An optical fiber device, a method for manufacturing an optical fiber device, and a coupling device

Abstract

The application discloses an optical fiber device, a preparation method of the optical fiber device and a coupling device, and belongs to the technical field of micro-nano photonics. The application sequentially arranges a mode field expansion area and a phase modulation area at an exit end of an optical fiber, uses the mode field expansion area to expand a beam mode field diameter, uses a substrate film matched with the mode field expansion area in refractive index and a micro-nano unit with high refractive index to form the phase modulation area, realizes a target phase distribution based on geometric sizes and / or a rotation angle of the micro-nano unit, and then performs phase modulation and wavefront shaping on the expanded beam, so as to output a target light field such as a focused beam, a collimated beam, a Bessel beam or a Bessel beam array. The optical fiber device can realize high coupling efficiency, high alignment tolerance and multi-functional wavefront regulation at the exit end of the optical fiber, can solve the mode field mismatch problem in optical fiber-chip coupling, can reduce system complexity and realize multi-functional integration.

Description

Technical Field

[0001] This application relates to the field of micro-nano photonics technology, and in particular to an optical fiber device, a method for fabricating the optical fiber device, and a coupling device. Background Technology

[0002] The rapid development of optical communication and optical interconnect technologies has led to a significant mismatch between the silicon waveguide mode field size of photonic integrated chips (only in the hundreds of nanometers range) and the micrometer-scale mode field diameter of single-mode optical fibers. This mismatch results in poor alignment tolerance and high loss in direct fiber-chip coupling. Existing fiber-chip coupling schemes primarily fall into two categories: grating couplers and edge couplers. Grating couplers achieve vertical optical coupling through periodic grating structures on the chip surface; edge couplers achieve fiber-waveguide coupling through lateral alignment, utilizing tapered fibers, end-face microlenses, or special waveguide designs for mode field conversion. Both of these schemes require additional special designs or components on the chip side, increasing cost and complexity. Furthermore, they offer limited functionality, lack flexibility in configuring multiple operating modes, and fail to meet diverse application requirements. Therefore, existing coupling schemes still have shortcomings in coupling efficiency, alignment tolerance, functional integration, and system complexity, necessitating the development of novel solutions that balance high performance and multifunctional integration. Summary of the Invention

[0003] The purpose of this application is to provide an optical fiber device, a method for fabricating the optical fiber device, and a coupling device that can achieve high coupling efficiency, high alignment tolerance, and multifunctional wavefront modulation at the optical fiber output end. While solving the mode field mismatch problem in optical fiber-chip coupling, it can reduce system complexity and achieve multifunctional integration.

[0004] To achieve the above objectives, this application provides an optical fiber device, comprising:

[0005] Optical fiber is used to transmit light beams;

[0006] A mode field expansion region is disposed on the exit end face of the optical fiber and is used to expand the mode field of the beam emitted from the optical fiber so that the mode field diameter of the beam emitted from the mode field expansion region is larger than the mode field diameter of the beam emitted from the optical fiber.

[0007] The phase modulation region includes a substrate film disposed on the emission end face of the mode field extension region and a micro / nano unit array disposed on the surface of the substrate film;

[0008] The refractive index of the substrate film is matched with the refractive index of the mode field extension region; the refractive index of the micro-nano units in the micro-nano unit array is greater than the refractive index of the substrate film, and the geometric dimensions and / or rotation angles of the micro-nano units are configured to make the phase distribution of the micro-nano unit array a target phase distribution;

[0009] The phase modulation region is used to perform phase modulation on the beam emitted from the mode field extension region according to the target phase distribution, so as to perform wavefront shaping on the beam emitted from the phase modulation region, so that the light field of the beam emitted from the phase modulation region is the target light field.

[0010] The target light field includes at least one corresponding light field among a focused beam, a collimated beam, a Bessel beam, and a Bessel beam array.

[0011] Optionally, the target phase distribution includes target phases that correspond one-to-one with the micro / nano units;

[0012] The micro / nano unit array employs a propagation phase modulation mechanism; the geometric dimensions of the micro / nano units are determined by a target phase corresponding to the micro / nano unit and a lookup table; the lookup table is established through electromagnetic simulation and records the correspondence between the geometric dimensions of the micro / nano units and the target phase; the geometric dimensions include at least one of length, width, and height;

[0013] And / or, the micro / nano unit array employs a geometric phase modulation mechanism; the geometric dimensions of each micro / nano unit are identical; the micro / nano unit is an anisotropic structure, and the rotation angle of the micro / nano unit and the target phase corresponding to the micro / nano unit satisfy:

[0014] ;

[0015] In the formula, The coordinates represent the position of the micro / nano unit on the surface of the substrate thin film. express The rotation angle of the micro / nano unit at the location; Indicates and The target phase corresponding to the micro / nano unit at the location.

[0016] Optionally, the target light field includes the light field corresponding to the focused beam; the target phase distribution is a spherical lens phase distribution; the spherical lens phase distribution satisfies:

[0017] ;

[0018] In the formula, The coordinates represent the position of the micro / nano unit on the surface of the substrate thin film. Indicates and The target phase corresponding to the micro / nano unit at the location, wherein the target phase is the spherical lens phase; Indicates the design focal length; Indicates the operating wavelength.

[0019] Optionally, the target optical field includes the optical field corresponding to the collimated beam; the target phase distribution is a hyperbolic phase distribution; the hyperbolic phase distribution satisfies:

[0020] ;

[0021] In the formula, The coordinates represent the position of the micro / nano unit on the surface of the substrate thin film. Indicates and The target phase corresponding to the micro / nano unit at the location, wherein the target phase is a hyperbolic phase; Indicates the design working distance; Indicates the operating wavelength.

[0022] Optionally, the target optical field includes the optical field corresponding to the Bessel beam; the target phase distribution is an axial conical mirror phase distribution; the axial conical mirror phase distribution satisfies:

[0023] ;

[0024] In the formula, The coordinates represent the position of the micro / nano unit on the surface of the substrate thin film. Indicates and The target phase corresponding to the micro / nano unit at the location, wherein the target phase is the phase of the axial conical mirror; Indicates the design numerical aperture; Indicates the operating wavelength.

