Dynamic degree of polarization meter and method for detecting polarization state of light

Abstract

The present application provides a dynamic polarimeter and a method for detecting the polarization state of light. The dynamic polarimeter includes a beam splitting element, a detection element, a first detector, a second detector, and a control module. Among them, the beam splitting element is used to split the incident light into a first light beam and a second light beam; the detection element has a metasurface and is arranged on the optical path of the second light beam; the second light beam forms a to-be-detected transmitted light after passing through the metasurface; the first detector is arranged on the optical path of the first light beam and is used to detect the power of the first light beam; the second detector is arranged on the optical path of the to-be-detected transmitted light and is used to detect the power of the to-be-detected transmitted light; the control module includes a data processing unit, which processes the measured power of the first light beam and the power of the to-be-detected transmitted light to obtain the polarization state parameters of the incident light. The polarimeter uses a detection element with a metasurface, making the device small in volume, simple in structure, and high in detection accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of polarization optics, and in particular, to a dynamic polarization meter and a method for detecting the polarization state of light. Background Art

[0002] Polarization is a fundamental property of light, and polarization contains very valuable information. Therefore, a polarization meter that can directly measure the polarization state of light has a wide range of applications in fields such as astronomy, material characterization, medical diagnosis, and remote sensing. Traditional polarization meters contain many and scattered optical elements and are bulky, and can no longer adapt to the trend of miniaturization and integration of optical systems.

[0003] In recent years, metasurfaces have been used to construct new instruments for measuring the full polarization state because they can flexibly control the amplitude, phase, and polarization of light in a nanoscale space and have the characteristics of small volume, light weight, and high integration. Currently, a variety of different polarization meters utilize metasurfaces to regulate incident light, or integrate metasurfaces with semiconductor elements for the photodetector of an integrated polarization meter to achieve the measurement of the polarization state of light.

[0004] However, these metasurface-based polarization meters are all static, contain many optical elements, have the problems of complex device structure, and the measurement errors of multiple measurement elements are superimposed, which easily leads to a large overall measurement error and requires the development of complex error reduction algorithms. Summary of the Invention

[0005] The present application provides a dynamic polarization meter and a method for detecting the polarization state of light. The dynamic polarization meter aims to solve the problems of complex device structure of existing polarization meters and large overall measurement error caused by the superposition of measurement errors of multiple measurement elements, which requires the development of complex error reduction algorithms.

[0006] To solve the above technical problems, a technical solution adopted by the present application is: to provide a dynamic polarization meter. The dynamic polarization meter includes a beam splitting element, a detection element, a first detector, a second detector, and a control module. Among them, the beam splitting element is used to split the incident light into a first light beam and a second light beam; the detection element has a metasurface and is arranged on the optical path of the second light beam; the second light beam forms a to-be-detected transmitted light after passing through the metasurface; the first detector is arranged on the optical path of the first light beam and is used to detect the power of the first light beam; the second detector is arranged on the optical path of the to-be-detected transmitted light and is used to detect the power of the to-be-detected transmitted light; the control module includes a data processing unit, which processes the measured power of the first light beam and the power of the to-be-detected transmitted light to obtain the polarization state parameters of the incident light.

[0007] Among them, the beam splitting element is a beam splitter, which is arranged on the optical path of the incident light and is used to reflect a part of the incident light to form a first light beam and transmit the other part of the incident light to form a second light beam; or the beam splitting element is a mirror and can be moved onto and away from the optical path of the incident light; the mirror is used to be arranged on the optical path of the incident light at a first time to reflect the incident light to form a first light beam, and move away from the optical path of the incident light at a second time so that the incident light forms a second light beam.

[0008] Among them, the detection element includes an insulating transparent substrate and a metal layer arranged on one surface of the insulating transparent substrate, and the metal layer includes a plurality of periodically arranged microstructures with chirality and anisotropy.

[0009] Among them, the plurality of microstructures are arranged at intervals to form an array; the microstructure includes a rectangular body and a rectangular tip protrusion extending from the rectangular body; the rectangular body and the rectangular tip protrusion are an integral structure; the rectangular tip protrusion is arranged near a corner, and one long side of the rectangular tip protrusion is flush with one side of the rectangular body.

[0010] Among them, the material of the metal layer is gold, silver, copper, iron, aluminum, nickel or their alloys; the thickness of the microstructure is 10 nanometers to 200 nanometers, the period is 300 nanometers to 600 nanometers, and the size is 200 nanometers to 500 nanometers; the material of the insulating transparent substrate is one or more of silicon oxide, silicon nitride, sapphire, ceramics, glass, quartz, diamond and polymers.

[0011] Among them, the dynamic polarization meter further includes a turntable, and the detection element is arranged on the turntable and can rotate with the turntable; the control module is further used to control the rotation angle and rotation speed of the turntable; the second detector is used to detect the power of the to-be-detected transmitted light of the detection element at different angles.

[0012] Among them, the second light beam is incident from the surface of the insulating transparent substrate where the metal layer is arranged; the data processing unit is further used to: control the turntable to rotate at least three different angles at a preset rotation speed, so that the second light beam is incident on the detection element at at least three different rotation angles; obtain the corresponding at least three groups of different powers of the to-be-detected transmitted light; process the power of the measured first light beam to obtain s0 of the Stokes vector, where s0 is the total power of the incident light; process the measured at least three groups of different powers of the to-be-detected transmitted light to obtain s1, s2 and s3 of the Stokes vector, where s1 is equal to the power difference between the horizontal and vertical components of the incident light, s2 is equal to the power difference between the ±45° components of the incident light, and s3 is equal to the power difference between the right-handed circularly polarized light and the left-handed circularly polarized light components.

