An equal-path adjustment and detection system and method for a non-polarizing beam splitter prism

Abstract

The present application relates to a kind of equal optical path adjustment and detection system and method for unpolarized light splitting prism, equal optical path adjustment and detection system includes adjusting mechanism, fixed base, wide spectrum light source, first wedge optical flat, second wedge optical flat, first confocal distance measuring module, second confocal distance measuring module and interference detection component;The plane of first wedge optical flat is towards the first exit surface of first half prism;The plane of second wedge optical flat is towards the exit surface of second half prism;The measuring end of first confocal distance measuring module is towards the inclined plane of first wedge optical flat;The measuring end of second confocal distance measuring module is towards the inclined plane of second wedge optical flat.The present application establishes external optical reference surface by two pieces of wedge optical flat, independently measures air gap of wedge optical flat and corresponding half prism by combining first confocal distance measuring module and second confocal distance measuring module respectively, makes air optical path difference zero, eliminates group velocity dispersion mismatch.

Description

Technical Field

[0001] This invention relates to the field of component manufacturing, assembly, and inspection technology, and specifically to an equal optical path assembly and inspection system and method for non-polarizing beam splitters. Background Technology

[0002] Broadband interferometry systems impose stringent physical requirements on non-polarizing beam splitters (NPBS): the transmission and reflection arms must achieve near-zero optical path difference on a nanometer scale across a broad spectral range (covering 400 nm to 700 nm), and the geometric orientations of the emitted beams from both arms must be highly consistent. A NPBS is typically constructed by joining two right-angled half-prisms at their hypotenuses using UV bonding or photopolymerization, with one half-prism having a pre-coated beam-splitting film on its hypotenuse. The assembly precision and curing stability during bonding directly determine the axial resolution, interference envelope contrast, and long-term stability of the interferometric system.

[0003] After bonding, the total optical path difference of the system can be decomposed into three independent physical components: the air optical path difference contributed by the length difference of the air segments in the two arms of the external detection optical path, the adhesive layer optical path difference contributed by the optical path of the beveled adhesive layer, and the glass optical path difference contributed by the difference in the geometric paths of the glass inside the two halves of the prism. Existing technologies typically find the zero point by changing the air gap during assembly and adjustment, resulting in different media compositions in the two arms (one arm is glass-air-glass, the other is glass-adhesive-glass), causing severe group velocity dispersion mismatch across a wide spectral range. Furthermore, traditional processes lack a complete reference system that simultaneously provides both optical path and angular references, making it difficult to separate the various error components; the cross-linking shrinkage of the UV adhesive causes tens of nanometers of optical path difference drift, lacking online compensation methods; and the detection methods are limited, making it difficult to simultaneously provide full-field attitude information and absolute optical path difference values. Summary of the Invention

[0004] Based on the above description, the present invention provides an equal optical path adjustment and detection system and method for non-polarizing beam splitters, aiming to solve the problems of dispersion mismatch, lack of a complete reference system, uncontrolled curing stress, and limited detection methods in the prior art.

[0005] In a first aspect, an equal optical path adjustment and detection system for a non-polarizing beam splitter prism is provided, wherein the non-polarizing beam splitter prism includes a first half-prism and a second half-prism, and a beam-splitting film is provided on the inclined surface of the first half-prism or the inclined surface of the second half-prism; the equal optical path adjustment and detection system includes: An adjustment mechanism is provided, on which the first half-prism is mounted, and the adjustment mechanism is used to adjust the position and orientation of the first half-prism. A fixed base is provided, and the second half-prism is mounted on the fixed base. A broadband light source, the output end of which faces the incident surface of the second half-prism, is used to provide a light beam; The first wedge-shaped optical flat has its plane facing the first exit surface of the first half-prism, and the first wedge-shaped optical flat is used to provide the first interference reference light; The second wedge-shaped optical flat has its plane facing the exit surface of the second half-prism, and is used to provide the second interference reference light. The first confocal ranging module has its measuring end facing the inclined surface of the first wedge-shaped optical flat. The first confocal ranging module is used to measure the air gap between the first wedge-shaped optical flat and the first half-prism. The second confocal ranging module has its measuring end facing the inclined surface of the second wedge-shaped optical flat. The second confocal ranging module is used to measure the air gap between the second wedge-shaped optical flat and the second half-prism. An interference detection component is provided, which is disposed opposite to the second exit surface of the first half-prism. The interference detection component is used to receive the two-beam interference light formed by the convergence of the first interference reference light and the second interference reference light at the beam splitter, and to acquire the interference fringe image of the two-beam interference light and demodulate the absolute optical path difference of the two-beam interference light.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: Furthermore, the adjustment mechanism is a six-degree-of-freedom displacement stage.

[0007] Furthermore, both the inclined surfaces of the first wedge-shaped optical flat and the inclined surfaces of the second wedge-shaped optical flat are provided with broadband antireflective coatings.

[0008] Furthermore, the angle between the inclined surface of the first wedge-shaped optical flat and the inclined surface of the second wedge-shaped optical flat is 1°~5°.

[0009] Furthermore, the interference detection assembly includes a beam splitter, a camera, and a spectrometer. The beam splitter is tilted, with its incident surface facing the second exit surface of the first semi-prism. The beam splitter is used to split the two-beam interference light into transmitted light and reflected light. The camera's imaging end faces the transmitted surface of the beam splitter, and the camera is used to receive the transmitted light to obtain an interference fringe image of the two-beam interference light. The spectrometer's measuring end faces the reflected surface of the beam splitter, and the spectrometer is used to receive the reflected light to demodulate the absolute optical path difference of the two-beam interference light.

