Optical mixer based on metasurface integration and preparation method thereof

Abstract

The invention provides an optical mixer based on metasurface integration and a preparation method thereof, and belongs to the field of mixers. The mixer comprises a circularly polarized light beam splitter which comprises a first substrate, a liquid crystal structure, a second substrate and a nanorod array which are stacked in sequence; the nanorod array is used for separating the signal light and the local oscillation light into signal light left-handed rotation light, signal light right-handed rotation light, local oscillation light left-handed rotation light and local oscillation light right-handed rotation light; the liquid crystal structure is used for regulating and controlling the initial phases of the output left-handed light and right-handed light; the first multimode interference coupler is used for receiving and mixing the signal light left-rotation light output by the circularly polarized light beam splitter with the local oscillation light left-rotation light to obtain four paths of left-rotation polarized light components with different phases; and the second multimode interference coupler is used for receiving and mixing the right-handed light of the signal light output by the circularly polarized light beam splitter with the right-handed light of the local oscillation light to obtain four paths of right-handed polarized light components with different phases.

Description

Technical Field

[0001] This application belongs to the field of mixers, and in particular relates to an optical mixer based on metasurface integration and its fabrication method. Background Technology

[0002] The 90-degree optical mixer is a core component in a coherent optical communication system. It outputs four optical signals with phase differences of 0°, 90°, 180°, and 270° by coherently interfering the signal light with the local oscillator light. This provides the basis for subsequent balanced detection to extract complex amplitude information of the optical field (in-phase I and quadrature Q components).

[0003] As optical communication rates evolve towards 400G / 1.2Tbps, higher requirements are placed on the phase accuracy, bandwidth, polarization compatibility, and environmental stability of devices. Existing 90-degree optical mixers are mostly based on multimode interference (MMI) couplers or cascaded phase shifter structures of 3dB couplers, relying on the geometric parameters (length, width) of the optical waveguide or the difference in the refractive index of the material to achieve phase modulation.

[0004] In recent years, metasurface technology, with its subwavelength-scale optical field manipulation capabilities (phase, polarization, amplitude), has provided a new approach to overcoming the performance bottlenecks of traditional devices, and its process compatibility with mainstream integration platforms such as silicon-based and silicon nitride has been verified. For example, CN107861257B discloses an optical mixer based on metasurface materials, which coherently mixes the input signal light and the local oscillator light, and then outputs the signals through four output ports: S+L, SL, S+JL, and S-JL. The four signals have the same amplitude and phase differences of 0°, 180°, 90°, and 270°, respectively. The four output ports undergo corresponding signal processing through subsequent photoelectric balanced detectors. Furthermore, by using polarization multiplexing technology, the original four outputs can be increased to eight outputs. This polarization multiplexing technology uses a circularly polarized beam splitter (whose surface is composed of a periodically arranged array of silicon nanopillars) to decompose incident light with random polarization into left-handed and right-handed circularly polarized light. Through this separation process, light with different polarization states becomes an independent information carrier. In practical applications such as optical communication, left-handed and right-handed circularly polarized light carry different signals, which greatly improves the parallelism and capacity of information transmission.

[0005] However, the existing technology has the following shortcomings: (1) The integration is too low. The original structure consists of multiple discrete components such as a circularly polarized beam splitter, a spatial beam splitter, a phase shifter, and a square lens. The connection and alignment between the components are complicated. (2) The phase control is not precise. The phase adjustment method of the traditional phase shifter (a PIN diode phase shifter at the laboratory level) will cause a phase error of about 10 degrees. (3) The insertion loss is relatively large. The connection of multiple discrete components in the existing structure will introduce additional insertion loss. (4) The flexibility is poor. The existing structure often requires changing the parameters of multiple discrete components. The process is relatively cumbersome and cannot be dynamically controlled. Summary of the Invention

[0006] In view of this, this application provides an optical mixer based on metasurface integration and its fabrication method, aiming to improve the integration density of the optical mixer and avoid insertion loss. Simultaneously, it improves the phase control accuracy of the optical mixer and reduces its phase error. Furthermore, it enables the optical mixer to possess dynamic phase control capabilities.

