Full-aperture measurement method and system for grating diffraction efficiency based on double light paths

Abstract

The present application relates to the field of precise optical element detection, and more particularly to a grating diffraction efficiency full-aperture measurement method and system based on double optical paths, which first simulates Littrow angle return light path by using a standard mirror, measures direct reflected light intensity and light intensity after attenuated by a beam splitter through a light detector, and calculates a reverse beam splitter ratio for correcting secondary attenuation of the beam splitter. On this basis, forward beam splitter ratio calibration is performed, and reference light intensity and diffraction light intensity are synchronously collected at Littrow angle. Through combining two calibration parameters and real-time measurement data, diffraction efficiency of the grating under Littrow configuration can be accurately calculated. To realize full-aperture measurement, the grating is placed on a two-dimensional translation stage for serpentine scanning, and motion and data collection are coordinated by a control unit. Finally, a diffraction efficiency distribution map is generated through data processing. The present application effectively eliminates system error in Littrow measurement, and realizes full-aperture, high-efficiency, high-precision and automatic detection.

Description

Technical Field

[0001] This invention belongs to the field of precision optical component testing technology, and particularly relates to a method and system for measuring the full-area diffraction efficiency of a grating based on dual optical paths. Background Technology

[0002] As a core beam-splitting element in precision optical systems such as metrology, space exploration, and high-end lithography machines, the performance of gratings directly determines the technical specifications of the entire system. Diffraction efficiency, a core parameter for evaluating grating performance, directly relates to the effective utilization efficiency of light energy and the accuracy of system design. Its value depends on the grating's microstructure (such as duty cycle, sidewall tilt angle, and groove depth). However, in actual manufacturing processes, influenced by factors such as mask uniformity, etching deviation, sidewall steepness, and surface roughness, the actual diffraction efficiency of the grating often deviates significantly from the theoretical design value. Theoretical design alone is insufficient to accurately predict and guarantee the actual performance of the grating, a problem that has become a key challenge restricting the reliable application of gratings in high-end optical systems. Therefore, accurately and efficiently measuring grating diffraction efficiency and establishing a feedback control closed loop between measurement results and process parameters has become a crucial step in optimizing grating manufacturing processes and ensuring finished product performance.

[0003] To accurately measure the diffraction efficiency of gratings, existing methods mainly fall into two categories: The first is the single-path sequential measurement method, which measures the intensity of incident and diffracted light sequentially. While simple, this method is susceptible to light source fluctuations, resulting in limited accuracy and repeatability. The second is the dual-path synchronous measurement method, which uses a beam splitter to simultaneously acquire reference and diffracted light signals, effectively offsetting light source fluctuations and improving accuracy. However, for optical systems employing the Littoral configuration, existing methods typically set the incident angle at a position deviating from the Littoral angle to avoid optical path conflicts. This leads to measurement results that fail to accurately reflect the actual performance of the grating under the Littoral configuration, introducing systematic errors. Furthermore, existing grating diffraction efficiency measurement methods are mostly limited to single-point measurements, making it difficult to measure the entire grating area. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and system for measuring the full-area diffraction efficiency of a grating based on dual optical paths, so as to solve the problem that the prior art cannot accurately measure the diffraction efficiency of a grating under a Littoral angle configuration, and the technical problem that single-point measurement is difficult to achieve full-area measurement.

[0005] To achieve the above objectives, the technical solution created by this invention is implemented as follows:

[0006] A full-frame measurement system for grating diffraction efficiency based on dual optical paths includes:

[0007] A light source, used to emit light beams;

[0008] A beam splitter is used to split a beam of light emitted from a light source into a reference beam and a measurement beam.

[0009] A reference photodetector is used to collect the intensity of a reference light.

[0010] A precision rotary stage is used to support and adjust the incident angle of the grating under test;

[0011] A two-dimensional precision displacement stage is used to support a precision rotary stage and the grating to be measured on it, and to move it in a two-dimensional plane.

[0012] The measurement photodetector is used to collect the intensity of specific-order diffracted light generated after the measurement light is diffracted by the grating under test when the measurement photodetector is placed in the diffraction direction of the grating under test; when the measurement photodetector is placed between the grating under test and the beam splitter, it is used to collect the incident light intensity of the measurement light.

[0013] The control unit is used to control the rotation of the precision rotary stage and the movement of the two-dimensional precision displacement stage, and to synchronously trigger the light intensity acquisition of the reference photodetector and the measurement photodetector.

