Method and device for extracting light spot centroid of four-quadrant detector

Abstract

The invention belongs to the technical field of laser spot positioning, and discloses a method and a device for extracting a spot centroid of a four-quadrant detector. A first linearly polarized light beam and a second linearly polarized light beam which are consistent in wavelength and orthogonal in polarization are generated through an emission optical system, the two linearly polarized light beams are modulated, different modulation frequencies are given to the two linearly polarized light beams, and the two linearly polarized light beams are combined into one beam of composite light to be emitted; receiving the composite light by using a receiving optical system; separating the composite light into first linearly polarized light and second linearly polarized light by using a polarization bifocus prism, and enabling the two beams of light to respectively form focuses which are staggered front and back; a four-quadrant detector is used for receiving a pre-focus light spot and a post-focus light spot, and the four-quadrant detector is arranged at the middle position of the two focuses; a signal processing system is used for processing signals output by the four-quadrant detector, and light spot centroid information is obtained through calculation. According to the invention, the weak signal detection efficiency of the four-quadrant detector is improved, and the precision of light spot position calculation is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser spot positioning, and more particularly relates to a four-quadrant detector spot centroid extraction method and device. BACKGROUND

[0002] Space laser communication is a research hotspot in the field of communication at home and abroad. Compared with traditional microwave communication and optical fiber communication, it has the advantages of high transmission rate, strong security and reliability, low transmission delay, and outstanding anti-electromagnetic interference ability.

[0003] In the construction of air-ground integrated communication network system, atmospheric optical communication as a bridge connecting space-based and ground-based communication nodes is a key link to realize real-time interaction of space information. Whether it is high-speed data transmission between satellites and ground stations or cooperative communication between unmanned aerial vehicle formations, the stability of the atmospheric optical communication link directly determines the communication quality of the entire network. In the space optical communication system, the acquisition, tracking and pointing (ATP) technology is the basis for establishing a communication link. Among them, the fine tracking system as the core module of ATP technology relies on high-precision position detectors to accurately position the light spot, laying the foundation for the subsequent fine tracking servo system to realize light spot alignment. Among various fine tracking position detection devices, the four-quadrant detector (QD) stands out due to its high detection sensitivity, high resolution, high bandwidth, small size and other advantages, and has become a widely used core component in the ATP fine tracking system.

[0004] Unlike devices such as cameras that use centroid positioning methods, QD can only rely on the light intensity of the four channels to solve the position. Under atmospheric channel conditions, the light spot is distorted due to atmospheric turbulence, resulting in changes in light spot shape, light intensity, and light spot uniformity, leading to large positioning errors of QD for the light spot, causing communication link jitter or even interruption. Current algorithms rely on the energy distribution state of the light spot, and in the face of random changes in light spot characteristics caused by atmospheric turbulence, it is difficult to accurately solve the position of the light spot. It is of great significance to explore how to solve the error problem of QD light spot position solving under atmospheric turbulence.

[0005] In the field of spot position solving based on four-quadrant detector, the bifocal positioning method has been widely studied and applied. The traditional bifocal positioning technology separates the incident light into two focal spots through an optical system, and uses the positional relationship of the two spots for high-precision positioning. However, the existing technology still has many deficiencies: first, in the light splitting process of the existing bifocal positioning technology, ordinary light splitting elements are often used, which can cause a large energy loss, further weaken the weak signal received by the four-quadrant detector, and reduce the detection efficiency; second, the influence of background light interference on the four-quadrant detector is difficult to effectively suppress, which reduces the signal-to-noise ratio of the detection signal and affects the accuracy of the spot position solving; third, the existing technology cannot guarantee the consistency of the energy of the two defocused spots, and the energy difference will introduce additional calculation error, which cannot realize high-precision spot position solving. Therefore, there is an urgent need in the field to propose a new method and device that can overcome the above defects. SUMMARY

[0006] The present application provides a four-quadrant detector spot centroid extraction method and device, which solves the problem of improving the detection efficiency and spot position solving accuracy of the four-quadrant detector in the prior art.

