Ultrahigh-precision birefringence detection system and method based on geometric phase jump effect

Abstract

The invention relates to the technical field of photoelectrons, in particular to an ultrahigh-precision birefringence detection system and method based on a geometric phase jump effect. The system comprises a laser, a half-wave plate, a quarter-wave plate, a polarizer, a crystal to be measured, a rotating table, a first beam splitter prism, a second beam splitter prism, a reflector and a charge coupling element. A linearly polarized light beam in the horizontal direction passes through a half-wave plate and a quarter-wave plate and then is split in a first beam splitting prism, an interference light beam after beam splitting is reflected and then enters a second beam splitting prism together with a main light beam passing through a crystal to be detected for beam combination, and then the interference light beam passes through a polarization analyzer and is collected by a charge coupling element; adjusting the voltage applied to the crystal, observing the brightness change of the interference fringes, recording the voltage required by the brightness change, and calculating the refractive index change. The change of the refractive index in the crystal material is observed by utilizing the geometric phase jump effect of the crystal material, and ultrahigh-precision measurement of the change of the refractive index of the crystal is realized.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and in particular to an ultra-high precision birefringence detection system and method based on a geometric phase jump effect. Background Art

[0002] Birefringence is commonly observed in certain materials, such as anisotropic crystals or stressed plastics. This birefringence arises from variations in the material's refractive index; these changes affect optical properties such as polarization, wavelength, and propagation direction of light passing through the material. By leveraging these changes in optical properties, birefringence can be used to further investigate the internal structure or molecular orientation of target materials, enabling a better understanding of their properties and improving applications in production and life. However, birefringence can also have adverse effects. For example, in fiber optic communications, variations in the refractive index within the fiber often distort the transmitted light field, reducing signal quality. In laser experiments, small changes in the refractive index within a laser crystal can alter key optical parameters such as the wavelength, polarization, and intensity of the light emitted by the crystal. Therefore, accurately detecting refractive index variations in the material under test is crucial, both in industry and scientific research.

[0003] At present, the detection of birefringence effects at home and abroad can be divided into two categories: direct measurement and indirect measurement. Direct measurement usually uses photoelastic polarization modulators, laser feedback effects, total internal reflection methods, Fabry-Perot cavities and other methods to detect birefringence effects. Indirect measurement usually uses quantum means, such as quantum weak measurement, which combines weak value amplification and ultrafast time delay technology to achieve high-precision detection of the birefringence effect of crystal materials. However, the current measurement accuracy of the above-mentioned methods can only reach 10 -8 This greatly limits the development of industrial production and scientific research.

[0004] Classical optics has systematically and thoroughly expounded on the concept of geometric phase, which emphasizes that the geometric phase of a photon is independent of the spacetime dynamics it experiences, but rather depends solely on its trajectory within the parameter space in which it evolves. Unlike the dynamical phase we are more familiar with, which is affected by time and space, the geometric phase is entirely determined by the parameter space in which it is defined and the geometric path of the photon's evolution on the Poincare sphere, unaffected by spacetime dynamics. This exceptional robustness to environmental interference and exceptional robustness have led many researchers to exploit this property of geometric phase to study well-known physical effects, such as the Aharonov-Bohm effect, the Sagnac effect, the Magnus effect, the quantum Hall effect, and the optical Hall effect. Furthermore, these physical effects have spawned a variety of cutting-edge applications, including optical sensing, photometry, optical imaging, and, most importantly, optical precision measurement. By leveraging the geometric phase's robustness to environmental interference and stability, it is possible to improve its stability and detection accuracy in these areas, further promoting the development of modern optical applications. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides an ultra-high precision birefringence detection system and method based on the geometric phase jump effect. By applying a small voltage to the crystal material to be measured, the geometric phase of the light field jumps, and then the outgoing light passing through the crystal interferes with the plane wave to observe the brightness changes of the central interference fringes, thereby utilizing the geometric phase jump effect of the crystal material to observe the changes in the refractive index inside the crystal material, thereby achieving ultra-high precision measurement of the crystal refractive index change.

