Method and apparatus for measuring the electro-optic coefficient of a crystal at low voltage

Abstract

The application discloses a method and device for measuring crystal electro-optic coefficient at low voltage, and relates to the technical field of photoelectric coefficient measurement. The method comprises the following steps: a wavelength tunable laser is used as an incident light source of a crystal electro-optic coefficient detection system; before the incident light source inputs a laser crystal to be measured, a wave plate is added as a phase compensator to generate a phase delay phi1, and meanwhile, the laser crystal to be measured generates a phase delay phi2 under the action of a direct current voltage; when the crystal electro-optic coefficient detection system is a half-wave voltage detection system, the wavelength of the tunable laser is adjusted to satisfy 3pi / 4 <= phi1 < pi; when the crystal electro-optic coefficient detection system is a full-wave voltage detection system, the wavelength of the tunable laser is adjusted to satisfy 7pi / 4 <= phi1 < 2pi. Since the light source used is a wavelength tunable laser, phi1 can be adjusted in a wide range by changing the wavelength, thereby changing phi2 and a test voltage, achieving the purpose of measuring the crystal electro-optic coefficient at low voltage, and improving test safety.

Description

Technical Field

[0001] This invention relates to the field of photoelectric coefficient measurement technology, and more specifically to a method and apparatus for measuring the electro-optic coefficient of a crystal under low voltage. Background Technology

[0002] Electro-optic crystal research is at the forefront of the intersection of optics, materials science, and information technology, and has a significant impact on the development of fields such as high-speed communication, quantum computing, and defense technology.

[0003] The electro-optic coefficient is the most important physical parameter of an electro-optic crystal, and the most common testing method is the half-wave voltage method. Its basic principle is to apply voltage to the crystal to generate an optical path difference of λ / 2 (corresponding to a phase delay of π), determine the half-wave voltage by observing the change in polarization state, and calculate the corresponding electro-optic coefficient using theoretical formulas. Since the half-wave voltage of many crystals reaches several kilovolts, this places high demands on the test power supply, and the entire testing process poses significant safety hazards.

[0004] Therefore, how to reduce the test voltage during the half-wave voltage method for testing the electro-optic coefficient of crystals, so as to minimize the requirements of the test power supply and ensure the safety of test personnel, is an urgent problem to be solved in this field. Summary of the Invention

[0005] This invention provides a method and apparatus for measuring the electro-optic coefficient of a crystal at low voltage. It employs a wavelength-tunable laser as the light source, thereby increasing the optical path difference of the waveplates in the optical path and reducing the electro-induced optical path difference required by the electro-optic crystal. This significantly reduces the test voltage of the crystal, down to one-eighth, one-sixteenth, or even lower. The technical solution of this invention is as follows:

[0006] This invention first discloses a method for measuring the electro-optic coefficient of a crystal under low voltage, comprising the following steps:

[0007] A wavelength-tunable laser is used as the incident light source for the crystal electro-optic coefficient detection system;

[0008] Before the incident light source is input into the laser crystal under test, a waveplate is added as a phase compensator to generate a phase delay φ1, and at the same time, the laser crystal under test generates a phase delay φ2 under the action of DC voltage.

[0009] When the crystal electro-optic coefficient detection system is a half-wave voltage detection system, the phase delays φ1 and φ2 satisfy:

[0010] φ1+φ2=π; At this time, adjust the wavelength of the tunable laser so that 3π / 4≤φ1<π, in order to reduce the DC voltage applied to the laser crystal under test;

[0011] When the crystal electro-optic coefficient detection system is a full-wave voltage detection system, the phase delays φ1 and φ2 satisfy:

[0012] φ1+φ2=2π. At this time, the wavelength of the tunable laser is adjusted so that 7π / 4≤φ1<2π to reduce the DC voltage applied to the laser crystal under test.

[0013] Furthermore, as an improved technical solution, the above-mentioned method for measuring the electro-optic coefficient of a crystal with low voltage also includes:

[0014] Adding a total reflection mirror to the crystal electro-optic coefficient detection system allows the light rays passing through the laser crystal under test to be reflected by the total reflection mirror and then pass through the laser crystal under test again, thereby further reducing the DC voltage applied to the laser crystal under test.

