A device and method for measuring phase delay of micro-nano size wave plates

Abstract

The present invention provides a device and method for measuring the phase retardation of a micro-nano-sized wave plate, which are used to solve the technical problems of existing wave plate phase retardation measurement methods, such as the inability to characterize and measure wave plates at micro-nano scales, the expensive optical detection equipment, the complex operation of the overall experimental measurement scheme, the poor system versatility, and the high instability of the measurement results of the wave plate phase retardation measurement scheme derived based on the Mueller matrix. The present invention uses an integrating sphere to modulate the light emitted by a tunable light source to form unpolarized light, and then uses a shaping reflection unit to shape the unpolarized light into a plane beam, which is then incident on a first linear polarizer to emit completely linearly polarized light of different polarization angles. At the same time, a second linear polarizer is provided between the microscope objective and the sleeve lens. By adjusting the analyzer angle of the second linear polarizer, the interference of factors such as light intensity jitter, system transmittance, and wave plate rotation positioning accuracy on the measurement results is reduced, effectively ensuring measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the measurement of the phase delay of a wave plate, and in particular to a device and method for measuring the phase delay of a micro-nano size wave plate. Background Art

[0002] A broadband full-Stokes vector detector chip is a photoelectric detection device that can measure the full polarization information of broadband incident light in a snapshot-like manner. It has broad application prospects in industrial inspection, materials science, and biomedicine. The wave plate, as the core component of a broadband full-Stokes vector detector chip, determines the accuracy and reliability of polarization measurements. Therefore, high-precision measurement of the wave plate's phase delay is crucial for ensuring the performance of broadband full-Stokes vector detector chips and is crucial for subsequent polarization correction and full-vector inversion parameter calibration in the detection system.

[0003] Chinese Patent Publication No. CN105628343A discloses a waveplate detection device and method, which uses parameter results obtained from ellipsometer measurements to calculate the optical parameters of the waveplate. Chinese Patent Publication No. CN110631806A discloses a device and method for rapidly measuring the phase delay of a wide-band waveplate. This method measures the maximum and minimum values ​​of the output light intensity by rotating the waveplate angle, and then substitutes them into the Mueller matrix to derive the waveplate's phase delay. Chinese Patent Publication No. CN114720095A discloses a device and method for measuring the phase delay and fast axis direction of a waveplate. This method calculates the phase delay and fast axis direction of the waveplate by recording the rotation angle and direction of the Laguerre-Gaussian beam interference pattern. However, all of the above solutions are only applicable to macro-sized waveplates and cannot characterize and measure micro- and nano-sized waveplates. Furthermore, all of the above solutions involve 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's versatility poor. In addition, the above-mentioned measurement scheme for deriving the wave plate phase delay based on the Mueller matrix adopts the method of rotating the wave plate, and only collects the light intensity values ​​under two incident states for calculation. It does not consider the error influence of the selection of the incident polarization state on the entire measurement model, resulting in 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 delay of micro-nano-sized wave plates to address the technical problems that the existing methods for measuring the phase delay of wave plates are unable to characterize and measure wave plates at micro-nano scale, the optical detection equipment is expensive, the overall experimental measurement scheme is complicated to operate, the system versatility is poor, and the measurement scheme for deriving the phase delay of wave plates based on the Mueller matrix has high instability of the measurement results.

[0005] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0006] A device for measuring the phase delay of a micro-nano wave plate is characterized in that it includes a tunable light source, an integrating sphere, a shaping reflection unit, a first linear polarizer, a microscope objective lens, a second linear polarizer, a tube lens, a detector, and a computer.

[0007] The light inlet of the integrating sphere is located on the light output path of the tunable light source, and is used to modulate the light emitted by the tunable light source, converting it into unpolarized light with uniform intensity, and then emitting it from the light output port of the integrating sphere;

[0008] The shaping reflection unit is located on the outgoing light path of the unpolarized light and is used to shape the unpolarized light into a plane beam and adjust the direction of the plane beam to form illumination light;

[0009] The first linear polarizer is located in 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 at different angles;

[0010] The microscope objective lens, the sleeve lens, and the detector are coaxially arranged in sequence along the optical transmission direction of the completely linearly polarized light, the sleeve lens is located within the working distance behind the microscope objective lens, 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 lens, and the completely linearly polarized light passing through the first linear polarizer is used to illuminate the wave plate to be measured, forming an optical signal loaded with information about the wave plate to be measured; the microscope objective lens and the sleeve lens are used to collect the optical signal loaded with information about the wave plate to be measured, and image it on the detector;

[0011] The second linear polarizer is arranged between the microscope objective lens and the tube lens to normalize the optical signal loaded with the wave plate information to be measured and magnified by the microscope objective lens into the same linear polarization state;

[0012] The input end of the computer is connected to the output end of the detector and is used to store the image acquired by the detector and determine the phase delay of the wave plate to be measured according to the image acquired by the detector.

