阅读说明：本技术 一种多芯光纤微准直器 (Multi-core optical fiber micro-collimator ) 是由 苑立波 孟令知 于 2020-05-10 设计创作，主要内容包括：本发明提供的是一种多芯光纤微准直器。其特征是：它由多芯光纤1、多芯光纤热扩散段2和渐变折射率大芯径多芯光纤3连接组成。本发明主要解决多芯光纤端出射光束扩束及准直的问题,同时降低各个信号之间的串扰。本发明具有制作简单、成本低、结构紧凑的优点。本发明可用于光纤通信传输系统和光纤传感系统,可广泛应用于光纤与光纤之间、光纤与波导之间以及光纤与其他光学器件之间的耦合连接。(The invention provides a multi-core optical fiber micro-collimator. The method is characterized in that: the optical fiber consists of a multi-core optical fiber 1, a multi-core optical fiber thermal diffusion section 2 and a gradient-refractive-index large-core-diameter multi-core optical fiber 3 which are connected. The invention mainly solves the problems of beam expansion and collimation of emergent light beams at the end of the multi-core optical fiber, and simultaneously reduces crosstalk among signals. The invention has the advantages of simple manufacture, low cost and compact structure. The invention can be used for optical fiber communication transmission systems and optical fiber sensing systems, and can be widely applied to coupling connection between optical fibers, between optical fibers and waveguides and between optical fibers and other optical devices.)

1. A multi-core optical fiber micro-collimator. The method is characterized in that: the optical fiber consists of a multi-core optical fiber 1, a multi-core optical fiber thermal diffusion section 2 and a gradient-refractive-index large-core-diameter multi-core optical fiber 3 which are connected. The multi-core optical fiber thermal diffusion section 2 in the multi-core optical fiber microcollimator is located between the multi-core optical fiber 1 and the gradient-index large-core-diameter multi-core optical fiber 3, and the multi-core optical fiber thermal diffusion section 2 is welded with the gradient-index large-core-diameter multi-core optical fiber 3. The multi-core optical fiber micro-collimator applies thermal diffusion on the multi-core optical fiber thermal diffusion section 2, the multi-core optical fiber thermal diffusion section 2 forms a refractive index gradient region, the transmission of a fundamental mode can be kept in a heat insulation mode, and light beams in the multi-core optical fiber are expanded. The multi-core optical fiber micro-collimator is specially designed for the multi-core optical fiber 3 with the gradually-changed refractive index and the large core diameter, and collimation of emergent light beams at the end of the multi-core optical fiber is achieved.

2. The multicore fiber 1 according to claim 1, including but not limited to a twin-core fiber, a three-core fiber, a five-core fiber, a seven-core fiber, i.e. the multicore fiber 1 has a number of cores equal to or greater than 2, and the multicore fibers may have different core profiles and core structures.

3. The multi-core fiber microcollimator of claim 1, wherein the length of the graded-index large-core multi-core fiber 3 is 0.25 pitch length, or 0.25 pitch length plus an integer multiple of 1 pitch length, i.e. the length is 0.25 pitch length, 1.25 pitch length, 2.25 pitch length, 3.25 pitch length, etc.

4. The multicore fiber microcollimator of claim 1, wherein the core profile of the graded-index large-core multicore fiber 3 is the same as the core profile of the multicore fiber 1, but the core diameter of the graded-index large-core multicore fiber 3 is greater than or equal to the core diameter of the multicore fiber 1.

5. The multi-core fiber microcollimator of claim 1, wherein the multi-core fiber 1, the multi-core fiber thermal diffusion section 2, and the graded-index large-core fiber 3 have one or more dopants.

6. The method for preparing the multi-core optical fiber microcollimator of claim 1, comprising the steps of:

1) specially designing the gradient-refractive-index large-core-diameter multi-core optical fiber 3

Two basic principles for specially designing the graded-index large-core multi-core fiber 3 are as follows: (1) the size of a cladding 8 of the large-core-diameter multi-core optical fiber 3 with the graded index is the same as that of a cladding 5 of the multi-core optical fiber 1, the number of fiber cores 9 is the same as that of the fiber cores 4, the fiber cores are in the same distribution mode, and the fiber cores are coaxial; (2) the core diameter of the core 9 of the graded-index large-core multicore fiber 3 is equal to or larger than the core diameter of the core 4 of the multicore fiber 1, but the cores 9 of the graded-index large-core multicore fiber 3 do not overlap each other.

