A system and method for measuring the thickness and refractive index of transparent samples

Abstract

This invention pertains to interferometric measurement techniques within the field of optical measurement, specifically a system and method for measuring the thickness and refractive index of transparent samples. The system includes: an SLD light source, a spectrometer, an optical fiber structure, a reference end structure, and a measurement end structure. The reference end structure comprises a mirror, a reference end collimator, and its angle adjustment frame; the measurement end structure includes an upper measurement end collimator and its angle adjustment frame, a lower measurement end collimator and its angle adjustment frame, an XYZ-axis displacement stage, a dual-axis electrically controlled stage, a first polarizer, and a second polarizer. This invention allows for the measurement of the thickness and refractive index of the sample without the need for a standard height sample, thereby eliminating the influence of standard height sample errors on the measurement results and achieving self-calibration measurement. By utilizing the characteristic of attenuating light intensity through the parallel placement of two polarizers, this invention weakens the intensity of the coupled beam between the upper and lower collimators at the measurement end, thus resolving the impact of transmitted light intensity on signal acquisition and processing during the measurement process.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement, and specifically relates to a system and method for measuring the thickness and refractive index of transparent samples. Background Technology

[0002] Methods for measuring the thickness of transparent samples are mainly divided into two categories: contact and non-contact. Contact measurement methods, such as mechanical probes and micrometers, while offering advantages in high precision and ease of operation, inevitably cause damage to the sample surface, especially when handling soft or fragile materials. Non-contact measurement methods, such as laser thickness gauges and ellipsometrists, avoid sample damage and are suitable for measurements in high-temperature, high-speed, or hazardous environments. However, these methods also have limitations; for example, laser thickness gauges are sensitive to surface reflectivity, and ellipsometrists require a high degree of surface smoothness in the sample.

[0003] Existing optical measurement techniques often require standard height samples to measure the thickness of the sample under test. For example, CN114894106A discloses an opaque sample thickness measurement system and method. This method uses dual probes to calibrate a standard height sample of known thickness, thereby obtaining the distance between the zero optical path difference positions of two interferometric systems on the upper and lower surfaces of the sample, and thus realizing the sample thickness measurement.

[0004] CN107167085A discloses a common optical path self-calibrating thin film thickness measurement device and method. The method uses dual probes to perform optical path scanning to obtain the absolute distance between the two probes, and then performs optical path scanning on the upper and lower surfaces of the sample to achieve sample thickness measurement. However, the method has a long measurement time, the measurement results are limited by the positioning accuracy of the scanning device, the system is complex, demodulation is difficult, and it cannot measure thicker samples.

[0005] Existing optical measurement techniques for measuring the thickness of opaque samples often require samples of standard height and face numerous challenges, such as long measurement times, system complexity, and limited measurement accuracy. Furthermore, when using reflection methods to measure transparent samples, the sample's transmittance is much greater than its reflectance. Therefore, the intensity of the transmitted beam is much greater than the required sample reflection intensity, affecting signal acquisition and processing. Thus, improving the application of optical measurement techniques in sample measurement has become one of the urgent problems to be solved in industrial production. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a system and method that can measure transparent samples with a certain thickness without the need for standard height samples, with fast measurement speed and high measurement accuracy, realize self-calibration measurement, and solve the problem of the influence of transmitted light intensity on signal acquisition and processing during the measurement process.

[0007] A first aspect of the present invention is to provide a transparent sample thickness and refractive index measurement system, comprising: an SLD light source, a spectrometer, an optical fiber structure, a column, a reference end structure, and a measurement end structure; the spectrometer is used to acquire interference spectral signals; the optical fiber structure is used to adjust beam intensity, beam splitting, and beam transmission.

[0008] The reference end structure mainly includes a reflector, a reference end collimator, and its angle adjustment frame;

[0009] The measuring end structure mainly includes an upper measuring end collimator and its angle adjustment frame, a lower measuring end collimator and its angle adjustment frame, an XYZ axis displacement stage, a dual-axis electrically controlled stage, a first polarizer and a second polarizer;

[0010] The XYZ axis displacement stage is connected to the lower measuring end collimator and is used to adjust the XYZ direction of the lower measuring end collimator. It is installed on the column.

[0011] The dual-axis electrically controlled stage is used for sample placement and coaxial adjustment of the upper and lower measuring collimators. The stage has two holes: one for coaxial measurement of the upper and lower measuring collimators and the other for measurement of the sample. The movement between the two holes of the stage is controlled by a controller. The stage is installed between the upper and lower measuring collimators at an appropriate distance. Through electrical control, XY direction displacement can be achieved.

