A device and method for measuring the group refractive index of a transparent optical material

Abstract

The application discloses a kind of transparent optical material group refractive index measuring device and measuring method, the measuring device includes: reference arm, sample arm, optical fiber coupler, light source, spectrometer, computer, metal flat plate and optical path motor installed on sample arm;The measuring method is mainly when target detection algorithm does not identify target, system automatically controls motor to drive the lens shift in sample arm, the image shown by system changes;When motor drives sample arm to move in the process, after algorithm identifies target, system controls motor to stop movement, then the image shown by system no longer changes;Finally reach the effect of automatic identification metal flat plate lower boundary.The application solves the problem of large workload and low precision in the existing method for measuring the group refractive index of transparent optical materials.

Description

Technical Field

[0001] This invention relates to the field of transparent optical material measurement technology, specifically to a device and method for measuring the refractive index of a group of transparent optical materials. Background Technology

[0002] The group refractive index is an important parameter of transparent optical materials. It refers to the overall speed of light waves propagating in a medium, that is, the ratio of the group velocity to the speed of light. In optical transmission, the group refractive index affects the transmission properties of light waves.

[0003] The group refractive index determines the propagation speed of light waves, thus affecting their phase and direction of propagation. While various methods exist for measuring this parameter, such as the minimum deviation angle method, grazing incidence method, polarization method, total internal reflection method, and displacement method, the minimum deviation angle method, for example, has a simple calculation formula, obvious critical phenomena in operation, and relatively small errors. However, finding the minimum deviation angle is tedious and time-consuming. In the total internal reflection method, the phenomenon of the experimental spectral lines disappearing is most obvious, intuitive, and clear, and the test results have relatively small errors. However, the position of total internal reflection is highly random, and the critical point of total internal reflection is more difficult to determine than the position of the minimum deviation angle.

[0004] Therefore, the above methods generally have problems such as requiring multiple measurements of the relevant parameters in the group refractive index calculation formula and multiple searches for suitable test angles and positions, which leads to some human error in the measurement, resulting in problems such as complicated operation steps and low measurement accuracy. Summary of the Invention

[0005] Purpose of the invention:

[0006] To address the technical problems of complex operation procedures and low measurement accuracy caused by human error in the aforementioned measurements, this technical solution provides a device and method for measuring the refractive index of a group of transparent optical materials. When the target detection algorithm fails to identify the target, it can automatically search for the target. The system automatically controls a motor to move the lens in the sample arm, changing the image displayed on the system. When the target detection algorithm identifies the target during the movement of the sample arm, the system stops the motor, and the displayed image no longer changes. Ultimately, this achieves the function of automatically identifying the lower boundary of the metal plate. The entire process is completed automatically by the equipment, requiring no human intervention, effectively solving the aforementioned problems.

[0007] This invention is achieved through the following technical solution:

[0008] A method for measuring the group refractive index of a transparent optical material is disclosed. The method involves measuring the group refractive index of the transparent optical material using a measuring device. This measuring device comprises an optical coherence tomography imaging system, consisting of a near-infrared laser diode light source, a 2-to-2 fiber optic coupler, a sample arm, a reference arm, a near-infrared spectrometer, a computer, an aluminum alloy metal plate, the sample to be measured, and a high-precision linear optical path stepper motor. The measurement method includes the following steps:

[0009] Step 1: Before measurement, the thickness of the transparent plate is known as T; input this value into the system; before placing the transparent plate to be measured, the system automatically captures and records the pixel height d1 and bending direction of the lower surface of the metal plate in the sample arm through the image processing algorithm, and reads the position Z0 of the optical path motor of the sample arm.

