Light path pointing error detection method and device

Abstract

The invention discloses a light path pointing error detection method and device, and belongs to the field of satellite laser communication. The device is used for solving the problems of system errors and low detection precision in the prior art and comprises an interferometer, a first laser beam emitted by the interferometer enters a detector through a transflective part, and the angle and / or position of the transflective part is adjustable; a second laser beam emitted by the tracking light source enters the detector through the PAT subsystem and the transflective part of the laser communication terminal; a third beam of laser emitted by the communication light source enters the detector through the PAT subsystem and the transmission and reflection part of the laser communication terminal; and the transmission and reflection part comprises a 45-degree reflecting mirror and a first adjustable inclined reference mirror, and is used for adjusting the angle of the first adjustable inclined reference mirror and / or the distance between the first adjustable inclined reference mirror and the 45-degree reflecting mirror and changing the period and definition of interference fringes formed on the detector.

Description

Technical Field

[0001] The present invention relates to the field of satellite laser communications, and more specifically to a method and device for detecting an optical path pointing error. Background Art

[0002] As technologies such as earth exploration, military confrontation, deep space imaging, meteorological analysis, and intersatellite networking develop towards smaller targets, faster actions, and higher speeds, the demand for communications has also exploded. Satellite optical communications, with its advantages of high communication speed (two orders of magnitude higher than microwave communications, up to 100Gbps), good confidentiality (beam divergence angle is urad orders of magnitude smaller), high beam pointing accuracy, and lightweight terminals (several kilograms to tens of kilograms), are expected to break through the bottleneck of low satellite microwave communication speed and meet the demand for significantly increased communication speed in the information age. Satellite optical communication terminals are mainly composed of three subsystems: modulation and demodulation subsystem, optical path transceiver subsystem (HOUSING), and pointing-acquisition-tracking (PAT) subsystem. Before communication, the laser communication payload needs to be aligned with the target and stably tracked before communication can be carried out. At this time, the laser communication terminal needs to have accurate beam pointing, which has high requirements for the HOUSING and PAT systems, especially for the communication transmission optical path and the communication receiving optical path, which affect the communication quality and the tracking quality of the target. At present, the coaxiality detection of the receiving and emitting paths of laser communication terminals is mainly carried out by detecting the centroid of the retroreflected light spot of the cube-corner retroreflector (CCR). This method has high requirements for the geometric error (surface error and dihedral error) of the CCR and the detection accuracy of the detector and the calculation accuracy of the centroid of the light spot. Since the laser communication beam is generally only a few dozen urads, a very small detection error will have a great impact on the stability of the laser link and the communication quality.

[0003] The interference pattern contains a wealth of information. By analyzing the density, shape or direction of the interference fringes, the angle deviation can be indirectly obtained. In addition, the interference detection is non-contact and has high resolution, which can achieve precise measurement. The literature Analysis of Coaxiality Error Induced by the cube corner retro-reflector Geometrical and Assembly Errors of an Acquisition, Pointing, and Tracking System analyzes the influence of geometric errors (reflection surface shape error and dihedral angle error) in the corner cube prism on the retroreflected light wavefront, and then analyzes the coaxiality error. Under the combined effect of the PAT system adjustment error and the CCR geometric error, the coaxiality error of the system reaches nearly 700urad. The problems with using CCR for detection are: 1. The detection accuracy of coaxiality is closely related to the manufacturing error of CCR. The manufacturing error causes geometric error, which in turn affects the wavefront. The wavefront in turn affects the positioning accuracy of the light spot, causing excessive coaxiality error during detection; 2. The detection of coaxiality is based on the positioning of the center of mass of the light spot, which mainly depends on the calculation accuracy of the center of mass. Therefore, the accuracy of the detector (for the pixel size of the array detector, for the four-quadrant detector, the calculation error caused by its dark area) also has a certain influence on the coaxiality; 3. This method uses the reflected light of a single light source for detection, that is, the outgoing light is reflected by the CCR into the APT system after passing through the optical path, and then reaches the detector surface through the tracking receiving branch. This will inevitably introduce a part of the installation error of the communication transmission optical path.

[0004] Therefore, reducing the impact of system errors, seeking high-precision coaxiality detection methods for laser communication terminals, and reducing the difficulty of detection are research difficulties for researchers in this field. Summary of the invention

[0005] The embodiments of the present invention provide a method and device for detecting an optical path pointing error, which are used to solve the problems of system error and low detection accuracy in the prior art.

[0006] An embodiment of the present invention provides a light path pointing error detection device, comprising:

[0007] A light source part, which is used to provide a laser light source to the interferometer, the tracking light source and the communication light source respectively;

[0008] an interferometer, through which a first laser beam emitted enters a detector through a transflective portion, wherein the angle and / or position of the transflective portion is adjustable;

[0009] A tracking light source emits a second laser beam which passes through the PAT subsystem of the laser communication terminal and the transflective part and enters the detector;

[0010] A communication light source, wherein a third laser beam emitted by the communication light source passes through the PAT subsystem of the laser communication terminal and the transflective part and enters the detector;

[0011] A PAT subsystem of the laser communication terminal, which is arranged between the tracking light source, the communication light source and the detector, and is used to refract and reflect the second laser beam and the third laser beam;

[0012] The transflective part includes a 45° reflector and a first adjustable tilt reference mirror, which is used to adjust the angle of the first adjustable tilt reference mirror and / or the distance between the first adjustable tilt reference mirror and the 45° reflector to change the period and clarity of the interference fringes formed on the detector, wherein the second laser beam and the first laser beam form interference fringes on the detector, and the third laser beam and the first laser beam form interference fringes on the detector.