[0015] Based on the method disclosed in this invention, in one specific embodiment, this invention also discloses a low-voltage measurement crystal electro-optic coefficient device, which is a half-wave voltage detection system, including a wavelength-tunable laser, a polarizer, a waveplate, an electro-optic crystal under test, an analyzer, and a power meter arranged sequentially along the optical path, and an adjustable DC power supply for applying a DC voltage to the electro-optic crystal under test.

[0016] Preferably, in the above-mentioned half-wave voltage detection system, when the wavelength-tunable laser generates 1402 nm incident laser light, the waveplate is set as a half-waveplate, and the transmission direction of the polarizer is set perpendicular to the transmission direction of the analyzer. The incident laser light, after being polarized by the polarizer, generates a phase delay φ1 of 3π / 4 after passing through the half-waveplate. At this time, the adjustable DC power supply applies an eighth-wave voltage to the electro-optic crystal under test, so that the phase delay φ2 generated by the electro-optic crystal under test is π / 4, and the electro-optic coefficient of the electro-optic crystal under test is measured according to the eighth-wave voltage.

[0017] Preferably, in the above-mentioned half-wave voltage detection system, when the wavelength-tunable laser generates 716 nm incident laser light, the waveplate is set as a quarter-wave plate, and the transmission direction of the polarizer is set perpendicular to the transmission direction of the analyzer. The incident laser light, after being polarized by the polarizer, generates a phase delay φ1 of 3π / 4 after passing through the quarter-wave plate. At this time, the adjustable DC power supply applies a quarter-wave voltage to the electro-optic crystal under test, so that the phase delay φ2 generated by the electro-optic crystal under test is π / 4, and the electro-optic coefficient of the electro-optic crystal under test is measured according to the quarter-wave voltage.

[0018] Based on the method disclosed in this invention, in another specific embodiment, this invention discloses another low-voltage measurement crystal electro-optic coefficient device. The low-voltage measurement crystal electro-optic coefficient device is a full-wave voltage detection system, including a wavelength-tunable laser, a polarizer, a waveplate, an electro-optic crystal under test, an analyzer, and a power meter arranged sequentially along the optical path, as well as an adjustable DC power supply for applying a DC voltage to the electro-optic crystal under test.

[0019] Preferably, in the above-mentioned full-wave voltage detection system, when the wavelength-tunable laser generates 620 nm incident laser light, the waveplate is set as a half-waveplate, and the transmission direction of the polarizer is set perpendicular to the transmission direction of the analyzer. The incident laser light, after being polarized by the polarizer, generates a phase delay φ1 of 7π / 4 after passing through the half-waveplate. At this time, the adjustable DC power supply applies an eighth-wave voltage to the electro-optic crystal under test, so that the phase delay φ2 generated by the electro-optic crystal under test is π / 4, and the electro-optic coefficient of the electro-optic crystal under test is measured according to the eighth-wave voltage.

[0020] Based on the improved technical solution disclosed in this invention, this invention discloses another low-voltage measurement crystal electro-optic coefficient device. The low-voltage measurement crystal electro-optic coefficient device is a half-wave voltage detection system, including a wavelength-tunable laser, a polarizer, a semi-reflecting mirror, a waveplate, an electro-optic crystal under test, and a total reflection mirror arranged sequentially along the optical path direction. The light reflected by the total reflection mirror returns to the electro-optic crystal under test and the waveplate, and after being reflected by the semi-reflecting mirror, it enters the analyzer and the power meter in sequence to complete the electro-optic coefficient measurement of the electro-optic crystal under test. During the electro-optic coefficient measurement process, the electro-optic crystal under test is supplied with a DC voltage through an adjustable DC power supply.

[0021] Preferably, in the above-mentioned half-wave voltage detection system, when the wavelength-tunable laser generates 1402 nm incident laser light, the waveplate is set as a quarter-wave plate, and the transmission direction of the polarizer is set perpendicular to the transmission direction of the analyzer. The incident laser light, after being polarized by the polarizer, generates a phase delay φ1ˊ of 3π / 8 after passing through the half-reflector and the half-wave plate. At this time, the adjustable DC power supply applies a one-sixteenth-wave voltage to the electro-optic crystal under test, so that the phase delay φ2ˊ generated by the electro-optic crystal under test is π / 8, and the electro-optic coefficient of the electro-optic crystal under test is measured according to the one-sixteenth-wave voltage.

