Laser Optical Power Stabilization Device Based on Differential Sampling Feedback and Its Debugging Method

Abstract

The present invention discloses a laser optical power stabilization device based on differential sampling feedback and a debugging method thereof. In the present invention, a voltage signal corresponding to the power of the laser to be stabilized is compared with a high-precision reference voltage source through a zero-drift differential circuit and differential sampling is performed. The sampled signal is fed back to the optical power controller through an analog proportional circuit. Finally, the laser power fluctuation is effectively reduced by up to 20 dB in the frequency band below several hundred Hz, and a long-term stability of several hundred PPM level within 1 hour is achieved. In the present invention, the DC component is removed through differential sampling, avoiding the contradiction between the circuit range and the resolution performance, and greatly improving the signal-to-noise ratio of the optical power signal relative to the circuit noise and the long-term stability effect. In short, through differential sampling feedback, the present invention provides a laser optical power stabilization method and device with excellent long-term stability and simple and reliable structure.

Description

Technical Field

[0001] The present invention relates to a laser optical power stabilizing device, and particularly to a high-stability laser optical power stabilizing device based on differential sampling feedback and a debugging method thereof.

[0002] Background Art

[0003] The power fluctuation of a laser mainly concentrates in the frequency band within several hundred Hz, and is mainly manifested as relative intensity noise. The relative intensity noise comes from the inherent fluctuation of the laser optoelectronic non-linear conversion process and the random changes of parameters such as the pump current of the laser and the cavity position caused by environmental factors such as air pressure, vibration, and temperature. In the frequency band above several hundred Hz, the power fluctuation of the laser is relatively weak, and is mainly manifested as optical shot noise. The optical shot noise comes from the quantum nature of light, and the optical shot noise is only related to the average optical power and cannot be suppressed by means of classical mechanics.

[0004] High power stability of a laser is a basic condition required in many scientific research and industrial production fields. For example, in the research of cold atom physics, the fluctuation of the laser light intensity will accelerate the collapse process of the coherent superposition state of cold atoms, reduce the available interaction time, and severely restrict the performance of the overall scientific device such as the accuracy of quantum measurement or the accuracy of quantum computing. Another example is that in the research of the optical momentum sensing device for suspending a transparent medium, the fluctuation of the optical power will cause a change in the optical radiation force exerted by the laser on the transparent medium, increase the motion background noise of the suspended transparent medium, and deteriorate the sensitivity index of the mechanical quantity sensing. However, even the long-term optical power stability (RMS value) of the direct output light of existing mid- to high-end commercial lasers within 1 hour is basically between 0.2% and 2%, that is, within the range of 2000 PPM (parts per million) to 20000 PPM, it is still difficult to meet the increasingly stringent application requirements now and in the future. Therefore, the exploration of preparing lasers with high power stability has quite important scientific value and practical significance.

[0005] Currently, the methods for stabilizing the optical power of lasers mainly include internal modulation of the pump current, saturated absorption, and external modulation of the light intensity transmittance, etc. Internal modulation of the pump current means that the pump current is feedback-controlled to make the output light of the laser stable. Generally, it has been integrated inside commercial lasers after leaving the factory, and its performance has been optimized by the manufacturer to a relatively good level without room for improvement. Saturated absorption utilizes the characteristic that when the input optical power of a semiconductor optical amplifier (SOA) exceeds a certain threshold, the gain will decrease as the input optical power increases. However, SOA will introduce additional noise when amplifying the optical power, and it is not suitable for application scenarios that require low optical power fluctuations in a relatively wide frequency band. External modulation of the light intensity transmittance means that the transmittance of electro-optic crystals, etc., is feedback-controlled to make the transmitted laser light intensity stable, and it has strong applicability. However, in the traditional direct sampling of the optical power signal method for external modulation of the light intensity transmittance, there is a useless strong DC component, which makes it difficult to reconcile the contradiction between the range of the operational amplifier or analog-to-digital converter and the circuit background noise, resulting in low sampling resolution and poor zero-drift performance, restricting the further improvement of the relative intensity noise and long-term stability performance of the optical power. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the present invention proposes a high-stability laser optical power stabilization method and device based on differential sampling feedback. The specific solutions of the present invention are as follows:

[0007] I. A laser optical power stabilization device based on differential sampling feedback

[0008] The device includes a laser source, a first beam splitter, a second beam splitter, a first photodetector, a second photodetector, a data acquisition card, a reference voltage source, a differential circuit, a proportional feedback circuit, and an optical power controller;

[0009] The laser source, the optical power controller, the first beam splitter, and the second beam splitter are arranged in sequence along the optical axis. The beam emitted by the laser source is incident on the first beam splitter through the optical power controller and undergoes transmission and reflection. The reflected light of the first beam splitter is incident on the photosensitive surface of the first photodetector. The first photodetector is connected to the second input end of the differential circuit. The first input end of the differential circuit is connected to the reference voltage source. The output end of the differential circuit is connected to the optical power controller through the proportional feedback circuit. The transmitted light of the first beam splitter is incident on the second beam splitter and undergoes transmission and reflection. The transmitted light of the second beam splitter is used as the output beam of the device. The reflected light of the second beam splitter is incident on the photosensitive surface of the second photodetector. The second photodetector is connected to the data acquisition card.

[0010] The laser source is a point laser source, and both the first beam splitter and the second beam splitter are polarization-independent optical beam splitters.

[0011] The shapes of the first beam splitter and the second beam splitter include cubic type and flat plate type.

[0012] Both the first photodetector and the second photodetector are reverse-biased photodiode structures, and the photosensitive surface size of the photodiode is greater than or equal to twice the laser beam waist diameter of the laser source.

[0013] The optical power controller includes an electro-optic modulator based on the Pockels effect, Kerr effect or liquid crystal effect and an acousto-optic modulator based on the acousto-optic effect.

[0014] II. A debugging method for a laser optical power stabilization device based on differential sampling feedback

[0015] 1) Turn on the working power supply of the reference voltage source, collect the output voltage signal of the reference voltage source and denote it as the reference voltage signal V ref , and calculate the corresponding equivalent optical power relative intensity noise spectrum according to the reference voltage signal V ref and denote it as the reference noise spectrum S ref,RIN (v);

[0016] 2) Turn on the working power supplies of the first photodetector, second photodetector, differential circuit, data acquisition card, proportional feedback circuit and optical power controller. Then set the gain parameter of the proportional feedback circuit. Next, use the data acquisition card to collect the output voltage signal of the second photodetector and denote it as the second voltage signal V2, and calculate the equivalent optical power relative intensity noise spectrum corresponding to the current gain parameter according to the debugging voltage signal V2 and denote it as the debugging noise spectrum;

[0017] 3) Change the gain parameter of the proportional feedback circuit N - 1 times, and collect and calculate the debugging noise spectra corresponding to N - 1 gain parameters;

[0018] 4) Compare the curves of the debugging noise spectra corresponding to N gain parameters with the reference noise spectrum S ref,RIN (ω). Select the debugging noise spectrum that is closest to the curve of the reference noise spectrum S ref,RIN (ω) from the N debugging noise spectra and denote it as the optimal noise spectrum. Take the gain parameter corresponding to the optimal noise spectrum as the optimal gain parameter of the proportional feedback circuit. At this time, the optical power stabilization device is debugged to the known best performance state.

[0019] In the step 4), calculate the integral value of the square of the difference between the debugging noise spectra corresponding to N gain parameters and the reference noise spectrum over the entire frequency band, and select the debugging noise spectrum with the minimum integral value from the N debugging noise spectra and denote it as the optimal noise spectrum.

