CN111624702A - Orthogonal double-shaft aspheric optical fiber micro lens - Google Patents

Abstract

The invention provides an orthogonal biaxial aspherical optical fiber microlens. It is characterized in that it is prepared by thermal diffusion of elliptical core optical fiber. Orthogonal biaxial aspheric fiber microlenses are prepared by thermal diffusion in a constant temperature field. After the elliptical core dopant of the finely designed elliptical core fiber is diffused, the refractive index distribution becomes a non-circumferentially symmetric quasi-Gaussian distribution. Can be equivalent to a microlens. The invention provides a fiber-integrated orthogonal biaxial aspherical optical fiber microlens, which has the advantages of simple manufacture and low cost. The invention can be used for the preparation of fiber-integrated microlenses, and can be widely used in micro-endoscopes, cellular biological optical fiber imaging systems, optical fiber optical tweezers systems, and micro-unmanned aerial vehicles based on fiber-integrated orthogonal biaxial aspherical optical fiber microlenses and other fields.

Description

An Orthogonal Biaxial Aspheric Fiber Microlens

(1) Technical field

The invention relates to an orthogonal biaxial aspherical optical fiber microlens, which can be used for the preparation of a fiber-integrated microlens, and can be widely used in microendoscopes based on the fiber-integrated orthogonal biaxial aspherical optical fiber microlens, Cell biological fiber imaging system, fiber optical tweezers system, micro-UAV and other fields.

(2) Background technology

With the development of modern industry and science and technology, people have gradually entered the information age. The rapid development of information technology requires that a complete information system can realize as many functions as possible in as small a space as possible.

Fiber-integrated micro-optical components have the advantages of small size, light weight, flexible design and manufacturing, low manufacturing cost, and easy to realize array and mass production. It has important application value in aerospace, biomedicine, laser technology, optical computing and other fields.

With the deepening of research, many preparation methods for micro-optical components have been proposed, mainly including semiconductor photolithography, single-point diamond turning, electron beam etching, and femtosecond laser direct writing. The semiconductor lithography process requires the use of a mask, which is exposed to ultraviolet light, and the microstructure is transferred to the photoresist through development. This method is mature in technology, suitable for mass production, and has a low average cost. The disadvantage is that the processed structure can only be flat, and multiple overlays are required when processing a multi-level structure, the alignment accuracy is high, and the cost rises sharply. The surface roughness of single-point diamond turning is small, and the general surface roughness is below 10nm, which is suitable for processing structures with arbitrary rotational topography. The machining accuracy depends on the cutter head and the machine tool. The machine tool requires high accuracy, the machining materials are limited, and the size of the machining structure cannot be too small. Electron beam etching is divided into scanning type and projection type. The scanning type does not require a mask, and the alignment and splicing are automatically controlled by the computer, and the processing accuracy is extremely high. The disadvantage is that the equipment is complicated, the cost is high, the single exposure area is small, and the production time of large-scale structures is too long. Projection processing is fast, but mask preparation is difficult. Both methods need to be performed in a vacuum, which greatly limits their applicability. Femtosecond laser processing is a non-contact, high-precision processing method for micro-nano optoelectronic devices, which has a strong wide range of applicable materials. The disadvantage is that the equipment cost is high, the processing technology is complex, and the processing efficiency is relatively low.

Due to the impact of the manufacturing process, the current lens system is limited in terms of shape and size. Fabrication techniques for fiber integration with micro-optics, different approaches have recently been proposed using fabrication techniques such as focused ion beam milling, interference lithography, nanoimprinting, lithography, polishing, etc., to directly integrate micro-optics. Processed and manufactured on the end face of the optical fiber. However, they have disadvantages such as difficult processing and complicated manufacturing equipment.

Thermal diffusion processing technology has the advantages of easy implementation, low cost and simple operation. Thermal diffusion technology has great application potential in MEMS, optical integrated devices, optical communication and optical fiber sensing. After the optical fiber is thermally diffused, a smooth gradient of refractive index will be formed in the thermally diffused area, and the smooth gradient of refractive index area has the effect of a microlens. Fiber-integrated orthogonal biaxial aspherical fiber microlenses can be prepared by thermal diffusion processing of finely designed elliptical core fibers.

