A mode multiplexing and demultiplexing device based on few-mode fiber

Abstract

This invention relates to the field of optical communication technology, and more particularly to a mode multiplexing and demultiplexing device based on few-mode fiber. It is characterized by comprising a base module, an outer ring fixing module, a central floating optical island module, a compliant support self-centering module, a differential fine-tuning drive module, an axial pre-compression focusing module, an input interface positioning module, an output interface positioning module, and a mode conversion optical path module. This invention, through the coordinated operation of the outer ring fixing module, the central floating optical island module, the compliant support self-centering module, and the differential fine-tuning drive module, integrates the input optical path, the mode conversion optical path, and the few-mode fiber output optical path into a finely adjustable optical assembly, reducing assembly complexity and improving optical axis consistency and mode coupling accuracy.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a mode multiplexing and demultiplexing device based on few-mode optical fiber. Background Technology

[0002] With the rapid development of cloud computing, the Internet of Things, 5G / 6G communications, and high-definition video, global data traffic is experiencing explosive growth. Traditional single-mode fiber (SMF) communication systems mainly rely on technologies such as time division multiplexing (TDM), wavelength division multiplexing (WDM), and polarization multiplexing (PDM) to improve transmission capacity. However, limited by the nonlinear effects of optical fibers (such as the Kerr effect) and the bandwidth limitations of optical amplifiers, the transmission capacity of single-mode fiber is rapidly approaching the nonlinear Shannon limit determined by Shannon's theorem. To overcome this "capacity crisis," space division multiplexing (SDM) technology has emerged as the most promising breakthrough direction for next-generation optical communication networks.

[0003] In the space division multiplexing technology system, mode multiplexing (MDM) technology based on few-mode fiber (FMF) has become a research hotspot in academia and industry because it can transmit multiple mutually orthogonal spatial modes (such as LP01, LP11, LP21, etc.) in a single fiber, thereby multiplying system capacity and spectral efficiency. At the same time, it has better compatibility and lower splicing difficulty compared to multi-core fiber.

[0004] The prior art disclosed in CN111736264A is an all-fiber mode multiplexer / demultiplexer comprising two identical few-mode fibers. The coating on the tapered region of the few-mode fibers has been stripped, and the fibers are fused and tapered to the diameter and length of the operating wavelength. The operating wavelength can be set according to actual needs, achieving mode multiplexing and demultiplexing functions. This process does not require pre-tapering of the few-mode fibers. This invention proposes for the first time a method for realizing all-fiber mode multiplexing / demultiplexing. The two few-mode fibers are coupled using an all-fiber fusion coupling method, resulting in a compact, simple-to-fabricate fiber mode multiplexer / demultiplexer with low insertion loss and high coupling efficiency.

[0005] Existing devices typically require repeated adjustments to the positional relationship between the input end, mode conversion element, and output few-mode fiber using an external precision displacement stage. This involves numerous adjustment steps, complex operation, and high engineering implementation costs. To address these common problems in the field, this invention was developed. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of current methods by proposing a mode multiplexing and demultiplexing device based on few-mode optical fiber.

[0007] To overcome the shortcomings of the prior art, the present invention adopts the following technical solution:

[0008] A mode multiplexing and demultiplexing device based on few-mode fiber includes:

[0009] Base module;

[0010] An outer ring fixing module is disposed on the base module;

[0011] The central floating optical island module is located inside the outer ring fixed module, and the central floating optical island module includes an input end and an output end;

[0012] A compliant self-centering module that connects the outer ring fixing module and the central floating optical island module;

[0013] The differential fine-tuning drive module acts on the compliant support self-centering module, and is used to indirectly fine-tune the central floating optical island module through the compliant support self-centering module.

[0014] An axially preloaded fixed-focus module used to define the axial position of the central floating optical island module and provide axial preload force;

[0015] The input interface positioning module and the output interface positioning module are respectively set on both sides of the central floating optical island module;

[0016] Mode conversion optical path module installed on the central floating optical island module;

[0017] The input interface positioning module is used to connect to a multi-channel input fiber or a single-mode fiber array, and the output interface positioning module is used to connect to a few-mode fiber. The mode conversion optical path module is located between the input interface positioning module and the output interface positioning module, and is used to convert and couple the optical fields of multiple input channels to the target mode of the few-mode fiber, or to separate the optical fields of different modes in the few-mode fiber and output them to different channels. The compliant support self-centering module is used to make the central floating optical island module slightly displaced in the lateral plane relative to the outer ring fixed module, and to make the central floating optical island module elastically return after the displacement. The differential fine-tuning drive module cooperates with the compliant support self-centering module to adjust the central floating optical island module. The axial pre-compression focusing module is used to maintain the axial spacing between the mode conversion optical path module, the input end and the output end to maintain stability, so as to improve the coupling efficiency and mode purity in the mode multiplexing and demultiplexing process.

[0018] Furthermore, the base module includes a base plate, a mounting reference surface, positioning pin holes, fastening holes, and a limiting shoulder. The base plate is used to support the entire device, the mounting reference surface is used to provide a reference position for device assembly, the positioning pin holes and fastening holes are used to enable the device to be repeatedly installed, and the limiting shoulder is used to limit the installation position of the outer ring fixing module.

[0019] The outer ring fixing module includes an annular frame, a circumferential mounting arm, a drive mounting seat, a limiting stop, and an inner guide space. The annular frame is fixedly mounted on the base module, forming an outer support structure surrounding the central floating optical island module. The circumferential mounting arm connects the base module and the annular frame and enhances the overall rigidity. The drive mounting seat is spaced circumferentially along the annular frame and is used to mount the differential fine-tuning drive module. The limiting stop limits the maximum offset of the central floating optical island module. The inner guide space accommodates the central floating optical island module and the compliant support self-centering module.