[0020] The beneficial effects of the present invention are as follows:

[0021] The present invention provides a laser optical power stabilization method and device with excellent long-term stability and simple and reliable structure through differential sampling feedback. The present invention is an improved version of the traditional optical intensity transmittance external modulation method. It compares the voltage signal corresponding to the power of the laser to be stabilized with a high-precision reference voltage source through a zero-drift differential circuit and performs differential sampling. The sampling signal is fed back to the optical power controller through an analog proportional circuit, and finally, the laser power fluctuation is effectively reduced in the frequency band below several hundred Hz, and the long-term stability of the laser power reaches the order of several hundred PPM. The present invention overcomes the problems of insufficient optical signal-to-noise ratio and poor long-term stability in the direct sampling of traditional external modulation, and provides a design and debugging method for a simplified proportional feedback module, reducing the cost of the stabilization system and improving the reliability required for long-term stable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic connection diagram of a high-stability laser optical power stabilization device based on differential sampling feedback according to the present invention.

[0023] Figure 2 Schematic diagram of the method flow according to the present invention.

[0024] Figure 3 Circuit schematic diagram of the attenuation module in the reference voltage source in Application Example 1.

[0025] Figure 4 Circuit schematic diagram of the differential circuit 8 in Application Example 2.

[0026] Figure 5 Circuit schematic diagram of the proportional feedback circuit 9 in Application Example 2.

[0027] Figure 6 For Application Examples 1 and 2, the relative intensity noise spectra S ref,RIN (ω) and S RIN,1 Comparison diagram of the optical power before and after stabilization.

[0028] Figure 7 For Application Example 3, the laser relative intensity noise spectra S RIN,k (ω) corresponding to three gain parameter settings of the proportional feedback circuit 9.

[0029] Figure 8 Comparison diagram of the long-term stability before and after optical power stabilization in Application Example 3.

[0030] In the figure: laser source 1, first beam splitter 2, second beam splitter 3, first photodetector 4, second photodetector 5, data acquisition card 6, reference voltage source 7, differential circuit 8, proportional feedback circuit 9, optical power controller 10. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0032] As Figure 1 shown, the device includes a laser source 1, a first beam splitter 2, a second beam splitter 3, a first photodetector 4, a second photodetector 5, a data acquisition card 6, a reference voltage source 7, a differential circuit 8, a proportional feedback circuit 9, and an optical power controller 10; among them, the dotted line represents the transmission of the electrical signal, and the solid line represents the transmission of the optical signal.

[0033] The laser source 1, the optical power controller 10, the first beam splitter 2, and the second beam splitter 3 are arranged in sequence along the optical axis. The beam emitted by the laser source 1 is incident on the first beam splitter 2 through the optical power controller 10 and undergoes transmission and reflection. The reflected light of the first beam splitter 2 is incident on the photosensitive surface of the first photodetector 4. The first photodetector 4 is connected to the second input terminal of the differential circuit 8, and the voltage signal output by the first photodetector 4 is input into the second input terminal of the differential circuit 8. The first input terminal of the differential circuit 8 is connected to the reference voltage source 7, and the output terminal of the differential circuit 8 is connected to the optical power controller 10 through the proportional feedback circuit 9. The transmitted light of the first beam splitter 2 is incident on the second beam splitter 3 and undergoes transmission and reflection. The transmitted light of the second beam splitter 3 is used as the output beam of the device. The ultimate goal of the optical power stabilization device is to maximize the stabilization of the optical power of the output beam of the device. The reflected light of the second beam splitter 3 is incident on the photosensitive surface of the second photodetector 5. The second photodetector 5 is connected to the data acquisition card 6, and the voltage signal output by the second photodetector 5 is collected by the data acquisition card and used as the analysis basis for the optical power fluctuation of the transmitted light of the second beam splitter 3. The optical power controller 10, the first beam splitter 2, the first photodetector 4, the differential circuit 8, and the proportional feedback circuit 9 form a closed loop. By controlling the transmittance (or diffraction efficiency) of the optical power controller 10, the change in the output optical power of the laser source 1 is offset, and the function of keeping the optical power of the final output beam stable is realized. The first beam splitter 3, the first photodetector 5, and the data acquisition card 6 form an external measurement part of the feedback loop for the optical power of the output beam, which is used for parameter debugging of the proportional feedback circuit 9 and monitoring whether the optical power stabilization system works properly in the long term.

