JPH04342183A - Frequency-stabilized light source - Google Patents
Frequency-stabilized light sourceInfo
- Publication number
- JPH04342183A JPH04342183A JP14258191A JP14258191A JPH04342183A JP H04342183 A JPH04342183 A JP H04342183A JP 14258191 A JP14258191 A JP 14258191A JP 14258191 A JP14258191 A JP 14258191A JP H04342183 A JPH04342183 A JP H04342183A
- Authority
- JP
- Japan
- Prior art keywords
- frequency
- light
- output
- light source
- laser
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 230000007704 transition Effects 0.000 claims description 7
- 238000001069 Raman spectroscopy Methods 0.000 claims description 6
- 230000004907 flux Effects 0.000 claims description 2
- 239000004065 semiconductor Substances 0.000 abstract description 16
- 230000031700 light absorption Effects 0.000 description 31
- 238000010521 absorption reaction Methods 0.000 description 25
- 230000003287 optical effect Effects 0.000 description 15
- 238000000034 method Methods 0.000 description 11
- 238000001514 detection method Methods 0.000 description 10
- 238000000862 absorption spectrum Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 3
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 description 3
- 230000010355 oscillation Effects 0.000 description 3
- 230000006641 stabilisation Effects 0.000 description 3
- 238000011105 stabilization Methods 0.000 description 3
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical group [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 229910052701 rubidium Inorganic materials 0.000 description 2
- IGLNJRXAVVLDKE-UHFFFAOYSA-N rubidium atom Chemical compound [Rb] IGLNJRXAVVLDKE-UHFFFAOYSA-N 0.000 description 2
- 230000000087 stabilizing effect Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- BJQHLKABXJIVAM-UHFFFAOYSA-N bis(2-ethylhexyl) phthalate Chemical compound CCCCC(CC)COC(=O)C1=CC=CC=C1C(=O)OCC(CC)CCCC BJQHLKABXJIVAM-UHFFFAOYSA-N 0.000 description 1
- 229910052792 caesium Inorganic materials 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Lasers (AREA)
- Semiconductor Lasers (AREA)
Abstract
Description
【０００１】0001
【産業上の利用分野】本発明は、レーザ光源の周波数安
定化装置に関するものであり、例えばアセチレン分子が
持つ１．５μｍ帯の光吸収スペクトルのうち、一つの光
吸収ピークを周波数基準とし、この光吸収ピークにレー
ザ光の周波数を固定して周波数を安定化させる周波数安
定化光源に関するものである。また、本発明は原理的に
無変調で光周波数を高確度に安定化できるため、次世代
通信方式として研究が進められている光ヘテロダイン通
信において雑音成分の少ない発信局光源及び受信局光源
として利用できる。[Field of Industrial Application] The present invention relates to a frequency stabilizing device for a laser light source. The present invention relates to a frequency-stabilized light source that stabilizes the frequency of a laser beam by fixing the frequency to a light absorption peak. In addition, since the present invention can in principle stabilize the optical frequency with high accuracy without modulation, it can be used as a transmitting station light source and a receiving station light source with low noise components in optical heterodyne communication, which is being researched as a next-generation communication system. can.
【０００２】0002
【従来技術】レーザ光源の光周波数を安定化させる方法
としては、特定周波数の光吸収ピークを持つ原子または
分子を封入した光吸収セルを周波数基準として用いる方
法、ファブリペロー共振器の光共振透過特性を周波数基
準として用いる方法等が検討されている。しかし、原子
または分子を封入した光吸収セルによる安定化の方法が
、最も周波数安定度が高く、簡単にシステム化ができる
等の利点がある。そのため、ルビジウムやセシウム原子
を封入した吸収セルにより、０．８μｍ帯の半導体レー
ザのレーザ光の周波数安定化光源の実用化がすでに行わ
れており、アラン分散評価で σ＝１０−１２
程度の安定度が実現されている。[Prior Art] Methods for stabilizing the optical frequency of a laser light source include a method using a light absorption cell containing atoms or molecules having a light absorption peak at a specific frequency as a frequency standard, and a method using optical resonance transmission characteristics of a Fabry-Perot cavity. Methods such as using this as a frequency standard are being considered. However, the stabilization method using a light absorption cell encapsulating atoms or molecules has advantages such as the highest frequency stability and easy systemization. Therefore, a frequency-stabilized light source for laser light from a 0.8 μm band semiconductor laser has already been put into practical use using an absorption cell filled with rubidium or cesium atoms, and Allan dispersion evaluation shows that σ = 10-12.
A certain degree of stability has been achieved.
【０００３】一方、この原子または分子を封入した光吸
収セルの吸収ピークを用いた特定周波数にレーザ周波数
を固定する方法としては、従来から様々な制御方法が提
案されている。代表的なものとしては次の４つの方法が
挙げられる。On the other hand, various control methods have been proposed to fix the laser frequency to a specific frequency using the absorption peak of a light absorption cell containing atoms or molecules. The following four methods are representative.
