Method and apparatus for measuring electro-optic coefficient of crystal by using wave-plate thermal-induced phase difference

Abstract

The application discloses a method and device for measuring crystal electro-optic coefficient by wave plate thermal phase difference, and belongs to the technical field of photoelectric measurement. The method comprises the following steps: constructing a crystal electro-optic coefficient measurement optical path, adjusting the temperature of a true zero-order half wave plate of the crystal electro-optic coefficient measurement optical path to make the optical path in an extinction state; continuously adjusting the temperature of the true zero-order half wave plate to make the optical path deviate from the extinction state; keeping the temperature of the extinction state unchanged, gradually applying a voltage on a to-be-measured electro-optic crystal to make the system return to the extinction state; and obtaining the electro-optic coefficient of the to-be-measured electro-optic crystal according to a compensation relationship between the thermal phase difference of the true zero-order half wave plate caused by the temperature difference of the wave plate and the electro-optic phase difference of the to-be-measured electro-optic crystal caused by the voltage difference. The method realizes the measurement of the crystal electro-optic coefficient by the mutual compensation of the thermal phase difference of the wave plate and the electro-optic effect of the crystal. Since the temperature change of the true zero-order wave plate has high sensitivity, the required voltage for actual measurement is extremely small, and the safety of the test and the accuracy of the test result are improved.

Description

Technical Field

[0001] This application relates to the field of photoelectric measurement technology, and more specifically to a method and apparatus for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate. Background Technology

[0002] The phenomenon of altering the optical properties of a crystal by applying an external electric field is called the electro-optic effect. Utilizing the electro-optic effect of electro-optic crystals, they can be fabricated into devices such as electro-optic modulators, electro-optic switches, and electro-optic deflectors, finding wide application in fields such as laser technology, optical communication, and quantum computing. The electro-optic coefficient is a key performance indicator of electro-optic crystals, and its accurate measurement is a core aspect of electro-optic crystal performance evaluation, device design, and system integration.

[0003] Currently, various methods have been developed for measuring the electro-optic coefficient of crystals, such as the half-wave voltage method, ellipsometric measurement method, interference compensation method, elasto-optic modulation method, and dispersion compensation method. Among these, the half-wave voltage method is the simplest to operate and the most commonly used. However, during the measurement process, the half-wave voltage of the electro-optic crystal sample changes slowly at the extreme value of light intensity, resulting in low accuracy and thus limiting the accuracy and sensitivity of the electro-optic coefficient measurement. The ellipsometric measurement method requires high accuracy of the ellipsometer, and high-precision ellipsometers are expensive, leading to relatively high measurement costs. Both the half-wave voltage method and the ellipsometric measurement method are direct measurement methods, with operating voltages often reaching thousands of volts. This places strict requirements on the performance of the high-voltage power supply and the insulation of the measurement environment, posing serious safety hazards to the personnel. Furthermore, the high-voltage power supply equipment is bulky and prone to introducing electromagnetic interference. For crystals with small electro-optic coefficients, tens of thousands of volts of high voltage need to be applied. For some crystals with even smaller electro-optic coefficients or low resistivity, which are prone to overheating or breakdown under high voltage, it is even difficult to obtain results using direct measurement methods. The remaining methods are all indirect testing methods. Compared with direct testing methods, the operating voltage is significantly reduced (e.g., 10-80 V for interference compensation, 100-400 V for photoelastic modulation, and 10-36 V for dispersion compensation). However, there is still a risk of electric shock in high humidity and highly conductive environments, and the personal safety of test personnel cannot be completely guaranteed. Furthermore, indirect testing methods suffer from varying degrees of problems such as expensive equipment, complex systems, cumbersome debugging, and high testing costs. For example, the optical path of interference compensation generally uses a Michelson or Mach-Zehnder interferometer structure. To extract weak phase signals under low voltage, it is necessary to rely on complex lock-in amplification, precise temperature control, vibration isolation, and multi-channel electrical modulation and demodulation systems. This results in very expensive equipment, extremely cumbersome optical and circuit debugging, and extreme sensitivity to environmental disturbances, making it difficult to apply stably and conveniently in conventional laboratories or industrial sites. Furthermore, the interference compensation method requires a crystal with a known electro-optic coefficient or inverse piezoelectric coefficient to compensate for the optical path difference caused by the electro-optic effect of the sample in order to measure the sample's electro-optic coefficient. The measurement results are heavily dependent on the type and quality of the reference sample, and there are no universally accepted standard samples on the market. The photoelastic modulation method requires lock-in amplifiers, photoelastic modulation (PEM), photoelastic modulation controllers, etc., while the dispersion compensation method requires wavelength-tunable light sources. The use of these devices and components increases the measurement cost.

[0004] In summary, the field currently faces a prominent technical contradiction: if low operating voltage is adopted in pursuit of test safety and sample compatibility, the problem of weak phase delay signal and low signal-to-noise ratio must be solved, forcing the measurement system to make sufficient compensation in the signal extraction and noise suppression stages, often resulting in an abnormally complex system, difficult operation, and harsh environmental requirements; if system simplicity and stability are pursued, it is necessary to return to the high-risk high-voltage test mode.

[0005] Therefore, there is an urgent need to develop a novel method for measuring electro-optic coefficients, which can achieve a balance between ultra-high security, system simplicity, ease of operation, and high measurement accuracy in crystal electro-optic coefficient measurement, thereby fundamentally breaking through the limitations of current technological approaches. Summary of the Invention

[0006] This application provides a method and apparatus for measuring the electro-optic coefficient of a crystal that can overcome (or at least partially overcome) the above-mentioned problems. The technical solution adopted in this application is as follows:

[0007] In a first aspect, embodiments of this application provide a method for measuring the electro-optic coefficient of a crystal using a waveplate-induced thermal phase difference, comprising the following steps: Step 1: Construct the optical path for measuring the electro-optic coefficient of the crystal, including a laser source, a polarizer, a true zero-order half-wave plate made of quartz material, the electro-optic crystal to be tested, an analyzer, and a power meter arranged sequentially along the propagation direction of the optical path; Step 2: Adjust the temperature of the true zero-order half-wave plate until the power meter reading reaches a minimum value, so that the measurement optical path is in the first extinction state and record the temperature value at this time as the first temperature; Step 3: Adjust the temperature of the true zero-order half-wave plate again to make the measurement optical path deviate from the extinction state, and record the temperature value at this time as the second temperature; Step 4: Maintain the second temperature and gradually apply voltage to the electro-optic crystal under test starting from zero volts until the measurement optical path reaches the extinction state again, and record the voltage difference applied to the electro-optic crystal under test; Step 5: Obtain the thermally induced phase difference calculation formula of the true zero-order half-wave plate based on the wave plate temperature difference obtained from the second temperature and the first temperature; at the same time, obtain the electro-induced phase difference calculation formula of the electro-optic crystal under test based on the voltage difference applied to the electro-optic crystal under test; obtain the electro-optic coefficient of the electro-optic crystal under test based on the compensation relationship between the thermally induced phase difference and the electro-induced phase difference.