[0012] The first polarizer is installed between the upper measuring end collimator and the dual-axis electrically controlled stage at a suitable distance, and the second polarizer is installed between the lower measuring end collimator and the dual-axis electrically controlled stage at a suitable distance. The two polarizers are used together to reduce the intensity of the coupled beam between the upper and lower collimators at the measuring end.

[0013] Furthermore, the optical fiber structure (3) includes a first optical fiber attenuator (301), a first optical fiber coupler (302), a second optical fiber coupler (303), and a second optical fiber attenuator (304);

[0014] The first fiber optic attenuator (301) is connected to the SLD light source (1) and is used to adjust the intensity of the light source beam;

[0015] The first fiber coupler (302) is connected to the first fiber attenuator (301) and the spectrometer (2) respectively, and is used to split the light and collect interference signals;

[0016] The second fiber coupler (303) is connected to the first fiber coupler (302) and is used for beam splitting at the reference end;

[0017] The second fiber attenuator (304) is connected to the first fiber coupler (302) and is used to adjust the intensity of the reference beam.

[0018] A second aspect of the present invention is to provide a method for measuring the thickness and refractive index of a transparent sample, comprising the following steps:

[0019] 1) Adjust the upper and lower collimators to be coaxial, ensuring that the two collimators are aligned with two points on the vertical lines of the upper and lower surfaces of the sample to be measured, thereby achieving point-to-point measurement of the upper and lower surfaces of the sample.

[0020] 2) Acquire interference signals and process the interference signals acquired by the spectrometer to obtain the optical path difference ΔR between the measuring end and the reference end;

[0021] 3) Place the sample to be tested, and control the biaxial electronically controlled stage to align the collimators on the upper and lower surfaces of the measurement end with the upper and lower surfaces of the sample to be tested, respectively. Collect interference signals and process the interference signals collected by the spectrometer to obtain the optical path difference Δa between the upper surface of the sample to be tested and the collimator at the upper measurement end and the reference end, the optical path difference Δb between the lower surface of the sample to be tested and the collimator at the lower measurement end and the reference end, the optical path difference Δc between the lower surface of the sample to be tested and the collimator at the upper measurement end and the reference end, and the optical path difference Δd between the upper surface of the sample to be tested and the collimator at the lower measurement end and the reference end.

[0022] 4) Calculate the thickness of the sample to be tested. Obtain the refractive index of the sample to be tested

[0023] Step 1) specifically includes the following steps:

[0024] (1.1) Turn on the SLD light source, place the flat crystal, adjust the upper measuring end collimator angle adjustment bracket so that the upper measuring end collimator is perpendicular to the upper surface of the flat crystal. When the light intensity returning from the upper surface of the flat crystal to the upper measuring end collimator reaches the maximum value, it is perpendicular. Adjust the lower measuring end collimator angle adjustment bracket so that the lower measuring end collimator is perpendicular to the lower surface of the flat crystal. When the light intensity returning from the lower surface of the flat crystal to the lower measuring end collimator reaches the maximum value, it is perpendicular.

[0025] (1.2) Remove the flat crystal and keep the upper measuring end collimator stationary. Using the upper measuring end collimator as a reference, move the lower measuring end collimator by changing the XY direction of the XYZ axis displacement stage until the light power value received by the spectrometer reaches the maximum. At this time, the upper and lower surface collimators of the measuring end are coaxial.

[0026] (1.3) Steps (1.1) and (1.2) are the initial adjustment steps of the system. After the system is built, it only needs to be adjusted once. In subsequent measurement steps, the upper measurement end collimator and the lower measurement end collimator are kept fixed.

[0027] Step 2) describes a specific method for obtaining the optical path difference ΔR between the measuring end and the reference end. This method involves using Fourier transform to transform the signal from the time domain to the frequency domain, extracting the phase information of the interference spectrum signal, and then using the slope method to calculate the optical path difference. The specific steps include:

[0028] (2.1) The acquired interference spectrum signal is the interference signal between the measurement end and the reference end. The acquired spectrum data is subjected to Fourier transform to extract the main frequency. A peak in the frequency domain signal is windowed and filtered to remove background light and noise interference.

[0029] (2.2) Perform inverse Fourier transform to obtain the phase information of the interference spectrum signal;

[0030] (2.3) Since the phase information in the interference spectrum signal is linearly related to the wavenumber, the slope value of the two can be obtained by fitting the linear relationship and calculating the optical path difference ΔR.

