Test system and test method suitable for acoustic optical modulator performance

Abstract

The invention discloses a test system suitable for the performance of an acousto-optic modulator, and the system comprises a light source directivity test unit, a zoom lens group, a pre-diffraction power monitoring unit, a response time test unit, a post-diffraction directivity test unit, a diffraction efficiency test unit, and an imaging efficiency test unit. The acousto-optic modulator to be tested is arranged between the pre-diffraction power monitoring unit and the response time testing unit, the acousto-optic modulator to be tested is in control connection with the stability control unit, and an isolator is arranged between the light source directivity testing unit and the zoom lens group. According to the method, the optimal use performance of the acousto-optic modulator in different laser application fields can be achieved, meanwhile, the method is also suitable for application of the optical fiber type acousto-optic modulator, and the method can be used for design of all wavebands, all powers and all laser modulation systems.

Description

Technical Field

[0001] This invention relates to the field of laser system modulation, and more particularly to a testing system and method for testing the performance of acousto-optic modulators. Background Technology

[0002] Laser technology, as a fundamental breakthrough, has greatly spurred the vigorous development of related scientific research. After fifty years of exploration and development, lasers are widely used in numerous fields, including national defense, medicine, communications, publishing, services, industrial applications, environmental monitoring, precision measurement, home entertainment, and scientific and engineering research, exerting a profound impact on the development of science, technology, and the economy and society. Lasers possess excellent temporal and spatial coherence, and their properties are similar to radio waves, making them easy to modulate. Currently, laser modulation mainly utilizes the acousto-optic effect, electro-optic effect, magneto-optic effect, and electroabsorption effect as its basic principles. Among these, acousto-optic modulators, based on the acousto-optic effect, can modulate parameters such as the intensity, frequency, and phase of a laser beam. Due to their advantages such as fast modulation speed, high diffraction efficiency, low control voltage, simple driving circuit, good temperature stability, large extinction ratio, and small device size, they are widely used in acousto-optic communication, laser measurement, and fiber optic sensor technologies.

[0003] Currently, most commercially available acousto-optic modulators only provide basic specifications and application ranges. For single-wavelength lasers, errors still exist in actual use. Furthermore, the use of acousto-optic modulators can introduce unstable factors such as loss, thermal effects, aberrations, and pointing drift into the system for different applications. Therefore, it is necessary to test and evaluate the performance of acousto-optic modulators for specific applications, and design and optimize the system based on the results to achieve the best effect of acousto-optic modulator application. Summary of the Invention

[0004] This invention discloses a testing system and method for the performance of acousto-optic modulators, in order to solve any of the above-mentioned and other potential problems in the prior art.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is: a testing system suitable for the performance of acousto-optic modulators, the testing system comprising:

[0006] A light source directivity testing unit is used to monitor the directivity of a laser beam;

[0007] A pre-diffraction power monitoring unit is used to monitor the system power before diffraction.

[0008] A zoom lens group is used to adjust the expansion or contraction of a laser beam in order to investigate the effect of spot size on rise time, diffraction efficiency, and beam quality.

[0009] The stability control unit is used to achieve stable control of system power;

[0010] The response time test unit is used to monitor the rising signal of the acousto-optic modulator;

[0011] The directivity testing unit after diffraction is used to monitor the directivity of the beam after diffraction.

[0012] The diffraction efficiency testing unit is used to monitor the diffraction power of the first-order light.

[0013] The imaging efficiency testing unit is used to monitor changes in image quality caused by the thermal effect of the acousto-optic modulator.

[0014] The light source directivity test unit, zoom lens group, pre-diffraction power monitoring unit, response time test unit, post-diffraction directivity test unit, diffraction efficiency test unit, and imaging efficiency test unit are arranged sequentially.

[0015] The acousto-optic modulator under test is positioned between the pre-diffraction power monitoring unit and the response time testing unit, and is controlled by the stabilization control unit. An isolator is provided between the light source directivity testing unit and the zoom lens group.

