System and method for directly adjusting optical power stability by using anti-phase power detection signal

Abstract

The invention discloses a system and a method for directly adjusting optical power stability by using an anti-phase power detection signal. The system comprises a laser emitting device, a detection device and an adjustment driving device, the laser emitting device emits laser and outputs laser with stable optical power, and the detection device detects the laser and outputs a power detection signal; and the adjustment driving device determines an optimal anti-phase gain parameter through the power detection signal and directly adjusts the laser. The system has the advantages of simple and stable structure, quick response and easy parameter adjustment, the reference voltage is used as the reference voltage in the method, the power stability effect can be effectively improved, an open-loop control structure is used, the stability effect better than that of closed-loop control can be achieved, and the system is suitable for large-scale popularization and application. And finally, optimal parameters can be determined, so that the system adapts to changes of an external environment and can be applied to the fields of precision measurement and laser precision machining.

Description

Technical Field

[0001] The invention relates to a system for regulating optical power stability, and in particular to a system and method for directly regulating optical power stability by using an inverted power detection signal. Background Art

[0002] Laser power stabilization technology is critical in precision measurement and laser precision processing applications. Taking a high-precision atomic spin gyroscope as an example, the detection of laser power fluctuations will lead to scale factor errors, and the pumping laser power fluctuations will directly cause fluctuations in the pumping rate, thereby affecting the stability of the polarizability. In the suspended optical force detection system, the laser power fluctuations are converted into momentum fluctuations of the sensitive unit, reducing the detection accuracy of acceleration and force. However, there are inevitable fluctuations in laser power, and its relative intensity noise RIN (Relative Intensity Noise) generally decreases with increasing frequency. It is higher in the frequency band within a few hundred Hz, and mainly manifests as shot noise in the high-frequency part. The main causes of laser power fluctuations include: the beat effect of each Fourier component in the laser line width, the fluctuation of the gain medium pump source, and the fluctuations of the cavity length, gain, etc. caused by environmental factors such as temperature and humidity changes and vibration. The power fluctuation value (standard deviation / mean) of a typical high-performance laser is around 0.2%, while the fiber laser is slightly worse than the spatial light laser, especially at high power output.

[0003] The current laser power stabilization schemes can be divided into intracavity regulation and extracavity regulation. Intracavity regulation includes feedback control of laser pump current, cavity length, and cavity temperature. Extracavity regulation generally achieves laser power stabilization after the laser emits light through optical power control devices such as liquid crystal variable phase delay, electro-optic modulator, and acousto-optic modulator combined with feedback control algorithms such as proportional integral differential PID control algorithm. Extracavity regulation has advantages over intracavity regulation. This is because intracavity regulation cannot compensate for power fluctuations caused by the external optical path and environment, including fluctuations in the splitting ratio of the splitter, and the impact of environmental factors on optical fiber loss.

[0004] However, the optical power stabilization system based on the PID control algorithm also has certain disadvantages. For example, it is difficult to adjust the parameters and the algorithm is complex. When the laser power changes significantly, it cannot enter the steady state in time. The effect of feedback control depends on the selection of feedback parameters. When the temperature changes, the performance of optical power modulation devices such as AOM changes, and the resistance value in the circuit drifts with temperature, the optimal parameters change and the feedback effect may deteriorate. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the present invention provides a system and method for directly adjusting the optical power stability by using the inverted power detection signal. Based on the linear relationship between the optical power and the detector output signal, and between the modulation signal and the modulated optical power (when the optical power modulation device is in the linear region), the present invention proposes a laser power stabilization system with intuitive structure, easy adjustment, low cost and obvious effect.

[0006] The technical solution adopted by the present invention is:

[0007] 1. A system for directly regulating optical power stability using an inverted power detection signal:

[0008] The laser emitting device is used to emit laser and output laser with stable optical power.

[0009] The detection device is used for detecting the laser emitted by the laser emitting device and outputting a power detection signal.

[0010] The regulating driving device is used to determine the optimal inverting gain parameter through the detection signal of the detection device and directly adjust the laser emitted by the laser emitting device.

[0011] The laser emitting device comprises a laser, a polarizer, a first beam splitter and a second beam splitter. The laser, the polarizer and the first beam splitter are connected in sequence through spatial light or optical fiber. The first beam splitter and the second beam splitter are respectively connected to the detection device through spatial light or optical fiber. The laser emits laser light and is divided into a first laser with lower power and a first laser with higher power after passing through the polarizer and the first beam splitter in sequence. The first laser with lower power is incident on the detection device and the adjustment drive device in sequence. The first laser with higher power is incident on the adjustment drive device and the second beam splitter in sequence and is divided into a second laser with lower power and a second laser with higher power. The second laser with lower power is incident on the detection device and the adjustment drive device in sequence. The second laser with higher power is finally output as a laser with stable power, which is finally applied to precision detection and laser processing, etc. After the laser passes through the polarizer, the change of the polarization state of the laser is converted into a change of power, so as to avoid the introduction of power fluctuation due to the change of the polarization state when the laser passes through the polarization optical element later.

