A metasurface spatial light modulator, a beam direction control method and related products

Abstract

The present application discloses a metasurface spatial light modulator, a beam direction control method and related products. The metasurface spatial light modulator includes a plurality of meta-units with periodic extension, and the meta-units extend along a direction parallel and / or perpendicular to the main axis of the metasurface spatial light modulator. The meta-units have different phase responses to light beams with polarization directions parallel and perpendicular to the main axis of the metasurface spatial light modulator, so as to achieve different reflection effects respectively. Anomalous reflection is performed on the light beam with a polarization direction parallel to the main axis of the metasurface spatial light modulator; normal reflection is performed on the light beam with a polarization direction perpendicular to the main axis of the metasurface spatial light modulator. The metasurface spatial light modulator is used to introduce a polarization control dimension for controlling the beam direction. By using the metasurface spatial light modulator, the control range of the beam direction is expanded. The metasurface spatial light modulator can be applied not only to infrared spatial optical communication, but also to many fields such as lidar, microwave photonic filtering and optical switching.

Description

Technical Field

[0001] This application relates to the field of optical technologies, and in particular, to a metasurface spatial light modulator, a beam direction control method, and related products. Background Art

[0002] With the rapid growth of broadband mobile devices and the explosion of small-scale sensing and driving devices in the Internet of Things, the demand for high-speed wireless communication has increased sharply. The huge demand for wireless communication capacity is about to exhaust the available radio spectrum. Against this background, due to the huge bandwidth and capacity resources of optical wireless communication, and at the same time having a relatively small coverage range, it has received increasing attention in the field of indoor high-speed communication.

[0003] Wireless optical communication can be mainly divided into two technical directions: (1) Visible light communication, which generally realizes high-speed communication by modulating the visible light beam of the lighting system; (2) Infrared light communication with beam control, which uses a directional infrared laser beam to achieve high-speed communication.

[0004] Visible light communication technology usually transmits data on a light-emitting diode (LED) lighting system. It has many deficiencies: (1) Since an actual lighting system usually includes multiple user devices, an appropriate MAC protocol is required to share the capacity of visible light communication, which may lead to congestion problems under high traffic loads. (2) In addition, using visible light communication requires turning on the lighting system, which consumes more extra power, making its efficiency relatively low, especially when lighting is not required during the day. (3) Moreover, the white LEDs used in visible light communication systems have limited bandwidth, and complex high spectral efficiency modulation techniques are required to achieve high transmission rates at the Gbit / s level.

[0005] In contrast, the infrared light communication system using a directional laser beam has many advantages: (1) A single beam is only used for a single user device, which avoids capacity sharing between devices, can easily achieve a high communication rate of >10 Gbit / s, and also avoids congestion problems; (2) By providing optical signals only where and when needed, it can be more energy-efficient and provide better privacy protection; (3) By using an infrared beam with a wavelength λ>1400 nm, the eye-safe standard allows an emission power of up to 10 dBm, which is at least 15 dB higher than the allowed power of visible light beams. Coupled with the directional laser beam, the link power budget of infrared light communication is significantly higher than that of visible light communication; (4) In addition, by operating in the S+L+C band (1460 - 1625 nm, a bandwidth of 20.9 THz), a variety of optical devices can be obtained from the mature fiber optic telecommunications market, greatly reducing the system cost.

[0006] However, in an infrared wireless communication system, the problem of area coverage is its main difficulty. In order to achieve area coverage, beam direction control technologies such as optical phased array antennas, blazed gratings, and spatial routers plus focal plane imaging have been widely studied. The above-mentioned solutions all achieve beam direction control by changing the optical wavelength, that is, different wavelengths of light are corresponding to different positions (directions) in space.

[0007] However, using only the wavelength as the control dimension limits the control range of the beam direction. How to expand the control range of the beam direction has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] Based on the above problems, the present application provides a metasurface spatial light modulator, a beam direction control method and related products, using polarization as a control dimension for controlling the beam direction to expand the control range of the beam direction.

[0009] The embodiments of the present application disclose the following technical solutions:

[0010] In a first aspect, the present application provides a metasurface spatial light modulator, including: a plurality of meta-units with periodic extension, and the extension directions of the meta-units include: directions parallel and / or perpendicular to the main axis of the metasurface spatial light modulator;

[0011] The meta-unit has different phase responses to the first polarization state and the second polarization state; the first polarization state is parallel to the main axis of the metasurface spatial light modulator; the second polarization state is perpendicular to the main axis of the metasurface spatial light modulator;

[0012] The meta-unit is configured to perform anomalous reflection on light in the first polarization state and normal reflection on light in the second polarization state.

[0013] Optionally, the meta-unit includes: a plurality of resonant units; the main axes of each of the resonant units are parallel to each other and are all parallel to the main axis of the metasurface spatial light modulator;

[0014] The resonant unit includes: a bottom layer, an intermediate layer and a top layer;

[0015] Among them, the bottom layer is a metal ground, which is used for reflecting light beams and resonant coupling;

[0016] The intermediate layer is a dielectric layer, which is used to separate the metal ground and the top layer to form a gap;

[0017] The top layer includes a metal block, and the major axis of the metal block is parallel to the main axis of the metasurface spatial light modulator.

[0018] Optionally, when the light in the first polarization state is incident on the resonant unit, gap surface plasmons (GPPs) are excited, and the GPPs resonate in the resonant cavity formed by the first pair of end faces of the metal block;

[0019] When the light in the second polarization state is incident on the resonant unit, the GPPs are excited, and the GPPs resonate in the resonant cavity formed by the second pair of end faces of the metal block;

[0020] The first pair of end faces includes: the two end faces of the metal block perpendicular to the long axis; the second pair of end faces includes: the two end faces of the metal block parallel to the long axis.

[0021] Optionally, the common parameters of each of the resonant units include:

[0022] The length of the resonant unit is between 10 nm and 1000 nm; the length direction of the resonant unit is parallel to the long axis of the metal block;

[0023] The thickness of the metal ground is greater than or equal to 10 nm;

[0024] The thickness of the dielectric layer is between 10 nm and 1000 nm;

[0025] The height of the metal block is between 10 nm and 1000 nm.

[0026] Optionally, the super unit includes: a first resonant unit and a second resonant unit;

[0027] Wherein, the top layer of the first resonant unit includes a metal block in a cuboid structure; the top layer of the second resonant unit includes a metal block in an I-shaped structure.

[0028] Optionally, the parameters of the first resonant unit further include:

[0029] The width of the first resonant unit is half of the length of the first resonant unit;

[0030] The length of the metal block in the cuboid structure is greater than or equal to 0 and less than the length of the first resonant unit;

[0031] The width of the metal block in the cuboid structure is greater than or equal to 0 and less than the width of the first resonant unit.

[0032] Optionally, the parameters of the second resonant unit further include:

[0033] The width of the second resonant unit is equal to the length of the second resonant unit;

[0034] The first length of the I-shaped metal block is greater than 0 and less than the length of the second resonant unit;

[0035] The second length of the I-shaped metal block is greater than 0 and less than half of the first length;

[0036] The first width of the I-shaped metal block is greater than 0 and less than the width of the second resonant unit;

[0037] The second width of the I-shaped metal block is greater than 0 and less than or equal to the first width.

[0038] Optionally, the super unit specifically includes: seven of the first resonant units and one of the second resonant units;

[0039] The relative phase responses of the seven first resonant units and the second resonant unit in the first polarization state are respectively: 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°;

[0040] The relative phase responses of the seven first resonant units and the second resonant unit in the second polarization state are respectively: 0°, k, k, k, k, k, k, 180°; where k represents any phase.

