Chip and design method supporting efficient interconnection of multiple heterogeneous hollow-core fibers

Abstract

The application relates to the technical field of optical fiber interconnection, and provides a chip supporting efficient interconnection of multiple heterogeneous hollow core optical fibers and a design method. The chip comprises a first grating, a second grating and a connecting waveguide; the first grating is used for coupling with a first hollow core optical fiber, the second grating is used for coupling with a second hollow core optical fiber; and the connecting waveguide is used for connecting the first grating and the second grating. The application provides a technical scheme for realizing the coupling of corresponding hollow core optical fibers through corresponding gratings, and realizing the interconnection of the hollow core optical fibers through the connection between the gratings and the connecting waveguide. Since the grating and the connecting waveguide are both designed based on a silicon-based chip, the preparation difficulty is low, and batch production is possible.

Description

Technical Field

[0001] This invention relates to the field of optical fiber interconnect technology, and in particular to a chip and design method that support efficient interconnection of various heterogeneous hollow optical fibers. Background Technology

[0002] Hollow-core fiber (HCF) has shown great promise in high-performance optical communication, high-power laser transmission, and precision optics due to its excellent characteristics such as ultra-low transmission loss, high nonlinear threshold, and low transmission delay. With the continuous development of hollow-core fiber technology, several fiber types with significantly different structures have emerged, such as nested antiresonant nodeless fiber (NANF) and double nested antiresonant nodeless fiber (DNANF). These fibers exhibit significant differences in core diameter, mode field diameter, and mode field distribution.

[0003] In practical applications, efficient interconnection between two hollow-core optical fibers with different parameters (i.e., heterogeneous hollow-core optical fibers) is often required. However, existing traditional interconnection schemes have many limitations. For example, the tapered / fusion splicing scheme using an intermediate single-mode fiber as a bridge requires first fusing and tapering one type of hollow-core fiber before connecting it to the other. This type of cascaded structure is not only complex to fabricate and prone to introducing additional dispersion and insertion loss, but it may also generate parasitic Fabry-Pérot (FP) resonances, leading to spectral jitter and thus reducing optical signal transmission performance. Furthermore, the fabrication process of this type of structure is not reproducible, making large-scale production difficult. Another commonly used spatial mode conversion scheme, while achieving mode matching to some extent, has a large system size and extremely high requirements for optical alignment accuracy, making it difficult to achieve high on-chip integration and large-scale mass production.

[0004] Therefore, overcoming the shortcomings of the existing technology is an urgent problem to be solved in this technical field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a chip and design method that support efficient interconnection of various heterogeneous hollow optical fibers, so as to solve the problem that the fabrication of heterogeneous hollow optical fiber interconnects is complicated and difficult to mass-produce in the prior art.

[0006] The present invention adopts the following technical solution: In a first aspect, the present invention provides a chip that supports efficient interconnection of various heterogeneous hollow optical fibers, including a first grating 1, a second grating 2 and a connecting waveguide 3; The first grating 1 is used for coupling with the first hollow fiber, and the second grating 2 is used for coupling with the second hollow fiber; The connecting waveguide 3 is used to connect the first grating 1 and the second grating 2.

[0007] Preferably, the grating period and duty cycle of the first grating 1 at each position are calculated based on the Gaussian optical field of the first hollow fiber, specifically including: Establish a mapping relationship between different grating periods and corresponding duty cycles in advance; Based on the Gaussian optical field of the first hollow fiber, the target leakage parameters at the first position along the longitudinal direction of the first grating 1 are determined. Among the optical field leakage parameters corresponding to each mapping relationship, a first optical field leakage parameter that matches the target leakage parameter is found. The grating period corresponding to the first optical field leakage parameter is used as the grating period of the first grating 1 at the first position, and the duty cycle corresponding to the first optical field leakage parameter is used as the duty cycle of the first grating 1 at the first position.

[0008] Preferably, the expression for the target leakage parameter at the first position along the longitudinal direction of the first grating 1 is: ; in, Indicates the position along the longitudinal direction of the first grating 1. This represents the target leakage parameters along the longitudinal position of the first grating 1. This represents the Gaussian optical field of the first hollow fiber.

[0009] Preferably, the pre-establishment of the mapping relationship between different grating periods and corresponding duty cycles specifically includes: By fixing the grating etching depth, the effective refractive index of the etched and unetched grating regions is obtained separately to obtain the equivalent effective refractive index within a single grating period for different duty cycles. Under the conditions of fixed operating wavelength and fixed grating radiation angle, the grating period and the equivalent effective refractive index within a single grating period satisfy a preset phase matching condition to obtain the duty cycle corresponding to the grating period, thereby establishing a mapping relationship between the grating period and the duty cycle.

[0010] Preferably, the expression for the equivalent effective refractive index within a single grating period for different duty cycles is: ; in, This indicates the effective refractive index of the unetched portion. Indicates the effective refractive index and duty cycle of the etched portion. This represents the proportion of the length of the unetched region to the length of the grating period within a single grating cycle.

[0011] Preferably, the expression for the preset phase matching condition is: ; in, Indicates a fixed operating wavelength. Indicates the fixed grating radiation angle. Indicates the grating period, Indicates the refractive index of the cladding layer on a silicon-based chip. It represents the equivalent effective refractive index within a single grating period.