[0012] The polarizer of the laser emitting device is composed of a half-wave plate and a Greenland prism arranged in sequence when the spatial light is connected, or a spatial light polarizer is used; the polarizer adopts a fiber optic polarizer when the optical fiber is connected; the polarizer should have a higher polarization extinction ratio.

[0013] The first beam splitter and the second beam splitter are composed of a half-wave plate and a Greenland prism arranged in sequence or a half-wave plate and a polarization beam splitter PBS (Polarization Beam Splitter) arranged in sequence when spatial light is connected. The first beam splitter and the second beam splitter adopt a polarization-maintaining coupling beam splitter when optical fiber is connected.

[0014] The detection device includes a first photodetector and a second photodetector, a first beam splitter and the first photodetector are connected through spatial light or optical fiber, the first photodetector and the adjustment drive device are electrically connected through a coaxial cable or a signal line, a second beam splitter and the second photodetector are connected through spatial light or optical fiber, and the second photodetector and the adjustment drive device are electrically connected through a coaxial cable or a signal line; the first beam splitter inputs a first laser with a relatively low power into the first photodetector and then outputs a first power detection signal to the adjustment drive device, and the second beam splitter inputs a second laser with a relatively low power into the second photodetector and then outputs a second power detection signal to the adjustment drive device. The first photodetector and the second photodetector are general low-noise photoelectric amplifier detectors or photodetectors capable of fast response, characterized by working in a linear amplification region and being able to achieve a linear response of input optical power and output signal.

[0015] The regulating drive device includes a control circuit, a high-performance reference voltage source, a driver, an optical power modulator and a host computer. The first photodetector, the control circuit, the driver and the optical power modulator are electrically connected in sequence through a coaxial cable or a signal line, the high-performance reference voltage source and the control circuit are electrically connected in sequence through a coaxial cable or a signal line, and the second photodetector and the host computer are electrically connected in sequence through a coaxial cable or a signal line; the first power detection signal of the first photodetector and the reference voltage of the high-performance reference voltage source are input into the control circuit for comparison to obtain a modulation signal, the reference voltage of the high-performance reference voltage source is divided to obtain a bias voltage and input into the control circuit, the modulation signal and the bias voltage are added in the control circuit and then input into the driver for processing and then output as a drive signal to the optical power modulator for control, the first optical splitter inputs the first laser with a larger power into the optical power modulator controlled by the driver and then into the second optical splitter; the second photodetector outputs a second power detection signal to the host computer, and the host computer adjusts the inverting gain parameter of the control circuit to the optimal inverting gain parameter according to the second power detection signal. The reference voltage of the high-performance reference voltage source is used as a bias voltage after voltage division to ensure that the optical power modulator works in the linear region. The role of the bias voltage is to ensure that the optical power modulation device such as the AOM works in the linear range.

[0016] The control circuit is composed of an inverting differential amplifier circuit, a low-pass filter circuit and a common-phase adder circuit connected in sequence, or an inverting differential amplifier circuit and a common-phase adder circuit connected in sequence. The control circuit realizes the differential and inverting amplification of the first power detection signal output by the first photodetector and the reference voltage.

[0017] The inverting differential amplifier circuit is a low-noise active inverting differential amplifier circuit, and the input of the inverting differential amplifier circuit is the first power detection signal V i and reference voltage V ref , reference voltage V ref After being divided by the precision adjustable resistor R3 and the low temperature drift coefficient resistor R4, it is used as a reference voltage to connect the in-phase terminal of the operational amplifier U1 input. The first power detection signal V i The inverting end of the operational amplifier U1 input is connected through the precision adjustable resistor R1, and the inverting end is connected to the output end of the operational amplifier U1 through the low temperature drift coefficient resistor R2. The inverting differential amplifier circuit finally outputs the amplified signal V o1 To the low-pass filter circuit, amplify the signal V o1 The details are as follows:

[0018]

[0019] The low temperature drift coefficient resistor can reduce the influence of external temperature change on the stability of the system. In addition, the positions of R1 and R2, R3 and R4 can be swapped to achieve similar effects. The value of the reference voltage can usually be taken as the average value of the power detection signal output by the first photodetector.

[0020] The low-pass filter circuit is a second-order Butterworth low-pass filter circuit. The amplified signal V o1 After processing, the output modulation signal V o2 To the in-phase adder circuit. The low-pass filter circuit has a flat passband, small signal distortion and low delay.

[0021] Modulation signal V o2 and bias voltage V D The signals are inputted into a common phase adder circuit and added together; the common phase adder circuit adopts resistors with low temperature drift coefficient.

