measured based on the detection output by the photodetector 260 that receives the laser light emitted from the nonlinear optical crystal element 250. Detecting the frequency component and the heterodyne (beat) component of the optical second harmonic component obtained by the optical second harmonic generation by the nonlinear optical crystal element 250, and feeding back the detected output to the second laser light source 230 Thus, control is performed to lock the frequency of the controlled laser light emitted from the second laser light source 230 to the target frequency given by the optical frequency comb.
[0036]
Like this laser light generation apparatus 200, an optical frequency comb composed of laser light having sidebands having a constant frequency interval on the low frequency side and high frequency side around the frequency of the reference laser light and the controlled laser light are mixed. , An optical second harmonic component obtained by optical second harmonic generation from the mixed light of the optical frequency comb and the controlled laser light, and the sum frequency of the optical frequency comb and the controlled laser light included in the mixed light The heterodyne component can be detected, and the heterodyne component can be detected with a high S / N ratio. The frequency of the controlled laser beam is controlled by feeding back the detection output of the heterodyne component and controlling the frequency of the controlled laser beam. Can be controlled with high accuracy over a wide range. Therefore, the laser beam generator 200 can generate controlled laser beams that are extremely stable over a wide frequency range.
[0037]
Here, in the laser light generation device 200, an optical frequency comb is generated by the optical frequency comb generation 220 based on the reference laser light emitted from the first laser light source 210, and is emitted from the second laser light source 230. The frequency of the laser beam to be controlled is controlled. Since the frequency control by detection of the heterodyne component is relative control, the first laser light source 210 and the second laser light source 230 are replaced, and the laser light to be measured is measured. Based on the above, an optical frequency comb may be generated by the optical frequency comb generation 220.
[0038]
Further, in the laser beam generator 200, the optical frequency comb and the laser to be measured are received by the nonlinear optical crystal element 250 to which a laser beam obtained by mixing the optical frequency comb and the controlled laser beam is incident via the optical system 240. Although the sum frequency component of light and the optical second harmonic component of the optical frequency comb are obtained, the sum frequency component of the optical frequency comb and the laser light to be measured and the optical second harmonic of the optical frequency comb The components may be obtained by individual nonlinear optical crystal elements. By optimizing each nonlinear optical crystal element individually, the SN ratio of the heterodyne component can be further increased.
[0039]
【The invention's effect】
In the laser frequency measurement method according to the present invention, an optical frequency comb composed of laser light having a sideband with a constant frequency interval is generated based on the first laser light, and the mixed light of the optical frequency comb and the second laser light. To obtain a second optical frequency comb component having the same frequency interval as the optical frequency comb and an optical second harmonic component of the optical frequency comb through one nonlinear optical crystal element. Since the heterodyne component and the optical second harmonic component of the optical frequency comb are detected, the heterodyne component can be detected with a high S / N ratio, and the second light is detected based on the detection output of the heterodyne component. The difference frequency between the frequency comb component and the optical second harmonic component of the optical frequency comb can be measured over a wide range with high measurement accuracy.
In the laser frequency measuring method according to the present invention, an optical frequency comb composed of laser light having a sideband with a constant frequency interval is generated based on the first laser light, and the optical frequency comb and the second laser light are A second optical frequency comb component having the same frequency interval as that of the optical frequency comb is obtained from the mixed light via the first nonlinear optical crystal element, and an optical first optical frequency comb is obtained from the optical frequency comb via the second nonlinear optical crystal element. An optical second harmonic component is obtained by second harmonic generation, and the second optical frequency comb component and the light are obtained from a mixed light of the second optical frequency comb component and the optical second harmonic component of the optical frequency comb. Since the heterodyne component with the optical second harmonic component of the frequency comb is detected, the heterodyne component can be detected with a high S / N ratio, and the second light can be detected based on the detection output of the heterodyne component. It can be measured to ensure high measurement accuracy the difference frequency between the wavenumber comb component and the optical frequency comb of the optical second harmonic component over a wide range. In this laser frequency measurement method, the first nonlinear optical crystal element and the optical second harmonic component of the optical frequency comb are obtained in order to obtain the second optical frequency comb component having the same frequency interval as the optical frequency comb. Therefore, since the characteristics of the second nonlinear optical crystal element can be individually optimized, the SN ratio of the heterodyne component can be further increased.
