An automatic test system for polarization devices

Abstract

The present invention discloses an automated testing system for a polarization device, comprising a testing optical path assembly and an automated control module; the testing optical path assembly is used to test the polarization response and / or phase response of the polarization device, and has at least one optical lens group, at least one tunable laser module, at least one photodetector and at least one camera; the automated control module has at least one adjustment mechanism, which is used to drive the at least one optical lens group to rotate and change the optical axis orientation, and to link the at least one tunable laser module and / or at least one photodetector and / or at least one camera. The automated testing system for the polarization device has the advantages of adjustable wavelength, adjustable power, adjustable polarization state, automated control, etc., and can realize automated measurement of polarization response and phase response according to the polarization analysis method and the interferometer method.

Description

Technical Field

[0001] The invention relates to the technical field of optoelectronic equipment, and in particular to an automatic testing system for a polarization device. Background Art

[0002] The phenomena of light diffraction, interference and polarization can prove the wave nature of light. Therefore, light can be used as a carrier to control the amplitude, polarization, phase, frequency and other dimensions of information transmission, transmission, reception and storage. As the core component for realizing dynamic control of light field, spatial light modulator has broad application prospects in digital holography, mode multiplexing in optical communication systems, laser radar ranging and other fields.

[0003] From digital holographic technology to optical communication modules, and to the hot automotive laser radar for autonomous driving in recent years, spatial light modulators play an important role. The core component of the spatial light modulator is silicon-based liquid crystal, which can be divided into amplitude type and phase type according to its type. By applying voltage to the pixel unit to control the spatial orientation of the liquid crystal molecules, the phase and polarization of the light field can be controlled by using the birefringence characteristics of the liquid crystal. Traditional silicon-based liquid crystal spatial light modulators have polarization-dependent optical responses and generally realize dynamic control of the light field in a single dimension. In order to meet the needs of practical applications, high-performance silicon-based liquid crystal spatial light modulators are crucial. However, the performance of the device during operation is limited by the inhomogeneity of the spatial distribution of liquid crystal molecules: 1) The inhomogeneity of the liquid crystal thickness; 2) The liquid crystal molecules may be "twisted" under the change of the applied voltage; 3) The liquid crystal molecules close to the alignment layer are insensitive to the change of the applied voltage.

[0004] As a typical polarization device, liquid crystal on silicon spatial light modulator has a wide range of adaptability. In order to meet the needs of practical applications, large bandwidth, low power consumption, high efficiency and high integration are the core issues in the field of optoelectronic device technology. The performance of polarization devices is usually related to physical quantities in multiple dimensions. For the design and performance optimization of polarization devices, accurate and efficient testing solutions for multiple dimensions are crucial. Summary of the invention

[0005] The present disclosure provides an automated testing system for polarization devices for the purpose of designing and optimizing the performance of polarization devices and accurately and efficiently measuring polarization response and phase response from multiple dimensions.

[0006] To solve the above problems, the present invention adopts the following technical solutions:

[0007] An automatic testing system for a polarization device comprises a testing optical path assembly and an automatic control module.

[0008] The test optical path assembly is used for testing the polarization response and / or phase response of a polarization device, and comprises at least one optical lens group, at least one tunable laser module, at least one photodetector and at least one camera.

[0009] The automation control module has at least one adjustment mechanism for driving the at least one optical lens group to rotate and change the orientation of the optical axis, and linking the at least one tunable laser module and / or at least one photodetector and / or at least one camera.

[0010] In the automated testing system for polarization devices provided by at least one embodiment of the present disclosure, the at least one optical lens group includes: at least one polarizer, at least one analyzer and at least one wave plate.

[0011] At least one polarizer is used to obtain linearly polarized light with adjustable polarization state and high linear polarization degree.

[0012] At least one polarizer is used to maintain parallelism or orthogonality with the optical axis of the at least one polarizer, so as to form a parallel or orthogonal polarizer system.

[0013] In the automated testing system for polarization devices provided by at least one embodiment of the present disclosure, the wave plate is a quarter wave plate.

[0014] In the automated testing system for polarization devices provided by at least one embodiment of the present disclosure, the polarizer includes a half-wave plate and a first linear polarizer.

[0015] In the automated testing system for polarization devices provided by at least one embodiment of the present disclosure, the polarizer is a second linear polarizer.

[0016] In the automated testing system for polarization devices provided by at least one embodiment of the present disclosure, the testing optical path assembly further comprises at least one polarization controller, at least one collimator, at least one third linear polarizer, at least one lens group, at least one beam splitter and at least one reflector.

