High-precision laser power stabilization control method based on built-in diode monitoring

Abstract

The application discloses a kind of high-precision light power stable control method of laser based on built-in diode monitoring.The method comprises: fluctuation signal is input to the control unit of light power control system, control unit calculates the control voltage of optical power attenuator according to the output of built-in diode and photodetector, so as to realize the stable control of system output light power under the condition of ambient temperature fluctuation.The output signal of laser tube built-in diode is added to the feedback input of original control system in the application, as the basis for monitoring the fluctuation of light splitting ratio, further improve the output light power stability of stable power system on the basis of maintaining the miniaturization of system, improve SERF inertial measurement accuracy.

Description

Technical Field

[0001] This invention belongs to the field of SERF inertial measurement laser power stabilization, specifically relating to a high-precision optical power stabilization control method for lasers based on built-in diode monitoring. Background Technology

[0002] Inertial measurement has wide applications in fundamental physics research and vehicle navigation. Navigation technology based on inertial measurement (INS) differs from other navigation technologies (such as satellite navigation, radio navigation, geomagnetic navigation, and astronomical navigation) in that it is independent of any external information, provides comprehensive, real-time, continuous, and highly autonomous navigation information. Furthermore, it can be applied to civilian fields such as drones, autonomous vehicles, and intelligent robots, serving the development of the national economy. The basic principle of INS is based on Newton's laws of motion. After measuring the angular and linear motion of the vehicle relative to inertial space, it obtains the vehicle's attitude and linear motion information through integration. The attitude information provides a spatial reference for calculating the position information. The measurement of angular and linear motion is accomplished by gyroscopes and accelerometers, respectively. Because the navigation information calculation process requires integration, measurement errors accumulate over time. Therefore, gyroscopes and accelerometers need to possess good long-term stability to complete long-term navigation tasks. The navigation and positioning error caused by the bias error of the gyroscope increases with the cube of the navigation time, while the navigation and positioning error caused by the bias error of the accelerometer increases with the square of the navigation time. Therefore, the gyroscope is usually the core component that restricts the improvement of the accuracy of the inertial navigation system. Traditional high-precision gyroscopes are usually large and expensive. Small size, low cost, and high precision gyroscopes are an important research direction and future development trend in the field of inertial navigation technology.

[0003] Laser power fluctuations are one of the key factors affecting the long-term stability of SERF (spin-free exchange relaxation) inertial measurements. Specifically, pump laser power fluctuations affect the scale factor stability and zero-bias stability of SERF inertial measurements by influencing longitudinal optical pump error and longitudinal optical frequency shift error. Detecting laser power fluctuations directly affects the scale factor stability of SERF inertial measurements. Furthermore, detecting lateral laser pump error and lateral optical frequency shift error directly affects the zero-bias stability of SERF inertial measurements. Therefore, suppressing laser power fluctuations is of great significance for improving the long-term stability of SERF inertial measurements. Summary of the Invention

[0004] To address the issue that temperature variations in traditional power stabilization schemes can cause changes in the splitting ratio of polarization beam splitters, resulting in splitting errors, this invention provides a high-precision optical power stabilization control method for lasers based on built-in diode monitoring. This method can reduce splitting errors caused by temperature changes and further improve power stability compared to traditional closed-loop power stabilization schemes.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for high-precision optical power stabilization control of a laser based on built-in diode monitoring includes the following steps:

[0007] Step 1: Define the optical propagation direction as the Z-axis, the X-axis as the horizontal direction perpendicular to the Z-axis, and the Y-axis as the direction perpendicular to both the X-axis and Z-axis. Adjust the laser to its normal operating state and set the laser's output power P. i As the input to the stable power system, the signal acquisition and amplification circuit converts the output signal of the built-in diode into a voltage signal V. i ;

[0008] The stable power system includes an optical isolator, a half-wave plate liquid crystal variable noise attenuator, a half-wave plate, and a polarizing beam splitter. The laser emitted from the laser passes through the stable power system to obtain two output beams. One output beam serves as the output of the stable power system, and the actual output optical power of the stable power system is denoted as P. out The other output beam serves as the feedback optical path, and the feedback optical power is denoted as P. in The signal acquisition and amplification circuit converts the intensity of the feedback beam into a voltage signal V. in ;

