JPH06152042A - Standard light source - Google Patents

Abstract

PURPOSE:To make it possible to implement a remarkably good stability concern ing a standard source using a laser diode and a rubidium atomic resonator. CONSTITUTION:A reference oscillator 41 generates a reference signal. A phase comparator 44 compares a phase of the reference signal generated by the reference oscillator 41 with a phase of the output signal of a VCO 29. In a filter circuit 45, a filtering is performed to a signal supplied from the phase comparator 44 and a current control signal is generated and is supplied to a laser diode drive circuit 14. The LD drive circuit 14, an LD 12, a resonator 16, a servo circuit 24, a VCO 29, the phase comparator 44 and the filter circuit 45 form a wavelength control loop of laser light. A current of the LD 12 is controlled so that a frequency of the output signal of the VCO 29 coincides with that of the reference signal of the reference oscillator 41 and as a result, a control is performed so that a wavelength lambda of the laser light becomes constant.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to standard light sources,
The present invention relates to a standard light source using a laser diode and a rubidium atomic resonator.

In recent years, coherent optical communication for future large-capacity optical communication has been considered, and there is a demand for development of a standard light source having extremely high stability for this purpose. Also, a standard light source with extremely high stability is required for optical measurement.

[0003]

2. Description of the Related Art Conventionally, there has been a stabilized light source in which a laser diode (hereinafter referred to as LD), an absorption cell, a photodetector, and a servo circuit are combined. In this stabilized light source, laser light passes through the absorption cell, based on the signal detected by the photodetector,
The servo circuit generates a signal for controlling the LD, controls the current of the LD, and controls the wavelength of the LD to be constant.

However, the above-mentioned stabilized light source has a problem that the wavelength stability is not so good and the frequency spectrum is wide. In order to solve this problem, the present applicant has proposed a stabilized light source described below in Japanese Patent Application No. 63-221816.

FIG. 6 is a block diagram of a conventional stabilized light source proposed by the present applicant. The optical microwave unit 11 includes a temperature control circuit 13, an LD 12, a half mirror 15, and a rubidium atomic resonator (hereinafter referred to as a resonator) 16.

The LD 12 is supplied with a current from the LD drive circuit 14 to generate a laser beam having a wavelength of 0.78 μm. The laser beam having a wavelength of 0.78 μm emitted from the LD 12 is divided into two by the half mirror 15, one of which is extracted as the output light of the light source, and the other is incident on the resonator 16. The resonator 16 includes a resonance cell 18 in which a rubidium atom is enclosed, and a cavity 1 containing the resonance cell 18.
7. Has a photodetector 22.

A coil 19 is wound around the cavity 17, and a DC current is supplied by a C-field current control circuit 20. This makes the cavities 17
A C-field (magnetic field) is formed inside the. The rubidium atom in the resonance cell 18 has a unique microwave resonance frequency f ₀ (6.834 GHz) and a unique resonance wavelength λ.
₀ (0.78 μm).

The microwave control means 23 for controlling the frequency f of the microwave applied to the resonator 16 is composed of the servo circuit 2
4, a voltage controlled oscillator (VCO) 29, and a frequency synthesizer 30.

The VCO 29 generates and outputs a signal of frequency f _V (for example, approximately 5 MHz). Frequency synthesizer 3
0 on the basis of a signal of a frequency f _V supplied from VCO 29, the frequency f _V constant relationship between the frequency f (approximately, 6.83
4 GHz) microwaves are combined and output. The microwave is phase-modulated at the low frequency fm by the low frequency signal fm supplied from the servo circuit 24 to the frequency synthesizer 30.

The microwave synthesized as described above and having a frequency f of approximately 6.834 GHz and a phase modulation at a low frequency f _m is transmitted from the frequency synthesizer 30 through the varactor diode 21 and the cavity 17 to the resonance cell. 18 is irradiated.

The laser beam incident on the resonance cell 18 passes through the resonance cell 18 and is incident on the photodetector 22.
At this time, atomic resonance occurs when the frequency f of the irradiation microwave coincides with the microwave resonance frequency f ₀ , the absorption amount of the laser beam in the resonance cell 18 becomes maximum, and the amount of light incident on the photodetector 22 is increased. Is the smallest. Therefore, the photodetector 22 outputs a photodetection signal corresponding to the difference between the microwave resonance frequency f ₀ and the irradiation microwave frequency f.

The servo circuit 24 uses the photodetection signal supplied from the photodetector 22 so that the frequency f of the microwave applied to the resonance cell 18 from the frequency synthesizer 30 matches the microwave resonance frequency f ₀ . The oscillation frequency f _V of the VCO 29 is controlled as described above.

Next, the control of the microwave frequency f by the servo circuit 24 will be described in detail. Servo circuit 2
4 is a preamplifier 25, a phase comparator 26, an integrator 27,
And an oscillator 28.

As described above, the frequency f _V of the VCO 29
(For example, 5 MHz) is synthesized based on the output signal and phase-modulated with the low-frequency signal f _m supplied from the oscillator 28,
The microwave of approximately 6.834 GHz is generated by the frequency synthesizer 30.
The resonance cell 18 is irradiated with the light. The photodetector 22 outputs a photodetection signal corresponding to the difference between the irradiation microwave frequency f and the microwave resonance frequency f ₀ .

FIG. 7 is an explanatory diagram of the photodetector output and the error signal generated by the phase comparator 26. FIG. 7 (A) shows the relationship between the irradiation microwave frequency and the output signal of the photodetector 22, and FIG. 7 (B) shows the relationship between the irradiation microwave frequency and the error signal.