[0013] Furthermore, it also includes a displacement clamping device for clamping the wave plate to be measured;

[0014] The displacement clamping device is a six-dimensional displacement device, which is used to achieve 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.

[0015] The shaping and reflecting unit includes a shaping module and a reflecting module;

[0016] The shaping module includes a focusing lens, a pinhole filter and an off-axis reflector; the reflecting module includes a first reflector and a second reflector;

[0017] The focusing lens is located on the optical 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 high-frequency noise in the unpolarized light; the off-axis reflector is located on the optical path of the filtered unpolarized light and is used to shape the filtered unpolarized light into a plane beam without chromatic aberration;

[0018] The focal plane of the focusing lens coincides with the focal plane of the off-axis reflector; the focus of the focusing lens, the pinhole of the pinhole filter, and the reflection focus of the off-axis reflector 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 reflector satisfy NA≤sin(Ψ);

[0019] The first reflector is located on the optical path of the plane light beam, and the second reflector is located on the optical path of the plane light beam reflected by the first reflector, and is used to adjust the direction of the plane light beam.

[0020] Furthermore, the extinction ratios of the first linear polarizer and the second linear polarizer are both greater than 5000:1.

[0021] Furthermore, the rotation steps of the first linear polarizer and the wave plate to be measured are respectively controlled by electric controllers.

[0022] Furthermore, the microscope objective is an infinity-corrected objective, and the relationship between the magnification β of the microscope objective when combined with the tube lens, the length L of the wave plate to be measured, the width W of the wave plate to be measured, and the pixel size p of the detector satisfies the following formula:

[0023] βL / p>200;

[0024] βW / p>200.

[0025] In addition, the present invention also provides a method for measuring the phase retardation of a micro-nano scale wave plate, which is based on the above-mentioned device for measuring the phase retardation of a micro-nano scale wave plate, and is special in that it includes the following steps:

[0026] 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 reflector and a first linear polarizer behind the integrating sphere so that the light emitted by the shaping reflector is incident on the surface of the first linear polarizer. Then, place a microscope objective lens, a tube lens, and a detector in sequence, and establish a communication connection between the detector and a computer.

[0027] Step 2: Based on the optical structure constructed in Step 1, the angle between the transmission axis of the first linear polarizer and the horizontal direction is fixed at 0°, and 0° is used as the initial angle. The first linear polarizer is controlled to rotate according to the set rotation step size, and the images obtained by the detector at the corresponding rotation angles are recorded and stored in a computer, and recorded as observation group A.

[0028] Step 3: Keeping the optical structure constructed in step 1 unchanged, the wave plate to be measured is coaxially arranged between the first linear polarizer and the microscope objective lens; fixing the angle between the transmission axis of the first linear polarizer and the horizontal direction to 0°, and using 0° as the initial angle, the first linear polarizer is controlled to rotate according to the set rotation step size, and the images obtained by the detector at the corresponding rotation angles are recorded, stored in the computer, and recorded as observation group B; at the same time, the imaging area of ​​the current wave plate to be measured on the detector is determined, which is recorded as imaging area B;

[0029] Step 4: Keep the optical structure built in step 3 unchanged, and set the second linear polarizer coaxially between the microscope objective and the tube lens; adjust the transmission axis of the second linear polarizer to form an angle with the horizontal direction. , ,or , fix the angle between the transmission axis of the first linear polarizer and the horizontal direction to 0°, control the wave plate to be measured to rotate according to the set rotation step length, and the set rotation step length corresponding to the wave plate to be measured is the same as the set rotation step length corresponding to the first linear polarizer; record the images obtained by the detector at the corresponding rotation angles respectively, store them in the computer, and record them as observation group C; at the same time, determine the imaging area of ​​the current wave plate to be measured on the detector, and record it as imaging area C;

[0030] Step 5: Use the imaging region B determined in step 3 as the integration region of the images in observation group A, and integrate all images in the integration region in observation group A to obtain first integral absolute values ​​at different rotation angles; integrate all images in the imaging region B in observation group B to obtain second integral absolute values ​​at different rotation angles; and integrate all images in the imaging region C in observation group C to obtain third integral absolute values ​​at different rotation angles.

[0031] Step 6: Calculate the phase delay of the wave plate to be measured according to the first integral absolute value, the second integral absolute value, and the third integral absolute value corresponding to each rotation angle.

[0032] Furthermore, step 6 is specifically as follows:

[0033] Step 6.1, calculate the ratio of the fast-axis transmittance to the slow-axis transmittance of the wave plate under test at different rotation angles using the following formula: :

[0034]

[0035] in, is the absolute value of the first integral at different rotation angles, is the absolute value of the second integral at different rotation angles;

[0036] Step 6.2, calculate the phase delay of the wave plate under test at different rotation angles using the following formula: :

[0037]

[0038] in, is the absolute value of the third integral at different rotation angles, , is the initial angle between the fast axis of the wave plate to be tested and the horizontal direction, i is the rotation step of the wave plate to be measured at the corresponding rotation angle, is the rotation step of the wave plate to be measured;

[0039] Step 6.3: Use the least square method to calculate the phase delay of the wave plate under different rotation angles. Perform optimization fitting to obtain the phase delay of the wave plate to be measured .