[0010] Furthermore, the equal optical path adjustment and detection system also includes a beam expander and collimator lens. The input end of the beam expander and collimator lens is connected to the output end of the broadband light source via an optical fiber. The output end of the beam expander and collimator lens faces the incident surface of the second half-prism. The beam expander and collimator lens is used to expand and collimate the light beam into parallel light.

[0011] Furthermore, the equal optical path adjustment and detection system also includes a first autocollimator and a second autocollimator, with the input end of the first autocollimator facing the inclined surface of the first wedge-shaped optical flat and the input end of the second autocollimator facing the inclined surface of the second wedge-shaped optical flat.

[0012] Furthermore, the equal optical path adjustment and detection system also includes a controller, which is electrically connected to the adjustment mechanism, the broadband light source, the first confocal ranging module, the second confocal ranging module, the camera, and the spectrometer.

[0013] In a second aspect, an equal optical path adjustment and detection method for a non-polarizing beam splitter prism is provided, applied to the equal optical path adjustment and detection system for a non-polarizing beam splitter described in the first aspect, wherein the equal optical path adjustment and detection method includes: With the broadband light source off, the first confocal ranging module measures the first initial air gap between the first wedge optical flat and the first half-prism, and the second confocal ranging module measures the second initial air gap between the second wedge optical flat and the second half-prism. If the first initial air gap and the second initial air gap are not equal, the distance between the first wedge optical flat and the first half-prism and / or the distance between the second wedge optical flat and the second half-prism are adjusted to make the first initial air gap and the second initial air gap equal. With the broadband light source off, the first half-prism is moved to fit against the beam-splitting film by the adjustment mechanism, and a pressing force is applied to form an adhesive layer. When the broadband light source is turned on, the beam of the broadband light source is split into a transmission arm and a reflection arm by a beam splitter. The transmission arm reaches the plane of the first wedge-shaped optical flat and is reflected back to the beam splitter. The reflection arm reaches the plane of the second wedge-shaped optical flat and is reflected back to the beam splitter. The beams converge at the beam splitter to form a double-beam interference beam. The interference fringe image of the double-beam interference beam and the demodulated absolute optical path difference are then detected by the interference detection component. Based on the interference fringe image, analyze the tilt direction and density of the interference fringes of the dual-beam interference light, calculate the required angle adjustment for the first half-prism, adjust the rotation angle of the first half-prism relative to the second half-prism according to the angle adjustment, until the interference fringes are eliminated from tilt, then adjust the translation position of the first half-prism along its own hypotenuse according to the absolute optical path difference, until the absolute optical path difference falls into the tolerance zone, and then record the first reference air gap measured by the first confocal ranging module and the second reference air gap measured by the second confocal ranging module. During the curing process of the adhesive layer, the first real-time air gap measured by the first confocal ranging module and the second real-time air gap measured by the second confocal ranging module are used to adjust the translation position of the first semi-prism for reverse compensation based on the deviation between the first reference air gap and the first real-time air gap, and the deviation between the second reference air gap and the second real-time air gap, so that the first real-time air gap approaches the first reference air gap and the second real-time air gap approaches the second reference air gap, until curing is completed.

[0014] Furthermore, the deviation between the first real-time air gap and the first reference air gap, and the deviation between the second real-time air gap and the second reference air gap, are less than or equal to 5 μm.

[0015] Compared with existing technologies, the technical solution of this application has the following beneficial technical effects: This invention establishes an external optical reference surface using two wedge-shaped optical flats. By combining a first confocal ranging module and a second confocal ranging module to independently measure the air gap between the wedge-shaped optical flat and the corresponding half-prism, the first and second initial air gaps can be forced to be equal in the absence of light, thus zeroing the air optical path difference. This avoids the insertion of heterogeneous media caused by subsequently changing the zero-point position of the air gap, eliminating group velocity dispersion mismatch. The interference detection component simultaneously acquires interference fringes and demodulates the absolute optical path difference, achieving parallel detection of angle and optical path, solving the problems of single detection methods and mixed error components. The separate design of the fixed base and the adjustment mechanism ensures that the first half-prism remains stable and the second half-prism is flexibly adjustable during assembly and adjustment, providing a foundation for nanometer-level optical path difference adjustment. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1This is a schematic diagram of an equal optical path adjustment and detection system for a non-polarizing beam splitter provided in an embodiment of the present invention; Figure 2 This is a flowchart of an equal optical path adjustment and detection method for a non-polarizing beam splitter provided in an embodiment of the present invention.

[0018] Explanation of reference numerals in the attached drawings: 1. First half-prism; 2. Second half-prism; 3. Adjustment mechanism; 4. Fixed base; 5. Broadband light source; 6. First wedge-shaped optical flat; 7. Second wedge-shaped optical flat; 8. First confocal ranging module; 9. Second confocal ranging module; 10. Beam splitter; 11. Camera; 12. Spectrometer; 13. Beam expander and collimator lens; 14. First autocollimator; 15. Second autocollimator. Detailed Implementation

[0019] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0021] It is understood that spatial relation terms such as "below," "under," "below," "below," "above," "above," etc., can be used here to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, the element or feature described as "below" or "below" of the other element or feature will be oriented "above" the other element or feature. Therefore, the exemplary terms "below" and "below" can include both upper and lower orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein will be interpreted accordingly.

[0022] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising,” “including,” or “having,” etc., specify the presence of the stated feature, whole, step, operation, component, part, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof.