[0025] Optionally, the target optical field includes the optical field corresponding to the Bessel beam array; the target phase distribution is a composite phase distribution; the composite phase distribution satisfies:

[0026] ;

[0027] In the formula, The coordinates represent the position of the micro / nano unit on the surface of the substrate thin film. express The target phase at the location corresponding to the micro / nano unit, wherein the target phase is a composite phase; Indicates and The phase of the axial conical mirror corresponding to the micro / nano unit at the location; Indicates and The beam splitter phase corresponding to the micro / nano unit at the location.

[0028] Optionally, the phase of the beam splitter is obtained by optimization using an improved iterative Fourier transform algorithm;

[0029] The improved iterative Fourier transform algorithm utilizes the central symmetry of the target intensity distribution to impose symmetry constraints on the initial random phase and the iteratively updated phase. During the iteration process, the complex amplitude of the light field between the input plane and the output plane is repeatedly projected through Fourier transform until the error converges, thus obtaining the beam splitter phase.

[0030] Optionally, the optical fiber includes single-sided optical fiber or multimode optical fiber;

[0031] The mode field extension region includes coreless optical fiber.

[0032] Optionally, the optical fiber device further includes a protective cladding that covers the output end face of the phase modulation region.

[0033] To achieve the above objectives, this application also provides a method for fabricating an optical fiber device, comprising:

[0034] A mode field extension region is formed at the output end face of the optical fiber;

[0035] A phase modulation region is formed at the exit end face of the mode field extension region; the phase modulation region includes a substrate film disposed at the exit end face of the mode field extension region and a micro / nano unit array disposed on the surface of the substrate film; the refractive index of the substrate film is matched with the refractive index of the mode field extension region; the refractive index of the micro / nano units in the micro / nano unit array is greater than the refractive index of the substrate film, and the geometric dimensions and / or rotation angles of the micro / nano units are configured to make the phase distribution of the micro / nano unit array a target phase distribution.

[0036] Optionally, forming a phase modulation region at the exit end face of the mode field extension region includes:

[0037] The substrate thin film and the functional thin film are sequentially deposited on the exit end face of the mold field extension region using a low-temperature sputtering process;

[0038] The functional thin film is patterned using photolithography to form the micro / nano unit array, thereby forming the phase modulation region.

[0039] To achieve the above objectives, this application also provides a coupling device, comprising: the optical fiber device described in any of the preceding claims.

[0040] Obviously, the optical fiber device provided in this application has the following beneficial effects:

[0041] (1) The mode field extension region is set on the fiber optic output end face to expand the small mode field diameter beam emitted from the fiber into a large mode field diameter beam. This can increase the geometric size of the phase modulation region processing area, accommodate more micro-nano units, and provide sufficient design freedom for complex phase control. At the same time, it can reduce the sensitivity coefficient of the center drift during the phase modulation region processing, effectively diluting the weight of the overlay error on the device performance.

[0042] (2) The substrate thin film is set at the incident end of the phase modulation region. Its refractive index matches that of the mode field extension region, which can isolate the high refractive index micro-nano units from the low refractive index mode field extension region, greatly reducing the reflection loss of the beam at the interface between the mode field extension region and the phase modulation region, and improving the optical transmission efficiency.

[0043] (3) The micro-nano unit array is located at the output end of the phase modulation region. It consists of multiple micro-nano units made of high refractive index materials and arranged in an array. It has strong optical phase modulation capability, and the geometric dimensions and / or rotation angle of each micro-nano unit can be configured independently, so that the micro-nano unit array can obtain the target phase distribution. Based on the target phase distribution, the micro-nano unit array can perform phase modulation on the beam after beam expansion, realize wavefront shaping of the output beam, and thus realize the control of the output light field.

[0044] When the target phase distribution is configured as a focused phase distribution, the outgoing beam is focused into a focused beam, which can convert the fiber mode field into a mode spot that matches the chip waveguide. This solves the mode field mismatch problem between the fiber and the chip waveguide, significantly improving the coupling efficiency and alignment tolerance of the fiber and the chip. At the same time, since the mode field extension region and the phase modulation region are integrated at the output end of the same fiber device, there is no need to fabricate grating couplers, tapered waveguides or other additional structures on the chip side, reducing the chip manufacturing cost and design complexity.

[0045] Furthermore, by configuring other target phase distributions, micro-nano unit arrays can achieve various wavefront modulation functions such as beam collimation, Bessel beam generation, and Bessel beam array generation to meet the needs of different application scenarios.

[0046] This application also provides a method for fabricating an optical fiber device and a coupling device, which have the above-mentioned beneficial effects. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of this application 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 only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the structure of an optical fiber device provided in an embodiment of this application;

[0049] Figure 2 This is a schematic diagram of the yz section of an optical fiber device provided in an embodiment of this application;

[0050] Figure 3 A flowchart illustrating a method for fabricating an optical fiber device according to an embodiment of this application;

[0051] Figure 4 An optical field distribution for a beam-focusing fiber optic device provided in this application embodiment;

[0052] Figure 5 An optical field distribution for a 0th-order Bessel beam generating fiber optic device provided in this application embodiment;

[0053] Figure 6 An optical field distribution for a first-order Bessel beam generating fiber optic device provided in this application embodiment;

[0054] Figure 7 The optical field distribution of a Bessel beam array generating fiber optic device is provided in the embodiments of this application.

[0055] The annotations in the attached figures are explained as follows:

[0056] 1-Fiber optic cable; 10-Beam beam; 11-Fiber core; 12-Clad layer; 2-Mode field extension region; 3-Phase modulation region; 31-Substrate thin film; 32-Micro / nano unit. Detailed Implementation

[0057] 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.