[0008] Furthermore, the above method also includes: repeating steps two to five to obtain multiple sets of electro-optic coefficients, and taking the average value of the multiple sets of electro-optic coefficients as the final electro-optic coefficient of the electro-optic crystal to be tested.

[0009] Furthermore, during the repetition of steps two through five, the temperature difference of the waveplate is different in each electro-optic coefficient measurement.

[0010] Furthermore, step five specifically includes: Construct the formula for calculating the thermally induced phase difference of a true zero-order half-wave plate:

[0011] Where λ is the wavelength of the incident laser emitted by the laser source; The birefringence of a true zero-order half-wave plate at the first temperature; The rate of change of birefringence of a true zero-order half-wave plate with temperature; The waveplate temperature difference between the second temperature and the first temperature; L Δ is the light transmission length of the waveplate at the first temperature, i.e., the initial thickness of the true zero-order half-wave plate; L This represents the change in the light transmission length of the waveplate when the temperature changes to the second temperature.

[0012] Formula for calculating the electroinduced phase difference of the electro-optic crystal under test:

[0013] in, This represents the o-ray refractive index of the electro-optic crystal under test. This represents the electro-optic coefficient of the electro-optic crystal under test. This represents the voltage difference applied to the electro-optic crystal under test when it is extinct again. l d is the length of the electro-optic crystal under test in the light transmission direction, and d is the electrode spacing of the electro-optic crystal under test; Based on the compensation relationship between thermally induced phase difference and electrically induced phase difference, let =

[0014] Then the electro-optic coefficient of the electro-optic crystal under test can be obtained.

[0015] Furthermore, in the constructed optical path for measuring the electro-optic coefficient of the crystal, the laser source shown is a laser that emits a fixed wavelength.

[0016] Furthermore, in the optical path for measuring the electro-optic coefficient of the crystal, the transmission directions of the polarizer and the analyzer are parallel to each other.

[0017] Secondly, embodiments of this application provide another method for measuring the electro-optic coefficient of a crystal using waveplate thermally induced phase difference. The adjustment steps for the voltage difference and temperature difference in this method differ from those in the first aspect, specifically including the following steps: Step 1: Construct the optical path for measuring the electro-optic coefficient of the crystal, including a laser source, a polarizer, a true zero-order half-wave plate made of quartz material, the electro-optic crystal to be tested, an analyzer, and a power meter arranged sequentially along the propagation direction of the optical path; Step 2: Adjust the temperature of the true zero-order half-wave plate until the power meter reading reaches a minimum value, so that the measurement optical path is in the first extinction state and record the temperature value at this time as the first temperature; Step 3: Starting from zero volts, gradually apply a safe voltage less than the set threshold to the electro-optic crystal under test, so that the measurement optical path deviates from the extinction state, and record the voltage difference applied to the electro-optic crystal under test; Step 4: Maintain the safe voltage from Step 3, and adjust the temperature of the true zero-order half-wave plate to make the measurement optical path reach the extinction state again, and record the temperature value at this time as the second temperature; Step 5: Obtain the thermally induced phase difference calculation formula of the true zero-order half-wave plate based on the wave plate temperature difference obtained from the second temperature and the first temperature; at the same time, obtain the electro-induced phase difference calculation formula of the electro-optic crystal under test based on the voltage difference applied to the electro-optic crystal under test; obtain the electro-optic coefficient of the electro-optic crystal under test based on the compensation relationship between the thermally induced phase difference and the electro-induced phase difference.

[0018] Furthermore, in step three, the set threshold is 1V.

[0019] Thirdly, this application discloses an apparatus for implementing the method of measuring the electro-optic coefficient of a crystal in the first aspect, including a crystal electro-optic coefficient measurement optical path and a data control and processing module, wherein the crystal electro-optic coefficient measurement optical path includes a laser source, a polarizer, a true zero-order half-wave plate made of quartz material, the electro-optic crystal to be measured, an analyzer and a power meter arranged sequentially along the propagation direction of the optical path; The electro-optic crystal under test is connected to an adjustable DC low-voltage power supply; the true zero-order half-wave plate is placed in a temperature-controlled furnace; The data control and processing module includes a voltage regulation unit, a temperature regulation unit, and a data recording and processing unit; The voltage adjustment unit shown is connected to an adjustable DC low-voltage power supply to adjust the DC voltage applied to the electro-optic crystal under test. The temperature regulation unit is connected to the temperature control furnace to regulate the temperature of the true zero-level half-wave plate in the temperature control furnace; The data recording and processing unit is used to record: the temperature difference when the minimum value of the power meter reading disappears by adjusting the temperature of the true zero-order half-wave plate while keeping the DC voltage constant; and the voltage difference when the DC voltage of the electro-optic crystal under test is adjusted so that the power meter reading reaches the minimum value again while keeping the temperature that caused the minimum value to disappear constant; and the electro-optic coefficient of the electro-optic crystal under test is obtained according to the compensation relationship between the thermal phase difference caused by the temperature difference and the electro-phase difference caused by the voltage difference.

