Mach-Zehnder interferometer-based gradient refractive index material wedge mirror compensation measurement method

Abstract

The invention discloses a gradient refractive index material wedge mirror compensation measurement method based on a Mach-Zehnder interferometer. The method comprises the following steps: building the Mach-Zehnder interferometer; putting the gradient refractive index material and the wedge mirror into an interference cavity of an interferometer; measuring a first wavefront superposed by the gradient refractive index material and the wedge mirror at the moment by using an interferometer; moving the gradient refractive index material out of the interference cavity to obtain a second wavefront with only a wedge mirror in the interference cavity; calculating transmission wavefront of the gradient refractive index material according to the first wavefront and the second wavefront; and calculating the refractive index change of the gradient refractive index material by using the obtained transmission wavefront. The gradient refractive index material exceeding the measurement range of the interferometer can be compensated, so that the refractive index change of the gradient refractive index material is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of optical interference measurement, in particular to a compensation measurement method of a gradient refractive index material wedge mirror based on a Mach-Zehnder interferometer. Background Art

[0002] Gradient refractive index (GRIN) material is a kind of inhomogeneous material, whose components and structure change continuously according to certain rules inside the material, so that the refractive index also changes continuously accordingly. Gradient refractive materials can be basically divided into three types according to the refractive gradient: radial gradient refractive material, axial gradient refractive material, and spherical gradient refractive material. Gradient refractive index optical devices can improve imaging quality, reduce the volume and weight of optical systems, simplify processing technology, and make optical systems miniaturized, lightweight, high-quality, and easier to assemble. They play an increasingly important role in optical communications, imaging, industry, and biomedical sensing. At present, gradient refractive index optics has been widely used in various fields, but its application range is still limited by its testing methods.

[0003] The refractive index distribution law of gradient refractive index materials has a great influence on their optical properties, so we need to accurately measure the refractive index distribution law of gradient refractive index materials. Methods for measuring the refractive index distribution of gradient refractive index materials include prism technology, schlieren method, interference method, beam deflection method, optical coherence tomography technology, etc. Among them, the use of Mach-Zehnder interferometer to measure gradient refractive index materials has been proven to be a more universal and reliable measurement method, which is not only applicable to visible light measurement, but also to infrared band measurement.

[0004] As the research on gradient refractive index materials deepens, the gradient steepness of some materials is getting bigger and bigger, that is, at the same lateral distance, the refractive index changes more and more, gradually exceeding the measurement range of general interferometers and making them impossible to measure. If the measurement range of the interferometer is to be expanded, it is necessary to redesign the imaging system, replace the lens with a smaller F number, and replace the detector with a higher resolution. This method is complicated and costly.

[0005] In summary, the gradient steepness of some gradient refractive index materials is too large to be directly measured by interferometer. When the interferometer is packaged, it is expensive and complicated to expand the measurement range of the interferometer. A simpler and more convenient method is needed to measure gradient refractive index materials that are beyond the measurement range. Summary of the invention

[0006] The object of the present invention is to provide a gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer which is simple to operate, low-cost and convenient to operate.

[0007] The technical solution to achieve the purpose of the present invention is: a gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer, comprising the following steps:

[0008] Step 1: Build a Mach-Zehnder interferometer;

[0009] Step 2, placing the gradient refractive index material and the wedge mirror into the interference cavity of the interferometer;

[0010] Step 3, using an interferometer to measure the first wavefront superimposed by the gradient refractive index material and the wedge mirror;

[0011] Step 4, moving the gradient refractive index material out of the interference cavity to obtain a second wavefront with only the wedge mirror in the interference cavity;

[0012] Step 5: Calculate the transmission wavefront of the gradient refractive index material based on the first wavefront and the second wavefront;

[0013] Step 6: Using the transmitted wavefront obtained in step 5, calculate the refractive index change of the gradient refractive index material.

[0014] Furthermore, it is characterized in that the compensation measurement includes two methods: using a single-mirror compensation measurement and using a dual-mirror compensation measurement.

[0015] Furthermore, when using single-mirror compensation measurement, the placement position of the wedge mirror in step 2 is specifically as follows:

[0016] After placing the gradient refractive index material in the test optical path, the wedge mirror is placed in the test optical path of the Mach-Zehnder interferometer, and the wedge mirror is placed as close to the gradient refractive index material as possible.

