Birefringence and polarization beam splitting ratio measuring system and method based on crystal rotation

Abstract

The invention discloses a birefringence and polarization beam splitting ratio measurement system and method based on crystal rotation, and relates to the technical field of optical characteristic measurement, and the system comprises a birefringence measurement module, a polarization beam splitting ratio measurement module and a data processing module. The birefringence measurement module comprises a sodium lamp, a collimator tube, a crystal rotation objective table, a first birefringence crystal, a first rotatable polarizing film and a spectrometer telescope which are arranged along a first light path. The polarization beam splitting ratio measuring module comprises a laser, a second birefringent crystal and a second rotatable polaroid which are arranged along a second light path, and the output end of the polarization beam splitting ratio measuring module is connected with a light screen with a scale and a photoelectric sensor in parallel. And the data processing module is respectively connected with the angle encoder, the double-vernier dial and the oscilloscope. The birefringence and polarization beam splitting ratio measuring device can realize synchronous and accurate measurement of birefringence and polarization beam splitting ratio parameters, and has the advantages of reducing measurement cost, improving data consistency, and being compact in structure and convenient to operate.

Description

Technical Field

[0001] The present invention relates to the field of optical characteristic measurement, and in particular to a system and method for measuring birefringence and polarization splitting ratio based on crystal rotation. Background Art

[0002] Birefringent crystals have important applications in the field of optics, and the precise measurement of their optical properties is crucial for material research and device development. Currently, the measurement methods for birefringent crystals mainly include two technical routes: ordinary spectral analysis and intensity detection. Although ordinary spectral analysis can obtain average spectral data of a macroscopic area, it has obvious limitations: on the one hand, it is difficult to distinguish directional differences in materials, and on the other hand, it cannot effectively obtain polarization information, resulting in a low signal-to-noise ratio for transparent or weakly absorbing samples. Although intensity detection technology can record changes in light intensity, it has many shortcomings in practical applications: it cannot accurately obtain key parameters such as optical path difference and refractive index changes, and the measurement process is easily affected by environmental interference.

[0003] Traditional measurement methods suffer from significant deficiencies in accuracy, system stability, and ease of use. Specifically, for the simultaneous measurement of two key parameters, birefringence and polarization splitting ratio, existing technologies often require separate measurement devices, increasing costs and potentially leading to inconsistent results. Furthermore, existing measurement systems are generally bulky and complex, hindering their widespread application in laboratories and industrial settings.

[0004] In view of the above problems, the existing technology is in urgent need of improvement. Summary of the Invention

[0005] In view of this, the present invention provides a system and method for measuring birefringence and polarization splitting ratio based on crystal rotation, which has the advantages of realizing synchronous measurement of birefringence and polarization splitting ratio, reducing measurement costs, improving data consistency, compact structure and convenient operation.

[0006] In a first aspect, the present invention provides a birefringence and polarization splitting ratio measurement system based on crystal rotation, comprising: a birefringence measurement module, a polarization splitting ratio measurement module, and a data processing module; A birefringence measurement module includes a sodium lamp, a collimator, a crystal rotating stage, a first birefringent crystal, a first rotatable polarizer, and a spectrometer telescope, which are sequentially arranged along a first optical path; The crystal rotating stage is provided with a double vernier scale and carries the first birefringent crystal, and the rotation angle is fed back in real time through a built-in angle encoder; the spectrometer telescope is connected to the double vernier scale and is used to dynamically capture the minimum deflection angle δ of the o-light and the e-light. min1 , δ min2 ; A polarization beam splitting ratio measurement module includes a laser, a second birefringent crystal, and a second rotatable polarizer arranged in sequence along a second optical path; Wherein, a light screen and a photoelectric sensor are arranged in parallel on the output light path of the second rotatable polarizer; the light screen has a position scale for marking the coordinates of the light spot of the o light and the spot coordinates of e-light The photoelectric sensor is connected to an oscilloscope to output the peak-to-peak voltage of o light / e light in real time V o,pp 、 V e,pp ; The data processing module is electrically connected to the angle encoder, the double vernier scale and the oscilloscope, and is used to calculate the minimum deflection angle δ of the o light and the e light. min1 , δ min2 , respectively calculate the refractive index of o light and e light; and, for peak-to-peak voltage according to o light and e light V o,pp 、 V e,pp , calculate the real-time polarization splitting ratio; and, for the spot coordinates of the o light and the spot coordinates of e-light , calculate the beam separation amount of o-light and e-light.

[0007] In an optional embodiment, the calculation formulas for the refractive indices of o-light and e-light are: ; ;

[0008] in, is the refractive index of o light; is the refractive index of e-light; is the apex angle of the birefringent crystal; δ min1 is the minimum deflection angle of o light, δ min2 is the minimum deflection angle of e-light.

[0009] In an optional implementation, the step of calculating the polarization splitting ratio is: ;

[0010] in, is the polarization splitting ratio; is the peak-to-peak voltage of o light V o,pp The value in the middle corresponds to the maximum light intensity; is the peak-to-peak voltage of e-light V e,pp The value in corresponds to the maximum light intensity.

