Electro-optic phase modulator for displacement measurement system and displacement measurement system

Abstract

The disclosure provides an electro-optic phase modulator for a displacement measurement system and the displacement measurement system. The electro-optic phase modulator comprises a housing with an accommodation space, an entrance and an exit are formed on the housing, and polarized measurement light enters the accommodation space through the entrance; a modulation crystal is arranged in the accommodation space and is configured to modulate the polarized measurement light from the entrance, and a polarization direction of the polarized measurement light is 45° to a modulation electric field direction of the modulation crystal; and a quarter-wave plate is located between the modulation crystal and the exit, an optical axis of the quarter-wave plate is 45° to the modulation electric field direction of the modulation crystal, the polarized measurement light passes through the quarter-wave plate and is emitted to a measured object through the exit, the measured object reflects the polarized measurement light back to the modulation crystal through the quarter-wave plate, and a polarization component direction of the polarized measurement light reflected back to the modulation crystal is changed by 90° compared with that of the polarized measurement light emitted to the modulation crystal through the entrance.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of laser displacement measurement, and in particular to an electro-optic phase modulator for a displacement measurement system and a displacement measurement system. BACKGROUND

[0002] Displacement measurement systems represented by laser trackers, laser range finders, total stations, laser radars, etc. are widely used in the production and construction processes of aerospace, marine vessels, large scientific devices, and large-scale civil engineering. With the improvement of technology, the requirements for displacement measurement range and measurement accuracy in these technical fields are constantly increasing.

[0003] Electro-optic modulation realizes displacement calculation by establishing a functional relationship between the spatial displacement and the laser modulation signal through electro-optic internal modulation or external modulation of the laser, and then realizes laser displacement measurement. Currently, laser ranging devices have been proposed based on the principles of time-of-flight method, phase method, frequency-modulated continuous wave method, femtosecond optical frequency comb method, etc. SUMMARY

[0004] To at least partially overcome the technical defects of at least one of the above-mentioned inventions or other inventions, at least one embodiment of the present disclosure provides an electro-optic phase modulator and a displacement measurement system. By providing a modulation crystal and a quarter-wave plate, the polarization direction and phase of the polarization measurement light can be adjusted, and the temperature self-compensation of the influence of the radio frequency modulation thermal effect on the refractive index of the modulation crystal can be realized, thereby improving the precision of the electro-optic phase modulator.

[0005] According to an aspect of the present disclosure, an electro-optic phase modulator is provided, comprising: a housing having an accommodation space built-in, an incident port and an exit port being formed on the housing, and a polarization measurement light being incident into the accommodation space from the incident port; a modulation crystal being disposed in the accommodation space and being configured to modulate the polarization measurement light from the incident port, a polarization direction of the polarization measurement light being 45° to a modulation electric field direction of the modulation crystal; and a quarter-wave plate being located between the modulation crystal and the exit port, an optical axis of the quarter-wave plate being 45° to the modulation electric field direction of the modulation crystal, the polarization measurement light being emitted to a measured object from the exit port after passing through the quarter-wave plate, and the measured object reflecting the polarization measurement light back to the modulation crystal via the quarter-wave plate, so that a polarization component direction of the polarization measurement light reflected back to the modulation crystal is changed by 90° from that of the polarization measurement light incident into the modulation crystal from the incident port.

[0006] In some embodiments, further comprising a resonant modulation driving circuit, the resonant modulation driving circuit comprising a signal receiving unit, an inductor, and a resistor connected in series, the signal receiving unit being configured to receive a modulation signal, the modulation crystal being connected to the signal receiving unit in series, different resonant modulation frequencies being obtained by adjusting the inductance value of the inductor.

[0007] In some embodiments, further comprising a temperature adjusting unit configured to adjust the temperature of the containing space, the temperature adjusting unit comprising: a temperature sensor configured to detect the temperature of the containing space; a thermoelectric refrigerator; and a temperature self-compensation control circuit connected with the temperature sensor and the temperature sensor respectively, and configured to control the thermoelectric refrigerator to refrigerate or heat based on the temperature detected by the temperature sensor.

