VCSEL (Vertical Cavity Surface Emitting Laser) array and multi-core fiber high-efficiency coupling and aligning system

Abstract

The invention discloses a VCSEL array and multi-core optical fiber high-efficiency coupling and aligning system, and belongs to the field of semiconductor lasers. The VCSEL array and multi-core optical fiber high-efficiency coupling system comprises a VCSEL array, a micro lens array and a multi-core optical fiber. A layer of microlens array is arranged between the VCSEL array and the multi-core optical fiber, and divergent light beams emitted by the VCSEL array are focused through the microlens array, so that the light beams can be respectively aligned with each fiber core of the multi-core optical fiber for incidence. The invention further discloses a VCSEL array and multi-core optical fiber alignment system, on the basis of the VCSEL array and multi-core optical fiber high-efficiency coupling system, the system further comprises a CCD camera, a high-magnification visual system and piezoelectric motors, the VCSEL array, the micro-lens array and the multi-core optical fiber are fixed in the three piezoelectric motors respectively, the plane where the piezoelectric motors are located is an x-y plane, and the plane where the piezoelectric motors are located is an x-y plane. A CCD camera is placed at the position parallel to the x-y plane, image information of the VCSEL array, the micro-lens array and the multi-core optical fiber is captured, and machine vision automatic alignment is carried out.

Description

Technical Field

[0001] The invention relates to a VCSEL array and multi-core optical fiber high-efficiency coupling and alignment system, belonging to the field of semiconductor lasers. Background Art

[0002] VCSEL (Vertical Cavity Surface Emitting Laser) is widely used in data centers, short-distance optical interconnects, and lidars due to its high conversion efficiency, low threshold current, low power consumption, and easy integration. Compared with DFB lasers, vertical cavity surface emitting lasers (VCSELs) have extremely low threshold currents, extremely low power consumption, and high photoelectric conversion efficiency. At the same time, VCSELs also have the advantages of small size, on-wafer testing, low manufacturing cost, and easy packaging, making them an ideal light source to replace DFB lasers. With the rapid development of information technology, VCSELs with higher modulation rates and greater output power are required. How to improve the modulation bandwidth of VCSELs has become the focus of academia and industry.

[0003] As the amount of data grows exponentially, existing optical communication systems based on single-mode fiber (SMF) are approaching capacity limits, and there is an increasing demand for increasing the capacity of optical communication channels through space division multiplexing (SDM). With the development of low-loss SMF, erbium-doped fiber amplifiers, multiplexing in possible fields such as time, wavelength, polarization and phase, and high spectral efficiency coding, the channel capacity has reached its limit. Multi-core fiber (MCF) can effectively expand channel capacity due to its multiple cores.

[0004] Multicore optical fibers can be divided into two types. One is uncoupled optical fiber, in which the center-to-center distance between adjacent cores (called core spacing) is designed to be large enough to reduce mode coupling between cores. The other is coupled optical fiber with a smaller core spacing, which allows strong coupling of isolated modes between adjacent cores and non-adjacent cores.

[0005] In order to meet the technical requirements of low power consumption, high speed and large capacity of internal optical interconnection in future ultra-large-scale data centers, research is conducted on how to effectively couple VCSEL arrays with multi-core optical fibers, including optical design, precision alignment technology and coupling efficiency optimization.

[0006] Microlenses offer an attractive solution for efficiently connecting individual cores of multicore fibers (MCFs) to standard arrays of VCSELs with industry standard pitches (e.g., 250 μm). Microlens elements are designed to collimate the associated beams to large diameters of tens of microns, which greatly relaxes alignment tolerances, allowing subsequent assembly steps to rely entirely on passive positioning using industry standard machine vision.

[0007] In actual operation, due to the small size of VCSEL array, microlens array and multi-core optical fiber, whether the components are aligned and the accuracy of alignment in the VCSEL array and multi-core optical fiber coupling model will affect the performance parameters of the model. Therefore, it is considered to use the method of visual assisted automatic alignment technology to align the various parts of the model. The specific implementation method is to use a charge coupled device (CCD) camera to determine the center of the reference point relative to the original coordinate, provide a position reference for motion control, and achieve alignment.