[0058] With the rapid development of optical communication and optical interconnect technologies, photonic integrated chips have become a key technology for reducing the cost and power consumption of communication modules. The mode field size of a typical single-mode silicon waveguide is on the order of hundreds of nanometers, while the mode field diameter of the ordinary single-mode fiber coupled to it is approximately 9μm-10μm, resulting in a significant mode field mismatch. This huge difference in mode field size leads to extremely small alignment tolerances and high optical coupling losses when the fiber is directly coupled to the chip, severely restricting the practical application of photonic integrated chips.

[0059] In existing technologies, fiber-to-chip coupling schemes mainly fall into two categories: grating couplers and side couplers. Grating couplers achieve vertical optical coupling through periodic grating structures on the chip surface, offering advantages such as large alignment tolerance and ease of on-chip testing. However, they suffer from drawbacks including polarization sensitivity, narrow operating bandwidth, and low coupling efficiency. Side couplers achieve fiber-to-waveguide coupling through lateral alignment, utilizing tapered fibers, end-face microlenses, or special waveguide designs to achieve mode field conversion. They offer advantages such as low loss and large bandwidth, but face challenges including system complexity, incompatibility with standard processes, and difficulty in scaling to multiple modes.

[0060] Both of these approaches require special structural designs or additional optical components on the chip side, increasing system complexity and manufacturing costs. More importantly, these traditional coupling solutions are limited in function, only capable of basic mode-field conversion, and cannot flexibly configure multiple operating modes according to application requirements, making it difficult to meet the increasingly diverse optical interconnect application scenarios.

[0061] Therefore, existing fiber-to-chip coupling schemes still have shortcomings in terms of coupling efficiency, alignment tolerance, functional integration and system complexity, making it difficult to simultaneously meet the practical application requirements of high efficiency, high tolerance and multi-functional integration.

[0062] To overcome the shortcomings of the prior art, this application provides an optical fiber device that integrates the mode field extension region and the phase modulation region at the output end of the same optical fiber device. This enables high coupling efficiency, high alignment tolerance, and multifunctional wavefront modulation at the optical fiber output end. While solving the mode field mismatch problem in fiber-chip coupling, it can reduce system complexity and achieve multifunctional integration.

[0063] Please refer to Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of the structure of an optical fiber device provided in an embodiment of this application. Figure 2 This is a schematic diagram of the yz section of an optical fiber device provided in an embodiment of this application; the optical fiber device may include:

[0064] Fiber 1 is used to transmit beam 10;

[0065] Mode field expansion region 2 is set at the exit end face of optical fiber 1 and is used to expand the mode field of the beam 10 emitted from optical fiber 1 so that the mode field diameter of the beam 10 emitted from mode field expansion region 2 is greater than the mode field diameter of the beam 10 emitted from optical fiber 1.

[0066] The phase modulation region 3 includes a substrate thin film 31 disposed on the emission end face of the mode field extension region 2 and an array of micro / nano units 32 disposed on the surface of the substrate thin film 31.

[0067] The refractive index of the substrate thin film 31 is matched with the refractive index of the mode field extension region 2; the refractive index of the micro-nano unit 32 in the micro-nano unit 32 array is greater than the refractive index of the substrate thin film 31, and the geometric dimensions and / or rotation angle of the micro-nano unit 32 are configured to make the phase distribution of the micro-nano unit 32 array the target phase distribution;

[0068] The phase modulation region 3 is used to perform phase modulation on the beam 10 emitted from the mode field extension region 2 according to the target phase distribution, so as to perform wavefront shaping on the beam 10 emitted from the phase modulation region 3, so that the light field of the beam 10 emitted from the phase modulation region 3 is the target light field.

[0069] The target light field includes at least one of the following: a focused beam, a collimated beam, a Bessel beam, and an array of Bessel beams.

[0070] It should be noted that, Figure 1 The x and y directions refer to two mutually perpendicular directions within the emitting end face, while the z direction refers to the extension direction of the optical fiber device, which is perpendicular to both the x and y directions.

[0071] It should be noted that the optical fiber 1 in this embodiment may include a fiber core 11 and a cladding 12 that surrounds the fiber core 11 in the circumferential direction; the light beam 10 is transmitted in the optical core, and the light beam 10 may be a Gaussian beam and carries target information as an optical signal. This embodiment does not limit the specific type of optical fiber 1, as long as it can transmit the light beam 10.

[0072] In one possible implementation, optical fiber 1 may comprise single-mode optical fiber. More preferably, the single-mode optical fiber may comprise Thorlabs SM600 single-mode optical fiber (a special single-mode optical fiber designed specifically for the visible to near-infrared short-wavelength band), with a core 11 diameter of 6 μm and a cladding 12 diameter of 125 μm, and an operating wavelength... It can be 633nm.

[0073] In another possible implementation, optical fiber 1 may include multimode optical fiber or other types of optical fiber. It should be noted that wavefront modulation function can also be achieved by adjusting the geometry (including length) of mode field extension region 2 and designing the structure of phase modulation region 3.

[0074] In one possible implementation, the exit end face of the optical fiber 1 may be provided with alignment marks to improve alignment accuracy during the subsequent formation of the phase modulation region 3. This embodiment does not limit the specific location of the alignment marks, as long as they facilitate alignment. In one possible implementation, the alignment marks may be located at the edge of the exit end face of the cladding 12 in the optical fiber 1.

[0075] This embodiment does not limit the specific type of alignment mark, as long as it facilitates alignment. In one possible implementation, the alignment mark may include a patterned groove; this groove can be formed by photolithography on the exit end face of the optical fiber 1. In another possible implementation, the alignment mark may include a patterned metal mark, which can be formed by chrome plating on the exit end face of the optical fiber 1.

[0076] This embodiment does not limit the specific type of the mode field expansion region 2, as long as it can ensure that mode field beam expansion can be achieved.