[0007] The present application provides a four-quadrant detector spot centroid extraction method, comprising the following steps: Two beams of first linearly polarized light and second linearly polarized light with consistent wavelengths and orthogonal polarizations are generated by using an emission optical system, the two beams of linearly polarized light are modulated, the two beams of linearly polarized light are given different modulation frequencies, and are combined into a composite light and then emitted; The composite light is received by using a receiving optical system; the composite light is separated into first linearly polarized light and second linearly polarized light by using a polarization bifocal prism in the receiving optical system, and the two beams of light form front and rear staggered focal points respectively; a four-quadrant detector in the receiving optical system receives the pre-focal spot and the post-focal spot, and the four-quadrant detector is arranged at a position between the two focal points; The signal output by the four-quadrant detector is processed by using a signal processing system, and the spot centroid information is solved.

[0008] Preferably, the emission optical system comprises a laser, an optical modulator, a light splitting prism and an emission end telescope; two lasers with consistent wavelengths are used as light sources to generate the first linearly polarized light and the second linearly polarized light; two optical modulators are used to modulate the first linearly polarized light and the second linearly polarized light respectively, so that the first linearly polarized light has a first frequency and the second linearly polarized light has a second frequency; the light splitting prism is used to combine the modulated first linearly polarized light and the second linearly polarized light into the composite light; and the emission end telescope is used to collimate and expand the composite light for emission.

[0009] Preferably, the receiving optical system further comprises a receiving end telescope and a lens; the receiving end telescope is used to receive the composite light transmitted through the channel; the lens is used to focus the composite light; the polarization bifocal prism receives the light beam focused by the lens.

[0010] Preferably, the polarization bifocal prism is an integrated prism.

[0011] Preferably, the polarization bifocal prism is composed of a first crystal, a second crystal and a third crystal; the first crystal is a total reflection single optical axis crystal; the second crystal and the third crystal are both double optical axis crystals. The composite light is incident to the second crystal; the second crystal is used to transmit and separate the first linearly polarized light and reflect and separate the second linearly polarized light; The first linearly polarized light transmitted and separated is incident to the third crystal and is emitted after being transmitted by the third crystal; The second linearly polarized light reflected and separated is incident to the third crystal again after being reflected by the first crystal and is emitted after being reflected by the third crystal.

[0012] Preferably, the signal processing system comprises a signal conditioning module, a signal acquisition module and a main control module. The signal conditioning module is used to perform signal conversion, amplification adjustment and filtering on the signal output by the four-quadrant detector; The signal acquisition module is used to synchronously acquire the four-channel voltage signals conditioned by the signal conditioning module; The main control module is used to receive the four-channel digital voltage signals acquired by the signal acquisition module, perform frequency separation and energy compensation on the signals, and calculate the light spot centroid information based on the centroid algorithm.

[0013] Preferably, the signal conditioning module comprises a transimpedance amplifier, a variable gain amplifier and a filter; the transimpedance amplifier is used to linearly convert the photocurrent output by the four-quadrant detector into a voltage signal; the variable gain amplifier is used to dynamically adjust the amplification multiple of the signal; and the filter is used to suppress high and low frequency noises.

[0014] Preferably, the main control module is used to perform fast Fourier transform on the four-channel digital voltage signals, extract the signal components corresponding to two modulation frequencies respectively, calculate the light intensities of each quadrant under the two modulation frequencies respectively, and compensate the signals according to the light intensities under the two modulation frequencies, so as to make the energies of the two light spots consistent.

[0015] Preferably, the implementation mode of compensating the signal according to the light intensity under two modulation frequencies comprises: scaling the four-quadrant signal of the pre-focal light spot by a compensation coefficient, so that the total intensity of the scaled pre-focal light spot matches the total intensity of the post-focal light spot.

[0016] In another aspect, the present application provides a four-quadrant detector light spot centroid extraction device, comprising: an emission optical system, a receiving optical system and a signal processing system. The four-quadrant detector light spot centroid extraction device is used to perform the steps in the four-quadrant detector light spot centroid extraction method as described above.