[0013] Preferably, the intensity of a laser light source provided by the light source part to the interferometer is adjustable; and / or

[0014] The intensity of a laser light source provided by the light source part to the tracking light source is adjustable; and / or

[0015] The intensity of a laser light source provided by the light source part to the communication light source is adjustable.

[0016] Preferably, the PAT subsystem of the laser communication terminal comprises two second adjustable tilt reference mirrors and two fixed tilt reference mirrors, and the second laser beam and the third laser beam first pass through the two fixed tilt reference mirrors respectively.

[0017] Preferably, the 45° reflector is a semi-transparent and semi-reflective mirror, and the transmittance and reflectivity are 1:1;

[0018] The fixed tilt reference mirror and the second adjustable tilt reference mirror included in the first adjustable tilt reference mirror and the PAT subsystem of the laser communication terminal are semi-transparent and semi-reflective mirrors, and the transmittance and reflectivity are 1:1.

[0019] An embodiment of the present invention provides a method for detecting an optical path pointing error, comprising:

[0020] Obtaining the light intensity value of the interference fringes obtained based on the optical path pointing error detection device, separating the interference fringes of different periods, and respectively obtaining the second spatial carrier frequency interference light intensity corresponding to the second laser beam and the third spatial carrier frequency interference light intensity corresponding to the third laser beam;

[0021] Performing two-dimensional Fourier space transformation on the second spatial carrier frequency interference light intensity and the third spatial carrier frequency interference light intensity respectively, and obtaining a second phase value corresponding to the second laser beam and a third phase value corresponding to the third laser beam in sequence;

[0022] Determine the relationship between the minimum error in the frequency domain and the sampling frequency or the sampling interval according to the measurement error of the sampling points in the frequency domain, the measurement error of the sampling points in the time domain, the number of sampling points and the sampling interval; determine the second wrapped phase value corresponding to the second phase value and the third wrapped phase value corresponding to the third phase value in turn by inverse trigonometric functions; obtain the true phase value according to the second wrapped phase value and the third wrapped phase value;

[0023] The true phase value is subjected to Zernike fitting to obtain coefficients of a Zernike polynomial, the coefficients of the Zernike polynomial are converted into Seidel coefficients commonly used to characterize aberrations, and the pointing error between the second laser beam and the third laser beam is obtained.

[0024] Preferably, after performing two-dimensional Fourier space transformation on the second interference light intensity and the third interference light intensity, the second Fourier interference light intensity and the third Fourier interference light intensity are obtained respectively:

[0025]

[0026] The second phase value and the third phase value are as follows:

[0027]

[0028] Among them, I1(f 11 , f 12 ) represents the third Fourier interference light intensity, A1(f 11 , f 12 ,) represents the zero-order spectrum distribution of the third laser beam, C1(f 11 -f x1 ,f 12 -f y1 ) represents the positive first-order spectrum distribution of the third laser beam, represents the negative first-order spectrum distribution of the third laser beam; I2(f 21 , f 22 ) represents the second Fourier interference light intensity, A2(f 21 , f 22 ) represents the zero-order spectrum distribution of the second laser beam, C2(f 21 -f x2 ,f 22 -f y2 ) represents the positive first-order spectrum distribution of the second laser beam; represents the negative first order spectrum distribution of the second laser beam; represents the third phase value, represents the second phase value, Im[C1(x,y)] represents the imaginary part of C1(x,y), Re[C1(x,y)] represents the real part of C1(x,y), Im[C2(x,y)] represents the imaginary part of C2(x,y), and Re[C2(x,y)] represents the real part of C2(x,y).

[0029] Preferably, the relationship between the minimum error value in the frequency domain and the sampling frequency or sampling interval is as follows:

[0030] S σ =S x ΔxN 1 / 2

[0031] Among them, S σ represents the standard deviation of the error in the frequency domain, S x represents the standard deviation of the error in the time domain, N represents the number of sampling points, Δx represents the sampling interval; E(x j ) represents the measurement error of the jth sampling point in the time domain, e(σ j ) represents the measurement error of the jth sampling point in the frequency domain.

[0032] Preferably, the true phase value is determined by the following formula:

[0033]

[0034] in, Indicates the true phase value; represents the wrapped phase value, and k(x,y) represents the integer wrapped field.

[0035] An embodiment of the present invention provides a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes any one of the above-mentioned optical path pointing error detection methods.

[0036] An embodiment of the present invention provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes any one of the above-mentioned optical path pointing error detection methods.