[0011] In an optional embodiment, the calculation formula for the beam separation amount is: ;

[0012] in, is the beam separation; are the abscissas of the light spots of o-light and e-light respectively; are the ordinates of the light spots of o-light and e-light respectively.

[0013] In an optional embodiment, the second birefringent crystal, the first rotatable polarizer and the light screen are on the same horizontal line.

[0014] In a second aspect, the present invention further provides a method for measuring birefringence and polarization splitting ratio based on crystal rotation, comprising: S1, based on the minimum deflection angle δ of o light and e light min1 , δ min2 , calculate the refractive index of o light and e light respectively; S2, according to the peak-to-peak voltage of o light and e light V o,pp 、 V e,pp , calculate the real-time polarization splitting ratio, and the spot coordinates of the o-light and the spot coordinates of e-light , calculate the beam separation amount of o-light and e-light.

[0015] In an optional embodiment, the S1 includes: The light beam is emitted by a sodium lamp, collimated by a collimator and then incident on a first birefringent crystal on a crystal rotating stage; Adjust the angle of the spectrometer telescope so that o-light and e-light appear in the field of view; Adjusting the angle of the first rotatable polarizer to enable the o-light and e-light to be distinguished in the field of view of the spectrometer telescope; Rotate the crystal rotating stage to dynamically capture the minimum deflection angle δ of o-light and e-light through the spectrometer telescope min1 , δ min2 , and record the dual vernier dial readings simultaneously; According to the minimum deflection angle δ min1 , δ min2 and the vertex angle of the first birefringent crystal to calculate the refractive index of o light and the refractive index of e light.

[0016] In an optional embodiment, the S2 includes: The laser is emitted by a laser, and the laser is incident on a second birefringent crystal and then modulated into linearly polarized light by a second rotatable polarizer; Performed in parallel at the output of the second rotatable polarizer: Mark the spot coordinates of the o light on the light screen with position scale and the spot coordinates of e-light ; and, collect the peak-to-peak voltage of o light and e light in real time through the photoelectric sensor V o,pp 、 V e,pp , and output by the oscilloscope; According to the peak-to-peak voltage V o,pp 、 V e,pp Calculate real-time polarization splitting ratio; According to the spot coordinates of the o light and the spot coordinates of e-light , calculate the beam separation of o-light and e-light.

[0017] In an optional embodiment, the rotating crystal rotating stage dynamically captures the minimum deflection angle δ of o-light and e-light through the spectrometer telescope. min1 , δ min2 ,include: Find the yellow spectral line refracted from the first birefringent crystal in the spectrometer telescope; Rotate the crystal stage to make the yellow spectrum line tend to the direction with decreasing deflection angle; when the yellow spectrum line starts to move in the opposite direction, use the left and right cursor readings at the current moment as the refraction angles of the left and right paths; Remove the first birefringent crystal, rotate the spectrometer telescope to align with the collimator, and align the crosshairs with the slits. Use the left and right cursor readings at the current moment as the incident angles of the left and right paths respectively. Calculate the minimum deflection angle δ of o light and e light min1 , δ min2 , and its calculation formula is: ;

[0018] in, 、 are the refraction angles of the left path and the right path respectively; are the incident angles of the left path and the right path, respectively.

[0019] From the above, it can be seen that the present application provides a crystal rotation-based birefringence and polarization splitting ratio measurement system and method, which realizes the synchronous and accurate measurement of birefringence and polarization splitting ratio parameters by integrating a birefringence measurement module, a polarization splitting ratio measurement module and a data processing module, and has the advantages of reducing measurement costs, improving data consistency, compact structure and convenient operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 1 is a schematic structural diagram of a system for measuring birefringence and polarization splitting ratio based on crystal rotation according to an embodiment of the present invention; Figure 2 is a schematic structural diagram of a birefringence measurement module according to an embodiment of the present invention; Figure 3 2 is a schematic structural diagram of a polarization splitting ratio measurement module according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0023] In existing technologies, spectral analysis and intensity detection are commonly used to measure the optical properties of birefringent crystals. Spectral analysis struggles to capture directional differences in materials and loses polarization information, resulting in low signal-to-noise ratios for transparent or weakly absorbing samples. Intensity detection is sensitive to environmental interference and cannot accurately measure optical path differences and refractive index changes. These limitations are particularly prominent in applications requiring dynamic birefringence measurement, such as optical communication device calibration and laser polarization control, hindering the development of high-precision optical devices.

[0024] To address the above issues, the inability of traditional methods to synchronously obtain polarization state changes and refractive index differences has been given special attention. Analysis revealed that the spectrometer's minimum deflection angle principle can accurately measure the refractive index, but static measurements suffer from cumulative angular errors. Further research revealed that dynamically rotating the crystal combined with dual vernier compensation can effectively reduce errors. At the same time, the parallel arrangement of the photoelectric sensor and the light screen can both detect light intensity changes and record spatial separation. Based on this, it is proposed to integrate birefringence measurement and polarization splitting ratio detection into a collaborative system, and to achieve synchronous calculation of multi-dimensional parameters through a data processing module.