[0007] In a first aspect, this application provides an optical mixer based on metasurface integration, comprising: A circularly polarized beam splitter comprises a substrate, a liquid crystal structure, and a nanopillar array stacked sequentially; the nanopillar array is used to separate the signal light and the local oscillator light into left-handed signal light, right-handed signal light, left-handed local oscillator light, and right-handed local oscillator light; the liquid crystal structure is used to control the initial phase of the output left-handed and right-handed light. The first multimode interference coupler is used to receive and mix the left-handed polarized light output from the circularly polarized beam splitter with the left-handed polarized light of the local oscillator to obtain four left-handed polarized light components with different phases. The second multimode interference coupler is used to receive and mix the right-handed polarized light output from the circularly polarized beam splitter with the right-handed polarized light of the local oscillator to obtain four right-handed polarized light components with different phases.

[0008] Optionally, the liquid crystal structure includes: A first transparent electrode layer, a second transparent electrode layer, and a liquid crystal layer located between the first transparent electrode layer and the second transparent electrode layer; A first alignment layer and a second alignment layer, wherein the first alignment layer is disposed between the first transparent electrode layer and the liquid crystal layer, and the second alignment layer is disposed between the second transparent electrode layer and the liquid crystal layer; The first and second transparent electrode layers are used to apply an electric field to the liquid crystal layer, control the orientation of liquid crystal molecules within the liquid crystal layer, and thereby modulate the phase of left-handed and right-handed light through the liquid crystal layer.

[0009] Optionally, the nanopillar array includes: A combination of several periodically repeating nanopillars, each nanopillar array including several nanopillars with different azimuth angles, wherein the length, width and height of the nanopillars are all within the subwavelength range.

[0010] Optionally, the nanopillars are silicon nanopillars or silicon nitride nanopillars.

[0011] Optionally, the nanopillars are prismatic or cylindrical.

[0012] Optionally, the first multimode interference coupler and the second multimode interference coupler constrain the signal light and the local oscillator light through a self-image mechanism.

[0013] Optionally, the first multimode interference coupler and the second multimode interference coupler comprise silicon nitride waveguides.

[0014] Optionally, the circularly polarized beam splitter is directly coupled to the first multimode interference coupler or coupled through a grating structure; the circularly polarized beam splitter is directly coupled to the second multimode interference coupler or coupled through a grating structure.

[0015] Secondly, this application provides a method for fabricating an optical mixer based on metasurface integration, comprising: A first substrate and a second substrate are provided, and a liquid crystal structure is formed between the first substrate and the second substrate; A nanopillar array is formed on the surface of a second substrate to obtain a circularly polarized beam splitter. A first multimode interference coupler and a second multimode interference coupler are provided. The first multimode interference coupler and the second multimode interference coupler are coupled to a circularly polarized beam splitter to obtain an optical mixer based on metasurface integration.

[0016] Optionally, the step of coupling the first multimode interference coupler and the second multimode interference coupler to the circularly polarized beam splitter includes: The first multimode interference coupler and the second multimode interference coupler are respectively placed at the focal point of the left-handed and right-handed light output from the circularly polarized beam splitter, and the first multimode interference coupler and the second multimode interference coupler are respectively directly coupled to the circularly polarized beam splitter.

[0017] The unexpected technical effects of the technical solution provided in this application are: This application provides an optical mixer based on metasurface integration, which includes a circularly polarized beam splitter, a first multimode interferometer, and a second multimode interferometer. The unexpected technical effects are: (1) By setting an alignment layer, a liquid crystal structure, and a nanopillar array in the circularly polarized beam splitter, the nanopillar array can separate the incident light into left-handed and right-handed light, while the liquid crystal structure can dynamically adjust the phase of the left-handed and right-handed light. Thus, adjusting the phase of the left-handed and right-handed light through the liquid crystal structure is simpler and does not require adjustment of complex discrete structures. (2) This application uses a highly integrated circularly polarized beam splitter, a first multimode interferometer, and a second multimode interferometer to form an optical mixer. The optical mixer includes only 3 discrete devices, with high integration, which can avoid the technical difficulties of complex connection and alignment caused by a large number of discrete components, and can also avoid the additional insertion loss introduced by the connection of multiple discrete components. (3) A multimode interference coupler (silicon nitride waveguide) is used, which covers the C+L band, has a large bandwidth, and good process tolerance. At the same time, the multimode interference coupler confines the light in the waveguide through the self-image mechanism, which reduces the scattering and radiation loss of light when it propagates in free space. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 A schematic diagram of the structure of an optical mixer based on metasurface integration provided in an embodiment of this application; Figure 2 This is a schematic diagram of the structure of a circularly polarized beam splitter provided in an embodiment of this application; Figure 3 This is a schematic diagram of a liquid crystal structure provided in an embodiment of this application; Figure 4 This is a schematic diagram of the structure of a nanopillar provided in an embodiment of this application; Figure 5 This is a schematic diagram of the structure of a nanopillar assembly provided in an embodiment of this application; Figure 6 This is a schematic diagram of a 2×4 type 90-degree optical mixer provided in one embodiment of this application; Figure 7 This is a flowchart illustrating a method for fabricating an optical mixer based on metasurface integration, as provided in an embodiment of this application.