[0037] An embodiment of the present invention provides a method and device for detecting an optical path pointing error, the device comprising: a light source part, which is used to provide a laser light source to an interferometer, a tracking light source and a communication light source respectively; an interferometer, through which a first laser beam emitted enters a detector through a transflective part; a tracking light source, through which a second laser beam emitted enters the detector through a PAT subsystem of the laser communication terminal and the transflective part; a communication light source, through which a third laser beam emitted enters the detector through the PAT subsystem of the laser communication terminal and the transflective part; the PAT subsystem of the laser communication terminal is arranged between the tracking light source, the communication light source and the detector, and is used to refract and reflect the second laser beam and the third laser beam; a transflective part, which comprises a 45° reflector and a first adjustable tilt reference mirror, which is used to adjust the angle of the first adjustable tilt reference mirror and / or the distance between the first adjustable tilt reference mirror and the 45° reflector, and change the period and clarity of interference fringes formed on the detector, wherein the second laser beam and the first laser beam form interference fringes on the detector, and the third laser beam and the first laser beam form interference fringes on the detector. When the device adopts the interference detection method, the light source part can divide the light beam into three parts, one of which passes through the tracking light path including the tracking light source, one passes through the communication light path including the communication light source, and one passes through the interferometer as a reference light. The above arrangement avoids the introduction of system errors due to a part of the light beam passing through the communication light path during the centroid method detection. Furthermore, the device includes a transflective part. By adjusting the position and tilt angle of the first adjustable tilt reference mirror included in the transflective part, the period and clarity of the interference fringes formed on the detector can be changed, thereby facilitating the acquisition of the best resolved interference fringes, which is better than the previous method of using a corner cube prism for coaxiality of the laser communication terminal. The detection avoids the influence of the dihedral angle error and surface shape error of the corner cube prism; further, based on the optical path pointing error detection method of the device, the wavefront shape is restored by phase unwrapping of the interference fringes, and then the pointing angle of the light beam is judged, and its accuracy can reach the wavelength level, which is one order of magnitude higher than the traditional detection accuracy of the detector spot centroid method; by converting the coefficients of the Zernike polynomial into the Seidel coefficients that characterize the aberration, not only the normal direction of the wavefront (i.e., the beam pointing) can be obtained, but also the information on the beam quality such as wavefront distortion, uneven energy distribution, etc. can be measured, which improves the level of detection information and enhances the reliability of the data. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 A schematic diagram of the structure of an optical path pointing error detection device provided by an embodiment of the present invention;

[0040] Figure 2 A schematic diagram of the structure of the PAT subsystem of the transflective part and the laser communication terminal provided in an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of a light path pointing error detection method provided by an embodiment of the present invention;

[0042] Figure 4 A schematic diagram of interference fringes superimposed in a spatial domain detected by a detector provided by an embodiment of the present invention;

[0043] Among them, interferometer ~1, collimator ~2, transflective part ~3, communication light source ~4, tracking light source ~5, detection light source ~6, fiber optic beam splitter ~7, PAT subsystem of laser communication terminal ~8, detector ~9, 45° reflector ~301, first adjustable tilt reference mirror ~302, second adjustable tilt reference mirror ~801, fixed tilt reference mirror ~802. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] The professional terms involved in the embodiments of the present invention are:

[0046] Seidel coefficients are very important concepts in optical systems. Seidel aberration coefficients are mainly used to describe the primary aberrations of optical systems, including spherical aberration, coma, astigmatism, field curvature and distortion.

[0047] In geometric optics, for a rotationally symmetric optical system, the Seidel coefficient can be calculated based on the structural parameters of the optical system (such as the radius of curvature, thickness, refractive index, etc. of the lens) by methods such as ray tracing. 11, W 20 , W 22 , W 31 , W 40 denote the Seidel coefficients associated with tilt, defocus, astigmatism, coma, and spherical aberration, respectively.

[0048] W 40 Related to spherical aberration, spherical aberration refers to the fact that light rays of different aperture angles intersect the optical axis at different positions, resulting in the imaging point being not an ideal point but a diffuse spot.

[0049] W 31 Related to coma, which causes off-axis imaging to produce comet-shaped diffuse spots.

[0050] W 22 Related to astigmatism, astigmatism causes the off-axis point to be imaged at different focal positions in two mutually perpendicular directions.

[0051] W 11 It is related to field curvature, which means that the imaging plane is not an ideal plane but a curved surface.

[0052] W 20 Related to distortion, distortion can distort the shape of the image and deviate from the ideal similar figure.

[0053] Figure 1 A schematic diagram of the structure of an optical path pointing error detection device provided by an embodiment of the present invention is shown in FIG. Figure 1 As shown, the optical path pointing error detection device provided by the embodiment of the present invention mainly includes: an interferometer, a collimator, a transflective part, a communication light source, a tracking light source, a detection light source, an optical fiber splitter, a PAT subsystem of a laser communication terminal, and a detector.

[0054] Specifically, the detection light source and the optical fiber beam splitter constitute the light source part, and the light source part is used to provide a laser light source to the interferometer, the tracking light source and the communication light source respectively. In order to distinguish the three laser beams, a laser beam passing through the interferometer is determined as the first laser beam, a laser beam passing through the tracking light source is determined as the second laser beam, and a laser beam passing through the communication light source is determined as the third laser beam. In practical applications, the light intensity of the three laser beams can be adjusted, and the specific distribution of the three laser beams is not limited here.

[0055] In an embodiment of the present invention, the light source part includes a detection light source and an optical fiber beam splitter, wherein the optical fiber beam splitter is located at the light output side of the detection light source and is used to split the laser from the detection light source.