[0010] Step 2: Place the transparent plate vertically into the mounting bracket on the reference arm. The optical path length in the reference arm changes. Let the thickness of the transparent plate be T, and the group refractive index be Ng. Then the increase in optical path length in the reference arm is:

[0011] ΔL=T×Ng-T×N 空 =T×(Ng-1),

[0012] Where, N 空 The refractive index of air is taken as 1.0;

[0013] The change in the optical path length in the reference arm causes a change in the image height of the metal plate in the image, and the surface of the metal plate may no longer be fully displayed or may no longer be in the image;

[0014] Step 3: The system detects the image in real time using a target detection algorithm. When the image quality does not meet the conditions of the target detection function in the algorithm, the system automatically controls the motor to move the lens in the sample arm, and the image displayed by the system changes. When the motor moves the sample arm, the algorithm identifies the target and the target detection function meets the conditions, the system controls the motor to stop moving, and the image displayed by the system no longer changes. This allows the metal plate to be fully displayed in a certain area of ​​the image again, and the bending direction of the metal plate is consistent with the bending direction of the metal plate when the transparent plate is not placed.

[0015] Step 4: Use image processing algorithms to capture the pixel height d2 of the lower boundary of the metal plate, and then read the current position Z1 of the optical path motor of the sample arm; to obtain:

[0016] |Z1-Z0|±|d2-d1|×AR 空 = (Ng-1)×T,

[0017] Among them, AR 空To determine the digital axial resolution of the system in air, we take 0.006692422; thus, the group refractive index Ng of the transparent plate is:

[0018] Ng=(|Z1-Z0|±|d2-d1|×AR 空 )÷T+1,

[0019] This refractive index is the group refractive index of the material at the system wavelength.

[0020] Furthermore, the operation steps of the target detection algorithm include:

[0021] Step 1: Perform adaptive thresholding binarization on the obtained image;

[0022] The grayscale values ​​of pixels in the image that are above a threshold are set to 255, and the grayscale values ​​of pixels that are below the threshold are set to 0, thereby converting the grayscale image into a binary image. The region with the most pixels with a value of 255 in the resulting binary image is extracted to obtain the image of the largest connected component.

[0023] Step 2: Perform an AND operation between the maximum connected component image obtained in Step 1 and the original grayscale image to extract the effective information in the original image and obtain a grayscale image containing only the effective information.

[0024] Step 3: For the grayscale image containing only valid information obtained in Step 2, evaluate the grayscale values ​​of the grayscale image using an object detection function. The optimal image is obtained when the value of the object detection function is minimized. The evaluation function is:

[0025]

[0026] Among them, X n X represents the number of pixels in the image whose grayscale value exceeds X, M represents the width of the image, and N represents the height of the image.

[0027] Furthermore, the operation steps of the image processing algorithm include:

[0028] Step S1: Binarize the obtained image by setting the gray values ​​of pixels above the threshold to 255 and the gray values ​​of pixels below the threshold to 0, thereby converting the grayscale image into a binary image. Then, use the remove-small-objects operator to denoise the image and remove some small signal blocks from the image.

[0029] Step S2: Perform connected component filling processing on the image processed in step S1. Extract all signal blocks in the entire image and mark them. Use the connected component filling operator to fill the missing signal regions in each connected component, thereby filling the small holes in each connected component in the image.

[0030] Step S3: Perform boundary removal processing on the image after step S2. By traversing the pixels of the entire image, mark and delete the connected components in the image that contain the index of the image boundary row or column, thereby removing the boundary information that does not belong to the valid signal.

[0031] Step S4: Perform maximum connected component filtering on the image processed in step S3. Use the maximum connected component extraction operator to filter all connected components contained in the entire image, remove all pixel blocks except for the pixel block with the largest area, and thus retain the final useful signal.

[0032] Step S5: Extract the lower boundary of the effective signal in the image processed in step S4 and map it to a black and white image of the same size as the original image. At the same time, perform B-spline fitting on the discrete coordinates of the extracted lower boundary to obtain the B-spline curve.

[0033] Step S6: Extract the vertices of the B-spline curve obtained in step S5, and subtract the y-value of the pixel coordinate of that point from the height of the image to obtain the image pixel height of the effective information in the image.