[0020] Furthermore, the central floating optical island module includes a floating island body, an input end mounting base, an output end mounting base, a mode conversion core mounting cavity, an optical reference surface, and a central light transmission channel;

[0021] The floating island body is suspended inside the outer ring fixing module by the compliant support self-centering module;

[0022] The input mounting bracket is used to install the input interface positioning module;

[0023] The output mounting bracket is used to install the output interface positioning module;

[0024] The mode conversion core mounting cavity is located between the input end mounting base and the output end mounting base, and is used to install the mode conversion optical path module;

[0025] The optical reference surface is used to ensure the relative positional accuracy of the input optical path, the mode conversion optical path, and the output optical path;

[0026] The central light-transmitting channel is used to provide space for beam transmission.

[0027] Furthermore, the compliant support self-centering module includes at least three sets of flexible support beams symmetrically distributed along the circumference, each set of flexible support beams including a fixed end, a floating end and a flexible necking section;

[0028] The fixed end is connected to the outer ring fixing module, the floating end is connected to the central floating optical island module, and the flexible necking section is disposed between the fixed end and the floating end.

[0029] Each flexible support beam group is evenly distributed in the circumferential direction so that the central floating optical island module can generate controlled lateral displacement or small-angle rotation when it is driven by the differential fine-tuning drive module, and provide restoring force after the external force is removed so that the central floating optical island module returns to its original position.

[0030] Furthermore, the axial preload focusing module includes an axial guide sleeve, a preload spring, a limiting ring, and a locking sleeve; the axial guide sleeve is used to provide axial guidance for the central floating optical island module or its input and output mounting seats; the preload spring is used to provide continuous axial preload; the limiting ring is used to limit the maximum axial displacement of the central floating optical island module; and the locking sleeve is used to maintain the assembled state.

[0031] Furthermore, both the input interface positioning module and the output interface positioning module include a plug-in base, a reference mating pair, and a clamping assembly. The plug-in base provides an insertion position for external input or output interface components. The reference mating pair includes a conical mating structure, a grooved guiding structure, and a planar limiting structure. The conical mating structure enables self-centering of the interface component, the grooved guiding structure constrains the lateral orientation of the interface component, and the planar limiting structure defines the axial positioning reference of the interface component. The clamping assembly stably presses the input or output interface component onto the corresponding plug-in base to improve repeatability and resistance to loosening.

[0032] Furthermore, the mode conversion optical path module includes an input collimation unit, a mode conversion core, and an output focusing unit; the input collimation unit is used to shape the beam from the input interface positioning module into a predetermined spatial optical field; the mode conversion core is used to perform mode mapping, mode synthesis, mode separation, or phase conversion on the spatial optical field; the output focusing unit is used to couple the converted optical field into a few-mode fiber, or to project the mode optical field output from the few-mode fiber onto the corresponding output channel; the mode conversion core is any one of a phase conversion element, a micro-optical mode conversion element, an integrated optical mode conversion element, or a fiber-optic mode conversion element.

[0033] Furthermore, the working process of this device includes the following steps:

[0034] S1, the input interface positioning module enables rapid and repeated positioning of the input optical fiber or single-mode array;

[0035] S2, the differential fine-tuning drive module indirectly drives the central floating optical island module through the compliant support self-centering module to perform lateral and angular fine-tuning within the range allowed by the compliant support self-centering module, so that the input optical axis, mode conversion optical path and few-mode fiber axis are kept consistent;

[0036] S3, the axial position between the mode conversion optical path module and the input and output ends is kept stable by the axial preload fixed focus module;

[0037] S4, the mode conversion optical path module completes the multiplexing of multiple single-mode channels to the target mode of few-mode fiber, or completes the demultiplexing of different modes in few-mode fiber to multiple output channels.

[0038] The beneficial effects achieved by the present invention are as follows: 1. The present invention integrates the input optical path, mode conversion optical path and few-mode fiber output optical path into an optical assembly that can be finely adjusted as a whole through the coordinated cooperation of the outer ring fixing module, the central floating optical island module, the compliant support self-centering module and the differential fine adjustment driving module, thereby reducing the assembly and adjustment complexity and improving the optical axis consistency and mode coupling accuracy.

[0039] 2. The present invention uses a compliant support self-centering module composed of flexible support beams, which enables the central floating optical island module to have both lateral fine adjustment and angular compensation capabilities, while still having elastic recovery and centering constraint functions, thereby improving the device's adaptability to assembly errors and external micro-vibrations.

[0040] 3. The present invention achieves precise setting and stable maintenance of axial focal length through the axial guide sleeve, preload spring, limiting ring, locking sleeve and distance shim in the axial preload focus module, which is beneficial to improving the long-term working stability of the mode conversion optical path.

[0041] 4. The overall structure of this invention integrates the lateral alignment, angular compensation, axial focusing, and circumferential orientation maintenance required for multiplexing and demultiplexing of few-mode fiber modes into one unit, which has the advantages of compact structure, fine adjustment, high consistency of repeated assembly, and strong adaptability to engineering applications. Attached Figure Description

[0042] The invention will be further understood from the following description taken in conjunction with the accompanying drawings. The components in the drawings are not necessarily drawn to scale, but rather the emphasis is on illustrating the principles of the embodiments. In different views, the same reference numerals designate the same parts.

[0043] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0044] Figure 2 This is a schematic diagram of the exploded structure of the present invention.

[0045] Figure 3 This is a cross-sectional view of the differential fine-tuning drive module of the present invention.

[0046] Figure 4 This is a flowchart of the process of the present invention.

[0047] Figure 5 This is a comparison diagram of the effects of the present invention and Comparative Example 1.

[0048] Figure 6 This is a comparison diagram of the effects of the present invention and Comparative Example 2.