[0012] Preferably, the connecting waveguide 3 includes a first tapered waveguide 31, a second tapered waveguide 32, and a straight waveguide 33; One end of the first tapered waveguide 31 is connected to the first grating 1, the other end of the first tapered waveguide 31 is connected to one end of the straight waveguide 33, one end of the straight waveguide 33 is connected to one end of the second tapered waveguide 32, and the other end of the second tapered waveguide 32 is connected to the second grating 2.

[0013] Preferably, the gradient angle of the first tapered waveguide 31 and the second tapered waveguide 32 is less than 2°.

[0014] Preferably, the width of the straight waveguide 33 is 400~500nm.

[0015] Secondly, the present invention provides a design method for a chip that supports efficient interconnection of multiple heterogeneous hollow optical fibers, wherein a first grating 1, a second grating 2 and a connecting waveguide 3 are designed on a silicon-based chip; The connecting waveguide 3 connects the first grating 1 and the second grating 2. The first grating 1 is used to couple with the first hollow fiber, and the second grating 2 is used to couple with the second hollow fiber.

[0016] Thirdly, the present invention provides a heterogeneous hollow fiber interconnection structure, including a first hollow fiber, a second hollow fiber, and the chip described in the first aspect that supports efficient interconnection of multiple heterogeneous hollow fibers; The first hollow fiber and the second hollow fiber are interconnected by the chip that supports efficient interconnection of multiple heterogeneous hollow fibers as described in the first aspect.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a technical solution to realize the coupling of corresponding hollow optical fibers through corresponding gratings, and then to connect gratings with connecting waveguides, thereby realizing the interconnection of hollow optical fibers with different or the same structure. Since both the gratings and the connecting waveguides are based on silicon-based chip design, the manufacturing difficulty is low, making mass production possible. Attached Figure Description

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

[0019] Figure 1 This is a schematic diagram of the structure of a chip that supports efficient interconnection of multiple heterogeneous hollow optical fibers, provided by an embodiment of the present invention; Figure 2 This is a flowchart illustrating a design method for a first grating in a chip that supports efficient interconnection of multiple heterogeneous hollow optical fibers, as provided in an embodiment of the present invention. Figure 3 This is a flowchart illustrating a design method for a first grating in a chip that supports efficient interconnection of multiple heterogeneous hollow optical fibers, as provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of a specific example of a chip hollow fiber-silicon-based optical chip coupling grating that supports efficient interconnection of multiple heterogeneous hollow fibers, provided by an embodiment of the present invention. Figure 5 This is a schematic diagram illustrating a specific example of a hollow optical fiber cross-section provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of a chip that supports efficient interconnection of multiple heterogeneous hollow optical fibers, provided by an embodiment of the present invention; Figure 7 This is a schematic diagram of an embodiment of the present invention, which uses a chip that supports efficient interconnection of multiple heterogeneous hollow optical fibers to interconnect a first hollow optical fiber and a second hollow optical fiber. Figure 8 This is a schematic diagram of the Gaussian light field at the first and second hollow optical coupling positions in a chip that supports efficient interconnection of multiple heterogeneous hollow optical fibers, provided by an embodiment of the present invention.

[0020] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1. First grating; 2. Second grating; 3. Connecting waveguide; 31. First tapered waveguide; 32. Second tapered waveguide; 33. Straight waveguide. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as openly inclusive, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples; that is, although they may be incorporated into embodiments or examples using the above terms for reasons such as order and position, it does not limit them to be incorporated in combination by a single embodiment or example.

[0023] In the description of this invention, the terms "inner", "outer", "longitudinal", "lateral", "upper", "lower", "top", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and do not require that this invention must be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0024] In this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0025] In this application, unless otherwise expressly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection, an indirect connection through an intermediate medium, or optical coupling. Furthermore, the term "coupled" can refer to an electrical connection method for achieving signal transmission.

[0026] In the description of this invention, the expression “A and / or B” (where A and B are used to formally represent specific features) will be used. The corresponding expression includes the following three combinations: only A, only B, and a combination of A and B.

[0027] As used in this invention, “about,” “approximately,” or “approximately” includes the stated value and the average value within an acceptable range of deviation from a particular value, wherein the acceptable range of deviation is determined by a person skilled in the art taking into account the measurement under discussion and the error associated with the measurement of the particular quantity (i.e., the limitations of the measurement system).

[0028] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] Example 1: To address the challenges of complex fabrication and mass production difficulties in existing heterogeneous hollow fiber interconnect technologies, Embodiment 1 of this invention provides a chip that supports efficient interconnection of various heterogeneous hollow fibers, such as... Figure 1 As shown, it includes a first grating 1, a second grating 2, and a connecting waveguide 3; the first grating 1 is used for coupling with a first hollow fiber, and the second grating 2 is used for coupling with a second hollow fiber; the connecting waveguide 3 is used to connect the first grating 1 and the second grating 2.