[0034] A device for measuring the refractive index of a transparent optical material group is provided, applicable to the aforementioned method for measuring the refractive index of a transparent optical material group. The device comprises an optical coherence tomography (OCT) imaging system, consisting of a near-infrared laser diode (SLD) light source, a 2-to-2 fiber optic coupler, a sample arm, a reference arm, a near-infrared spectrometer, a computer, an aluminum alloy metal plate, the sample to be tested, and a high-precision linear optical path stepper motor. The SLD light source, sample arm, and reference arm are fixed to an optical breadboard, with a mounting base in the reference arm for placing the sample. The aluminum alloy metal plate is fixed to the optical breadboard via a bracket, located at the focal length of the sample arm's front end. The high-precision linear optical path stepper motor is controlled by the computer; its movement changes the position of the lens in the sample arm, thus altering the optical path of the sample arm. The scanning range, amplitude, and period of the galvanometer are controlled by the computer. Signals reflected from the sample arm and reference arm interfere and are then transmitted through the 2-to-2 fiber optic coupler to the near-infrared spectrometer for conversion into an interference spectrum. Data acquired by the near-infrared spectrometer is transmitted to the computer and processed by the testing client.

[0035] Furthermore, the near-infrared laser diode (SLD) light source emits a low-coherence light source with a wide near-infrared wavelength range.

[0036] Furthermore, the 2-to-2 fiber coupler uses single-mode fiber to split the laser beam at a certain ratio, with one beam passing through the sample arm and the other through the reference arm.

[0037] Furthermore, the sample arm uses an X-ray galvanometer and an optical system to scan the SLD light source into a line and project it onto a metal plate.

[0038] Furthermore, the reference arm includes a rear-facing mirror and a mounting base for placing the sample to be tested.

[0039] Furthermore, the near-infrared spectrometer is a spectral measuring instrument in the near-infrared band.

[0040] Furthermore, the aluminum alloy metal plate can reflect the light emitted from the sample arm back at a high intensity.

[0041] Furthermore, the sample to be tested is a transparent flat plate with a known thickness.

[0042] Furthermore, the high-precision linear optical path stepper motor is a high-precision linear stepper motor with a low step loss rate.

[0043] Beneficial effects

[0044] The present invention provides a device and method for measuring the group refractive index of transparent optical materials, which, compared with the prior art, has the following advantages:

[0045] (1) When the target detection algorithm fails to identify the target, the present invention can automatically search for the target; the system automatically controls the motor to move the lens in the sample arm, and the image displayed by the system changes; when the target detection algorithm identifies the target during the movement of the sample arm driven by the motor, the system controls the motor to stop moving, and the image displayed by the system no longer changes; ultimately achieving the function of automatically identifying the lower boundary of the metal plate. The measuring device is easy to operate. The entire process only requires placing the sample to be tested in the designated position. The calculation and measurement process is completed autonomously by the system, avoiding the generation of human error and realizing a fully automatic testing function; at the same time, the image processing algorithm used by the measuring device automatically identifies the lower boundary of the metal plate, and the measurement accuracy is accurate to the pixel level, thereby making the calculation accuracy higher; if the group refractive index of the sample at other main wavelengths is to be tested, it is only necessary to replace it with a spectrometer of other system wavelengths. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0047] Figure 2 This is a flowchart illustrating the target detection algorithm in this invention.

[0048] Figure 3 This is a schematic diagram of the image recognition algorithm in this invention.

[0049] Figure 4 This is a schematic diagram showing the analysis results of the refractive index measurement group of two different sized glass rods.