The horizontal axis of FIG. 7A shows the irradiation microwave frequency, and the vertical axis shows an example of the output of the photodetector 22. The relationship between the microwave frequency f and the photodetector output is shown in FIG.
As shown in a of (A), the curve becomes a valley at f = f ₀ .

As shown below the horizontal axis, the illuminating microwave is phase-modulated at a low frequency f _m . As shown in FIG. 7A, when the irradiation microwave frequency f = f ₀ , the photodetector 22 outputs a signal including a frequency component of 2f _m . Further, when the frequency f of the microwave slightly differs from f ₀ is different in phase by π by the sign of f-f _0, and outputs a signal containing a component of the frequency f _m.

The output signal (photodetection signal) of the photodetector 22 is amplified by the preamplifier 25, and then the phase comparator 2
At 6, synchronous detection is performed based on the signal of the frequency f _m supplied from the oscillator 28, and an error signal is obtained.

FIG. 7B shows an example of the error signal generated by the synchronous detection by the phase comparator 26. As shown in b of FIG. 7B as an example, this error signal is positive when the frequency f of the microwave is smaller than the microwave resonance frequency f ₀ , and f
The DC signal is ₀ when = f ₀ and is negative when f> f ₀ .

Incidentally, due to the characteristics of the VCO 29, FIG.
The sign is opposite to that of (B), and is negative when the microwave frequency f <the microwave resonance frequency f ₀ , ₀ when f = f ₀ , and f> f.
_A configuration in which a DC signal that is positive when ₀ is obtained is also possible.

This error signal is integrated by the integrator 27 and supplied to the VCO 29 as a frequency control signal. Servo circuit 24, VCO 29, frequency synthesizer 30, resonator 16
Since the microwave control loop is formed by
The oscillation frequency f _{V of} O29 is controlled so that the above error signal becomes zero.

Therefore, from the frequency synthesizer 30 to the resonance cell 1
The frequency f of the microwave supplied to 8 is automatically controlled to be equal to the microwave resonance frequency f ₀ , and V
The oscillating frequency of the CO 29 (that is, the frequency of the output signal of the VCO 29) f _V is controlled so as to match the frequency f _V0 (for example, 5 MHz) having a fixed relationship with the microwave resonance frequency f ₀ .

On the other hand, the photodetection signal of the photodetector 22 is supplied to the servo circuit 34. The photodetection signal of the photodetector 22 is the wavelength λ of the laser beam incident on the resonance cell 18.
And a resonance wavelength λ ₀ of the resonance cell 18 is included in the signal.

The servo circuit 34 generates a current control signal according to the difference between the wavelength λ of the laser beam and the resonance wavelength λ ₀ of the resonance cell 18, based on the photo detection signal of the photo detector 22. This current control signal is added to the drive voltage output from the LD drive voltage source 37 by the adder 38 and supplied to the LD 12.

By the way, the wavelength λ of the light generated by the LD 12
Varies with the current supplied. Therefore, by the current control signal supplied from the servo circuit 34, the wavelength λ of the light generated by the LD 12, that is, the output light, is controlled so as to match the resonance wavelength λ ₀ of the resonance cell 18 = 0.78 μm.

The LD 12 is controlled by the temperature control circuit 13 so that the temperature is constant, and the wavelength λ of the generated light is stabilized.

[0027]

However, in the conventional stabilized light source shown in FIG. 5, the structure of the servo circuit 34 is complicated, and it is difficult to design the servo circuit 34 in order to achieve extremely high stability. There was a problem.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a standard light source that can realize extremely high stability and that can easily design a control circuit for the output light wavelength.

[0029]

According to a first aspect of the present invention, a current is supplied from a laser diode drive circuit to obtain 0.78.
A laser diode that emits a laser beam of μm, a half mirror that extracts the output light by branching the laser beam, and a photodetection signal that is irradiated with the 0.78 μm laser beam and a microwave phase-modulated with a low-frequency signal. Outputting a rubidium atomic resonator, a servo circuit for generating a frequency control signal for controlling the frequency based on the photodetection signal, and outputting a signal having a frequency according to the frequency control signal supplied from the servo circuit. Voltage-controlled oscillator, based on the signal supplied from the voltage-controlled oscillator, a frequency synthesizer for generating the phase-modulated microwave, based on the photodetection signal, the rubidium atomic resonator to The phase modulation is performed so that the frequency of the irradiated phase-modulated microwave matches the microwave resonance frequency of the rubidium atomic resonator. Microwave control means for controlling the frequency of the generated microwave, a reference oscillator for generating a reference signal, a phase comparison between the reference signal generated by the reference oscillator and the output signal of the voltage controlled oscillator to obtain a current control signal. A control signal generating circuit for generating and supplying the current control signal to the laser diode driving circuit.

According to a second aspect of the invention, a laser diode which is supplied with a current from a laser diode drive circuit and emits a laser beam of 0.78 μm, a half mirror which branches the laser beam to extract output light, and the above-mentioned 0 .78
A rubidium atomic resonator that outputs a photodetection signal when irradiated with a μm laser beam and a microwave phase-modulated with a low-frequency signal, and a servo circuit that generates a frequency control signal that controls the frequency based on the photodetection signal. And a voltage-controlled oscillator that outputs a signal having a frequency corresponding to the frequency control signal supplied from the servo circuit, and the phase-modulated microwave is generated based on the signal supplied from the voltage-controlled oscillator. A frequency synthesizer, based on the photodetection signal, the frequency of the phase-modulated microwave irradiating the rubidium atomic resonator matches the microwave resonance frequency of the rubidium atomic resonator, A microwave control means for controlling the frequency of the phase-modulated microwave, a reference oscillator for generating a reference signal, and a reference oscillator generated by the reference oscillator. And a control signal generation circuit that generates a temperature control signal by phase comparison of a signal and an output signal of the voltage controlled oscillator, and supplies the temperature control signal to a temperature control circuit that controls the temperature of the laser diode. To do.