[0020] Fourthly, this application discloses an apparatus for implementing the method of measuring the electro-optic coefficient of a crystal in the second aspect, comprising a crystal electro-optic coefficient measurement optical path and a data control and processing module, wherein the crystal electro-optic coefficient measurement optical path comprises a laser source, a polarizer, a true zero-order half-wave plate made of quartz material, the electro-optic crystal to be measured, an analyzer, and a power meter arranged sequentially along the optical path propagation direction; The electro-optic crystal under test is connected to an adjustable DC low-voltage power supply; the true zero-level half-wave plate is placed in a temperature-controlled furnace. The data control and processing module includes a voltage regulation unit, a temperature regulation unit, and a data recording and processing unit; The voltage adjustment unit shown is connected to an adjustable DC low-voltage power supply to adjust the DC voltage applied to the electro-optic crystal under test. The temperature regulation unit is connected to the temperature control furnace to regulate the temperature of the true zero-level half-wave plate in the temperature control furnace; The data recording and processing unit is used to record: the voltage difference when the DC voltage on the electro-optic crystal under test is adjusted to make the minimum value of the power meter reading disappear while keeping the temperature constant; and the temperature difference when the temperature of the true zero-order half-wave plate is adjusted to make the power meter reading reach the minimum again while keeping the DC voltage that caused the minimum value to disappear constant; and to obtain the electro-optic coefficient of the electro-optic crystal under test based on the compensation relationship between the thermal phase difference caused by the temperature difference and the electro-phase difference caused by the voltage difference.

[0021] Compared with the prior art, this application has the following beneficial effects: The operating voltage is significantly lower than that of traditional methods. As representative low-voltage detection techniques, the operating voltage range of the interference compensation method is typically 10-80 V, and that of the dispersion compensation method is typically 10-36 V. However, the minimum operating voltage of these methods is still 10 V or higher, posing a risk of electric shock in high-humidity and highly conductive environments. This application utilizes the high sensitivity of a true zero-order waveplate to temperature changes (for every 1 volt change in waveplate temperature...). Approximately 1.06 The optical path change corresponding to λ / 18894 is one order of magnitude higher than that of the previous interference compensation method (λ / 2000) and two orders of magnitude higher than that of the dispersion compensation method (λ / 200), and has the highest sensitivity among known electro-optic coefficient testing methods. By compensating for the thermally induced phase difference caused by temperature and the electro-induced phase difference caused by voltage difference, the electro-optic coefficient of the electro-optic crystal under test can be solved. Due to the high sensitivity of the true zero-order waveplate to temperature change, the operating voltage range of the electro-optic crystal under test can reach 0-6 V, and the lowest operating voltage can even be as low as below 1 V (only a voltage below 1 V is needed to obtain the electro-optic coefficient test result). This value is even lower than the voltage of a common dry cell battery (1.5 V). Therefore, this application provides an absolutely safe electro-optic coefficient testing method, completely eliminating the safety hazards in the electro-optic coefficient testing process and thoroughly protecting the personal safety of the test personnel. Meanwhile, due to the extremely low operating voltage, the problem of crystal heating or breakdown that may be caused by strong electric fields is avoided. This makes the method applicable to measuring special electro-optic crystals that are difficult to handle by traditional high-voltage methods, such as those with low resistivity and easy breakdown, thus broadening the application range of electro-optic coefficient measurement.

[0022] This method uses a true zero-order quartz waveplate, which is one of the most commercially mature, widely used, and standardized optical components with consistent quality. The key physical parameter relied upon by this method is the thermo-optical coefficient of the quartz crystal. The known values ​​have extremely high precision (up to 10). -8 / o (C) This method has been widely accepted and recognized by society. Based on this, the developed testing methods and devices have unified standards, resulting in high-precision, easily repeatable, and widely accepted test results. In contrast, other methods primarily use self-made reference samples, such as self-made electro-optic crystals, inverse piezoelectric crystals, and elasto-optic crystals. The development maturity, quality consistency, and processing standardization of these materials are far inferior to commercially available quartz waveplates. The relative immaturity and individual differences of the reference samples introduce significant uncertainty into the test results, which is detrimental to the large-scale market application of these methods.

[0023] The system is simple and economical. The optical path structure used in this application is simple, consisting of basic optical components, and does not include sophisticated and complex lock-in amplification, vibration isolation, high-voltage power supply, multi-channel electrical modulation and demodulation systems, etc. There are no mechanical adjustment or moving parts, so the manufacturing cost is low, the operation is very convenient, and it is easy to integrate into automation for stable and convenient application in conventional laboratories or industrial sites. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the electro-optic coefficient measuring device disclosed in the embodiments of this application.

[0026] The components represented by each number are listed below: 1 is the detection light source, 2 is the polarizer, 3 is the half-wave plate placed in the temperature-controlled furnace, 4 is the temperature-regulating power supply, 5 is the electro-optic crystal under test, 6 is the adjustable DC low-voltage power supply, 7 is the analyzer, and 8 is the power meter.

[0027] Figure 2 This is a schematic diagram of the test results for Embodiment 1 of this application.

[0028] Figure 3 This is a schematic diagram of the test results for Embodiment 2 of this application.

[0029] Figure 4 This is a schematic diagram of the test results for Embodiment 3 of this application.

[0030] Figure 5 This is a schematic diagram of the test results for Embodiment 4 of this application. Detailed Implementation

[0031] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] This application provides a method for measuring the electro-optic coefficient of a crystal using a waveplate-induced thermal phase difference, the method comprising the following steps: Step 1: Construct the optical path for measuring the electro-optic coefficient of the crystal, including a detection light source, a polarizer, a true zero-order half-wave plate, the electro-optic crystal under test, an analyzer, and a power meter arranged sequentially along the propagation direction of the optical path. The true zero-order half-wave plate is placed in a temperature-controlled furnace, which is connected to a temperature-regulating power supply. The electro-optic crystal under test is connected to an adjustable low-voltage DC power supply.

[0033] Step 2: Adjust the temperature of the half-wave plate to bring the system to an extinction state.

[0034] Step 3: Continue to adjust the waveplate temperature to make the system deviate from the extinction state.

[0035] Step 4: Apply pressure to the electro-optic crystal under test to return the system to the extinction state.

[0036] Step 5: Based on the waveplate temperature at the end of Step 3 and the waveplate temperature at the end of Step 2, the waveplate temperature difference can be calculated, and then the phase difference change (thermally induced phase difference) of the true zero-order waveplate during Step 3 can be calculated. From the regression of the extinction state in Step 4, it can be seen that the above-mentioned thermally induced phase difference and the phase difference change (electro-induced phase difference) introduced by the pressure on the electro-optic crystal under test in Step 4 have a mutually compensating relationship (i.e., the absolute values ​​of the thermally induced phase difference and the electro-induced phase difference are equal, but their signs are opposite). Thus, a compensation relationship expression is established, and the electro-optic coefficient of the electro-optic crystal under test can be obtained.

