Coupling lens structure, optical module and manufacturing method

Abstract

The invention discloses a coupling lens structure, an optical module and a manufacturing method, the coupling lens structure is composed of an optical focusing unit and an optical reflection unit, the optical focusing unit receives an optical signal transmitted by a multimode fiber and collimates or focuses the optical signal, and the optical reflection unit changes the propagation direction of the optical signal of an optical input path and reflects the optical signal to an optical output path. The light reflection unit forms a BESSEL-TIR reflection surface, and the BESSEL-TIR reflection surface modulates the propagation phase of a light signal, and enables the light spot of the light signal to be an annular light spot. According to the technical scheme, a traditional TIR plane reflecting surface is replaced by the BESSEL-TIR reflecting surface with the quasi-axial conical surface structure, on the premise that the overall structure and the manufacturing process of an original optical module are not changed, phase modulation of incident Gaussian beams is achieved, light spots can be effectively shaped to be annularly distributed, the annular flux control performance of optical signals is remarkably optimized, and the optical module can be applied to the field of optical modules. High-order mode excitation in the multimode optical fiber is reduced, dispersion and pulse broadening phenomena are further reduced, and therefore the transmission rate and the transmission distance of the optical module are improved.

Description

A coupling lens structure, optical module and its fabrication method Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a coupling lens structure, an optical module, and a manufacturing method thereof. Background Technology

[0002] In the field of optical communication, existing 850nm optical modules often adopt an integrated plastic lens structure, which collimates the optical signal from the multimode fiber through the lens, turns the optical signal 90 degrees through the total internal reflection surface, and then couples the optical signal to the optical fiber or photodetector through the focusing lens, thereby realizing the efficient coupling of the optical signal between the optical fiber and the chip in the optical module.

[0003] However, for 850nm wavelength optical modules, the presence of numerous propagation modes in the multimode fiber easily leads to phenomena such as mode dispersion and pulse broadening, severely limiting the transmission distance and rate of the optical signal. To improve transmission performance, related technologies typically require controlling the ring flux of the optical signal during the actual coupling process to match the mode field distribution of the high-speed optical module and reduce the impact of mode dispersion.

[0004] However, the integrated coupling lenses in related technologies are usually designed based on Gaussian spots, which cannot meet the optimization requirements for annular flux in terms of spot shape. Therefore, most lens solutions have significant shortcomings in controlling annular flux, making it difficult to meet the requirements of high-performance 850nm optical modules for long-distance and high-speed transmission. Summary of the Invention

[0005] The main objective of this invention is to provide a coupling lens structure, an optical module, and a manufacturing method, so as to at least solve the problem that most lens structures in related technologies cannot meet the requirements of high-performance 850nm optical modules for long-distance and high-speed transmission.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a coupling lens structure applied in an optical module, the coupling lens structure comprising: an optical focusing unit for receiving optical signals transmitted by a multimode optical fiber and collimating or focusing them; and an optical reflection unit for changing the propagation direction of the optical signal in the optical input path and reflecting it to the optical output path; wherein the optical reflection unit forms a BESSEL-TIR reflective surface, the BESSEL-TIR reflective surface being used to modulate the propagation phase of the optical signal so that the light spot of the optical signal is an annular light spot.

[0007] In a second aspect, the present invention provides an optical module, the optical module being an 850nm optical module, and including the coupling lens structure as described in the first aspect.

[0008] A third aspect of the present invention provides a method for manufacturing a coupling lens structure, comprising the following steps: designing a quasi-axial conical structure for forming a BESSEL-TIR reflective surface based on a target BESSEL phase function; machining a mold corresponding to the quasi-axial conical structure having the BESSEL-TIR reflective surface on a mold workpiece using a mold processing method; preparing the quasi-axial conical structure forming the BESSEL-TIR reflective surface through an injection molding process and the mold; and installing the quasi-axial conical structure in the coupling lens structure.