[0049] Figure descriptions: 1. Base module; 2. Outer ring fixing module; 3. Central floating optical island module; 4. Compliant support self-centering module; 5. Differential fine-tuning drive module; 6. Axial preload focusing module; 7. Input interface positioning module; 8. Output interface positioning module; 9. Mode conversion optical path module. Detailed Implementation

[0050] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can understand the advantages and effects of the present invention from the content disclosed in this specification. The present invention can be implemented or applied through other different specific embodiments, and various details in this specification can also be modified and changed based on different viewpoints and applications without departing from the spirit of the present invention. Furthermore, the accompanying drawings of the present invention are for simple illustrative purposes only and are not depictions of actual dimensions; this is stated beforehand. The following embodiments will further describe the relevant technical content of the present invention in detail, but the disclosed content is not intended to limit the scope of protection of the present invention.

[0051] Example 1: This example provides a mode multiplexing and demultiplexing device based on few-mode fiber, including:

[0052] Base module;

[0053] An outer ring fixing module is disposed on the base module;

[0054] The central floating optical island module is located inside the outer ring fixed module, and the central floating optical island module includes an input end and an output end;

[0055] A compliant self-centering module that connects the outer ring fixing module and the central floating optical island module;

[0056] The differential fine-tuning drive module acts on the compliant support self-centering module, and is used to indirectly fine-tune the central floating optical island module through the compliant support self-centering module.

[0057] An axially preloaded fixed-focus module used to define the axial position of the central floating optical island module and provide axial preload force;

[0058] The input interface positioning module and the output interface positioning module are respectively set on both sides of the central floating optical island module;

[0059] Mode conversion optical path module installed on the central floating optical island module;

[0060] The input interface positioning module is used to connect to a multi-channel input fiber or a single-mode fiber array, and the output interface positioning module is used to connect to a few-mode fiber. The mode conversion optical path module is located between the input interface positioning module and the output interface positioning module, and is used to convert and couple the optical fields of multiple input channels to the target mode of the few-mode fiber, or to separate the optical fields of different modes in the few-mode fiber and output them to different channels. The compliant support self-centering module is used to make the central floating optical island module slightly displaced in the lateral plane relative to the outer ring fixed module, and to make the central floating optical island module elastically return after the displacement. The differential fine-tuning drive module cooperates with the compliant support self-centering module to adjust the central floating optical island module. The axial pre-compression focusing module is used to maintain the axial spacing between the mode conversion optical path module, the input end and the output end to maintain stability, so as to improve the coupling efficiency and mode purity in the mode multiplexing and demultiplexing process.

[0061] Furthermore, the base module includes a base plate, a mounting reference surface, positioning pin holes, fastening holes, and a limiting shoulder. The base plate is used to support the entire device, the mounting reference surface is used to provide a reference position for device assembly, the positioning pin holes and fastening holes are used to enable the device to be repeatedly installed, and the limiting shoulder is used to limit the installation position of the outer ring fixing module.

[0062] The outer ring fixing module includes an annular frame, a circumferential mounting arm, a drive mounting seat, a limiting stop, and an inner guide space. The annular frame is fixedly mounted on the base module, forming an outer support structure surrounding the central floating optical island module. The circumferential mounting arm connects the base module and the annular frame and enhances the overall rigidity. The drive mounting seat is spaced circumferentially along the annular frame and is used to mount the differential fine-tuning drive module. The limiting stop limits the maximum offset of the central floating optical island module. The inner guide space accommodates the central floating optical island module and the compliant support self-centering module.

[0063] Furthermore, the central floating optical island module includes a floating island body, an input end mounting base, an output end mounting base, a mode conversion core mounting cavity, an optical reference surface, and a central light transmission channel;

[0064] The floating island body is suspended inside the outer ring fixing module by the compliant support self-centering module;

[0065] The input mounting bracket is used to install the input interface positioning module;

[0066] The output mounting bracket is used to install the output interface positioning module;

[0067] The mode conversion core mounting cavity is located between the input end mounting base and the output end mounting base, and is used to install the mode conversion optical path module;

[0068] The optical reference surface is used to ensure the relative positional accuracy of the input optical path, the mode conversion optical path, and the output optical path;

[0069] The central light-transmitting channel is used to provide space for beam transmission.

[0070] Furthermore, the compliant support self-centering module includes at least three sets of flexible support beams symmetrically distributed along the circumference, each set of flexible support beams including a fixed end, a floating end and a flexible necking section;

[0071] The fixed end is connected to the outer ring fixing module, the floating end is connected to the central floating optical island module, and the flexible necking section is disposed between the fixed end and the floating end.

[0072] Each flexible support beam group is evenly distributed in the circumferential direction so that the central floating optical island module can generate controlled lateral displacement or small-angle rotation when it is driven by the differential fine-tuning drive module, and provide restoring force after the external force is removed so that the central floating optical island module returns to its original position.

[0073] Specifically, the number of flexible support beam groups is three, four, or six, preferably three or six. When set to three groups, each flexible support beam group is evenly arranged along a 120° circumference. When set to six groups, adjacent flexible support beam groups form a pair and are symmetrically arranged along the circumference to improve lateral support stiffness and angular stability.

[0074] Furthermore, the differential fine-tuning drive module includes at least three fine-tuning drive units distributed circumferentially along the outer ring fixing module. Each fine-tuning drive unit includes a drive screw, a differential threaded pair, a push head, a pre-tightening elastic element, and a locking element. The drive screw is threadedly connected to the drive mounting seat. The differential threaded pair is used to convert the rotational displacement of the drive screw into a linear displacement with a smaller step. The push head is disposed on the differential threaded pair and contacts the compliant support self-centering module. The pre-tightening elastic element is used to eliminate backlash. The locking element is used to fix the position of the drive screw after the differential fine-tuning drive module has been adjusted.

[0075] Specifically, the push head adopts any one of a spherical end, a circular arc end, or a flat end. The compliant support self-centering module is provided with a force-bearing recess, a force-bearing plane, or a wear-resistant pad corresponding to the push head, so as to reduce lateral friction and local wear during the driving process and improve the accuracy of repeated adjustment.