[0014] The data processing unit is used to calculate the diffraction efficiency of the grating under test based on the light intensity collected by the measuring photodetector and the reference photodetector.

[0015] Furthermore, the light source is a diode laser or a fiber laser.

[0016] Furthermore, when the light source is a fiber laser, a beam expander and collimator and a polarizer are placed between the light source and the beam splitter. The beam expander and collimator is used to collimate the beam emitted by the light source into parallel light and to modulate the parallel light into polarized light. When the light source is a diode laser, only a polarizer is placed between the light source and the beam splitter.

[0017] Furthermore, it further includes a standard reflector disposed between the beam splitter and the light source. First, the standard reflector is adjusted so that the reflected light coincides with the measurement light, so that the reflected light is reflected by the beam splitter. By moving the position of the measurement photodetector, the light intensity of the reflected light attenuated by the beam splitter is collected. Then, the standard reflector is rotated so that the reflected light does not pass through the beam splitter. By moving the position of the measurement photodetector, the light intensity of the reflected light that has not been attenuated by the beam splitter is collected.

[0018] A method for measuring the full-frame diffraction efficiency of a grating based on a dual-optical-path system, implemented using the aforementioned full-frame grating diffraction efficiency measurement system, includes the following steps:

[0019] S1: Construct a full-area measurement system for grating diffraction efficiency: Adjust the measurement system to make the measurement light coaxial with the 0th order reflected light generated by the diffraction of the grating under test, and ensure that the measurement light is incident on the grating surface along the normal direction of the grating surface under test.

[0020] S2: Forward beam splitting ratio calibration and diffraction intensity acquisition:

[0021] S21: Place a measurement photodetector between the grating under test and the beam splitter, and use the measurement photodetector to collect the incident light intensity of the measurement light at the calibration time. Simultaneously, a reference photodetector is used to collect the light intensity of the reference light at the calibration time. And calculate the forward beam splitting ratio. The calculation formula is: ;

[0022] S22: The incident angle of the grating under test is adjusted to a preset angle using a precision rotating stage, and the intensity of the specific order diffracted light generated after diffraction by the grating under test is collected by moving the measuring photodetector. Simultaneously, a reference photodetector is used to collect the intensity of the reference light at the measurement time. And calculate the relative diffraction ratio. The calculation formula is: ;

[0023] S3: Calculate the single-point diffraction efficiency of the grating under test: using the data processing unit based on the forward beam splitting ratio and relative diffraction ratio Calculate the single-point diffraction efficiency of the grating under test. The calculation formula is: ;

[0024] S4: Full-width scanning measurement: The two-dimensional precision displacement stage is controlled by the synchronous control unit to move along the preset path, and steps S2 and S3 are repeated to obtain the full-width diffraction efficiency of the grating under test.

[0025] Furthermore, prior to step S2, the following steps are also included:

[0026] S10: Reverse beam splitting ratio calibration:

[0027] S10a: Place a standard mirror between the grating under test and the beam splitter;

[0028] S10b: Adjust the standard mirror so that the reflected light coincides with the measurement light, so that the reflected light is reflected by the beam splitter. By moving the position of the measurement photodetector, collect the intensity of the reflected light attenuated by the beam splitter. ;

[0029] S10c: Rotate the standard mirror again so that the reflected light does not pass through the beam splitter. By moving the position of the measuring photodetector, the intensity of the reflected light that has not been attenuated by the beam splitter is collected. ;

[0030] S10d: Based on light intensity With light intensity Calculate the reverse beam splitting ratio The calculation formula is: ;

[0031] In step S3, the data processing unit uses the forward beam splitting ratio... and relative diffraction ratio and reverse beam splitting ratio Calculate the single-point diffraction efficiency of the grating under test at the Littoral incident angle. The calculation formula is: ;

[0032] Finally, in step S4, steps S10, S2 and S3 are repeated to obtain the full-area diffraction efficiency of the grating under test at the Littoral incident angle.

[0033] Furthermore, the preset path in step S4 is a serpentine scanning path, with a lateral displacement distance greater than the length of the grating to be measured and a longitudinal displacement distance less than or equal to the diameter of the measuring light spot.

[0034] Furthermore, after step S4, the following steps are also included:

[0035] S5: Diffraction efficiency visualization: The full-area diffraction efficiency obtained in step S4 is processed by the data processing unit to generate a diffraction efficiency distribution map corresponding to the position on the surface of the grating under test.