[0008] In some embodiments, further comprising a substrate, the modulation crystal and the quarter-wave plate being disposed on the substrate, and a line connecting the center of the modulation crystal and the center of the quarter-wave plate being collinear with a line connecting the incident port and the exit port.

[0009] In some embodiments, the modulation crystal is a lithium niobate crystal.

[0010] In some embodiments, the shell is an electromagnetic shielding shell to isolate interference from external signals.

[0011] In some embodiments, the resonant modulation driving circuit further comprises: two metal electrodes respectively disposed on opposite sides of the modulation crystal, the modulation crystal being connected with the signal receiving unit and the resistor via the two metal electrodes.

[0012] According to another aspect of the present disclosure, a displacement measurement system configured to measure displacement of an object under test is provided, comprising: a light source unit configured to emit an initial light source; a polarization beam splitter prism configured to polarize the initial light source to form a polarization measurement light; the above-mentioned electro-optical phase modulator configured to modulate the polarization direction and phase of the polarization measurement light; a mirror disposed on the object under test and configured to reflect the polarization measurement light from the electro-optical phase modulator back to the electro-optical phase modulator; a photodetector configured to receive the polarization measurement light and convert the optical signal of the polarization measurement light into an electrical signal; and a control unit connected with the photodetector and configured to send a modulation signal to the electro-optical phase modulator and calculate the displacement of the object under test based on the electrical signal of the polarization measurement light.

[0013] In some embodiments, the light source unit comprises: a laser configured to emit a laser light; and a polarization isolator configured to emit the initial light source based on the laser light.

[0014] In some embodiments, further comprising: a sampling unit configured to sample the electrical signal output by the photodetector and transmit the sampled electrical signal to the control unit.

[0015] According to the embodiments of the present disclosure, by setting the polarization direction of the polarization measurement light to be 45° to the modulation electric field direction of the modulation crystal, the two polarization components of the polarization measurement light orthogonal to each other can generate a phase difference. By setting a quarter-wave plate inside the electro-optical phase modulator, the optical axis of the quarter-wave plate is 45° to the modulation electric field direction of the modulation crystal, so that the direction of the two polarization components of the polarization measurement light orthogonal to each other can be changed by 90°. The modulation crystal can modulate the two polarization components of the polarization measurement light orthogonal to each other respectively when the polarization measurement light passes through the modulation crystal twice, and then the temperature self-compensation of the influence of the radio frequency modulation thermal effect on the refractive index of the modulation crystal can be realized, the precision of the electro-optical phase modulator 1 is improved, and then the measurement precision of the displacement measurement system is improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A cross-sectional view of an electro-optical phase modulator according to an embodiment of the present disclosure is schematically shown;

[0017] Figure 2 A working principle diagram of an electro-optical phase modulator according to an embodiment of the present disclosure is schematically shown;

[0018] Figure 3 A circuit diagram of a resonant modulation driving circuit according to an embodiment of the present disclosure is schematically shown;

[0019] Figure 4 A working principle diagram of a displacement measurement system according to an embodiment of the present disclosure is schematically shown;

[0020] Figure 5 A perspective view of a modulation crystal according to an embodiment of the present disclosure is schematically shown; and

[0021] Figure 6 A cross-sectional view of a modulation crystal and two metal electrodes connected according to an embodiment of the present disclosure is schematically shown.