[0009] Step 2: Ideally, the laser source output light is purely linearly polarized. However, in reality, the laser output has a slight ellipticity, meaning that a small amount of linearly polarized light component exists in the direction perpendicular to the linearly polarized light. Therefore, its Jones vector E... α Represented as:

[0010]

[0011] Where ε represents the angle between the overall polarization direction of the polarized light and the X-axis of the light path, i.e., the polarization angle; α represents the angle between the line connecting the major and minor axes of the polarized light with ellipticity and its major axis, i.e., the ellipticity angle; and i represents the unit imaginary number.

[0012] The Jones vector of the output beam after passing through the power stabilization system is expressed as:

[0013] E out =G GL_T G HWP2 G ANA G LCVR (δ)G POL G HWP1 E α

[0014] In the formula, G GL_T G HWP2 G ANA GLCVR (δ), G POL G HWP1 These are the Jones matrix of the polarizing beam splitter transmission direction, half-wave plate, analyzer, liquid crystal variable phase retarder, polarizer, and half-wave plate, respectively.

[0015] in,

[0016] Among them, T S1 T S2 T S3 T represents the transmittance of S-rays from the polarizer, analyzer, and polarizing beam splitter, respectively. P1 T P2 T P3 Let θ1 represent the transmittance of P-beams in the polarizer, analyzer, and polarizing beam splitter, respectively; θ2 represent the angle between the fast axis of the half-wave plate and the X-axis of the optical path; θ3 represent the angle between the fast axis of the half-wave plate and the X-axis of the optical path; and δ represent the phase delay of the liquid crystal variable phase retarder, the magnitude of which is controlled by the input voltage of the liquid crystal. The expression for calculating the intensity of the output beam is as follows:

[0017]

[0018] In the formula, For E out The transpose of the matrix, L1, L2, and N1-N4 are constant algebraic expressions, and:

[0019] L1=N1(cosεcosα-isinεsinα)+iN2(sinεcosα+icosεsinα)

[0020] L2=N3(cosεcosα-isinεsinα)+iN4(sinεcosα+icosεsinα)

[0021] in:

[0022]

[0023]

[0024]

[0025]

[0026] Based on the above formula, the theoretical output optical power of the stable power system optical path can be derived from the power value at the built-in diode as follows:

[0027]

[0028] In the formula, k is the power efficiency from the optical power at the built-in monitoring diode of the laser to the output beam power of the stable power system, and P is the power efficiency. o ′ ut The corresponding voltage signal is represented as V o ′ ut :

[0029]

[0030] The Jones vector representation of the feedback light in a stable power system is:

[0031] E in =G GL_R G HWP2 G ANA G LCVR (δ)G POL G HWP1 E α

[0032] in,

[0033]

[0034] G GL_R It is the Jones matrix of the reflected light from the polarizing beam splitter, R P3 R S3 These are the P-ray reflectance and S-ray reflectance of the polarizing beam splitter, respectively. The relationship between the output light and the feedback light can be obtained as follows:

[0035]

[0036] The splitting ratio of a polarizing beam splitter is related to the polarization state of the incident light. Temperature changes will cause changes in the polarization state of the laser beam. Due to the imperfections of polarization devices, the laser beam that passes through the polarizer will retain a certain ellipticity and azimuth angle of the original laser beam. Therefore, changes in the ellipticity and azimuth angle of the laser beam will partially pass through the polarization device. This causes the changes in the laser polarization state caused by temperature drift to be coupled into the system output, resulting in splitting errors.

[0037] Take a set of theoretical output optical power values ​​obtained from the initial short-term stable operation of the stable power system, and average them, denoted as P′. out0 The corresponding voltage value is V′ out0 Let V′ be the denoted V′. out With V′ out0 The difference is Err′, which is the theoretical value of the output optical power obtained from the derivation relative to P′. out0 Voltage signal error:

[0038] Err′=V′ out -V′ out0

[0039] Step 3: The photodetector acquires the feedback optical power signal and converts the intensity of the feedback beam into a voltage signal V. in Let h be the ratio of the transmittance to the refractive index of the polarizing beam splitter, and V″ be the simulated output optical power voltage signal. out =hV in , V″ out With feedback optical power setting value V set By subtracting the values, we obtain the error Err″ = V″ between the feedback optical power and the setpoint. out -V set ;

[0040] Step 4: Relative the theoretical value of the output optical power to P′ out0 The total error value of the stable power system, Err = Err′ + Err″, is obtained by adding the voltage signal error and the error signal between the feedback optical power and the feedback optical power setpoint.