[0034] The laser source 1 is a point laser source, and both the first beam splitter 2 and the second beam splitter 3 are polarization-independent optical beam splitters.

[0035] The shapes of the first beam splitter 2 and the second beam splitter 3 include, but are not limited to, cubic and flat plate types.

[0036] Both the first photodetector 4 and the first photodetector 5 are reverse-biased photodiode structures, and the photosensitive surface size of the photodiode is greater than or equal to twice the laser beam waist diameter of the laser source 1; when the voltages at both input terminals of the differential circuit 8 remain unchanged, the output voltage of the differential circuit 8 does not drift with time.

[0037] The optical power controller 10 includes, but is not limited to, an electro-optic modulator based on the Pockels effect, Kerr effect, or liquid crystal effect, and an acousto-optic modulator based on the acousto-optic effect. The transmittance and / or reflectivity of the laser by the optical power controller 10 changes with the change of the input voltage.

[0038] As Figure 2 shown, the debugging method includes the following steps:

[0039] 1) Turn on the working power supply of the reference voltage source 7. After waiting for the warm-up and stabilization time required by the reference voltage source 7, directly collect the output voltage signal of the reference voltage source 7 using the data acquisition card 6 and record it as the reference voltage signal V ref , and calculate the corresponding equivalent optical power relative intensity noise spectrum according to the reference voltage signal V ref and record it as the reference noise spectrum S ref,RIN (ω);

[0040] 2) Turn on the working power supplies of the first photodetector 4, the second photodetector 5, the differential circuit 8, the data acquisition card 6, the proportional feedback circuit 9, and the optical power controller 10. After waiting for the warm-up and stabilization times required by each module, then set the gain parameter of the proportional feedback circuit 9. Then, use the data acquisition card 6 to collect the output voltage signal of the second photodetector 5 and record it as the second voltage signal V2. Calculate the equivalent optical power relative intensity noise spectrum corresponding to the current gain parameter according to the debugging voltage signal V2 and record it as the debugging noise spectrum;

[0041] 3) In specific implementation, change the gain parameter of the proportional feedback circuit 9 N - 1 times within the preset gain range, collect and calculate the debugging noise spectra corresponding to N - 1 gain parameters, and record them as S RIN,k (ω), k = 1, 2,..., N;

[0042] 4) Calculate the integral value of the square of the difference between the debugging noise spectra corresponding to N gain parameters and the reference noise spectrum over the entire frequency band. Select the debugging noise spectrum with the minimum integral value from the N debugging noise spectra and record it as the optimal noise spectrum. Use the gain parameter corresponding to the optimal noise spectrum as the optimal gain parameter of the proportional feedback circuit 9. At this time, the optical power stabilization device is debugged to the known best performance state.

[0043] Application Example 1

[0044] The following gives a specific example of the reference noise spectrum S in step 1) of the method of the present inventionref,RIN (ω) The calculation process will be described.