2) Carrying out thermal diffusion treatment on the multi-core optical fiber thermal diffusion section 2

And carrying out thermal diffusion treatment on the multi-core optical fiber thermal diffusion section 2, wherein the refractive index distribution of the multi-core optical fiber thermal diffusion section 2 is gradually changed into stable quasi-Gaussian distribution, so that the emergent light beam at the end of the multi-core optical fiber is expanded.

(I) technical field

The invention relates to a multi-core optical fiber micro-collimator which can be used for an optical fiber communication transmission system and an optical fiber sensing system, can be widely applied to coupling connection between optical fibers, between the optical fibers and waveguides and between the optical fibers and other optical devices, and belongs to the field of optical fiber communication.

(II) background of the invention

The optical fiber communication system is an indispensable nervous system in the information age, and the optical fiber collimator is an important component in an optical passive device and has extremely common application in the optical fiber communication system and the optical fiber sensing system. The optical fiber collimator mainly functions to change light beams emitted from the optical fiber end into parallel light or converge the parallel light to be incident into the optical fiber end. Currently, there are three main types of fiber collimating lenses: self-focusing lens, microsphere lens, and diffraction lens.

The self-focusing lens is formed by adding a rod with gradient refractive index and diameter larger than that of the optical fiber to the end of the optical fiber. This type of collimator, generally because of the large diameter of the self-focusing rods, is about 1mm and the diameter of the optical fiber is 125 μm. And therefore cannot be made compact and small.

The microsphere lens is a spherical lens manufactured at the tail end of an optical fiber by a special manufacturing method. The micro-ball lens has high manufacturing difficulty and high equipment requirement, and because a micro-lens is manufactured at the tail end of the optical fiber, the possibility of inserting and connecting the optical fiber is limited.

The diffractive lens is produced by photolithography at the end of a silica rod and then soldered to the fiber. This technique has the disadvantage of requiring precise alignment of the reticle and the fiber ends, and is therefore difficult to manufacture and incapable of mass production.

Along with the popularization of optical fiber networks and the rapid development of the internet industry, the requirements of various industries on information communication are higher and higher, and higher requirements are provided for ultra-large capacity transmission and long-distance transmission of an optical fiber communication system. Based on this, the single mode fiber cannot meet the current requirement, and the multi-core fiber is inevitably applied to the optical fiber communication system and the optical fiber sensing system more and more generally, so a multi-core fiber micro-collimator is urgently needed to meet the application requirement of the multi-core fiber in the optical fiber communication system and the optical fiber sensing system, and meanwhile, the advantages of low cost, simple manufacture and compact structure are needed.

Patent CN201110226192.4 discloses a thermal core-expanding optical fiber collimator, which is composed of a thermal core-expanding optical fiber head, a quartz optical fiber, an aspheric lens and an outer sleeve. The collimating device is characterized in that an aspheric lens is used as a collimator, the collimation of a single-mode optical fiber is realized, but the collimation of emergent light beams at the end of a multi-core optical fiber cannot be realized.

Patent CN201110226340.2 discloses a broad spectrum optical fiber collimator, which is characterized in that an achromatic lens is adopted to be parallel to the central axis of a thermal core-expanding optical fiber head, and collimation is performed by using the achromatic lens, but the collimation of emergent light beams at the end of a multi-core optical fiber cannot be solved, and the mode of installing an outer sleeve cannot be used universally with a standard interface.

Patent CN201721647567.3 discloses a laser fiber collimation focusing lens, which is characterized in that an optical fiber is connected to one end of a glass tube, and the other end is connected with a lens. The use range is limited because the light beam is collimated by using the micro lens, the insertion connection cannot be performed, and the collimation of the light beam emitted from the end of the multi-core optical fiber cannot be realized because the manufacturing is difficult.

