Device and method for measuring refractive index of lens

Abstract

The invention discloses a device and a method for measuring the refractive index of a lens, belongs to the technical field of optical measurement, and particularly relates to a non-contact type device and a method for measuring the refractive index of the lens. According to the invention, double-side measurement is carried out on the lens based on a frequency sweep OCT system, information of four surfaces of the lens is extracted, real upper and lower surfaces of the lens are reconstructed, and the refractive index n of the lens is calculated by using a ray tracing method, so that non-contact measurement of the refractive index of the measured lens is realized. The measuring device does not damage the lens, has no requirement for the placing posture of the lens, and has the advantages of being rapid in detection and high in measuring precision. Compared with a traditional immersion method for measuring the refractive index of the lens to be measured, the measurement time is greatly shortened. According to the device, the data acquisition card synchronously records interference signals detected by the balance detector, the maximum acquisition rate is 500 MS / s, namely 500 M sampling points per second, the sensitivity to mechanical vibration is far lower than that of a traditional interferometer, and the measurement stability can be kept.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement, and particularly relates to a lens refractive index measurement device and a measurement method for measuring the refractive index of a lens in industry. Background Art

[0002] As a core component in an optical imaging system, the refractive index parameter of a lens directly affects the imaging quality. With the wide application of optical technology in fields such as aerospace, automotive, and photography, the demand for accurate measurement of the refractive index of lenses is increasing day by day.

[0003] Currently, the main methods for measuring the refractive index of a lens are the immersion method, the interference fringe method, and the confocal method. In the immersion method, the lens is placed in a certain immersion liquid, and the refractive index information of the lens is obtained by adjusting the refractive index of the immersion liquid. The interference method is based on the analysis of interference fringes, locates the lens, measures the optical path difference using phase demodulation technology, and calculates the refractive index in combination with lens parameters, which can measure the lens without damage. The confocal method measures the vertices of the front and back surfaces of the lens, combines parameters such as the radius of curvature and thickness of the lens, and calculates the refractive index of the lens using optical formulas, with relatively high measurement accuracy. For example, Patent No. CN 112556990A uses a diopter module to detect the diopter of a lens, uses a confocal reflection measurement module to detect the confocal reflection positions of the upper and lower surfaces of the lens, and then obtains the refractive index of the lens using a formula. However, the above traditional methods for measuring the refractive index of a lens have the following technical problems:

[0004] (1) The immersion method requires precise preparation of a refractive index matching liquid, and the solution preparation process is time-consuming and cumbersome. The solution is easily affected by temperature, volatilization, or contamination, and some solutions may also contaminate the lens, making it difficult to meet the requirements of rapid and high-precision detection in industrial fields.

[0005] (2) The interference fringe method is sensitive to environmental changes, and air flow or temperature fluctuations will cause the interference fringes to drift. The surface of the lens to be measured needs to be highly polished, and if the surface is too rough, clear fringes may not be generated, all of which will affect the measurement accuracy.

[0006] (3) The confocal method requires precise adjustment of the coaxiality between the center of the lens and the optical axis, and has strict requirements for the placement posture of the lens.

[0007] The existing several measurement methods in the prior art are difficult to meet the multiple requirements of industrial applications for measurement accuracy, efficiency, and cost, and there is an urgent need to develop a new measurement solution. Summary of the Invention

[0008] In view of the deficiencies of the prior art, the present invention discloses a lens refractive index measurement device and a measurement method, which are realized through the following technical solutions:

[0009] The technical solution adopted by the present invention is a lens refractive index measuring device, which includes a swept source, a first fiber coupler fiber-connected to the swept source, a reference arm module and a sample arm module fiber-connected to the first fiber coupler respectively, a second fiber coupler fiber-connected to the reference arm module and the sample arm module in sequence, and a balanced detector; a data acquisition card, a function generator and a computer in the computer connected to the balanced detector in sequence by lines, and the swept source is connected to the data acquisition card by a line.

