Method for testing the absorption of a grating structure region
By cutting the test grating in the grating structure region and adjusting its micro-nano structure period, the accuracy problem of grating structure region absorptivity testing was solved, and accurate absorptivity calculation was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GOERTEK OPTICAL TECH CO LTD
- Filing Date
- 2025-12-03
- Publication Date
- 2026-07-21
AI Technical Summary
Existing technologies have poor accuracy in testing the absorptivity of grating structure regions, and it is difficult to effectively capture diffracted light other than zero-order transmitted light and zero-order reflected light, resulting in inaccurate tests.
The test grating is cut out from the grating under test, and the target period is determined according to the incident wavelength and the refractive index of the waveguide substrate. The period of the micro-nano structure is adjusted to suppress the generation of diffracted light, and the absorption rate is calculated using the transmittance and reflectance.
This technology enables accurate acquisition of transmittance and reflectance in the absorptivity test of the grating structure region, eliminating diffraction interference and ensuring the accuracy and reliability of the test results.
Smart Images
Figure CN121702697B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of material property testing technology for grating structures, and in particular to a method for testing the absorption rate of a grating structure region. Background Technology
[0002] The characteristic of a diffractive waveguide is that it folds light within the waveguide, allowing the light to be transmitted to various regions through repeated total internal reflection. Therefore, the absorptivity of the material constituting the waveguide is a key parameter affecting its optical efficiency.
[0003] Currently, spectrophotometers and other equipment are commonly used to test the absorptivity of diffractive waveguides. However, this testing method only has good accuracy in the unstructured regions of the diffractive waveguide, while its accuracy is poor in the grating structure regions. Summary of the Invention
[0004] The main objective of this application is to provide a method for testing the absorption rate of a grating structure region, which aims to accurately test the absorption rate of the grating structure region.
[0005] This application provides a method for testing the absorption rate of a grating structure region, the method comprising: A portion of the grating to be tested is cut out as a test grating, and the test grating is placed on the waveguide substrate on which the grating to be tested is to be placed. Based on the incident wavelength of the test light and the refractive index of the waveguide substrate, the target period is determined, and the micro-nano structure period of the test grating is adjusted to the target period to suppress the generation of diffracted light when the test light is incident on the test grating at a preset angle. The test light beam is incident on the test grating after the adjustment period at the preset angle to obtain the transmittance and reflectance of the test grating; Based on the transmittance and the reflectance, the absorptivity of the test grating is calculated and used as the absorptivity of the grating under test.
[0006] In one embodiment, the step of determining the target period based on the incident wavelength of the test light and the refractive index of the waveguide substrate includes: The periodic range of the micro / nano structure is determined based on the incident wavelength of the test light and the refractive index of the waveguide substrate. One period is selected from the periodic range of the micro / nano structure as the target period.
[0007] In one embodiment, the step of determining the periodic range of the micro / nano structure based on the incident wavelength of the test light and the refractive index of the waveguide substrate includes: Calculate the difference between the refractive index and the sine of the preset angle to obtain a first value; Calculate the ratio between the incident wavelength and the first value to obtain the reference period; The micro-nano structure period range is generated by using the reference period as the upper limit of the period range.
[0008] In one embodiment, prior to the step of obtaining the transmittance and reflectance of the test grating, the method further includes: When the test light is incident on the test grating after the adjustment period at the preset angle, it is determined whether diffracted light exists. If so, the target period is reduced to obtain a new target period, and the process returns to the step of adjusting the micro / nano structure period of the test grating to the target period. If not, then proceed with the step of obtaining the transmittance and reflectance of the test grating.
[0009] In one embodiment, the step of detecting whether diffracted light exists when the test light is incident on the test grating after the adjustment period at the preset angle includes: At least one prism is coupled onto the surface of the waveguide substrate that supports the test grating. During the process of the test light beam being incident on the test grating after the adjustment period at the preset angle, the intensity of the emitted light from the prism is obtained; If the intensity of the emitted light is zero, then it is determined that when the test light is incident on the test grating after the adjustment period at the preset angle, there is no diffraction light. If the intensity of the emitted light is greater than zero, then it is determined that when the test light is incident on the test grating after the adjustment period at the preset angle, there is diffracted light.