[0036] Furthermore, step S5 specifically includes the following steps:

[0037] S51: Data filtering: Extract the diffraction efficiency sequence corresponding to each scan line from the diffraction efficiency collected in time series.

[0038] S52: Data rearrangement: The order of the diffraction efficiency sequence of alternating rows in the serpentine scanning path is reversed so that the row and column order of the diffraction efficiency matrix corresponds one-to-one with the two-dimensional physical position on the surface of the grating under test.

[0039] S53: Visualization output: Based on the rearranged diffraction efficiency matrix, generate a diffraction efficiency distribution map of the entire grating under test or a specified area.

[0040] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0041] 1. By adopting dual-optical-path synchronous measurement technology, the incident light is split into reference light and measurement light by a beam splitter. The reference photodetector captures the energy fluctuation information of the light source in real time and performs dynamic compensation in the diffraction efficiency calculation. This fundamentally solves the problems of light source fluctuation and environmental interference errors caused by the non-simultaneous measurement of incident light and diffracted light in the single-optical-path sequential measurement method, thereby improving the repeatability and accuracy of grating diffraction efficiency measurement.

[0042] 2. For optical systems employing Litterow configurations, such as external cavity diode lasers, high-precision grating interferometers, and augmented reality diffraction waveguides, this invention introduces a standard mirror and calculates the reverse beam splitting ratio, combining it with the forward beam splitting ratio to accurately measure the grating diffraction efficiency at the Litterow angle. This design allows the measurement process to directly reproduce the diffraction performance of the grating in the actual working scenario without deviating from the Litterow angle of the grating's actual application, completely eliminating the inherent systematic errors caused by non-Litterow angle measurements. This provides core data assurance for the design and performance optimization of optical systems relying on Litterow configurations.

[0043] 3. This invention adds a two-dimensional precision displacement stage and a control unit to the single-point measurement, achieving continuous scanning measurement of the grating surface through a preset serpentine displacement path. The control unit coordinates the movement speed of the two-dimensional precision displacement stage and the response time of the detector to ensure the synchronization and data integrity of the full-area measurement process. Compared with the traditional point-by-point detection method, efficiency is significantly improved, while solving the problems of limited positioning accuracy and incomplete full-area coverage of the traditional method. Combined with diffraction efficiency screening, inversion calibration, and visualization functions, the diffraction efficiency distribution of the entire grating surface and local areas can be intuitively presented, providing comprehensive data support for the evaluation of the uniformity of the grating microstructure.

[0044] 4. The measurement system of this invention consists only of conventional optical and mechanical components such as a light source, beam splitter, detector, precision rotary stage, and two-dimensional precision displacement stage. It eliminates the need for complex and expensive custom-designed equipment, thus keeping hardware costs under control. At the software level, it is compatible with the Windows operating system, and the efficiency detection and data recording software supports common development platforms such as LabVIEW. Data processing code can be implemented using general-purpose tools such as Matlab, reducing the difficulty of technical deployment and secondary development. Furthermore, the measurement system eliminates the need for complex optical path debugging procedures. Through a standardized process of "optical path calibration - angle adjustment - data acquisition - automatic processing," it significantly reduces manual intervention, lowers the technical threshold for operators, and facilitates large-scale application on industrial production lines.

[0045] 5. This invention possesses strong scene adaptability: In terms of grating type, universal testing of reflective and transmissive gratings can be achieved through the design of a dedicated fixture; in terms of grating line direction, it supports grating measurement at angles perpendicular, horizontal, and arbitrary to the side of the substrate (only the equivalent incident angle needs to be calculated); in terms of measurement conditions, it can flexibly switch between various incident angle modes such as vertical incident (0°), Littoral angle incident, and specific required angles, adapting to various polarization measurement needs such as vertical and horizontal; in terms of grating parameters, it can cover mainstream grating specifications in fields such as metrology, aerospace exploration, and high-end lithography machines, providing an integrated solution for grating performance testing in different application scenarios. Attached Figure Description

[0046] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0047] Figure 1 This is a schematic diagram of the structure of the full-width measurement system for grating diffraction efficiency based on dual optical paths according to an embodiment of the present invention;

[0048] Figure 2 This is a schematic flowchart of the full-area measurement method for grating diffraction efficiency based on dual optical paths according to an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of the interface and serpentine scanning path settings of the two-dimensional precision displacement stage control software according to an embodiment of the present invention.

[0050] Figure 4 This is a schematic diagram of the interface of the efficiency detection and data recording software according to an embodiment of the present invention.