[0017] The automated testing system for polarization devices provided by at least one embodiment of the present disclosure further includes: an optical 4F system; wherein the lens group is used to change the spot size after passing through the collimator through the optical 4F system.

[0018] In the automated testing system for polarization devices provided by at least one embodiment of the present disclosure, the second linear polarizer is further configured to be moved to the rear of the beam splitter through the adjustment mechanism, and to be kept parallel to the optical axis orientation of the first linear polarizer for polarization, so that object light incident at a small angle can be reflected by the sample and then collected by the photodetector to measure the polarization response.

[0019] The automated testing system for polarization devices provided by at least one embodiment of the present disclosure further includes: a terminal; wherein the test optical path assembly and the automated control module are both electrically connected to the terminal.

[0020] The invention has the advantages of adjustable wavelength, adjustable power, adjustable polarization state, automatic control, etc., and can realize automatic measurement of polarization response and phase response according to polarization analysis method and interference method. The automatic test system and method thereof can accurately and efficiently realize comprehensive testing of polarization device performance from multiple dimensions (such as wavelength, polarization and voltage), such as polarization conversion efficiency, insertion loss, phase modulation, polarization-dependent loss and other parameter indicators, and point out the relationship between polarization conversion efficiency and phase modulation, which is of great significance for the design and performance optimization of polarization devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 A schematic diagram of an automated testing system for polarization devices.

[0023] Figure 2 Schematic diagram of the test light path of a polarization device at normal incidence.

[0024] Figure 3 Schematic diagram of the test light path of a polarization device at small angle of incidence.

[0025] Figure 4 Orientation test results at different wavelengths.

[0026] Figure 5 These are the polarization conversion efficiency test results at different wavelengths.

[0027] Figure 6 The polarization conversion efficiency test results at different wavelengths and grayscales.

[0028] Figure 7 The phase modulation test results of the polarization method at a wavelength of 1550nm and different grayscales.

[0029] Figure 8 Insertion loss test results at different wavelengths and grayscales at a 0-degree starting angle.

[0030] Fig. 9 These are the insertion loss test results at different wavelengths and grayscales when the starting angle is 90 degrees.

[0031] Fig.10 The phase modulation test results of the interferometry method at a wavelength of 1550nm and different grayscales.

[0032] Fig.11 The insertion loss test results at different wavelengths and polarization angles at small angle of incidence.

[0033] Fig.12 These are the polarization-dependent loss test results at different wavelengths at small angles of incidence.

[0034] Fig.13 A schematic diagram of an automated testing system for polarization devices.

[0035] In the figure:

[0036] 10. Test optical path assembly; 101. Tunable laser module; 102. Polarization controller; 103. Collimator; 104. Lens group; 105. First polarizer; 106. Second polarizer; 107. Third polarizer; 108. Half-wave plate; 109. Quarter-wave plate; 110. Beam splitter; 111. Reflector; 112. Detection mechanism;

[0037] 20. Automation control module; 201. Electric rotating table; 202. Voltage source;

[0038] 30. PC terminal;

[0039] 40. Samples. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments will be described clearly and completely below in conjunction with the drawings in the embodiments. Obviously, the described embodiments are only a part of the embodiments, rather than all the embodiments.

[0041] In the embodiments, it should be understood that the terms "middle", "upper", "lower", "top", "right side", "left end", "above", "back", "middle", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, which are only for the convenience of description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be the usual meanings understood by people with ordinary skills in the field to which the present disclosure belongs. The "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprising" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0042] In addition, in the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms such as installation, connection and connection should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] At least one embodiment of the present disclosure provides an automated test system for a polarization device, including a test optical path assembly, an automated control module, and a PC terminal. The test optical path assembly includes a tunable laser module, a polarization controller, a collimator, a lens group, a first polarizer, a second polarizer, a third polarizer, a half-wave plate, a quarter-wave plate, a beam splitter, a reflector, a photodetector, and a CCD camera; the automated control module includes an electric rotating stage, a rotation controller, and a voltage source, which controls the electric rotating stage to change the optical axis orientation of the first polarizer, the second polarizer, and the quarter-wave plate, and links the tunable laser module, the electric rotating stage, the rotation controller, the voltage source, the photodetector, and the CCD camera to complete the automated acquisition of optical power and images. The voltage source is used to load an AC voltage and is used as a signal generator or a driving device for a spatial light modulator.