[0077] In one possible implementation, the mode field extension region 2 may include a coreless optical fiber. More preferably, the coreless optical fiber may include a silica coreless optical fiber. It should be noted that when the Gaussian beam emitted from the front-end optical fiber 1 is incident into the coreless optical fiber, the mode field diameter of the beam 10 will increase due to the absence of the constraint of the fiber core 11. When the Gaussian beam propagates in the coreless optical fiber, its mode field radius... With propagation distance The changes can satisfy:

[0078] ;

[0079] In the formula, Let be the mode field radius at the output end face of fiber 1 (taking Thorlabs SM600 single-mode fiber as an example). ), where n is the refractive index of the coreless optical fiber ( By precisely controlling the length of the coreless fiber, the mode field diameter can be expanded from the original 6μm (mode field radius of 3μm) to over 40μm. The target mode field radius... Substituting into the above equation, we get:

[0080] ;

[0081] Calculated Considering the actual machining and polishing allowance, take... At this point, the mode field diameter is approximately 51 μm, which meets the beam expansion requirements.

[0082] In one possible implementation, the coreless optical fiber can be fused to optical fiber 1.

[0083] It should be noted that, in this embodiment, refractive index matching means that the difference in refractive index between the two media is small enough that the reflection energy generated by the beam 10 at the interface can be effectively suppressed. Preferably, the refractive index of the substrate thin film 31 can be equal to the refractive index of the mode field extension region 2.

[0084] This embodiment does not limit the specific type of the substrate film 31, as long as it can match the refractive index of the mode field extension region 2. In one possible implementation, the substrate film 31 can be made of silicon dioxide. It should be noted that the micro / nano unit 32 in this embodiment has a high refractive index, which can ensure strong optical phase modulation capability.

[0085] This embodiment does not limit the specific shape of the micro / nano unit 32, as long as phase modulation can be achieved. In one possible implementation, the micro / nano unit 32 may include nanopillars.

[0086] This embodiment does not limit the specific type of micro / nano unit 32, as long as phase modulation can be achieved. In one possible implementation, the micro / nano unit 32 can be any of the materials such as amorphous silicon, silicon nitride, and polymers.

[0087] This embodiment does not limit the specific thickness of the phase modulation region 3, which can be determined according to actual needs. In one possible implementation, the thickness of the phase modulation region 3 can be less than 2 μm. More preferably, the thickness of the substrate film 31 can be 1 μm; the thickness of the micro / nano unit 32 can be 300 nm or 500 nm. It should be noted that the overall thickness of the phase modulation region 3 is less than 2 μm, which hardly increases the rigid length of the fiber tip 1, allowing for flexible operation.

[0088] This embodiment can employ various phase modulation mechanisms, including but not limited to propagation phase modulation mechanisms, geometric phase modulation mechanisms, or composite phase modulation mechanisms. Depending on the phase modulation method, the phase modulation region 3 may include a propagation phase-type metasurface, a geometric phase-type metasurface, or a composite phase-type metasurface.

[0089] It should be noted that the target phase distribution in this embodiment may include the target phase corresponding to the micro / nano unit 32.

[0090] In one possible implementation, the array of micro / nano units 32 can employ a propagation phase modulation mechanism; the geometric dimensions of the micro / nano units 32 are determined by the target phase corresponding to each micro / nano unit 32 and a lookup table; the lookup table is established through electromagnetic simulation and records the correspondence between the geometric dimensions of the micro / nano units 32 and the target phase; the geometric dimensions include at least one of length, width, and height. It should be noted that the propagation phase type metasurface modulates the phase delay of the beam 10 by designing the geometric dimensions of the micro / nano units 32, thereby achieving wavefront modulation.

[0091] In one possible implementation, the array of micro / nano units 32 can employ a geometric phase modulation mechanism; each micro / nano unit 32 has the same geometric dimensions; the micro / nano units 32 are anisotropic structures, and the rotation angle of the micro / nano units 32 and the target phase corresponding to the micro / nano units 32 satisfy the following:

[0092] ;

[0093] In the formula, This indicates the position coordinates of the micro / nano unit 32 on the surface of the substrate thin film 31. express The rotation angle of the micro / nano unit 32 at the location; Indicates and The target phase corresponding to the micro / nano unit 32 at the location.

[0094] It should be noted that geometric phase-type metasurfaces are based on the Pancharatnam-Berry (PB) phase principle; according to the PB phase principle, when circularly polarized light is incident, the component of the outgoing light with the opposite rotation direction to the incident light will acquire a geometric phase. (The sign depends on the incident polarization direction). Therefore, by controlling the rotation angle of the micro / nano unit 32 By introducing geometric phase, arbitrary phase modulation of the wavefront can be achieved.

[0095] In one possible implementation, the array of micro / nano units 32 can employ a geometric phase control mechanism; the target phase corresponding to the micro / nano units 32 includes both the propagation phase and the geometric phase. It should be noted that the composite phase metasurface combines the propagation phase and the geometric phase to achieve more flexible control.

[0096] This embodiment does not limit the specific type of target phase distribution. The target phase distribution can be determined according to the target light field, and different target light fields can achieve different functions.

[0097] In one possible implementation, to achieve beam focusing, i.e., when the target light field includes the light field corresponding to the focused beam, the target phase distribution can be a spherical lens phase distribution (belonging to the focusing phase distribution); the spherical lens phase distribution can satisfy:

[0098] ;

[0099] In the formula, This indicates the position coordinates of the micro / nano unit 32 on the surface of the substrate thin film 31. Indicates and The target phase corresponding to the micro / nano unit 32 at the location is the spherical lens phase; Indicates the design focal length; Indicates the operating wavelength.

[0100] It should be noted that the design focal length f refers to the theoretical distance between the focal point and the micro-nano unit 32 array when the micro-nano unit 32 array converges the incident light beam 10 at the working wavelength λ.

[0101] In one possible implementation, to achieve beam collimation, i.e., when the target optical field includes the optical field corresponding to the collimated beam, the target phase distribution can be a hyperbolic phase distribution; the hyperbolic phase distribution can satisfy:

[0102] ;

[0103] In the formula, This indicates the position coordinates of the micro / nano unit 32 on the surface of the substrate thin film 31. Indicates and The target phase corresponding to the micro / nano unit 32 at the location is a hyperbolic phase. Indicates the design working distance; Indicates the operating wavelength.