[0013] To solve the above technical problems, another technical solution adopted in this application is: to provide a method for detecting the polarization state of light. The method for detecting the polarization state of light includes: splitting the incident light into a first light beam and a second light beam; detecting the power of the first light beam; making the second light beam pass through a detection element with a metasurface to form a transmitted light to be detected, and detecting the power of the transmitted light to be detected; processing the measured power of the first light beam and the power of the transmitted light to be detected to obtain the polarization state parameters of the incident light.

[0014] Among them, the step of making the second light beam pass through a detection element with a metasurface to form a transmitted light to be detected and detecting the power of the transmitted light to be detected specifically includes: rotating the detection element by at least three different angles, making the second light beam incident on the detection element at at least three different rotation angles to form at least three corresponding different transmitted lights to be detected; respectively detecting the powers of at least three different transmitted lights to be detected. The step of processing the measured power of the first light beam and the power of the transmitted light to be detected to obtain the polarization state parameters of the incident light specifically includes: processing the measured power of the first light beam to obtain s0 of the Stokes vector, where s0 is the total power of the incident light; processing the measured powers of at least three different transmitted lights to be detected to obtain s1, s2, and s3 of the Stokes vector, where s1 is equal to the power difference between the horizontal and vertical components of the incident light, s2 is equal to the power difference between the ±45° components of the incident light, and s3 is equal to the power difference between the right-handed circularly polarized light and the left-handed circularly polarized light components.

[0015] Among them, the step of processing the measured powers of at least three different transmitted lights to be detected to obtain s1, s2, and s3 of the Stokes vector specifically includes: calculating s1, s2, and s3 of the Stokes vector through the following formula,

[0016] S t =(A T A) -1 A T B

[0017]

[0018]

[0019] Among them, S t represents the column vector composed of s1, s2, and s3 of the Stokes vector of the second light beam, that is, S t =[s1,s2,s3] T , s0(θ) represents the intensity of the second light beam when the rotation angle of the detection element is θ, s′0(θ) represents the intensity of the transmitted light to be detected when the rotation angle of the detection element is θ, and θ is the rotation angle of the detection element; processing the Stokes vector of the second light beam to obtain the Stokes vector of the incident light.

[0020] The dynamic degree-of-polarization meter provided by the embodiment of the present application divides the incident light into a first light beam and a second light beam through a beam splitting element, and sets a first detector on the optical path of the first light beam to detect the power of the first light beam, so as to obtain the power of the incident light; by setting a detection element with a metasurface on the optical path of the second light beam, the second light beam forms a transmitted light to be detected after passing through the metasurface. Since the metasurface has different responses to lights with different polarization states, the powers of the transmitted lights to be detected formed by the second light beams of different incident lights after passing through the metasurface are different. Therefore, different polarization states of the incident light can be distinguished by detecting the power of the transmitted light to be detected; and by rotating the detection element with the metasurface by different angles, the same second light beam can form different transmitted lights to be detected through the detection element at different rotation angles; by setting a second detector on the optical path of the transmitted light to be detected to detect the powers of the transmitted lights to be detected at different rotation angles; the data processing unit of the control module obtains the power of the detected first light beam and the powers of the transmitted lights to be detected at different rotation angles and processes them to obtain the polarization state parameters of the incident light; while completing the detection of the polarization state of the incident light, due to the characteristics of the metasurface, such as small volume, high integration, and different responses to incident lights with different polarization states, the dynamic degree-of-polarization meter can use a detection element with a metasurface of small volume and high integration to detect the incident light without using more other optical elements. Compared with the existing degree-of-polarization meters, it has a smaller volume, a simpler device structure, and the detection error will not be too large due to error superposition, effectively improving the detection accuracy of the dynamic degree-of-polarization meter and avoiding the problem of developing a complex error reduction algorithm due to the large overall measurement error caused by the superposition of measurement errors of multiple measurement elements. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings, where:

[0022] Figure 1 It is a schematic structural diagram of the dynamic degree-of-polarization meter provided by an embodiment of the present application;

[0023] Figure 2a It is a schematic diagram of the beam splitting element set on the optical path of the incident light provided by another embodiment of the present application;

[0024] Figure 2b It is a schematic diagram of the beam splitting element moved away from the optical path of the incident light provided by another embodiment of the present application;

[0025] Figure 3 Schematic diagram of the structure of the detection element provided by an embodiment of the present application;

[0026] Figure 4 Scanning electron microscope image of the metasurface structure provided by an embodiment of the present application;

[0027] Figure 5 Schematic diagram of the structure of the microstructure provided by an embodiment of the present application;

[0028] Figure 6 Experimental result diagram of the response of the metasurface to polarized light provided by an embodiment of the present application;

[0029] Figure 7 Experimental result diagram of the annotation of the first row elements of the Mueller matrix provided by an embodiment of the present application;

[0030] Figure 8 Method flowchart for detecting the polarization state of light provided by an embodiment of the present application;

[0031] Figure 9 Distribution diagram of multiple incident lights on the Poincaré sphere provided by an embodiment of the present application;

[0032] Figure 10a Experimental result diagram of the theoretical values and detected values of the Stokes vectors of multiple incident lights provided by an embodiment of the present application;

[0033] Figure 10b Experimental result diagram of the theoretical values and detected values of the azimuth angles and ellipticity angles of multiple incident lights provided by an embodiment of the present application. Specific implementation manners

[0034] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0035] The terms "first", "second", and "third" in this application are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", and "third" may explicitly or implicitly include at least one of such features. In the description of this application, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined. All directional indications (such as up, down, left, right, front, back...) in the embodiments of this application are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly. In addition, the terms "comprise" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but optionally further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products, or devices.

