Optical material refractive index curve measuring device and method based on frequency domain interference

Abstract

The invention provides a device and a method for measuring a refractive index curve of an optical material based on frequency domain interference. The method comprises the following steps: S1, collecting three groups of interference signals; s2, acquiring an interference signal of the rotary optical material sample; s3, performing spectrum correction on the interference signal obtained in the S1; s4, performing spectrum correction on the interference signal obtained in the S2; and S5, carrying out digital filtering on the frequency domain signal in the step S4, solving phase data of the quartz glass by utilizing Hilbert transform after inverse fast Fourier transform, and unrolling the whole phase data according to columns to obtain a phase difference under the wavelength. S6, constructing a physical equation between the optical thickness variation and the phase variation; and S7, substituting the data obtained in S4 and S5 into the equation established in S6, and calculating to obtain the refractive index n (k) of the optical material sample. The method provided by the invention can be used for high-precision nondestructive measurement of the dispersion of the optical material.

Description

Technical Field

[0001] The invention relates to the technical field of non-contact optical coherence tomography, and in particular to a device and method for measuring the refractive index curve of an optical material based on frequency domain interference. Background Art

[0002] The refractive index is an optical parameter determined by the molecular polarizability of a medium, which provides insight into the interaction of light with matter and the structure of matter. Dispersion is a physical property of a substance that describes the relationship between its refractive index and wavelength. Dispersion leads to different propagation speeds at different wavelengths and has a significant impact on the performance of optical components and optical waveguides.

[0003] At present, the main method for measuring refractive index is refraction method, in which the refractive index of each wavelength is calculated by the deflection angle of light in the sample and using Fresnel's law. However, these methods require multiple repeated steps to measure the refractive index curve. Frequency domain optical coherence tomography has the advantages of high resolution, high efficiency, fast speed and flexible application. However, it only obtains the equivalent value of the group refractive index in the entire wavelength range and does not really give the refractive index information. Therefore, a method for accurately obtaining the refractive index curve of the sample using frequency domain optical coherence tomography is proposed. Summary of the invention

[0004] In view of this, an object of the present invention is to provide an optical material refractive index curve measurement device and method based on frequency domain interferometry, which can non-destructively measure the dispersion of optical materials with high precision.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a device for measuring the refractive index curve of an optical material based on frequency domain interference, comprising a grating spectrometer, a superluminescent diode, a fiber coupler, a reference arm, a detection arm and a computer; wherein a broadband light source with a central wavelength of 850nm emitted by the superluminescent diode is divided into a reference light and a detection light through a fiber coupler, the reference light enters the reference arm and is reflected by the quartz glass in the reference arm, the detection light enters the optical material sample through the detection arm and is reflected by the optical material sample, the two beams of light return to the fiber coupler and interfere in the fiber coupler, and finally the interference signal is collected by the grating spectrometer.

[0006] In a preferred embodiment, the reference arm includes an optical fiber APC connector, a collimating lens, a focusing lens, quartz glass and a plurality of sleeves. The light source enters the sleeve through the optical fiber APC connector, becomes parallel light after passing through the collimating lens, is then focused on the upper surface of the quartz glass by the focusing lens, and is finally reflected back into the optical fiber coupler. The structure of the detection arm is the same as that of the reference arm.

[0007] In a preferred embodiment, the grating spectrometer includes an optical fiber APC connector, a collimating lens, a reflection grating, a focusing lens and a linear array CCD camera. The light source enters the sleeve through the optical fiber APC connector, is collimated into parallel light by the collimating lens, and then is reflected and split by the reflection grating. Under the action of the focusing lens, it is focused on the photosensitive element of the linear array CCD camera. Finally, the linear array CCD camera collects the spectral information and transmits it back to the computer for data processing.

[0008] The present invention also provides a method for measuring the refractive index curve of an optical material based on frequency domain interferometry, which adopts the above-mentioned device for measuring the refractive index curve of an optical material based on frequency domain interferometry; the method comprises the following steps:

[0009] S1. placing the sample and the quartz glass in three different combinations at the detection end of the frequency domain optical coherence tomography system and using the frequency domain optical coherence tomography system to collect three groups of interference signals respectively;

[0010] S2, placing the sample and the quartz glass at the detection end of the frequency domain optical coherence tomography system and using the frequency domain optical coherence tomography system to collect the interference signal of the rotating optical material sample;

[0011] S3, performing spectral correction on the interference signal obtained in S1, obtaining the position data corresponding to each reflection layer in the frequency domain signal by using the Hanning window energy center of gravity correction algorithm after fast Fourier transform, and obtaining the group refractive index of the sample by using the relationship between optical thickness and geometric thickness;