In the laser frequency measurement method according to the present invention, for example, based on the heterodyne component detected by the heterodyne detection means with reference to one of the first laser light or the second laser light, The frequency of the other laser beam can be measured over a wide range while ensuring high measurement accuracy.
[0040]
In the laser frequency control method according to the present invention, the optical frequency comb generated from the first laser light and the mixed light of the second laser light are passed through one nonlinear optical crystal element, and the first optical frequency comb having the same frequency interval as the optical frequency comb is used. Since the second optical frequency comb component and the optical second harmonic component of the optical frequency comb are obtained, the heterodyne component of the second optical frequency comb component and the optical second harmonic component of the optical frequency comb is detected. The heterodyne component can be detected with a high S / N ratio, and feedback control is performed so that the difference frequency between the first laser beam and the second laser beam is constant based on the detection output of the heterodyne component. Thus, the difference frequency can be controlled with high accuracy over a wide range.
In the laser frequency control method according to the present invention, the same frequency as that of the optical frequency comb is obtained from the mixed light of the optical frequency comb generated from the first laser light and the second laser light through the first nonlinear optical crystal element. A second optical frequency comb component having an interval is obtained, and an optical second harmonic component of the optical frequency comb due to optical second harmonic generation is obtained via a second nonlinear optical crystal element, and the second light Since the heterodyne component of the second optical frequency comb component and the optical second harmonic component of the optical frequency comb is detected from the mixed light of the frequency comb component and the optical second harmonic component of the optical frequency comb, a high SN The heterodyne component can be detected by the ratio, and feedback control is performed so that the difference frequency between the first laser beam and the second laser beam is constant based on the detection output of the heterodyne component. It can be controlled over the wave number in a wide range with high accuracy. Further, in this laser frequency control method, a first nonlinear optical crystal element and an optical second harmonic component of the optical frequency comb are obtained in order to obtain a second optical frequency comb component having the same frequency interval as the optical frequency comb. Therefore, since the characteristics of the second nonlinear optical crystal element can be individually optimized, the SN ratio of the heterodyne component can be further increased.
[0041]
In the laser frequency measuring device according to the present invention, the optical frequency comb generating means generates an optical frequency comb composed of laser light having a sideband with a constant frequency interval based on the first laser light, and the optical frequency comb and the second optical frequency comb A second optical frequency comb component having the same frequency interval as that of the optical frequency comb obtained from the mixed light of the laser light through one nonlinear optical crystal element, and the light of the optical frequency comb generated by optical second harmonic generation Since the heterodyne component of the second harmonic component is detected by the heterodyne detection means, the heterodyne component can be detected with a high S / N ratio. Based on the detection output of the heterodyne component by the heterodyne detection means, the second Measure the difference frequency between the optical frequency comb component and the optical second harmonic component of the optical frequency comb over a wide range with high measurement accuracy. It is possible.
In the laser frequency measuring device according to the present invention, the optical frequency comb generating means generates an optical frequency comb composed of laser light having a sideband with a constant frequency interval based on the first laser light, A second optical frequency comb component having the same frequency interval as that of the optical frequency comb obtained from the mixed light of the second laser light via the first nonlinear optical crystal element, and obtained via the second nonlinear optical crystal element. The heterodyne component of the second optical frequency comb component and the optical second harmonic component of the optical frequency comb is heterodyne from the mixed light of the optical second harmonic component of the optical frequency comb generated by the generated optical second harmonic. Since it is detected by the detection means, the heterodyne component can be detected with a high S / N ratio, and the difference frequency can be detected over a wide range based on the detection output of the heterodyne component. It can be measured to ensure have measurement accuracy. Further, in this laser frequency measurement method, a first nonlinear optical crystal element and an optical second harmonic component of the optical frequency comb are obtained in order to obtain a second optical frequency comb component having the same frequency interval as the optical frequency comb. Therefore, since the characteristics of the second nonlinear optical crystal element can be individually optimized, the SN ratio of the heterodyne component can be further increased.