[0050] The labels in the attached diagram are as follows: 1-Near-infrared laser diode (SLD) light source, 2-2-to-2 fiber optic coupler, 3-Sample arm, 4-Reference arm, 5-Near-infrared spectrometer, 6-Computer, 7-Aluminum alloy metal plate, 8-Sample to be tested, 9-High-precision linear optical path stepper motor. Detailed Implementation

[0051] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. The described embodiments are merely some embodiments of the present invention, and not all embodiments. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the design concept of the present invention should fall within the protection scope of the present invention.

[0052] Example 1:

[0053] A method for measuring the group refractive index of a transparent optical material, comprising measuring the group refractive index of the transparent optical material using a measuring device, such as... Figure 1 As shown, the system includes an optical coherence tomography imaging system, which consists of a near-infrared laser diode light source 1, a 2-to-2 fiber optic coupler 2, a sample arm 3, a reference arm 4, a near-infrared spectrometer 5, a computer 6, an aluminum alloy metal plate 7, a sample to be tested 8, and a high-precision linear optical path stepper motor 9.

[0054] The measurement method includes the following steps:

[0055] Step 1: Before measurement, the thickness of the transparent plate is known as T; input this value into the system; before placing the transparent plate to be measured, the system automatically captures and records the pixel height d1 and bending direction of the lower surface of the metal plate in the sample arm through an image processing algorithm, and reads the position Z0 of the optical path motor of the sample arm.

[0056] Step 2: Place the transparent plate vertically into the mounting bracket on the reference arm. The optical path length in the reference arm changes. Let the thickness of the transparent plate be T, and the group refractive index be Ng. Then the increase in optical path length in the reference arm is:

[0057] ΔL=T×Ng-T×N 空 =T×(Ng-1),

[0058] Where, N 空 Let be the refractive index of air, taken as 1.0.

[0059] The change in optical path length in the reference arm causes a change in the image height of the metal plate, and the surface of the metal plate may no longer be fully displayed or may no longer be in the image.

[0060] Step 3: The system detects the image in real time using a target detection algorithm. When the image quality does not meet the conditions of the target detection function in the algorithm, the system automatically controls the motor to move the lens in the sample arm, and the image displayed by the system changes. When the motor moves the sample arm, the algorithm identifies the target and the target detection function meets the conditions, the system controls the motor to stop moving, and the image displayed by the system no longer changes. This allows the metal plate to be fully displayed in a certain area of ​​the image again, and the bending direction of the metal plate is consistent with the bending direction of the metal plate when the transparent plate is not placed.

[0061] Step 4: Use image processing algorithms to capture the pixel height d2 of the lower boundary of the metal plate, and then read the current position Z1 of the optical path motor of the sample arm; to obtain:

[0062] |Z1-Z0|±|d2-d1|×AR 空 = (Ng-1)×T,

[0063] Among them, AR 空 To determine the digital axial resolution of the system in air, we take 0.006692422; thus, the group refractive index Ng of the transparent plate is:

[0064] Ng=(|Z1-Z0|±|d2-d1|×AR 空 )÷T+1,

[0065] This refractive index is the group refractive index of the material at the system wavelength.

[0066] The above-mentioned target detection algorithm has the following operation steps: Figure 2 As shown, it includes:

[0067] Step 1: Perform adaptive threshold binarization on the obtained image; set the grayscale value of pixels in the image above the threshold to 255 and the grayscale value of pixels below the threshold to 0, thereby converting the grayscale image into a binary image. Extract the region in the obtained binary image that contains the most pixels with a value of 255 to obtain the largest connected component image.

[0068] Step 2: Perform an AND operation between the maximum connected component image obtained in Step 1 and the original grayscale image to extract the effective information in the original image, resulting in a grayscale image containing only the effective information.

[0069] Step 3: For the grayscale image containing only valid information obtained in Step 2, evaluate the grayscale values ​​of the grayscale image using an object detection function. The optimal image is obtained when the value of the object detection function is minimized. The evaluation function is:

[0070]

[0071] Among them, X n X represents the number of pixels in the image whose grayscale value exceeds X, M represents the width of the image, and N represents the height of the image.