[0031] In step 3), since the spectral signal required for calculation is the superposition of four interference signals, before acquiring the interference spectrum, the Z-axis direction of the displacement stage must be adjusted to ensure that the four optical path differences have a certain distance, thus guaranteeing that the peaks of the four interference signals in the frequency domain do not overlap. Specific steps include...

[0032] (3.1) By controlling the dual-axis electrically controlled stage, the collimators on the upper and lower surfaces of the measuring end are aligned with the upper and lower surfaces of the sample, respectively.

[0033] (3.2) Because the transmittance of the sample to be measured is much greater than its reflectance, the intensity of the coupled beam between the upper and lower collimators at the measuring end is much greater than the required sample reflection intensity, affecting signal acquisition and processing. According to Malus's law, if the light emitted from the first polarizer passes through the second polarizer, the light intensity I after passing through the two polarizers varies with the angle θ between the transmission axes of the two polarizers, that is...

[0034] I = I0COS 2 θ

[0035] Wherein, I0 represents the transmitted light intensity when the transmission axes of the two polarizers are parallel, at which point the transmitted light intensity is at its maximum; when the transmission axes of the two polarizers are perpendicular, the transmitted light intensity is 0, which is the ideal state to be adjusted in this invention; when the two polarizers rotate relative to each other, the transmitted light intensity changes with the angle between the transmission axes of the two polarizers, so the device with the two polarizers placed vertically parallel can also attenuate the light intensity. Therefore, this invention, by fixing the first polarizer and rotating the second polarizer, adjusts the angle between the transmission axes of the two polarizers to 90°, thereby reducing the intensity of the coupled beam between the upper and lower collimators at the measuring end to a negligible level;

[0036] (3.3) The collected interference spectral signals include the interference signals between the upper surface of the sample and the reference end, the interference signals between the lower surface of the sample and the reference end, and the interference signals between the upper and lower surfaces of the sample. Fourier transform is performed on the collected spectral data.

[0037] (3.4) Block the reference end signal. The collected interference spectrum signal is the interference signal between the upper and lower surfaces of the sample. This part of the signal is an unwanted interference signal. Perform Fourier transform on the collected spectrum data.

[0038] (3.5) Subtract the Fourier transform result obtained in (3.3) from the Fourier transform result obtained in (3.4) to obtain the Fourier transform result of the required interference signal. Window the four peaks in the frequency domain signal and filter to remove background light and noise interference.

[0039] (3.6) Perform inverse Fourier transform to obtain the phase information of the interference spectrum signal;

[0040] (3.7) Since the phase information in the interference spectrum signal is linearly related to the wavenumber, by fitting the linear relationship, the slope values ​​of the two can be obtained, and the optical path difference Δa, Δb, Δc and Δd can be obtained at the same time.

[0041] The system can perform single-point, line profile, and area measurements of the thickness and refractive index of transparent samples. Specifically, when measuring line profile thickness, area thickness, and refractive index, the signal only needs to be measured once when the sample is not placed for a short period. Line profile measurement is achieved by controlling the movement of the biaxial electrically controlled stage in the X or Y direction, setting the movement step size and number of movements to measure the thickness and refractive index of the transparent sample's line profile. Area measurement is achieved by setting the movement direction and distance of the biaxial electrically controlled stage, controlling the sample's position within the measurement area, and measuring point by point to achieve measurement of the entire area.

[0042] The dual-axis electrically controlled stage will generate straightness error during movement. The change in angle during the movement will cause the following error in the thickness of the sample to be measured:

[0043]

[0044] In the formula, a1 is the distance from the upper collimator to the upper surface of the sample, a2 is the distance from the lower collimator to the lower surface of the sample, and θ is the tilt angle of the stage relative to the alignment direction of the two collimators. Measurement data shows that θ does not exceed 0.36", a1, and a2 do not exceed 10 cm, and the resulting theoretical error in the thickness of the sample does not exceed 0.18 pm, which is negligible compared to the sample thickness.

[0045] The dual-axis electrically controlled stage will produce straightness error during movement. However, the change in displacement perpendicular to the sample during movement will not cause a fundamental error in the thickness of the sample because the optical path difference calculated from the two interference signals on the upper and lower surfaces of the sample can cancel each other out. This can offset the measurement error caused by the change in displacement perpendicular to the sample during movement.

[0046] This invention proposes a system and method for measuring the thickness and refractive index of transparent samples. The system utilizes a dual-probe coaxial measurement system to measure the optical path difference between the reference and measurement ends, and acquires interference spectral information using a spectrometer. Subsequently, the dual probes measure the optical path difference between the upper and lower surfaces of the sample and the reference end, and interference spectral information is acquired again using a spectrometer. The phase information of the interference spectral signal is obtained using the Fourier transform method, and the optical path difference is calculated using the slope method, ultimately achieving the measurement of the thickness and refractive index of the transparent sample. This measurement system does not require calibration using standard height samples, the measurement method is simple and easy to implement, and the system structure is compact, greatly facilitating the measurement of sample thickness and refractive index.

