A few-mode fiber mode multiplexer and demultiplexer based on metasurface

Abstract

This application relates to a few-mode fiber mode multiplexer and demultiplexer based on a metasurface, comprising a first polarizing beam splitter prism, a metasurface, and a polarization control element. The first polarizing beam splitter has a first port and a second port. The polarization control element and the metasurface are configured to: perform polarization modulation and multiple phase modulation on linearly polarized light transmitted from the first port with a first polarization direction, and reflect linearly polarized light with a second polarization direction from the second port, wherein the first direction and the second direction are perpendicular. This application can solve the problem of alignment difficulties between phase plates in related technologies.

Description

Technical Field

[0001] This application relates to the field of optical communication technology, and in particular to a few-mode fiber mode multiplexer and demultiplexer based on metasurface. Background Technology

[0002] Currently, spatial division multiplexing (SDM) and mode division multiplexing (MDM) technologies have become methods for increasing capacity in optical fiber communication systems. For the output optical field of few-mode fibers, before demodulating the signal, it is necessary to separate the optical signals of different modes. The current approach is to first divide the output optical field of the few-mode fiber into three equal parts, and then use a spatial light modulator to guide one mode of light into the single-mode fiber or receiver in each optical path. The drawback of this method is that it uses many large-sized devices, and loses two-thirds of the optical energy while receiving each mode of light.

[0003] In recent years, a fiber mode demultiplexer based on multi-layer cascaded phase plates has been proposed, which can solve the above problems. However, regardless of the type of phase plate used, the alignment between the phase plates remains a challenge in the fabrication of this device. Summary of the Invention

[0004] This application provides a few-mode fiber mode multiplexer and demultiplexer based on metasurfaces to solve the problem of alignment difficulties between phase plates in related technologies.

[0005] This application provides a few-mode fiber mode multiplexer and demultiplexer based on a metasurface, which includes:

[0006] The first polarizing beam splitter has a first port and a second port;

[0007] Metasurface;

[0008] And a polarization control element, which, together with the metasurface, is configured to: perform polarization modulation and multiple phase modulation on linearly polarized light transmitted from the first port with a polarization direction of a first direction, and reflect linearly polarized light with a polarization direction of a second direction from the second port, wherein the first direction is perpendicular to the second direction.

[0009] In some embodiments, the polarization control element includes a Faraday rotator and a first reflector, and along the polarization light transmission direction, the first polarization beam splitter, the metasurface, the Faraday rotator and the first reflector are arranged sequentially at intervals, and the Faraday rotator is also equipped with a magnetic field generating device.

[0010] In some embodiments, the metasurface is a single-layer metasurface, comprising a substrate and nanobricks disposed on one of the walls of the substrate, wherein the structural symmetry of the nanobricks is configured such that the polarization direction of linearly polarized light transmitted from the metasurface remains unchanged; the Faraday rotator is used to perform 45° polarization modulation on the linearly polarized light transmitted through the Faraday rotator; and the first mirror is used to reflect the linearly polarized light transmitted from the Faraday rotator back to the Faraday rotator.

[0011] Alternatively, the metasurface is a bilayer metasurface, comprising a substrate and nanobricks disposed on two walls of the substrate. The structural symmetry of the nanobricks is configured such that linearly polarized light transmitted from the metasurface undergoes 90° polarization modulation. The Faraday rotator is used to perform 45° polarization modulation on the linearly polarized light transmitted through the Faraday rotator, and the first mirror is used to reflect the linearly polarized light transmitted from the Faraday rotator back to the Faraday rotator.

[0012] In some embodiments, the polarization control element and the first polarization beam splitter are located on opposite sides of the metasurface, and the polarization control element includes a first reflector, a half-wave plate, a second reflector, a third reflector, and a second polarization beam splitter that are sequentially spaced and arranged in a ring.

[0013] The metasurface is a single-layer metasurface, comprising a substrate and nanobricks disposed on one of the walls of the substrate. The structural symmetry of the nanobricks is configured such that the polarization direction of linearly polarized light transmitted from the metasurface remains unchanged. A second polarizing beam splitter is used to transmit the linearly polarized light transmitted from the metasurface to a third reflecting mirror. The third reflecting mirror and the second reflecting mirror are jointly configured to reflect the linearly polarized light to a half-wave plate. The half-wave plate is used to perform 90° polarization modulation on the linearly polarized light transmitted through the half-wave plate, and the light is reflected to the metasurface via the first reflecting mirror and the second polarizing beam splitter.

[0014] In some embodiments, the polarization control element and the first polarization beam splitter are located on opposite sides of the metasurface, and the polarization control element includes a first reflector, a half-wave plate, a second reflector, a third reflector, and a second polarization beam splitter that are sequentially spaced and arranged in a ring.