[0072] The operation steps of the image processing algorithm are as follows: Figure 3 As shown, Figure 3 This corresponds to the visualization of each step in the image recognition algorithm through image processing. The final image height is the difference between the ordinate of the lower boundary vertex of the automatically identified marker in Figure d and the total image height. The specific steps of the image processing algorithm include:

[0073] Step S1: Binarize the obtained image by setting the grayscale values ​​of pixels above the threshold to 255 and the grayscale values ​​of pixels below the threshold to 0, thereby converting the grayscale image into a binary image. Then, use the remove-small-objects operator to denoise the image and remove some small signal blocks in the image.

[0074] Step S2: Perform connected component filling on the image processed in step S1. Extract all signal blocks in the entire image and mark them. Use the connected component filling operator to fill the missing signal regions in each connected component, thereby filling the small holes in each connected component in the image.

[0075] Step S3: Perform boundary removal processing on the image processed in step S2. By traversing the pixels of the entire image, the connected components containing the indices of the image boundary rows or columns are marked and deleted, thereby removing boundary information that does not belong to the valid signal; for example... Figure 3 As shown in b.

[0076] Step S4: Perform maximum connected component filtering on the image processed in step S3. Use the maximum connected component extraction operator to filter all connected components contained in the entire image, remove all pixel blocks except for the pixel block with the largest area, and thus retain the final useful signal.

[0077] Step S5: Extract the lower boundary of the effective signal in the image processed in Step S4 and map it onto a black and white image of the same size as the original image. Simultaneously, perform B-spline fitting on the discrete coordinates of the extracted lower boundary to obtain a B-spline curve; for example... Figure 3 As shown in c.

[0078] Step S6: The smooth lower boundary fitting line obtained in step S5 is mapped to the original image, as shown below. Figure 3 As shown in d; at the same time, the vertex of the B-spline curve obtained in step S5 is extracted, and the image pixel height of the effective information in the image is obtained by subtracting the y-value of the pixel coordinate of the point from the height of the image.

[0079] Automatic capture and precise positioning of the lower boundary of a metal plate are achieved through target detection and image processing algorithms. The lower boundary of the metal plate in the processed image was identified and captured at least fifteen times, and the repeatability of the pixel height of the captured metal plate was verified. Testing showed that the repeatability was within 1.5 pixels. The repeatability calculation formula is as follows:

[0080]

[0081] Where σ represents measurement repeatability, x i Let N be the pixel height of the lower boundary of the metal plate being grasped in the i-th measurement, and N be the number of measurements, thus greatly improving the measurement accuracy.

[0082] Example 2:

[0083] A device for measuring the group refractive index of transparent optical materials is provided, which can be used in the method for measuring the group refractive index of transparent optical materials described in Example 1. The measuring device includes an optical coherence tomography imaging system, consisting of a near-infrared laser diode (SLD) light source 1, a 2-to-2 fiber optic coupler 2, a sample arm 3, a reference arm 4, a near-infrared spectrometer 5, a computer 6, an aluminum alloy metal plate 7, a sample to be tested 8, and a high-precision linear optical path stepper motor 9. The near-infrared laser diode (SLD) light source 1, the sample arm 3, and the reference arm 4 are fixed on an optical breadboard, and the mounting base in the reference arm 4 is used to place the sample to be tested. 8; The aluminum alloy metal plate 7 is fixed to the optical breadboard by a bracket and is located at the focal length of the front end of the sample arm 3; The high-precision linear optical path stepper motor 9 is controlled by the computer 6. The movement of the high-precision linear optical path stepper motor 9 can change the position of the lens in the sample arm 3, thereby changing the optical path of the sample arm; The scanning range, amplitude and period of the galvanometer are controlled by the computer 6; After the signal reflected back from the sample arm 3 and the reference arm 4 interferes, it enters the near-infrared spectrometer 5 through the 2-to-2 fiber optic coupler 2 and is converted into an interference spectrum; The data collected by the near-infrared spectrometer 5 is transmitted to the computer 6 and processed by the test client.