[0047] Compared with the prior art, the main advantages of the present invention are as follows:

[0048] (1) This invention does not require calibration with standard height samples, and there is no influence of the thickness error of standard height samples on the thickness measurement of the sample to be tested, thus improving the accuracy of the measurement results.

[0049] (2) By utilizing the characteristic of two polarizers placed parallel to each other, the present invention can attenuate the light intensity and reduce the intensity of the coupled beam between the upper and lower collimators at the measurement end, thus solving the problem of the influence of transmitted light intensity on signal acquisition and processing during the measurement process.

[0050] (3) This invention can not only measure the single-point thickness and refractive index of the sample to be tested, but also measure the line profile or region thickness of the sample to be tested by controlling the biaxial electrically controlled stage.

[0051] (4) The present invention uses dual probes for measurement, which effectively offsets the error caused by external vibration or displacement of the biaxial electronically controlled stage in the direction perpendicular to the sample to be measured during the measurement process.

[0052] (5) The sample to be tested in this invention can be a transparent sample or an opaque sample. The measurement steps for the thickness of the opaque sample are the same as those for the transparent sample. Since it is not necessary to measure the optical thickness of the sample itself, the thickness measurement range of the sample is larger than that of the transmission method. It is mainly determined by the resolution of the spectrometer. Different resolution spectrometers can be selected according to the measurement requirements.

[0053] (6) This invention controls the biaxial electrically controlled stage to quickly move it to the positions of the collimators on the upper and lower surfaces of the measuring end, respectively, after measuring the optical path difference between the reference end and the measuring end when there is no sample. This reduces the measurement time, minimizes the impact of system drift over time on the measurement results, and improves measurement efficiency. Furthermore, when measuring the thickness of the sample to be measured in a short time, the optical path difference ΔR between the reference end and the measuring end only needs to be measured once when there is no sample, improving the accuracy of the measurement results and greatly improving measurement efficiency. Attached Figure Description

[0054] Figure 1 This is a structural diagram of a transparent sample thickness and refractive index measurement system according to the present invention;

[0055] Figure 2 This is an optical path diagram of a transparent sample thickness and refractive index measurement system according to the present invention;

[0056] Figure 3a This is a schematic diagram of the angle error during the movement of the dual-axis electrically controlled stage in this invention;

[0057] Figure 3b This is a schematic diagram of the displacement error during the movement of the dual-axis electrically controlled stage in this invention;

[0058] Figure 4a The result is obtained by performing Fourier transforms on the interference signals between the upper surface of the sample and the reference end, the interference signals between the lower surface of the sample and the reference end, and the interference signals between the upper and lower surfaces of the sample.

[0059] Figure 4b The Fourier transform of the interference signals on the upper and lower surfaces of the sample is performed to block the reference signal.

[0060] Figure 4c for Figure 4a Fourier transform and Figure 4b The result of subtracting the Fourier transforms.

[0061] Figure 1 1. SLD light source; 2. Spectrometer; 3. Fiber optic structure; 4. Column;

[0062] First fiber optic attenuator 301, first fiber optic coupler 302, second fiber optic coupler 303, second fiber optic attenuator 304;

[0063] Reference end structure 5; reflector 501, reference end collimator 502 and reference end collimator angle adjustment bracket 503;

[0064] Measurement end structure 6; upper measurement end collimator 601 and angle adjustment frame 602 of upper measurement end collimator, lower measurement end collimator 603 and angle adjustment frame 604 of lower measurement end collimator, XYZ axis displacement stage 605, dual-axis electrically controlled stage 606, first polarizer 607 and second polarizer 608.

[0065] E0: Light emitted by the collimator 502 at the reference end and reflected by the mirror 501 at the reference end;

[0066] E1: When there is no sample, the light coupled between the upper and lower collimators at the measuring end;

[0067] E2: Light emitted by the upper measuring end collimator 601, reflected by the upper surface of the sample to be measured, and received by the upper measuring end collimator 601;

[0068] E3: Light emitted by the lower measuring end collimator 603, reflected by the lower surface of the sample to be measured, and received by the lower measuring end collimator 603;

[0069] E4: Light emitted by the upper measuring end collimator 601, reflected by the lower surface of the sample to be measured, and received by the upper measuring end collimator 601;

