JPH09297065A - Optical-frequency measuring device and optical-reference-frequency generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to perform the highly accurate measurement of the optical frequency of a laser light source by determining the optical frequency ratio of both first and second laser light sources, and determining the optical frequency of the first laser light source from the optical-frequency difference obtained by the optical-frequency-difference measuring means. SOLUTION: The optical frequency ratio of a first laser light source 1 and a second laser light source 2 is determined, and the optical frequency of the first laser light source obtained by an optical-frequency-difference measuring means. The optical- frequency difference is determined by using the resonance-frequency control means, wherein a resonator length L of an optical resonator 7 is made to vary and one resonance frequency of it is made to agree with the first laser light souce 1, and the optical-frequency control means, wherein the optical frequency of the second laser light source 2 is varied and the optical frequency is a made to agree with the other resonance optical frequency. The optical frequency difference is obtained as follows; the output light of any of the first and secon laser light sources is inputted into an optical frequency comb generator, a side band is generated and the beat frequency of the beat signal of one of the side bands and the output light of the other laser light source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical frequency measuring device for measuring an optical frequency of a laser light source and an optical reference frequency generating device for generating a predetermined optical reference frequency.

[0002]

2. Description of the Related Art Laser light of unknown frequency (frequency ν _u ),
When a laser beam with a known frequency (frequency ν _k ) and a microwave with a known frequency (frequency ν _m ) are mixed using a non-linear element, a beat signal with a frequency δν can be generated. Frequency .DELTA..nu is, .DELTA..nu = | represented ... as _{(1) | ν u -N k} ν k ± N m ν m. Here, N _k and N _m are integers. The conventional optical frequency measuring device has a frequency δν of this beat signal.
Is measured by a frequency counter or the like, and the frequency ν _u of the laser light of unknown frequency is obtained. For the non-linear element, for example, a Josephson point contact diode or a tungsten-nickel point contact diode is used.

FIG. 6 shows an example of the configuration of a conventional optical frequency measuring device for measuring the optical frequency of a CH ₃ stabilized He-Ne laser. In the figure, the laser light output from the CH ₃ OH laser 61 and the microwave (frequency 90 GHz) output from the microwave oscillator 71 are mixed by the non-linear element 81, and the difference frequency is measured by the frequency counter 91. ₃ OH
The frequency of the laser 61, 4.2 THz, is determined. Then this C
Laser light output from the H ₃ OH laser 61 (frequency
4.2 THz), the microwave (frequency 70 GHz) output from the microwave oscillator 72, and the laser light output from the CO ₂ laser 62 are mixed by the nonlinear element 82, and the difference frequency is measured by the frequency counter 92. CO ₂ laser 62
Confirm the frequency of 29 THz. Next, this CO ₂ laser 6
2 and the laser light (frequency 29 THz) output from the microwave oscillator 73 (frequency 55 G
And Hz), the frequency of CH ₃ stabilized He-Ne laser beam output from the laser 63 is mixed with a non-linear element 83, CH ₃ stabilized He-Ne laser 63 to measure the difference frequency by the frequency counter 93 88THz Confirm (wavelength 3.39 μm). Microwave oscillators 71-73 and frequency counters 91-9
3 is controlled by the cesium atomic oscillator 100.

[0004]

As shown in FIG. 6, the conventional optical frequency measuring device has a complicated structure that requires a plurality of laser light sources over a wide wavelength range, a microwave oscillator, and a non-linear element. The range was limited. It is an object of the present invention to provide an optical frequency measurement device and an optical reference frequency generation device that can measure the optical frequency of a laser light source with a simple configuration and with high accuracy.

[0005]

The optical frequency measuring device of the present invention determines the optical frequency ratio between the first laser light source and the second laser light source, and determines from the optical frequency difference obtained by the optical frequency difference measuring means. The optical frequency of the first laser light source is determined. The optical frequency ratio is such that the resonator length of the optical resonator can be varied and the resonance frequency control means for matching one resonance frequency with the optical frequency of the first laser light source and the optical frequency of the second laser light source can be varied. , Optical frequency control means for matching the optical frequency with other resonant frequencies of the optical resonator. The optical frequency difference is that the output light of either the first or second laser light source is input to an optical frequency comb generator or a mode-locked laser to generate sidebands, and one of the sidebands and the other laser light source. It is obtained by measuring the frequency of the beat signal with the output light of.