[0022] The driver and optical power modulator adopt an acousto-optic modulator (AOM) or an electro-optic modulator (EOM), which can achieve a linear response between the modulated optical power and the modulated signal.

[0023] 2. A method for adjusting the optical power stability of the system by directly adjusting the optical power stability using the inverse power detection signal:

[0024] Step 1) When the laser is transmitted in the laser emitting device, the detection device and the adjustment drive device, the inverting gain coefficient of the control circuit is changed in real time by the host computer to increase or decrease with a preset gradient. The inverting gain of the inverting differential amplifier circuit can be adjusted by adjusting the value of R1, and the inverting gain coefficient is the value of R2 / R1.

[0025] Step 2) After each change of the inverting gain coefficient, the host computer receives the second power detection signal input by the second photodetector in the next preset time period and obtains the relative power fluctuation of the second power detection signal, and then uses the Welch method to obtain the power spectral density PSD (Power Spectral Density) of the relative power fluctuation.

[0026] Step 3) According to the power spectral density PSD, the pwelch function is used to obtain the relative intensity noise of the second power detection signal, and the low-frequency part of the relative intensity noise is integrated to obtain the final result. When the final result is the smallest, the inverting gain coefficient at this time is obtained as the optimal inverting gain coefficient, and the control circuit under the optimal inverting gain coefficient is used to directly adjust the laser to achieve stable optical power.

[0027] To determine the optimal inverting gain parameter more accurately, the value of R2 / R1 can be controlled to increase or decrease with a smaller gradient near the current optimal parameter, and steps 2) and 3) can be repeated; finally, the inverting gain coefficient is monitored and adjusted regularly. Since the performance of devices such as optical power modulators may change with changes in ambient temperature, etc., regular monitoring and adjustment of the inverting gain coefficient will help the system adapt to changes in the external environment.

[0028] In the step 2), the relative power fluctuation ΔP of the second power detection signal is specifically as follows:

[0029]

[0030] Among them, V det represents a second power detection signal of the second photodetector, Represents the average value of the second power detection signal of the second photodetector within a preset time period.

[0031] In the step 3), the range of the low frequency part in the relative intensity noise is 0.1 Hz-10 Hz.

[0032] The relative intensity noise RIN of the second power detection signal is as follows:

[0033] RIN=20*log 10 S

[0034] Where S represents the power spectral density PSD of the relative power fluctuation.

[0035] The present invention is based on the linear relationship between optical power and detector output signal, and between modulation signal and diffracted optical power (taking AOM as an example). The power detection signal after input laser beam splitting can be compared with the reference voltage and then amplified in reverse phase, and directly used as the adjustment signal of the optical power modulator to compensate for optical power fluctuations. At the same time, the compensated optical power is monitored to determine the optimal inverse gain coefficient, and corresponding parameter adjustments are made when external influencing factors change. In addition, in the present invention, the reference voltage and its divided voltage are used as the reference voltage and bias voltage, which effectively improves the effect of power stabilization. Compared with the classical feedback regulation system using the proportional integral differential PID (Proportion Integral Differential) algorithm, the scheme proposed by the present invention has the advantages of simple and stable structure, rapid response, and easy parameter adjustment, and can be applied to the fields of precision measurement and laser precision processing.

[0036] The beneficial effects of the present invention are:

[0037] The present invention is based on the stable linear relationship between optical power and detector output signal, and between modulation signal and diffraction optical power, and proposes that the optical power can be regulated stably by using an inverted power detection signal. The structure is simple and stable, the delay is small, and the parameters are easy to adjust.

[0038] In the present invention, the reference voltage is used as the reference voltage, which can effectively improve the power stability effect. The low temperature drift coefficient resistor is selected to reduce the influence of the external environment temperature change on the system stability effect.

[0039] The present invention also uses simulation methods to discuss the optical power stabilization effect under different inverting gains, different delay times, with or without filters, and open / closed loop conditions. In the power regulation part, the open-loop control structure is used, which is expected to achieve a better stabilization effect than the closed-loop control. After the power regulation part, a second split light path and a photoelectric detector are set to monitor the power, thereby determining the optimal parameters and making the system adapt to changes in the external environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of a system for directly regulating optical power stability using an inverted power detection signal according to the present invention;

[0041] Figure 2 It is a schematic diagram of an inverting differential amplifier circuit of the system of the present invention;

[0042] Figure 3 A schematic diagram of a second-order Butterworth low-pass filter circuit of the system of the present invention;

[0043] Figure 4 A schematic diagram of a circuit of a common-phase adder of the system of the present invention;

[0044] Figure 5 It is a simulation implementation flow chart of the method of the present invention, wherein: Figure 5 (a) is a simulation implementation flow chart of the open-loop power stabilization system of the method of the present invention, Figure 5 (b) is a simulation implementation flow chart of a comparative closed-loop power stabilization system;