[0022] Based on the improved technical solution disclosed in this invention, this invention discloses another low-voltage measurement crystal electro-optic coefficient device. The low-voltage measurement crystal electro-optic coefficient device is a full-wave voltage detection system, including a wavelength-tunable laser, a polarizer, a half-reflecting mirror, a waveplate, an electro-optic crystal under test, and a total reflection mirror arranged sequentially along the optical path direction. The light reflected by the total reflection mirror returns to the electro-optic crystal under test and the waveplate, and after being reflected by the half-reflecting mirror, it enters the analyzer and the power meter in sequence to complete the measurement of the electro-optic coefficient of the electro-optic crystal under test. During the electro-optic coefficient measurement process, the electro-optic crystal under test is supplied with a DC voltage through an adjustable DC power supply.

[0023] This invention discloses a method and apparatus for measuring the electro-optic coefficient of a crystal under low voltage. Compared with existing techniques for measuring the electro-optic coefficient of crystals, this invention has the following advantages:

[0024] (1) Since the present invention uses a wavelength-tunable laser as a light source, the phase delay φ1 of the laser after passing through the waveplate can be adjusted over a wide range by changing the wavelength, thereby changing the phase delay φ2 of the laser crystal under test and the test voltage applied to the laser crystal under test, so as to achieve the purpose of measuring the electro-optic coefficient of the crystal with low voltage and low cost, and improve the safety of test personnel, test equipment and test materials.

[0025] The test voltage required by this invention is significantly reduced, and the test voltage can be infinitely close to the required voltage, regardless of the convenience of waveplate calibration.

[0026] (2) The test results are more accurate and reliable. Since the electro-optic coefficient is obtained at a lower test voltage, it effectively avoids the loss caused by high voltage, as well as the interference of various factors such as inverse piezoelectric effect and elasto-optic effect. Therefore, it can better reflect the intrinsic electro-optic characteristics of the material.

[0027] (3) Low cost of optical components. In practical applications, the waveplate used in this invention does not need to be customized. Existing conventional waveplates or even self-made birefringent crystals with arbitrary thickness can be used directly. Therefore, the structure of this invention is simple and saves on complicated waveplate stators.

[0028] (4) The crystal electro-optic coefficient detection device involved in this invention has a simple optical path, few optical components, and small device size. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0030] Figure 1This is a schematic diagram of the electro-optic coefficient testing device corresponding to Embodiments 1, 2, and 3 of the present invention.

[0031] Figure 2 This is a schematic diagram of the test results of Embodiment 1 of the present invention.

[0032] Figure 3 This is a schematic diagram of the test results for Embodiment 2 of the present invention.

[0033] Figure 4 This is a schematic diagram of the test results in Embodiment 3 of the present invention.

[0034] Figure 5 A schematic diagram of the electro-optic coefficient testing device corresponding to Embodiment 4 of the present invention.

[0035] In the figure, 1 is a wavelength-tunable laser source, 2 is a polarizer, 3 is a waveplate, 4 is an adjustable DC power supply, 5 is the electro-optic crystal under test, 6 is an analyzer, 7 is a power meter, 8 is a semi-reflecting mirror, and 9 is a total reflection mirror. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] One embodiment of the present invention discloses a method for measuring the electro-optic coefficient of a crystal at low voltage, comprising the following steps:

[0038] A wavelength-tunable laser is used as the incident light source for the crystal electro-optic coefficient detection system;

[0039] Before the incident light source is input into the laser crystal under test, a waveplate is added as a phase compensator to generate a phase delay φ1. At the same time, the laser crystal under test generates a phase delay φ2 under the action of DC voltage.

[0040] When the crystal electro-optic coefficient detection system is a half-wave voltage detection system, the phase delays φ1 and φ2 satisfy:

[0041] φ1+φ2=π; At this time, adjust the wavelength of the tunable laser so that 3π / 4≤φ1<π, in order to reduce the DC voltage applied to the laser crystal under test;

[0042] When the crystal electro-optic coefficient detection system is a full-wave voltage detection system, the phase delays φ1 and φ2 satisfy:

[0043] φ1+φ2=2π. At this time, the wavelength of the tunable laser is adjusted so that 7π / 4≤φ1<2π to reduce the DC voltage applied to the laser crystal under test.