[0040] The beneficial effects of the present invention compared to the prior art are as follows:

[0041] 1. The present invention provides a device for measuring the phase delay of a micro-nano-sized wave plate, which uses an integrating sphere to modulate light emitted by a tunable light source to form unpolarized light, and then uses a shaping reflection unit to shape the unpolarized light into a plane light beam, which is then incident on a first linear polarizer, so as 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 microscope objective lens and a sleeve lens collects an optical signal loaded with information about 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 microscope 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 of different sizes and polarization characteristic parameters, making the measuring device more versatile. The present invention also provides a second linear polarizer between the microscope objective lens and the sleeve lens, which is used to minimize the interference of factors such as light intensity jitter, system transmittance and wave plate rotation positioning accuracy on the measurement results by adjusting the analyzer angle of the second linear polarizer. The device has high stability and effectively ensures measurement accuracy.

[0042] 2. The present invention provides a device for measuring the phase delay of a micro-nano-sized wave plate. It does not contain 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. It has strong versatility and scalability and can be flexibly applied to various measurement needs and environments.

[0043] 3. The present invention provides a method for measuring the phase delay of a micro-nano-sized wave plate. The method regards the wave plate to be measured and the measuring device as a complete system, and uses the Mueller matrix and Stokes vector to parameterize and model its various polarization optical indicators to form a Mueller-Stokes polarization modulation model. By repeatedly collecting light intensity information of the wave plate to be measured under different polarization modulation characteristics, the information is substituted into the system Mueller-Stokes polarization modulation model to calculate the phase delay under multiple sets of polarization modulation characteristics (at different rotation angles), and then the least squares method is used for optimization fitting to obtain the phase delay of the wave plate to be measured. This method can effectively suppress the inherent errors in the Mueller-Stokes polarization modulation model, is easy to operate, and simple to process data. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic structural diagram of an embodiment of a device for measuring phase delay of a micro-nano-sized wave plate according to the present invention;

[0045] Figure 2 Schematic diagram of the change of the device condition number under different analyzer angles and rotation step sizes when the starting angle of the wave plate to be measured is within the range of [-90°, 90°] in an embodiment of a device for measuring the phase retardation of a micro-nano size wave plate of the present invention;

[0046] Figure 3 This is a flow chart of a method for measuring phase delay of a micro-nano size wave plate according to the present invention;

[0047] Figure 4 Schematic diagram of the principle structure of step 2 in a method for measuring the phase retardation of a micro-nano size wave plate of the present invention;

[0048] Figure 5 Schematic diagram of the principle structure of step 3 in a method for measuring the phase retardation of a micro-nano size wave plate of the present invention;

[0049] Figure 6 Schematic diagram of the principle structure of step 4 in a method for measuring the phase retardation of a micro-nano size wave plate according to the present invention;

[0050] Figure 7 Schematic diagram of a curve between the rotation angle and phase delay of the wave plate to be measured in an embodiment of the present invention;

[0051] Figure 8 This is a schematic diagram of the fitting results of the phase retardation of the wave plate to be measured obtained by the method for measuring the phase retardation of the micro-nano size wave plate of the present invention.

[0052] The specific reference numerals are as follows:

[0053] 1-tunable light source; 2-integrating sphere; 3-focusing lens; 4-pinhole filter; 5-off-axis reflector; 6-first reflector; 7-second reflector; 8-first linear polarizer; 9-wave plate to be measured; 10-displacement clamping device; 11-microscope objective; 12-second linear polarizer; 13-tube lens; 14-detector; 15-computer. DETAILED DESCRIPTION

[0054] In order to make the advantages and features of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] like Figure 1 As shown, a device for measuring the phase delay of a micro-nano size wave plate includes a tunable light source 1, an integrating sphere 2, a focusing lens 3, a pinhole filter 4, an off-axis reflector 5, a first reflector 6, a second reflector 7, a first linear polarizer 8, a microscope objective 11, a second linear polarizer 12, a tube lens 13, a detector 14 and a computer 15.

[0056] The tunable light source 1 is used to provide a light source, and the light inlet of the integrating sphere 2 is located on the light output path of the tunable light source 1. It is used to modulate the light emitted by the tunable light source 1 and convert it into unpolarized light with uniform intensity, that is, convert it into completely unpolarized light, which is convenient for subsequent representation using the Stokes vector. 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 via an optical fiber to achieve light transmission. The light emitted by the tunable light source 1 is converted into unpolarized light with uniform intensity within the integrating sphere 2 and then emitted from the light output port of the integrating sphere 2 to the subsequent light path.

