Laser bias frequency stabilization device and method based on four-wave mixing ultra-narrow spectrum

Abstract

The present invention discloses a laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum, the device includes an alkali metal atomic vapor chamber, pump light and signal light are incident on the alkali metal atomic vapor chamber at a phase matching angle required for four-wave mixing, and gain signal light and conjugate light are obtained, and the gain signal light or conjugate light is used as a frequency stabilization reference light signal of a second coherent light source that emits signal light. The present invention also discloses a laser bias frequency stabilization method based on four-wave mixing ultra-narrow spectrum, the Raman gain signal light or the newly generated conjugate light generated in the four-wave mixing process is used as a frequency stabilization reference signal to obtain an ultra-narrow linewidth atomic frequency discrimination signal, and the laser bias frequency stabilization with a large detuning amount from the atomic resonance frequency can be realized. The ultra-narrow linewidth laser bias frequency stabilization scheme of the present invention can be applied to fields such as atomic interferometers, atomic magnetometers, and nuclear magnetic resonance gyroscopes.

Description

Technical Field

[0001] The present invention relates to the fields of atomic physics, optics, laser technology, and more particularly to a laser bias (deviation from atomic resonance frequency) frequency stabilization device based on four-wave mixing ultra-narrow spectrum, and also to a laser bias frequency stabilization method based on four-wave mixing ultra-narrow spectrum. The present invention is applicable to the fields of laser detection, quantum sensing, quantum precision measurement, and the like. Background Art

[0002] At present, precision measurement technology has developed rapidly and has been widely used in many fields such as physics, biology, materials, and navigation. As the main measurement tool in the field of precision measurement, the frequency stability of laser itself is the main factor affecting the measurement accuracy of the system. The frequency stability of the laser is affected by many factors such as changes in temperature and humidity in the outside world, mechanical vibration, changes in the position of optical components, and electrical noise inside the laser. Traditional frequency stabilization methods are mainly divided into passive and active. The passive frequency stabilization method uses passive measures such as physical vibration isolation and temperature control to stabilize the output power of the laser; the active frequency stabilization method uses a stable optical frequency reference to obtain the frequency discrimination error signal of laser frequency stabilization through the optical frequency reference, and then uses the feedback system to correct the output frequency of the laser in real time. For example, the commonly used saturation absorption frequency stabilization technology and polarization spectrum frequency stabilization technology both use the atomic spectrum line that eliminates Doppler broadening as the reference signal for laser frequency stabilization to achieve the frequency stabilization of the laser for a specific atomic transition frequency. However, the above frequency stabilization schemes based on atomic spectral lines can usually only achieve laser frequency stabilization with the atomic resonance frequency. The frequency-stabilized laser line width is limited by the natural line width of the atom, and the stability of the laser frequency needs to be further improved. In addition, this method and a set of equipment can only obtain a frequency-stabilized light source of a certain frequency, and it is difficult to achieve a frequency-stabilized laser light source with a relatively stable frequency difference between two beams at the same time. Through the PDH (Pound-Drever-Hall) technology, an external optical cavity is used to obtain a frequency-stabilization reference signal, which can achieve the frequency stabilization of the laser relative to the atomic non-resonance frequency. However, PDH frequency stabilization uses the resonant frequency of the optical resonant cavity as the frequency stabilization reference frequency, and its frequency stabilization accuracy depends on the fineness and stability of the external cavity, and it is not easy to obtain good long-term stability. Summary of the invention

[0003] Aiming at the shortcomings of the existing laser frequency stabilization technology, the present invention proposes a laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum and a laser bias frequency stabilization method based on four-wave mixing ultra-narrow spectrum.

[0004] In order to achieve the above-mentioned purpose, the present invention is implemented by the following technical measures:

[0005] The laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum includes an alkali metal atomic vapor chamber. Pump light and signal light are incident on the alkali metal atomic vapor chamber at a phase matching angle required for four-wave mixing to obtain gain signal light and conjugate light. The gain signal light or conjugate light is used as a frequency stabilization reference light signal for a second coherent light source that emits signal light.

[0006] The gain signal light or conjugate light obtains a detection signal through a photoelectric detector and a modulation signal output by a laser modulation module, and simultaneously inputs the detection signal into a laser frequency locking module, and the laser frequency locking module outputs a discrimination signal to a laser control module of a second coherent light source.

