A non-imaging goniometer device and method based on birefringent polarization encoding

Abstract

The application discloses a kind of based on birefringent polarization encoding non-imaging goniometer device and method, belong to precision optical measurement and photoelectric detection technical field, the device is by polarization unit, birefringent encoding unit, polarization correlation diffraction decoding unit, coupling light collection unit, power detection unit and signal processing unit composition, incident light is polarized after polaroid, with the incident angle to be measured incident to birefringent encoding unit, by the birefringent encoding unit between ordinary light component and non-ordinary light component introduce relative phase delay varying with incident angle.Polarization correlation diffraction decoding unit will two kinds of opposite handedness circular polarization components respectively distribute to spatial separation +1 level and-1 level diffraction order, coupling light collection unit is coupled to two power detectors, respectively obtains corresponding optical power, signal processing unit calculates normalized difference index, and according to the mapping relationship in preselected monotone working interval calibration output incident angle.The application does not need array imaging, compact structure, and differential readout can suppress common-mode disturbance, suitable for laser pointing control, free space optical communication and precision alignment etc.

Description

Technical Field

[0001] This application belongs to the field of precision optical measurement and photoelectric detection technology, and in particular relates to a non-imaging angle measurement device and method based on birefringence polarization encoding. Background Technology

[0002] In applications such as laser pointing and tracking, free-space optical communication, and alignment and stabilization control of precision optomechanical systems, high-precision measurement of the incident angle is a key link in achieving closed-loop pointing and stabilization.

[0003] In existing incident angle measurement schemes, imaging methods typically rely on lenses and array detectors to estimate the incident angle through spot position, centroid, or image correlation algorithms. These systems are large in size and costly, and may be affected by factors such as aberrations, focal plane drift, wavefront distortion, spot morphology changes, and pixel response inconsistencies. While interferometric methods can achieve higher resolution, they are sensitive to multi-path stability, coherence, and environmental disturbances, and are complex to implement in engineering.

[0004] Therefore, there is a need for an incident angle measurement technology that is compact, has strong anti-disturbance capabilities, is easy to calibrate, and does not require array imaging, in order to adapt to complex application scenarios such as high dynamics or strong vibrations. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the prior art by providing a non-imaging angle measurement device and method based on birefringence polarization encoding, which can achieve high-precision measurement of the incident angle without the need for an array imaging detector, and reduce the influence of common-mode factors such as light source power fluctuation, link coupling efficiency change and detection channel gain drift on the measurement results.

[0006] The objective of this application is achieved through the following technical solution: A non-imaging angle measurement device based on birefringence polarization encoding, the device comprising: A polarization unit, which is used to polarize incident light into linearly polarized light in a preset direction; A birefringence encoding unit performs polarization encoding on the linearly polarized light, introducing a relative phase delay that varies with the incident angle between the ordinary light component and the extraordinary light component, so that the outgoing polarization state carries information related to the incident angle. A polarization-dependent diffraction decoding unit, which assigns the two opposite-chiral circular polarization components in the outgoing polarization state to spatially separated +1 and -1 order diffraction orders, respectively. A coupling light-collecting unit, wherein the coupling light-collecting unit couples the +1st order and -1st order diffracted light to the power detection unit respectively; A power detection unit detects the +1st and -1st order diffracted light respectively to obtain the corresponding optical power; The signal processing unit acquires the optical power, calculates the normalized differential index based on the optical power, and outputs the incident angle according to the pre-selected monotonic working interval calibrated mapping relationship.

[0007] Furthermore, the polarization-dependent diffraction decoding unit satisfies the half-wave delay condition at the working wavelength, with a phase delay of (2m+1)π, where m is an integer, so that the main energy enters the +1 and -1 order diffraction orders.

[0008] Furthermore, the polarization unit includes a linear polarizer, and the device defines a preset direction of the linearly polarized light according to the transmission direction of the polarizer.

[0009] Furthermore, the birefringent encoding unit includes a phase delayer, and the phase delayer is made of a birefringent material, which includes quartz, calcite, or magnesium fluoride.

[0010] Furthermore, the coupling light-gathering unit includes a lens, a mirror, an aperture, or a fiber coupler, configured to receive the corresponding +1st and -1st order diffraction orders within a preset incident angle range.