According to a third aspect of the present invention, a laser diode is supplied with a current from a laser diode drive circuit to emit a laser beam of 1.56 μm, a half mirror for branching the laser beam to extract output light, and the laser. A subharmonic generator that emits a laser beam of 0.78 μm when irradiated with a laser beam from a diode;
A rubidium atomic resonator that outputs a photodetection signal when irradiated with a μm laser beam and a microwave phase-modulated with a low-frequency signal, and a servo circuit that generates a frequency control signal that controls the frequency based on the photodetection signal. And a voltage-controlled oscillator that outputs a signal having a frequency corresponding to the frequency control signal supplied from the servo circuit, and the phase-modulated microwave is generated based on the signal supplied from the voltage-controlled oscillator. A frequency synthesizer, based on the photodetection signal, the frequency of the phase-modulated microwave irradiating the rubidium atomic resonator matches the microwave resonance frequency of the rubidium atomic resonator, A microwave control means for controlling the frequency of the phase-modulated microwave, a reference oscillator for generating a reference signal, and a reference oscillator generated by the reference oscillator. It generates a current control signal and an output signal of the signal and the voltage controlled oscillator and a phase comparator, a configuration and a control signal generating circuit for supplying the current control signal to the laser diode drive circuit.

According to a fourth aspect of the invention, a laser diode which is supplied with a current from a laser diode drive circuit and emits a laser beam of 1.56 μm, a half mirror which branches the laser beam to extract output light, and the laser A subharmonic generator that emits a laser beam of 0.78 μm when irradiated with a laser beam from a diode;
A rubidium atomic resonator that outputs a photodetection signal when irradiated with a μm laser beam and a microwave phase-modulated with a low-frequency signal, and a servo circuit that generates a frequency control signal that controls the frequency based on the photodetection signal. And a voltage-controlled oscillator that outputs a signal having a frequency corresponding to the frequency control signal supplied from the servo circuit, and the phase-modulated microwave is generated based on the signal supplied from the voltage-controlled oscillator. A frequency synthesizer, based on the photodetection signal, the frequency of the phase-modulated microwave irradiating the rubidium atomic resonator matches the microwave resonance frequency of the rubidium atomic resonator, A microwave control means for controlling the frequency of the phase-modulated microwave, a reference oscillator for generating a reference signal, and a reference oscillator generated by the reference oscillator. And a control signal generation circuit that generates a temperature control signal by phase comparison of a signal and an output signal of the voltage controlled oscillator, and supplies the temperature control signal to a temperature control circuit that controls the temperature of the laser diode. To do.

[0033]

According to the present invention, the voltage of the output signal of the voltage controlled oscillator, which has a constant relationship with the wavelength of the light emitted by the laser diode, is controlled by the current of the laser diode so that the frequency of the output signal of the voltage controlled oscillator matches the frequency of the reference oscillator. Controls the wavelength of light from the laser diode. Therefore, the wavelength of light of 0.78 μm generated by the laser diode can be stabilized with high accuracy, and the design of the control signal generation circuit can be facilitated.

According to the second aspect of the present invention, the temperature of the laser diode is controlled so that the frequency of the output signal of the voltage controlled oscillator, which has a constant relationship with the wavelength of the light emitted by the laser diode, matches the frequency of the reference oscillator. Controls the wavelength of light from the laser diode. Therefore, the wavelength of light of 0.78 μm generated by the laser diode can be stabilized with high accuracy, and the design of the control signal generation circuit can be facilitated.

According to the third aspect of the invention, the current of the laser diode is adjusted so that the frequency of the output signal of the voltage controlled oscillator, which has a constant relationship with the wavelength of the light emitted by the laser diode, matches the frequency of the reference oscillator. Controls the wavelength of light from the laser diode. Therefore, the wavelength of the light of 1.56 μm generated by the laser diode can be stabilized with high accuracy, and the control signal generation circuit can be easily designed.

According to a fourth aspect of the invention, the temperature of the laser diode is controlled so that the frequency of the output signal of the voltage controlled oscillator, which has a constant relationship with the wavelength of the light emitted by the laser diode, matches the frequency of the reference oscillator. Controls the wavelength of light from the laser diode. Therefore, the wavelength of the light of 1.56 μm generated by the laser diode can be stabilized with high accuracy, and the control signal generation circuit can be easily designed.

[0037]

1 is a block diagram of the first embodiment of the present invention.
6, those parts that are the same as those corresponding parts in FIG. 6 are designated by the same reference numerals, and a description thereof will be omitted. As shown in FIG. 1, the optical microwave unit 11 includes a temperature control circuit 13, an LD 12, a half mirror 15, and a rubidium atomic resonator (resonator) 16. In addition, the frequency f of the microwave applied to the resonator 16
The microwave control means 23 for controlling the
4, VCO 29, and frequency synthesizer 30.