[0037] In the above method, the measurement optical path system is determined to be in an extinction state under the current conditions by the power meter reading reaching its minimum value. In step four, when the power meter reading reaches its minimum value, the electro-optic phase difference caused by the applied voltage in the electro-optic crystal compensates for the thermo-optic phase difference and thermal expansion phase difference (collectively referred to as thermally induced phase difference) caused by temperature changes in the half-wave plate, causing the total phase difference of the crystal electro-optic coefficient measurement optical path to return to the state π at the end of step two. Furthermore, in step five, based on the thermally induced phase difference of the half-wave plate... By combining the theoretical expressions for the voltage ΔV applied to the electro-optic crystal under test and its electroinduced phase difference, the electro-optic coefficient under test can be obtained.

[0038] Repeat steps three through five, continuously adjusting the waveplate temperature and the voltage applied to the electro-optic crystal under test by the DC low-voltage power supply, and record multiple sets of waveplate temperature and voltage values ​​that meet the optical path extinction conditions, to obtain multiple sets of electro-optic coefficient measurement values.

[0039] When step three ends, after the temperature of the true zero-order quartz half-wave plate changes, the change in phase difference of the incident light relative to the initial temperature can be expressed as:

[0040]

[0041]

[0042]

[0043] Where λ is the incident light wavelength. Birefringence at initial temperature The rate of change of birefringence with temperature, For waveplate temperature change, L Let Δ be the light transmission length of the waveplate at its initial temperature. L This represents the change in the light transmission length of the waveplate after a temperature change. The phase difference of the waveplate after temperature change. Let be the waveplate phase difference at the initial temperature. Assuming the incident light wavelength λ is 532 nm, the waveplate is typically fabricated using... The corresponding true zero-order quartz half-wave plate thickness L It is 28.9 μm, so =0.0092 28.9μm=2.66 , representing the extinction state at the end of step two, multiplied by 2π / λ (λ=532nm) equals the phase difference π at the initial temperature. When the waveplate temperature changes by 2... ,in Let be the coefficient of thermal expansion of the quartz crystal in the direction of light transmission (i.e., perpendicular to the C-axis). Analyzing the last step of the above equation: the first term within the parentheses represents the individual effect of thermal expansion. The second item in parentheses represents the individual effect of the thermo-optical effect. ) ,in , which is the difference in thermo-optical coefficients between the two principal axis refractive indices; the third term in parentheses represents the cross-effect of the thermo-optical effect and the thermal expansion effect, ( ) The above analysis shows that the second term within the parentheses is 8.7 times the first term and 3.65 times the third term. Therefore, regarding the thermally induced phase difference of the waveplate, only the first term (the sole effect of thermal expansion) and the second term (the sole effect of thermo-optical effect) need to be considered. Furthermore, the above analysis shows that for every 1 unit change in temperature... This optical path change, λ / 18894, means that the thermal effect can be precisely adjusted in phase with extremely high resolution, if a common precision of 0.1 is used. The temperature controller can theoretically achieve a resolution of λ / 188940 for optical path variation. This property provides the necessary conditions for measuring the electro-optic coefficient of crystals at ultra-low voltage.

[0044] In summary, the phase difference change caused by the waveplate temperature used in step five can be approximated as the phase difference change caused by the waveplate's thermo-optical effect and thermal expansion effect (thermally induced phase difference). The corresponding calculation formula is as follows:

[0045] Based on the fundamental principle of the electro-optic effect of crystals, the expression for the electroinduced phase difference is: ; The compensation formula is derived based on the fact that the absolute values ​​of the thermally induced phase difference and the electrically induced phase difference are equal: =

[0046] Where λ is the wavelength of the incident laser emitted by the laser source; The birefringence of a true zero-order half-wave plate at the first temperature; The rate of change of birefringence of a true zero-order half-wave plate with temperature; The waveplate temperature difference between the second temperature and the first temperature; L Δ is the light transmission length of the waveplate at the first temperature, i.e., the initial thickness of the true zero-order half-wave plate; L This represents the change in the light transmission length of the waveplate when the temperature changes to the second temperature. This represents the o-ray refractive index of the electro-optic crystal under test. This represents the electro-optic coefficient of the electro-optic crystal under test. This represents the voltage difference applied to the electro-optic crystal under test when it is extinct again. l d represents the length of the electro-optic crystal under test in the light transmission direction, and d represents the electrode spacing of the electro-optic crystal under test.

[0047] Finally, the electro-optic coefficient of the electro-optic crystal under test is obtained according to the compensation relationship.

[0048] It should be noted that in another embodiment of this application, after the first extinction state described in step two is reached, in step three, the temperature can be kept constant and the voltage on the electro-optic crystal under test can be adjusted to make the extinction state disappear, and the voltage difference when the extinction state disappears can be recorded; while in step four, the voltage value when the extinction state disappears is maintained, and the temperature value of the true zero-order half-wave plate is adjusted to record the temperature difference of the wave plate when the extinction state is reached again; thereby establishing the compensation relationship between the voltage-induced electro-phase difference and the temperature-induced thermal phase difference, and thus obtaining the electro-optic coefficient of the electro-optic crystal under test.

[0049] The above method can be implemented using the device disclosed in this application for measuring the electro-optic coefficient of a crystal using waveplate thermally induced phase difference. This device mainly consists of a crystal electro-optic coefficient measurement optical path and a data control and processing module, wherein the reference... Figure 1 The optical path for measuring the electro-optic coefficient of a crystal includes a laser source 1, a polarizer 2, a true zero-order half-wave plate 3 made of quartz material, an electro-optic crystal under test 5, an analyzer 7, and a power meter 8, arranged sequentially along the propagation direction of the optical path. The true zero-order half-wave plate 3 is placed in a temperature-controlled furnace, which is connected to a temperature regulation device 4 in a data control and processing module. The electro-optic crystal under test 5 is connected to an adjustable DC low-voltage power supply 6. Two transparent electrodes of the adjustable DC low-voltage power supply are applied to the two light-transmitting end faces of the electro-optic crystal under test 5, respectively. In this application, the temperature-controlled furnace is a tubular temperature-controlled furnace (not shown in the figure) with a tubular temperature control component. The true zero-order half-wave plate is fixed by a heat-conducting annular clamp and embedded in the tubular temperature control component of the temperature-controlled furnace. The tubular temperature control component has a transparent structure and is at the same horizontal position as the polarizer, allowing the laser light after passing through the polarizer to pass smoothly through the true zero-order half-wave plate 3 in the temperature-controlled furnace. The temperature of the temperature-controlled furnace is regulated by the temperature regulation device 4.