[0008] In addition to semiconductor manufacturing, the electronics industry is another sector that has incorporated machine vision into its production process, especially automatic alignment operations. With the help of machine vision-assisted automatic alignment technology, high-quality electronic devices with good precision can be produced efficiently, thereby reducing production costs and enhancing industry competitiveness. Summary of the invention

[0009] The purpose of the present invention is to provide a high-efficiency coupling and alignment system for a VCSEL array and a multi-core optical fiber. By arranging a microlens array between the VCSEL array and the multi-core optical fiber, the relevant light beam is collimated to a large diameter of tens of microns, and the alignment tolerance is relaxed. At the same time, a two-dimensional VCSEL array is designed and manufactured so that its size and spacing match the core diameter and core spacing of a single-mode multi-core optical fiber (SM-MCF) to allow MCF transmission based on microlens array coupling for parallel optical data links.

[0010] The objective of the present invention is achieved through the following technical solutions:

[0011] The invention discloses a VCSEL array and multi-core optical fiber high-efficiency coupling system, comprising a VCSEL array, a microlens array and a multi-core optical fiber. A layer of microlens array is arranged between the VCSEL array and the multi-core optical fiber, and the divergent light beam emitted by the VCSEL array is focused by the microlens array so that the light beam can be respectively aligned with each core of the multi-core optical fiber for incidence.

[0012] Furthermore, the design method of the microlens array is as follows: setting the profile and vertex focal length of the microlenses in the microlens array;

[0013] The lens profile h(r) of an axisymmetric plano-convex microlens is expressed as:

[0014]

[0015] Where h(r) is a function of the microlens height and the distance r from the optical axis, R is the vertex radius of curvature, and K is the aspheric constant; the radius of curvature at the vertex is expressed as:

[0016]

[0017] where h L is the height of the microlens vertex;

[0018] The vertex focal length f of the plano-convex refractive microlens is expressed as:

[0019]

[0020] where n is the refractive index of the microlens material.

[0021] Furthermore, the distance between the microlens array and the VCSEL array, and the distance between the microlens array and the multi-core optical fiber are set so that the coupling efficiency is maximized and the loss of the light beam is minimized;

[0022] Define Z1 as the distance from the VCSEL array to the microlens surface, and Z2 as the distance from the microlens surface to the incident end of the multi-core fiber, where both Z1 and Z2 are equal to the vertex focal length f, and the coupling efficiency is obtained:

[0023]

[0024] in:

[0025]

[0026] ω VCSEL is the mode size of the VCSEL beam at the cavity surface, ω MCF is the mode size of the multi-core optical fiber, T is the thickness of the microlens substrate, and n is the refractive index of the microlens material; Z'2 is the distance from the microlens surface to the incident end of the multi-core optical fiber minus the error of the microlens substrate thickness.

[0027] Furthermore, the design method of the multi-core optical fiber is as follows:

[0028] Interference XT between two adjacent cores in a multi-core optical fiber μ It can be expressed as where P and P' are the output powers of core p and adjacent core q, respectively;

[0029] Interference XT between two adjacent cores in a multi-core optical fiber μ Written in terms of fiber parameters:

[0030]

[0031] Among them, h pq is the power coupling coefficient between the fiber cores p and q, L is the length of the fiber, k pq is the mode coupling coefficient, R b is the bending radius of the optical fiber, and the mode propagation constant β = k × n eff , k is the wave number, k = 2π / λ, λ is the wavelength of light in vacuum, n effis the effective refractive index, Λ is the core-to-core distance, γ is the fiber twist rate, and j represents an imaginary number.

[0032] The present invention also discloses a method for high-efficiency coupling of a VCSEL array and a multi-core optical fiber, which is implemented based on a high-efficiency coupling system of the VCSEL array and the multi-core optical fiber. A method for high-efficiency coupling of a VCSEL array and a multi-core optical fiber comprises the following steps:

[0033] Step 1: A layer of microlens array is set between the VCSEL array and the multi-core optical fiber to focus the divergent light beam emitted by the VCSEL array so that the light beam can be incident on each core of the multi-core optical fiber.

[0034] Step 2: Set the profile and focal length of the microlenses in the microlens array, as well as the distance between the microlens array, the VCSEL array, and the multi-core optical fiber to maximize the coupling efficiency and minimize the loss of the light beam.

[0035] The lens profile h(r) of an axisymmetric plano-convex microlens is expressed as:

[0036]

[0037] Where h(r) is a function of the microlens height and the optical axis distance r, R is the vertex curvature radius, K is the aspheric constant, and the curvature radius at the vertex is expressed as:

[0038]

[0039] where h L is the height of the microlens vertex; the vertex focal length f of the plano-convex refractive microlens is expressed as:

[0040]

[0041] where n is the refractive index of the microlens material.

