CN116231445A

CN116231445A - Device for stabilizing laser frequency and power

Info

Publication number: CN116231445A
Application number: CN202211679625.6A
Authority: CN
Inventors: 朱傲男; 桑建芝; 刘院省; 李嘉华; 张慧松
Original assignee: Beijign Institute of Aerospace Control Devices
Current assignee: Beijign Institute of Aerospace Control Devices
Priority date: 2022-12-26
Filing date: 2022-12-26
Publication date: 2023-06-06

Abstract

The application relates to the field of laser frequency and power stabilization, and particularly discloses a device for laser frequency and power stabilization, which comprises an AOM, a lens, an optical isolator, a lambda/2 wave plate, a polarization beam splitter prism, rb atomic bubbles, a lambda/4 wave plate, a reflecting mirror, a photoelectric detector, an acousto-optic modulator, a signal processing circuit and an AOM driver. The invention does not need to directly control the current and the temperature of the laser, can greatly improve the flexibility of a frequency stabilization and power stabilization system, and can further cascade and improve the stabilizing effect of the frequency and the power after integrating the device.

Description

Device for stabilizing laser frequency and power

Technical Field

The application relates to the technical field of laser frequency and power stabilization, in particular to a device for laser frequency and power stabilization.

Background

Cold atom interference technology is widely applied to products such as a gravity meter, a gyroscope and the like due to the advantages of high sensitivity, strong stability and the like. Optical path simplification is the most important ring in cold atom interference gravimeter and gyroscope engineering. The conventional frequency stabilization scheme needs to directly control the laser, and generally locks the laser frequency on a stable reference frequency, wherein the reference frequency generally selects a high-stability characteristic transition spectral line of atoms or molecules, a transmission peak center frequency of a high-Q-value Fabry-Perot cavity or a laser frequency with stable frequency. When the laser frequency deviates from the reference frequency, an error signal is generated, and the temperature and the current of the laser are regulated by the closed-loop control system, so that the laser frequency is consistent with the reference frequency, and the purpose of laser frequency stabilization is achieved. This requires control of the laser itself. For a laser with larger volume, the occupied space is larger and less flexible in application, and the laser can still be influenced by mechanical vibration noise, thermal disturbance noise and the like in the transmission process, so that the precision of frequency and power is lower than before when the laser is used.

Disclosure of Invention

Aiming at the requirements of flexible control and stabilization of laser frequency power in cold atom interference gyroscope experiments, the invention provides a device for stabilizing laser frequency power, which can realize the stabilization of laser power and frequency through an acousto-optic modulator without controlling the current and the temperature of a laser.

In a first aspect, an apparatus for laser frequency and power stabilization is provided, comprising:

the device comprises an acousto-optic modulator AOM, a first lambda/2 wave plate, a first polarization beam splitter prism, a first photoelectric detector, a lens, an optical isolator, a second lambda/2 wave plate, a second polarization beam splitter prism, a second photoelectric detector, rb atomic bubbles, a lambda/4 wave plate and a reflecting mirror;

the AOM is used for emitting negative first-order diffraction light, the negative first-order diffraction light is emitted into a first polarization beam splitter prism through the first lambda/2 wave plate, the first polarization beam splitter prism splits the negative first-order diffraction light into two beams of negative first-order diffraction light, a first part of negative first-order diffraction light emitted by the first polarization beam splitter prism is sequentially emitted into the lens, the optical isolator, the second lambda/2 wave plate and the second polarization beam splitter prism through the first polarization beam splitter prism, and a second part of negative first-order diffraction light emitted by the first polarization beam splitter prism is reflected to the first photoelectric detector through the first polarization beam splitter prism;

the first photoelectric detector is used for detecting second partial negative first-order diffraction light emitted by the first polarization splitting prism, and deviation between an electric signal output by the first photoelectric detector and a reference voltage is used for executing power stabilization operation;

the negative first-order diffraction light from the optical isolator is split into two beams of negative first-order diffraction light after entering the second polarization beam splitter prism, the first part of negative first-order diffraction light emitted by the second polarization beam splitter prism penetrates through the second polarization beam splitter prism to sequentially enter the rubidium atomic bubble, the lambda/4 wave plate and the reflecting mirror, and the negative first-order diffraction light reflected by the reflecting mirror and the negative first-order diffraction light emitted by the second polarization beam splitter prism form a correlation beam;

the light reflected by the reflecting mirror is reflected to the second photoelectric detector when entering the second polarization splitting prism, the second photoelectric detector is used for converting a saturated absorption spectrum signal into an electric signal, and the deviation of the electric signal output by the second photoelectric detector and a reference frequency is used for executing frequency stabilization operation.