[0104] It should be noted that the beam 10 emitted from fiber 1 can be approximated as a diverging spherical wave emitted from the end face of fiber 1, and the design working distance... This refers to the theoretical distance between the point source emitting diverging spherical waves and the 32-unit micro / nano array. Phase modulation based on the hyperbolic phase distribution can compensate for the spherical wavefront and achieve beam collimation.

[0105] In one possible implementation, to achieve Bessel beam generation, i.e., when the target optical field includes the optical field corresponding to the Bessel beam, the target phase distribution can be an axial conical mirror phase distribution; the axial conical mirror phase distribution can satisfy:

[0106] ;

[0107] In the formula, This indicates the position coordinates of the micro / nano unit 32 on the surface of the substrate thin film 31. Indicates and The target phase corresponding to the micro / nano unit 32 at the location is the phase of the axial conical mirror. Indicates the design numerical aperture; Indicates the operating wavelength.

[0108] It should be noted that the numerical aperture design This represents the theoretical numerical aperture of the Bessel beam, which determines the size of the central spot and the non-diffraction distance of the Bessel beam.

[0109] In one possible implementation, to achieve the generation of a Bessel beam array, i.e., when the target optical field includes the optical field corresponding to the Bessel beam array, the target phase distribution can be a composite phase distribution; the composite phase distribution can satisfy:

[0110] ;

[0111] In the formula, This indicates the position coordinates of the micro / nano unit 32 on the surface of the substrate thin film 31. express The target phase at the location corresponds to the micro / nano unit 32, and the target phase is a composite phase; Indicates and The phase of the axial conical mirror corresponding to the micro / nano unit 32 at the location; Indicates and The beam splitter phase corresponding to the micro / nano unit 32 at the location.

[0112] More preferably, the beam splitter phase can be obtained by optimization using the Modified Iterative Fourier Transform Algorithm (MIFTA).

[0113] The improved iterative Fourier transform algorithm utilizes the central symmetry of the target intensity distribution (including a 4×4 uniform dot matrix) to impose symmetry constraints on the initial random phase and the iteratively updated phase. During the iteration process, the complex amplitude of the light field between the input and output planes is repeatedly projected through Fourier transform until the error converges, thus obtaining the beam splitter phase.

[0114] In one possible implementation, the optical fiber device may further include a protective cladding covering the emitting end face of the phase modulation region 3. It should be noted that the protective cladding covers the micro / nano unit array 32 and can be used to prevent environmental factors from contaminating and damaging the micro / nano unit array 32, ensuring the long-term stability of the device.

[0115] This embodiment does not limit the specific type of protective cladding, as long as it provides adequate protection. In one possible implementation, the protective cladding may be made of silicon dioxide. This embodiment does not limit the specific thickness of the protective cladding, which can be selected according to actual needs. In one possible implementation, the thickness of the protective cladding may be 800 nm.

[0116] Based on the above embodiments, this application has the following beneficial effects:

[0117] (1) The mode field extension region is set on the fiber optic output end face to expand the small mode field diameter beam emitted from the fiber into a large mode field diameter beam. This can increase the geometric size of the phase modulation region processing area, accommodate more micro-nano units, and provide sufficient design freedom for complex phase control. At the same time, it can reduce the sensitivity coefficient of the center drift during the phase modulation region processing, effectively diluting the weight of the overlay error on the device performance.

[0118] (2) The substrate thin film is set at the incident end of the phase modulation region. Its refractive index matches that of the mode field extension region, which can isolate the high refractive index micro-nano units from the low refractive index mode field extension region, greatly reducing the reflection loss of the beam at the interface between the mode field extension region and the phase modulation region, and improving the optical transmission efficiency.

[0119] (3) The micro-nano unit array is located at the output end of the phase modulation region. It consists of multiple micro-nano units made of high refractive index materials and arranged in an array. It has strong optical phase modulation capability, and the geometric dimensions and / or rotation angle of each micro-nano unit can be configured independently, so that the micro-nano unit array can obtain the target phase distribution. Based on the target phase distribution, the micro-nano unit array can perform phase modulation on the beam after beam expansion, realize wavefront shaping of the output beam, and thus realize the control of the output light field.

[0120] When the target phase distribution is configured as a focused phase distribution, the outgoing beam is focused into a focused beam, which can convert the fiber mode field into a mode spot that matches the chip waveguide. This solves the mode field mismatch problem between the fiber and the chip waveguide, significantly improving the coupling efficiency and alignment tolerance of the fiber and the chip. At the same time, since the mode field extension region and the phase modulation region are integrated at the output end of the same fiber device, there is no need to fabricate grating couplers, tapered waveguides or other additional structures on the chip side, reducing the chip manufacturing cost and design complexity.

[0121] Furthermore, by configuring other target phase distributions, micro-nano unit arrays can achieve various wavefront modulation functions such as beam collimation, Bessel beam generation, and Bessel beam array generation to meet the needs of different application scenarios.

[0122] Please refer to Figure 3 , Figure 3 This is a flowchart illustrating a method for fabricating an optical fiber device according to an embodiment of this application. The method may include:

[0123] S101: A mode field extension region is formed at the output end face of the optical fiber.

[0124] It should be noted that step S101 is a preprocessing step for the output end face of the optical fiber, the purpose of which is to form a mode field extension region on the output end face of the optical fiber.

[0125] This embodiment does not limit the specific method of forming the mode field extension region, and can be determined according to the specific type of mode field extension region. In one possible implementation, step S101 may include: splicing a coreless optical fiber at the emitting end face of the optical fiber.

[0126] Studies have shown that the flatness of the output end face has a significant impact on the quality of subsequent processing. In one possible implementation, the coreless fiber can be cut and polished after fusion splicing to make the output end face of the coreless fiber flat.