[0023] Reference Figure 1 As shown, the present invention provides a technical solution: an equal optical path adjustment and detection system for a non-polarizing beam splitter prism. The non-polarizing beam splitter prism includes a first half-prism 1 and a second half-prism 2. A beam splitting film is provided on the inclined surface of the first half-prism 1 or the inclined surface of the second half-prism 2. The equal optical path adjustment and detection system includes an adjustment mechanism 3, a fixed base 4, a broadband light source 5, a first wedge-shaped optical flat 6, a second wedge-shaped optical flat 7, a first confocal ranging module 8, a second confocal ranging module 9, and an interference detection component. The first half-prism 1 is mounted on the adjustment mechanism 3, which is used to adjust the position and orientation of the first half-prism 1. The second half-prism 2 is mounted on the fixed base 4. The output end of the broadband light source 5 faces the incident surface of the second half-prism 2, and the broadband light source 5 is used to provide a light beam. The plane of the first wedge-shaped optical flat 6 faces the first exit surface of the first half-prism 1, and the first wedge-shaped optical flat 6 is used to provide a light beam. The first interference reference light is provided; the plane of the second wedge-shaped optical flat 7 faces the exit surface of the second half-prism 2, and the second wedge-shaped optical flat 7 is used to provide the second interference reference light; the measuring end of the first confocal ranging module 8 faces the inclined surface of the first wedge-shaped optical flat 6, and the first confocal ranging module 8 is used to measure the air gap between the first wedge-shaped optical flat 6 and the first half-prism 1; the measuring end of the second confocal ranging module 9 faces the inclined surface of the second wedge-shaped optical flat 7, and the second confocal ranging module 9 is used to measure the air gap between the second wedge-shaped optical flat 7 and the second half-prism 2; the interference detection component is set opposite to the second exit surface of the first half-prism 1, and the interference detection component is used to receive the double-beam interference light formed by the convergence of the first interference reference light and the second interference reference light at the beam splitter, and to acquire the interference fringe image of the double-beam interference light and demodulate the absolute optical path difference of the double-beam interference light.

[0024] For example, the adjustment mechanism 3 can be a six-degree-of-freedom displacement stage. The broadband light source 5 can be a white light source. The first confocal ranging module 8 and the second confocal ranging module 9 can be confocal ranging sensors.

[0025] In this embodiment, when the broadband light source 5 is not turned on, the first confocal ranging module 8 reads the first initial air gap, and the second confocal ranging module 9 reads the second initial air gap, determining whether the first initial air gap and the second initial air gap are equal. If they are not equal, the distance between the first wedge-shaped optical flat 6 and the first half-prism 1, and the distance between the second wedge-shaped optical flat 7 and the second half-prism 2 are adjusted until the first initial air gap and the second initial air gap are equal. At this time, the air optical path difference has been forced to zero.

[0026] When the broadband light source 5 is turned on, the beam emitted by the broadband light source 5 is incident on the second half-prism 2. Simultaneously, the beam is split into a transmission arm and a reflection arm by the beam splitter. The transmission arm enters the first half-prism 1 and reaches the plane of the first wedge-shaped optical flat 6, while the reflection arm enters the second half-prism 2 and reaches the plane of the second wedge-shaped optical flat 7. Both produce approximately 4% Fresnel reflection, and the reflected light returns along the original path, converging at the beam splitter to form a double-beam interference beam. The double-beam interference beam is output from the second exit surface of the first half-prism 1 and enters the interference detection component. The interference detection component acquires the interference fringe image and simultaneously performs FFT demodulation to obtain the absolute optical path difference. Based on the tilt direction and density of the interference fringes, the required angle adjustment amount for the first half-prism 1 is calculated. The adjustment mechanism 3 adjusts the first half-prism 1 according to the angle adjustment amount (around the normal direction of the inclined surface of the first half-prism 1) until the fringes are no longer tilted. Then, based on the absolute optical path difference, the adjustment mechanism 3 drives the first half-prism 1 to translate along its own inclined side, making the absolute optical path difference approach zero. During the adhesive layer curing stage, the first real-time air gap measured by the first confocal ranging module 8 and the second real-time air gap measured by the second confocal ranging module 9 are used to adjust the translation position of the first half-prism 1 for reverse compensation based on the deviation between the first reference air gap and the first real-time air gap and the deviation between the second reference air gap and the second real-time air gap. This brings the first real-time air gap closer to the first reference air gap and the second real-time air gap closer to the second reference air gap until curing is complete, thereby suppressing optical path drift caused by adhesive layer shrinkage.

[0027] By adjusting mechanism 3, fixed base 4, broadband light source 5, double wedge optical flat, double confocal ranging module, and interferometric detection component, it is possible to first geometrically lock the air optical path and then decouple and close the loop based on the interference signal. This avoids the drawbacks of mutual interference between air optical path and glass optical path in traditional methods, and provides a physical basis for subsequent nanoscale equal optical path adjustment.

[0028] In some embodiments, the equal optical path adjustment and detection system further includes a first optical flat displacement stage and a second optical flat displacement stage, with the first wedge-shaped optical flat 6 mounted on the first optical flat displacement stage and the second wedge-shaped optical flat 7 mounted on the second optical flat displacement stage.

[0029] In this embodiment, when the first initial air gap is equal to the second initial air gap, the first flat optical stage and the second flat optical stage are locked to lock the first wedge-shaped optical flat 6 and the second wedge-shaped optical flat 7, thereby forcing the air optical path difference to be zero.

[0030] In some embodiments, both the inclined surfaces of the first wedge-shaped optical flat 6 and the second wedge-shaped optical flat 7 are provided with broadband antireflective coatings.

[0031] For example, a broadband antireflective coating can cover a wide spectral range of 400 nm to 700 nm.

[0032] In this embodiment, the residual reflectivity of the wedge-shaped optical flat is reduced to less than 0.5% by a broadband antireflection film. The reflected light from the inclined surface of the wedge-shaped optical flat is significantly attenuated and deflected out of the receiving optical path due to its own wedge angle, thereby eliminating ghosting interference.

[0033] Optionally, the angle between the inclined surface of the first wedge-shaped optical flat 6 and the inclined surface of the second wedge-shaped optical flat 7 is 1° to 5°.