[0016] Furthermore, the light source directivity testing unit includes a first beam splitter and a first CCD camera;

[0017] The diffraction pre-power monitoring unit includes a second beam splitter and a first power meter;

[0018] The stability control unit includes a driver, an attenuator, an RF switch, and a signal generator;

[0019] The response time testing unit includes a third beam splitter, an oscilloscope, and a photodetector;

[0020] The diffraction-based directivity testing unit includes a fourth beam splitter and a second CCD camera.

[0021] The diffraction efficiency testing unit includes a fifth beam splitter, a second power meter, and a third power meter;

[0022] The imaging efficiency testing unit includes a beam quality analyzer.

[0023] Furthermore, the zoom lens group consists of several lenses. The materials are selected according to the needs of different laser systems. Based on the beam waist size and position of the laser beam, physical optical simulation design is performed using Zemax software to achieve adjustable beam expansion and contraction of the laser beam.

[0024] Furthermore, the number of lenses is at least three, including plano-convex lenses and concave lenses; arranged at intervals.

[0025] Another object of the present invention is to provide a testing method for implementing the above-described testing system, the testing method specifically including the following steps:

[0026] First, input the beam waist size and beam waist position of the target laser, and design the setting method, focal length and surface shape of the zoom lens group through simulation.

[0027] The beam is introduced and its directivity is monitored before and after entering the acousto-optic modulator under test. It is determined whether there is a change in directivity. If there is, the beam direction stability is corrected; otherwise, the next step is performed.

[0028] By symmetrically placing a pair of convex and concave lenses before and after the acousto-optic modulator, the thermal effect on the crystal caused by excessive incident laser power can be corrected without introducing additional aberrations. The selection of the photodetector requires its response bandwidth to be greater than or equal to 5 times the rise frequency of the acousto-optic modulator, and the spot size and power need to be optimized to obtain the minimum rise time.

[0029] By combining the zoom lens group with the adjustment of the laser power, comparative analysis is conducted to give the insertion loss Δp and the maximum diffraction efficiency η of the first-order light of the acousto-optic modulator under test under different operating conditions.

[0030] Furthermore, the fast-reflecting mirror control system includes a first fast-reflecting mirror, a second fast-reflecting mirror, a sixth beam splitter, a beam position monitoring subsystem, and a feedback control subsystem. Through closed-loop control, the correction method is to feed back the beam position drift detected by the beam position monitoring subsystem to the feedback control subsystem, perform closed-loop control through the feedback control subsystem, and output a signal to the fast-reflecting mirror to achieve beam pointing stability correction.

[0031] Furthermore, the specific steps for correcting and optimizing the image quality are as follows: First, the thermal effects introduced by the target laser parameters are simulated using Comsol Multiphysics simulation software, and the deformation of the front and back surfaces of the acousto-optic modulator crystal is analyzed.

[0032] Then, the Zenic polynomial is used to fit the simulated deformation results to obtain the Zenic polynomial coefficients;

[0033] Secondly, the correlation coefficient is input into zemax to obtain the equivalent lens of the acousto-optic modulator;

[0034] Finally, a pair of symmetrical equivalent lenses are placed symmetrically in front of and behind the acousto-optic modulator for aberration correction.

[0035] Furthermore, the specific steps for obtaining the insertion loss Δp are as follows:

[0036] The system power P1 before diffraction, the power P2 of the first-order diffracted light, and the power P3 of the zero-order light were obtained respectively. The insertion loss Δp was calculated using the comparison method. The specific calculation formula is as follows:

[0037] ΔP = P1 - P2 - P3.