[0045] Figure 6 is the amplitude response and group delay diagram of the second-order Butterworth low-pass filter of the present invention, wherein, Figure 6 (a) is the amplitude response diagram of the second-order Butterworth low-pass filter of the present invention, Figure 6 (b) is a group delay diagram of the second-order Butterworth low-pass filter of the present invention;

[0046] Figure 7 is a typical simulation result diagram of the open-loop power stabilization system of the present invention, wherein: Figure 7 (a) is a time domain result diagram of the input and output of the open-loop power stabilization system of the present invention, Figure 7 (b) is a frequency domain result diagram of the input and output of the open-loop power stabilization system of the present invention;

[0047] Figure 8 : is a simulation result diagram of the open-loop power stabilization system of the present invention with and without filtering the detection signal, wherein: Figure 8 (a) is a simulation result diagram of an open-loop power stabilization system of the present invention after the detection signal is filtered. Figure 8 (b) is a simulation result diagram of the open-loop power stabilization system of the present invention in which the detection signal is not filtered;

[0048] Fig. 9 It is a simulation result diagram of the open-loop power stabilization system with different gains of the present invention;

[0049] Fig.10 is a typical simulation result diagram of the closed-loop power stabilization system of the present invention, wherein: Fig.10 (a) is a time domain result diagram of the input and output of the closed-loop power stabilization system of the present invention, Fig.10 (b) is a frequency domain result diagram of the input and output of the closed-loop power stabilization system of the present invention;

[0050] In the figure: laser 1, polarizing optical path 2, first splitting optical path 3, first photodetector 4, control circuit 5, reference voltage 6, driver 7, optical power modulator 8, second splitting optical path 9, second photodetector 10, host computer 11. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0052] like Figure 1 As shown, the system for directly regulating optical power stability by using an inverted power detection signal of the present invention includes a laser emitting device, a detection device and an adjustment drive device. The laser emitting device emits laser and outputs laser after optical power is stabilized. The detection device detects the laser emitted by the laser emitting device and outputs a power detection signal. The adjustment drive device determines the optimal inverted gain parameter through the detection signal of the detection device and directly adjusts the laser emitted by the laser emitting device.

[0053] The laser emitting device comprises a laser 1, a polarizer 2, a first beam splitter 3 and a second beam splitter 9. The laser 1, the polarizer 2 and the first beam splitter 3 are connected in sequence through spatial light or optical fiber. The first beam splitter 3 and the second beam splitter 9 are respectively connected to the detection device through spatial light or optical fiber. The laser 1 emits laser light and is divided into a first laser light with a smaller power and a first laser light with a larger power after passing through the polarizer 2 and the first beam splitter 3 in sequence. The first laser light with a smaller power is incident on the detection device and the adjustment drive device in sequence. The first laser light with a larger power is incident on the adjustment drive device and the second beam splitter 9 in sequence and is divided into a second laser light with a smaller power and a second laser light with a larger power. The second laser light with a smaller power is incident on the detection device and the adjustment drive device in sequence. The second laser light with a larger power is finally output as a laser light with a stable power, which is finally applied to precision detection and laser processing. After the laser light passes through the polarizer 2, the change of the polarization state of the laser light is converted into a change of power, so as to avoid the introduction of power fluctuation due to the change of the polarization state of the laser light when it passes through the polarization optical element in the future.

[0054] The polarizer 2 of the laser emitting device is composed of a half-wave plate and a Greenland prism arranged in sequence when the spatial light is connected, or a spatial light polarizer is used; the polarizer 2 is a fiber polarizer when the optical fiber is connected; the polarizer 2 should have a high polarization extinction ratio. The first beam splitter 3 and the second beam splitter 9 are composed of a half-wave plate and a Greenland prism arranged in sequence or a half-wave plate and a polarization beam splitter PBS arranged in sequence when the spatial light is connected, and the first beam splitter 3 and the second beam splitter 9 use a polarization-maintaining coupling beam splitter when the optical fiber is connected. The lasers with smaller and larger powers of the first beam splitter 3 and the second beam splitter 9 are the detection light and the transmission light respectively, and the splitting ratio of the detection light to the transmission light is α:(1-α), and α=0.01 can be taken as a typical example. The splitting ratio of the first beam splitter 3 and the second beam splitter 9 is set to 99:1, and the detection light occupies 1%, which can achieve a better effect. This ratio can be adjusted according to the input laser power and the selected photoelectric detector range during application.

[0055] The detection device includes a first photodetector 4 and a second photodetector 10, a first optical splitter 3 and the first photodetector 4 are connected through spatial light or optical fiber, the first photodetector 4 and the adjustment drive device are electrically connected through a coaxial cable or a signal line, a second optical splitter 9 and the second photodetector 10 are connected through spatial light or optical fiber, and the second photodetector 10 and the adjustment drive device are electrically connected through a coaxial cable or a signal line; the first optical splitter 3 inputs a first laser with a relatively low power into the first photodetector 4 and then outputs a first power detection signal to the adjustment drive device, and the second optical splitter 9 inputs a second laser with a relatively low power into the second photodetector 10 and then outputs a second power detection signal to the adjustment drive device. The first photodetector 4 and the second photodetector 10 are general low-noise photoelectric amplifier detectors or photodetectors capable of fast response, characterized by working in a linear amplification region and being able to achieve a linear response of input optical power and output signal.

