Measuring device and measuring method for phase retardation of micro-nano-sized wave plate

Abstract

The invention provides a device and a method for measuring the phase retardation of a micro-nano-sized wave plate, which are used for solving the problems that an existing method for measuring the phase retardation of the wave plate cannot characterize and measure the wave plate in the micro-nano size, optical detection equipment is expensive, an overall experimental measurement scheme is complicated to operate, the system universality is poor, and the measurement cost is high. And the instability of the measurement result of the measurement scheme for deducing the phase retardation of the wave plate based on the Mueller matrix is relatively high. Light emitted by the tunable light source is modulated by the integrating sphere to form unpolarized light, the unpolarized light is shaped into a planar light beam through the shaping reflection unit, and the planar light beam is normally incident to the first linear polarizer so as to emit completely linearly polarized light with different polarization angles; meanwhile, the second linear polarizer is arranged between the microscope objective and the sleeve lens, interference of factors such as light intensity jitter, system transmittance and wave plate rotation positioning precision on a measurement result is reduced by adjusting the deflection angle of the second linear polarizer, and the measurement precision is effectively guaranteed.

Description

Technical Field

[0001] The present invention relates to the measurement of the phase retardation of a wave plate, and particularly to a device and method for measuring the phase retardation of a wave plate with micro-nano dimensions. Background Art

[0002] A broadband full Stokes vector detection chip is an optoelectronic detection device that can measure the snapshot full polarization information of broadband incident light and has broad application prospects in fields such as industrial inspection, materials science, and biomedicine. Among them, the wave plate, as the core component of the broadband full Stokes vector detection chip, its performance determines the accuracy and reliability of the polarization measurement results. Therefore, high-precision measurement of the phase retardation of the wave plate is a key link to ensure the performance of the broadband full Stokes vector detection chip and is crucial for the polarization information correction of the subsequent detection system and the calibration of the full vector inversion parameters.

[0003] The Chinese patent with the publication number CN105628343A discloses a wave plate detection device and method, which calculates the optical parameters of the wave plate using the parameter results measured by an ellipsometer. The Chinese patent with the publication number CN110631806A discloses a device and method for quickly measuring the phase retardation of a wide-band wave plate. This method measures the maximum and minimum values of the output light intensity by rotating the angle of the wave plate, and then substitutes them into the Mueller matrix to deduce the phase retardation of the wave plate. The Chinese patent with the publication number CN114720095A discloses a device and method for measuring the phase retardation and fast axis direction of a wave plate, which calculates the phase retardation and fast axis direction of the wave plate by recording the rotation angle and direction of the Laguerre-Gaussian beam interference pattern. However, the above schemes are only applicable to wave plates with macroscopic dimensions and cannot realize the characterization and measurement of wave plates with micro-nano dimensions. At the same time, the above schemes all include expensive optical detection equipment, and the measurement results depend on the debugging and stability of the equipment, making the overall experimental measurement scheme complex to operate and the system versatility poor. In addition, the above measurement scheme for deducing the phase retardation of the wave plate based on the Mueller matrix uses the method of rotating the wave plate and only collects the light intensity values under two incident states for calculation, without considering the influence of the selection of the incident polarization state on the error of the entire measurement model, resulting in a relatively high instability of the measurement results. Summary of the Invention

[0004] The purpose of the present invention is to provide a device and method for measuring the phase retardation of a wave plate with micro-nano dimensions in view of the technical problems existing in the existing methods for measuring the phase retardation of a wave plate, such as the inability to characterize and measure wave plates with micro-nano dimensions, expensive optical detection equipment, complex operation of the overall experimental measurement scheme, poor system versatility, and relatively high instability of the measurement results of the measurement scheme for deducing the phase retardation of the wave plate based on the Mueller matrix.

[0005] To achieve the above object, the technical solution provided by the present invention is as follows: A measuring device for the phase retardation of a micro-nano sized wave plate, characterized in that it includes a tunable light source, an integrating sphere, a shaping reflection unit, a first linear polarizer, a microscope objective, a second linear polarizer, a sleeve lens, a detector, and a computer; The light inlet of the integrating sphere is located on the light path of the light emitted by the tunable light source, and is used to modulate the light emitted by the tunable light source, so that it is converted into unpolarized light with uniform intensity and then emitted from the light outlet of the integrating sphere; The shaping reflection unit is located on the light path of the emitted unpolarized light, and is used to shape the unpolarized light into a plane light beam and adjust the direction of the plane light beam to form illumination light; The first linear polarizer is located on the light path of the illumination light, and the illumination light is converted into completely linearly polarized light with different polarization angles by rotating the first linear polarizer at different angles; The microscope objective, the sleeve lens, and the detector are coaxially arranged in sequence along the light path transmission direction of the completely linearly polarized light. The sleeve lens is located within the working distance behind the microscope objective, and the detector is located at the focal position of the sleeve lens; the wave plate to be measured is coaxially arranged between the first linear polarizer and the microscope objective, and the completely linearly polarized light passing through the first linear polarizer is used to illuminate the wave plate to be measured to form an optical signal loaded with the information of the wave plate to be measured; the microscope objective and the sleeve lens are used to collect the optical signal loaded with the information of the wave plate to be measured and image it on the detector; The second linear polarizer is used to be arranged between the microscope objective and the sleeve lens to normalize the optical signal loaded with the information of the wave plate to be measured amplified by the microscope objective into the same linear polarization state; The input end of the computer is connected to the output end of the detector, and is used to store the image obtained by the detector and determine the phase retardation of the wave plate to be measured according to the image obtained by the detector.