[0036] Reference to "embodiment" in this context means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of this application. The phrase may appear in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0037] The following provides a detailed description of this application in conjunction with the drawings and embodiments.

[0038] Please refer to Figure 1 , Figure 1 which is a schematic structural diagram of a dynamic polarimeter provided by an embodiment of this application. An embodiment of this application provides a dynamic polarimeter, which includes a beam splitting element 10, a detection element 20, a first detector 31, a second detector 32, and a control module 40. Among them, the beam splitting element 10 is used to split the incident light 70 into a first light beam 71 and a second light beam 72; the first detector 31 is arranged on the optical path of the first light beam 71 and is used to detect the power of the first light beam 71; the detection element 20 has a metasurface 220 and is arranged on the optical path of the second light beam 72. After the second light beam 72 passes through the metasurface 220, a to-be-detected transmitted light 73 is formed; the second detector 32 is arranged on the optical path of the to-be-detected transmitted light 73 and is used to detect the power of the to-be-detected transmitted light 73; the control module 40 includes a data processing unit 41. After receiving the detected power of the first light beam 71 and the power of the to-be-detected transmitted light 73, the data processing unit 41 performs processing, that is, uses a corresponding program algorithm to process the received data to obtain the polarization state parameters of the incident light 70.

[0039] Among them, the beam splitting element 10 is used to split the incident light 70 into a first light beam 71 and a second light beam 72; generally, the beam splitting element 10 can be a beam splitter, which is arranged on the optical path of the incident light 70. When the incident light 70 is incident on the beam splitter, the beam splitter reflects a part of the incident light 70 to form the first light beam 71, and transmits the other part of the incident light 70 to form the second light beam 72; it is easy to understand that in this embodiment, the beam splitting element 10 spatially splits the incident light 70 into the first light beam 71 and the second light beam 72. Specifically, the beam splitter reflects x% of the incident light 70 to form the first light beam 71, and the other part of the incident light 70 (i.e., (1 - x%) of the incident light 70) is transmitted through the beam splitter to form the second light beam 72. x% can be between 10% and 80%, and the present application does not make specific limitations in this regard. Generally, considering that light may be attenuated during propagation, if the power of the first light beam 71 (the reflected part of the incident light 70) or the second light beam 72 (the transmitted part of the incident light 70) is too small, the measurement result will not be accurate enough. Therefore, in order to make the measurement result more accurate, neither the reflected part of the incident light 70 (i.e., x% of the incident light 70) nor the transmitted part (i.e., (1 - x%) of the incident light 70) should be too small or too large. Therefore, x% is generally selected to be 40% - 60%; for example, if x% is 50%, then the first light beam 71 is 50% of the incident light 70, and the power of the first light beam 71 detected by the first detector 31 is s 01 , then the power of the incident light 70 is s0 (s0 = s 01 ÷50% = 2s 01 ), and the second light beam 72 is 50% of the incident light 70.

[0040] In another embodiment, the beam splitting element 10 can also split the incident light 70 into the first light beam 71 and the second light beam 72 in terms of time; please refer to Figure 2a and Figure 2b . In this embodiment, the beam splitting element 10 is a mirror, and the mirror can move onto the optical path of the incident light 70 and move away from the optical path of the incident light 70, for example, the beam splitting element 10 is driven to move by a motor; as Figure 2a shown, at the first time, the beam splitting element 10 is arranged on the optical path of the incident light 70, and totally reflects the incident light 70 to form the first light beam 71. The first detector 31 detects the power s of the first light beam 71 01 , and the detected power s of the first light beam 71 01 is the power s0 of the incident light 70, that is, s0 = s 01 ; as Figure 2b shown, at the second time, the beam splitting element 10 moves away from the optical path of the incident light 70, so that the incident light 70 forms the second light beam 72. Compared with Figure 1Compared with the beam splitter element 10 provided in the embodiment, the beam splitter element 10 in this embodiment enables both the first light beam 71 and the second light beam 72 to be the entirety of the incident light 70, so that the power of the first light beam 71 measured by the first detector 31 is equal to the power of the incident light 70, and the power of the light to be detected measured by the second detector 32 is equal to the power of the light after the incident light 70 is transmitted through the metasurface 220. After the data processing unit 41 of the control module 40 obtains the power of the first light beam 71 and the power of the light to be detected, it can be directly processed without conversion, simplifying the data processing process; however, since the beam splitter element 10 needs to be moved onto the optical path of the incident light 70 and moved away from the optical path of the incident light 70, an additional driving device needs to be connected to the beam splitter element 10 to drive the beam splitter element 10 to move onto the optical path of the incident light 70 at the first time and drive the beam splitter element 10 to move away from the optical path of the incident light 70 at the second time, which increases the device complexity of the dynamic polarimeter to a certain extent.

[0041] Please refer to Figure 3 , Figure 3 FIG. is a schematic structural diagram of a detection element provided in an embodiment of the present application. In the embodiment of the present application, the detection element 20 includes an insulating transparent substrate 21 and a metal layer 22 disposed on one surface of the insulating transparent substrate 21. Among them, the insulating transparent substrate 21 has a planar or curved structure and mainly functions as a support; the insulating transparent substrate 21 can be made of a rigid or flexible transparent material; specifically, the rigid transparent material can be selected from one or more of silicon oxide, silicon nitride, sapphire, ceramic, glass, quartz, diamond, and polymers, and the flexible transparent material can be selected from polyester materials such as polycarbonate (PC), polymethyl methacrylate (PMMA), polyethylene (PE), polyimide (PI), or polyethylene terephthalate (PET), or materials such as polyethersulfone (PES), cellulose ester, polyvinyl chloride (PVC), benzocyclobutene (BCB), or acrylic resin; of course, the material for preparing the insulating transparent substrate 21 is not limited to the materials listed above, as long as it can make the insulating transparent substrate 21 function as a support and be transparent. The shape, size, and thickness of the insulating transparent substrate 21 can be selected according to actual needs. In this embodiment, the insulating transparent substrate 21 is a transparent quartz layer with a thickness of 500 microns.