Compared with the prior art, the scheme provided by the application at least comprises the following beneficial technical effects:

an acousto-optic modulator (AOM) based frequency and power stabilizing device. The principle of the acousto-optic modulator is that the piezoelectric transducer is controlled by voltage to generate sound waves with corresponding frequency and amplitude, when the sound waves are transmitted into the acousto-optic crystal, the refractive index of the sound waves is changed, and as the wavelength of the sound waves is far greater than that of the light waves, the sound waves can be regarded as a grating, diffraction can be generated when light beams pass through the crystal, and the control of the frequency and the amplitude of voltage signals of the piezoelectric transducer can be realized. The negative first-order diffraction light modulated by the acousto-optic frequency is modulated, error signals of frequency and power are directly fed back to the AOM driver, so that current or temperature control of a laser is not needed, and an optical path and a circuit are integrated, so that the optical path is more concise and flexible. The self-developed acousto-optic modulator driver can obtain higher frequency power accuracy and stability.

With reference to the first aspect, in certain implementation manners of the first aspect, the apparatus further includes:

the first signal processing circuit is used for obtaining a power deviation correcting signal according to the deviation between the electric signal output by the first photoelectric detector and the reference voltage;

the second signal processing circuit is used for obtaining a frequency deviation correcting signal according to the deviation between the electric signal output by the second photoelectric detector and the reference frequency;

and the AOM driver is used for performing power stabilizing operation on the AOM according to the power deviation correcting signal and performing frequency stabilizing operation on the AOM according to the frequency deviation correcting signal.

With reference to the first aspect, in certain implementation manners of the first aspect, the first signal processing circuit obtains the power deviation rectifying signal through a reference voltage source, a comparator and a digital PID module.

Thus, a deviation correcting signal between the optical power and a preset expected value can be obtained.

With reference to the first aspect, in certain implementation manners of the first aspect, the second signal processing circuit obtains the frequency deviation rectifying signal through phase sensitive detection, low-pass filtering, a comparator and an analog PID circuit.

Thus, the deviation correcting signal of the optical frequency and the saturated absorption peak can be obtained.

With reference to the first aspect, in some implementations of the first aspect, the AOM driver selects a 32-bit DDS chip AD9910, a built-in PLL circuit and a clock, and uses 1GHz as a reference clock.

With reference to the first aspect, in some implementations of the first aspect, the output frequency range of the AOM driver is 0-250 MHz, the precision is 0.012Hz, the output amplitude output range is 0-40 v, the 16 bits are adjustable, and the phase is 0-360 degrees 16 bits are adjustable.

The design of the AOM driver with high precision and quick response can be realized.

With reference to the first aspect, in some implementations of the first aspect, the apparatus further includes a mixer, the signal output by the DDS chip AD9910 is filtered and input to the mixer, and the signal output by the mixer is amplified and input to the AOM.

Therefore, the control voltage and the DDS output signal can be directly mixed, and the response speed of the amplitude of the driving source can be greatly improved.

With reference to the first aspect, in certain implementations of the first aspect, the mixer is a ring diode double balanced mixer.

In a second aspect, there is provided a cold atom interference device comprising an apparatus as described in any one of the implementations of the first aspect above.

Drawings

Fig. 1 is a schematic diagram of a laser frequency power control device according to the present invention.

Fig. 2 is a block diagram of the key device AOM driver of the present invention.

Fig. 3 is a simplified schematic diagram of a circular double balanced mixer.

Detailed Description

The present application is described in further detail below with reference to the drawings and specific examples.

As shown in fig. 1, the device for stabilizing frequency power comprises an acousto-optic modulator (acoustic optic modulator, AOM), a lambda/2 wave plate 1, a polarization splitting prism 1, a lens, an optical isolator, a lambda/2 wave plate 2, a polarization splitting prism 2, rb atomic bubbles, a lambda/4 wave plate and a reflecting mirror.