As shown in FIG. 1, in the first embodiment, the LD
A reference oscillator 41 and a control signal generation circuit 42 including a phase comparator 44 and a filter circuit 45 are provided in order to stabilize the wavelength λ of light generated by 12, ie, the wavelength λ of output light.

The rubidium atomic oscillator including the laser diode 12, the resonator 16, the servo circuit 24, the VCO 29, and the frequency synthesizer 30 has the same structure as the conventional stabilized light source shown in FIG. 6 and operates in the same manner. .

Wavelength of 0.78 μm emitted from LD12
Of the laser beam is divided into two by the half mirror 15, one of which is extracted as the output light of the light source and the other of which is the resonator 16
Is incident on.

In the coil 19 around the cavity 17, C
-DC current is supplied by the field current control circuit 20 and C-field (magnetic field) is generated inside the cavity 17.
Are formed. The rubidium atom in the resonance cell 18 has a unique microwave resonance frequency f ₀ (f ₀ = 6.834G).
Hz. However, it has a unique resonance wavelength λ ₀ (0.78 μm) and a wavelength λ of the incident laser light.

The microwave control means 23 for controlling the frequency f of the microwave applied to the resonator 16 is composed of the servo circuit 2
4, VCO 29, and frequency synthesizer 30.

The VCO 29 generates and outputs a signal of frequency f _V (eg, about 5 MHz). Frequency synthesizer 3
0 on the basis of a signal of a frequency f _V supplied from VCO 29, the frequency f _V constant relationship between the frequency f (approximately, 6.83
4 GHz) microwaves are combined and output. The microwave is phase-modulated at the low frequency fm by the low frequency signal fm supplied from the servo circuit 24 to the frequency synthesizer 30.

The microwave synthesized as described above, which has a frequency f of approximately 6.834 GHz and is phase-modulated at a low frequency f _m , is transmitted from the frequency synthesizer 30 via the varactor diode 21 and the cavity 17 to the resonance cell. 18 is irradiated.

The laser beam incident on the resonance cell 18 passes through the resonance cell 18 and is incident on the photodetector 22.
At this time, atomic resonance occurs when the frequency f of the irradiation microwave coincides with the microwave resonance frequency f ₀ , the absorption amount of the laser beam in the resonance cell 18 becomes maximum, and the amount of light incident on the photodetector 22 is increased. Is the smallest. Therefore, the photodetector 22 outputs a photodetection signal corresponding to the difference between the microwave resonance frequency f ₀ and the irradiation microwave frequency f.

In the servo circuit 24, the above photodetector
The light detection signal (see FIG. 7A) output from the
After being amplified by the amplifier 25, the phase comparator 26
Frequency f supplied from 28_mIs synchronously detected based on the signal of
Microwave resonance frequency f ₀And irradiation microwave frequency
An error signal (see FIG. 7B) corresponding to the difference from f is obtained.
It This error signal is integrated by the integrator 27 to obtain the frequency control.
It is supplied to the VCO 29 as a control signal.

Since the microwave control loop is formed by the servo circuit 24, the VCO 29, the frequency synthesizer 30 and the resonator 16 which constitute the microwave control means 23, the oscillation frequency f _V of the VCO 29 is The error signal of is controlled to be zero.

Therefore, from the frequency synthesizer 30 to the resonance cell 1
The frequency f of the microwave supplied to 8 is automatically controlled to be equal to the microwave resonance frequency f ₀ , and V
The oscillating frequency of the CO 29 (that is, the frequency of the output signal of the VCO 29) f _V is controlled so as to match the frequency f _V0 (for example, 5 MHz) having a fixed relationship with the microwave resonance frequency f ₀ .

Next, the wavelength control loop in the first embodiment will be described. In the rubidium atomic oscillator in which the frequency f of the microwave applied to the resonator 16 is controlled by the microwave control loop so as to match the microwave resonance frequency f ₀ of the resonator 16, the LD 12 is incident on the resonator 16. There is a proportional relationship between the wavelength λ of the laser light and the microwave resonance frequency f ₀ .

Therefore, even between the wavelength λ of the laser light incident on the resonator 16 and the output frequency f _V0 of the VCO 29,
There is a proportional relationship as shown in FIG. In the first embodiment, the wavelength λ of the incident light on the resonator 16, that is, the wavelength λ of the LD 12 and V
Using the proportional relationship with the output frequency f _{V0 of} CO29, L
The wavelength λ of the light generated by D12 is a constant value (0.78 μm)
Control so that. In the first embodiment, LD1
The characteristic that the wavelength λ changes with the current of 2 is used.

As the reference oscillator 41, an oscillator, for example, a cesium atomic oscillator or a rubidium atomic oscillator, which generates a reference signal with a frequency accuracy sufficiently higher than that required for a standard light source is used. With a cesium atomic oscillator, 1
A reference signal having a frequency accuracy of × 10 ^-11 or less, which is sufficiently higher than the accuracy required for a standard light source, is generated. Phase comparator 4
Reference numeral 4 compares the output signal of the VCO 29 with the reference signal generated by the reference oscillator 41 in phase, and outputs the signal of the comparison result.

The filter circuit 45 is supplied with the comparison result signal from the phase comparator 44, filters the signal, and generates a current control signal for controlling the current of the LD 12. This current control signal is supplied to the LD drive circuit 14. The output voltage of the LD drive voltage source 37 and the current control signal supplied from the filter circuit 45 are added by the adder 38 of the LD drive circuit 14 and supplied to the LD 12 as the drive voltage of the LD 12.