[0042] Among them, the material of the metal layer 22 can be selected from gold, silver, iron, aluminum, nickel, etc. or their alloys to generate surface plasmon polaritons; the thickness of the metal layer 22 is 10 nanometers to 200 nanometers. In this embodiment, the thickness of the metal layer 22 is 100 nanometers. Please refer to Figure 4 , Figure 4SEM image of the metasurface structure provided by an embodiment of the present application. In the embodiment of the present application, the metal layer 22 includes a plurality of periodically arranged microstructures 221 with chirality and anisotropy; the plurality of periodically arranged microstructures 221 are processed on the metal layer 22 by techniques such as focused ion beam etching or electron beam lithography, that is, the microstructures 221 are the hollow parts of the metal layer 22. The plurality of microstructures 221 are arranged at intervals to form an array, so as to form the metasurface 220. Among them, the thickness of the microstructure 221 is the same as that of the metal layer 22, the period is 300 nm to 600 nm, and the size is 200 nm to 500 nm. The pattern of the microstructure 221 is not limited as long as it has chirality and anisotropy. Further refer to Figure 5 , in this embodiment, the microstructure 221 includes a rectangular body 2211 and a rectangular tip protrusion 2212 extending from the rectangular body 2211, and the rectangular body 2211 and the rectangular tip protrusion 2212 are an integral structure; the rectangular tip protrusion 2212 is arranged near a corner of the rectangular body 2211, and one long side of the tip protrusion is flush with one side of the rectangular body 2211. Specifically, the side length of the rectangular body 2211 is 200 nm, the length of the rectangular tip protrusion 2212 is 45 nm, and the width is 28 nm. The metasurface 220 formed by a plurality of microstructures 221 has a small size, so that the detection element 20 with the metasurface 220 has a small volume and a high integration degree, thereby making the volume of the dynamic polarization meter smaller.

[0043] It can be understood that the metasurface 220 is a plurality of periodically arranged microporous structures formed on the metal layer 22, so that light can pass through the metal layer 22; at the same time, in order to protect the metasurface 220 of the metal layer 22 and prevent its structure from being damaged, a transparent protective layer can also be provided on the surface of the metal layer 22 facing away from the insulating transparent substrate 21, and the material of the transparent protective layer can be selected from the materials for preparing the insulating transparent substrate 21 mentioned above.

[0044] The metasurface 220 has anisotropy, so that it has different optical responses to different linearly polarized lights; please refer to Figure 6, in this embodiment, experiments are carried out taking linearly polarized light at horizontal, vertical, and ±45° as examples. Different linearly polarized lights are made to pass through the metasurface 220 to form transmitted light. The right column in the figure is the response diagram of the metasurface 220 to lights with different polarization states. The abscissa represents the wavelength of the polarized light, and the ordinate represents the transmittance of the metasurface 220 to the polarized light. The transmittance is equal to the percentage of the light intensity of the transmitted light to the light intensity of the incident light 70; it can be seen from the results of the first four rows in the figure that for different linearly polarized lights, the metasurface 220 has obvious changes in its transmittance; this is because when the light is incident on the metasurface 220, the microstructures 221 of the metasurface 220 effectively induce the electromagnetic multipole characteristic charge distribution, and in addition, it can effectively excite vortex currents. When different polarized lights are incident on the metasurface 220, the excited charges and the current distribution and magnitude are different, so the intensity of the transmitted light will be different, that is, the transmittance will be different.

[0045] At the same time, the metasurface 220 has chirality, making it have different optical responses to different circularly polarized lights. Taking left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP) as examples, it can be seen from the results of the last two rows in the figure that obvious resonance peaks appear in both the LCP and RCP spectra at about 710 nanometers, but the transmittance amplitudes are completely different; it can be understood that compared with LCP, RCP excites stronger currents, which is caused by the chiral selective resonant cavity composed of the chiral plasmonic nanostructures of the metasurface 220. According to the above analysis, it can be found that the detection element 20 with the metasurface 220 provided in the embodiment of the present application can distinguish the linear polarization and circular polarization components of light, so that the power of the detected transmitted light 73 formed after the second light beam 72 of different incident lights 70 passes through the metasurface 220 is different. Furthermore, by detecting the power of the first light beam 71 and the power of the detected transmitted light 73 and then performing data processing, the polarization state parameters of the incident light 70 can be obtained. While completing the detection of the polarization state of the incident light 70, due to the characteristics of the metasurface 220 being small in volume, high in integration, and having different responses to incident lights 70 with different polarization states, the dynamic polarimeter can use the detection element 20 with the metasurface 220 that is small in volume and high in integration to detect the incident light 70 without using more other optical elements. Compared with the existing polarimeters, it is smaller in volume, simpler in device structure, and the detection error will not be too large due to error superposition, effectively improving the detection accuracy of the dynamic polarimeter and avoiding the problem of developing a complex error reduction algorithm due to the measurement error superposition of multiple measurement elements resulting in a large overall measurement error. In addition, it can be understood that in order to protect the metasurface 220 of the metal layer 22 and prevent its structure from being damaged, a transparent protective layer can also be provided on the surface of the metal layer 22 facing away from the insulating transparent substrate 21. The material of the transparent protective layer can be selected from the materials for preparing the insulating transparent substrate 21 mentioned above.