And in the laser frequency measuring device according to the present invention, for example, based on the heterodyne component detected by the heterodyne detection means with reference to one of the first laser light or the second laser light, The frequency of the other laser beam can be measured over a wide range while ensuring high measurement accuracy.
[0042]
In the laser beam generator according to the present invention, an optical frequency comb composed of laser beams having sidebands having a constant frequency interval is generated based on the first laser beam emitted from the first laser light source by the optical frequency comb generator. The optical frequency obtained from the mixed light of the optical frequency comb generated by the optical frequency comb generating means and the second laser light emitted from the second laser light source through one nonlinear optical crystal element Since the heterodyne component of the second optical frequency comb component having the same frequency interval as the comb and the optical second harmonic component of the optical frequency comb generated by the optical second harmonic generation is detected by the heterodyne detection means, the heterodyne has a high SN ratio. Component can be detected, and based on the detection output of the heterodyne component, the control means controls the difference frequency between the first laser beam and the second laser beam. It can be extremely stable feedback control over the wide frequency range to a constant.
In the laser beam generator according to the present invention, the optical frequency comb generator generates an optical frequency comb composed of laser beams having sidebands having a constant frequency interval based on the first laser beam, A second optical frequency comb component having the same frequency interval as that of the optical frequency comb obtained from the mixed light of the second laser light via the first nonlinear optical crystal element, and obtained via the second nonlinear optical crystal element. The heterodyne component of the second optical frequency comb component and the optical second harmonic component of the optical frequency comb is heterodyne from the mixed light of the optical second harmonic component of the optical frequency comb generated by the generated optical second harmonic. Since it is detected by the detection means, the heterodyne component can be detected with a high S / N ratio, and the first laser is detected by the control means based on the detection output of the heterodyne component. If it is possible to extremely stable feedback control over the difference frequency of the second laser beam in a wide frequency range such that a constant. Furthermore, in this laser beam generator, in order to obtain a second optical frequency comb component having the same frequency interval as the optical frequency comb, a first nonlinear optical crystal element and an optical second harmonic component of the optical frequency comb are obtained. Since the characteristics of the second nonlinear optical crystal element can be individually optimized, the SN ratio of the heterodyne component can be further increased.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a laser frequency measurement system to which the present invention is applied.
FIG. 2 is a diagram showing a result of observing a laser beam obtained by mixing a laser beam to be measured and an optical frequency comb with an optical spectrum analyzer having a resolution of 0.1 nm in the laser frequency measurement system.
FIG. 3 is a diagram showing a result of observing laser light emitted from a nonlinear optical crystal element with an optical spectrum analyzer having a resolution of 0.1 nm in the laser frequency measurement system, wherein FIG. The spectrum of the SHG optical frequency comb emitted from the nonlinear optical crystal element when the light source is turned off is shown, and (B) is emitted from the nonlinear optical crystal element when the second laser light source is turned on. The spectrum of the SHG optical frequency comb is shown.
FIG. 4 is a diagram showing a result of observation of a heterodyne (beat) component of a laser beam to be measured and an optical frequency comb with a radio frequency spectrum analyzer having a resolution of 1 MHz and a span of 100 MHz in the laser frequency measurement system; Indicates the spectrum of the heterodyne (beat) component of the controlled laser light and optical frequency comb included in the laser light mixed with the measured laser light and the optical frequency comb, and (B) indicates the laser light emitted from the nonlinear optical crystal element. The spectrum of the heterodyne (beat) component of the optical frequency comb of the sum frequency which mixed the said to-be-measured laser beam and optical frequency comb contained in SHG, and the SHG optical frequency comb is shown.
FIG. 5 is a block diagram showing another configuration example of a laser frequency measurement system to which the present invention is applied.
FIG. 6 is a block diagram showing a configuration of a laser beam generator to which the present invention is applied.