[0041] Optionally, the common parameters of the seven first resonant units and one second resonant unit include:

[0042] The length of the resonant unit is 500 nm;

[0043] The thickness of the metal ground is 250 nm;

[0044] The thickness of the dielectric layer is 100 nm;

[0045] The height of the metal block is 50 nm;

[0046] The widths of the seven first resonant units are respectively 250 nm; the widths of the metal blocks of the seven first resonant units are respectively 90 nm; the lengths of the metal blocks of the seven first resonant units are respectively: 0 nm, 210 nm, 252 nm, 285 nm, 308 nm, 340 n, 420 nm;

[0047] The width of the second resonant unit is 500 nm; the first width of the metal block of the second resonant unit is 290 nm, the second width is 120 nm, the first length is 390 nm, and the second length is 100 nm.

[0048] Optionally, in the super unit, the number of the seven first resonant units is two;

[0049] The relative phase response arrangement order of the first resonant unit and the second resonant unit in the supercell at the first polarization state is as follows:

[0050] 0°, 0°, 45°, 45°, 90°, 90°, 135°, 135°, 180°, 180°, 225°, 225°, 270°, 270°, 315°;

[0051] The arrangement direction of each resonant unit in the supercell is perpendicular to the main axis of the metasurface spatial light modulator.

[0052] Optionally, each of the resonant units in the supercell is a sub-wavelength resonant unit, and the light incident on the supercell is infrared light.

[0053] Optionally, the central wavelength of the light incident on the supercell is 1550 nm.

[0054] Optionally, the supercell is specifically configured to anomalously reflect the light in the first polarization state according to the following formula:

[0055] sinθ a = sinθ i + λ / Λ

[0056] where Λ is the length of the supercell, λ is the wavelength of the light in the first polarization state, θ a is the anomalous reflection angle, and θ i is the incident angle.

[0057] Optionally, the metal used for the top layer and the bottom layer of the resonant unit is gold; the dielectric used for the intermediate layer is silica.

[0058] In a second aspect, the present application provides a method for controlling the beam direction, the method including:

[0059] Receiving incident light by using the metasurface spatial light modulator provided in the first aspect;

[0060] Using the metasurface spatial light modulator to anomalously reflect the light in the incident light whose polarization direction is parallel to the main axis of the metasurface spatial light modulator, and to normally reflect the light in the incident light whose polarization direction is perpendicular to the main axis of the metasurface spatial light modulator.

[0061] Optionally, before receiving the incident light, it further includes:

[0062] Controlling the polarization state of the incident light by using a polarization control element.

[0063] Optionally, the controlling the polarization state of the incident light by using a polarization control element specifically includes:

[0064] According to the target reflection coverage area and / or the target reflection energy distribution ratio, the polarization state of the incident light is controlled by using the polarization control element.

[0065] Optionally, before controlling the polarization state of the incident light by using the polarization control element, it further includes:

[0066] The incident light is processed by using a spatial router so that lights with different wavelengths in the incident light are emitted at different output positions of the spatial router.

[0067] In a third aspect, the present application provides a beam direction control system, including: the metasurface spatial light modulator provided in the first aspect; and further including: a polarization control element;

[0068] The polarization control element is configured to control the polarization state of the beam incident on the metasurface spatial light modulator and provide the beam to the metasurface spatial light modulator;

[0069] The metasurface spatial light modulator is configured to anomalously reflect the light in the beam whose polarization direction is parallel to the main axis of the metasurface spatial light modulator, and normally reflect the light in the beam whose polarization direction is perpendicular to the main axis of the metasurface spatial light modulator.

[0070] Optionally, the system further includes: a spatial router, configured to process the incident light before the beam enters the polarization control element so that lights with different wavelengths in the beam are emitted at different output positions of the spatial router.

[0071] Optionally, the system further includes: a first lens, configured to refract the beam from the polarization control element to the metasurface spatial light modulator;

[0072] The surface of the metasurface spatial light modulator includes a point that coincides with the focal point of the first lens.

[0073] In a fourth aspect, the present application provides a microwave photonic filter, including: the metasurface spatial light modulator provided in the first aspect; and further including: a light source, a polarization control element, an intensity modulator, an optical combiner, and a photodetector;

[0074] The light source is configured to generate an optical carrier;

[0075] The intensity modulator is configured to modulate an externally applied microwave signal onto the optical carrier to form a modulated optical signal;

[0076] The metasurface spatial light modulator is configured to anomalously reflect the optical signals with polarization directions parallel to the main axis of the metasurface spatial light modulator according to the polarization states of the optical signals, so as to form a first reflected optical signal; and normally reflect the optical signals with polarization directions perpendicular to the main axis of the metasurface spatial light modulator to form a second reflected optical signal;

[0077] The optical combiner is configured to receive the first reflected optical signal and the second reflected optical signal, perform interference superposition on the first reflected optical signal and the second reflected optical signal, and then provide the optically interfered and superposed signal to the photodetector;

[0078] The photodetector is configured to receive the optically interfered and superposed signal and perform optoelectronic conversion.

[0079] In a fifth aspect, the present application provides a configurable multi-tap microwave photonic filter, including: the metasurface spatial light modulator provided in the first aspect; further including: a tunable laser source, an intensity modulator, a spatial router, a polarization control element, a line focusing lens, a reflection cavity, a second lens, and a photodetector array;

[0080] The tunable laser source is configured to generate an optical carrier and control the wavelength of the optical carrier;

[0081] The intensity modulator is configured to modulate a microwave signal onto the optical carrier to form a modulated optical signal, and provide the modulated optical signal to the spatial router;

[0082] The spatial router is configured to process the modulated optical signal, so that lights with different wavelengths in the optical signal exit at different output positions of the spatial router;

[0083] The polarization control element is configured to receive the light beam exiting from the spatial router and perform polarization regulation on it, so that the polarization direction of the light beam is parallel to the main axis of the metasurface spatial light modulator;

[0084] The line focusing lens is configured to deflect the light beam regulated by the polarization control element and emit a divergent light beam towards the metasurface spatial light modulator;

[0085] The metasurface spatial light modulator is configured to anomalously reflect the incident divergent light beam to the reflection cavity;

[0086] The reflection cavity is configured to reflect the light beam from the metasurface spatial light modulator at least once and then output it;

[0087] The second lens is configured to converge and transmit the light beam output from the reflection cavity to the photodetector array;

[0088] The optoelectronic detection array includes a plurality of detection units, and the positions of different detection units are different, and are respectively used to receive optical signals incident at different positions and perform optoelectronic conversion; different detection units respectively output microwave signals with different phase delays.

[0089] In a sixth aspect, the present application provides a lidar detection system, including: the metasurface spatial light modulator provided in the first aspect; further including: a lidar, a first receiver, and a second receiver;

[0090] The lidar is used to emit a detection signal to a reflection source;

[0091] The metasurface spatial light modulator is used to receive the echo signal reflected by the reflection source, anomalously reflect the light in the echo signal whose polarization direction is parallel to the main axis of the metasurface spatial light modulator, and normally reflect the light in the echo signal whose polarization direction is perpendicular to the main axis of the metasurface spatial light modulator;

[0092] The first receiver is used to receive the first optical signal anomalously reflected by the metasurface spatial light modulator;

[0093] The second receiver is used to receive the second optical signal normally reflected by the metasurface spatial light modulator;

[0094] The first optical signal, the second optical signal, and the detection signal are used to detect information about the reflection source.