[0127] In one possible implementation, after the fusion splicing is completed, the optical fiber can be fixed on a special fixture with the output end face of the optical fiber facing upwards, so as to facilitate the subsequent step of forming the phase modulation region.

[0128] In one possible implementation, alignment marks can also be formed on the exit end face of the optical fiber before fusion splicing to improve the alignment accuracy of subsequent electron beam exposure.

[0129] This embodiment does not limit the specific method of forming the alignment mark, and can be determined according to the specific type of alignment mark. In one possible implementation, when the alignment mark includes a patterned groove, the alignment mark can be formed by photolithography on the exit end face of the optical fiber. In another possible implementation, when the alignment mark includes a patterned metal mark, the alignment mark can be formed by chrome plating on the exit end face of the optical fiber.

[0130] S102: A phase modulation region is formed at the exit end face of the mode field extension region; the phase modulation region includes a substrate thin film disposed at the exit end face of the mode field extension region and a micro / nano unit array disposed on the surface of the substrate thin film; the refractive index of the substrate thin film is matched with the refractive index of the mode field extension region; the refractive index of the micro / nano units in the micro / nano unit array is greater than the refractive index of the substrate thin film, and the geometric dimensions and / or rotation angles of the micro / nano units are configured to make the phase distribution of the micro / nano unit array the target phase distribution.

[0131] This embodiment does not limit the specific method of forming the phase modulation region, and can be determined according to the specific type of phase modulation region. In one possible implementation, step S102 may include:

[0132] Step 21: Deposit the substrate film and the functional film sequentially on the exit face of the mold field extension area using a low-temperature sputtering process.

[0133] It should be noted that using a low-temperature sputtering process can avoid damage to the ejection end face of the mold field expansion zone due to thermal stress.

[0134] In one possible implementation, the cryogenic sputtering process may include magnetron sputtering or ion beam sputtering.

[0135] Step 22: The functional thin film is patterned using photolithography to form a micro / nano unit array, thereby forming a phase modulation region.

[0136] It should be noted that this embodiment uses an in-situ preparation process, which directly processes the phase modulation region on the exit end face of the mold field extension area. This avoids the structural damage and positional deviation caused by the direct transfer method to the mold field extension area, and can achieve high-precision alignment, good process controllability, and high yield.

[0137] In one possible implementation, step 22 may include:

[0138] Step 221: Spin-coat electron beam resist onto the surface of the functional thin film and bake to cure;

[0139] In one possible implementation, the electron beam resist may include ZEP520A (methyl styrene / chloromethyl methacrylate copolymer) electron beam resist or PMMA (poly(methyl methacrylate) electron beam resist.

[0140] In one possible implementation, a hot plate can be used for baking and curing.

[0141] Step 222: Expose the film using an electron beam exposure system, aligning the center of the exposure area with the core of the optical fiber, and expose the functional thin film according to the target phase distribution.

[0142] In one possible implementation, alignment marks can be identified using a scanning electron microscope to align the center of the exposure area with the center of the fiber core. It should be noted that this method can achieve an alignment accuracy of ±50 nm.

[0143] It should be noted that exposing a functional thin film according to the target phase distribution means converting the target phase distribution into the position and rotation angle of the micro / nano units, and then exposing the functional thin film according to the converted position and rotation angle of the micro / nano units.

[0144] It should be noted that when the optical fiber is fixed on the special fixture, the special fixture can be placed on the sample stage of the electron beam exposure system and step 222 can be performed.

[0145] Step 223: Develop after exposure.

[0146] In one possible implementation, the exposed optical fiber can be immersed in a developing solution to remove the electron beam resist from the exposed area.

[0147] Step 224: After development, the micro-nano unit array pattern is transferred to the functional thin film using an etching process to form a micro-nano unit array, thereby forming a phase modulation region.

[0148] In one possible implementation, the etching process may include inductively coupled plasma etching.

[0149] Step 225: Remove the remaining electron beam resist.

[0150] In one possible implementation, oxygen plasma can be used to remove the remaining electron beam resist.

[0151] In one possible implementation, step 22 may be followed by step 23: depositing a protective cladding layer on the emitting end face of the phase modulation region and performing planarization.

[0152] In one possible implementation, a protective cladding can be deposited on the exit face of the phase modulation region by plasma-enhanced chemical vapor deposition.

[0153] Based on the above embodiments, this application is able to prepare the above-mentioned optical fiber device, which also has the above-mentioned beneficial effects.

[0154] This application also provides a coupling device, including the above-described optical fiber device.

[0155] It should be noted that, in addition to optical fiber devices, the coupling device in this embodiment may also include chips or other waveguide devices.

[0156] Based on the above embodiments, this application uses the above-described optical fiber device, which also has the above-described beneficial effects.

[0157] The functions of the aforementioned fiber optic devices are illustrated below with specific examples.

[0158] Example 1:

[0159] This embodiment provides a beam-focusing fiber optic device, in which:

[0160] The optical fiber used is Thorlabs SM600 single-mode fiber with a core diameter of 6μm, a cladding diameter of 125μm, and an operating wavelength λ of 633nm.

[0161] The mode field extension region uses coreless quartz fiber with a refractive index n of 1.46 and a length of 500 μm. After expansion, the mode field diameter is 51 μm.

[0162] The substrate film is made of silicon dioxide, with a thickness of 1 μm and a refractive index of 1.46;

[0163] The micro / nano unit array consists of multiple amorphous silicon nanopillars arranged in an array. It adopts a propagation phase modulation method. The amorphous silicon nanopillars have a period of 400 nm, a height of 500 nm, and a length and width that vary in the range of 100-400 nm. Phase modulation is achieved by changing the geometric dimensions of the amorphous silicon nanopillars.

[0164] To achieve beam focusing, the micro / nano unit array employs a spherical lens phase distribution, which satisfies the following: Among them, the design focal length ;

[0165] The optical field distribution obtained by simulating the beam-focusing fiber optic device is as follows: Figure 4 As shown, Figure 4 (a) represents the optical field distribution at the xy section in a beam-focusing fiber optic device; Figure 4 (b) shows the optical field distribution at the xz section of the beam-focusing fiber optic device. Simulation results show that this beam-focusing fiber optic device can achieve beam focusing.