[0011] Furthermore, the power detection unit includes a photodiode, an avalanche photodiode, a photomultiplier tube, or an integrated power detection chip, and is connected to the signal processing unit.

[0012] Furthermore, the signal processing unit is also used to perform dark current subtraction and probe channel gain matching calibration.

[0013] On the other hand, this application also provides a non-imaging angle measurement method based on birefringence polarization coding, the method comprising: Under multiple known incident angles, the incident light is sequentially subjected to polarization, polarization encoding, and spatial diffraction decoding to obtain spatially separated +1st and -1st order diffracted light; The optical power of the coupled +1st and -1st order diffracted beams is detected, and the normalized difference index is calculated based on the optical power. The normalized difference index is substituted into the pre-selected monotonic working interval and the calibrated mapping relationship is used to output the incident angle measurement result.

[0014] Furthermore, the mapping relationship calibrated within the pre-selected monotonic working interval is established using a known incident angle and the corresponding normalized difference index.

[0015] Furthermore, the method also includes: The normalized difference index is obtained by scanning the angle within a preset range and the multi-branch response curve of the normalized difference index as a function of the incident angle. Then, a working interval is selected that makes the normalized difference index strictly monotonic with respect to the incident angle and avoids extreme points. A mapping relationship is established within the working interval using a linear or polynomial model to achieve real-time inversion.

[0016] The beneficial effects of this application are as follows: (1) Compared with the prior art, the non-imaging angle measurement device based on birefringence polarization coding proposed in this application does not require array detectors and imaging lenses. It only requires two single-pixel power detectors to realize the incident angle measurement. It has a compact structure and is easy to integrate, which greatly reduces the size of the device.

[0017] (2) The non-imaging angle measurement method based on birefringence polarization coding proposed in this application can suppress common-mode errors such as light source power fluctuation and link loss change through normalized differential index, and reduce the error introduced by the inconsistency of the detection channel through channel gain matching calibration.

[0018] (3) This application can establish a mapping relationship in the monotonic working interval through linear or polynomial methods, which is convenient for engineering implementation. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the non-imaging incident angle measuring device in the embodiments of this application.

[0020] Explanation of reference numerals in the attached figures: 1-Polarizer; 2-Birefringence encoding unit; 3-Polarization correlation diffraction decoding unit; 4-First coupling light collecting unit; 5-Second coupling light collecting unit; 6-First power detector; 7-Second power detector; 8-Signal processing unit. Detailed Implementation

[0021] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0022] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] In existing incident angle measurement schemes, imaging methods typically rely on lenses and array detectors to estimate the incident angle through spot position, centroid, or image correlation algorithms. These systems are large in size and costly, and may be affected by factors such as aberrations, focal plane drift, wavefront distortion, spot morphology changes, and pixel response inconsistencies. While interferometric methods can achieve higher resolution, they are sensitive to multi-path stability, coherence, and environmental disturbances, and are complex to implement in engineering.

[0024] To address the aforementioned technical problems, the present application proposes the following embodiments of a non-imaging angle measurement device and method based on birefringence polarization encoding.

[0025] Example 1: A non-imaging incident angle measurement device based on A-cut quartz crystal and liquid crystal polarization grating.

[0026] Reference Figure 1 ,like Figure 1 The diagram shows a schematic of the non-imaging incident angle measurement device in this embodiment. The +1st order diffracted light is coupled to the first power detector 6 via the first coupling light-collecting unit 4, and the -1st order diffracted light is coupled to the second power detector 7 via the second coupling light-collecting unit 5. In this embodiment, the incident light is generated by an external light source and incident on the device (the external light source and collimating element are not shown in the diagram). Preferably, the light source is a laser with a center wavelength of 1550 nm. The non-imaging optical incident angle measurement device includes: a polarizer 1, a birefringence encoding unit 2, a polarization correlation diffraction decoding unit 3, a first coupling light-collecting unit 4, a second coupling light-collecting unit 5, a first power detector 6, a second power detector 7, and a signal processing unit 8.

[0027] (1) Polarizer 1: used to polarize the incident beam to form linearly polarized light in a preset direction to match the working requirements of the subsequent birefringence encoding unit.