[0025] Therefore, if Figure 1-Figure 3As shown, the present application proposes a birefringence and polarization splitting ratio measurement system based on crystal rotation, a birefringence measurement module, a polarization splitting ratio measurement module, and a data processing module. The birefringence measurement module includes a sodium lamp, a collimator, a crystal rotation stage, a first birefringent crystal, a first rotatable polarizer, and a spectrometer telescope arranged in sequence along a first optical path; wherein, a dual vernier scale is provided on the crystal rotation stage, and the first birefringent crystal is carried, and the rotation angle is fed back in real time via a built-in angle encoder; the spectrometer telescope is connected to the dual vernier scale to dynamically capture the minimum deflection angle δ of the o-light and the e-light. min1 , δ min2 The polarization splitting ratio measurement module includes a laser, a second birefringent crystal, and a second rotatable polarizer arranged in sequence along the second optical path; wherein, a light screen and a photoelectric sensor are arranged in parallel on the output optical path of the second rotatable polarizer; the light screen has a position scale for marking the coordinates of the o-light spot and the spot coordinates of e-light ;The photoelectric sensor is connected to an oscilloscope to output the peak-to-peak voltage of o light / e light in real time V o,pp 、 V e,pp The data processing module is electrically connected to the angle encoder, the double vernier scale and the oscilloscope, and is used to calculate the minimum deflection angle δ of the o-light and the e-light. min1 , δ min2 , respectively calculate the refractive index of o light and e light; and, for peak-to-peak voltage according to o light and e light V o,pp 、 V e,pp , calculate the real-time polarization splitting ratio; and, for the spot coordinates of the o light and the spot coordinates of e-light , calculate the beam separation amount of o-light and e-light.

[0026] The crystal rotation stage refers to a precision rotating platform equipped with dual vernier scales and an angle encoder. Specifically, it can be implemented using a stepper motor-driven rotation stage in conjunction with a photoelectric encoder. It is used to precisely control the crystal rotation angle and provide real-time position data feedback. The spectrometer telescope refers to an optical observation device with a dual vernier readout function. Specifically, it can be implemented using an Abbe autocollimation telescope in conjunction with a CCD image sensor. It is used to dynamically capture changes in the minimum deflection angle. The parallel arrangement of the photoelectric sensor and the light screen refers to combining a charge-coupled device and a calibration grid plate in the same optical path. Specifically, it can be implemented using a silicon photodiode array in conjunction with a precision ruled glass plate. It is used to simultaneously acquire light intensity signals and spatial coordinate data. The data processing module refers to a computing unit with multi-channel data acquisition capabilities. Specifically, it can be implemented using an embedded processor in conjunction with an analog-to-digital conversion circuit. It is used to fuse angle data, voltage signals, and coordinate information for joint calculations.

[0027] Specifically, the light beam emitted by a sodium lamp is collimated into parallel light by a collimator and incident on a rotating crystal stage. As the stage rotates the first birefringent crystal, the spectrometer telescope records the minimum deflection angles of the o and e beams in real time using dual vernier scales. The first rotatable polarizer filters out non-target polarized light, ensuring the spectrometer accurately distinguishes the two polarization states. During polarization splitting ratio measurement, the laser output beam is polarized by the second birefringent crystal. The second rotatable polarizer adjusts the incident polarization direction. A photoelectric sensor detects the peak-to-peak voltage of the o and e beams, and a light screen records the spatial coordinate offset of the two beams. The data processing module synchronously receives the rotation angle of the angle encoder, the deflection angle data from the dual vernier scales, the voltage signal from the oscilloscope, and the coordinate data from the light screen. It calculates the birefringence using the minimum deflection angle formula, the polarization splitting ratio using the voltage ratio, and the amount of beam splitting based on the coordinate difference.

[0028] Compared with the existing technology, the traditional method uses a single detection mode, resulting in incomplete parameter acquisition. However, this solution achieves synchronous detection of refractive index, polarization splitting ratio and spatial offset through dual optical path collaborative measurement. In the existing technology, the spectrometer measurement is a static single reading. The present invention improves the angle measurement accuracy by an order of magnitude through the dynamic coordination of the crystal rotating stage and the dual vernier system. Compared with traditional photoelectric detection that can only obtain light intensity signals, the present invention innovatively combines the calibration of light screen coordinates to provide a spatial dimension verification basis for polarization splitting.

[0029] Through the above-mentioned technical solution, the present invention effectively solves the problem of insufficient directional identification in birefringence measurement, enabling multi-angle data acquisition through a crystal rotating stage. The lack of polarization information is overcome by the combined detection of a first rotatable polarizer and a photoelectric sensor, ensuring accurate differentiation of o- and e-light. The measurement signal-to-noise ratio is significantly improved by dynamically capturing the minimum deflection angle using a spectrometer. Simultaneously, the parallel detection of the light screen coordinates and the photoelectric signal provides a dual verification mechanism for the polarization splitting ratio, enhancing the reliability of the measurement results.

[0030] In an optional embodiment, the calculation formulas for the refractive index of o-light and e-light are: ; ;

[0031] in, is the refractive index of o light; is the refractive index of e-light; is the apex angle of the birefringent crystal; δ min1 is the minimum deflection angle of o light, δ min2 is the minimum deflection angle of e-light.