[0056] The regulating driving device includes a control circuit 5, a high-performance reference voltage source 6, a driver 7, an optical power modulator 8 and a host computer 11. The first photodetector 4, the control circuit 5, the driver 7 and the optical power modulator 8 are electrically connected in sequence through a coaxial cable or a signal line, the high-performance reference voltage source 6 and the control circuit 5 are electrically connected in sequence through a coaxial cable or a signal line, and the second photodetector 10 and the host computer 11 are electrically connected in sequence through a coaxial cable or a signal line; the first power detection signal of the first photodetector 4 and the reference voltage of the high-performance reference voltage source 6 are input into the control circuit 5 for comparison to obtain a modulation signal The reference voltage of the high-performance reference voltage source 6 is divided to obtain the bias voltage and input into the control circuit 5. The modulation signal and the bias voltage are added in the control circuit 5 and input into the driver 7 for processing and then output the driving signal to the optical power modulator 8 for control. The first optical splitter 3 inputs the first laser with a larger power into the optical power modulator 8 controlled by the driver 7 and then inputs it into the second optical splitter 9; the second photodetector 10 outputs the second power detection signal to the host computer 11, and the host computer 11 adjusts the inverting gain parameter of the control circuit 5 to the optimal inverting gain parameter according to the second power detection signal. The reference voltage of the high-performance reference voltage source 6 is divided as the bias voltage to ensure that the optical power modulator 8 works in the linear region. The role of the bias voltage is to ensure that the optical power modulation device such as AOM works in the linear range. The driver 7 and the optical power modulator 8 use an acousto-optic modulator AOM or an electro-optic modulator EOM, which can achieve a linear response of the modulated optical power and the modulation signal.

[0057] The control circuit 5 is composed of an inverting differential amplifier circuit, a low-pass filter circuit and a common-phase adder circuit connected in sequence, or is composed of an inverting differential amplifier circuit and a common-phase adder circuit connected in sequence. The control circuit 5 realizes the differential and inverting amplification of the first power detection signal output by the first photodetector 4 and the reference voltage.

[0058] like Figure 2 As shown, the inverting differential amplifier circuit is a low-noise active inverting differential amplifier circuit, and the input of the inverting differential amplifier circuit is the first power detection signal V i and reference voltage V ref , reference voltage V ref After being divided by the precision adjustable resistor R3 and the low temperature drift coefficient resistor R4, it is used as a reference voltage to connect the in-phase terminal of the operational amplifier U1 input. The first power detection signal V i The inverting end of the operational amplifier U1 input is connected through the precision adjustable resistor R1, and the inverting end is connected to the output end of the operational amplifier U1 through the low temperature drift coefficient resistor R2. The inverting differential amplifier circuit finally outputs the amplified signal V o1 To the low-pass filter circuit, amplify the signal V o1 The details are as follows:

[0059]

[0060] The low temperature drift coefficient resistor can reduce the influence of the external temperature change on the stability of the system. In addition, the positions of R1 and R2, R3 and R4 can be swapped to achieve a similar effect. The value of the reference voltage can usually be taken as the average value of the power detection signal output by the first photodetector 4.

[0061] like Figure 3 As shown, it is a schematic diagram of a second-order Butterworth low-pass filter circuit. The low-pass filter circuit is a second-order Butterworth low-pass filter circuit. The amplified signal V o1 After processing, the output modulation signal V o2 To the in-phase adder circuit. The low-pass filter circuit has a flat passband, small signal distortion, and low delay. The modulation signal V o2 and bias voltage V D The two signals are input to the common phase adder circuit and added together; the common phase adder circuit uses low temperature drift coefficient resistors. O1 The input terminal is V O2 The output terminal is U2, and the operational amplifier is U2. The second-order Butterworth low-pass filter is widely used due to its flat passband, excellent characteristics, and convenient design. However, its transition band decreases at a normal speed, and there is signal distortion caused by nonlinear dependence. Figure 3It can be seen that the passband gain of the low-pass filter is 1, and R5=R6=R, C1=C2=C, then ω0=2πf0=1 / RC, ω0 and f0 are the cutoff angular frequency and frequency of the first-order filter respectively, and the 3dB cutoff frequency is equal to 0.37f0. The capacitor C can generally be 1μF, so the value of the resistor R can be determined. The function of the filter is to remove high-frequency glitches in the detection optical power signal. Because of the delay, these glitches may cause oscillations in the closed-loop system. In the open-loop system proposed by the present invention, although there is no oscillation, due to the delay, the high-frequency power fluctuation is difficult to be compensated, but it will increase the high-frequency RIN of the stabilized optical power.