[Explanation of symbols]
100, 100A laser frequency measurement system, 110 first laser light source, 120 optical frequency comb generator, 121 fiber amplifier, 130 second laser light source, 140, 140A, 140B optical system, 150, 150A, 150B nonlinear optical crystal element , 160 photodetector, 170 frequency measuring device, 200 laser light generator, 210 first laser light source, 220 optical frequency comb generator, 230 second laser light source, 240 optical system, 250 nonlinear optical crystal element and 260 light Detector, 270 controller

Claims (20)

第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、
上記光周波数コムと第２のレーザ光とを混合し、その混合光から１つの非線形光学結晶素子を介して、上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と上記光周波数コムの光第２高調波成分を得て、
上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分のヘテロダイン成分を検出し、
上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を測定することを特徴とするレーザ周波数測定方法。Generating an optical frequency comb composed of laser light having sidebands having a constant frequency interval based on the first laser light;
The optical frequency comb and the second laser light are mixed, and the second optical frequency comb component and the optical frequency comb having the same frequency interval as the optical frequency comb are transmitted from the mixed light through one nonlinear optical crystal element. The optical second harmonic component of
Detecting a heterodyne component of the second optical frequency comb component and an optical second harmonic component of the optical frequency comb;
A laser frequency measuring method, comprising: measuring a difference frequency between the second optical frequency comb component and the optical second harmonic component of the optical frequency comb based on the detection output of the heterodyne component. 上記第２の光周波数コム成分は、上記光周波数コムと上記第２のレーザ光の和周波数成分であることを特徴とする請求項１記載のレーザ周波数測定方法。  2. The laser frequency measuring method according to claim 1, wherein the second optical frequency comb component is a sum frequency component of the optical frequency comb and the second laser light. 上記第１のレーザ光又は第２のレーザ光の一方を基準レーザ光として、検出されたヘテロダイン成分に基づいて、上記他方のレーザ光の周波数を測定することを特徴とする請求項１記載のレーザ周波数測定方法。  2. The laser according to claim 1, wherein one of the first laser beam and the second laser beam is used as a reference laser beam, and the frequency of the other laser beam is measured based on the detected heterodyne component. Frequency measurement method. 第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、
上記光周波数コムと第２のレーザ光とを混合し、その混合光から第１の非線形光学結晶素子を介して上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分を得るとともに、上記光周波数コムから第２の非線形光学結晶素子を介して光第２高調波発生により光第２高調波成分を得て、
上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とを混合し、その混合光から上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分を検出し、
上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を測定することを特徴とするレーザ周波数測定方法。Generating an optical frequency comb composed of laser light having sidebands having a constant frequency interval based on the first laser light;
The optical frequency comb and the second laser light are mixed, and a second optical frequency comb component having the same frequency interval as the optical frequency comb is obtained from the mixed light via the first nonlinear optical crystal element. An optical second harmonic component is obtained by optical second harmonic generation from the optical frequency comb through the second nonlinear optical crystal element,
The second optical frequency comb component and the optical second harmonic component of the optical frequency comb are mixed, and the second optical frequency comb component and the optical second harmonic component of the optical frequency comb are mixed from the mixed light. The heterodyne component of
A laser frequency measuring method, comprising: measuring a difference frequency between the second optical frequency comb component and the optical second harmonic component of the optical frequency comb based on the detection output of the heterodyne component. 上記第２の光周波数コム成分は、上記光周波数コムと上記第２のレーザ光の和周波数成分であることを特徴とする請求項４記載のレーザ周波数測定方法。  5. The laser frequency measuring method according to claim 4, wherein the second optical frequency comb component is a sum frequency component of the optical frequency comb and the second laser light. 上記第１のレーザ光又は第２のレーザ光の一方のレーザ光を基準として、検出された上記ヘテロダイン成分に基づいて、他方のレーザ光の周波数を測定することを特徴とする請求項４記載のレーザ周波数測定方法。  5. The frequency of the other laser beam is measured based on the detected heterodyne component with reference to one of the first laser beam and the second laser beam. Laser frequency measurement method. 第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、