[0012] S4, performing spectral correction on the interference signal obtained in S2, obtaining the position data corresponding to the quartz glass in the frequency domain signal by using the Hanning window energy center of gravity correction algorithm after fast Fourier transform, and obtaining the thickness of the sample during rotation by using the relationship between the group refractive index and the optical thickness;

[0013] S5, digitally filtering the frequency domain signal in S4, obtaining the phase data of the quartz glass by using Hilbert transform after inverse fast Fourier transform, and deconvolving the entire phase data by column to obtain the phase difference under wavelength;

[0014] S6, constructing a physical equation between the optical thickness change and the phase change;

[0015] S7, the data obtained in S4 and S5 are put into the equation established in S6 to calculate the refractive index n of the optical material sample (k) .

[0016] In a preferred embodiment: in S1, three groups of interference signals are collected respectively according to the following steps:

[0017] S11: placing the quartz glass as a sample on the detection arm of the frequency domain optical coherence tomography system, and collecting a set of interference signals corresponding to the upper surface of the quartz glass. At this time, the interference signals correspond to the position data of the upper surface of the quartz glass;

[0018] S12: On the basis of S11, the sample is suspended in the air at a certain position above the quartz glass, and a set of interference signals corresponding to this condition are collected using a frequency domain optical coherence tomography system. At this time, the interference signal corresponds to the position data of the upper surface of the quartz glass changed by the refractive index of the sample;

[0019] S13: Based on S11, the sample is placed on the quartz glass surface, and a set of interference signals corresponding to this condition is collected using a frequency domain optical coherence tomography system. At this time, the interference signals correspond to the position data of the upper and lower surfaces of the sample.

[0020] In a preferred embodiment: in S2, the quartz glass is placed on the detection arm of the frequency domain optical coherence tomography system, the optical material sample is suspended and horizontally placed at a certain position above the quartz glass and its tilt angle is continuously changed, and the frequency domain optical coherence tomography system is used to collect a set of interference signals corresponding to this condition. At this time, the interference signal corresponds to the position data of the upper surface of the quartz glass changed by the refractive index of the sample.

[0021] In a preferred embodiment: in step S3, the relationship between the optical thickness and the geometric thickness is:

[0022]

[0023] Wherein, d0 is the position data of the upper surface of the quartz glass measured by S11, d1 is the position data of the upper surface of the quartz glass measured by S12, and n air is the refractive index of air, n s is the group refractive index of the sample, d s is the thickness of the sample, d2 and d3 are the upper and lower surface position data of the sample measured by S1 respectively.

[0024] In a preferred embodiment: in S4, the relationship between the group refractive index and the optical thickness is:

[0025]

[0026] Wherein, d4 is the position data of the upper surface of the quartz glass measured in S3, d r is the thickness of the sample during rotation.

[0027] In a preferred embodiment: in step S6, the physical equation between the optical thickness change and the phase change is:

[0028]

[0029] where n (k) is the refractive index of the sample, k is the wave number, Δd is the thickness change of the dispersion material sample, is the phase change at different wave numbers.

[0030] Compared with the prior art, the present invention has the following beneficial effects: by establishing the physical relationship between the refractive index and the phase and thickness, the present invention can non-destructively measure the dispersion of optical materials with high precision, thus overcoming the problem that previous detection methods require multiple repeated steps to obtain the refractive index curve and that frequency domain optical coherence tomography can only obtain its group refractive index. This technology can be used for the determination of parameters of new optical materials, the identification of samples and the study of light propagation in media. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the structure and principle of a frequency domain optical coherence tomography system in an embodiment of the present invention;

[0032] Figure 2 Schematic diagram of three groups of collection experiments in step S1 of an embodiment of the present invention;

[0033] Figure 3 This is a diagram of the signal processing result of step S4 in an embodiment of the present invention;

[0034] Figure 4 This is a signal processing flow chart of step S5 in an embodiment of the present invention;

[0035] Figure 5 This is a diagram of the signal processing result of step S5 in an embodiment of the present invention.