【０００４】（１）吸収スペクトルの微分信号による制
御
この方法は、発振周波数に直接変調をかけたレーザ光を
、光吸収セルに入射させ、光検出器でレーザ光の発振周
波数に応じた透過光強度を検知して周波数制御を行う方
法である。この方法で検知される透過光強度は、レーザ
光の周波数に変調がかかっているため光吸収セルの吸収
ピーク曲線に従った強度変化を持つ。この強度変化に対
応した光検出器の出力信号をロックインアンプに入力し
、半導体レーザに変調を加えるときに利用した変調信号
と位相同期検波することにより、吸収スペクトルの周波
数に対する微分値出力を得る。(1) Control using a differential signal of the absorption spectrum In this method, a laser beam whose oscillation frequency is directly modulated is incident on a light absorption cell, and a photodetector detects the transmitted light according to the oscillation frequency of the laser beam. This method detects the intensity and controls the frequency. The transmitted light intensity detected by this method has an intensity change that follows the absorption peak curve of the light absorption cell because the frequency of the laser light is modulated. The output signal of the photodetector corresponding to this intensity change is input to a lock-in amplifier, and by performing phase synchronization detection with the modulation signal used when modulating the semiconductor laser, a differential value output with respect to the frequency of the absorption spectrum is obtained. .
【０００５】この微分値出力は、レーザ光の周波数が、
光吸収セルの吸収周波数と一致したとき零となり、周波
数が吸収周波数を原点として正負にずれたときは、それ
ぞれ負と正の値となる。そのため、微分値出力は周波数
弁別特性をもつことになるのである。したがって、微分
値出力を駆動電流源に負帰還し、この微分値出力が零と
なるように出力電流を制御することにより、レーザ光の
周波数を光吸収セルの吸収周波数に安定化することがで
きる。[0005] This differential value output is determined when the frequency of the laser beam is
When it matches the absorption frequency of the light absorption cell, it becomes zero, and when the frequency deviates from the absorption frequency in the positive and negative directions, it becomes a negative value and a positive value, respectively. Therefore, the differential value output has frequency discrimination characteristics. Therefore, by feeding back the differential value output negatively to the drive current source and controlling the output current so that the differential value output becomes zero, the frequency of the laser beam can be stabilized to the absorption frequency of the light absorption cell. .
【０００６】（２）音響光学変調器による制御音響光学
変調器による制御とは、半導体レーザのレーザ光を、任
意の周波数でＯＮ，ＯＦＦさせている音響光学変調器に
入射し、ＯＮのときには、０ＦＦのときのレーザ光の周
波数に音響光学変調器の駆動周波数の変調分が加わるよ
うにする。また、音響光学変調器をＯＮとＯＦＦさせた
ときに、それぞれの状態のレーザ光の周波数が光吸収セ
ルの吸収ピークの中心周波数を挟むように半導体レーザ
を調整し、音響光学変調器の出射光を再度光吸収セルに
入射させて、その透過光を光検出器で検知する。この信
号をロックインアンプに入力し、音響光学変調器をＯＮ
，ＯＦＦさせている発振器の周波数と位相同期検波する
ことにより、吸収ピークの周波数に対する微分の近似値
を得る。この近似値を駆動電流源に負帰還し、近似値が
零となるように出力電流を制御することにより、レーザ
光の周波数を光吸収セルの吸収周波数に安定化すること
ができる。(2) Control using an acousto-optic modulator Control using an acousto-optic modulator means that the laser light of a semiconductor laser is incident on an acousto-optic modulator that turns on and off at an arbitrary frequency. The modulation amount of the driving frequency of the acousto-optic modulator is added to the frequency of the laser beam at 0FF. In addition, when the acousto-optic modulator is turned ON and OFF, the semiconductor laser is adjusted so that the frequency of the laser light in each state is sandwiched between the center frequency of the absorption peak of the light absorption cell, and the output light of the acousto-optic modulator is is made incident on the light absorption cell again, and the transmitted light is detected by a photodetector. Input this signal to the lock-in amplifier and turn on the acousto-optic modulator.
, an approximate value of the differential with respect to the frequency of the absorption peak is obtained by performing phase synchronized detection with the frequency of the oscillator that is turned off. By feeding back this approximate value negatively to the drive current source and controlling the output current so that the approximate value becomes zero, the frequency of the laser beam can be stabilized at the absorption frequency of the light absorption cell.
