High-precision wide-range angle signal measurement system

Abstract

The invention relates to a high-precision wide-range angle signal measurement system. In order to ensure that reference measurement light is always propagated on the same optical axis in a target rotation process and an optical interference signal is not damaged due to rotation, a lens group is designed to image the centers of light spots incident on a target on the center of a detector, so that light spot migration caused by the target in the rotation process is inhibited. Under the design of the invention, a stable optical interference signal can be obtained as long as the target rotation angle is within the view field range of the lens group. Sensitivity to phase measurement noise can be reduced through a linear displacement measurement method, angle signals are amplified through the lever effect, influences of translational motion can be eliminated through differential readout, and the wide-angle optical path has the large-angle measurement capacity superior to that of an existing optical path.

Description

Technical Field

[0001] The invention belongs to the field of space signal measurement and relates to a high-precision and large-range angular signal measurement system. Background Art

[0002] Space gravitational wave detection uses space laser interferometry technology to invert gravitational wave signals by reading the distance changes between free-falling test masses. With the support of drag-free technology, the test masses freely fall along the direction of the interstellar center of mass line, strictly unaffected by external forces, thereby providing a stable inertial reference for gravitational wave measurements, while the laser interferometer provides high-precision displacement signals of the test masses in the direction of the center of mass line.

[0003] Affected by the constellation breathing angle, the center of mass line will change over time relative to the satellite body. To ensure normal operation without drag, the angle of the proof mass needs to be adjusted in real time so that its reflecting surface is always facing the center of mass line. To this end, it is necessary to read out the angle signal of the proof mass relative to the satellite with high precision. On the other hand, the satellite attitude will undergo random jitter within the detection frequency band, resulting in laser interferometry displacement signal noise of the center of mass line, which is called jitter-optical path coupling noise. This noise is the second largest noise source in space gravitational wave detection. If there is high-precision attitude angle measurement data, the jitter-optical path coupling noise of the proof mass readout part can be suppressed through data processing.

[0004] On the other hand, in order to verify the working modes of the space gravitational wave inertial sensor such as drag-free control on the ground, a torsion balance is generally used to simulate the state of the inspection mass, and high-precision torsion pendulum angle readout is also one of its key technologies. For this reason, nanoradian-level high-precision angular signal readout is one of the goals of the development of laser interferometry technology for space gravitational wave detection.

[0005] In order to achieve nanoradian-level high-precision angle signal readout capability in heterodyne interferometry, two measurement schemes have been proposed internationally. The first is to use a four-quadrant detector based on differential wavefront sensing technology to obtain the angle between the reference light and the signal light involved in the interference.

[0006] The advantage of this method is that the angle signal can be perfectly integrated with the axial optical path signal, and because the four-quadrant detector has a small facet, the four quadrant signals of the wavefront interference have a very high common-mode suppression capability against environmental noise; however, due to the small facet of the four-quadrant detector, the phase measurement noise requirements for the differential signal are higher. Generally speaking, the relationship between the wavefront phase differential signal caused by the angle signal is:

[0007]

[0008] Where d represents the pixel center distance, δθ represents the angle signal, Represents the phase difference between quadrants, and λ represents the laser wavelength. It can be seen that the smaller the facet size and the smaller the pixel center distance, the more sensitive the angle signal is to phase noise. In addition, due to the limitations of its detection principle, this detection method also has the problem of a small angle measurement range: in order to achieve the coupling of wavefront difference and angle signal, the reference light must be fixed, and the measurement light is reflected by the target. The reference measurement light must have an angle, which is the measurement signal that is desired to be obtained. However, when the angle of the reference measurement light is too large, the interference efficiency will decay rapidly, resulting in signal loss. According to the LISA team's simulation of the interferometer, the corresponding angle when the interference efficiency decays to 0.1 is about 1 mrad.