[0095] Compared with the prior art, the present application has the following beneficial effects:

[0096] The metasurface spatial light modulator provided by the present application includes: a plurality of meta-units with periodic extension, and the extension directions of the meta-units include: directions parallel and / or perpendicular to the main axis of the metasurface spatial light modulator. The meta-units have different phase responses to light beams with polarization directions parallel and perpendicular to the main axis of the metasurface spatial light modulator, so as to respectively achieve different reflection effects. Specifically, for the light beam with a polarization direction parallel to the main axis of the metasurface spatial light modulator, anomalous reflection is performed, that is, the reflection angle is not equal to the incident angle; for the light beam with a polarization direction perpendicular to the main axis of the metasurface spatial light modulator, normal reflection is performed, that is, the reflection angle is equal to the incident angle. Thus, it can be seen that using this metasurface spatial light modulator can introduce a polarization control dimension for controlling the beam direction. Using this metasurface spatial light modulator, the control range of the beam direction can be expanded. The metasurface spatial light modulator provided by the present application can be applied not only to infrared free-space optical communication, but also to many fields such as lidar, microwave photonic filtering, and optical switching. Description of the Drawings

[0097] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0098] Figure 1 A two-dimensional schematic diagram of a metasurface spatial light modulator structure provided by an embodiment of the present application;

[0099] Figure 2 A three-dimensional structure schematic diagram of a first resonant unit provided by an embodiment of the present application;

[0100] Figure 3 A three-dimensional structure schematic diagram of a second resonant unit provided by an embodiment of the present application;

[0101] Figure 4 An arrangement schematic diagram of the resonant units in a supercell provided by an embodiment of the present application;

[0102] Figure 5 For Figure 4 A schematic diagram of a metasurface spatial light modulator formed by periodically extending the shown supercell;

[0103] Figure 6 A schematic diagram of the phase response of a supercell to the first polarization state provided by an embodiment of the present application;

[0104] Figure 7 A schematic diagram of the phase response of a supercell to the second polarization state provided by an embodiment of the present application;

[0105] Figure 8a A schematic diagram of a scenario where a metasurface spatial light modulator provided by an embodiment of the present application realizes beam splitting;

[0106] Figure 8b A relationship diagram of the variation of the abnormal reflection angle and the incident angle of a metasurface spatial light modulator provided by an embodiment of the present application;

[0107] Figure 8c A relationship diagram of the variation of the included angle between the abnormal reflection and the normal reflection and the incident angle of a metasurface spatial light modulator provided by an embodiment of the present application;

[0108] Figure 9 A flowchart of a beam direction control method provided by an embodiment of the present application;

[0109] Figure 10 A schematic diagram of the structure of a beam direction control system provided by an embodiment of the present application;

[0110] Figure 11a Schematic structural diagram of a microwave photonic filter provided by an embodiment of the present application;

[0111] Figure 11b is Figure 11a Measured filter characteristic diagram under different free spectral range configurations;

[0112] Figure 12 Schematic structural diagram of a configurable multi-tap microwave photonic filter provided by an embodiment of the present application;

[0113] Figure 13 Schematic diagram of a lidar detection system provided by an embodiment of the present application. Detailed implementation manners

[0114] As described above, the current common beam control scheme usually controls the beam direction by changing the light wavelength, that is, different wavelengths of light are corresponding to different positions in space. However, when using this scheme to control the beam direction, the achieved beam control range is relatively small, while in many actual application scenarios, a wider requirement for the beam control range exists.

[0115] Based on the above problems, the present application provides a metasurface spatial light modulator (Spatial Light Modulator, SLM), a beam direction control method and related products. The related products include: a beam direction control system, a microwave photonic filter, a configurable multi-tap microwave photonic filter, and a lidar detection system. In the present application, by introducing a polarization control mechanism, a polarization control type metasurface spatial light modulator can reflect the beams with orthogonal polarization directions at different reflection angles respectively. Thus, the beam control range is greatly expanded.

[0116] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0117] Embodiment of metasurface spatial light modulator

[0118] See Figure 1 , this figure is a two-dimensional schematic diagram of the structure of a metasurface spatial light modulator SLM provided by an embodiment of the present application.

[0119] As Figure 1 shown, the SLM includes: a plurality of supercells c0 with periodic extension.Figure 1 Among them, the double-arrow s1 represents the direction parallel to the main axis of the SLM, and the double-arrow s2 is perpendicular to the double-arrow s1, representing the direction perpendicular to the main axis of the SLM.

[0120] In practical applications, the extension direction of the supercell c0 of the SLM can be parallel to the main axis of the SLM or perpendicular to the main axis of the SLM. That is to say, the supercell c0 can extend within the surface range R of the SLM along any one of the arrow directions of the double-arrow s1 and / or along any one of the arrow directions of the double-arrow s2. Figure 1 Only the rectangular surface range R is taken as an example here. In practical applications, the surface range R of the SLM can also be circular or elliptical, etc. Here, the shape and area of the surface range R of the SLM are not limited.

[0121] In the SLM provided in this embodiment, multiple supercells c0 form the metasurface of the SLM. The supercell has different phase responses to the light beams polarized in the s1 direction and the s2 direction. Therefore, the supercell c0 has different reflection effects on the light beams with different polarization states. For the sake of easy understanding, the first polarization state and the second polarization state are taken as examples for illustration.

[0122] The first polarization state is parallel to the main axis of the SLM, and its polarization direction can refer to Figure 1 the double-arrow s1; the second polarization state is perpendicular to the main axis of the SLM, and its polarization direction can refer to Figure 1 the double-arrow s2. For the first polarization state, the supercell c0 is equivalent to a plane wavefront. Therefore, when the light of the first polarization state is incident on the SLM, due to the action of the supercell c0, an anomalous reflected light is formed. It should be noted that in this embodiment, the anomalous reflection means that the magnitude of the reflection angle is not equal to the magnitude of the incident angle. For the second polarization state, the supercell c0 is equivalent to a mirror. Therefore, when the light of the second polarization state is incident on the SLM, due to the action of the supercell c0, a normal reflected light is formed. It should be noted that in this embodiment, the normal reflection means that the reflection angle is equal to the magnitude of the incident angle.

[0123] Because in the SLM provided in this embodiment, the supercell c0 can reflect the lights with different polarization directions in the same light beam at different angles respectively. Therefore, by controlling the polarization state of the incident light, the direction of the reflected light of the SLM can be controlled to meet the actual requirements. For example, when it is necessary to make the reflected light cover a large range, the polarization direction and the incident angle of the incident light can be controlled to make the reflected light be reflected at different angles.

[0124] It can be seen that using this SLM can introduce a polarization control dimension for controlling the beam direction and expand the control range of the beam direction. The SLM provided in this application can be applied not only to infrared free-space optical communication, but also to many fields such as lidar, microwave photonic filtering, and optical switching. Before introducing many application scenarios of the SLM, first, various possible structural implementation methods of the supercell c0 will be introduced below.

[0125] As a possible implementation method, the supercell c0 includes: a plurality of resonant units; the main axes of each resonant unit are parallel to each other and are all parallel to the main axis of the SLM. The multiple resonant units included in the supercell c0 can be arranged in a variety of possible arrangements. For example, the arrangement direction of each resonant unit in the supercell c0 is perpendicular to the main axis of the SLM, and this arrangement direction can be seen in Figure 1 the double arrow s2 in, and the main axis direction of each resonant unit can be seen in Figure 1 the double arrow s1 in.

[0126] The structure of each supercell c0 can be the same or different. It should be noted that for any supercell c0, it includes a variety of different resonant units, and the number of one type of resonant unit in the supercell c0 is one or more.

[0127] For each resonant unit, it includes at least three layers, namely: a bottom layer, a middle layer, and a top layer. Among them, the bottom layer is a metal ground, which is used to reflect the beam and resonate and couple; the middle layer is a dielectric layer, which is used to separate the metal ground and the top layer to form a gap; the top layer includes a metal block, and the long axis of the metal block is parallel to the main axis of the SLM, and the long axis direction can be seen in Figure 1 the double arrow s1 in. And the long axis of the metal block is also parallel to the main axis of the unit.

[0128] The resonant unit can be fabricated on different substrates (such as silica wafers, quartz wafers, silicon wafers, etc.). Due to the existence of the metal ground, the substrate has nothing to do with resonance and only plays a role of support and substrate.

[0129] It can be seen that both the top layer and the bottom layer of the resonant unit use metal. As an example, this metal is gold. The dielectric used in the middle layer can be silica. It can be understood that in practical applications, the top layer and the bottom layer of the resonant unit can also use other metals other than gold. In addition, the metals used in the top layer and the bottom layer can be the same or different. The dielectric used in the middle layer can also be other dielectrics other than silica.