[0034] In this embodiment, a wedge angle of 1° to 5° can ensure that the reflected light from the inclined surface of the wedge-shaped optical flat is completely deflected out of the optical path, without affecting the surface accuracy and light transmission quality of the wedge-shaped optical flat.

[0035] Reference Figure 1 As shown, in some embodiments, the interference detection assembly includes a beam splitter 10, a camera 11, and a spectrometer 12. The beam splitter 10 is tilted, with its incident surface facing the second exit surface of the first half-prism 1. The beam splitter 10 is used to split the two-beam interference light into transmitted light and reflected light. The imaging end of the camera 11 faces the transmission surface of the beam splitter 10, and the camera 11 is used to receive the transmitted light to obtain an interference fringe image of the two-beam interference light. The measuring end of the spectrometer 12 faces the reflection surface of the beam splitter 10, and the spectrometer 12 is used to receive the reflected light to demodulate the absolute optical path difference of the two-beam interference light.

[0036] For example, camera 11 can be a complementary metal-oxide-semiconductor area array camera. Spectrometer 12 can be a fiber optic spectrometer.

[0037] In this embodiment, the two-beam interference light converging at the beam splitter exits from the second exit surface of the first half-prism 1 and first enters the beam splitter 10. The beam splitter 10 splits the incident light into transmitted light and reflected light. The transmitted light passes through the transmission surface of the beam splitter 10 and enters the camera 11, while the reflected light exits from the reflection surface of the beam splitter 10 and enters the spectrometer 12. The camera 11 acquires an image of the spatial distribution of the interference light, and the tilt direction and density of the interference fringes in the image directly reflect the relative angular deviation between the transmitted and reflected arms. The spectrometer 12 receives the interference spectrum and calculates the absolute optical path difference using a frequency-domain white light interferometry demodulation algorithm (such as FFT + peak localization).

[0038] Reference Figure 1 As shown, in some embodiments, the equal optical path adjustment and detection system further includes a beam expander and collimator lens 13. The input end of the beam expander and collimator lens 13 is connected to the output end of the broadband light source 5 via an optical fiber. The output end of the beam expander and collimator lens 13 faces the incident surface of the second half-prism 2. The beam expander and collimator lens is used to expand and collimate the light beam into parallel light.

[0039] In this embodiment, the beam expanding and collimating lens 13 expands the diverging light emitted from the optical fiber and converts it into parallel light, outputting a collimated beam that faces the incident surface of the second half-prism 2, ensuring that the light incident on the non-polarizing beam splitter has good collimation and spectral purity.

[0040] Reference Figure 1 As shown, in some embodiments, the equal optical path adjustment and detection system further includes a first autocollimator 14 and a second autocollimator 15, with the input end of the first autocollimator 14 facing the inclined surface of the first wedge-shaped optical flat 6, and the input end of the second autocollimator 15 facing the inclined surface of the second wedge-shaped optical flat 7.

[0041] In this embodiment, the autocollimator is used to calibrate the normal direction of the corresponding wedge-shaped optical flat before the broadband light source 5 is turned on, so that the wedge-shaped optical flat is perpendicular to the principal optical axis, thereby establishing an angular reference. After the broadband light source 5 is turned on, the first autocollimator 14 measures the angular difference between the exit surface of the first half-prism 1 and the plane of the first wedge-shaped optical flat 6, and the second autocollimator 15 measures the angular difference between the exit surface of the second half-prism 2 and the plane of the second wedge-shaped optical flat 7.

[0042] Reference Figure 1 As shown, in some embodiments, the equal optical path adjustment and detection system further includes a controller, which is electrically connected to the adjustment mechanism 3, the broadband light source 5, the first confocal ranging module 8, the second confocal ranging module 9, the camera 11 and the spectrometer 12, respectively.

[0043] In this embodiment, the controller can perform the following operations: send displacement and rotation commands to the adjustment mechanism 3 to drive the first half-prism 1 to translate along its own hypotenuse or rotate around the normal direction of the hypotenuse; send a switch command to the broadband light source 5; read the measurement data of the air gap from the first confocal ranging module 8 and the second confocal ranging module 9; receive interference fringe image data from the camera 11; and receive interference spectrum data from the spectrometer 12.

[0044] Reference Figure 2 As shown, the present invention provides a technical solution: an equal optical path adjustment and detection method for a non-polarizing beam splitter prism, applied to the aforementioned equal optical path adjustment and detection system for a non-polarizing beam splitter prism. The equal optical path adjustment and detection method includes the following steps: S11, with the broadband light source 5 off, the first confocal ranging module 8 measures the first initial air gap between the first wedge optical flat 6 and the first half-prism 1, and the second confocal ranging module 9 measures the second initial air gap between the second wedge optical flat 7 and the second half-prism 2. If the first initial air gap and the second initial air gap are not equal, the distance between the first wedge optical flat 6 and the first half-prism 1 and / or the distance between the second wedge optical flat 7 and the second half-prism 2 are adjusted to make the first initial air gap and the second initial air gap equal.

[0045] For example, the difference between the first initial air gap and the second initial air gap can be <10nm.

[0046] S12, with the broadband light source 5 off, the first half-prism 1 is moved to fit with the beam splitter film by the adjustment mechanism 3, and a pressing force is applied to form an adhesive layer.

[0047] For example, a clamping force can be applied to the first half-prism 1 by means of a clamping force control device.

[0048] S13, turn on the broadband light source 5. The beam of the broadband light source 5 is split into a transmission arm and a reflection arm by the beam splitter. The transmission arm reaches the plane of the first wedge-shaped optical flat 6 and is reflected back to the beam splitter. The reflection arm reaches the plane of the second wedge-shaped optical flat 7 and is reflected back to the beam splitter. After converging at the beam splitter, a double-beam interference beam is formed. The interference fringe image of the double-beam interference beam and the demodulated absolute optical path difference are then detected by the interference detection component.