[0022] REFERENCE SIGNS

[0023] 1: electro-optical phase modulator;

[0024] 11: housing;

[0025] 111: accommodation space;

[0026] 112: entrance;

[0027] 113: exit;

[0028] 12: modulation crystal;

[0029] 13: quarter-wave plate;

[0030] 14: resonant modulation driving circuit;

[0031] 141: signal receiving unit;

[0032] 142: inductor;

[0033] 143: resistor;

[0034] 144: metal electrode;

[0035] 145: gold-plated film;

[0036] 146: conductive silver paste;

[0037] 15: radio frequency modulation port;

[0038] 161: temperature sensor;

[0039] 162: thermoelectric cooler;

[0040] 163: temperature self-compensation control circuit;

[0041] 17: base;

[0042] 2: light source part;

[0043] 21: laser;

[0044] 22: polarizing isolator;

[0045] 3: polarization beam splitter prism;

[0046] 4: mirror;

[0047] 5: photodetector;

[0048] 6: control unit;

[0049] 7: sampling unit;

[0050] 8: modulation driving unit. DETAILED DESCRIPTION

[0051] To make the objectives, technical solutions and advantages of the present disclosure clearer, the present disclosure is further described in detail below with reference to specific embodiments and drawings. However, the present disclosure can be implemented in different forms, and should not be interpreted as limited to the embodiments presented herein. On the contrary, these embodiments are provided to make the disclosure complete and fully, and to fully convey the scope of the present disclosure to those skilled in the art. In the drawings, the sizes and relative sizes of layers and regions can be exaggerated for clarity, and the same reference numerals represent the same elements throughout.

[0052] Embodiments of the present disclosure will be described below with reference to the accompanying drawings. It should be understood, however, that the description that follows is merely exemplary and is not intended to limit the scope of the present disclosure. In the following detailed description of embodiments of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that one or more embodiments of the present disclosure can be practiced without these specific details. In other instances, well-known structures and functions have not been described in detail in order to avoid obscuring aspects of the present disclosure.

[0053] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the term "including" "comprising" and the like are meant to be inclusive, but not limiting to the components, steps, operations and / or features that were listed.

[0054] All terms used herein including technical and scientific terms have the meanings commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein are defined as consistent with the context where used, and should not be interpreted in an idealized or overly formal way.

[0055] To facilitate understanding of the technical solutions of the present disclosure, the following technical terms are explained.

[0056] In the case of using expressions similar to "at least one of A, B, and C, etc.", it should generally be interpreted to include any of them, singly or in combination. In the case of using expressions similar to "at least one of A, B, or C, etc.", it should generally be interpreted to include any of them, singly or in combination. In the case of using expressions similar to "at least one of A, B, and C, etc.", it should generally be interpreted to include any of them, singly or in combination. In the case of using expressions similar to "at least one of A, B, or C, etc.", it should generally be interpreted to include any of them, singly or in combination.

[0057] Figure 1 A cross-sectional view of an electro-optic phase modulator according to embodiments of the present disclosure is schematically shown.

[0058] As Figure 1As shown, this disclosure provides an electro-optic phase modulator 1. The electro-optic phase modulator 1 is suitable for displacement measurement systems and is configured to modulate the polarization direction and phase of polarization measurement light in the displacement measurement system. The electro-optic phase modulator includes a housing 11, a modulation crystal 12, and a quarter-wave plate 13. The housing 11 has a built-in receiving space 111, and an entrance port 112 is provided on the housing 11. Figure 1 The left side of the housing 11 and the outlet 113 Figure 1 (On the right side of the housing 11), polarization measurement light is incident into the receiving space 111 through the entrance port 112. A modulation crystal 12 is disposed within the receiving space 111 and configured to modulate the polarization measurement light from the entrance port 112. The polarization direction of the polarization measurement light is at 45° to the modulation electric field direction of the modulation crystal 12. A quarter-wave plate 13 is located between the modulation crystal 12 and the exit port 113. The optical axis of the quarter-wave plate 13 is at 45° to the modulation electric field direction of the modulation crystal 12. After passing through the quarter-wave plate 13, the polarization measurement light exits through the exit port 113 onto the object under test. The object under test reflects the polarization measurement light back to the modulation crystal 12 via the quarter-wave plate 13, causing the polarization component direction of the reflected polarization measurement light to change by 90° compared to the polarization measurement light incident into the modulation crystal 12 through the entrance port 112.