[0009] The second scheme is based on the linear displacement measurement method. This method uses the piston effect of the target rotation on the laser incident point to generate a displacement signal. After the laser returns to the detector and interferes with the reference light, the displacement signal is read out through the phase signal of the interference signal, thereby inverting the target's angular rotation. The advantage of this method is that the lateral distance from the incident point to the rotation center can be set very large, that is, d in formula (1). For example, in LISA, the size of the inspection mass is approximately a square with a side length of 46 mm, so d can be a maximum of 23 mm, which can reduce the impact of phase measurement noise on angle reading by orders of magnitude; however, similar to the differential wavefront sensing method, the angle measurement range of the linear displacement method is also affected by the interference efficiency. Under large angle rotation, there will be a problem of interference signal loss. In addition, since the piston signal is used as the angle signal in linear displacement angle measurement, it is impossible to distinguish between true translation signals and rotation signals. Figure 1 Schematic diagram of the principle of linear displacement angle measurement.

[0010] In order to solve the problem of mixing true translation and rotation signals, an improvement to linear displacement angle measurement is the differential linear displacement angle measurement method. The principle is to allow both reference light and measurement light to be incident on the measurement target. At this time, the true translation signal will be automatically eliminated in the interference signal. However, this method also has a small measurement range. When the angle is too large, signal loss will occur, especially when the optical path between the detector and the incident point is large. Summary of the invention

[0011] The technical problem solved by the present invention is to overcome the deficiencies of the prior art and provide a high-precision and large-range angle signal measurement system.

[0012] The solution of the present invention is:

[0013] A high-precision, large-range angular signal measurement system, comprising a light source preparation module, a spatial optical path module, and a signal acquisition and solution module; the spatial optical path module comprises a first detector, a second detector, a first polarizer, a second polarizer, a non-polarizing beam splitter, a first polarizing beam splitter, a second polarizing beam splitter, a first 1 / 4 wave plate, a second 1 / 4 wave plate, a third 1 / 4 wave plate, a fourth 1 / 4 wave plate, a 1 / 2 wave plate, a first plane mirror, a second plane mirror, and an imaging system; a spatial rectangular coordinate system is defined, wherein the laser emitted by the collimator propagates along the -x direction, and the +z direction is perpendicular to the paper surface and outward;

[0014] The light source preparation module is used to provide dual-frequency lasers with orthogonal polarizations, which are transmitted to the fiber collimator through polarization-maintaining optical fiber; the fiber collimator generates dual-frequency collimated linearly polarized lasers with orthogonal polarizations, one of which is polarized along the z-axis, recorded as 1 light, and the other is polarized along the y-axis, recorded as 2 light; the dual-frequency collimated linearly polarized lasers with orthogonal polarizations are split into reflected light and transmitted light by a non-polarizing beam splitter, wherein the reflected light is used as a reference light, and is projected by the first polarizer to generate an interference light beat signal, which is received by the first detector for photoelectric conversion, and the electrical signal is transmitted to the signal acquisition and resolution module; the transmitted light is transmitted to the first polarization beam splitter, the 1 light polarized along the z-axis is emitted as s light, and the 2 light polarized along the y-axis is directly transmitted as p light;

[0015] Light 1 reflected by the first polarization beam splitter is incident on the target surface after passing through the first 1 / 4 wave plate, and after being reflected, it passes through the first 1 / 4 wave plate again to become p light polarized along the y axis, enters the first polarization beam splitter, and is transmitted by the first polarization beam splitter and then passes through the second 1 / 4 wave plate to be incident on the first plane mirror, and is reflected by the first plane mirror and then transmitted by the second 1 / 4 wave plate again. At this time, light 1 becomes s light polarized along the z axis, and after returning to the first polarization beam splitter, it is reflected by the first polarization beam splitter and propagates coaxially with light 2 to the 1 / 2 wave plate again. The 1 / 2 wave plate rotates the polarization directions of both by 90°. At this time, light 1 is polarized along the y direction, and light 2 is polarized along the Z direction; light 1 polarized along the y direction and light 2 polarized along the z direction are incident on the second polarization beam splitter, light 1 is directly transmitted to the imaging system, and light 2 is reflected;

[0016] The 2 light reflected by the second polarization beam splitter is incident on the target surface after passing through the third 1 / 4 wave plate, and after being reflected, it passes through the third 1 / 4 wave plate again to become the p light polarized along the y axis, enters the second polarization beam splitter, and is transmitted through the second polarization beam splitter and then passes through the fourth 1 / 4 wave plate to be incident on the second plane mirror, and is reflected by the second plane mirror and then transmitted through the fourth 1 / 4 wave plate again. At this time, the 2 light becomes the s light polarized along the z axis, and after returning to the second polarization beam splitter, it is reflected by the second polarization beam splitter and propagates coaxially with the 1 light again, and enters the imaging system;