[0049] In this embodiment, the beam splitter 10 in the interference detection assembly splits the interference light into transmitted light and reflected light: the transmitted light enters the camera 11, and the camera 11 acquires the interference fringe image; the reflected light enters the spectrometer 12, and the spectrometer 12 acquires the interference spectrum and demodulates the absolute optical path difference. The controller reads the image data from the camera 11 and the optical path difference data from the spectrometer 12.

[0050] S14. Analyze the tilt direction and density of the interference fringes based on the interference fringe image, calculate the required angle adjustment amount for the first half-prism 1, adjust the rotation angle of the first half-prism 1 relative to the second half-prism 2 according to the angle adjustment amount, until the interference fringes are eliminated from tilt, and then adjust the translation position of the first half-prism 1 along its own hypotenuse according to the absolute optical path difference, until the absolute optical path difference falls into the tolerance zone, and then record the first reference air gap measured by the first confocal ranging module 8 and the second reference air gap measured by the second confocal ranging module 9.

[0051] For example, the angle adjustment may include the rotation direction and the rotation step. The rotation angle is the rotation of the second half-prism 2 about the normal direction of its own hypotenuse. The translation adjustment may include the translation direction and the distance.

[0052] In this embodiment, the controller analyzes the tilt direction and density of the interference fringes using an image processing algorithm based on the interference fringe image acquired from the camera 11. Specifically, it calculates the tilt angle of the fringes relative to the horizontal direction and the number of fringes per millimeter. Based on the fringe tilt direction and density, the controller calculates the required angle adjustment amount for the first half-prism 1. Then, the controller controls the adjustment mechanism 3 to adjust the rotation angle of the first half-prism 1 relative to the second half-prism 2. The camera 11 provides real-time feedback of new fringe images, and the controller iteratively calculates new adjustment amounts until the interference fringes are no longer tilted (residual tilt less than 0.1″). At this point, the geometric orientation of the emitted beams from the transmission arm and the reflection arm is consistent.

[0053] Subsequently, the controller calculates the required translation adjustment of the first half-prism 1 based on the absolute optical path difference value demodulated by the spectrometer 12. The controller controls the adjustment mechanism 3 to adjust the translation position of the first half-prism 1 along its own hypotenuse. During the translation process, the geometric path of the light beam within the glass changes, thereby altering the optical path difference of the glass and offsetting the optical path difference of the adhesive layer and processing errors. The spectrometer 12 provides real-time feedback of the optical path difference value, and the controller gradually converges using a proportional-integral-differential algorithm until the absolute optical path difference falls into the tolerance band (e.g., ±5nm). At this point, the total optical path difference of the system approaches zero.

[0054] After completing the above adjustments, the controller reads the currently measured first air gap from the first confocal ranging module 8 and records it as the first reference air gap; it also reads the currently measured second air gap from the second confocal ranging module 9 and records it as the second reference air gap. The first and second reference air gaps will be used for stress compensation during the curing process.

[0055] S15, during the curing process of the adhesive layer, the first real-time air gap measured by the first confocal distance measuring module 8 and the second real-time air gap measured by the second confocal distance measuring module 9 are used to adjust the translation position of the first half-prism 1 for reverse compensation based on the deviation between the first reference air gap and the first real-time air gap and the deviation between the second reference air gap and the second real-time air gap, so that the first real-time air gap approaches the first reference air gap and the second real-time air gap approaches the second reference air gap until curing is completed.

[0056] In this embodiment, during the UV adhesive curing process (e.g., when UV light-emitting diodes are turned on), the cross-linking and shrinkage of the adhesive layer causes a slight displacement of the first half-prism 1, resulting in the air gaps on both sides deviating from the first reference air gap and the second reference air gap. The first confocal ranging module 8 and the second confocal ranging module 9 monitor the first and second real-time air gaps in real time at a high frequency (e.g., 5kHz~10kHz). The controller calculates the deviation between the first reference air gap and the first real-time air gap, and the deviation between the second reference air gap and the second real-time air gap.

[0057] Once a deviation is detected to exceed the allowable range, the controller controls the adjustment mechanism 3 to adjust the translational position of the first half-prism 1, pulling the real-time air gap back to near the reference air gap. This closed-loop control operates continuously at a kilohertz frequency until curing is complete. After curing, the real-time air gap is locked near the first and second reference air gaps, thereby controlling the optical path difference drift caused by adhesive layer shrinkage to the nanometer level.

[0058] In some embodiments, after S13, the method further includes: if the tilt angle of the interference fringes exceeds the adjustable range of the rotational degrees of freedom of the adjustment mechanism 3, or the demodulated absolute optical path difference exceeds the adjustable range of the translational degrees of freedom of the adjustment mechanism 3, then the non-polarizing beam splitter is determined to be unqualified and is subjected to a return process.

[0059] In some embodiments, the deviation between the first real-time air gap and the first reference air gap, and the deviation between the second real-time air gap and the second reference air gap, are less than or equal to 5 μm.

[0060] In this embodiment, controlling the deviation to less than or equal to 5 μm ensures that the final absolute optical path difference of the non-polarizing beam splitter remains within the nanometer tolerance band (e.g., ≤5 nm) after curing.

[0061] Example 1: UV adhesive process The core parameters of the equal optical path adjustment and testing system are as follows: First half-prism 1 and second half-prism 2: H-K9L glass, refractive index 1.516 (@550nm), single side length 25.4mm.

[0062] Spectrophotometer: Deposited on the inclined surface of the first half-prism 1, with a transmission / reflection ratio of ≈50 / 50 and an operating wavelength range of 400nm~700nm.