[0010] In one embodiment, the step of cutting a portion of the grating from the grating to be tested as the test grating includes: A region containing at least a predetermined number of micro-nano structure periods of the grating under test is cut out from the grating under test and used as the test grating.
[0011] In one embodiment, the step of obtaining the transmittance and reflectance of the test grating includes: A transmission light detector and a reflection light detector are respectively set along the transmission light path and the reflection light path formed on the test grating along the test light ray; The transmittance of the test grating is obtained through the transmission photodetector, and the reflectance of the test grating is obtained through the reflection photodetector.
[0012] In one embodiment, the step of obtaining the transmittance of the test grating through the transmission photodetector and obtaining the reflectance of the test grating through the reflection photodetector includes: The transmittance and reflectance of the waveguide substrate without the test grating are obtained by the transmitted light detector and the reflected light detector, respectively, and used as the reference transmittance and reference reflectance. With the test grating placed on the waveguide substrate and the test light incident on the test grating after the adjustment period at the preset angle, the transmittance and reflectance are obtained by the transmission light detector and the reflection light detector, respectively, as the initial transmittance and initial reflectance. The difference between the initial transmittance and the reference transmittance is used as the transmittance of the test grating, and the difference between the initial reflectance and the reference reflectance is used as the reflectance of the test grating.
[0013] In one embodiment, the method further includes: Obtain the absorption rate of the test grating under different target periods; The average absorptivity under each target period is taken as the absorptivity of the grating under test.
[0014] In one embodiment, the method further includes: The absorptivity of the test grating is obtained when the test light is incident on the test grating at different preset angles. The preset angles and their corresponding absorption rates are correlated to generate the absorption rate characteristic curve of the test grating. The absorption rate characteristic curve is displayed on the test equipment.
[0015] This application provides a method for testing the absorptivity of a grating structure region. First, a portion of the grating to be tested is cut out as the test grating, and the test grating is placed on the waveguide substrate on which the grating to be tested is to be placed. Then, based on the incident wavelength of the test light and the refractive index of the waveguide substrate, the target period is determined, and the micro-nano structure period of the test grating is adjusted to the target period to suppress diffraction when the test light is incident on the test grating at a preset angle. As a result, when the test light is incident on the test grating after the period adjustment at the preset angle, no diffraction will be generated, only transmitted and reflected light will be generated. At this time, by obtaining the transmittance and reflectance of the test grating, the accurate absorptivity of the test grating can be calculated.
[0016] Therefore, the technical solution provided in this application can flexibly adjust the micro-nano structure period of the test grating according to the actual test conditions when testing the absorption rate of the grating structure region, so that no diffraction light is generated when the test light is incident on the test grating at a preset angle, thereby accurately testing the absorption rate of the grating structure region. Attached Figure Description
[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.
[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 This is a diffraction principle diagram of the incident light entering the grating structure region provided in this embodiment; Figure 2 This is another diffraction principle diagram provided in this embodiment after the incident light enters the grating structure region; Figure 3 A schematic flowchart of the absorption rate testing method for the grating structure region provided in the first embodiment of this application; Figure 4 A schematic diagram showing the installation position of the transmission light detector provided in the first embodiment of this application; Figure 5 A schematic diagram showing the installation position of the reflected light detector provided in the first embodiment of this application; Figure 6 This is a schematic diagram showing the placement of the prism according to the second embodiment of this application.
[0020] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0021] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application.
[0022] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.
[0023] The characteristic of a diffractive waveguide is that it folds light within the waveguide, allowing the light to be transmitted to various regions through repeated total internal reflection. Therefore, the absorptivity of the material constituting the waveguide is a key parameter affecting its optical efficiency.