[0044] As an improved technical solution, based on the above method, it also includes:

[0045] Adding a total reflection mirror to the crystal electro-optic coefficient detection system allows the light rays passing through the laser crystal under test to be reflected by the total reflection mirror and then pass through the laser crystal under test again, thereby further reducing the DC voltage applied to the laser crystal under test.

[0046] In this invention, the wavelength range of the incident laser of the wavelength-tunable laser can be selected from 300 nm to 2400 nm.

[0047] To reduce testing costs, waveplate 3 does not need to be specially made; existing waveplate devices commonly found on the market can be selected. The phase delay φ1 generated by waveplate 3 in this device can be determined based on the wavelength of the laser used for testing and the thickness and refractive index of the waveplate material.

[0048] To ensure the accuracy of the test results using the test method described in this invention, the optical path difference of the waveplates in the optical path must be experimentally calibrated before the test. This ensures that the optical path difference generated by the electro-optic crystal used in the calculation process is accurate. The calibration method for the 3λ / 8 waveplate (i.e., the 3π / 4 waveplate) is as follows: Based on the birefringence of the material used in the waveplate and the wafer thickness, the theoretical wavelength can be obtained first. Then, four identical waveplates are connected in series to obtain a 3λ / 2 waveplate. This waveplate is placed between two orthogonal polarizers to perform an extinction experiment. The wavelength of the tunable laser source is adjusted to near the theoretical wavelength and fine-tuned until extinction occurs. This determines the accurate wavelength corresponding to the 3λ / 8 waveplate, thus completing the waveplate calibration work before the electro-optic coefficient test. The calibration method for a 3λ / 16 waveplate (i.e., a 3π / 8 waveplate) is as follows: Based on the birefringence of the material used in the waveplate and the wafer thickness, the theoretically calculated wavelength can be obtained first. Then, four identical waveplates are connected in series to obtain a 3λ / 4 waveplate. This waveplate is placed between the back-and-forth propagating optical paths. Ideally, the reflected light will produce an optical path difference of 3λ / 2 relative to the incident light. The wavelength of the tunable laser source is tuned to near the theoretically calculated wavelength and fine-tuned. Simultaneously, the reflected light is sampled, and its polarization characteristics are detected until the polarization of the reflected light becomes a linear polarization state completely perpendicular to the polarization of the incident light. The wavelength of the source at this point is the accurate wavelength corresponding to the 3λ / 16 waveplate, thus completing the waveplate calibration work before the electro-optic coefficient test. The calibration of other optical path difference waveplates follows the same method.

[0049] To better illustrate the principles of the present invention, based on the method of the present invention, the present invention also discloses several low-voltage measurement crystal electro-optic coefficient devices to demonstrate and illustrate the specific implementation steps and principles of the present invention.

[0050] Example 1

[0051] A device for measuring the electro-optic coefficient of a crystal using a 1402 nm light source and a one-eighth wave voltage.

[0052] The measuring device consists of a wavelength-tunable laser (1), a polarizer (2), a waveplate (3), a DC power supply (4), the electro-optic crystal under test (5), an analyzer (6), and a power meter (7), as shown in the attached diagram. Figure 1 As shown. The method of using this device is as follows: Set the transmission direction of polarizer 2 to be perpendicular to the transmission direction of analyzer 6. The laser emitted by the wavelength-tunable laser 1 is converted into highly polarized linear light by polarizer 2. After passing through waveplate 3, the phase delay φ1=3π / 4 is generated. After passing through the electro-optic crystal 5 under test, which is powered by DC power supply 4, the phase delay φ2=π / 4 is generated. Since the applied voltage satisfies the condition φ1 + φ2 =π, the polarization direction of the linearly polarized light generated by polarizer 2 is rotated by 90°. o The transmitted light intensity of the analyzer 6 is at its maximum, meaning the entire system is in a fully open state. The electro-optic coefficient of the electro-optic crystal 5 under test is determined based on the one-eighth wave voltage applied by the DC power supply 4 (corresponding to a π / 4 phase delay).