[0063] Adjustment mechanism 3: a six-degree-of-freedom displacement stage with a translation resolution of 1 nm and a stroke of 100 μm; an angular resolution of 0.1″ and a range of ±60″.

[0064] Broadband light source 5: Halogen tungsten lamp, power ≥50W.

[0065] Expander collimating lens 13: Contains a 400nm long-pass filter.

[0066] First wedge optical flat 6 and second wedge optical flat 7: made of fused silica, wedge angle 3°, planar shape better than λ / 20, light-transmitting aperture Φ30mm; the inclined surface is coated with a broadband antireflection film (residual reflectivity <0.5%).

[0067] First confocal ranging module 8 and second confocal ranging module 9: axial resolution 10nm, sampling frequency 10kHz.

[0068] Camera 11: Complementary metal-oxide-semiconductor area array camera, resolution 2048×2048 pixels, 5.5μm pixel size, ≥30fps.

[0069] Spectrometer 12: Fiber optic spectrometer, wavelength range 400nm~700nm, resolution 0.2nm.

[0070] First autocollimator 14 and second autocollimator 15: resolution 0.01″, measurement range ±300″.

[0071] The implementation steps are as follows: S21, the system preheats for 30 minutes to reach thermal equilibrium. The perpendicularity of the normals of the first wedge optical flat 6 and the second wedge optical flat 7 to the principal optical axis is calibrated to within 0.05″. With the broadband light source 5 off, the first confocal ranging module 8 measures the first initial air gap as 152.35 μm; the second confocal ranging module 9 measures the second initial air gap as 147.80 μm, with a difference of 4.55 μm. The spacing between the first wedge optical flat 6 and the first half-prism 1, and / or the spacing between the second wedge optical flat 7 and the second half-prism 2, is adjusted to make the first initial air gap 150.07 μm and the second initial air gap 150.08 μm, with a difference of approximately 10 nm. Then, the optical flats are mechanically locked, and the confocal reading drift before and after locking is verified to be less than 3 nm. At this point, the forced air path difference is zero.

[0072] S22, the broadband light source 5 remains off. UV adhesive (NOA61) is coated on the surface of the spectrophotometer. The controller controls the adjustment mechanism 3 to move the first half-prism 1 to contact the spectrophotometer at a speed of 0.5 μm / s. The clamping force control device applies a total force of approximately 1.2 N in force balance mode, with a deviation of <0.05 N on both sides. Wait 10 seconds for the adhesive layer to flow and stabilize, with an average thickness of approximately 10 μm.

[0073] S23, the controller activates the broadband light source 5. The light emitted from the broadband light source 5 passes through an optical fiber and the beam expander / collimating lens 13, outputting a collimated beam that points towards the incident surface of the second half-prism 2. The beam enters the unpolarized beam splitter prism, where it splits into a transmission arm and a reflection arm at the beam splitter. The transmission arm passes sequentially through the adhesive layer and the second half-prism 2, reaching the plane of the first wedge-shaped optical flat 6 and being reflected back; the reflection arm passes through the first half-prism 1, reaching the plane of the second wedge-shaped optical flat 7 and being reflected back. The two reflected beams converge at the beam splitter to form a double-beam interference beam. The double-beam interference beam is incident from the first half-prism 1 to the beam splitter 10. Beam splitter 10 separates the interference light into transmitted and reflected light: the transmitted light enters camera 11, which acquires an image of the interference fringes, displaying approximately 5 fringes per field of view, with a fringe skew of approximately 8″; the reflected light enters spectrometer 12, which demodulates the absolute optical path difference to approximately 310 nm. The controller reads the image from camera 11 and the absolute optical path difference from spectrometer 12. Both are within adjustable ranges. First autocollimator 14 measures the angle difference between the exit face of the first semi-prism 1 and the plane of the first wedge-shaped optical flat 6 as +0.8″, and second autocollimator 15 measures the angle difference between the exit face of the second semi-prism 2 and the plane of the second wedge-shaped optical flat 7 as -2.5″, and archives the data.

[0074] S24, the controller analyzes the tilt direction and density of the interference fringes based on the interference fringe image, and calculates the required angle adjustment for the first semi-prism 1. Initially tilted by 8″, the controller sends a rotation command to the adjustment mechanism 3, coarsely adjusting in 0.5″ steps for 4 steps, reducing the tilt to 1.0″; then finely adjusting in 0.5″ steps for 2 steps to 0.1″; finally, adjusting in 0.1″ steps to less than 0.05″. The camera 11 provides real-time feedback, showing that the fringes are no longer tilted and the image is basically uniform. At this time, the spectrometer 12 displays an absolute optical path difference that changes from 310nm to 265nm (the change in optical path difference caused by angle adjustment coupling is approximately 45nm). Based on the absolute optical path difference (265nm) demodulated by the spectrometer 12, the controller controls the adjustment mechanism 3 to adjust the translational position of the first semi-prism 1 along its own tilt direction. Proportional-integral-derivative control is used: the first translation... At 74nm, the absolute optical path difference decreased to 106nm; a second shift of 30nm reduced the absolute optical path difference to 42nm; a third shift of 12nm reduced the absolute optical path difference to 16nm; subsequent shifts were made in 3-5nm increments to gradually converge. After 11 iterations, the absolute optical path difference stabilized at 3.2nm, falling within the tolerance band (≤±5nm). At this point, the image from camera 11 showed a uniform light field with no visible fringes. The controller read the first air gap value currently measured by the first confocal ranging module 8 as 150.07μm and recorded it as the first reference air gap; it also read the second air gap value currently measured by the second confocal ranging module 9 as 150.08μm and recorded it as the second reference air gap.