[0024] Currently, spectrophotometers and similar equipment are commonly used to test the absorptivity of diffractive waveguides. However, this testing method only has good accuracy in the unstructured regions of the diffractive waveguide, while its accuracy is poor in the grating structure regions. Specifically, see [reference needed]. Figure 1 and Figure 2 When incident light enters the grating structure region, it not only produces reflected and transmitted light, but also diffracted light of various orders. After being coupled into the waveguide, the diffracted light will undergo multiple reflections, making it difficult for integrating spheres or other detectors to capture. Therefore, conventional testing methods cannot accurately measure the absorption rate of the grating structure region.
[0025] Based on this, this application provides a method for testing the absorptivity of a grating structure region. First, a portion of the grating to be tested is cut out as the test grating, and the test grating is placed on the waveguide substrate on which the grating to be tested is to be placed. Then, based on the incident wavelength of the test light and the refractive index of the waveguide substrate, the target period is determined, and the micro-nano structure period of the test grating is adjusted to the target period to suppress diffraction when the test light is incident on the test grating at a preset angle. As a result, when the test light is incident on the test grating after the period adjustment at the preset angle, no diffraction will be generated, only transmitted and reflected light will be generated. At this time, by obtaining the transmittance and reflectance of the test grating, the accurate absorptivity of the test grating can be calculated.
[0026] Therefore, the technical solution provided in this application can flexibly adjust the micro-nano structure period of the test grating according to the actual test conditions when testing the absorption rate of the grating structure region, so that no diffraction light is generated when the test light is incident on the test grating at a preset angle, thereby accurately testing the absorption rate of the grating structure region.
[0027] The diffracted light mentioned in this application specifically refers to all higher-order diffracted light except for zero-order transmitted light and zero-order reflected light.
[0028] This application proposes a method for testing the absorption rate of the grating structure region according to the first embodiment. Please refer to [link / reference]. Figure 3 The method for testing the absorption rate of the grating structure region may include steps S10 to S40: Step S10: Cut out a portion of the grating from the grating to be tested as the test grating, and place the test grating on the waveguide substrate on which the grating to be tested is to be placed; It should be noted that the grating under test is the grating whose absorption rate needs to be tested, and the test grating is the sample separated from the grating under test and used for actual testing. A waveguide substrate is a transparent dielectric layer that constrains and guides light propagation through the principle of total internal reflection.
[0029] It is understandable that by cutting a portion of the grating under test as a test grating and placing the test grating on the waveguide substrate on which the grating under test is to be placed, the test environment is made consistent with the actual working state of the grating under test. Thus, the test results of the absorbance of the test grating can accurately reflect the absorbance of the grating under test.
[0030] When cutting the grating to be tested, a portion of the grating can be cut out from the grating by means of focused ion beam etching, laser ablation, or precision scribing and dicing. This embodiment does not make specific limitations on this.
[0031] In one feasible implementation, to ensure that the absorption rate of a portion of the grating cut out from the grating under test truly reflects the macroscopic performance of the entire grating under test, rather than local defects, thus making the data more representative, the step of cutting out a portion of the grating under test as a test grating may include: cutting out a region from the grating under test that contains at least a predetermined number of micro / nano structure periods of the grating under test, as the test grating.
[0032] The preset quantity can be a default value, such as 10, or it can be flexibly set by the user according to the actual situation. This embodiment does not impose a specific limitation on this. The micro-nano structure period of the grating under test refers to the size of the most basic, repeatable nanometer or micrometer-level unit that constitutes the grating under test.
[0033] It is understood that this embodiment limits the cut portion of the grating to contain a sufficient number of complete periods to ensure that the cut portion of the grating can accurately and completely reproduce the periodic optical characteristics of the entire grating under test, and to ensure that the interaction between light and the grating is sufficient and stable, thereby making the final test data accurate and reliable.
[0034] Step S20: Determine the target period based on the incident wavelength of the test light and the refractive index of the waveguide substrate, and adjust the micro-nano structure period of the test grating to the target period in order to suppress the generation of diffracted light when the test light is incident on the test grating at a preset angle. It should be noted that the target period refers to the specific period to which the test grating needs to be adjusted in order to suppress diffraction when the test light is incident on the test grating at a preset angle. The micro / nano structure period refers to the spacing between two adjacent grooves or ridges of the grating.