[0017] Furthermore, when using dual-mirror compensation measurement, the wedge mirror placement position in step 2 is specifically:

[0018] After placing the gradient refractive index material in the test optical path, the first wedge mirror is placed in the test optical path of the Mach-Zehnder interferometer, so that the first wedge mirror is as close to the gradient refractive index material as possible; then the second wedge mirror is placed in the reference optical path of the Mach-Zehnder interferometer, so that the second wedge mirror is as close to the beam combiner and beam splitter as possible.

[0019] Furthermore, the first wedge mirror and the second wedge mirror have the same angle, material and size, and the wavefront inclination directions caused by the first wedge mirror and the second wedge mirror are consistent.

[0020] Furthermore, in step 2, the wavefront tilt direction caused by the wedge mirror should be opposite to the direction of the gradient refractive index steepness, and the angle of the wedge mirror increases as the gradient slope of the gradient refractive index sample to be measured increases.

[0021] Furthermore, in step 3, the first wavefront superimposed by the gradient refractive index material and the wedge mirror is measured by using an interferometer, as follows:

[0022] Turn on the interferometer, place the area with a large gradient slope in the gradient refractive index material in the middle of the measurement area, and use the interferometer to measure the first wavefront W1 (x, y) superimposed by the gradient refractive index material and the wedge mirror.

[0023] Furthermore, in step 4, the gradient refractive index material is moved out of the interference cavity to obtain a second wavefront with only the wedge mirror in the interference cavity, as follows:

[0024] The position of the wedge mirror is kept unchanged, and only the gradient refractive index material is removed. The second wavefront W2(x, y) containing only the wedge mirror in the interference cavity is measured using an interferometer.

[0025] Furthermore, the transmission wavefront of the gradient refractive index material in step 5 is W(x,y), and the calculation formula is as follows:

[0026] W(x,y)=W1(x,y)-W2(x,y)

[0027] Among them, W1(x, y) is the first wavefront obtained in step 2, and W2(x, y) is the second wavefront obtained in step 3.

[0028] Furthermore, in step 6, the refractive index change of the gradient refractive index material is calculated using the transmitted wavefront obtained in step 5, as follows:

[0029] The peak-to-valley value of the optical path difference PV is expressed as OPD PV :

[0030] OPD PV =W max (x,y)-W min (x,y)

[0031] Among them, W max (x,y),W min (x, y) are the maximum and minimum values ​​of the transmitted wavefront of the gradient refractive index material, respectively;

[0032] The refractive index change Δn of the gradient refractive index material is:

[0033] Δn=OPD PV / t

[0034] Where t is the thickness of the gradient index material.

[0035] Compared with the prior art, the present invention has the following significant advantages: (1) the range of measurable gradient refractive index materials can be expanded by simply adding a wedge mirror without destroying the existing structure of the interferometer; (2) the gradient refractive index sample that cannot be directly measured using the Mach-Zehnder interferometer can be measured with the help of the wedge mirror, and the method has high accuracy, simple operation and low cost, which can meet the demand of expanding the measurement range of the interferometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The schematic diagram of the compensation measurement method of the gradient refractive index material wedge mirror based on Mach-Zehnder interferometer of the present invention.

[0037] Figure 2 The interference pattern and measurement results of the GASS sample directly measured using an interferometer, where (a) is the interference pattern and (b) is the measurement result.

[0038] Figure 3 is the single mirror compensation measurement result, where Figure 3 (a) is the wavefront of the gradient refractive index sample and the wedge mirror. Figure 3 (b) is the wavefront data with only the wedge mirror. Figure 3 (c) is the wavefront data obtained by subtracting the wavefront data of only the wedge mirror from the wavefront of the gradient refractive index sample and the wedge mirror.