LD drive circuit 14, LD 12, resonator 1
6, the servo circuit 24, the VCO 29, the phase comparator 44, and the filter circuit 45 form a wavelength control loop of the laser light generated by the LD 12. Therefore, the current of the LD 12, that is, the wavelength λ, is adjusted so that the frequency f _V0 of the output signal of the VCO 29 matches the frequency f _R of the reference signal of the reference oscillator 41.
Is controlled.

The frequency f _R of the reference signal generated by the reference oscillator 41 is set as follows.
The microwave resonance frequency f ₀ of the resonator 16 when the wavelength λ of the LD 12 is exactly 0.78 μm is f _0C, and at this time, the frequency of the output signal of the VCO 29 having a constant relationship with f _0C is f _VC . . The frequency f _R of the reference signal of the reference oscillator 41 is the frequency f _{VC of} this VCO 29 (for example, 5 MH).
The frequency is set exactly equal to z).

Therefore, when the frequency f _V0 of the VCO 29 is controlled so as to match the frequency f _R = f _VC of the reference signal of the reference oscillator 41, as a result, the wavelength λ of the light generated by the LD 12 is exactly 0. Controlled to match 0.78 μm.

As described above, as the reference oscillator 41, a cesium atomic oscillator, a rubidium atomic oscillator, or the like having an accuracy sufficiently higher than the accuracy required by the standard light source is used. Therefore, the wavelength control loop described above can stabilize the wavelength λ of the light generated by the LD 12 with extremely high accuracy. Therefore, the standard light source of the first embodiment can be used as a standard light source for optical measurement that requires extremely high stability. Further, since the control signal generation circuit 42 has a simple configuration, the control signal generation circuit 42 can be easily designed.

FIG. 3 is a block diagram of the second embodiment of the present invention. 3, the same components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted as appropriate. As shown in FIG. 3, the optical microwave unit 11 includes a temperature control circuit 13, an LD 12,
Half mirror 15, rubidium atomic resonator (resonator) 1
It consists of 6 and 6.

As shown in FIG. 3, in the second embodiment, LD
A reference oscillator 41 and a control signal generation circuit 43 including a phase comparator 44 and a filter circuit 46 are provided in order to stabilize the wavelength λ of light generated by 12, ie, the wavelength of output light.

The rubidium atomic oscillator including the laser diode 12, the resonator 16, the servo circuit 24, the VCO 29, and the frequency synthesizer 30 has the same configuration as that of the first embodiment and operates in the same manner.

Next, the wavelength control loop in the second embodiment will be described. In the second embodiment, the wavelength λ of the incident light on the resonator 16, that is, the wavelength λ and V of the LD 12 shown in FIG.
Using the proportional relationship with the output frequency f _{V0 of} CO29, L
The wavelength λ of the light generated by D12 is a constant value (0.78 μm)
Control so that. In the second embodiment, LD1
The characteristic that the wavelength λ changes with the temperature of 2 is used.

The phase comparator 44 compares the phase of the output signal of the VCO 29 with the reference signal generated by the reference oscillator 41, and outputs the signal of the comparison result. The filter circuit 46 is
The signal of the comparison result is supplied from the phase comparator 44, the signal is filtered, and a temperature control signal for controlling the temperature of the LD 12 is generated. This temperature control signal is supplied to the temperature control circuit 13.

In the second embodiment, the temperature control circuit 13, LD
12, the resonator 16, the servo circuit 24, the VCO 29, the phase comparator 44, and the filter circuit 46 form a wavelength control loop of the laser light generated by the LD 12. Therefore, the frequency f _V0 of the output signal of the VCO 29 is set to the reference oscillator 4
The temperature of the LD 12, that is, the wavelength λ is controlled so as to match the frequency f _R of the reference signal of 1.

By the way, the frequency f _R of the reference signal generated by the reference oscillator 41 is set as follows.
The microwave resonance frequency f ₀ of the resonator 16 when the wavelength λ of the LD 12 is exactly 0.78 μm is f _0C, and at this time, the frequency of the output signal of the VCO 29 having a constant relationship with f _0C is f _VC . . The frequency f _R of the reference signal of the reference oscillator 41 is the frequency f _{VC of} this VCO 29 (for example, 5 MH).
The frequency is set exactly equal to z).

Therefore, when the frequency f _V0 of the VCO 29 is controlled so as to match the frequency f _R = f _VC of the reference signal of the reference oscillator 41, as a result, the wavelength λ of the light generated by the LD 12 is exactly 0. Controlled to match 0.78 μm.

As described above, as the reference oscillator 41, a cesium atomic oscillator, a rubidium atomic oscillator, or the like having an accuracy sufficiently higher than the accuracy required by the standard light source is used. Therefore, the wavelength control loop described above can stabilize the wavelength λ of the light generated by the LD 12 with extremely high accuracy. Therefore, the standard light source of the second embodiment can be used as a standard light source for optical measurement that requires extremely high stability. Further, since the configuration of the control signal generation circuit 43 is simple, the design of the control signal generation circuit 43 can be facilitated.

FIG. 4 shows a block diagram of the third embodiment of the present invention. 4, parts that are the same as the parts shown in FIG. 1 are given the same reference numerals, and descriptions thereof will be omitted as appropriate. As shown in FIG. 4, the optical microwave unit 11 includes a temperature control circuit 13, an LD 52,
It comprises a half mirror 15, a harmonic generator (SHG) 47, and a rubidium atomic resonator (resonator) 16.