[0015] The metasurface is a bilayer metasurface, comprising a substrate and nanobricks disposed on two walls of the substrate. The structural symmetry of the nanobricks is configured such that linearly polarized light transmitted from the metasurface undergoes 90° polarization modulation. A second polarizing beam splitter is used to reflect the linearly polarized light transmitted from the metasurface to a first mirror. The first mirror is used to reflect the linearly polarized light to a half-wave plate. The half-wave plate is used to perform 90° polarization modulation on the linearly polarized light transmitted through the half-wave plate and direct it toward a second mirror. The second and third mirrors are jointly configured to reflect the linearly polarized light to the second polarizing beam splitter. The second polarizing beam splitter is also used to transmit the reflected linearly polarized light back to the metasurface.

[0016] In some embodiments, the polarization control element includes a quarter-wave plate and a reflective element, and the first polarization beam splitter, the quarter-wave plate, the metasurface, and the reflective element are arranged sequentially along the polarization light transmission direction.

[0017] In some embodiments, the metasurface is a single-layer metasurface, comprising a substrate and nanobricks disposed on the wall of the substrate near the quarter-wave plate. The reflective element is a reflective layer made of a metallic material, disposed on the wall of the substrate away from the nanobricks. The structural symmetry of the nanobricks is configured such that the polarization direction of circularly polarized light transmitted from the nanobricks is reversed. The quarter-wave plate is used to modulate the polarization between circularly polarized and linearly polarized light transmitted through the quarter-wave plate. The reflective layer is used to reflect the circularly polarized light incident from the nanobricks into the substrate back to the nanobricks.

[0018] Alternatively, the metasurface is a double-layer metasurface, comprising a substrate and nanobricks disposed on two walls of the substrate. The reflecting element is a fourth mirror, which is arranged at intervals from the metasurface. The structural symmetry of the nanobricks is configured such that the polarization direction of circularly polarized light transmitted from the metasurface remains unchanged. The quarter-wave plate is used to modulate the polarization between circularly polarized and linearly polarized light transmitted through the quarter-wave plate. The fourth mirror is used to reflect the circularly polarized light transmitted from the metasurface back to the metasurface.

[0019] In some embodiments, the metasurface is a bilayer metasurface, which includes a substrate and nanobricks disposed on two walls of the substrate;

[0020] The polarization control element includes a photoresist layer and a reflective element, wherein the reflective element is a reflective layer made of metal.

[0021] Furthermore, along the direction of polarized light transmission, the first polarizing beam splitter, the metasurface, the photoresist layer, and the reflective element are arranged sequentially, with the nanobrick and the reflective element respectively connected to both sides of the photoresist layer;

[0022] The structural symmetry of the nanobrick is configured such that the polarization direction of linearly polarized light transmitted from the nanobrick near the first polarizing beam splitter on the metasurface remains unchanged, and the linearly polarized light transmitted in the substrate is polarized by 90° after being reflected by another wall surface of the substrate on which the nanobrick is disposed.

[0023] In some embodiments, the metasurface is a bilayer metasurface, which includes a substrate and nanobricks disposed on two walls of the substrate;

[0024] The polarization control element includes a quarter-wave plate, a photoresist layer, and a reflective element, wherein the reflective element is a reflective layer made of metal.

[0025] Furthermore, along the direction of polarization light transmission, the first polarization beam splitter, quarter-wave plate, metasurface, photoresist layer and reflective element are arranged in sequence, with nanobricks and reflective elements connected to both sides of the photoresist layer, respectively.

[0026] The structural symmetry of the nanobrick is configured such that the polarization direction of circularly polarized light transmitted from the nanobrick near the first polarizing beam splitter on the metasurface is reversed, and the circularly polarized light transmitted in the substrate is reflected by another wall surface of the substrate on which the nanobrick is disposed, and then polarization modulation with reversed polarization direction is performed. The quarter-wave plate is used to perform polarization modulation between circularly polarized light and linearly polarized light transmitted through the quarter-wave plate.

[0027] In some embodiments, when the polarized light in the input first port is a multi-positionally independent single-mode optical field, the metasurface-based few-mode fiber mode multiplexer and demultiplexer is a multiplexer.

[0028] When the polarized light in the input first port is a multimode optical field with multiple overlapping positions, the few-mode fiber mode multiplexer and demultiplexer based on metasurface is a demultiplexer.

[0029] The beneficial effects of the technical solution provided in this application include:

[0030] This application provides a few-mode fiber mode multiplexer and demultiplexer based on a metasurface. The principle of this application is as follows: by utilizing the different forward and reverse propagation characteristics of the metasurface, the metasurface and polarization control element are used together to allow the light field to pass through the metasurface sequentially from the front and back sides to achieve multiple phase control, thereby realizing mode multiplexing or demultiplexing. Since this device only uses a single metasurface to achieve multiple phase modulations, it simplifies the traditional optical path that requires multiple phase plates cascaded, reduces the size of the device, and reduces the difficulty of optical path alignment, making it suitable for widespread application.