[0007] The pump light sequentially passes through the shaping prism, the first variable-power beam expander and the first λ / 2 wave plate, and then the polarized pump light obtained by reflection from the first polarization beam splitter is incident on the second polarization beam splitter and reflected by the second polarization beam splitter to the alkali metal atomic vapor chamber; the signal light sequentially passes through the second variable-power beam expander and the second λ / 2 wave plate, and then transmits the second polarization beam splitter to obtain the polarized signal light and is incident on the alkali metal atomic vapor chamber.

[0008] The pump light transmitted by the first polarization beam splitter is incident on the saturated absorption frequency stabilization system, and the obtained frequency stabilization feedback signal of the first coherent light source is then input into the laser wavelength frequency locking module of the first coherent light source.

[0009] The alkali metal atomic vapor chamber is placed in an insulation module, which is also provided with a temperature measuring platinum resistor and a heating device. The temperature measuring platinum resistor converts the detected temperature information into an electrical signal and outputs it to a precision temperature control device. The precision temperature control device outputs the difference between the electrical signal and the temperature value set by the precision temperature control device to a DC regulated power supply, and the DC regulated power supply outputs a regulated current to the heating device.

[0010] After four-wave mixing, the remaining output pump light is still emitted from the alkali metal atomic vapor chamber. After the remaining output pump light, gain signal light and conjugate light exit the alkali metal atomic vapor chamber, they simultaneously pass through the third λ / 2 wave plate and the λ / 4 wave plate in sequence. The remaining output pump light is then reflected to the optical baffle by the third polarization beam splitter, and the gain signal light and conjugate light transmit the third polarization beam splitter.

[0011] The laser bias frequency stabilization method based on four-wave mixing ultra-narrow spectrum uses the laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum, and the specific steps are as follows:

[0012] Step 1: Build a laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum;

[0013] Step 2, adjusting the saturated absorption frequency stabilization system to select and stabilize the pump light frequency on the alkali metal atom resonance transition line of the saturated absorption frequency stabilization system;

[0014] Step 3, adjusting the temperature range of the alkali metal atom vapor chamber to 60° C. to 120° C. by a precise temperature control device so that the metal atom vapor chamber emits gain signal light and conjugate light;

[0015] Step 4, scanning the laser frequency of the second coherent light source with a scanning width of 10 GHz, collecting the first detection signal of the first photodetector or the second detection signal of the second photodetector, and then connecting the first detection signal or the second detection signal to the signal amplifier, and the output of the signal amplifier then passes through the signal filtering circuit and the laser frequency locking module in sequence, and finally connected to the laser control module of the second coherent light source;

[0016] Step 5: Adjust the laser modulation module and apply a frequency of ω to the scanning signal of the second coherent light source through the laser frequency locking module. mod The modulation signal has a modulation frequency greater than the scanning frequency of the second coherent light source itself.

[0017] In step 5, the scanning signal frequency of the second coherent light source is ω(t)=ω 0 +Δω×sin(ω mod ×t), where ω 0 is the initial frequency of the second coherent light source, Δω is the scanning frequency of the second coherent light source itself, and t is the time; the detection signal of the photodetector is S(t)=S 0 +S'(ω 0 )×Δω×sin(ω mod × t), S 0 The frequency of the second coherent light source is ω 0 The detection signal detected by the electrical detector, S'(ω 0 ) is the photodetector receiving frequency ω 0 The derivative of the detection signal output after the laser is emitted; the detection signal is connected to the laser frequency locking module, and then multiplied by the modulation signal to obtain the modulated detection signal:

[0018] S(t)×sin(ω mod ×t)

[0019] =1 / 2×S'(ω 0 )×Δω+S 0 ×sin(ω mod ×t)-S'(ω 0 )×Δω×cos(2×ω mod ×t)

[0020] The modulated detection signal is passed through the low-pass filter in the laser frequency locking module to obtain the modulation and demodulation signal Output = 1 / 2 × S'(ω 0 )×Δω.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The laser frequency stabilization method of the present invention uses the Raman gain signal light or the newly generated conjugate light generated by the four-wave mixing process in the atomic vapor as a frequency stabilization reference light signal for frequency discrimination, and can obtain an atomic frequency discrimination signal with an ultra-narrow linewidth lower than the natural linewidth of the atom, thereby achieving better laser frequency stability.