[0006] The detection system of the present invention is implemented by the following technical solutions: an ultra-high-precision birefringence detection system based on the geometric phase jump effect, comprising a laser, a half-wave plate, a quarter-wave plate, a polarizer, a crystal to be measured, a rotating stage, a first beam-splitting prism, a second beam-splitting prism, a reflector, and a charge-coupled device; the rotating stage is mounted on the crystal to be measured, and the rotating stage is rotated to rotate the crystal to be measured along the optical axis; voltage is applied to the upper and lower plates of the crystal to be measured;

[0007] The horizontal linearly polarized beam emitted by the laser passes through a half-wave plate and a quarter-wave plate to set the initial polarization state of the initial incident light field of the crystal to be measured. The beam emitted from the quarter-wave plate is incident on the first beam splitting prism for beam splitting. The main beam after the splitting passes through the crystal to be measured. The interference beam after the splitting is reflected and incident on the second beam splitting prism together with the main beam that passed through the crystal to be measured for beam combination. The combined beam passes through the analyzer and is collected by the charge coupled device.

[0008] Adjust the voltage applied to the crystal to be tested at preset voltage intervals, observe the changes in the brightness of the interference fringes, record the voltage required for the changes in the brightness of the interference fringes, and calculate the change in refractive index.

[0009] The detection method of the present invention is implemented based on the above detection system and includes the following steps:

[0010] S1. Processing the horizontal linear polarized light emitted by the laser through a half-wave plate and a quarter-wave plate to set the initial polarization state of the initial incident light field of the crystal to be measured;

[0011] S2. After the light beam has been processed by the half-wave plate and the quarter-wave plate, a polarizer is set to eliminate the influence of the phase difference between the outgoing light field of the crystal to be tested and the initial incident light field, and then the light beam is incident on the crystal to be tested; the crystal to be tested is rotated at any angle using a rotating stage; a voltage is applied to the crystal to control the evolution of the photon state on the Poincare sphere; and finally, the light and dark interference fringes are collected using a charge-coupled device.

[0012] S3. Observe the interference fringes. By adjusting the voltage applied to the crystal to be tested, record the voltage value required when the interference fringes change from light to dark, and calculate the change in refractive index.

[0013] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0014] 1. Unlike existing direct measurement methods such as photoelastic polarization modulators, laser negative feedback effects, Fabry-Perot cavities, total internal reflection, and quantum weak measurements, the present invention utilizes the geometric phase jump effect in quantum mechanics and optics. By applying a small voltage to the crystal material to be measured, the geometric phase of the light field emitted by the crystal material jumps (for example, a jump of π). The small voltage required to change the bright and dark interference fringes is recorded, and then the change in the refractive index of the measured crystal is accurately calculated based on the geometric phase expression on which the magnetic field depends. The detection accuracy of the refractive index change can reach 10 -11 It is of an order of magnitude, greatly improving the detection accuracy of the birefringence effect, and has good robustness, high detection accuracy and strong anti-interference ability.

[0015] 2. The present invention utilizes the geometric phase jump effect to achieve ultra-high-precision detection of the birefringence effect of the crystal material to be tested, so that the birefringence effect, an optical phenomenon that is vague and difficult to observe, can be vividly displayed in front of the observer. The designed detection scheme has the advantages of good stability of the experimental device, high detection accuracy, high response sensitivity, and a wide range of adaptability. In the future, it can greatly promote industrial production and scientific research, and detect material defects and material properties, and realize low-cost, high-precision detection of material refractive index changes (i.e., birefringence effect). BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the structure of an ultra-high-precision birefringence detection system based on the geometric phase jump effect in an embodiment of the present invention;

[0017] Figure 2 Schematic diagrams of the wave plate rotation and placement in the main steps of determining the position of the initial incident light field of the crystal to be tested on the Poincare sphere in an embodiment of the present invention; (a) a half-wave plate is used to convert horizontal linear polarization to +45° linear polarization; (b) a quarter-wave plate is added to convert +45° linear polarization to right-handed circular polarization; (c) the quarter-wave plate is removed to maintain the same rotation angle of the quarter-wave plate, and the half-wave plate is rotated to convert the +45° linear polarization to a position close to vertical polarization; (d) a quarter-wave plate is added to rotate the light to above the same meridian as the vertical polarization transition point;