[0076] Furthermore, the axial preload focusing module includes an axial guide sleeve, a preload spring, a limiting ring, and a locking sleeve; the axial guide sleeve is used to provide axial guidance for the central floating optical island module or its input and output mounting seats; the preload spring is used to provide continuous axial preload; the limiting ring is used to limit the maximum axial displacement of the central floating optical island module; and the locking sleeve is used to maintain the assembled state.

[0077] Furthermore, both the input interface positioning module and the output interface positioning module include a plug-in base, a reference mating pair, and a clamping assembly. The plug-in base provides an insertion position for external input or output interface components. The reference mating pair includes a conical mating structure, a grooved guiding structure, and a planar limiting structure. The conical mating structure enables self-centering of the interface component, the grooved guiding structure constrains the lateral orientation of the interface component, and the planar limiting structure defines the axial positioning reference of the interface component. The clamping assembly stably presses the input or output interface component onto the corresponding plug-in base to improve repeatability and resistance to loosening.

[0078] Furthermore, the mode conversion optical path module includes an input collimation unit, a mode conversion core, and an output focusing unit; the input collimation unit is used to shape the beam from the input interface positioning module into a predetermined spatial optical field; the mode conversion core is used to perform mode mapping, mode synthesis, mode separation, or phase conversion on the spatial optical field; the output focusing unit is used to couple the converted optical field into a few-mode fiber, or to project the mode optical field output from the few-mode fiber onto the corresponding output channel; the mode conversion core is any one of a phase conversion element, a micro-optical mode conversion element, an integrated optical mode conversion element, or a fiber-optic mode conversion element.

[0079] Furthermore, the working process of this device includes the following steps:

[0080] S1, the input interface positioning module enables rapid and repeated positioning of the input optical fiber or single-mode array;

[0081] S2, the differential fine-tuning drive module indirectly drives the central floating optical island module through the compliant support self-centering module to perform lateral and angular fine-tuning within the range allowed by the compliant support self-centering module, so that the input optical axis, mode conversion optical path and few-mode fiber axis are kept consistent;

[0082] S3, the axial position between the mode conversion optical path module and the input and output ends is kept stable by the axial preload fixed focus module;

[0083] S4, the mode conversion optical path module completes the multiplexing of multiple single-mode channels to the target mode of few-mode fiber, or completes the demultiplexing of different modes in few-mode fiber to multiple output channels.

[0084] Specifically, the device is a bidirectional reversible optical path structure, which is used as a mode multiplexing device in one transmission direction and as a mode demultiplexing device in the opposite transmission direction, without changing the basic structure of the central floating optical island module, the compliant support self-centering module and the differential fine-tuning drive module.

[0085] Existing devices typically require repeated adjustments to the positional relationship between the input end, mode conversion element, and output few-mode fiber using an external precision displacement stage. This involves numerous adjustment steps, complex operation, and high engineering implementation costs. Compared with existing technologies, this invention has at least the following advantages:

[0086] The beneficial effects of this solution are as follows: 1. By coordinating the outer ring fixing module, the central floating optical island module, the compliant support self-centering module, and the differential fine-tuning drive module, this invention integrates the input optical path, the mode conversion optical path, and the few-mode fiber output optical path into an optical assembly that can be finely adjusted as a whole, thereby reducing the complexity of assembly and adjustment and improving the optical axis consistency and mode coupling accuracy.

[0087] 2. The present invention uses a compliant support self-centering module composed of flexible support beams, which enables the central floating optical island module to have both lateral fine adjustment and angular compensation capabilities, while still having elastic recovery and centering constraint functions, thereby improving the device's adaptability to assembly errors and external micro-vibrations.

[0088] 3. The present invention achieves precise setting and stable maintenance of axial focal length through the axial guide sleeve, preload spring, limiting ring, locking sleeve and distance shim in the axial preload focus module, which is beneficial to improving the long-term working stability of the mode conversion optical path.

[0089] 4. The overall structure of this invention integrates the lateral alignment, angular compensation, axial focusing, and circumferential orientation maintenance required for multiplexing and demultiplexing of few-mode fiber modes into one unit, which has the advantages of compact structure, fine adjustment, high consistency of repeated assembly, and strong adaptability to engineering applications.

[0090] Example 2: This example should be understood as including all the features of any of the foregoing examples, and further improving upon them. It also includes a method for setting a pressure threshold for the axial preload of the axial preload fixed focus module. This method is used to limit the maximum value of the axial preload to avoid excessive pressure that could damage the central floating optical island module.

[0091] In existing spatial optical path coupling or fiber array packaging technologies, the setting of axial preload (such as the force provided by the preload spring in Example 1) is usually based on a purely mechanical perspective, only considering "preventing parts from loosening," "overcoming the influence of gravity," or relying on the engineer's "experience value," without directly linking the mechanical preload to the core optical indicators of few-mode fiber transmission (i.e., mode orthogonality and intermode crosstalk). This design approach, which separates mechanical and optical aspects, is prone to the hidden defect of "appearing mechanically stable, but optically causing mode distortion due to stress." The difference between this solution and existing technologies lies in breaking down the isolation between mechanical and optical aspects and establishing a pressure threshold setting method that considers both "mechanical force input" and "optical mode purity output."

[0092] Specifically, in this method, a pressure threshold is set. During actual assembly and debugging, the device must ensure that the actual pre-pressure provided by the pre-pressure spring is strictly less than the pressure threshold calculated by the formula. This ensures that the axial distance between the mode conversion optical path module and the input and output ends is stable, while absolutely avoiding structural micro-deformation or stress birefringence caused by excessive pre-tightening, thereby avoiding the deterioration of mode reuse purity.