The optical reference frequency generator of the present invention determines the optical frequency ratio between the first laser light source and the second laser light source,
Based on the optical frequency difference obtained by the optical frequency difference measuring means, the resonator length of the optical resonator is controlled to determine the optical frequency of the first laser light source. The optical frequency ratio is a first optical frequency control means for matching the optical frequency of the first laser light source with one resonance frequency of the optical resonator, the optical frequency of the second laser light source and the other resonance of the optical resonator. And the second optical frequency control means for matching the frequencies. The optical frequency difference is that the output light of either the first or second laser light source is input to an optical frequency comb generator or a mode-locked laser to generate sidebands, and one of the sidebands and the other laser light source. It is obtained by measuring the frequency of the beat signal with the output light of.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment of Optical Frequency Measuring Apparatus) FIG. 1 shows a first embodiment of the optical frequency measuring apparatus of the present invention. In the figure, 1 is a laser light source whose optical frequency is to be measured and whose frequency is stabilized by using absorption lines of atoms or molecules, and 2 is a laser light source whose optical frequency can be controlled. The resonance frequency control means is composed of an oscillator 3-1, a phase modulator 4-1, an optical coupler 5, an optical circulator 6, a Fabry-Perot resonator 7 having a vacuum between reflection surfaces, a photodetector 8, a bandpass filter (BP).
F) 9-1, a mixer 10-1, and a resonator length control circuit 11. The optical frequency control means is an oscillator 3-2,
Phase modulator 4-2, optical coupler 5, optical circulator 6,
Fabry-Perot resonator 7 having a vacuum between the reflecting surfaces, a photodetector 8, a bandpass filter (BPF) 9-2, and a mixer 1.
0-2, optical frequency control circuit 12. The optical frequency difference measuring means includes optical couplers 21-1 and 21-2, an optical frequency comb generator 22, an optical coupler 23, a light receiver 24, a high precision oscillator 25 using a cesium atomic oscillator or a rubidium atomic oscillator, a counter 26, and frequency control. It is composed of a circuit 27, a microwave synthesizer 28, and a counter 29. The optical coupler 20 is used to take out the output light of the laser light source 1 to the outside.

First, the measurement of the optical frequency ratio of the laser light sources 1 and 2 will be described. Output light of laser light source 1 (frequency ν
₀ ) is branched by the optical coupler 20, one of the lights is further branched by the optical coupler 21-1, the one light is input to the phase modulator 4-1, and the output of the oscillator 3-1 (frequency f ₁ ) Is modulated. Output light of laser light source 2 (frequency ν
₁ ) is branched by the optical coupler 21-2, one light of which is input to the phase modulator 4-2, and is modulated by the output (frequency f ₂ ) of the oscillator 3-2. The two lights that have been phase-modulated are combined by the optical coupler 5 and input to the Fabry-Perot resonator 7 via the optical circulator 6.

The Fabry-Perot resonator 7 has a vacuum between its reflecting surfaces, and its electric field reflectance r (ν) and mode interval Δν.
Is

[0010]

[Equation 1] Given in. Here, r ₁ and r ₂ are electric field reflectances of the reflecting surface. L is the resonator length, which can be controlled by the voltage applied to the PZT (electrostrictive element). c is the speed of light in vacuum (= 2.99792458 × 10 ⁸ m / s). In addition,
The resonator length of the Fabry-Perot resonator can be controlled not only by PZT but also by temperature.