[0059] Figure 2 The schematic diagram illustrates the working principle of an electro-optic phase modulator according to an embodiment of the present disclosure.

[0060] like Figure 2 As shown, after the polarization measurement light enters the electro-optic phase modulator 1 through the entrance port 112, the polarization direction of the polarization measurement light is at a 45° angle to the modulation electric field direction of the modulation crystal 12. The polarization measurement light can be decomposed into two mutually orthogonal polarization state components E. x E y Due to changes in electric field strength and direction, the refractive index of modulation crystal 12 changes. After the polarization measurement light passes through modulation crystal 12, the polarization state component E... x and polarization state component E y Transmission delays can occur between them. After the polarization measurement light is modulated by the modulation crystal 12 inside the electro-optic phase modulator 1, the polarization state component E x and polarization state component E y It can produce a relative phase difference.

[0061] Furthermore, after the polarization measurement light is modulated by the modulation crystal 12, it reaches the quarter-wave plate 13. The optical axis of the quarter-wave plate 13 is at 45° to the direction of the modulation electric field of the modulation crystal 12. After the polarization measurement light reaches the object under test through the exit port 113, it can return along the original optical path and pass through the quarter-wave plate 13 again. Figure 2As shown, the polarization measurement light passes through the quarter-wave plate 13 twice, and after being modulated by the quarter-wave plate 13 again, the polarization measurement light has two mutually perpendicular polarization states E x , E y , and the directions of the two polarization states are changed by 90°.

[0062] According to the embodiments of the present disclosure, by setting the polarization direction of the polarization measurement light to be 45° to the modulation electric field direction of the modulation crystal 12, a phase difference can be generated between the two mutually orthogonal polarization components of the polarization measurement light. By setting the optical axis of the quarter-wave plate 13 to be 45° to the modulation electric field direction of the modulation crystal 12, the directions of the two mutually orthogonal polarization components of the polarization measurement light can be changed by 90°. The polarization measurement light passes through the modulation crystal 12 twice, and the modulation crystal 12 can modulate the two mutually orthogonal polarization components of the polarization measurement light, respectively, thereby achieving temperature self-compensation of the influence of the radio frequency modulation thermal effect on the refractive index of the modulation crystal 12, improving the accuracy of the electro-optic phase modulator 1, and further improving the measurement accuracy of the displacement measurement system.

[0063] In the process of implementing the present disclosure, the inventors found that the higher the modulation frequency of the electro-optic phase modulator 1, the wider the modulation bandwidth, and the higher the measurement accuracy of the displacement measurement system. Therefore, the measurement accuracy of the displacement measurement system can be improved by improving the modulation frequency of the electro-optic phase modulator 1.

[0064] Figure 3 A circuit diagram of a resonant modulation driving circuit according to an embodiment of the present disclosure is schematically shown.

[0065] As Figure 3 shown, in some embodiments, the electro-optic phase modulator 1 can further include a resonant modulation driving circuit 14. The resonant modulation driving circuit 14 can include a signal receiving unit 141, an inductor 142, and a resistor 143 connected in series. The signal receiving unit 141 is configured to receive a modulation signal, and the modulation crystal 12 is connected to the signal receiving unit 141 in series, and different resonant modulation frequencies can be obtained by adjusting the inductance value of the inductor 142.

[0066] Specifically, the resonant modulation driving circuit 14 can perform high-frequency modulation, and the modulation crystal 12 can be equivalent to a capacitor, as Figure 3 shown, the resonant frequency ω0 of the resonant modulation driving circuit 14 can be represented as Wherein, C can be represented as the capacitance value of the modulation crystal 12, L can be represented as the inductance value of the inductor 142, the inductor 142 can be selected to use a radio frequency inductor 142 to improve the resonant modulation frequency, and the inductor 142 can be selected to use a tuning inductor 142 to obtain different resonant modulation frequencies by adjusting the inductance value of the inductor 142, so as to improve the measurement accuracy of the displacement measurement system. The signal receiving unit 141 can include a triode amplification circuit or a transformer to obtain greater gain. The resistance 143 can be selected according to the electrical parameters of the modulation crystal 12 to meet the impedance matching requirements of the displacement measurement system.