[0062] like Figure 4 As shown, it is a schematic diagram of the in-phase adder circuit, where V O2 The input terminal is V O3 The output terminal is R 10 is the feedback resistor, and U3 is the operational amplifier. D is the bias voltage, which is obtained by dividing the reference voltage to ensure that the optical power modulator works in the linear region. The modulation signal V O3 The details are as follows:

[0063]

[0064] The method for adjusting the optical power stability system by directly adjusting the optical power stability by using the reverse power detection signal of the present invention is as follows:

[0065] Step 1) When the laser is transmitted in the laser emitting device, the detection device and the adjustment drive device, the inverting gain coefficient of the control circuit 5 is changed in real time by the host computer 11 to increase or decrease with a preset gradient. The inverting gain of the inverting differential amplifier circuit can be adjusted by adjusting the value of R1, and the inverting gain coefficient is the value of R2 / R1.

[0066] Step 2) After each change of the inverting gain coefficient, the host computer 11 receives the second power detection signal input by the second photodetector 10 in the next preset time period and obtains the relative power fluctuation of the second power detection signal, and then uses the Welch method to obtain the power spectral density PSD of the relative power fluctuation. The relative power fluctuation ΔP of the second power detection signal is as follows:

[0067]

[0068] Among them, V det represents the second power detection signal of the second photodetector 10, It represents the average value of the second power detection signal of the second photodetector 10 within a preset time period.

[0069] Step 3) According to the power spectrum density PSD, the relative intensity noise of the second power detection signal is obtained by using the pwelch function, and the low-frequency part in the relative intensity noise is integrated to obtain the final result, until the final result is the smallest, the inverting gain coefficient at this time is obtained as the best inverting gain coefficient, and the control circuit 5 under the best inverting gain coefficient directly adjusts the laser to achieve stable optical power. The range of the low-frequency part in the relative intensity noise is 0.1Hz-10Hz.

[0070] The relative intensity noise RIN of the second power detection signal is as follows:

[0071] RIN=20*log 10 S

[0072] Where S represents the power spectral density PSD of the relative power fluctuation.

[0073] To determine the optimal inverting gain parameter more accurately, the value of R2 / R1 can be controlled to increase or decrease with a smaller gradient near the current optimal parameter, and steps 2) and 3) can be repeated; finally, the inverting gain coefficient is monitored and adjusted regularly. Since the performance of devices such as optical power modulators may change with changes in ambient temperature, etc., regular monitoring and adjustment of the inverting gain coefficient will help the system adapt to changes in the external environment.

[0074] In the power stabilization system of the present invention, the fluctuation of the reference voltage determines the upper limit of the final stabilization result. Selecting a reference voltage with less fluctuation as the reference voltage can effectively improve the effect of power stabilization. At the same time, this requires that the resistance of the voltage divider resistors R3 and R4 drifts little with temperature. The current typical ultra-low temperature drift coefficient resistor can reach a temperature drift coefficient of 5PPM.

[0075] According to the above adjustment ideas, the power adjustment part of the present invention is simulated to verify the feasibility of the present invention. Figure 5 As shown in the figure, it is a simulation implementation flow chart. Figure 5As shown in (a), it is the open-loop power stabilization system of the system of the present invention during the simulation process. First, the measured AOM diffraction optical power signal is differentially inverted and input into a second-order Butterworth low-pass filter for filtering, and then multiplied by the AOM linear corresponding coefficient. Then, it is delayed and added to the measured AOM diffraction optical power signal and output as an open-loop output. The input data of the system is the measured +1 level 1550nm diffraction optical power of the optical fiber AOM that has not been power stabilized. The sampling rate is 10kHz, and the detector used is the DET20C2 indium gallium arsenide bias detector. The simulated output signal is the stabilized optical power signal, which is also the monitoring signal received by the second photodetector 10. The simulation process takes into account the influence of the inverting gain deviation, circuit delay and filter on the power stabilization effect of the system, but does not consider the fluctuation of the reference voltage, the nonlinearity of optical power modulation devices such as AOM, and the noise of the photodetector. At the same time, in addition to the open-loop structure proposed in the present invention, the simulation also compares the power stabilization effect under the closed-loop condition, such as Figure 5 As shown in (b), it is a closed-loop power stabilization system for comparison in the simulation process. First, the measured AOM diffraction light power signal is differentially inverted and input into a second-order Butterworth low-pass filter for filtering, then multiplied by the AOM linear response coefficient, and then delayed and added to the measured AOM diffraction light power signal before being output as a closed-loop output and the above-mentioned differential inversion processing is repeated.