[0010] As a further improvement, the reference arm module of the present invention includes a first optical circulator, a first polarizer and a first collimating lens fiber-connected in sequence, a first focusing lens and a reflector connected to the optical path of the first collimating lens and connected to the optical path of the first collimating lens; the sample arm module includes a second optical circulator, a second polarizer, a third fiber coupler fiber-connected in sequence, a second collimating lens and a third collimating lens fiber-connected to the third fiber coupler respectively, a second focusing lens connected to the optical path of the second collimating lens and connected to the optical path of the second collimating lens, a third focusing lens connected to the optical path of the third collimating lens and connected to the optical path of the third collimating lens, a lens under test located between the second focusing lens and the third focusing lens and on their optical paths, and a translation stage for fixing the lens under test, and the translation stage is connected to the function generator by a line.

[0011] As a further improvement, both the first optical circulator and the second optical circulator of the present invention are fiber-connected to the second fiber coupler. The light reflected back by the reference arm module and the sample arm module passes through the input end connected to the second fiber coupler. The output end of the second fiber coupler is connected to the balanced detector. The output end of the balanced detector is connected to the data acquisition card built in the computer. The output end of the swept source is connected to the data acquisition card. One end of the output of the function generator is connected to the data acquisition card, and the other end is connected to the translation stage in the sample arm. The output end of the computer is connected to the input end of the function generator.

[0012] As a further improvement, the light emitted by the swept-source light source of the present invention is split by a first fiber coupler and then enters the reference arm module and the sample arm module respectively; in the reference arm module, after the optical signal passes through a first optical circulator and a first polarizer in sequence, it is collimated into parallel light by a first collimating lens, and then focused by a first focusing lens onto a mirror and returns along the original path. Subsequently, the reference light is obtained through the first optical circulator; in the sample arm module, after the optical signal passes through a second optical circulator and a second polarizer, it is equally split by a third fiber coupler. The left-side light after splitting passes through a second collimating lens and a second focusing lens in sequence and is incident on the lens under test and then reflected back. The right-side light passes through a third collimating lens and a third focusing lens in sequence and is incident on the lens under test and then returns. The returned light is combined by the third fiber coupler and the sample light is obtained through the second optical circulator; the two paths of light are jointly transmitted to a second fiber coupler, and interference occurs in the second fiber coupler to obtain an interference signal.

[0013] As a further improvement, the interference signal of the present invention is detected by a balanced detector and then input into a data acquisition card; the swept-source light source provides a clock signal and a trigger signal to the data acquisition card, the function generator provides a synchronization signal to the data acquisition card and a drive signal to the translation stage, and the computer uniformly processes and analyzes all the signals collected by the data acquisition card and generates a scanning signal to the function generator.

[0014] As a further improvement, the sample arm module of the present invention is split into two by a third fiber coupler and respectively incident on the left side and the right side of the lens under test. The optical paths of the light incident on both sides of the lens under test are not equal, and the right-side optical path is slightly greater than the left-side optical path, and a preset distance difference is maintained between the two.

[0015] As a further improvement, the translation stage of the present invention is a three-dimensional translation stage, wherein the Z-axis translation stage is a manual translation stage, and the XY-axis translation stage is an electric translation stage, which is used to realize the two-dimensional scanning of the lens under test, and the thickness direction of the lens under test is consistent with the Z-axis direction.

[0016] As a further improvement, the splitting ratio of the first fiber coupler of the present invention is 90:10, and the splitting ratios of the second fiber coupler and the third fiber coupler are 50:50.

[0017] As a further improvement, the exit diameters of the first collimating lens, the second collimating lens, and the third collimating lens of the present invention are 3.4 mm.

[0018] As a further improvement, the focal lengths of the first focusing lens, the second focusing lens, and the third focusing lens of the present invention are 50 mm.

[0019] The present invention also discloses a method for measuring the refractive index of a lens, including the following steps:

[0020] Step 1: Before placing the lens to be measured, process the interference signal to obtain its position zp in the axial depth;

[0021] The interference signal refers to the interference between the reference light in the reference arm and the sample light in the sample arm in the second fiber optic coupler with the reference light, and the interference signal obtained through the balanced detector. At this time, the sample light refers to the light that enters the sample arm, is split by the third fiber optic coupler, and then passes through the second collimating lens, the second focusing lens, the third focusing lens, and the third collimating lens in sequence and then returns to the third fiber optic coupler.