[0067] In some embodiments, the electro-optical phase modulator 1 can further include a radio frequency modulation port 15. The radio frequency modulation port 15 can be configured to receive a high frequency modulation signal from a high frequency signal source and process the high frequency modulation signal into a modulation signal to match the back-end circuit.

[0068] In some embodiments, the electro-optical phase modulator 1 can further include a temperature adjustment unit. The temperature adjustment unit can be configured to adjust the temperature of the accommodation space 111, and the temperature adjustment unit can include a temperature sensor 161, a thermoelectric cooler 162, and a temperature self-compensation control circuit 163. Specifically, the temperature sensor 161 can be configured to detect the temperature of the accommodation space 111. The temperature self-compensation control circuit 163 can be connected with the temperature sensor 161 and the temperature sensor 161 respectively, and configured to control the thermoelectric cooler 162 (TEC) to cool or heat based on the temperature detected by the temperature sensor 161. The temperature sensor 161 can include but not limited to a thermocouple, a platinum resistance 143, and the like.

[0069] In some embodiments, the electro-optical phase modulator 1 can further include a substrate 17, and the modulation crystal 12 and the quarter-wave plate 13 are arranged on the substrate 17, and the line connecting the center of the modulation crystal 12 and the center of the quarter-wave plate 13 is collinear with the line connecting the incident port 112 and the exit port 113. The substrate 17 can be a ceramic substrate 17. By fixing the modulation crystal 12 and the quarter-wave plate 13 together on the ceramic substrate 17, the influence of thermal effects on the relative positions of the modulation crystal 12 and the quarter-wave plate 13 and the transmission optical axis can be effectively suppressed, and the accuracy of the electro-optical phase modulator 1 can be improved.

[0070] The quarter-wave plate 13 can compensate for the thermal-induced phase change of the two orthogonal linear polarization components of the polarization measurement light due to the temperature change in the electro-optical phase modulator 1 caused by the heat of the high-frequency signal source sending the high-frequency modulation signal. The temperature self-compensation control circuit 163 can compensate for the influence of the ambient temperature change on the refractive index of the modulation crystal 12. By using the above two-stage temperature compensation method, the influence of the ambient temperature and the heat of the high-frequency modulation signal on the modulation of the electro-optical phase modulator 1 can be eliminated, and thus the modulation accuracy of the electro-optical phase modulator 1 can be improved, and the measurement accuracy of the displacement measurement system can be improved.

[0071] In some embodiments, the modulation crystal 12 can be an electro-optical crystal that can generate the Pockels effect, such as a lithium niobate crystal. The lithium niobate crystal can change the refractive index of the lithium niobate crystal by applying an electric field, and thus can modulate the phase of the polarization measurement light and change the polarization state of the polarization measurement light.

[0072] In some embodiments, the shell 11 is an electromagnetic shielding shell 11 to isolate the interference of external signals.

[0073] In some embodiments, the resonant modulation driving circuit 14 further includes two metal electrodes 144. The metal electrodes 144 are respectively arranged on the opposite sides of the modulation crystal 12, and the modulation crystal 12 is connected to the signal receiving unit 141 and the resistor 143 via the two metal electrodes 144.

[0074] Figure 4 The working principle diagram of the displacement measurement system according to an embodiment of the present disclosure is schematically shown. As shown in Figure 4 Another aspect provided by the present disclosure provides a displacement measurement system. The displacement measurement system is configured to measure the displacement of an object to be measured, and includes an optical source part 2, a polarization beam splitter 3, an electro-optical phase modulator 1, a mirror 4, a photodetector 5, and a control unit 6.