[0042] Define Z1 as the distance from the VCSEL array to the microlens surface, and Z2 as the distance from the microlens surface to the incident end of the multi-core fiber, where Z1 and Z2 are equal to the focal length f, and the coupling efficiency is obtained:

[0043]

[0044] in:

[0045]

[0046] ω VCSEL is the mode size of the VCSEL beam at the cavity surface, ω MCFis the mode size of the multi-core optical fiber, T is the thickness of the microlens substrate, and n is the refractive index of the microlens material; Z'2 is the distance from the microlens surface to the incident end of the multi-core optical fiber minus the error of the microlens substrate thickness.

[0047] Step 3: Design and manufacture uncoupled multi-core optical fibers to suppress crosstalk between fiber cores.

[0048] Interference XT between two adjacent cores in a multi-core optical fiber μ Expressed as where P and P' are the output powers of core p and adjacent core q, respectively.

[0049] Interference XT between two adjacent cores in a multi-core optical fiber μ Written in terms of fiber parameters:

[0050]

[0051] Among them, h pq is the power coupling coefficient between the fiber cores p and q, L is the length of the fiber, k pq is the mode coupling coefficient, R b is the bending radius of the optical fiber, and the mode propagation constant β = k × n eff , k is the wave number, k = 2π / λ, λ is the wavelength of light in vacuum, n eff is the effective refractive index, Λ is the core-to-core distance, γ is the fiber twist rate, and j represents an imaginary number.

[0052] Step 4: Design and manufacture a two-dimensional VCSEL array so that its size and spacing match the core diameter and core spacing of the multi-core optical fiber to allow multi-core optical fiber transmission based on microlens array coupling for parallel optical data links. The size and spacing of the VCSEL array are designed according to the actual size of the multi-core optical fiber used. The two-dimensional VCSEL array is designed to ensure that its arrangement is consistent with the arrangement of the cores inside the multi-core optical fiber, and the spacing of a single VCSEL device should be slightly smaller than the distance between each core, so that its size and spacing match the core diameter and core spacing of the single-mode multi-core optical fiber (SM-MCF) to allow MCF transmission based on microlens array coupling for parallel optical data links.

[0053] Furthermore, the diameter of a single VCSEL device in the VCSEL array is 9.5μm~10.5μm; the diameter of each core of the 16-core multi-core optical fiber is 7.5μm~8.5μm, the distance between each core is 39.5μm~40.5μm, and the cladding diameter is 199.5μm~200.5μm; the microlens spacing is about 99.5μm~100.5μm; the designed microlens diameter is 9.5μm~10.5μm, and the material is Si. By adding a microlens array, the maximum coupling efficiency is increased to 90%.

[0054] The present invention also discloses a VCSEL array and multi-core optical fiber alignment system, which includes a CCD camera, a high-magnification visual system and a piezoelectric motor in addition to the VCSEL array, the microlens array and the multi-core optical fiber. The VCSEL array, the microlens array and the multi-core optical fiber are respectively fixed in three piezoelectric motors, the plane where the piezoelectric motors are located is the xy plane, and a CCD camera is placed at a position parallel to the xy plane to capture the image information of the VCSEL array, the microlens array and the multi-core optical fiber, and perform automatic machine vision alignment.

[0055] The method for realizing automatic alignment of a VCSEL array and a multi-core optical fiber alignment system comprises the following steps:

[0056] Step 1: Set P1 as the target position: record the coordinates of the image of the object at the target position captured by the CCD camera in the system as the target position P1. Set P2 as the position to be aligned: record the coordinates of the image of the object to be aligned captured by the CCD camera in the system as the position to be aligned P2. Then match position P2 with position P1.

[0057] The target vector of the CCD camera is [X1 Y1] T Because P1≠P2, there are position differences Δx and Δy between them. The characteristic matrix can be obtained as follows:

[0058]

[0059] in is the feature matrix, expressed as matrix A, is the bias vector, expressed as a matrix Z, is the target matrix, denoted as matrix B.

[0060] Therefore, equation (8) is equivalent to AZ = B. Since the target vector and feature matrix can be obtained from the relative coordinates of the CCD camera, the expression of the offset vector Z is:

[0061] Z=(A T A) -1 A T B (9)

[0062] The solution of equation (9) is a general solution. Using the correlation between the input signal and the output feedback, the feature matrix issues reference commands to move along the x and y directions to compensate for the position difference. The change of the reference point after the translation movement will be recorded by the CCD and analyzed as follows:

[0063]

[0064] in, Provide input, represented as a matrix C, with m ≥ 2, is a subvector of the feature matrix A, represented as a matrix M, is the x subvector of the target matrix B, represented by the matrix D. Therefore, equation (10) is equivalent to CM=D.