[0023] 2. The Raman gain signal light or newly generated conjugate light used to generate the frequency-stabilized frequency discrimination signal in the present invention has a large detuning amount relative to the atomic resonance frequency (much larger than the Doppler broadening of the atom at room temperature), so that the laser frequency can be stabilized at the non-atomic transition resonance frequency. Compared with the currently commonly used laser frequency stabilization schemes based on atomic spectral lines, such as saturated absorption spectrum and polarization spectrum, the present invention solves the shortcomings of the existing laser bias frequency stabilization method, and provides a new laser bias frequency stabilization method based on narrow linewidth atomic discrimination signals, realizing a laser frequency stabilization system with a large detuning amount relative to the atomic resonance frequency, which can be applied to precision sensors such as atomic laser cooling, atomic interferometers, atomic magnetometers and nuclear magnetic resonance gyroscopes.

[0024] 3. The laser bias frequency stabilization device and method based on four-wave mixing ultra-narrow spectrum in the present invention can also be used to realize a relatively stable frequency-stabilized laser light source with two-beam frequency difference. The present invention can be applied to quantum precision measurement based on double-beam intensity difference compressed light, Raman light in atomic interference experiments, and the associated detection light source of atomic magnetometers, further improving the measurement stability of quantum sensors such as atomic interferometers and nuclear magnetic resonance gyroscopes. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0026] Figure 1 In: 1-first coherent light source; 2-second coherent light source; 3-shaping prism; 4-first variable-power beam expander; 5-first λ / 2 wave plate; 6-first polarization beam splitter; 7-second variable-power beam expander; 8-second λ / 2 wave plate; 9-second polarization beam splitter; 10-alkali metal atomic vapor chamber; 11-third λ / 2 wave plate; 12-λ / 4 wave plate; 13-third polarization beam splitter; 14-optical baffle; 15-first photodetector; 16-second photodetector Detector; 17-signal amplifier; 18-computer; 19-laser frequency locking module; 20-laser modulation module; 21-signal filtering circuit; 22-precision temperature control device; 23-DC voltage-stabilized power supply; 24-temperature measuring platinum resistor; 25-heating device; 26-insulation module; 27-gain signal light (signal light enhanced by four-wave mixing process); 28-conjugate light (light newly generated by four-wave mixing process); 29-data acquisition card; 30-saturated absorption frequency stabilization system. DETAILED DESCRIPTION

[0027] In order to facilitate those skilled in the art to understand and implement the present invention, Figure 1 As well as implementation methods for further elaboration of the present invention, it should be understood that the implementation examples described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0028] like Figure 1 As shown, a laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum includes an optical path unit, an atomic vapor chamber unit, a signal detection unit, and a frequency stabilization unit. In this embodiment, the atomic vapor chamber unit uses alkali metal rubidium atoms.

[0029] The optical path unit includes: a first coherent light source 1, a second coherent light source 2, a shaping prism 3, a first variable magnification beam expander 4, a first λ / 2 wave plate 5, a first polarization beam splitter 6, a second variable magnification beam expander 7, a second λ / 2 wave plate 8, a second polarization beam splitter 9, a third λ / 2 wave plate 11, a λ / 4 wave plate 12, a third polarization beam splitter 13, and an optical baffle 14.

[0030] The atomic vapor chamber unit comprises: an alkali metal atomic vapor chamber 10, a precision temperature control device 22, a DC voltage-stabilized power supply 23, a temperature-measuring platinum resistor 24, a heating device 25, and a heat-insulating module 26. In the alkali metal atomic vapor chamber 10, a four-wave mixing process is performed.

[0031] The signal detection unit includes: a first photodetector 15 , a second photodetector 16 , a signal amplifier 17 , a signal filtering circuit 21 , a data acquisition card 29 , and a computer 18 .

[0032] The frequency stabilization unit includes: a laser modulation module 20 and a laser frequency locking module 19 .