[0075] S25, the controller activates the ultraviolet LED light source (365nm, power density 80mW / cm²) to begin curing. The first confocal ranging module 8 and the second confocal ranging module 9 monitor the first and second real-time air gaps in real time at a sampling frequency of 10kHz. The controller calculates the deviation between the first reference air gap and the first real-time air gap, as well as the deviation between the second reference air gap and the second real-time air gap. During the initial curing phase (0-3 seconds), the adhesive layer shrinks rapidly, with the maximum transient deviation occurring at 1.2 seconds, approximately 8nm. The controller then controls the adjustment mechanism 3 to adjust the translation position of the first semi-prism 1, pulling each real-time air gap back to the vicinity of its corresponding reference air gap. Within 3-10 seconds, the deviation between each real-time air gap and its corresponding reference air gap stabilizes within ±3nm; after 10-15 seconds, the compensation displacement of the adjustment mechanism 3 approaches zero, and curing is complete. The controller was turned off with the UV LED, and after waiting for thermal equilibrium, a retest was performed: the final absolute optical path difference was 4.8 nm (tolerance ≤ 5 nm), the stripes were indistinguishable (less than 0.05 stripes / mm), the optical path difference offset caused by curing was 1.6 nm (≤ 3 nm), the maximum transient gap deviation was 8 nm (≤ 10 nm), and the attitude change was less than 0.1″ (≤ 0.2″). All standards were met, and the product was shipped.

[0076] Example 2 The beveled surface shape of the first half-prism 1 and the second half-prism 2 is better than λ / 20, and the roughness is less than 0.3 nm root mean square, so the clamping force control device is eliminated from applying clamping force. The core parameters of the remaining equal optical path adjustment and detection system are the same as in Example 1.

[0077] The steps for implementing the photopolymerization process are as follows: S31 is the same as S21 in Example 1.

[0078] S32, the first half-prism 1 is moved by the adjustment mechanism 3 until it is in direct contact with the inclined beam-splitting film of the second half-prism 2, forming molecular bonds. No UV adhesive is applied during this process, and the absolute optical path difference of the adhesive layer is approximately 0. The bonds expand rapidly within seconds, and the adjustable window is short.

[0079] S33, within 1 second after bonding, the controller activates the broadband light source 5. The collimated beam is split into a transmission arm and a reflection arm by the beam splitter. The transmission arm passes through the adhesive layer and the second half-prism 2 in sequence, reaches the plane of the first wedge-shaped optical flat 6, and is reflected back; the reflection arm passes through the first half-prism 1, reaches the plane of the second wedge-shaped optical flat 7, and is reflected back. The two reflected beams converge at the beam splitter to form a double-beam interference beam. The double-beam interference beam is incident from the first half-prism 1 to the beam splitter 10. The beam splitter 10 splits the interference beam into transmitted and reflected beams: the transmitted beam enters the camera 11, and the camera 11 acquires the interference fringe image. Camera 11 displays approximately 2 fringes per field of view, with a skew of approximately 2″. Spectrometer 12 demodulates an absolute optical path difference of approximately 95 nm. First autocollimator 14 measures the angle difference between the exit face of the first semi-prism 1 and the plane of the first wedge-shaped optical flat 6 as +0.3″, and second autocollimator 15 measures the angle difference between the exit face of the second semi-prism 2 and the plane of the second wedge-shaped optical flat 7 as -0.4″. Both the angle difference and the absolute optical path difference are within adjustable range.

[0080] In step S34, the controller performs a coarse adjustment of 4 steps with a step size of 0.5″ based on the interference fringe image, followed by a fine adjustment of 2 steps, reducing the skewness to less than 0.05″ in approximately 3 seconds. At this point, the absolute optical path difference becomes approximately 85 nm due to coupling. Based on the absolute optical path difference of the spectrometer 12, the controller drives the adjustment mechanism 3 to translate the first half-prism 1 along its own inclined side. After approximately 15 iterations, the absolute optical path difference converges to 2.1 nm in approximately 5 seconds. The controller reads and records the first reference air gap of 150.07 μm and the second reference air gap of 150.08 μm.

[0081] S35, the controller keeps the broadband light source 5 on, and the first confocal ranging module 8 and the second confocal ranging module 9 monitor the first and second initial air gaps at a sampling frequency of 1kHz for 60 seconds. The drift is less than 0.5nm / min. The broadband light source 5 is turned off, and the optical path difference is remeasured to be 2.3nm. The fringes are indistinguishable, and the product is ready for shipment.

[0082] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An equal optical path adjustment and detection system for a non-polarizing beam splitter, wherein the non-polarizing beam splitter includes a first half-prism (1) and a second half-prism (2), wherein a beam splitting film is provided on the inclined surface of the first half-prism (1) or the inclined surface of the second half-prism (2), characterized in that, The equal optical path adjustment and detection system includes: Adjustment mechanism (3), the first half-prism (1) is mounted on the adjustment mechanism (3), the adjustment mechanism (3) is used to adjust the position and orientation of the first half-prism (1); A fixed base (4) is provided, on which the second half-prism (2) is mounted; A broadband light source (5) is provided, the output end of which faces the incident surface of the second half-prism (2). The broadband light source (5) is used to provide a light beam. The first wedge-shaped optical flat (6) has its plane facing the first exit surface of the first half-prism (1), and the first wedge-shaped optical flat (6) is used to provide the first interference reference light; The second wedge-shaped optical flat (7) has its plane facing the exit surface of the second half-prism (2), and the second wedge-shaped optical flat (7) is used to provide the second interference reference light; The first confocal ranging module (8) has its measuring end facing the inclined surface of the first wedge optical flat (6). The first confocal ranging module (8) is used to measure the air gap between the first wedge optical flat (6) and the first half-prism (1). The second confocal ranging module (9) has its measuring end facing the inclined surface of the second wedge optical flat (7). The second confocal ranging module (9) is used to measure the air gap between the second wedge optical flat (7) and the second half prism (2). An interference detection component is provided, which is disposed opposite to the second exit surface of the first half-prism (1). The interference detection component is used to receive the double-beam interference light formed by the first interference reference light and the second interference reference light converging at the beam splitter, and to acquire the interference fringe image of the double-beam interference light and demodulate the absolute optical path difference of the double-beam interference light.