The reflected light from the Fabry-Perot resonator 7 is input to the light receiver 8 via the optical circulator 6,
Converted to electrical signals. A band-pass filter 9-1 extracts a component of frequency f ₁ from this electric signal, and the output of the oscillator 3-1 is mixed with the mixer 10-1. If the M-th resonance frequency MΔν of the Fabry-Perot resonator 7 is near the frequency ν ₀ of the laser light source 1, the mixer 10-
At the output of 1, a frequency error signal V ₁ proportional to ν ₀ -MΔν represented by V ₁ ∝ (ν ₀ -MΔν) Re [r '(f ₁ )] (3) is obtained. Here, r ′ (ν) represents the differential of the electric field reflectance (Equation (2)) of the Fabry-Perot resonator 7. The resonator length control circuit 11 is controlled so that the frequency error signal V ₁ becomes 0.
When the Fabry-Perot resonator 7 is controlled by, the relationship of ν ₀ = MΔν (4) holds between the frequency ν ₀ of the laser light source 1 and the resonance frequency MΔν of the Fabry-Perot resonator 7 (see FIG. 2). ).

Similarly, the component of frequency f ₂ is extracted from the electric signal output from the photodetector 8 by the bandpass filter 9-2, and this is mixed with the output of the oscillator 3-2 by the mixer 10-2. If the M + 1th resonance frequency (M + 1) Δν of the Fabry-Perot resonator 7 is near the frequency ν ₁ of the laser light source 2, the output of the mixer 10-2 is V ₂ ∝ {ν _1- (M + 1) Δν} Re [r ′ (f ₂ )] (5) A frequency error signal V ₂ is obtained which is proportional to ν ₁ − (M + 1) Δν. When the laser light source 2 is controlled by the optical frequency control circuit 12 so that the frequency error signal V ₂ becomes 0, the frequency between the frequency ν ₁ of the laser light source 2 and the resonance frequency (M + 1) Δν of the Fabry-Perot resonator 7 becomes. , Ν ₁ = (M + 1) Δν (6) holds (see FIG. 2). That is, the optical frequency ratio of the laser light sources 1 and 2 is ν ₀ / ν ₁ = M / (M + 1) (7)

Next, the measurement of the optical frequency difference between the laser light sources 1 and 2 will be described. A part of the output light (frequency ν ₁ ) of the laser light source 2 branched by the optical coupler 21-2 is input to the optical frequency comb generator 22. Optical frequency comb generator 22
Is a Fabry-Perot resonator in which both end surfaces of the optical phase modulator are highly reflectively coated to form reflecting mirror surfaces, and the modulation signal (frequency f ₀ ) is input from the microwave synthesizer 28. This optical frequency comb generator 2
The light input to 2 is repeatedly phase-modulated, and many sidebands (frequency ν ₁ ± f ₀ , around the center frequency ν ₁
ν ₁ ± 2f ₀ , ν ₁ ± 3f ₀ ,…) occur. The output of the optical frequency comb generator 22 and a part of the output light (frequency ν ₀ ) of the laser light source 1 branched by the optical coupler 21-1 are combined by the optical coupler 23 and converted into an electric signal by the light receiver 24. To be done.

Here, if the frequency ν ₀ of the laser light source 1 is in the vicinity of _{one of the} sidebands generated by the optical frequency comb generator 22 (frequency ν ₁ -Nf ₀ , N is an integer), then the light receiver The electrical signal output from 24 becomes a beat signal between the output light of the laser light source 1 and one of the sidebands generated in the optical frequency comb generator 22. The frequency of this beat signal is ν
_It can be measured if the difference between ₀ and ν ₁ −Nf ₀ is sufficiently small. In the present embodiment, the frequency of the beat signal is measured by the counter 26 using the output of the high precision oscillator 27 as a reference signal, and the frequency control circuit 2 controls the value to be exactly Δf.
Controlling the microwave synthesizer 28 at 7, the frequency difference [nu ₁ -v ₀ frequency [nu ₁ frequency [nu ₀ and the laser light source 2 of the laser light source _{1, ν 1 -ν 0 = Nf 0} + Δf ... as (8) Can be obtained (see FIG. 2).

