An apparatus for laser frequency and power stabilization

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, an Rb atom bubble, a lambda / 4 wave plate, a mirror, a photodetector, an acousto-optic modulator, a signal processing circuit and an AOM driver. The application does not need to directly control the current and temperature of a laser, can greatly improve the flexibility of a frequency stabilization and power stabilization system, and can further improve the frequency and power stabilization effect after integration of the device.

Description

Technical Field

[0001] This application relates to the technical field of laser frequency and power stabilization, and in particular to a device for laser frequency and power stabilization. Background Technology

[0002] Cold atom interferometry (CAI) technology, due to its high sensitivity and stability, is now widely used in products such as gravimeters and gyroscopes. Simplifying the optical path is the most crucial aspect of the engineering of CAI gravimeters and gyroscopes. Traditional frequency stabilization schemes require direct control of the laser, typically locking the laser frequency to a stable reference frequency. This reference frequency is generally chosen from highly stable characteristic transition lines of atoms or molecules, the center frequency of the transmission peak of a high-Q Fabry-Perot cavity, or an already stabilized laser frequency. When the laser frequency deviates from the reference frequency, an error signal is generated. A closed-loop control system adjusts the laser's temperature and current to maintain consistency with the reference frequency, achieving laser frequency stabilization. This requires control over the laser itself. For larger lasers, this occupies a significant amount of space, making it less flexible. Furthermore, during transmission, the laser is still affected by mechanical vibration noise and thermal disturbance noise, resulting in lower frequency and power accuracy during laser use. Summary of the Invention

[0003] To address the need for flexible and stable control of laser frequency and power in cold atom interferometric gyroscope experiments, this invention provides a device for stabilizing laser frequency and power. This device eliminates the need to control the laser current and temperature, and can achieve laser power and frequency stability through an acousto-optic modulator.

[0004] In a first aspect, a device for stabilizing laser frequency and power is provided, comprising:

[0005] The acousto-optic modulator (AOM), first λ / 2 waveplate, first polarizing beam splitter, first photodetector, lens, optical isolator, second λ / 2 waveplate, second polarizing beam splitter, second photodetector, Rb atom bubble, λ / 4 waveplate, and mirror are included.

[0006] The AOM is used to emit negative first-order diffracted light. The negative first-order diffracted light enters the first polarizing beam splitter through the first λ / 2 waveplate and is split into two negative first-order diffracted beams by the first polarizing beam splitter. The first part of the negative first-order diffracted light emitted from the first polarizing beam splitter passes through the first polarizing beam splitter and enters the lens, the optical isolator, the second λ / 2 waveplate, and the second polarizing beam splitter in sequence. The second part of the negative first-order diffracted light emitted from the first polarizing beam splitter is reflected by the first polarizing beam splitter to the first photodetector.

[0007] The first photodetector is used to detect the second part of the negative first-order diffraction light emitted from the first polarizing beam splitter, and the deviation between the electrical signal output by the first photodetector and the reference voltage is used to perform power stabilization operation.

[0008] The negative first-order diffracted light from the optical isolator is split into two negative first-order diffracted beams after entering the second polarizing beam splitter. The first part of the negative first-order diffracted light emitted from the second polarizing beam splitter passes through the second polarizing beam splitter and enters the rubidium atom bubble, the λ / 4 waveplate and the mirror in sequence. The negative first-order diffracted light reflected by the mirror and the negative first-order diffracted light emitted from the second polarizing beam splitter form a beam of opposing light.

[0009] When the light reflected by the mirror enters the second polarizing beam splitter, it is reflected to the second photodetector. The second photodetector is used to convert the saturated absorption spectrum signal into an electrical signal. The deviation between the electrical signal output by the second photodetector and the reference frequency is used to perform frequency stabilization operation.

[0010] Compared with the prior art, the solution provided in this application has at least the following beneficial technical effects:

[0011] A frequency and power stabilization device based on an acousto-optic modulator (AOM) is disclosed. The principle of the acousto-optic modulator is to generate sound waves of corresponding frequency and amplitude by controlling a piezoelectric transducer with voltage. When the sound waves enter the acousto-optic crystal, they change its refractive index. Since the wavelength of the sound wave is much larger than that of the light wave, it can be regarded as a kind of grating. Therefore, diffraction occurs when the light beam passes through the crystal. Controlling the frequency and amplitude of the voltage signal of the piezoelectric transducer allows for control of the beam frequency and power. Frequency modulation is achieved through the negative first-order diffracted light of the acousto-optic modulator. The frequency and power error signals are directly fed back to the AOM driver, eliminating the need for current or temperature control of the laser. Integrating the optical and electrical paths results in a simpler and more flexible design. Using a self-developed acousto-optic modulator driver, high frequency and power accuracy and stability can be achieved.