[0093] Furthermore, the pressure threshold is calculated according to the following formula:

[0094]

[0095] in, The pressure threshold, This is the operating wavelength of the device, which is directly given by the design specifications of the optical communication system served by the device (e.g., 1500nm is commonly used in the C-band). The orthogonality degradation coefficient allowed by the device means the maximum degradation ratio of mode orthogonality allowed by the system design. It is obtained by those skilled in the art based on the tolerance index of inter-mode crosstalk of the specific optical communication system. For example, in harsh scenarios, the orthogonality degradation coefficient can be set to 0.01 (that is, 1% orthogonality degradation is allowed). This refers to the average refractive index of the few-mode fiber. It can be obtained by referring to the fiber manufacturer's parameter manual or by measurement using a near-field refractive index meter. The target mode is the refractive index difference between the target mode groups, and the target mode is determined by the mode transformation optical path module. For example, if the target modes are the LP01 fundamental mode and the LP11 higher-order mode, then... The intrinsic refractive index difference between the LP01 fundamental mode and the LP11 higher-order modes can be obtained by constructing a cross-sectional model of the few-mode fiber using vector finite element simulation software (such as COMSOL Multiphysics), performing electromagnetic field frequency domain simulation, extracting the effective refractive indices of different modes, and then subtracting them. The effective interaction length of the mode-conversion optical path (i.e., the length of the mode-conversion core). The normalized stress-optical displacement coupling coefficient is used to characterize the average lateral displacement caused by a unit normal stress within the optically effective region. Its formula is shown below:

[0096]

[0097] in, The mode field radius can be calculated by those skilled in the art based on the fiber parameters and using the Marcuse formula, or it can be directly measured using a near-field scanner at the target operating wavelength. The root mean square (RMS) of the lateral displacement of the mode-changing core is obtained as follows: a load is applied at the preload position using finite element software. Given the load force value, extract the lateral displacement field of the mounting cavity region of the mode transform core, and calculate its root mean square value. .

[0098] The beneficial effects of this embodiment are: Traditional mechanical design focuses on stress or strain, and traditional optical design focuses on phase or light intensity, while... The parameter "lateral geometric displacement caused by a unit mechanical force input in a specific optically sensitive area" is defined. This parameter allows designers to intuitively discover that even if two design schemes have the same macroscopic rigidity, the force transmission paths may differ (e.g., whether the preload spring is offset or centered). The values ​​can vary by orders of magnitude. It quantifies "how force is transmitted and distorts the path of light";

[0099] Technicians can actively reduce the wall thickness of the core mounting cavity by adjusting the position or mode of the axial guide sleeve in Embodiment 1. value; The smaller, the more accurate the calculation The larger the value, the better. This means that the device can apply a larger preload to achieve excellent seismic stability without compromising mode orthogonality, thus resolving the contradiction between stability and optical purity in traditional designs.

[0100] For different mode groups (such as LP01 / LP11 multiplexing and LP01 / LP21 multiplexing), due to its Different formulas can be used to derive different upper limits of pre-pressure, enabling the same mechanical structure to be configured in a refined and adaptive manner for different optical tasks.

[0101] Example 3: This example should be understood as including all the features of any of the foregoing examples, and further improving upon them. It also supplements the above examples with more equipment details and implementation details, and provides a comparison example between this solution and the prior art.

[0102] Specifically, the preferred operating wavelength in this embodiment is 1550nm, corresponding to C-band communication scenarios; the output few-mode fiber is preferably a step-index few-mode fiber supporting LP01 and LP11 mode transmission, with a cladding diameter of 125μm, a core diameter of 18μm to 22μm, and a numerical aperture of 0.10 to 0.14. The input end preferably employs a two-way or four-way single-mode fiber input structure. When using two inputs, they can correspond to the fundamental mode channel and the higher-order mode channel respectively; when using four inputs, they can be combined to form the target spatial mode according to the design requirements of the mode conversion core.

[0103] Furthermore, the base module includes a base plate, a mounting reference surface, positioning pin holes, fastening holes, and a limiting shoulder. The base plate is preferably made of 6061-T6 aluminum alloy, 7075 aluminum alloy, or stainless steel. In this embodiment, a 6061-T6 aluminum alloy plate with a thickness of 10mm to 15mm is preferred. After aging treatment, the surface is anodized black to balance structural rigidity, ease of processing, and surface anti-reflective properties. The planar dimensions of the base plate are preferably 100mm×100mm to 140mm×140mm, and in this embodiment, 120mm×120mm is preferred. The base plate thickness is preferably 12mm. The flatness of the mounting reference surface is preferably no greater than 0.01mm. The positioning pin holes are preferably two precision positioning pin holes spaced 40mm to 60mm apart, with a hole diameter preferably φ3H7. The fastening holes are preferably M3 or M4 threaded holes to allow for repeated installation of the device on experimental platforms or in chassis.

[0104] Furthermore, the outer ring fixing module includes an annular frame, a circumferential mounting arm, a drive mounting base, a limiting stop, and an inner guide space. The outer diameter of the annular frame is preferably 70mm–90mm, the inner diameter is preferably 35mm–50mm, and in this embodiment, the outer diameter is preferably 78mm, the inner diameter is preferably 42mm, and the thickness is preferably 8mm–12mm. The drive mounting base is preferably arranged in three evenly spaced 120° intervals along the circumference, or in six intervals of 60°. Using three drive mounting bases allows for lateral fine-tuning and small-angle attitude compensation in a two-dimensional plane; using six drive mounting bases further improves drive redundancy and adjustment precision. The limiting gap between the limiting stop and the central floating optical island module is preferably 80μm–150μm to prevent excessive displacement of the central floating optical island module in case of misoperation.

[0105] Furthermore, the central floating optical island module includes a floating island body, an input mounting base, an output mounting base, a mode conversion core mounting cavity, an optical reference surface, and a central light transmission channel. The floating island body is preferably made of 4J36 low-expansion alloy, stainless steel, or ceramic-based material. In this embodiment, 4J36 low-expansion alloy is preferred to reduce optical axis drift caused by temperature changes. The external dimensions of the floating island body are preferably 30mm×18mm×8mm to 40mm×25mm×12mm, and in this embodiment, 34mm×20mm×10mm is preferred. The mode conversion core mounting cavity is preferably located in the center of the floating island body, with a cavity length preferably of 8mm~18mm, a width preferably of 4mm~8mm, and a depth preferably of 1.5mm~4mm. In this embodiment, 12mm×5mm×2.5mm is preferred. The flatness of the optical reference surface is preferably no greater than 0.005 mm, and the coaxiality of the input and output mounting bases on both sides is preferably no greater than 0.01 mm, so as to ensure the relative positional accuracy between the mode conversion optical path module, the input end, and the output end.