[0006] Furthermore, it further includes a displacement clamping device for clamping the wave plate to be measured; The displacement clamping device is a six-dimensional displacement device, and is used to realize the displacement of the wave plate to be measured in three directions, as well as the adjustment of the rotation angle, tilt angle, and pitch angle.

[0007] The shaping reflection unit includes a shaping module and a reflection module; The shaping module includes a focusing lens, a pinhole filter, and an off-axis mirror; the reflection module includes a first mirror and a second mirror; The focusing lens is located on the light path of the unpolarized light emitted from the light outlet of the integrating sphere, and is used to focus the unpolarized light; the pinhole filter is located at the focal position of the focusing lens, and is used to filter out the high-frequency noise in the unpolarized light; the off-axis mirror is located on the light path of the filtered unpolarized light, and is used to shape the filtered unpolarized light into a plane light beam without chromatic aberration; The focal plane of the focusing lens coincides with the focal plane of the off-axis mirror. The focus of the focusing lens, the pinhole of the pinhole filter, and the reflection focus of the off-axis mirror are collinear and parallel to the optical axis of the unpolarized light. The numerical aperture NA of the focusing lens and the working angle Ψ of the off-axis mirror satisfy NA ≤ sin(Ψ). The first mirror is located on the optical path of the plane light beam, and the second mirror is located on the optical path of the plane light beam reflected by the first mirror, for adjusting the direction of the plane light beam.

[0008] Furthermore, the extinction ratios of the first linear polarizer and the second linear polarizer are both greater than 5000:1.

[0009] Furthermore, the first linear polarizer and the waveplate under test are respectively controlled by an electric controller to rotate in a set step size.

[0010] Furthermore, the microscope objective is an infinity-corrected objective. The relationship between the magnification β after the microscope objective is paired with the tube lens, the length L of the waveplate under test, the width W of the waveplate under test, and the pixel size p of the detector satisfies the following formula: βL / p > 200; βW / p > 200.

[0011] In addition, the present invention also provides a method for measuring the phase retardation of a micro-nano scale waveplate. Based on the above-mentioned measuring device for the phase retardation of a micro-nano scale waveplate, the special features are as follows. It includes the following steps: Step 1: Place the light inlet of the integrating sphere on the optical path of the light emitted by the tunable light source, and place a shaping reflection unit and a first linear polarizer behind the integrating sphere, so that the light emitted by the shaping reflection unit is incident perpendicularly on the surface of the first linear polarizer. Then, sequentially place a microscope objective, a tube lens, and a detector, and establish a communication connection between the detector and the computer. Step 2: On the basis of the optical structure built in Step 1, fix the angle between the transmission axis of the first linear polarizer and the horizontal direction at 0°, and use 0° as the initial angle. Control the first linear polarizer to rotate in a set step size, respectively record the images obtained by the detector at the corresponding rotation angles, store them in the computer, and record them as observation group A. Step 3: Keep the optical structure built in Step 1 unchanged. Coaxially set the waveplate under test between the first linear polarizer and the microscope objective. Fix the angle between the transmission axis of the first linear polarizer and the horizontal direction at 0°, and use 0° as the initial angle. Control the first linear polarizer to rotate in a set step size, respectively record the images obtained by the detector at the corresponding rotation angles, store them in the computer, and record them as observation group B. At the same time, determine the imaging area of the current waveplate under test on the detector, and record it as imaging area B. Step 4, while keeping the optical structure established in Step 3 unchanged, coaxially set the second linear polarizer between the microscope objective and the sleeve lens; adjust the transmission axis of the second linear polarizer to an angle with the horizontal direction , , or , fix the angle between the transmission axis of the first linear polarizer and the horizontal direction at 0°, control the waveplate under test to rotate according to the set rotation step size, and the set rotation step size corresponding to the waveplate under test is the same as the set rotation step size corresponding to the first linear polarizer; respectively record the images obtained by the detector at the corresponding rotation angles, store them in the computer, and denote them as Observation Group C; at the same time, determine the imaging area of the current waveplate under test on the detector, and denote it as Imaging Area C; Step 5, use the imaging area B determined in Step 3 as the integration area for the images in Observation Group A, and integrate all the images in Observation Group A within the integration area to obtain the first integral absolute values at different rotation angles; integrate all the images in Observation Group B within Imaging Area B to obtain the second integral absolute values at different rotation angles; integrate all the images in Imaging Area C of Observation Group C to obtain the third integral absolute values at different rotation angles; Step 6, calculate the phase retardation of the waveplate under test according to the first integral absolute value, the second integral absolute value, and the third integral absolute value corresponding to each rotation angle.

[0012] Further, Step 6 is specifically as follows: Step 6.1, solve the ratio of the transmission rates of the fast and slow axes of the waveplate under test at different rotation angles through the following formula :

[0013] where is the first integral absolute value at different rotation angles, is the second integral absolute value at different rotation angles; Step 6.2, solve the phase retardation of the waveplate under test at different rotation angles through the following formula :

[0014] where is the third integral absolute value at different rotation angles, , is the initial angle between the fast axis of the waveplate under test and the horizontal direction, i is the rotation step number of the waveplate under test at the corresponding rotation angle, is the rotation step size of the waveplate under test; Step 6.3, use the least squares method for the phase retardation of the waveplate under test obtained at different rotation angles Optimize and fit to obtain the phase delay of the wave plate to be measured 。