[0065] By M=(C T C) -1 C T D gets the matrix

[0066] Similarly, the subvector of the feature matrix A is obtained from formula (11): Represented as matrix N:

[0067]

[0068] in, Provide input, represented as a matrix E, and m ≥ 2; is a subvector of the feature matrix A, represented as a matrix N, is the y subvector of the target matrix B, represented by the matrix F; therefore, equation (11) is equivalent to EN = F, and N = (E T E) -1 E T F gets the matrix

[0069] In the known feature matrix In the case of Substituting into equation (8), we get the bias vector Z = (A T A) -1 A T B; Finally, It is converted into actual instructions, so that the two-axis piezoelectric motors compensate for Δx and Δy, so that the position to be aligned P2 is accurately matched with the target position P1, thus achieving precise alignment.

[0070] Beneficial effects:

[0071] 1. The present invention discloses a high-efficiency coupling system and method of a VCSEL array and a multi-core optical fiber. The coupling of the VCSEL array and the single-mode multi-core optical fiber based on a microlens array can improve the maximum coupling efficiency to 90% compared with butt coupling. The lateral alignment tolerance required for the maximum 1dB excess coupling loss of each component is ±4μm.

[0072] 2. The present invention discloses a VCSEL array and multi-core optical fiber high-efficiency coupling system and coupling method, which designs the spacing between each VCSEL in the VCSEL array and the core distance of the MCF, and designs the arrangement of the VCSEL array to be consistent with the arrangement of the cores inside the MCF, so that the spacing between a single VCSEL device should be slightly smaller than the distance between each core. When the transmission distance is 10km or more, the coupling coefficient between adjacent cores is <0.01 / m, and the core spacing is 40μm or more, the crosstalk XT level between the cores can be guaranteed to be <-30dB.

[0073] 3. The present invention discloses a high-efficiency coupling system and coupling method of a VCSEL array and a multi-core optical fiber, which uses a CCD camera to define the center of a reference mark relative to the original coordinates, thereby providing a position reference for motion control to achieve alignment. Through image processing and matrix transformation, a characteristic matrix of the system function between the input and output signals is established. Using the matrix established when the object to be aligned falls within the field of view FOV of the CCD, the position change between the reference mark and the original coordinates is calculated through matrix transformation. Based on the difference obtained, a command can be issued to the piezoelectric motor to make it move to compensate for the above difference, thereby achieving fast and accurate alignment, and the alignment accuracy range can achieve ±20nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 It is a schematic diagram of coupling between VCSEL array and multi-core optical fiber;

[0075] Figure 2 is a schematic diagram of the automatic alignment system.

[0076] Among them: 1-VCSEL array, 2-microlens array, 3-multi-core optical fiber, 4-CCD camera, 5-high magnification visual system, 6-first piezo motor, 7-second piezo motor, 8-third piezo motor. DETAILED DESCRIPTION

[0077] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0078] Embodiment 1:

[0079] like Figure 1As shown, a VCSEL array and multi-core optical fiber high-efficiency coupling system disclosed in this embodiment includes, from left to right, a VCSEL array 1, a microlens array 2, and a multi-core optical fiber 3. The divergent light beams emitted by the VCSEL array 1 are focused by the microlens array 2 so that the light beams can be respectively directed to the single cores of the multi-core optical fiber 3 for incidence. At the same time, the two-dimensional VCSEL array 2 is designed and manufactured so that its size and spacing match the core diameter and core spacing of the multi-core optical fiber 3, so as to allow multi-core optical fiber transmission based on microlens array coupling for parallel optical data links.

[0080] Embodiment 2:

[0081] This embodiment also discloses a method for high-efficiency coupling of a VCSEL array and a multi-core optical fiber, which is implemented based on the high-efficiency coupling system of a VCSEL array and a multi-core optical fiber, and includes the following steps:

[0082] Step 1: A layer of microlens array 2 is arranged between the VCSEL array 1 and the multi-core optical fiber 3 to focus the divergent light beam emitted by the VCSEL array 1 so that the light beam can be incident on each core of the multi-core optical fiber 3 respectively.

[0083] Step 2: Set the profile and focal length of the microlenses in the microlens array 2, the distance between the microlens array 2 and the VCSEL array 1, and the distance between the microlens array 2 and the multi-core optical fiber 3 to maximize the coupling efficiency and minimize the light beam loss.

[0084] Combined with the microlens array 2 set in step 1, the changes of the Gaussian beam generated by the VCSEL array 1 after passing through the microlens array 2 are analyzed.