Patent CN201410777215.4 discloses a monolithic integrated multi-core fiber splitter and a manufacturing method thereof, which refers to using a self-focusing lens to collimate a multi-core fiber, but the parameters of the self-focusing lens are not specially designed, so that the emitted light beams of different cores at the end of the multi-core fiber cannot be collimated, and the light beams of different cores are emitted in parallel. This patent also can not realize expanding the beam to the multicore optic fibre light beam.

Patent CN201510518584.6 discloses an optical fiber collimator and a manufacturing method thereof, which is characterized in that a single mode fiber is connected with a coreless fiber and a self-focusing fiber, so as to expand and collimate an output beam, but does not relate to collimating an exit beam at the end of a multicore fiber.

Patent CN201410777241.7 discloses a multicore fiber connector based on gradient index lens, which connects multicore fiber and single mode fiber with the same number of cores as multicore fiber through a double gradient index lens group, because the size of the double gradient index lens group is large, the collimation of emergent light beam at the end of multicore fiber with compact size can not be realized, and no special design is performed on the double gradient index lens group, so as to solve the problem of signal crosstalk between cores of multicore fiber.

Patent US20050201701a1 discloses a single-mode fiber collimator for collimating a single-mode fiber using a graded-index fiber, which enables collimation of a single-mode fiber, but does not collimate an exit beam from the end of a multi-core fiber.

Patent US7155096B2 discloses an optical collimator for single-mode fibers, which thermally expands the core of the single-mode fiber, and then connects a section of step-index fiber, thereby expanding and collimating the beam, but does not relate to collimating the emergent beam at the end of the multi-core fiber.

Patent US20070147733a1 discloses a fiber collimation system that primarily collimates the light beam of a single mode fiber with a self-focusing lens, but does not expand the light beam of a single mode fiber nor does it relate to collimating the light beam exiting the end of a multi-core fiber.

Patent US20050220401a1 discloses a single-mode fiber collimating lens and a method thereof, which mainly uses a section of special single-mode fiber to respectively connect a standard single-mode fiber and a graded-index fiber, so as to realize beam expansion and collimation of emergent light beams of the single-mode fiber. However, this patent does not address collimating the light exiting from the end of the multi-core fiber.

The invention discloses a multi-core optical fiber micro-collimator which can be used for an optical fiber communication transmission system and an optical fiber sensing system and can be widely applied to coupling connection between optical fibers, between the optical fibers and waveguides and between the optical fibers and other optical devices. The multi-core optical fiber micro-collimator adopts a thermal diffusion technology to expand the core of a multi-core optical fiber, and a section of specially designed gradient-index large-core-diameter multi-core optical fiber is connected with the multi-core optical fiber, so that the emergent light beam at the end of the multi-core optical fiber is expanded and collimated. Compared with the prior art, the multi-core optical fiber is subjected to thermal diffusion treatment, and the specially designed gradient-index large-core-diameter multi-core optical fiber is adopted, so that the emergent light beams at the ends of the multi-core optical fiber are expanded and collimated, and the problem of signal crosstalk among the cores is solved. The multi-core optical fiber micro-collimator has the advantages of simple manufacture, low cost and compact structure.

Disclosure of the invention

The invention aims to provide a multi-core optical fiber micro-collimator which is simple to manufacture, low in cost and compact in structure.

The purpose of the invention is realized as follows:

the multi-core optical fiber micro-collimator is formed by connecting a multi-core optical fiber 1, a multi-core optical fiber thermal diffusion section 2 and a multi-core optical fiber 3 with a large core diameter and a gradually-changing refractive index. The multi-core optical fiber thermal diffusion section 2 in the multi-core optical fiber microcollimator is located between the multi-core optical fiber 1 and the gradient-index large-core-diameter multi-core optical fiber 3, and the multi-core optical fiber thermal diffusion section 2 is welded with the gradient-index large-core-diameter multi-core optical fiber 3. The multi-core optical fiber micro-collimator applies thermal diffusion on the multi-core optical fiber thermal diffusion section 2, the multi-core optical fiber thermal diffusion section 2 forms a refractive index gradient region, the transmission of a fundamental mode can be kept in a heat insulation mode, and light beams in the multi-core optical fiber are expanded. The multi-core optical fiber micro-collimator is specially designed for the multi-core optical fiber 3 with the gradually-changed refractive index and the large core diameter, and collimation of emergent light beams at the end of the multi-core optical fiber is achieved.