[0050] The data recording and processing unit (not shown in the attached diagram) in the data control and processing module is used to record: the temperature difference when the minimum value of the power meter reading disappears by adjusting the temperature of the true zero-order half-wave plate while keeping the DC voltage constant; and the voltage difference when the DC voltage of the electro-optic crystal under test is adjusted to make the power meter reading reach the minimum value again while keeping the temperature that caused the minimum value to disappear constant; and the electro-optic coefficient of the electro-optic crystal under test is obtained based on the compensation relationship between the thermally induced phase difference caused by the temperature difference and the electro-induced phase difference caused by the voltage difference. Preferably, multiple sets of temperature and voltage data can be recorded, an electro-optic coefficient can be calculated based on each set of data, and the average value can be taken as the final measurement result of the electro-optic coefficient under test.

[0051] The data recording and processing unit can also record: the voltage difference when the DC voltage on the electro-optic crystal under test is adjusted to make the minimum value of the power meter reading disappear while keeping the temperature constant; and the temperature difference when the temperature of the true zero-order half-wave plate is adjusted to make the power meter reading reach the minimum again while keeping the DC voltage that caused the minimum value to disappear constant; and obtain the electro-optic coefficient of the electro-optic crystal under test based on the compensation relationship between the thermally induced phase difference caused by the temperature difference and the electro-induced phase difference caused by the voltage difference.

[0052] Based on the fundamental principles of this application, the above-mentioned device automatically performs multiple temperature measurements, and the final electro-optic coefficient is obtained from the average value of multiple measurement points. This can reduce the random error of single-point measurement, improve the test accuracy, and automate the entire measurement process.

[0053] The inventive principles and specific testing steps of this application will be further explained below through different embodiments.

[0054] Example 1 Example 1 discloses the measurement of the electro-optic coefficient γ of a BBO crystal using this application. 22 The method, measuring device such as Figure 1 As shown. The detection light source 1 is a linearly polarized continuous-wave green laser with a wavelength of 532 nm. Both the polarizer 2 and analyzer 7 are Glan-Taylor prisms with a 12.7 mm aperture. The half-wave plate 3 is a true zero-order half-wave plate made of quartz, with a working wavelength λ0 of 532 nm, and is placed inside a temperature-controlled furnace. The temperature regulating power supply 4 can maintain a temperature between 20 and 200 degrees Celsius. o Continuous adjustment within the range of C, with a temperature resolution of 0.1. o C. The electro-optic crystal 5 under test is a commercially available electro-optic Pockel cell (CASTECH, BPA-3AS-L), and the electro-optic material used is... β -BBO crystals, processed into a hexahedral shape, with a manufacturer-specified size of 3 mm. 3 mm 20 mm (X) Y The light transmission direction is along the Z-axis, and the electric field direction is along the X-axis. The two light-transmitting Z-side faces are polished and coated with an anti-reflection film, while the two electric field-applied X-side faces are coated with silver electrodes. The output voltage of the DC low-voltage power supply 6 can be continuously adjusted within the range of 0-12 V, with a voltage resolution of 0.1 V. Its positive and negative terminals are connected to the power supply via power lines. β - On the side electrode of the BBO crystal. The power meter 8 consists of a 3A probe and a power meter head, with a minimum resolution of 0.1 μW, which is sufficient to determine the extinction state of the system.

[0055] Using the measurement steps described above, the thermally induced phase difference of the variable-temperature waveplate was obtained. Based on the fundamental principle of the electro-optic effect in crystals, the expression for the electroinduced phase difference is: Regarding the application of the transverse electro-optic effect of the BBO crystal in this embodiment, which involves "applying an electric field in the X direction and allowing light to pass through in the Z direction", Based on the relationship that the magnitudes of the two phase differences are equal, the electro-optic crystal BBO under test can be obtained. like Figure 2 As shown in Table 1. During the calculation, a 532 nm true zero-order quartz waveplate was used. , , With a thickness L = 28.9 μm, the o-ray refractive index of the BBO crystal is... =1.6742, light transmission direction length l = 20 mm, thickness between the two electrodes d = 3 mm, and For measurement data. Under the condition that no voltage is applied to the crystal under test, when the waveplate temperature is adjusted to 25.6... o At time C, the power meter reading is at its lowest, indicating the system is in a static extinction state, i.e., the extinction state described in step two. Increase the waveplate temperature to 27.6°C. o C. The system deviates from the extinction state, and then voltage is slowly applied to the crystal under test. When the voltage is increased from 0 to 0.7 V, the power meter reading reaches its lowest point again. At this time, the system is in the dynamic extinction state for the first time, which is the extinction state described in step four. =2 and =0.7 V Substitute = The calculation relationship allows us to obtain the first electro-optic coefficient test data. At this point, step five is completed for the first time. Subsequently, a new test is conducted every 2°C increase in waveplate temperature, repeating steps three through five to obtain the remaining electro-optic coefficient test data. Table 1 shows that five electro-optic coefficient test data points were obtained from six experimental points, with an average value of 2.69 pm / V. This is very close to the measured value (2.78 pm / V) obtained using the half-wave voltage method on the same device, and also to the reported value (2.70 pm / V) in the literature, with differences of only 3.2% and 0.37%, respectively. These results indicate that this testing method has high accuracy and operates at extremely low voltages (maximum 3.3 V), and can be as low as below 1 V (e.g., a waveplate temperature of 27.6°C corresponds to a crystal voltage of only 0.7 V).