[0046] Refer again to Figure 1 In the embodiment of the present application, both the first detector 31 and the second detector 32 are photodetectors. A mechanical chopper and a lock-in amplifier are provided in the photodetector to perform photoelectric conversion and modulation on the received light to complete the detection of the power of the light.

[0047] In the embodiment of the present application, the dynamic degree of polarization meter further includes a turntable 50. The detection element 20 with the metasurface 220 is disposed on the turntable 50 and can rotate with the turntable 50. Among them, the rotation center of the turntable 50 is located on the optical path of the second light beam 72, and there is a through hole at the rotation center. The detection element 20 is disposed on the through hole. The size and shape of the through hole are not specifically limited as long as the second light beam 72 can completely pass through the through hole after passing through the metasurface 220 and the insulating transparent substrate 21. Specifically, the metal layer 22 of the detection element 20 is located on the surface of the insulating transparent substrate 21 facing away from the turntable 50, and the second light beam 72 is incident from the surface of the insulating transparent substrate 21 provided with the metal layer 22. The turntable 50 is connected to the control module 40. The control module 40 controls the turntable 50 to rotate at different angles, so that the metasurface 220 of the detection element 20 can rotate at different angles. The second light beam 72 passes through the metasurface 220 at different rotation angles to form different detected transmitted lights 73. The second detector 32 detects the power of the detected transmitted lights 73 at different rotation angles. At the same time, the control module 40 can also control the rotation speed of the turntable 50. Specifically, before detecting the polarization state of the incident light 70, a preset rotation rate can be input to the control module 40. During the detection, the control module 40 can control the turntable 50 to rotate at different angles at the preset rotation rate to measure the polarization state of the incident light 70. It is easy to understand that under the condition that the response speed of the data processing unit 41 can adapt to the rotation rate of the turntable 50, the faster the rotation rate, the faster the detection speed, and the rotation rate can be specifically set according to needs. Of course, in another embodiment, the turntable 50 may not be connected to the control module 40, and the rotation angle of the turntable 50 is completed by manual operation. That is, after manually operating the turntable 50 to rotate to corresponding different angles, the second light beam 72 passes through the metasurface 220 at different rotation angles to form different detected transmitted lights 73. It can be understood that when detecting the polarization state of the incident light 70 in this way, the rotation angle of the detection element 20 needs to be input to the data processing unit 41 of the control module 40, and the data processing unit 41 can correctly process to obtain the polarization state of the incident light 70. However, manual operation is prone to human error, making the measurement result prone to unnecessary errors. Therefore, the embodiment of the present application preferably adopts the technical solution of the control module 40 controlling the rotation angle of the turntable 50 to avoid unnecessary errors.

[0048] Further, the dynamic polarization meter provided by the embodiments of the present application further includes a first microscope 61 and a second microscope 62 respectively disposed on both sides of the detection element 20; the first microscope 61 is a lens or an objective lens disposed between the spectroscopic element 10 and the detection element 20, and is located on the optical path of the second light beam 72, and is used for collecting and collimating the second light beam 72, so that the second light beam 72 is incident on the detection element 20 after passing through the first microscope 61. The second microscope 62 is a lens or an objective lens disposed between the detection element 20 and the second detector 32, and is located on the optical path of the transmitted light 73 to be detected, and is used for collecting and collimating the transmitted light 73 to be detected. Specifically, the parameters and models of the first microscope 61 and the second microscope 62 can be selected according to the detection needs, and no specific limitation is made thereto; for example, in this embodiment, both the first microscope 61 and the second microscope 62 are 10×(N.A. = 0.25) microscopic objective lenses.

[0049] In the embodiments of the present application, the polarization state of the incident light 70 is described by the Stokes vector, and the Stokes vector is a four-element vector S = [s0, s1, s2, s3] T , where s0 is the total power of the incident light 70, s1 is equal to the power difference between the horizontal and vertical components of the incident light 70, s2 is equal to the power difference between the ±45° components of the incident light 70, and s3 is equal to the power difference between the right-handed circularly polarized light and the left-handed circularly polarized light components. Among them, s0 can be obtained by converting the power of the first light beam 71 detected by the first detector 31. To obtain s1, s2, and s3, it is also necessary to perform data processing after detecting the power of the transmitted light 73 to be detected at at least three different rotation angles. Therefore, to obtain the Stokes vector S of the incident light 70, the data processing unit 41 of the control module 40 is further configured to:

[0050] Control the turntable 50 to rotate at least three different angles, so that the second light beam 72 is incident on the detection element 20 at at least three different rotation angles;

[0051] Obtain the corresponding at least three groups of different powers of the transmitted light 73 to be detected;

[0052] Perform corresponding conversion on the measured power of the first light beam 71 to obtain s0; perform corresponding data processing algorithms on the measured powers of at least three groups of different transmitted lights 73 to be detected to obtain s1, s2, and s3 of the Stokes vector of the incident light 70.

[0053] Specifically, the interaction between the second light beam 72 and the metasurface 220 can be represented by a 4×4 Mueller matrix M, and the relationship between the Stokes vector S' of the transmitted light 73 to be detected and the incident light 70 can be expressed as:

[0054] S' = M·S (1)

[0055] From the expression (1), the relationship expression between the power s′0 of the transmitted light 73 to be detected and the Stokes vector S of the incident light 70 can be obtained as follows:

[0056] s′0 = m1s0 + m2s1 + m3s2 + m4s3 (2)

[0057] Where m1, m2, m3, and m4 are the elements of the first row of the Mueller matrix, that is, m i = M 1i (i = 1, 2, 3, 4).