[0033] In the optical path unit, the first coherent light source 1 serves as the pump light source for the four-wave mixing process. The pump light emitted by the first coherent light source 1 passes through the shaping prism 3, the first variable-power beam expander 4 and the first λ / 2 wave plate 5 in sequence, and then is split by the first polarization beam splitter 6. The polarized pump light is reflected by the first polarization beam splitter 6 to obtain the polarized pump light. The polarized pump light is incident on the second polarization beam splitter 9 and is reflected by the second polarization beam splitter 9 to the alkali metal atomic vapor chamber 10. The pump light transmitted by the first polarization beam splitter 6 is incident on the saturated absorption frequency stabilization system 30, and the frequency stabilization feedback signal of the first coherent light source 1 is obtained and then input into the laser wavelength frequency locking module of the first coherent light source 1, so as to achieve the frequency stabilization of the pump light output by the first coherent light source 1. The laser emitted by the second coherent light source 2 is used as the signal light of the four-wave mixing process. The signal light and the pump light have a certain angle and pass through the second variable-power beam expander 7 and the second λ / 2 wave plate 8 in sequence, and then transmit the second polarization beam splitter 9 to obtain polarized signal light, which is then incident on the alkali metal atomic vapor chamber 10. The polarized signal light and the polarized pump light are incident on the alkali metal atomic vapor chamber 10 at a certain angle and cross and merge at the center of the alkali metal atomic vapor chamber 10.

[0034] The alkali metal atom vapor chamber 10 is placed in a heat preservation module 26, and a temperature measuring platinum resistor 24 and a heating device 25 are also arranged in the heat preservation module 26. The temperature measuring platinum resistor 24 converts the detected temperature information into an electrical signal and outputs it to the precision temperature control device 22. The precision temperature control device 22 can set the temperature in the alkali metal atom vapor chamber 10. The precision temperature control device 22 outputs the difference between the electrical signal and the set temperature value of the precision temperature control device 22 to the DC voltage-stabilized power supply 23. The DC voltage-stabilized power supply 23 outputs a corresponding adjustment current to the heating device 25 according to the difference between the electrical signal and the set temperature value, so that the temperature information detected by the temperature measuring platinum resistor 24 corresponds to the set temperature value, thereby adjusting and stabilizing the temperature in the alkali metal atom vapor chamber 10 so that the alkali metal atom vapor chamber 10 has a suitable optical depth. When the angle between the polarized signal light and the polarized pump light meets the phase matching condition, a four-wave mixing process occurs in the alkali metal atom vapor chamber 10, which will generate the Raman gain of the signal light, obtain the gain signal light 27 and generate the conjugate light 28 of a new frequency. Due to the conservation of momentum, the gain signal light 27 and the conjugate light 28 are symmetrically distributed on both sides of the polarized pump light. The gain signal light 27 and the conjugate light 28 can be used as frequency-stabilized reference light signals of the second coherent light source 2, respectively.

[0035] After the four-wave mixing process, three coherent lights are emitted from the alkali metal atomic vapor cell 10, which are the remaining output pump light, the gain signal light 27 and the newly generated conjugate light 28. The three coherent lights simultaneously pass through the third λ / 2 wave plate 11 and the λ / 4 wave plate 12 in sequence to restore the changes in the polarization planes that have occurred in each of them passing through the alkali metal atomic vapor cell 10, wherein the remaining output pump light passes through the λ / 4 wave plate 12, and then is reflected to the optical baffle 14 by the third polarization beam splitter 13 and filtered out, and the gain signal light 27 and the conjugate light 28 transmit the third polarization beam splitter 13.

[0036] After the gain signal light 27 and the newly generated conjugate light 28 obtained by Raman gain are transmitted through the third polarization beam splitter 13 respectively, the gain signal light 27 or the conjugate light 28 obtains a detection signal through the photodetector and the modulation signal output by the laser modulation module 20 is simultaneously input to the laser frequency locking module 19, and the laser frequency locking module 19 outputs a discrimination signal to the laser control module of the second coherent light source 2 to achieve frequency stabilization of the second coherent light source 2. In this embodiment, the gain signal light 27 is incident on the second photodetector 16, and the conjugate light 28 is incident on the first photodetector 15. The second photodetector 16 and the first photodetector 15 output a second detection signal and a first detection signal respectively, and the second detection signal and the first detection signal are selectively connected to the signal amplifier 17 through the switch in the signal amplifier 17. In order to record data, the detection amplified signal obtained after the second detection signal or the first detection signal passes through the signal amplifier 17 is divided into two paths, and the first path of the signal is recorded in the computer 18 via the data acquisition card 29. The second path of the signal is input to the signal filter circuit 21 to obtain the filtered detection signal as the reference electrical signal for frequency stabilization. The modulation signal output by the laser modulation module 20 and the frequency stabilization reference electrical signal are simultaneously input to the laser frequency locking module 19 , and the laser frequency locking module 19 outputs the discrimination signal required for frequency stabilization to the laser control module of the second coherent light source 2 , thereby achieving frequency stabilization of the second coherent light source 2 .