[0130] In a possible implementation, the multiple resonance units included in the super unit c0 are divided into: a first resonance unit and a second resonance unit. The top layer of the first resonance unit includes a metal block with a rectangular structure; the top layer of the second resonance unit includes a metal block with an I-shaped structure. That is, there is a difference in the structure of the metal block at the top layer of the first resonance unit and the second resonance unit.

[0131] Figure 2 is a schematic diagram of the three-dimensional structure of the first resonance unit, Figure 3 Schematic diagram of the three-dimensional structure of the second resonance unit. Figure 2 and Figure 3 In the figure, the direction indicated by the double arrow K is the long axis direction of the metal block. Figure 2 The first resonance unit is taken as an example to describe the resonance condition after light is incident on the super unit c0.

[0132] In an embodiment of the present application, when light is incident on the resonance unit of the super unit c0, it can excite the gap plasmon (GPP) to resonate in the resonance cavity formed by the end face of the top metal block. Specifically: when the light of the first polarization state is incident on the first resonance unit, the GPP is excited, so that the GPP resonates in the resonance cavity formed by the first pair of end faces of the rectangular metal block. The first pair of end faces are the two end faces of the rectangular metal block perpendicular to its long axis. When the light of the second polarization state is incident on the first resonance unit, the GPP is excited, so that the GPP resonates in the resonance cavity formed by the second pair of end faces of the rectangular metal block. The second pair of end faces are the two end faces of the rectangular metal block parallel to its long axis. The wavelength of the GPP is much smaller than the wavelength of the incident light.

[0133] Although the structures of the top metal blocks are different, the first resonant unit and the second resonant unit have some common parameters, including:

[0134] The length L of the resonance unit is between 10 nm and 1000 nm; the length direction of the resonance unit is parallel to the long axis of the metal block;

[0135] The thickness g of the metal ground is greater than or equal to 10 nm;

[0136] The thickness d of the dielectric layer is between 10 nm and 1000 nm;

[0137] The height h of the metal block is between 10 nm and 1000 nm.

[0138] Different from the structure of the second resonance unit, in the embodiment of the present application, the parameters of the first resonance unit, in addition to the above L, g, d and h, also include:

[0139] The width W1 of the first resonant unit is half of the length L of the first resonant unit;

[0140] The length l1 of the metal block with a cuboid structure is greater than or equal to 0 and less than the length L of the first resonant unit;

[0141] The width w1 of the metal block with a cuboid structure is greater than or equal to 0 and less than the width W1 of the first resonant unit.

[0142] Different from the structure of the first resonant unit, in the embodiment of the present application, the parameters of the second resonant unit, in addition to the above L, g, d, and h, further include:

[0143] The width W2 of the second resonant unit is equal to the length L of the second resonant unit;

[0144] The first length l2 of the metal block with an I-shaped structure is greater than 0 and less than the length L of the second resonant unit;

[0145] The second length l3 of the metal block with an I-shaped structure is greater than 0 and less than half of the first length l2;

[0146] The first width w2 of the metal block with an I-shaped structure is greater than 0 and less than the width W2 of the second resonant unit;

[0147] The second width w3 of the metal block with an I-shaped structure is greater than 0, and w3 is less than or equal to the first width w2.

[0148] From the above parameters, it can be known that the width W2 of the second resonant unit is twice the width W1 of the first resonant unit.

[0149] In a possible implementation manner, the first resonant unit is divided into multiple types.

[0150] For example, the super unit c0 specifically includes: seven of the first resonant units (listed as U1 to U7 respectively) and one second resonant unit U8. It should be noted that U1 to U8 are not shown in Figure 1 ~ Figure 3 shown.

[0151] The relative phase responses of U1 to U8 in the first polarization state are respectively: 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°;

[0152] The relative phase responses of U1 to U8 in the second polarization state are respectively: 0°, k, k, k, k, k, k; where k represents an arbitrary phase.

[0153] It should be noted that the relative phase response described herein may be the phase of U1 to U8 relative to U1 (i.e., U1 is set to 0°). That is to say, in the first polarization state, the phase response of U1 to U8 relative to U1 increases in steps of 45°. In the second polarization state, the phase responses of U2 to U7 relative to U1 are the same or nearly the same (for example, the variation range is within a preset phase difference).

[0154] In a possible implementation, the common parameters of U1 to U8 include:

[0155] The length L of the resonant unit is 500 nm; the thickness g of the metal ground is 250 nm; the thickness d of the dielectric layer is 100 nm; the height h of the metal block is 50 nm;

[0156] The widths W1 of the first resonant units U1 to U7 are 250 nm respectively; the widths w1 of the metal blocks of U1 to U7 are 90 nm respectively; the lengths l1 of the metal blocks of U1 to U7 are: 0 nm, 210 nm, 252 nm, 285 nm, 308 nm, 340 n, 420 nm respectively. It should be noted that the length l1 of the metal block of U1 is 0, that is, it is equivalent to that there is no metal block on the top layer of U1.

[0157] The width of the second resonant unit U8 is 500 nm; the first width w2 of the metal block of U8 is 290 nm, the second width w3 is 120 nm, the first length l2 is 390 nm, and the second length l3 is 100 nm.

[0158] See Figure 4 , which is a schematic diagram of the arrangement of resonant units in a supercell provided by an embodiment of the present application. As Figure 4 shown, the supercell c0 includes 15 resonant units. In terms of the arrangement quantity, there are two of U1 to U7 each and one of U8. Figure 5 is a schematic diagram of a metasurface SLM formed by periodic extension of the supercell shown Figure 4 .

[0159] In the supercell c0, the resonant units are arranged in a direction perpendicular to the main axis of the SLM. Since the main axis of the SLM is parallel to the main axis of each resonant unit and parallel to the long axis of the metal block of the resonant unit, it can also be understood that in the supercell c0, the resonant units are arranged in a direction perpendicular to the main axis of the resonant unit or perpendicular to the long axis of the metal block. In addition, the main axes of the resonant units are parallel to each other during the arrangement.

[0160] As Figure 4As shown, U1, U1, U2, U2, U3, U3, U4, U4, U5, U5, U6, U6, U7, U7, and U8 are arranged in sequence according to the above arrangement direction. If U1 to U8 are set according to the above parameters, the length of the supercell c0 (along the direction perpendicular to the long axis of the metal block) is 4 μm. Every two first resonant units of the same type form a resonant group, and U8 alone forms a resonant group, that is, there are a total of 8 resonant groups. The size of each resonant group is 500 nm × 500 nm, and the thickness is only 400 nm. If this SLM is applied to the infrared band, the three-dimensional sizes of each resonant group are all less than one-third of the wavelength.

[0161] Based on the previous description, it can be known that in Figure 4 the relative phase response arrangement order of each resonant unit in the supercell c0 shown in the first polarization state is:

[0162] 0°, 0°, 45°, 45°, 90°, 90°, 135°, 135°, 180°, 180°, 225°, 225°, 270°, 270°, 315°;

[0163] In Figure 4 the relative phase response arrangement order of each resonant unit in the supercell c0 shown in the second polarization state is: 0°, 0°, k, k, k, k, k, k, k, k, k, k, k, k, 180°.

[0164] In the embodiments of the present application, the number of resonant units arranged in the supercell c0 is not limited to 15, and more resonant units can also be included, such as 4 U1s, 4 U2s, 4 U3s, 4 U4s, 4 U5s, 4 U6s, 4 U7s, and 1 U8. The same type of first resonant units are repeatedly arranged in the supercell c0 to ensure a spatially uniform phase response.

[0165] From the above description, it can be known that in Figure 4 the supercell c0 shown, for the first polarization state where the polarization direction is parallel to the main axis of the SLM, the phase responses of the sub-wavelength resonant units U1 to U8 relative to U1 change in equal steps and cover 2π, which forms an artificially designed plane wavefront, generates an anomalous reflection phenomenon, and forms a beam of anomalous reflected light. See Figure 6 This figure is a schematic diagram of the phase response of the supercell c0 to the first polarization state.