[0058] From the expression (2), it can be known that the data processing unit 41 can, according to the power s′0 of the transmitted light 73 to be detected at at least three different rotation angles measured, the elements m1, m2, m3, m4 of the first row of the Mueller matrix M, and the power s0 of the incident light 70 obtained by the first beam processing, obtain s1, s2, and s3 in the Stokes vector S of the incident light 70 through inverse operation.

[0059] Among them, the elements m1, m2, m3, and m4 of the first row in the Mueller matrix M can be calibrated through experiments, and the specific method is as follows:

[0060] In the experiment, a supercontinuum laser is used as the light source, and the wavelength can be adjusted by a filter to form k kinds of incident lights 70 with different known polarization states, so as to obtain the Stokes vectors of k kinds of incident lights 70 with different known polarization states. Inputting the k Stokes vectors into the data processing unit 41, a matrix I composed of the k Stokes vectors can be obtained. The expression of the matrix I is:

[0061]

[0062] Respectively, make the k kinds of incident lights 70 with different known polarization states pass through the detection element 20 with the metasurface 220 to form k kinds of incident lights 70 to be detected. The second detector 32 respectively detects the powers of the k kinds of incident lights 70 to be detected. The data processing unit 41 forms a matrix O with the powers of the k kinds of incident lights 70 to be detected obtained. The expression of the matrix O is:

[0063]

[0064] According to the expression (1), the relationship between the matrix I and the matrix O is:

[0065] O = M1·I T (5)

[0066] Where M1 = [m1, m2, m3, m4] is composed of the elements of the first row of the Mueller matrix M. In order to make the calculation result more accurate, the least squares method can be used for fitting, and it is required that the matrices O, M1, and I satisfy:

[0067]

[0068] The data processing unit 41 performs inverse operations through the relational expressions (5) and (6) to obtain M1:

[0069] M1 = OI T (I T I) -1 (7)

[0070] Please refer to Figure 7 , Figure 7 , which is the calculation result diagram of the first row elements of the Mueller matrix provided by an embodiment of the present application. In this embodiment, six different known polarization state incident lights 70 are used in the experiment to calibrate the first row elements m1, m2, m3, m4 in the Mueller matrix M. The six different known polarization state incident lights 70 include horizontal polarized light (Horizontal), vertical polarized light (Vertical), +45° polarized light, -45° polarized light, left-handed circularly polarized light, and right-handed circularly polarized light; lights of different wavelengths are respectively used in the experiment, so as to obtain M1 corresponding to different wavelengths in the spectrum. It can be understood that if the parameters m1, m2, m3, m4 in M1 are inaccurate or not applicable to the metasurface 220 of the detection element 20, the calibration can be re-performed through experiments. In another embodiment, the metal layer 22 of the detection element 20 is located on the surface of the insulating transparent substrate 21 close to the turntable 50. The second light beam 72 passes through the insulating transparent substrate 21 and then is incident on the metal layer 22. Due to the chirality of the microstructure 221 of the metal layer 22, the response of the metasurface 220 to the second light beam 72 is different from that in the above embodiment, that is, the elements in the Mueller matrix of the interaction between the second light beam 72 and the metasurface 220 are different. Therefore, it is also necessary to re-calibrate the parameters m1, m2, m3, m4 in M1 through experiments.

[0071] Please refer to Figure 8 , Figure 8 , which is the flowchart of the method for detecting the polarization state of the detection light provided by the embodiment of the present application. The method for detecting the polarization state of the detection light specifically includes the following steps:

[0072] Step S10: Divide the incident light 70 into a first light beam 71 and a second light beam 72.

[0073] Specifically, as described above, the beam splitter 10 can divide the incident light 70 into the first light beam 71 and the second light beam 72 in space or time, which will not be elaborated here.

[0074] Step S20: Detect the power of the first light beam 71.

[0075] Among them, the first detector 31 is arranged on the optical path of the first light beam 71 for detecting the power of the first light beam 71.

[0076] In step S30, the second light beam 72 is transmitted through the detection element 20 with the metasurface 220 to form a to-be-detected transmitted light 73, and the power of the to-be-detected transmitted light 73 is detected.

[0077] In step S40, the measured power of the first light beam 71 and the power of the to-be-detected transmitted light 73 are processed to obtain the polarization state parameters of the incident light 70.

[0078] In step S30, when the second light beam 72 is transmitted through the detection element 20 with the metasurface 220 to form the to-be-detected transmitted light 73, specifically, the detection element 20 is rotated by at least three different angles, and the second light beam 72 is respectively transmitted through the detection element 20 at three different rotation angles to form at least three corresponding different to-be-detected transmitted lights 73; the second detector 32 respectively detects the powers of the at least three different to-be-detected transmitted lights 73.

[0079] In step S40, the data processing unit 41 acquires the detected power of the first light beam 71 and the powers of the at least three different to-be-detected transmitted lights 73; the data processing unit 41 performs conversion processing on the measured power of the first light beam 71 to obtain s0 of the Stokes vector of the incident light 70, that is, the total power of the incident light 70; the powers of the at least three different to-be-detected transmitted lights 73 are processed to obtain s1, s2, and s3 of the Stokes vector of the incident light 70; where s1 is equal to the power difference between the horizontal and vertical components of the incident light 70, s2 is equal to the power difference between the ±45° components of the incident light 70, and s3 is equal to the power difference between the right-handed circularly polarized light and the left-handed circularly polarized light components.