[0031] To achieve high-efficiency optical mode multiplexing or demultiplexing, the output optical field of the optical fiber needs to pass through multiple independent phase control elements in sequence. The alignment accuracy between these phase control elements determines the overall performance of the device. This application uses a metasurface to replace the traditional multiple phase control elements to achieve multiple phase control operations without the need for alignment between multiple phase control elements. Therefore, the efficiency of optical mode multiplexing or demultiplexing can be improved. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of a multiplexer and demultiplexer provided in the first embodiment of this application;

[0034] Figure 2 This is a schematic diagram of a multiplexer and demultiplexer provided in the second embodiment of this application;

[0035] Figure 3 This is a schematic diagram of a multiplexer and demultiplexer provided in the third embodiment of this application;

[0036] Figure 4 This is a schematic diagram of a multiplexer and demultiplexer provided in the fourth embodiment of this application;

[0037] Figure 5 This is a schematic diagram of a multiplexer and demultiplexer provided in the fifth embodiment of this application;

[0038] Figure 6 This is a schematic diagram of a multiplexer and demultiplexer provided in the sixth embodiment of this application;

[0039] Figure 7 This is a schematic diagram of a multiplexer and demultiplexer provided in the seventh embodiment of this application;

[0040] Figure 8 This is a schematic diagram of a multiplexer and demultiplexer provided in the eighth embodiment of this application;

[0041] Figure 9 This is a schematic diagram of the nanobricks provided in the embodiments of this application in the XYZ rectangular coordinate system.

[0042] In the figure: 1. First polarizing beam splitter; 2. First port; 3. Second port; 4. Metasurface; 40. Substrate; 41. Nanobrick; 5. Faraday rotator; 6. First mirror; 7. Half-wave plate; 8. Second mirror; 9. Third mirror; 10. Second polarizing beam splitter; 11. Quarter-wave plate; 12. Reflective element; 13. Photoresist layer. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] Combination Figure 1 As shown, this application provides a few-mode fiber mode multiplexer and demultiplexer based on a metasurface. The multiplexer and demultiplexer includes a first polarizing beam splitter 1, a metasurface 4, and a polarization control element. The first polarizing beam splitter 1 has a first port 2 and a second port 3. After the optical signal in the few-mode fiber enters the first polarizing beam splitter 1, part of it is reflected and part is transmitted. The transmitted polarized light continues to be directed toward the metasurface 4. The polarization control element and the metasurface 4 are configured to perform polarization modulation and multiple phase modulation on the linearly polarized light transmitted from the first port 2 with a polarization direction of the first direction, and reflect the linearly polarized light with a polarization direction of the second direction from the second port 3. The first direction and the second direction are perpendicular.

[0045] The principle of this application is as follows: by utilizing the different forward and reverse propagation characteristics of a metasurface, the metasurface and polarization control element are used together to enable the light field to pass through the metasurface sequentially from the front and back sides to achieve multiple phase control, thereby realizing mode multiplexing or demultiplexing. Since this device only uses one metasurface to achieve multiple phase modulations, it simplifies the traditional optical path that requires multiple phase plates to be cascaded, reduces the size of the device, and reduces the difficulty of optical path alignment, making it suitable for widespread application.

[0046] To achieve high-efficiency optical mode multiplexing or demultiplexing, the output optical field of the optical fiber needs to pass through multiple independent phase control elements in sequence. The alignment accuracy between these phase control elements determines the overall performance of the device. This application uses a metasurface to replace the traditional multiple phase control elements to achieve multiple phase control operations without the need for alignment between multiple phase control elements. Therefore, the efficiency of optical mode multiplexing or demultiplexing can be improved.

[0047] To achieve the aforementioned multiplexing and demultiplexing, this application also provides several implementation methods. In these implementation methods, the specific structure of the polarization control element is related to the structure of the metasurface 4.

[0048] See Figure 1 As shown, in the first embodiment, the polarization control element includes a Faraday rotator 5 and a first reflector 6. Along the direction of polarized light transmission, the first polarizing beam splitter 1, the metasurface 4, the Faraday rotator 5, and the first reflector 6 are arranged sequentially at intervals. The Faraday rotator 5 is also equipped with a magnetic field generating device. The metasurface 4 is a single-layer metasurface, specifically a transmissive single-layer metasurface. The single-layer metasurface includes a substrate 40 and nano-bricks 41 disposed on one of the walls of the substrate 40. Multiple nano-bricks 41 are arranged in an array to form a nano-brick array. The structural symmetry of the nano-bricks 41 is configured such that the polarization direction of the linearly polarized light transmitted from the metasurface 4 remains unchanged. The Faraday rotator 5 is used to perform 45° polarization modulation on the linearly polarized light transmitted from the Faraday rotator 5. The first reflector 6 is used to reflect the linearly polarized light transmitted from the Faraday rotator 5 back to the Faraday rotator 5.