[0017] After the imaging system receives light 1 and light 2, it shrinks the beam, and the interference light beat signal is projected by the second polarizer, which is received by the second detector for photoelectric conversion to generate an electrical signal, which is transmitted to the signal acquisition and solution module;

[0018] The signal acquisition and solution module calculates the phase difference between the two light beats and the target rotation angle according to the electrical signals transmitted by the first detector and the second detector.

[0019] Preferably, the polarization extinction ratio of the non-polarization beam splitter is greater than 20 dB.

[0020] Preferably, the polarizations of the coaxially propagated light 1 and light 2 emitted from the first polarization beam splitter still remain orthogonal.

[0021] Preferably, the polarizations of the coaxially propagated light 1 and light 2 emitted from the second polarization beam splitter still remain orthogonal.

[0022] Preferably, the target rotation angle

[0023]

[0024] λ is the laser wavelength, d 4 is the center distance between the light spot of the 1st light and the 2nd light reflection point on the target emitting surface, is the phase difference between the two light shots.

[0025] Preferably, the propagation optical path of the light 1 and the light 2 at the front end of the imaging system satisfies the formula:

[0026] 2d 1 +d 4 =2d 3

[0027] where d 1 is the optical path between the center of the first polarization beam splitter and the first plane mirror, d3 is the optical path between the center of the second polarization beam splitter and the second plane mirror, and d4 is the optical path between the center of the first polarization beam splitter and the center of the second polarization beam splitter.

[0028] Preferably, the imaging system matrix is ​​described as The following imaging relationship and beam reduction relationship are satisfied from the target reflection point to the detector center:

[0029]

[0030] Among them l 1 =2d 3 =2d 1 +d 4 Represents the optical path from the reflection point of the laser on the target to the entrance pupil of the imaging system; l 2 =d 6 Represents the optical path from the exit pupil of the imaging system to the center of the detector.

[0031] Preferably, wherein l 1 =2d 3 =2d 1 +d 4 , l 2 =d 6 , where d 1 is the optical path between the center of the first polarization beam splitter and the first plane mirror, d3 is the optical path between the center of the second polarization beam splitter and the second plane mirror, and d4 is the optical path between the center of the first polarization beam splitter and the center of the second polarization beam splitter.

[0032] Preferably, the light source preparation module uses an AOM frequency shift method or a dual-laser heterodyne phase-locking method to generate dual-frequency lasers with orthogonal polarizations.

[0033] The beneficial effects of the present invention compared with the prior art are:

[0034] The present invention proposes an optical path based on differential linear displacement angle measurement. First, it ensures that the reference measurement light always propagates along the optical axis during the rotation of the target, and the optical interference signal will not be destroyed due to the rotation; however, since there is still a distance between the incident point and the detector, the interference spot will wander on the photosensitive surface of the detector when the target rotates. When the rotation angle is too large, the interference spot will completely move away from the detector. Although the optical interference signal can be maintained, it cannot be received by the detector. To this end, the present invention designs a lens group to image the center of the light spot incident on the target at the center of the detector, thereby suppressing the wandering of the light spot caused by the rotation of the target. Under the design of the present invention, as long as the target rotation angle is within the field of view of the lens group, it is theoretically within the normal working range. Therefore, the present invention can reduce the sensitivity to phase measurement noise through the linear displacement measurement method, amplify the angle signal by lever effect, and eliminate the influence of translation through differential readout, and has the ability to measure large angles beyond the existing optical path. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the principle of linear displacement angle measurement;

[0036] Figure 2 Schematic diagram of the angle measurement system of the present invention;

[0037] Figure 3 This is a schematic diagram of the spatial optical path object-image relationship design of the present invention;

[0038] Figure 4 To verify the quality angle signal readout example;

[0039] Figure 5 Example for breathing angle readout. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings.