[0080] Among them, the specific method for processing the powers of the at least three different to-be-detected transmitted lights 73 to obtain s1, s2, and s3 of the Stokes vector of the incident light 70 is as follows:

[0081] When the turntable 50 rotates by an angle θ, that is, when the metasurface 220 of the detection element 20 rotates by an angle θ, the interaction between the second light beam 72 and the metasurface 220 changes, and the Mueller matrix M also changes accordingly. The Mueller matrix M(θ) at the angle θ can be calculated according to the following formula;

[0082] M(θ) = R(-θ)MR(θ) (8)

[0083] Among them, R(θ) is a rotation matrix, and the expression is:

[0084]

[0085] If the beam splitting element 10 is a beam splitter, the data processing unit 41 converts the power of the first beam 71 when the metasurface 220 is rotated by an angle θ to obtain the power s0(θ) of the second beam 72 when the metasurface 220 is rotated by an angle θ, and forms a matrix B with the power s′0(θ) of the to-be-detected transmitted light 73 at at least three different angles. The expression of the matrix B is:

[0086]

[0087] Further, the data processing unit 41 reorganizes the matrix M1(θ) composed of the first row elements of the Mueller matrix M(θ) at different rotation angles into a new matrix A. The expression of the matrix A is:

[0088]

[0089] The column vector composed of s1, s2, and s3 of the Stokes vector of the second beam 72 is S t , that is, S t = [s1, s2, s3] T , where s1 is equal to the power difference between the horizontal and vertical components of the second beam 72, s2 is equal to the power difference between the ±45° components of the second beam 72, and s3 is equal to the power difference between the right-handed circularly polarized light and the left-handed circularly polarized light components of the second beam 72; where the total power s of the second beam 72 20 is equal to the power s0(θ) of the second beam 72 when the metasurface 220 is rotated by an angle θ. The column vector S t composed of s1, s2, and s3 of the Stokes vector of the second beam 72 satisfies the following relationship with the matrix A and the matrix B:

[0090] B = A·S t (12)

[0091] Further, the data processing unit 41 performs an inverse operation according to the relationship (12) to obtain the column vector S t composed of s1, s2, and s3 of the Stokes vector of the second beam 72. Its operation expression is:

[0092] S t = (A T A) -1 A T B (13)

[0093] Furthermore, the data processing unit 41 obtains the Stokes vector S of the second beam 72 through the above calculation y = [s0(θ), s1, s2, s3] T , and according to the ratio relationship between the second beam 72 and the incident light 70, for the Stokes vector S of the second beam 72y By performing the corresponding conversion, the Stokes vector S of the incident light 70 can be obtained.

[0094] In another embodiment, if the beam splitting element 10 is a mirror, and the beam splitting element 10 divides the incident light 70 into a first light beam 71 and a second light beam 72 in terms of time, then the powers of both the first light beam 71 and the second light beam 72 are equal to the power of the incident light 70. The power of the first light beam 71 detected by the first detector 31 is equal to the power of the incident light 70, and is also equal to the incident power of the second light beam 72. Then, the data processing unit 41 does not need to perform conversion on the power of the obtained first light beam 71, nor does it need to perform corresponding conversion on the calculated Stokes vector S of the second light beam 72 t perform the corresponding conversion, that is, S = S t .

[0095] Furthermore, based on the calculated Stokes vector S of the incident light 70 obtained by the data processing unit 41, the azimuth angle φ and the ellipticity angle χ of the incident light 70 can also be calculated through the following formulas:

[0096]

[0097]

[0098] In the embodiments of the present application, the accuracy of the dynamic polarimeter involved in the above embodiments is verified through experiments. Specifically, an ultra - continuous laser is used as the light source in the experiment. Taking the light source with a wavelength of 690 nanometers as an example, the light source is adjusted through a combination of a Glan - Taylor polarizer, a half - wave plate, and a quarter - wave plate to form incident light 70 with different polarization states, so that the polarization state of the incident light 70 can cover the entire surface of the Poincaré sphere. Please refer to Figure 9 , 26 different polarization states of incident light 70 are selected in the experiment, and the 26 different polarization states of incident light 70 are evenly distributed on the surface of the Poincaré sphere; in the figure, the abscissa is s1, representing the power difference between the horizontal and vertical components of the incident light 70; the ordinate is s2, representing the power difference between the ±45° components of the incident light 70; the vertical coordinate is s3, representing the power difference between the right - hand circularly polarized light and the left - hand circularly polarized light components. The experiment respectively detects the 26 different polarization states of incident light 70 by using the method for detecting the polarization state of light provided in the above embodiments; the detection results are as shown in Figure 10a and Figure 10b . In the figure, the hollow dots represent the theoretical values of the polarization state of the incident light 70, and the solid dots represent the experimental detection values of the polarization state of the incident light 70. It can be seen from Figure 10a that for s1, s2, and s3 in the Stokes vectors of the 26 different polarization states of incident light 70, the points of the detection values basically all coincide with the points of the theoretical values, and the degree of coincidence is very high; from Figure 10bAs can be seen, for the azimuth angle φ and the ellipticity angle χ of the incident light 70 with 26 different polarization states, the points of the detected values basically coincide with those of the theoretical values, and the degree of coincidence is also very high. Therefore, it can also be seen from the experimental results that the detection accuracy of the dynamic polarization meter provided by the embodiments of the present application is relatively high and the performance is good.

[0099] The above are only the implementation manners of the present application, and do not limit the patent scope of the present application accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present application.