As shown in FIG. 4, in the third embodiment, LD
52 generates a laser beam having a wavelength of 1.56 μm, and one beam split by the half mirror 15 is extracted as output light. The other beam is transmitted through the half mirror 15 and is incident on the SHG 47, and a 0.78 μm laser beam is generated and output. This wavelength 0.78 μm
The laser beam of is incident on the resonator 16.

As shown in FIG. 4, in the third embodiment, LD
In order to stabilize the wavelength λ _D of the light generated by 52, that is, the wavelength λ _{D of} the output light, the reference oscillator 41 and the phase comparator 44
And a control signal generation circuit 42 including a filter circuit 45. Laser diode 52, SHG4
7, the rubidium atomic oscillator composed of the resonator 16, the servo circuit 24, the VCO 29, and the frequency synthesizer 30
Except for the HG 47, it has the same configuration as that of the first embodiment and operates similarly.

Next, the wavelength control loop in the third embodiment will be described. In the third embodiment, the incident light wavelength λ of the resonator 16 and the output frequency f _{V0 of the} VCO 29 shown in FIG.
, And therefore the wavelength λ _{D of} LD52 and VCO2
LD52 using the proportional relationship with the output frequency f _{V0 of} 9
The wavelength λ _{D of} the light generated by is controlled to be a constant value (1.56 μm). In the third embodiment, the characteristic that the wavelength λ _D changes with the current of the LD 52 is used.

The phase comparator 44 compares the phase of the output signal of the VCO 29 with the reference signal generated by the reference oscillator 41, and outputs the signal of the comparison result. The filter circuit 45 is
The signal of the comparison result is supplied from the phase comparator 44, the signal is filtered, and a current control signal for controlling the current of the LD 52 is generated.

This current control signal is supplied to the LD drive circuit 14. In the adder 38 of the LD drive circuit 14, the output voltage of the LD drive voltage source 37 and the current control signal supplied from the filter circuit 45 are added and supplied to the LD 52 as the drive voltage of the LD 52.

LD drive circuit 14, LD52, SHG4
6, the resonator 16, the servo circuit 24, the VCO 29, the phase comparator 44, and the filter circuit 45 form a wavelength control loop of the laser light generated by the LD 52. Therefore,
The current of the LD 52, that is, the wavelength λ _D is controlled so that the frequency f _V0 of the output signal of the VCO 29 matches the frequency f _R of the reference signal of the reference oscillator 41.

By the way, the frequency f _R of the reference signal generated by the reference oscillator 41 is set as follows.
The microwave resonance frequency f ₀ of the resonator 16 when the wavelength λ _{D of the} LD 52 is exactly 1.56 μm is f _0C, and at this time, the frequency of the output signal of the VCO 29 having a constant relationship with f _0C is f _VC . To do. The frequency f _R of the reference signal of the reference oscillator 41 is the frequency f _{VC of} this VCO 29 (for example, 5 MH).
The frequency is set exactly equal to z).

Therefore, when the frequency f _V0 of the VCO 29 is controlled so as to match the frequency f _R = f _VC of the reference signal of the reference oscillator 41, as a result, the wavelength λ _D of the light generated by the LD 52 becomes accurate. It is controlled to match 1.56 μm.

As described above, as the reference oscillator 41, a cesium atomic oscillator, a rubidium atomic oscillator, or the like having an accuracy sufficiently higher than the accuracy required by the standard light source is used. Therefore, the wavelength control loop described above can stabilize the wavelength λ _D of the light generated by the LD 52 with extremely high accuracy. Therefore, the standard light source of the third embodiment can be used as a standard light source for coherent optical communication that requires extremely high stability. Further, since the control signal generation circuit 42 has a simple configuration, the control signal generation circuit 42 can be easily designed.

FIG. 5 shows a block diagram of the fourth embodiment of the present invention. 5, parts that are the same as the parts shown in FIG. 1 are given the same reference numerals, and descriptions thereof will be omitted. As shown in FIG. 5, the optical microwave unit 11 includes a temperature control circuit 13, an LD 52,
It comprises a half mirror 15, a harmonic generator (SHG) 47, and a rubidium atomic resonator (resonator) 16.

As shown in FIG. 5, in the fourth embodiment, LD
52 generates a laser beam having a wavelength of 1.56 μm, and one beam split by the half mirror 15 is extracted as output light. The other beam is transmitted through the half mirror 15 and is incident on the SHG 47, and a 0.78 μm laser beam is generated and output. This wavelength 0.78 μm
The laser beam of is incident on the resonator 16.

As shown in FIG. 5, in the fourth embodiment, LD
A reference oscillator 41 and a control signal generation circuit 43 including a phase comparator 44 and a filter circuit 46 are provided to stabilize the wavelength λ _{D of} the light generated by 52, that is, the wavelength of the output light.

Laser diode 52, SHG 47, resonator 16, servo circuit 24, VCO 29, frequency synthesizer 3
A rubidium atomic oscillator composed of 0 is SHG47
Except for the above, the configuration is the same as that of the first embodiment, and operates similarly.

Next, the wavelength control loop in the fourth embodiment will be described. In the fourth embodiment, the incident light wavelength λ of the resonator 16 and the output frequency f _{V0 of the} VCO 29 shown in FIG.
, And therefore the wavelength λ _{D of} LD52 and VCO2
LD52 using the proportional relationship with the output frequency f _{V0 of} 9
The wavelength λ _{D of} the light generated by is controlled to be a constant value (1.56 μm). In the fourth embodiment, the characteristic that the wavelength λ _D changes with the temperature of the LD 52 is used.