[0049] See Figure 2 As shown, in the second embodiment, the polarization control element includes a Faraday rotator 5 and a first reflector 6. Along the direction of polarized light transmission, the first polarizing beam splitter 1, the metasurface 4, the Faraday rotator 5, and the first reflector 6 are arranged sequentially at intervals. The Faraday rotator 5 is also equipped with a magnetic field generating device. The metasurface 4 is a double-layer metasurface, specifically a transmissive double-layer metasurface. The double-layer metasurface includes a substrate 40 and nano-bricks 41 disposed on two walls of the substrate 40. Multiple nano-bricks 41 are arranged in an array to form a nano-brick array. The structural symmetry of the nano-bricks 41 is configured such that the linearly polarized light transmitted from the metasurface 4 undergoes 90° polarization modulation. The Faraday rotator 5 is used to perform 45° polarization modulation on the linearly polarized light transmitted from the Faraday rotator 5. The first reflector 6 is used to reflect the linearly polarized light transmitted from the Faraday rotator 5 back to the Faraday rotator 5.

[0050] See Figure 3As shown, in the third embodiment, the polarization control element and the first polarization beam splitter 1 are located on opposite sides of the metasurface 4. The polarization control element includes a first reflecting mirror 6, a half-wave plate 7, a second reflecting mirror 8, a third reflecting mirror 9, and a second polarization beam splitter 10 arranged in a ring shape at intervals. The metasurface 4 is a single-layer metasurface and a transmissive single-layer metasurface. The single-layer metasurface includes a substrate 40 and a nano-brick 41 disposed on one of the walls of the substrate 40. The structural symmetry of the nano-brick 41 is configured such that the polarization direction of the linearly polarized light transmitted from the metasurface 4 remains unchanged. The second polarization beam splitter 10 is used to transmit the linearly polarized light transmitted from the metasurface 4 to the third reflecting mirror 9. The third reflecting mirror 9 and the second reflecting mirror 8 are jointly configured to reflect the linearly polarized light to the half-wave plate 7. The half-wave plate 7 is used to perform 90° polarization modulation on the linearly polarized light transmitted through the half-wave plate 7, and then reflects it to the metasurface 4 via the first reflecting mirror 6 and the second polarization beam splitter 10.

[0051] See Figure 4 As shown, in the fourth embodiment, the polarization control element and the first polarization beam splitter 1 are located on opposite sides of the metasurface 4. The polarization control element includes a first reflecting mirror 6, a half-wave plate 7, a second reflecting mirror 8, a third reflecting mirror 9, and a second polarization beam splitter 10, which are sequentially spaced and arranged in a ring shape. The metasurface 4 is a double-layer metasurface, and it is a transmissive double-layer metasurface. The double-layer metasurface includes a substrate 40 and nano-bricks 41 disposed on two walls of the substrate 40. There are multiple nano-bricks 41, which are arranged in an array to form a nano-brick array. The structural symmetry of the nano-bricks 41 is configured. The purpose is to: modulate the linearly polarized light transmitted from the metasurface 4 by 90°; the second polarizing beam splitter 10 is used to reflect the linearly polarized light transmitted from the metasurface 4 to the first reflecting mirror 6, the first reflecting mirror 6 is used to reflect the linearly polarized light to the half-wave plate 7, the half-wave plate 7 is used to modulate the linearly polarized light transmitted through the half-wave plate 7 by 90° and direct it to the second reflecting mirror 8, the second reflecting mirror 8 and the third reflecting mirror 9 are configured together to reflect the linearly polarized light to the second polarizing beam splitter 10, and the second polarizing beam splitter 10 is also used to transmit the reflected linearly polarized light back to the metasurface 4.

[0052] In the third and fourth embodiments described above, the arrangement of the polarization control elements can be exactly the same. For example, see [link to example]. Figure 3 and Figure 4 As shown, the beam-splitting surface of the second polarizing beam splitter 10, the beam-splitting surface of the first polarizing beam splitter 1, the first reflecting mirror 6, and the third reflecting mirror 9 are parallel; the first reflecting mirror 6 and the second reflecting mirror 8 are perpendicular, and the half-wave plate 7 is arranged at a 45° angle to the first reflecting mirror 6.

[0053] The aforementioned beam-splitting surface refers to the surface of a beam-splitting prism that can transmit and reflect light after it enters.