[0070] E5: Light emitted by the lower measuring end collimator 603, reflected by the upper surface of the sample to be measured, and received by the lower measuring end collimator 603;

[0071] E6: Light coupled between the upper and lower collimators at the measuring end when placing the sample;

[0072] d: Thickness of the sample to be tested;

[0073] n: Refractive index of the sample to be tested;

[0074] ΔR: Optical path difference between E0 and E1;

[0075] Δa: Optical path difference between E0 and E2;

[0076] Δb: Optical path difference between E0 and E3;

[0077] Δc: Optical path difference between E0 and E4;

[0078] Δd: Optical path difference between E0 and E5;

[0079] a1: Optical path from the upper measuring end collimator 601 to the upper surface of the sample to be measured;

[0080] a1': Optical path length from the upper surface of the sample to the collimator 601 on the upper surface of the measuring end;

[0081] a2: Optical path from collimator 603 on the lower surface of the measuring end to the lower surface of the sample to be measured;

[0082] a2': Optical path length from the lower surface of the sample to the collimator 603 on the lower surface of the measuring end;

[0083] θ: The tilt angle of the sample relative to the alignment direction of the collimators at the upper and lower surface measuring ends, caused by the straightness error during the movement of the dual-axis electrically controlled stage 606. Detailed Implementation

[0084] The present invention will now be described in detail with reference to the accompanying drawings.

[0085] This invention pertains to interferometric measurement within the field of optical measurement, specifically a system and method for measuring the thickness and refractive index of transparent samples. This invention eliminates the need for a standard height sample to measure the thickness and refractive index of the sample, thus removing the influence of errors from the standard height sample on the measurement results and achieving self-calibration. Utilizing dual probes can counteract the effects of external vibrations or changes in the straightness of the stage during movement on the measurement results. This invention occupies a small space, is less affected by the surrounding environment, and simplifies the system adjustment process.

[0086] like Figure 1 As shown, the present invention provides a transparent sample thickness and refractive index measurement system, comprising: an SLD light source 1, a spectrometer 2, an optical fiber structure 3, a column 4, a reference end structure 5, and a measurement end structure 6.

[0087] The optical fiber structure 3 is used to adjust the beam intensity, split the beam, and transmit the beam; the optical fiber structure 3 includes a first optical fiber attenuator 301, a first optical fiber coupler 302, a second optical fiber coupler 303, and a second optical fiber attenuator 304.

[0088] The first fiber optic attenuator 301 is connected to the SLD light source 1 and is used to adjust the intensity of the light source beam.

[0089] The first fiber coupler 302 is connected to the first fiber attenuator 301 and the spectrometer 2 respectively, and is used to split the light and collect interference signals.

[0090] The second fiber coupler 303 is connected to the first fiber coupler 302 and is used for beam splitting at the reference end;

[0091] The second fiber attenuator 304 is connected to the first fiber coupler 302 and is used to adjust the intensity of the beam at the reference end.

[0092] The reference end structure 5 includes: a reflector 501; a reference end collimator 502; and an angle adjustment bracket 503 for the reference end collimator.

[0093] The measuring end structure 6 includes: an upper measuring end collimator 601 and an angle adjustment frame 602 for the upper measuring end collimator; a lower measuring end collimator 603 and an angle adjustment frame 604 for the lower measuring end collimator; an XYZ axis displacement stage 605; a dual-axis electrically controlled stage 606; a first polarizer 607; and a second polarizer 608.

[0094] The XYZ axis displacement stage 605 is connected to the lower measuring end collimator 603 and is used to adjust the XYZ direction of the lower measuring end collimator 603. It is installed on the column 4.

[0095] A dual-axis electrically controlled stage 606 is used for sample placement and coaxial adjustment of the upper measuring end collimator 601 and the lower measuring end collimator 603. The stage has two holes: one for coaxial measurement of the upper measuring end collimator 601 and the lower measuring end collimator 603, and the other for measurement of the sample. The movement between the two holes of the electrically controlled stage is controlled by a controller. The stage is installed between the upper measuring end collimator 601 and the lower measuring end collimator 603 at an appropriate distance. Through electrical control, XY direction displacement can be achieved.

[0096] The first polarizer 607 is installed between the upper measuring end collimator 601 and the dual-axis electrically controlled stage 606 at a suitable distance. The second polarizer 608 is installed between the lower measuring end collimator 603 and the dual-axis electrically controlled stage 606 at a suitable distance. The two polarizers are used together to reduce the intensity of the coupled beam between the upper and lower collimators at the measuring end.