[0022] Step 2: Place the lens to be measured for acquisition, and process the three-dimensional data to obtain the OCT image of the lens to be measured;

[0023] The three-dimensional data in Step 2 refers to after placing the lens to be measured, the interference between the reference light and the sample light is detected by the balanced detector and input into the data acquisition card. The computer controls the function generator to generate a driving signal to ensure that the translation stage performs two-dimensional scanning. At the same time, the function generator also generates a synchronous signal to the data acquisition card to ensure synchronous acquisition during the movement of the translation stage to obtain three-dimensional data. At this time, the sample light refers to the light that enters the sample arm, is split by the third fiber optic coupler, and is reflected after being incident on the left and right sides of the lens to be measured respectively.

[0024] Step 3: Extract four surface signal positions on the front and back surfaces of the lens to be measured on both sides from the OCT image, and reconstruct the true front and back surfaces of the lens to be measured without distortion in combination with the position zp;

[0025] Step 3 specifically includes: Extracting four surfaces from the OCT image: The A surface and B surface of the lens to be measured measured from the left are denoted as the 1A surface and 1B surface, and the A surface and B surface of the lens to be measured measured from the right are denoted as the 2A surface and 2B surface; Randomly select a point M on the 1A surface, and its Z-axis position is denoted as z1Am. Find a point M1 on the 2B surface with the same X and Y coordinates as point M, and its Z-axis position is z2Bm. Calculate the physical thickness dm of point M in the real space: dm = 2×zp - (z1Am + z2Bm); Extract the 2B surface and perform a vertical flip, and translate it upward to obtain the 2B' surface. Select a point M2 on the 2B' surface with the same X and Y coordinates as point M, and the surface where the Z-axis distance between M2 and point M is dm is the 2B' surface that meets the conditions, and the true front surface 1A surface and the back surface 2B' surface of the lens to be measured without distortion are reconstructed.

[0026] Step 4: Combine the positions of the true front and back surfaces of the lens to be measured, calculate the refraction optical path MN of light in the lens to be measured based on the ray tracing method, calculate the actual optical path MM3 in combination with the four surface positions, compare the refraction optical path MN and the actual optical path MM3, and screen out the refractive index n of the lens to be measured that meets the conditions.

[0027] Step 4 specifically includes: Select a point M3 on the 1B surface with the same X and Y coordinates as point M. The actual optical path of the light passing through point M in the lens to be measured is MM3. Calculate the path of the light parallel to the Z-axis after refraction through point M, determine the intersection point N of the refracted light with the actual rear surface 2B' of the true lens to be measured, and calculate the length of MN. With the refractive index varying within the range of 1.400 to 1.600 in steps of 0.0005 to 0.002, select the refractive index that satisfies MN×n = MM3 as the refractive index of the lens to be measured.

[0028] As a further improvement, the number of point M selected in the present invention is greater than or equal to 3, and the refractive indices corresponding to each point are calculated respectively. Finally, the average value is taken as the refractive index of the lens to be measured.

[0029] The beneficial effects of the present invention are as follows:

[0030] Compared with the existing techniques for measuring the refractive index of a lens, the device of the present invention adopts an OCT system, without the need for immersion liquid or physical contact with the lens, avoiding damage to the lens. At the same time, the combination of a high-speed swept-source (scanning rate of 100 kHz) and a point-balanced detector realizes fast OCT image acquisition, greatly reducing the measurement time required for measuring the refractive index of the lens to be measured compared with the traditional immersion method.

[0031] Compared with the existing techniques for measuring the refractive index of a lens, the data acquisition card of the device of the present invention synchronously records the interference signals detected by the balanced detector, with a maximum acquisition rate of 500 MS / s, that is, 500 million sampling points per second, and the sensitivity to mechanical vibration is much lower than that of traditional interferometers, capable of maintaining measurement stability.

[0032] Compared with the existing techniques for measuring the refractive index of a lens, the device of the present invention divides the sampling arm into two through the third fiber coupler and measures from both sides of the lens to be measured, and 4 surface signal positions can be obtained. The A surface and B surface of the lens to be measured measured from the left are denoted as the 1A surface and 1B surface; the A surface and B surface of the lens to be measured measured from the right are denoted as the 2A surface and 2B surface. Randomly select a point M on the 1A surface, and its Z-axis position is denoted as z1Am. Find a point M1 on the 2B surface with the same X and Y coordinates as point M, and its Z-axis position is z2Bm. Calculate the physical thickness dm of point M in the real space as dm = 2×zp - (z1Am + z2Bm); extract the 2B surface and perform a vertical flip, and translate it upward to obtain the 2B' surface. Select a point M2 on the 2B' surface with the same X and Y coordinates as point M, and the surface with the distance between the Z coordinates of M2 and M being dm is the 2B' surface that meets the conditions, reconstructing the true front surface 1A and rear surface 2B' of the lens to be measured without distortion. The error in calculating the refractive index of the lens for a single point M is within 0.005, and the error in calculating the refractive index by taking the average value of 10 points M is within 0.001, and a high-precision refractive index of the lens can be obtained.