[0020] The attached figures are labeled as follows: 11: Circularly polarized beam splitter; 111: First substrate; 112: Liquid crystal structure; 1121: First transparent electrode layer; 1122: Second transparent electrode layer; 1123: Liquid crystal layer; 1124: First alignment layer; Second alignment layer; 1125: Second substrate; 113: Nanopillar array; 1140: Nanopillar combination; 1141: Nanopillar; 1142: First nanopillar; 1143: Second nanopillar; 1144: Third nanopillar; 1145: Fourth nanopillar; 1146: Fifth nanopillar; 12: First multi-membrane interference coupler; 13: Second multi-membrane interference coupler. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0022] See Figures 1 to 3 This application provides an optical mixer based on metasurface integration, comprising: A circularly polarized beam splitter 11 includes a first substrate 111, a liquid crystal structure 112, a second substrate 113, and a nanopillar array 114 stacked sequentially. The nanopillar array 114 is used to separate the signal light and the local oscillator light into left-handed signal light, right-handed signal light, left-handed local oscillator light, and right-handed local oscillator light. The liquid crystal structure 112 is used to control the initial phase of the output left-handed and right-handed light. The first multimode interference coupler 12 is used to receive and mix the left-handed polarized light of the signal light output from the circularly polarized beam splitter 11 with the left-handed polarized light of the local oscillator to obtain four left-handed polarized light components with different phases. The second multimode interference coupler 13 is used to receive and mix the right-handed polarized light output from the circularly polarized beam splitter 11 with the right-handed polarized light of the local oscillator to obtain four right-handed polarized light components with different phases.

[0023] This application provides an optical mixer based on metasurface integration, which includes a circularly polarized beam splitter, a first multimode interferometer, and a second multimode interferometer. The unexpected technical effects are: (1) By setting an alignment layer, a liquid crystal structure, and a nanopillar array in the circularly polarized beam splitter, the nanopillar array can separate the incident light into left-handed and right-handed light, while the liquid crystal structure can dynamically adjust the phase of the left-handed and right-handed light. Thus, adjusting the phase of the left-handed and right-handed light through the liquid crystal structure is simpler and does not require adjustment of complex discrete structures. (2) This application uses a highly integrated circularly polarized beam splitter, a first multimode interferometer, and a second multimode interferometer to form an optical mixer. The optical mixer includes only 3 discrete devices, with high integration, which can avoid the technical difficulties of complex connection and alignment caused by a large number of discrete components, and can also avoid the additional insertion loss introduced by the connection of multiple discrete components. (3) A multimode interference coupler (silicon nitride waveguide) is used, which covers the C+L band, has a large bandwidth, and good process tolerance. At the same time, the multimode interference coupler confines the light in the waveguide through the self-image mechanism, which reduces the scattering and radiation loss of light when it propagates in free space.

[0024] In some examples provided in this application, the first substrate 111 and the second substrate 113 comprise silicon dioxide substrates. The substrates must be made of a light-transmitting material to ensure that they do not interfere with the signal light and the local oscillator light.