[0097] like Figure 2 As shown in Figure 3, a method for measuring the thickness and refractive index of a transparent sample according to the present invention includes the following steps:

[0098] 1) Adjust the upper measuring end collimator 601 and the lower measuring end collimator 603 to be coaxial, so that the two collimators are respectively aligned with two points on the vertical lines of the upper and lower surfaces of the sample to be tested, so as to realize point-to-point measurement of the upper and lower surfaces of the sample to be tested;

[0099] (1.1) Turn on the SLD light source 1, insert the flat crystal, adjust the angle adjustment bracket 602 of the upper measuring end collimator so that the upper measuring end collimator 601 is perpendicular to the upper surface of the flat crystal. When the light intensity returning from the upper surface of the flat crystal to the upper measuring end collimator 601 reaches the maximum value, it is perpendicular. Adjust the angle adjustment bracket 604 of the lower measuring end collimator so that the lower measuring end collimator 603 is perpendicular to the lower surface of the flat crystal. When the light intensity returning from the lower surface of the flat crystal to the lower measuring end collimator 603 reaches the maximum value, it is perpendicular.

[0100] (1.2) Remove the flat crystal and keep the upper measuring end collimator 601 stationary. Using the upper measuring end collimator 601 as a reference, move the lower measuring end collimator 603 by changing the XY direction of the XYZ axis displacement stage 605 until the light power value received by the spectrometer 2 reaches the maximum. At this time, the upper and lower surface collimators of the measuring end are coaxial.

[0101] (1.3) Steps (1.1) and (1.2) are the initial adjustment steps of the system. After the system is built, it only needs to be adjusted once. In subsequent measurement steps, the upper measuring end collimator 601 and the lower measuring end collimator 603 are kept fixed.

[0102] 2) Acquire interference signals and process the interference signals acquired by spectrometer 2 to obtain the optical path difference ΔR between the measuring end and the reference end;

[0103] (2.1) The acquired interference spectrum signal is the interference signal between the measurement end and the reference end. The acquired spectrum data is subjected to Fourier transform to extract the main frequency. A peak in the frequency domain signal is windowed and filtered to remove background light and noise interference.

[0104] (2.2) Perform inverse Fourier transform to obtain the phase information of the interference spectrum signal;

[0105] (2.3) Since the phase information in the interference spectrum signal is linearly related to the wavenumber, the slope value of the two can be obtained by fitting the linear relationship and calculating the optical path difference ΔR.

[0106] 3) Place the sample to be tested, and control the dual-axis electrically controlled stage 606 to align the upper and lower surface collimators of the measuring end with the upper and lower surfaces of the sample to be tested, respectively. Collect interference signals and process the interference signals collected by the spectrometer 2 to obtain the optical path difference Δa between the upper surface of the sample to be tested and the upper measuring end collimator 601 and the reference end, the optical path difference Δb between the lower surface of the sample to be tested and the lower measuring end collimator 603 and the reference end, the optical path difference Δc between the lower surface of the sample to be tested and the upper measuring end collimator 601 and the reference end, and the optical path difference Δd between the upper surface of the sample to be tested and the lower measuring end collimator 603 and the reference end.

[0107] (3.1) By controlling the dual-axis electrically controlled stage 606, the collimators of the upper and lower surfaces of the measuring end are aligned with the upper and lower surfaces of the sample, respectively.

[0108] (3.2) Because the transmittance of the sample to be measured is much greater than its reflectance, the intensity of the coupled beam between the upper and lower collimators at the measuring end is much greater than the required sample reflection intensity, affecting signal acquisition and processing. According to Malus's law, if the light emitted from the first polarizer 607 passes through the second polarizer 608, the light intensity I after passing through the two polarizers varies with the angle θ between the transmission axes of the two polarizers, i.e.

[0109] I = I0COS 2 θ

[0110] Wherein, I0 represents the transmitted light intensity when the transmission axes of the two polarizers are parallel, at which point the transmitted light intensity is at its maximum; when the transmission axes of the two polarizers are perpendicular, the transmitted light intensity is 0, which is the ideal state to be adjusted in this invention; when the two polarizers rotate relative to each other, the transmitted light intensity changes with the angle between the transmission axes of the two polarizers, so the device with the two polarizers placed vertically parallel can also attenuate the light intensity. Therefore, this invention fixes the first polarizer 607, rotates the second polarizer 608, and adjusts the angle between the transmission axes of the two polarizers to 90°, so that the intensity of the coupled beam between the upper and lower collimators at the measuring end is reduced to negligible levels;

[0111] (3.3) The collected interference spectral signals include the interference signals between the upper surface of the sample and the reference end, the interference signals between the lower surface of the sample and the reference end, and the interference signals between the upper and lower surfaces of the sample. Fourier transform is performed on the collected spectral data.