[0053] In this embodiment 1, the laser source 1 can be an optical parametric oscillator (OPO) laser, with the wavelength fixed at 1402 nm for the half-wave plate used. The polarizer 2 and analyzer 6 are both Glan prisms. The wave plate 3 is a commercially available 1064 nm true zero-order half-wave plate, which can produce an optical path difference of 532 nm for the incident laser. If used as a 3λ / 8 wave plate, the corresponding wavelength is 1418 nm. Actual calibration shows that the optimal wavelength for the 3λ / 8 wave plate is 1402 nm, at which point φ1 = 3π / 4. The DC power supply 4 is connected to the electro-optic crystal 5 under test, providing the required voltage and generating a positive phase delay φ2.

[0054] The electro-optic crystal 5 under test is a DKDP crystal with X×Y×Z=20mm×20mm×10mm. The electro-optic crystal 5 is either rod-shaped or hexahedral. When measuring the longitudinal electro-optic effect, the voltage output from the DC power supply 4 is applied to the front and rear light-transmitting end faces of the electro-optic crystal 5 through transparent electrodes. When measuring the transverse electro-optic effect, the voltage output from the DC power supply 4 is applied to the two opposite sides of the electro-optic crystal 5 coated with metal electrodes. The electro-optic coefficient γ is measured through the longitudinal electro-optic effect. 63 .

[0055] The actual test results are as follows Figure 2As shown, it can be seen that when the phase difference φ2 = π / 4, the transmitted light intensity of the system is at its maximum, U λ / 8 =2200V. Substitute this into the phase difference formula. Combined with λ=1402 nm, DKDP crystal n o =1.4865, the electro-optic coefficient of the sample is obtained as γ 63 =24.25pm / V, which is very close to the literature reported value of DKDP crystal (25.98pm / V), confirming the reliability of the test method.

[0056] Example 2

[0057] A device for measuring the electro-optic coefficient of a crystal using a 716 nm light source and a half-wave voltage.

[0058] In Example 2, the measuring device is a half-wave voltage detection system, capable of measuring the electro-optic coefficient of a crystal using a half-wave voltage. This device consists of a wavelength-tunable laser 1, a polarizer 2, a waveplate 3, an adjustable DC power supply 4, the electro-optic crystal under test 5, an analyzer 6, and a power meter 7, as shown in the attached diagram. Figure 1 As shown. The method of using this device is as follows: Set the transmission direction of polarizer 2 to be perpendicular to the transmission direction of analyzer 6. The laser emitted by the wavelength-tunable laser 1 is converted into highly polarized linear light by polarizer 2. After passing through waveplate 3, the phase delay φ1=3π / 4 is generated. After passing through the electro-optic crystal 5 under test, which is energized by adjustable DC power supply 4, the phase delay φ2=π / 4 is generated. Since the applied voltage satisfies the condition φ1 + φ2 =π, the polarization direction of the linearly polarized light generated by polarizer 2 is rotated by 90°. o The transmitted light intensity of the analyzer 6 is at its maximum, meaning the entire system is fully open. The electro-optic coefficient of the electro-optic crystal 5 under test is determined based on the one-eighth wave voltage (corresponding to a π / 4 phase delay) shown by the DC power supply 4.

[0059] In Example 2, the wavelength-tunable laser 1 can be an optical parametric oscillator (OPO) laser, with the wavelength fixed at 716 nm for the waveplate used. Both the polarizer 2 and analyzer 6 are Glan prisms. The waveplate 3 is a commercially available 1064 nm true zero-order quarter-wave plate, which can produce an optical path difference of 266 nm for the incident laser. If used as a 3λ / 8 waveplate, the corresponding wavelength is 709 nm. Actual calibration shows the optimal wavelength for the 3λ / 8 waveplate is 716 nm, at which point φ1 = 3π / 4. The adjustable DC power supply 4 is connected to the electro-optic crystal 5 under test, providing the required eighth-wave voltage to the electro-optic crystal 5, generating a positive phase delay φ2.

[0060] The electro-optic crystal under test, 5, is a DKDP with X×Y×Z=20mm×20mm×10mm. The electro-optic coefficient γ is measured by longitudinal electro-optic effect. 63The voltage output from DC power supply 4 is applied to the front and rear light-transmitting surfaces of crystal 5 through transparent electrodes.