[0039] Figure 4 is the double mirror compensation measurement result, where Figure 4 (a) is the wavefront of the gradient refractive index sample and the wedge mirror. Figure 4 (b) is the wavefront data with only the wedge mirror. Figure 4 (c) is the wavefront data obtained by subtracting the wavefront data of only the wedge mirror from the wavefront of the gradient refractive index sample and the wedge mirror. DETAILED DESCRIPTION

[0040] It is easy to understand that according to the technical solution of the present invention, without changing the essential spirit of the present invention, a person skilled in the art can imagine various implementation methods of the present invention. Therefore, the following specific implementation methods and drawings are only exemplary descriptions of the technical solution of the present invention, and should not be regarded as the whole of the present invention or as a limitation or restriction of the technical solution of the present invention.

[0041] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0042] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0043] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0044] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0045] Combination Figure 1 The present invention provides a method for measuring gradient refractive index materials using wedge mirror compensation based on Mach-Zehnder interferometer, comprising the following steps:

[0046] Step 1: Build a Mach-Zehnder interferometer;

[0047] Step 2, placing the gradient refractive index material and the wedge mirror into the interference cavity of the interferometer;

[0048] Step 3, using an interferometer to measure the first wavefront superimposed by the gradient refractive index material and the wedge mirror;

[0049] Step 4, moving the gradient refractive index material out of the interference cavity to obtain a second wavefront with only the wedge mirror in the interference cavity;

[0050] Step 5: Calculate the transmission wavefront of the gradient refractive index material based on the first wavefront and the second wavefront;

[0051] Step 6: Using the transmitted wavefront obtained in step 5, calculate the refractive index change of the gradient refractive index material.

[0052] As a specific example, the compensation measurement includes two methods: single-mirror compensation measurement and dual-mirror compensation measurement.

[0053] As a specific example, when using single-mirror compensation measurement, the wedge mirror placement position in step 2 is specifically as follows:

[0054] After placing the gradient refractive index material in the test optical path, the wedge mirror is placed in the test optical path of the Mach-Zehnder interferometer, and the wedge mirror is placed as close to the gradient refractive index material as possible.

[0055] As a specific example, when using dual-mirror compensation measurement, the wedge mirror placement position in step 2 is specifically as follows:

[0056] After placing the gradient refractive index material in the test optical path, the first wedge mirror is placed in the test optical path of the Mach-Zehnder interferometer, so that the first wedge mirror is as close to the gradient refractive index material as possible; then the second wedge mirror is placed in the reference optical path of the Mach-Zehnder interferometer, so that the second wedge mirror is as close to the beam combiner and beam splitter as possible.

[0057] As a specific example, the first wedge mirror and the second wedge mirror have the same angle, material, and size, and the wavefront inclination directions caused by the first wedge mirror and the second wedge mirror are consistent.

[0058] As a specific example, in step 2, the wavefront tilt direction caused by the wedge mirror should be opposite to the direction of the gradient refractive index steepness, and the angle of the wedge mirror increases as the gradient slope of the gradient refractive index sample to be measured increases.

[0059] As a specific example, the first wavefront superimposed by the gradient refractive index material and the wedge mirror is measured by using an interferometer in step 3, as follows:

[0060] Turn on the interferometer, place the area with a large gradient slope in the gradient refractive index material in the middle of the measurement area, and use the interferometer to measure the first wavefront W1 (x, y) superimposed by the gradient refractive index material and the wedge mirror.

[0061] As a specific example, in step 4, the gradient refractive index material is moved out of the interference cavity to obtain a second wavefront with only a wedge mirror in the interference cavity, as follows:

[0062] The position of the wedge mirror is kept unchanged, and only the gradient refractive index material is removed. The second wavefront W2(x, y) containing only the wedge mirror in the interference cavity is measured using an interferometer.

[0063] As a specific example, the transmission wavefront of the gradient refractive index material in step 5 is W(x, y), and the calculation formula is as follows:

[0064] W(x,y)=W1(x,y)-W2(x,y)

[0065] Among them, W1(x, y) is the first wavefront obtained in step 2, and W2(x, y) is the second wavefront obtained in step 3.

[0066] As a specific example, step 6 uses the transmitted wavefront obtained in step 5 to calculate the refractive index change of the gradient refractive index material, as follows:

[0067] The peak-to-valley value of the optical path difference PV is expressed as OPD PV :

[0068] OPD PV =W max (x,y)-W min (x,y)

[0069] Among them, W max (x,y),W min (x, y) are the maximum and minimum values ​​of the transmitted wavefront of the gradient refractive index material, respectively;

[0070] The refractive index change Δn of the gradient refractive index material is:

[0071] Δn=OPD PV / t

[0072] Where t is the thickness of the gradient index material.