[0084] The near-infrared laser diode (SLD) light source 1 emits a low-coherence light source with a wide near-infrared wavelength range. The 2-to-2 fiber optic coupler 2 uses single-mode fiber to split the laser beam at a certain ratio, with one beam passing through the sample arm and the other through the reference arm. The sample arm 3 scans the SLD light source 1 into a line and projects it onto a metal plate using an X-ray mirror and optical system. The reference arm 4 includes a rear-reflecting mirror and a mounting base for placing the sample 8 under test. The near-infrared spectrometer 5 is a spectrometer for the near-infrared band. The aluminum alloy metal plate 7 reflects the light emitted from the sample arm 3 back with high intensity. The sample 8 under test is a transparent plate with a known thickness. The high-precision linear optical path stepper motor 9 is a high-precision linear stepper motor with a low step loss rate.

[0085] Matters not covered in this invention are common knowledge.

[0086] Taking a commonly used K9 glass rod as an example, its group velocity refractive index was obtained by measuring in the 800-880nm wavelength band using the method described in Example 1 and the device described in Example 2.

[0087] During measurement, the thickness of the glass rod is known as T. Before placing the transparent plate to be measured, an image processing algorithm is used to identify and control the automatic grasping and recording of the pixel height d1 and bending direction of the lower surface of the metal plate in the sample arm. The image processing algorithm automatically identifies the current image pixel height d1 and reads the position Z0 of the optical path motor of the sample arm at this time.

[0088] Then, the glass rod is placed vertically on the fixed stage in the reference arm, so that the light is incident perpendicularly on the surface of the glass rod. As the optical path changes in the reference arm, the image height of the metal plate also changes, moving closer to the zero frequency position. When the change distance exceeds d1, the image will flip and continue to move away from the zero frequency. The target detection algorithm and image processing algorithm in the system will automatically judge the image and control the optical path motor to move so that the image of the metal plate reaches the appropriate height of the whole image and is consistent with the bending direction of the metal plate when the glass rod is not placed.

[0089] The image processing algorithm is used again to automatically identify the image height d2 and read the current optical path motor position Z1. Since the image pixel height for automatic movement is not explicitly specified, cases where d2 ≥ d1 or d2 < d1 may occur. For this system, as the image pixel height moves away from zero frequency, the motor position becomes smaller. Therefore, the change in motor height |Z0-Z1| plus the pixel height change (d1-d2) represents the change in optical path.

[0090] Input the thickness of the glass rod, and the software will automatically calculate the thickness based on the results of the two recognitions and the formula Ng=(|Z1-Z0|+|d2-d1|×AR). 空The group refractive index of the glass rod is calculated by dividing T by 1, where Ng is the group refractive index of the glass rod; Z0 is the optical path length position before the glass rod is placed, in millimeters (mm); Z1 is the optical path length position after the glass rod is placed, in millimeters (mm); d1 is the pixel height of the lower boundary of the metal plate before the glass rod is placed, in pixels; d2 is the pixel height of the lower boundary of the metal plate after the glass rod is placed, in pixels; AR 空 The calibrated digital axial resolution of the system in air is 0.006692422, in millimeters per pixel (mm / pixel); T is the thickness of the glass rod being measured, in millimeters (mm).

[0091] Figure 4 The results are obtained using the test method described in Example 1. In the figure, Z0 is the position of the optical path motor before the glass rod is placed, in millimeters (mm); Z1 is the position of the optical path motor after the glass rod is placed, in millimeters (mm); d1 is the pixel height of the lower boundary of the metal plate when the glass rod is not placed, in pixels; d2 is the pixel height of the lower boundary of the metal plate after the glass rod is placed, in pixels. Finally, the obtained test results are substituted into the group refractive index calculation formula described in this patent to obtain the group refractive index of the sample.