[0012] In conjunction with the first aspect, in some implementations of the first aspect, the apparatus further includes:

[0013] The first signal processing circuit is used to obtain a power correction signal based on the deviation between the electrical signal output by the first photodetector and the reference voltage.

[0014] The second signal processing circuit is used to obtain a frequency correction signal based on the deviation between the electrical signal output by the second photodetector and the reference frequency.

[0015] An AOM driver is configured to perform power stabilization operation on the AOM according to the power correction signal, and to perform frequency stabilization operation on the AOM according to the frequency correction signal.

[0016] In conjunction with the first aspect, in some implementations of the first aspect, the first signal processing circuit obtains the power correction signal through a reference voltage source, a comparator, and a digital PID module.

[0017] This allows us to obtain the correction signal between the optical power and the pre-set desired value.

[0018] In conjunction with the first aspect, in some implementations of the first aspect, the second signal processing circuit obtains the frequency correction signal through phase-sensitive detection, low-pass filtering, comparator, and analog PID circuit.

[0019] This allows us to obtain the polarization correction signal for the optical frequency and the saturation absorption peak.

[0020] In conjunction with the first aspect, in some implementations of the first aspect, the AOM driver uses a 32-bit DDS chip AD9910, which has a built-in PLL circuit and clock, and uses 1GHz as the reference clock.

[0021] In conjunction with the first aspect, in some implementations of the first aspect, the AOM driver has an output frequency range of 0 to 250 MHz, an accuracy of 0.012 Hz, an output amplitude range of 0 to 40 V, is 16-bit adjustable, and a phase range of 0 to 360 degrees, which is also 16-bit adjustable.

[0022] It enables the design of AOM drivers with high precision and fast response.

[0023] In conjunction with the first aspect, in some implementations of the first aspect, the device further includes a mixer, wherein the signal output by the DDS chip AD9910 is filtered and then input to the mixer, and the signal output by the mixer is amplified and then input to the AOM.

[0024] This allows for direct mixing of the control voltage and the DDS output signal, which can greatly improve the response speed of the driver source amplitude.

[0025] In conjunction with the first aspect, in some implementations of the first aspect, the mixer is a ring diode double-balanced mixer.

[0026] In a second aspect, a cold atom interference device is provided, comprising the apparatus described in any of the implementations of the first aspect above. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the laser frequency and power control device in this invention.

[0028] Figure 2 This is a structural block diagram of the AOM driver, a key component in this invention.

[0029] Figure 3 This is a simplified schematic diagram of a ring double-balanced mixer. Detailed Implementation

[0030] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] like Figure 1 As shown, the frequency power stabilization device includes an acousto-optic modulator (AOM), a λ / 2 waveplate 1, a polarizing beam splitter 1, a lens, an optical isolator, a λ / 2 waveplate 2, a polarizing beam splitter 2, an Rb atom bubble, a λ / 4 waveplate, and a reflector.

[0032] After passing through an acousto-optic modulator (AOM), the laser beam produces 0th-order light and negative first-order diffracted light. The negative first-order diffracted light obtained via an AOM can be modulated by an AOM driver. Specifically, the AOM driver adds modulation and frequency sweep signals to the light emitted by the AOM, which are then reflected onto the negative first-order diffracted light. The negative first-order diffracted light can pass through a λ / 2 waveplate 1 into a polarizing beam splitter 1, where it is split into two beams. The first portion of the negative first-order diffracted light emitted from the polarizing beam splitter 1 can pass through the polarizing beam splitter 1 sequentially into a lens and optical isolator, a λ / 2 waveplate 2, and another polarizing beam splitter 2 for frequency stabilization. The second portion of the negative first-order diffracted light emitted from the polarizing beam splitter 1 can be reflected by the polarizing beam splitter 1 to a photodetector 1 for laser power stabilization.

[0033] Photodetector 1 can detect the optical power of the second part of the negative first-order diffracted light. Photodetector 1 can then send the electrical signal it receives to signal processing circuit 1. Signal processing circuit 1 mainly includes a reference voltage source, a comparator, and an analog PID circuit. The signal is compared with the reference voltage source to obtain a correction signal. Signal processing circuit 1 can then feed the correction signal back to the amplitude control module of the AOM driver to stabilize the laser power.