[0009] The coupling lens structure, optical module, and manufacturing method of this invention consist of an optical focusing unit and an optical reflection unit. A BESSEL-TIR reflective surface is formed based on the optical reflection unit, that is, the traditional TIR planar reflective surface is replaced with a BESSEL-TIR reflective surface with a quasi-axial conical structure. Without changing the original overall structure and manufacturing process of the optical module, phase modulation of the incident Gaussian beam is achieved, which can effectively shape the light spot into a ring distribution, significantly optimize the ring flux control performance of the optical signal, reduce the excitation of higher-order modes in multimode fiber, and thus reduce dispersion and pulse broadening, thereby improving the transmission rate and transmission distance of the optical module. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies 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.

[0011] Figure 1 is a schematic diagram of the internal structure of an 850nm optical module coupling lens in the related art; Figure 2 is a schematic diagram of the internal structure of the coupling lens structure provided in the embodiment of this application; Figure 3 is a schematic diagram of the Gaussian spot of the optical signal modulated by a conventional TIR total internal reflection surface in the related art; Figure 4 is a schematic diagram of the BESSEL ring spot of the optical signal modulated by a BESSEL-TIR reflective surface in the embodiment of this application; Figure 5 is a schematic diagram of the azimuth angle formed by the geometric center O of the BESSEL-TIR reflective surface and the target point A on the surface in the embodiment of this application; Figure 6 is a schematic diagram of Figure 2 after adding the box selection line B; Figure 7 is a partially enlarged schematic diagram of part B in Figure 6; Figure 8 is a schematic diagram of the height change law of a design example in the embodiment of this application; Figure 9 is a schematic diagram of the height change law of a design example in the embodiment of this application; Figure 10 is a schematic diagram of the color dimension of the BESSEL-TIR reflective surface in the embodiment of this application; Figure 11 is a schematic diagram of the height z change effect of the surface shape of the BESSEL-TIR reflective surface on a circle in the embodiment of this application. Detailed Implementation

[0012] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0013] It should be noted that related terms such as "first" and "second" can be used to describe various components, but these terms do not limit the component. These terms are only used to distinguish one component from another. For example, without departing from the scope of the invention, the first component can be referred to as the second component, and the second component can similarly be referred to as the first component. The term "and / or" refers to any one or more combinations of related and descriptive terms.

[0014] In related technologies, most 850nm optical module coupling lenses (850nm being the operating wavelength of the optical signal) use an integrated plastic lens to collimate the light from the VCSEL (laser) or fiber through lens 201, then redirect it by 90 degrees through a TIR total internal reflection surface 202 (here, the TIR total internal reflection surface is a conventional reflective surface structure with a straight cross-section), and finally converge it onto the fiber or PD 203 (photodetector) through the lens. The overall structure is shown in Figure 1. This integrated lens enables the coupling and transmission of optical information between the fiber and the chips on the PCBA board.

[0015] For 850nm optical modules (which typically require multimode fiber), the multiple propagation modes, dispersion, and pulse broadening in multimode fiber severely impact the application distance and transmission rate. Therefore, 850nm optical modules are generally used only for short-distance transmission. To ensure transmission rate, it is usually necessary to control the actual coupling ring flux. However, traditional integrated coupling lenses are designed with Gaussian spots, making it impossible to optimize the ring flux from the design perspective. Existing coupling lenses have poor ring flux control and cannot meet ideal requirements.

[0016] The following explains multimode optical communication systems and encircled flux in related technologies: In multimode optical communication systems, VCSELs are commonly used as the light source and multimode optical fibers as the optical guiding medium. Generally, the bandwidth relationship between the VCSEL and the multimode optical guiding medium can be obtained through simulation calculations, which is used to determine and improve the performance of the multimode optical guiding medium. That is, the encircled flux (EF) of the VCSEL is used to define the optical characteristics of VCSEL transmission and transmission.