[0015] The beneficial effects of the present invention compared with the prior art are as follows: 1. A measuring device for the phase delay of a micro-nano sized wave plate provided by the present invention uses an integrating sphere to modulate the light emitted by a tunable light source to form unpolarized light, and then shapes the unpolarized light into a plane light beam through a shaping reflection unit and makes it incident perpendicularly to the first linear polarizer to emit completely linearly polarized light with different polarization angles to illuminate the wave plate to be measured. Then, a microscopic system formed by a microscopic objective lens and a sleeve lens collects the optical signal loaded with the information of the wave plate to be measured and images it on a detector, thereby obtaining the phase delay of the wave plate to be measured; the microscopic system formed by the microscopic objective lens and the sleeve lens enables the measuring device to be compatible with the measurement of both micro-nano sized wave plates and macro-sized wave plates, and can detect wave plates with different sizes and polarization characteristic parameters, making the measuring device more versatile; a second linear polarizer is further provided between the microscopic objective lens and the sleeve lens of the present invention, which is used to adjust the analyzer angle of the second linear polarizer to minimize the interference of factors such as light intensity jitter, system transmittance, and wave plate rotation positioning accuracy on the measurement result, and the device has high stability, effectively ensuring the measurement accuracy.

[0016] 2. A measuring device for the phase delay of a micro-nano sized wave plate provided by the present invention does not include expensive and complex special optoelectronic equipment, the system is easy to operate, and data acquisition and processing are intuitive. It not only simplifies the experimental operation process, but also greatly reduces the measurement cost, has strong versatility and scalability, and can be flexibly applied to various different measurement requirements and environments.

[0017] 3. A measuring method for the phase delay of a micro-nano sized wave plate provided by the present invention regards the wave plate to be measured and the measuring device as a complete system, uses the Mueller matrix and Stokes vector to parameterize and model its various polarization optical indexes to form a Mueller-Stokes polarization modulation model, and by collecting the light intensity information of the wave plate to be measured under different polarization modulation characteristics multiple times and substituting them into the system Mueller-Stokes polarization modulation model respectively to calculate the phase delay under multiple polarization modulation characteristics (at different rotation angles), and then using the least squares method for optimization and fitting to obtain the phase delay of the wave plate to be measured, which can effectively suppress the inherent errors existing in the Mueller-Stokes polarization modulation model, and the operation is simple and the data processing is easy. Brief Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of an embodiment of a measuring device for the phase delay of a micro-nano sized wave plate of the present invention; Figure 2Schematic diagram of the variation of the device condition number under different analyzer angles and rotation steps when the starting angle of the wave plate to be measured is in the range of [-90°, 90°] in an embodiment of the measuring device for the phase retardation of a micro-nano sized wave plate according to the present invention; Figure 3 Schematic flow chart of a method for measuring the phase retardation of a micro-nano sized wave plate according to the present invention; Figure 4 Schematic diagram of the principle structure of step 2 in a method for measuring the phase retardation of a micro-nano sized wave plate according to the present invention; Figure 5 Schematic diagram of the principle structure of step 3 in a method for measuring the phase retardation of a micro-nano sized wave plate according to the present invention; Figure 6 Schematic diagram of the principle structure of step 4 in a method for measuring the phase retardation of a micro-nano sized wave plate according to the present invention; Figure 7 Schematic diagram of the curve between the rotation angle of the wave plate to be measured and the phase retardation in an embodiment of the present invention; Figure 8 Schematic diagram of the fitting result of the phase retardation of the wave plate to be measured obtained by using the method for measuring the phase retardation of a micro-nano sized wave plate according to the present invention.

[0019] The specific reference numerals are as follows: 1 - Tunable light source; 2 - Integrating sphere; 3 - Focusing lens; 4 - Pinhole filter; 5 - Off-axis mirror; 6 - First mirror; 7 - Second mirror; 8 - First linear polarizer; 9 - Wave plate to be measured; 10 - Displacement clamping device; 11 - Microscope objective; 12 - Second linear polarizer; 13 - Sleeve lens; 14 - Detector; 15 - Computer. Specific embodiments

[0020] To make the advantages and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] As Figure 1 shown, a measuring device for the phase retardation of a micro-nano sized wave plate includes a tunable light source 1, an integrating sphere 2, a focusing lens 3, a pinhole filter 4, an off-axis mirror 5, a first mirror 6, a second mirror 7, a first linear polarizer 8, a microscope objective 11, a second linear polarizer 12, a sleeve lens 13, a detector 14 and a computer 15.

[0022] The tunable light source 1 is used to provide a light source. The light input port of the integrating sphere 2 is located on the light output path of the tunable light source 1 and is used to modulate the light emitted by the tunable light source 1 so that it is converted into unbiased light with uniform intensity, that is, converted into completely unpolarized light, which is convenient for subsequent representation using Stokes vectors. Preferably, in this embodiment, the light output port of the tunable light source 1 is connected to the light input port of the integrating sphere 2 through an optical fiber to achieve light transmission. The light emitted by the tunable light source 1 is converted into unbiased light with uniform intensity in the integrating sphere 2 and then emitted from the light output port of the integrating sphere 2 to the subsequent optical path.

[0023] The focusing lens 3, the pinhole filter 4, and the off-axis mirror 5 form a shaping module, which is used to shape the unbiased light emitted from the light output port of the integrating sphere 2. In other embodiments of the present invention, other forms of shaping modules can also be used for beam shaping. Specifically, the focusing lens 3 is located on the optical path of the unbiased light emitted from the light output port of the integrating sphere 2 and is used to focus the unbiased light; the pinhole filter 4 is located at the focal position of the focusing lens 3 and is used to filter out high-frequency noise in the unbiased light; the off-axis mirror 5 is located on the optical path of the filtered unbiased light and is used to shape the filtered unbiased light into a plane beam without chromatic aberration.

