Compact optical fiber coupling system and design method thereof

Abstract

The invention relates to a compact optical fiber coupling system and a design method thereof, and belongs to the technical field of beam shaping, the compact optical fiber coupling system comprises a broadband light source, a first metasurface device, a magneto-optical material, a second metasurface device and an optical fiber, the magneto-optical material is used for rotating a light beam passing through the first metasurface device in a polarization state, the second metasurface device is located at the downstream of the magneto-optical material, the second metasurface device is used for shaping emergent light in a specific polarization state, and the optical fiber is located at the downstream of the second metasurface device. The invention has the advantages of miniaturization, high efficiency and high isolation.

Description

Technical Field

[0001] The present application belongs to the field of beam shaping, and in particular to a compact optical fiber coupling system and a design method thereof. Background Art

[0002] Fiber-based communication and sensing technologies play an important role in various industries. Limited by the mode of optical fiber, a coupling lens group consisting of multiple lenses is usually required to couple the laser emitted by the laser into the optical fiber, which greatly increases the size and cost of the fiber coupling system. At the same time, in order to increase the reverse isolation of the coupling system, an additional optical isolator is required. The common optical isolator is composed of magneto-optical material and two polarizers, which further increases the size of the coupling system. Summary of the invention

[0003] The present application provides a compact optical fiber coupling system and a design method thereof to at least solve the above technical problems existing in the prior art.

[0004] On the one hand, an embodiment of the present application provides a compact fiber coupling system, including a broadband light source, a first metasurface device, a magneto-optical material, a second metasurface device and an optical fiber, wherein the first metasurface device is located downstream of the broadband light source, the magneto-optical material is used to rotate the polarization state of a light beam passing through the first metasurface device, the second metasurface device is located downstream of the magneto-optical material, the second metasurface device is used to shape the output light of a specific polarization state, and the optical fiber is located downstream of the second metasurface device.

[0005] In one possible implementation manner, the broadband light source is one of a light emitting diode, a vertical cavity surface emitting laser and a fiber laser; the magneto-optical material is one of rare earth orthoferrite, yttrium iron garnet magneto-optical crystal, terbium niobate and rare earth molybdate; and the optical fiber is a single-mode optical fiber or a multi-mode optical fiber.

[0006] In one possible implementation, the first metasurface device includes a substrate and a metasurface unit disposed on the substrate.

[0007] In one possible implementation manner, the metasurface unit is composed of a microstructure array, and the phase distribution of the metasurface is changed by the type, size and arrangement of the microstructures, and the phase change range is within 0-2π.

[0008] In one embodiment, the microstructure is in the shape of a nanorod or a nanohole.

[0009] In one possible implementation manner, the microstructure is a rectangular nanorod, a nanocross rod, a rectangular nanohole, a nanocross hole, and a microstructure having a specific shape obtained by optimizing the method.

[0010] In one possible implementation, the microstructure is anisotropic; the arrangement of the microstructure may be a tetragonal arrangement or a hexagonal arrangement.

[0011] Another aspect of the present application provides a design method for a compact optical fiber coupling system, comprising the following steps:

[0012] S1. By changing the size and shape of the microstructure, a parameter library of phase distribution, transmittance and structural parameters under two orthogonal polarization incidences is obtained;

[0013] S2. Designing the phase of the first metasurface device according to the intensity and divergence angle distribution of the broadband light source;

[0014] S3. Design the phase of the second metasurface device to achieve matching between the incident light and the numerical aperture and mode of the optical fiber.

[0015] In one possible implementation, the phase design formula of the first metasurface device is as follows:

[0016]

[0017] Where (x, y) is the spatial coordinate of the hypersurface, and f1 and f2 are the focal lengths, respectively.

[0018] In one possible implementation, the phase design formula of the second metasurface device is as follows:

[0019]

[0020] Where (x, y) is the spatial coordinate of the hypersurface and f is the focal length.

[0021] Compared with the prior art, this application has the following advantages:

[0022] 1. The compact fiber coupling system of the present application realizes high-isolation fiber coupling by using the phase and polarization simultaneous control characteristics of the metasurface and combining it with magneto-optical materials, effectively solving the shortcomings of the traditional optical lens system such as large volume and high cost;

[0023] 2. By changing the shape and arrangement of the microstructure, the metasurface can regulate the parameters of light within the sub-wavelength scale to achieve laser shaping;

[0024] 3. This application realizes a miniaturized, high-efficiency, and high-isolation coupling device by combining the polarization control characteristics of the metasurface with an isolator. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic structural diagram of a compact optical fiber coupling system in an embodiment of the present application;