[0035] In one feasible implementation, step S20 may include steps S21-S22: Step S21: Determine the periodic range of the micro / nano structure based on the incident wavelength of the test light and the refractive index of the waveguide substrate. It should be noted that the micro-nano structure period range refers to the range of values for the micro-nano structure period. By adjusting the micro-nano structure period of the test grating to this range, diffraction light can be suppressed when the test light is incident on the test grating at a preset angle.
[0036] Step S23: Select a period from the periodic range of the micro / nano structure as the target period.
[0037] It should be noted that when selecting a period from the range of micro-nano structure periods as the target period, any micro-nano structure period can be selected as the target period, or a default micro-nano structure period (such as the upper limit of the range of micro-nano structure periods) can be selected as the target period. This embodiment does not make any specific limitations on this.
[0038] Furthermore, in one feasible implementation, step S21 may include steps S211 to S213: Step S211: Calculate the difference between the refractive index and the sine value of the preset angle to obtain the first value; Step S212: Calculate the ratio between the incident wavelength and the first value to obtain the reference period; Step S213: Using the reference period as the upper limit of the period range of the micro / nano structure, the period range of the micro / nano structure is generated.
[0039] It should be noted that after performing the above steps S211~S213, the periodic range of the generated micro / nano structure can be expressed as follows: Formula 1: Formula 1; in, For micro / nano structure periodicity, The incident wavelength, For refractive index, This is a preset angle.
[0040] It should be noted that Formula 1 above is derived from the grating diffraction equation (i.e. Formula 2 below), specifically derived by assuming that no diffraction order exists, that is, assuming that the diffraction angle is greater than 90°.
[0041] Formula 2; in, denoted as the diffraction angle, and m as the diffraction order.
[0042] This embodiment does not specifically limit the implementation of step S21. For example, in other feasible implementations, the micro-nano structure period corresponding to different incident wavelengths and refractive indices can be determined in advance and recorded using a relational table. Thus, the range of micro-nano structure periods corresponding to the incident wavelength of the test light and the refractive index of the waveguide substrate can be quickly determined by looking up the table, thereby improving the efficiency of determining the micro-nano structure period range.
[0043] Step S30: The test light is incident on the test grating after the adjustment period at a preset angle to obtain the transmittance and reflectance of the test grating; It should be noted that the preset angle is the pre-set angle of light incidence, which is usually consistent with the angle used in the design of the grating. It can be a default value or it can be flexibly set by the user according to the actual situation. This embodiment does not impose specific limitations on this. Transmittance is the ratio of transmitted light intensity to incident light intensity, and reflectance is the ratio of reflected light intensity to incident light intensity.
[0044] In one feasible implementation, please refer to Figure 4 and Figure 5 Step S30 may include steps S31 to S32: Step S31: Set up a transmission light detector and a reflection light detector respectively along the transmission light path and the reflection light path formed on the test grating by the test light ray; It should be noted that the transmitted light path refers to the path of the test light after passing through the test grating and waveguide substrate; the light intensity on the transmitted light path represents the transmission capability of the grating. The reflected light path refers to the path of the test light returning from the surface of the test grating (or after coupling through the waveguide substrate); the light intensity on the reflected light path represents the reflection capability of the grating. A transmitted light detector is a photoelectric conversion device used to receive and quantify the intensity of the transmitted light signal, and a reflected light detector is a photoelectric conversion device used to receive and quantify the intensity of the reflected light signal. Transmitted and reflected light detectors can be spectrophotometers, integrating spheres, or other devices capable of detecting light signal intensity, etc., and this implementation does not specifically limit their application.
[0045] Step S32: Obtain the transmittance of the test grating through a transmission light detector and the reflectance of the test grating through a reflection light detector.