[0018] Figure 3 Schematic diagram of the theoretical and experimental results of the geometric phase transition when the crystal rotation angle α = 3π / 4, the parameters of the incident photon state φ = π / 2, and θ = 8π / 15 in an embodiment of the present invention; (a) shows the geometric phase as a function of voltage, (b) shows the interference fringes before the geometric phase transition, and (c) shows the interference fringes after the geometric phase transition;

[0019] Figure 4 Schematic diagram of the theoretical and experimental results of the geometric phase jump when the crystal rotation angle α = 3π / 4, the parameters of the incident photon state φ = π / 2, θ = 31π / 60 in an embodiment of the present invention; wherein (a) is the function of the change of geometric phase with voltage; (b) is the interference fringes before the geometric phase jump; and (c) is the interference fringes after the geometric phase jump. DETAILED DESCRIPTION

[0020] The present invention utilizes the geometric phase jump effect of crystal materials to clearly observe the change in the refractive index inside the crystal material. Specifically, a plane wave is used to interfere with the light field passing through the crystal material, and a small voltage is applied to the crystal material. The light and dark changes of the interference fringes can be observed. Then, by calculating the voltage required for the transition between light and dark interference fringes, the geometric phase change carried by the light field can be determined, for example, the geometric phase jump is π; further, the refractive index change of the crystal material to be tested can be accurately calculated using the refractive index calculation formula. The present invention can detect a refractive index change of 10 -11 Magnitude.

[0021] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0022] Example 1

[0023] like Figure 1As shown, the ultra-high-precision birefringence detection system based on the geometric phase jump effect in this embodiment includes: a laser, a half wave plate (HWP), a quarter wave plate (QWP), a polarizer (P), a lithium niobate crystal (LN), a rotating stage (RS), a beam splitter (BS), a mirror (M), and a charge-coupled device (CCD). The beam splitter includes a first beam splitter prism and a second beam splitter prism, and the mirror includes a first reflector and a second reflector.

[0024] Among them, the laser emits horizontal linear polarized light, and the direction of polarization can be changed by rotating the half wave plate and the quarter wave plate. Rotating the half wave plate can make the polarization state of the initial incident light field of the crystal evolve along the same latitude, while rotating the quarter wave plate can make it evolve along the same longitude.

[0025] A 360° rotating table is applied to the crystal to be tested, so that the crystal can be rotated along the optical axis. A gold film can be coated on the upper and lower plates of the crystal material to be tested, and a voltage source can be connected using wires to apply voltage. The changes in the bright and dark interference fringes are observed, and the maximum accuracy of the system in detecting the birefringence effect is further calculated.

[0026] The polarizer is set after the second beam-splitting prism to eliminate the interference fringe error caused by the phase difference between the outgoing light field and the initial incident light field, so that it only allows the polarized light beam in a single direction (horizontal or vertical) to pass through. The movement of the interference fringes represents the change in the geometric phase.

[0027] Specifically, in this embodiment, a helium-neon laser is used as the laser. The horizontal linearly polarized light beam emitted by the laser passes through a half-wave plate and a quarter-wave plate, thereby setting the initial polarization state of the initial incident light field of the crystal to be measured on the Poincare sphere. The light beam emitted from the quarter-wave plate is incident on a first beam-splitting prism for beam splitting. The main beam after splitting passes through the crystal to be measured. The crystal to be measured is mounted on a rotating stage that can rotate 360° along the optical axis, and a voltage can be applied to the upper and lower plates of the crystal to be measured. The interference light path of the first beam-splitting prism consists of two reflectors. After reflection, the interference light beam after splitting is incident on a second beam-splitting prism together with the main light beam that has passed through the crystal to be measured for beam combination. The combined light beam passes through a polarizer and is collected and recorded by a charge-coupled device. The function of the polarizer is to eliminate the influence of the phase difference between the output light field and the initial incident light field. By observing the changes in brightness of the interference fringes in the charge-coupled device, recording the voltage required for the interference fringes to switch between light and dark, and calculating the refractive index change using the formula for refractive index change, the accuracy of the birefringence effect that the system can detect is obtained.