[0034] The negative first-order diffracted light from the optical isolator is split into two beams by the polarizing beam splitter prism 2. The first portion of the negative first-order diffracted light emitted from the polarizing beam splitter prism 2 passes through the prism 2 and sequentially enters the rubidium atomic bubble, the λ / 4 waveplate, and the mirror. The negative first-order diffracted light reflected by the mirror can form an opposing beam with the negative first-order diffracted light emitted from the polarizing beam splitter prism 2. The second portion of the negative first-order diffracted light emitted from the polarizing beam splitter prism 2 can enter the main optical path.

[0035] The diffracted beam consists of two parts: a pump beam and a probe beam. The probe beam, reflected by the mirror, is polarized twice by the waveplate, resulting in a polarization state orthogonal to that of the pump beam. Upon returning to the polarization beam splitter prism 2 upstream of the Rb atom bubble, it is reflected to the photodetector 2, forming a saturated absorption spectrum. The photodetector 2 converts the saturated absorption spectrum signal into an electrical signal, which is then provided to the signal processing circuit 2. The signal processing circuit 2, through phase-sensitive detection, low-pass filtering, and analog PID (P, I, D refer to proportional, integral, and derivative circuits, respectively), generates a correction signal. The signal processing circuit 2 feeds this correction signal back to the adder in the AOM driver circuit, ultimately feeding it back to the AOM, thereby locking the frequency on the rubidium atom saturated absorption spectrum line and achieving frequency stabilization of the diffracted light.

[0036] The AOM (Area-Operating Module) can be controlled via an AOM driver module. This module can employ an RF drive circuit based on a Direct Digital Synthesis (DDS) chip. The AOM driver module may include an amplitude control module, a frequency control module, and a modulation triangular sweep module. The modulation triangular sweep module controls the modulation signal required for the saturated absorption spectrum. The frequency control module controls the frequency shift of the AOM, directly feeding the frequency-controlled correction signal back to the laser. The amplitude control module controls the diffraction efficiency of the AOM, feeding the power-controlled correction signal back to the laser. The frequency control response speed of the AOM can reach the order of hundreds of nanoseconds. The amplitude control module uses a double-balanced mixer, different from conventional voltage-controlled attenuators, improving the response speed from tens of microseconds to tens of nanoseconds.

[0037] The AOM driver has an output frequency range of 0–250 MHz, an accuracy of 0.012 Hz, an output amplitude range of 0–40 V (16-bit adjustable), and a phase range of 0–360 degrees (16-bit adjustable).

[0038] The signal processing circuit comprises two parts: signal processing circuit 1 and signal processing circuit 2. Signal processing circuit 1 includes a reference voltage source, a comparator, and a digital PID module, used to obtain a correction signal between the optical power and a pre-set desired value. Signal processing circuit 2 includes modules such as phase-sensitive detector, low-pass filter, comparator, and analog PID, used to obtain a correction signal between the optical frequency and the saturation absorption peak.

[0039] like Figure 2As shown, the working principle of this invention is as follows: Using an AOM (Analog-Organic Oscillator) as the core, the dependence on the laser itself is reduced. When the laser frequency deviates from the center frequency of the absorption peak, a phase difference occurs between the modulation signal and the light intensity signal. At this time, the light intensity signal is multiplied by the reference signal, and the error signal is obtained by phase-locked amplification and low-pass filtering. The error signal is then calculated by a PID circuit to obtain a correction signal, which is fed back to the AOM driver. Frequency stabilization is achieved by controlling the frequency shift of the AOM through the AOM driver. Power stabilization is achieved by using a high-precision reference voltage source to pre-set the desired value. A comparator compares the desired value with the actual measured value of the optical power to obtain the error signal. After the PID calculates the magnitude of the correction signal, it is fed back to the amplitude control terminal of the AOM driver. The power of the laser light diffracted by the negative first order of the AOM is proportional to the amplitude of the driving source, thus achieving laser power stabilization.

[0040] like Figure 2 As shown, the core of this invention lies in the design of a high-precision, fast-response AOM driver. The AOM driver uses a 32-bit DDS chip AD9910, with a built-in PLL circuit and clock, employing 1GHz as the reference clock, and can achieve a frequency output of 0–250MHz, with adjustable frequency, amplitude, and phase. The amplitude amplification section uses a mixer. The signal output from the DDS chip AD9910 is filtered and then input to the mixer. The signal output from the mixer can be amplified and then input to the AOM. This allows for direct mixing of the control voltage and the DDS output signal, significantly improving the amplitude response speed of the driver source.