[0061] The actual test results are as follows Figure 3 As shown, it can be seen that when the phase difference φ2 = π / 4, the transmitted light intensity of the system is at its maximum, U λ / 8 =1000V. Substitute this into the phase difference formula. Combined with λ=716 nm, DKDP crystal n o =1.5016, the electro-optic coefficient of the sample is obtained as γ 63 =26.44 pm / V, which is very close to the literature reported value of DKDP crystal (25.98 pm / V), confirming the reliability of the test method.

[0062] Example 3

[0063] A device for measuring the electro-optic coefficient of a crystal using a 620 nm light source and a half-wave voltage.

[0064] In Example 3, the measuring device is a full-wave voltage detection system, capable of measuring the electro-optic coefficient of a crystal using a one-eighth wave voltage. This device consists of a wavelength-tunable laser 1, a polarizer 2, a waveplate 3, an adjustable DC power supply 4, the electro-optic crystal under test 5, an analyzer 6, and a power meter 7, as shown in the attached diagram. Figure 1 As shown. The method of using this device is as follows: Set the transmission direction of polarizer 2 to be perpendicular to the transmission direction of analyzer 6. The laser emitted by the wavelength-tunable laser 1 is converted into highly polarized linear light by polarizer 2. After passing through waveplate 3, the phase delay φ1=7π / 4 is generated, and after passing through the electro-optic crystal 5 under test energized by DC power supply 4, the phase delay φ2=π / 4 is generated. Since the applied voltage satisfies the condition φ1 + φ2 = 2π, the polarization state of the linearly polarized light generated by polarizer 2 does not change after passing through waveplate 3 and crystal 5. The transmitted light intensity of analyzer 6 is minimal, that is, the entire system is in an extinction state. The electro-optic coefficient of the electro-optic crystal 5 under test is determined according to the one-eighth wave voltage shown by the adjustable DC power supply 4 (corresponding to π / 4 phase delay).

[0065] In Example 3, the tunable laser source 1 can be an optical parametric oscillator (OPO) laser, with the wavelength fixed at 620 nm for the waveplate used. Both the polarizer 2 and analyzer 6 are Glan prisms. The waveplate 3 is a commercially available 1064 nm true zero-order half-waveplate, which can generate an optical path difference of 532 nm for the incident laser. If used as a 7λ / 8 waveplate, the corresponding wavelength is 608 nm. Actual calibration shows the optimal wavelength for the 7λ / 8 waveplate is 620 nm, at which point φ1 = 7π / 4. The DC power supply 4 is connected to the electro-optic crystal 5 under test, providing the required half-wave voltage to the electro-optic crystal 5, generating a positive phase delay φ2.

[0066] The electro-optic crystal under test, 5, is a DKDP with X×Y×Z=20 mm × 20 mm × 10 mm. The electro-optic coefficient γ is measured by the longitudinal electro-optic effect. 63 The voltage output from the adjustable DC power supply 4 is applied to the front and rear light-transmitting surfaces of the crystal 5 through transparent electrodes.

[0067] The actual test results are as follows Figure 4 As shown, it can be seen that when the phase difference φ2 = π / 4, the transmitted light intensity of the system is minimal, U λ / 8 =850 V. Substitute this into the phase difference formula. Combined with λ=620 nm, DKDP crystal n o =1.5044, the electro-optic coefficient of the sample is obtained as γ 63 =26.78pm / V, which is very close to the literature reported value of DKDP crystal (25.98pm / V), confirming the reliability of the test method.

[0068] Example 4

[0069] A device for measuring the electro-optic coefficient of a crystal using a 1402 nm light source and a 1 / 16th wave voltage.