[0025] In some examples provided in this application, the liquid crystal structure 112 includes: A first transparent electrode layer 1121 and a second transparent electrode layer 1122, and a liquid crystal layer 1123 located between the first transparent electrode layer and the second transparent electrode layer; A first alignment layer 1124 and a second alignment layer 1125 are disposed between a first transparent electrode layer 1121 and a liquid crystal layer 1123, and the second alignment layer 1125 is disposed between a second transparent electrode layer 1122 and a liquid crystal layer 1123. The first transparent electrode layer 1121 and the second transparent electrode layer 1122 are used to apply an electric field to the liquid crystal layer 1123, control the orientation of liquid crystal molecules in the liquid crystal layer 1123, and thereby regulate the phase of left-handed and right-handed light through the liquid crystal layer 1123.

[0026] In some examples provided in this application, the first orientation layer 1124 and the second orientation layer 1125 include a polyimide orientation layer (PI orientation layer).

[0027] In some examples provided in this application, the working principle of the liquid crystal structure 112 is as follows: The first transparent electrode layer 1121 (typically an indium tin oxide (ITO) electrode) and the second transparent electrode layer 1121 (typically an indium tin oxide (ITO) electrode) are connected to an external adjustable power supply. By changing the applied voltage amplitude and polarity, the reorientation of liquid crystal molecules within the liquid crystal layer 1123 is controlled. At low voltage, the liquid crystal molecules within the liquid crystal layer 1123 maintain their initial parallel alignment. As the voltage increases, the molecules gradually reorient along the electric field direction, causing the effective refractive index of light in the liquid crystal layer 1123 to gradually change, thereby achieving continuous phase modulation. When no voltage is applied, the liquid crystal molecules maintain their initial alignment direction (the first and second alignment layers are used to align the liquid crystal molecules within the liquid crystal layer according to the initial alignment direction), and their birefringence effect adds a fixed additional phase delay to the entire optical path. When a voltage is applied, the electric field forces the liquid crystal molecules to reorient, and their birefringence effect changes accordingly, thereby dynamically changing the additional phase delay.

[0028] The orientation angle of the liquid crystal molecules within liquid crystal layer 1123 determines the effective refractive index for light propagation within it. When the target phase difference... When the condition is known, the relationship can be determined based on the birefringence properties of liquid crystals:

[0029] in, For the operating wavelength, The thickness of the liquid crystal layer. and These represent the extraordinary and ordinary refractive indices under voltage, respectively. By measuring the refractive index-voltage response curve of the liquid crystal material, the method for obtaining the target phase difference can be deduced. Required applied voltage .

[0030] When using the optical mixer provided in this application to mix the local oscillator light and the signal light, it is necessary to ensure that the phases of the output signal light and the local oscillator light meet the mixing requirements. If the phases of the signal light and the local oscillator light do not meet the mixing requirements, the target phase difference must be determined. According to the target phase difference The required voltage to be applied to the liquid crystal layer is calculated. By applying a voltage to the liquid crystal layer 1123, the orientation of the liquid crystal molecules within the layer is affected, thereby changing the phase of the signal light and the local oscillator light, ensuring that their phases meet the requirements for mixing. Finally, when the signal light and the local oscillator light enter the multimode interference coupler, mixing occurs.

[0031] In some examples provided in this application, the nanopillar array 114 includes: A plurality of periodically repeating nanopillars 1140 are combined, each of the nanopillars 1140 including a plurality of nanopillars 1141 with different azimuth angles, wherein the length, width and height of the nanopillars 1141 are all within the subwavelength range.

[0032] In some examples, the size of the nanopillars 1141 is limited, making them smaller. This allows for a greater number of periodically repeating nanopillar combinations 1140 to be included in the nanopillar array 1140 on a unit area of ​​the liquid crystal structure 112 surface. Each nanopillar combination 1140 includes several nanopillars 1141 with different orientation angles. By controlling the orientation angles of the nanopillars 1141, the nanopillar combination 1140 can separate the signal light and local oscillator light into left-handed and right-handed light. A higher number of nanopillar combinations 1140 per unit area improves light separation efficiency.

[0033] In some examples, the nanopillar 1141 is a silicon nanopillar or a silicon nitride nanopillar.

[0034] In some examples provided in this application, the nanopillar 1141 is prismatic or cylindrical. If a cylindrical nanopillar is used, the cylindrical nanopillar design ensures that the phase modulation and reflection / transmission efficiency of light with different polarization states are consistent on the metasurface, that is, regardless of whether the incident light is horizontally polarized, vertically polarized, left-handed / right-handed circularly polarized, or arbitrarily elliptical polarized, the output performance of the device remains stable.