[0017] The one or more technical solutions provided in the present application have at least the following technical effects or advantages: (1) The present application first generates two first linearly polarized lights and second linearly polarized lights with consistent wavelengths and orthogonal polarizations by using the emission optical system, modulates the two linearly polarized lights to give them different modulation frequencies, and emits a combined light after being combined; then receives the combined light by using the receiving optical system; separates the combined light into the first linearly polarized light and the second linearly polarized light by using the polarization bifocal prism in the receiving optical system, and makes the two lights form pre-focal and post-focal points staggered in front and back; receives the pre-focal and post-focal spots by using the four-quadrant detector in the receiving optical system, and the four-quadrant detector is arranged at a position between the two focal points; finally, processes the signal output by the four-quadrant detector by using the signal processing system to obtain the light spot centroid information. The present application adopts polarization multiplexing, which not only effectively suppresses the influence of turbulence in the propagation of the light beam in the atmospheric environment, but also reduces energy loss and improves the efficiency of weak signal detection of the four-quadrant detector and the accuracy of light spot position calculation by using the polarization state and the polarization bifocal prism for beam splitting at the receiving end.

[0018] (2) The present application adopts intensity modulation and performs correlation demodulation at the receiving end, which not only reduces the interference of background light on the four-quadrant detector, but also ensures the consistency of the energy of the conjugate light spots on the four-quadrant detector by corresponding compensation of the energy (i.e. intensity or amplitude), thereby further improving the accuracy of light spot position calculation.

[0019] (3) The polarization bifocal prism in the present application adopts an integrated prism, which reduces the volume and improves the stability and reduces the complexity of the optical path compared with the traditional discrete double-focal optical path. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A flow chart corresponding to a four-quadrant detector light spot centroid extraction method provided for the embodiment 1 of the present application; Figure 2 An optical path schematic diagram of the polarization bifocal prism in the four-quadrant detector light spot centroid extraction method provided for the embodiment 1 of the present application; Figure 3 Structure diagram of the polarization bifocal prism.

[0021] Wherein, 100 - transmitting optical system, 200 - receiving optical system, 300 - signal processing system; 110 - first laser, 120 - second laser, 130 - first light modulator, 140 - second light modulator, 150 - beam splitter prism, 160 - transmitting telescope; 210 - receiving telescope, 220 - lens, 230 - polarization bifocal prism, 240 - four-quadrant detector; 231 - first crystal, 232 - second crystal, 233 - third crystal; 310 - signal conditioning module, 320 - signal acquisition module, 330 - main control module. DETAILED DESCRIPTION

[0022] In order to better understand the above technical solutions, the above technical solutions will be described in detail in the following in combination with the description of the drawings and specific embodiments.

[0023] Embodiment 1: Embodiment 1 provides a four-quadrant detector light spot centroid extraction method, referring to Figure 1 , comprising the following steps: The transmitting optical system 100 generates two beams of first linearly polarized light and second linearly polarized light with consistent wavelength and orthogonal polarization. The two beams of linearly polarized light are modulated, and the two beams of linearly polarized light are given different modulation frequencies, and then combined into a composite light for emission. The receiving optical system 200 receives the composite light. The polarization bifocal prism 230 in the receiving optical system 200 separates the composite light into first linearly polarized light and second linearly polarized light, and makes the two beams of light form front and rear staggered focal points respectively. The four-quadrant detector 240 in the receiving optical system 200 receives the front focal spot and the rear focal spot. The four-quadrant detector 240 is arranged at a position between the two focal points. The signal processing system 300 processes the signal output by the four-quadrant detector 240, and calculates the light spot centroid information.

[0024] The emission optical system 100 comprises a laser (specifically, a first laser 110 and a second laser 120), an optical modulator (specifically, a first optical modulator 130 and a second optical modulator 140), a light splitting prism 150, and an emission end telescope 160; the two lasers (i.e., the first laser 110 and the second laser 120) with the same wavelength are used as light sources to generate the first linearly polarized light and the second linearly polarized light; the two optical modulators (i.e., the first optical modulator 130 and the second optical modulator 140) are used to modulate the first linearly polarized light and the second linearly polarized light respectively, so that the first linearly polarized light has a first frequency and the second linearly polarized light has a second frequency; the light splitting prism 150 is used to combine the modulated first linearly polarized light and the second linearly polarized light into the composite light; and the emission end telescope 160 is used to collimate and expand the composite light for emission.