[0056] Furthermore, the first laser beam entering the interferometer passes through the interferometer and then enters the detector through the transflective part; the second laser beam entering the tracking light source passes through the reflection or transmission of the PAT subsystem of the laser communication terminal and the transflective part and then enters the detector; the third laser beam entering the communication light source passes through the reflection or transmission of the PAT subsystem of the laser communication terminal and the transflective part and then enters the detector.

[0057] In the embodiment of the present invention, the second laser beam from the tracking light source will interfere with the first laser beam from the interferometer, and correspondingly, the third laser beam from the communication light source will also interfere with the first laser beam from the interferometer; due to the existence of the transflective part and the PAT subsystem of the laser communication terminal, if there is an angular error between the second laser beam from the tracking light source and the third laser beam from the communication light source, the second laser beam and the third laser beam will respectively generate interference fringes of different spatial frequencies with the first laser beam on the detector, and by analyzing these interference fringes, the pointing angle of the tracking light source and the communication light source and the coaxiality between the two can be obtained.

[0058] Furthermore, the PAT subsystem of the laser communication terminal is arranged between the tracking light source, the communication light source and the detector; in an embodiment of the present invention, the PAT subsystem of the laser communication terminal is composed of a fixed tilt reference mirror and a second adjustable tilt reference mirror, and the fixed tilt reference mirror and the second adjustable tilt reference mirror are used to refract and / or reflect the second laser beam, so that the optical path of the second laser beam can be deflected; accordingly, the fixed tilt reference mirror and the second adjustable tilt reference mirror are also used to refract and / or reflect the third laser beam, so that the optical path of the third laser beam can be deflected.

[0059] Further, since the transflective part is arranged between the interferometer, the tracking light source, the communication light source and the detector, in the embodiment of the present invention, the transflective part includes a 45° reflector and a first adjustable tilt reference mirror, and the period and clarity of the interference fringes formed on the detector can be changed by adjusting the distance between the first adjustable tilt reference mirror and the 45° reflector and the setting angle of the first adjustable tilt reference mirror; specifically, in one way, the period and clarity of the interference fringes formed on the detector can be changed by adjusting the distance between the first adjustable tilt reference mirror and the 45° reflector; the period and clarity of the interference fringes formed on the detector can be changed by adjusting the angle of the first adjustable tilt reference mirror and the distance between the first adjustable tilt reference mirror and the 45° reflector; the period and clarity of the interference fringes formed on the detector can be changed by adjusting the angle of the first adjustable tilt reference mirror and the distance between the first adjustable tilt reference mirror and the 45° reflector at the same time. That is, in the optical path pointing error detection device provided by the embodiment of the present invention, the period and clarity of the interference fringes formed on the detector can be changed by adjusting the angle of the first adjustable tilt reference mirror included in the transflective part and the distance between the first adjustable tilt reference mirror and the 45° reflector. In the embodiment of the present invention, the specific adjustment method for changing the period and clarity of the interference fringes formed on the detector is not limited.

[0060] The optical path pointing error detection device provided by the embodiment of the present invention adopts the interference detection method, in which the light source part divides the light beam into three, one beam passes through the tracking light path including the tracking light source, one beam passes through the communication light path including the communication light source, and one beam passes through the interferometer as a reference light, thereby avoiding the introduction of system errors by part of the light beam passing through the communication light path during the centroid method detection; furthermore, the device includes a transflective part and a PAT subsystem of the laser communication terminal, and the period and clarity of the interference fringes formed on the detector can be changed by adjusting the angle of the first adjustable tilt reference mirror included in the transflective part and the distance between the mirror and the 45° reflector, thereby facilitating the acquisition of the interference fringes with the best resolution.

[0061] For example, in the optical path pointing error detection device provided by the embodiment of the present invention, the PAT subsystem of the laser communication terminal includes two second adjustable tilt reference mirrors and two fixed tilt reference mirrors. Specifically, the second laser beam and the third laser beam first pass through the two fixed tilt reference mirrors. The PAT subsystem of the laser communication terminal includes two second adjustable tilt reference mirrors, which are rigidly connected to the PAT azimuth axis system and the pitch axis system, and can rotate with the rotation of the PAT axis system, that is, the two second adjustable tilt reference mirrors rotate around the optical axis direction, thereby realizing the pointing of the PAT system to any direction. Theoretically, the azimuth axis can be rotated from 0 to 360° and the pitch axis from 0 to 360°, that is, if there is no pointing error, the optical axis and the axis system are completely coincident. In the embodiment of the present invention, for the convenience of display, the angle of the second adjustable tilt reference mirror set here is 135°, but in actual applications, it can also be set to 45°.

[0062] Furthermore, the 45° reflector provided in the embodiment of the present invention is actually a semi-transparent and semi-reflective mirror, and the ratio of its transmittance to reflectance is half each, that is, transmittance:reflectance=1:1.

[0063] Furthermore, the first adjustable tilt reference mirror provided in the embodiment of the present invention and the fixed tilt reference mirror included in the PAT subsystem of the laser communication terminal are essentially semi-transparent and semi-reflective mirrors. At the same time, the coating types of the 45° reflector, the first adjustable tilt reference mirror, the second adjustable tilt reference mirror and the fixed tilt reference mirror are consistent, and the ratio of transmittance and reflectivity in the optical band is the same, which is half respectively.