[0035] See Figure 4 If cuboid nanopillars 1141 are used, their length, width, and height are all subwavelength. When light waves enter the cuboid nanopillars 1141, a phase delay occurs along the major and minor axes of the nanopillars 1141, while maintaining consistent amplitude. That is, each cuboid silicon nanopillar is equivalent to a miniature phase retarder. When the phase delay of the phase retarder is π, the phase modulation function of a half-wave plate is achieved.

[0036] The Jones matrix of a half-wave plate is , Let be the orientation angle of the long axis of the silicon nanobrick in the silicon nanobrick coordinate system.

[0037] When the incident light wave is circularly polarized, the Jones vector of the incident light wave is: , Represents the direction of rotation. The imaginary unit is given by the emitted light wave: The light waves emitted from the silicon nanobricks are transformed into circularly polarized light with opposite rotation, and an additional polarization is added. The phase delay is achieved; continuous phase modulation of the incident light wave can be realized simply by changing the rotation angle of the silicon nanobrick.

[0038] See Figure 5 To further illustrate the specific structure of the periodically repeating nanopillar assembly 1140, this application provides a schematic diagram of the nanopillar assembly 1140. Figure 4 (Top view). In some examples, the nanopillar assembly 1140 includes a first nanopillar 1142, a second nanopillar 1143, a third nanopillar 1144, a fourth nanopillar 1145, and a fifth nanopillar 1146. The first and fifth nanopillars are horizontal (along...). (Direction), the third nanopillar is vertical (along) (Direction), the second and fourth nanopillars are tilted.

[0039] Each cell of the circularly polarized beam splitter 11 has a number of linearly polarized beams arranged on its liquid crystal structure 112. Nanopillars rotating continuously in the direction of rotation, cell cells in The length in the direction is ,exist The length in the direction is , Determined by the grating constant, , Given the side length of the square cell and the orientation angle of the nanopillar. Based on the coordinates of the location Confirmed, satisfied .

[0040] When the cell is and When repeated periodically in a direction, it forms a phase grating, with a grating constant. The other diffraction orders of this grating completely disappear, leaving only The levels represent circularly polarized light with different rotation directions, combined with the grating equation. , The diffraction angle of the emitted beam. Where is the wavelength of the incident light. For diffraction orders, when At that time, the diffraction angle of the emitted beam From grating constant The only certainty: .

[0041] See you again Figure 1 In some examples provided in this application, the first multimode interference coupler 12 and the second multimode interference coupler 13 constrain the signal light and the local oscillator light through a self-image mechanism. By confining the light within the waveguide through the self-image mechanism, scattering and radiation losses during free space propagation are reduced.

[0042] In some examples provided in this application, the first multimode interference coupler 12 and the second multimode interference coupler 13 include silicon nitride waveguides.

[0043] In some examples, the circularly polarized beam splitter 11 is directly coupled to the first multimode interference coupler 12 or coupled through a grating structure; the circularly polarized beam splitter 11 is directly coupled to the second multimode interference coupler 13 or coupled through a grating structure. If coupled through a grating structure, the grating structure can be disposed on the substrate surface of the circularly polarized beam splitter.

[0044] In some examples, after the corresponding left-handed signal light and left-handed local oscillator light, right-handed signal light, and right-handed local oscillator light enter the multimode interference coupler (2×4 MMI input waveguide), it is assumed that the electric fields of the local oscillator light and the signal light are respectively... and The expression for the electric field is:

[0045]

[0046] in and These are the optical powers of the local oscillator light and the signal light, respectively. and These are the frequencies of the local oscillator light and the signal light, respectively. Similarly, and These are the phases of the local oscillator light and the signal light, respectively.

[0047] See Figure 6 Taking the most common 6-port 90-degree optical mixer as an example, and They are respectively signal light ( ) and local oscillator ( The electric field strength of ) to These represent the electric field strengths at the four output ports.

[0048] The function of a 90-degree optical mixer can be represented using an optical transfer matrix. The expressions for the electric field strength at the four output ports of the 90-degree optical mixer are as follows:

[0049]

[0050]

[0051]

[0052] The above process can be represented using an optical transfer matrix:

[0053] , The optical signal at the output port enters the in-phase detector. , The optical signal from the port enters the quadrature detector and is then processed into electrical signals.