[0025] The receiving optical system 200 further comprises a receiving end telescope 210 and a lens 220; the receiving end telescope 210 is used to receive the composite light transmitted through the channel; the lens 220 is used to focus the composite light; and the polarization bifocal prism 230 receives the light beam focused by the lens 220.

[0026] The polarization bifocal prism 230 is an integrated prism. Specifically, referring to Figure 2 and Figure 3 , the polarization bifocal prism 230 is composed of a first crystal 231, a second crystal 232, and a third crystal 233; the first crystal 231 is a total reflection single optical axis crystal, and the second crystal 232 and the third crystal 233 are both double optical axis crystals; the composite light is incident to the second crystal 232, which transmits the first linearly polarized light and reflects the second linearly polarized light; the first linearly polarized light transmitted is incident to the third crystal 233 and exits after being transmitted by the third crystal 233; and the second linearly polarized light reflected is incident to the third crystal 233 again after being reflected by the first crystal 231, and exits after being reflected by the third crystal 233.

[0027] The signal processing system 300 comprises a signal conditioning module 310, a signal acquisition module 320, and a main control module 330; the signal conditioning module 310 is used to perform signal conversion, amplification adjustment, and filtering on the signals output by the four-quadrant detector 240; the signal acquisition module 320 is used to synchronously acquire the four-channel voltage signals conditioned by the signal conditioning module 310; the main control module 330 is used to receive the four-channel digital voltage signals acquired by the signal acquisition module 320, perform frequency separation and energy compensation on the signals, and calculate the spot centroid information based on the centroid algorithm.

[0028] Specifically, the signal conditioning module 310 includes a transimpedance amplifier, a variable gain amplifier and a filter; the transimpedance amplifier is used to linearly convert the photocurrent output by the four-quadrant detector 240 into a voltage signal; the variable gain amplifier is used to dynamically adjust the amplification multiple of the signal; and the filter is used to suppress high and low frequency noises.

[0029] Specifically, the main control module 330 is used to perform fast Fourier transform on the four-channel digital voltage signal, and extract the signal components corresponding to two modulation frequencies respectively; the main control module 330 is used to calculate the light intensity of each quadrant under the two modulation frequencies respectively, and compensate the signal according to the light intensity under the two modulation frequencies, so as to make the energy of the two light spots consistent.

[0030] The implementation manner of compensating the signal according to the light intensity under the two modulation frequencies includes: scaling the four-quadrant signal of the pre-focus light spot by a compensation coefficient, so that the total intensity of the scaled pre-focus light spot matches the total intensity of the post-focus light spot.

[0031] The main steps or operations included in the present application are further illustrated below.

[0032] (1) Transmission end light beam modulation and synthesis: two lasers (specifically including a first laser 110 and a second laser 120) with the same wavelength are used as light sources to generate linearly polarized light respectively. The polarization directions of the two light beams can be adjusted by a half-wave plate to be orthogonal to each other, forming a first linearly polarized light (s linearly polarized light) and a second linearly polarized light (p linearly polarized light). An optical modulator (specifically including a first optical modulator 130 and a second optical modulator 140) is used to modulate the intensity of the two linearly polarized lights respectively, so as to give the first linearly polarized light a modulation frequency and give the second linearly polarized light a modulation frequency . Then, the two modulated linearly polarized lights are combined into a composite light through the beam splitter prism 150, and the light beam modulation and synthesis of the transmission end are completed.

[0033] (2) Light beam transmission and reception: the composite light after modulation and synthesis of the transmission end is transmitted through the transmission end telescope 160, and is received by the receiving end telescope 210 after channel transmission.

[0034] (3) Light beam focusing: the light beam received by the receiving end telescope 210 is focused by the lens 220 to converge the incident light beam to form a focal point.