[0045] First, use the ultra-precision voltage reference chip LTZ1000 module of Analog Devices (ADI) company. Its long-term stability can reach The input of this module is +12V DC, the output is +7V, with an SMA RF interface, and the maximum output current is 2mA. A fixed-gain RF attenuation circuit board is used to transform and build an attenuation module. The circuit schematic diagram of the attenuation module is as Figure 3 shown. V ref,in is the input voltage, equal to +7V. C1 uses a 10μF 5% precision X7R chip capacitor to decouple the +7V power supply. R1 and R2 are 6.8kΩ and 200Ω ultra-low temperature drift coefficient 0.1% precision metal film through-hole resistors respectively, which play a voltage division role, and the temperature drift coefficient is 5PPM. C2 is composed of four 100μF 5% precision X7R chip capacitors in parallel, and together with R2, it forms a first-order low-pass filter, and the cut-off frequency f c1 = 1 / (2πR2C2) ≈ 2Hz. The output voltage V ref,out is about 194mV. The LTZ1000 module and the attenuation module are connected in series to form the reference voltage source 7.

[0046] Then, the data acquisition card 6 uses the precision single-channel 24-bit analog-to-digital conversion chip AD7764 of ADI. Its output rate reaches 312kSPS, and the signal-to-noise ratio is 112dB. Turn on the working power supply of the reference voltage source 7 and wait for the warm-up and stabilization time required by the reference voltage source 7, generally 3 hours. Use the data acquisition card 6 to directly collect the output voltage signal V ref (t) of the reference voltage source 7, with a continuous sampling duration of 1000s, and obtain the voltage random power density spectrum S vv,ref (ω). According to the formula Calculate the equivalent optical power relative intensity noise spectrum S ref,RIN (ω) represented in logarithm, where <> represents taking the DC value of the time-domain signal. In this example, the calculation result of S ref,RIN (ω) is as shown by the solid line in Figure 6 .

[0047] Application Example 2

[0048] Next, a specific example is given to illustrate the calculation process of the debugging noise spectrum S RIn,1 (ω) in steps 2) to 3) of the method of the present invention.

[0049] First, build a highly stable laser optical power stabilization device based on differential sampling feedback. Turn on the laser source 1, and turn on the working power supplies of the first photodetector 4, the second photodetector 5, the data acquisition card 6, the differential circuit 8, the proportional feedback circuit 9, and the optical power controller 10 to achieve the optical power stabilization function. Wait for the preheating and stabilization time required by each module, generally 3 hours.

[0050] Among them, the laser source 1 uses a fiber amplifier 1064nm laser pumped by a laser diode with a maximum optical power of 500mW, and outputs p-polarized light. Both the first photodetector and the second one use DET100A2 from Thorlab, which is a large photosensitive surface PIN silicon photodiode with a reverse bias of a 12V battery, and is externally connected with a 50-ohm SMA terminal. The diameter of the photosensitive surface is 9.5mm, and the large photosensitive area can fully reduce the adverse effects of the laser beam pointing drift on the optical power stabilization performance.

[0051] The differential circuit 8 is a typical single-op amp differential amplification circuit, and the schematic diagram is as Figure 4 shown. Among them, the op amp U1 uses a single op amp OPA189 from Texas Instruments (TI) with ultra-low drift, low noise, and large bandwidth, and the input temperature drift coefficient is 0.005 μV / °C. All resistors in the differential circuit 8 must use 0.1% precision metal film through-hole resistors with ultra-low temperature drift coefficients, generally with a temperature drift coefficient of 5 PPM. The DC gain of the differential circuit 8 is set to 150 times and includes a first-order low-pass filter with a bandwidth of 10 kHz. Except for the differential circuit 8, the resistors and operational amplifiers in other circuits of the optical power stabilization device in the present invention do not require ultra-low temperature drift performance.

[0052] The proportional feedback circuit 9 is a typical single-op amp inverting input amplification circuit, and the schematic diagram is as Figure 5 shown. Among them, the op amp U2 selects a non-zero drift, ultra-low noise single op amp OPA1611. The resistors in the circuit 9 use ordinary chip resistors with a temperature drift coefficient of 300 PPM and a precision of 0.1%. Among them, the resistor R6 = 200 Ω. The gain G2 of the circuit 9 = R7 / R6, and it can be changed by rotating the knob on the multi-turn precision adjustable resistor R4. The resistance value range is 0 - 10 kΩ, so the maximum gain is 50 times, and the minimum is generally not less than 1 time. The bandwidth of the circuit 9, that is, the cut-off frequency f of the first-order low-pass filter c1 = 1 / (2πR7C4).