[0166] For the second polarization state with the polarization direction perpendicular to the main axis of the SLM, among the six sub-wavelength resonant units U2 - U7, there is an almost identical phase response relative to U1. Therefore, the supercell c0 acts as a mirror for the second polarization state. For the other two resonant units U1 and U8, there is a phase difference of about 180°. Due to the periodic extension structure of the supercell c0, U1 and U8 are adjacent in space. Thus, the scattered light of the two cancels each other out. Overall, it still acts as a mirror, thereby forming a specularly reflected light beam. See Figure 7 , which is a schematic diagram of the phase response of the supercell c0 to the second polarization state.

[0167] Since the relationships between the anomalous reflection angle and the normal reflection angle and the incident angle are different, the angle between the specularly reflected light and the anomalously reflected light can be adjusted by changing the incident angle. The supercell c0 is specifically used to anomalously reflect the light of the first polarization state according to the following formula:

[0168] sinθ a = sinθ i + λ / Λ

[0169] In the above formula, Λ is the length of the supercell c0, λ is the wavelength of the light of the first polarization state, θ a is the anomalous reflection angle, and θ i is the incident angle.

[0170] That is, the incident angle of the light of the first polarization state can be controlled according to the above formula, thereby realizing the control of the reflection angle of the light beam. In addition, the anomalous reflection angle is related to the wavelength of the light of the first polarization state. Therefore, it can be known that for the light of the first polarization state with the polarization direction parallel to the main axis, if it contains multiple wavelengths, the anomalous reflection angles of the lights with different wavelengths after reflection are different. That is, the SLM can reflect lights with different wavelengths having the same incident angle and the same polarization direction in different directions.

[0171] Since the directions of the reflected lights in the two orthogonal polarization cases are different, by changing the polarization of the incident light, the energy of the reflected light can be distributed in two different directions. For example, by changing the polarization state of the incident light so that the light incident on the SLM is completely polarized in the direction parallel to the main axis of the SLM, the energy of the light beam reflected at the anomalous reflection angle is maximized; by changing the polarization state of the incident light so that the light incident on the SLM is completely polarized in the direction perpendicular to the main axis of the SLM, the energy of the light beam reflected at the normal reflection angle is maximized, and so on.

[0172] In addition, based on the above formula, it can be known that for the light of the first polarization state with the polarization direction parallel to the main axis of the SLM, the angle of its anomalously reflected light changes non-linearly with the incident light angle, and the anomalous reflection angle is greater than the incident angle. Therefore, using this SLM, non-linear tuning (angle amplification) of the input angle and the output angle can be achieved.

[0173] Figures 8a - 8c This is a schematic diagram for realizing the distribution of beam energy in two directions and the non - linear tuning of the input angle and output angle in the embodiments of the present application. Figure 8a This is a schematic diagram of the scenario for realizing beam distribution by a metasurface spatial light modulator provided in the embodiments of the present application; Figure 8b This is the variation relationship between the extraordinary reflection angle and the incident angle of a metasurface spatial light modulator provided in the embodiments of the present application; Figure 8c This is the variation relationship between the angle between the extraordinary reflection and the normal reflection and the incident angle of a metasurface spatial light modulator provided in the embodiments of the present application.

[0174] Combined with Figures 8a - 8c , because the directions of the reflected light are different in two orthogonal polarization cases, by changing the polarization of the incident light, the energy of the reflected light can be gradually transferred from one direction to another, realizing the distribution of beam energy in two regions, which can be used in optical switching systems, such as Figure 8a shown. In Fig. 8a, θ a is the extraordinary reflection angle, θ i is the incident angle, and θ n is the normal reflection angle. For the incident light with the polarization direction parallel to the main axis of the SLM, the angle θ a of its extraordinary reflected light varies non - linearly with the incident light angle θ i , and non - linear tuning (angle amplification) of the input angle and output angle can be realized. The relationship between the extraordinary reflection angle and the incident angle is as Figure 8b shown. In addition, because the relationships between the extraordinary reflection angle and the normal reflection angle and the incident angle are different, the angle (θ a -θ n ) between the normal reflected light and the extraordinary reflected light can be adjusted by changing the incident angle θ i , and its angle relationship is as Figure 8c shown.

[0175] In a possible implementation manner, the SLM provided in this embodiment can be applied to the infrared communication scenario. Each resonant unit of the super - cell c0 can be a sub - wavelength resonant unit, that is, the size is comparable to or smaller than the working infrared wavelength. The light of the first polarization state and / or the second polarization state incident on the SLM is infrared light, and its respective central wavelength is the working infrared wavelength in the infrared communication scenario. As an example, the central wavelength of the incident light is 1550 nm.

[0176] It should be noted that the light of the first polarization state and / or the second polarization state can be linearly polarized light without polarization modulation, or the components of other types of polarized light without polarization modulation in the direction parallel to the main axis of the SLM and / or perpendicular to the main axis of the SLM. Additionally, it can also be polarized light after polarization modulation.

[0177] When the SLM is applied to the infrared band, the top metal block of each resonant unit can specifically be a metal block of nanoscale size, simply referred to as a metal nanoblock.

[0178] It can be seen from the above technical solutions that applying the above SLM has the following advantages:

[0179] (1) It has a high efficiency. By using the gap plasmon polariton subwavelength resonant unit to achieve precise control of the optical phase at the subwavelength scale, it is possible to reconstruct the wavefront phase of the reflected light at the subwavelength scale, so that the vast majority of the energy of the reflected light is concentrated in the desired direction, obtaining a high reflection efficiency.

[0180] (2) It avoids beam expansion in the non - linear tuning (angle magnification) of the input angle and output angle. Since the anomalous reflection is achieved by reconstructing the wavefront phase of the plane wave at the subwavelength scale (including horizontally and vertically), beam expansion in devices such as lenses, which have a relatively large volume compared to the SLM metasurface, can be avoided.

[0181] (3) Polarization - controlled beam direction control mechanism: 1) For incident light with a polarization direction parallel to the main axis, the reflection angle of its reflected light varies non - linearly with the incident angle, enabling non - linear tuning (angle magnification) of the input angle and output angle, and thus can be used to expand the beam direction control range; 2) By changing the polarization of the incident light, the energy of the reflected light can be distributed in two different directions to achieve beam direction control, and the angle between the two reflection directions can be adjusted by changing the incident angle.

[0182] (4) It is very small in volume and very conducive to integration. The SLM is a two - dimensional metasurface device, whose longitudinal scale is much smaller than the wavelength and can be fabricated on various planar or curved surfaces; secondly, due to the use of subwavelength resonant units, the complete functions of the device can be realized in a planar space of the wavelength scale, which is conducive to large - scale integration.

[0183] It can be understood that the SLM provided in this embodiment may also be applied to other bands through reasonable parameter settings, such as the visible light band or the ultraviolet band. The band range of the SLM application is not limited here.

[0184] Based on the metasurface spatial light modulator provided in the foregoing embodiment, correspondingly, the present application also provides a beam control method. A description will be given below in conjunction with the embodiments.

[0185] Embodiment of method

[0186] See Figure 9 , which is a flowchart of a beam direction control method provided by an embodiment of the present application.

[0187] As Figure 9 shown, the method includes:

[0188] Step 901: Receive incident light using a metasurface spatial light modulator.

[0189] It should be noted that, in the embodiment of the present application, the metasurface spatial light modulator adopted is any one of the metasurface spatial light modulators SLM provided in the foregoing embodiment. Since the implementation manner of the SLM has been described in detail in the foregoing embodiment, its structure will not be elaborated herein.

[0190] Step 902: Use the metasurface spatial light modulator to anomalously reflect the light in the incident light whose polarization direction is parallel to the main axis of the metasurface spatial light modulator, and normally reflect the light in the incident light whose polarization direction is perpendicular to the main axis of the metasurface spatial light modulator.

[0191] It can be understood that since the SLM can reflect light with different polarization directions in different directions, compared with reflecting the light beam in a single direction, the beam control range can be expanded. Controlling the light beam from the polarization dimension enriches the control dimension compared with only controlling the beam direction from the wavelength dimension, and can meet more complex beam control requirements, solving the problem of a small regional coverage range.