[0057] The focusing lens 3, pinhole filter 4, and off-axis reflector 5 form a beam shaping module for shaping the unpolarized light emitted from the light outlet of the integrating sphere 2. Other beam shaping modules may also be used in other embodiments of the present invention. Specifically, the focusing lens 3 is located in the optical path of the unpolarized light emitted from the light outlet of the integrating sphere 2 and is used to focus the unpolarized light. The pinhole filter 4 is located at the focal point of the focusing lens 3 and is used to filter out high-frequency noise in the unpolarized light. The off-axis reflector 5 is located in the optical path of the filtered unpolarized light and is used to shape the filtered unpolarized light into a planar beam without chromatic aberration.

[0058] In this embodiment, the shaping module composed of the focusing lens 3, pinhole filter 4, and off-axis reflector 5 is predicated on the fact that the focal plane of the focusing lens 3 coincides with the focal plane of the off-axis reflector 5, and that the focal point of the focusing lens 3, the pinhole of the pinhole filter 4, and the reflection focus of the off-axis reflector 5 are collinear and parallel to the optical axis of the unpolarized light. The numerical aperture NA of the focusing lens 3 and the operating angle Ψ of the off-axis reflector 5 must satisfy NA ≤ sin(Ψ). By restricting the relative positions of the focusing lens 3, off-axis reflector 5, and pinhole filter 4, the shaping accuracy of the unpolarized light can be improved, thereby enhancing the accuracy of phase delay measurement.

[0059] The first reflector 6 and the second reflector 7 are used to adjust the direction of the plane light beam to facilitate the arrangement of the subsequent light path. Specifically, the first reflector 6 is located on the light path of the plane light beam, and the second reflector 7 is located on the light path of the plane light beam reflected by the first reflector 6, and is used to adjust the direction of the plane light beam to form illumination light.

[0060] The first linear polarizer 8 is located in 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 external electric controller according to the rotation step size. The rotation step size of the first linear polarizer 8 is Need to meet: .

[0061] The microscope objective lens 11, the sleeve lens 13, and the detector 14 are coaxially arranged in sequence along the optical transmission direction of the completely linearly polarized light. The sleeve lens 13 is located within the working distance behind the microscope objective lens 11, and the detector 14 is located at the focal position of the sleeve lens 13. The wave plate 9 to be measured is coaxially arranged between the first linear polarizer 8 and the microscope objective lens 11, and is clamped and fixed by a displacement clamping device 10. The displacement clamping device 10 is a six-dimensional displacement device, which defines 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 linear polarized light and perpendicular to the optical axis of the completely linear polarized light as the Y direction, and the direction perpendicular to the plane containing the X and Y directions as the Z direction. The displacement clamping device 10 can drive the wave plate 9 to be measured to achieve displacement in the X, Y, and Z directions. At the same time, the displacement clamping device 10 can also adjust the rotation angle, tilt angle, and pitch angle of the wave plate 9 to be measured. In addition, the wave plate 9 to be tested needs to be rotated during the test. In this embodiment, the rotation of the wave plate 9 to be tested is controlled by an externally arranged electric controller according to the rotation step length. The rotation step length of the wave plate 9 to be tested is Need to meet: .

[0062] The completely linearly polarized light passing through the first linear polarizer 8 is used to illuminate the wave plate 9 to be measured, forming an optical signal loaded with information about the wave plate 9 to be measured. The microscope objective 11 and the tube lens 13 collect the optical signal loaded with information about the wave plate 9 to be measured, and image it on the detector 14, that is, the detector 14 obtains the light intensity information of the wave plate 9 to be measured. In this embodiment, the microscope objective 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 of the microscope objective 11 after being matched with the tube lens 13 and the length L of the wave plate 9 to be measured, the width W of the wave plate 9 to be measured, and the pixel size p of the detector 14 satisfies: βL / p>200, βW / p>200. By limiting the above relationship, the microscopic performance of the microscopic system composed of the microscope objective 11 and the tube lens 13 can be guaranteed, and not only the phase delay of macro-sized wave plates can be measured, but also the phase delay of micro-nano-sized wave plates can be well measured.

[0063] The second linear polarizer 12 is coaxially arranged between the microscope objective 11 and the tube lens 13 to normalize the optical signal carrying the information of the wave plate 9 to be measured and magnified by the microscope objective 11 to the same linear polarization state. When the second linear polarizer 12 is arranged, the angle between its transmission axis and the horizontal direction needs to be fixed at a certain angle for polarization analysis, which is recorded as the polarization analysis angle. , then the deflection angle Need to meet: ,or .

[0064] In the present invention, the wave plate 9 to be measured and the second linear polarizer 12 are preferably configured as quick-detachable structures, so that the wave plate 9 to be measured and the second linear polarizer 12 can be quickly set in the optical path structure, and can also be quickly removed without affecting other optical path structures, thereby facilitating subsequent measurements.

[0065] The operating bandwidth of the first linear polarizer 8 and the second linear polarizer 12 should be as wide as possible to cover the operating bands of different wave plates, enabling phase retardation measurement across all operating bands for wave plates with different bandwidths. Furthermore, the corresponding wavelength ranges of the tunable light source 1, integrating sphere 2, and detector 14 should also be as large as possible to cover the operating 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, 6000:1, 7000:1, etc. A larger extinction ratio can improve the accuracy of phase retardation measurement.