[0106] Furthermore, the compliant support self-centering module includes three or six sets of flexible support beams symmetrically arranged circumferentially. In this embodiment, three sets of flexible support beams are preferably used, with each set evenly distributed along a 120° angle. Each set of flexible support beams includes a fixed end, a floating end, and a flexible necking section. The flexible necking section is preferably composed of SUS301 spring stainless steel sheets, beryllium copper spring sheets, or integrally machined thin-walled elastic beams. In this embodiment, the flexible support beams preferably use beryllium copper spring sheets with a thickness of 0.20mm to 0.35mm. The effective length of a single support beam is preferably 6mm to 10mm, and the width is preferably 0.8mm to 1.5mm. In this embodiment, the preferred length is 8mm, the width is 1.2mm, and the thickness is 0.25mm. Therefore, the effective fine-tuning range of the central floating optical island module in the transverse plane is preferably ±30μm to ±60μm, the small angle compensation range is preferably ±0.2° to ±0.5°, and the center recovery deviation after the external force is removed is preferably no greater than 2μm.

[0107] Furthermore, the differential fine-tuning drive module includes at least three fine-tuning drive units, each of which includes a drive screw, a differential thread pair, a push head, a preload elastic element, and a locking element. The drive screw is preferably a stainless steel precision screw, and the differential thread pair can be formed by two sets of threads with different pitches. In this embodiment, the outer thread is preferably M6×0.50, and the inner differential thread is preferably M4×0.45, with an equivalent differential step distance of 0.05 mm / revolution; when the drive knob is circumferentially divided into 50 equal divisions, the theoretical displacement resolution per division is 1 μm. The push head is preferably a spherical end, with a ball diameter preferably φ1.5 mm to φ2.5 mm; in this embodiment, a φ2 mm silicon nitride ball head is preferred to reduce friction and wear. The preload elastic element is preferably a small compression spring or disc spring assembly, with a preload force preferably 1 N to 3 N; in this embodiment, 2 N is preferred, used to eliminate backlash. The locking element is preferably a locking nut or a radial set screw, used to fix the position of the differential thread pair after adjustment is completed.

[0108] Furthermore, the axial pre-compression focusing module includes an axial guide sleeve, a pre-compression spring, a limiting ring, a locking sleeve, and a spacer. The fit clearance between the axial guide sleeve and the central floating optical island module is preferably 3μm to 8μm, and in this embodiment, it is preferably 5μm, to balance guiding accuracy and assembly feasibility. The pre-compression spring is preferably a helical compression spring, with a spring stiffness preferably 0.10N / mm to 0.30N / mm, and in this embodiment, preferably 0.18N / mm; its initial preload is preferably 0.4N to 0.9N, and in this embodiment, preferably 0.6N. The limiting ring is used to limit the maximum axial displacement, which is preferably no greater than 0.15mm. The spacer preferably uses a combination of three standard thicknesses: 50μm, 100μm, and 200μm, to achieve graded setting of the axial focal length between the mode-changing core mounting cavity and the input and output ends. The locking sleeve preferably uses a fine-thread locking structure to ensure that the axial spacing does not change significantly during long-term operation.

[0109] Furthermore, both the input interface positioning module and the output interface positioning module include a connector, a reference mating pair, and a clamping assembly. The input interface positioning module is preferably used to install a single-mode fiber array, which can be a V-groove array structure composed of 125μm clad fiber, with an array pitch preferably of 127μm or 250μm; in this embodiment, a 127μm pitch is preferred. The output interface positioning module is preferably used to install a few-mode fiber ferrule, which is preferably a ceramic or metal ferrule with an outer diameter of 2.5mm. The cone angle of the tapered mating structure is preferably 60°, the guide width tolerance of the grooved guide structure is preferably controlled within ±3μm, and the axial reference repeatability of the planar limiting structure is preferably no greater than 2μm. The clamping force of the clamping assembly is preferably 8N to 12N to ensure stable crimping of the interface and facilitate repeated assembly and disassembly.

[0110] Further, the mode conversion optical path module includes an input collimation unit, a mode conversion core, and an output focusing unit. The input collimation unit preferably uses a GRIN collimating lens, a microsphere lens, or a small aspherical collimating lens. In this embodiment, a GRIN collimating lens with an outer diameter of 1.8 mm, a length of 4.0 mm, and a numerical aperture of 0.23 is preferred. The mode conversion core preferably uses a phase converter or a micro-optical mode conversion element. In this embodiment, a quartz-based phase converter is preferred, with an effective aperture of 2 mm and a thickness of 0.5 mm to 1 mm. The output focusing unit preferably uses a miniature aspherical lens with a focal length of 4 mm to 6 mm, preferably 4.5 mm in this embodiment. The distance from the input fiber end face to the front surface of the input collimation unit is preferably 0.05 mm to 0.20 mm, the distance between the mode conversion core and the output focusing unit is preferably 1.5 mm to 3.0 mm, and the distance between the output focusing unit and the few-mode fiber end face is preferably 0.10 mm to 0.40 mm. After adjustment by the differential fine-tuning drive module and the axial pre-compression focusing module, the lateral optical axis deviation is preferably controlled within ±1.5μm, the angular deviation is preferably controlled within ±0.15°, and the axial defocusing amount is preferably controlled within 5μm.