Thermal diffusion technology is commonly used for expanding the fundamental mode field, and the thermal diffusion can enable the dopant distribution in the multi-core optical fiber to be gradually changed into stable quasi-Gaussian distribution. As shown in fig. 1, the multi-core fiber thermal diffusion section 2 is heated, and a thermal diffusion process is introduced, so that the dopant distribution in the multi-core fiber thermal diffusion section 2 gradually changes to a stable quasi-gaussian distribution, and the normalized frequency of the fiber is not changed in the heating process. The quasi-Gaussian distribution of the dopant makes the refractive index distribution of the multi-core optical fiber thermal diffusion section 2 gradually change into quasi-Gaussian distribution, so that the fundamental mode field in the multi-core optical fiber is expanded, adiabatic transmission can be realized, and the beam expansion of the emergent light beam at the end of the multi-core optical fiber is realized.

During thermal diffusion, the local doping concentration C can be expressed as:

d in formula (1) is the dopant diffusion coefficient; t is the heating time. D depends mainly on the type of different dopants, the host material and the local heating temperature. In most cases, considering the diffusion of germanium in the core of an optical fiber, the heating temperature of the fiber is almost uniformly constant with respect to the radial position r on its axisymmetric geometry, and the diffusion coefficient D is assumed to be constant with respect to the radial position r. In practice, neglecting the diffusion of dopants in the axial direction, the simplified diffusion equation (1) in cylindrical coordinates is:

the doping concentration C of the dopant is a function of the radial distance r and the heating time t. The diffusion coefficient D is also affected by the heating temperature and is expressed as:

t (z) in the formula (3) represents the heating temperature in K, which is related to the longitudinal position of the optical fiber in the furnace; r-8.3145 (J/K/mol) is an ideal gas constant; parameter D₀And Q can be obtained from experimental data. Considering initial boundary conditions

The dopant local doping concentration profile C can be expressed as:

in the formula (5), f (r) is an initial concentration distribution, and the concentration at the fiber boundary surface r ═ a is 0. J. the design is a square₀Is a first class zero order Bessel function with characteristic value α_nIs the root of it

J₀(aα_n)＝0 (6)

Assuming that the refractive index profile of the optical fiber over the thermal diffusion region is proportional to the dopant profile, the refractive index profile of the optical fiber after thermal diffusion can be expressed as:

n in formula (7)_clAnd n_coThe refractive indices of the fiber cladding and the core, respectively. The refractive index profiles of the two-core fiber (fig. 2a) and the three-core fiber (fig. 2b) change with the heating time t when the heating temperature field is 1600 ℃. Curves 21, 22, 23, and 24 are refractive index distributions along the radial direction of the optical fiber after the dual-core optical fiber is heated for 0 hour, 0.1 hour, 0.2 hour, and 0.3 hour, respectively; curves 25, 26, 27, and 28 are refractive index profiles in the radial direction of the optical fiber after heating the three-core optical fiber for 0 hour, 0.1 hour, 0.2 hour, and 0.3 hour, respectively. After a certain period of thermal diffusion treatment, the refractive index profile of the fiber tends to be more stable in a quasi-gaussian profile.

Graded index lenses have been widely used in optical components and devices for collimation, focusing and coupling. A graded index lens refers to a lens in which the refractive index varies continuously in the axial, radial, or spherical directions. For radial graded index lenses, it is most common that the refractive index is greatest at the central axis and decreases with increasing radial distance from the central axis. The refractive index profile follows a square ratio profile:

n in formula (8)₀Is the refractive index on the axis of the graded index lens, r is the radial distance from the central axis, and g is the focusing parameter of the graded index lens.

In a graded index lens, light rays travel along a sinusoidal curve until reaching the back surface of the lens. The length of the light ray that completes a sinusoidal periodic propagation, represented as a pitch, is shown in fig. 3. Curve 31 shows that the light ray travels a length 32 of one period, one pitch, following a sinusoidal progression. One pitch is denoted by P.