[0030] It should be noted that since both waveguides and gratings are structures existing on silicon-based chips, this embodiment can be understood as a scheme to realize hollow fiber interconnection using silicon-based chips. Furthermore, this embodiment does not limit the hierarchical structure of the silicon-based chip. Any silicon-based chip that can be designed to produce the first grating 1, the second grating 2, and the connecting waveguide 3 is within the protection scope of this embodiment.

[0031] The first hollow fiber and the second hollow fiber can be hollow fibers with different parameters or hollow fibers with the same parameters.

[0032] This invention provides a technical solution for achieving the coupling of corresponding hollow optical fibers through corresponding gratings, and then connecting gratings with connecting waveguide 3, thereby realizing the interconnection of hollow optical fibers with different or the same structure. Since both the gratings and the connecting waveguide 3 are based on silicon-based chip design, the manufacturing difficulty is low, making mass production possible.

[0033] In practice, it has been found that existing grating designs typically focus only on matching the radiation angle with the wavelength, making it difficult to precisely control the lateral distribution of the emitted light field (especially the Gaussian mode field distribution). This results in insufficient mode field matching with the hollow fiber, limited coupling efficiency, and low interconnection efficiency in the hollow fiber. To address this issue, this embodiment provides a preferred implementation method where the first grating 1 and / or the second grating 2 are graded gratings. The first grating 1 and / or the second grating 2 are designed using a silicon-based hollow fiber high-efficiency coupling method based on mode field matching. Taking the first grating 1 as an example, the grating period and duty cycle of the first grating 1 at each position are calculated based on the Gaussian light field of the first hollow fiber. Figure 2 As shown, it specifically includes: In step 201, a mapping relationship between different grating periods and their corresponding duty cycles is established in advance. The grating period refers to the spatial repetition distance between two adjacent grating units, used to determine the phase-matching condition of the grating and is a key parameter controlling the emitted light angle and wavelength. The duty cycle refers to the ratio of the width of the unetched silicon material to the entire period length within one grating period. The duty cycle reflects the density of the grating structure and mainly affects the scattering intensity of the grating.

[0034] For a given grating cell, its grating period and duty cycle jointly determine the local grating structure. The grating structure directly affects two key physical quantities at that point: the modulation depth of the local effective refractive index and the light leakage (scattering) intensity, thus affecting the optical field leakage parameters at various positions along the grating's longitudinal direction. Therefore, this embodiment of the invention establishes multiple sets of mapping relationships between grating periods and duty cycles. Since the grating period and duty cycle of each set of mapping relationships are determined, it can be understood that the grating structure is determined, and therefore has determined optical field leakage parameters.

[0035] In step 202, the target leakage parameters at the first position along the longitudinal direction of the first grating 1 are determined based on the Gaussian light field of the first hollow fiber.

[0036] In step 203, among the optical field leakage parameters corresponding to each mapping relationship, a first optical field leakage parameter that matches the target leakage parameter is found. The grating period corresponding to the first optical field leakage parameter is used as the grating period of the first grating 1 at the first position, and the duty cycle corresponding to the first optical field leakage parameter is used as the duty cycle of the first grating 1 at the first position.

[0037] By taking each position along the longitudinal direction of the first grating 1 as the first position and performing the above steps 202 and 203, the grating period and duty cycle of the first grating 1 at each position can be obtained, thus obtaining the specific gradient grating structure.

[0038] In one optional implementation, the optical field leakage parameters of the mapping relationship are obtained through simulation. Specifically, a gradient grating is constructed based on the mapping relationship to achieve a Gaussian radiation field distribution, and the optical field leakage parameters at each position of the grating are obtained. That is, for different combinations of grating periods and duty cycles, the corresponding optical field leakage parameters are calculated using the finite-difference time-domain method (FDTD) simulation. .

[0039] In the framework of coupled-mode theory, the optical leakage parameter is usually described by an attenuation coefficient α(z), which represents the ratio of optical power leaking to the outside per unit length due to grating scattering when light propagates along position z in the waveguide. The larger α(z) is, the stronger the ability of the grating at that position to leak to the outside due to grating scattering.

[0040] The first optical field leakage parameter that matches the target leakage parameter is the optical field leakage parameter whose difference from the target leakage parameter is within a preset range (e.g., under ideal conditions, the optical field leakage parameter that is equal to the target leakage parameter is used as the first optical field leakage parameter). The preset range is obtained by those skilled in the art based on experience.

[0041] Unlike traditional uniform gratings (i.e., all periods and duty cycles are the same), the gradient grating's grating period and / or duty cycle change continuously along the length of the grating (i.e., the light propagation direction, denoted as the z-axis). This characteristic allows the grating's coupling properties (e.g., coupling strength, phase) to be adjustable with position. Since the embodiments of this invention require the grating's output radiation field to have a Gaussian distribution across its cross-section, the grating's light leakage capability along the z-direction also needs to change accordingly to generate a uniformly decreasing (i.e., Gaussian) radiation field. That is, more light needs to leak out at the beginning of the grating (i.e., the center of the corresponding Gaussian spot), while less light needs to leak out at the end (i.e., the edge of the spot). Through the above mapping relationship, the calculated first light field leakage parameters of the target, which vary with z-position, are mapped inversely to a set of physical structural parameters (i.e., grating period and duty cycle) that vary with z-position, thus forming a gradient grating where both the period and duty cycle change with position.