[0037] The first coherent light source 1 is an external cavity semiconductor laser, which is used to generate four-wave mixing pump light (power is about 200mW). It has a laser wavelength scanning module and a laser wavelength locking module of the first coherent light source 1. The saturated absorption atomic spectrum line is obtained by the saturated absorption frequency stabilization system 30 as the frequency stabilization reference signal of the first coherent light source 1. The saturated absorption frequency stabilization system 30 is then connected to the laser wavelength locking module of the first coherent light source 1 itself to realize laser frequency stabilization.

[0038] The second coherent light source 2 is also an external cavity semiconductor laser, which is used to generate four-wave mixing signal light (power is about 100uW).

[0039] The shaping prism 3 is used to improve the quality of the outgoing pump light beam of the first coherent light source 1.

[0040] The first variable-power beam expander 4 and the second variable-power beam expander 7 are used to shrink the laser spots generated by the pump light and the signal light, respectively, so that the pump light and the signal light enter the alkali metal atomic vapor chamber 10 with appropriate sizes, thereby generating a four-wave mixing process more efficiently.

[0041] The first λ / 2 wave plate 5 and the first polarization beam splitter 6 are used to change the polarization plane of the pump light so that the pump light enters the alkali metal atomic vapor chamber 10 in a horizontal polarization direction after being reflected by the second polarization beam splitter 9 .

[0042] The second λ / 2 wave plate 8 and the second polarization beam splitter 9 are used to change the polarization plane of the signal light so that the signal light is transmitted into the alkali metal atomic vapor chamber 10 through the second polarization beam splitter 9 in a vertical polarization direction.

[0043] The alkali metal atomic vapor cell 10 uses rubidium Rb atomic vapor as a medium for generating four-wave mixing. The polarized signal light and the polarized pump light meet at a certain angle at the center of the alkali metal atomic vapor cell 10 .

[0044] The gain signal light 27 is the light field amplified after the polarized pump light and the polarized signal light generate a four-wave mixing process in the alkali metal atom vapor chamber 10. The emission direction of the gain signal light 27 is consistent with the direction of the incident signal light.

[0045] The conjugate light 28 is a newly generated light field after the polarized pump light and the polarized signal light undergo four-wave mixing in the alkali metal atomic vapor chamber 10 . The conjugate light 28 is symmetrically distributed on both sides of the remaining outgoing pump light with respect to the gain signal light 27 .

[0046] The third λ / 2 wave plate 11 and the λ / 4 wave plate 12 are used to adjust the polarization state of the remaining outgoing pump light and the gain signal light 27 and the conjugate light 28 exiting the alkali metal atomic vapor cell 10, so that the remaining outgoing pump light maintains horizontal polarization, while the outgoing gain signal light 27 and the conjugate light 28 maintain vertical polarization, so as to be separated by the third polarization beam splitter 13 later.

[0047] The third polarization beam splitter 13 is used to separate the remaining outgoing pump light and the gain signal light 27 and the conjugate light 28 .

[0048] The optical baffle 14 is used to filter the remaining outgoing pump light after being reflected by the alkali metal atomic vapor cell 10 and the third polarization beam splitter 13 .

[0049] The first photodetector 15 and the second photodetector 16 are used to detect the spatially split conjugate light 28 and the gain signal light 27 respectively.

[0050] The signal amplifier 17 is used to selectively amplify the voltage signal detected by the first photodetector 15 or the second photodetector 16, namely the first detection signal or the second detection signal, and transmit it to the computer 18 through the data acquisition card 29 to record the time domain signal of the signal light 27 or the conjugate light 28.