The light beams are emitted from the multi-core optical fiber thermal diffusion section 2, and after being input into the multi-core optical fiber 3 with the gradually-changed refractive index and the large core diameter, the light beams are changed into parallel light after the length of the multi-core optical fiber 3 is 0.25P, and the collimation effect is realized; the light beam is emitted from the multi-core fiber thermal diffusion section 2, and after being input into the multi-core fiber 3 with the gradually-changed refractive index and the large core diameter, the light beam is converged at the rear surface through the length of 0.5P, so that the focusing effect is realized.

When the multi-core fiber micro-collimator is prepared, in order to realize the beam expansion of the emergent light beam at the end of the multi-core fiber, the multi-core fiber containing one or more doped different dopants can be used according to the requirement of the beam expansion, the heating time and the heating temperature of the thermal diffusion section 2 of the multi-core fiber are designed, and the heating time is prolonged and the heating temperature is increased by a thermal diffusion method, so that the beam diameter of the multi-core fiber can be increased. One or more doped different dopants are used, and the realization of the function of the multi-core optical fiber micro-collimator is not influenced.

When the multi-core fiber micro-collimator is prepared, in order to realize collimation of emergent light beams at the end of the multi-core fiber and solve the problem of signal crosstalk among cores of the multi-core fiber, the structure of the multi-core fiber 3 with the gradually-changing refractive index and the large core diameter needs to be specially designed. Two basic principles for the special design of the graded-index large-core multi-core fiber 3 are as follows: (1) the size of a cladding 8 of the large-core-diameter multi-core optical fiber 3 with the graded index is the same as that of a cladding 5 of the multi-core optical fiber 1, the number of fiber cores 9 is the same as that of the fiber cores 4, the fiber cores are in the same distribution mode, and the fiber cores are coaxial; (2) the core diameter of the core 9 of the graded-index large-core multicore fiber 3 is equal to or larger than the core diameter of the core 4 of the multicore fiber 1, but the cores 9 of the graded-index large-core multicore fiber 3 do not overlap each other.

When the multi-core fiber micro-collimator is prepared, in order to realize collimation of light beams emitted from the end of the multi-core fiber, the light beams are emitted from the multi-core fiber thermal diffusion section 2, and after the light beams are input into the multi-core fiber 3 with the gradually-changing refractive index and the large core diameter, the light beams are changed into parallel light after the length of the multi-core fiber 3 is 0.25P, namely the collimation effect is realized. The total length of the input graded-index large-core multi-core fiber 3 may be 0.25P length plus an integral multiple of 1P length, i.e., 0.25P, 1.25P, 2.25P, 3.25P, or the like.

When the multi-core optical fiber micro-collimator is prepared, the special design is carried out on the multi-core optical fiber 3 with the gradually-changing refractive index and the large core diameter, so that the core diameter of the multi-core optical fiber 3 with the gradually-changing refractive index and the large core diameter is larger than or equal to the maximum core diameter of the multi-core optical fiber thermal diffusion section 2, and the expanded beam and collimation of the emergent light beam at the end of the multi-core optical fiber are. The graded-index large-core-diameter multi-core fiber 3 is specially designed, the size of a cladding 8 of the graded-index large-core-diameter multi-core fiber 3 is the same as that of a cladding 5 of the multi-core fiber 1, the number of fiber cores 9 is the same as that of the fiber cores 4, the fiber cores have the same distribution, and the fiber cores are coaxial. The core diameter of each fiber core 9 in the large-core-diameter multi-core fiber 3 with the graded index can be specially designed, and the numerical aperture and the self-focusing constant can also be specially designed, so that the core diameter, the numerical aperture and the self-focusing constant of each fiber core are different, but the requirement that the fiber cores 9 of the large-core-diameter multi-core fiber 3 with the graded index do not overlap each other is met.