[0075] Specifically, the light source part 2 is configured to emit an initial light source. The initial light source can be a broadband light source. The light source part 2 includes but is not limited to an ASE, an SLD light source. The polarization beam splitter prism 3 can be configured to polarize the initial light source to form a polarization measurement light. The electro-optical phase modulator 1 is configured to modulate the polarization direction and phase of the polarization measurement light. The mirror 4 is arranged on the object to be measured and is configured to reflect the polarization measurement light from the electro-optical phase modulator 1 back to the electro-optical phase modulator 1. The photodetector 5 is configured to receive the polarization measurement light and convert the optical signal of the polarization measurement light into an electrical signal. The control unit 6 is connected with the photodetector 5 and is configured to send a modulation signal to the electro-optical phase modulator 1 and calculate the displacement of the object to be measured based on the electrical signal of the polarization measurement light. The control unit 6 can be a high-frequency signal source to send a high-frequency modulation signal to the electro-optical phase modulator 1 and transmit to the signal receiving unit 141 via the radio frequency modulation port 15.

[0076] In some embodiments, the displacement measurement system can further include a modulation driving unit 8. The modulation driving unit 8 is configured to receive the modulation signal from the control unit 6, and the control unit 6 controls the modulation driving unit 8 to send the modulation signal to the electro-optical phase modulator 1.

[0077] Further, by analyzing the polarization state change of the polarization measurement light in the transmission process using the polarization light Jones matrix, the relationship between the optical signal intensity I at the photodetector 5 and the phase difference change Δ of the modulation signal sent by the control unit 6 in the round trip flight process of the polarization measurement light between the electro-optical phase modulator and the mirror 4 can be shown as formula (1):

[0078]

[0079] Wherein, M can represent the modulation depth of the electro-optical phase modulator 1, and E0 can represent the applied electric field intensity.

[0080] As can be seen from formula (1), when , the optical signal intensity I is a minimum value, and the phase calculation of may not be needed, which is beneficial to improve the measurement accuracy of the displacement measurement system.

[0081] Further, the displacement of the object to be measured can be shown as formula (2):

[0082]

[0083] Wherein, L can represent the displacement of the object to be measured, λ can represent the wavelength value of the modulation signal corresponding to the minimum light intensity, N can represent the integer multiple of the wavelength value of the modulation signal, c can represent the speed of light, and f can represent the frequency of the modulation signal corresponding to the wavelength λ.

[0084] By continuously sweeping the frequency modulation of the electro-optic phase modulator 1, the frequency values ​​corresponding to two or more adjacent light intensity minima can be obtained, and then the unique spatial distance value can be solved to eliminate the ambiguity of distance caused by multiple cycles.

[0085] Furthermore, assuming that f1 and f2 are the frequencies of the modulation electrical signals at two adjacent minimum light intensity points, and the corresponding integer wavelengths can be expressed as N1 and N2 respectively, the relationship between the frequency values ​​of two adjacent minimum light intensity points and the displacement L of the object under test can be shown in formula (3):

[0086]

[0087] Furthermore, after differentiating equation (2) above, the measurement accuracy ΔL of the displacement measurement system can be expressed as shown in equation (4):

[0088]

[0089] Where f can be represented as the frequency of the modulation signal. As can be seen from formula (4), continuous sweep frequency modulation of the electro-optic phase modulator 1 is beneficial for the displacement measurement system to measure the displacement of the object under test, and the higher the modulation frequency, the higher the measurement accuracy.

[0090] In some embodiments, the light source unit 2 includes a laser 21 and a polarizing isolator 22. Specifically, the laser 21 is configured to emit a laser beam. The polarizing isolator 22 can emit an initial light source based on the laser beam.

[0091] In some embodiments, the displacement measurement system may further include a sampling unit 7, which is configured to sample the electrical signal output by the photodetector 5 and transmit the sampled electrical signal to the control unit 6.