[0017] The beam emitted by a VCSEL is typically circular, and its near-field intensity propagating along the multimode fiber is distributed in a circular shape, with the intensity at the center of the fiber core approaching zero. For a typical 10Gbps communication system, less than 30% of the optical energy is distributed within a 9µm diameter circle, while more than 86% is distributed within a 38µm diameter circle (the "maximum energy at the center" beam pattern is not applicable to VCSELs).

[0018] The transmission performance of multimode fiber is primarily limited by the Differential Mode Delay (DMD) phenomenon. During transmission, optical pulses in multimode fiber diverge and broaden. When this divergence becomes severe enough, consecutive pulses can overlap, making it impossible for the receiving detector to distinguish each individual pulse signal. The main reasons for this are: First, the fiber core refractive index distribution is imperfect. DMD in multimode fiber is a combined effect of the propagation time of incident pulses at different radial positions and the intermodal dispersion characteristics of the fiber. Although a good refractive index distribution function can be designed and DMD controlled for exponentially graded-index multimode fibers, the DMD phenomenon is highly sensitive to the fiber's refractive index distribution; even a small deviation can lead to significant DMD. Therefore, precise control and design are essential to achieve the most perfect refractive index distribution value during multimode fiber fabrication. Second, there is a central dip in the fiber. A central dip refers to a significant decrease in the refractive index distribution at the center of the fiber core, which affects the fiber's transmission characteristics and reduces its performance.

[0019] In summary, the energy distribution (ring flux EF) characteristics of the emitted light spot in the multimode optical communication system based on VCSEL, and the limitations imposed by the multimode fiber's multiple propagation modes, dispersion, and pulse broadening on the application distance and transmission rate of the 850nm optical module, result in most coupling lens structures (using conventional TIR surfaces with linear cross-sections) having significant shortcomings in controlling the ring flux.

[0020] To address the technical problems of insufficient transmission rate and insufficient control ring flux in most coupling lens structures when applied to 850nm optical modules, please refer to Figure 2. This application provides a coupling lens structure 1, which includes at least a light focusing unit 12 and a light reflecting unit 13.

[0021] The optical focusing unit 12, as the first-stage optical signal processing unit in the coupling lens structure 1, is used to receive the optical signal (typically with a wavelength of 850 nm) transmitted from the multimode fiber 11 and collimate or focus the optical signal so that the optical signal is focused in the optical input path and transmitted to the next-stage optical signal processing unit in a first direction (e.g., to the right in Figure 2).

[0022] Optionally, the optical focusing unit 12 may employ an aspherical lens or other optical lens with good beam shaping performance, which can effectively reduce aberrations and improve the collimation or focusing quality of the beam.

[0023] The light reflection unit 13 serves as the second-stage optical signal processing unit in the coupling lens structure 1. It is located in the light reflection position (between the light input path and the light output path) and is used to change the propagation direction of the light signal in the light input path (approximately 90 degrees) and reflect the light signal to the light output path so that the light signal is transmitted along the second direction in the light output path, and finally reaches the light receiver 14 on the PCBA board 15.

[0024] The light reflecting unit 13 forms a BESSEL-TIR reflecting surface 131. The overall structure of the BESSEL-TIR reflecting surface 131 is a quasi-axial conical surface with a continuous undulating profile that is symmetrical about the center.

[0025] Furthermore, unlike traditional flat TIR reflectors, the BESSEL-TIR reflector 131 modulates the propagation phase of the optical signal by controlling the relative height of each target point on the reflector, according to the requirements of Bessel beam shaping. The mechanism is as follows: after light enters the reflector, it undergoes spatial reconstruction after reflection through a non-planar structure with phase modulation capabilities. The original Gaussian distribution (as shown in Figure 3, which is the light spot modulated by a conventional TIR total reflection surface 202) gradually transforms into an approximate BESSEL spot with a ring-shaped energy distribution (i.e., a BESSEL ring spot, as shown in Figure 4). This BESSEL-TIR reflector allows the optical signal coupled into the multimode fiber to have better ring flux matching, thereby reducing dispersion and pulse broadening caused by higher-order mode excitation and effectively improving the performance of the 850nm optical module in short-distance, high-speed transmission applications.