Patent CN01144937.3 discloses an optical fiber with a lens function and a manufacturing method thereof, using a graded-index optical fiber whose period length shows the lens function, which is effective for abrupt refractive index optical fiber. This method can collimate single-mode fibers, but does not have the function of orthogonal biaxial aspheric fiber microlenses.

Patent CN201210011571.6 discloses a single-mode optical fiber connector with a large mode area and a manufacturing method. The step-type multi-mode optical fiber is subjected to thermal diffusion of core doping elements to form a gradient of refractive index that decreases radially outward. The lens is mainly used for single-mode fiber connection with large mode area, and does not have the function of orthogonal biaxial aspheric fiber microlens.

Patent CN201721647567.3 discloses a laser fiber collimation focusing lens, which is characterized in that one end of the glass tube is connected to an optical fiber, and the other end is connected to a lens. Because the beam collimation is performed by using a micro lens, it cannot be used for insertion and connection, which limits the scope of use and is difficult to manufacture.

Patent US4269648A discloses a method of mounting a microsphere coupling lens on an optical fiber, and the microsphere coupling lens can be mounted on the end of the optical fiber by using an adhesive. A method for manufacturing a microlens at the end of an optical fiber is disclosed, but the method has a complicated manufacturing process and does not have the function of an orthogonal biaxial aspherical optical fiber microlens.

Patent US7013678B2 discloses a manufacturing method of a graded-index fiber lens. The graded-index fiber lens is an important component in an optical fiber communication system and can be used as a lens, but the graded-index fiber lens does not have an orthogonal biaxial aspheric fiber microlens. The function of the lens is relatively complicated, and the production cost of this method is relatively high.

Patent US7228033B2 discloses an optical waveguide lens and its manufacturing method, by fusing a uniform glass lens blank to the distal end of an optical fiber, heating and stretching the lens blank to divide it into two sections, and connecting the section to a defined taper The lens blank is then heated above its softening point to form a spherical lens. The optical waveguide lens can be used for beam collimation or focusing, but the lens manufactured by this method does not have the function of an orthogonal biaxial aspherical fiber microlens.

The invention discloses an orthogonal biaxial aspherical optical fiber microlens. The invention can be used for the preparation of a fiber-integrated microlens, and can be widely used in microendoscopes based on the fiber-integrated orthogonal biaxial aspherical optical fiber microlens. , cell biological fiber imaging system, fiber optic tweezers system, micro-UAV and other fields. It adopts thermal diffusion technology to carry out thermal diffusion treatment on finely designed elliptical core fibers in a constant temperature field, and forms a non-circumferentially symmetrical quasi-Gaussian distribution refractive index gradient region in the thermal diffusion area, and then conducts thermal diffusion treatment on the thermally diffused elliptical core fibers. By cutting to length, orthogonal biaxial aspherical fiber microlenses of different sizes can be prepared. Compared with the prior art, due to the use of thermal diffusion technology and finely designed elliptical core fiber, microlenses can be integrated into the fiber, and the function of the fiber-integrated aspheric lens can be realized on the fiber. Batch and Efficient Fabrication of Fiber-Integrated Orthogonal Biaxial Aspheric Fiber Microlenses.

(3) Contents of the invention

The purpose of the present invention is to provide an orthogonal biaxial aspherical optical fiber microlens which is simple to manufacture, low in cost and can be mass produced.

The object of the present invention is achieved in this way:

The orthogonal biaxial aspherical optical fiber microlenses are prepared by thermal diffusion of elliptical core optical fibers. Orthogonal biaxial aspheric fiber microlenses are prepared by thermal diffusion in a constant temperature field. After the elliptical core dopant of the finely designed elliptical core fiber is diffused, the refractive index distribution becomes a non-circumferentially symmetric quasi-Gaussian distribution. Can be equivalent to a microlens.

Thermal diffusion technology is often used to expand the fundamental mode field. Thermal diffusion can gradually change the dopant distribution in the fiber to a stable quasi-Gaussian distribution. When the finely designed elliptical core fiber is heated in a constant temperature field, the dopant distribution in the elliptical core gradually changes into a stable non-circumferential quasi-Gaussian distribution, and the normalized frequency of the fiber remains unchanged during the heating process. The non-circumferential quasi-Gaussian distribution of the dopant makes the refractive index distribution of the elliptical core fiber gradually change to a non-circularly symmetric quasi-Gaussian distribution. The elliptical core fiber has the function of an aspherical microlens.