[0028] Figure 2 The method and steps for determining the initial incident light field on the Poincare sphere are illustrated, where (a) is the first step, in which the horizontally polarized light is converted to +45° linearly polarized light through a half-wave plate; (b) is the second step, in which a quarter-wave plate is added to convert the +45° linearly polarized light to right-handed circular polarization; (c) is the third step, in which the quarter-wave plate rotation angle is kept unchanged, the quarter-wave plate is removed, and the half-wave plate is rotated to convert the +45° linearly polarized light to a position close to vertical polarization; and (d) is the fourth step, in which a quarter-wave plate is added to rotate it to above the same meridian as the vertical polarization transition point.

[0029] Figure 3 The figure shows the theoretical and experimental results of the geometric phase transition in this embodiment when the rotation angle of the crystal to be tested is α = 3π / 4, the ellipticity angle of the photon state of the initial incident light field of the crystal to be tested is φ = π / 2, and the pitch angle θ = 8π / 15. (a) is the function of the change of geometric phase with voltage, the solid line represents the result of theoretical simulation, and the asterisk represents the result of experimental measurement; (b) is the interference fringes before the geometric phase transition (i.e., voltage U = 15.541V), with the interference fringes at the center being bright fringes; (c) is the interference fringes after the geometric phase transition (i.e., voltage U = 15.542V), with the interference fringes at the center being dark fringes. The scale bars in the figures are all 100μm. By observing the changes in the bright and dark interference fringes, it is used to calculate and detect the change in the refractive index (i.e., the birefringence effect).

[0030] like Figure 1 As shown in the figure, the experimental device for the detection of correlated birefringence is constructed and collimated, wherein the initial polarization of the laser is set to the direction of horizontal linear polarization, and passes through the half wave plate and the quarter wave plate in sequence. Figure 2The method steps include rotating the half wave plate and the quarter wave plate to ensure that the state of the photon incident on the crystal to be measured is above the geometric phase transition point, and determining the initial ellipsometric angle φ = π / 2 and the pitch angle θ = 8π / 15 through the Jones matrix. The light beam then passes through a polarizer, and the polarizer is set to horizontal polarization to eliminate the influence of the phase difference between the outgoing light field and the initial incident light field. At this time, the voltage applied to the crystal to be measured is adjusted at a preset voltage interval (for example, the voltage can be slowly applied to the crystal to be measured starting from 0V, and the preset voltage interval can be 1mV), and at the same time, the brightness changes of the interference fringes are observed through a charge-coupled element, and the voltage required for the interference fringes to transition to brightness and darkness is recorded. As Figure 3 As shown in (a), the solid line is the result of theoretical simulation, the asterisk is the value in the experiment, and the light and dark jump of the interference fringes indicates that the phase of the light field jumps by π. Figure 3 (a) can be used to determine that the voltage at which the geometric phase jump occurs is U1 = 12.541V. When the voltage U2 = 12.542V, the central interference fringe changes from a bright fringe to a dark fringe. At this time, the voltage required for the interference fringe to jump from light to dark is U = U1 – U2 = 0.001V. The change of refractive index is calculated. -11 Order of magnitude. The jumping interference spot is as follows Figure 3 As shown in (b) and (c), an ultra-high-precision birefringence detection based on the geometric phase jump effect is realized.

[0031] This embodiment also proposes an ultra-high-precision birefringence detection method based on the geometric phase jump effect. Because the geometric phase jump occurs at the point of vertical linear polarization on the Poincare sphere, rotating the half-wave plate and quarter-wave plate can position the initial photon state above the same meridian at this point. Furthermore, by applying a small voltage (e.g., less than 20V) to the crystal under test, the state evolves along the same meridian, and the light and dark variations of the interference fringes are observed at the point where the light passes through the vertical polarization point.

[0032] The detection method of this embodiment includes the following steps:

[0033] S1. Process the horizontal linear polarized light emitted by the laser through a half-wave plate and a quarter-wave plate to set the initial polarization state of the initial incident light field of the crystal to be measured.

[0034] Since the Poincare sphere is generally used to describe the polarization state of the light field, this step sets the initial polarization state of the initial incident light field in the Poincare sphere.