[0038] Furthermore, the specific steps for obtaining the maximum diffraction efficiency η of the first-order light are as follows:

[0039] By adjusting the zoom lens group, the beam can be expanded and contracted. Then, by comparing different spot size conditions, the minimum insertion loss of the acousto-optic modulator is obtained. The maximum diffraction efficiency η of the first-order diffracted light is calculated using the following formula:

[0040]

[0041] Compared with the prior art, the design method of the present invention has the following advantages:

[0042] 1. The present invention proposes a design method for achieving the best performance of acousto-optic modulators, which is applicable to the design of all bands, all powers, and all laser modulation systems.

[0043] 2. This invention proposes a test system to achieve the best performance of an acousto-optic modulator, which can evaluate the loss, diffraction efficiency, rise time introduced by the use of the acousto-optic modulator to the laser system, and correct for the introduced thermal effects, aberrations, power instability and other factors.

[0044] 3. This invention proposes a design method to achieve the best performance of an acousto-optic modulator, which is beneficial for guiding the research and development and application of acousto-optic modulators. Attached Figure Description

[0045] Figure 1 This is a schematic diagram illustrating the performance of an acousto-optic modulator applied to an arbitrary wavelength laser system according to the present invention.

[0046] Figure 2 It is a zoom lens group; in the figure, ①②③ are plano-convex lens, concave lens, and plano-convex lens, respectively. Among them, Figure (a) is a beam-expanding design and Figure (b) is a beam-contracting design.

[0047] Figure 3 The diagram shows a beam pointing stabilization control system. In the diagram, ① and ② are fast-reflecting mirrors, ③ is a beam splitter, ④ is a beam position monitoring system, and ⑤ is a feedback control system.

[0048] Figure 4 To correct aberrations caused by the thermal effect of the acousto-optic modulator, ① and ④ in the figure are plano-convex lenses, ② and ③ are concave lenses, and ⑤ is the equivalent lens of the acousto-optic modulator.

[0049] Figure 5 This is a power stabilization control system for an acousto-optic modulator. In the figure, ① is a beam splitter and ② is a PID controller.

[0050] In the picture:

[0051] 1. Target laser, 2. First beam splitter, 3. Isolator, 4. Zoom lens group, 5. Second beam splitter, 6. Acousto-optic modulator, 7. Third beam splitter, 8. Fourth beam splitter, 9. Fifth beam splitter, 10. First CCD camera, 11. First power meter, 12. Driver, 13. Attenuator, 14. RF switch, 15. Signal generator, 16. Oscilloscope, 17. Photodetector, 18. CCD camera, 19. Second power meter, 21. Third power meter, 20. Beam quality analyzer, 21. First fast mirror, 22. Second fast mirror, 23. Sixth beam splitter, 24. Beam position monitoring subsystem, 25. Feedback control subsystem. Detailed Implementation

[0052] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0053] The technical problem to be solved by this invention is to propose a design and optimization method for achieving the best performance of acousto-optic modulators for different laser systems and applications, without introducing new unstable factors.

[0054] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: an acousto-optic modulator can be applied to laser modulation systems with different needs to achieve the evaluation of its optimal performance. Specifically, it consists of a target laser (1), beam splitters (2), (5), (7), (8), (9), isolator (3), zoom lens group (4), acousto-optic modulator (6), CCD camera (10) and (18), power meter (11), (19) and (21), driver (12), attenuator (13), radio frequency switch (14), signal generator (15), oscilloscope (16), photodetector (17), and beam quality analyzer (20). The beam splitter (2) and CCD camera (10) are used to monitor the directivity of the laser; the beam splitter (5) and power meter (11) are used to monitor the system power before diffraction; the driver (12), attenuator (13), RF switch (14), and signal generator (15) are used to control the acousto-optic modulator (6); the beam splitter (7), oscilloscope (16), and photodetector (17) are used to monitor the rising signal of the acousto-optic modulator; the beam splitter (8) and CCD camera (18) are used to monitor the beam directivity after diffraction; the beam splitter (9) and power meter (19) are used to monitor the diffraction power of the first-order light; the power meter (21) is used to monitor the power of the zero-order light; and the beam splitter (9) and beam quality analyzer (20) are used to monitor the image quality changes caused by the thermal effect of the system.