[0054] See Figure 5 As shown, in the fifth embodiment, the polarization control element includes a quarter-wave plate 11 and a reflective element 12, and the first polarization beam splitter 1, the quarter-wave plate 11, the metasurface 4 and the reflective element 12 are arranged sequentially along the polarization light transmission direction. The metasurface 4 is a single-layer metasurface, which includes a substrate 40 and nano-bricks 41 disposed on the wall of the substrate 40 near the quarter-wave plate 11. There are multiple nano-bricks 41, which are arranged in an array to form a nano-brick array. The reflective element 12 is a reflective layer made of metal, such as gold or aluminum. The reflective layer is disposed on the wall of the substrate 40 away from the nano-bricks 41, so that the metasurface 4 becomes a reflective single-layer metasurface. The structural symmetry of the nano-bricks 41 is configured such that the polarization direction of the circularly polarized light transmitted from the nano-bricks 41 is reversed. The quarter-wave plate 11 is used to modulate the polarization between circularly polarized light and linearly polarized light transmitted through the quarter-wave plate 11. The reflective layer is used to reflect the circularly polarized light that enters the substrate 40 from the nano-bricks 41 back to the nano-bricks 41.

[0055] See Figure 6 As shown, in the sixth embodiment, the polarization control element includes a quarter-wave plate 11 and a reflective element 12. Along the direction of polarization light transmission, the first polarization beam splitter 1, the quarter-wave plate 11, the metasurface 4, and the reflective element 12 are arranged sequentially. The metasurface 4 is a double-layer metasurface, specifically a transmissive double-layer metasurface. The double-layer metasurface includes a substrate 40 and nano-bricks 41 disposed on two walls of the substrate 40. Multiple nano-bricks 41 are arranged in an array to form a nano-brick array. The reflective element 12 is a fourth reflector, which is spaced apart from the metasurface 4. The structural symmetry of the nano-bricks 41 is configured to maintain the polarization direction of the circularly polarized light transmitted from the metasurface 4. The quarter-wave plate 11 is used to modulate the polarization between circularly polarized and linearly polarized light transmitted through the quarter-wave plate 11. The fourth reflector is used to reflect the circularly polarized light transmitted from the metasurface 4 back to the metasurface 4.

[0056] See Figure 7As shown, in the seventh embodiment, the metasurface 4 is a double-layer metasurface, which includes a substrate 40 and nano-bricks 41 disposed on two walls of the substrate 40. Multiple nano-bricks 41 are arranged in an array to form a nano-brick array. The polarization control element includes a photoresist layer 13 and a reflective element 12. The reflective element 12 is a reflective layer made of a metal material, such as gold or aluminum. The photoresist layer 13 can be made of Su-8 material. Along the polarization light transmission direction, the first polarization beam splitter 1 and the metasurface... The surface 4, photoresist layer 13 and reflective element 12 are arranged in sequence. The photoresist layer 13 is connected to the nanobrick 41 and the reflective element 12 on both sides, so that the metasurface 4 becomes a reflective double-layer metasurface. The structural symmetry of the nanobrick 41 is configured such that the polarization direction of the linearly polarized light transmitted from the nanobrick 41 near the first polarizing beam splitter 1 on the metasurface 4 remains unchanged, and the linearly polarized light transmitted in the substrate 40 is reflected by another wall surface of the substrate 40 on which the nanobrick 41 is provided, and then undergoes 90° polarization modulation.

[0057] See Figure 8 As shown, in the eighth embodiment, the metasurface 4 is a double-layer metasurface, which includes a substrate 40 and nano-bricks 41 disposed on two walls of the substrate 40. Multiple nano-bricks 41 are arranged in an array to form a nano-brick array. The polarization control element includes a quarter-wave plate 11, a photoresist layer 13, and a reflective element 12. The reflective element 12 is a reflective layer made of a metal material, such as gold or aluminum. The photoresist layer 13 can be made of SU-8 material. Along the polarization light transmission direction, the first polarization beam splitter 1, the quarter-wave plate 11, the metasurface 4, the photoresist layer 13, and the reflective element... The photoresist layer 13 is arranged in sequence, with the nano-bricks 41 and the reflective element 12 connected to both sides of the photoresist layer 13, so that the metasurface 4 becomes a reflective double-layer metasurface. The structural symmetry of the nano-bricks 41 is configured such that the polarization direction of the circularly polarized light transmitted from the nano-bricks 41 near the first polarizing beam splitter 1 on the metasurface 4 is reversed, and the circularly polarized light transmitted in the substrate 40 is reflected by another wall surface of the substrate 40 on which the nano-bricks 41 are disposed, and then polarization modulation with the polarization direction reversed is performed. The quarter-wave plate 11 is used to perform polarization modulation between circularly polarized light and linearly polarized light transmitted through the quarter-wave plate 11.

[0058] It should be noted that in the first to eighth embodiments described above, when the polarized light input to the first port 2 is a single-mode optical field with multiple independent positions, the few-mode fiber mode multiplexer and demultiplexer based on the metasurface is a multiplexer; while when the polarized light input to the first port 2 is a multimode optical field with multiple overlapping positions, the few-mode fiber mode multiplexer and demultiplexer based on the metasurface is a demultiplexer.