[0035] (4) Polarization bifocal beam splitting: the light beam after the lens 220 is incident to the polarization bifocal prism 230, and the polarization bifocal prism 230 is used to separate the composite light into s linearly polarized light and p linearly polarized light, and generate front and back focal points respectively.

[0036] Referring to Figure 2 and Figure 3 , the polarization bifocal prism 230 designed by the present application is composed of three crystals, wherein the second crystal 232 and the third crystal 233 can both transmit s-polarized light and reflect p-polarized light. The polarization bifocal prism 230 can realize the decomposition of incident composite polarized light into two linearly polarized lights with different focal points, which can be respectively denoted as focal point 1 and focal point 2.

[0037] Specifically, when the incident light is composite light with orthogonal polarization, the composite light is transmitted and separated into s-polarized light and reflected and separated into p-polarized light by the second crystal 232. Among them, the s-polarized light continues to be transmitted through the third crystal 233, and since the third crystal 233 only transmits s-polarized light, theoretically there is no other light separation; similarly, the p-polarized light is reflected by the first crystal 231 and then incident on the third crystal 233 for reflection, and since the third crystal 233 only reflects p-polarized light, theoretically there is no other light separation. The p-polarized light has experienced different reflection paths of s-polarized light, and there is a difference in optical path between the two lights, so that two focal points at front and back positions can be obtained at the receiving end. The polarization bifocal prism 230 designed by the present application utilizes the polarization state of the light beam, and can reduce the energy loss caused by light separation.

[0038] (5) Fusion beam detection: the four-quadrant detector 240 is installed at a position between the two focal points. Since one light beam is a pre-focal spot and the other is a post-focal spot, the surface of the four-quadrant detector 240 can receive two conjugate defocused spots in terms of light intensity spatial distribution. The pre-focal spot received by the four-quadrant detector 240 is a second polarized light (with a frequency of ), and the post-focal spot is a first polarized light (with a frequency of ).

[0039] (6) Photoelectric conversion and signal conditioning: the photocurrent generated by the four-quadrant detector 240 is converted into a voltage signal, and then the signal is amplified and filtered to ensure that the signal meets the parameter requirements of the subsequent signal acquisition.

[0040] Specifically, for the weak photocurrent signal output by the four-quadrant detector 240, three-stage signal processing is performed to realize dynamic range adaptation and noise suppression. First, the current signal is converted into a voltage signal by a transimpedance amplifier (TIA), and then the signal is amplified to the effective input range of the subsequent sampling input by a variable gain amplifier (VGA). A band-pass filter is added at a suitable position in the link to filter out high-frequency and low-frequency noise, and four stable voltage signals are output.

[0041] (7) Signal acquisition: the processed four-quadrant detector signal is acquired, and the analog signal is converted into a digital signal for subsequent data processing.

[0042] Specifically, the signal conditioning module 310 is reliably connected to the signal acquisition module 320. The signal acquisition module 320 must have low noise, high gain, and a wide bandwidth to accurately capture weak optical signals. The gain of the signal acquisition module 320 can be adjusted based on the actual light intensity to ensure the captured signal has an appropriate amplitude.

[0043] (8) Signal compensation and spot position calculation: The main control module 330 receives the collected four-channel digital voltage signal and extracts the frequency and The signal components are calculated to calculate the light intensity of the signals of different frequencies in each quadrant. Based on the light intensity information of the two frequencies, the signals are compensated to ensure that the energy of the two light spots is consistent, which can improve the accuracy of subsequent light spot position detection. The main control module 330 calculates the light spot coordinates based on the centroid algorithm. For example, parallel computing can be implemented through hardware to reduce solution delay and ultimately output high-precision light spot position coordinates.

[0044] The present invention utilizes the main control module 330 to improve the accuracy of light spot positioning and suppress background light through frequency separation and energy compensation: after receiving the four-channel digital voltage signal, the main control module 330 first performs fast Fourier transform on the signal to convert the time domain signal into a frequency domain signal. and The narrowband filter centered at is used to extract the signal components corresponding to the two modulation frequencies to suppress the background light. and Based on the dual-focus energy balance compensation mechanism, when the energy deviation is detected to exceed the preset threshold, the system dynamically adjusts the energy of the two light spots to ensure that the energy of the two light spots is consistent, thereby improving the accuracy of light spot positioning.