[0044] A polarization and analysis system can be built by combining a wave plate and a polarizer. By linking a tunable laser module, an electric rotating stage, a rotation controller, a voltage source and a photodetector, the wavelength and voltage can be adjusted, the orthogonal analysis and parallel analysis systems can be rotated, and the optical power can be collected, thereby realizing the automatic measurement of polarization response from multiple dimensions (such as wavelength, polarization and voltage). A beam splitter is used to first split the light into two paths, in which the object light passes through the sample and the reference light passes through a quarter-wave plate and a reflector. After the two paths of light are reflected, they pass through the beam splitter again to form interference fringes. By linking a tunable laser module, an electric rotating stage, a rotation controller, a voltage source and a CCD camera, the wavelength and voltage can be adjusted, the orthogonal analysis or parallel analysis system can be rotated, and the interference pattern can be collected, thereby realizing the automatic measurement of phase response from multiple dimensions (such as wavelength, polarization and voltage).

[0045] This automated test system can accurately and efficiently perform comprehensive tests on the performance of polarization devices from multiple dimensions (such as wavelength, polarization, and voltage), such as polarization conversion efficiency (PCR), insertion loss (IL), phase modulation (Δδ), polarization-dependent loss (PDL), and other parameter indicators.

[0046] To understand the relationship between polarization conversion efficiency and phase modulation, consider the birefringence characteristics of the polarization device and construct the following rotation Jones matrix:

[0047]

[0048] At this time, the angle between the optical axis of the birefringent molecule and the x-axis is θ, φ = A L -A S exp(iδ),A L and A S denote the amplitude response along the long and short axes of the birefringent molecule, δ(δ=φ S -φ L ) represents the phase difference between the long and short axis responses of the birefringent molecule. Considering the amplitude responses are equal (A L =A S =A), the response of the parallel and quadrature detection systems can be expressed as:

[0049]

[0050]

[0051]

[0052]

[0053] According to formula (4), in the orthogonal polarization analyzer system, no matter how the complex amplitude along the long and short axes of the birefringent molecule responds, when θ = nπ / 2 (n is an integer, the optical axis of the analyzer is parallel or orthogonal to the optical axis of the birefringent molecule), the optical power reaches a minimum value, and the orientation of the birefringent molecule can be considered as the θ value when the optical power reaches a minimum value under the orthogonal polarization analyzer. At this time, the polarization conversion efficiency (PCR, unit: dB) can be expressed as:

[0054] PCR(θ)=10log[P outy (θ)]-10log[P outx (θ)]; (5)

[0056]

[0057] When θ = (2n + 1)π / 4 (n is an integer, and the angle between the optical axis of the analyzer and the optical axis of the birefringent molecule is 45 degrees or 135 degrees), the polarization conversion efficiency reaches a maximum value and can be expressed as:

[0058]

[0059] According to formula (7), the relationship between polarization conversion efficiency (PCR) and phase difference (δ) can be obtained. Since both polarization conversion efficiency and phase difference vary with wavelength and voltage, the relationship between polarization conversion efficiency (PCR) and phase modulation amount (Δδ) can be obtained.

[0060] The combination of the tunable laser module, polarization controller, collimator and linear polarizer is used to obtain linearly polarized light with adjustable wavelength, adjustable power and high linear polarization degree.

[0061] The lens group is used to change the size of the light spot after passing through the collimator through the 4F system.

[0062] The combination of the half-wave plate and the first polarizer is used as a polarizer to obtain linearly polarized light with adjustable polarization state and high polarization degree.

[0063] The second linear polarizer is used as an analyzer, and the object light reflected by the sample passes through the beam splitter and the analyzer and then the light power is collected by the photodetector.

[0064] The beam splitter divides the light into two paths, and the combination of a quarter wave plate and a reflector is used to change the polarization state of the reference light. The object light reflected by the sample interferes with the reference light after passing through the beam splitter and the analyzer, and the interference image is collected by the CCD camera.

[0065] The second linear polarizer can be moved behind the beam splitter and kept parallel to the optical axis orientation of the first linear polarizer in front of the beam splitter as a polarizer. When the object light is incident at a small angle, the light power is collected by the photodetector after being reflected by the sample.

[0066] The following uses a liquid crystal on silicon spatial light modulator as an example to further illustrate the solution of the present disclosure in conjunction with the accompanying drawings of the specification.

[0067] like Figure 1 and Figure 2 As shown, an automated testing system and method for polarization devices include a test optical path assembly 10, an automated control module 20, and a PC terminal; the test optical path assembly 10 includes a tunable laser module 101, a polarization controller 102, a collimator 103, a first polarizer 105, a second polarizer 106, a third polarizer 107, a lens group 104, a half-wave plate 108, a beam splitter 110, a detection mechanism 112, a quarter-wave plate 109, and a reflector 111; the detection mechanism 112 includes a photodetector and a CCD camera. The automated control module includes an electric rotating stage 201, a rotation controller (not shown), and a voltage source 202. The automation control module 20 uses Python on the PC terminal to establish the connection between the tunable laser module 101, the electric rotating stage 201, the rotation controller, the voltage source 202, the photodetector and the CCD camera, controls the first polarizer 105, the second polarizer 106, the half-wave plate 108 and the quarter-wave plate 109 through the electric rotating stage 201, and links the tunable laser module 101, the electric rotating stage 201, the rotation controller, the voltage source 202, the photodetector and the CCD camera to complete the automatic acquisition of light power and image.