[0028] (2) Birefringence encoding unit 2: A-cut quartz crystal with a thickness of d=8 mm is used as the birefringence encoding unit. When the incident light is obliquely incident on the quartz crystal at an incident angle θ, the relative phase delay δ accumulated in the crystal between the ordinary light and the extraordinary light changes with θ, thereby driving the outgoing polarization state to evolve continuously with θ, realizing polarization encoding of the incident angle.

[0029] (3) Polarization-dependent diffraction decoding unit 3: A liquid crystal polarization grating (LCPG) is used as the decoder. The LCPG applies opposite phase gradients to the left and right circularly polarized components using geometric phase, thereby diffracting the left and right circularly polarized components to spatially separated +1 and -1 order diffraction orders, respectively. Preferably, the LCPG satisfies the half-wave delay condition at the operating wavelength, with a phase delay of (2m+1)π, where m is an integer. Thus, the two circularly polarized components with opposite chirality in the incident polarization state can be converted and diffracted to the +1 and -1 order diffraction orders, respectively, allowing the main energy to enter the +1 and -1 order diffracted light, thereby improving the polarization-dependent diffraction decoding efficiency. In a specific embodiment, the grating period Λ of the LCPG is 29.6 μm, and the +1 and -1 order diffraction angles at a wavelength of 1550 nm are approximately ±3°.

[0030] (4) The first coupling light-collecting unit 4 and the second coupling light-collecting unit 5 are used to couple the +1st order and -1st order diffracted light to the corresponding power detectors, respectively. In this embodiment, two lenses with a focal length of f=30 mm are used to couple the +1st order diffracted light to the first power detector 6 and the second power detector 7, respectively.

[0031] (5) First power detector 6 and second power detector 7: In this embodiment, there are two single-pixel power detectors, which measure the power of the +1st order diffracted light and the -1st order diffracted light respectively. The power of the +1st order diffracted light is denoted as Pa, and the power of the -1st order diffracted light is denoted as Pb. The power detectors can be photodiodes or other power detectors, and their outputs are sampled and sent to the signal processing unit 8.

[0032] (6) Signal processing unit 8: Used to synchronously read Pa and Pb, calculate the normalized differential index S=(Pa-Pb) / (Pa+Pb), and output the incident angle θ according to the pre-calibrated mapping relationship θ=F(S). To further improve measurement accuracy, signal processing unit 8 can perform dark current subtraction and channel gain matching calibration. Signal processing unit 8 can be implemented based on hardware platforms such as microcontrollers, field-programmable gate arrays, or digital signal processors. The analog output of the detector is sampled by an analog-to-digital converter and then processed by the hardware platform.

[0033] Example 2: Calibration and Inversion Method.

[0034] After the device is built, the mapping relationship between the normalized difference index S and the incident angle θ can be established through calibration. The optimization process includes: (1) Angle scanning calibration: Within the preset incident angle range, the incident angle θ is changed in steps with known angles. The optical power Pa and Pb of the +1st and -1st order diffracted beams measured by the first power detector and the second power detector are collected respectively. The normalized difference index S=(Pa-Pb) / (Pa+Pb) is calculated to obtain the calibration data between S and θ.

[0035] (2) Selection of monotonic working interval: Since S(θ) usually exhibits periodic or multi-branch characteristics, in order to ensure the single-valuedness and numerical stability of the inversion, the interval in which S is strictly monotonic with respect to θ is selected from the calibration curve as the working interval.

[0036] (3) Establishing the mapping relationship: Establish the incident angle mapping relationship θ=F(S) within the working interval. The mapping relationship θ=F(S) can be a linear model, a piecewise linear model, a polynomial model of order 3 or less, or a spline model. In a specific embodiment, a polynomial model θ=∑c can be used. k Sᵏ establishes a mapping relationship, where c k These are the coefficients obtained during calibration.

[0037] (4) Online measurement: Pa and Pb are collected and S is calculated when the measurement is to be performed. The measurement result of the incident angle θ is obtained according to the mapping relationship θ=F(S).

[0038] Among them, the operations in (1) to (3) are calibration steps; the "collect Pa and Pb and calculate S" in the operation in (4) is a measurement step; the "calculate the measurement result of the incident angle θ according to the mapping relationship θ=F(S)" in the operation in (4) is an inversion step.