[0059] For linearly polarized light, its polarization direction remains unchanged after passing through the aforementioned mirror or reflective layer. For circularly polarized light, its polarization direction is reversed after passing through the aforementioned mirror or reflective layer.

[0060] For linearly polarized light, after passing through a half-wave plate, its polarization direction will be modulated by 90°.

[0061] For polarized light, after passing through a quarter-wave plate, modulation occurs between left-handed circularly polarized light and horizontally linearly polarized light, as well as between right-handed circularly polarized light and vertically linearly polarized light. For example, left-handed circularly polarized light is modulated into horizontally linearly polarized light after passing through a quarter-wave plate, and horizontally linearly polarized light is modulated into left-handed circularly polarized light after passing through a quarter-wave plate.

[0062] Combination Figures 1 to 6 As shown, in the first to sixth embodiments described above, by designing the structural symmetry of each nanobrick in the metasurface, the multiplexer and demultiplexer perform two independent phase modulations on the output light of the optical fiber. In the first, second, third, fourth, and sixth embodiments, forward transmission (transmission from left to right in the figure) passes through the metasurface and reverse transmission (transmission from right to left in the figure) passes through the metasurface, respectively. In the fifth embodiment, forward transmission (transmission from left to right in the figure) passes through the nanobrick on the left wall of the metasurface (the nanobrick on the left wall is called the first metasurface layer) and is reflected by the reflective layer on the right wall of the metasurface, respectively.

[0063] Combination Figure 1 and Figure 3 As shown, the transmittance of forward-propagating vertical (horizontal) linearly polarized light and the transmittance of reverse-propagating horizontal (vertical) linearly polarized light on the metasurface in the first and third embodiments are completely different.

[0064] Combination Figure 2 and Figure 4 As shown, in the second and fourth embodiments, the transmittance of forward-propagating vertical (horizontal) linearly polarized light and the conversion rate of reverse-propagating horizontal (vertical) linearly polarized light on the metasurface are completely different.

[0065] Combination Figure 5 As shown, in the fifth embodiment, the transmittance of forward-propagating left-handed (right-handed) circularly polarized light and the conversion rate of reverse-propagating right-handed (left-handed) circularly polarized light on the metasurface are completely different.

[0066] Combination Figure 6 As shown, in the sixth embodiment, the transmittance of forward-propagating left-handed (right-handed) circularly polarized light and the transmittance of reverse-propagating right-handed (left-handed) circularly polarized light on the metasurface are completely different.

[0067] In the seventh and eighth embodiments described above, by designing the structural symmetry of each nanobrick in the metasurface, the multiplexer and demultiplexer perform three independent phase modulations on the output light of the optical fiber: forward transmission (transmission from left to right in the figure) through the nanobrick on the left wall of the metasurface (the nanobrick on the left wall is called the first layer of the metasurface), reflection by the nanobrick on the right wall of the metasurface (the nanobrick on the right wall is called the second layer of the metasurface), and reverse transmission (transmission from right to left in the figure) through the nanobrick on the left wall of the metasurface (the first layer of the metasurface).

[0068] Combination Figure 7 As shown in the seventh embodiment, for the first metasurface, the transmittance of forward-propagating vertical (horizontal) linearly polarized light and the transmittance of reverse-propagating horizontal (vertical) linearly polarized light are completely different. For the second metasurface, efficient conversion of vertical (horizontal) linearly polarized light to horizontal (vertical) linearly polarized light can be achieved, and the phase distribution of reflected light can be controlled at the same time.

[0069] Combination Figure 8 As shown in the eighth embodiment, for the first metasurface, the conversion rate of forward-propagating left-handed (right-handed) circularly polarized light and the conversion rate of reverse-propagating right-handed (left-handed) circularly polarized light are completely different. For the second metasurface, efficient conversion of left-handed (right-handed) circularly polarized light to right-handed (left-handed) circularly polarized light can be achieved, and the phase distribution of reflected light can be controlled at the same time.

[0070] It should be noted that the following steps can be taken when designing metasurfaces: First, the phase distribution on each phase plate is calculated using wavefront matching or deep neural network algorithms; then, the phase changes generated by metasurface units of different sizes and structures are calculated using electromagnetic wave simulation software; finally, the arrangement of cubes on the specific metasurface is obtained according to the required phase distribution.

[0071] The structural symmetry of nanobricks includes two types: rotational symmetry and mirror symmetry. Rotational symmetry means that the structure remains identical to the original structure after being rotated around a certain axis by a certain angle. Mirror symmetry means that the structure remains identical to the original structure after being mirrored with respect to a certain plane. In design, combining... Figure 9 As shown, the structural symmetry of the nanobricks in the above embodiments should satisfy the following conditions:

[0072]

[0073]

[0074] A rectangular coordinate system XYZ is established with the length of the nanobrick as the Z-axis, the width as the Y-axis, and the height as the Z-axis. Figure 9 This is a schematic diagram of a nanobrick on a metasurface in the XYZ Cartesian coordinate system, where the Z-axis is the direction of light transmission and is perpendicular to the substrate of the metasurface.