[0024] In this embodiment, the prerequisite for the focusing lens 3, the pinhole filter 4, and the off-axis mirror 5 to form a shaping module is that the focal plane of the focusing lens 3 coincides with the focal plane of the off-axis mirror 5, and the focus of the focusing lens 3, the pinhole of the pinhole filter 4, and the reflection focus of the off-axis mirror 5 are collinear and parallel to the optical axis of the unbiased light. The numerical aperture NA of the focusing lens 3 and the working angle Ψ of the off-axis mirror 5 need to satisfy NA ≤ sin(Ψ). By restricting the relative positions among the focusing lens 3, the off-axis mirror 5, and the pinhole filter 4, the shaping accuracy of the unbiased light can be improved, and thus the measurement accuracy of the phase delay amount can be improved.

[0025] The first mirror 6 and the second mirror 7 are used to adjust the direction of the plane beam to facilitate the layout of the subsequent optical path. Specifically, the first mirror 6 is located on the optical path of the plane beam, and the second mirror 7 is located on the optical path of the plane beam reflected by the first mirror 6 and is used to adjust the direction of the plane beam to form illumination light.

[0026] The first linear polarizer 8 is located on the optical path of the illumination light, and the illumination light is converted into completely linearly polarized light with different polarization angles by rotating the first linear polarizer 8 at different angles. Preferably, in this embodiment, the rotation of the first linear polarizer 8 is controlled by an externally provided electronic controller according to the rotation step, and the rotation step of the first linear polarizer 8 needs to satisfy: .

[0027] The microscopic objective lens 11, the sleeve lens 13, and the detector 14 are coaxially arranged in sequence along the optical path transmission direction of the completely linearly polarized light. The sleeve lens 13 is located within the working distance behind the microscopic objective lens 11, and the detector 14 is located at the focal position of the sleeve lens 13. The waveplate 9 to be measured is coaxially arranged between the first linear polarizer 8 and the microscopic objective lens 11, and is clamped and fixed by the displacement clamping device 10. The displacement clamping device 10 is a six-dimensional displacement device. Defining the optical axis direction of the completely linearly polarized light as the X direction, the direction in the same horizontal plane as the optical axis direction of the completely linearly polarized light and perpendicular to the optical axis of the completely linearly polarized light as the Y direction, and the direction perpendicular to the plane where the X direction and the Y direction are located as the Z direction, the displacement clamping device 10 can drive the waveplate 9 to be measured to achieve displacements in the X direction, Y direction, and Z direction. At the same time, the displacement clamping device 10 can also adjust the rotation angle, tilt angle, and pitch angle of the waveplate 9 to be measured. In addition, the waveplate 9 to be measured needs to rotate during the test. In this embodiment, the rotation of the waveplate 9 to be measured is controlled by an externally provided electronic controller according to the rotation step size. The rotation step size shall satisfy: .

[0028] The completely linearly polarized light passing through the first linear polarizer 8 is used to illuminate the waveplate 9 to be measured, forming an optical signal loaded with the information of the waveplate 9 to be measured. The microscopic objective lens 11 and the sleeve lens 13 collect the optical signal loaded with the information of the waveplate 9 to be measured and image it on the detector 14, that is, the detector 14 obtains the light intensity information of the waveplate 9 to be measured. In this embodiment, the microscopic objective lens 11 is an infinity-corrected objective lens, and the detector 14 is a traditional detection device such as a CMOS camera; preferably, the relationship between the magnification β after the microscopic objective lens 11 is matched with the sleeve lens 13, the length L of the waveplate 9 to be measured, the width W of the waveplate 9 to be measured, and the pixel size p of the detector 14 satisfies: βL / p > 200, βW / p > 200. Through the above relationship limitation, the microscopic performance of the microscopic system composed of the microscopic objective lens 11 and the sleeve lens 13 can be guaranteed, and not only the phase retardation amount of the waveplate with macroscopic size can be measured, but also the phase retardation amount of the waveplate with micro-nano size can be well measured.

[0029] The second linear polarizer 12 is used to be coaxially arranged between the microscopic objective lens 11 and the sleeve lens 13 to normalize the optical signal loaded with the information of the waveplate 9 to be measured, which is magnified by the microscopic objective lens 11, into the same linear polarization state. When the second linear polarizer 12 is set, the included angle between its transmission axis and the horizontal direction needs to be fixed at an angle for polarization analysis. Denote this included angle as the polarization analysis angle , then the polarization analysis angle shall satisfy: , or .

[0030] In the present invention, the wave plate 9 to be measured and the second linear polarizer 12 are preferably arranged in a quick-release structure, which enables the wave plate 9 to be measured and the second linear polarizer 12 to be quickly arranged in the optical path structure and can also be quickly removed without affecting other optical path structures, facilitating the implementation of subsequent measurements.

[0031] The working bandwidths of the first linear polarizer 8 and the second linear polarizer 12 should be as wide as possible to cover the working bands of different wave plates and achieve the measurement of the phase delay amounts of wave plates with different bandwidths in all working bands. At the same time, the corresponding wavelength ranges of the tunable light source 1, the integrating sphere 2, and the detector 14 also need to be as large as possible to cover the working bands of different wave plates. Preferably, the extinction ratios of the first linear polarizer 8 and the second linear polarizer 12 are both greater than 5000:1. For example, the extinction ratios are 6000:1, 7000:1, etc. A larger extinction ratio can improve the measurement accuracy of the phase delay amount.