[0042] It should be noted that the first grating 1 and / or the second grating 2 are graded gratings, and the first grating 1 and / or the second grating 2 are designed using a silicon-based hollow fiber high-efficiency coupling method based on mode field matching, specifically including the following three optional implementation methods: The first type: The first grating 1 is a graded-gradient grating, designed using a silicon-based hollow fiber high-efficiency coupling method based on mode field matching. The structure of the second grating 2 is not limited.

[0043] The second type: The second grating 2 is a graded-gradient grating, designed using a silicon-based hollow fiber high-efficiency coupling method based on mode field matching. The structure of the first grating 1 is not limited.

[0044] The third type: Both the first grating 1 and the second grating 2 are graded gratings. Both the first grating 1 and the second grating 2 are designed using a silicon-based hollow fiber high-efficiency coupling method based on mode field matching.

[0045] The design process of the first grating 1 is only used as an example here. In actual use, the design process of the second grating 2 in the second and third embodiments above is based on the same concept as the design process of the first grating 1, and will not be described in detail here.

[0046] This invention, through the obtained leakage parameter distribution, uses a mapping relationship to assign a specific grating period and duty cycle to each position z on the grating. The corresponding coupling process is as follows: the guided mode light in the silicon photonic chip waveguide encounters the graded grating designed in this invention during propagation. Based on the leakage parameter distribution, the grating leaks light from the waveguide at appropriate positions with appropriate intensity. The light leaking from all positions coherently superimposes in free space. Because the graded grating precisely controls the amplitude and phase of the leaked light in space, these wavelets, after superposition, form a high-quality approximate Gaussian beam in the far field (or, at the fiber end face), thereby achieving efficient and stable coupling between silicon-based hollow fiber, ensuring stable and efficient coupling between the first grating 1 and the first hollow fiber, and ensuring stable and efficient coupling between the second grating 2 and the second hollow fiber.

[0047] This invention designs coupling gratings (i.e., first grating 1 and / or second grating 2) for silicon-based hollow fiber based on mode field matching. By precisely adjusting the period and duty cycle of the silicon-based grating, the leakage parameters at each position of the grating are distributed and controlled without changing the radiation direction. This results in a Gaussian distribution of the radiated light field that highly matches the receiving mode field of the hollow fiber, thereby significantly improving coupling efficiency and achieving direct and efficient coupling between the silicon-based chip and the hollow fiber. By adjusting the structural parameters of the silicon-based grating to actively match the target mode field of the hollow fiber, efficient and stable coupling of optical signals from the silicon-based chip to the hollow fiber is achieved.

[0048] To achieve a Gaussian radiation field that matches the mode field of a hollow fiber, this invention employs a graded grating with leakage parameters distributed according to a specific pattern. These leakage parameters are mapped to the geometric parameters of the grating to achieve efficient coupling by precisely controlling leakage at each location. In one embodiment, step 203 may involve: pre-recording the optical field leakage coefficients of different duty cycles and their corresponding grating periods in a database; for the target leakage value at each location on the grating, finding the duty cycle that achieves the leakage value through database search or interpolation, and directly using the grating period corresponding to that duty cycle that satisfies the phase-matching condition. This transforms the abstract function controlling radiation intensity (i.e., the leakage parameter) into a specific geometric parameter distribution that guides manufacturing.

[0049] In a specific application scenario, the expression for the target leakage parameter at the first position along the longitudinal direction of the first grating 1 is: ;in, Indicates the position along the longitudinal direction of the first grating 1. This represents the target leakage parameters along the longitudinal position of the first grating 1. This represents the Gaussian optical field of the first hollow fiber.

[0050] In practical applications, the pre-established mapping relationship between different grating periods and corresponding duty cycles is as follows: Figure 3 As shown, it specifically includes: In step 301, the grating etching depth is fixed, and the effective refractive indices of the etched and unetched grating regions are obtained separately to obtain the equivalent effective refractive indices within a single grating period for different duty cycles. Specifically, the grating etching depth is fixed, and the effective refractive indices of the etched and unetched grating regions are obtained separately through finite-difference time-domain simulation. Here, the grating unit is a complete etched periodic structure etched on a silicon waveguide, such as... Figure 4 As shown, a grating unit consists of a raised portion (i.e., the unetched area of ​​the grating) and a recessed portion (i.e., the etched area of ​​the grating). Since a grating unit is composed of alternating etched areas (recesses, typically made of silicon dioxide or air) and unetched areas (ridges, made of silicon), light propagating within it actually experiences a path with periodic, drastic jumps in refractive index; directly analyzing this complex path is very difficult. Therefore, this embodiment of the invention calculates the equivalent effective refractive index, replacing the real, non-uniform grating unit with a hypothetical, uniform waveguide segment with a constant refractive index, and requires that this hypothetical waveguide be optically (especially in terms of phase accumulation) equivalent to the real grating unit. The equivalent effective refractive index directly determines the phase-matching condition of the grating, so it needs to be calculated. For the silicon waveguide containing the grating, its effective refractive index refers to the overall refractive index received by light propagating in the waveguide. Effective refractive index is not an inherent property of a material, but rather a mode-field dependent equivalent parameter determined by the refractive index of the waveguide's core layer (i.e., silicon), cladding (e.g., silica or air), geometry (e.g., waveguide width, thickness), and the mode of light. Effective refractive index describes the phase velocity of light propagating within a waveguide.