[0092] Figure 5 A perspective view of a modulation crystal according to an embodiment of the present disclosure is shown schematically.

[0093] Figure 6 A schematic cross-sectional view of a modulation crystal connected to two metal electrodes according to an embodiment of the present disclosure is shown.

[0094] In some embodiments, the method for fabricating an electro-optic phase modulator includes:

[0095] Step 1: Cut the lithium niobate crystal into cuboids with a length of 2mm, a width of 20mm, and a height of 2mm to form modulation crystal 12, as shown. Figure 5 As shown.

[0096] Step 2: On the two sides of the modulation crystal 12 formed by the width and height ( Figure 5 The left and right sides are coated with a gold-plated film, adding 145 gold film.

[0097] Step 3: Fix the metal electrodes 144 to the outside of the gold-plated film 145 respectively by using conductive silver glue 146, as shown in FIG. 3. Figure 6

[0098] Step 4: Fix the modulating crystal 12 and the quarter-wave plate 13 to the ceramic substrate 17, and make the center of the entrance 112, the center of the exit 113, the center of the modulating crystal 12 and the center of the quarter-wave plate 13 on the same straight line, to form the transmission optical axis of the electro-optical phase modulator 1, as shown in FIG. 4. Figure 1

[0099] Step 5: Connect the modulating crystal 12 to the resonant modulation driving circuit 14 through the metal electrodes 144.

[0100] Step 6: Fix the temperature sensor 161 at the middle position between the modulating crystal 12 and the quarter-wave plate 13, connect the temperature sensor 161 to the temperature self-compensation control circuit 163, and set a thermoelectric cooler in the electro-optical phase modulator 1, and the thermoelectric cooler is electrically connected to the temperature self-compensation control circuit 163. The temperature self-compensation control circuit 163 can realize the self-compensation control of the temperature in the electro-optical phase modulator 1 by collecting the thermal resistance 143 value of the temperature sensor 161 in real time, and controlling the direction and size of the driving current of the thermoelectric cooler.

[0101] Step 7: Lock the shell 11 to form an electromagnetic shielding shell 11 to avoid the influence of external signals on the modulating signal.

[0102] According to the above description, those skilled in the art should have a clear understanding of the electro-optical phase modulator and displacement measurement system of the present disclosure.

[0103] It should be further noted that the directional terms mentioned in the embodiments, such as "up", "down", "front", "back", "left", "right", etc., are only the directions of the drawings, and are not used to limit the protection scope of the present disclosure. Throughout the drawings, the same elements are represented by the same or similar reference numerals. When it may cause confusion to the understanding of the present disclosure, the conventional structures or configurations will be omitted, and the shapes and sizes of the components in the drawings do not reflect the true size and proportion, but only illustrate the content of the embodiments of the present disclosure.

[0104] ​​Unless otherwise indicated, the numerical parameters in the description and the claims are approximations, and can vary depending upon the desired properties sought to be obtained by the compositions of the disclosure. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Preferably, numerical parameters in the exemplary embodiments of the present disclosure are reported with three significant digits and can vary within 10%, in other embodiments within 5%, in other embodiments within 1%, and in other embodiments within 0.5% of the reported value in the specification and claims.

[0105] The use of ordinal terms such as "first", "second", "third", etc. in the specification and claims to modify a claim element does not imply a sequence or order to the elements modified, but instead is used wherein "first" comes before "second" which comes before "third", etc. in an abstract sense. As such, a description of a "first" element does not mean that the element must be among a series of elements and neither requires or imply any physical or logical order of its placement.

[0106] In addition, unless specifically stated or otherwise required, the order of steps in the above-described embodiments is not limited to the order described and can vary or be rearranged according to design. Also, the above-described embodiments can be used in combination with each other or with other embodiments, based on design and reliability considerations, i.e., technical features in different embodiments can be freely combined to form further embodiments.