[0068] More specifically, linearly polarized light with adjustable wavelength, adjustable power and high linear polarization degree is obtained through the tunable laser module 101 , the polarization controller 102 , the collimator 103 and the third polarizer 107 , and the spot size is changed through the lens group 104 .

[0069] More specifically, the half-wave plate 108 and the first linear polarizer are controlled by the electric rotating stage 201 and used as a polarizer to obtain linearly polarized light with adjustable polarization state and high linear polarization degree.

[0070] More specifically, the second linear polarizer is controlled by the electric rotating stage 201 and used as an analyzer, so that it is kept parallel or orthogonal to the optical axis of the polarizer, forming a parallel or orthogonal analyzer system.

[0071] More specifically, the tunable laser module 101, the electric rotating stage 201, the rotation controller and the photodetector are linked to rotate the parallel polarization analyzer system and the orthogonal polarization analyzer system, and the light power is collected by the photodetector to obtain the test results of the liquid crystal orientation and polarization conversion efficiency at different wavelengths, such as Figure 4 and Figure 5 When the optical axis of the analyzer is parallel or orthogonal to the optical axis of the liquid crystal, the optical power (unit: dBm) reaches its minimum value; when the angle between the optical axis of the analyzer and the optical axis of the liquid crystal is 45 or 135 degrees, the polarization conversion efficiency (PCR, unit: dB) reaches its maximum value.

[0072] More specifically, the tunable laser module 101, the electric rotating stage 201, the rotation controller, the voltage source 202 and the photodetector are linked, the polarization angle is set to 45 degrees and 135 degrees according to the orientation test results, different gray scales are loaded to the silicon-based liquid crystal spatial light modulator under the parallel and orthogonal polarization systems, and the polarization conversion efficiency test results under different wavelengths and gray scales can be obtained by collecting the light power through the photodetector, such as Figure 6 As shown. The polarization conversion efficiency (PCR, unit: dB) is defined as the difference between the optical power under orthogonal polarization and parallel polarization. After two modulations by liquid crystal, when the phase difference satisfies an odd multiple of π, the polarization conversion efficiency reaches a maximum value; when the phase difference satisfies an even multiple of π, the polarization conversion efficiency reaches a minimum value. As the gray scale increases, the polarization conversion efficiency successively reaches a maximum and a minimum value and finally returns to the vicinity of the initial value, indicating that the phase difference has changed by 2π. Taking the wavelength of 1550nm as an example, the phase difference under different gray scales is calculated according to formula (7), and the minimum and maximum values ​​of the phase difference are used as the reference points of 0 and π. The phase modulation test results of the polarization method at a wavelength of 1550nm and different gray scales can be obtained, as shown Figure 7 shown.

[0073] More specifically, the tunable laser module 101, the electric rotating stage 201, the rotation controller, the voltage source 202 and the photodetector are linked, the starting angle is set to 0 degrees and 90 degrees according to the orientation test results, different gray scales are loaded to the silicon-based liquid crystal spatial light modulator under the parallel and orthogonal polarization systems, and the optical power is collected by the photodetector. Referring to the reflector 111, the insertion loss test results at different wavelengths and gray scales can be obtained by collecting the optical power according to the above steps, such as Figure 8 and Fig. 9 As shown. Insertion loss (IL, unit: dB) is defined as the difference in total optical power after passing through the reflector 111 and the sample 40, and the total optical power is the sum of the optical power under the parallel and orthogonal polarization systems. Due to the interface reflection caused by the refractive index mismatch between the air, the glass cover and the liquid crystal layer, the insertion loss of the linearly polarized light oriented along the long axis of the liquid crystal (0 degrees) changes significantly after being modulated by the liquid crystal at different wavelengths and grayscales; the insertion loss of the linearly polarized light oriented along the long axis of the liquid crystal (90 degrees) changes significantly after being modulated by the liquid crystal at different wavelengths.