[0056] Table 1 Test results of BBO crystals

[0057] Depend on Figure 2As shown in Table 1, some experimental data may differ significantly from the final average value, such as the first electro-optic coefficient test value (2.57 pm / V). This is mainly due to the accuracy of the testing instrument. During the test, the temperature controller reading may vary. 0.1 o The fluctuations of C, for 2 o The test temperature interval of C introduces an error of 5-10%. Using higher precision testing instruments can reduce measurement errors and improve the consistency of measurement data. Furthermore, the algorithm for averaging multiple measurement points effectively improves reliability, resulting in final results closer to those obtained using other methods and reported values ​​in the literature, effectively reducing the impact of random errors from single-point measurements.

[0058] Example 2 Example 2 discloses the measurement of the electro-optic coefficient γ of a 98% DKDP crystal using this application. 63 The method, measuring device such as Figure 1 As shown. The detection light source 1 is a linearly polarized continuous-wave green laser with a wavelength of 532 nm. Both the polarizer 2 and analyzer 7 are Glan-Taylor prisms with a 12.7 mm aperture. The half-wave plate 3 is a true zero-order half-wave plate made of quartz, with a working wavelength λ0 of 532 nm, and is placed inside a temperature-controlled furnace. The temperature regulating power supply 4 can maintain a temperature between 20 and 200 degrees Celsius. o The temperature was continuously adjustable within the range of C, with a temperature resolution of 0.1 ℃. The electro-optic crystal under test, 5, is a DKDP crystal with a deuterium content of 98%, processed into a hexahedral shape with a size of 15 mm. 15 mm 10 mm (X) Y The light transmission direction is along the Z-axis, and transparent electrodes and voltages are applied to the two light-transmitting end faces of the crystal. The output voltage of the DC low-voltage power supply 6 can be continuously adjusted within the range of 0-12 V, with a voltage resolution of 0.1 V. Its positive and negative terminals are connected to the two transparent electrodes of the 98% DKDP crystal via power lines, respectively. The power meter 8 consists of a 3A probe and a power meter head, with a minimum resolution of 0.1 μW, which is sufficient to determine the extinction state of the system.

[0059] Using the measurement steps described above, the thermally induced phase difference of the variable-temperature waveplate was obtained. Based on the fundamental principle of the electro-optic effect in crystals, the expression for the electroinduced phase difference is: Regarding the application of the longitudinal electro-optic effect of "applying an electric field in the Z direction and allowing light to pass through in the Z direction" in the 98% DKDP crystal in this embodiment, Based on the relationship that the magnitudes of the two phase differences are equal, the 98% DKDP of the electro-optic crystal under test can be obtained. like Figure 3As shown in Table 2.

[0060] Table 2. Test results of 98% DKDP crystals

[0061] During the calculation, a 532 nm true zero-order quartz wave plate was used. , Thickness L=28.9 μm, 98% DKDP crystal o-ray refractive index =1.5087, and For measurement data. Under the condition that no voltage is applied to the crystal under test, when the waveplate temperature is adjusted to 25.2... o At time C, the power meter reading is at its lowest, indicating the system is in a static extinction state, i.e., the extinction state described in step two. Increase the waveplate temperature to 27.2°C. o C. The system deviates from the extinction state, and then voltage is slowly applied to the crystal under test. When the voltage is increased from 0 to 0.6 V, the power meter reading reaches its lowest point again. At this time, the system is in the dynamic extinction state for the first time, which is the extinction state described in step four. =2 and =0.6 V Substitute = The calculation relationship allows us to obtain the first electro-optic coefficient test data. At this point, step five is completed for the first time. Subsequently, a test is performed every 2°C increase in waveplate temperature, repeating steps three through five to obtain the remaining electro-optic coefficient test data. Table 2 shows that five electro-optic coefficient test data points were obtained from six experimental points, with an average value of 25.85 pm / V. This is very close to the measured value (24.97 pm / V) obtained using the half-wave voltage method on the same device, and also to the value reported in the literature (25.98 pm / V), with differences of 3.5% and 0.5%, respectively. These results indicate that this testing method has high accuracy and operates at extremely low voltages (maximum 3.2 V), and can be as low as below 1 V (e.g., the crystal voltage corresponding to a waveplate temperature of 27.2°C is only 0.6 V).

[0062] Example 3 Example 3 discloses the measurement of the electro-optic coefficient γ of a KDP crystal using this application. 63 The method, measuring device such as Figure 1 As shown. The detection light source 1 is a linearly polarized continuous-wave green laser with a wavelength of 532 nm. Both the polarizer 2 and analyzer 7 are Glan-Taylor prisms with a 12.7 mm aperture. The half-wave plate 3 is a true zero-order half-wave plate made of quartz, with a working wavelength λ0 of 532 nm, and is placed inside a temperature-controlled furnace. The temperature regulating power supply 4 can maintain a temperature between 20 and 200 degrees Celsius. oThe temperature can be continuously adjusted within the range of C, with a temperature resolution of 0.1 ℃. The electro-optic crystal under test, 5, is a KDP crystal, processed into a hexahedral shape with a size of 15 mm. 15 mm 10 mm (X) Y The light transmission direction is along the Z-axis, and transparent electrodes and voltages are applied to the two light-transmitting end faces of the crystal. The output voltage of the DC low-voltage power supply 6 can be continuously adjusted within the range of 0-12 V, with a voltage resolution of 0.1 V. Its positive and negative terminals are connected to the two transparent electrodes of the KDP crystal via power lines, respectively. The power meter 8 consists of a 3A probe and a power meter head, with a minimum resolution of 0.1 μW, which is sufficient to determine the extinction state of the system.

[0063] Using the measurement steps described above, the thermally induced phase difference of the variable-temperature waveplate was obtained. Based on the fundamental principle of the electro-optic effect in crystals, the expression for the electroinduced phase difference is: Regarding the application of the longitudinal electro-optic effect of the KDP crystal in this embodiment, which involves "applying an electric field in the Z direction and allowing light to pass through in the Z direction", Based on the relationship that the magnitudes of the two phase differences are equal, the KDP of the electro-optic crystal under test can be obtained. like Figure 4 As shown in Table 3. During the calculation, a 532 nm true zero-order quartz waveplate was used. , , With a thickness L = 28.9 μm, the o-ray refractive index of the KDP crystal is... =1.5129, and For measurement data. Under the condition that no voltage is applied to the crystal under test, when the waveplate temperature is adjusted to 25.3... o At time C, the power meter reading is at its lowest, indicating the system is in a static extinction state, i.e., the extinction state described in step two. Increase the waveplate temperature to 26.3°C. o C. The system deviates from the extinction state, and then voltage is slowly applied to the crystal under test. When the voltage increases from 0 to 0.9 V, the power meter reading reaches its lowest point again. At this time, the system is in the dynamic extinction state for the first time, which is the extinction state described in step four. =1 and =0.9 V Substitute = The calculation relationship allows us to obtain the first electro-optic coefficient test data. At pm / V, step five is completed for the first time. Afterward, a test is performed every 1°C increase in waveplate temperature, repeating steps three through five to obtain the remaining electro-optic coefficient test data.