[0064] In order to more completely introduce the application method of the optical path pointing error detection device provided by the embodiment of the present invention, the processing of the interference fringe pattern obtained by the optical path pointing error detection device is further introduced below.

[0065] Figure 2 A schematic diagram of a light path pointing error detection method provided by an embodiment of the present invention is shown in FIG. Figure 2 As shown, a method for detecting an optical path pointing error provided by an embodiment of the present invention mainly comprises the following steps:

[0066] Step 101, obtaining the light intensity value of the interference fringes obtained based on the optical path pointing error detection device, separating the interference fringes of different periods, and respectively obtaining the second spatial carrier frequency interference light intensity corresponding to the second laser beam and the third spatial carrier frequency interference light intensity corresponding to the third laser beam;

[0067] Step 102, performing two-dimensional Fourier space transformation on the second spatial carrier frequency interference light intensity and the third spatial carrier frequency interference light intensity respectively, to obtain a second phase value corresponding to the second laser beam and a third phase value corresponding to the third laser beam in sequence;

[0068] Step 103, determining the relationship between the minimum error in the frequency domain and the sampling frequency or the sampling interval according to the measurement error of the sampling points in the frequency domain, the measurement error of the sampling points in the time domain, the number of sampling points and the sampling interval; determining the second wrapped phase value corresponding to the second phase value and the third wrapped phase value corresponding to the third phase value in turn by using an inverse trigonometric function; obtaining the true phase value according to the second wrapped phase value and the third wrapped phase value;

[0069] Step 104 performs Zernike fitting on the real phase value to obtain coefficients of a Zernike polynomial, converts the coefficients of the Zernike polynomial into Seidel coefficients for characterizing aberrations, and obtains a pointing error between the second laser beam and the third laser beam.

[0070] Before step 101, it is necessary to calibrate the position and optical path parameters of the 45° reflector, the fixed tilt reference mirror, the first adjustable tilt reference mirror and the second adjustable tilt reference mirror, and obtain the optical path between the tracking light path and the communication light path included in the optical path pointing error detection device, which is used as a data basis for subsequent data extraction and processing; at the same time, it is also necessary to adjust the light intensity provided by the light source part and the tilt angle of the first adjustable tilt reference mirror, so as to obtain interference fringes of different widths and brightness and superposition on the detector. It should be noted that the adjustment of the position and tilt angle of the 45° reflector, the fixed tilt reference mirror, the first adjustable tilt reference mirror and the second tilt reference mirror is mainly to make the optical axis on the same straight line.

[0071] After the adjustment of the optical path pointing error detection device is completed and the light source is turned on, the light spot on the detector needs to be at the center of mass position. When adjusting the position of the light spot on the detector, the communication optical path is used as a reference, and the optical axes are made to coincide by adjusting the posture and position of the interferometer, thereby avoiding the uncertainty caused by adjusting the terminal under test.

[0072] Furthermore, by adjusting the angle and position of the first adjustable tilt reference mirror, clear interference fringes with different periods can be seen on the detector. The interference fringes here can be as follows: Figure 3 shown.

[0073] In step 101 and step 102, after obtaining interference fringes with different frequencies superimposed, the interference fringes with different periods must first be separated, and the fringes in the spatial domain are converted into the frequency domain to achieve separation and extraction.

[0074] Specifically, the third laser beam emitted by the communication light source interferes with the first laser beam emitted by the interferometer, and the initial interference light intensity is:

[0075]

[0076] Wherein, I1(x, y) represents the interference light intensity of the third laser beam and the first laser beam, and I1(x, y) is referred to as the third initial interference light intensity here; A1(x, y) represents the background light intensity of the interference of the third laser beam and the first laser beam; B1(x, y) represents the amplitude of the interference of the third laser beam and the first laser beam; Indicates the desired phase value of the interference between the third laser beam and the first laser beam.

[0077] In the interference diagram of the third laser beam interfering with the first laser beam, f is introduced along the x and y directions respectively. x1 and f y1 The third spatial carrier frequency interference intensity can be expressed by the following formula:

[0078]

[0079] Among them, I 11 (x, y) represents the interference light intensity of the third spatial carrier after the spatial carrier is introduced, and A1(x, y) represents the background light intensity of the interference between the third laser beam and the first laser beam;

[0080] Furthermore, by performing a two-dimensional Fourier space transform on formula (2), we can obtain:

[0081]

[0082] Among them, I1(f 11 , f 12 ) represents the third Fourier interference light intensity, A1(f 11 , f 12 ,) represents the zero-order spectrum distribution of the third laser beam, C1(f 11 -f x1 ,f 12 -f y1 ) represents the positive first-order spectrum distribution of the third laser beam, Represents the negative first order spectrum distribution of the third laser beam.

[0083] Furthermore, choosing a suitable f x1 and f y1 The zero-order, positive-order and negative-order spectra in the interference spectrum can be separated, and the positive-order spectrum contains the information to be measured without distortion. Then, the bandwidth is appropriately selected, and the center frequency is (f x1 , f y1 ) filter, the positive first order spectrum can be separated. In the frequency domain, C1(f 11 -f x1 ,f 12 -f y1 ) from (f x1 , f y1 ) is translated to the origin to obtain C1(f 11 ,f 12 ) to eliminate the background light intensity. Then, the third phase value can be obtained by inverse Fourier transform, as shown below:

[0084]

[0085] Among them, Re[C1(x,y)] is the real part of C1(x,y), and Im[C1(x,y)] is the imaginary part of C1(x,y).