[0026] Here, we distinguish between Gaussian spot and BESSEL ring spot: Gaussian spot generally has the highest light intensity at the center, gradually decreasing towards the periphery; while ring spot has almost zero light intensity at the center, with energy mainly concentrated within a certain radius, distributed in a ring shape. The BESSEL ring spot formed in this application embodiment is based on matching the spot energy to the optimal coupling region (outer ring region) of the multimode fiber, reducing transmission distortion (dispersion, DMD), and improving the coupling efficiency and transmission distance of the 850nm optical module.

[0027] As can be seen, the coupling lens structure of this application embodiment is composed of an optical focusing unit and an optical reflection unit. Based on the optical reflection unit, a BESSEL-TIR reflective surface is formed, that is, the traditional TIR planar reflective surface is replaced with a BESSEL-TIR reflective surface with a quasi-axial conical surface structure. Without changing the original overall structure and manufacturing process of the optical module, the phase modulation of the incident Gaussian beam is achieved, which can effectively shape the light spot into a ring distribution, significantly optimize the ring flux control performance of the optical signal, reduce the excitation of higher-order modes in multimode fiber, and thus reduce dispersion and pulse broadening, thereby improving the transmission rate and transmission distance of the optical module.

[0028] In an optional embodiment of this application, the quasi-axial cone surface is a quasi-conical microstructure constructed according to the target phase function.

[0029] Specifically, these conical microstructures typically form an undulating structure, designed according to the phase shaping requirements of the target light spot. The undulations can be arranged radially or circumferentially. In a radial arrangement, the undulations are distributed from the center to the edge along the reflecting surface, suitable for achieving ring-shaped symmetrical phase modulation of the beam. In a circumferential arrangement, the undulations are distributed around the circumference of the reflecting surface, suitable for shaping the light spot with angular variations or vortex-like phase characteristics. Thus, through this arrangement and periodic design, the undulating structure can effectively achieve continuous phase modulation of the optical signal, shaping the original light spot into a ring-shaped light spot that meets the requirements of multimode fiber transmission, thereby improving coupling efficiency, reducing dispersion, and enhancing system performance.

[0030] Please refer to Figures 5 to 7. The heights of the target points (A, 131A, 131B) on the quasi-axial conical surface (i.e., the BESSEL-TIR reflector) satisfy the following relationship:

[0031] in, N represents the height of the target point in the BESSEL-TIR reflector relative to the reference plane (which is the plane corresponding to the conventional TIR total reflection surface 202 selected at this location, as shown by the dashed line in Figure 6), where N is a positive integer greater than 0 (determined by design optimization to control the phase modulation depth). The wavelength of the optical signal (generally selected as 850nm in this application). Rmax is the refractive index of the material used to manufacture the BESSEL-TIR reflector, Rmax is the maximum radius of the BESSEL-TIR reflector, and r is the distance from a point on the BESSEL-TIR reflector to the center.

[0032] Specifically, the target point refers to the reference point with the highest height within one period of the BESSEL-TIR reflector, which determines the spatial distribution of phase modulation on the surface of the diffractive optical element. Generally, since the undulating structure in the BESSEL-TIR reflector has periodic height variations, there are often multiple target points.

[0033] Furthermore, by defining the height of the target point in the undulating structure using the aforementioned height relationship formula, it can be seen that the height of the undulating structure continuously changes with the azimuth angle, thereby achieving optical phase control in different regions. Preferably, when the azimuth angle φ = 180°, the height of the undulating structure is equal to the corresponding height of the conventional TIR reflector, while the height at other azimuth angles deviates functionally from that of the conventional TIR surface.

[0034] Therefore, it can be seen that each target point in the BESSEL-TIR reflector can be defined according to the height relationship formula, which is related to multiple parameters. This indicates that the undulating structure is designed according to the requirements of ring spot shaping, and can apply predetermined phase modulation to incident light signals at different azimuth angles, thereby converting the original Gaussian spot into a ring spot that conforms to the target ring flux. This design fully considers the mode dispersion and pulse broadening phenomena existing in multimode fiber transmission, effectively improving the coupling efficiency and transmission performance of optical signals.