The phase comparator 44 compares the phase of the output signal of the VCO 29 and the reference signal generated by the reference oscillator 41, and outputs the signal of the comparison result. The filter circuit 46 is
The signal of the comparison result is supplied from the phase comparator 44, the signal is filtered, and a temperature control signal for controlling the temperature of the LD 12 is generated. This temperature control signal is supplied to the temperature control circuit 13.

In the fourth embodiment, the temperature control circuit 13, LD
52, SHG 46, resonator 16, servo circuit 24, VC
O29, the phase comparator 44, and the filter circuit 46 are L
A wavelength control loop for the laser light generated by D52 is formed. Therefore, the temperature of the LD 52, that is, the wavelength λ _D is controlled so that the frequency f _V0 of the output signal of the VCO 29 matches the frequency f _R of the reference signal of the reference oscillator 41.

By the way, the frequency f _R of the reference signal generated by the reference oscillator 41 is set as follows.
The microwave resonance frequency f ₀ of the resonator 16 when the wavelength λ _{D of the} LD 52 is exactly 1.56 μm is f _0C, and at this time, the frequency of the output signal of the VCO 29 having a constant relationship with f _0C is f _VC . To do. The frequency f _R of the reference signal of the reference oscillator 41 is the frequency f _{VC of} this VCO 29 (for example, 5 MH).
The frequency is set exactly equal to z).

Therefore, when the frequency f _V0 of the VCO 29 is controlled so as to match the frequency f _R = f _VC of the reference signal of the reference oscillator 41, as a result, the wavelength λ _D of the light generated by the LD 52 becomes accurate. It is controlled to match 1.56 μm.

As described above, as the reference oscillator 41, a cesium atomic oscillator, a rubidium atomic oscillator, or the like having an accuracy sufficiently higher than the accuracy required by the standard light source is used. Therefore, the wavelength control loop described above can stabilize the wavelength λ _D of the light generated by the LD 52 with extremely high accuracy. Therefore, the standard light source of the fourth embodiment can be used as a standard light source for coherent optical communication that requires extremely high stability. Further, since the configuration of the control signal generation circuit 43 is simple, the design of the control signal generation circuit 43 can be facilitated.

In each of the above embodiments, the frequency f _VC of the output signal of the VCO is not limited to 5 MHz but 10 MH.
Of course, it is possible to set another frequency such as z. Further, the output signal of the VCO can be used as an electric signal with extremely high stability.

[0087]

As described above, according to the invention of claim 1,
Has a fixed relationship with the wavelength of the light emitted by the laser diode,
Since the wavelength of the laser diode light is controlled by the laser diode current so that the frequency of the output signal of the voltage controlled oscillator matches the frequency of the reference oscillator, the wavelength of the 0.78 μm light generated by the laser diode is increased. It has the features that it can be stabilized with accuracy and that the design of the control signal generation circuit can be facilitated.

According to the second aspect of the present invention, the temperature of the laser diode is adjusted so that the frequency of the output signal of the voltage controlled oscillator, which has a constant relationship with the wavelength of the light emitted by the laser diode, matches the frequency of the reference oscillator. Since the wavelength of the light of the laser diode is controlled, the wavelength of the light of 0.78 μm generated by the laser diode can be stabilized with high accuracy, and the control signal generation circuit can be easily designed.

According to the third aspect of the present invention, the current of the laser diode is adjusted so that the frequency of the output signal of the voltage controlled oscillator, which has a constant relationship with the wavelength of the light emitted by the laser diode, matches the frequency of the reference oscillator. Since the wavelength of the light of the laser diode is controlled, the wavelength of the light of 1.56 μm generated by the laser diode can be stabilized with high accuracy, and the design of the control signal generation circuit can be facilitated.

According to the fourth aspect of the invention, the temperature of the laser diode is adjusted so that the frequency of the output signal of the voltage controlled oscillator, which has a constant relationship with the wavelength of the light emitted by the laser diode, matches the frequency of the reference oscillator. Since the wavelength of the light of the laser diode is controlled, the wavelength of the light of 1.56 μm generated by the laser diode can be stabilized with high accuracy, and the design of the control signal generation circuit can be facilitated.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a wavelength of incident light of a resonator and a VCO output frequency.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a configuration diagram of a third embodiment of the present invention.

FIG. 5 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 6 is a configuration diagram of an example of a conventional stabilized light source.

FIG. 7 is an explanatory diagram of a photodetector output and an error signal.

[Explanation of symbols]

 11 Optical Microwave Unit 12 Laser Diode 13 Temperature Control Circuit 14 Laser Diode Drive Circuit 15 Half Mirror 16 Rubidium Atom Resonator 17 Cavity 18 Resonance Cell 19 Coil 20 C-Field Current Control Circuit 21 Varactor Diode 22 Photodetector 23 Microwave Control Means 24 Servo circuit 25 Preamplifier 26 Phase comparator 27 Integrator 28 Oscillator 29 VCO 30 Frequency synthesizer 37 LD drive voltage source 38 Adder 41 Reference oscillator 42, 43 Control signal generation circuit 44 Phase comparator 45, 46 Filter circuit 47 SHG

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Atami 1-2-25, 1-chome, Aoba-ku, Sendai City, Miyagi Prefecture Fujitsu Tohoku Digital Technology Co., Ltd. 1015 Kamitadanaka, Fujitsu Limited