[0041] The present invention can be directly used to measure the rotation signal of a rigid body. Its application fields include multi-degree-of-freedom readout of space gravitational wave detection inspection mass and readout of torsion balance angle signals in weak force measurement. It can also be scalably applied to fields such as laser interferometer truss angle signal measurement.

[0042] The present invention adopts the principle of differential displacement angle measurement and combines the high-precision measurement capability of laser heterodyne interferometer on displacement signal to design an interference optical path that can adapt to the wide range of angle changes of the target. The spatial optical path design is as follows: Figure 2 shown.

[0043] The measurement system of the present invention comprises a light source preparation module, a spatial optical path module and a signal acquisition and solution module. A spatial rectangular coordinate system is defined, wherein the laser emitted by the collimator propagates along the -x direction and the +z direction is perpendicular to the paper surface and outward.

[0044] The light source preparation module is used to provide dual-frequency lasers with orthogonal polarizations, which are transmitted to the fiber collimator by the fast and slow axes of the polarization-maintaining fiber. This design does not require the preparation method of the light source. For example, it can use the AOM frequency shift method or it can be generated by dual laser heterodyne phase locking, and there is no restriction on the laser wavelength.

[0045] The prepared light source is connected to a fiber collimator through a polarization-maintaining fiber to generate collimated laser. The collimation parameters can be designed according to specific measurement requirements. For example, for a cube test mass with a side length of 46 mm in space gravitational waves, the collimation waist diameter can be designed to be 0.5 mm.

[0046] The collimator outputs dual-frequency collimated linearly polarized lasers with orthogonal polarizations, one of which is polarized along the z-axis (shown by the green line in the figure, defined as light 1), and the other is polarized along the y-axis (shown by the red line in the figure, defined as light 2).

[0047] The collimated laser beam is output through the fiber collimator and split by the non-polarizing beam splitter, where the reflected light is used as the reference light. After being projected by the first polarizer, the interference light beat signal is received by the first detector for photoelectric conversion and the electrical signal is transmitted to the signal acquisition and solution module. The polarization extinction ratio (polarization maintaining capability) of the non-polarizing beam splitter is required to be greater than 20dB.

[0048] The transmitted light of the non-polarizing beam splitter is transmitted to the first polarizing beam splitter (PBS), the 2 light polarized along the y-axis is the p light, and the 1 light polarized along the z-axis is the s light, so the 1 light will be reflected and the 2 light will be directly transmitted;

[0049] Light 1 reflected by the first polarization beam splitter is incident on the target surface after passing through the first 1 / 4 wave plate. After reflection, it passes through the first 1 / 4 wave plate again to become p light polarized along the y-axis, enters the first polarization beam splitter, and is transmitted by the first polarization beam splitter and then passes through the second 1 / 4 wave plate to be incident on the first plane mirror. After being reflected by the first plane mirror, it is transmitted by the second 1 / 4 wave plate again. At this time, light 1 becomes s light polarized along the z-axis, and after returning to the first polarization beam splitter, it is reflected by the first polarization beam splitter and propagates coaxially with light 2 again, and at this time, the polarizations of light 1 and light 2 still remain orthogonal.

[0050] After passing through the first PBS, light 1 and light 2 pass through a 1 / 2 wave plate, which rotates the polarization directions of both light 1 and light 2 by 90°. At this time, light 1 is polarized along the y direction and light 2 is polarized along the z direction.

[0051] The 2 light reflected by the second polarization beam splitter is incident on the target surface after passing through the third 1 / 4 wave plate. After reflection, it passes through the third 1 / 4 wave plate again to become the p light polarized along the y-axis, enters the second polarization beam splitter, and is transmitted by the second polarization beam splitter and then passes through the fourth 1 / 4 wave plate to be incident on the second plane mirror. After being reflected by the second plane mirror, it is transmitted by the fourth 1 / 4 wave plate again. At this time, the 2 light becomes the s light polarized along the z-axis. After returning to the second polarization beam splitter, it is reflected by the second polarization beam splitter and propagates coaxially with the 1 light again. At this time, the polarizations of the two are still orthogonal.