Claims

1. A method for measuring the group refractive index of a transparent optical material, characterized in that: The group refractive index of a transparent optical material is measured using a measuring device, which includes an optical coherence tomography imaging system consisting of a near-infrared laser diode light source (1), a 2-to-2 fiber optic coupler (2), a sample arm (3), a reference arm (4), a near-infrared spectrometer (5), a computer (6), an aluminum alloy metal plate (7), the sample to be tested (8), and a high-precision linear optical path stepper motor (9). The measurement method includes the following steps: Step 1: Before measurement, the thickness of the transparent plate is known as T; input this value into the system; before placing the transparent plate to be measured, the system automatically captures and records the pixel height d1 and bending direction of the lower surface of the metal plate in the sample arm through the image processing algorithm, and reads the position Z0 of the optical path motor of the sample arm. Step 2: Place the transparent plate vertically into the mounting bracket on the reference arm. The optical path length in the reference arm changes. Let the thickness of the transparent plate be T, and the group refractive index be Ng. Then the increase in optical path length in the reference arm is: ΔL=T×Ng-T×N 空 =T×(Ng-1), Where, N 空 The refractive index of air is taken as 1.0; The change in the optical path length in the reference arm causes a change in the image height of the metal plate in the image, and the surface of the metal plate may no longer be fully displayed or may no longer be in the image; Step 3: The system detects the image in real time using a target detection algorithm. When the image quality does not meet the conditions of the target detection function in the algorithm, the system automatically controls the motor to move the lens in the sample arm, and the image displayed by the system changes. When the motor moves the sample arm, the algorithm identifies the target and the target detection function meets the conditions, the system controls the motor to stop moving, and the image displayed by the system no longer changes. This allows the metal plate to be fully displayed in a certain area of ​​the image again, and the bending direction of the metal plate is consistent with the bending direction of the metal plate when the transparent plate is not placed. Step 4: Use image processing algorithms to capture the pixel height d2 of the lower boundary of the metal plate, and then read the current position Z1 of the optical path motor of the sample arm; to obtain: |Z1-Z0|±|d2-d1|×AR 空 = (Ng-1)×T, Among them, AR 空 To determine the digital axial resolution of the system in air, we take 0.006692422; thus, the group refractive index Ng of the transparent plate is: Ng=(|Z1-Z0|±|d2-d1|×AR 空 )÷T+1, This refractive index is the group refractive index of the material at the system wavelength.

2. The method for measuring the refractive index of a transparent optical material group according to claim 1, characterized in that: The operation steps of the target detection algorithm include: Step 1: Perform adaptive thresholding binarization on the obtained image; The grayscale values ​​of pixels in the image that are above a threshold are set to 255, and the grayscale values ​​of pixels that are below the threshold are set to 0, thereby converting the grayscale image into a binary image. The region with the most pixels with a value of 255 in the resulting binary image is extracted to obtain the image of the largest connected component. Step 2: Perform an AND operation between the maximum connected component image obtained in Step 1 and the original grayscale image to extract the effective information in the original image and obtain a grayscale image containing only the effective information. Step 3: For the grayscale image obtained in Step 2 that contains only valid information, evaluate the grayscale values ​​of the grayscale image using an object detection function. The optimal image is obtained when the value of the object detection function is minimized. The evaluation function is: Among them, X n X represents the number of pixels in the image whose grayscale value exceeds X, M represents the width of the image, and N represents the height of the image.