[0051] When periodic etching (i.e., grating) is introduced on the waveguide surface, the local effective refractive index of each grating element undergoes periodic or gradual modulation with changes in etching depth and duty cycle. This modulation provides the momentum required to scatter or couple guided mode light within the waveguide into free space. Therefore, the effective refractive index parameter needs to be calculated first.

[0052] The expression for the equivalent effective refractive index within a single grating period for different duty cycles is as follows: ;in, This indicates the effective refractive index of the unetched portion. This indicates the effective refractive index of the etched portion. Duty cycle is the ratio of the length of the unetched area to the length of the grating period within a single grating period.

[0053] In step 302, under the conditions of fixed working wavelength and fixed grating radiation angle, the grating period and the equivalent effective refractive index within a single grating period are made to satisfy a preset phase matching condition, thereby obtaining the duty cycle corresponding to the grating period and establishing a mapping relationship between the grating period and the duty cycle.

[0054] The preset phase matching condition can be selected by those skilled in the art based on the specific application scenario. In one practical application scenario, the expression for the preset phase matching condition is: ;in, Indicates a fixed operating wavelength. Indicates the fixed grating radiation angle. Indicates the grating period, Indicates the refractive index of the cladding layer on a silicon-based chip. It represents the equivalent effective refractive index within a single grating period.

[0055] The principle by which a grating directs light propagating within a waveguide to emit radiation is based on momentum conservation or phase matching. The periodic structure of the grating compensates for the momentum difference between the optical modes within the waveguide and those in free space (or optical fiber). This embodiment constrains these three factors to achieve equilibrium by setting phase matching conditions. Once the operating wavelength and desired radiation angle are preset, the grating period can be constrained.

[0056] Under the conditions of fixed wavelength and radiation angle, grating design is to find a set of grating periods and duty cycles that are compatible with each grating unit, so that the local equivalent effective refractive index determined by the duty cycle can satisfy the preset phase matching equation that determines the radiation direction together with the duty cycle.

[0057] like Figure 5 The diagram shows a cross-sectional view of a first hollow fiber provided in an embodiment of the present invention. In actual fabrication, process adaptation adjustments can be made to ensure the machinability of the grating. In one embodiment, the method further includes: when the duty cycle corresponding to the optical field leakage parameter required at a certain location exceeds the minimum etch size achievable by the process, a combination of period and duty cycle closest to the leakage parameter within the process allowable range is used as a substitute. That is, when the ideal duty cycle at a certain location determined according to the target leakage parameter in step 203 exceeds the minimum feature size achievable by the process (e.g., the required etch line width is smaller than the lithographic resolution), within the value range allowed by the process rules, a set of achievable period and duty cycle combinations that can produce the leakage parameter closest to the target is selected from the aforementioned pre-established leakage parameter database for substitution.

[0058] This invention achieves direct coupling with high mode matching, significantly improving efficiency. By actively controlling the distribution of the grating period and duty cycle, the silicon-based grating radiation field is precisely shaped into a target Gaussian distribution, achieving a high degree of matching with the ideal receiving mode field of the hollow-core fiber. Compared to the traditional indirect coupling method of "hollow-core fiber → single-mode fiber → optical chip," this avoids the additional insertion loss, mode field mismatch, and coupling alignment errors introduced by intermediate conversion stages, thus significantly improving coupling efficiency and reducing system complexity and instability. Furthermore, it provides a clear and controllable grating parameter design method, eliminating the reliance on trial and error: Existing grating designs often rely on parameter scanning and iterative optimization, which is inefficient and lacks physical intuition. Based on the analytical relationship between leakage parameters and the target optical field, this invention establishes a direct design process for deriving the required grating geometric parameters (i.e., grating period and duty cycle) from the target Gaussian optical field. This method has clear physical meaning, a short design cycle, and can be customized for different hollow-core fiber mode fields, enhancing the adaptability and predictability of the design. It also balances ideal performance with process feasibility, demonstrating good implementability: During the grating parameter mapping process, this invention explicitly considers the actual process limits (such as the minimum etching size) and replaces them with the unit structure that has the closest performance within the process allowance, ensuring the fabrication feasibility of the grating structure without significantly affecting the overall coupling performance. This design concept enables high-performance grating couplers to be compatible with existing semiconductor micro-nano fabrication processes, which is conducive to promoting their large-scale application in practical integrated photonic chips.

[0059] In a practical application scenario, such as Figure 6 As shown, the connecting waveguide 3 includes a first tapered waveguide 31, a second tapered waveguide 32, and a straight waveguide 33; one end of the first tapered waveguide 31 is connected to the first grating 1, the other end of the first tapered waveguide 31 is connected to one end of the straight waveguide 33, one end of the straight waveguide 33 is connected to one end of the second tapered waveguide 32, and the other end of the second tapered waveguide 32 is connected to the second grating 2.