[0107] The above detailed description has shown, described, and pointed out the fundamental aspects of the present disclosure. It will be understood that various modifications and variations can be made to the present disclosure, in view of the above teachings, without departing from the spirit of the present disclosure. It will be understood that the present disclosure is not limited to the embodiments described above, but encompasses all modifications and variations within the scope and spirit of the present disclosure.

Claims

1. An electro-optical phase modulator for a displacement measurement system, comprising: a housing having an accommodation space therein, the housing having an entrance port and an exit port formed therein, the entrance port being configured to allow a polarized measurement light to enter the accommodation space; a modulation crystal disposed in the accommodation space, a polarization direction of the polarized measurement light being 45° to a modulation electric field direction of the modulation crystal; and a quarter wave plate disposed between the modulation crystal and the exit port, an optical axis of the quarter wave plate being 45° to the modulation electric field direction of the modulation crystal, the polarized measurement light passing through the quarter wave plate and being emitted from the exit port to a target object, the target object reflecting the polarized measurement light back to the modulation crystal via the quarter wave plate, the polarized measurement light reflected back to the modulation crystal having a polarization component direction changed by 90° from a polarization component direction of the polarized measurement light entering the modulation crystal from the entrance port; a temperature adjusting unit configured to adjust a temperature of the accommodation space, the temperature adjusting unit comprising: a temperature sensor configured to detect the temperature of the accommodation space; a thermoelectric cooler; and a temperature self-compensation control circuit connected to the temperature sensor and the thermoelectric cooler, respectively, and configured to control the thermoelectric cooler to cool or heat based on the temperature detected by the temperature sensor; wherein the modulation crystal is configured to modulate two mutually orthogonal polarization components of the polarized measurement light, respectively.

2. The electro-optic phase modulator of claim 1, wherein, further comprising a resonant modulation driving circuit, the resonant modulation driving circuit comprising a signal receiving unit, an inductor and a resistor connected in series, the signal receiving unit being configured to receive a modulation signal, the modulation crystal being connected to the signal receiving unit in series, and different resonant modulation frequencies being obtained by adjusting an inductance value of the inductor.

3. The electro-optic phase modulator of claim 1, wherein, further comprising a substrate, the modulation crystal and the quarter wave plate being disposed on the substrate, a line connecting a center of the modulation crystal and a center of the quarter wave plate being collinear with a line connecting the entrance port and the exit port.

4. The electro-optic phase modulator of claim 1, wherein, the modulation crystal is a lithium niobate crystal.

5. The electro-optic phase modulator of claim 1, wherein, the housing is an electromagnetic shielding housing to shield interference from external signals.

6. The electro-optic phase modulator of claim 2, wherein, the resonant modulation driving circuit further comprises: two metal electrodes disposed on opposite sides of the modulation crystal, the modulation crystal being connected to the signal receiving unit and the resistor via the two metal electrodes.

7. A displacement measurement system configured to measure displacement of an object under test, characterized by, comprising: a light source configured to emit an initial light source; a polarizing beam splitter prism configured to polarize the initial light source to form the polarized measurement light; the electro-optical phase modulator of any one of claims 1 to 6, configured to modulate a polarization direction and a phase of the polarized measurement light; a mirror disposed on the target object and configured to reflect the polarized measurement light from the electro-optical phase modulator back to the electro-optical phase modulator; a photodetector configured to receive the polarized measurement light and convert an optical signal of the polarized measurement light into an electrical signal; and a control unit connected to the photodetector and configured to send a modulation signal to the electro-optical phase modulator and calculate a displacement of the target object based on the electrical signal of the polarized measurement light. the light source comprises:

8. The displacement measurement system of claim 7, wherein, ​ a laser configured to emit a laser light; a polarizing isolator configured to emit an initial light source based on the laser light.

9. The displacement measurement system of claim 7, wherein, Further comprising: a sampling unit configured to sample an electrical signal output by the photodetector and transmit the sampled electrical signal to the control unit.

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