[0041] This invention uses a ring diode double-balanced mixer as an attenuator to control the power level. The intermediate frequency signal is the output signal of the AD9910 after differential-to-single-ended conversion and passive filtering. The reference signal is a TTL DC voltage control signal, and the mixing signal is the final radio frequency signal. Figure 3 This is a simplified schematic diagram of a ring double-balanced mixer. The transmission loss of the signal between the local oscillator port L and the RF port R of the mixer is controlled by the magnitude of the intermediate frequency current I. When the voltage signal provided by the TTL is controlled, the magnitude of the intermediate frequency current signal is controlled, thereby controlling the magnitude of the output signal.

[0042] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims of the present invention.

Claims

1. A device for stabilizing laser frequency and power, characterized in that, include: Acousto-optic modulator AOM, first Waveplate, first polarizing beam splitter, first photodetector, lens, optical isolator, second Waveplate, second polarizing beam splitter, second photodetector, rubidium atom bubble, Wave plate, mirror; The AOM is used to emit negative first-order diffracted light, which passes through the first... A waveplate enters a first polarizing beam splitter and is split into two negative first-order diffracted beams. The first portion of the negative first-order diffracted beam emitted from the first polarizing beam splitter passes through the first polarizing beam splitter and sequentially enters the lens, the optical isolator, and the second... Wave plate, second polarizing beam splitter, the second part of the negative first order diffracted light emitted from the first polarizing beam splitter is reflected by the first polarizing beam splitter to the first photodetector; The first photodetector is used to detect the second part of the negative first-order diffraction light emitted from the first polarizing beam splitter, and the deviation between the electrical signal output by the first photodetector and the reference voltage is used to perform power stabilization operation. The negative first-order diffracted light from the optical isolator is split into two beams of negative first-order diffracted light after entering the second polarizing beam splitter. The first part of the negative first-order diffracted light emitted from the second polarizing beam splitter passes through the second polarizing beam splitter and sequentially enters the rubidium atom bubble, the... The waveplate and the reflector, wherein the negative first-order diffracted light reflected by the reflector and the negative first-order diffracted light emitted from the second polarizing beam splitter form an opposing beam; When the light reflected by the mirror enters the second polarizing beam splitter, it is reflected to the second photodetector. The second photodetector is used to convert the saturated absorption spectrum signal into an electrical signal. The deviation between the electrical signal output by the second photodetector and the reference frequency is used to perform frequency stabilization operation.

2. The apparatus according to claim 1, characterized in that, The device further includes: The first signal processing circuit is used to obtain a power correction signal based on the deviation between the electrical signal output by the first photodetector and the reference voltage. The second signal processing circuit is used to obtain a frequency correction signal based on the deviation between the electrical signal output by the second photodetector and the reference frequency. An AOM driver is configured to perform power stabilization operation on the AOM according to the power correction signal, and to perform frequency stabilization operation on the AOM according to the frequency correction signal.

3. The apparatus according to claim 2, characterized in that, The first signal processing circuit obtains the power correction signal through a reference voltage source, a comparator, and a digital PID module.

4. The apparatus according to claim 2, characterized in that, The second signal processing circuit obtains the frequency correction signal through phase-sensitive detection, low-pass filtering, comparator, and analog PID circuit.

5. The apparatus according to claim 2, characterized in that, The AOM driver uses a 32-bit DDS chip AD9910, which has a built-in PLL circuit and clock, and uses 1GHz as the reference clock.

6. The apparatus according to claim 2, characterized in that, The AOM driver has an output frequency range of 0~250MHz, an accuracy of 0.012Hz, an output amplitude range of 0~40V (16-bit adjustable), and a phase range of 0~360 degrees (16-bit adjustable).

7. The apparatus according to claim 5, characterized in that, The device also includes a mixer. The signal output by the DDS chip AD9910 is filtered and then input to the mixer. The signal output by the mixer is amplified and then input to the AOM.

8. The apparatus according to claim 7, characterized in that, The mixer is a ring diode double-balanced mixer.

9. A cold atom interferometer, characterized in that, Includes the apparatus as described in any one of claims 1 to 8.

Images