[0053] The optical power controller 10 uses the large-aperture acousto-optic crystal AOMO 3110-197 from Gooch&Houseg and the supporting RF driver 1080AF-AIN0-3.0HCR. The input pin voltage range of the RF driver is 0 to 1V. When the input voltage is 0V, the first-order diffracted optical power output by the acousto-optic crystal is the smallest, only 0.1mW; when the input voltage is 0.8V, the first-order diffracted optical power output by the acousto-optic crystal is the largest and enters the saturation region, reaching 430mW.

[0054] Both the first beam splitter 2 and the second beam splitter 3 use the polarization-independent cube beam splitter BS038 from Thorlab. The nominal splitting ratio is R:T = 1:9, and the actual splitting ratio is R:T = 0.4:8.6. After the optical power stabilization starts to work, the proportional feedback makes the DC value of the output voltage V1(t) of the first photodetector 4 connected to the 50-ohm SMA terminal equal to the DC value of the output voltage V ref (t) of the reference voltage source 7. At this time, the DC value of the input voltage of the RF driver is about 0.4V, and the DC value of the output voltage V2(t) of the first photodetector 4 connected to the 50-ohm SMA terminal is about 165mV.

[0055] In the first process of performing steps (4) and (5), the gain of the proportional feedback circuit 9 is set to 10, and the bandwidth is equal to 100Hz. Use the data acquisition card 6 to collect the output voltage signal V2(t) of the second photodetector 5, with a continuous sampling duration of 1000s, and obtain the voltage random power density spectrum S vv,RIN,1 (ω). According to the formula k = 1..N to calculate the equivalent optical power relative intensity noise spectrum S RIN,1 (ω) in logarithmic form, where <> represents taking the DC value of the time-domain signal. In this example, the calculation result of S RIN,1 (ω) is as shown by the dashed line in Figure 4 .

[0056] In Figure 1 , disconnect the connection between the proportional feedback circuit 9 and the optical power controller 10, and connect the input pin of the power controller 10 to the output pin of the reference voltage source 7, that is, the optical power stabilization is in the non-working state. At this time, use the data acquisition card 6 to collect the output voltage signal V2( t ) of the second photodetector 5, with a continuous sampling duration of 1000s, and obtain the voltage random power density spectrum S vv,RIN,0 (ω). According to the formula As shown by the dash-dot line in Figure 4 , it can be seen that the optical power stabilization device effectively suppresses the fluctuations of the optical power in the frequency range of 0.01Hz to 300Hz, and the typical suppression value of the relative intensity noise reaches 20dB. As shown in Figure 6As shown, the output voltage of the reference voltage source in the device required by the present invention corresponds to the spectral line S ref,RIN (ω) (solid line) is always lower than the spectral line S corresponding to the laser power before stabilization in almost all frequency bands RIN,1 (ω) (dotted line), so that there is a stabilization effect. Moreover, the spectral line S corresponding to the output voltage of the reference voltage source ref,RIN (ω) (solid line) constitutes the lowest value that can be achieved by the spectral line S corresponding to the laser power after the parameters of the proportional feedback circuit 9 are adjusted and the optical power stabilization is turned on RIN,1 (ω) (dashed line), which characterizes the performance optimization limit of the optical power stabilization of the device of the present invention. It can be seen that in Figure 6 , after the optical power stabilization of the device of the present invention is turned on, the spectral line S corresponding to the laser power RIN,1 (ω) (dashed line) reaches the optimization limit in the frequency band above 0.1 Hz. The optical power stabilization performance in the frequency band below 0.1 Hz is limited by other limiting factors such as ambient temperature, air flow disturbance, and vibration, and there is still room for optimization. The circuit structures in the present invention, such as the differential circuit 8 and the proportional feedback circuit 9, have simple structures and low costs, and have the advantages of simplicity and reliability.