【０００７】（３）透過率測定による制御半導体レーザ
の出力光を、ビームスプリッタで一定の強度比率に２分
岐する。一方の光は第１の光検出器に直接入射させ、他
方の光は光吸収セルに通過させた後、第２の光検出器で
検知する。吸収ピーク曲線の傾きが最も大きくなる周波
数において、それぞれの光検出器の出力が等しくなるよ
うにゲインを調整する。それぞれの検出器の出力を差動
アンプに入力し、その差分を出力させる。
この差動出力は、特定周波数において０、特定周波数か
らずれた場合、正負の電圧を出力する周波数弁別信号と
なる。そして、差動出力が零になるように、駆動電流源
に、この差動出力を負帰還させることにより、レーザ光
の周波数を光吸収セルの吸収ピーク近傍の特定周波数に
安定化することができる。(3) Control by transmittance measurement The output light of the semiconductor laser is split into two parts at a constant intensity ratio by a beam splitter. One of the lights is directly incident on the first photodetector, and the other light is passed through a light absorption cell and then detected by the second photodetector. The gain is adjusted so that the outputs of the respective photodetectors are equal at the frequency where the slope of the absorption peak curve is the largest. The output of each detector is input to a differential amplifier, and the difference is output. This differential output becomes a frequency discrimination signal that outputs 0 at a specific frequency and a positive or negative voltage when it deviates from the specific frequency. By feeding back this differential output negatively to the drive current source so that the differential output becomes zero, the frequency of the laser light can be stabilized to a specific frequency near the absorption peak of the light absorption cell. .
【０００８】（４）２個の音響光学変調器による制御被
安定化半導体レーザからのレーザ光をビームスプリッタ
で一定の強度比率に２分岐する。一方の光は、第１の音
響光学変調器で周波数変調した後、光吸収セルを透過さ
せ、第１の光検出器でその透過光量を検出する。他方の
光は、第１の音響光学変調器と周波数遷移量が等しく、
かつ遷移方向が逆となる第２の音響光学変調器で周波数
変調した後、光吸収セルを透過させ、第２の光検出器で
検出する。そして、それぞれの検出器からの出力を差動
アンプに入力し、その差分を出力させる。この差動出力
は、光吸収セルの吸収ピーク周波数において０、この周
波数からずれた場合、正負の電圧を出力する周波数弁別
信号となる。そして、差動出力が０と成るように、駆動
電流源に、この差動出力を負帰還させることにより、被
安定化レーザの発振周波数を光吸収セルの吸収ピークに
安定化することができる。(4) Controlled by two acousto-optic modulators The laser light from the stabilized semiconductor laser is split into two parts at a constant intensity ratio by a beam splitter. One of the lights is frequency-modulated by a first acousto-optic modulator, then transmitted through a light absorption cell, and the amount of transmitted light is detected by a first photodetector. The amount of frequency transition of the other light is equal to that of the first acousto-optic modulator, and
After being frequency-modulated by a second acousto-optic modulator whose transition direction is opposite, the light is transmitted through a light absorption cell and detected by a second photodetector. Then, the output from each detector is input to a differential amplifier, and the difference is output. This differential output becomes a frequency discrimination signal that is 0 at the absorption peak frequency of the light absorption cell and outputs a positive or negative voltage when it deviates from this frequency. By feeding back this differential output negatively to the drive current source so that the differential output becomes 0, the oscillation frequency of the laser to be stabilized can be stabilized to the absorption peak of the light absorption cell.
【０００９】[0009]
【発明が解決しようとする課題】しかしながら、これら
の制御には、それぞれ次のような課題がある。
（１）の制御は、半導体レーザに加える微弱な変調と、
ロックインアンプを用いた位相同期検波により光吸収セ
ルの光吸収微分曲線を得て、半導体レーザ出力光の中心
周波数の安定化を図っている。そのために、どうしても
半導体レーザの出力光周波数に微弱な変調が載ってしま
う欠点が有る。さらに位相同期検波を行っているために
ロックインアンプの時定数よりも短い時間での周波数安
定化が不可能である。
（２）の制御も（１）の制御と同様な課題を有する。[Problems to be Solved by the Invention] However, each of these controls has the following problems. Control (1) is achieved by applying weak modulation to the semiconductor laser,
The optical absorption differential curve of the optical absorption cell is obtained by phase synchronization detection using a lock-in amplifier, and the center frequency of the semiconductor laser output light is stabilized. Therefore, there is a drawback that a weak modulation is inevitably added to the output optical frequency of the semiconductor laser. Furthermore, since phase synchronization detection is performed, it is impossible to stabilize the frequency in a time shorter than the time constant of the lock-in amplifier. The control (2) also has the same problem as the control (1).