Claims

1. A dynamic degree of polarization meter, characterized in that, Comprising: A beam-splitting element for splitting incident light into a first light beam and a second light beam; A detection element having a metasurface, disposed on the optical path of the second light beam; the second light beam forms a transmitted light to be detected after passing through the metasurface; A first detector disposed on the optical path of the first light beam for detecting the power of the first light beam; A turntable, on which the detection element is disposed and can rotate with the turntable; A second detector disposed on the optical path of the transmitted light to be detected for detecting the power of the transmitted light to be detected, and also for detecting the power of the transmitted light to be detected at different angles of the detection element; A control module, including a data processing unit, which processes the measured power of the first light beam and the power of the transmitted light to be detected to obtain the polarization state parameters of the incident light; the control module is also used to control the rotation angle and rotation rate of the turntable; The data processing unit is further used for: Controlling the turntable to rotate at least three different angles at a preset rotation rate, so that the second light beam is incident on the detection element at at least three different rotation angles; Obtaining at least three corresponding different powers of the transmitted light to be detected.

2. The dynamic polarization degree meter according to claim 1, characterized in that The beam-splitting element is a beam splitter disposed on the optical path of the incident light for reflecting a part of the incident light to form the first light beam and transmitting the other part of the incident light to form the second light beam; or The beam-splitting element is a mirror and can move onto and away from the optical path of the incident light; the mirror is used to be disposed on the optical path of the incident light to reflect the incident light to form the first light beam at a first time, and move away from the optical path of the incident light at a second time so that the incident light forms the second light beam.

3. The dynamic polarization degree meter according to claim 1, characterized in that, The detection element includes an insulating transparent substrate and a metal layer disposed on one surface of the insulating transparent substrate, and the metal layer includes a plurality of periodically arranged microstructures with chirality and anisotropy.

4. The dynamic polarization degree meter according to claim 3, characterized in that The plurality of microstructures are spaced apart to form an array; the microstructure includes a rectangular body and a rectangular tip protrusion extending from the rectangular body; the rectangular body and the rectangular tip protrusion are an integral structure; the rectangular tip protrusion is disposed near a corner, and one long side of the rectangular tip protrusion is flush with one side of the rectangular body.

5. The dynamic polarization degree meter according to claim 4, wherein The material of the metal layer is gold, silver, copper, iron, aluminum, nickel or their alloys; the thickness of the microstructure is 10 nanometers to 200 nanometers, the period is 300 nanometers to 600 nanometers, and the size is 200 nanometers to 500 nanometers; the material of the insulating transparent substrate is one or more of silicon oxide, silicon nitride, sapphire, ceramic, glass, quartz, diamond and polymer.

6. The dynamic degree of polarization meter according to claim 3, wherein The second light beam is incident from the surface of the insulating transparent substrate where the metal layer is disposed; the data processing unit is further used for: Processing the measured power of the first light beam to obtain s0 of the Stokes vector, where s0 is the total power of the incident light; Processing the measured power of at least three different groups of the transmitted light to be detected to obtain s1, s2, and s3 of the Stokes vector of the incident light, where s1 is equal to the power difference between the horizontal and vertical components of the incident light, s2 is equal to the power difference between the ±45° components of the incident light, and s3 is equal to the power difference between the right-handed circularly polarized light and the left-handed circularly polarized light components.

7. A method for detecting the polarization state of light, characterized in that, Including: Dividing the incident light into a first light beam and a second light beam; Detecting the power of the first light beam; Making the second light beam pass through a detection element at at least three different rotation angles to form at least three groups of transmitted light to be detected, and respectively detecting the power of at least three groups of the transmitted light to be detected; wherein, the detection element has a metasurface; Processing the measured power of the first light beam and the power of at least three groups of the transmitted light to be detected to obtain the polarization state parameters of the incident light.

8. The method for detecting the polarization state of light according to claim 7, characterized in that, The step of making the second light beam pass through a detection element with a metasurface to form transmitted light to be detected and detecting the power of the transmitted light to be detected specifically includes: Rotating the detection element by at least three different angles, and making the second light beam pass through the detection element at at least three different rotation angles to form corresponding at least three different groups of the transmitted light to be detected; Respectively detecting the power of at least three different groups of the transmitted light to be detected; The step of processing the measured power of the first light beam and the power of the transmitted light to be detected to obtain the polarization state parameters of the incident light specifically includes: Processing the measured power of the first light beam to obtain s0 of the Stokes vector, where s0 is the total power of the incident light; Processing the measured power of at least three different groups of the transmitted light to be detected to obtain s1, s2, and s3 of the Stokes vector, where s1 is equal to the power difference between the horizontal and vertical components of the incident light, s2 is equal to the power difference between the ±45° components of the incident light, and s3 is equal to the power difference between the right-handed circularly polarized light and the left-handed circularly polarized light components.

9. The method for detecting the polarization state of light according to claim 8, wherein, The step of processing the measured power of at least three different groups of the transmitted light to be detected to obtain s1, s2, and s3 of the Stokes vector specifically includes: The s1, s2, and s3 of the Stokes vector of the second light beam are calculated through the following formula, S t =(A T A) -1 A T B where S t represents the column vector composed of s1, s2, and s3 of the Stokes vector of the second light beam, that is, S t = [s1, s2, s3] T , s0(θ) represents the intensity of the second light beam when the rotation angle of the detection element is θ, s′0(θ) represents the intensity of the transmitted light to be detected when the rotation angle of the detection element is θ, and θ is the rotation angle of the detection element; Processing the Stokes vector of the second light beam to obtain the Stokes vector of the incident light.

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