[0032] The input end of the computer 15 is connected to the output end of the detector 14, which is used to store the light intensity information of the wave plate 9 to be measured obtained by the detector 14 and determine the phase delay amount of the wave plate 9 to be measured based on the light intensity information of the wave plate 9 to be measured obtained by the detector 14.

[0033] Regarding the wave plate 9 to be measured and the measuring device for the phase delay amount of the micro-nano-sized wave plate (hereinafter referred to as the measuring device) as a complete system, the Mueller matrix and Stokes vector are used to parametrically model its various polarization optical indexes to form a Mueller-Stokes polarization modulation model, and the phase delay amount of the wave plate 9 to be measured is obtained by inverse calculation through collecting the light intensity information of the wave plate 9 to be measured under different polarization modulations multiple times.

[0034] According to the optical path structure of the above-mentioned measuring device, the light modulated by the integrating sphere 2 is unpolarized light, so the Stokes vector of the unpolarized light at the corresponding wavelength is: (1) where , , , are the four values corresponding to the Stokes vector .

[0035] In addition, since the extinction ratios of the first linear polarizer 8 and the second linear polarizer 12 are both greater than 5000:1 and can be regarded as ideal polarizers, the Mueller matrices of the first linear polarizer 8 and the second linear polarizer 12 can be expressed as: (2) where j takes 1 or 2, is the Mueller matrix of the first linear polarizer 8, is the initial angle between the transmission axis of the first linear polarizer 8 and the horizontal direction, is the Mueller matrix of the second linear polarizer 12, is the initial angle between the transmission axis of the second linear polarizer 12 and the horizontal direction. According to the optical path structure of the measuring device, can be fixed.

[0036] Let the phase retardation of the waveplate 9 to be measured be , the angle between the fast axis of the waveplate 9 to be measured and the horizontal direction be , the transmittance of the fast axis of the waveplate 9 to be measured be , the ratio of the transmittances of the fast and slow axes of the waveplate 9 to be measured be , then the Mueller matrix of the waveplate 9 to be measured can be expressed as: (3) According to the positional relationship of each optical element and the Mueller matrix of the waveplate 9 to be measured, the Stokes vector of the light intensity of the waveplate 9 to be measured detected by the detector 14 at the corresponding wavelength can be expressed as: (4) where, , , , are the four values corresponding to the Stokes vector .

[0037] For the convenience of analyzing the noise influence of the measuring device, it is assumed that the transmittances of the fast axis and the slow axis of the waveplate 9 to be measured are both 1, that is, the ratio of the transmittances of its fast and slow axes is also 1, and its ideal Mueller matrix is denoted as . Since the detector 14 can only detect the light intensity, then: (5) where, is the light intensity of the emitted light of the tunable light source 1, is the light intensity of the waveplate 9 to be measured detected by the detector 14, is the transmittance of the entire measuring device, is the initial angle between the fast axis of the waveplate 9 to be measured and the horizontal direction, is the rotation step of the waveplate 9 to be measured.

[0038] Substitute Eqs. (2) and (3) into Eq. (5) and simplify and expand to obtain: (6) where, is an n×1 column vector, and each element in the column vector corresponds to the light intensity value obtained by each detection; is an n×2 transmission matrix, n is the total number of rotation steps of the waveplate 9 to be measured, , when is a decimal, round down.

[0039] .

[0040] As can be seen from Equation (6), the light intensity of the waveplate 9 to be measured detected by the detector 14 and the cosine of the phase delay of the waveplate 9 to be measured constitute a linear system. To fully reduce the random error of the measurement device, it is necessary to determine the appropriate polarization angle of the second polarizer 12 and the rotation step of the waveplate 9 to be measured during the experimental operation, so that the condition number of the transmission matrix G is as small as possible.

[0041] Figure 2 is a schematic diagram of the change in the condition number of the device of the waveplate 9 to be measured in the present invention embodiment with the starting angle in the range of [-90°, 90°] at different polarization angles and rotation steps . It can be seen that when the polarization angle is ±45°, and the rotation step of the waveplate 9 to be measured is less than 20°, the condition number of the measurement system is small and relatively stable, that is, the accuracy requirement for the repeated positioning of the rotation angle of each optical element is not high, which is beneficial to fully reducing the interference of factors such as light intensity jitter, system transmittance, and waveplate rotation positioning accuracy in the Mueller-Stokes system on the measurement result, and improving the measurement accuracy and stability. Therefore, in this embodiment, the polarization angle is taken as 45°, and the rotation step of the waveplate 9 to be measured is taken as 10°.

[0042] Based on the above principle, a method for measuring the phase delay of a micro-nano scale waveplate of the present invention, as shown in Figure 3 , specifically includes the following steps: Step 1: First, connect and fix the light output port of the tunable light source 1 to the light input port of the integrating sphere 2. Then, sequentially place a focusing lens 3, a pinhole filter 4, and an off-axis mirror 5 behind the integrating sphere 2. When placing them, adjust the focal point of the focusing lens 3, the pinhole of the pinhole filter 4, and the reflection focal point of the off-axis mirror 5 to the same height and collinear, and fix the pinhole filter 4 at the focal point position of the focusing lens 3. Then, turn on the light source and move the spatial position of the off-axis mirror 5 until the light reflected by the off-axis mirror 5 is a plane light beam, and then fix the spatial position of the off-axis mirror 5. Next, sequentially place a first mirror 6, a second mirror 7, and a first linear polarizer 8, so that the centers of the optical elements are at the same height. Adjust the first mirror 6 and the second mirror 7 so that the light passing through the second mirror 7 is normally incident on the surface of the first linear polarizer 8. Finally, sequentially place a microscope objective 11, a sleeve lens 13, and a detector 14, and establish a communication connection between the detector 14 and the computer 15. Among them, the sleeve lens 13 is placed within the working distance behind the microscope objective 11, and the detector 14 is located at the focal point position of the sleeve lens 13. At this time, except for the waveplate under test 9 and the second linear polarizer 12, the rest of the optical elements of the measuring device are built.