[0045] In the calculation of the spot position, the Fourier transform method can be used to calculate the signal intensity. :

[0046] Where, is the collected four-quadrant detector signal, is the amplitude corresponding to the first linear polarization light, is the modulation frequency (angular frequency) corresponding to the first linear polarization light, is the phase corresponding to the first linear polarization light, is the amplitude corresponding to the second linear polarization light, is the modulation frequency (angular frequency) corresponding to the second linearly polarized light, is the phase corresponding to the second linear polarization light, is a noise signal.

[0047] Right now Contains two sine wave signals and a noise signal.

[0048] Sample the signal and convert it into a discrete signal. Let the sampling frequency be , in Hz, and ,(in is the sampling angular frequency), we get:

[0049] Where, for The corresponding discrete signal, is the sampling interval, , are the frequencies of the two sinusoidal signals (in Hz), for The corresponding discrete signal.

[0050] For discrete signals Perform N-point discrete Fourier transform (DFT) to obtain the frequency domain sequence , add the DFT results of the two sine waves and the noise to get:

[0051] Where, For discrete signals The frequency domain sequence of the four-quadrant detector signal obtained by discrete Fourier transform is For discrete signals The noise frequency domain sequence obtained by discrete Fourier transform is and They are the DFT results of two sine waves, 、 and 、 There will be a peak here. , express Corresponding frequency point; , express The corresponding frequency point; N is the number of transformation points of discrete Fourier transform.

[0052] turn up Corresponding frequency , calculate the amplitude of the frequency point ,but .

[0053] turn up Corresponding frequency , calculate the amplitude of the frequency point ,but .

[0054] In the light spot position calculation, in order to solve the problem of unequal total intensity of the two light spot signals (total intensity of the pre-focus light spot , the total intensity of the focused spot ,and ,in, The light spot before focus is in the quadrant a The strength of The light spot before focus is in the quadrant b The strength of The light spot before focus is in the quadrant c The strength of The light spot before focus is in the quadrant d The strength of After focusing, the spot is in the quadrant a The strength of After focusing, the spot is in the quadrant b The strength of After focusing, the spot is in the quadrant c The strength of After focusing, the spot is in the quadrant d The coordinate solution deviation caused by the strength of the , scale the four-quadrant signal of the pre-focus spot according to the compensation coefficient K (i.e. ,in, The pre-focus spot is scaled by the compensation coefficient in the quadrant a The strength of The pre-focus spot is scaled by the compensation coefficient in the quadrant b The strength of The pre-focus spot is scaled by the compensation coefficient in the quadrant c The strength of The pre-focus spot is scaled by the compensation coefficient in the quadrant d intensity), so that the total intensity of the pre-focus spot after scaling , which matches the total intensity of the focused spot. The coordinate solution formula after correction is:

[0055] Where, The centroid of the four-quadrant light spot is x The coordinates on the axis, The centroid of the four-quadrant light spot is y Coordinates on the axis.

[0056] The present invention eliminates the weighted interference of the difference in the intensity of two light spots on the sum and difference calculation by normalizing the total intensity, which can effectively improve the accuracy and stability of coordinate solution.

[0057] Embodiment 2: Embodiment 2 provides a four-quadrant detector light spot centroid extraction device, comprising: a transmitting optical system, a receiving optical system and a signal processing system; the four-quadrant detector light spot centroid extraction device is used to execute the steps in the four-quadrant detector light spot centroid extraction method as described in Embodiment 1.

[0058] The transmitting optical system comprises a laser, an optical modulator, a light splitting prism and a transmitting end telescope.