[0057] Application Example Three

[0058] A specific example is given below to illustrate the gain bandwidth optimization process of the proportional feedback circuit 9 in step 4) of the method of the present invention.

[0059] Take N = 3, that is, three cases of the gain of the proportional feedback circuit 9 are set in steps 3) to 6). Figure 7 The laser relative intensity noise spectral lines corresponding to the three gain parameter setting cases are given. Compare the optical power relative intensity noise spectra S RIN,1 (ω) (solid line) and S RIN,2 (ω) (dashed line). Within a certain range, the relative intensity noise spectrum decreases as the gain increases. The stability of the laser optical power can be characterized by the relative intensity noise spectrum in the low frequency band. It can be seen that when the gain is too small, the device has insufficient optimization of the stability of the laser optical power on the time scale of 0.1 s (10 Hz) to longer. Compare the optical power relative intensity noise spectra S RIN,1 (ω) (solid line) and S RIN,3 (ω) (dotted line). It can be seen that when the gain is set too large, although the relative intensity noise continues to decrease as the gain increases in the frequency band below 10 Hz, the relative intensity noise spectrum in the frequency band above 10 Hz will increase as the gain increases. Calculate the integral value D of the square of the difference between the debug noise spectra S RIN,k (ω), k = 1..3 and the noise spectrum S ref,RIN (ω) over the entire frequency band k = ∫[S RIN,k (ω) - S ref,RIN (ω)] 2, k = 1..3. The results are D1 = 3.4×10 -4 , D2 = 8.2×10 -4 and D3 = 1.5×10 -3 . Therefore, the appropriate gain value of the proportional feedback circuit 9 should be as shown by S Figure 7 (ω) (solid line) in RIN,1 to be 20, so that the overall relative intensity noise spectrum of the laser optical power is at a relatively low level.

[0060] After setting the gain value of the proportional feedback circuit 9 to the optimal value of 20 and turning on the optical power stabilization device for a long time, the time-domain curves of the power before and after stabilization are as shown in Figure 8 , which characterizes the improvement effect of long-term stability. The RMS value of the optical power fluctuation within one hour after the device is stabilized decreases from 2255 PPM to 313 PPM. In summary, the present invention can effectively reduce the laser power fluctuation by up to 20 dB in the frequency band below several hundred Hz and achieve a long-term stability of several hundred PPM within one hour. <l

[0061] Application Example 4

[0062] A specific example is given below to illustrate the improvement effect of the signal-to-noise ratio of differential sampling relative to direct sampling of the present invention.

[0063] The range of the operational amplifier is limited by the power supply voltage range and chip parameters, generally not exceeding ±18V. Assume that in the traditional direct sampling method, the voltage signal converted from the optical power signal is amplified by the operational amplifier circuit to be close to the range; while in the present invention, after differential sampling, the strong DC component is subtracted by the reference voltage source, and then the voltage signal fluctuation amplitude is amplified to be close to the range. Both of the above methods maximize the signal-to-noise ratio of the optical signal relative to the circuit noise as much as possible. On the premise that the low-pass cut-off frequency of the operational amplifier is 100 Hz, the DC value of the voltage signal converted from the optical power signal is taken as V0 = 194 mV, and the fluctuation amplitude is ΔV = 1.1 mV. The equivalent input voltage noise amplitude of the operational amplifier is V amp,in = 1.5 μV, and the range is V max = 18V. The output voltage noise amplitude of the reference voltage source is V ref,out = 1U.3 μV. Then the signal-to-noise ratio of the traditional direct sampling method is The signal-to-noise ratio of the differential sampling method of the present invention is In summary, in the traditional method of directly sampling the optical signal for power stabilization, there is a useless strong DC component. The present invention uses the reference voltage source and differential sampling to remove the limitation of the strong DC component, and can improve the signal-to-noise ratio of the optical signal relative to the circuit noise in the optical power stabilization system by up to 28.1 dB, promoting the further improvement of the relative intensity noise and long-term stability performance of the optical power, which is an excellent laser optical power stabilization scheme.