[0070] In Example 4, the measuring device is a half-wave voltage detection system, capable of measuring the electro-optic coefficient of a crystal using a one-sixteenth-wave voltage. This device consists of a wavelength-tunable laser 1, a polarizer 2, a waveplate 3, an adjustable DC power supply 4, the electro-optic crystal under test 5, an analyzer 6, a power meter 7, a semi-reflecting mirror 8, and a total reflection mirror 9, as shown in the attached diagram. Figure 5 As shown. The method of using this device is as follows: Set the transmission direction of polarizer 2 to be perpendicular to the transmission direction of analyzer 6. The laser emitted by the wavelength-tunable laser 1 is converted into highly polarized linear light after passing through polarizer 2. After passing through the semi-reflecting mirror 8 and waveplate 3, the phase delay φ1ˊ=3π / 8 is generated. After passing through the electro-optic crystal 5 under test, which is energized by the adjustable DC power supply 4, the phase delay φ2ˊ=π / 8 is generated. Subsequently, when the beam passes through the total reflection mirror 9, the electro-optic crystal 5 under test, and the waveplate 3 in sequence and returns to the semi-reflecting mirror 8 along the original optical path, the total phase delay doubles to 2×(3π / 8+π / 8)=π. The polarized light reflected from the semi-reflecting mirror 8 to the analyzer 6 is linearly polarized, and the polarization direction is rotated by 90° relative to the linear polarization of polarizer 2. o The transmitted light intensity of the analyzer 6 is at its maximum, meaning the entire system is in a fully open state. The electro-optic coefficient of the electro-optic crystal 5 under test is determined based on the one-sixteenth wave voltage applied by the adjustable DC power supply 4 (corresponding to a π / 8 phase delay).

[0071] In Example 4, the wavelength-tunable laser source 1 can be an optical parametric oscillator (OPO) laser, with the wavelength fixed at 1402 nm for the waveplate used. Both the polarizer 2 and analyzer 6 are Glan prisms. The waveplate 3 is a commercially available 1064 nm true zero-order quarter-wave plate, which can generate an optical path difference of 266 nm for the incident laser. If used as a 3λ / 16 waveplate, the corresponding wavelength is 1418 nm. Actual calibration shows the optimal wavelength for the 3λ / 16 waveplate is 1402 nm, at which point φ1ˊ = 3π / 8. The adjustable DC power supply 4 is connected to the electro-optic crystal 5 under test, providing the required voltage and generating a phase delay φ2ˊ of π / 8. Due to the use of a round-trip optical path, the detection voltage applied to the crystal under test is only half that of Example 1. The electro-optic crystal under test, 5, is a DKDP with X×Y×Z=20 mm × 20 mm × 10 mm. The electro-optic coefficient γ is measured by the longitudinal electro-optic effect. 63 The voltage output from DC power supply 4 is applied to the front and rear light-transmitting surfaces of crystal 5 through transparent electrodes.

[0072] 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.

[0073] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. 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 the invention. Therefore, the invention 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 of measuring the electro-optic coefficient of a crystal at low voltage, characterized in that, The method comprises the following steps: The wavelength tunable laser is used as the incident light source of the crystal electro-optic coefficient detection system; The crystal electro-optic coefficient detection system is a half-wave voltage detection system or a full-wave voltage detection system, comprising, in sequence along the light path direction, a wavelength tunable laser (1), a polarizer (2), a wave plate (3), a to-be-measured electro-optic crystal (5), a detection polarizer (6), and a power meter (7), and an adjustable direct current power supply (4) for applying a direct current voltage to the to-be-measured electro-optic crystal (5); The wave plate (3) acts as a phase compensator to produce a phase delay before the incident light source enters the laser crystal to be tested At the same time, the laser crystal to be tested produces a phase delay under the action of a direct current voltage ; When the crystal electro-optic coefficient detection system is a half-wave voltage detection system, the wavelength of the tunable laser is adjusted to satisfy 3π / 4≤ <π, so as to reduce the direct current voltage applied to the laser crystal to be detected. When the crystal electro-optic coefficient detection system is a full-wave voltage detection system, the wavelength of the tunable laser is adjusted to satisfy 7π / 4≤ <2π, so as to reduce the direct current voltage applied to the laser crystal to be detected.

2. A method of measuring the electro-optic coefficient of a crystal at low voltage as claimed in claim 1, wherein, In the half-wave voltage detection system, when the wavelength tunable laser (1) generates 1402 nm incident laser, the wave plate (3) is set as a half wave plate, the transmission direction of the polarizer (2) and the transmission direction of the analyzer (6) are set as perpendicular, the incident laser after being polarized by the polarizer (2) generates 3π / 4 phase delay after the half wave plate At this time, the adjustable DC power supply (4) applies an eighth-wave voltage to the to-be-measured electro-optical crystal (5), so that the to-be-measured electro-optical crystal (5) generates a phase delay π / 4, and the electro-optical coefficient measurement of the to-be-measured electro-optical crystal (5) is completed according to the eighth-wave voltage.