[0075] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0076] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0077] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A plasmonic mode multiplexer and demultiplexer based on a superstructured surface, characterized in that, It comprises: a first polarization beam splitter prism (1) having a first port (2) and a second port (3); a metasurface (4); and a polarization control element, which is configured together with the metasurface (4) to perform polarization modulation and multiple phase modulation on linearly polarized light with a first direction of polarization transmitted from the first port (2) and reflect linearly polarized light with a second direction of polarization from the second port (3), the first direction being perpendicular to the second direction.

2. The metasurface-based few-mode fiber mode multiplexer and demultiplexer according to claim 1, wherein: the polarization control element comprises a Faraday rotator (5) and a first mirror (6), and the first polarization beam splitter prism (1), the metasurface (4), the Faraday rotator (5) and the first mirror (6) are sequentially and spacedly arranged along the direction of polarization light transmission, and the Faraday rotator (5) is further provided with a magnetic field generating device.

3. The metasurface-based few-mode fiber mode multiplexer and demultiplexer according to claim 2, wherein: the metasurface (4) is a single-layer metasurface, which comprises a substrate (40) and nano bricks (41) arranged on one wall surface of the substrate (40), and the structural symmetry of the nano bricks (41) is configured to keep the polarization direction of linearly polarized light transmitted from the metasurface (4) unchanged; the Faraday rotator (5) is used to perform 45° polarization modulation on linearly polarized light transmitted through the Faraday rotator (5), and the first mirror (6) is used to reflect linearly polarized light transmitted from the Faraday rotator (5) to the Faraday rotator (5); or, the metasurface (4) is a double-layer metasurface, which comprises a substrate (40) and nano bricks (41) arranged on two wall surfaces of the substrate (40), and the structural symmetry of the nano bricks (41) is configured to perform 90° polarization modulation on linearly polarized light transmitted from the metasurface (4); the Faraday rotator (5) is used to perform 45° polarization modulation on linearly polarized light transmitted through the Faraday rotator (5), and the first mirror (6) is used to reflect linearly polarized light transmitted from the Faraday rotator (5) to the Faraday rotator (5).

4. The metasurface-based few-mode fiber mode multiplexer and demultiplexer according to claim 1, wherein: the polarization control element and the first polarization beam splitter prism (1) are respectively located on two sides of the metasurface (4), and the polarization control element comprises a first mirror (6), a half-wave plate (7), a second mirror (8), a third mirror (9) and a second polarization beam splitter prism (10) which are sequentially and spacedly arranged and form a ring. The super-structured surface (4) is a single-layer super-structured surface, which comprises a substrate (40) and nano-bricks (41) arranged on one wall of the substrate (40), and the structural symmetry of the nano-bricks (41) is configured to keep the polarization direction of linearly polarized light transmitted from the super-structured surface (4) unchanged; the second polarization beam splitter prism (10) is configured to transmit the linearly polarized light transmitted from the super-structured surface (4) to the third mirror (9), and the third mirror (9) and the second mirror (8) are jointly configured to reflect the linearly polarized light to the half-wave plate (7), and the half-wave plate (7) is configured to perform 90° polarization modulation on the linearly polarized light transmitted through the half-wave plate (7) and reflect the linearly polarized light to the super-structured surface (4) through the first mirror (6) and the second polarization beam splitter prism (10).

5. The super-structured surface-based few-mode fiber mode multiplexer and demultiplexer of claim 1, wherein: the polarization control element and the first polarization beam splitter prism (1) are respectively located on two sides of the super-structured surface (4), and the polarization control element comprises a first mirror (6), a half-wave plate (7), a second mirror (8), a third mirror (9) and a second polarization beam splitter prism (10) which are sequentially and spacedly arranged and form a ring; the super-structured surface (4) is a double-layer super-structured surface, which comprises a substrate (40) and nano-bricks (41) arranged on two walls of the substrate (40), and the structural symmetry of the nano-bricks (41) is configured to perform 90° polarization modulation on the linearly polarized light transmitted from the super-structured surface (4); the second polarization beam splitter prism (10) is configured to reflect the linearly polarized light transmitted from the super-structured surface (4) to the first mirror (6), the first mirror (6) is configured to reflect the linearly polarized light to the half-wave plate (7), the half-wave plate (7) is configured to perform 90° polarization modulation on the linearly polarized light transmitted through the half-wave plate (7) and reflect the linearly polarized light to the second mirror (8), the second mirror (8) and the third mirror (9) are jointly configured to reflect the linearly polarized light to the second polarization beam splitter prism (10), and the second polarization beam splitter prism (10) is further configured to transmit the reflected linearly polarized light to the super-structured surface (4).