[0085] The light beam emitted by the VCSEL array 1 is a Gaussian beam, which is expressed by the following formula:

[0086]

[0087] H m (x) and H n (x) represents the mth and nth Hermite polynomials, ω is the beam waist, and the basic Gaussian beam satisfies m=n=0; x and y represent the two directional components of the incident wave transmission, Represents the unit vector in the x direction.

[0088] The transmission and transformation of Gaussian beams can be expressed by the ABCD matrix. In a linear, uniform, isotropic medium with a refractive index of n, the relationship between the beam waist ω0 of a Gaussian beam and its half-divergence θ can be expressed as:

[0089]

[0090] Where λ0 is the wavelength in vacuum.

[0091] Its Rayleigh length is:

[0092]

[0093] Where ω0 is the beam waist of the Gaussian beam, n is the refractive index of the medium, and λ0 is the wavelength in vacuum.

[0094] For any horizontal coordinate z, its local radius ω(z) and curvature R(z) are as follows:

[0095]

[0096] Where ω0 is the beam waist of the Gaussian beam and z0 is the Rayleigh length.

[0097] The complex curvature q(z) can be defined as:

[0098]

[0099] where R(z) is the curvature, ω(z) is the local radius, n is the refractive index of the medium, and λ0 is the wavelength in vacuum.

[0100] Propagation from abscissa z to abscissa z' = z L in the same medium converts the complex curvature q(z) to q(z') according to the following rule:

[0101]

[0102] Through the microlens array 2, it is equivalent to the spherical interface separating two linear, uniform, isotropic media with refractive indices n and n', and the complex curvature is converted according to the rule. ABCD can be expressed as:

[0103]

[0104] Where S is the vertex and C is the center. represents the distance between two points in SC, Indicates the focal length of the interface.

[0105] The change of the Gaussian beam after passing through the microlens array 2 is expressed according to equation (19).

[0106] The coupling efficiency is calculated according to formulas (1) to (6).

[0107] The diameter of a single VCSEL device in the VCSEL array 1 is 9.5 μm to 10.5 μm, and the diameter of each core of the 16-core multi-core optical fiber 3 is 7.5 μm to 8.5 μm. In order to effectively focus the VCSEL beam, the NA should be greater than 0.5.

[0108] The diameter of a single microlens in the designed microlens array 2 is 9.5 μm to 10.5 μm, the thickness T of the microlens substrate is 399.5 μm to 400.5 μm, and the material is Si, which can increase the maximum coupling efficiency to 90%.

[0109] Step 3: Design and manufacture a multi-core optical fiber 3 to suppress crosstalk between the fiber cores.

[0110] Suppressing crosstalk between cores is one of the key issues in the practical use of multi-core optical fiber 3. While maintaining the single-mode condition of multi-core optical fiber 3, there is a trade-off relationship between crosstalk between cores, fiber nonlinearity, and core density.

[0111] XT μ Defined as the disturbance caused by the magnetic / electric field of a signal in one core, which affects the signal in an adjacent core.

[0112] Interference XT between two adjacent cores in multi-core optical fiber 3 μ It can be expressed as where P and P' are the output powers of core p and adjacent core q, respectively.

[0113] Interference XT between two adjacent cores in multi-core optical fiber 3 μ Calculate using formula (7).

[0114] Design multi-core optical fiber 3, maintain XT level <-30dB, design transmission distance of 10km or more, coupling coefficient between adjacent cores <0.01 / m, and core spacing of 40μm or more.

[0115] Step 4: Design and manufacture the VCSEL array 1 so that its size and spacing match the core diameter and core spacing of the multi-core optical fiber 3 to allow multi-core optical fiber 3 transmission based on microlens array 2 coupling for parallel optical data links. The size and spacing of the VCSEL array 1 should be designed according to the actual size of the multi-core optical fiber 3 used. When designing the VCSEL array 1, it is necessary to ensure that its arrangement is consistent with the arrangement of the cores inside the multi-core optical fiber 3, and the spacing of a single VCSEL device in the VCSEL array 1 should be slightly smaller than the distance between each core.

[0116] The diameter of a single VCSEL device in the VCSEL array 1 is 9.5 μm to 10.5 μm; the diameter of each core of the 16-core multi-core optical fiber 3 is 7.5 μm to 8.5 μm, the distance between each fiber core is 39.5 μm to 40.5 μm, and the cladding diameter is 199.5 μm to 200.5 μm; the spacing between a single microlens in the microlens array 2 is about 99.5 μm to 100.5 μm; the diameter of a single microlens in the microlens array 2 is 9.5 μm to 10.5 μm, and the material is Si. By adding the microlens array 2, the maximum coupling efficiency is increased to 90%.