[0046] This embodiment sets up a transmission light detector and a reflection light detector respectively on the transmission light path and the reflection light path formed on the test grating along the test light ray, so as to accurately capture the intensity of the transmission light signal and the intensity of the reflection light signal, thereby accurately determining the transmittance and reflectance of the test grating, and thus ensuring the accuracy and reliability of the absorptivity of the grating to be determined subsequently.
[0047] Furthermore, in one feasible implementation, step S32 may include steps S321-S323: Step S321: The transmittance and reflectance of the waveguide substrate when no test grating is placed are obtained by using a transmittance light detector and a reflectance light detector, respectively, and used as reference transmittance and reference reflectance. Step S322: With the test grating already placed on the waveguide substrate and the test light incident on the test grating after the adjustment period at a preset angle, the transmittance and reflectance are obtained respectively through the transmission light detector and the reflection light detector, and used as the initial transmittance and initial reflectance. Step S323: The difference between the initial transmittance and the reference transmittance is used as the transmittance of the test grating, and the difference between the initial reflectance and the reference reflectance is used as the reflectance of the test grating.
[0048] In this embodiment, the transmittance and reflectance of the waveguide substrate without a test grating are obtained using a transmission light detector and a reflection light detector, respectively, and are used as reference transmittance and reference reflectance. When a test grating is placed on the waveguide substrate and the test light is incident on the test grating at a preset angle after the adjustment period, the transmittance and reflectance are obtained using the transmission light detector and the reflection light detector, respectively, and are used as initial transmittance and initial reflectance. The difference between the initial transmittance and the reference transmittance is used as the transmittance of the test grating, and the difference between the initial reflectance and the reference reflectance is used as the reflectance of the test grating. This effectively removes the interference introduced by the waveguide substrate, improves the accuracy of the determined transmittance and reflectance of the test grating, and ensures the accuracy of the subsequently determined absorptivity of the grating under test.
[0049] Step S40: Based on the transmittance and reflectance, the absorptivity of the test grating is calculated and used as the absorptivity of the grating under test.
[0050] It should be noted that the calculation process for the absorptivity of the test grating based on transmittance and reflectance can be expressed as the following formula 3.
[0051] Loss=1-RT formula 3; Where Loss is the absorptivity of the test grating, R is the reflectivity of the test grating, and T is the transmittance of the test grating.
[0052] When determining the absorptivity of the grating under test, the absorptivity of the test grating under one target period can be directly used as the absorptivity of the grating under test. However, to improve the accuracy of the determined absorptivity, the absorptivity of the test grating under different target periods can also be determined, and the average absorptivity of the test grating under different target periods can then be used as the absorptivity of the grating under test. This embodiment does not specifically limit the specific implementation method for determining the absorptivity of the grating under test.
[0053] Based on the above, this embodiment provides a method for testing the absorptivity of a grating structure region. First, a portion of the grating to be tested is cut out as the test grating, and the test grating is placed on the waveguide substrate on which the grating to be tested is to be placed. Then, based on the incident wavelength of the test light and the refractive index of the waveguide substrate, the target period is determined, and the micro-nano structure period of the test grating is adjusted to the target period to suppress diffraction when the test light is incident on the test grating at a preset angle. As a result, when the test light is incident on the test grating after the period adjustment at the preset angle, no diffraction will be generated, only transmitted and reflected light will be generated. At this time, by obtaining the transmittance and reflectance of the test grating, the accurate absorptivity of the test grating can be calculated.
[0054] Therefore, the technical solution provided in this embodiment can flexibly adjust the micro-nano structure period of the test grating according to the actual test conditions when testing the absorption rate of the grating structure region, so that no diffraction light is generated when the test light is incident on the test grating at a preset angle, thereby accurately testing the absorption rate of the grating structure region.