[0059] The receiving optical system comprises a receiving end telescope, a lens, a polarization bifocal prism and a four-quadrant detector. When the optical path is set up, the lens and the polarization bifocal prism are installed along the optical axis to ensure that the optical path is axially aligned and that the incident light beam still propagates along the axis after being transmitted through each element. When the four-quadrant detector is installed, the four-quadrant detector is arranged between the focal point 1 and the focal point 2, i.e. the four-quadrant detector is installed at the middle position to ensure that the two defocused light spots can fall in the detection area at the same time. By fine-tuning the posture of the detector and the incident direction of the light beam, the two light spots are symmetrically distributed on the detector.

[0060] The signal processing system comprises a signal conditioning module, a signal acquisition module and a main control module.

[0061] The devices or modules are further illustrated below.

[0062] (1) Laser: used to generate two orthogonal linearly polarized lights, i.e. s-polarized light and p-polarized light.

[0063] (2) Optical modulator: modulates the laser beam to generate two beams with frequencies of and .

[0064] (3) Light splitting prism: combines the modulated s-polarized light and p-polarized light into a composite light to realize multiplex transmission of the two polarized lights.

[0065] (4) Transmitting end telescope: collimates and expands the composite light for emission.

[0066] (5) Receiving end telescope: receives the composite light transmitted through the channel to complete the collection and preliminary collimation of the spatial light signal.

[0067] (6) Lens: focuses the incident parallel tracking beacon light to ensure that the front and rear light spots can be generated.

[0068] (7) Polarization bifocal prism: receives the light beam of the focusing lens, separates the composite light into s linearly polarized light and p linearly polarized light, and makes the two light beams form front and rear staggered focal points (s linearly polarized light is a rear focal spot and p linearly polarized light is a front focal spot).

[0069] (8) Four-quadrant detector: located between the two focal points, receiving two light spots before and after the focus, and determining the final beacon light spot centroid position by the centroid algorithm.

[0070] (9) Signal conditioning module: This module integrates a transimpedance amplifier to linearly convert the photoelectric current output by the four-quadrant detector into a voltage signal, which is suitable for subsequent circuit processing. The variable gain amplifier dynamically adjusts the amplification multiple according to the input light intensity, ensuring that strong and weak light signals are within the effective acquisition range of the analog-to-digital converter (ADC), avoiding saturation or noise distortion. The filter module suppresses high and low frequency noise through filtering, improving the signal-to-noise ratio and stability; (10) Signal acquisition module: uses a high-speed ADC to synchronously acquire four-channel voltage signals, supports high-precision signal sampling, ensures the time consistency of signals in each quadrant, provides high-precision raw data for subsequent centroid calculation, and meets the real-time requirements of dynamic tracking scenarios; (11) Main control module: receives the collected four-channel digital voltage signals, extracts signal components with frequencies of and , calculates the light intensity of each quadrant corresponding to different frequency signals, compensates the signals according to the light intensity information of the two frequencies to ensure consistent energy of the two light spots, and calculates the light spot coordinates based on the centroid algorithm. Parallel computing is realized through hardware to reduce the calculation delay, and finally the high-precision light spot position coordinates are output.

[0071] Since the functions of the systems and devices in the four-quadrant detector light spot centroid extraction device provided in Embodiment 2 correspond to the steps in the four-quadrant detector light spot centroid extraction method provided in Embodiment 1, the description of Embodiment 1 can be referred to for understanding, and will not be repeated here.

[0072] In summary, by improving the light beam transmission and processing method, the present application solves the problems of atmospheric turbulence influence, large energy loss, serious background light interference, and inconsistent light spot energy in the existing double-focus positioning technology, and can significantly improve the accuracy and stability of light spot position calculation, and improve the efficiency of four-quadrant detector weak signal detection.

[0073] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the examples, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and all should be covered in the scope of the claims of the present application.

Claims

1. A four-quadrant detector spot centroid extraction method, characterized by, The method comprises the following steps: Two first linearly polarized lights and second linearly polarized lights with the same wavelength and orthogonal polarization are generated by using a transmitting optical system, the two linearly polarized lights are modulated, the two linearly polarized lights are given different modulation frequencies, and then the two linearly polarized lights are combined into a composite light and transmitted; The composite light is received by using a receiving optical system; the composite light is separated into the first linearly polarized light and the second linearly polarized light by using a polarization bifocal prism in the receiving optical system, and the two lights form front and rear staggered foci respectively; the front and rear light spots are received by using a four-quadrant detector in the receiving optical system, and the four-quadrant detector is arranged at a position between the two foci; The signal output by the four-quadrant detector is processed by using a signal processing system, and the light spot centroid information is obtained by calculation.