[0073] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0074] Example

[0075] The Mach-Zehnder interferometer used in this embodiment is an Interface CMIZ-I long-wave infrared interferometer, with an operating wavelength of λ=10.6 μm and a test aperture of Φ30 mm.

[0076] This embodiment adopts a wedge mirror compensation measurement method for gradient refractive index materials based on Mach-Zehnder interferometer of the present invention to perform compensation measurement on gradient refractive index materials that are beyond the measurement range of Interface CMIZ-I long-wave infrared interferometer.

[0077] The gradient refractive index sample used in this embodiment is the GASS sample of Ningbo University, with a thickness of t=1.21 mm and a refractive index change Δn=0.22. Figure 2 , Figure 2 (a) is the interference pattern, Figure 2 (b) is the measurement result. The interferometer is used to directly measure the gradient refractive index sample to be tested. The sample to be tested is only placed in the test light path. The middle fringes of the obtained interference pattern are unclear and the information is missing. The measurement result is significantly different from the nominal value of the sample.

[0078] Combination Figure 3 ,in Figure 3 (a) is the wavefront of the gradient refractive index sample and the wedge mirror. Figure 3 (b) in the figure shows the wavefront data with only the wedge mirror. Figure 3 (c) in the figure is the wavefront data obtained by subtracting the wavefront data of the wedge mirror from the wavefront of the gradient refractive index sample and the wedge mirror. Using single-mirror compensation measurement, the sample to be tested is placed in the test optical path, and then the wedge mirror is placed in the test optical path of the Mach-Zehnder interferometer, with the wedge mirror as close to the material to be tested as possible. The interferometer is used to measure the wavefront of the gradient refractive index sample and the wedge mirror at this time. The gradient refractive index sample is moved out of the interferometer cavity to obtain the wavefront data of the wedge mirror in the interferometer cavity. The wavefront data of the gradient refractive index sample is obtained by subtracting the wavefront data of the wedge mirror from the wavefront of the gradient refractive index sample and the wedge mirror. The measurement result Δn=0.211 is calculated according to the formula.

[0079] Combination Figure 4 ,in Figure 4 (a) is the wavefront of the gradient refractive index sample and the wedge mirror. Figure 4 (b) in the figure shows the wavefront data with only the wedge mirror. Figure 4 (c) in the figure is the wavefront data obtained by subtracting the wavefront data of the wedge mirror from the wavefront of the gradient refractive index sample and the wedge mirror. Using dual-mirror compensation measurement, after the sample to be tested is placed in the test optical path, wedge mirror ① is placed in the test optical path of the Mach-Zehnder interferometer, the wedge mirror is as close to the material to be tested as possible, and wedge mirror ② is placed in the reference optical path of the Mach-Zehnder interferometer, as close to the beam combiner and beam splitter as possible. The interferometer is used to measure the wavefront of the gradient refractive index sample and the wedge mirror at this time, and the gradient refractive index sample is moved out of the interferometer cavity to obtain the wavefront data of the wedge mirror in the interferometer cavity. The wavefront data of the gradient refractive index sample is obtained by subtracting the wavefront data of the wedge mirror from the wavefront of the gradient refractive index sample and the wedge mirror. The measurement result Δn=0.217 is calculated according to the formula. The measurement error is 1.36%.

[0080] In order to verify the reliability of the experimental results of the present invention, the results obtained by the wedge mirror compensation method were compared with the nominal values ​​of the gradient refractive index samples. When using single-mirror compensation measurement, the gradient refractive index deviation value is about 0.009, and the relative measurement error is 4.09%. When using double-mirror compensation measurement, the gradient refractive index deviation value is about 0.003, and the relative measurement error is 1.36%. The experimental results show that the method proposed by the present invention has high measurement accuracy and stable results, and the angle and number of wedge mirrors can be selected according to different samples to be tested.