[0043] Step 2: As Figure 4 shown, on the basis of the optical structure built in Step 1, that is, when the waveplate under test 9 and the second linear polarizer 12 are not set in the measuring device, fix the initial angle between the transmission axis of the first linear polarizer 8 and the horizontal direction at 0°, and control the first linear polarizer 8 to rotate according to the rotation step = 10°, so that the angle between the transmission axis of the first linear polarizer 8 and the horizontal direction changes steadily. Respectively record the images obtained by the detector 14 at different angles , and store them in the computer 15, which is recorded as the observation group A. At this time, the Stokes vector of the detection light corresponding to the observation group A at the corresponding wavelength can be expressed as: (7) (8) Among them, , , , are the four values corresponding to the Stokes vector .

[0044] Step 3: As Figure 5As shown in the figure, while keeping the optical structure established in Step 1 unchanged, after clamping the waveplate 9 to be measured on the displacement clamping device 10, it is placed between the first linear polarizer 8 and the microscope objective 11. At this time, the displacement clamping device 10 is adjusted respectively along the X direction, Y direction, and Z direction, so that the waveplate 9 to be measured is at the working distance of the microscope objective 11, and at the same time, the waveplate 9 to be measured corresponds to the objective center position of the microscope objective 11, that is, a clear image of the waveplate 9 to be measured can be obtained on the detector 14. In addition, it is also necessary to adjust the rotation angle, tilt angle, and pitch angle of the waveplate 9 to be measured so that the light passing through the first linear polarizer 8 is incident perpendicularly to the surface of the waveplate 9 to be measured.

[0045] After the waveplate 9 to be measured is placed, when the second linear polarizer 12 is not set in the measuring device, the initial angle between the transmission axis of the first linear polarizer 8 and the horizontal direction is fixed at 0°, and the first linear polarizer 8 is controlled by the electric controller to rotate according to the rotation step = 10°, so that the angle between the transmission axis of the first linear polarizer 8 and the horizontal direction changes steadily. The images obtained by the detector 14 at different angles are respectively recorded and stored in the computer 15, and are denoted as the observation group B. At this time, the Stokes vector of the detection light corresponding to the observation group B at the corresponding wavelength can be expressed as: (9) (10) Among them, , , , are the four values corresponding to the Stokes vector , is the phase retardation amount of the waveplate 9 to be measured, is the angle between the fast axis of the waveplate 9 to be measured and the horizontal direction, is the transmittance of the fast axis of the waveplate 9 to be measured, is the ratio of the transmittances of the fast and slow axes of the waveplate 9 to be measured.

[0046] At the same time, determine the imaging area of the current waveplate 9 to be measured on the detector 14, and denote it as the imaging area B.

[0047] Step 4, as Figure 6 shown, while keeping the optical structure established in Step 2 unchanged, the second linear polarizer 12 is coaxially set between the microscope objective 11 and the sleeve lens 13. When the waveplate 9 to be measured and the second linear polarizer 12 are set in the measuring device, the angle between the transmission axis of the second linear polarizer 12 and the horizontal direction is fixed at 45°, and the angle between the transmission axis of the first linear polarizer 8 and the horizontal direction is fixed at 0°. The waveplate 9 to be measured is controlled by the electric controller to rotate according to the rotation step Rotate by = 10° so that the included angle between the fast axis of the wave plate 9 to be measured and the horizontal direction changes steadily. Record the images obtained by the detector 14 at different included angles , store them in the computer 15, and denote them as the observation group C. At this time, the Stokes vector of the detection light corresponding to the observation group C at the corresponding wavelength can be expressed as: (11) (12) where , , , , , , are the four values corresponding to the Stokes vector .

[0048] , can be substituted into Equation (2) and solved according to formula (3).

[0049] At the same time, determine the imaging area of the wave plate 9 to be measured on the detector 14, denoted as the imaging area C.

[0050] It should be noted that there is no fixed order between the acquisition operations of the observation groups A, B, and C in the present invention.

[0051] Step 5, obtain the phase retardation amount of the wave plate 9 to be measured.

[0052] In the images of the observation group A, since the wave plate 9 to be measured has not been set in the measurement device, the imaging area of the wave plate 9 to be measured on the detector 14 cannot be determined, so the images in the observation group A cannot be integrated. Therefore, in the present invention, after setting the wave plate 9 in step 3, the imaging area B is used as the integration area of the images in the observation group A. Then, integrate all the images in the integration area in the observation group A to obtain the first integrated absolute value at different rotation angles .

[0053] At the same time, integrate all the images in the imaging area B in the observation group B to obtain the second integrated absolute value at different rotation angles ; integrate all the images in the imaging area C in the observation group C to obtain the third integrated absolute value at different rotation angles .