Claims (4)

[Claims] 1. A laser diode (12) which is supplied with a current from a laser diode drive circuit (14) and emits a laser beam of 0.78 μm, and a half mirror (15) which branches the laser beam to extract output light. And a rubidium atomic resonator (16) which outputs a photodetection signal by being irradiated with the 0.78 μm laser beam and a microwave phase-modulated with a low-frequency signal, and the frequency is controlled based on the photodetection signal. A servo circuit (24) for generating a frequency control signal, and the servo circuit (2
4) a voltage controlled oscillator (29) for outputting a signal having a frequency corresponding to the frequency controlled signal supplied from the above, and the phase-modulated microwave based on the signal supplied from the voltage controlled oscillator (29). Frequency synthesizer (3
0), and the frequency of the phase-modulated microwave irradiating the rubidium atomic resonator (16) matches the microwave resonant frequency of the rubidium atomic resonator (16) based on the photodetection signal. As described above, a microwave control means (23) for controlling the frequency of the phase-modulated microwave, a reference oscillator (41) for generating a reference signal, a reference signal generated by the reference oscillator (41), and A phase comparison is made with the output signal of the voltage controlled oscillator (29) to generate a current control signal, and the laser diode drive circuit (1
4) A standard light source having a control signal generating circuit (42) for supplying the current control signal to 4). 2. A laser diode (12) which is supplied with a current from a laser diode drive circuit (14) and emits a laser beam of 0.78 μm, and a half mirror (15) which branches the laser beam to extract output light. And a rubidium atomic resonator (16) which outputs a photodetection signal by being irradiated with the 0.78 μm laser beam and a microwave phase-modulated with a low-frequency signal, and the frequency is controlled based on the photodetection signal. A servo circuit (24) for generating a frequency control signal, and the servo circuit (2
4) a voltage controlled oscillator (29) for outputting a signal having a frequency corresponding to the frequency controlled signal supplied from the above, and the phase-modulated microwave based on the signal supplied from the voltage controlled oscillator (29). Frequency synthesizer (3
0), and the frequency of the phase-modulated microwave irradiating the rubidium atomic resonator (16) matches the microwave resonant frequency of the rubidium atomic resonator (16) based on the photodetection signal. As described above, a microwave control means (23) for controlling the frequency of the phase-modulated microwave, a reference oscillator (41) for generating a reference signal, a reference signal generated by the reference oscillator (41), and Control signal generation for generating a temperature control signal by phase comparison with the output signal of the voltage controlled oscillator (29) and supplying the temperature control signal to a temperature control circuit (13) for controlling the temperature of the laser diode (12). A standard light source having a configuration including a circuit (43). 3. A laser diode (52) which is supplied with a current from a laser diode drive circuit (14) and emits a laser beam of 1.56 μm, and a half mirror (15) which branches the laser beam to extract output light. And a subharmonic generator (47) which emits a laser beam of 0.78 μm by being irradiated with a laser beam from the laser diode (52), and phase-modulated with the laser beam of 0.78 μm and a low frequency signal. A rubidium atomic resonator (16) that is irradiated with microwaves and outputs a photodetection signal, a servo circuit (24) that generates a frequency control signal that controls a frequency based on the photodetection signal, and the servo circuit (2).
4) a voltage controlled oscillator (29) for outputting a signal having a frequency corresponding to the frequency controlled signal supplied from the above, and the phase-modulated microwave based on the signal supplied from the voltage controlled oscillator (29). Frequency synthesizer (3
0) and the frequency of the phase-modulated microwave irradiating the rubidium atomic resonator (16) matches the microwave resonant frequency of the rubidium atomic resonator (16) based on the photodetection signal. As described above, a microwave control means (23) for controlling the frequency of the phase-modulated microwave, a reference oscillator (41) for generating a reference signal, a reference signal generated by the reference oscillator (41), and A phase comparison is made with the output signal of the voltage controlled oscillator (29) to generate a current control signal, and the laser diode drive circuit (1
4) A standard light source having a control signal generating circuit (42) for supplying the current control signal to 4). 4. A laser diode (52) which is supplied with a current from a laser diode drive circuit (14) and emits a laser beam of 1.56 μm, and a half mirror (15) which branches the laser beam to extract output light. And a subharmonic generator (47) which emits a laser beam of 0.78 μm by being irradiated with a laser beam from the laser diode (52), and phase-modulated with the laser beam of 0.78 μm and a low frequency signal. A rubidium atomic resonator (16) that is irradiated with microwaves and outputs a photodetection signal, a servo circuit (24) that generates a frequency control signal that controls the frequency based on the photodetection signal, and the servo circuit (2
4) a voltage controlled oscillator (29) for outputting a signal having a frequency corresponding to the frequency controlled signal supplied from the above, and the phase-modulated microwave based on the signal supplied from the voltage controlled oscillator (29). Frequency synthesizer (3
0), and the frequency of the phase-modulated microwave irradiating the rubidium atomic resonator (16) matches the microwave resonant frequency of the rubidium atomic resonator (16) based on the photodetection signal. As described above, a microwave control means (23) for controlling the frequency of the phase-modulated microwave, a reference oscillator (41) for generating a reference signal, a reference signal generated by the reference oscillator (41), and Control signal generation for phase-comparing the output signal of the voltage-controlled oscillator (29) to generate a temperature control signal and supplying the temperature control signal to a temperature control circuit (13) for controlling the temperature of the laser diode (12). A standard light source having a configuration including a circuit (43).