2. The four-quadrant detector spot centroid extraction method of claim 1, wherein, The transmitting optical system comprises a laser, an optical modulator, a light splitting prism and a transmitting end telescope; the two lasers with the same wavelength are used as light sources to generate the first linearly polarized light and the second linearly polarized light; the two optical modulators are used to modulate the first linearly polarized light and the second linearly polarized light respectively, so that the first linearly polarized light has a first frequency and the second linearly polarized light has a second frequency; the light splitting prism is used to combine the modulated first linearly polarized light and the second linearly polarized light into the composite light; and the transmitting end telescope is used to collimate and expand the composite light for transmission.

3. The four-quadrant detector spot centroid extraction method of claim 1, wherein, The receiving optical system further comprises a receiving end telescope and a lens; the receiving end telescope is used to receive the composite light transmitted through a channel; the lens is used to focus the composite light; and the polarization bifocal prism receives the light beam focused by the lens.

4. The four-quadrant detector spot centroid extraction method of claim 1, wherein, The polarization bifocal prism is an integrated prism.

5. The four-quadrant detector spot centroid extraction method of claim 4, wherein, The polarization bifocal prism is composed of a first crystal, a second crystal and a third crystal; the first crystal is a total reflection single optical axis crystal, and the second crystal and the third crystal are both double optical axis crystals; The composite light is incident to the second crystal, the first linearly polarized light is transmitted and separated by the second crystal, and the second linearly polarized light is reflected and separated by the second crystal; The first linearly polarized light after transmission separation is incident to the third crystal and is emitted after transmission by the third crystal; The second linearly polarized light after reflection separation is reflected by the first crystal and then is incident to the third crystal, and is emitted after reflection by the third crystal.

6. The four-quadrant detector spot centroid extraction method of claim 1, wherein, The signal processing system comprises a signal conditioning module, a signal acquisition module and a main control module; The signal conditioning module is used to perform signal conversion, amplification adjustment and filtering on the signal output by the four-quadrant detector; The signal acquisition module is used to synchronously acquire the four-channel voltage signals conditioned by the signal conditioning module; The main control module is used to receive the four-channel digital voltage signals acquired by the signal acquisition module, perform frequency separation and energy compensation on the signals, and calculate the light spot centroid information based on a centroid algorithm.

7. The four-quadrant detector spot centroid extraction method of claim 6, wherein, The signal conditioning module comprises a transimpedance amplifier, a variable gain amplifier and a filter; the photoelectric current output by the four-quadrant detector is linearly converted into a voltage signal by the transimpedance amplifier; the variable gain amplifier is used to dynamically adjust the amplification multiple of the signal; The filter is used to suppress high and low frequency noise.

8. The four-quadrant detector spot centroid extraction method of claim 6, wherein, The main control module is used to perform fast Fourier transform on the four-channel digital voltage signal, and extract the signal components corresponding to two modulation frequencies respectively; the main control module is used to calculate the light intensity of each quadrant under the two modulation frequencies respectively, and compensate the signal according to the light intensity under the two modulation frequencies, so that the energy of the two light spots is consistent.

9. The four-quadrant detector spot centroid extraction method of claim 8, wherein, The implementation mode of compensating the signal according to the light intensity under the two modulation frequencies comprises: scaling the four-quadrant signal of the pre-focal light spot according to a compensation coefficient, so that the total intensity of the scaled pre-focal light spot matches the total intensity of the post-focal light spot.

10. A four-quadrant detector spot centroid extraction apparatus, characterized by, It comprises: An emission optical system, a receiving optical system and a signal processing system; The four-quadrant detector light spot centroid extraction device is used to execute the steps in the four-quadrant detector light spot centroid extraction method according to any one of claims 1-9.

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