【００１０】一方、（３）の制御は、（１）（２）の制
御と比較して半導体レーザの出力光周波数に変調が載る
ことはない上にロックインアンプを必要としないため短
期安定度がよいと言う長所があるが、その反面、光吸収
セルの光吸収ピークでの周波数にレーザ光の周波数を安
定化することが不可能なため（１）及び（２）の制御と
比較し、周波数の確度が失われてしまうという問題があ
る。（４）の制御は、（３）の制御が有している長所を
そのまま所持し、さらに、光吸収セルの吸収ピークに安
定化することが可能なため安定周波数の確度が高いと言
う特徴がある。しかしながら、独立な周波数変調器を２
個用いているために周波数変調器自体の温度ドリフトな
どの外乱による影響を受け易く、さらに光学系の構成部
品が多いという欠点があった。On the other hand, the control (3) has lower short-term stability than the controls (1) and (2) because it does not cause modulation on the output optical frequency of the semiconductor laser and does not require a lock-in amplifier. However, on the other hand, it is impossible to stabilize the frequency of the laser light to the frequency at the light absorption peak of the light absorption cell, so compared to (1) and (2), There is a problem that frequency accuracy is lost. Control (4) has the same advantages as control (3), and has the additional feature that the stable frequency is highly accurate because it can be stabilized at the absorption peak of the light absorption cell. be. However, two independent frequency modulators
Since the frequency modulator is used individually, it is easily affected by disturbances such as temperature drift of the frequency modulator itself, and has the disadvantage of having a large number of optical system components.
【００１１】[0011]
【課題を解決するための手段】そこで、本発明では、光
学系において半導体レーザのレーザ光をラマン・ナース
回折セルを用いて複数の光束に分割させながら周波数遷
移させ、その周波数遷移したレーザ光を光吸収セルに通
した後に透過光量を検出する構成とする。ただし、周波
数遷移した２つのレーザ光は半導体レーザへの注入電流
または温度によってそれぞれの光周波数が光吸収ピーク
の高周波数側のスロープと低周波数側のスロープになる
ように調整する。また、フィードバック系においては検
出されたおのおのの透過光量を比較し、その比較出力が
零となるように半導体レーザの注入電流に負帰還をかけ
ることで周波数を安定化する構成とする。[Means for Solving the Problems] Therefore, in the present invention, in an optical system, the laser beam of a semiconductor laser is frequency-transitioned while being divided into a plurality of light beams using a Raman-Nurss diffraction cell, and the frequency-transitioned laser beam is The structure is such that the amount of transmitted light is detected after passing through a light absorption cell. However, the two frequency-shifted laser beams are adjusted so that their respective optical frequencies become slopes on the high frequency side and slopes on the low frequency side of the optical absorption peak, depending on the current injected into the semiconductor laser or the temperature. Furthermore, the feedback system is configured to compare the amounts of each detected transmitted light, and to stabilize the frequency by applying negative feedback to the current injected into the semiconductor laser so that the comparison output becomes zero.
【００１２】0012
【作用】本発明で使用するラマン・ナ−ス回折現象につ
いて、以下に説明する。一般に知られている光周波数シ
フタの原理であるブラック回折現象は、光束と音波の相
互作用領域が十分に広く、しかも斜めに入射した光束が
音波面を何度も横切るときに起こる現象であり、入射光
の周波数をシフトさせた単一の輝点を生成するのに利用
させる。これに対して、ラマン・ナ−ス回折現象は光束
に対し音波ビ−ムの幅が狭く、かつ光束と音波の相互作
用領域が有限である場合に生ずる現象である。[Operation] The Raman Naas diffraction phenomenon used in the present invention will be explained below. The black diffraction phenomenon, which is the principle of a generally known optical frequency shifter, is a phenomenon that occurs when the interaction area between a light beam and a sound wave is sufficiently wide, and the light beam that is incident obliquely crosses the sound wave surface many times. It is used to generate a single bright spot by shifting the frequency of the incident light. On the other hand, the Raman Nurse diffraction phenomenon is a phenomenon that occurs when the width of the acoustic beam is narrower than the beam of light and the area of interaction between the beam of light and the acoustic wave is finite.
【００１３】しかし、ラマン・ナ−ス回折現象では、フ
ォノンとフォトン間の運動量保存の法則及びエネルギ−
保存の法則を満たしているため、入射光束が複数の光束
に空間分割され、かつ、各光束の光周波数も異なって出
力する。このことを音波の伝搬によって生ずる媒質中粗
密波が理想的な位相格子として働くものとして、図５に
より説明する。光束が音波面に平行に入射して、音場を
直線で横切ると、出射光は音波によって位相のみを変調
される。つまり、音波が密で屈折率の高くなった部分を
通過した光は位相が遅れ、逆に粗な部分を通過した光は
位相が進む。その結果、音場を通過した光束の波面はａ
のように波打つことになり、変調波が遠距離に達したと
き、いいかえれば、フ−リエ変換したとき ０次、±
１次、±２次等の回折光ができることになる。このとき
、音波は光に対して回折格子として働くが、振幅も光の
向きには影響せず位相のみに影響している。However, in the Raman Naas diffraction phenomenon, the law of conservation of momentum between phonons and photons and the energy
Since the law of conservation is satisfied, the incident light beam is spatially divided into a plurality of light beams, and each light beam is output with a different optical frequency. This will be explained with reference to FIG. 5, assuming that the compression waves in the medium produced by the propagation of sound waves act as an ideal phase grating. When a light beam is incident parallel to a sound wave surface and crosses the sound field in a straight line, only the phase of the output light is modulated by the sound wave. In other words, light that passes through areas where the acoustic waves are dense and has a high refractive index will have a delayed phase, and conversely, light that has passed through areas where the acoustic waves are dense will have an advanced phase. As a result, the wavefront of the light flux passing through the sound field is a
When the modulated wave reaches a long distance, in other words, when it is Fourier transformed, the 0th order, ±
This results in the formation of first-order, ±second-order, etc. diffracted light. At this time, the sound waves act as a diffraction grating for the light, but the amplitude does not affect the direction of the light, only the phase.