[0036] Figure numerals: 1. superluminescent diode light source; 2. optical fiber coupler; 3. reference arm; 3-1. reference arm optical fiber APC connector; 3-2. reference arm collimating lens; 3-3. reference arm focusing lens; 3-4. reference arm quartz glass; 4. detection arm; 4-1. detection arm optical fiber APC connector; 4-2. detection arm collimating lens; 4-3. detection arm focusing lens; 4-4. detection arm quartz glass; 5. optical material sample; 6. computer; 7. grating spectrometer; 7-1. spectrometer optical fiber APC connector; 7-2. spectrometer collimating lens; 7-3. reflection grating; 7-4. spectrometer focusing lens; 7-5. linear array CCD camera. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0038] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0039] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0040] This embodiment provides a device and method for measuring the refractive index curve of an optical material based on frequency domain interferometry, comprising the following steps:

[0041] S1. Place the sample and quartz glass in three different combinations at the detection end of the frequency domain optical coherence tomography system and use the system to collect three groups of interference signals respectively;

[0042] In this embodiment, if Figure 1 As shown, the frequency domain optical coherence tomography system includes a superluminescent diode light source 1, a fiber coupler 2, a reference arm 3, a detection arm 4, a sample 5, a computer 6 and a grating spectrometer 7. The broadband light source with a central wavelength of 840nm emitted by the superluminescent diode light source 1 is divided into a reference light and a detection light by the fiber coupler 2. The reference light enters the reference arm 3 through the reference arm fiber APC connector 3-1, is collimated into parallel light under the action of the reference arm collimating lens 3-2, is then focused on the reference arm quartz glass 3-4 through the reference arm focusing lens 3-3, and is finally reflected back to the fiber coupler 2. The detection light enters the detection arm 4 through the detection arm fiber APC connector 4-1, is collimated into parallel light under the action of the detection arm collimating lens 4-2, and is then focused on the reference arm quartz glass 3-4 through the detection arm focusing lens 3-3. The focusing lens 4-3 focuses, first passes through the optical material sample 5, then focuses on the detection arm quartz glass 4-4, and finally reflects back to the fiber coupler 2. After returning to the fiber coupler 2, the reference light and the detection light interfere with each other, and then enter the grating spectrometer 7 through the spectrometer fiber APC connector 7-1. Under the action of the spectrometer collimating lens 7-2, it is collimated into parallel light, and then reflected and split by the reflection grating 7-3. It is focused by the spectrometer focusing lens 7-4 on the linear array CCD camera 7-5, and finally the spectral interference signal is transmitted to the computer 6 for data processing.

[0043] Specifically, three groups of interference signals are collected respectively according to the following steps:

[0044] (1): Place quartz glass as a sample on the detection arm of the frequency domain optical coherence tomography system, and collect a set of interference signals corresponding to the upper surface of the quartz glass. At this time, the interference signal corresponds to the position data of the upper surface of the quartz glass;

[0045] (2): On the basis of step (1), the optical material sample is suspended and placed 3 cm above the quartz glass, and a set of interference signals corresponding to this condition are collected using a frequency domain optical coherence tomography system. At this time, the interference signal corresponds to the position data of the upper surface of the quartz glass changed by the refractive index of the sample;

[0046] (3): Based on step (1), the optical material sample is placed on the quartz glass surface, and a set of interference signals corresponding to this condition is collected using a frequency domain optical coherence tomography system. At this time, the interference signal corresponds to the position data of the upper and lower surfaces of the sample.

[0047] S2, placing the sample and the quartz glass at the detection end of the frequency domain optical coherence tomography system and using the system to collect the interference signal of the rotating optical material sample;

[0048] Specifically, the quartz glass is placed on the detection arm of the frequency domain optical coherence tomography system, the optical material sample is suspended and horizontally placed at a certain position above the quartz glass and its tilt angle is continuously changed, and the frequency domain optical coherence tomography system is used to collect a set of interference signals corresponding to this condition. At this time, the interference signal corresponds to the position data of the upper surface of the quartz glass changed by the refractive index of the sample.

[0049] S3, performing spectral correction on the obtained interference signal, obtaining the position data corresponding to each reflection layer in the frequency domain signal by using the Hanning window energy center of gravity correction algorithm after fast Fourier transform, and obtaining the group refractive index of the sample by using the relationship between optical thickness and geometric thickness;

[0050] Specifically, the relationship between the optical thickness and the geometric thickness is:

[0051]

[0052] Wherein, d0 is the position data of the upper surface of the quartz glass measured in step S11, d1 is the position data of the upper surface of the quartz glass measured in step S12, and n air is the refractive index of air, n s is the group refractive index of the sample, d s is the thickness of the sample, d2 and d3 are the upper and lower surface position data of the sample measured in step S13 respectively.