[0033] Compared with the existing technologies for measuring the refractive index of a lens, the method of the present invention first proposes to use the ray tracing method to calculate the refractive index of a lens. At the 1B surface, a point M3 with the same X and Y coordinates as the point M is selected. The actual optical path of the light passing through the point M in the lens to be measured is MM3. Calculate the path of the light parallel to the Z axis after refraction through the point M, determine the intersection point N of the refracted light and the actual surface 2B' of the lens to be measured, and calculate the length of MN. With the refractive index varying within the range of 1.400 to 1.600 in steps of 0.0005 to 0.002, select the refractive index that satisfies MN×n = MM3 as the refractive index of the lens to be measured. This method has no requirements for the placement posture of the lens to be measured, allows a large angular deviation between the incident light path and the central optical axis of the lens, is compatible with various surface types such as convex, concave, and flat surfaces, and can be applied to production measurement. Description of the Drawings

[0034] Figure 1 It is a schematic diagram of a lens refractive index measuring device;

[0035] Figure 2 It is a schematic diagram of obtaining the refractive index of a lens by the ray tracing method;

[0036] Figure 3 It is a flow chart for calculating the refractive index of a lens.

[0037] In the figure: 1. Swept-source optical fiber; 2. First fiber optic coupler; 3. Second fiber optic coupler; 4. Balanced detector; 5. Data acquisition card; 6. Function generator; 7. Computer; 8. First optical circulator; 9. First polarizer; 10. First collimating lens; 11. First focusing lens; 12. Plane mirror; 13. Second optical circulator; 14. Second polarizer; 15. Third fiber optic coupler; 16. Second collimating lens; 17. Second focusing lens; 18. Third collimating lens; 19. Third focusing lens; 20. Translation stage; 21. Lens to be measured; 22. 1A surface; 23. 2B surface; 24. 1B surface; 25. 2A surface; 26. 2B' surface. Detailed Embodiments

[0038] The following further describes the invention with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can implement it according to the text of the specification.

[0039] Those skilled in the art should understand that in the disclosure of the present invention, the orientations indicated by the terms "left" and "right" are based on the orientation of the lens 21 to be measured shown in the accompanying drawings. It is only for the sake of simplifying the description and does not mean that the indicated devices or elements must have a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

[0040] The present invention relates to a lens refractive index measuring device, as Figure 1As shown in the figure, it includes a swept-source optical fiber laser 1, a first fiber coupler 2 fiber-connected to the swept-source optical fiber laser 1, a reference arm module and a sample arm module fiber-connected to the first fiber coupler 2 respectively, a second fiber coupler 3 fiber-connected to the reference arm module and the sample arm module in sequence, and a balanced detector 4; a data acquisition card 5, a function generator 6 and a computer 7 in the computer 7 connected in sequence to the balanced detector 4 by lines, and the swept-source optical fiber laser 1 is connected to the data acquisition card 5 by lines;

[0041] The reference arm module includes a first optical circulator 8, a first polarizer 9 and a first collimating lens 10 fiber-connected in sequence, and a first focusing lens 11 and a plane mirror 12 connected to the optical path of the first collimating lens 10 and on the optical path of the first collimating lens 10; the sample arm module includes a second optical circulator 13, a second polarizer 14, a third fiber coupler 15, a second collimating lens 16 and a third collimating lens 18 fiber-connected to the third fiber coupler 15 respectively, a second focusing lens 17 connected to the optical path of the second collimating lens 16 and on the optical path of the second collimating lens 16, a third focusing lens 19 connected to the optical path of the third collimating lens 18 and on the optical path of the third collimating lens 18, a lens under test 21 located between the second focusing lens 17 and the third focusing lens 19 and on their optical paths, and a translation stage 20 for fixing the lens under test 21, and the translation stage 20 is connected to the function generator 6 by lines.