[0066] The input end of the computer 15 is connected to the output end of the detector 14 , and is used to store the light intensity information of the wave plate 9 to be tested obtained by the detector 14 , and determine the phase delay of the wave plate 9 to be tested according to the light intensity information of the wave plate 9 to be tested obtained by the detector 14 .

[0067] The wave plate to be measured 9 and the device for measuring the phase delay of the micro-nano-sized wave plate (hereinafter referred to as the measurement device) are regarded as a complete system. The Mueller matrix and Stokes vector are used to parameterize modeling of their various polarization optical indicators to form a Mueller-Stokes polarization modulation model. The phase delay of the wave plate to be measured is obtained by inversion calculation by repeatedly collecting the light intensity information of the wave plate to be measured 9 under different polarization modulations.

[0068] According to the optical path structure of the above-mentioned measuring device, the light modulated by the integrating sphere 2 is unpolarized light, and the Stokes vector of the unpolarized light at the corresponding wavelength is for:

[0069] (1)

[0070] in, 、 、 、 is the Stokes vector The corresponding four values.

[0071] In addition, since the extinction ratios of the first linear polarizer 8 and the second linear polarizer 12 are both greater than 5000:1, they can be regarded as ideal polarizers. Therefore, the Mueller matrices of the first linear polarizer 8 and the second linear polarizer 12 can be expressed as:

[0072] (2)

[0073] in, j Take 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. Fix it.

[0074] Assume that the phase delay of the wave plate 9 to be measured is , the angle between the fast axis of the wave plate 9 to be measured and the horizontal direction is The fast axis transmittance of the wave plate 9 to be tested is , the ratio of the fast-axis transmittance to the slow-axis transmittance of the wave plate 9 to be tested is , then the Mueller matrix of the wave plate 9 to be measured is It can be expressed as:

[0075] (3)

[0076] According to the positional relationship of each optical element and the Mueller matrix of the wave plate 9 to be measured , the light intensity of the wave plate 9 to be measured detected by the detector 14 is the Stokes vector at the corresponding wavelength It can be expressed as:

[0077] (4)

[0078] in, 、 、 、 is the Stokes vector The corresponding four values.

[0079] To analyze the noise effect of the measuring device, it is assumed that the fast axis transmittance and slow axis transmittance of the wave plate 9 to be measured are both 1, that is, the ratio of its fast axis transmittance to its slow axis transmittance is also 1. Its ideal Mueller matrix is ​​expressed as Since the detector 14 can only detect light intensity, we have:

[0080] (5)

[0081] in, is the output light intensity of the tunable light source 1, is the light intensity of the wave plate 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 wave plate 9 to be tested and the horizontal direction, is the rotation step length of the wave plate 9 to be measured.

[0082] Substitute equations (2) and (3) into equation (5) and simplify and expand them to obtain:

[0083] (6)

[0084] in, is an n×1 column vector, each element of which corresponds to the light intensity value obtained at each detection; is an n×2 transmission matrix, n is the total number of rotation steps of the wave plate 9 to be measured, ,when If the result is a decimal, round it down.

[0085] .

[0086] From formula (6), we can know that the light intensity of the wave plate 9 to be measured detected by the detector 14 is The cosine of the phase delay of the wave plate 9 to be measured In order to fully reduce the random error of the measuring device, it is necessary to determine the appropriate analyzer angle of the second linear polarizer 12 during the experimental operation. The rotation step of the wave plate 9 to be measured , so that the condition number of the transfer matrix G is as small as possible.

[0087] Figure 2 In the embodiment of the present invention, the starting angle of the wave plate 9 to be measured is within the range of [-90°, 90°] at different analyzer angles. and rotation step size The schematic diagram of the change of the device condition number under the condition of At ±45°, and the rotation step of the wave plate 9 to be measured is When the angle 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 conducive to fully reducing the interference of factors such as light intensity jitter, system transmittance and wave plate rotation positioning accuracy in the Mueller-Stokes system on the measurement results, thereby improving the measurement accuracy and stability. Take 45°, the rotation step of the wave plate 9 to be measured Take 10°.

[0088] Based on the above principle, the present invention provides a method for measuring the phase delay of a micro-nano size wave plate, such as Figure 3 As shown, the specific steps include:

[0089] Step 1: First, connect and secure the light outlet of the tunable light source 1 to the light inlet of the integrating sphere 2. Place the focusing lens 3, pinhole filter 4, and off-axis reflector 5 in sequence behind the integrating sphere 2. When placing the focusing lens 3, the pinhole of the pinhole filter 4, and the reflection focus of the off-axis reflector 5 to the same height and collinearity, and secure the pinhole filter 4 to the focal position of the focusing lens 3. Then, turn on the light source and move the off-axis reflector 5 until the light reflected by the off-axis reflector 5 forms a plane beam. Then, place the first reflector 6, second reflector 7, and first linear polarizer 8 in sequence, ensuring that the centers of each optical element are at the same height. Adjust the first and second reflectors 6 and 7 so that the light passing through the second reflector 7 is incident directly on the surface of the first linear polarizer 8. Finally, microscope objective 11, tube lens 13, and detector 14 are placed in sequence, and communication between detector 14 and computer 15 is established. Tube lens 13 is placed within the working distance behind microscope objective 11, and detector 14 is located at the focal point of tube lens 13. At this point, with the exception of wave plate 9 to be measured and second linear polarizer 12, the remaining optical components of the measurement apparatus are complete.