[0041] Step 5: Allocate appropriate proportional, integral, and derivative PID parameters according to the total error Err value of the stable power system. The PID algorithm calculates the required input voltage of the liquid crystal variable phase delay device based on the Err value and changes the transmittance of the liquid crystal variable noise attenuator.

[0042] Furthermore, the simulated temperature drift value is obtained by reading the liquid crystal driving voltage output from the stable power system and the output signal of the built-in diode of the laser tube; the relationship between the phase delay δ of the liquid crystal variable phase delayer and the driving voltage V is as follows:

[0043]

[0044] Among them, V0, V C M and d are the performance parameters of the liquid crystal variable phase retarder, d is the diameter of the mirror of the liquid crystal variable phase retarder, Δn is the thickness of the waveplate of the liquid crystal variable phase retarder, λ is the incident light wavelength, V is the driving voltage applied to the liquid crystal variable phase retarder, and δ0 is a constant value related to the liquid crystal variable phase retarder and the incident wavelength.

[0045] Once the laser, optical components, and optical path are determined, the actual output optical power P of the stable power system is... out The power value P at the monitoring diode of the input power stabilization system. i Given that the input voltage-phase delay relationship of the liquid crystal variable phase delay device (LCD) is known, and is a function of the phase delay δ, the theoretical value of the output optical power P′ can be derived by reading the driving voltage and built-in diode data of the LCD by the control system. out :

[0046] P′ out =f(P i ,δ)

[0047] P′ out The corresponding voltage signal V′ out for:

[0048] V′ out =f(V i ,V)

[0049] Furthermore, steps two and four include acquiring the output of the built-in diode of the laser tube and modeling it to obtain the temperature drift error, and adding the temperature drift error to the error signal of the feedback control.

[0050] Let I be the current of the output signal from the built-in diode. i The voltage signal after the built-in diode output signal passes through the signal acquisition and amplification circuit is V. i The theoretical value of the output optical power voltage signal obtained by the power compensation model is:

[0051] V′ out =f(V i ,V)

[0052] Take the average of a set of theoretical output optical power values ​​obtained from the initial short-term stable operation of the stable power system, denoted as P′. out0 The corresponding voltage value is V′ out0 Let V′ be the denoted V′. out With V′ out0 The difference is Err′, which only contains the error data of the spectral error caused by temperature drift. When using the feedback light signal separated by the polarizing beam splitter for feedback control, Err′, which only contains the spectral error, is added to the error signal Err″ between the feedback light power and the feedback light power set value described in step three to compensate for the spectral error caused by temperature drift in the feedback control.

[0053] The beneficial effects of this invention are as follows:

[0054] This invention proposes a high-precision optical power stabilization control method for lasers based on built-in diode monitoring. By modeling and processing the output signal of the built-in diode of the laser to obtain an error signal containing only temperature drift error, this error signal is added to the error signal of traditional closed-loop control. This reduces the problem of beam splitting error in traditional closed-loop control. This method is more accurate than the method of using temperature data to model and compensate for temperature drift, and can achieve a higher level of laser power stabilization. Attached Figure Description

[0055] Figure 1 A schematic diagram showing the elliptic angle and azimuth angle of the original laser polarization state emitted from the laser.