[0076] like Figure 6 As shown in the figure, it is the amplitude response and group delay of the second-order Butterworth low-pass filter. The filter is generated by the filterDesigner tool, with the cutoff frequency set to 1000Hz. The passband is flat, but the transition band decreases at an average speed, with a maximum delay of nearly 3 samples, i.e. 0.3ms (sampling rate 10kHz). The amplitude response of the filter is basically stable at 0dB within the passband, as shown in the figure below. Figure 6 (a) and Figure 6 As shown in (b), at different frequencies, the delay caused by the filter is different, and the maximum delay will be 2.8 samples. The delay will cause a certain degree of distortion in the signal, affecting the effect of the anti-phase regulation. A flat amplitude response is conducive to the stability and performance of the system.

[0077] like Figure 7 As shown in Figure 1, it is a typical simulation result of an open-loop power stabilization system. Figure 7 (a) and Figure 7As shown in (b), the optimal inverting gain under this simulation condition is G = -100. When a 1kHz second-order Butterworth low-pass filter is added at the optimal inverting gain and a delay of 0.3ms, a low-frequency power stabilization effect of more than -30dB can be achieved in the frequency band of 10Hz and below, where the vertical axis is the output optical power in watts W, and std represents the standard deviation of the output optical power, which reflects the power fluctuation of the output light to a certain extent.

[0078] like Figure 8 As shown in Figure 1, it is the simulation result diagram of the open-loop power stabilization system with and without filtering of the detection signal. Figure 8 (a) and Figure 8 As shown in (b), when the detection signal passes through the filter first, the high-frequency component of the output optical power is reduced, and the standard deviation drops from 0.03086mW without passing through the filter to 0.029933mW. Since the filter itself will introduce a maximum delay of 0.3ms and a certain degree of signal distortion, the RIN of the output optical power is generally raised at low frequencies.

[0079] like Fig. 9 As shown in FIG. 1 , it is a simulation result diagram of an open-loop power stabilization system with different gains. The sensitivity of the open-loop system to the inverting gain parameter is more reflected at the low frequency of RIN. The deviation from the optimal parameter will reduce the compensation effect of the power stabilization system for low-frequency power fluctuations. Therefore, by monitoring the RIN of the optical power at the host computer 11, the optimal gain can be determined in practical applications.

[0080] Fig.10 This is a typical simulation result diagram of a closed-loop power stabilization system. Fig.10 (a) and Fig.10 As shown in (b), when the inverting gain G = -99.5 and the delay is 0.3ms, the RIN of the output optical power is reduced by 6dB compared to the input when a 1kHz second-order Butterworth low-pass filter is added. In this method, the open-loop regulation can achieve a low-frequency power stabilization effect of more than -30dB in the frequency band of 10Hz and below. When the power has a large offset, the open-loop system can achieve more effective and rapid compensation. One of the reasons for the poor closed-loop effect in this method is the existence of delays and signal distortion. The presence of delays may also cause oscillations in the output power. The defect of the open-loop system is that it is more sensitive to parameter changes and depends on the linearity of the adjustment drive device, so regular monitoring and adjustment are required. In addition, the closed-loop result is sensitive to the inverting gain parameter. When the inverting gain G>100, the output optical result will diverge.

[0081] In summary, the simulation results verify the feasibility of the present invention. Therefore, the system solution of directly modulating optical power with an inverted power detection signal of the present invention has a simple and stable structure, can respond quickly, has easy parameters to adjust, and achieves a good control effect.

[0082] What is disclosed above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or modifications within the technical scope disclosed in the present invention, which should be covered within the protection scope of the present invention.

Claims

1. A system for directly regulating optical power stability using an inverted power detection signal, characterized in that: include: A laser emitting device, used for emitting laser light and outputting laser light with stable optical power; A detection device, used for detecting the laser emitted by the laser emitting device and outputting a power detection signal; The regulating driving device is used to determine the optimal inverting gain parameter through the detection signal of the detection device and directly adjust the laser emitted by the laser emitting device.

2. The system for directly regulating optical power stability using an inverted power detection signal according to claim 1, characterized in that: The laser emitting device comprises a laser (1), a polarizer (2), a first beam splitter (3) and a second beam splitter (9). The laser (1), the polarizer (2) and the first beam splitter (3) are connected in sequence through spatial light or optical fiber. The first beam splitter (3) and the second beam splitter (9) are respectively connected to a detection device through spatial light or optical fiber. The laser (1) emits laser light and is divided into a first laser light with a smaller power and a first laser light with a larger power after passing through the polarizer (2) and the first beam splitter (3) in sequence. The first laser light with a smaller power is incident on the detection device and the adjustment drive device in sequence. The first laser light with a larger power is incident on the adjustment drive device in sequence and the second beam splitter (9) is divided into a second laser light with a smaller power and a second laser light with a larger power. The second laser light with a smaller power is incident on the detection device and the adjustment drive device in sequence. The second laser light with a larger power is finally output as a laser light with a stable power.