[0055] The zoom lens group (4) consists of 3 lenses. According to the requirements of different laser systems, the material is selected. Based on the beam waist size and beam waist position of the laser, physical optical simulation design is carried out through Zemax software to realize adjustable beam expansion and contraction of the laser beam in order to explore the influence of the spot size on rise time, diffraction efficiency and beam quality.

[0056] The directivity test is specifically as follows: a beam splitter and a CCD camera are used to monitor the directivity of the laser, and a beam splitter (8) and a CCD camera (18) are used to monitor the directivity of the diffracted beam. The difference between the two is the directivity change introduced by the acousto-optic modulator. If there is beam directivity drift or change, two fast-reflecting mirrors and corresponding control systems are required to correct the beam position in the actual application optical system.

[0057] The image quality correction caused by the thermal effect is specifically as follows: Excessive incident laser power per unit crystal area can lead to thermal effects in the crystal, affecting the quality of the optical system. Therefore, image quality correction and optimization are needed without introducing additional aberrations. This can be achieved by symmetrically placing a set of convex and concave lenses before and after the acousto-optic modulator, using Zemax software to design the optimal configuration.

[0058] The specific test of the rise time of the acousto-optic modulation crystal is as follows: the selection of the photodetector requires that its response bandwidth be greater than or equal to the rise frequency of the acousto-optic modulator, and the spot size and power need to be optimized to obtain the minimum rise time.

[0059] The insertion loss and first-order diffraction efficiency tests are specifically conducted as follows: a beam splitter and a power meter are used to monitor the system power before diffraction; a beam splitter (9) and a power meter (19) are used to monitor the diffraction efficiency of the first-order light; and a power meter (21) is used to monitor the power of the zero-order diffracted light. The insertion loss of the acousto-optic modulator under different operating conditions is then given by comparative analysis.

[0060] The control of the acousto-optic modulator is specifically as follows: the control of the acousto-optic modulator (6) consists of a driver (12), an attenuator (13), an RF switch (14), and a signal generator (15). The RF switch is used for laser systems that require pulse modulation. If the system has high power stability requirements, a photodetector and a PID control system can be added to form a closed loop with the driver (12), attenuator (13), and RF switch (14) to achieve stable control of the system power.

[0061] like Figure 1 As shown, according to Figure 1 The schematic diagram shown illustrates the platform setup for testing and evaluating the performance of an acousto-optic modulator applied to a single-wavelength laser system.

[0062] The zoom lens group 4 consists of three lenses. Specifically, it is designed using physical optics simulation with Zemax software. First, the beam waist size and position of the target laser are input. Through simulation, the focal lengths and surface shapes of the plano-convex lens, concave lens, and plano-convex lenses ①②③ are designed respectively. The lens materials are selected based on the laser's wavelength. Secondly, as... Figure 2 As shown, during assembly and adjustment, lens ① remains stationary, while lenses ② and ③ expand the beam according to the system's specifications. Figure 2 (a) or the need for bundle contraction ( Figure 2 (b)) Adjust them separately.

[0063] The directivity test involves a beam splitter (2) and a CCD camera (10) used to monitor the laser's directivity, and a beam splitter (8) and a CCD camera (18) used to monitor the directivity of the diffracted beam. The difference between the two is the directivity change introduced by the acousto-optic modulator. If there is beam directivity drift or change, it can be determined according to... Figure 3 Control is achieved using a fast-reflecting mirror control system, where ① and ② are fast-reflecting mirrors, ③ is a beam splitter, ④ is a beam position monitoring system, and ⑤ is a feedback control system. Through closed-loop control, the beam position drift detected by ④ is fed back to ⑤, and closed-loop control is performed through ⑤ to output a signal to the fast-reflecting mirror, thereby achieving beam pointing stability correction.