[0042] Both the first optical circulator 8 and the second optical circulator 13 are fiber-connected to the second fiber coupler 3. The light reflected back by the reference arm module and the sample arm module passes through the input end connected to the second fiber coupler 3. The output end of the second fiber coupler 3 is connected to the balanced detector 4. The output end of the balanced detector 4 is connected to the data acquisition card 5 built in the computer 7. The output end of the swept-source optical fiber laser 1 is connected to the data acquisition card 5. One end of the output of the function generator 6 is connected to the data acquisition card 5, and the other end is connected to the translation stage 20 in the sample arm. The output end of the computer 7 is connected to the input end of the function generator 6.

[0043] The light emitted by the swept-source optical fiber laser 1 is split by the first fiber coupler 2 and then enters the reference arm module and the sample arm module respectively. In the reference arm module, after the optical signal passes through the first optical circulator 8 and the first polarizer 9 in sequence, it is collimated into parallel light by the first collimating lens 10, and then focused by the first focusing lens 11 onto the plane mirror 12 and returns along the original path. Subsequently, the reference light is obtained through the first optical circulator 8. In the sample arm module, after the optical signal passes through the second optical circulator 13 and the second polarizer 14, it is equally split by the third fiber coupler 15. The left-side light after splitting passes through the second collimating lens 16 and the second focusing lens 17 in sequence and is incident on the lens under test 21 and then reflected back. The right-side light passes through the third collimating lens 18 and the third focusing lens 19 in sequence and is incident on the lens under test 21 and then returns. The returned light is combined by the third fiber coupler 15 and then passes through the second polarizer 14 and the second optical circulator 13 to obtain the sample light. The two paths of light are jointly transmitted to the second fiber coupler 3, and interference occurs in the second fiber coupler 3 to obtain an interference signal.

[0044] The interference signal is detected by the balanced detector 4 and then input into the data acquisition card 5. The swept-source optical fiber laser 1 provides a clock signal and a trigger signal to the data acquisition card 5. The function generator 6 provides a synchronization signal to the data acquisition card 5 and a driving signal to the translation stage 20. The computer 7 uniformly processes and analyzes all the signals collected by the data acquisition card 5 and generates a scanning signal for the function generator 6.

[0045] The sample arm module is split into two by the third fiber coupler 15 and is respectively incident on the left side and the right side of the lens under test 21. The optical paths of the light incident on both sides of the lens under test 21 are not equal. The right-side optical path is slightly greater than the left-side optical path, and a preset distance difference is maintained between the two.

[0046] The translation stage 20 is a three-dimensional translation stage 20, where the Z-axis translation stage 20 is a manual translation stage 20, and the XY-axis translation stage 20 is an electric translation stage 20, which is used to realize the two-dimensional scanning of the lens under test 21. The thickness direction of the lens under test 21 is consistent with the Z-axis direction.

[0047] Preferably, the splitting ratio of the first fiber coupler 2 is 90:10, and the splitting ratios of the second fiber coupler 3 and the third fiber coupler 15 are 50:50.

[0048] Preferably, the exit diameters of the first collimating lens 10, the second collimating lens 16, and the third collimating lens 18 are 3.4 mm.

[0049] Preferably, the focal lengths of the first focusing lens 11, the second focusing lens 17, and the third focusing lens 19 are 50 mm.

[0050] A method for measuring the refractive index of a lens includes the following steps:

[0051] Step 1: Before placing the lens 21 to be measured, process the interference signal to obtain its position zp in the axial depth;

[0052] The interference signal refers to the interference signal obtained by the interference of the reference light in the reference arm and the sample light in the sample arm with the reference light in the second fiber coupler 3 and detected by the balanced detector 4. At this time, the sample light refers to the light that enters the sample arm, is split by the third fiber coupler 15, and then passes through the second collimating lens 16, the second focusing lens 17, the third focusing lens 19, and the third collimating lens 18 in sequence and then returns to the third fiber coupler 15.

[0053] Step 2: Place the lens 21 to be measured for acquisition, and process the three-dimensional data to obtain the OCT image of the lens 21 to be measured;

[0054] The three-dimensional data in Step 2 refers to the interference of the reference light and the sample light after placing the lens 21 to be measured, which is detected by the balanced detector 4 and input into the data acquisition card 5. The computer 7 controls the function generator 6 to generate a driving signal to ensure that the translation stage 20 performs two-dimensional scanning. At the same time, the function generator 6 also generates a synchronous signal to the data acquisition card 5 to ensure synchronous acquisition during the movement of the translation stage 20 to obtain three-dimensional data. At this time, the sample light refers to the light that enters the sample arm, is split by the third fiber coupler 15, and is reflected after being incident on the left and right sides of the lens 21 to be measured respectively.