[0035] In one alternative implementation, when the reflecting surface is a standard right-angle TIR structure, the radial distance r of the target point can be determined by the following formula: r^2 = x^2 + y^2, where x and y are the planar coordinates of the target point relative to the center of the reflecting surface. Correspondingly, the maximum radial distance Rmax (i.e., the maximum radius) can be expressed as the maximum sum of squares of the coordinates of the boundary of the reflecting area: Rmax^2 = Xmax^2 + Ymax^2.

[0036] In another alternative implementation, considering the effects of reflective surface tilt or light incident angle compensation, an angle compensation parameter can be introduced. , After adjusting the coordinates, the radial distance and maximum radius become: r^2 = (x* )^2+(y* Rmax^2 = (Xmax)^2; Rmax^2 = (Xmax)^2 )^2+(Ymax) )^2; where, , These are tilt angle compensation parameters used to compensate for the influence of the tilt angle of the slope on the deviation of the ideal BESSEL beam. Typically, for a 45-degree slope, the requirements are θ1=45 degrees, θ2=0 degrees, or θ1=0 degrees, θ2=45 degrees. For a 41-degree slope, you can choose θ1=41 degrees, θ2=0 degrees, or θ1=0 degrees, θ2=41 degrees.

[0037] Please refer to Figures 8 and 10. The BESSEL-TIR reflector is a non-planar structure with phase modulation capabilities, and its reflector height gradually changes along the radial direction. Specifically, the surface height of each target point on the reflector is determined by the radial distance between that point and the center point, forming a quasi-axial conical structure with the center as the axis of symmetry.

[0038] The height at the center point is set to match the center height of a conventional TIR reflector to maintain the matching of the overall optical path and the consistency of the coupling focus. The surface height of the region outside the center is constructed based on the Bessel beam phase control function, exhibiting continuously varying undulations to modulate the phase delay of the reflected light.

[0039] This continuously undulating surface structure allows the original Gaussian-distributed light spot to form a beam with an approximately ring-shaped energy distribution after reflection, i.e., a Bessel-type light spot. The resulting output light spot more closely approximates the ring-shaped flux coupling requirements in optical module applications, effectively suppressing the propagation of higher-order modes in multimode fibers, reducing dispersion and pulse broadening, and improving link performance in short-distance high-speed communication.

[0040] Please refer to Figures 9 and 11. In one specific embodiment of the present invention, the BESSEL-TIR reflective surface constitutes a non-planar reflective structure, exhibiting a height variation with axisymmetric characteristics in space (Figure 9 shows the height z variation of the reflective surface on a standard circle, and Figure 11 shows the three-dimensional effect of the surface structure). In this embodiment, to compensate for the incident tilt angle of light in the optical system, angle compensation parameters are set, where θ1 = 45° and θ2 = 0°. Because this compensation parameter causes the projection distance in the X direction to be stretched compared to the Y direction, under the same circumferential radius, the surface height z values ​​corresponding to the X and Y directions will differ, reflecting the structural characteristics of non-uniform stretching.

[0041] Specifically, in this structure: the height of the central region (x = 0, y = 0) of the BESSEL-TIR surface is consistent with that of the conventional TIR surface; as it shifts radially outward from the center, the surface height gradually changes according to the Bessel function modulation formula; due to angle compensation, the phase delay path in the X direction is longer, and correspondingly, at the same radius position, its surface height changes faster than in the Y direction.

[0042] It should be noted that the reflecting surface in related technologies (such as the TIR total internal reflection surface 202) is a regular plane or simple undulation, which cannot perform regular phase modulation on light rays at different azimuth angles, resulting in uneven energy distribution or poor directionality of the reflected beam. In contrast, this embodiment improves the directionality and energy uniformity of the reflected beam by periodically changing the height with the azimuth angle.