[0051] Explanation of reference numerals in the attached figures: 1. Light source; 2. Beam splitter; 3. Precision rotary stage; 4. Two-dimensional precision displacement stage; 5. Reference photodetector; 6. Measurement photodetector; 7. Grating under test; 8. Polarizer; 9. Standard mirror. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0053] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0054] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0055] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0056] The invention will now be described in detail with reference to the figures and embodiments.

[0057] Figure 1 The structure of a full-area measurement system for grating diffraction efficiency based on a dual-path optical path, according to an embodiment of the present invention, is shown.

[0058] like Figure 1 As shown, the structure of the full-area measurement system for grating diffraction efficiency based on dual optical paths provided in this embodiment of the invention includes a light source 1, a beam splitter 2, a precision rotating stage 3, a two-dimensional precision displacement stage 4, a reference photodetector 5, a measurement photodetector 6, a control unit (not shown) and a data processing unit (not shown).

[0059] Light source 1 emits a light beam, which serves as the incident light for the grating 7 under test. Light source 1 can be a diode laser or a fiber laser (as above). When a fiber laser is used, a beam expander / collimator is placed between light source 1 and beam splitter 2 to expand and collimate the emitted beam into parallel light, ensuring a uniform and stable spot size incident on the surface of the grating 7. If the beam emitted by the fiber laser is not collimated, the spot size will change with the propagation distance, resulting in inconsistent light intensity distribution at different scanning positions. Furthermore, the uncollimated beam, due to divergence or convergence, will cause distribution errors in the actual incident angle illuminating the surface of the grating 7, thus introducing systematic errors. When a diode laser is used, the laser emitted by the diode laser is collimated, eliminating the need for a beam expander / collimator. A polarizer 8 is placed between light source 1 and beam splitter 2 to modulate the collimated light into polarized light. When a beam expander / collimator is placed between light source 1 and beam splitter 2, the polarizer 8 is positioned between the beam splitter 2 and the beam expander / collimator. Polarizer 8 can filter out a single, stable linearly polarized light, ensuring that each measurement is performed under exactly the same polarization conditions, thereby improving the repeatability and accuracy of the diffraction efficiency measurement of the grating 7 under test.

[0060] After the incident light is incident on the beam splitter 2, part of the incident light is reflected by the beam splitter 2 and then incident on the reference photodetector 5 as reference light, and the reference photodetector 5 collects the light intensity of the reference light; the other part of the incident light is transmitted through the beam splitter 2 and then incident on the grating to be measured 7 as measurement light. The measurement photodetector 6 is set at different positions according to the light intensity to be measured.

[0061] The precision rotary stage 3 is used to support and adjust the incident angle of the grating 7 under test. The precision rotary stage 3 can be a commercially available high-precision rotary platform, so the specific structure of the precision rotary stage 3 will not be described in detail in this invention.

[0062] The two-dimensional precision displacement stage 4 is used to support the precision rotary stage 3 and the optical grating 7 to be measured on it, and to move it in a two-dimensional plane. The two-dimensional precision displacement stage 4 adopts a commercially available high-precision two-dimensional displacement platform, so the specific structure of the two-dimensional precision displacement stage 4 will not be described in detail in this invention.

[0063] When calibrating the forward beam splitting ratio, the measuring photodetector 6 is placed between the beam splitter 2 and the grating under test 7 to collect the incident light intensity of the measuring light at the calibration time. At this time, the intensity of the reference light at the calibration time is synchronously acquired by reference photodetector 5. Thus, the forward beam splitting ratio can be calculated. .

[0064] When measuring the diffraction efficiency of the grating 7 under test, the measuring photodetector 6 is moved to the diffraction direction of the grating 7 under test to collect the light intensity of the specific order diffracted light generated after the measurement light is diffracted by the grating 7 under test. Specifically, the incident angle of the grating 7 under test is adjusted to a preset angle by the precision rotating stage 3, and the measuring photodetector 6 collects the light intensity of the specific order diffracted light generated after the diffraction by the grating 7 under test. At this time, the intensity of the reference light at the measurement moment is synchronously acquired by the reference photodetector 5. Thus, the relative diffraction ratio can be calculated. .

[0065] To measure diffracted light of different orders, multiple photodetectors 6 can be set up to collect the light intensity of diffracted light of different orders. .

[0066] The control unit is used to implement three types of control: first, to control the rotation of the precision rotary table 3 and the movement of the two-dimensional precision displacement stage 4; second, to synchronously trigger the light intensity acquisition of the reference photodetector 5 and the measuring photodetector 6. The reference photodetector 5 and the measuring photodetector 6 can be power meters.