[0039] In one specific embodiment, scanning calibration can be performed within a preset incident angle range to obtain the response curve of S as a function of the incident angle θ. When the scanning range covers multiple monotonic branches, a strictly monotonic interval can be selected for working interval calibration. Within this interval, a mapping relationship θ=F(S) can be established using a linear model, polynomial model, piecewise linear model, or spline model, thereby achieving stable and unambiguous angle inversion.

[0040] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A non-imaging angle measuring device based on birefringence polarization encoding, characterized in that, The device includes: A polarization unit, which is used to polarize incident light into linearly polarized light in a preset direction; A birefringence encoding unit performs polarization encoding on the linearly polarized light, introducing a relative phase delay that varies with the incident angle between the ordinary light component and the extraordinary light component, so that the outgoing polarization state carries information related to the incident angle. A polarization-dependent diffraction decoding unit, which assigns the two opposite-chiral circular polarization components in the outgoing polarization state to spatially separated +1 and -1 order diffraction orders, respectively. A coupling light-collecting unit, wherein the coupling light-collecting unit couples the +1st order and -1st order diffracted light to the power detection unit respectively; A power detection unit detects the +1st and -1st order diffracted light respectively to obtain the corresponding optical power; The signal processing unit acquires the optical power, calculates the normalized differential index based on the optical power, and outputs the incident angle according to the pre-selected monotonic working interval calibrated mapping relationship.

2. The non-imaging angle measuring device based on birefringence polarization encoding as described in claim 1, characterized in that, The polarization-dependent diffraction decoding unit satisfies the half-wave delay condition at the working wavelength, with a phase delay of (2m+1)π, where m is an integer, so that the main energy enters the +1 and -1 order diffraction orders.

3. The non-imaging angle measuring device based on birefringence polarization encoding as described in claim 1, characterized in that, The polarization unit includes a linear polarizer, and the device defines a preset direction of the linearly polarized light according to the transmission direction of the polarizer.

4. The non-imaging angle measuring device based on birefringence polarization encoding as described in claim 1, characterized in that, The birefringent encoding unit includes a phase delayer, and the phase delayer is made of a birefringent material, which may include quartz, calcite, or magnesium fluoride.

5. The non-imaging angle measuring device based on birefringence polarization encoding as described in claim 1, characterized in that, The coupling light-gathering unit includes a lens, a mirror, an aperture, or a fiber coupler, and is configured to receive the corresponding +1st and -1st order diffraction orders within a preset incident angle range.

6. The non-imaging angle measuring device based on birefringence polarization encoding as described in claim 1, characterized in that, The power detection unit includes a photodiode, an avalanche photodiode, a photomultiplier tube, or an integrated power detection chip, and is connected to the signal processing unit.

7. The non-imaging angle measuring device based on birefringence polarization encoding as described in claim 1, characterized in that, The signal processing unit is also used to perform dark current subtraction and probe channel gain matching calibration.

8. A non-imaging angle measurement method based on birefringence polarization encoding, characterized in that, The method includes: Under multiple known incident angles, the incident light is sequentially subjected to polarization, polarization encoding, and spatial diffraction decoding to obtain spatially separated +1st and -1st order diffracted light; The optical power of the coupled +1st and -1st order diffracted beams is detected, and the normalized difference index is calculated based on the optical power. The normalized difference index is substituted into the pre-selected monotonic working interval and the calibrated mapping relationship is used to output the incident angle measurement result.

9. The non-imaging angle measurement method based on birefringence polarization encoding as described in claim 8, characterized in that, The mapping relationship calibrated within the pre-selected monotonic working interval is established using a known incident angle and the corresponding normalized difference index.

10. The non-imaging angle measurement method based on birefringence polarization encoding as described in claim 9, characterized in that, The method further includes: The normalized difference index is obtained by scanning the angle within a preset range and the multi-branch response curve of the normalized difference index as a function of the incident angle. Then, a working interval is selected that makes the normalized difference index strictly monotonic with respect to the incident angle and avoids extreme points. A mapping relationship is established within the working interval using a linear or polynomial model to achieve real-time inversion.

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