上記光周波数コムと第２のレーザ光とを混合し、その混合光から１つの非線形光学結晶素子を介して上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、上記光周波数コムの光第２高調波成分を得て、
上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分のヘテロダイン成分を検出し、
上記ヘテロダイン成分の検出出力に基づいて上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように帰還制御することを特徴とするレーザ周波数制御方法。Generating an optical frequency comb composed of laser light having sidebands having a constant frequency interval based on the first laser light;
The optical frequency comb and the second laser light are mixed, a second optical frequency comb component having the same frequency interval as the optical frequency comb is transmitted from the mixed light through one nonlinear optical crystal element, and the optical frequency comb The optical second harmonic component of
Detecting a heterodyne component of the second optical frequency comb component and an optical second harmonic component of the optical frequency comb;
A laser frequency control method, wherein feedback control is performed so that a difference frequency between the first laser beam and the second laser beam is constant based on the detection output of the heterodyne component. 上記第２の光周波数コム成分は、上記光周波数コムと上記第２のレーザ光の和周波数成分であることを特徴とする請求項７記載のレーザ周波数制御方法。  8. The laser frequency control method according to claim 7, wherein the second optical frequency comb component is a sum frequency component of the optical frequency comb and the second laser light. 第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを生成し、
上記光周波数コムと第２のレーザ光とを混合し、その混合光から第１の非線形光学結晶素子を介して上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分を得るとともに、第２の非線形光学結晶素子を介して光第２高調波発生による上記光周波数コムの光第２高調波成分を得て、
上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とを混合し、その混合光から上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分を検出し、
上記ヘテロダイン成分の検出出力に基づいて上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように帰還制御することを特徴とするレーザ周波数制御方法。Generating an optical frequency comb composed of laser light having sidebands having a constant frequency interval based on the first laser light;
The optical frequency comb and the second laser light are mixed, and a second optical frequency comb component having the same frequency interval as the optical frequency comb is obtained from the mixed light via the first nonlinear optical crystal element. Obtaining the optical second harmonic component of the optical frequency comb by the optical second harmonic generation through the two nonlinear optical crystal elements;
The second optical frequency comb component and the optical second harmonic component of the optical frequency comb are mixed, and the second optical frequency comb component and the optical second harmonic component of the optical frequency comb are mixed from the mixed light. The heterodyne component of
A laser frequency control method, wherein feedback control is performed so that a difference frequency between the first laser beam and the second laser beam is constant based on the detection output of the heterodyne component. 上記第２の光周波数コム成分は、上記光周波数コムと上記第２のレーザ光の和周波数成分であることを特徴とする請求項９記載のレーザ周波数制御方法。  10. The laser frequency control method according to claim 9, wherein the second optical frequency comb component is a sum frequency component of the optical frequency comb and the second laser light. 第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを発生する光周波数コム発生手段と、
上記光周波数コム発生手段により生成された光周波数コムと第２のレーザ光とを混合する光学系と、
上記光学系により混合された上記光周波数コムと第２のレーザ光の混合光が入射される非線形光学結晶素子と、
上記非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、光第２高調波発生による上記光周波数コムの光第２高調波成分のヘテロダイン成分を検出するヘテロダイン検波手段とを備え、
上記ヘテロダイン検波手段による上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を測定することを特徴とするレーザ周波数測定装置。Optical frequency comb generating means for generating an optical frequency comb composed of laser light having a sideband with a constant frequency interval based on the first laser light;
An optical system for mixing the optical frequency comb generated by the optical frequency comb generating means and the second laser beam;
A nonlinear optical crystal element on which the mixed light of the optical frequency comb and the second laser light mixed by the optical system is incident;
A second optical frequency comb component having the same frequency interval as that of the optical frequency comb obtained through the nonlinear optical crystal element, and a heterodyne component of the optical second harmonic component of the optical frequency comb due to optical second harmonic generation are obtained. Heterodyne detection means for detecting,