[0067] The data processing unit is used to determine the relative diffraction ratio. and forward beam splitting ratio Calculate the diffraction efficiency of the grating 7 under test. .

[0068] By employing dual-optical-path synchronous measurement technology, the incident light is split into reference light and measurement light by a beam splitter. The reference photodetector captures the energy fluctuation information of the light source in real time and performs dynamic compensation in the diffraction efficiency calculation. This fundamentally solves the problems of light source fluctuation and environmental interference errors caused by the non-simultaneous measurement of incident light and diffracted light in the single-optical-path sequential measurement method, thereby improving the repeatability and accuracy of grating diffraction efficiency measurement.

[0069] The full-frame measurement system for grating diffraction efficiency further includes a standard mirror 9, which works in conjunction with the measurement photodetector 6 to calibrate the reverse beam splitting ratio.

[0070] When calibrating the reverse beam splitting ratio, a standard mirror 9 is placed between the grating 7 under test and the beam splitter 2. The standard mirror 9 is first adjusted so that the reflected light coincides with the measurement light, so that the reflected light is reflected by the beam splitter 2. By moving the position of the measurement photodetector 6, the intensity of the reflected light attenuated by the beam splitter 2 is collected. Then rotate the standard mirror 9 so that the reflected light does not pass through the beam splitter 2. By moving the position of the measuring photodetector 6, the intensity of the reflected light that has not been attenuated by the beam splitter 2 is collected. Thus, the reverse beam splitting ratio can be calculated. .

[0071] Of course, the present invention can employ two measuring photodetectors 6 to respectively collect the light intensity of the reflected light attenuated by the beam splitter 2. The intensity of reflected light without attenuation by beam splitter 2 .

[0072] After calculating the reverse beam splitting ratio, the standard mirror 9 is removed to avoid affecting the subsequent measurement of the diffraction efficiency of the grating 7 under test.

[0073] With the standard reflector 9 introduced, the data processing unit then calculates based on the forward beam splitting ratio. and relative diffraction ratio and reverse beam splitting ratio Calculate the diffraction efficiency of the grating 7 under test. .

[0074] For optical systems employing Litterow configurations, such as external cavity diode lasers, high-precision grating interferometers, and augmented reality diffraction waveguides, this invention introduces a standard mirror 9 and calculates the reverse beam splitting ratio. Combined with the forward beam splitting ratio, it achieves accurate measurement of the grating diffraction efficiency at the Litterow angle. This design allows the measurement process to directly reproduce the diffraction performance of the grating in the actual working scenario without deviating from the Litterow angle of the grating's actual application. It completely eliminates the inherent systematic errors caused by non-Litterow angle measurements, providing core data assurance for the design and performance optimization of optical systems that rely on Litterow configurations.

[0075] The foregoing describes in detail the structure of the full-frame grating diffraction efficiency measurement system provided by the embodiments of the present invention. The embodiments of the present invention also provide a method for full-frame grating diffraction efficiency measurement using the full-frame grating diffraction efficiency measurement system.

[0076] Figure 2 The flowchart of the full-area measurement method for grating diffraction efficiency based on dual optical paths according to an embodiment of the present invention is shown.

[0077] like Figure 2 As shown in the embodiment of the present invention, the method for full-area measurement of grating diffraction efficiency based on dual optical paths includes the following steps:

[0078] S1: Construct a full-area measurement system for grating diffraction efficiency.

[0079] Adjust the measurement system so that the measurement light is coaxial with the 0th order reflected light generated by the diffraction of the grating under test, ensuring that the measurement light is incident on the grating surface along the normal direction of the grating surface under test.

[0080] S2: Forward beam splitting ratio calibration and diffraction intensity acquisition.

[0081] Step S2 specifically includes the following steps:

[0082] S21: Place a measurement photodetector between the grating under test and the beam splitter, and use the measurement photodetector to collect the incident light intensity of the measurement light at the calibration time. Simultaneously, the intensity of the reference light at the calibration time is synchronously acquired using a reference photodetector. And calculate the forward beam splitting ratio. The calculation formula is: .

[0083] S22: The incident angle of the grating under test is adjusted to a preset angle using a precision rotating stage, and the intensity of the specific order diffracted light generated after diffraction by the grating under test is collected by moving the measuring photodetector. Simultaneously, a reference photodetector is used to collect the intensity of the reference light at the measurement time. And calculate the relative diffraction ratio. The calculation formula is: .