[0055] Step 3: Extract four surface signal positions on the front and back surfaces of the lens 21 to be measured on both sides from the OCT image, and reconstruct the true front and back surfaces of the lens 21 to be measured without distortion in combination with the position zp;

[0056] Step 3 specifically includes: Extract four surfaces from the OCT image: The A surface and B surface of the lens 21 measured from the left are denoted as the 1A surface 22 and the 1B surface 24, and the A surface and B surface of the lens 21 measured from the right are denoted as the 2A surface 25 and the 2B surface 23; Randomly select a point M on the 1A surface 22, and its Z-axis position is denoted as z1Am. Find a point M1 on the 2B surface 23 with the same X and Y coordinates as point M, and its Z-axis position is z2Bm. Calculate the physical thickness dm = 2×zp - (z1Am + z2Bm) corresponding to point M in the real space; Extract the 2B surface 23 and perform a vertical flip, and translate it upward to obtain the 2B' surface 26. Select a point M2 on the 2B' surface 26 with the same X and Y coordinates as point M, and the surface where the Z-axis distance between M2 and point M is dm is the 2B' surface 26 that meets the conditions, and the true front surface 1A surface 22 and the back surface 2B' surface 26 of the lens 21 to be measured without distortion are reconstructed.

[0057] Step 4: Combine the actual front and rear surface positions of the lens under test 21, calculate the refraction optical path MN of light in the lens under test 21 based on the ray tracing method, calculate the actual optical path MM3 by combining the four surface positions, compare the refraction optical path MN with the actual optical path MM3, and select the refractive index n of the lens under test 21 that meets the conditions.

[0058] Specifically, Step 4 includes: Select a point M3 on the 1B surface 24 with the same X and Y coordinates as point M. The actual optical path of the light passing through point M in the lens under test 21 is MM3. Calculate the path of the light parallel to the Z-axis after refraction through point M, determine the intersection point N of the refracted light with the rear surface 2B' surface 26 of the actual lens under test 21, and calculate the length of MN. With the refractive index varying in the range of 1.400 to 1.600 in steps of 0.001, select the refractive index that satisfies MN×n = MM3 as the refractive index of the lens under test 21.

[0059] The number of selected points M is 10, calculate the refractive index corresponding to each point respectively, and finally take the average value as the refractive index of the lens under test 21.

[0060] The preferred embodiments of the present invention have been specifically described above, but the present invention is not limited to the embodiments. Those skilled in the art can also make various equivalent variations or substitutions without departing from the spirit of the present invention, and these equivalent variations or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A lens refractive index measuring device, characterized in that, It includes a swept-source optical fiber, a first fiber coupler fiber-connected to the swept-source optical fiber, a reference arm module and a sample arm module fiber-connected to the first fiber coupler respectively, a second fiber coupler fiber-connected to the reference arm module and the sample arm module in sequence, and a balanced detector; A data acquisition card, a function generator and a computer in the computer connected to the balanced detector in sequence by lines, and the swept-source optical fiber is connected to the data acquisition card by a line.

2. The lens refractive index measuring device according to claim 1, wherein The reference arm module includes a first optical circulator, a first polarizer and a first collimating lens fiber-connected in sequence, a first focusing lens and a reflector connected to the optical path of the first collimating lens and on the optical path of the first collimating lens; the sample arm module includes a second optical circulator, a second polarizer, a third fiber coupler fiber-connected in sequence, a second collimating lens and a third collimating lens fiber-connected to the third fiber coupler respectively, a second focusing lens connected to the optical path of the second collimating lens and on the optical path of the second collimating lens, a third focusing lens connected to the optical path of the third collimating lens and on the optical path of the third collimating lens, a lens under test located between the second focusing lens and the third focusing lens and on their optical paths, and a translation stage for fixing the lens under test, and the translation stage is connected to the function generator by a line.