[0055] Based on the first embodiment described above, a second embodiment of the method for testing the absorptivity of the grating structure region of this application is proposed. In the second embodiment, before the steps of obtaining the transmittance and reflectance of the test grating, the method for testing the absorptivity of the grating structure region may further include steps S01 to S03: Step S01: Detect whether diffracted light exists when the test light is incident on the test grating after the adjustment period at a preset angle; In one feasible implementation, please refer to Figure 6 Step S01 may include steps S011 to S014: Step S011: At least one prism is coupled onto the surface of the waveguide substrate carrying the test grating. It should be noted that, on the surface of the waveguide substrate carrying the test grating, coupling at least one prism means that the prism is in close contact with the surface of the waveguide substrate in a specific way (usually its bottom surface) to form a temporary optical integration.
[0056] Furthermore, in one feasible implementation, in order to achieve efficient optical coupling, a refractive index matching liquid can be coated between the prism and the waveguide substrate to eliminate reflection loss caused by air gaps.
[0057] Step S012: During the process of the test light being incident on the test grating after the adjustment period at a preset angle, the intensity of the outgoing light from the prism is obtained. It should be noted that when obtaining the intensity of the emitted light from a prism, measuring devices such as photodiodes or photomultiplier tubes can be used to measure the emitted light intensity by aligning them with the prism's exit surface.
[0058] Step S013: If the intensity of the outgoing light is zero, it is determined that when the test light is incident on the test grating after the adjustment period at a preset angle, there is no diffraction light. Step S014: If the intensity of the emitted light is greater than zero, it is determined that when the test light is incident on the test grating after the adjustment period at a preset angle, there is diffracted light.
[0059] In this embodiment, by coupling at least one prism onto the surface of the waveguide substrate carrying the test grating, the intensity of the emitted light from the prism can be determined to accurately determine whether diffracted light exists when the test light is incident on the test grating after the adjustment period at a preset angle.
[0060] Step S02: If yes, then reduce the target period to obtain a new target period, and return to the step of adjusting the micro / nano structure period of the test grating to the target period. It should be noted that when reducing the target period, the target period can be reduced by the default reduction amount or reduction ratio; or the reduction amount or reduction ratio can be flexibly determined according to the intensity of the generated diffracted light, so as to reduce the target period accordingly. This embodiment does not specifically limit the specific implementation of step S02.
[0061] Step S03: If not, proceed to the step of obtaining the transmittance and reflectance of the test grating.
[0062] This embodiment limits the process by requiring, after adjusting the micro / nano structure period of the test grating to the target period, to further detect whether diffracted light exists when the test light is incident on the adjusted test grating at a preset angle. If diffracted light exists, the target period can be reduced to obtain a new target period, and the process returns to the step of adjusting the micro / nano structure period of the test grating to the target period. This process continues until it is determined that no diffracted light is generated when the test light is incident on the adjusted test grating at a preset angle. Only then is the step of obtaining the transmittance and reflectance of the test grating executed, thereby further ensuring the accuracy of the grating's absorptivity test.
[0063] Based on the first and / or second embodiments described above, a third embodiment of the absorption rate testing method for the grating structure region of this application is proposed. In the third embodiment, the absorption rate testing method for the grating structure region may further include steps S50 to S70: Step S50: Obtain the absorption rate of the test grating when the test light is incident on the test grating at different preset angles; Step S60: Correlate each preset angle with the corresponding absorption rate to generate the absorption rate characteristic curve corresponding to the test grating. Step S70: Display the absorption rate characteristic curve on the test equipment.
[0064] In this embodiment, by associating each preset angle with the absorptivity of the test grating when the test light is incident on the test grating at each preset angle, an absorptivity characteristic curve corresponding to the test grating is generated and displayed on the test equipment. This provides users with the law and trend of the grating's absorptivity changing with the incident angle, thereby enabling evaluators to accurately and comprehensively evaluate the grating performance and precisely locate the optimal working range of the grating, thus effectively improving the product development efficiency.
[0065] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.
[0066] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.
[0067] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent scope of this application.
Claims
1. A method for testing the absorption rate of a grating structure region, characterized in that, The method includes: A portion of the grating to be tested is cut out as a test grating, and the test grating is placed on the waveguide substrate on which the grating to be tested is to be placed. Based on the incident wavelength of the test light and the refractive index of the waveguide substrate, the target period is determined, and the micro-nano structure period of the test grating is adjusted to the target period to suppress the generation of diffracted light when the test light is incident on the test grating at a preset angle. The test light beam is incident on the test grating after the adjustment period at the preset angle to obtain the transmittance and reflectance of the test grating; Based on the transmittance and the reflectance, the absorptivity of the test grating is calculated and used as the absorptivity of the grating under test.