[0084] S3: Calculate the single-point diffraction efficiency of the grating under test: using the data processing unit based on the forward beam splitting ratio and relative diffraction ratio Calculate the single-point diffraction efficiency of the grating under test. The calculation formula is: .

[0085] S4: Full-width scanning measurement: The two-dimensional precision displacement stage is controlled by the synchronous control unit to move along the preset path, and steps S2 and S3 are repeated to obtain the full-width diffraction efficiency of the grating under test.

[0086] Before step S2, step S10 is also included: reverse beam splitting ratio calibration.

[0087] Step S10 specifically includes the following steps:

[0088] S10a: Place a standard mirror between the grating under test and the beam splitter.

[0089] S10b: Adjust the standard mirror so that the reflected light coincides with the measurement light, so that the reflected light is reflected by the beam splitter. By moving the position of the measurement photodetector, collect the intensity of the reflected light attenuated by the beam splitter. .

[0090] S10c: Rotate the standard mirror again so that the reflected light does not pass through the beam splitter. By moving the position of the measuring photodetector, the intensity of the reflected light that has not been attenuated by the beam splitter is collected. .

[0091] S10d: Based on light intensity With light intensity Calculate the reverse beam splitting ratio The calculation formula is: .

[0092] In step S3, the data processing unit uses the forward beam splitting ratio... and relative diffraction ratio and reverse beam splitting ratio Calculate the single-point diffraction efficiency of the grating under test at the Littoral incident angle. The calculation formula is: .

[0093] Finally, in step S4, steps S10, S2 and S3 are repeated to obtain the full-area diffraction efficiency of the grating under test at the Littoral incident angle.

[0094] The preset path in step S4 is a serpentine scanning path, with a lateral displacement distance greater than the length of the grating to be measured and a longitudinal displacement distance less than or equal to the diameter of the measuring light spot.

[0095] This invention addresses the rotation of a precision rotary table and the motion control of a two-dimensional precision displacement stage. A two-dimensional precision displacement stage control software was developed based on the Windows operating system, with the user interface as shown below. Figure 3 As shown, a serpentine displacement path is set in the two-dimensional precision displacement stage control software.

[0096] This invention addresses the full-width diffraction efficiency of a grating under test. Based on common development platforms such as LabVIEW, a software program for efficiency detection and data recording has been developed. The user interface is as follows: Figure 4 As shown, by clicking the "Band Splitting Ratio Calculation" switch, the forward or reverse beam splitting ratio can be calculated. Clicking the "Efficiency Real-time Calculation" switch enables single-point diffraction efficiency calculation. Clicking the "Efficiency Real-time Recording" switch starts the serpentine displacement recording of the two-dimensional precision displacement stage and exports the full-area diffraction efficiency data.

[0097] Following step S4, the following steps are also included:

[0098] S5: Diffraction efficiency visualization: The full-area diffraction efficiency obtained in step S4 is processed by the data processing unit to generate a diffraction efficiency distribution map corresponding to the position on the surface of the grating under test.

[0099] Step S5 specifically includes the following steps:

[0100] S51: Data filtering: Extract the diffraction efficiency sequence corresponding to each scan line from the diffraction efficiency collected in time series.

[0101] S52: Data rearrangement: The order of the diffraction efficiency sequence in the alternating rows of the serpentine scanning path is reversed so that the row and column order of the diffraction efficiency matrix corresponds one-to-one with the two-dimensional physical position of the grating surface under test.

[0102] S53: Visualization output: Based on the rearranged diffraction efficiency matrix, generate a diffraction efficiency distribution map of the entire grating under test or a specified area.

[0103] Steps S51 to S53 above can be implemented using data processing scripts such as Python or MATLAB. Specifically, the following operations are performed:

[0104] Data import and filtering: Read the raw diffraction efficiency data, and according to the motion logic (speed, step size) and acquisition timing of the two-dimensional precision displacement stage, parse the time series data into a two-dimensional data array arranged by scan rows.

[0105] Data rearrangement: Because adjacent rows in a serpentine scan have opposite scanning directions, the directly obtained data matrix does not correspond one-to-one with the physical position of the grating under test. The orientation reversal module is responsible for reversing the order of the data in even-numbered rows (or odd-numbered rows) to generate a diffraction efficiency matrix that completely corresponds to the spatial position of the grating surface under test (from left to right, from top to bottom).