[0060] When an optical signal enters the chip from the first hollow fiber via the first grating 1, its large spatial Gaussian mode field is forcibly constrained and converted into the TE fundamental mode in the silicon waveguide. This fundamental mode is guided through the first tapered waveguide 31 on the chip to the single-mode straight waveguide 33, achieving stable transmission within the submicron waveguide. Subsequently, this fundamental mode is guided through the straight waveguide 33 to the second tapered waveguide 32 and then to the second grating 2. It undergoes reverse radiation modulation through the specific non-uniform apodization parameter distribution of the second grating 2, redistributing and reconstructing it into a radiation field matching the characteristics of the second hollow fiber. This step, through a "spatial field—waveguide field—spatial field" conversion mechanism, eliminates the losses caused by phase mismatch and inconsistent mode field diameters when heterogeneous fibers are directly interconnected. Similarly, the optical signal travels from the second hollow fiber through the second grating 2, the second tapered waveguide 32, the straight waveguide 33, the first tapered waveguide 31, and the first grating 1 to reach the first hollow fiber, with a transmission mechanism consistent with that of the optical signal from the first hollow fiber to the second hollow fiber.

[0061] To further optimize coupling efficiency, this embodiment also provides a preferred implementation where the gradient angle between the first tapered waveguide 31 and the second tapered waveguide 32 is less than 2°. The width of the straight waveguide 33 is 400~500nm. In one embodiment, the width of the straight waveguide 33 can be 450nm.

[0062] This embodiment achieves efficient and low-loss interconnection between heterogeneous hollow-core fibers, significantly improving mode matching accuracy. By integrating two customized non-uniform apodized gratings (i.e., grating 1 and grating 2) on a silicon-based chip for different hollow-core fiber mode fields (such as NANF and DNANF with different core diameters), this embodiment solves the coupling loss problem caused by mode field mismatch and phase discontinuity in traditional solutions. Using a silicon waveguide as an intermediary, the complex spatial mode conversion is transformed into controlled on-chip waveguide mode evolution. Experimental measurements show that this embodiment can achieve a total coupling loss as low as 3.01 dB at both ends. Compared with traditional tapered or spatial lens coupling, this embodiment effectively suppresses higher-order mode excitation, significantly reduces insertion loss, and ensures high fidelity of optical signals transmitted between hollow-core fibers with different structures. Furthermore, the chip described in this embodiment possesses excellent polarization stability and wide bandwidth characteristics, improving the robustness of the communication system.

[0063] In some embodiments, this example further enhances upward radiation efficiency by introducing an integrated metal bottom mirror on the silicon-on-insulator (SOI) chip and optimizing the silicon dioxide substrate thickness, thereby achieving a high polarization extinction ratio (PER) exceeding 29 dB through selective coupling of specific polarization states. This structure not only enhances the device's immunity to environmental disturbances but also ensures stable conversion efficiency over a wide operating wavelength range (e.g., a 3 dB bandwidth exceeding 30 nm) through synchronous optimization of the dispersion of the heterogeneous gratings at both ends. This effectively solves the problems of polarization state instability and spectral jitter (such as FP resonance) in traditional heterogeneous interconnect schemes.

[0064] This embodiment achieves high device integration and mass production capability, significantly reducing system complexity and cost. It integrates complex mode conversion functions onto millimeter- or even sub-millimeter-scale silicon-based photonic chips, completely transforming previous interconnection methods that relied on manual tapering, fusion splicing, or large-scale spatial optical alignment systems. Because the entire chip is manufactured using mature Complementary Metal Oxide Semiconductor (CMOS) compatible micro-nano fabrication processes, the device's geometric parameters (such as grating period, duty cycle, and etching depth) exhibit extremely high processing accuracy and repeatability. This not only greatly reduces the physical size of heterogeneous hollow-core fiber interconnect modules, facilitating on-chip multi-path parallel integration, but also significantly improves production efficiency and reliability, providing a low-cost, scalable hardware foundation for the deployment of large-scale hollow-core fiber communication networks.

[0065] Example 2: Based on the method described in Embodiment 1, this invention combines specific application scenarios and uses technical descriptions in relevant scenarios to illustrate the implementation process of the features of this invention in those scenarios.

[0066] This embodiment provides a chip that supports efficient interconnection of various heterogeneous hollow optical fibers, such as... Figure 7 The image shows a scenario where the chip is used to interconnect the first and second hollow optical fibers. The Gaussian light field at the coupling points of the hollow optical fibers after interconnection is as follows: Figure 8 As shown, the core technical solution involves integrating two independently designed non-uniform apodized grating couplers for different hollow fiber mode field characteristics on the same silicon substrate, and connecting them using a single-mode silicon waveguide. The specific implementation steps are as follows: (1) For two hollow optical fibers of different specifications to be interconnected (such as NANF and DNANF with different radii) (i.e., the first hollow optical fiber and the second hollow optical fiber), extract the mode field and Gaussian optical field G1(z) and G2(z) of their fundamental mode respectively.