[0052] The coaxially propagated lights 1 and 2 after passing through the second polarization beam splitter are received by the imaging system and focused onto the second detector. After the interference light beat signal is projected by the second polarizer in front of the second detector, the second detector performs photoelectric conversion to generate an electrical signal, which is finally transmitted to the signal acquisition and solution module.

[0053] The signal acquisition and resolution module converts the electrical signal transmitted by the detector into digital form and uses the phase resolution algorithm to calculate the phase difference between the two light beats. The present invention does not restrict the phase solution method, and can use an orthogonal phase demodulation algorithm or a zero-crossing phase detection method, etc.

[0054] The target rotation angle is calculated using the following formula:

[0055]

[0056] λ is the laser wavelength, d 4 It is the center distance of the light spot of the reflection point 1 and the reflection point 2 on the target emitting surface.

[0057] In the present invention:

[0058] (1) Optical path relationship

[0059] In order to achieve the coaxial propagation of light 1 and light 2 and the coincidence of the virtual images of the incident points, the design key point of the present invention is that the propagation optical path of light 1 and light 2 at the front end of the imaging system satisfies the formula:

[0060] 2d 1 +d 4 =2d 3

[0061] where d 1 ,d 2 ,d 3 Represents the optical path as shown in the figure; d 1 is the optical path between the center of the first polarization beam splitter and the first plane mirror, d3 is the optical path between the center of the second polarization beam splitter and the second plane mirror, and d4 is the optical path between the center of the first polarization beam splitter and the center of the second polarization beam splitter. At this time, after the second polarization beam splitter propagates coaxially again, the virtual images of the 1 and 2 light beams formed by the plane system they pass through on the target reflection surface overlap.

[0062] (2) Imaging system design

[0063] The key point of the present invention is to use an imaging system to shrink the incident points of the above-mentioned lights 1 and 2 at the target from a plane system into a virtual image, which is then imaged again with the center of the detector through a subsequent imaging system, so that the incident points of the lights 1 and 2 at the target and the center of the detector form imaging conjugate points. At this time, according to the object-image relationship, since the incident points of the lights 1 and 2 at the target mainly undergo axial movement during the rotation process, the positions of their image points on the detector remain almost unchanged, and can adapt to a wide range of angular rotation changes.

[0064] like Figure 2 As shown, the imaging system matrix is ​​described as The following imaging relationship and beam reduction relationship are satisfied from the target reflection point to the detector center:

[0065]

[0066] Among them l 1 =2d 3 =2d 1 +d 4 Represents the optical path from the reflection point of the laser on the target to the entrance pupil of the imaging system; l 2 =d 6 Represents the optical path from the exit pupil of the imaging system to the center of the detector. 1 =2d 3 =2d 1 +d 4 , l 2 =d 6 .

[0067] Figure 3This is a schematic diagram of the design principle of the spatial optical path object-image relationship of the present invention. On the basis of differential displacement angle measurement, the reflection points of light 1 and light 2 on the target are projected from a plane system to the same virtual image point through an optical path design. Moreover, since light 1 and light 2 are emitted from the same optical fiber through the same collimator, light 1 and light 2 appear to be collimated lasers generated by the same surface light source located at the virtual image point in the subsequent imaging system. This ensures that during the rotation of the target, even if the laser optical axis rotates relative to the optical axis of the imaging system, light 1 and light 2 can still maintain the coaxial propagation characteristics. If a polarizing plate is used to allow projection interference, it can be proved that the heterodyne interference efficiency of the interference signal remains almost unchanged during the rotation of the target. Compared with the previous angle readout optical path design, the present invention solves the problem of rapid attenuation of interference efficiency during large-angle rotation.

[0068] After achieving co-optical axis propagation, the present invention further designs an imaging system so that the virtual image point of the reflection point on the target is re-projected by the imaging system and imaged at the center of the second detector. This can fix the interference spot in the central area of ​​the second detector, ensuring that sufficient energy can be received during the rotation process without losing the interference signal; and based on the analysis of the equal optical path properties of the object and the optical simulation of space gravitational wave detection on the jitter-optical path coupling noise, this design can minimize the coupling of the optical axis tilt to the optical path signal, and highlight the sensing relationship of the Piston signal to the rotation angle.