[0192] In addition, as a possible implementation manner, before step 901 of this method is executed, it further includes:

[0193] Step 900: Control the polarization state of the incident light using a polarization control element.

[0194] In practical applications, the polarization control element can be a polarization control liquid crystal. The specific type of the polarization control element is not limited herein. Specifically, the polarization state of the incident light can be controlled according to actual needs, for example, polarization control can be performed according to requirements such as reflection direction, reflection coverage area, and reflection energy distribution.

[0195] As a possible implementation manner, when specifically implementing this step 900, the polarization state of the incident light is controlled using the polarization control element according to the target reflection coverage area and / or the target reflection energy distribution ratio.

[0196] For example, if maximizing the extraordinary reflection energy is required, the light polarized parallel to the main axis of the SLM is controlled to be incident on the metasurface SLM. If maximizing the normal reflection energy is required, the light polarized perpendicular to the main axis of the SLM is controlled to be incident on the metasurface SLM.

[0197] In addition, before performing step 900, the incident light can also be processed by a spatial router so that lights of different wavelengths in the incident light exit at different output positions of the spatial router. That is, in this implementation, the light first passes through the spatial router and exits according to the wavelength, and then the polarization state of the light is regulated by the polarization control element; the light beam exiting from the polarization control element is the light beam after polarization regulation, and this light beam is incident on the SLM and is reflected by the SLM in a normal or extraordinary reflection manner according to the polarization direction.

[0198] Based on the SLM and the beam direction control method provided in the foregoing embodiments, correspondingly, the present application also provides corresponding products based on the possible applications of this method and this SLM in different scenarios. The product implementation forms of this SLM in various scenarios are described below in conjunction with the drawings and embodiments.

[0199] Embodiment of SLM product

[0200] See Figure 10 , which is a schematic structural diagram of a beam direction control system provided by an embodiment of the present application.

[0201] As Figure 10 shown, the beam direction control system includes: the metasurface spatial light modulator SLM provided in the foregoing embodiment; and further includes: a polarization control element 101;

[0202] The polarization control element 101 is configured to control the polarization state of the light beam incident on the metasurface spatial light modulator SLM and provide the light beam to the metasurface spatial light modulator SLM;

[0203] The metasurface spatial light modulator SLM is configured to perform extraordinary reflection on the light in the light beam whose polarization direction is parallel to the main axis of the SLM, and perform normal reflection on the light in the light beam whose polarization direction is perpendicular to the main axis of the SLM.

[0204] As a possible implementation, the above beam direction control system further includes: a spatial router 102, configured to process the incident light before the light beam enters the polarization control element 101 so that lights of different wavelengths in the light beam exit at different output positions of the spatial router 102.

[0205] In one example, the spatial router 102 includes an Array Waveguide Grating Router (AWGR). The polarization control element 101 is a polarization control liquid crystal.

[0206] As a possible implementation, the above beam direction control system further includes: a first lens 103 for refracting the light beam from the polarization control element 101 to the metasurface spatial light modulator SLM;

[0207] The surface of the metasurface spatial light modulator SLM includes a point that coincides with the focal point of the first lens.

[0208] Figure 10 The shown beam direction control system can increase the polarization control dimension on the basis of wavelength control to further expand the beam direction regulation range. This system can control the beam direction in two dimensions of wavelength and polarization: 1) By changing the input light wavelength, after passing through the spatial router 102, lights of different wavelengths are emitted at different output positions of the spatial router 102, and then are emitted in different directions through the lens array of the spatial router 102, realizing the beam direction control regulated by wavelength; 2) Add a polarization control element 101 after the spatial router 102, and properly place the polarization control type metasurface SLM at the focal point of the first lens 103 to reflect the light passing through the first lens 103 once, then the beam direction can be further controlled through polarization regulation, doubling the coverage area. By adjusting each pixel unit of the polarization control element 101, the polarization of each beam can be independently and parallelly controlled, and further the direction of each beam can be independently and parallelly controlled, greatly improving the polarization control freedom degree.

[0209] See Figure 11a , which is a schematic structural diagram of a microwave photonic filter provided by an embodiment of the present application. As Figure 11a shown, the microwave photonic filter includes: the metasurface spatial light modulator SLM described in the foregoing embodiment; further includes: a light source 111, a polarization control element, an Intensity Modulator (IM), an Optical Combiner (OC), and a Photo Detector (PD).

[0210] The light source 111 is used to generate an optical carrier. In this embodiment, the light source may specifically be a Tunable Laser Source (TLS).

[0211] An IM is used to modulate an externally applied microwave signal (MWS) onto an optical carrier generated by a light source 111 to form a modulated optical signal.

[0212] An SLM is used to anomalously reflect the optical signal with a polarization direction parallel to its own main axis according to the polarization state of the optical signal to form a first reflected optical signal; and normally reflect the optical signal with a polarization direction perpendicular to its own main axis to form a second reflected optical signal.

[0213] An OC is used to receive the first reflected optical signal and the second reflected optical signal, interfere and superimpose the first reflected optical signal and the second reflected optical signal, and then provide the optically signal after interference and superposition to a PD.

[0214] A PD is used to receive the optically signal after interference and superposition and perform optoelectronic conversion.

[0215] In addition, as a possible implementation, the optically signal after the first optical signal and the second optical signal are interfered and superimposed by an OC can also be amplified by an erbium-doped fiber amplifier (EDFA) and then provided to the PD.

[0216] In this microwave photonic filter, polarization control elements can be added between two devices, such as PC1, PC2, and PC3 in Fig. 11a. In addition, before the optical signal modulated by the IM is incident on the SLM, it can also pass through a collimator 112, a polarizer 113, and a lens 114.

[0217] Figure 11a A microwave photonic filter based on the SLM provided in this application is shown. First, the MWS is input and modulated onto an optical carrier via an intensity modulator (IM) to form a modulated optical signal. After being reflected by the SLM, the optical signal becomes two paths (with different polarizations). Subsequently, the two paths of signals are respectively received and interfered and superimposed. Finally, an output microwave signal is obtained after passing through the PD. By adjusting the optical path and the optical path difference between the two reflection optical paths, the phase and the phase difference of the two paths of signals can be changed, and thus different frequency selectivities can be realized at the output end, realizing the function of a configurable microwave photonic filter. The energy distribution of the two reflected signals can be precisely controlled by changing the emission polarization state. Figure 11b For Figure 11a The measured filtering characteristics of the microwave photonic filter shown in the different free spectral range (FSR) configurations. The measured FSR can be configured between 20 GHz and 0.5 GHz, realizing a very wide configuration range.

[0218] Figure 12 This is a schematic structural diagram of a configurable multi-tap microwave photonic filter provided by an embodiment of this application.

[0219] As shown Figure 12 in the figure, the configurable multi-tap microwave photonic filter includes: the aforementioned SLM; and further includes: a tunable laser source TLS, an intensity modulator IM, a spatial router 121, a polarization control element 122, a line focusing lens 123, a reflection cavity 124, a second lens 125, and a photodetector array 126;

[0220] The TLS is used to generate an optical carrier and control the wavelength of the microwave signal;

[0221] The IM is used to modulate the microwave signal onto the optical carrier to form a modulated optical signal, and provide the modulated optical signal to the spatial router 121;

[0222] The spatial router 121 is used to process the modulated optical signal, so that lights of different wavelengths in the optical signal are emitted at different output positions of the spatial router 121;

[0223] The polarization control element 122 is used to receive the light beam emitted from the spatial router 121 and perform polarization regulation on it, so that the polarization direction of the light beam is parallel to the main axis of the SLM;

[0224] The line focusing lens 123 is used to deflect the light beam regulated by the polarization control element 122 and emit a divergent light beam to the SLM;

[0225] The SLM is used to anomalously reflect the incident divergent light beam to the reflection cavity 124;

[0226] The reflection cavity 124 is used to reflect the light beam from the metasurface spatial light modulator SLM at least once and then output it;

[0227] The second lens 125 is used to converge and transmit the light beam output from the reflection cavity 124 to the photodetector array 126;

[0228] The photodetector array 126 includes a plurality of detection units. The positions of different detection units are different and are respectively used to receive the optical signals incident at different positions and perform photoelectric conversion; different detection units respectively output microwave signals with different phase delays. Assuming that the photodetector array 126 is an M×1 array, where M is a positive integer greater than 1, then microwave signals MWS1, MWS2, MWS3, MWS4…MWSM are respectively output.