[0032] The vertex angle refers to the angle between two opposite crystal faces of a birefringent crystal. It can be calibrated using a spectrometer with a standard angle block. This parameter is pre-measured as an inherent property of the crystal and substituted into the formula. min1 and δ min2 It refers to the minimum deflection angle of the o-ray and e-ray captured by the rotating crystal stage in the spectrometer. It can be read dynamically through the dual vernier dial and the spectrometer telescope. This parameter eliminates the angular error in traditional static measurement through a real-time feedback mechanism.

[0033] Specifically, when the light beam emitted by the sodium lamp passes through the collimator and becomes parallel light and enters the crystal, the o-light and e-light have different propagation paths due to the birefringence effect. By rotating the crystal stage and synchronously observing the movement direction of the spectrum line in the spectrometer telescope, the minimum deflection angle of the two polarized lights is dynamically determined. The vertex angle is used as a known geometric parameter and is compared with the dynamically captured δ min1 and δ min2 Substituting these into the formula, the refractive index can be directly calculated from the geometric relationship of the optical propagation path. This calculation process, by combining the mathematical relationship between the crystal apex angle and the minimum deviation angle, avoids the cumulative error caused by fixed-angle measurement in traditional methods, thereby accurately distinguishing the refractive index difference between o-light and e-light.

[0034] Through the above technical solution, the present invention can accurately calculate the numerical difference in the refractive index of o-light and e-light in birefringent crystals, solve the problem of insufficient measurement accuracy caused by angular error and lack of directionality in traditional methods, and provide high-precision quantitative data support for the optical property analysis of birefringent crystals.

[0035] In an optional implementation, the steps for calculating the polarization splitting ratio are: ;

[0036] in, is the polarization splitting ratio; is the peak-to-peak voltage of o light V o,pp The value in the middle corresponds to the maximum light intensity; is the peak-to-peak voltage of e-light V e,pp The value in corresponds to the maximum light intensity.

[0037] The peak-to-peak voltage refers to the difference between the maximum and minimum values ​​of the voltage fluctuation range of the electrical signal output by the photoelectric sensor, as displayed on an oscilloscope. This can be achieved using a silicon photodiode as the photoelectric sensor. Its response time must be less than one-tenth of the polarizer rotation period to ensure dynamic sampling accuracy. The value at maximum light intensity refers to the voltage signal corresponding to the peak intensity of the o-light or e-light when the polarizer is rotated. This can be achieved by using an oscilloscope's trigger mode to capture the highest point of the voltage waveform. This method effectively eliminates interference from ambient light noise on the measurement results.

[0038] Specifically, during the rotation of the second rotatable polarizer, the photoelectric sensor collects the changes in the light intensity passing through the polarizer in real time, converts it into an electrical signal, and transmits it to the oscilloscope. The oscilloscope processes the electrical signal into a peak-to-peak voltage waveform, and records the voltage data when the intensity of the o light and the e light reaches the maximum value as and Because light intensity and voltage signals have a linear relationship, selecting the voltage value corresponding to maximum light intensity eliminates measurement errors caused by optical path deviation or light source fluctuations during polarizer angle adjustment. Calculating the ratio of the two directly reflects the polarization splitting capability of the birefringent crystal for o- and e-light, enabling continuous analysis of the splitting ratio during dynamic measurement.

[0039] Through this technical solution, the present invention achieves dynamic, high-precision measurement of the polarization splitting ratio, resolving the inability of traditional methods to track polarization state changes in real time and their poor anti-interference capabilities. By selecting the voltage value corresponding to the maximum light intensity for ratio calculation, light intensity fluctuations and environmental noise are effectively suppressed, ensuring that the splitting ratio calculation reflects only the differences in the polarization properties of the crystal itself, providing a reliable quantitative basis for the performance evaluation of birefringent crystals.

[0040] In an optional embodiment, the calculation formula for the beam separation amount is: ;

[0041] in, is the beam separation; are the abscissas of the light spots of o-light and e-light respectively; are the ordinates of the light spots of o-light and e-light respectively.

[0042] Beam separation refers to the actual spatial separation between the O- and E-beams. This can be achieved using a screen with a position scale. A two-dimensional coordinate system is provided on the screen surface to mark the horizontal and vertical coordinates of the O- and E-beams. The formula for calculating beam separation is based on the Euclidean distance principle and is calculated by taking the square root of the sum of the differences between the horizontal and vertical coordinates of the two light spots.

[0043] Specifically, the structure of the light screen with position scale converts the spot positions of the o-light and e-light into specific coordinate data through a preset two-dimensional coordinate system. For example, when the laser passes through the birefringent crystal, the o-light and e-light form two separate spots on the light screen. By reading the horizontal coordinates of the spots on the scale and the vertical axis , and the actual spatial distance between the two can be calculated by substituting . This formula eliminates the positive and negative effects of the coordinate difference through a square operation, and then restores it to a linear distance by taking the square root, thus accurately reflecting the separation effect of the birefringent crystal on the light beam.

[0044] Compared to existing technologies, traditional methods typically measure beam deviation in only a single direction, such as recording only the horizontal or vertical coordinate difference. This fails to fully reflect the actual degree of beam separation in a two-dimensional plane. However, this solution, by introducing a two-dimensional coordinate system and Euclidean distance calculation, can simultaneously capture both horizontal and vertical separation components, thereby more accurately quantifying the amount of beam separation.