[0090] Step 2, such as Figure 4As shown, based on the optical structure built in step 1, that is, when the wave plate 9 to be measured and the second linear polarizer 12 are 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 to 0°, and the first linear polarizer 8 is controlled by the electronic controller to rotate according to the step size =10°, so that the angle between the transmission axis of the first linear polarizer 8 and the horizontal direction is Steady change. Record different angles separately The image captured by the lower detector 14 is stored in the computer 15 and recorded as observation group A. At this time, the Stokes vector of the detection light corresponding to the observation group A at the corresponding wavelength is It can be expressed as:

[0091] (7)

[0092] (8)

[0093] in, 、 、 、 is the Stokes vector The corresponding four values.

[0094] Step 3, such as Figure 5 As shown, keeping the optical structure constructed in step 1 unchanged, the wave plate 9 to be measured is clamped on the displacement clamping device 10 and placed between the first linear polarizer 8 and the microscope objective 11; at this time, the displacement clamping device 10 is adjusted along the X direction, Y direction and Z direction respectively, so that the wave plate 9 to be measured is located at the working distance of the microscope objective 11, and at the same time, the wave plate 9 to be measured corresponds to the objective center position of the microscope objective 11, that is, a clear image of the wave plate 9 to be measured can be obtained on the detector 14; in addition, the rotation angle, tilt angle and pitch angle of the wave plate 9 to be measured need to be adjusted so that the light passing through the first linear polarizer 8 is incident on the surface of the wave plate 9 to be measured.

[0095] After the wave plate 9 to be measured is placed, in the case that the measuring device is only not provided with the second linear polarizer 12, the initial angle between the transmission axis of the first linear polarizer 8 and the horizontal direction is fixed to 0°, and the first linear polarizer 8 is controlled by the electronic controller to rotate according to the step size =10°, so that the angle between the transmission axis of the first linear polarizer 8 and the horizontal direction is Steady change. Record different angles separately The image captured by the lower detector 14 is stored in the computer 15 and recorded as observation group B. At this time, the Stokes vector of the detection light corresponding to the observation group B at the corresponding wavelength is It can be expressed as:

[0096] (9)

[0097] (10)

[0098] in, 、 、 、 is the Stokes vector The corresponding four values ​​are is the phase delay of the wave plate 9 to be measured, is the angle between the fast axis of the wave plate 9 to be measured and the horizontal direction, is the fast axis transmittance of the wave plate 9 to be tested, is the ratio of the fast-axis transmittance to the slow-axis transmittance of the wave plate 9 to be tested.

[0099] At the same time, the imaging area of ​​the wave plate 9 to be tested on the detector 14 is determined, and is recorded as imaging area B.

[0100] Step 4, such as Figure 6 As shown, the optical structure built in step 2 remains unchanged, and the second linear polarizer 12 is coaxially set between the microscope objective lens 11 and the tube lens 13. When the measuring device is provided with the wave plate 9 to be measured and the second linear polarizer 12, the angle between the transmission axis of the second linear polarizer 12 and the horizontal direction is fixed to 45°, and the angle between the transmission axis of the first linear polarizer 8 and the horizontal direction is fixed to 0°. The wave plate 9 to be measured is controlled by the electronic controller according to the rotation step size. =10° to make the angle between the fast axis of the wave plate 9 to be measured and the horizontal direction Steady change. Record different angles separately The image captured by the lower detector 14 is stored in the computer 15 and recorded as observation group C. At this time, the Stokes vector of the detection light corresponding to the observation group C at the corresponding wavelength is It can be expressed as:

[0101] (11)

[0102] (12)

[0103] in, 、 、 、 is the Stokes vector The corresponding four values.

[0104] 、 It can be substituted into formula (2) to obtain, Solve according to formula (3).

[0105] At the same time, the imaging area of ​​the wave plate 9 to be tested on the detector 14 is determined, which is recorded as the imaging area C.

[0106] It should be noted that there is no fixed order among the acquisition operations of observation group A, observation group B, and observation group C in the present invention.

[0107] Step 5: Obtain the phase delay of the wave plate 9 to be measured.

[0108] In the images of observation group A, since the wave plate 9 to be measured has not yet been set in the measurement device, the imaging area of ​​the wave plate 9 to be measured on the detector 14 cannot be determined, and therefore the images in observation group A cannot be integrated. Therefore, after the wave plate 9 to be measured is set in step 3, the present invention uses the imaging area B as the integration area of ​​the images in observation group A. Then, all images in the integration area of ​​observation group A are integrated to obtain the first integral absolute value at different rotation angles. .