3. The method for measuring the refractive index of a transparent optical material group according to claim 1, characterized in that: The operation steps of the image processing algorithm include: Step S1: Binarize the obtained image by setting the gray values ​​of pixels above the threshold to 255 and the gray values ​​of pixels below the threshold to 0, thereby converting the grayscale image into a binary image. Then, use the remove-small-objects operator to denoise the image and remove some small signal blocks from the image. Step S2: Perform connected component filling processing on the image processed in step S1. Extract all signal blocks in the entire image and mark them. Use the connected component filling operator to fill the missing signal regions in each connected component, thereby filling the small holes in each connected component in the image. Step S3: Perform boundary removal processing on the image after step S2. By traversing the pixels of the entire image, mark and delete the connected components in the image that contain the index of the image boundary row or column, thereby removing the boundary information that does not belong to the valid signal. Step S4: Perform maximum connected component filtering on the image processed in step S3. Use the maximum connected component extraction operator to filter all connected components contained in the entire image, remove all pixel blocks except for the pixel block with the largest area, and thus retain the final useful signal. Step S5: Extract the lower boundary of the effective signal in the image processed in step S4 and map it to a black and white image of the same size as the original image. At the same time, perform B-spline fitting on the discrete coordinates of the extracted lower boundary to obtain the B-spline curve. Step S6: Extract the vertices of the B-spline curve obtained in step S5, and subtract the y-value of the pixel coordinate of that point from the height of the image to obtain the image pixel height of the effective information in the image.

4. A device for measuring the refractive index of a transparent optical material group, which can be used in the method for measuring the refractive index of a transparent optical material group according to any one of claims 1-3; characterized in that: The measuring device includes an optical coherence tomography imaging system, consisting of a near-infrared laser diode (SLD) light source (1), a 2-to-2 fiber optic coupler (2), a sample arm (3), a reference arm (4), a near-infrared spectrometer (5), a computer (6), an aluminum alloy metal plate (7), a sample to be tested (8), and a high-precision linear optical path stepper motor (9). The near-infrared laser diode (SLD) light source (1), sample arm (3), and reference arm (4) are fixed on the optical breadboard, and the mounting base in the reference arm (4) is used to place the sample to be tested (8). The aluminum alloy metal plate (7) is fixed to the optical breadboard by a bracket. On the breadboard, at the focal length of the front end of the sample arm (3); the high-precision linear optical path stepper motor (9) is controlled by the computer (6). The movement of the high-precision linear optical path stepper motor (9) can change the position of the lens in the sample arm (3), thereby changing the optical path of the sample arm; the scanning range, amplitude and period of the galvanometer are controlled by the computer (6); after the signal reflected back by the sample arm (3) and the reference arm (4) interferes, it enters the near-infrared spectrometer (5) through the 2-to-2 fiber coupler (2) and is converted into an interference spectrum; the data collected by the near-infrared spectrometer (5) is transmitted to the computer (6) and processed by the test client.

5. The device for measuring the refractive index of a transparent optical material group according to claim 4, characterized in that: The near-infrared laser diode SLD light source (1) emits a low-coherence light source with a wide near-infrared wavelength range.

6. The device for measuring the refractive index of a transparent optical material group according to claim 4, characterized in that: The 2-to-2 fiber coupler (2) uses single-mode fiber to split the laser beam according to a certain ratio, with one beam passing through the sample arm and the other through the reference arm.

7. The device for measuring the refractive index of a group of transparent optical materials according to claim 4, characterized in that: The sample arm (3) scans the SLD light source (1) into a line and projects it onto a metal plate using an X-ray mirror and an optical system; the reference arm (4) includes a rear-facing mirror and a mounting base for placing the sample (8) to be tested.

8. The device for measuring the refractive index of a transparent optical material group according to claim 4, characterized in that: The near-infrared spectrometer (5) is a spectral measuring instrument in the near-infrared band.

9. The device for measuring the refractive index of a transparent optical material group according to claim 4, characterized in that: The aluminum alloy metal plate (7) can reflect the light emitted from the sample arm (3) back with a high intensity; the sample to be tested (8) is a transparent plate with a known thickness.

10. The device for measuring the refractive index of a transparent optical material group according to claim 4, characterized in that: The high-precision linear optical path stepper motor (9) is a high-precision linear stepper motor with a low step loss rate.

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