【００１４】したがって、幾何的な回折格子の理論から
θｍ ＝ ａｒｃ Ｓｉｎ（ｍλ／Λ） で求め
られるｍ次の回折角θｍ ごとに入射光束が分割される
。ここで、λは真空中の光波長、Λは音波長を示してい
る。[0014] Therefore, the incident light beam is divided for each m-th diffraction angle θm, which is determined by θm = arc Sin (mλ/Λ) from the theory of geometric diffraction gratings. Here, λ is the wavelength of light in vacuum, and Λ is the length of the sound wave.
【００１５】一方、音波による媒質中の粗密波により光
の位相に影響を与える位相格子が形成されているため、
音波の位相速度は ｆΛ という値をもっている。
したがって、前記ｍ次の回折光の周波数νｍ は、ドッ
プラ−効果により、νｍ＝νｉ ＋ｍｆ で表される周
波数にシフトされることになる。ここで、νｉ は入射
光の周波数、ｍは次数、ｆは音波周波数を示す。以上述
べたように、ラマン・ナ−ス回折現象を用いると、入射
光を複数の光束に分割し、かつ、その分割したそれぞれ
の光束をｍｆ（ｍ＝±１，±２，・・・）だけ周波数シ
フトさせることができる。On the other hand, since compression waves in the medium caused by sound waves form a phase grating that affects the phase of light,
The phase velocity of a sound wave has a value fΛ. Therefore, the frequency νm of the m-th order diffracted light is shifted to the frequency expressed by νm=νi +mf due to the Doppler effect. Here, νi is the frequency of the incident light, m is the order, and f is the sound wave frequency. As mentioned above, when using the Raman-Nurs diffraction phenomenon, the incident light is divided into a plurality of light beams, and each of the divided light beams is divided into mf (m=±1, ±2,...) Only the frequency can be shifted.
【００１６】[0016]
【実施例】図１は、本発明による周波数安定化光源の一
実施例を示したものである。レ−ザ光源（半導体レーザ
）１からの周波数ｆＬＤのレーザ光を、ラマン・ナース
回折セル２に入力し、複数のレーザ光束に回折して分割
した場合、その分割された複数のレーザ光束の周波数は
、例えば ＋１次回折光であればラマン・ナース回折
セル２の駆動周波数ｆｒを加えたｆＬＤ＋ｆｒに、＋２
次回折光であればｆＬＤ＋２ｆｒに遷移し、一方、−１
次回折光であればラマン・ナース回折セル２の駆動周波
数ｆｒを減じたｆＬＤ−ｆｒ に、−２次回折光であれ
ばｆＬＤ−２ｆｒ に成る。本実施例では、この複数の
回折光のうち、２つの回折光を利用したものを示す。DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a frequency stabilized light source according to the present invention. When a laser beam with a frequency fLD from a laser light source (semiconductor laser) 1 is input to the Raman-Nurse diffraction cell 2 and is diffracted and divided into a plurality of laser beams, the frequency of the plurality of divided laser beams is For example, if it is +1st-order diffracted light, +2
If it is the second order diffracted light, it will transition to fLD+2fr, while -1
If it is the second-order diffracted light, it becomes fLD-fr, which is obtained by subtracting the driving frequency fr of the Raman Nurse diffraction cell 2, and if it is the -second-order diffracted light, it becomes fLD-2fr. In this embodiment, two diffracted lights out of the plurality of diffracted lights are used.