3. A method of measuring the electro-optic coefficient of a crystal at low voltage as claimed in claim 1, wherein, In the half-wave voltage detection system, when the wavelength tunable laser (1) generates 716 nm incident laser, the wave plate (3) is set as a quarter wave plate, the transmission direction of the polarizer (2) and the transmission direction of the analyzer (6) are set as perpendicular, the incident laser after being polarized by the polarizer (2) generates 3π / 4 phase delay after the quarter wave plate At this time, the adjustable DC power supply (4) applies an eighth-wave voltage to the to-be-measured electro-optical crystal (5), so that the to-be-measured electro-optical crystal (5) generates a phase delay π / 4, and the electro-optical coefficient measurement of the to-be-measured electro-optical crystal (5) is completed according to the eighth-wave voltage.

4. The method of claim 1, wherein the low voltage is in the range of 0.1 to 10 volts. In the full-wave voltage detection system, when the wavelength tunable laser (1) generates 620 nm incident laser, the wave plate (3) is set as a half wave plate, the transmission direction of the polarizer (2) and the transmission direction of the analyzer (6) are set as perpendicular, the incident laser after the polarization of the polarizer (2) generates 7π / 4 phase delay after the half wave plate At this time, the adjustable DC power supply (4) applies an eighth-wave voltage to the to-be-measured electro-optic crystal (5), so that the to-be-measured electro-optic crystal (5) generates a phase delay π / 4, and the electro-optic coefficient measurement of the to-be-measured electro-optic crystal (5) is completed according to the eighth-wave voltage.

5. A method of measuring the electro-optic coefficient of a crystal at low voltage, characterized by, The method comprises the following steps: The wavelength tunable laser is used as the incident light source of the crystal electro-optic coefficient detection system; The crystal electro-optic coefficient detection system is a half-wave voltage detection system or a full-wave voltage detection system, comprising, in sequence along the light path direction, a wavelength tunable laser (1), a polarizer (2), a half mirror (8), a wave plate (3), a to-be-measured electro-optic crystal (5), and a full mirror (9); after the light reflected by the full mirror (9) returns to the to-be-measured electro-optic crystal (5) and the wave plate (3) again, the light is reflected by the half mirror (8) and then enters the detection polarizer (6) and the power meter (7) in sequence to complete the electro-optic coefficient measurement of the to-be-measured electro-optic crystal (5); during the electro-optic coefficient measurement, the to-be-measured electro-optic crystal (5) is applied with a direct current voltage by the adjustable direct current power supply (4). The wave plate (3) acts as a phase compensator to produce a phase delay before the incident light source enters the laser crystal to be tested At the same time, the laser crystal to be tested produces a phase delay under the action of a direct current voltage ; When the crystal electro-optic coefficient detection system is a half-wave voltage detection system, the wavelength of the tunable laser is adjusted to satisfy 3π / 8≤ <π, so as to reduce the direct current voltage applied to the laser crystal to be detected. When the crystal electro-optic coefficient detection system is a full-wave voltage detection system, the wavelength of the tunable laser is adjusted to satisfy 7π / 4≤ <2π, so as to reduce the direct current voltage applied to the laser crystal to be detected.

6. A method of measuring the electro-optic coefficient of a crystal at low voltage as claimed in claim 5, wherein, In the half-wave voltage detection system, when the wavelength tunable laser (1) generates 1402 nm incident laser, the wave plate (3) is set as a quarter wave plate, the transmission direction of the polarizer (2) and the transmission direction of the analyzer (6) are set as perpendicular, the incident laser after being polarized by the polarizer (2) generates 3π / 8 phase delay after the half mirror (8) and the half wave plate At this time, the adjustable DC power supply (4) applies a sixteenth wave voltage to the to-be-measured electro-optical crystal (5), so that the to-be-measured electro-optical crystal (5) generates a phase delay It is π / 8, and the electro-optic coefficient measurement of the to-be-measured electro-optical crystal (5) is completed according to the sixteenth wave voltage.

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