[0229] Figure 12Disclosed is a configurable multi-tap microwave photonic filter according to an embodiment of the present application. An input microwave signal (MWS) is modulated onto an optical carrier via an intensity modulator (IM) to form a modulated optical signal, and the wavelength of the optical carrier is controlled by a tunable laser source (TLS). The modulated optical signal is output from corresponding output positions after passing through a spatial router (an arrayed waveguide grating router in the example), and then the polarization of the light beam is adjusted by a polarization control liquid crystal so that the polarization direction of the light beam is consistent with the main axis direction of the metasurface SLM. The light beam after polarization adjustment passes through a line focusing lens for deflection. The line focusing lens should be placed at an appropriate distance so that the light beam is still divergent after passing through, and the divergence angle can also be controlled by adjusting the distance of the line focusing lens. The polarization control type metasurface SLM is placed at an appropriate position behind the lens. The divergent light beam after passing through the lens is reflected by the metasurface SLM and enters a reflection cavity. After multiple reflections, it is output from the other end of the reflection cavity. The output light is converged by another lens and projected onto an array of PDs. The receiving units at different positions of the array of PDs output microwave signals with different phase delays, realizing a multi-tap microwave photonic filter. The filter configuration (phase difference of each tap) can be changed by adjusting the wavelength of the optical carrier.

[0230] The specific working principle is as follows: (1) The polarization direction of the light is adjusted to the main axis direction of the metasurface SLM through the polarization control liquid crystal. At this time, only extraordinary reflection occurs on the surface of the metasurface SLM, and the non-linear relationship between the reflection angle and the incident angle has been described in the previous text. (2) The light beam reaching the metasurface SLM has a divergence angle, so the incident angles at the upper and lower ends of the light beam are different (such as Figure 12 θ i1 and θ i2)。Due to the non-linear relationship between the incident angle and the reflection angle in the abnormal reflection described above, the divergence angle of the reflected light beam will be enlarged (angle magnification). Each time the light beam reflected by the metasurface SLM is reflected in the reflection cavity, an optical path difference will be added when the upper and lower ends of the light beam reach the PD array. The final optical path difference between the upper and lower ends of the PD array is determined by the direction of the light beam entering the reflection cavity, the divergence angle of the light beam after being reflected by the metasurface SLM, and the number of reflections in the reflection cavity. Since the optical paths corresponding to the respective receiving units of the PD array are different, there is a phase difference between the respective microwave signals (MWS 1 to MWS M) output, forming a multi-tap microwave photon filter. Different filtering characteristics can be obtained by selecting different output signals for superposition. (3) By adjusting the TSL, the optical carrier wavelength can be changed, so that the light beam is output from different ports (spatial positions) of the spatial router, and after passing through the line-focusing lens, it is transmitted in different directions. The angles of the light beams in different transmission directions reaching the metasurface SLM are different, and thus the diffusion angles and directions after being reflected by the metasurface SLM are also different. Finally, the optical path difference corresponding to the upper and lower ends of the PD array is changed, thereby changing the phase difference of each tap and realizing the configuration of the filter characteristics. The non-linear relationship between the incident angle and the reflection angle in the metasurface SLM and the polarization sensitivity of the abnormal reflection are the keys to realizing the configurable multi-tap microwave photon filter.

[0231] Figure 13 Schematic diagram of a lidar detection system provided by an embodiment of the present application.

[0232] As Figure 13 , the lidar detection system includes the aforementioned metasurface spatial light modulator SLM; and further includes: lidar 131, first receiver R1, and second receiver R2;

[0233] The lidar 131 is configured to emit a detection signal to a reflection source 132. The detection purpose may be to detect a position, distance, etc. The reflection source is an object in the scenario where the lidar detection system is applied, such as a wall, an animal, etc. The specific type of the reflection source is not limited herein.

[0234] The SLM is configured to receive the echo signal reflected by the reflection source 132, perform abnormal reflection on the light with a polarization direction parallel to the main axis of the SLM in the echo signal, and perform normal reflection on the light with a polarization direction perpendicular to the main axis of the SLM in the echo signal;

[0235] The first receiver R1 is configured to receive the first optical signal abnormally reflected by the SLM;

[0236] The second receiver R2 is configured to receive the second optical signal normally reflected by the SLM.

[0237] In practical applications, the system can detect the information of the reflection source by using the first optical signal, the second optical signal, and the initially transmitted detection signal.

[0238] Figure 13 The application of the embodiment of the present application in a lidar is shown. The reflection signal of the object 132 to be detected can obtain two orthogonally polarized received signals after passing through the polarization control type metasurface SLM. After separate detection, richer reflection information can be obtained using different polarization states. It can be understood that by obtaining the rich reflection information of the first optical signal and the second optical signal, the object 132 can be detected more accurately.

[0239] As described above, it is only a specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A metasurface spatial light modulator, It is characterized in that include: A plurality of periodically extended superunits, wherein the extension direction of the superunits includes: a direction parallel to and / or perpendicular to the main axis of the metasurface spatial light modulator; the superunits include: a plurality of resonant units; the resonant units include: a bottom layer, a middle layer and a top layer; the plurality of resonant units are divided into: a first resonant unit and a second resonant unit, the top layer of the first resonant unit includes a metal block of a rectangular parallelepiped structure; the top layer of the second resonant unit includes a metal block of an I-shaped structure; the long axis of the metal block is parallel to the main axis of the metasurface spatial light modulator; The supercell has different phase responses to a first polarization state and a second polarization state; the first polarization state is parallel to the main axis of the metasurface spatial light modulator; the second polarization state is perpendicular to the main axis of the metasurface spatial light modulator; The super unit is used to perform abnormal reflection on the light of the first polarization state and normal reflection on the light of the second polarization state; When the light in the first polarization state is incident on the resonance unit, gap plasmons GPP are excited, and the GPP resonates in the resonance cavity formed by the first pair of end faces of the metal block; When the light in the second polarization state is incident on the resonance unit, the GPP is excited, and the GPP resonates in the resonance cavity formed by the second pair of end faces of the metal block; The first pair of end surfaces includes: two end surfaces of the metal block perpendicular to the long axis; the second pair of end surfaces includes: two end surfaces of the metal block parallel to the long axis.

2. The metasurface spatial light modulator according to claim 1, It is characterized in that The main axes of the resonance units are parallel to each other and to the main axis of the metasurface spatial light modulator; Wherein, the bottom layer is a metal ground, which is used for light beam reflection and resonant coupling; The middle layer is a dielectric layer, which is used to separate the metal ground and the top layer to form a gap.

3. The metasurface spatial light modulator according to claim 2, It is characterized in that The common parameters of each of the resonance units include: The length of the resonance unit is between 10 nm and 1000 nm; the length direction of the resonance unit is parallel to the long axis of the metal block; The thickness of the metal ground is greater than or equal to 10 nm; The thickness of the dielectric layer is between 10nm and 1000nm; The height of the metal block is between 10 nm and 1000 nm.

4. The metasurface spatial light modulator according to claim 1, It is characterized in that The parameters of the first resonance unit also include: The width of the first resonance unit is half of the length of the first resonance unit; The length of the metal block of the rectangular parallelepiped structure is greater than 0 and less than the length of the first resonant unit; The width of the metal block of the rectangular parallelepiped structure is greater than 0 and smaller than the width of the first resonance unit.