[0069] In space gravitational wave detection, high-precision angular signal readout for mass verification is one of the important technologies. An angular signal measurement system that can adapt to a wide range of angle readouts will greatly improve the robustness of the system. When it comes to breathing angle readouts over a large angle range (the angle range is approximately ±1°), although the previous methods can meet the requirements in terms of accuracy, they are limited in the measurement range and cannot guarantee the acquisition of interference signals.

[0070] For the inspection mass readout, it is only necessary to adjust the measurement system designed by the present invention on the inspection mass electrode cage. The light source preparation module is provided by the laser interferometer measurement payload light source system. According to the gravitational wave laser interferometer measurement payload design, the heterodyne signal is generated by dual laser phase locking, and the polarization-maintaining fiber beam combiner forms a dual-frequency linear polarized laser with orthogonal polarization and inputs it into the spatial optical path; the signal processing can be uniformly processed by the onboard phase meter.

[0071] According to the current mainstream space gravitational wave payload working mode design, the MOSA mechanism is used to continuously compensate for the influence of the orbital breathing angle, and the jitter noise requirement within the MOSA mechanism frequency band is on the order of 1nrad / √Hz, while the breathing angle variation range is about ±1° (±17.3mrad). To achieve large-scale and high-precision continuous adjustment of pointing, a wide-range and high-precision angle readout sensor is required, while the differential wavefront sensing readout does not have large-angle measurement capabilities. In this case, the present invention can meet both the accuracy requirements (the accuracy is comparable to the accuracy of the scientific interferometer DWS angle signal) and the measurement needs of a large angle range. Figure 4 An example of checking the quality angle signal readout. Figure 5 Example for breathing angle readout.

[0072] The present invention can be applied to multi-degree-of-freedom optical readout of space gravitational wave detection test mass and breathing angle optical readout. Its advantages are that it inherits the high precision of linear displacement angle measurement and greatly enhances the robustness of measurement due to its tolerance for the rotation angle of the test mass, and can adapt to the large range of changes in the breathing angle (±1°) and high-precision control requirements (the pointing noise in the detection band is at least lower than 10nrad / √Hz); at the same time, the invention can also be used in weak force measurement performed by a torsion balance to perform high-precision measurement of the torsion pendulum signal; finally, the invention can be scalably applied to the fields of angle measurement that require large angles and high precision, such as the primary and secondary mirror postures and the calibration of rotating mirrors in engineering.