[0166] Example 2:

[0167] This embodiment provides a beam-collimating fiber optic device, which is basically the same as that in Embodiment 1, except that the phase distribution used is different.

[0168] To achieve beam collimation, the micro / nano unit array employs a hyperbolic phase distribution to compensate for the spherical wavefront. The hyperbolic phase distribution satisfies: Among them, the design working distance .

[0169] Example 3:

[0170] This embodiment provides a Bessel beam generating fiber optic device, in which:

[0171] The optical fiber, mode field extension region, and substrate thin film are the same as in Example 1;

[0172] The micro / nano unit array employs geometric phase modulation. The amorphous silicon nanopillars have a period of 250 nm, a height of 300 nm, a length of 135 nm, and a width of 85 nm. The rotation angle of each amorphous silicon nanopillar is... Phase modulation is achieved by changing the rotation angle of the amorphous silicon nanopillars within the range of 0° to 180°.

[0173] To achieve Bessel beam generation, the micro / nano unit array employs an axial conical mirror phase distribution, which satisfies the following: Among them, design numerical aperture ;

[0174] According to the PB phase principle, the rotation angle The rotation angle of the amorphous silicon nanopillars was obtained.

[0175] This embodiment describes a 0th-order Bessel beam generating fiber optic device. Simulation of this 0th-order Bessel beam generating fiber optic device yields the following optical field distribution: Figure 5As shown, Figure 5 (a) represents the optical field distribution of the xy section in a 0th-order Bessel beam generating fiber device; Figure 5 (b) shows the optical field distribution of the xz section in the 0th-order Bessel beam generating fiber device. Simulation results show that this beam-focusing fiber device can achieve beam focusing. Simulation results also show that the diffraction-free distance of this 0th-order Bessel beam generating fiber device is 122 μm, and the full width at half maximum (FWHM) is 1.10 μm, which is in good agreement with the theoretical value of 124.92 μm. This embodiment also simulates another 1st-order Bessel beam generating fiber device, and the obtained optical field distribution is as follows. Figure 6 As shown, Figure 6 (a) represents the optical field distribution of the xy section in a first-order Bessel beam generating fiber device; Figure 6 (b) represents the optical field distribution of the xz section in a first-order Bessel beam generating fiber device. The first-order Bessel beam is similar to the zero-order Bessel beam, and will not be described in detail here.

[0176] Example 4:

[0177] This embodiment provides a Bessel beam array generating fiber optic device, in which:

[0178] The optical fiber, mode field extension region, and substrate thin film are the same as in Example 1;

[0179] The micro / nano unit array is the same as in Example 3;

[0180] To achieve Bessel beam generation, the micro / nano unit array employs a composite phase distribution, which satisfies the following: Among them, the beam splitter phase The target intensity distribution is obtained by optimization using an improved iterative Fourier transform algorithm, and the distribution is a 4×4 uniform lattice. The improved iterative Fourier transform algorithm utilizes the central symmetry of the target intensity distribution to impose symmetry constraints on the initial random phase and the iteratively updated phase. The specific steps are as follows:

[0181] Let the phase distribution of the input plane be... The target amplitude distribution on the focal plane is (A constant representing uniform intensity). The algorithm iterative process is as follows:

[0182] Step 1: Initialize the phase;

[0183] Randomly generate initial phase value range Using the central symmetry prior of the desired target distribution, a symmetry constraint is imposed on the initial phase:

[0184] ;

[0185] In the formula, for Triangular portion (e.g., the upper half-plane or the right half-plane). This indicates a transpose operation that makes the phase distribution centrally symmetric.

[0186] Step 2: Fourier transform;

[0187] Performing a Fourier transform on the phase distribution after applying symmetry constraints yields the complex amplitude distribution at the focal plane:

[0188] ;

[0189] In the formula, This represents the Fourier transform operator;

[0190] Step 3: Amplitude replacement;

[0191] Using the target amplitude distribution Replace the calculated amplitude with (constant, uniform intensity), while preserving the phase:

[0192] ;

[0193] Step 4: Inverse Fourier Transform;

[0194] Perform an inverse Fourier transform on the replaced complex amplitude to obtain the updated input plane complex amplitude:

[0195] ;

[0196] Extract its phase portion:

[0197] ;

[0198] Step 5: Apply symmetry constraints;

[0199] Applying a central symmetry constraint to the updated phase again, we obtain the... Phase distribution of the next iteration:

[0200] ;

[0201] Step 6: Error calculation and convergence judgment;

[0202] Calculate the error of this iteration:

[0203] ;

[0204] In the formula, Represents a certain norm (such as root mean square error); if Less than the preset threshold or number of iterations The algorithm terminates when the maximum number of iterations (e.g., 200) is reached, and the optimized beam splitter phase is output. Otherwise, return to step 2 and continue iterating.

[0205] After 200 iterations, the optimized beam splitter phase was obtained. ;

[0206] Composite phase converted to rotation angle: ;

[0207] Simulation of the Bessel beam array generating fiber device yields the following optical field distribution: Figure 7 As shown, Figure 7 (a) represents the optical field distribution at the xy section in a Bessel beam array generating fiber device; Figure 7 (b) represents the optical field distribution of the xz section in a Bessel beam array generating fiber device.

[0208] Simulation results show that the diffraction-free distance of this 0th-order Bessel beam generating fiber device is about 121 μm, and the array uniformity reaches 90%.

[0209] This document uses specific examples to illustrate the principles and implementation methods of this application. The various embodiments are progressive, with each embodiment focusing on its differences from others. Similar or identical parts between embodiments can be referred to interchangeably. The descriptions of the above embodiments are merely for the purpose of helping to understand the method and core ideas of this application. For those skilled in the art, various improvements and modifications can be made to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of this application.