[0111] The assembly process in this embodiment is as follows: First, the base module is fixed on the assembly platform, and initial installation positioning is completed using the locating pin holes; then, the outer ring fixing module is installed at the limiting shoulder position of the base module, and the circumferential mounting arm is locked; next, the central floating optical island module is suspended in the guide space inside the outer ring fixing module by three sets of flexible support beams, and three differential fine-tuning drive units are installed so that their push heads correspond to the force-bearing positions of the compliant support self-centering module; then, the mode conversion core mounting cavity of the central floating optical island module is sequentially... Install the input collimation unit, mode conversion core, and output focusing unit, and set the initial axial focal length using a spacer. Then, install the axial guide sleeve, preload spring, limit ring, and locking sleeve to achieve stable axial preload on the central floating optical island module. Next, insert the input single-mode fiber array into the input interface positioning module and the few-mode fiber into the output interface positioning module. Finally, with the aid of a laser source and an optical power meter or mode analyzer, adjust the three differential fine-tuning drive units to achieve the target values ​​for coupling efficiency and mode purity, and then lock each drive unit.

[0112] Without altering the technical concept and overall structural relationship of this embodiment, the following modifications and replacements are also possible: First, the materials of the base module and the outer ring fixing module can be replaced from 6061-T6 aluminum alloy to 7075 aluminum alloy, stainless steel, or low-expansion alloy to adapt to different mechanical stiffness and thermal stability requirements; Second, the compliant support self-centering module can be replaced from three sets of flexible support beams to six sets of flexible support beams to improve lateral support stiffness and anti-disturbance capability; Third, the pitch combination of the differential thread pair can be between 0.50mm / 0.45mm, 0.40mm / 0.35mm, or 0.25mm / 0.20mm. The choice of mode conversion core, as long as it is still used to convert rotational displacement into linear displacement with smaller step sizes, does not change the technical essence of this embodiment; fourth, the mode conversion core can be replaced by a quartz phase conversion plate with a micro-optical mode conversion element, an integrated optical mode conversion element, or a fiber-optic mode conversion element, but it is still installed in the mode conversion core mounting cavity of the central floating optical island module and works in conjunction with the input collimation unit and the output focusing unit; fifth, the input interface positioning module can be applied to multi-channel single-mode fiber arrays or single-channel single-mode fiber access, and the output interface positioning module can be connected to few-mode fibers or to standard ferrule assemblies encapsulated with few-mode fibers.

[0113] The following are comparative examples of existing technologies:

[0114] Comparative Example 1: Rigid Split Adjustment Structure with No Compliant Support Self-Centering Module

[0115] Comparative Example 1 uses the same input single-mode fiber array, mode conversion core, and output few-mode fiber as this embodiment, with the same operating wavelength of 1550nm. The difference is that Comparative Example 1 does not use the integrated floating fine-tuning structure composed of a central floating optical island module and a compliant support self-centering module. Instead, the input end, mode conversion core, and output end are rigidly fixed separately and adjusted step by step using an external two-dimensional displacement stage. All other optical components and test conditions remain the same.

[0116] At 25±2℃, both this embodiment and Comparative Example 1 underwent 10 repeated assembly and debugging cycles, and the assembly and debugging time, insertion loss, inter-mold crosstalk, and repeatability error were recorded. The results are shown in the table below. Figure 5 The images show a comparison of the corresponding effects.

[0117]

[0118] As can be seen from the table above, this embodiment uses the compliant support self-centering module and the differential fine-tuning drive module to perform overall indirect fine-tuning of the central floating optical island module, which significantly shortens the assembly and adjustment time, significantly reduces the insertion loss and loss fluctuation after repeated assembly, and significantly improves inter-mode crosstalk. This shows that this embodiment has significant advantages in improving assembly and adjustment efficiency, repeatability positioning accuracy, and mode coupling quality.

[0119] Comparative Example 2: Ordinary rigid distance-fixed structure with no axial preload focus module

[0120] Comparative Example 2 uses the same base module, outer ring fixing module, central floating optical island module, compliant support self-centering module, and differential fine-tuning drive module as this embodiment. The difference is that Comparative Example 2 eliminates the axial preload spring and locking sleeve, and only uses a single rigid washer for initial axial spacing. It does not provide continuous axial preload force, nor does it provide axial compensation and limiting coordination. All other conditions remain the same.

[0121] After initial debugging, temperature cycling and vibration tests were conducted on this embodiment and Comparative Example 2, respectively. The temperature cycling conditions were 5 cycles from 20℃ to 60℃, with each temperature point held for 30 minutes; the vibration conditions were 10Hz to 200Hz sweep vibration for 30 minutes. The test results are shown in the table below. Figure 6 The corresponding effect image is shown below.

[0122]

[0123] As can be seen from the table above, this embodiment, through the coordinated operation of the axial guide sleeve, preload spring, limiting ring, locking sleeve and spacer, can continuously maintain the axial distance between the mode conversion optical path module and the input and output ends under temperature changes and vibration environments, thereby effectively reducing focus drift, suppressing coupling efficiency decay and inter-mode crosstalk deterioration, indicating that the axial preload focus module has a significant promoting effect on the long-term stable operation of the device.

[0124] The above-disclosed content is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Therefore, all equivalent technical changes made based on the description and drawings of the present invention are included within the scope of protection of the present invention. Furthermore, the elements therein can be updated as technology develops. The above units are merely examples, and those skilled in the art can adopt corresponding units according to actual needs when implementing this solution.