[0086] Similar to the interference between the third laser beam and the first laser beam emitted by the interferometer, the second Fourier interference light intensity generated by the second laser beam emitted by the tracking light source and the first laser beam emitted by the interferometer is as follows:

[0087]

[0088] Among them, I2(f 21 , f 22 ) represents the second Fourier interference light intensity; A2(f 21 , f 22 ) represents the zero-order spectrum distribution of the second laser beam; C2(f 21 -f2,f 22 -f y2 ) represents the positive first-order spectrum distribution of the second laser beam; Represents the negative first order spectrum distribution of the second laser beam.

[0089] The second phase value of the interference between the second laser beam and the first laser beam As shown below:

[0090]

[0091] Among them, Re[C2(x,y)] is the real part of C2(x,y), and Im[C2(x,y)] is the imaginary part of C2(x,y).

[0092] In step 103, in practical applications, when performing time domain-frequency domain transformation, the error of Fourier transform needs to be considered. This error is related to the detection accuracy requirement. Assuming that E(x) is the measurement error of the light intensity function I0(x), that is, the actual measurement value I(x)=I0(x)+E(x), it can be known from the Fourier transform characteristics that:

[0093] ∫|E(x)| 2 dx=∫|e(σ)| 2 dσ (7)

[0094] Among them, E(x) represents the measurement error in the time domain; e(σ) represents the measurement error in the frequency domain after Fourier transform.

[0095] Since the Fourier transform of the sampled data only contains useful data below the Nyquist frequency, the calculation of σ N Ending, therefore:

[0096]

[0097] Among them, Δσ represents the frequency resolution, that is, the interval between two adjacent points; σ N =1 / 2Δx, which represents the Nyquist frequency; N represents the number of sampling points, and Δx represents the sampling interval.

[0098] In practical applications, the standard deviation of the Fourier transform error of a discrete signal is:

[0099]

[0100] Among them, S x represents the standard deviation of the error in the time domain, S σ represents the standard deviation of the error in the frequency domain, N represents the number of sampling points, E(x j ) represents the measurement error of the jth sampling point in the time domain, e(σ j ) represents the measurement error of the jth sampling point in the frequency domain.

[0101] Furthermore, by combining formula (7) and formula (8), we can get S σ for:

[0102] S σ =S x ΔxN 1 / 2 (10)

[0103] In the embodiment of the present invention, the relationship between the minimum error in the frequency domain and the sampling frequency or the sampling interval is obtained based on formula (10), that is, if the error of Fourier transform is to be reduced, it can be achieved by shortening the sampling interval or increasing the sampling range.

[0104] After obtaining interference fringes of different frequencies in step 101, they can be converted to the time domain space again through the inverse Fourier transform, and then the phase unwrapping process is performed to extract the wavefront features. The wrapped phase obtained by the inverse Fourier transform through the inverse trigonometric function is discontinuous, and its true phase is limited to the range of [-π, π]. It is necessary to perform corresponding processing on the obtained wrapped phase to obtain the true phase of the continuous wavefront to be measured. The relationship between the true phase and the wrapped phase can be expressed by the following formula:

[0105]

[0106] in, Indicates the true phase value; represents the wrapped phase value, and k(x,y) represents the integer wrapped field.

[0107] Based on this, it can be determined that the key to unwrapping is to determine the wrapping field. Under ideal conditions, the difference in the absolute value of the real phase of two adjacent points in the real phase field needs to be less than or equal to π. At this time, the wrapped phase field is equivalent to the phase gradient wrapping value of the real phase field. By traversing the wrapped phase field, the difference in the absolute value of the phase of two adjacent points is not greater than π by adding or subtracting integer multiples of 2π, so as to achieve phase unwrapping.

[0108] In step 104, after the true phase value is obtained according to the second wrapped phase value and the third wrapped phase value, Zernike fitting is performed in combination with the true phase value to obtain the coefficients of the Zernike polynomial. After the coefficients of the Zernike polynomial are obtained, the coefficients of the Zernike polynomial are converted into Seidel coefficients which are commonly used to characterize aberrations in optical design. By further analyzing the Seidel coefficients, the pointing error between the second laser beam and the third laser beam in the embodiment of the present invention is obtained.

[0109] In practical engineering applications, the coefficients of the 36th-order Zernike polynomial are generally used to characterize the wavefront. Table 1 shows some Zernike polynomials and their meanings.

[0110] Table 1 Some Zernike polynomials and their meanings

[0111]

[0112]

[0113] Since Seidel coefficients are often used to analyze aberrations in optical design, Seidel coefficients can be represented by coefficients of Zernike polynomials, and their relationship is shown in Table 2.