[0026] Figure 2 is a schematic diagram of the structure of a super surface unit in an embodiment of the present application;

[0027] Figure 3 is a schematic diagram of the change of transmittance under two polarization states of incidence in the embodiment of the present application;

[0028] Figure 4 Schematic diagram of the laser shaping and polarization selection characteristics of the first metasurface device in the embodiment of the present application;

[0029] Figure 5 is a schematic diagram of the intensity and phase distribution of the laser before and after passing through the first metasurface device in the embodiment of the present application;

[0030] Figure 6 is a schematic diagram of laser shaping and polarization selection characteristics of the second metasurface device in an embodiment of the present application;

[0031] Figure 7 is a schematic diagram of the intensity distribution of the laser before and after passing through the second metasurface device in the embodiment of the present application;

[0032] Description of reference numerals:

[0033] 1. Broadband light source; 21. First metasurface device; 22. Magneto-optical material; 23. Second metasurface device; 3. Optical fiber. DETAILED DESCRIPTION

[0034] The present application is further described in detail below in conjunction with the accompanying drawings.

[0035] In the description of the present application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0036] The present application discloses a compact fiber coupling system, which includes a broadband light source 1, a first metasurface device 21, a magneto-optical material 22, a second metasurface device 23 and an optical fiber 3. The first metasurface device 21 is located downstream of the broadband light source 1. The first metasurface device 21 can collimate and polarize the incident laser spot. The magneto-optical material 22 is used to rotate the polarization state of the light beam passing through the first metasurface device 21. The second metasurface device 23 is located downstream of the magneto-optical material 22. The second metasurface device 23 is used to shape the output light of a specific polarization state to achieve matching with the optical fiber mode. The optical fiber 3 is located downstream of the second metasurface device 23.

[0037] The broadband light source 1 may be a light emitting diode, a vertical cavity surface emitting laser, a fiber laser or other light sources.

[0038] The first metasurface device 21 includes a substrate and a metasurface unit disposed on the substrate. The metasurface unit is composed of a microstructure array, and the phase distribution of the metasurface is changed by the type, size and arrangement of the microstructure, and the phase change range is within 0-2π. The material of the substrate can be silicon dioxide, calcium fluoride, aluminum oxide, etc. The material of the microstructure can be amorphous silicon, polycrystalline silicon, silicon nitride, titanium dioxide, gallium nitride, sulfur compounds, etc. The shape of the microstructure is a nanocolumn or a nanohole, and its structure is anisotropic to achieve polarization control. The microstructure includes but is not limited to rectangular nanocolumns, nanocross columns, rectangular nanoholes, nanocross holes, and microstructures with specific shapes obtained by optimization. The arrangement of the microstructure can be a square arrangement or a hexagonal arrangement. The structure of the second metasurface device 23 is inconsistent with the first metasurface device 21. Specifically, the phase distribution of the second metasurface device 23 is inconsistent with the first metasurface device 21. The materials constituting the second metasurface device 23 are the materials mentioned above. The materials constituting the second metasurface device 23 and the materials constituting the first metasurface device 21 may be the same or different.

[0039] The magneto-optical material 22 may be rare earth orthoferrite, yttrium iron garnet magneto-optical crystal (YIG), terbium-containing niobate, rare earth molybdate, etc. The optical fiber 3 is a single-mode optical fiber or a multi-mode optical fiber.

[0040] The present application also discloses a design method for a compact optical fiber coupling system. After passing through the second metasurface device 23, the light spot is shaped into a mode field distribution supported by the optical fiber 3 for propagation. The design steps are as follows:

[0041] S1. By changing the size and shape of the microstructure, a parameter library of phase distribution, transmittance and structural parameters under two orthogonal polarization incidences is obtained.

[0042] Figure 2 A schematic diagram of one of the microstructures is given. By changing the length (l) and width (w) of the microstructure, the phase and transmittance response to the incident light in two polarization states can be adjusted. In order to achieve a better isolation effect, the structure needs to have a higher polarization extinction ratio. Figure 3 The transmittance of a part of the structure under linear polarization in the x-direction and linear polarization in the y-direction is shown in the figure. The same structure has different transmittance responses to the two orthogonal polarizations.

[0043] S2. According to the intensity and divergence angle distribution of the light source 1, the phase of the first metasurface device 21 can be designed, wherein one phase distribution can be written as:

[0044]

[0045] Where (x, y) is the spatial coordinate of the hypersurface, and f1 and f2 are the focal lengths, respectively.