[0210] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only 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 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 the element.

Claims

1. An optical fiber device, characterized in that, include: Optical fiber is used to transmit light beams; A mode field expansion region is disposed on the exit end face of the optical fiber and is used to expand the mode field of the beam emitted from the optical fiber so that the mode field diameter of the beam emitted from the mode field expansion region is larger than the mode field diameter of the beam emitted from the optical fiber. The phase modulation region includes a substrate film disposed on the emission end face of the mode field extension region and a micro / nano unit array disposed on the surface of the substrate film; The refractive index of the substrate film is matched with the refractive index of the mode field extension region; the refractive index of the micro-nano units in the micro-nano unit array is greater than the refractive index of the substrate film, and the geometric dimensions and / or rotation angles of the micro-nano units are configured to make the phase distribution of the micro-nano unit array a target phase distribution; The phase modulation region is used to perform phase modulation on the beam emitted from the mode field extension region according to the target phase distribution, so as to perform wavefront shaping on the beam emitted from the phase modulation region, so that the light field of the beam emitted from the phase modulation region is the target light field. The target light field includes at least one corresponding light field among a focused beam, a collimated beam, a Bessel beam, and a Bessel beam array.

2. The optical fiber device according to claim 1, characterized in that, The target phase distribution includes target phases that correspond one-to-one with the micro / nano units; The micro / nano unit array employs a propagation phase modulation mechanism; the geometric dimensions of the micro / nano units are determined by a target phase corresponding to the micro / nano unit and a lookup table; the lookup table is established through electromagnetic simulation and records the correspondence between the geometric dimensions of the micro / nano units and the target phase; the geometric dimensions include at least one of length, width, and height; And / or, the micro / nano unit array employs a geometric phase modulation mechanism; the geometric dimensions of each micro / nano unit are identical; the micro / nano unit is an anisotropic structure, and the rotation angle of the micro / nano unit and the target phase corresponding to the micro / nano unit satisfy: ； In the formula, The coordinates represent the position of the micro / nano unit on the surface of the substrate thin film. express The rotation angle of the micro / nano unit at the location; Indicates and The target phase corresponding to the micro / nano unit at the location.

3. The optical fiber device according to claim 1, characterized in that, The target light field includes the light field corresponding to the focused beam; the target phase distribution is a spherical lens phase distribution; the spherical lens phase distribution satisfies: ； In the formula, The coordinates represent the position of the micro / nano unit on the surface of the substrate thin film. Indicates and The target phase corresponding to the micro / nano unit at the location, wherein the target phase is the spherical lens phase; Indicates the design focal length; Indicates the operating wavelength.

4. The optical fiber device according to claim 1, characterized in that, The target optical field includes the optical field corresponding to the collimated beam; the target phase distribution is a hyperbolic phase distribution; the hyperbolic phase distribution satisfies: ； In the formula, The coordinates represent the position of the micro / nano unit on the surface of the substrate thin film. Indicates and The target phase corresponding to the micro / nano unit at the location, wherein the target phase is a hyperbolic phase; Indicates the design working distance; Indicates the operating wavelength.

5. The optical fiber device according to claim 1, characterized in that, The target optical field includes the optical field corresponding to the Bessel beam; the target phase distribution is an axial conical mirror phase distribution; the axial conical mirror phase distribution satisfies: ； In the formula, The coordinates represent the position of the micro / nano unit on the surface of the substrate thin film. Indicates and The target phase corresponding to the micro / nano unit at the location, wherein the target phase is the phase of the axial conical mirror; Indicates the design numerical aperture; Indicates the operating wavelength.

6. The optical fiber device according to claim 1, characterized in that, The target optical field includes the optical field corresponding to the Bessel beam array; the target phase distribution is a composite phase distribution; the composite phase distribution satisfies: ； In the formula, The coordinates represent the position of the micro / nano unit on the surface of the substrate thin film. express The target phase at the location corresponding to the micro / nano unit, wherein the target phase is a composite phase; Indicates and The phase of the axial conical mirror corresponding to the micro / nano unit at the location; Indicates and The beam splitter phase corresponding to the micro / nano unit at the location.

7. The optical fiber device according to claim 6, characterized in that, The phase of the beam splitter is obtained by optimization using an improved iterative Fourier transform algorithm; The improved iterative Fourier transform algorithm utilizes the central symmetry of the target intensity distribution to impose symmetry constraints on the initial random phase and the iteratively updated phase. During the iteration process, the complex amplitude of the light field between the input plane and the output plane is repeatedly projected through Fourier transform until the error converges, thus obtaining the beam splitter phase.

8. The optical fiber device according to claim 1, characterized in that, The optical fiber includes single-sided optical fiber or multimode optical fiber; The mode field extension region includes coreless optical fiber.

9. The optical fiber device according to claim 1, characterized in that, Also includes: The protective cladding covers the output end face of the phase modulation region.

10. A method for fabricating an optical fiber device, characterized in that, include: A mode field extension region is formed at the output end face of the optical fiber; A phase modulation region is formed at the exit end face of the mode field extension region; the phase modulation region includes a substrate film disposed at the exit end face of the mode field extension region and a micro / nano unit array disposed on the surface of the substrate film; the refractive index of the substrate film is matched with the refractive index of the mode field extension region; the refractive index of the micro / nano units in the micro / nano unit array is greater than the refractive index of the substrate film, and the geometric dimensions and / or rotation angles of the micro / nano units are configured to make the phase distribution of the micro / nano unit array a target phase distribution.

11. The method for fabricating an optical fiber device according to claim 10, characterized in that, The formation of a phase modulation region at the exit end face of the mode field extension region includes: The substrate thin film and the functional thin film are sequentially deposited on the exit end face of the mold field extension region using a low-temperature sputtering process; The functional thin film is patterned using photolithography to form the micro / nano unit array, thereby forming the phase modulation region.

12. A coupling device, characterized in that, include: The optical fiber device according to any one of claims 1 to 9.

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