【００１７】今、２つの回折光をそれぞれａ光、ｂ光と
名付ける。光の進路は２本の実線で成る矢印で示してあ
る。ａ光は、レーザ光源１より出力されたレーザ光束を
ラマン・ナース回折セル２に透過させた場合に空間分割
と周波数遷移が生じて、ｆＬＤ＋ｆｒの周波数を持った
レ−ザ光を示し、一方、ｂ光はレーザ光源１より出力さ
れたレーザ光束をラマン・ナース回折セル２に透過させ
た場合に空間分割と周波数遷移が生じて、ｆＬＤ−ｆｒ
の周波数を持ったレーザ光を示す。The two diffracted lights will now be named a-light and b-light, respectively. The path of the light is shown by two solid arrows. When the laser beam output from the laser light source 1 is transmitted through the Raman Nurse diffraction cell 2, the a-light undergoes space division and frequency transition, and exhibits a laser beam with a frequency of fLD+fr. When the laser beam output from the laser light source 1 is transmitted through the Raman Nurse diffraction cell 2, the b light undergoes space division and frequency transition, resulting in fLD-fr.
Indicates a laser beam with a frequency of .
【００１８】ａ光、ｂ光をそれぞれ周波数弁別器３に入
射する。周波数弁別器３は、所定の周波数だけを吸収す
る特性（光吸収特性）を有し、所望の光吸収特性が得ら
れるようにした光吸収セルやエタロンなどを用いること
ができる。The a-light and the b-light are respectively input to the frequency discriminator 3. The frequency discriminator 3 has a characteristic of absorbing only a predetermined frequency (light absorption characteristic), and can use a light absorption cell, an etalon, or the like that can obtain a desired light absorption characteristic.
【００１９】以上に述べた本実施例では、光吸収セルを
用いた場合について説明する。光吸収セルの中には、ア
セチレン（１．５μｍ）、水蒸気（０．８μｍ）、ルビ
ジウム（０．７８μｍ）、セシウム（０．８５μｍ）等
のガスが単独または２以上封入されており、その封入物
質で定まる特定の周波数において吸収スペクトルを有す
る。In this embodiment described above, a case will be explained in which a light absorption cell is used. Inside the light absorption cell, one or more gases such as acetylene (1.5 μm), water vapor (0.8 μm), rubidium (0.78 μm), and cesium (0.85 μm) are sealed. It has an absorption spectrum at a specific frequency determined by the substance.
【００２０】図２は、光吸収ガスとしてアセチレンを封
入した場合の光吸収セルにおける吸収スペクトルの一例
を示したものである。図から明らかなように、横軸に示
すレーザ光の周波数（Ｈｚ）が変化するのに対応してレ
ーザ光が光吸収セルを透過した場合の縦軸に示す透過光
強度（横軸）も変化する。周波数弁別器３を透過したａ
光とｂ光はそれぞれ２つの光検出機能を有する受光器４
で電気信号Ｖａ 、Ｖｂ に変換される。吸収ピークの
周波数をｆ０ とし、ｆＬＤ＝ｆ０ のときにＶａ ＝
Ｖｂ となるように受光器４の出力ゲイン等を調整して
おく。差動アンプ５にそれぞれＶａ とＶｂ を入力す
る。この差動アンプ５は、差動出力値Ｖｄｅｆ （＝Ｖ
ａ −Ｖｂ ）を出力することができる。FIG. 2 shows an example of an absorption spectrum in a light absorption cell when acetylene is sealed as a light absorption gas. As is clear from the figure, as the frequency (Hz) of the laser light shown on the horizontal axis changes, the transmitted light intensity (horizontal axis) shown on the vertical axis also changes when the laser light passes through the light absorption cell. do. a transmitted through frequency discriminator 3
The light and b light each have a light receiver 4 with two light detection functions.
are converted into electrical signals Va and Vb. Let the absorption peak frequency be f0, and when fLD=f0, Va=
Adjust the output gain of the photoreceiver 4 so that the voltage becomes Vb. Va and Vb are input to the differential amplifier 5, respectively. This differential amplifier 5 has a differential output value Vdef (=V
a −Vb ).
【００２１】図３に示すとおり、横軸にレ−ザ光の周波
数ｆＬＤ、縦軸に差動出力値Ｖｄｅｆ をとると、この
曲線は吸収ピークの一次微分の近似となる。この差動出
力値Ｖｄｅｆの値は、（１）ｆＬＤ＜ｆ０ ではＶｄｅ
ｆ ＜０、（２）ｆＬＤ＝ｆ０ ではＶｄｅｆ＝０、（
３）ｆＬＤ＞ｆ０ ではＶｄｅｆ ＞０ となる。As shown in FIG. 3, when the frequency fLD of the laser beam is plotted on the horizontal axis and the differential output value Vdef is plotted on the vertical axis, this curve becomes an approximation of the first derivative of the absorption peak. The value of this differential output value Vdef is (1) When fLD<f0, Vde
f < 0, (2) fLD=f0 then Vdef=0, (
3) When fLD>f0, Vdef>0.