[0067] (2) On the same silicon-on-insulator (SOI) platform, based on the heterogeneous parameters extracted in step (1) (i.e., the Gaussian optical field G1(z) of the first hollow fiber and the Gaussian optical field G2(z) of the second hollow fiber), calculate the geometry of the gratings at both ends (i.e., calculate the grating period and duty cycle at each position of the first grating 1, and calculate the grating period and duty cycle at each position of the second grating 2). During the calculation, ensure phase matching consistency, that is, to ensure on-chip interconnection, the equivalent refractive index of the gratings at both ends at the connection with the silicon waveguide must remain continuous to suppress reflection loss.

[0068] (3) Using on-chip waveguides to achieve constrained evolution and reconfiguration of heterogeneous modes: The silicon waveguide connecting the first grating 1 and the second grating 2 is used as a mode transfer and adaptation platform. When the optical signal enters the chip from the first hollow fiber through the first grating 1, its large spatial Gaussian mode field is forcibly constrained and converted into the TE fundamental mode in the silicon waveguide. This fundamental mode is guided to the single-mode straight waveguide (i.e., straight waveguide 33) through the on-chip long tapered waveguide (i.e., the first tapered waveguide 31), realizing stable transmission in the submicron waveguide; wherein, the long tapered waveguide is a trapezoidal waveguide with a gradient angle of less than 2°, and the single-mode straight waveguide is a 450nm silicon-based waveguide; subsequently, this fundamental mode is guided to the second grating 2 through the on-chip straight waveguide 33 via the long tapered waveguide (i.e., the second tapered waveguide 32), and is back-radiated and modulated by the specific non-uniform apodization parameter distribution of the second grating 2, redistributing and reconfiguring it into a radiation field that matches the characteristics of the second hollow fiber. This step eliminates the loss caused by phase mismatch and inconsistent mode field diameters when heterogeneous optical fibers are directly interconnected through a "space field - waveguide field - space field" conversion mechanism.

[0069] (4) Constructing a broadband high-polarization enhancement structure to optimize global performance: To address the potential differences in dispersion distribution between the two end gratings in a heterogeneous coupling system, a global optimization strategy is adopted to improve the overall robustness of the device, including: a. Interference Enhancement Synergistic Design: An aluminum bottom mirror is integrated above the silicon substrate. By precisely controlling the thickness of the buried oxide layer (BOX) between the mirror and the grating layer, the downward-leaking radiation is highly reflected at the aluminum mirror and forms constructive interference with the upward-leaking radiation after returning to the grating region. This improves the coupling directionality and overall coupling efficiency within the target operating wavelength band, achieving synchronous gain for the heterogeneous coupling efficiency at both ends and compensating for the additional insertion loss caused by mode field mismatch. For the 1550 nm band, the BOX thickness typically needs to be optimized to approximately the equivalent optical path length corresponding to a quarter wavelength condition to ensure a suitable phase relationship between the reflected light and the original radiation field, thereby achieving the maximum interference enhancement effect.

[0070] b. Polarization Selectivity Control: By uniformly optimizing the etching depth of the gratings at both ends and combining the bottom mirror to control the reflection phase of specific polarization states, higher-order mode excitation is suppressed and fundamental mode coupling is enhanced, ensuring that the device maintains a high polarization extinction ratio over a wide spectral range, and ultimately achieving low-loss, high-purity on-chip mode conversion between heterogeneous hollow-core fibers.

[0071] Specifically, the calculation of the geometric structure of the gratings at both ends includes: (1) Determine the effective refractive index of the grating unit: With the grating etching depth fixed, the effective refractive index of the etched and unetched regions of the grating is obtained through finite-difference time-domain simulation. Based on this, the equivalent effective refractive index within a single grating period is determined. It is given by the following formula: ; In the formula, This indicates the effective refractive index of the unetched portion. This indicates the effective refractive index of the etched portion. This represents the grating duty cycle.

[0072] (2) Establish the correspondence between period and duty cycle (i.e., mapping relationship): at a fixed working wavelength and grating radiation angle Under the condition of grating period Equivalent effective refractive index within a single grating period The following phase matching conditions must be met: ; In the formula, This represents the refractive index of the cladding layer on a silicon-based chip. This formula is used to compare the equivalent effective refractive index... By combining the formulas, the duty cycle corresponding to different periods can be determined.

[0073] (3) Constructing a gradient grating to achieve a Gaussian radiation field distribution: To achieve a Gaussian distribution of the grating output light field, the following steps are performed: a. Obtaining unit leakage parameters: For different combinations of period and duty cycle (i.e., mapping relationships), calculate the corresponding optical field leakage parameters using FDTD simulation. .

[0074] b. Establish the distribution of leakage parameters along the grating length: based on the target Gaussian light field intensity distribution. The longitudinal position along the grating is determined by the following relationship. Required leakage parameters (i.e., target leakage parameters): ; This allows us to obtain the positions of the grating. The leakage parameters to be realized are mapped to the corresponding grating period and duty cycle, thereby achieving efficient coupling of the large-size mode field of the first hollow fiber into the on-chip single-mode silicon waveguide.

[0075] (4) Process adaptation adjustment: In actual fabrication, if the duty cycle corresponding to the leakage parameter required at a certain position exceeds the minimum etching size that the process can achieve, the cycle and duty cycle combination that is closest to the leakage parameter within the process allowable range will be used as a substitute to ensure the machinability of the grating.