6. The super-structured surface-based few-mode fiber mode multiplexer and demultiplexer of claim 1, wherein: the polarization control element comprises a quarter-wave plate (11) and a reflecting element (12), and along the polarization light transmission direction, the first polarization beam splitter prism (1), the quarter-wave plate (11), the super-structured surface (4) and the reflecting element (12) are sequentially arranged.

7. The super-structured surface-based few-mode fiber mode multiplexer and demultiplexer of claim 6, wherein: The super-structured surface (4) is a single-layer super-structured surface, the single-layer super-structured surface comprises a substrate (40) and nano-bricks (41) arranged on the wall surface of the substrate (40) close to a quarter-wave plate (11), the reflective element (12) is a reflective layer made of metal material, the reflective layer is arranged on the wall surface of the substrate (40) away from the nano-bricks (41), the structural symmetry of the nano-bricks (41) is configured to reverse the polarization direction of circularly polarized light transmitted from the nano-bricks (41), the quarter-wave plate (11) is used for performing polarization modulation between circularly polarized light and linearly polarized light on the polarized light transmitted through the quarter-wave plate (11), and the reflective layer is used for reflecting the circularly polarized light incident from the nano-bricks (41) into the substrate (40) to the nano-bricks (41). Alternatively, the super-structured surface (4) is a double-layer super-structured surface, the double-layer super-structured surface comprises a substrate (40) and nano-bricks (41) arranged on two wall surfaces of the substrate (40), the reflective element (12) is a fourth mirror, the fourth mirror is arranged in space with the super-structured surface (4), the structural symmetry of the nano-bricks (41) is configured to keep the polarization direction of circularly polarized light transmitted from the super-structured surface (4) unchanged, the quarter-wave plate (11) is used for performing polarization modulation between circularly polarized light and linearly polarized light on the polarized light transmitted through the quarter-wave plate (11), and the fourth mirror is used for reflecting the circularly polarized light transmitted from the super-structured surface (4) to the super-structured surface (4).

8. The super-structured surface-based few-mode fiber mode multiplexer and demultiplexer of claim 1, wherein: the super-structured surface (4) is a double-layer super-structured surface, the double-layer super-structured surface comprises a substrate (40) and nano-bricks (41) arranged on two wall surfaces of the substrate (40); the polarization control element comprises a photoresist layer (13) and a reflective element (12), the reflective element (12) is a reflective layer made of metal material; and along the polarization light transmission direction, the first polarization beam splitter prism (1), the super-structured surface (4), the photoresist layer (13) and the reflective element (12) are arranged in sequence, the photoresist layer (13) is connected with the nano-bricks (41) and the reflective element (12) on both sides respectively; the structural symmetry of the nano-bricks (41) is configured to keep the polarization direction of linearly polarized light transmitted from the nano-bricks (41) of the super-structured surface (4) close to the first polarization beam splitter prism (1) unchanged, and after the linearly polarized light transmitted in the substrate (40) is reflected by the other wall surface of the substrate (40) provided with the nano-bricks (41), the linearly polarized light is subjected to 90° polarization modulation.

9. The super-structured surface-based few-mode fiber mode multiplexer and demultiplexer of claim 1, wherein: the super-structured surface (4) is a double-layer super-structured surface, the double-layer super-structured surface comprises a substrate (40) and nano-bricks (41) arranged on two wall surfaces of the substrate (40); The polarization control element comprises a quarter-wave plate (11), a photoresist layer (13) and a reflective element (12), the reflective element (12) is a reflective layer made of metal material; And along the polarization light transmission direction, the first polarization light splitting prism (1), the quarter-wave plate (11), the super-structured surface (4), the photoresist layer (13) and the reflective element (12) are arranged in sequence, the photoresist layer (13) is connected with the nano brick (41) and the reflective element (12) on both sides respectively; The structural symmetry of the nano brick (41) is configured to reverse the polarization direction of the circularly polarized light transmitted by the nano brick (41) of the super-structured surface (4) close to the first polarization light splitting prism (1), and the circularly polarized light transmitted in the substrate (40) is reflected by the wall surface of the substrate (40) provided with the nano brick (41) on the other side, and then the polarization modulation of the polarization direction is performed, and the quarter-wave plate (11) is used for performing polarization modulation between circularly polarized light and linearly polarized light on the polarization light transmitted through the quarter-wave plate (11).

10. The super-structured surface-based few-mode fiber mode multiplexer and demultiplexer according to claim 1, wherein: When the polarization light input into the first port (2) is a plurality of position-independent single-mode light fields, the super-structured surface-based few-mode fiber mode multiplexer and demultiplexer is a multiplexer; When the polarization light input into the first port (2) is a plurality of position-overlapping multi-mode light fields, the super-structured surface-based few-mode fiber mode multiplexer and demultiplexer is a demultiplexer.

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