A laser frequency measurement characterized by measuring a difference frequency between the second optical frequency comb component and an optical second harmonic component of the optical frequency comb based on a detection output of the heterodyne component by the heterodyne detection means. apparatus. 上記第２の光周波数コム成分は、上記光周波数コムと上記第２のレーザ光の和周波数成分であることを特徴とする請求項１１記載のレーザ周波数測定装置。  12. The laser frequency measuring device according to claim 11, wherein the second optical frequency comb component is a sum frequency component of the optical frequency comb and the second laser light. 上記第１のレーザ光又は第２のレーザ光の一方を基準レーザ光として、上記ヘテロダイン検波手段により検出されたヘテロダイン成分に基づいて、上記他方のレーザ光の周波数を測定することを特徴とする請求項１１記載のレーザ周波数測定装置。  The frequency of the other laser beam is measured based on the heterodyne component detected by the heterodyne detection means using either the first laser beam or the second laser beam as a reference laser beam. Item 12. The laser frequency measuring device according to Item 11. 第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを発生する光周波数コム発生手段と、
上記光周波数コム発生手段により発生された光周波数コムと第２のレーザ光とを混合する第１の光学系と、
上記第１の光学系により混合された上記光周波数コムと第２のレーザ光の混合光が入射される第１の非線形光学結晶素子と、
上記光周波数コム発生手段により発生された光周波数コムが入射される第２の非線形光学結晶素子と、
上記第１の非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、上記第２の非線形光学結晶素子を介して得られる光第２高調波発生による上記光周波数コムの光第２高調波成分とを混合する第２の光学系と、
上記第２の光学系により混合された上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分の混合光から、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分を検出するヘテロダイン検波手段と、
上記ヘテロダイン検波手段による上記ヘテロダイン成分の検出出力に基づいて、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分との差周波数を測定することを特徴とするレーザ周波数測定装置。Optical frequency comb generating means for generating an optical frequency comb composed of laser light having a sideband with a constant frequency interval based on the first laser light;
A first optical system for mixing the optical frequency comb generated by the optical frequency comb generating means and the second laser beam;
A first nonlinear optical crystal element on which the mixed light of the optical frequency comb and the second laser light mixed by the first optical system is incident;
A second nonlinear optical crystal element on which the optical frequency comb generated by the optical frequency comb generating means is incident;
Second optical frequency comb component having the same frequency interval as that of the optical frequency comb obtained through the first nonlinear optical crystal element, and optical second harmonic generation obtained through the second nonlinear optical crystal element A second optical system for mixing the optical second harmonic component of the optical frequency comb by
From the mixed light of the second optical frequency comb component and the optical second harmonic component of the optical frequency comb mixed by the second optical system, the light of the second optical frequency comb component and the optical frequency comb Heterodyne detection means for detecting a heterodyne component with the second harmonic component;
A laser frequency measurement characterized by measuring a difference frequency between the second optical frequency comb component and an optical second harmonic component of the optical frequency comb based on a detection output of the heterodyne component by the heterodyne detection means. apparatus. 上記第２の光周波数コム成分は、上記光周波数コムと上記第２のレーザ光の和周波数成分であることを特徴とする請求項１４記載のレーザ周波数測定装置。  15. The laser frequency measuring device according to claim 14, wherein the second optical frequency comb component is a sum frequency component of the optical frequency comb and the second laser beam. 上記第１のレーザ光又は第２のレーザ光の一方のレーザ光を基準として、上記ヘテロダイン検波手段により検出された上記ヘテロダイン成分に基づいて、他方のレーザ光の周波数を測定することを特徴とする請求項１４記載のレーザ周波数測定装置。  The frequency of the other laser beam is measured based on the heterodyne component detected by the heterodyne detection means with reference to one of the first laser beam and the second laser beam. The laser frequency measuring device according to claim 14. 第１のレーザ光を出射する第１のレーザ光源と、
上記第１のレーザ光源から出射された第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを発生する光周波数コム発生手段と、
第２のレーザ光を出射する第２のレーザ光源と、
上記光周波数コム発生手段により生成された光周波数コムと上記第２のレーザ光源から出射された第２のレーザ光とを混合する光学系と、
上記光学系により混合された上記光周波数コムと第２のレーザ光の混合光が入射される非線形光学結晶素子と、
上記非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、光第２高調波発生による上記光周波数コムの光第２高調波成分のヘテロダイン成分を検出するヘテロダイン検波手段と、
上記ヘテロダイン検波手段による上記ヘテロダイン成分の検出出力に基づいて上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように上記第１のレーザ光源と第２のレーザ光源の一方を帰還制御する制御手段と
を備えることを特徴とするレーザ光発生装置。A first laser light source that emits a first laser beam;