The temperature field distribution of the heating zone of the furnace during the thermal diffusion process is shown in fig. 4, and a curve 41 is the temperature distribution on the central axis of the heating zone of the furnace; the position 42 is the central position of the temperature field, and the temperature is highest. When the multi-core optical fiber micro-collimator is prepared, a section of long multi-core optical fiber is placed on a central shaft of a heating zone of a furnace for thermal diffusion treatment, and after heating for a certain time, the concentration distribution of the dopant in the thermal diffusion zone of the multi-core optical fiber is gradually changed into quasi-Gaussian distribution. The length of the heating zone of the furnace is typically in the order of centimeters or more, ensuring a slow change of the refractive index in the gradient temperature field to a quasi-gaussian distribution.

After heating for a certain time, the multi-core fiber is heated, and then the multi-core fiber is cut at the position with the highest heating temperature in the multi-core fiber thermal diffusion area, so that two identical multi-core fibers 1 and 2 capable of expanding the light beams of the multi-core fiber 1 can be manufactured.

And aligning each fiber core axis of the specially designed gradient-index large-core-diameter multi-core fiber 3 with each fiber core axis of the multi-core fiber thermal diffusion section 2, and welding fiber ends. Then, the GI large-core multi-core fiber 3 is cut to a predetermined length by a fiber cutter, and after the cutting, the length of the GI large-core multi-core fiber 3 is 0.25P, or the total length of the GI large-core multi-core fiber 3 may be 0.25P plus an integral multiple of 1P, i.e., 0.25P, 1.25P, 2.25P, 3.25P, etc. The collimation of the emergent light beam after the multi-core optical fiber thermal diffusion section 2 is realized.

The multi-core fiber 1 includes, but is not limited to, a dual-core fiber, a three-core fiber, a five-core fiber, and a seven-core fiber, i.e., the number of cores of the multi-core fiber 1 is greater than or equal to 2. Moreover, as for different fiber core distributions and fiber core structures of the multi-core fiber, as long as two basic principles of special design of the multi-core fiber 3 with the gradually-changing refractive index and the large core diameter are met, beam expansion and collimation of emergent light beams at the end of the multi-core fiber can be realized, and the problem of signal crosstalk among cores of the multi-core fiber can be solved.

The multi-core optical fiber micro-collimator provided by the invention is formed by connecting a multi-core optical fiber 1, a multi-core optical fiber thermal diffusion section 2 and a multi-core optical fiber 3 with a large core diameter and a gradually-changing refractive index. Compared with the prior art, the multi-core optical fiber is subjected to thermal diffusion treatment, and the specially designed gradient-index large-core-diameter multi-core optical fiber is adopted, so that the emergent light beams at the ends of the multi-core optical fiber are expanded and collimated, and the problem of signal crosstalk among the cores is solved. The multi-core optical fiber micro-collimator has the advantages of simple manufacture, low cost and compact structure.

(IV) description of the drawings

Fig. 1 is a schematic structural diagram of a multi-core fiber microcollimator.

Fig. 2a is a graph showing the change in refractive index profile of a two-core optical fiber with a heating time t in a temperature field of 1600 c, and fig. 2b is a graph showing the change in refractive index profile of a three-core optical fiber with a heating time t in a temperature field of 1600 c.

FIG. 3 is a schematic representation of light propagating along a sinusoidal curve in a graded index lens.

FIG. 4 is a schematic illustration of the temperature profile at the central axis of the heating zone of the furnace when heating a multi-core fiber.

FIG. 5 is a schematic cross-sectional view of a dual core optical fiber.

Fig. 6a is a refractive index distribution of the dual-core fiber microcollimator, fig. 6b is a light beam propagation pattern in a fiber core of the dual-core fiber microcollimator, fig. 6c is a light field distribution of light beams emitted from a dual-core fiber end, fig. 6d is a light field distribution of light beams emitted from a dual-core fiber microcollimator, fig. 6e is a light intensity distribution of light fields emitted from a dual-core fiber end, and fig. 6f is a light intensity distribution of light fields emitted from a dual-core fiber microcollimator end.

Fig. 7 is a schematic cross-sectional view of a three-core optical fiber.