[0064] Table 3 Test results of KDP crystals

[0065] Table 3 shows that five electro-optic coefficient test data points were obtained from six experimental points, with an average value of 9.52 pm / V. This value is very close to the measurement value (9.70 pm / V) obtained by us using the half-wave voltage method on the same device, as well as the value reported in the literature (9.60 pm / V), with differences of 1.9% and 0.8%, respectively. The above results indicate that the proposed test method has high accuracy and operates at extremely low voltages (maximum 4.2 V), and can be as low as below 1 V (e.g., the crystal voltage corresponds to only 0.9 V at a waveplate temperature of 26.3℃).

[0066] Example 4 Example 4 discloses the measurement of the electro-optic coefficient γ of an ADP crystal using this application. 63 The method, measuring device such as Figure 1 As shown. The detection light source 1 is a linearly polarized continuous-wave green laser with a wavelength of 532 nm. Both the polarizer 2 and analyzer 7 are Glan-Taylor prisms with a 12.7 mm aperture. The half-wave plate 3 is a true zero-order half-wave plate made of quartz, with a working wavelength λ0 of 532 nm, and is placed inside a temperature-controlled furnace. The temperature regulating power supply 4 can maintain a temperature between 20 and 200 degrees Celsius. o The temperature can be continuously adjusted within the range of C, with a temperature resolution of 0.1 ℃. The electro-optic crystal under test, 5, is an ADP crystal, processed into a hexahedral shape with a size of 15 mm. 15 mm 10 mm (X) Y The light transmission direction is along the Z-axis, and transparent electrodes and voltages are applied to the front and rear light-transmitting end faces of the crystal. The output voltage of the DC low-voltage power supply 6 can be continuously adjusted within the range of 0-12 V, with a voltage resolution of 0.1 V. Its positive and negative terminals are connected to the front and rear transparent electrodes of the ADP crystal via power lines, respectively. The power meter 8 consists of a 3A probe and a power meter head, with a minimum resolution of 0.1 μW, which is sufficient to determine the extinction state of the system.

[0067] Using the measurement steps described above, the thermally induced phase difference of the variable-temperature waveplate was obtained. Based on the fundamental principle of the electro-optic effect in crystals, the expression for the electroinduced phase difference is: Regarding the application of the longitudinal electro-optic effect of "applying an electric field in the Z direction and allowing light to pass through in the Z direction" in the ADP crystal of this embodiment, Based on the relationship that the magnitudes of the two phase differences are equal, the ADP of the electro-optic crystal under test can be obtained. like Figure 5 As shown in Table 4.

[0068] Table 4 Test results of ADP crystals

[0069] During the calculation, a 532 nm true zero-order quartz wave plate was used. , , With a thickness L = 28.9 μm, the o-ray refractive index of the ADP crystal is... =1.5271, and For measurement data. Under the condition that no voltage is applied to the crystal under test, when the waveplate temperature is adjusted to 26.8... o At time C, the power meter reading is at its lowest, indicating the system is in a static extinction state, i.e., the extinction state described in step two. Increase the waveplate temperature to 27.8°C. o C. The system deviates from the extinction state, and then voltage is slowly applied to the crystal under test. When the voltage increases from 0 to 0.9 V, the power meter reading reaches its lowest point again. At this time, the system is in the dynamic extinction state for the first time, which is the extinction state described in step four. = and =0.9 V Substitute = The calculation relationship allows us to obtain the first electro-optic coefficient test data. At this point, step five is completed for the first time. Subsequently, a new round of testing is conducted for every 1°C increase in waveplate temperature, repeating steps three through five to obtain the remaining electro-optic coefficient test data. Table 4 shows that five electro-optic coefficient test data points were obtained from six experimental points, with an average value of 8.46 pm / V. This is very close to the measured value (8.39 pm / V) obtained using the half-wave voltage method on the same device, and also to the value reported in the literature (8.40 pm / V), with differences of 0.8% and 0.7%, respectively. These results indicate that this testing method has high accuracy and operates at extremely low voltages (maximum 4.7V), as low as 0.9V (e.g., a waveplate temperature of 27.8°C corresponds to a crystal voltage of only 0.9V).

[0070] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0071] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate, characterized in that, Includes the following steps: Step 1: Construct the optical path for measuring the electro-optic coefficient of the crystal, including a laser source, a polarizer, a true zero-order half-wave plate made of quartz material, the electro-optic crystal to be tested, an analyzer, and a power meter arranged sequentially along the propagation direction of the optical path; Step 2: Adjust the temperature of the true zero-order half-wave plate until the power meter reading reaches a minimum value, so that the measurement optical path is in the first extinction state and record the temperature value at this time as the first temperature; Step 3: Adjust the temperature of the true zero-order half-wave plate again to make the measurement optical path deviate from the extinction state, and record the temperature value at this time as the second temperature; Step 4: Maintain the second temperature and gradually apply voltage to the electro-optic crystal under test starting from zero volts until the measurement optical path reaches the extinction state again, and record the voltage difference applied to the electro-optic crystal under test; Step 5: Obtain the thermally induced phase difference calculation formula for the true zero-order half-wave plate based on the wave plate temperature difference obtained from the second temperature and the first temperature; simultaneously, obtain the electro-induced phase difference calculation formula for the electro-optic crystal under test based on the voltage difference applied to the electro-optic crystal under test. The electro-optic coefficient of the electro-optic crystal under test is obtained based on the compensation relationship between thermally induced phase difference and electro-induced phase difference.