[0114] Table 2 Relationship between Seidel coefficients and coefficients of Zernike polynomials

[0115]

[0116] In practical applications, it is assumed that the coefficients of the Zernike polynomials of the interference wavefronts of the second laser beam and the third laser beam respectively interfering with the first laser beam emitted by the interferometer have been obtained by using the above steps, and the coefficients of the Zernike polynomials are used in conjunction with Table 2 to represent the amplitude and angle of the Seidel coefficient. In the examples of the present invention, the W representing the tilt term in the Seidel coefficient is generally used. 11 To determine whether the PAT communication optical path and the PAT tracking optical path are coaxial, use the angle formula of the tilt item in Table 2 The actual pointing angle of the tracking optical path where the second laser beam is located can be obtained, which is recorded as θ. The same method can be used to obtain the actual pointing angle of the communication optical path where the third laser beam is located, which is recorded as β. Then the coaxiality error between the tracking optical path and the communication optical path is θ-β. By calculating the size of θ-β, the coaxiality of the satellite optical communication PAT system corresponding to the optical path pointing error detection device can be detected.

[0117] At the same time, by analyzing other coefficients of the Seidel coefficient, it can be used to evaluate the quality of the outgoing beam, and the beam quality has an important reference value for other indicators of the laser communication terminal. The specific analysis is as follows:

[0118] W stands for defocus 20 , represents the translation of the focus along the optical axis. The presence of defocus will reduce the clarity and contrast of the image; W represents astigmatism 22 The existence of astigmatism causes the off-axis field beam to separate into the meridian and sagittal directions after passing through the pupil, forming a diffuse spot; W represents coma 31 , coma is used to indicate the asymmetry of a wide beam of an off-axis object point after imaging by an optical system. Its existence will disperse the energy of the beam, thus affecting the imaging quality; W, which represents spherical aberration 40 , represents the deviation between the actual image point and the ideal image point, W 40 The larger it is, the larger the diffusion spot on the Gaussian image plane will be, and the less clear the image will be.

[0119] After calculating the coefficients of the Zernike polynomials, and using them to characterize the Seidel coefficients used to characterize aberrations in optical design, not only can the coaxiality of the satellite optical communication PAT system be determined, but also the magnitude of aberrations such as defocus, astigmatism, coma, and spherical aberration can be obtained, which can be used to evaluate the quality of the imaging beam of the system.

[0120] In summary, an embodiment of the present invention provides a method and device for detecting an optical path pointing error, the device comprising: a light source part, which is used to provide a laser light source to an interferometer, a tracking light source and a communication light source respectively; an interferometer, wherein the first laser beam emitted by the interferometer enters the detector through a transflective part; a tracking light source, wherein the second laser beam emitted by the tracking light source enters the detector through a PAT subsystem of the laser communication terminal and the transflective part; a communication light source, wherein the third laser beam emitted by the communication light source enters the detector through the PAT subsystem of the laser communication terminal and the transflective part; the PAT subsystem of the laser communication terminal is arranged between the tracking light source, the communication light source and the detector, and is used to refract and reflect the second laser beam and the third laser beam; a transflective part, which comprises a 45° reflector and a first adjustable tilt reference mirror, which is used to adjust the angle of the first adjustable tilt reference mirror and / or the distance between the first adjustable tilt reference mirror and the 45° reflector, and change the period and clarity of the interference fringes formed on the detector, wherein the second laser beam and the first laser beam form interference fringes on the detector, and the third laser beam and the first laser beam form interference fringes on the detector. When the device adopts the interference detection method, the light source part divides the light beam into three parts: one beam passes through the tracking light path including the tracking light source, one beam passes through the communication light path including the communication light source, and one beam passes through the interferometer as a reference light, thereby avoiding the introduction of system errors by part of the light beam passing through the communication light path during the centroid method detection; furthermore, the device includes a transflective part, and by adjusting the position and tilt angle of the first adjustable tilt reference mirror included in the transflective part, the period and clarity of the interference fringes formed on the detector can be changed, thereby facilitating the acquisition of the interference fringes with the best resolution, and compared with the previous use of a corner cube prism for coaxiality detection of laser communication terminals, this avoids the problem of angle error. The influence of the dihedral angle error and surface shape error of the conical prism; further, based on the optical path pointing error detection method of the device, the wavefront shape is restored by phase unwrapping of the interference fringes, and then the pointing angle of the light beam is determined, and its accuracy can reach the wavelength level, which is one order of magnitude higher than the traditional detection accuracy using the detector spot centroid method; by converting the coefficients of the Zernike polynomial into the Seidel coefficients used to characterize the aberration in optical design, not only the normal direction of the wavefront, that is, the beam pointing, can be obtained; the beam quality, such as wavefront distortion, uneven energy distribution and other information can also be measured, which improves the level of detection information and enhances the reliability of the data.

[0121] Another embodiment of the present invention also provides a computer device, which includes: a processor and a memory; the memory is used to store computer program code, and the computer program code includes computer instructions; when the processor executes the computer instructions, the electronic device executes the various steps shown in the above-mentioned optical path pointing error detection method embodiment.

[0122] Another embodiment of the present invention further provides a computer-readable storage medium, in which computer instructions are stored. When the computer instructions are executed on a computer device, the computer device executes the various steps shown in the above-mentioned optical path pointing error detection method embodiment.