[0045] In an optional embodiment, the second birefringent crystal, the first rotatable polarizer and the light screen are on the same horizontal line.

[0046] Among them, the second birefringent crystal refers to a transparent optical element that decomposes the incident laser into o-light and e-light. Specifically, it can be implemented by calcite or quartz crystal, and its optical axis direction forms a specific angle with the propagation direction of the incident light. The second rotatable polarizer refers to a polarization element that can rotate around the optical axis. Specifically, it can be implemented by a polarizer bracket with an angle scale, which is used to adjust the polarization direction of the outgoing light. The light screen refers to a planar receiving device with a position scale. Specifically, it can be implemented by a diffuse reflection plate with a coordinate grid covered on the surface, which is used to record the spot position of o-light and e-light. The structural design of the three arranged horizontally in a straight line can constrain the propagation direction of the light path and avoid unexpected tilt or deviation of the light beam during spatial propagation.

[0047] Specifically, after the second birefringent crystal decomposes the incident laser into o-light and e-light, the two beams propagate along the transmission axis of the second rotatable polarizer. Since the three are on the same horizontal line, the o-light and e-light continue to propagate in their original directions to the light screen after passing through the polarizer, ensuring that the measurement reference of the light spot coordinates is strictly aligned with the axis of the optical path. This design eliminates the lateral displacement error caused by the tilt of the optical path, so that the coordinate difference marked on the light screen only reflects the amount of beam separation caused by birefringence. At the same time, the horizontal straight line layout provides a stable light intensity detection path for the photoelectric sensor, so that the peak-to-peak voltage collected by the oscilloscope is synchronized with the change in the light spot position, avoiding signal delays caused by differences in optical path length.

[0048] Through the above technical solution, the present invention effectively eliminates the coordinate measurement error caused by the tilt of the optical path, ensures the time synchronization of the light spot position and the photoelectric signal, and improves the dynamic measurement accuracy of the beam separation amount and the polarization splitting ratio.

[0049] In addition, the present invention also provides a method for measuring birefringence and polarization splitting ratio based on crystal rotation, comprising: Step S1: Based on the minimum deflection angle δ of the o-light and the e-light min1 , δ min2 , calculate the refractive index of o light and e light respectively; Step S2: Peak-to-peak voltage of o-light and e-light V o,pp 、 V e,pp , calculate the real-time polarization splitting ratio, and the spot coordinates of the o-light and the spot coordinates of e-light , calculate the beam separation amount of o-light and e-light.

[0050] In an optional embodiment, step S1 includes: Step S11: a sodium lamp emits a light beam, which is collimated by a collimator and then incident on a first birefringent crystal on a crystal rotating stage; Step S12: adjusting the angle of the spectrometer telescope so that light o and light e appear in the field of view; Step S13: adjusting the angle of the first rotatable polarizer so that the o-light and the e-light can be distinguished in the field of view of the spectrometer telescope; Step S14: Rotate the crystal rotating stage to dynamically capture the minimum deflection angle δ of the o-light and the e-light through the spectrometer telescope. min1 , δ min2 , and record the dual vernier dial readings simultaneously; Step S15: According to the minimum deflection angle δ min1 , δ min2 and the vertex angle of the first birefringent crystal to calculate the refractive index of o light and the refractive index of e light.

[0051] A sodium lamp is a light source that emits monochromatic light. Specifically, a sodium D-line light source with a wavelength of 589.3 nanometers can be used. Its function is to provide stable monochromatic incident light for birefringence measurements, avoiding measurement errors caused by polychromatic light. A collimator is an optical element that converts a divergent light beam into a parallel beam. Specifically, a lens assembly or a reflector system can be used. Its function is to ensure that the incident light enters the birefringent crystal in a collimated state, reducing the impact of beam divergence on angle measurement. A spectrometer telescope is a device used to observe and measure the angle of light deflection. Specifically, a telescope structure with an eyepiece scale and an objective lens focusing mechanism can be used. Its function is to capture the minimum deflection angle in real time by dynamically tracking changes in the optical path. A double vernier scale is a device with two symmetrically distributed vernier readouts. Specifically, a mechanical or photoelectric angle encoder can be used. Its function is to eliminate eccentricity errors through symmetrical readings, improving angle measurement accuracy to within 1 minute. Dynamic capture of the minimum deflection angle refers to tracking the minimum value of light deflection by adjusting the crystal rotation angle in real time. This can be achieved by using a servo motor to drive the stage and synchronously recording the angle data. Its function is to avoid errors caused by angle positioning deviation in static measurements through continuous monitoring.