[0056] Figure 2This is a hardware system block diagram of the laser high-precision optical power stabilization control method based on built-in diode monitoring according to the present invention;

[0057] Figure 3 This is a flowchart of the high-precision optical power stabilization control method for lasers based on built-in diode monitoring, as described in this invention. Specific implementation methods

[0058] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0059] Figure 2 This is a hardware structure diagram of the present invention, where 1 represents a laser, 2 represents an optical isolator, 3 represents a half-wave plate, 4 represents a Glan prism used as a polarizer, 5 represents a liquid crystal variable phase delay unit, 6 represents a Glan prism used as an analyzer, 4, 5, and 6 together constitute a liquid crystal variable noise attenuator, 7 represents a half-wave plate used to adjust the beam splitting ratio, 8 represents a polarizing beam splitter, 9 represents a photodetector, and 10 represents an electronic control system. The electronic control system performs analog-to-digital conversion on the signals acquired by the system, executes the control algorithm and completes the digital-to-analog conversion, outputs the required liquid crystal driving voltage, and thereby changes the transmittance of the liquid crystal variable noise attenuator to achieve control over the optical power. Figure 3 The flowchart for this method is as follows:

[0060] Step 1: Define the optical propagation direction as the Z-axis, the X-axis as the horizontal direction perpendicular to the Z-axis, and the Y-axis as the direction perpendicular to both the X-axis and Z-axis. A schematic diagram of the polarization state of the laser beam emitted is shown below. Figure 1 As shown in the figure, ε represents the angle between the overall polarization direction of the polarized light and the X-axis of the optical path, i.e., the polarization angle; α represents the angle between the line connecting the major and minor axes of the elliptic polarized light and its major axis, i.e., the ellipticity angle. The laser is adjusted to its normal operating state, and the laser's output power P... i As the input to the stable power system, the signal acquisition and amplification circuit converts the output signal of the built-in diode of the laser tube into a voltage signal V. i .

[0061] The laser beam passes sequentially through an optical isolator, a half-wave plate, a liquid crystal variable noise attenuator, another half-wave plate, and a polarizing beam splitter, resulting in two output beams. One output beam serves as the output of the stable power system, and the actual output optical power of the stable power system is denoted as P. out The other output beam serves as the feedback optical path, and the feedback optical power is denoted as P. inThe signal acquisition and amplification circuit converts the intensity of the feedback beam into a voltage signal V. in ;

[0062] Step 2: The main control chip reads V i The theoretical value of the output optical power voltage signal is obtained after calculation, based on the liquid crystal control voltage V.

[0063] V′ out =f(V i ,V)

[0064] The main control chip records a set of simulated external optical power voltage signals obtained during the initial 120 seconds of stable system operation and takes the average value, which is denoted as V′. out0 In actual working environments, temperature fluctuations are slow, and a traditional PID control scheme is used within 120 seconds.

[0065] After 120 seconds, subtract V′ from the voltage signal of the theoretical output optical power value. out0 ,get:

[0066] Err′=V′ out -V′ out0

[0067] Step 3: The photodetector collects the feedback optical power signal and converts it into a voltage signal V. in Let h be the ratio of the transmittance to the refractive index of the polarizing beam splitter. From this, the output optical power obtained after model fitting is V″. out =hV in , V″ out With feedback optical power setting value V set By subtracting the values, we obtain the error Err″ = V″ between the feedback optical power and the setpoint. out -V set ;

[0068] Step 4: Relative to P′ the theoretical value of the output optical power out0 The total error value of the stable power system, Err = Err′ + Err″, is obtained by adding the voltage signal error and the error signal between the feedback optical power and the feedback optical power setpoint.

[0069] Step 5: Allocate PID (proportional, integral, derivative) parameters according to the total error value of the stable power system. The PID algorithm calculates the required input voltage of the liquid crystal variable phase delayer based on the Err value. The main control chip drives the DA chip to provide the corresponding driving voltage to the liquid crystal variable phase delayer, thereby changing the transmittance of the liquid crystal variable noise attenuator and stabilizing the system output optical power.

[0070] The simulated temperature drift value is obtained by reading the liquid crystal driving voltage and the output signal of the laser tube's built-in diode from the system output in step two. The relationship between the phase delay δ of the liquid crystal variable phase delayer and the driving voltage V is as follows:

[0071]

[0072] Among them, V0, V C M and d are the performance parameters of the liquid crystal variable phase retarder, d is the diameter of the mirror of the liquid crystal variable phase retarder, Δn is the thickness of the waveplate of the liquid crystal variable phase retarder, λ is the incident light wavelength, V is the driving voltage applied to the liquid crystal variable phase retarder, and δ0 is a constant value related to the liquid crystal variable phase retarder and the incident wavelength.