[0073] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A high-precision, large-range angle signal measurement system, characterized in that: It includes a light source preparation module, a spatial optical path module, and a signal acquisition and solution module; the spatial optical path module includes a first detector, a second detector, a first polarizer, a second polarizer, a non-polarizing beam splitter, a first polarizing beam splitter, a second polarizing beam splitter, a first 1 / 4 wave plate, a second 1 / 4 wave plate, a third 1 / 4 wave plate, a fourth 1 / 4 wave plate, a 1 / 2 wave plate, a first plane mirror, a second plane mirror, and an imaging system; a spatial rectangular coordinate system is defined, wherein the laser emitted by the collimator propagates along the -x direction, and the +z direction is perpendicular to the paper surface and outward; The light source preparation module is used to provide dual-frequency lasers with orthogonal polarizations, which are transmitted to the fiber collimator through polarization-maintaining optical fiber; the fiber collimator generates dual-frequency collimated linearly polarized lasers with orthogonal polarizations, one of which is polarized along the z-axis, recorded as 1 light, and the other is polarized along the y-axis, recorded as 2 light; the dual-frequency collimated linearly polarized lasers with orthogonal polarizations are split into reflected light and transmitted light by a non-polarizing beam splitter, wherein the reflected light is used as a reference light, and is projected by the first polarizer to generate an interference light beat signal, which is received by the first detector for photoelectric conversion, and the electrical signal is transmitted to the signal acquisition and resolution module; the transmitted light is transmitted to the first polarization beam splitter, the 1 light polarized along the z-axis is emitted as s light, and the 2 light polarized along the y-axis is directly transmitted as p light; Light 1 reflected by the first polarization beam splitter is incident on the target surface after passing through the first 1 / 4 wave plate, and after being reflected, it passes through the first 1 / 4 wave plate again to become p light polarized along the y axis, enters the first polarization beam splitter, and is transmitted by the first polarization beam splitter and then passes through the second 1 / 4 wave plate to be incident on the first plane mirror, and is reflected by the first plane mirror and then transmitted by the second 1 / 4 wave plate again. At this time, light 1 becomes s light polarized along the z axis, and after returning to the first polarization beam splitter, it is reflected by the first polarization beam splitter and propagates coaxially with light 2 to the 1 / 2 wave plate again. The 1 / 2 wave plate rotates the polarization directions of both by 90°. At this time, light 1 is polarized along the y direction, and light 2 is polarized along the Z direction; light 1 polarized along the y direction and light 2 polarized along the z direction are incident on the second polarization beam splitter, light 1 is directly transmitted to the imaging system, and light 2 is reflected; The 2 light reflected by the second polarization beam splitter is incident on the target surface after passing through the third 1 / 4 wave plate, and after being reflected, it passes through the third 1 / 4 wave plate again to become the p light polarized along the y axis, enters the second polarization beam splitter, and is transmitted through the second polarization beam splitter and then passes through the fourth 1 / 4 wave plate to be incident on the second plane mirror, and is reflected by the second plane mirror and then transmitted through the fourth 1 / 4 wave plate again. At this time, the 2 light becomes the s light polarized along the z axis, and after returning to the second polarization beam splitter, it is reflected by the second polarization beam splitter and propagates coaxially with the 1 light again, and enters the imaging system; After the imaging system receives light 1 and light 2, it shrinks the beam, and the interference light beat signal is projected by the second polarizer, which is received by the second detector for photoelectric conversion to generate an electrical signal, which is transmitted to the signal acquisition and solution module; The signal acquisition and solution module calculates the phase difference between the two light beats and the target rotation angle according to the electrical signals transmitted by the first detector and the second detector.

2. A high-precision and large-range angle signal measurement system according to claim 1, characterized in that: The polarization extinction ratio of the non-polarizing beam splitter is greater than 20dB.

3. The high-precision and large-range angle signal measurement system according to claim 1, characterized in that: The polarizations of the coaxially propagating light 1 and light 2 emitted from the first polarization beam splitter still remain orthogonal.

4. The high-precision and large-range angle signal measurement system according to claim 1, characterized in that: The polarizations of the coaxially propagating light 1 and light 2 emitted from the second polarization beam splitter still remain orthogonal.

5. The high-precision and large-range angle signal measurement system according to claim 1, characterized in that: Target rotation angle λ is the laser wavelength, d4 is the center distance between the light spot of the 1st light and the 2nd light reflection point on the target emitting surface, is the phase difference between the two light shots.

6. The high-precision and large-range angle signal measurement system according to claim 1, characterized in that: The propagation optical path of light 1 and light 2 at the front end of the imaging system satisfies the formula: 2d1+d4=2d3 Wherein d1 is the optical path between the center of the first polarization beam splitter and the first plane mirror, d3 is the optical path between the center of the second polarization beam splitter and the second plane mirror, and d4 is the optical path between the center of the first polarization beam splitter and the center of the second polarization beam splitter.

7. The high-precision and large-range angle signal measurement system according to claim 1, characterized in that: The imaging system matrix is ​​described as The following imaging relationship and beam reduction relationship are satisfied from the target reflection point to the detector center: Among them, l1=2d3=2d1+d4 represents the optical path from the reflection point of the laser on the target to the entrance pupil of the imaging system; l2=d6 represents the optical path from the exit pupil of the imaging system to the center of the detector.

8. The high-precision and large-range angle signal measurement system according to claim 7, characterized in that: Among them, l1=2d3=2d1+d4, l2=d6, wherein d1 is the optical path between the center of the first polarization beam splitter and the first plane mirror, d3 is the optical path between the center of the second polarization beam splitter and the second plane mirror, and d4 is the optical path between the center of the first polarization beam splitter and the center of the second polarization beam splitter.

9. The high-precision and large-range angle signal measurement system according to claim 1, characterized in that: The light source preparation module uses an AOM frequency shift method or a dual-laser heterodyne phase-locking method to generate dual-frequency lasers with orthogonal polarizations.

Images