On the other hand, the counter 29 measures the frequency f ₀ of the microwave synthesizer 28 using the output of the high precision oscillator 27 as a reference signal. By using the result and the equations (4), (6) and (8), the frequency ν ₀ of the laser light source 1 is determined as ν ₀ = M (Nf ₀ + Δf) (9) You can

Next, the values of M and N are determined, and the laser light source 1
A specific example of obtaining the frequency ν ₀ of will be described. Here, an optical wavelength meter (for example, Michelson interferometer) is used supplementarily. Even with a commercially available optical wavemeter, an accuracy of ± 0.05 ppm is obtained. This is, for example, in the wavelength 1.5 μm band (frequency 200
When measuring light of about THz), frequency conversion is ± 10
Indicates that an accuracy of 0 MHz can be obtained.

Assuming that the laser light source 1 is stabilized at the absorption line P (27) of HCN (hydrocyanic acid gas) (wavelength 1.556373 μm), its optical frequency ν ₀ is ν ₀ ≈ by using the above optical wavelength meter. It can be estimated as 192.6225 ± 0.0001 [THz]. Here, the resonator length L (≈0.3 mm) of the Fabry-Perot resonator 7 is controlled, and the M-th resonance frequency MΔν is locked to this optical frequency ν ₀ . Next, the optical frequency ν ₁ of the laser light source 2 is locked to the M + 1th resonance frequency (M + 1) Δν. Since the mode interval Δν of the Fabry-Perot resonator 7 is about 500 GHz, M
+ 1st resonance frequency is around 193.1 THz (wavelength 1.552μ
m neighborhood). The optical frequency ν ₁ of the laser light source 2 is measured by the above optical wavelength meter. If this value is ν ₁ ≈193.1065 ± 0.0001 [THz], the mode interval Δν of the Fabry-Perot resonator 7 is Δν = 484.0 ± 0.2 [GHz], and M from Equations (4) and (6) = 398 can be determined.

Next, when the modulation frequency f ₀ of the optical frequency comb generator 22 is set to about 5 GHz and the frequency Δf of the beat signal is accurately selected to 4.0 GHz, N = 96 can be determined from the equation (8). . Here, if the controlled modulation frequency f ₀ is f ₀ = 4.9997499 [GHz], the optical frequency ν ₀ of the laser light source 1 is given by the formula (9).
Therefore, it can be determined that ν ₀ = 192.622444 [THz].

(Second Embodiment of Optical Frequency Measuring Apparatus) FIG. 3 shows a second embodiment of the optical frequency measuring apparatus of the present invention. The feature of this embodiment is that the optical frequency comb generator 22 in the first embodiment of FIG. 1 is replaced with a mode-locked laser 30. Other configurations are the same as those of the first embodiment.

The center frequency of the mode-locked laser 30 is pulled to the optical frequency ν ₁ of the laser light source 2. The modulation signal (frequency f ₀ ) of the mode-locked laser 30 is input from the microwave synthesizer 28. Mode-locked laser 3
Since the longitudinal mode interval of ₀ is almost equal to this modulation frequency f ₀ , many sidebands (frequency ν ₁ ± f ₀ , ν ₁ ± 2f ₀ , ν ₁ ± 3f ₀ , ...) are formed around the center frequency ν _1. appear. The output of this mode-locked laser 30 and the optical coupler 21
Output light of laser light source 1 branched at -1 (frequency ν ₀ ).
Is partly combined by the optical coupler 23 and converted into an electric signal by the light receiver 24. The subsequent operation is similar to that of the first embodiment.