【００２２】そのため、この差動出力値Ｖｄｅｆ を、
駆動電流源６に負帰還させることによって、レーザ光の
周波数ｆＬＤを、常に吸収ピ−クの周波数ｆ０ に安定
化することができる。試作した本発明による周波数安定
化光源のアラン分散値を図４に示す。図４（ａ）におい
て、○印は位相検波法による周波数安定度を示し、図４
（ｂ）において、●印は本発明による周波数安定度を示
す。これらのデ−タから、本発明による周波数安定化光
源は、従来における位相検波法による安定度のような時
定数による帯域の制限がないため、位相検波法では実現
不可能であった短期安定度１ｍｓ以下でも実現できるこ
とがわかる。Therefore, this differential output value Vdef is
By providing negative feedback to the drive current source 6, the frequency fLD of the laser beam can always be stabilized at the absorption peak frequency f0. FIG. 4 shows the Allan dispersion value of a prototype frequency-stabilized light source according to the present invention. In Fig. 4(a), the circle mark indicates the frequency stability based on the phase detection method.
In (b), the ● mark indicates the frequency stability according to the present invention. From these data, it was found that the frequency-stabilized light source according to the present invention has short-term stability that could not be achieved using the phase detection method, since there is no band limitation due to the time constant, which is achieved by the conventional phase detection method. It can be seen that this can be achieved even in 1 ms or less.
【００２３】[0023]
【発明の効果】以上、述べたように、本発明によるラマ
ン・ナ−ス回折セルを利用した周波数安定化光源は、ラ
マン・ナ−ス回折現象により、光の周波数をラマン・ナ
−ス回折の駆動周波数ｆｒだけ、プラス・マイナス両方
向にシフトさせ、周波数弁別器として光の吸収ピ−クを
利用し、そのピ−クの前後のスロ−プを利用して光源の
周波数安定をはかるものとしたから、次に示すような固
有の効果を有することができた。Effects of the Invention As described above, the frequency stabilized light source using the Raman Nass diffraction cell according to the present invention changes the frequency of light by the Raman Nass diffraction phenomenon. The driving frequency fr is shifted in both plus and minus directions, and the light absorption peak is used as a frequency discriminator, and the slope before and after the peak is used to stabilize the frequency of the light source. Therefore, it was possible to have the following unique effects.
【００２４】（１）一般的な差動法ではレーザ光の周波
数を吸収ピークの側面に安定化させることになるのに対
して、本発明では吸収ピークの周波数にレーザ光の周波
数を安定化することができるため、安定周波数の確度が
高く、また１個の周波数変調器を用いて２つの周波数遷
移光を作り出しているために、少ない構成部品で、かつ
周波数変調器自体の温度ドリフトの影響も受けにくく、
長期安定度が非常に優れた周波数安定化光源（δ＝１×
１０−９：τ＝１ｓ）が実現できた。
（２）本発明は位相検波法による安定化のような時定数
による帯域の制限がないため制御系の帯域を広げること
により、位相検波法では実現不可能であった無変調で周
波数の短期安定度が非常に優れた周波数安定化光源（δ
＝９×１０−９：τ＝１ｍｓ）が実現できた。(1) In the general differential method, the frequency of the laser beam is stabilized to the side of the absorption peak, whereas in the present invention, the frequency of the laser beam is stabilized to the frequency of the absorption peak. This allows for high accuracy of stable frequency, and since one frequency modulator is used to generate two frequency transition lights, there are fewer components and there is no effect of temperature drift of the frequency modulator itself. difficult to receive,
A frequency-stabilized light source with excellent long-term stability (δ=1×
10-9:τ=1s) was realized. (2) Since the present invention does not have the band limitation due to a time constant like stabilization by phase detection method, by widening the band of the control system, short-term frequency stabilization without modulation, which was impossible to achieve with phase detection method, is achieved. Frequency stabilized light source (δ
=9×10-9:τ=1ms).
【００２５】このように、本発明の周波数安定化光源は
、回折セルとして使用されてきたものをピ−ク特性をも
つ周波数弁別器と組み合わせて安定化光源を得るために
使用することとした点に特徴がある。実施例では、周波
数弁別器として吸収ピ−クを利用したが、ピ−クは吸収
特性に必ずしも限定されない。要すれば、±ｆｒだけ周
波数シフトした光をスロ−プの異なるところで検出でき
るようなものであればよい。As described above, the frequency-stabilized light source of the present invention is characterized in that what has been used as a diffraction cell is used in combination with a frequency discriminator having peak characteristics to obtain a stabilized light source. There are characteristics. In the embodiment, an absorption peak is used as a frequency discriminator, but the peak is not necessarily limited to absorption characteristics. In short, it may be any device that can detect light whose frequency has been shifted by ±fr at different slopes.
【図１】本発明による周波数安定化光源の一実施例の構
成を示す。FIG. 1 shows the configuration of an embodiment of a frequency-stabilized light source according to the present invention.
【図２】吸収セル中のアセチレンの光吸収スペクトルを
示す。FIG. 2 shows the optical absorption spectrum of acetylene in an absorption cell.