[0073] Once the laser, optical components, and optical path are determined, the actual output optical power P of the stable power system is... out The power value P at the built-in diode of the stable power system i Given the input voltage-phase delay relationship of the liquid crystal variable phase delay device as a function of phase delay δ, the theoretical output optical power, simulated from the data of the built-in diodes, can be obtained by reading the control voltage of the liquid crystal through the control system.

[0074]

[0075] It can be written as:

[0076] P′ out =f(P i ,δ)

[0077] The corresponding voltage signal is:

[0078] V′ out =f(V i ,V)

[0079] According to step five, the main control chip performs PID calculations and applies the PID algorithm to the total error Err of the stable power system. The algorithm is characterized by calculating the control quantity based on Err at this moment and the previous moments.

[0080]

[0081] Where del is the voltage control quantity, T is the integral time constant, and T D The differential time constant;

[0082] Discretize the PID:

[0083] del=kp·Err1+ki·SUM+kd(Err1-Err2)

[0084] Where SUM is the sum of the differences Err from the previous time step, Err1 represents the total error value of the steady-state system at this time step, Err2 represents the total error value of the steady-state system at the previous time step, and kp, ki, and kd are the proportional, integral, and derivative parameters of the PID control algorithm, respectively.

[0085] The contents not described in detail in this specification are prior art known to those skilled in the art. Those skilled in the art will readily understand that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for high-precision optical power stabilization control of a laser based on built-in diode monitoring, characterized in that, Includes the following steps: Step 1: Define the optical propagation direction as the Z-axis, the X-axis as the horizontal direction perpendicular to the Z-axis, and the Y-axis as the direction perpendicular to both the X-axis and Z-axis; adjust the laser to its normal operating state, and set the laser's output power P... i As the input to the stable power system, the signal acquisition and amplification circuit converts the output signal of the built-in diode into a voltage signal V. i ; The stable power system includes an optical isolator, half-wave plate 1, a liquid crystal variable noise attenuator, half-wave plate 2, and a polarizing beam splitter. The laser beam emitted from the laser passes through the stable power system to obtain two output beams. One output beam serves as the output of the stable power system, and the actual output optical power of the stable power system is denoted as P. out The other output beam serves as the feedback optical path, and the feedback optical power is denoted as P. in The signal acquisition and amplification circuit converts the beam intensity of the feedback optical path into a voltage signal V. in ; The liquid crystal variable noise attenuator consists of a polarizer, a liquid crystal variable phase delayer, and a polarizer. Step 2: Determine the theoretical value of the output photovoltage signal of the stable power system and V. i The relationship; the Jones vector E of the laser beam emitted from the laser. α Represented as: Where ε represents the angle between the overall polarization direction of the polarized light and the X-axis of the light path, i.e., the polarization angle; α represents the angle between the line connecting the major and minor axes of the polarized light with ellipticity and its major axis, i.e., the ellipticity angle; and i represents the unit imaginary number. The Jones vector of the output beam after passing through the power stabilization system is expressed as: E out =G GL_T G HWP2 G ANA G LCVR (δ)G POL G HWP1 E α In the formula, G GL_T G HWP2 G ANA G LCVR (δ), G POL G HWP1 These are the Jones matrix of the polarizing beam splitter transmission direction, half-wave plate 2, analyzer, liquid crystal variable phase retarder, polarizer, and half-wave plate 1, respectively. in, Among them, T S1 T S2 T S3 T represents the transmittance of S-rays from the polarizer, analyzer, and polarizing beam splitter, respectively. P1 T P2 T P3 θ1 represents the transmittance of P-beams from the polarizer, analyzer, and polarizing beam splitter, respectively; θ1 represents the angle between the fast axis of half-wave plate 1 and the X-axis of the optical path; θ2 represents the angle between the fast axis of half-wave plate 2 and the X-axis of the optical path; δ represents the phase delay of the liquid crystal variable phase retarder, the magnitude of which is controlled by the input voltage of the liquid crystal; and I0 represents the light intensity of the output beam after passing through the stabilizing power system. out The calculation expression is as follows: In the formula, For E out The transpose of the matrix, L1, L2, and N1-N4 are constant algebraic expressions, and: L1=N1(cosεcosα-isinεsinα)+iN2(sinεcosα+icosεsinα) L2=N3(cosεcosα-isinεsinα)+iN4(sinεcosα+icosεsinα) in: Based on the above formula, the theoretical output optical power P′ of the stable power system can be derived from the power value at the built-in diode. out for: In the formula, k represents the power efficiency from the optical power at the laser's built-in diode to the output beam of the stable power system, and P′ represents the power efficiency. out The corresponding voltage signal is represented as V′ out and Take a set of simulated off-loop optical powers obtained from the initial short-term stable operation of the stable power system, and average them, denoted as P′. out0 The corresponding average voltage is V′ out0 Let V′ be the denoted V′. out With V′ out0 The difference is the theoretical value of the output optical power relative to P′. out0 Voltage signal error Err′: Err′=V′ out -V′ out0 Step 3: The photodetector acquires the feedback optical power signal and converts the beam intensity of the feedback optical path into a voltage signal V. in Let h be the ratio of the transmittance to the refractive index of the polarizing beam splitter, and V″ be the simulated output optical power voltage signal. out =hV in , V″ out With feedback optical power setting value V set By subtracting the values, we obtain the error Err″ = V″ between the feedback optical power and the setpoint. out -V set ; Step 4: Relative to P′ the theoretical value of the output optical power out0 The total error value of the stable power system is obtained by adding the voltage signal error Err′ and the error Err″ between the feedback optical power and the set value of the feedback optical power. Err = Err′ + Err″. Step 5: Allocate proportional, integral, and derivative PID parameters according to the total error value Err of the stable power system. The PID algorithm calculates the required input voltage of the liquid crystal variable phase delay device based on the Err value and changes the transmittance of the liquid crystal variable noise attenuator.