(First Embodiment of Optical Reference Frequency Generator) FIG. 4 shows a first embodiment of the optical reference frequency generator of the present invention. In the figure, 1 is a laser light source whose optical frequency can be controlled, and 2 is a laser light source whose optical frequency can be controlled. The first optical frequency control means includes an oscillator 3-1, a phase modulator 4-1, an optical coupler 5, an optical circulator 6, a Fabry-Perot resonator 7 having a vacuum between reflection surfaces, a light receiver 8, and a bandpass filter. (BPF) 9-1, mixer 10
-1, and an optical frequency control circuit 12-1. The second optical frequency control means includes an oscillator 3-2 and a phase modulator 4
-2, the optical coupler 5, the optical circulator 6, the Fabry-Perot resonator 7 having a vacuum between the reflecting surfaces, the photodetector 8, the bandpass filter (BPF) 9-2, the mixer 10-2, the optical frequency control circuit 12- It is composed of two. The optical frequency difference measuring means is composed of the optical couplers 21-1 and 21-2, the optical frequency comb generator 22, the optical coupler 23, the light receiver 24, the cesium atomic oscillator and the rubidium atomic oscillator, which are high-precision oscillators 2.
5, a counter 26, and a microwave synthesizer 28. The resonance frequency control means is composed of the resonator length control circuit 11 that operates according to the output of the counter 26. The optical coupler 20 is used to take out the output light of the laser light source 1 to the outside.

First, the measurement of the optical frequency ratio of the laser light sources 1 and 2 will be described. Output light of laser light source 1 (frequency ν
₀ ) is branched by the optical coupler 20, one light of which is extracted as output light to the outside, and the other light is further extracted by the optical coupler 2.
The light is branched at 1-1, and one of the lights is input to the phase modulator 4-1 and is modulated by the output (frequency f ₁ ) of the oscillator 3-1. The output light (frequency ν ₁ ) of the laser light source 2 is branched by the optical coupler 21-2, and one of the lights is phase modulator 4-2.
And is modulated by the output (frequency f ₂ ) of the oscillator 3-2. The two lights that have been phase-modulated are combined by the optical coupler 5 and input to the Fabry-Perot resonator 7 via the optical circulator 6.

The reflected light from the Fabry-Perot resonator 7 is input to the photodetector 8 via the optical circulator 6,
Converted to electrical signals. A band-pass filter 9-1 extracts a component of frequency f ₁ from this electric signal, and the output of the oscillator 3-1 is mixed with the mixer 10-1. If the M-th resonance frequency MΔν of the Fabry-Perot resonator 7 is near the frequency ν ₀ of the laser light source 1, the mixer 10-
At the output of 1, the frequency error signal V ₁ proportional to ν ₀ -MΔν is obtained. When the optical frequency control circuit 12-1 controls the laser light source 1 so that the frequency error signal V ₁ becomes 0, the frequency ν ₀ of the laser light source 1 and the resonance frequency MΔν of the Fabry-Perot resonator 7 are ν ₀ = The relation is MΔν (4 ').

Similarly, a component of frequency f ₂ is extracted from the electric signal output from the photodetector 8 by the bandpass filter 9-2, and this is mixed with the output of the oscillator 3-2 by the mixer 10-2. If the M + 1th resonance frequency (M + 1) Δν of the Fabry-Perot resonator 7 is near the frequency ν ₁ of the laser light source 2, the output of the mixer 10-2 is ν ₁ −.
A frequency error signal V ₂ proportional to (M + 1) Δν is obtained. When the laser light source 2 is controlled by the optical frequency control circuit 12-2 so that the frequency error signal V ₂ becomes 0, the frequency ν ₁ of the laser light source 2 and the resonance frequency (M + 1) Δν of the Fabry-Perot resonator 7 become ν ₁ = (M + 1) Δν (6 ′).

On the other hand, a part of the output light (frequency ν ₁ ) of the laser light source 2 branched by the optical coupler 21-2 is input to the optical frequency comb generator 22. The modulation signal (frequency f ₀ ) of the optical frequency comb generator 22 is input from the microwave synthesizer 28. The light input to the optical frequency comb generator 22 is repeatedly phase-modulated, and many sidebands (frequency ν ₁ ± f ₀ , ν ₁ ± 2f ₀ , ν ₁ around the center frequency ν ₁ are generated.
± 3f ₀ ,…) occurs. This optical frequency comb generator 22
And a part of the output light (frequency ν ₀ ) of the laser light source 1 branched by the optical coupler 21-1 is combined by the optical coupler 23 and converted into an electric signal by the light receiver 24.