[0051] The signal filtering circuit 21 is used to filter the high-frequency noise of the detection amplified signal obtained by the signal amplifier 17 .

[0052] The laser modulation module 20 is used to generate a frequency of ω mod The modulation signal sin(ω mod × t).

[0053] After being filtered by the signal filter circuit 21, the detected amplified signal is connected to the laser frequency locking module 19 and multiplied by the modulation signal sin(ω) generated by the laser modulation module 20. mod ×t) to obtain a modulated detection signal. The modulated detection signal passes through a low-pass filter in the laser frequency locking module 19 to filter out high-frequency components, and the result is the derivative of the filtered detection signal, that is, the discrimination signal required for frequency stabilization. Combined with adjusting the PID parameters in the laser frequency locking module 19, the second coherent light source 2 is feedback-adjusted so that the output laser frequency of the second coherent light source 2 is stabilized at the spectral peak of the gain signal light 27 or the conjugate light 28.

[0054] The precision temperature control device 22 adopts Omron precision temperature control with a temperature stability of 0.1° C., and is used for feedback control to stabilize the temperature in the alkali metal atom vapor chamber 10 .

[0055] The DC regulated power supply 23 is used to generate a temperature-controlled current to control the heating device 25 .

[0056] The temperature measuring platinum resistor 24 , model Pt100, is used to measure the temperature of the alkali metal atomic vapor chamber 10 .

[0057] The heating device 25 is used to heat the alkali metal atom vapor chamber 10 .

[0058] In the present invention, the heat preservation module 26 adopts a heat preservation furnace to reduce the heat dissipation inside the alkali metal atomic vapor chamber 10 and improve the heating efficiency and temperature stability.

[0059] Example 2

[0060] The present invention also includes a method for laser bias frequency stabilization based on four-wave mixing ultra-narrow spectrum, comprising the following steps:

[0061] Step 1: According to Example 1, a laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum is constructed.

[0062] Step 2: Adjust the saturated absorption frequency stabilization system 30. The first coherent light source 1 can selectively stabilize the pump light frequency on any resonant transition line of the alkali metal atoms in the saturated absorption frequency stabilization system 30 through the saturated absorption optical path frequency stabilization method.

[0063] Step 3, start the precision temperature control device 22, monitor the temperature of the alkali metal atomic vapor chamber 10 through the temperature measuring platinum resistor 24, the temperature measuring platinum resistor 24 is connected to the precision temperature control device 22, and the precision temperature control device 22 PID feedback adjusts and controls the input of the DC regulated power supply 23, so that the alkali metal atomic vapor chamber 10 reaches a stable temperature, and the alkali metal atomic vapor chamber 10 has a suitable atomic number density to meet the requirements of the four-wave mixing process. In the experiment, the setting operating temperature range of the alkali metal atomic vapor is 60℃~120℃. The alkali metal atomic vapor chamber 10 emits gain signal light 27 and conjugate light 28.

[0064] Step 4, scan the laser frequency of the second coherent light source 2 with a scanning width of 10 GHz, collect the first detection signal of the first photodetector 15 or the second detection signal of the second photodetector 16, and then connect the first detection signal or the second detection signal to the signal amplifier 17. The output of the signal amplifier 17 then passes through the signal filtering circuit 21 and the laser frequency locking module 19 in sequence, and is finally connected to the laser control module of the second coherent light source 2. In this embodiment, the first detection signal of the first photodetector 15 is collected.

[0065] Step 5: Adjust the laser modulation module 20 and apply a frequency of ω to the scanning signal of the second coherent light source 2 through the laser frequency locking module 19. mod The modulation signal has a modulation frequency much greater than the scanning frequency Δω of the second coherent light source 2 itself, and the modulation frequency range is selected to be 1-10kHz. At this time, the scanning signal frequency ω(t) of the second coherent light source 2 is ω 0 +Δω×sin(ω mod ×t), where ω 0 is the initial frequency of the second coherent light source 2, t is time; the detection signal of the photodetector is S(t), and in this embodiment, the first detection signal of the first photodetector 15 is selected, and S(t) can be approximated as S(t)=S 0 +S'(ω 0 )×Δω×sin(ω mod × t), where S 0 is the frequency ω of the second coherent light source 2 0 The detection signal of the photodetector, S'(ω 0 ) is the photodetector receiving frequency ω 0 The derivative of the detection signal output after the laser is, in this embodiment, the first photodetector 15 receives the frequency ω 0The derivative of the first detection signal is output after the laser; the detection signal is connected to the laser frequency locking module 19, and then multiplied by the modulation signal to obtain the modulated detection signal:

[0066] S(t)×sin(ω mod ×t)

[0067] =S 0 ×sin(ω mod ×t)+S'(ω 0 )×Δω×sin(ω mod ×t) 2

[0068] =1 / 2×S'(ω 0 )×Δω+S 0 ×sin(ω mod ×t)-S'(ω 0 )×Δω×cos(2×ω mod ×t)

[0069] The modulated detection signal passes through a low-pass filter in the laser frequency locking module 19 to filter out the high-frequency components in the signal. The result can be expressed as:

[0070] Output=low pass(S(t)×sin(ω mod ×t))=1 / 2×S'(ω 0 )×Δω

[0071] Among them, Output is the modulation and demodulation signal, low pass is the low-pass filtering process, and the modulation and demodulation signal obtained by this method is 1 / 2×S'(ω 0 )×Δω∝S'(ω 0 ), that is, in this embodiment, the first photodetector 15 measures the derivative of the first detection signal.

[0072] The laser frequency of the gain signal light 27 or the newly generated conjugate light 28, i.e., the laser frequency corresponding to the peak of the laser signal, has a certain detuning amount compared to the resonance frequency of the first coherent light source 1, i.e., the pump light frequency. Then, the gain signal light 27 or the newly generated conjugate light 28 is collected and converted and processed to obtain a signal connected to the laser frequency locking module 19, and the modulation and demodulation signal obtained thereby is used as the frequency discrimination signal of the laser. The PID feedback circuit of the second coherent light source 2 is stabilized at the frequency of the Raman gain signal light 27 or the newly generated conjugate light 28 generated by the second coherent light source 2. According to the principle of four-wave mixing in the atomic system, the gain signal light 27 and the newly generated conjugate light 28 have a larger detuning amount compared to the pump light output by the first coherent light source 1 whose frequency is stabilized on the atomic resonance transition line, thereby realizing laser frequency stabilization with a large detuning amount from the atomic resonance frequency, and at the same time obtaining a laser light source with a relatively stable frequency difference between the gain signal light 27 and the conjugate light 28.

[0073] The technical contents described herein are merely examples of the spirit of the present invention. Those skilled in the art of the present invention may make various modifications or additions to the specific technical solutions described or replace them in similar ways. However, they will not deviate from the spirit of the present invention or exceed the scope defined by the attached claims.

Claims

1. Laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum, It is characterized in that The invention comprises an alkali metal atom vapor chamber (10), wherein pump light and signal light are incident on the alkali metal atom vapor chamber (10) at a phase matching angle required for four-wave mixing, and gain signal light (27) and conjugate light (28) are obtained. The gain signal light (27) or the conjugate light (28) is used as a frequency stabilization reference light signal for a second coherent light source (2) that emits the signal light, and the second coherent light source (2) is feedback-regulated so that the laser frequency output by the second coherent light source (2) is stabilized at the spectrum peak of the gain signal light (27) or the conjugate light (28); The light source of the pump light is a first coherent light source (1); The alkali metal atomic vapor chamber (10) is placed in a heat preservation module (26).

2. According to claim 1, the laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum, It is characterized in that The gain signal light (27) or the conjugate light (28) is passed through a photoelectric detector to obtain a detection signal and a modulation signal output by a laser modulation module (20), which are simultaneously input into a laser frequency locking module (19). The laser frequency locking module (19) outputs a discrimination signal to a laser control module of a second coherent light source (2).

3. According to claim 2, the laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum, It is characterized in that The pump light sequentially passes through a shaping prism (3), a first variable-power beam expander (4) and a first λ / 2 wave plate (5), and then the polarized pump light obtained by reflection from the first polarization beam splitter (6) is incident on a second polarization beam splitter (9) and is reflected by the second polarization beam splitter (9) to an alkali metal atom vapor chamber (10); the signal light sequentially passes through a second variable-power beam expander (7) and a second λ / 2 wave plate (8), and then transmits through the second polarization beam splitter (9) to obtain polarized signal light and is incident on the alkali metal atom vapor chamber (10).