[0054] To facilitate the analysis of the noise influence of the measurement device, assume that the transmittance of the fast axis and the slow axis of the wave plate 9 to be measured are both 1, but the accuracy of the phase retardation amount calculated in this way is relatively low. And the first integrated absolute value at different rotation angles obtained by integrating the observation group A in the present invention​​​​​​​​​​​​​​​​​​​​​​​ and the second integral absolute value at different rotation angles obtained by integrating with the observation group B , first determine the ratio of the transmission rates of the fast and slow axes of the waveplate 9 to be measured at different rotation angles more accurately , and then based on the ratio of the transmission rates of the fast and slow axes of the waveplate 9 to be measured , and the corresponding first integral absolute value and the third integral absolute value jointly determine the phase delay amount of the waveplate 9 to be measured at different rotation angles , effectively improving the measurement accuracy of the phase delay amount of the waveplate to be measured.

[0055] Specifically, since the Stokes vector is the result after normalization, therefore , so the ratio of the transmission rates of the fast and slow axes of the waveplate (9) to be measured at different rotation angles can be solved respectively by the following formula : (13) Since , therefore there is: (14) Substitute the first integral absolute value corresponding to each rotation angle , the third integral absolute value and the ratio of the transmission rates of the fast and slow axes of the waveplate 9 to be measured into formula (14) respectively, and we can get:

[0056] Among them, , is the initial angle between the fast axis of the waveplate 9 to be measured and the horizontal direction, i is the rotation step of the waveplate 9 to be measured at the corresponding rotation angle, is the rotation step size of the waveplate 9 to be measured.

[0057] Finally, use the least squares method to fit the phase delay amount of the waveplate 9 to be measured obtained at different rotation angles, and obtain the phase delay amount of the waveplate 9 to be measured.

[0058] When the waveplate 9 to be measured is a bandwidth waveplate, change the wavelength of the light emitted by the tunable light source 1, and perform measurements according to the content of steps 2 to 5, so as to obtain the phase delay amount of the waveplate 9 to be measured under different wavelength irradiations.

[0059] Figure 7 is a schematic curve diagram of the rotation angle of the waveplate to be measured and the phase delay amount of the waveplate to be measured under different wavelength irradiations in the embodiment of the present invention, that is Figure 7The phase delay results of multiple measurements under irradiation of different wavelengths by the method for measuring the phase delay amount of a micro-nano scale wave plate provided by the present invention are shown. Figure 8 It is a schematic diagram of the fitting result of the phase delay amount of the wave plate to be measured obtained by using the method for measuring the phase delay amount of the micro-nano scale wave plate of the present invention, that is Figure 8 It is the calculation result of the phase delay amount after being processed. It can be seen that the measuring device and the measuring method provided by the present invention can accurately measure the phase delay amount of the wave plate to be measured 9.

[0060] As mentioned above, it is only used to illustrate the technical solution of the present invention, rather than to limit it. For those of ordinary professional skills in the art, the specific technical solution recorded in the above embodiments can be modified, or some of the technical features can be equivalently replaced, and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution protected by the present invention.

Claims

1. A measuring device for the phase retardation of a micro-nano sized wave plate, characterized in that: It includes a tunable light source (1), an integrating sphere (2), a shaping reflection unit, a first linear polarizer (8), a microscope objective (11), a second linear polarizer (12), a sleeve lens (13), a detector (14) and a computer (15); The light input port of the integrating sphere (2) is located on the light output path of the tunable light source (1), and is used to modulate the light emitted by the tunable light source (1) so that it is converted into unbiased light with uniform intensity and then exits from the light output port of the integrating sphere (2); The shaping reflection unit is located on the light output path of the unbiased light, and is used to shape the unbiased light into a plane light beam and adjust the direction of the plane light beam to form illumination light; The first linear polarizer (8) is located on the light path of the illumination light, and the illumination light is converted into completely linearly polarized light with different polarization angles by rotating the first linear polarizer (8) at different angles; The microscope objective (11), the sleeve lens (13), and the detector (14) are coaxially arranged in sequence along the light path transmission direction of the completely linearly polarized light. The sleeve lens (13) is located within the working distance behind the microscope objective (11), and the detector (14) is located at the focal position of the sleeve lens (13); The wave plate to be measured (9) is coaxially arranged between the first linear polarizer (8) and the microscope objective (11). The completely linearly polarized light passing through the first linear polarizer (8) is used to illuminate the wave plate to be measured (9) to form an optical signal carrying the information of the wave plate to be measured (9); The microscope objective (11) and the sleeve lens (13) are used to collect the optical signal carrying the information of the wave plate to be measured (9) and image it on the detector (14); The second linear polarizer (12) is used to be arranged between the microscope objective (11) and the sleeve lens (13) to normalize the optical signal carrying the information of the wave plate to be measured (9) magnified by the microscope objective (11) into the same linear polarization state; The input end of the computer (15) is connected to the output end of the detector (14), and is used to store the image obtained by the detector (14) and determine the phase retardation of the wave plate to be measured (9) according to the image obtained by the detector (14).

2. The measuring device for the phase retardation of a micro-nano sized wave plate according to claim 1, characterized in that: It further includes a displacement clamping device (10) for clamping the wave plate to be measured (9); The displacement clamping device (10) is a six-dimensional displacement device.