Here, the frequency ν of the laser light source 1₀But the light
One of the sidebands (frequency) generated by the frequency comb generator 22
Wave number ν₁-Nf₀ , N is an integer)
The electric signal output from the device 24 is the output light of the laser light source 1.
And one of the sidebands generated by the optical frequency comb generator 22
It becomes a beat signal. Therefore, the output of the high precision oscillator 27
With the force as a reference signal, the frequency of the beat signal is counted by the counter 26.
Resonator length is measured so that the measured value is exactly Δf.
The control circuit 11 controls the Fabry-Perot resonator 7.
And the frequency ν of the laser light source 1₀And the frequency of laser light source 2
ν₁Frequency difference ν ₁−ν₀Is ν₁−ν₀= Nf₀+ Δf (8 ') Therefore, use equations (4 '), (6'), (8 ') and
Therefore, the frequency ν of the laser light source 1₀Is ν₀= M (Nf₀+ Δf) can be determined as in (9 ').

(Second Embodiment of Optical Reference Frequency Generator) FIG. 5 shows a second embodiment of the optical reference frequency generator of the present invention. The feature of this embodiment is that the optical frequency comb generator 22 in the first embodiment of FIG. 4 is replaced with a mode-locked laser 30. Other configurations are the same as those of the first embodiment.

The center frequency of the mode-locked laser 30 is pulled to the optical frequency ν ₁ of the laser light source 2. The modulation signal (frequency f ₀ ) of the mode-locked laser 30 is input from the microwave synthesizer 28. Mode-locked laser 3
Since the longitudinal mode interval of ₀ is almost equal to this modulation frequency f ₀ , many sidebands (frequency ν ₁ ± f ₀ , ν ₁ ± 2f ₀ , ν ₁ ± 3f ₀ , ...) are formed around the center frequency ν _1. appear. The output of this mode-locked laser 30 and the optical coupler 21
Output light of laser light source 1 branched at -1 (frequency ν ₀ ).
Is partly combined by the optical coupler 23 and converted into an electric signal by the light receiver 24. The subsequent operation is similar to that of the first embodiment.

In each of the embodiments described above, as the optical resonator, a Mach-Zehnder type optical filter can be used in addition to the Fabry-Perot resonator. Further, a fiber Fabry-Perot resonator in which two fiber ends are close to each other can be used.

[0030]

As described above, the optical frequency measuring device of the present invention has a simple structure, but has a high accuracy in optical frequency measurement, as compared with the conventional device using a plurality of laser light sources and nonlinear elements. It can be performed. Further, the optical reference frequency measuring device of the present invention can also be used as a reference light source having high frequency accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of an optical frequency measuring device of the invention.

FIG. 2 is a diagram for explaining the operation principle of the optical frequency measuring device of the present invention.

FIG. 3 is a diagram showing a second embodiment of the optical frequency measuring device of the invention.

FIG. 4 is a diagram showing a first embodiment of an optical reference frequency generator of the present invention.

FIG. 5 is a diagram showing a second embodiment of the optical reference frequency generator of the present invention.

FIG. 6 is a diagram showing a configuration example of a conventional optical frequency measurement device for measuring the optical frequency of a CH ₃ stabilized He—Ne laser.

[Explanation of symbols]

 1, 2 Laser light source 3 Oscillator 4 Phase modulator 5, 20, 21, 23 Optical coupler 6 Optical circulator 7 Fabry-Perot resonator 8, 24 Photodetector 9 Bandpass filter (BPF) 10 Mixer 11 Resonator length control circuit 12 Optical frequency control circuit 22 Optical frequency comb generator 25 High precision oscillator 26,29 Counter 27 Frequency control circuit 28 Microwave synthesizer 30 Mode lock laser

Claims (9)