4. According to claim 3, the laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum, It is characterized in that The pump light transmitted by the first polarization beam splitter (6) is incident on a saturation absorption frequency stabilization system (30), and the obtained frequency stabilization feedback signal of the first coherent light source (1) is then input into a laser wavelength frequency locking module of the first coherent light source (1).

5. According to claim 4, the laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum, It is characterized in that The heat preservation module (26) is also provided with a temperature measuring platinum resistor (24) and a heating device (25). The temperature measuring platinum resistor (24) converts the detected temperature information into an electrical signal and outputs it to the precision temperature control device (22). The precision temperature control device (22) outputs the difference between the electrical signal and the temperature value set by the precision temperature control device (22) to a DC regulated power supply (23). The DC regulated power supply (23) outputs a regulated current to the heating device (25).

6. The laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum according to claim 1, It is characterized in that After four-wave mixing, remaining output pump light is also output from the alkali metal atomic vapor chamber (10); the remaining output pump light, gain signal light (27) and conjugate light (28) are simultaneously and sequentially passed through a third λ / 2 wave plate (11) and a λ / 4 wave plate (12) after outputting the alkali metal atomic vapor chamber (10); the remaining output pump light is then reflected by a third polarization beam splitter (13) to an optical baffle (14); and the gain signal light (27) and conjugate light (28) are transmitted through the third polarization beam splitter (13).

7. A method for laser bias frequency stabilization based on four-wave mixing ultra-narrow spectrum, using the laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum as claimed in claim 5, and the specific steps are as follows: Step 1: Build a laser bias frequency stabilization device based on four-wave mixing ultra-narrow spectrum; Step 2, adjusting the saturated absorption frequency stabilization system (30) to select and stabilize the pump light frequency on the alkali metal atom resonance transition line of the saturated absorption frequency stabilization system (30); Step 3, adjusting the temperature in the alkali metal atom vapor chamber (10) to a range of 60° C. to 120° C. by means of a precision temperature control device (22) so that the metal atom vapor chamber (10) emits gain signal light (27) and conjugate light (28); Step 4, scanning the laser frequency of the second coherent light source (2), with a scanning width of 10 GHz, collecting the first detection signal of the first photodetector (15) or the second detection signal of the second photodetector (16), and then connecting the first detection signal or the second detection signal to the signal amplifier (17), and the output of the signal amplifier (17) then passes through the signal filtering circuit (21) and the laser frequency locking module (19) in sequence, and finally connected to the laser control module of the second coherent light source (2); Step 5: Adjust the laser modulation module (20) and apply a frequency of ω to the scanning signal of the second coherent light source (2) through the laser frequency locking module (19). mod The modulation signal has a modulation frequency greater than the scanning frequency of the second coherent light source (2) itself.

8. According to the laser bias frequency stabilization method based on four-wave mixing ultra-narrow spectrum according to claim 7, It is characterized in that In the said step 5, the scanning signal frequency ω(t) of the second coherent light source (2) = ω 0 + Δω × sin(ω mod × t), where ω 0 is the initial frequency of the second coherent light source (2), Δω is the scanning frequency of the second coherent light source (2) itself, and t is the time; the detection signal S(t) of the photodetector = S 0 + S’(ω 0 ) × Δω × sin(ω mod × t), S 0 is the detection signal detected by the electric detector when the frequency of the second coherent light source (2) is ω 0 , and S’(ω 0 ) is the derivative of the detection signal output after the photodetector receives the laser with the frequency of ω 0 ; the detection signal is connected to the laser frequency locking module (19), and then multiplied by the modulation signal to obtain the modulated detection signal: S(t)×sin(ω mod ×t) =1 / 2×S'(ω 0 )×D+S 0 ×sin(ω mod ×t)-S'(ω 0 )×Dω×cos(2×ω mod ×t) The modulated detection signal is passed through a low-pass filter in a laser frequency locking module (19) to obtain a modulation and demodulation signal Output = 1 / 2 × S' (ω 0 )×Δω.

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