After passing through the acousto-optic modulator, the laser obtains 0-order light and negative-order diffraction light. The negative first order diffracted light of the laser light obtained by the AOM may be modulated by an AOM driver. Specifically, the AOM driver may add modulation and sweep signals to the light emitted by the AOM, which react to the negative order diffracted light via the AOM effect. The negative first-order diffraction light can be emitted into the polarization beam splitter prism 1 through the lambda/2 wave plate 1, and is split into two beams of negative first-order diffraction light by the polarization beam splitter prism 1. The first part of the negative first-order diffraction light emitted by the polarization splitting prism 1 can be sequentially emitted into a lens, an optical isolator, a lambda/2 wave plate 2 and the polarization splitting prism 2 through the polarization splitting prism 1 so as to be used for stabilizing the frequency. The second part of the negative first-order diffraction light emitted by the polarization splitting prism 1 can be reflected to the photoelectric detector 1 by the polarization splitting prism 1 for laser stable power.

The photodetector 1 can detect the optical power of the second portion of the negative first order diffracted light. The photodetector 1 may supply the electric signal obtained by the photodetector 1 to the signal processing circuit 1. The signal processing circuit 1 mainly comprises a reference voltage source, a comparator, an analog PID circuit and the like, and the signal processing circuit 1 is compared with the reference voltage source to obtain a deviation rectifying signal. The signal processing circuit 1 can feed back the deviation correcting signal to the amplitude control module of the AOM driver so as to realize the stability of laser power.

The negative first order diffracted light from the optical isolator is incident on the polarization beam splitter prism 2 and then split into two beams of negative first order diffracted light. The first part of the negative first-order diffraction light emitted by the polarization splitting prism 2 can be sequentially emitted into the rubidium atomic bubble, the lambda/4 wave plate and the reflecting mirror through the polarization splitting prism 2. The negative first order diffracted light reflected by the reflecting mirror may form an opposite beam with the negative first order diffracted light emitted from the polarization beam splitter prism 2. The second portion of the negative first order diffracted light emitted from the polarization splitting prism 2 may be incident on the main optical path.

The correlation beam comprises pumping light and detection light. The detection light reflected by the reflecting mirror is the detection light, and the detection light is reflected to the photoelectric detector 2 when the detection light returns to the polarizing beam splitter prism 2 at the upstream of the Rb atomic bubble due to the fact that the polarization state of the detection light is orthogonal to the polarization state of pumping light by passing through the wave plate twice, so that a saturated absorption spectrum is formed. The photodetector 2 may convert the saturated absorption spectrum signal into an electrical signal, which is provided to the signal processing circuit 2. The signal processing circuit 2 is subjected to phase sensitive detection, low-pass filtering, analog PID (P, I, D respectively refers to proportional, integral and derivative) circuits and the like to obtain deviation rectifying signals. The signal processing circuit 2 can feed back the deviation correcting signal to an adder in the AOM driver circuit and finally feeds back to the AOM, so that the frequency is locked on the rubidium atom saturated absorption spectrum line, and the frequency stability of diffracted light is realized.

The AOM may be controlled by an AOM driver module. The AOM driver module may employ a radio frequency drive circuit based on a direct digital frequency synthesis (DDS) chip. The AOM driver module may include an amplitude control module, a frequency control module, and a modulation triangle sweep module. The modulation triangle sweep frequency module is used for controlling a modulation signal required by the saturated absorption spectrum. The frequency control module is used for controlling the AOM frequency shift quantity and directly feeding back the deviation correcting signal controlled by the frequency to the laser. The amplitude control module is used for controlling the diffraction efficiency of the AOM and feeding back a deviation correcting signal of power control to the laser. The frequency control response speed of the AOM can reach the order of hundreds of ns. The amplitude control module adopts a double-balance mixer which is different from a conventional voltage-controlled attenuator to control, and the response speed is improved from the conventional magnitude of tens of us to tens of ns.

The output frequency range of the AOM driver is 0-250 MHz, the precision is 0.012Hz, the output amplitude output range is 0-40V, 16 bits are adjustable, and the phase is 0-360 degrees and 16 bits are adjustable.