[0117] Embodiment 3:

[0118] like Figure 2 As shown, this embodiment also discloses a VCSEL array and multi-core optical fiber alignment system, which includes a CCD camera 4, a high-magnification visual system 5, a first piezo motor 6, a second piezo motor 7, and a third piezo motor 8 in addition to the VCSEL array 1, the microlens array 2, and the multi-core optical fiber 3. The connection relationship is: in the system, the VCSEL array 1 is fixed in the first piezo motor 6, the microlens array 2 is fixed in the second piezo motor 7, and the multi-core optical fiber 3 is fixed in the third piezo motor 8. The plane where the first piezo motor 6, the second piezo motor 7, and the third piezo motor 8 are located is the xy plane, and the CCD camera 4 and the high-magnification visual system 5 connected together are placed at a position parallel to the xy plane to capture the image information of the VCSEL array 1, the microlens array 2, and the multi-core optical fiber 3, and perform automatic machine vision alignment.

[0119] The automatic alignment of the VCSEL array 1 and the multi-core optical fiber 3 is realized by using machine vision technology. The working method of the alignment system of the VCSEL array 1 and the multi-core optical fiber 3 is as follows:

[0120] Let P1 be the target position: the coordinates of the image of the object at the target position captured by the CCD camera 4 are recorded in the system as the target position P1. Let P2 be the position to be aligned: the coordinates of the image of the object to be aligned captured by the CCD camera 4 are recorded in the system as the position to be aligned P2. Then match the position P2 with the position P1.

[0121] like Figure 2 As shown, since the plane where the first piezo motor 6, the second piezo motor 7 and the third piezo motor 8 are located is the xy plane, the target vector of the CCD camera 4 is [X1 Z1] T Because P1≠P2, there are position differences Δx and Δz between them. The characteristic matrix can be obtained as follows:

[0122]

[0123] in is the feature matrix, expressed as matrix A, is the bias vector, expressed as a matrix Z, is the target matrix, denoted as matrix B.

[0124] Therefore, equation (20) is equivalent to AZ = B. Since the target vector and feature matrix can be obtained from the relative coordinates of the CCD camera, the expression of the offset vector Z is:

[0125] Z=(A T A) -1 A T B (21)

[0126] The solution of equation (21) is a general solution. Using the correlation between the input signal and the output feedback, the characteristic matrix issues reference commands to move along the x and z directions to compensate for the position difference. The change of the reference point after the translation movement will be recorded by the CCD and analyzed as follows:

[0127]

[0128] in, Provide input, represented as a matrix C, with m ≥ 2, is a subvector of the feature matrix A, represented as a matrix M, is the x subvector of the target matrix B, represented by the matrix D. Therefore, equation (22) is equivalent to CM=D.

[0129] By M=(C T C) -1 C T D gets the matrix

[0130] Similarly, the subvector of the feature matrix A is obtained from formula (23): Represented as matrix N:

[0131]

[0132] in, Provide input, represented as a matrix E, and m ≥ 2; is a subvector of the feature matrix A, represented as a matrix N, is the y subvector of the target matrix B, represented by the matrix F; therefore, equation (23) is equivalent to EN = F, and N = (E T E) -1 E T F gets the matrix

[0133] In the known feature matrix In the case of Substituting into equation (20), we get the bias vector Z = (A T A) -1 A T B; Finally, It is converted into actual instructions, so that the first piezo motor 6, the second piezo motor 7 and the third piezo motor 8 compensate for Δx and Δz, so that the position to be aligned P2 is accurately matched with the target position P1, thereby achieving precise alignment.

[0134] The third piezo motor 8 is controlled to move the multi-core optical fiber 3 to the center of the operating table to facilitate subsequent operations.

[0135] Use a high-magnification visual system 5 to detect the coordinates of the yz plane of the center position of the multi-core optical fiber 3 as the target coordinates, calculate the position differences Δx1 and Δz1 between the microlens array 2 and the multi-core optical fiber 3, and control the second piezo motor 7 to compensate for Δx1 and Δz1 so that the position of the microlens array 2 accurately matches the position of the multi-core optical fiber 3.

[0136] Then, the position differences Δx2 and Δz2 between the VCSEL array 1 and the multi-core optical fiber 3 are calculated, and the first piezo motor 6 is controlled to compensate for Δx2 and Δz2, so that the position of the VCSEL array 1 is accurately matched with the position of the multi-core optical fiber 3.