[0035] In this step, the helium-neon laser emitted by the laser is horizontally polarized. First, the horizontal linear polarized light is rotated to a +45° linear polarization position through a half-wave plate; then a quarter-wave plate is added to rotate the +45° linear polarization light to a right-handed circular polarization position; then the quarter-wave plate is removed, and the angle of the quarter-wave plate is kept unchanged, and the half-wave plate is continued to be rotated to rotate the +45° linear polarization light to a position close to vertical polarization; finally, a quarter-wave plate is added to rotate it to above the same longitude as the vertical polarization transition point, thereby realizing that the photon state is located above the same longitude as the geometric phase transition point on the Poincare sphere, and then by calculating the polarization angle, the required initial polarization state on the Poincare sphere is obtained.

[0036] S2. For the light beam processed by the half-wave plate and the quarter-wave plate in step S1, a polarizer is set to eliminate the influence of the phase difference between the outgoing light field and the initial incident light field, and then the light beam is incident on the lithium niobate crystal to be measured; a rotating stage is applied to the crystal to realize the rotation of the crystal at any angle; tiny positive and negative voltages are applied to the upper and lower plates of the crystal to realize the control of the evolution of the photon state on the Poincare sphere; finally, the light and dark interference fringes are collected through a charge-coupled device.

[0037] According to the paraxial wave equation, after the derivation and change of the slowly varying envelope approximation, the Hamiltonian of the Schrödinger-like equation can be written as (H):

[0038]

[0039] In the above formula, i represents an imaginary number, β represents the propagation constant, and γ represents the anisotropy coefficient of the crystal. and Represents the second-order partial derivative of xy and yx. Where α is the rotation angle of the crystal to be measured, k0 represents the wave vector, and n ox and n oy Represents the principal refractive index of the crystal to be measured after rotation. Δβ=β x -β y is the phase mismatch, β x is the propagation constant along the x-axis, β y is the propagation constant along the y-axis.

[0040] In order to further derive the refractive index-sensitive synthetic magnetic field, a rotation transformation is introduced:

[0041]

[0042] In the above formula, A x represents the polarization component along the x-axis, A y represents the polarization component along the y-axis; Represents the polarization component along the x-axis after the rotation transformation, Represents the polarization component along the y-axis after the rotation transformation. In the rotation transformation, the phase factor exp(iβz) that carries two forward propagations and accumulates distance is called the dynamic phase. After the rotation transformation, and The accumulated phase process becomes a pure geometric phase, and the Hamiltonian (H) without dynamic phase is obtained. ′ ):

[0043]

[0044] In this embodiment, by applying voltage to the crystal material to be tested, the geometric phase of the outgoing light field of the crystal material to be tested can be further changed, thereby causing a jump in the bright and dark interference fringes. Each bright and dark jump of the interference fringes represents a phase change of π in the outgoing light field.

[0045] By checking the Lant connection <Φ(B0=0)|Φ(B0≠0)>, where Φ=[cosθ;sinθ·exp(iφ)] is the initial function expression of the photon state, θ is the pitch angle of the photon state defined by the Jones vector, φ is the ellipsoid angle of the photon state defined by the Jones vector, |B0|=|k0(n ox -n oy )| is the magnetic field intensity, the geometric phase expression of the magnetic field B can be obtained as follows:

[0046]

[0047] Among them, x=cos(2α)cosθ+sin(2α)sin(θ)exp(iφ), χ r and χ i Represent the real part (r) and imaginary part (i) of χ respectively.

[0048] When the geometric phase jump condition is: ( ±1, ±2, ... are all integers), Substituting into equation (5), the photon state will evolve along the same meridian of the Poincare sphere, following the Hamiltonian rule of equation (4). From equations (4) and (5), we can see that the transition between bright and dark interference fringes is caused by a change in the geometric phase of π. Therefore, the detected refractive index change can be further obtained by simply recording the required transition voltage U applied to the crystal under test.