[0106] Visualization Output: The processed efficiency matrix is ​​presented as a pseudo-color image, 3D surface plot, or contour map, generating an intuitive full-area diffraction efficiency distribution map. Users can interactively select specific areas for local magnification, statistical analysis (such as uniformity calculation, maximum / minimum value location), and export reports.

[0107] Experiments verified that the repeatability error for grating diffraction efficiency detection is less than 0.03% in the range of 300 gr / mm to 3500 gr / mm. Furthermore, for a 60 mm × 60 mm grating, full-area diffraction efficiency measurement using both vertical and horizontal polarization modes takes only 10 minutes, significantly improving detection efficiency and accuracy.

[0108] By changing the fixture and adjusting the optical path, the method of this invention is also applicable to the full-area detection of diffraction efficiency of transmission or reflection gratings. In the grating line direction, it supports grating measurements at arbitrary angles (perpendicular to the substrate side, horizontal, and at only the equivalent incident angle needs to be calculated). Regarding measurement conditions, it allows for flexible switching between various incident angle modes, such as vertical incident (0°), Littoral angle incident, and specific required angles, adapting to various polarization measurement needs, including vertical and horizontal. Within the range of 300gr / mm to 3500gr / mm, it covers mainstream grating specifications in fields such as metrology, aerospace exploration, and high-end lithography, providing an integrated solution for grating performance testing in different application scenarios.

[0109] Compared to single-point measurement methods, this invention adds a two-dimensional precision displacement stage and a control unit to the single-point measurement process. Through a preset serpentine displacement path, continuous scanning measurement of the grating surface is achieved. The control unit coordinates the movement speed of the two-dimensional precision displacement stage and the response time of the detector to ensure the synchronization and data integrity of the full-area measurement process. Compared to traditional point-by-point detection methods, efficiency is significantly improved, while solving the problems of limited positioning accuracy and incomplete full-area coverage in traditional methods. Combined with diffraction efficiency screening, inversion calibration, and visualization functions, the diffraction efficiency distribution of the entire grating surface and local areas can be intuitively presented, providing comprehensive data support for evaluating the uniformity of the grating's microstructure.

[0110] Furthermore, the measurement system of this invention consists only of conventional optical and mechanical components such as a light source, beam splitter, detector, precision rotary stage, and two-dimensional precision displacement stage, eliminating the need for complex and expensive custom-designed equipment and keeping hardware costs under control. On the software side, it is compatible with the Windows operating system, and the efficiency detection and data recording software supports common development platforms such as LabVIEW. Data processing code can be implemented using general-purpose tools such as Matlab, reducing the difficulty of technical deployment and secondary development. Simultaneously, the measurement system eliminates the need for complex optical path debugging procedures. Through a standardized process of "optical path calibration - angle adjustment - data acquisition - automatic processing," it significantly reduces manual intervention, lowers the technical threshold for operators, and facilitates large-scale application on industrial production lines.

[0111] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0112] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A full-frame measurement system for grating diffraction efficiency based on dual optical paths, characterized in that, include: A light source, used to emit light beams; A beam splitter is used to split a beam of light emitted from a light source into a reference beam and a measurement beam. A reference photodetector is used to collect the intensity of a reference light. A precision rotary stage is used to support and adjust the incident angle of the grating under test; A two-dimensional precision displacement stage is used to support a precision rotary stage and the grating to be measured on it, and to move it in a two-dimensional plane. The measurement photodetector is used to collect the intensity of specific-order diffracted light generated after the measurement light is diffracted by the grating under test when the measurement photodetector is placed in the diffraction direction of the grating under test; when the measurement photodetector is placed between the grating under test and the beam splitter, it is used to collect the incident light intensity of the measurement light. The control unit is used to control the rotation of the precision rotary stage and the movement of the two-dimensional precision displacement stage, and to synchronously trigger the light intensity acquisition of the reference photodetector and the measurement photodetector. The data processing unit is used to calculate the diffraction efficiency of the grating under test based on the light intensity collected by the measuring photodetector and the reference photodetector. A standard reflector is placed between the beam splitter and the light source. First, the standard reflector is adjusted so that the reflected light coincides with the measurement light, so that the reflected light is reflected by the beam splitter. By moving the position of the measurement photodetector, the intensity of the reflected light attenuated by the beam splitter is collected. Then, the standard reflector is rotated so that the reflected light does not pass through the beam splitter. By moving the position of the measurement photodetector, the intensity of the reflected light that has not been attenuated by the beam splitter is collected.

2. The full-width measurement system for grating diffraction efficiency based on dual optical paths according to claim 1, characterized in that, The light source is a diode laser or a fiber laser.