[0109] At the same time, all images in the imaging area B in the observation group B are integrated to obtain the second integral absolute value at different rotation angles ; Integrate the images of all imaging areas C in the observation group C to obtain the third integral absolute value at different rotation angles .

[0110] In order to analyze the noise influence of the measuring device, it is assumed that the fast axis transmittance and slow axis transmittance of the wave plate 9 to be measured are both 1, but the phase delay calculated in this way is less accurate. The absolute value of the second integral at different rotation angles obtained by integrating the observation group B First, determine the more accurate ratio of the fast and slow axis transmittance of the wave plate 9 to be tested at different rotation angles. , and then based on the ratio of the fast and slow axis transmittance of the wave plate 9 to be tested , and the corresponding absolute value of the first integral and the absolute value of the third integral Determine the phase delay of the wave plate 9 under test at different rotation angles , effectively improving the measurement accuracy of the phase delay of the wave plate to be measured.

[0111] Specifically, since the Stokes vector is the normalized result, , so the ratio of the fast and slow axis transmittance of the wave plate (9) to be tested at different rotation angles can be solved by the following formula: :

[0112] (13)

[0113] because , so we have:

[0114] (14)

[0115] The absolute value of the first integral corresponding to each rotation angle , the absolute value of the third integral And the ratio of the fast and slow axis transmittance of the wave plate 9 to be tested Substituting them into formula (14) we can get:

[0116]

[0117] in, , is the initial angle between the fast axis of the wave plate 9 to be tested and the horizontal direction, i is the rotation step of the wave plate 9 to be measured at the corresponding rotation angle, is the rotation step length of the wave plate 9 to be measured.

[0118] Finally, the phase delay of the wave plate 9 to be measured obtained at different rotation angles is calculated using the least squares method. Perform fitting to obtain the phase delay of the wave plate 9 to be measured .

[0119] When the wave plate 9 to be measured is a broadband wave plate, the wavelength of the light emitted by the tunable light source 1 is changed, and the measurement is performed according to the contents of steps 2 to 5, so as to obtain the phase delay of the wave plate 9 to be measured under different wavelengths.

[0120] Figure 7 Schematic diagram of the curve between the rotation angle of the wave plate to be measured and the phase delay of the wave plate to be measured under different wavelengths of illumination in an embodiment of the present invention, that is, Figure 7 The phase delay results of multiple measurements under different wavelengths of illumination are shown according to the method for measuring the phase delay of micro-nano size wave plates provided by the present invention. Figure 8 This is a schematic diagram of the fitting results of the phase retardation of the wave plate to be measured obtained by the method for measuring the phase retardation of the micro-nano size wave plate of the present invention, that is, Figure 8 is the calculated result of the phase delay after processing. It can be seen that the measuring device and the measuring method provided by the present invention can accurately measure the phase delay of the wave plate 9 to be measured.

[0121] The above description is only used to illustrate the technical solution of the present invention, rather than to limit it. For ordinary professional and technical personnel in this field, the specific technical solutions recorded in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents. These modifications or replacements do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solution protected by the present invention.

Claims

1. A device for measuring the phase delay of a micro-nano wave plate, characterized by: It includes a tunable light source (1), an integrating sphere (2), a shaping reflection unit, a first linear polarizer (8), a microscope objective lens (11), a second linear polarizer (12), a sleeve lens (13), a detector (14), and a computer (15); The light inlet 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 as to convert the light into non-polarized light with uniform intensity and then emit the light from the light output port of the integrating sphere (2); The shaping reflection unit is located on the outgoing light path of the unpolarized light and is used to shape the unpolarized light into a plane beam and adjust the direction of the plane beam to form illumination light; The first linear polarizer (8) is located in 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; The microscope 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 microscope objective lens (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 lens (11), and the completely linearly polarized light passing through the first linear polarizer (8) is used to illuminate the wave plate to be measured (9), thereby forming an optical signal loaded with information of the wave plate to be measured (9); the microscope objective lens (11) and the sleeve lens (13) are used to collect the optical signal loaded with information of the wave plate to be measured (9), and image it on the detector (14); The second linear polarizer (12) is arranged between the microscope objective lens (11) and the sleeve lens (13) to normalize the optical signal loaded with the information of the wave plate (9) to be measured and magnified by the microscope objective lens (11) to 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 acquired by the detector (14) and determine the phase delay of the wave plate (9) to be measured based on the image acquired by the detector (14).