2. The equal optical path adjustment and detection system for a non-polarizing beam splitter according to claim 1, characterized in that, The adjustment mechanism (3) is a six-degree-of-freedom displacement stage.

3. The equal optical path adjustment and detection system for a non-polarizing beam splitter according to claim 1, characterized in that, Both the inclined surfaces of the first wedge-shaped optical flat (6) and the second wedge-shaped optical flat (7) are provided with broadband anti-reflection coatings.

4. The equal optical path adjustment and detection system for a non-polarizing beam splitter according to claim 1, characterized in that, The angle between the inclined surface of the first wedge-shaped optical flat (6) and the inclined surface of the second wedge-shaped optical flat (7) is 1°~5°.

5. The equal optical path adjustment and detection system for a non-polarizing beam splitter according to claim 1, characterized in that, The interference detection assembly includes a beam splitter (10), a camera (11), and a spectrometer (12). The beam splitter (10) is tilted, with its incident surface facing the second exit surface of the first half-prism (1). The beam splitter (10) is used to split the two-beam interference light into transmitted light and reflected light. The camera (11) has its imaging end facing the transmission surface of the beam splitter (10) and is used to receive the transmitted light to obtain an interference fringe image of the two-beam interference light. The spectrometer (12) has its measuring end facing the reflection surface of the beam splitter (10) and is used to receive the reflected light to demodulate the absolute optical path difference of the two-beam interference light.

6. The equal optical path adjustment and detection system for a non-polarizing beam splitter according to claim 1, characterized in that, The equal optical path adjustment and detection system also includes a beam expander collimator (13). The input end of the beam expander collimator (13) is connected to the output end of the broadband light source (5) via an optical fiber. The output end of the beam expander collimator (13) faces the incident surface of the second half prism (2). The beam expander collimator is used to expand and collimate the beam into parallel light.

7. The equal optical path adjustment and detection system for a non-polarizing beam splitter according to claim 1, characterized in that, The equal optical path adjustment and detection system further includes a first autocollimator (14) and a second autocollimator (15). The input end of the first autocollimator (14) faces the inclined surface of the first wedge-shaped optical flat (6), and the input end of the second autocollimator (15) faces the inclined surface of the second wedge-shaped optical flat (7).

8. The equal optical path adjustment and detection system for a non-polarizing beam splitter according to claim 5, characterized in that, The equal optical path adjustment and detection system also includes a controller, which is electrically connected to the adjustment mechanism (3), the broadband light source (5), the first confocal ranging module (8), the second confocal ranging module (9), the camera (11), and the spectrometer (12).

9. A method for equal optical path adjustment and detection of a non-polarizing beam splitter prism, applied to the equal optical path adjustment and detection system for a non-polarizing beam splitter prism according to any one of claims 1 to 8, characterized in that, The equal optical path adjustment and detection method includes: When the broadband light source (5) is not turned on, the first confocal ranging module (8) measures the first initial air gap between the first wedge optical flat (6) and the first half-prism (1), and the second confocal ranging module (9) measures the second initial air gap between the second wedge optical flat (7) and the second half-prism (2). If the first initial air gap and the second initial air gap are not equal, the distance between the first wedge optical flat (6) and the first half-prism (1) and / or the distance between the second wedge optical flat (7) and the second half-prism (2) is adjusted so that the first initial air gap and the second initial air gap are equal. When the broadband light source (5) is not turned on, the first half-prism (1) is moved to fit with the beam splitter film by the adjustment mechanism (3), and a pressing force is applied to form an adhesive layer; When the broadband light source (5) is turned on, the beam of the broadband light source (5) is split into a transmission arm and a reflection arm by the beam splitter. The transmission arm reaches the plane of the first wedge-shaped optical flat (6) and is reflected back to the beam splitter. The reflection arm reaches the plane of the second wedge-shaped optical flat (7) and is reflected back to the beam splitter. The beams converge at the beam splitter to form a double-beam interference beam. The interference fringe image of the double-beam interference beam and the demodulated absolute optical path difference are then detected by the interference detection component. Based on the interference fringe image, analyze the tilt direction and density of the interference fringes of the dual-beam interference light, calculate the required angle adjustment amount of the first half-prism (1), adjust the rotation angle of the first half-prism (1) relative to the second half-prism (2) according to the angle adjustment amount, until the interference fringes are eliminated from tilt, and then adjust the translation position of the first half-prism (1) along its own hypotenuse direction according to the absolute optical path difference, until the absolute optical path difference falls into the tolerance zone, and then record the first reference air gap measured by the first confocal ranging module (8) and the second reference air gap measured by the second confocal ranging module (9); During the curing process of the adhesive layer, the first real-time air gap measured by the first confocal distance measuring module (8) and the second real-time air gap measured by the second confocal distance measuring module (9) are used to adjust the translation position of the first half-prism (1) for reverse compensation based on the deviation between the first reference air gap and the first real-time air gap and the deviation between the second reference air gap and the second real-time air gap, so that the first real-time air gap approaches the first reference air gap and the second real-time air gap approaches the second reference air gap until curing is completed.

10. The method for equal optical path adjustment and detection of a non-polarizing beam splitter according to claim 9, characterized in that, The deviation between the first real-time air gap and the first reference air gap, and the deviation between the second real-time air gap and the second reference air gap, are less than or equal to 5 μm.

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