3. The system for directly regulating optical power stability using an inverted power detection signal according to claim 2, characterized in that: The polarizer (2) of the laser emitting device is composed of a half-wave plate and a Greenland prism arranged in sequence when the spatial light is connected, or a spatial light polarizer is used; the polarizer (2) is a fiber optic polarizer when the optical fiber is connected; The first optical splitter (3) and the second optical splitter (9) are composed of a half-wave plate and a Greenland prism arranged in sequence or a half-wave plate and a polarization beam splitter PBS arranged in sequence when spatial light is connected. The first optical splitter (3) and the second optical splitter (9) use a polarization-maintaining coupling beam splitter when optical fiber is connected.

4. The system for directly regulating optical power stability using an inverted power detection signal according to claim 2, characterized in that: The detection device comprises a first photodetector (4) and a second photodetector (10); a first beam splitter (3) and the first photodetector (4) are connected via spatial light or optical fiber, the first photodetector (4) and an adjustment drive device are electrically connected, a second beam splitter (9) and the second photodetector (10) are connected via spatial light or optical fiber, the second photodetector (10) and the adjustment drive device are electrically connected; the first beam splitter (3) inputs a first laser with a relatively small power into the first photodetector (4) and then outputs a first power detection signal to the adjustment drive device; the second beam splitter (9) inputs a second laser with a relatively small power into the second photodetector (10) and then outputs a second power detection signal to the adjustment drive device.

5. The system for directly regulating optical power stability using an inverted power detection signal according to claim 4, characterized in that: The regulating drive device comprises a control circuit (5), a reference voltage source (6), a driver (7), an optical power modulator (8) and a host computer (11); the first photodetector (4), the control circuit (5), the driver (7) and the optical power modulator (8) are electrically connected in sequence; the reference voltage source (6) and the control circuit (5) are electrically connected in sequence; the second photodetector (10) and the host computer (11) are electrically connected in sequence; the first power detection signal of the first photodetector (4) and the reference voltage of the reference voltage source (6) are input into the control circuit (5) for comparison to obtain a modulation signal; the reference voltage of the reference voltage source (6) is electrically connected to ... The bias voltage is obtained by dividing the voltage in the control circuit (5), and then input into the control circuit (5); the modulation signal and the bias voltage are added in the control circuit (5), and then input into the driver (7), and then processed and output as a drive signal to the optical power modulator (8) for control; the first optical splitter (3) inputs the first laser with a larger power into the optical power modulator (8) controlled by the driver (7), and then inputs into the second optical splitter (9); the second photodetector (10) outputs a second power detection signal to the host computer (11), and the host computer (11) adjusts the inverting gain parameter of the control circuit (5) to an optimal inverting gain parameter according to the second power detection signal.

6. The system for directly regulating optical power stability by using an inverted power detection signal according to claim 5, characterized in that: The control circuit (5) is composed of an inverting differential amplifier circuit, a low-pass filter circuit and an in-phase adder circuit connected in sequence, or is composed of an inverting differential amplifier circuit and an in-phase adder circuit connected in sequence.

7. The system for directly regulating optical power stability by using an inverted power detection signal according to claim 5, characterized in that: The driver (7) and the optical power modulator (8) are acousto-optic modulators (AOM) or electro-optic modulators (EOM).

8. The method for adjusting a system for directly adjusting optical power stability by using an inverted power detection signal according to any one of claims 1 to 7, characterized in that: include: Step 1) When the laser is transmitted in the laser emitting device, the detection device and the adjustment drive device, the inverting gain coefficient of the control circuit (5) is changed in real time by the host computer (11) to increase or decrease by a preset gradient; Step 2) after each change of the inverting gain coefficient, the host computer (11) receives the second power detection signal input by the second photodetector (10) in the next preset time period and obtains the relative power fluctuation of the second power detection signal, and then uses the Welch method to obtain the power spectral density PSD of the relative power fluctuation; Step 3) Obtain the relative intensity noise of the second power detection signal according to the power spectral density PSD, integrate the low-frequency part of the relative intensity noise to obtain the final result, until the final result is minimum, obtain the inverting gain coefficient at this time as the optimal inverting gain coefficient, and use the control circuit (5) under the optimal inverting gain coefficient to directly adjust the laser to achieve stable optical power.

9. The method for adjusting a system for directly adjusting optical power stability by using an inverted power detection signal according to claim 8, characterized in that: In the step 2), the relative power fluctuation ΔP of the second power detection signal is specifically as follows: Among them, V det represents a second power detection signal of the second photodetector (10), Represents the average value of the second power detection signal of the second photodetector (10) within a preset time period.

10. The method for adjusting a system for directly adjusting optical power stability by using an inverted power detection signal according to claim 8, characterized in that: In the step 3), the range of the low frequency part in the relative intensity noise is 0.1 Hz-10 Hz.

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