[0074] More specifically, the tunable laser module 101, the electric rotating stage 201, the rotation controller, the voltage source 202 and the CCD camera are linked, the wavelength is set to 1550nm, the polarization angle is set to 0 degree and 90 degree according to the orientation test result, and the orientation angle of the quarter wave plate 109 is 0 degree. The beam splitter 110 is used to split the light into two paths, wherein the object light passes through the silicon-based liquid crystal spatial light modulator, and the reference light passes through the quarter wave plate 109 and the reflector 111. After the two paths of light are reflected, they pass through the beam splitter 110 again to form interference fringes. When different gray scales are loaded on the silicon-based liquid crystal spatial light modulator under the parallel and orthogonal polarization system, the interference fringes will move, and the phase modulation amount test results of the interference method at a wavelength of 1550nm and different gray scales can be obtained by collecting the interference pattern with a CCD camera, such as Fig.10 As shown in Figure 1, the phase modulation changes by 2π every time the dark interference fringe moves through one cycle.

[0075] More specifically, an automated testing system for a polarization device at small angles of incidence is implemented by the following steps:

[0076] First, the half-wave plate 108 and the first linear polarizer are controlled by the electric rotating stage 201 to obtain linearly polarized light with adjustable polarization state and high linear polarization degree. Then, the second linear polarizer is moved to the beam splitter 110, and then the first polarizer 105 and the second polarizer 106 are controlled by the electric rotating stage 201 as polarizers to keep their optical axes parallel.

[0077] In the specific implementation process, the tunable laser module 101, the electric rotating stage 201, the rotation controller and the photodetector are linked to rotate the polarizer. When the object light is incident at a small angle, it is reflected by the silicon liquid crystal spatial light modulator, and then the photodetector is used to collect the light power. Referring to the reflector 111, the insertion loss and polarization-dependent loss test results at different wavelengths and polarization angles can be obtained by collecting the light power according to the above steps, such as Fig.11 and Fig.12 As shown. Insertion loss (IL, unit: dB) is defined as the difference in total optical power after passing through the reflector 111 and the sample 40, and polarization-dependent loss (PDL, unit: dB) is defined as the maximum difference in insertion loss under different polarization states. This scheme uses a combination of three polarization states to analyze polarization-dependent loss: linearly polarized light at all angles; linearly polarized light from 0 to 180 degrees; linearly polarized light at special angles such as 0 degrees, 45 degrees, 90 degrees and 135 degrees. It is found that the results are roughly equal, indicating that polarization-dependent loss mainly comes from the difference in amplitude response of the long and short axes (0 degrees and 90 degrees) of the liquid crystal.

[0078] In the description of this specification, the description with reference to the terms "this embodiment", "some embodiments", "other embodiments" or "specific example" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0079] Although the embodiments of the present application have been shown and described above, the scope of protection of the present invention is not limited thereto, and any changes or substitutions that are not conceivable through creative work should be included in the scope of protection of the present invention; unless explicitly stated, any elements, actions or instructions used in this document should not be interpreted as critical or necessary.

Claims

1. An automated testing system for polarization devices, It is characterized in that include: A test optical path assembly, used for testing the polarization response and / or phase response of a polarization device, and comprising at least one optical lens group, at least one tunable laser module, at least one photodetector and at least one camera; An automated control module having at least one adjustment mechanism for driving the at least one optical lens group to rotate and change the orientation of the optical axis, and for linking the at least one tunable laser module and / or at least one photodetector and / or at least one camera; as well as Optical 4F system; The at least one optical lens set comprises: At least one polarizer, used to obtain linearly polarized light with adjustable polarization state and high linear polarization degree; At least one polarizer, used to maintain parallelism or orthogonality with the optical axis of the at least one polarizer, so as to form a parallel or orthogonal polarizer system; as well as at least one wave plate; The test optical path assembly also has at least one polarization controller, at least one collimator, at least one third linear polarizer, at least one lens group, at least one beam splitter and at least one reflector; Wherein, the lens group is used to change the spot size after passing through the collimator through the optical 4F system; The wave plate is a quarter wave plate, and the quarter wave plate is located between the beam splitter and the reflector; The polarizer includes a half-wave plate and a first linear polarizer; The polarizer is also configured to be moved to the back of the beam splitter through the adjustment mechanism and to be kept parallel to the optical axis orientation of the first linear polarizer for polarization, so that object light incident at a small angle can be reflected by the sample and then collected by the photodetector to measure the polarization response.

2. The automated testing system for polarization devices according to claim 1, It is characterized in that The polarizer is a second linear polarizer.

3. The automated testing system for a polarization device according to claim 1, It is characterized in that Also includes: terminal; Wherein, the test optical path assembly and the automatic control module are both electrically connected to the terminal.

4. The automatic testing system for polarization devices according to claim 1, It is characterized in that The automation control module also includes: a voltage source.

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