[Claims] 1. A first laser light source for measuring an optical frequency, a second laser light source capable of controlling the optical frequency, an optical resonator having a periodic resonance characteristic, and a resonator of the optical resonator. Resonance frequency control means for varying the length and matching one resonance frequency with the optical frequency of the first laser light source; and varying the optical frequency of the second laser light source, the optical frequency and the optical resonator. And an optical frequency difference measuring unit for measuring an optical frequency difference between the optical frequency of the first laser light source and the optical frequency of the second laser light source. The resonance frequency control means and the optical frequency control means are used to determine the optical frequency ratio between the first laser light source and the second laser light source, and the optical frequency difference obtained by the optical frequency difference measuring means is used to determine the optical frequency ratio. First ray Optical frequency measurement device, characterized in that the arrangement for determining the optical frequency of the light source. 2. The optical frequency measuring device according to claim 1, wherein the first laser light source is a laser light source stabilized to an absorption line of an atom or a molecule. 3. The optical frequency measuring device according to claim 1, wherein the optical resonator is a Fabry-Perot resonator having a vacuum between reflecting surfaces. 4. The optical frequency measuring device according to claim 1, wherein the optical frequency difference measuring means includes an optical frequency comb generator in which an optical phase modulator is provided between the reflecting mirror surfaces of the Fabry-Perot resonator. The output light of one laser light source is input to the optical frequency comb generator to generate a sideband, and the frequency of the beat signal between one of the sidebands and the output light of the other laser light source is measured, and one laser light source An optical frequency measuring device having a configuration for measuring an optical frequency difference between the optical frequency of the laser light source and the optical frequency of the other laser light source. 5. The optical frequency measuring device according to claim 1, wherein the optical frequency difference measuring means includes a mode-locked laser injection-locked with the output light of one laser light source, and one of the generated side hand and the other side hand is generated. An optical frequency measuring device having a configuration in which a frequency of a beat signal with respect to an output light of a laser light source is measured, and an optical frequency difference between an optical frequency of one laser light source and an optical frequency of the other laser light source is measured. 6. A first laser light source capable of controlling an optical frequency, a second laser light source capable of controlling an optical frequency, an optical resonator having a periodic resonance characteristic, and the first laser. First optical frequency control means for varying the optical frequency of the light source and matching the optical frequency with one resonance frequency of the optical resonator; and varying the optical frequency of the second laser light source with the optical frequency A second one for matching the other resonance frequencies of the optical resonator
Optical frequency control means, optical frequency difference measuring means for measuring the optical frequency difference between the optical frequency of the first laser light source and the optical frequency of the second laser light source, and the resonator length of the optical resonator is variable. And a resonance frequency control means for matching the interval of the resonance frequency with an integer multiple of the optical frequency difference, and using the first optical frequency control means and the second optical frequency control means, the first optical frequency control means is used. The optical frequency ratio between the laser light source and the second laser light source is determined, and the resonator length of the optical resonator is controlled based on the optical frequency difference obtained by the optical frequency difference measuring means to control the first optical frequency. An optical reference frequency generator having a configuration for determining an optical frequency of a laser light source. 7. The optical reference frequency generator according to claim 6, wherein the optical resonator is a Fabry-Perot resonator having a vacuum between reflection surfaces. 8. The optical reference frequency generator according to claim 6, wherein the optical frequency difference measuring means includes an optical frequency comb generator in which an optical phase modulator is provided between the reflecting mirror surfaces of the Fabry-Perot resonator. , The output light of one of the laser light sources is input to the optical frequency comb generator to generate sidebands, the frequency of the beat signal between one of the sidebands and the output light of the other laser light source is measured, and one of the lasers is measured. An optical reference frequency generator having a configuration for measuring an optical frequency difference between an optical frequency of a light source and an optical frequency of the other laser light source. 9. The optical reference frequency generator according to claim 6, wherein the optical frequency difference measuring means includes a mode-locked laser injection-locked with the output light of one of the laser light sources, and one of the generated side hand and the other. The optical reference frequency generator is characterized in that the beat signal frequency with the output light of the laser light source is measured, and the optical frequency difference between the optical frequency of one laser light source and the optical frequency of the other laser light source is measured. apparatus.