[0081] In summary, the method for measuring gradient refractive index materials with wedge mirror compensation based on Mach-Zehnder interferometer proposed in the present invention can expand the measurement range. With the help of wedge mirror, gradient refractive index samples that cannot be directly measured using Mach-Zehnder interferometer can be measured. It has high accuracy, simple operation and low cost, and can meet the demand for expanding the measurement range of the interferometer.

Claims

1. A gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer, characterized in that: The following steps are involved: Step 1: Build a Mach-Zehnder interferometer; Step 2, placing the gradient refractive index material and the wedge mirror into the interference cavity of the interferometer; Step 3, using an interferometer to measure the first wavefront superimposed by the gradient refractive index material and the wedge mirror; Step 4, moving the gradient refractive index material out of the interference cavity to obtain a second wavefront with only the wedge mirror in the interference cavity; Step 5: Calculate the transmission wavefront of the gradient refractive index material based on the first wavefront and the second wavefront; Step 6: Using the transmitted wavefront obtained in step 5, calculate the refractive index change of the gradient refractive index material.

2. The gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer according to claim 1, characterized in that: The compensation measurement includes two methods: using a single mirror compensation measurement and using a double mirror compensation measurement.

3. The gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer according to claim 2, characterized in that: When using single-mirror compensation measurement, the specific placement of the wedge mirror in step 2 is: After placing the gradient refractive index material in the test optical path, the wedge mirror is placed in the test optical path of the Mach-Zehnder interferometer, and the wedge mirror is placed as close to the gradient refractive index material as possible.

4. The gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer according to claim 2, characterized in that: When using dual-mirror compensation measurement, the wedge mirror placement in step 2 is as follows: After placing the gradient refractive index material in the test optical path, the first wedge mirror is placed in the test optical path of the Mach-Zehnder interferometer, so that the first wedge mirror is as close to the gradient refractive index material as possible; then the second wedge mirror is placed in the reference optical path of the Mach-Zehnder interferometer, so that the second wedge mirror is as close to the beam combiner and beam splitter as possible.

5. The gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer according to claim 4, characterized in that: The first wedge mirror and the second wedge mirror have the same angle, material and size, and the wavefront tilt directions caused by the first wedge mirror and the second wedge mirror are consistent.

6. The gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer according to claim 3 or 4, characterized in that: In step 2, the wavefront tilt direction caused by the wedge mirror should be opposite to the direction of the gradient refractive index steepness, and the angle of the wedge mirror increases as the gradient slope of the gradient refractive index sample to be measured increases.

7. The gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer according to claim 1, characterized in that: In step 3, the interferometer is used to measure the first wavefront superimposed by the gradient refractive index material and the wedge mirror, as follows: Turn on the interferometer, place the area with a large gradient slope in the gradient refractive index material in the middle of the measurement area, and use the interferometer to measure the first wavefront W1 (x, y) superimposed by the gradient refractive index material and the wedge mirror.

8. The gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer according to claim 1, characterized in that: In step 4, the gradient refractive index material is moved out of the interference cavity to obtain the second wavefront with only the wedge mirror in the interference cavity, as follows: The position of the wedge mirror is kept unchanged, and only the gradient refractive index material is removed. The second wavefront W2(x, y) containing only the wedge mirror in the interference cavity is measured using an interferometer.

9. The gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer according to claim 1, characterized in that: The transmitted wavefront of the gradient refractive index material in step 5 is W(x,y), which is calculated as follows: W(x,y)=W1(x,y)-W2(x,y) Among them, W1(x, y) is the first wavefront obtained in step 2, and W2(x, y) is the second wavefront obtained in step 3.

10. The gradient refractive index material wedge mirror compensation measurement method based on Mach-Zehnder interferometer according to claim 1, characterized in that: Step 6 uses the transmitted wavefront obtained in step 5 to calculate the refractive index change of the gradient refractive index material, as follows: The peak-to-valley value of the optical path difference PV is expressed as OPD PV : OPD PV =W max (x,y)-W min (x,y) Among them, W max (x,y),W min (x, y) are the maximum and minimum values ​​of the transmitted wavefront of the gradient refractive index material, respectively; The refractive index change Δn of the gradient refractive index material is: Δn=OPD PV / t Where t is the thickness of the gradient index material.

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