3. The full-width measurement system for grating diffraction efficiency based on dual optical paths according to claim 2, characterized in that, When the light source is a fiber laser, a beam expander and collimator and a polarizer are placed between the light source and the beam splitter. The beam expander and collimator is used to collimate the beam emitted by the light source into parallel light and to modulate the parallel light into polarized light. When the light source is a diode laser, only a polarizer is placed between the light source and the beam splitter.

4. A method for measuring the full-width diffraction efficiency of a grating based on a dual-optical-path system, implemented using the full-width diffraction efficiency measurement system according to any one of claims 1 to 3, characterized in that... Includes the following steps: S1: Constructing a full-area measurement system for grating diffraction efficiency: Adjust the measurement system to ensure that the measurement light and the 0th-order reflected light generated by the diffraction of the grating under test are coaxial, ensuring that the measurement light is incident on the grating surface along the normal direction of the grating surface; S2: Forward beam splitting ratio calibration and diffraction intensity acquisition: S21: Place a measurement photodetector between the grating under test and the beam splitter, and use the measurement photodetector to collect the incident light intensity of the measurement light at the calibration time. Simultaneously, a reference photodetector is used to collect the light intensity of the reference light at the calibration time. And calculate the forward beam splitting ratio. The calculation formula is: ; S22: The incident angle of the grating under test is adjusted to a preset angle using a precision rotating stage, and the intensity of the specific order diffracted light generated after diffraction by the grating under test is collected by moving the measuring photodetector. Simultaneously, a reference photodetector is used to collect the intensity of the reference light at the measurement time. And calculate the relative diffraction ratio. The calculation formula is: ; S3: Calculate the single-point diffraction efficiency of the grating under test: using the data processing unit based on the forward beam splitting ratio and relative diffraction ratio Calculate the single-point diffraction efficiency of the grating under test. The calculation formula is: ; S4: Full-width scanning measurement: The two-dimensional precision displacement stage is controlled by the synchronous control unit to move along the preset path, and steps S2 and S3 are repeated to obtain the full-width diffraction efficiency of the grating under test. Before step S2, the following steps are also included: S10: Reverse beam splitting ratio calibration: S10a: Place a standard mirror between the grating under test and the beam splitter; S10b: Adjust the standard mirror so that the reflected light coincides with the measurement light, so that the reflected light is reflected by the beam splitter. By moving the position of the measurement photodetector, collect the intensity of the reflected light attenuated by the beam splitter. ; S10c: Rotate the standard mirror again so that the reflected light does not pass through the beam splitter. By moving the position of the measuring photodetector, the intensity of the reflected light that has not been attenuated by the beam splitter is collected. ; S10d: Based on light intensity With light intensity Calculate the reverse beam splitting ratio The calculation formula is: ; In step S3, the data processing unit uses the forward beam splitting ratio... and relative diffraction ratio and reverse beam splitting ratio Calculate the single-point diffraction efficiency of the grating under test at the Littoral incident angle. The calculation formula is: ; Finally, in step S4, steps S10, S2 and S3 are repeated to obtain the full-area diffraction efficiency of the grating under test at the Littoral incident angle.

5. The method for full-width measurement of grating diffraction efficiency based on dual optical paths according to claim 4, characterized in that, The preset path in step S4 is a serpentine scanning path, with a lateral displacement distance greater than the length of the grating to be measured and a longitudinal displacement distance less than or equal to the diameter of the measuring light spot.

6. The method for full-width measurement of grating diffraction efficiency based on dual optical paths according to claim 5, characterized in that, Following step S4, the following steps are also included: S5: Diffraction efficiency visualization: The full-area diffraction efficiency obtained in step S4 is processed by the data processing unit to generate a diffraction efficiency distribution map corresponding to the position on the surface of the grating under test.

7. The method for full-width measurement of grating diffraction efficiency based on dual optical paths according to claim 6, characterized in that, Step S5 specifically includes the following steps: S51: Data filtering: Extract the diffraction efficiency sequence corresponding to each scan line from the diffraction efficiency collected in time series. S52: Data rearrangement: The order of the diffraction efficiency sequence of alternating rows in the serpentine scanning path is reversed so that the row and column order of the diffraction efficiency matrix corresponds one-to-one with the two-dimensional physical position on the surface of the grating under test. S53: Visualization output: Based on the rearranged diffraction efficiency matrix, generate a diffraction efficiency distribution map of the entire grating under test or a specified area.

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