[0137] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A VCSEL array and multi-core optical fiber high-efficiency coupling system, characterized by: It includes a VCSEL array, a microlens array and a multi-core optical fiber; a layer of microlens array is arranged between the VCSEL array and the multi-core optical fiber, and the divergent light beam emitted by the VCSEL array is focused by the microlens array so that the light beam can be respectively aligned with each core of the multi-core optical fiber for incidence.

2. A VCSEL array and multi-core optical fiber high-efficiency coupling system as claimed in claim 1, characterized in that: The design method of the microlens array is as follows: setting the profile and vertex focal length of the microlenses in the microlens array; The lens profile h(r) of an axisymmetric plano-convex microlens is expressed as: Where h(r) is a function of the microlens height and the distance r from the optical axis, R is the vertex radius of curvature, and K is the aspheric constant; the radius of curvature at the vertex is expressed as: where h L is the height of the microlens vertex; The vertex focal length f of the plano-convex refractive microlens is expressed as: where n is the refractive index of the microlens material.

3. A VCSEL array and multi-core optical fiber high-efficiency coupling system as claimed in claim 1, characterized in that: The distance between the microlens array and the VCSEL array, and the distance between the microlens array and the multi-core optical fiber are set to maximize the coupling efficiency and minimize the loss of the light beam; Define Z1 as the distance from the VCSEL array to the microlens surface, and Z2 as the distance from the microlens surface to the incident end of the multi-core fiber, where both Z1 and Z2 are equal to the vertex focal length f, and the coupling efficiency is obtained: in: ω VCSEL is the mode size of the VCSEL beam at the cavity surface, ω MCF is the mode size of the multi-core optical fiber, T is the thickness of the microlens substrate, and n is the refractive index of the microlens material; Z'2 is the distance from the microlens surface to the incident end of the multi-core optical fiber minus the error of the microlens substrate thickness.

4. A VCSEL array and multi-core optical fiber high-efficiency coupling system as claimed in claim 1, characterized in that: The design method of the multi-core optical fiber is as follows: Interference XT between two adjacent cores in a multi-core optical fiber μ Expressed as where P and P' are the output powers of core p and adjacent core q, respectively; Interference XT between two adjacent cores in a multi-core optical fiber μ Written in terms of fiber parameters: Among them, h pq is the power coupling coefficient between the fiber cores p and q, L is the length of the fiber, k pq is the mode coupling coefficient, R b is the bending radius of the optical fiber, and the mode propagation constant β = k × n eff , k is the wave number, k = 2π / λ, λ is the wavelength of light in vacuum, n eff is the effective refractive index, Λ is the core-to-core distance, γ is the fiber twist rate, and j represents an imaginary number.

5. A VCSEL array and multi-core optical fiber high-efficiency coupling system as claimed in claim 1, characterized in that: The diameter of a single VCSEL device in the VCSEL array is 9.5μm to 10.5μm; the diameter of each core of the 16-core multi-core optical fiber is 7.5μm to 8.5μm, the distance between each core is 39.5μm to 40.5μm, and the cladding diameter is 199.5μm to 200.5μm; the microlens spacing is about 99.5μm to 100.5μm; the designed microlens diameter is 9.5μm to 10.5μm, and the material is Si. By adding a microlens array, the maximum coupling efficiency is increased to 90%.