[0064] Excessive incident laser power per unit crystal area can lead to thermal effects in the crystal, affecting the quality of the optical system. Therefore, image quality correction and optimization are necessary without introducing additional aberrations. First, the thermal effects introduced by the target laser parameters are simulated using Comsol Multiphysics simulation software to analyze the deformation of the front and rear surfaces of the acousto-optic modulator crystal. Second, the simulated deformation results are fitted using Zenick polynomials to obtain the Zenick polynomial coefficients. Third, the correlation coefficients are input into Zemax to obtain the equivalent lens of the acousto-optic modulator, which is generally empirically equivalent to a convex lens. Fourth, a pair of symmetrical convex and concave lenses are placed symmetrically before and after the acousto-optic modulator for aberration correction, such as... Figure 4 As shown in the figure, ① and ④ are plano-convex lenses, and ② and ③ are concave lenses. The system is simulated and designed based on Zemax software to correct aberrations without changing the laser spot size.

[0065] The rise time test of the acousto-optic modulation crystal requires that the selected photodetector has a response bandwidth greater than or equal to 5 times the rise frequency of the acousto-optic modulator. The rise time of the first-order diffracted light and the size of the laser spot can be expressed as:

[0066]

[0067] Where d is the beam diameter and υ is the speed of sound. By adjusting the zoom lens group, the beam expansion and contraction of the laser system can be achieved, thereby exploring the minimum rise time of the laser system and making it better suited for pulsed, Q-switched, and other laser systems.

[0068] The insertion loss test is mainly calculated by comparison: the beam splitter (5) and power meter (11) are used to monitor the system power P1 before diffraction; the beam splitter (9) and power meter (19) are used to monitor the power P2 of the first-order diffracted light; the power meter (21) is used to monitor the power P3 of the zero-order light. The insertion loss can then be expressed as:

[0069] ΔP=P1-P2-P3(2)

[0070] The efficiency of first-order diffracted light can be expressed as:

[0071]

[0072] By adjusting the zoom lens group, the beam system can be expanded and contracted. Then, by comparing different spot size conditions, the minimum insertion loss of the acousto-optic modulator can be given, and the maximum diffraction efficiency of the first-order diffracted light can be achieved.

[0073] The control of the acousto-optic modulator is specifically as follows: the control of the acousto-optic modulator (6) consists of a driver 12, an attenuator 13, an RF switch 14, and a signal generator 15. The RF switch is used in laser systems requiring pulse modulation. If the system has high power stability requirements, a photodetector and a PID control system can be added to form a closed loop with the driver 12, attenuator 13, and RF switch 14 to achieve stable power control of the system. Figure 5 As shown.

[0074] The foregoing has provided a detailed description of a testing system and method for the performance of acousto-optic modulators, as provided in the embodiments of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and its core ideas; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

[0075] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0076] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0077] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0078] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A testing system suitable for the performance of acousto-optic modulators, characterized in that, The testing system includes: A light source directivity testing unit is used to monitor the directivity of a laser beam; A pre-diffraction power monitoring unit is used to monitor the system power before diffraction. A zoom lens group is used to adjust the expansion or contraction of a laser beam in order to investigate the effect of spot size on rise time, diffraction efficiency, and beam quality. The stability control unit is used to achieve stable control of system power; The response time test unit is used to monitor the rising signal of the acousto-optic modulator; The directivity testing unit after diffraction is used to monitor the directivity of the beam after diffraction. The diffraction efficiency testing unit is used to monitor the diffraction power of the first-order light. The imaging efficiency testing unit is used to monitor changes in image quality caused by the thermal effect of the acousto-optic modulator. The light source directivity test unit, zoom lens group, pre-diffraction power monitoring unit, response time test unit, post-diffraction directivity test unit, diffraction efficiency test unit, and imaging efficiency test unit are arranged sequentially. The acousto-optic modulator under test is positioned between the pre-diffraction power monitoring unit and the response time testing unit, and is controlled by the stabilization control unit. An isolator is provided between the light source directivity testing unit and the zoom lens group.