[0043] In an optional embodiment of this application, please return to and continue referring to Figures 2, 6 and 7, where the coupling lens structure forms an internal cavity.

[0044] In addition to the light focusing unit 12 and the light reflecting unit 13, the internal cavity is also provided with a chip lens 16 for focusing or collimating the reflected light signal and a light receiver 14 for receiving the light signal.

[0045] Specifically, an optical path is formed between the light focusing unit 12, the light reflecting unit 13, and the chip lens 16. This optical path includes a light input path 301 and a light output path 302 that are approximately 90 degrees apart (90 degrees ± 0-2 degrees). The light reflecting unit is located between the light input path 301 and the light output path 302 to facilitate total internal reflection of the light signal.

[0046] As can be seen, through the above optical path design, the optical signal from the multimode fiber 11 passes through the optical focusing unit 12 and the optical reflection unit 13 in sequence, and is transmitted to the optical receiver 14 through the chip lens 16, thereby achieving efficient optical signal coupling and transmission.

[0047] This embodiment also provides an optical module, which is an 850nm optical module, and includes the coupling lens structure as described in the above embodiments.

[0048] This embodiment also provides a method for fabricating a coupled lens structure, including the following steps: First, optical design is performed based on the target BESSEL phase function to determine the required quasi-axial conical structure profile, which is used to construct a reflective surface shape capable of converting a Gaussian spot to a ring-shaped spot. The phase function can be used to generate corresponding height distribution data through optical field simulation and phase delay analysis.

[0049] Secondly, a mold processing method is adopted, using ultra-precision CNC machining and ultra-smooth polishing to form a reflective surface mold with a quasi-axial conical surface structure on the surface of the metal mold workpiece. The surface of this mold is precisely etched with the continuous undulating microstructure required for the BESSEL-TIR reflective surface, which can meet the requirements for optical-grade surface shape error control.

[0050] Next, injection molding is performed using the aforementioned mold to completely transfer the quasi-axial conical structure with the BESSEL-TIR reflective surface into the plastic lens product. This lens molding surface is the final functional reflective surface used for reflection control, possessing the required non-planar morphology.

[0051] Finally, the lens assembly forming the BESSEL-TIR reflective surface is assembled into the coupling lens structure to achieve the functions of deflection, reflection, and phase modulation of the optical signal propagation path.

[0052] The coupling lens structure, optical module, and manufacturing method of this invention consist of an optical focusing unit and an optical reflection unit. A BESSEL-TIR reflective surface is formed based on the optical reflection unit, that is, the traditional TIR planar reflective surface is replaced with a BESSEL-TIR reflective surface with a quasi-axial conical structure. Without changing the original overall structure and manufacturing process of the optical module, phase modulation of the incident Gaussian beam is achieved, which can effectively shape the light spot into a ring distribution, significantly optimize the ring flux control performance of the optical signal, reduce the excitation of higher-order modes in multimode fiber, and thus reduce dispersion and pulse broadening, thereby improving the transmission rate and transmission distance of the optical module.

[0053] Finally, it should be added that the embodiments of this application target optical signals with a wavelength of 850nm, rather than other wavelengths (such as 1000nm or 2000nm), mainly based on the following technical considerations: 1) 850nm is the mainstream operating wavelength for short-distance high-speed communication of multimode fiber. Currently, short-distance communication systems such as data centers and local area networks generally use 850nm wavelength VCSEL light sources paired with OM3 and OM4 grade multimode fibers. Devices in this wavelength range have high maturity and low cost, and are the most widely used solution in the market.

[0054] 2) Multimode dispersion is particularly prominent at 850nm wavelength. Because the 850nm wavelength is shorter, it supports more modes under the same fiber core conditions, resulting in significant differential mode delay (DMD), which is the key technical bottleneck that limits the transmission distance of 850nm system.