Fig. 8a is a refractive index distribution of the three-core optical fiber microcollimator, fig. 8b is a light beam propagation diagram in a fiber core of the three-core optical fiber microcollimator, fig. 8c is a light field distribution of light beams emitted from an end of the three-core optical fiber, fig. 8d is a light field distribution of light beams emitted from an end of the three-core optical fiber microcollimator, fig. 8e is a light intensity distribution of a light field emitted from a light beam from an end of the three-core optical fiber, and fig. 8f is a light intensity distribution of a light field emitted from an end of the.

Fig. 9 is a schematic cross-sectional view of a five-core optical fiber.

Fig. 10a is a refractive index distribution of the five-core optical fiber microcollimator, fig. 10b is a light beam propagation diagram in a fiber core of the five-core optical fiber microcollimator, fig. 10c is a light field distribution of light beams emitted from an end of the five-core optical fiber, fig. 10d is a light field distribution of light beams emitted from an end of the five-core optical fiber microcollimator, fig. 10e is a light intensity distribution of a light field emitted from an end of the five-core optical fiber, and fig. 10f is a light intensity distribution of a light field emitted from an end of the five-core optical.

FIG. 11 is a schematic cross-sectional view of a seven-core optical fiber.

Fig. 12a is a refractive index distribution of the seven-core optical fiber microcollimator, fig. 12b is a light beam propagation pattern in a fiber core of the seven-core optical fiber microcollimator, fig. 12c is a light field distribution of light beams emitted from a seven-core optical fiber end, fig. 12d is a light field distribution of light beams emitted from a seven-core optical fiber microcollimator end, fig. 12e is a light intensity distribution of a light field emitted from a seven-core optical fiber end, and fig. 12f is a light intensity distribution of a light field emitted from a seven-core optical fiber microcollimator end.

(V) detailed description of the preferred embodiments

The invention is further illustrated below with reference to specific examples.

The multi-core optical fiber micro-collimator provided by the invention is formed by connecting a multi-core optical fiber 1, a multi-core optical fiber thermal diffusion section 2 and a gradient-refractive-index large-core-diameter multi-core optical fiber 3. The multi-core optical fiber thermal diffusion section 2 in the multi-core optical fiber microcollimator is located between the multi-core optical fiber 1 and the gradient-index large-core-diameter multi-core optical fiber 3, and the multi-core optical fiber thermal diffusion section 2 is welded with the gradient-index large-core-diameter multi-core optical fiber 3. The multi-core optical fiber micro-collimator applies thermal diffusion on the multi-core optical fiber thermal diffusion section 2, the multi-core optical fiber thermal diffusion section 2 forms a refractive index gradient region, the transmission of a fundamental mode can be kept in a heat insulation mode, and light beams in the multi-core optical fiber are expanded. The multi-core optical fiber micro-collimator is specially designed for the multi-core optical fiber 3 with the gradually-changed refractive index and the large core diameter, and collimation of emergent light beams at the end of the multi-core optical fiber is achieved.

When the multi-core fiber micro-collimator is prepared, in order to realize the beam expansion of the emergent light beam at the end of the multi-core fiber, the multi-core fiber containing one or more doped different dopants can be used according to the requirement of the beam expansion, the heating time and the heating temperature of the thermal diffusion section 2 of the multi-core fiber are designed, and the heating time is prolonged and the heating temperature is increased by a thermal diffusion method, so that the beam diameter of the multi-core fiber can be increased. One or more doped different dopants are used, and the realization of the function of the multi-core optical fiber micro-collimator is not influenced.

When the multi-core fiber micro-collimator is prepared, in order to realize collimation of emergent light beams at the end of the multi-core fiber and solve the problem of signal crosstalk among cores of the multi-core fiber, the structure of the multi-core fiber 3 with the gradually-changing refractive index and the large core diameter needs to be specially designed. Two basic principles for the special design of the graded-index large-core multi-core fiber 3 are as follows: (1) the size of a cladding 8 of the large-core-diameter multi-core optical fiber 3 with the graded index is the same as that of a cladding 5 of the multi-core optical fiber 1, the number of fiber cores 9 is the same as that of the fiber cores 4, the fiber cores are in the same distribution mode, and the fiber cores are coaxial; (2) the core diameter of the core 9 of the graded-index large-core multicore fiber 3 is equal to or larger than the core diameter of the core 4 of the multicore fiber 1, but the cores 9 of the graded-index large-core multicore fiber 3 do not overlap each other.