[0046] After passing through the first metasurface device 21, the incident laser will be collimated while being polarized. Figure 4 As shown, at this time, the polarized light in the x-direction will be collimated, while the polarized light in the y-direction will not be transmitted due to the polarization filtering effect of the metasurface itself. Figure 5 The design effect of one of the first super lens devices 21 is given. After the elliptical light spot passes through the first super lens device 21, the spot size changes slightly, while the phase plane is almost a uniform value, indicating that the laser is collimated after passing through the first super lens device 21.

[0047] S3. After the collimated laser passes through the magneto-optical material 22, its polarization state will rotate. The deflection can be 0° to 360°, one of which is 45°. This deflection can isolate all reflected light.

[0048] S4, the second metasurface device 23 is located downstream of the magneto-optical material 22, and its function is to shape the light beam through phase control to achieve the matching of the incident light with the numerical aperture and mode of the optical fiber. The shaping phase can be directly given by an analytical formula or calculated by a phase recovery algorithm, such as the GS algorithm, where one phase can be written as:

[0049]

[0050] Where (x, y) is the spatial coordinate of the hypersurface and f is the focal length.

[0051] The metasurface also has polarization selection. One of the optional methods is that when 45° polarized light is incident, the incident light will pass through the metasurface and be shaped. When 135° polarized light is incident, all energy will be blocked. The result is as follows: Figure 6 shown. Figure 7 The design effect of one of the second super lens devices 23 is given. After the collimated elliptical light beam passes through the second super lens, its spot will be shaped into a circle, and the intensity distribution also matches the mode field distribution of the optical fiber 3.

[0052] If reflection occurs at the end face of the optical fiber 3, after the reflected light passes through the second super lens device 23, the polarization state is rotated 45° by the magneto-optical material. At this time, the polarization state of the reflected light is exactly the low-transmittance polarization state of the first super lens device 21. Therefore, the light beam 3 will be blocked by the first super surface device 21, which plays the role of an optical isolator.

[0053] The above are only specific embodiments of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present disclosure, which should be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.

Claims

1. A compact optical fiber coupling system, characterized in that: It includes a broadband light source, a first metasurface device, a magneto-optical material, a second metasurface device and an optical fiber, wherein the first metasurface device is located downstream of the broadband light source, the magneto-optical material is used to rotate the polarization state of the light beam passing through the first metasurface device, the second metasurface device is located downstream of the magneto-optical material, the second metasurface device is used to shape the output light of a specific polarization state, and the optical fiber is located downstream of the second metasurface device.

2. A compact optical fiber coupling system according to claim 1, characterized in that: The broadband light source is one of a light emitting diode, a vertical cavity surface emitting laser and a fiber laser; The magneto-optical material is one of rare earth orthoferrite, yttrium iron garnet magneto-optical crystal, terbium-containing niobate and rare earth molybdate; The optical fiber is a single-mode optical fiber or a multi-mode optical fiber.

3. A compact optical fiber coupling system according to claim 1, characterized in that: The first metasurface device includes a substrate and a metasurface unit disposed on the substrate.

4. A compact optical fiber coupling system according to claim 3, characterized in that: The metasurface unit is composed of a microstructure array, and the phase distribution of the metasurface is changed by the type, size and arrangement of the microstructure, and the phase change range is within 0-2π.

5. A compact optical fiber coupling system according to claim 4, characterized in that: The microstructure is in the shape of nanorods or nanoholes.

6. A compact optical fiber coupling system according to claim 5, characterized in that: The microstructures are rectangular nanorods, nanocross rods, rectangular nanoholes, nanocross holes, and microstructures with specific shapes obtained by optimizing methods.

7. A compact optical fiber coupling system according to claim 4, characterized in that: The microstructure is anisotropic; The microstructures may be arranged in a tetragonal arrangement or a hexagonal arrangement.

8. The method for designing a compact optical fiber coupling system according to any one of claims 1 to 7, characterized in that: The steps include: S1. By changing the size and shape of the microstructure, a parameter library of phase distribution, transmittance and structural parameters under two orthogonal polarization incidences is obtained; S2. Designing the phase of the first metasurface device according to the intensity and divergence angle distribution of the broadband light source; S3. Design the phase of the second metasurface device to achieve matching between the incident light and the numerical aperture and mode of the optical fiber.

9. The design method according to claim 8, characterized in that: The phase design formula of the first metasurface device is as follows: Where (x, y) is the spatial coordinate of the hypersurface, and f1 and f2 are the focal lengths, respectively.

10. The design method according to claim 8, characterized in that: The phase design formula of the second metasurface device is as follows: Where (x, y) is the spatial coordinate of the hypersurface and f is the focal length.

Images