Claims

1. A mode multiplexing and demultiplexing device based on few-mode fiber, characterized in that, include: Base module; An outer ring fixing module is disposed on the base module; The central floating optical island module is located inside the outer ring fixed module, and the central floating optical island module includes an input end and an output end; A compliant self-centering module that connects the outer ring fixing module and the central floating optical island module; The differential fine-tuning drive module acts on the compliant support self-centering module, and is used to indirectly fine-tune the central floating optical island module through the compliant support self-centering module. An axially preloaded fixed-focus module used to define the axial position of the central floating optical island module and provide axial preload force; The input interface positioning module and the output interface positioning module are respectively set on both sides of the central floating optical island module; Mode conversion optical path module installed on the central floating optical island module; The input interface positioning module is used to connect to a multi-channel input fiber or a single-mode fiber array, and the output interface positioning module is used to connect to a few-mode fiber. The mode conversion optical path module is located between the input interface positioning module and the output interface positioning module, and is used to convert and couple the optical fields of multiple input channels to the target mode of the few-mode fiber, or to separate the optical fields of different modes in the few-mode fiber and output them to different channels. The compliant support self-centering module is used to make the central floating optical island module slightly displaced in the lateral plane relative to the outer ring fixed module, and to make the central floating optical island module elastically return after the displacement. The differential fine-tuning drive module cooperates with the compliant support self-centering module to adjust the central floating optical island module. The axial pre-compression focusing module is used to maintain the axial spacing between the mode conversion optical path module, the input end and the output end to maintain stability, so as to improve the coupling efficiency and mode purity in the mode multiplexing and demultiplexing process.

2. The mode multiplexing and demultiplexing device based on few-mode fiber according to claim 1, characterized in that, The base module includes a base plate, a mounting reference surface, positioning pin holes, fastening holes, and a limiting shoulder. The base plate is used to support the entire device, the mounting reference surface is used to provide a reference position for device assembly, the positioning pin holes and fastening holes are used to enable the device to be repeatedly installed, and the limiting shoulder is used to limit the installation position of the outer ring fixing module. The outer ring fixing module includes an annular frame, a circumferential mounting arm, a drive mounting seat, a limiting stop, and an inner guide space. The annular frame is fixedly mounted on the base module, forming an outer support structure surrounding the central floating optical island module. The circumferential mounting arm connects the base module and the annular frame and enhances the overall rigidity. The drive mounting seat is spaced circumferentially along the annular frame and is used to mount the differential fine-tuning drive module. The limiting stop limits the maximum offset of the central floating optical island module. The inner guide space accommodates the central floating optical island module and the compliant support self-centering module.

3. The mode multiplexing and demultiplexing device based on few-mode fiber according to claim 1, characterized in that, The central floating optical island module includes a floating island body, an input end mounting base, an output end mounting base, a mode conversion core mounting cavity, an optical reference surface, and a central light transmission channel. The floating island body is suspended inside the outer ring fixing module by the compliant support self-centering module; The input mounting bracket is used to install the input interface positioning module; The output mounting bracket is used to install the output interface positioning module; The mode conversion core mounting cavity is located between the input end mounting base and the output end mounting base, and is used to install the mode conversion optical path module; The optical reference surface is used to ensure the relative positional accuracy of the input optical path, the mode conversion optical path, and the output optical path; The central light-transmitting channel is used to provide space for beam transmission.

4. The mode multiplexing and demultiplexing device based on few-mode fiber according to claim 1, characterized in that, The compliant support self-centering module includes at least three sets of flexible support beams symmetrically distributed along the circumference, each set of flexible support beams including a fixed end, a floating end and a flexible necking section; The fixed end is connected to the outer ring fixing module, the floating end is connected to the central floating optical island module, and the flexible necking section is disposed between the fixed end and the floating end. Each flexible support beam group is evenly distributed in the circumferential direction so that the central floating optical island module can generate controlled lateral displacement or small-angle rotation when it is driven by the differential fine-tuning drive module, and provide restoring force after the external force is removed so that the central floating optical island module returns to its original position.

5. The mode multiplexing and demultiplexing device based on few-mode fiber according to claim 1, characterized in that, The axial preload focusing module includes an axial guide sleeve, a preload spring, a limiting ring, and a locking sleeve. The axial guide sleeve provides axial guidance for the central floating optical island module or its input and output mounting seats. The preload spring provides continuous axial preload. The limiting ring limits the maximum axial displacement of the central floating optical island module. The locking sleeve maintains the assembled state.

6. The mode multiplexing and demultiplexing device based on few-mode fiber according to claim 1, characterized in that, Both the input interface positioning module and the output interface positioning module include a plug-in base, a reference mating pair, and a clamping assembly. The plug-in base provides an insertion position for external input or output interface components. The reference mating pair includes a conical mating structure, a grooved guiding structure, and a planar limiting structure. The conical mating structure enables self-centering of the interface component, the grooved guiding structure constrains the lateral orientation of the interface component, and the planar limiting structure defines the axial positioning reference of the interface component. The clamping assembly stably presses the input or output interface component onto the corresponding plug-in base to improve repeatability and resistance to loosening.

7. The mode multiplexing and demultiplexing device based on few-mode fiber according to claim 1, characterized in that, The mode conversion optical path module includes an input collimation unit, a mode conversion core, and an output focusing unit. The input collimation unit is used to shape the beam from the input interface positioning module into a predetermined spatial optical field. The mode conversion core is used to perform mode mapping, mode synthesis, mode separation, or phase conversion on the spatial optical field. The output focusing unit is used to couple the converted optical field into a few-mode fiber, or to project the mode optical field output from the few-mode fiber onto a corresponding output channel. The mode conversion core is any one of a phase conversion element, a micro-optical mode conversion element, an integrated optical mode conversion element, or a fiber-optic mode conversion element.

8. The mode multiplexing and demultiplexing device based on few-mode fiber according to claim 1, characterized in that, The device's workflow includes the following steps: S1, the input interface positioning module enables rapid and repeated positioning of the input optical fiber or single-mode array; S2, the differential fine-tuning drive module indirectly drives the central floating optical island module through the compliant support self-centering module to perform lateral and angular fine-tuning within the range allowed by the compliant support self-centering module, so that the input optical axis, mode conversion optical path and few-mode fiber axis are kept consistent; S3, the axial position between the mode conversion optical path module and the input and output ends is kept stable by the axial preload fixed focus module; S4, the mode conversion optical path module completes the multiplexing of multiple single-mode channels to the target mode of few-mode fiber, or completes the demultiplexing of different modes in few-mode fiber to multiple output channels.

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