2. The testing system according to claim 1, characterized in that, The light source directivity testing unit includes a first beam splitter and a first CCD camera; The diffraction pre-power monitoring unit includes a second beam splitter and a first power meter; The stability control unit includes a driver, an attenuator, an RF switch, and a signal generator; The response time testing unit includes a third beam splitter, an oscilloscope, and a photodetector; The diffraction-based directivity testing unit includes a fourth beam splitter and a second CCD camera. The diffraction efficiency testing unit includes a fifth beam splitter, a second power meter, and a third power meter; The imaging efficiency testing unit includes a beam quality analyzer.

3. The testing system according to claim 1, characterized in that, The zoom lens group consists of several lenses. The materials are selected according to the needs of different laser systems. Based on the beam waist size and position of the laser beam, physical optical simulation design is performed using Zemax software to achieve adjustable beam expansion and contraction of the laser beam.

4. The testing system according to claim 3, characterized in that, The number of lenses is at least three, including plano-convex lenses and concave lenses; they are arranged at intervals.

5. A test method for implementing the test system as described in any one of claims 1-4, characterized in that, The testing method specifically includes the following steps: First, input the beam waist size and beam waist position of the target laser, and design the setting method, focal length and surface shape of the zoom lens group through simulation. The beam is introduced and its directivity is monitored before and after entering the acousto-optic modulator under test. It is determined whether there is a change in directivity. If there is, the beam direction stability is corrected; otherwise, the next step is performed. By symmetrically placing a pair of convex and concave lenses before and after the acousto-optic modulator, the thermal effect on the crystal caused by excessive incident laser power can be corrected without introducing additional aberrations. The selection of the photodetector requires its response bandwidth to be greater than or equal to 5 times the rise frequency of the acousto-optic modulator, and the spot size and power need to be optimized to obtain the minimum rise time. By combining the zoom lens group with the adjustment of the laser power, comparative analysis is conducted to give the insertion loss Δp and the maximum diffraction efficiency η of the first-order light of the acousto-optic modulator under test under different operating conditions.

6. The test method according to claim 5, characterized in that, The fast-reflecting mirror control system includes a first fast-reflecting mirror, a second fast-reflecting mirror, a sixth beam splitter, a beam position monitoring subsystem, and a feedback control subsystem. Through closed-loop control, the correction method is to feed back the beam position drift detected by the beam position monitoring subsystem to the feedback control subsystem, and then perform closed-loop control through the feedback control subsystem to output a signal to the fast-reflecting mirror, thereby achieving beam pointing stability correction.

7. The test method according to claim 5, characterized in that, The specific steps for image quality correction and optimization are as follows: First, the thermal effect introduced by the target laser parameters is simulated using Comsol Multiphysics simulation software, and the deformation of the front and back surfaces of the acousto-optic modulator crystal is analyzed. Then, the Zenic polynomial is used to fit the simulated deformation results to obtain the Zenic polynomial coefficients; Secondly, the correlation coefficient is input into zemax to obtain the equivalent lens of the acousto-optic modulator; Finally, a pair of symmetrical equivalent lenses are placed symmetrically in front of and behind the acousto-optic modulator for aberration correction.

8. The test method according to claim 5, characterized in that, The specific steps for obtaining the insertion loss Δp are as follows: The system power P1 before diffraction, the power P2 of the first-order diffracted light, and the power P3 of the zero-order light were obtained respectively. The insertion loss Δp was calculated using the comparison method. The specific calculation formula is as follows: ΔP = P1 - P2 - P3.

9. The test method according to claim 5, characterized in that, The specific steps for obtaining the maximum diffraction efficiency η of the first-order light are as follows: By adjusting the zoom lens group, the beam can be expanded and contracted. Then, by comparing different spot size conditions, the minimum insertion loss of the acousto-optic modulator is obtained. The maximum diffraction efficiency η of the first-order diffracted light is calculated using the following formula:

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