6. A method for high-efficiency coupling of a VCSEL array and a multi-core optical fiber, based on the high-efficiency coupling system of a VCSEL array and a multi-core optical fiber as claimed in claim 1, characterized in that: The steps include: Step 1: A layer of microlens array is set between the VCSEL array and the multi-core optical fiber to focus the divergent light beam emitted by the VCSEL array so that the light beam can be incident on each core of the multi-core optical fiber respectively; Step 2: Setting the profile and focal length of the microlenses in the microlens array, as well as the distance between the microlens array, the VCSEL array, and the multi-core optical fiber, to maximize the coupling efficiency and minimize the loss of the light beam; The lens profile h(r) of an axisymmetric plano-convex microlens is expressed as: Where h(r) is a function of the microlens height and the optical axis distance r, R is the vertex curvature radius, K is the aspheric constant, and the curvature radius at the vertex is expressed as: where h L is the height of the microlens vertex; the vertex focal length f of the plano-convex refractive microlens is expressed as: Where n is the refractive index of the microlens material; Define Z1 as the distance from the VCSEL array to the microlens surface, and Z2 as the distance from the microlens surface to the incident end of the multi-core fiber, where Z1 and Z2 are equal to the focal length f, and the coupling efficiency is obtained: in: ω VCSEL is the mode size of the VCSEL beam at the cavity surface, ω MCF is the mode size of the multi-core optical fiber, T is the thickness of the microlens substrate, and n is the refractive index of the microlens material; Z'2 is the distance from the microlens surface to the incident end of the multi-core optical fiber minus the error of the microlens substrate thickness; Step 3: Design and manufacture uncoupled multi-core optical fibers to suppress crosstalk between cores; Interference XT between two adjacent cores in a multi-core optical fiber μ Expressed as where P and P' are the output powers of core p and adjacent core q, respectively; Interference XT between two adjacent cores in a multi-core optical fiber μ Written in terms of fiber parameters: Among them, h pq is the power coupling coefficient between the fiber cores p and q, L is the length of the fiber, k pq is the mode coupling coefficient, R b is the bending radius of the optical fiber, and the mode propagation constant β = k × n eff , k is the wave number, k = 2π / λ, λ is the wavelength of light in vacuum, n eff is the effective refractive index, Λ is the core-to-core distance, γ is the fiber twist rate, and j represents an imaginary number; Step 4: Design and manufacture a two-dimensional VCSEL array so that its size and spacing match the core diameter and core spacing of the multi-core optical fiber to allow multi-core optical fiber transmission based on microlens array coupling for parallel optical data links; the size and spacing of the VCSEL array are designed according to the actual size of the multi-core optical fiber used; the two-dimensional VCSEL array is designed to ensure that its arrangement is consistent with the arrangement of the cores inside the multi-core optical fiber, and the spacing of a single VCSEL device should be slightly smaller than the distance between each core, so that its size and spacing match the core diameter and core spacing of the single-mode multi-core optical fiber to allow MCF transmission based on microlens array coupling for parallel optical data links.

7. A VCSEL array and multi-core optical fiber alignment system, based on the VCSEL array and multi-core optical fiber high-efficiency coupling system as claimed in claim 1, 2, 4 or 5, characterized in that: It also includes a CCD camera, a high-magnification vision system, and a piezo motor; The VCSEL array, microlens array and multi-core optical fiber are fixed in three piezoelectric motors respectively. The plane where the piezoelectric motors are located is the xy plane. A CCD camera is placed at a position parallel to the xy plane to capture the image information of the VCSEL array, microlens array and multi-core optical fiber for automatic machine vision alignment.

8. A method for realizing automatic alignment of a VCSEL array and a multi-core optical fiber alignment system according to claim 7, characterized in that: Let P1 be the target position: record the coordinates of the image of the object at the target position captured by the CCD camera in the system as the target position P1; let P2 be the position to be aligned: record the coordinates of the image of the object to be aligned captured by the CCD camera in the system as the position to be aligned P2; then match the position P2 with the position P1; The target vector of CCD is [X1 Y1] T ; Because P1≠P2, there are position differences Δx and Δy between them; From equation (8), we get: in is the feature matrix, expressed as matrix A, is the bias vector, expressed as a matrix is the target matrix, expressed as matrix B; Formula (8) is equivalent to AZ = B. Since the target vector and feature matrix can be obtained from the relative coordinates of the CCD camera, the expression of the offset vector Z is: Z=(A T A) -1 A T B (9) Using the correlation between the input signal and the output feedback, the feature matrix issues reference commands to move in the x and y directions to compensate for the position difference; the change of the position to be aligned P2 after the translation movement will be recorded by the CCD and analyzed as follows: in, Provide input, represented as a matrix C, and m ≥ 2; is a subvector of the feature matrix A, represented as a matrix M, is the x subvector of the target matrix B, represented by the matrix D; therefore, equation (10) is equivalent to CM = D; from M = (C T C) - 1 C T D gets the matrix Similarly, the subvector of the feature matrix A is obtained from formula (11): Represented as matrix N: in, Provide input, represented as a matrix E, and m ≥ 2; is a subvector of the feature matrix A, represented as a matrix N, is the y subvector of the target matrix B, represented by the matrix F; therefore, equation (11) is equivalent to EN = F, and N = (E T E) - 1 E T F gets the matrix In the known feature matrix In the case of Substituting into equation (8), we get the bias vector Z = (A T A) -1 A T B; Finally, It is converted into actual instructions, so that the two-axis piezoelectric motors compensate for Δx and Δy, so that the position to be aligned P2 is accurately matched with the target position P1, thus achieving precise alignment.

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