5. The metasurface spatial light modulator according to claim 1, It is characterized in that The parameters of the second resonance unit also include: The width of the second resonance unit is equal to the length of the second resonance unit; The first length of the I-shaped metal block is greater than 0 and less than the length of the second resonant unit; The second length of the I-shaped metal block is greater than 0 and less than half of the first length; The first width of the I-shaped metal block is greater than 0 and less than the width of the second resonant unit; The second width of the I-shaped metal block is greater than 0 and less than or equal to the first width.

6. The metasurface spatial light modulator according to claim 1, wherein, the supercell specifically includes: seven of the first resonant units and one of the second resonant units; The relative phase responses of the seven first resonant units and the second resonant unit at the first polarization state are respectively: 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°; The relative phase responses of the seven first resonant units and the second resonant unit at the second polarization state are respectively: 0°, k, k, k, k, k, k, 180°; where k represents an arbitrary phase.

7. The metasurface spatial light modulator according to claim 6, wherein, The common parameters of the seven first resonant units and one second resonant unit include: The length of the resonant unit is 500 nm; The thickness of the metal ground is 250 nm; The thickness of the dielectric layer is 100 nm; The height of the metal block is 50 nm; The widths of the seven first resonant units are respectively 250 nm; the widths of the metal blocks of the seven first resonant units are respectively 90 nm; the lengths of the metal blocks of the seven first resonant units are respectively: 0 nm, 210 nm, 252 nm, 285 nm, 308 nm, 340 n, 420 nm; The width of the second resonant unit is 500 nm; the first width of the metal block of the second resonant unit is 290 nm, the second width is 120 nm, the first length is 390 nm, and the second length is 100 nm.

8. The metasurface spatial light modulator according to claim 6 or 7, wherein, in the supercell, the number of the seven first resonant units is two; The arrangement order of the relative phase responses of the first resonant unit and the second resonant unit in the supercell at the first polarization state is: 0°，0°，45°，45°，90°，90°，135°，135°，180°，180°，225°，225°，270°，270°，315°； The arrangement direction of each resonant unit in the supercell is perpendicular to the main axis of the metasurface spatial light modulator.

9. The metasurface spatial light modulator according to claim 2, wherein, each resonant unit in the supercell is a sub-wavelength resonant unit, and the light incident on the supercell is infrared light.

10. The metasurface spatial light modulator according to claim 9, wherein, the central wavelength of the light incident on the supercell is 1550 nm.

11. The metasurface spatial light modulator according to claim 1, wherein, the supercell is specifically used to perform anomalous reflection on the light in the first polarization state according to the following formula: ； wherein, the is the length of the supercell, the is the wavelength of the light in the first polarization state, the is the extraordinary reflection angle, and the is the incident angle.

12. The metasurface spatial light modulator according to any one of claims 2-7, wherein, The metal used for the top layer and the bottom layer of the resonant unit is gold; the dielectric used for the middle layer is silicon dioxide.

13. A method for controlling the beam direction, characterized in that, the method includes: receiving incident light by using the metasurface spatial light modulator according to any one of claims 1-12; using the metasurface spatial light modulator to anomalously reflect the light in the incident light whose polarization direction is parallel to the main axis of the metasurface spatial light modulator, and to normally reflect the light in the incident light whose polarization direction is perpendicular to the main axis of the metasurface spatial light modulator.

14. The method for controlling the beam direction according to claim 13, characterized in that, before receiving the incident light, it further includes: controlling the polarization state of the incident light by using a polarization control element.

15. The method for controlling the beam direction according to claim 14, characterized in that, the controlling the polarization state of the incident light by using a polarization control element specifically includes: controlling the polarization state of the incident light by using the polarization control element according to the target reflection coverage area and / or the target reflection energy distribution ratio.

16. The method for controlling the beam direction according to claim 14 or 15, characterized in that, before controlling the polarization state of the incident light by using the polarization control element, it further includes: processing the incident light by using a spatial router so that lights of different wavelengths in the incident light are emitted at different output positions of the spatial router.

17. A beam direction control system, characterized in that, it includes: the metasurface spatial light modulator according to any one of claims 1-12; it further includes: a polarization control element; the polarization control element is used to control the polarization state of the beam incident on the metasurface spatial light modulator and supply the beam to the metasurface spatial light modulator; the metasurface spatial light modulator is used to anomalously reflect the light in the beam whose polarization direction is parallel to the main axis of the metasurface spatial light modulator, and to normally reflect the light in the beam whose polarization direction is perpendicular to the main axis of the metasurface spatial light modulator.

18. The beam direction control system according to claim 17, characterized in that, it further includes: a spatial router, which is used to process the incident light before the beam enters the polarization control element so that lights of different wavelengths in the beam are emitted at different output positions of the spatial router.

19. The beam direction control system according to claim 18, characterized in that, it further includes: a first lens, which is used to refract the beam from the polarization control element to the metasurface spatial light modulator; a point on the surface of the metasurface spatial light modulator coincides with the focus of the first lens.

20. A microwave photonic filter, characterized in that, it includes: the metasurface spatial light modulator according to any one of claims 1-12; it further includes: a light source, a polarization control element, an intensity modulator, an optical combiner and a photodetector; the light source is used to generate an optical carrier; the intensity modulator is used to modulate an externally applied microwave signal onto the optical carrier to form a modulated optical signal; The metasurface spatial light modulator is configured to anomalously reflect the optical signals with polarization directions parallel to the main axis of the metasurface spatial light modulator according to the polarization states of the optical signals, so as to form a first reflected optical signal; and normally reflect the optical signals with polarization directions perpendicular to the main axis of the metasurface spatial light modulator to form a second reflected optical signal. The optical combiner is configured to receive the first reflected optical signal and the second reflected optical signal, perform interference superposition on the first reflected optical signal and the second reflected optical signal, and then provide the optically interfered and superposed signal to the photodetector. The photodetector is configured to receive the optically interfered and superposed signal and perform optoelectronic conversion.

21. A configurable multi-tap microwave photonic filter Characterized in that it includes: The metasurface spatial light modulator according to any one of claims 1-12; it further includes: a tunable laser source, an intensity modulator, a spatial router, a polarization control element, a line focusing lens, a reflection cavity, a second lens, and a photodetector array. The tunable laser source is configured to generate an optical carrier and control the wavelength of the optical carrier. The intensity modulator is configured to modulate a microwave signal onto the optical carrier to form a modulated optical signal, and provide the modulated optical signal to the spatial router. The spatial router is configured to process the modulated optical signal so that lights with different wavelengths in the optical signal exit at different output positions of the spatial router. The polarization control element is configured to receive the light beam exiting from the spatial router and perform polarization regulation on it so that the polarization direction of the light beam is parallel to the main axis of the metasurface spatial light modulator. The line focusing lens is configured to deflect the light beam regulated by the polarization control element and emit a divergent light beam towards the metasurface spatial light modulator. The metasurface spatial light modulator is configured to anomalously reflect the incident divergent light beam into the reflection cavity. The reflection cavity is configured to reflect the light beam from the metasurface spatial light modulator at least once and then output it. The second lens is configured to converge and transmit the light beam output from the reflection cavity to the photodetector array. The photodetector array includes a plurality of detection units. The positions of different detection units are different and are respectively configured to receive optical signals incident at different positions and perform optoelectronic conversion; different detection units respectively output microwave signals with different phase delays.

22. A lidar detection system Characterized in that it includes: The metasurface spatial light modulator according to any one of claims 1-12; it further includes: a lidar, a first receiver, and a second receiver. The lidar is configured to emit a detection signal towards a reflection source. The metasurface spatial light modulator is configured to receive the echo signal reflected by the reflection source, anomalously reflect the light with a polarization direction parallel to the main axis of the metasurface spatial light modulator in the echo signal, and normally reflect the light with a polarization direction perpendicular to the main axis of the metasurface spatial light modulator in the echo signal. The first receiver is configured to receive a first optical signal anomalously reflected by the metasurface spatial light modulator; The second receiver is configured to receive a second optical signal normally reflected by the metasurface spatial light modulator; The first optical signal, the second optical signal, and the detection signal are used to detect information of the reflection source.

Images