3. The measuring device for the phase retardation of a micro-nano sized wave plate according to claim 2, characterized in that: The shaping reflection unit includes a shaping module and a reflection module; The shaping module includes a focusing lens (3), a pinhole filter (4) and an off-axis mirror (5); The reflection module includes a first mirror (6) and a second mirror (7); The focusing lens (3) is located on the optical path of the unpolarized light emitted from the light outlet of the integrating sphere (2) for focusing the unpolarized light; the pinhole filter (4) is located at the focal position of the focusing lens (3) for filtering out high-frequency noise in the unpolarized light; the off-axis mirror (5) is located on the optical path of the filtered unpolarized light for shaping the filtered unpolarized light into a planar light beam without chromatic aberration; The focal plane of the focusing lens (3) coincides with the focal plane of the off-axis mirror (5), and the focus of the focusing lens (3), the pinhole of the pinhole filter (4), and the reflection focus of the off-axis mirror (5) are collinear and parallel to the optical axis of the unpolarized light; the numerical aperture NA of the focusing lens (3) and the working angular aperture Ψ of the off-axis mirror (5) satisfy NA ≤ sin(Ψ); The first mirror (6) is located on the optical path of the planar light beam, and the second mirror (7) is located on the optical path of the planar light beam reflected by the first mirror (6) for adjusting the direction of the planar light beam.

4. The measuring device for the phase retardation amount of a micro-nano sized wave plate according to claim 3, wherein: The extinction ratios of the first linear polarizer (8) and the second linear polarizer (12) are both greater than 5000:

1.

5. The measuring device for the phase retardation amount of a micro-nano sized wave plate according to claim 4, wherein: The first linear polarizer (8) and the wave plate under test (9) are respectively controlled by an electric controller to rotate in step sizes.

6. The measuring device for the phase retardation amount of a micro-nano sized wave plate according to any one of claims 1-5, wherein: The microscope objective (11) is an infinity-corrected objective, and the magnification β after the microscope objective (11) is combined with the tube lens (13) satisfies the following relationship with the length L of the wave plate under test (9), the width W of the wave plate under test (9), and the pixel size p of the detector (14): βL / p > 200; βW / p > 200.

7. A method for measuring the phase delay amount of a micro-nano wave plate, based on the measuring device for the phase delay amount of the micro-nano wave plate according to any one of claims 1-6, characterized in that, It includes the following steps: Step 1, place the light inlet of the integrating sphere (2) on the optical path of the light emitted from the tunable light source (1), and place a shaping reflection unit and the first linear polarizer (8) behind the integrating sphere (2) so that the light emitted from the shaping reflection unit is normally incident on the surface of the first linear polarizer (8); then sequentially place the microscope objective (11), the tube lens (13), and the detector (14), and establish a communication connection between the detector (14) and the computer (15); Step 2, based on the optical structure established in Step 1, fix the included angle between the transmission axis of the first linear polarizer (8) and the horizontal direction at 0°, and use 0° as the initial included angle. Control the first linear polarizer (8) to rotate according to a set rotation step size, record the images obtained by the detector (14) at the corresponding rotation angles respectively, store them in the computer (15), and denote them as observation group A; Step 3: Keeping the optical structure established in Step 1 unchanged, coaxially set the waveplate under test (9) between the first linear polarizer (8) and the microscope objective (11); fix the angle between the transmission axis of the first linear polarizer (8) and the horizontal direction at 0°, and use 0° as the initial angle. Control the first linear polarizer (8) to rotate according to the set rotation step size, record the images obtained by the detector (14) at the corresponding rotation angles respectively, store them in the computer (15), and denote them as Observation Group B; at the same time, determine the imaging area of the current waveplate under test (9) on the detector (14), and denote it as Imaging Area B; Step 4, keeping the optical structure established in Step 3 unchanged, coaxially set the second linear polarizer (12) between the microscope objective lens (11) and the sleeve lens (13); adjust the transmission axis of the second linear polarizer (12) to form an angle with the horizontal direction , , or , fix the angle between the transmission axis of the first linear polarizer (8) and the horizontal direction at 0°, control the wave plate under test (9) to rotate according to the set rotation step, and the set rotation step corresponding to the wave plate under test (9) is the same as the set rotation step corresponding to the first linear polarizer (8); respectively record the images obtained by the detector (14) at the corresponding rotation angles, store them in the computer (15), and denote them as the observation group C; at the same time, determine the imaging area of the current wave plate under test (9) on the detector (14), and denote it as the imaging area C; Step 5: Take the Imaging Area B determined in Step 3 as the integration area of the images in Observation Group A, and integrate all the images in Observation Group A within the integration area to obtain the first integral absolute values at different rotation angles; Integrate all the images in Observation Group B within Imaging Area B to obtain the second integral absolute values at different rotation angles; Integrate all the images in Imaging Area C of Observation Group C to obtain the third integral absolute values at different rotation angles; Step 6: Calculate the phase retardation of the waveplate under test (9) according to the first integral absolute value, the second integral absolute value, and the third integral absolute value corresponding to each rotation angle.

8. A method for measuring the phase retardation of a micro-nano wave plate according to claim 7, characterized in that Step 6 is specifically as follows: Step 6.1, respectively solve the ratio of the transmission rates of the fast and slow axes of the waveplate under test (9) at different rotation angles through the following formula : ； Among them, is the first integral absolute value at different rotation angles, is the second integral absolute value at different rotation angles; Step 6.2, solve the phase retardation of the wave plate (9) to be measured at different rotation angles respectively by the following formula :[[]]END]] ； Among them, is the absolute value of the third integral at different rotation angles, , is the initial angle between the fast axis of the waveplate (9) to be measured and the horizontal direction, i is the rotation step of the waveplate (9) to be measured at the corresponding rotation angle, is the rotation step size of the waveplate (9) to be measured. Step 6.3, use the least squares method to optimize and fit the phase delay amount of the waveplate (9) to be measured obtained at different rotation angles to obtain the phase delay amount of the waveplate (9) to be measured .

Images