[0123] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0124] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. An optical path pointing error detection device, characterized in that: include: A light source part, which is used to provide a laser light source to the interferometer, the tracking light source and the communication light source respectively; An interferometer, which emits a first laser beam that enters a detector through a transflective part; A tracking light source emits a second laser beam which passes through the PAT subsystem of the laser communication terminal and the transflective part and enters the detector; A communication light source, wherein a third laser beam emitted by the communication light source passes through the PAT subsystem of the laser communication terminal and the transflective part and enters the detector; A PAT subsystem of the laser communication terminal, which is arranged between the tracking light source, the communication light source and the detector, and is used to refract and reflect the second laser beam and the third laser beam; The transflective part includes a 45° reflector and a first adjustable tilt reference mirror, which is used to adjust the angle of the first adjustable tilt reference mirror and / or the distance between the first adjustable tilt reference mirror and the 45° reflector to change the period and clarity of the interference fringes formed on the detector, wherein the second laser beam and the first laser beam form interference fringes on the detector, and the third laser beam and the first laser beam form interference fringes on the detector.

2. The device according to claim 1, characterized in that The intensity of a laser light source provided by the light source part to the interferometer is adjustable; and / or The intensity of a laser light source provided by the light source part to the tracking light source is adjustable; and / or The intensity of a laser light source provided by the light source part to the communication light source is adjustable.

3. The device according to claim 1, characterized in that The PAT subsystem of the laser communication terminal includes two second adjustable tilt reference mirrors and two fixed tilt reference mirrors, and the second laser beam and the third laser beam first pass through the two fixed tilt reference mirrors respectively.

4. The device according to claim 1, characterized in that The 45° reflector is a semi-transparent and semi-reflective mirror, and the transmittance and reflectivity are 1:1; The fixed tilt reference mirror and the second adjustable tilt reference mirror included in the first adjustable tilt reference mirror and the PAT subsystem of the laser communication terminal are semi-transparent and semi-reflective mirrors, and the transmittance and reflectivity are 1:

1.

5. A method for detecting an optical path pointing error, characterized in that: include: Obtaining the light intensity value of the interference fringes obtained based on the optical path pointing error detection device, separating the interference fringes of different periods, and respectively obtaining the second spatial carrier frequency interference light intensity corresponding to the second laser beam and the third spatial carrier frequency interference light intensity corresponding to the third laser beam; Performing two-dimensional Fourier space transformation on the second spatial carrier frequency interference light intensity and the third spatial carrier frequency interference light intensity respectively, and obtaining a second phase value corresponding to the second laser beam and a third phase value corresponding to the third laser beam in sequence; Determine the relationship between the minimum error in the frequency domain and the sampling frequency or the sampling interval according to the measurement error of the sampling points in the frequency domain, the measurement error of the sampling points in the time domain, the number of sampling points and the sampling interval; determine the second wrapped phase value corresponding to the second phase value and the third wrapped phase value corresponding to the third phase value in turn by inverse trigonometric functions; obtain the true phase value according to the second wrapped phase value and the third wrapped phase value; The true phase value is subjected to Zernike fitting to obtain coefficients of a Zernike polynomial, the coefficients of the Zernike polynomial are converted into Seidel coefficients for characterizing aberrations, and the pointing error between the second laser beam and the third laser beam is obtained.

6. The method according to claim 5, characterized in that After performing two-dimensional Fourier space transformation on the second interference light intensity and the third interference light intensity, the second Fourier interference light intensity and the third Fourier interference light intensity are obtained respectively: The second phase value and the third phase value are as follows: Among them, I1(f 11 , f 12 ) represents the third Fourier interference light intensity, A1(f 11 , f 12 ,) represents the zero-order spectrum distribution of the third laser beam, C1(f 11 -f x1 ,f 12 -f y1 ) represents the positive first-order spectrum distribution of the third laser beam, represents the negative first-order spectrum distribution of the third laser beam; I2(f 21 , f 22 ) represents the second Fourier interference light intensity, A2(f 21 , f 22 ) represents the zero-order spectrum distribution of the second laser beam, C2(f 21 -f x2 ,f 22 -f y2 ) represents the positive first-order spectrum distribution of the second laser beam; represents the negative first order spectrum distribution of the second laser beam; represents the third phase value, represents the second phase value, Im[C1(x,y)] represents the imaginary part of C1(x,y), Re[C1(x,y)] represents the real part of C1(x,y), Im[C2(x,y)] represents the imaginary part of C2(x,y), and Re[C2(x,y)] represents the real part of C2(x,y).

7. The method according to claim 5, characterized in that The relationship between the minimum error value in the frequency domain and the sampling frequency or sampling interval is as follows: S σ =S x ΔxN 1 / 2 Among them, S σ represents the standard deviation of the error in the frequency domain, S x represents the standard deviation of the error in the time domain, N represents the number of sampling points, Δx represents the sampling interval; E(x j ) represents the measurement error of the jth sampling point in the time domain, e(σ j ) represents the measurement error of the jth sampling point in the frequency domain.

8. The method according to claim 5, characterized in that The true phase value is determined by the following formula: in, Indicates the true phase value; represents the wrapped phase value, and k(x,y) represents the integer wrapped field.

9. A computer device, characterized in that: The computer device includes a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the optical path pointing error detection method as described in any one of claims 5-9.

10. A computer-readable storage medium, characterized in that: A computer program is stored, and when the computer program is executed by a processor, the processor executes the optical path pointing error detection method as described in any one of claims 5-9.

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