[0049] The interference light spots emitted by the crystal are recorded by a charge-coupled device. By fine-tuning (for example, adjusting in intervals of 0.001V (1 millivolt)) the voltage applied to the crystal to be measured, the changes in the bright and dark interference fringes can be observed on a computer connected to the charge-coupled device. Among them, the theoretical calculation of the crystal refractive index measured with ultra-high precision through geometric phase jump is: the refractive index along the x-axis is and the refractive index along the y-axis is Obtain the refractive index change of the crystal to be tested along the x-axis and y-axis directions (i.e., birefringence effect):

[0050]

[0051] The Δn in the above expression represents the change in the refractive index of the crystal to be measured, that is, the change in the birefringence effect, n x and n y Respectively represent the refractive index of the lithium niobate crystal to be measured along the x-axis and y-axis directions, n o Represents the ordinary refractive index of the lithium niobate crystal to be measured, γ 22 represents the electro-optical coefficient of the lithium niobate crystal to be measured, U represents the voltage applied to the crystal, and d represents the thickness of the crystal. From Equation (6), we can see that by simply adjusting the voltage U applied to the crystal to be measured, the change in the crystal's refractive index can be observed and measured on a computer connected to a charge-coupled device.

[0052] S3. By connecting a computer to a charge-coupled device, light and dark interference fringes can be observed. By adjusting the voltage applied to the lithium niobate crystal to be tested, the voltage value required for the light and dark transition of the interference fringes can be recorded. The value of the refractive index change is obtained, that is, the accuracy value of the birefringence effect can be detected.

[0053] Example 2

[0054] This embodiment is basically the same as the embodiment 1, the main difference being that the initial position of the photon state of the geometric phase jump is different.

[0055] Figure 4 The figure illustrates the theoretical and experimental results of the geometric phase jump in this embodiment when the crystal rotation angle α = 3π / 4, the ellipticity angle φ of the incident photon state = π / 2, and the pitch angle θ = 31π / 60. Among them, (a) is the function of the change of geometric phase with voltage, the solid line represents the result of theoretical simulation, and the asterisk represents the result of experimental measurement. (b) is the interference fringes before the geometric phase jump (i.e., voltage U = 7.770V), and the interference fringes in the center are bright fringes. (c) is the interference fringes after the geometric phase jump (i.e., voltage U = 7.771V), and the interference fringes in the center are dark fringes. The scale bars in the figures are all 100μm.

[0056] according to Figure 1 As shown in the figure, the experimental device for birefringence detection is built and collimated, in which the initial polarization of the HeNe laser is horizontal linear polarization, which passes through the half wave plate and the quarter wave plate in turn. Figure 2 The method steps are to rotate the half wave plate and the quarter wave plate to ensure that the initial state of the photon incident on the crystal to be tested is above the geometric phase transition point, and the initial ellipticity angle φ = π / 2 and the pitch angle θ = 31π / 60 are determined by the Jones matrix. Then, the polarizer is set to horizontal polarization to eliminate the influence of the initial phase. At this time, the voltage can be slowly applied to the crystal to be tested starting from 0V, while observing the changes in the light and dark interference fringes, and recording the voltage required for the light and dark interference fringes to transition. Figure 4 As shown in (a), the solid line is the result of theoretical simulation, while the asterisk is the numerical value in the experiment. The jump of bright and dark interference fringes indicates that the phase of the light field jumps by π.

[0057] according to Figure 4 (a) can be used to determine that the voltage at which the geometric phase jump occurs is U1 = 7.770V. When the voltage U2 = 7.771V, the interference fringes in the center change from bright fringes to dark fringes. At this time, the voltage required for the phase jump π of the light field passing through the lithium niobate crystal is U = U1 – U2 = 0.001V. The change in refractive index is calculated to be Δn~10 -11 Order of magnitude. The jumping interference spot is as follows Figure 4 As shown in (b) and (c), an ultra-high-precision birefringence detection based on the geometric phase jump effect is realized.

[0058] In summary, the present invention proposes an ultra-high-precision birefringence detection system and method based on the crystal geometric phase jump effect, which realizes high-precision detection of the birefringence effect of the crystal to be measured. It has relatively broad industrial and economic value and is in line with the trend of high-tech development of the times. This technology is expected to be widely used in solid materials, stress detection, laser physics, and ophthalmology.