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

In formula (1), D is the dopant diffusion coefficient; t is the heating time. D mainly depends on the type of different dopants, host material and local heating temperature. In most cases, considering the diffusion of germanium in the core of the fiber, the heating temperature of the fiber is almost uniform with respect to the radial position r over its axisymmetric geometry, and it is assumed that the diffusion coefficient D is relative to The radial position r is constant. In practice, ignoring the diffusion of dopants in the axial direction, the simplified diffusion equation (1) in the cylindrical coordinate system 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:

In formula (3), T(z) represents the heating temperature, the unit is K, which is related to the longitudinal position of the optical fiber in the furnace; R=8.3145 (J/K/mol) is the ideal gas constant; the parameters D ₀ and Q can be obtained from the experimental data obtained in. Consider the initial boundary conditions:

where a is a constant and represents the diameter of the fiber.

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

In formula (5), f(r) is the initial concentration distribution, and the concentration at the fiber boundary surface r=a is 0. J ₀ is a zero-order Bessel function of the first kind, and the eigenvalue α _n is its positive root

J ₀ (aα _n )=0 (6)

Assuming that the refractive index distribution of the fiber in the entire thermal diffusion region is proportional to the dopant distribution, the refractive index distribution of the fiber after thermal diffusion can be expressed as:

In formula (7), n _cl and n _co are the refractive indices of the fiber cladding and the central core, respectively. When the heating temperature field is 1600℃, the refractive index distribution of the elliptical core fiber varies with the heating time t. Curves 21, 22, and 23 are the refractive index distributions along the radial direction of the a-axis of the fiber after the elliptical core fiber is heated for 0h, 0.2h, and 0.4h, respectively (as shown in Figure 2a); After 0h, 0.2h, and 0.4h, the refractive index distribution along the radial direction of the b-axis of the fiber (as shown in Figure 2c). After 0.4h of thermal diffusion treatment, the refractive index distributions of the a-axis (as shown in Figure 2b) and b-axis (as shown in Figure 2d) of the elliptical core fiber tend to be stable quasi-Gaussian distributions. The thermal diffusivity of the a-axis and b-axis of the elliptical core is the same, but the diameters are different, so after thermal diffusion, the refractive index distribution is different.

Graded index lenses have been widely used in optical components and devices such as collimation, focusing and coupling. A graded index lens refers to a lens whose refractive index changes continuously along the axial, radial or spherical surface. For the orthorhombic biaxial aspheric fiber microlenses with radially graded refractive index, the central refractive index of the fiber is the highest and decreases with increasing radial distance from the central axis.

After the elliptical core fiber is thermally diffused for 0.4 h, the cross-sectional refractive index of the fiber-integrated orthogonal biaxial aspheric fiber microlens is shown in Figure 3. Figure 4 is a three-dimensional display of the cross-sectional refractive index of a fiber-integrated orthogonal biaxial aspheric fiber microlens. It can be seen from the figure that the refractive index distribution of the orthogonal biaxial aspheric optical fiber microlens is elliptical, that is, a non-circumferentially symmetric quasi-Gaussian distribution. The central refractive index is the highest and increases with the radial distance from the central axis. and decrease.

When the fiber-integrated orthogonal biaxial aspherical optical fiber microlens is prepared by the invention, the elliptical core optical fiber can be finely designed, including the design of the geometric size of the elliptical core, the type of dopant, the numerical aperture and the like.

When the fiber-integrated orthogonal biaxial aspherical optical fiber microlenses are prepared by the invention, the microlenses are prepared by thermal diffusion in a constant temperature field. The temperature of the constant temperature field is above 1000°C. The thermal diffusivity of elliptical core fibers with different elliptical core dopants is different.

When the fiber-integrated orthogonal biaxial aspherical optical fiber microlenses are prepared by the present invention, after heating and diffusing in a constant temperature field for a certain period of time, the thermally diffused elliptical core fiber is cut to a fixed length to prepare orthogonal biaxial optical fibers of different sizes. Aspheric Fiber Microlenses.