[0112] (3.4) Block the reference end signal. The collected interference spectrum signal is the interference signal between the upper and lower surfaces of the sample. This part of the signal is an unwanted interference signal. Perform Fourier transform on the collected spectrum data.

[0113] (3.5) Subtract the Fourier transform result obtained in (3.3) from the Fourier transform result obtained in (3.4) to obtain the Fourier transform result of the required interference signal. Window the four peaks in the frequency domain signal and filter to remove background light and noise interference.

[0114] (3.6) Perform inverse Fourier transform to obtain the phase information of the interference spectrum signal;

[0115] (3.7) Since the phase information in the interference spectrum signal is linearly related to the wavenumber, by fitting the linear relationship, the slope values ​​of the two can be obtained, and the optical path difference Δa, Δb, Δc and Δd can be obtained at the same time.

[0116] 4) Calculate the thickness of the sample to be tested. Obtain the refractive index of the sample to be tested

[0117] The embodiments of the present invention have been described in detail above. However, it should be understood that those skilled in the art can make various improvements and modifications to the present invention without departing from the spirit and scope of the invention, and these improvements and modifications should be considered within the scope of protection of the present invention.

Claims

1. A system for measuring the thickness and refractive index of a transparent sample, characterized in that, include: SLD light source (1); Spectrometer (2), the spectrometer (2) is used to acquire interference spectral signals; The optical fiber structure (3) is used to adjust the beam intensity, split the beam and transmit the beam; Columns (4); The reference end structure (5) is mounted on the column (4) and includes a reflector (501), a reference end collimator (502) and an angle adjustment bracket (503) for the reference end collimator. The measuring end structure (6) includes an upper measuring end collimator (601) and an angle adjustment frame (602) for the upper measuring end collimator, a lower measuring end collimator (603) and an angle adjustment frame (604) for the lower measuring end collimator, an XYZ axis displacement stage (605), a dual-axis electrically controlled stage (606), a first polarizer (607), and a second polarizer (608). The XYZ axis displacement stage (605) is connected to the lower measuring end collimator (603) and is used to adjust the XYZ direction of the lower measuring end collimator (603). The XYZ axis displacement stage (605) is mounted on the column (4). The dual-axis electrically controlled stage (606) is used for sample placement and coaxial adjustment of the upper measuring end collimator (601) and the lower measuring end collimator (603). The dual-axis electrically controlled stage (606) has two holes. One hole is used for coaxial measurement of the upper measuring end collimator (601) and the lower measuring end collimator (603), and the other hole is used for measurement of the sample to be tested. The movement between the two holes of the dual-axis electrically controlled stage (606) is controlled by a controller. The dual-axis electrically controlled stage (606) is installed between the upper measuring end collimator (601) and the lower measuring end collimator (603) at an appropriate distance. Through electrical control, displacement in the XY directions can be achieved. The first polarizer (607) is installed between the upper measuring end collimator (601) and the dual-axis electrically controlled stage (606) at a suitable distance, and the second polarizer (608) is installed between the lower measuring end collimator (603) and the dual-axis electrically controlled stage (606) at a suitable distance. The two polarizers are used together to reduce the intensity of the coupled beam between the upper and lower collimators at the measuring end.

2. The transparent sample thickness and refractive index measurement system according to claim 1, characterized in that, The optical fiber structure (3) includes a first optical fiber attenuator (301), a first optical fiber coupler (302), a second optical fiber coupler (303), and a second optical fiber attenuator (304); The first fiber optic attenuator (301) is connected to the SLD light source (1) and is used to adjust the intensity of the light source beam; The first fiber coupler (302) is connected to the first fiber attenuator (301) and the spectrometer (2) respectively, and is used to split the light and collect interference signals; The second fiber coupler (303) is connected to the first fiber coupler (302) and is used for beam splitting at the reference end; The second fiber optic attenuator (304) is connected to the first fiber optic coupler (302) and is used to adjust the intensity of the beam at the reference end.