[0054] Figure 7 A flowchart illustrating the fabrication method of a metasurface-integrated optical mixer according to an embodiment of this application. See also... Figure 7 ,include: S101, A first substrate and a second substrate are provided, and a liquid crystal structure is formed between the first substrate and the second substrate.

[0055] In some examples, step S101 includes: S1011. A first transparent electrode layer is formed on the surface of the first substrate, and a second transparent electrode layer is formed on the surface of the second substrate.

[0056] In some examples, the first and second transparent electrode layers are indium tin oxide layers, which can be prepared by magnetron sputtering.

[0057] S1012, A first orientation layer is formed on the surface of the first transparent electrode layer, and a second orientation layer is formed on the surface of the second transparent electrode layer.

[0058] In some examples, step S1012 includes: Step 1: Coat the surfaces of the first and second substrates with a polyimide (PI) solution.

[0059] A polyimide (PI) solution can be coated onto the substrate surface by spin coating.

[0060] Step 2, Pre-curing.

[0061] Perform on a hot plate or in an oven at a relatively low temperature (e.g., 80°C to 120°C for several minutes).

[0062] Pre-curing evaporates most of the organic solvent in the polyimide (PI) solution, causing the film to change from a liquid to a solid state, but the imidization reaction has not yet fully occurred. This step is also known as "soft baking".

[0063] Step 3: High-temperature baking to cure polyimide (PI).

[0064] In a high-temperature oven, the polyimide (PI) on the substrate surface is baked at a baking temperature of 180°C to 200°C for 30 to 60 minutes.

[0065] Step 4: Tribo-orient the polyimide (PI) to obtain the first orientation layer and the second orientation layer.

[0066] A substrate covered with a polyimide (PI) layer is fixed on a friction machine. A metal roller wrapped with a felt rotates at a certain speed and direction. The substrate passes under the roller at a set speed, and the fibers of the felt scrape the polyimide (PI) surface.

[0067] Tiny, aligned grooves are formed on the surface of the polyimide (PI) layer to guide the liquid crystal molecules to align along that direction.

[0068] S1013. A liquid crystal layer is formed between the first alignment layer and the second alignment layer.

[0069] In some examples, the fabrication process of the liquid crystal layer is as follows: UV-curable frame adhesive is printed at the edge of the lower structure to define the thickness of the liquid crystal layer. At the edge of the lower structure (first transparent electrode layer + first alignment layer), UV-curable frame adhesive is applied by screen printing or dispensing process to define the thickness of the liquid crystal layer (usually 3~5μm).

[0070] Vacuum infusion: The lower structure and the upper structure to be bonded (including the second orientation layer + the second transparent electrode layer) are placed together in a vacuum chamber, and liquid crystal (such as nematic liquid crystal E7) is injected into the cavity surrounded by the frame adhesive using capillary action.

[0071] Sealing and curing: After injecting liquid crystal, the frame adhesive is irradiated with ultraviolet light to cure it and seal the liquid crystal layer.

[0072] S102. A nanopillar array is formed on the surface of the second substrate to obtain a circularly polarized beam splitter.

[0073] Nanopillar arrays can be fabricated using deposition, photolithography, and etching processes. A material layer is deposited using a deposition process, and then etched using photolithography and etching processes to obtain the nanopillar array.

[0074] S103. Provide a first multimode interference coupler and a second multimode interference coupler, and couple the first multimode interference coupler and the second multimode interference coupler to a circularly polarized beam splitter to obtain an optical mixer based on metasurface integration.

[0075] In some examples, step S103 includes: The first multimode interference coupler and the second multimode interference coupler are respectively placed at the focal point of the left-handed and right-handed light output from the circularly polarized beam splitter, and the first multimode interference coupler and the second multimode interference coupler are respectively directly coupled to the circularly polarized beam splitter.

[0076] In other examples, step S103 includes: A grating structure is formed on the surface of a first substrate, and a circularly polarized beam splitter, a first multimode interference coupler, and a second multimode interference coupler are coupled through the grating structure.