【図３】差動アンプ出力とレーザ光の周波数の関係をそ
れぞれ示す。FIG. 3 shows the relationship between the differential amplifier output and the frequency of laser light.
【図４】本発明による周波数安定化光源のアラン分散値
を示す。FIG. 4 shows Allan dispersion values of a frequency-stabilized light source according to the invention.
【図５】音波の伝搬により生ずる媒質中粗密波が理想的
な位相格子として働く様子を示す。
１ レ−ザ光源（半導体レーザ）
２ ラマン・ナース回折セル
３ 周波数弁別器
４ 受光器
５ 差動アンプ
６ 駆動電流源FIG. 5 shows how compression waves in a medium generated by the propagation of sound waves function as an ideal phase grating. 1 Laser light source (semiconductor laser) 2 Raman Nurse diffraction cell 3 Frequency discriminator 4 Light receiver 5 Differential amplifier 6 Drive current source
Claims (1)
駆動するための駆動電流源（６）と、該レーザ光源から
出力されたレーザ光を複数の光束に分割し、かつ、該複
数の光束をそれぞれ異なった周波数に遷移するラマン・
ナース回折セル（２）と、該ラマン・ナース回折セルで
周波数遷移した該複数の光束を弁別する周波数弁別器（
３）と、該周波数弁別器により弁別したレーザ光の光強
度を検出し、その検出した光強度に応じた信号を出力す
る少なくとも２つの受光器（４）と、該受光器の出力信
号に応じて前記レーザ光源からの出力光の周波数を前記
周波数弁別器の出力に一致せしめるように，前記駆動電
流源を制御する差動アンプ（５）とからなる周波数安定
化光源。1. A laser light source (1), a drive current source (6) for driving the laser light source, and a laser light source that divides the laser light output from the laser light source into a plurality of light beams, and divides the laser light output from the laser light source into a plurality of light beams, and Raman, which transitions the light flux to different frequencies,
a Nath diffraction cell (2), and a frequency discriminator (
3), at least two light receivers (4) that detect the light intensity of the laser light discriminated by the frequency discriminator and output a signal corresponding to the detected light intensity; and a differential amplifier (5) that controls the drive current source so that the frequency of the output light from the laser light source matches the output of the frequency discriminator.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14258191A JPH04342183A (en) | 1991-05-17 | 1991-05-17 | Frequency-stabilized light source |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14258191A JPH04342183A (en) | 1991-05-17 | 1991-05-17 | Frequency-stabilized light source |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH04342183A true JPH04342183A (en) | 1992-11-27 |
Family
ID=15318639
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP14258191A Pending JPH04342183A (en) | 1991-05-17 | 1991-05-17 | Frequency-stabilized light source |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH04342183A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1998043327A3 (en) * | 1997-03-26 | 1998-12-23 | Siemens Ag | Method for stabilizing the wavelength of a laser and arrangement for implementing said method |
| DE102007007677A1 (en) * | 2007-02-13 | 2008-09-04 | Deutsches Zentrum für Luft- und Raumfahrt e.V. | Method for frequency stabilization of laser beam emitted by laser, which is subjected to pre-determined frequency of acoustic-optical modulation, involves determining intensities of frequency-modulated partial beams |
| WO2011049486A1 (en) * | 2009-10-19 | 2011-04-28 | Фгуп "Вниифтри" | Phase-sensitive frequency stabilization of laser radiation |
| JP2021114579A (en) * | 2020-01-21 | 2021-08-05 | 株式会社ミツトヨ | Laser frequency stabilizer and laser frequency-stabilizing method |
-
1991
- 1991-05-17 JP JP14258191A patent/JPH04342183A/en active Pending
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1998043327A3 (en) * | 1997-03-26 | 1998-12-23 | Siemens Ag | Method for stabilizing the wavelength of a laser and arrangement for implementing said method |
| DE102007007677A1 (en) * | 2007-02-13 | 2008-09-04 | Deutsches Zentrum für Luft- und Raumfahrt e.V. | Method for frequency stabilization of laser beam emitted by laser, which is subjected to pre-determined frequency of acoustic-optical modulation, involves determining intensities of frequency-modulated partial beams |
| DE102007007677B4 (en) * | 2007-02-13 | 2009-03-05 | Deutsches Zentrum für Luft- und Raumfahrt e.V. | Method for stabilizing the frequency of a laser with the aid of acousto-optical modulation and a device for frequency stabilization of a laser by means of acousto-optical modulation |
| WO2011049486A1 (en) * | 2009-10-19 | 2011-04-28 | Фгуп "Вниифтри" | Phase-sensitive frequency stabilization of laser radiation |
| JP2021114579A (en) * | 2020-01-21 | 2021-08-05 | 株式会社ミツトヨ | Laser frequency stabilizer and laser frequency-stabilizing method |
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