[0052] Specifically, the monochromatic light beam emitted by the sodium lamp is collimated by a collimator to form parallel beams. Upon entering the first birefringent crystal, birefringence occurs, producing o- and e-rays. The spectrometer telescope is adjusted to simultaneously observe the refraction paths of both polarized light, resulting in two separate spectral lines in the field of view. The angle of the first rotatable polarizer is adjusted to a specific orientation, creating a contrast difference between the o- and e-rays in the spectrometer telescope's field of view, thereby clearly distinguishing the two polarization states. The crystal rotating stage rotates, changing the relative angle between the birefringent crystal and the incident light. The spectrometer telescope monitors the changes in the deflection angles of the o- and e-rays in real time. When the deflection angle reaches its minimum, the dual vernier scales simultaneously record the left and right vernier readings. The minimum deflection angle is calculated by comparing the difference between the refraction angle and the incident angle. Finally, the refractive index values ​​for the o- and e-rays are obtained by substituting the crystal's vertex angle into the refractive index formula, respectively.

[0053] Compared with existing technologies, traditional methods use fixed-angle measurements or single readings, which are unable to track the changing trend of the minimum deflection angle in real time, resulting in limited measurement accuracy. Dynamic capture technology, by continuously rotating the crystal and synchronously recording the angle data, accurately captures the minimum point of light deflection, avoiding systematic errors caused by angular positioning deviations. Furthermore, the use of a dual vernier scale further eliminates eccentricity errors, improving angle measurement accuracy by an order of magnitude and resolving the difficulty in distinguishing directional differences in traditional spectral analysis.

[0054] Through the above-mentioned technical solution, the present invention achieves high-precision dynamic measurement of the minimum deflection angle of o- and e-light in birefringent crystals, effectively distinguishing the directional differences between the two polarization states and fully preserving the polarization information. The use of a collimated monochromatic light source and a symmetrical vernier readout significantly reduces environmental interference and system errors, improving the signal-to-noise ratio. Ultimately, the refractive index is directly calculated using geometric optical relationships, avoiding the difficulty in quantifying optical path differences in traditional intensity detection methods, providing a reliable experimental data foundation for analyzing the optical properties of birefringent crystals.

[0055] Through the above technical solution, the present invention solves the problem in the prior art that the spatial separation of light beams caused by birefringent crystals cannot be accurately measured, and realizes high-precision measurement of the actual separation distance of o-light and e-light on a two-dimensional plane, providing a reliable spatial separation data basis for the optical property analysis of birefringent crystals.

[0056] In an optional embodiment, step S2 includes: Step S21, emitting laser light through a laser, the laser light is incident on a second birefringent crystal and then modulated into linearly polarized light by a second rotatable polarizer; Step S22, execute in parallel at the output end of the second rotatable polarizer: mark the spot coordinates of the o light on the light screen with position scale and the spot coordinates of e-light ; and, collect the peak-to-peak voltage of o light and e light in real time through the photoelectric sensor V o,pp 、 V e,pp , and output by the oscilloscope; Step S23: According to the peak-to-peak voltage V o,pp 、 V e,pp Calculate real-time polarization splitting ratio; Step S24: according to the spot coordinates of the o light and the spot coordinates of e-light , calculate the beam separation of o-light and e-light.

[0057] The second rotatable polarizer is a polarization modulator that can rotate about the optical axis. Specifically, this can be implemented using a polarizer holder driven by a stepper motor. It is used to adjust the polarization direction of the outgoing light to match the detection reference of the photoelectric sensor. A light screen with a position scale is a projection plane with gridded coordinate markings on its surface, such as a transparent acrylic plate printed with millimeter-scale scale lines. This is used to directly quantify the spatial separation effect caused by birefringence by differences in the position of the light spots. A photoelectric sensor is a detection unit that converts optical signals into electrical signals. For example, a silicon photodiode combined with a transimpedance amplifier circuit is used to capture the intensity changes of the o- and e-lights in real time and output a peak-to-peak voltage signal. The beam separation refers to the spatial offset distance between the o- and e-lights. This can be calculated by coordinate difference, such as using the Pythagorean theorem to calculate the distance between the centers of the two light spots. This characterizes the beam separation capability of a birefringent crystal.

[0058] Specifically, the collimated light beam output by the laser undergoes birefringent splitting after passing through the second birefringent crystal, forming two beams of light with orthogonal polarization directions, o-light and e-light. The second rotatable polarizer adjusts the rotation angle so that the polarization directions of the two beams are aligned with the detection axis of the photoelectric sensor, ensuring the effective extraction of the light intensity signal. At the output end of the optical path, the position scale on the light screen records the coordinate data by capturing the projection positions of the two light spots, while the photoelectric sensor synchronously collects the instantaneous light intensity of the two beams and converts it into a peak-to-peak voltage signal. The data processing module calculates the polarization splitting ratio based on the peak-to-peak voltage ratio to reflect the energy distribution characteristics; at the same time, it calculates the beam separation amount based on the coordinate difference to characterize the degree of spatial offset. This parallel detection mechanism realizes the synchronous acquisition of the intensity and spatial parameters of the polarization splitting, avoiding the timing error caused by the step-by-step measurement in the traditional method.

[0059] Compared with existing technologies, traditional polarization beam splitting measurements typically rely on a combination of a beam splitter prism and a power meter, which can only obtain light intensity ratios but cannot record spatial separation, and requires multiple adjustments to the position of optical components. However, the present invention uses dual-modal detection, combining optical screen coordinate calibration with synchronous acquisition of photoelectric signals, to simultaneously obtain both beam splitting ratio and separation data in a single measurement, eliminating the operational complexity associated with repeated equipment configuration. Furthermore, existing technologies often use microscopic imaging or CCD scanning to measure beam separation, which suffers from slow response speeds and complex data processing. This solution simplifies the spatial parameter acquisition process by directly reading coordinates using an optical screen with a scale.