2. The method for high-precision optical power stabilization control of a laser based on built-in diode monitoring according to claim 1, characterized in that, The analog temperature drift value is obtained by reading the liquid crystal driving voltage output from the stable power system and the output signal of the built-in diode of the laser tube; the relationship between the phase delay δ of the liquid crystal variable phase delayer and the driving voltage V is as follows: Among them, V0, V C M and d are the performance parameters of the liquid crystal variable phase retarder, d is the diameter of the mirror of the liquid crystal variable phase retarder, Δn is the thickness of the waveplate of the liquid crystal variable phase retarder, λ is the incident light wavelength, V is the driving voltage applied to the liquid crystal variable phase retarder, and δ0 is a constant value related to the liquid crystal variable phase retarder and the incident wavelength. Once the laser, optical components, and optical path are determined, the actual output optical power P of the stable power system is... out The power value P at the monitoring diode of the input power stabilization system. i Given that the input voltage-phase delay relationship of the liquid crystal variable phase delay device (LCD) is known as a function of the phase delay δ, the theoretical output optical power value P′ of the stable power system can be derived by reading the driving voltage and built-in diode data of the LCD by the control system. out : P′ out =f(P i ,δ) P′ out The corresponding voltage signal V′ out for: V′ out =f(V i ,V)。 3. The high-precision optical power stabilization control method for lasers based on built-in diode monitoring according to claim 1, characterized in that, Steps two and four include: acquiring the output of the built-in diode of the laser tube and modeling it to obtain the temperature drift error, and adding the temperature drift error to the error signal of the feedback control. Let I be the current of the output signal from the built-in diode. i The voltage signal after the built-in diode output signal passes through the signal acquisition and amplification circuit is V. i The theoretical value of the output optical power voltage signal obtained by the power compensation model is: V′ out =f(V i ,V) Take the average of a set of theoretical output optical power values ​​obtained from the initial short-term stable operation of the stable power system, denoted as P′. out0 The corresponding voltage value is V′ out0 Let V′ be the denoted V′. out With V′ out0 The difference is Err′, which only contains the error data of the spectral error caused by temperature drift. When using the feedback light signal separated by the polarizing beam splitter for feedback control, Err′, which only contains the spectral error, is added to the error signal Err″ between the feedback light power and the feedback light power set value described in step three to compensate for the spectral error caused by temperature drift in the feedback control.

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