[0059] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. An ultra-high precision birefringence detection system based on geometric phase jump effect, characterized in that: The device comprises a laser, a half-wave plate, a quarter-wave plate, a polarizer, a crystal to be measured, a rotating stage, a first beam splitting prism, a second beam splitting prism, a reflector and a charge coupled device; the rotating stage is placed on the crystal to be measured, and the rotating stage is rotated to rotate the crystal to be measured along the optical axis; voltage is applied to the upper and lower plates of the crystal to be measured; The horizontal linear polarized light beam emitted by the laser passes through a half wave plate and a quarter wave plate to set the initial polarization state of the initial incident light field of the crystal to be measured; The light beam emitted from the quarter-wave plate is incident on the first beam splitting prism for beam splitting. The main beam after the splitting passes through the crystal to be measured. The interference beam after the splitting is reflected and then incident on the second beam splitting prism together with the main beam passing through the crystal to be measured for beam combination. The combined beam passes through the analyzer and is collected by the charge coupled device. Adjust the voltage applied to the crystal to be tested at preset voltage intervals, observe the changes in the brightness of the interference fringes, record the voltage required for the changes in the brightness of the interference fringes, and calculate the change in refractive index.

2. The ultra-high precision birefringence detection system according to claim 1, characterized in that: Set the initial polarization state of the initial incident light field of the crystal to be tested, specifically: The horizontally polarized light is converted to +45° linear polarized light by a half-wave plate; the +45° linear polarized light is converted to right-handed circular polarization by adding a quarter-wave plate; while the quarter-wave plate rotation angle remains unchanged, the quarter-wave plate is removed and the half-wave plate is rotated to convert the +45° linear polarized light to a position close to vertical polarization; Add a quarter-wave plate to rotate it above the same longitude as the vertical polarization transition point.

3. The ultra-high precision birefringence detection system according to claim 1, characterized in that: The preset voltage interval is 1mV.

4. The ultra-high precision birefringence detection system according to claim 1, characterized in that: The refractive index changes from 10 -11 Order of magnitude.

5. The ultra-high precision birefringence detection system according to claim 1, characterized in that: The formula for calculating the refractive index change is in is the refractive index of the crystal to be measured along the x-axis; is the refractive index of the crystal to be measured along the y-axis; n o Represents the ordinary refractive index of the crystal to be measured, γ 22 represents the electro-optic coefficient of the crystal to be measured, U represents the voltage applied to the crystal to be measured, and d represents the thickness of the crystal to be measured.

6. The ultra-high precision birefringence detection system according to claim 1, characterized in that: The laser is a helium-neon laser and the crystal to be tested is a lithium niobate crystal.

7. The ultra-high precision birefringence detection system according to claim 1, characterized in that: The rotation angle of the crystal to be measured is α=3π / 4, the ellipsoid angle φ of the photon state of the initial incident light field of the crystal to be measured is π / 2, and the pitch angle θ=8π / 15.

8. The ultra-high precision birefringence detection system according to claim 1, characterized in that: The rotation angle of the crystal to be measured is α=3π / 4, the ellipsoid angle φ of the photon state of the initial incident light field of the crystal to be measured is π / 2, and the pitch angle θ=31π / 60.

9. The ultra-high precision birefringence detection system according to claim 1, characterized in that: The detection system also includes a computer connected to the charge coupled device, and the light and dark changes of the interference fringes are observed through the computer.

10. An ultra-high precision birefringence detection method based on geometric phase jump effect, characterized in that: Based on the detection system according to any one of claims 1 to 9, the detection method comprises the steps of: S1. Processing the horizontal linear polarized light emitted by the laser through a half-wave plate and a quarter-wave plate to set the initial polarization state of the initial incident light field of the crystal to be measured; S2. After the light beam has been processed by the half-wave plate and the quarter-wave plate, a polarizer is set to eliminate the influence of the phase difference between the outgoing light field of the crystal to be tested and the initial incident light field, and then the light beam is incident on the crystal to be tested; the crystal to be tested is rotated at any angle using a rotating stage; a voltage is applied to the crystal to control the evolution of the photon state on the Poincare sphere; and finally, the light and dark interference fringes are collected using a charge-coupled device. S3. Observe the interference fringes. By adjusting the voltage applied to the crystal to be tested, record the voltage value required when the interference fringes change from light to dark, and calculate the change in refractive index.

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