[0060] Through the above-mentioned technical solution, the present invention achieves the simultaneous execution of dynamic measurement of the polarization splitting ratio and spatial positioning of the beam separation amount, solving the problems of single-dimensional characterization of beam splitting characteristics and asynchronous spatiotemporal data in traditional methods. The parallel data acquisition mechanism of the photoelectric sensor and the optical screen improves the real-time measurement, while the direct reading of the coordinate scale enhances the spatial resolution. In the detection of the optical properties of birefringent crystals, this solution can simultaneously output quantitative parameters of energy distribution and spatial offset, providing multidimensional data support for the performance evaluation of polarization devices.

[0061] In an optional embodiment, as Figure 2 As shown, the crystal rotating stage is rotated to dynamically capture the minimum deflection angle δ of o-light and e-light through the spectrometer telescope. min1 , δ min2 include: Step a, finding the yellow spectral line refracted from the first birefringent crystal in the spectrometer telescope; Step b, rotating the crystal rotating stage so that the yellow spectrum line tends to move in the direction of decreasing deflection angle; when the yellow spectrum line begins to move in the opposite direction, the left and right cursor readings at the current moment are used as the refraction angles of the left path and the right path; Step c: Remove the first birefringent crystal, rotate the spectrometer telescope to align it with the collimator, and align the crosshairs with the slits. Use the current left and right vernier readings as the incident angles of the left and right paths, respectively. Step d: Calculate the minimum deflection angle δ of o-light and e-light min1 , δ min2 , and its calculation formula is: ;

[0062] in, 、 are the refraction angles of the left path and the right path respectively; are the incident angles of the left path and the right path, respectively.

[0063] Among them, the yellow spectral line refers to the characteristic spectral line produced by the sodium lamp light source after passing through the birefringent crystal. Specifically, it can be achieved by using a sodium lamp to emit light with a wavelength of 589.3nm and identifying it through a spectrometer telescope, which is used to locate the refraction paths of o-light and e-light. The crystal rotation stage refers to a mechanical structure that can rotate around an axis and carry a birefringent crystal. Specifically, it can be achieved by using a stepper motor drive and an integrated angle encoder, which is used to dynamically adjust the crystal angle to track the minimum deviation angle position. The double vernier scale refers to an angle measuring device with left-right symmetrical vernier readings. Specifically, it can be achieved by using a double vernier system that comes with a spectrometer. The eccentricity error of a single vernier is eliminated by synchronously recording the readings on the left and right sides. The angle of incidence and the angle of refraction refer to the angular parameters of light when it enters and leaves the crystal. Specifically, it can be achieved by aligning the spectrometer telescope with the collimator slit and recording the vernier readings. It is used to construct the geometric relationship of the optical path and calculate the minimum deviation angle.

[0064] Specifically, the spectrometer telescope is used to capture the yellow spectrum produced by the sodium lamp light source passing through the birefringent crystal, and the angle of the crystal rotating stage is dynamically adjusted. When the direction of movement of the spectrum line reverses, it indicates that the critical point of the minimum deflection angle has been reached. At this time, the refraction angle readings of the left and right cursors are recorded synchronously, and then the crystal is removed and realigned with the collimator slit, and the incident angle reading is recorded. The refraction angle and the incident angle are calculated using the average value of the left and right cursor readings, respectively, and the minimum deflection angle is substituted into the formula. This process effectively eliminates manual judgment bias and instrument mechanical errors by dynamically tracking changes in the direction of movement of the spectrum line and combining dual cursor redundant data acquisition.

[0065] Compared to existing technologies, traditional methods rely on static angle measurement and single vernier readings, making them susceptible to operator visual error and instrument assembly errors. This present invention employs dynamic path tracking technology, determining the minimum deflection angle position by reversing the direction of spectral line movement. Combined with a dual-vernier symmetrical reading mechanism, this reduces angle measurement errors to within the instrument's inherent accuracy. Furthermore, the separate measurement of incident and refracted angles prevents interference from crystal assembly errors in optical path calculations.

[0066] Through the above-mentioned technical solution, the present invention achieves precise measurement of the minimum deflection angle of birefringent crystals, eliminating the measurement deviation problems caused by manual reading errors and angle drift. The combination of dynamic tracking and dual-vernier redundancy check ensures that the accuracy of minimum deflection angle capture is limited only by the mechanical accuracy of the spectrometer, eliminating the need for operator experience. The separate measurement method of the incident and refraction angles further reduces the impact of crystal mounting position deviations on the calculated results, providing a reliable data foundation for high-precision calculations of birefringence.