[0077] Finally, it should be noted that the metasurface-type 90-degree optical mixer structure proposed in this application employs a metasurface coupled with two 2×4 MMIs. Compared to traditional spatial transmission mixer structures, the proposed new structure is smaller in size and easier to integrate; it also reduces insertion loss, offers superior performance, and allows for dynamic phase control. The metasurface-type 90-degree optical mixer structure proposed in this application is based on a silicon nitride waveguide, operates in the C+L band, has a large bandwidth, and exhibits good process tolerance; simultaneously, the MMIs confine light within the waveguide through a self-image mechanism, reducing scattering and radiation losses during free-space propagation.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optical mixer based on metasurface integration, characterized in that, include: A circularly polarized beam splitter comprises a first substrate, a liquid crystal structure, a second substrate, and a nanopillar array stacked sequentially. The nanopillar array is used to separate the signal light and the local oscillator light into left-handed signal light, right-handed signal light, left-handed local oscillator light, and right-handed local oscillator light; the liquid crystal structure is used to regulate the initial phase of the output left-handed and right-handed light. The first multimode interference coupler is used to receive and mix the left-handed polarized light output from the circularly polarized beam splitter with the left-handed polarized light of the local oscillator to obtain four left-handed polarized light components with different phases. The second multimode interference coupler is used to receive and mix the right-handed polarized light output from the circularly polarized beam splitter with the right-handed polarized light of the local oscillator to obtain four right-handed polarized light components with different phases.

2. The optical mixer based on metasurface integration according to claim 1, characterized in that, The liquid crystal structure includes: A first transparent electrode layer, a second transparent electrode layer, and a liquid crystal layer located between the first transparent electrode layer and the second transparent electrode layer; A first alignment layer and a second alignment layer, wherein the first alignment layer is disposed between the first transparent electrode layer and the liquid crystal layer, and the second alignment layer is disposed between the second transparent electrode layer and the liquid crystal layer; The first and second transparent electrode layers are used to apply an electric field to the liquid crystal layer, control the orientation of liquid crystal molecules within the liquid crystal layer, and thereby modulate the phase of left-handed and right-handed light through the liquid crystal layer.

3. The optical mixer based on metasurface integration according to claim 1 or 2, characterized in that, Nanopillar arrays include: A combination of several periodically repeating nanopillars, each nanopillar array including several nanopillars with different azimuth angles, wherein the length, width and height of the nanopillars are all within the subwavelength range.

4. The optical mixer based on metasurface integration according to claim 3, characterized in that, The nanopillars are silicon nanopillars or silicon nitride nanopillars.

5. The optical mixer based on metasurface integration according to claim 3, characterized in that, The nanopillars are prismatic or cylindrical.

6. The optical mixer based on metasurface integration according to claim 1 or 2, characterized in that, The first multimode interference coupler and the second multimode interference coupler constrain the signal light and the local oscillator light through a self-image mechanism.

7. The optical mixer based on metasurface integration according to claim 6, characterized in that, The first multimode interference coupler and the second multimode interference coupler both include silicon nitride waveguides.

8. The optical mixer based on metasurface integration according to claim 6, characterized in that, The circularly polarized beam splitter is directly coupled to the first multimode interference coupler or coupled through a grating structure; the circularly polarized beam splitter is directly coupled to the second multimode interference coupler or coupled through a grating structure.

9. A method for fabricating an optical mixer based on metasurface integration, characterized in that, include: A first substrate and a second substrate are provided, and a liquid crystal structure is formed between the first substrate and the second substrate; A nanopillar array is formed on the surface of a second substrate to obtain a circularly polarized beam splitter. A first multimode interference coupler and a second multimode interference coupler are provided. The first multimode interference coupler and the second multimode interference coupler are coupled to a circularly polarized beam splitter to obtain an optical mixer based on metasurface integration.

10. The method for fabricating an optical mixer based on metasurface integration according to claim 9, characterized in that, The steps of coupling the first multimode interference coupler and the second multimode interference coupler to the circularly polarized beam splitter respectively include: The first multimode interference coupler and the second multimode interference coupler are respectively placed at the focal point of the left-handed and right-handed light output from the circularly polarized beam splitter, and the first multimode interference coupler and the second multimode interference coupler are respectively directly coupled to the circularly polarized beam splitter.

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