3. The lens refractive index measuring device according to claim 1 or 2, characterized in that, The sample arm module is split into two by the third fiber coupler and respectively incident on the left and right sides of the lens under test. The optical paths of the light incident on both sides of the lens under test are not equal. The optical path on the right side is slightly greater than the optical path on the left side, and a preset distance difference is maintained between the two.

4. The lens refractive index measuring device according to claim 2, characterized in that The translation stage is a three-dimensional translation stage, wherein the Z-axis translation stage is a manual translation stage, and the XY-axis translation stage is an electric translation stage, which is used to realize the two-dimensional scanning of the lens under test, and the thickness direction of the lens under test is consistent with the Z-axis direction.

5. A method for measuring the refractive index of a lens using the lens refractive index measuring device of claim 1 or 2 or 4, characterized in that, It includes the following steps: Step 1: Before the lens under test is placed, the interference signal is processed to obtain its position zp in the axial depth; Step 2: Place the lens under test for acquisition, and after processing the three-dimensional data, obtain the OCT image of the lens under test; Step 3: Extract four surface signal positions on the front and back surfaces of the lens under test measured on both sides from the OCT image, and combine the position zp to reconstruct the true front and back surfaces of the lens under test without distortion; Step 4: Combine the true front and back surface positions of the lens under test, calculate the refraction optical path MN of light in the lens under test based on the ray tracing method, calculate the actual optical path MM3 based on the four surface positions, compare the refraction optical path MN and the actual optical path MM3, and screen out the refractive index n of the lens under test that meets the conditions.

6. The method for measuring the refractive index of a lens according to claim 5, wherein The interference signal in Step 1 refers to the interference between the reference light in the reference arm and the sample light in the sample arm in the second fiber coupler, and the interference signal obtained by the balanced detector. At this time, the sample light refers to the light that enters the sample arm, is split by the third coupler, and then passes through the second collimating lens, the second focusing lens, the third focusing lens, and the third collimating lens in sequence and then returns to the third coupler.

7. The method for measuring the refractive index of a lens according to claim 5, characterized in that The 3D data in the second step refers to the interference of the reference light and the sample light after the lens is placed, which is detected by the balanced detector and input into the data acquisition card. The computer controls the function generator to generate a driving signal to ensure that the translation stage performs two-dimensional scanning. At the same time, the function generator also generates a synchronous signal to the data acquisition card to ensure synchronous acquisition during the movement of the translation stage to obtain 3D data. At this time, the sample light refers to the light that enters the sample arm, is split by the third coupler, and is respectively incident on the left and right sides of the lens to be measured and then reflected.

8. The lens refractive index measurement method according to claim 6 or 7, characterized in that, The specific content of the third step includes: Extract four surfaces from the OCT image: The A surface and B surface of the lens to be measured measured from the left are denoted as the 1A surface and 1B surface, and the A surface and B surface of the lens to be measured measured from the right are denoted as the 2A surface and 2B surface; Randomly select a point M on the 1A surface, and record its Z-axis position as z 1Am , find a point M1 on the 2B surface with the same X and Y coordinates as point M, and its Z-axis position is z 2Bm , calculate the physical thickness d corresponding to point M in the real space m =2×zp-( z 1Am + z 2Bm )); Extract the 2B surface and perform a vertical flip, then translate it upward to obtain the 2B' surface. Select a point M2 on the 2B' surface with the same X and Y coordinates as point M. The surface where the Z-axis coordinate distance between M2 and point M is dm is the 2B' surface that meets the conditions, and the true front surface 1A and the rear surface 2B' of the lens to be measured without distortion are reconstructed.

9. The method for measuring the refractive index of a lens according to claim 8, wherein The specific content of the fourth step includes: Select a point M3 on the 1B surface with the same X and Y coordinates as the point M. The actual optical path of the light passing through the point M in the lens to be measured is MM3. Calculate the path of the light parallel to the Z axis after refraction through the point M, determine the intersection point N of the refracted light and the actual back surface 2B' of the lens to be measured, and calculate the length of MN. Select the refractive index that satisfies MN×n = MM3 as the refractive index of the lens to be measured with the refractive index varying in the range of 1.400 to 1.600 in steps of 0.0005 to 0.

002.

10. The method for measuring the refractive index of a lens according to claim 9, wherein The number of selected points M is greater than or equal to 3, and the refractive index corresponding to each point is calculated respectively. Finally, the average value is taken as the refractive index of the lens to be measured.

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