When the multi-core fiber micro-collimator is prepared, in order to realize collimation of light beams emitted from the end of the multi-core fiber, the light beams are emitted from the multi-core fiber thermal diffusion section 2, and after the light beams are input into the multi-core fiber 3 with the gradually-changing refractive index and the large core diameter, the light beams are changed into parallel light after the length of the multi-core fiber 3 is 0.25P, namely the collimation effect is realized. The total length of the input graded-index large-core multi-core fiber 3 may be 0.25P length plus an integral multiple of 1P length, i.e., 0.25P, 1.25P, 2.25P, 3.25P, or the like.

When the multi-core optical fiber micro-collimator is prepared, the special design is carried out on the multi-core optical fiber 3 with the gradually-changing refractive index and the large core diameter, so that the core diameter of the multi-core optical fiber 3 with the gradually-changing refractive index and the large core diameter is larger than or equal to the maximum core diameter of the multi-core optical fiber thermal diffusion section 2, and the expanded beam and collimation of the emergent light beam at the end of the multi-core optical fiber are. The graded-index large-core-diameter multi-core fiber 3 is specially designed, the size of a cladding 8 of the graded-index large-core-diameter multi-core fiber 3 is the same as that of a cladding 5 of the multi-core fiber 1, the number of fiber cores 9 is the same as that of the fiber cores 4, the fiber cores have the same distribution, and the fiber cores are coaxial. The core diameter of each fiber core 9 in the large-core-diameter multi-core fiber 3 with the graded index can be specially designed, and the numerical aperture and the self-focusing constant can also be specially designed, so that the core diameter, the numerical aperture and the self-focusing constant of each fiber core are different, but the requirement that the fiber cores 9 of the large-core-diameter multi-core fiber 3 with the graded index do not overlap each other is met.

When the multi-core fiber micro-collimator is prepared, a section of long multi-core fiber is placed on a central shaft of a heating zone of a furnace for thermal diffusion treatment, and after heating for a certain time, the concentration distribution of a dopant in the thermal diffusion zone of the multi-core fiber is gradually changed into quasi-Gaussian distribution. The length of the heating zone of the furnace is typically in the order of centimeters or more, ensuring a slow change of the refractive index in the gradient temperature field to a quasi-gaussian distribution.

When the multi-core optical fiber micro-collimator is prepared, a section of long multi-core optical fiber is heated for a certain time, after the thermal diffusion treatment is completed, the position with the highest heating temperature in the multi-core optical fiber thermal diffusion area is cut, and two identical multi-core optical fibers 1 and a multi-core optical fiber thermal diffusion section 2 which can expand the light beams of the multi-core optical fiber 1 can be prepared.

When the multi-core fiber micro-collimator is prepared, the axes of the fiber cores of the specially designed gradient-refractive-index large-core-diameter multi-core fiber 3 are aligned with the axes of the fiber cores of the multi-core fiber thermal diffusion section 2, and the fiber ends are welded. Then, the GI large-core multi-core fiber 3 is cut to a predetermined length by a fiber cutter, and after the cutting, the length of the GI large-core multi-core fiber 3 is 0.25P, or the total length of the GI large-core multi-core fiber 3 may be 0.25P plus an integral multiple of 1P, i.e., 0.25P, 1.25P, 2.25P, 3.25P, etc. The collimation of the emergent light beam after the multi-core optical fiber thermal diffusion section 2 is realized.

When the multi-core fiber micro-collimator is prepared, the multi-core fiber 1 comprises but is not limited to a double-core fiber, a three-core fiber, a five-core fiber and a seven-core fiber, namely the number of the cores of the multi-core fiber 1 is more than or equal to 2. Moreover, as for different fiber core distributions and fiber core structures of the multi-core fiber, as long as two basic principles of special design of the multi-core fiber 3 with the gradually-changing refractive index and the large core diameter are met, beam expansion and collimation of emergent light beams at the end of the multi-core fiber can be realized, and the problem of signal crosstalk among cores of the multi-core fiber can be solved.