[0053] S4, performing spectral correction on the interference signal obtained in S2, obtaining the position data corresponding to the quartz glass in the frequency domain signal by using the Hanning window energy center of gravity correction algorithm after fast Fourier transform, and obtaining the thickness of the sample during rotation by using the relationship between the group refractive index and the optical thickness;

[0054] Specifically, the relationship between the group refractive index and the optical thickness is:

[0055]

[0056] Wherein, d4 is the position data of the upper surface of the quartz glass measured in step S3, d r is the thickness of the sample during rotation.

[0057] S5, digitally filtering the frequency domain signal in S4, obtaining the phase data of the quartz glass by using Hilbert transform after inverse fast Fourier transform, and deconvolving the entire phase data by column to obtain the phase difference under wavelength;

[0058] S6, constructing a physical equation between the optical thickness change and the phase change;

[0059] Specifically, the physical equation between the optical thickness change and the phase change is:

[0060]

[0061] where n (k) is the refractive index of the sample, k is the wave number, Δd is the thickness change of the dispersion material sample, is the phase change at different wave numbers.

[0062] S7, the data obtained in S4 and S5 are put into the equation established in S6 to calculate the refractive index n of the optical material sample (k) ;

[0063] According to the above method, in an application example of this embodiment, a sampling position is selected on the sample and 10 different points are selected near the sampling position for experiment and the results are substituted into the above formula for calculation. Table 1 shows the experimental data at the sampling position, and the mean group refractive index is 1.5342.

[0064] Table 1 Experimental results of group refractive index measurement at sample sampling position

[0065] Sampling point <![CDATA[d0(μm)]]> <![CDATA[d1(μm)]]> <![CDATA[d2(μm)]]> <![CDATA[d3(μm)]]> <![CDATA[n s ]]> 1 1771.4987 1239.1963 1032.8674 2561.5268 1.5342 2 1771.4813 1239.2046 1032.8601 2561.4837 1.5342 3 1771.4936 1239.1913 1032.8505 2561.4814 1.5343 4 1771.4923 1239.1947 1032.8355 2561.5287 1.5342 5 1771.4890 1239.1923 1032.8276 2561.5473 1.5342 6 1771.4965 1239.1780 1032.8315 2561.5346 1.5342 7 1771.4898 1239.1697 1032.8377 2561.5831 1.5342 8 1771.4789 1239.1646 1032.8312 2561.5667 1.5342 9 1771.4727 1239.1487 1032.8302 2561.4670 1.5343 10 1771.4693 1239.1287 1032.8334 2561.5285 1.5343 average value 1771.4862 1239.1769 1032.8405 2561.5248 1.5342

[0066] The optical material sample used in this embodiment is standard N-BK7 glass. A sampling position is selected on the sample for experiment and the result is substituted into the above formula for calculation. The change in thickness is 2.1510 μm. The refractive index values ​​at different wavelengths are compared with the theoretical values ​​and the errors between the data and the theoretical values ​​at 10 wavelengths are calculated. The specific results are shown in Table 2. The maximum refractive index error at 10 wavelengths is 0.0029. The experimental results prove the feasibility and accuracy of this method.

[0067] Table 2 Refractive index measurement results

[0068]

[0069] The above experiments and results show that the method proposed in the present invention can detect the refractive index of the sample based on the measurement of the group refractive index by frequency domain optical coherence tomography technology, and has strong practicality and broad application prospects.

[0070] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

[0071] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of optical material refractive index curve measurement devices and methods based on frequency domain interference under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by this patent.

Claims

1. A device for measuring the refractive index curve of an optical material based on frequency domain interferometry, characterized in that: The invention comprises a grating spectrometer, a superluminescent diode, an optical fiber coupler, a reference arm, a detection arm and a computer; wherein the broadband light source with a central wavelength of 850nm emitted by the superluminescent diode is divided into reference light and detection light through the optical fiber coupler; the reference light enters the reference arm and is reflected by the quartz glass in the reference arm; the detection light enters the optical material sample through the detection arm and is reflected by the optical material sample; the two beams of light return to the optical fiber coupler and interfere in the optical fiber coupler; finally, the interference signal is collected by the grating spectrometer.

2. The optical material refractive index curve measuring device based on frequency domain interferometry according to claim 1, characterized in that: The reference arm includes an optical fiber APC connector, a collimating lens, a focusing lens, quartz glass and several sleeves. The light source enters the sleeve through the optical fiber APC connector, becomes parallel light after passing through the collimating lens, and is then focused on the upper surface of the quartz glass by the focusing lens, and finally reflected back into the optical fiber coupler; the detection arm structure is the same as the reference arm.