The signal processing circuit includes two parts of content, a signal processing circuit 1 and a signal processing circuit 2. The signal processing circuit 1 comprises a reference voltage source, a comparator and a digital PID module, and is used for obtaining a deviation rectifying signal between the optical power and a preset expected value. The signal processing circuit 2 comprises phase sensitive detection, low-pass filtering, a comparator, an analog PID and other modules and is used for obtaining a deviation correcting signal of the optical frequency and the saturated absorption peak.

As shown in fig. 2, the working principle of the present invention is as follows. And the AOM is used as a core, so that the dependence on the laser is reduced. When the laser frequency deviates from the center frequency of the absorption peak, the modulating signal and the light intensity signal generate a phase difference, at the moment, the light intensity signal is multiplied by the reference signal, the size of an error signal can be obtained through phase-locking amplification and low-pass filtering, a deviation correcting signal is obtained through calculation of a PID circuit, the deviation correcting signal is fed back to the AOM driver, and the frequency stabilization is realized by controlling the frequency shift quantity of the AOM through the AOM driver. The power stabilization is to set an expected value in advance by using a high-precision reference voltage source, compare the expected value with an actual measured value of the optical power by using a comparator to obtain an error signal, calculate the magnitude of a deviation correcting signal through PID, feed back to an amplitude control end of an AOM driver, and realize the power stabilization of laser by the proportional relation between the negative first-order diffraction optical power of the AOM and the amplitude of the driving source.

As shown in fig. 2, the core of the present invention is the design of an AOM driver with high accuracy and fast response. The AOM driver selects a 32-bit DDS chip AD9910, a built-in PLL circuit and a clock, and adopts 1GHz as a reference clock, so that frequency output of 0-250 MHz can be realized, and the frequency, amplitude and phase are adjustable. The amplitude amplifying part adopts a mixer, the signal output by the DDS chip AD9910 is filtered and then input into the mixer, and the signal output by the mixer can be amplified and then input into the AOM. Therefore, the control voltage and the DDS output signal can be directly mixed, and the response speed of the amplitude of the driving source can be greatly improved.

The invention uses the annular diode double-balance mixer as an attenuator to control the power, wherein the frequency signal is a signal obtained by converting an output signal of AD9910 into a single-ended and passive filtered signal, the reference signal is a TTL direct-current voltage control signal, the mixing signal is a final radio frequency signal, and fig. 3 is a simplified schematic diagram of the annular double-balance mixer. The transmission loss of signals at the local oscillation port L and the radio frequency end R of the mixer is controlled by the intermediate frequency current I. When the voltage signal given by the TTL is controlled, the magnitude of the intermediate frequency current signal is controlled, so that the magnitude of the output signal is controlled.

While the invention has been described in terms of the preferred embodiment, it is not intended to limit the invention, but it will be apparent to those skilled in the art that variations and modifications can be made without departing from the spirit and scope of the invention, and therefore the scope of the invention is defined in the appended claims.

Claims

1. An apparatus for laser frequency and power stabilization, comprising:

2. The apparatus of claim 1, wherein the apparatus further comprises:

3. The apparatus of claim 2, wherein the first signal processing circuit obtains the power correction signal via a reference voltage source, a comparator, a digital PID module.

4. The apparatus of claim 2, wherein the second signal processing circuit obtains the frequency deviation correcting signal by phase sensitive detection, low pass filtering, comparator, analog PID circuit.

5. The device of claim 2, wherein the AOM driver is a 32-bit DDS chip AD9910, a built-in PLL circuit and a clock, and uses 1GHz as a reference clock.

6. The device according to claim 2, wherein the output frequency range of the AOM driver is 0-250 MHz, the precision is 0.012Hz, the output amplitude output range is 0-40 v, the 16 bits are adjustable, and the phase is 0-360 degrees 16 bits are adjustable.

7. The device according to claim 1, further comprising a mixer, wherein the signal output by the DDS chip AD9910 is filtered and input to the mixer, and the signal output by the mixer is amplified and input to the AOM.

8. The apparatus of claim 1, wherein the mixer is a ring diode double balanced mixer.

9. Cold atom interference device, characterized by comprising an apparatus according to any of claims 1 to 8.