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

3. The device for measuring phase delay of a micro-nano wave plate according to claim 2, characterized in that: The shaping and reflecting unit includes a shaping module and a reflecting module; The shaping module comprises a focusing lens (3), a pinhole filter (4) and an off-axis reflector (5); the reflection module comprises a first reflector (6) and a second reflector (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) and is used to focus the unpolarized 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 unpolarized light; the off-axis reflector (5) is located on the optical 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 (3) coincides with the focal plane of the off-axis reflector (5); the focus of the focusing lens (3), the pinhole of the pinhole filter (4), and the reflection focus of the off-axis reflector (5) are collinear and parallel to the optical axis of the non-polarized light; the numerical aperture NA of the focusing lens (3) and the working angle Ψ of the off-axis reflector (5) satisfy NA≤sin(Ψ); The first reflector (6) is located on the optical path of the plane light beam, and the second reflector (7) is located on the optical path of the plane light beam reflected by the first reflector (6), and is used to adjust the direction of the plane light beam.

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

1.

5. The device for measuring phase delay of a micro-nano wave plate according to claim 4, characterized in that: The first linear polarizer (8) and the wave plate to be measured (9) are respectively controlled in rotation step length by an electric controller.

6. A device for measuring phase retardation of a micro-nano wave plate according to any one of claims 1 to 5, characterized in that: The microscope objective lens (11) is an infinity-corrected objective lens. The relationship between the magnification β of the microscope objective lens (11) when combined with the sleeve lens (13), the length L of the wave plate (9) to be measured, the width W of the wave plate (9) to be measured, and the pixel size p of the detector (14) satisfies the following formula: βL / p>200; βW / p>200.

7. A method for measuring the phase retardation of a micro-nano scale wave plate, based on the device for measuring the phase retardation of a micro-nano scale wave plate according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1, the light inlet of the integrating sphere (2) is positioned on the optical path of the light emitted by the tunable light source (1), and a shaping reflection unit and a first linear polarizer (8) are placed behind the integrating sphere (2), so that the light emitted by the shaping reflection unit is incident on the surface of the first linear polarizer (8); then, a microscope objective lens (11), a sleeve lens (13), and a detector (14) are placed in sequence, and a communication connection is established between the detector (14) and a computer (15); Step 2: Based on the optical structure constructed in step 1, the angle between the transmission axis of the first linear polarizer (8) and the horizontal direction is fixed to 0°, and 0° is used as the initial angle. The first linear polarizer (8) is controlled to rotate according to the set rotation step length, and the images obtained by the detector (14) at the corresponding rotation angles are recorded, stored in the computer (15), and recorded as observation group A; Step 3, keeping the optical structure constructed in step 1 unchanged, coaxially setting the wave plate to be measured (9) between the first linear polarizer (8) and the microscope objective (11); fixing the angle between the transmission axis of the first linear polarizer (8) and the horizontal direction to 0°, and taking 0° as the initial angle, controlling the first linear polarizer (8) to rotate according to the set rotation step, respectively recording the images obtained by the detector (14) at the corresponding rotation angles, storing them in the computer (15), and recording them as observation group B; at the same time, determining the imaging area of ​​the current wave plate to be measured (9) on the detector (14), recording them as imaging area B; Step 4: Keep the optical structure built in step 3 unchanged, and 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 , fixing the angle between the transmission axis of the first linear polarizer (8) and the horizontal direction to 0°, controlling the wave plate to be measured (9) to rotate according to the set rotation step, the set rotation step corresponding to the wave plate to be measured (9) is the same as the set rotation step corresponding to the first linear polarizer (8); recording the images obtained by the detector (14) at the corresponding rotation angles respectively, storing them in the computer (15), and recording them as observation group C; and at the same time determining the imaging area of ​​the current wave plate to be measured (9) on the detector (14), recording them as imaging area C; Step 5: Using the imaging area B determined in step 3 as the integration area of ​​the images in the observation group A, and integrating all images in the integration area in the observation group A to obtain first integral absolute values ​​at different rotation angles; Integrate all images in imaging area B in observation group B to obtain second integral absolute values ​​at different rotation angles; Integrate the images of all imaging areas C in the observation group C to obtain third integral absolute values ​​at different rotation angles; Step 6, calculating the phase delay of the wave plate (9) to be measured according to the first integral absolute value, the second integral absolute value and the third integral absolute value corresponding to each rotation angle.

8. The method for measuring the phase delay of a micro-nano wave plate according to claim 7, characterized in that: Step 6 is as follows: Step 6.1, calculate the ratio of the fast-axis transmittance to the slow-axis transmittance of the wave plate (9) under different rotation angles by the following formula: : ； in, is the absolute value of the first integral at different rotation angles, is the absolute value of the second integral at different rotation angles; Step 6.2, calculate the phase delay of the wave plate (9) under different rotation angles by the following formula: : ； in, is the absolute value of the third integral at different rotation angles, , is the initial angle between the fast axis of the wave plate (9) to be tested and the horizontal direction, i is the rotation step of the wave plate (9) to be measured at the corresponding rotation angle, is the rotation step length of the wave plate (9) to be measured; Step 6.3, use the least square method to calculate the phase delay of the wave plate (9) under different rotation angles. Perform optimization fitting to obtain the phase delay of the wave plate (9) to be measured .

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