3. The optical material refractive index curve measuring device based on frequency domain interferometry according to claim 2, characterized in that: The grating spectrometer includes an optical fiber APC connector, a collimating lens, a reflection grating, a focusing lens and a linear array CCD camera. The light source enters the sleeve through the optical fiber APC connector, is collimated into parallel light by the collimating lens, and then is reflected and split by the reflection grating. Under the action of the focusing lens, it is focused on the photosensitive element of the linear array CCD camera. Finally, the linear array CCD camera collects the spectral information and transmits it back to the computer for data processing.

4. A method for measuring the refractive index curve of an optical material based on frequency domain interferometry, characterized in that: An optical material refractive index curve measuring device based on frequency domain interference as described in any one of claims 1 to 3 is used; comprising the following steps: S1. placing the sample and the quartz glass in three different combinations at the detection end of the frequency domain optical coherence tomography system and using the frequency domain optical coherence tomography system to collect three groups of interference signals respectively; S2, placing the sample and the quartz glass at the detection end of the frequency domain optical coherence tomography system and using the frequency domain optical coherence tomography system to collect the interference signal of the rotating optical material sample; S3, performing spectral correction on the interference signal obtained in S1, obtaining the position data corresponding to each reflection layer in the frequency domain signal by using the Hanning window energy center of gravity correction algorithm after fast Fourier transform, and obtaining the group refractive index of the sample by using the relationship between optical thickness and geometric thickness; S4, performing spectral correction on the interference signal obtained in S2, obtaining the position data corresponding to the quartz glass in the frequency domain signal by using the Hanning window energy center of gravity correction algorithm after fast Fourier transform, and obtaining the thickness of the sample during rotation by using the relationship between the group refractive index and the optical thickness; S5, digitally filtering the frequency domain signal in S4, obtaining the phase data of the quartz glass by using Hilbert transform after inverse fast Fourier transform, and deconvolving the entire phase data by column to obtain the phase difference under wavelength; S6, constructing a physical equation between the optical thickness change and the phase change; S7, the data obtained in S4 and S5 are put into the equation established in S6 to calculate the refractive index n of the optical material sample (k) .

5. The method for measuring the refractive index curve of an optical material based on frequency domain interferometry according to claim 4, characterized in that: In S1, three groups of interference signals are collected respectively according to the following steps: S11: placing the quartz glass as a sample on the detection arm of the frequency domain optical coherence tomography system, and collecting a set of interference signals corresponding to the upper surface of the quartz glass. At this time, the interference signals correspond to the position data of the upper surface of the quartz glass; S12: On the basis of S11, the sample is suspended in the air at a certain position above the quartz glass, and a set of interference signals corresponding to this condition are collected using a frequency domain optical coherence tomography system. At this time, the interference signal corresponds to the position data of the upper surface of the quartz glass changed by the refractive index of the sample; S13: Based on S11, the sample is placed on the quartz glass surface, and a set of interference signals corresponding to this condition is collected using a frequency domain optical coherence tomography system. At this time, the interference signals correspond to the position data of the upper and lower surfaces of the sample.

6. The method for measuring the refractive index curve of an optical material based on frequency domain interferometry according to claim 4, characterized in that: In S2, the quartz glass is placed on the detection arm of the frequency domain optical coherence tomography system, the optical material sample is suspended and horizontally placed at a certain position above the quartz glass and its tilt angle is continuously changed, and a set of interference signals corresponding to this condition are collected by the frequency domain optical coherence tomography system. At this time, the interference signal corresponds to the position data of the upper surface of the quartz glass changed by the refractive index of the sample.

7. The method for measuring the refractive index curve of an optical material based on frequency domain interferometry according to claim 5, characterized in that: In step S3, the relationship between the optical thickness and the geometric thickness is: Wherein, d0 is the position data of the upper surface of the quartz glass measured by S11, d1 is the position data of the upper surface of the quartz glass measured by S12, and n air is the refractive index of air, n s is the group refractive index of the sample, d s is the thickness of the sample, d2 and d3 are the upper and lower surface position data of the sample measured by S1 respectively.

8. The method for measuring the refractive index curve of an optical material based on frequency domain interferometry according to claim 4, characterized in that: In S4, the relationship between the group refractive index and the optical thickness is: Wherein, d4 is the position data of the upper surface of the quartz glass measured in S3, d r is the thickness of the sample during rotation.

9. The method for measuring the refractive index curve of an optical material based on frequency domain interferometry according to claim 4, characterized in that: In step S6, the physical equation between the optical thickness change and the phase change is: where n (k) is the refractive index of the sample, k is the wave number, Δd is the thickness change of the dispersion material sample, is the phase change at different wave numbers.

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