[0064] Finally, it should be noted that the above embodiments and descriptions are only used to illustrate the technical solutions of the present invention and not to limit them. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced, and as long as they do not depart from the spirit and scope of the disclosure of the technical solutions of the present invention, they should all be covered by the protection scope of the claims of the present invention.

Claims

1. A debugging method for a laser optical power stabilization device based on differential sampling feedback, characterized in that The described laser optical power stabilization device based on differential sampling feedback includes a laser source (1), a first beam splitter (2), a second beam splitter (3), a first photodetector (4), a second photodetector (5), a data acquisition card (6), a reference voltage source (7), a differential circuit (8), a proportional feedback circuit (9), and an optical power controller (10); The laser source (1), the optical power controller (10), the first beam splitter (2), and the second beam splitter (3) are arranged in sequence along the optical axis. The beam emitted by the laser source (1) is incident on the first beam splitter (2) through the optical power controller (10), and transmission and reflection occur. The reflected light of the first beam splitter (2) is incident on the photosensitive surface of the first photodetector (4). The first photodetector (4) is connected to the second input terminal of the differential circuit (8). The first input terminal of the differential circuit (8) is connected to the reference voltage source (7). The output terminal of the differential circuit (8) is connected to the optical power controller (10) through the proportional feedback circuit (9). The transmitted light of the first beam splitter (2) is incident on the second beam splitter (3) and transmission and reflection occur. The transmitted light of the second beam splitter (3) is used as the output beam of the device. The reflected light of the second beam splitter (3) is incident on the photosensitive surface of the second photodetector (5). The second photodetector (5) is connected to the data acquisition card (6); The debugging method includes the following steps: 1) Turn on the working power supply of the reference voltage source (7), collect the output voltage signal of the reference voltage source (7) and denote it as the reference voltage signal V ref , and according to the reference voltage signal V ref calculate the corresponding equivalent optical power relative intensity noise spectrum and denote it as the reference noise spectrum S ref,RIN (ω); 2) Turn on the working power supplies of the first photodetector (4), the second photodetector (5), the differential circuit (8), the data acquisition card (6), the proportional feedback circuit (9), and the optical power controller (10). Then set the gain parameter of the proportional feedback circuit (9). Next, use the data acquisition card (6) to collect the output voltage signal of the second photodetector (5) and denote it as the second voltage signal V2. Calculate the equivalent optical power relative intensity noise spectrum corresponding to the current gain parameter and denote it as the debugging noise spectrum according to the debugging voltage signal V2; 3) Change the gain parameter of the proportional feedback circuit (9) N - 1 times, and collect and calculate the debugging noise spectra corresponding to N - 1 gain parameters; 4) Compare the debugging noise spectra corresponding to the N gain parameters with the reference noise spectrum S ref,RIN (ω) by curve comparison, and select the debugging noise spectrum from the N debugging noise spectra that is closest to the curve of the reference noise spectrum S ref,RIN (ω) and denote it as the optimal noise spectrum. Use the gain parameter corresponding to the optimal noise spectrum as the optimal gain parameter of the proportional feedback circuit (9). At this time, the optical power stabilization device is debugged to the known best performance state.

2. The debugging method of a laser optical power stabilizing device based on differential sampling feedback according to claim 1, characterized in that, In the described step 4), calculate the integral value of the square of the difference between the debugging noise spectra corresponding to N gain parameters and the reference noise spectrum over the entire frequency band. Select the debugging noise spectrum with the minimum integral value from the N debugging noise spectra and denote it as the optimal noise spectrum.

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