[0067] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A birefringence and polarization splitting ratio measurement system based on crystal rotation, characterized in that: include: Birefringence measurement module, polarization splitting ratio measurement module and data processing module; A birefringence measurement module includes a sodium lamp, a collimator, a crystal rotating stage, a first birefringent crystal, a first rotatable polarizer, and a spectrometer telescope, which are sequentially arranged along a first optical path; The crystal rotating stage is provided with a double vernier scale and carries the first birefringent crystal, and the rotation angle is fed back in real time through a built-in angle encoder; the spectrometer telescope is connected to the double vernier scale and is used to dynamically capture the minimum deflection angle δ of the o-light and the e-light. min1 , δ min2 ; A polarization beam splitting ratio measurement module includes a laser, a second birefringent crystal, and a second rotatable polarizer arranged in sequence along a second optical path; Wherein, a light screen and a photoelectric sensor are arranged in parallel on the output light path of the second rotatable polarizer; the light screen has a position scale for marking the coordinates of the light spot of the o light and the spot coordinates of e-light The photoelectric sensor is connected to an oscilloscope to output the peak-to-peak voltage of o light / e light in real time V o,pp 、 V e,pp ; The data processing module is electrically connected to the angle encoder, the double vernier scale and the oscilloscope, and is used to calculate the minimum deflection angle δ of the o light and the e light. min1 , δ min2 , respectively calculate the refractive index of o light and e light; and, for peak-to-peak voltage according to o light and e light V o,pp 、 V e,pp , calculate the real-time polarization splitting ratio; and, for the spot coordinates of the o light and the spot coordinates of e-light , calculate the beam separation amount of o-light and e-light.

2. The system according to claim 1, wherein: The calculation formulas for the refractive index of o-light and e-light are: ； ； in, is the refractive index of o light; is the refractive index of e-light; is the apex angle of the birefringent crystal; δ min1 is the minimum deflection angle of o light, δ min2 is the minimum deflection angle of e-light.

3. The system according to claim 1, wherein: The calculation steps of the polarization splitting ratio are: ； in, is the polarization splitting ratio; is the peak-to-peak voltage of o light V o,pp The value in the middle corresponds to the maximum light intensity; is the peak-to-peak voltage of e-light V e,pp The value in corresponds to the maximum light intensity.

4. The system according to claim 1, wherein: The formula for calculating the amount of beam separation is: ； in, is the beam separation; are the abscissas of the light spots of o-light and e-light respectively; are the ordinates of the light spots of o-light and e-light respectively.

5. The system according to claim 1, wherein: The second birefringent crystal, the first rotatable polarizer and the light screen are on the same horizontal line.

6. A method for measuring birefringence and polarization splitting ratio based on crystal rotation, characterized in that: include: S1, based on the minimum deflection angle δ of o light and e light min1 , δ min2 , calculate the refractive index of o light and e light respectively; S2, according to the peak-to-peak voltage of o light and e light V o,pp 、 V e,pp , calculate the real-time polarization splitting ratio, and the spot coordinates of the o-light and the spot coordinates of e-light , calculate the beam separation amount of o-light and e-light.

7. The method according to claim 6, characterized in that Said S1 comprises: The light beam is emitted by a sodium lamp, collimated by a collimator and then incident on a first birefringent crystal on a crystal rotating stage; Adjust the angle of the spectrometer telescope so that o-light and e-light appear in the field of view; Adjusting the angle of the first rotatable polarizer to enable the o-light and e-light to be distinguished in the field of view of the spectrometer telescope; Rotate the crystal rotating stage to dynamically capture the minimum deflection angle δ of o-light and e-light through the spectrometer telescope min1 , δ min2 , and record the dual vernier dial readings simultaneously; According to the minimum deflection angle δ min1 , δ min2 and the vertex angle of the first birefringent crystal to calculate the refractive index of o light and the refractive index of e light.

8. The method according to claim 6, characterized in that The S2 includes: The laser is emitted by a laser, and the laser is incident on a second birefringent crystal and then modulated into linearly polarized light by a second rotatable polarizer; Performed in parallel at the output of the second rotatable polarizer: Mark the spot coordinates of the o light on the light screen with position scale and the spot coordinates of e-light ; and, collect the peak-to-peak voltage of o light and e light in real time through the photoelectric sensor V o,pp 、 V e,pp , and output by the oscilloscope; According to the peak-to-peak voltage V o,pp 、 V e,pp Calculate real-time polarization splitting ratio; According to the spot coordinates of the o light and the spot coordinates of e-light , calculate the beam separation of o-light and e-light.

9. The method according to claim 7, characterized in that The rotating crystal rotating stage dynamically captures the minimum deflection angle δ of o-light and e-light through the spectrometer telescope min1 , δ min2 ,include: Find the yellow spectral line refracted from the first birefringent crystal in the spectrometer telescope; Rotate the crystal stage to make the yellow spectrum line tend to the direction with decreasing deflection angle; when the yellow spectrum line starts to move in the opposite direction, use the left and right cursor readings at the current moment as the refraction angles of the left and right paths; Remove the first birefringent crystal, rotate the spectrometer telescope to align with the collimator, and align the crosshairs with the slits. Use the left and right cursor readings at the current moment as the incident angles of the left and right paths respectively. Calculate the minimum deflection angle δ of o light and e light min1 , δ min2 , and its calculation formula is: ； in, 、 are the refraction angles of the left path and the right path respectively; are the incident angles of the left path and the right path, respectively.

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