Optical frequency comb generating means for generating an optical frequency comb composed of laser light having a sideband with a constant frequency interval based on the first laser light emitted from the first laser light source;
A second laser light source that emits a second laser light;
An optical system for mixing the optical frequency comb generated by the optical frequency comb generating means and the second laser light emitted from the second laser light source;
A nonlinear optical crystal element on which the mixed light of the optical frequency comb and the second laser light mixed by the optical system is incident;
A second optical frequency comb component having the same frequency interval as that of the optical frequency comb obtained through the nonlinear optical crystal element, and a heterodyne component of the optical second harmonic component of the optical frequency comb due to optical second harmonic generation are obtained. Heterodyne detection means to detect;
Based on the detection output of the heterodyne component by the heterodyne detection means, one of the first laser light source and the second laser light source is set so as to make the difference frequency between the first laser light and the second laser light constant. And a control means for performing feedback control. 上記第２の光周波数コム成分は、上記光周波数コムと上記第２のレーザ光の和周波数成分であることを特徴とする請求項１７記載のレーザ光発生装置。  18. The laser light generator according to claim 17, wherein the second optical frequency comb component is a sum frequency component of the optical frequency comb and the second laser light. 第１のレーザ光を出射する第１のレーザ光源と、
上記第１のレーザ光源から出射された第１のレーザ光に基づいて周波数間隔一定のサイドバンドを持つレーザ光からなる光周波数コムを発生する光周波数コム発生手段と、
第２のレーザ光を出射する第２のレーザ光源と、
上記光周波数コム発生手段により発生された光周波数コムと上記第２のレーザ光源から出射された第２のレーザ光とを混合する第１の光学系と、
上記第１の光学系により混合された上記光周波数コムと上記第２のレーザ光の混合光が入射される第１の非線形光学結晶素子と、
上記光周波数コム発生手段により発生された光周波数コムが入射される第２の非線形光学結晶素子と、
上記第１の非線形光学結晶素子を介して得られる上記光周波数コムと同じ周波数間隔の第２の光周波数コム成分と、上記第２の非線形光学結晶素子を介して得られる光第２高調波発生による上記光周波数コムの光第２高調波成分とを混合する第２の光学系と、
上記第２の光学系により混合された上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分の混合光から、上記第２の光周波数コム成分と上記光周波数コムの光第２高調波成分とのヘテロダイン成分を検出するヘテロダイン検波手段と、
上記ヘテロダイン検波手段による上記ヘテロダイン成分の検出出力に基づいて上記第１のレーザ光と第２のレーザ光の差周波数を一定にするように上記第１のレーザ光源と第２のレーザ光源の一方を帰還制御する制御手段と
を備えることを特徴とするレーザ光発生装置。A first laser light source that emits a first laser beam;
Optical frequency comb generating means for generating an optical frequency comb composed of laser light having a sideband with a constant frequency interval based on the first laser light emitted from the first laser light source;
A second laser light source that emits a second laser light;
A first optical system that mixes the optical frequency comb generated by the optical frequency comb generating means with the second laser light emitted from the second laser light source;
A first nonlinear optical crystal element on which a mixed light of the optical frequency comb mixed by the first optical system and the second laser light is incident;
A second nonlinear optical crystal element on which the optical frequency comb generated by the optical frequency comb generating means is incident;
Second optical frequency comb component having the same frequency interval as that of the optical frequency comb obtained through the first nonlinear optical crystal element, and optical second harmonic generation obtained through the second nonlinear optical crystal element A second optical system for mixing the optical second harmonic component of the optical frequency comb by
From the mixed light of the second optical frequency comb component and the optical second harmonic component of the optical frequency comb mixed by the second optical system, the light of the second optical frequency comb component and the optical frequency comb Heterodyne detection means for detecting a heterodyne component with the second harmonic component;
Based on the detection output of the heterodyne component by the heterodyne detection means, one of the first laser light source and the second laser light source is set so as to make the difference frequency between the first laser light and the second laser light constant. And a control means for performing feedback control. 上記第２の光周波数コム成分は、上記光周波数コムと上記第２のレーザ光の和周波数成分であることを特徴とする請求項１９記載のレーザ光発生装置。  The laser light generator according to claim 19, wherein the second optical frequency comb component is a sum frequency component of the optical frequency comb and the second laser light.
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