[0055] 3) Ring flux control is more critical in 850nm multimode systems. Unlike single-mode or few-mode fiber systems with wavelengths of 1000nm, 1300nm or 2000nm, the energy coupling efficiency of 850nm multimode systems is directly related to the matching degree of the ring spot. If Gaussian spots are continued to be used, it will lead to significant energy loss and transmission performance degradation.

[0056] 4) System design requirements differ for other wavelengths (such as 1000nm or 2000nm): 1000nm-1300nm: commonly used in single-mode fiber optic communication, single-mode dispersion is low and no complex ring flux control is required; 2000nm: mostly used in laser medical or gas sensing fields, the requirements for spot shaping are different from those for data communication.

[0057] Therefore, the phase modulation method of the undulating structure of the diffractive optical element used in the embodiments of this application is particularly suitable for solving the problems of dispersion and coupling efficiency in 850nm multimode optical communication.

[0058] The specific embodiments of the invention have been described in detail above, but these are merely examples, and the invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications or substitutions to the invention are also within the scope of this invention. Therefore, all equivalent transformations, modifications, and improvements made without departing from the spirit and principles of this invention should be covered within the scope of this invention.

Claims

1. A coupling lens structure, characterized in that, When applied in an optical module, the coupling lens structure includes: an optical focusing unit for receiving and collimating or focusing the optical signal transmitted by the multimode fiber; and an optical reflection unit for changing the propagation direction of the optical signal in the optical input path and reflecting it to the optical output path. The optical reflection unit forms a BESSEL-TIR reflective surface, which modulates the propagation phase of the optical signal to make the optical signal spot an annular spot.

2. The coupling lens structure as described in claim 1, characterized in that, The BESSEL-TIR reflector is a quasi-axial conical surface, used to modulate the Gaussian spot into a ring-shaped spot.

3. The coupling lens structure as described in claim 2, characterized in that, The quasi-axial cone surface is a cone-shaped microstructure constructed based on the target phase function.

4. The coupling lens structure as described in claim 2, characterized in that, The height of the target point on the axial conical surface satisfies the following relationship: Where N is a positive integer greater than 0, λ is the wavelength, r is the distance from a point on the BESSEL-TIR reflector to the center, and Rmax is the maximum radius of the BESSEL-TIR reflector. It is the refractive index of the material used to manufacture the BESSEL-TIR reflective surface.

5. The coupling lens structure as described in claim 4, characterized in that, r^2 = x^2 + y^2, and Rmax^2 = Xmax^2 + Ymax^2; where x and y are the planar coordinates of the target point relative to the center of the reflecting surface.

6. The coupling lens structure as described in claim 4, characterized in that, r^2=（x* ）^2+（y* )^2, and Rmax^2=(Xmax)^2 )^2+(Ymax )^2; where, and These are the angle compensation parameters.

7. The coupling lens structure as described in claim 4, characterized in that, The surface height of the BESSEL-TIR reflector varies radially according to the distance between the target point and the center point; wherein, the height of the BESSEL-TIR reflector at the center point is used to maintain consistency with the center height of the conventional TIR reflector, and the height at other positions is used to form a continuous undulating surface shape to achieve phase modulation of the Gaussian spot.

8. The coupling lens structure as described in claim 1, characterized in that, The coupling lens structure forms an internal cavity; the light input unit, the light focusing unit, and the light reflection unit are all located in the internal cavity, forming an optical path with a light input path and a light output path; the light reflection unit is located between the light input path and the light output path.

9. An optical module, characterized in that, The optical module is an 850nm optical module for use with external multimode optical fiber, and includes a coupling lens structure as described in any one of claims 1 to 8.

10. A method for manufacturing a coupling lens structure as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Based on the target BESSEL phase function, a quasi-axial conical structure for forming a BESSEL-TIR reflector is designed; a mold with the quasi-axial conical structure corresponding to the BESSEL-TIR reflector is processed on a mold workpiece using a mold processing method; the quasi-axial conical structure forming the BESSEL-TIR reflector is prepared by injection molding process and mold, and the quasi-axial conical structure is installed in the coupling lens structure.

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