2. The method for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate as described in claim 1, characterized in that, Also includes: Repeat steps two through five to obtain multiple sets of electro-optic coefficients, and take the average value of the multiple sets of electro-optic coefficients as the final electro-optic coefficient of the electro-optic crystal under test.

3. The method for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate as described in claim 2, characterized in that, During the repetition of steps two through five, the temperature difference of the waveplate is different in each electro-optic coefficient measurement.

4. The method for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate as described in claim 1, characterized in that, Step five specifically includes: Construct the formula for calculating the thermally induced phase difference of a true zero-order half-wave plate: Where λ is the wavelength of the incident laser emitted by the laser source; The birefringence of a true zero-order half-wave plate at the first temperature; The rate of change of birefringence of a true zero-order half-wave plate with temperature; The waveplate temperature difference between the second temperature and the first temperature; L Δ is the light transmission length of the waveplate at the first temperature, i.e., the initial thickness of the true zero-order half-wave plate; L This represents the change in the light transmission length of the waveplate when the temperature changes to the second temperature. Formula for calculating the electroinduced phase difference of the electro-optic crystal under test: in, This represents the o-ray refractive index of the electro-optic crystal under test. This represents the electro-optic coefficient of the electro-optic crystal under test. This represents the voltage difference applied to the electro-optic crystal under test when it is extinct again. l d is the length of the electro-optic crystal under test in the light transmission direction, and d is the electrode spacing of the electro-optic crystal under test; Based on the compensation relationship between thermally induced phase difference and electrically induced phase difference, let = Then the electro-optic coefficient of the electro-optic crystal under test can be obtained.

5. The method for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate as described in claim 1, characterized in that, In the constructed optical path for measuring the electro-optic coefficient of the crystal, the laser source shown is a laser emitting a fixed wavelength.

6. The method for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate as described in claim 1, characterized in that, In constructing the optical path for measuring the electro-optic coefficient of a crystal, the transmission directions of the polarizer and the analyzer are parallel to each other.

7. A method for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate, characterized in that, Includes the following steps: Step 1: Construct the optical path for measuring the electro-optic coefficient of the crystal, including a laser source, a polarizer, a true zero-order half-wave plate made of quartz material, the electro-optic crystal to be tested, an analyzer, and a power meter arranged sequentially along the propagation direction of the optical path; Step 2: Adjust the temperature of the true zero-order half-wave plate until the power meter reading reaches a minimum value, so that the measurement optical path is in the first extinction state and record the temperature value at this time as the first temperature; Step 3: Starting from zero volts, gradually apply a safe voltage less than the set threshold to the electro-optic crystal under test, so that the measurement optical path deviates from the extinction state, and record the voltage difference applied to the electro-optic crystal under test; Step 4: Maintain the safe voltage from Step 3, and adjust the temperature of the true zero-order half-wave plate to make the measurement optical path reach the extinction state again, and record the temperature value at this time as the second temperature; Step 5: Obtain the thermally induced phase difference calculation formula for the true zero-order half-wave plate based on the wave plate temperature difference obtained from the second temperature and the first temperature; simultaneously, obtain the electro-induced phase difference calculation formula for the electro-optic crystal under test based on the voltage difference applied to the electro-optic crystal under test. The electro-optic coefficient of the electro-optic crystal under test is obtained based on the compensation relationship between thermally induced phase difference and electro-induced phase difference.

8. The method for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate as described in claim 7, characterized in that, In step three, the set threshold is 1V.

9. A device for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate, characterized in that, The device includes a crystal electro-optic coefficient measurement optical path and a data control and processing module. The crystal electro-optic coefficient measurement optical path includes a laser source, a polarizer, a true zero-order half-wave plate made of quartz material, an electro-optic crystal under test, an analyzer, and a power meter arranged sequentially along the optical path propagation direction. The electro-optic crystal under test is connected to an adjustable DC low-voltage power supply; the true zero-order half-wave plate is placed in a temperature-controlled furnace; The data control and processing module includes a voltage regulation unit, a temperature regulation unit, and a data recording and processing unit; The voltage adjustment unit shown is connected to an adjustable DC low-voltage power supply to adjust the DC voltage applied to the electro-optic crystal under test. The temperature regulation unit is connected to the temperature control furnace to regulate the temperature of the true zero-level half-wave plate in the temperature control furnace; The data recording and processing unit is used to record: the temperature difference when the minimum value of the power meter reading disappears by adjusting the temperature of the true zero-order half-wave plate while keeping the DC voltage constant; and the voltage difference when the DC voltage of the electro-optic crystal under test is adjusted so that the power meter reading reaches the minimum value again while keeping the temperature that caused the minimum value to disappear constant; and the electro-optic coefficient of the electro-optic crystal under test is obtained according to the compensation relationship between the thermal phase difference caused by the temperature difference and the electro-phase difference caused by the voltage difference.

10. A device for measuring the electro-optic coefficient of a crystal using the thermally induced phase difference of a waveplate, characterized in that, The device includes a crystal electro-optic coefficient measurement optical path and a data control and processing module. The crystal electro-optic coefficient measurement optical path includes a laser source, a polarizer, a true zero-order half-wave plate made of quartz material, an electro-optic crystal under test, an analyzer, and a power meter arranged sequentially along the optical path propagation direction. The electro-optic crystal under test is connected to an adjustable DC low-voltage power supply; the true zero-order half-wave plate is placed in a temperature-controlled furnace; The data control and processing module includes a voltage regulation unit, a temperature regulation unit, and a data recording and processing unit; The voltage adjustment unit shown is connected to an adjustable DC low-voltage power supply to adjust the DC voltage applied to the electro-optic crystal under test. The temperature regulation unit is connected to the temperature control furnace to regulate the temperature of the true zero-level half-wave plate in the temperature control furnace; The data recording and processing unit is used to record: the voltage difference when the DC voltage on the electro-optic crystal under test is adjusted to make the minimum value of the power meter reading disappear while keeping the temperature constant; and the temperature difference when the temperature of the true zero-order half-wave plate is adjusted to make the power meter reading reach the minimum again while keeping the DC voltage that caused the minimum value to disappear constant; and to obtain the electro-optic coefficient of the electro-optic crystal under test based on the compensation relationship between the thermal phase difference caused by the temperature difference and the electro-phase difference caused by the voltage difference.

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