3. A method for measuring the thickness and refractive index of a transparent sample using a transparent sample thickness and refractive index measurement system according to claim 1 or 2, characterized in that, Includes the following steps: 1) Adjust the upper measuring end collimator (601) and the lower measuring end collimator (603) to be coaxial, so that the two collimators are respectively aligned with two points on the vertical lines of the upper and lower surfaces of the sample to be measured, so as to realize point-to-point measurement of the upper and lower surfaces of the sample to be measured. 2) Acquire interference signals and process the interference signals acquired by the spectrometer (2) to obtain the optical path difference ΔR between the measuring end and the reference end; 3) Place the sample to be tested, and control the dual-axis electrically controlled stage (606) to align the upper and lower surface collimators of the measuring end with the upper and lower surfaces of the sample to be tested, respectively. Collect interference signals and process the interference signals collected by the spectrometer (2) to obtain the optical path difference Δa between the upper surface of the sample to be tested and the upper measuring end collimator (601) and the reference end, the optical path difference Δb between the lower surface of the sample to be tested and the lower measuring end collimator (603) and the reference end, the optical path difference Δc between the lower surface of the sample to be tested and the upper measuring end collimator (601) and the reference end, and the optical path difference Δd between the upper surface of the sample to be tested and the lower measuring end collimator (603) and the reference end. 4) Calculate the thickness of the sample to be tested. Obtain the refractive index of the sample to be tested 4. The method according to claim 3, characterized in that, Step 1) specifically includes the following steps: (1.1) Turn on the SLD light source (1), place the flat crystal, adjust the angle adjustment bracket (602) of the upper measuring end collimator so that the upper measuring end collimator (601) is perpendicular to the upper surface of the flat crystal. When the light intensity returned from the upper surface of the flat crystal to the upper measuring end collimator (601) reaches the maximum value, it is perpendicular. Adjust the angle adjustment bracket (604) of the lower measuring end collimator so that the lower measuring end collimator (603) is perpendicular to the lower surface of the flat crystal. When the light intensity returned from the lower surface of the flat crystal to the lower measuring end collimator (603) reaches the maximum value, it is perpendicular. (1.2) Remove the flat crystal and keep the upper measuring end collimator (601) stationary. Using the upper measuring end collimator (601) as a reference, move the lower measuring end collimator (603) by changing the XY direction of the XYZ axis displacement stage (605) until the optical power value received by the spectrometer (2) reaches the maximum. At this time, the upper and lower surface collimators of the measuring end are coaxial. (1.3) Steps (1.1) and (1.2) are the initial adjustment steps of the system. After the system is built, it only needs to be adjusted once. In subsequent measurement steps, the upper measuring end collimator (601) and the lower measuring end collimator (603) are kept fixed.

5. The method according to claim 3, characterized in that, Step 2) describes a specific method for obtaining the optical path difference ΔR between the measuring end and the reference end. This method involves using Fourier transform to transform the signal from the time domain to the frequency domain, extracting the phase information of the interference spectrum signal, and then using the slope method to calculate the optical path difference.

6. The method according to claim 5, characterized in that, Step 2) The specific steps include: (2.1) The acquired interference spectrum signal is the interference signal between the measurement end and the reference end. The acquired spectrum data is subjected to Fourier transform to extract the main frequency. A peak in the frequency domain signal is windowed and filtered to remove background light and noise interference. (2.2) Perform inverse Fourier transform to obtain the phase information of the interference spectrum signal; (2.3) Since the phase information in the interference spectrum signal is linearly related to the wave number, the slope value of the two can be obtained by fitting the linear relationship, and the optical path difference ΔR can be obtained.

7. The method according to claim 3, characterized in that, Step 3) specifically includes the following steps: (3.1) By controlling the dual-axis electrically controlled stage (606), the collimators of the upper and lower surfaces of the measuring end are aligned with the upper and lower surfaces of the sample, respectively. (3.2) Fix the first polarizer (607), rotate the second polarizer (608), and adjust the angle between the transmission axes of the two polarizers to 90° so that the intensity of the coupled beam between the upper and lower collimators at the measuring end is reduced to negligible. (3.3) The collected interference spectral signals include the interference signals between the upper surface of the sample and the reference end, the interference signals between the lower surface of the sample and the reference end, and the interference signals between the upper and lower surfaces of the sample. Fourier transform is performed on the collected spectral data. (3.4) Block the reference end signal. The collected interference spectrum signal is the interference signal between the upper and lower surfaces of the sample. This part of the signal is an unwanted interference signal. Perform Fourier transform on the collected spectrum data. (3.5) Subtract the Fourier transform result obtained in (3.3) from the Fourier transform result obtained in (3.4) to obtain the Fourier transform result of the required interference signal. Window the four peaks in the frequency domain signal and filter to remove background light and noise interference. (3.6) Perform inverse Fourier transform to obtain the phase information of the interference spectrum signal; (3.7) The phase information in the interference spectrum signal is linearly related to the wavenumber. By fitting the linear relationship, the slope values ​​of the two are obtained, and the optical path difference Δa, Δb, Δc and Δd are obtained at the same time.

Images