[0076] Example 3: Based on Embodiments 1 and 2 above, this embodiment also provides a heterogeneous hollow fiber interconnection structure, including a first hollow fiber, a second hollow fiber, and a chip that supports efficient interconnection of multiple heterogeneous hollow fibers as described in Embodiment 1 or Embodiment 2; the first hollow fiber and the second hollow fiber are interconnected through the chip that supports efficient interconnection of multiple heterogeneous hollow fibers as described in Embodiment 1 or Embodiment 2.

[0077] Those skilled in the art will understand that all or part of the steps in the various methods of the embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, which may include: read-only memory (ROM), random access memory (RAM), magnetic disk or optical disk, etc.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A chip supporting high-efficiency interconnection of multiple heterogeneous hollow optical fibers, characterized in that, It includes a first grating (1), a second grating (2), and a connecting waveguide (3); The first grating (1) is used for coupling with the first hollow fiber, and the second grating (2) is used for coupling with the second hollow fiber; The connecting waveguide (3) is used to connect the first grating (1) and the second grating (2).

2. The chip supporting high-efficiency interconnection of multiple heterogeneous hollow optical fibers according to claim 1, characterized in that, The grating period and duty cycle of the first grating (1) at each position are calculated based on the Gaussian optical field of the first hollow fiber, specifically including: Establish a mapping relationship between different grating periods and corresponding duty cycles in advance; Based on the Gaussian light field of the first hollow fiber, the target leakage parameters at the first position along the longitudinal direction of the first grating (1) are determined; Among the light field leakage parameters corresponding to each mapping relationship, find the first light field leakage parameter that matches the target leakage parameter, take the grating period corresponding to the first light field leakage parameter as the grating period of the first grating (1) at the first position, and take the duty cycle corresponding to the first light field leakage parameter as the duty cycle of the first grating (1) at the first position.

3. The chip supporting high-efficiency interconnection of multiple heterogeneous hollow optical fibers according to claim 2, characterized in that, The expression for the target leakage parameter at the first longitudinal position of the first grating (1) is: ； in, Indicates the longitudinal position along the first grating (1), This indicates the target leakage parameters along the longitudinal position of the first grating (1). This represents the Gaussian optical field of the first hollow fiber.

4. The chip supporting high-efficiency interconnection of multiple heterogeneous hollow optical fibers according to claim 2, characterized in that, The pre-established mapping relationship between different grating periods and corresponding duty cycles specifically includes: By fixing the grating etching depth, the effective refractive index of the etched and unetched grating regions is obtained separately to obtain the equivalent effective refractive index within a single grating period for different duty cycles. Under the conditions of fixed operating wavelength and fixed grating radiation angle, the grating period and the equivalent effective refractive index within a single grating period satisfy a preset phase matching condition to obtain the duty cycle corresponding to the grating period, thereby establishing a mapping relationship between the grating period and the duty cycle.

5. The chip supporting high-efficiency interconnection of multiple heterogeneous hollow optical fibers according to claim 4, characterized in that, The expression for the equivalent effective refractive index within a single grating period for different duty cycles is as follows: ； in, This indicates the effective refractive index of the unetched portion. Indicates the effective refractive index and duty cycle of the etched portion. This represents the proportion of the length of the unetched region to the length of the grating period within a single grating cycle.

6. The chip supporting high-efficiency interconnection of multiple heterogeneous hollow optical fibers according to claim 4, characterized in that, The expression for the preset phase matching condition is: ； in, Indicates a fixed operating wavelength. Indicates the fixed grating radiation angle. Indicates the grating period. Indicates the refractive index of the cladding layer on a silicon-based chip. It represents the equivalent effective refractive index within a single grating period.

7. The chip supporting high-efficiency interconnection of multiple heterogeneous hollow optical fibers according to claim 1, characterized in that, The connecting waveguide (3) includes a first tapered waveguide (31), a second tapered waveguide (32), and a straight waveguide (33). One end of the first tapered waveguide (31) is connected to the first grating (1), the other end of the first tapered waveguide (31) is connected to one end of the straight waveguide (33), one end of the straight waveguide (33) is connected to one end of the second tapered waveguide (32), and the other end of the second tapered waveguide (32) is connected to the second grating (2).

8. The chip supporting high-efficiency interconnection of multiple heterogeneous hollow optical fibers according to claim 7, characterized in that, The gradient angles of the first tapered waveguide (31) and the second tapered waveguide (32) are less than 2°.

9. The chip supporting high-efficiency interconnection of multiple heterogeneous hollow optical fibers according to claim 7, characterized in that, The width of the straight waveguide (33) is 400~500nm.

10. A design method for a chip supporting efficient interconnection of multiple heterogeneous hollow optical fibers, characterized in that, A first grating (1), a second grating (2), and a connecting waveguide (3) are designed on a silicon-based chip. The connecting waveguide (3) connects the first grating (1) and the second grating (2). The first grating (1) is used to couple with the first hollow fiber, and the second grating (2) is used to couple with the second hollow fiber.

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