2. The method as described in claim 1, characterized in that, The step of determining the target period based on the incident wavelength of the test light and the refractive index of the waveguide substrate includes: The periodic range of the micro / nano structure is determined based on the incident wavelength of the test light and the refractive index of the waveguide substrate. One period is selected from the periodic range of the micro / nano structure as the target period.
3. The method as described in claim 2, characterized in that, The step of determining the periodic range of the micro / nano structure based on the incident wavelength of the test light and the refractive index of the waveguide substrate includes: Calculate the difference between the refractive index and the sine of the preset angle to obtain a first value; Calculate the ratio between the incident wavelength and the first value to obtain the reference period; The micro-nano structure period range is generated by using the reference period as the upper limit of the period range.
4. The method as described in claim 1, characterized in that, Before the step of obtaining the transmittance and reflectance of the test grating, the method further includes: When the test light is incident on the test grating after the adjustment period at the preset angle, it is determined whether diffracted light exists. If so, the target period is reduced to obtain a new target period, and the process returns to the step of adjusting the micro / nano structure period of the test grating to the target period. If not, then proceed with the step of obtaining the transmittance and reflectance of the test grating.
5. The method as described in claim 4, characterized in that, The step of detecting whether diffracted light exists when the test light is incident on the test grating after the adjustment period at the preset angle includes: At least one prism is coupled onto the surface of the waveguide substrate that supports the test grating. During the process of the test light beam being incident on the test grating after the adjustment period at the preset angle, the intensity of the emitted light from the prism is obtained; If the intensity of the emitted light is zero, then it is determined that when the test light is incident on the test grating after the adjustment period at the preset angle, there is no diffraction light. If the intensity of the emitted light is greater than zero, then it is determined that when the test light is incident on the test grating after the adjustment period at the preset angle, there is diffracted light.
6. The method as described in claim 1, characterized in that, The step of cutting a portion of the grating from the grating to be tested as the test grating includes: A region containing at least a predetermined number of micro-nano structure periods of the grating under test is cut out from the grating under test and used as the test grating.
7. The method as described in claim 1, characterized in that, The steps for obtaining the transmittance and reflectance of the test grating include: A transmission light detector and a reflection light detector are respectively set along the transmission light path and the reflection light path formed on the test grating along the test light ray; The transmittance of the test grating is obtained through the transmission photodetector, and the reflectance of the test grating is obtained through the reflection photodetector.
8. The method as described in claim 7, characterized in that, The steps of obtaining the transmittance of the test grating through the transmission photodetector and obtaining the reflectance of the test grating through the reflection photodetector include: The transmittance and reflectance of the waveguide substrate without the test grating are obtained by the transmitted light detector and the reflected light detector, respectively, and used as the reference transmittance and reference reflectance. With the test grating placed on the waveguide substrate and the test light incident on the test grating after the adjustment period at the preset angle, the transmittance and reflectance are obtained by the transmission light detector and the reflection light detector, respectively, as the initial transmittance and initial reflectance. The difference between the initial transmittance and the reference transmittance is used as the transmittance of the test grating, and the difference between the initial reflectance and the reference reflectance is used as the reflectance of the test grating.
9. The method according to any one of claims 1 to 8, characterized in that, The method further includes: Obtain the absorption rate of the test grating under different target periods; The average absorptivity of the grating under test is taken as the average absorptivity of each target period.
10. The method according to any one of claims 1 to 8, characterized in that, The method further includes: The absorptivity of the test grating is obtained when the test light is incident on the test grating at different preset angles. The preset angles and their corresponding absorption rates are correlated to generate the absorption rate characteristic curve of the test grating. The absorption rate characteristic curve is displayed on the test equipment.