The method for preparing a fiber-integrated orthogonal biaxial aspherical optical fiber microlens according to the present invention is characterized by comprising the following steps:

The first step is to finely design the elliptical core fiber, including the design of the geometric size of the elliptical core, the types of dopants, and the numerical aperture.

In the second step, the elliptical core fiber is subjected to thermal diffusion treatment, and the elliptical core fiber is placed in a constant temperature field for thermal diffusion treatment. After heating for a certain period of time, the refractive index distribution of the elliptical core fiber gradually changes into a stable non-circumferentially symmetric quasi-Gaussian distribution .

In the third step, the elliptical core optical fiber is cut, and the thermally diffused elliptical core optical fiber is cut to a fixed length to prepare orthogonal biaxial aspherical optical fiber microlenses of different sizes.

When the fiber-integrated orthogonal biaxial aspherical optical fiber microlens is prepared by the invention, after a certain time of thermal diffusion treatment, the refractive index distribution of the elliptical core fiber tends to be a stable non-circumferentially symmetrical quasi-Gaussian distribution, and the central refractive index of the optical fiber highest and decreases with increasing radial distance from the central axis. After the elliptical core fiber is thermally diffused, the dopant forms a smooth, non-circumferentially symmetric quasi-Gaussian distribution in the thermally diffused processing region. The distribution of the dopant is a non-circular symmetric quasi-Gaussian distribution, and the refractive index distribution of the elliptical core fiber is also a non-circularly symmetric quasi-Gaussian distribution. During the propagation of the beam, it bends toward the area with higher refractive index, so the heat spreads. The latter elliptical core fiber has a microlens function.

As shown in Figure 3, the cross-sectional refractive index distribution of the fiber-integrated orthogonal biaxial aspherical fiber microlens is elliptical, that is, a non-circumferentially symmetric quasi-Gaussian distribution. The central refractive index of the fiber is the highest, and with the radial direction The distance from the central axis increases and decreases. In the process of beam propagation, it bends toward the area with higher refractive index. When the incident beam passes through the microlens, the light in the center and edge will gradually bend toward the area with high refractive index, and the a-axis and b-axis have different ability to bend light. Equivalent to an aspherical microlens. Therefore, after transmitting a certain distance in the orthogonal biaxial aspherical fiber microlens, the light beam will become an elliptical light field distribution.

The fiber-integrated orthogonal biaxial aspherical optical fiber microlenses prepared by the invention can realize the function of beam shaping, so that Gaussian beams and the like can be shaped into elliptical light field distribution. By cutting the fiber-integrated orthogonal biaxial aspherical fiber microlenses to a fixed length, orthogonal biaxial aspherical fiber microlenses of different sizes can be prepared to realize the beam shaping function of different requirements.

When the present invention finely designs the elliptical core optical fiber, the dopant of the elliptical core can be one or more doped different dopants as required. When using elliptical core fiber for the preparation of orthogonal biaxial aspheric fiber microlenses, designing a larger elliptical core diameter, or increasing the heating time and heating temperature, can prepare orthogonal biaxial aspheric fiber microlenses with larger mode field diameters. lens. The use of one or more doped different dopants does not affect the realization of the beam shaping function of the orthogonal biaxial aspherical fiber microlens.

The fiber-integrated orthogonal biaxial aspherical optical fiber microlens provided by the invention is prepared by thermal diffusion of elliptical core optical fibers. Compared with the prior art, due to the use of thermal diffusion technology and finely designed elliptical core fiber, microlenses can be integrated into the fiber, and the function of the fiber-integrated aspheric lens can be realized on the fiber. Batch and Efficient Fabrication of Fiber-Integrated Orthogonal Biaxial Aspheric Fiber Microlenses.

(4) Description of drawings

Fig. 1 is a schematic diagram of the change of refractive index distribution before and after the preparation of a fiber-integrated orthogonal biaxial aspheric optical fiber microlens by thermal diffusion.

Figure 2a is a schematic diagram of the change of the refractive index distribution along the a-axis of the elliptical core fiber with the heating time t in a temperature field of 1600 °C, and Figure 2b is the refractive index distribution of the elliptical core fiber along the a-axis after heating for 0.4h Schematic diagram, Figure 2c is a schematic diagram of the change of the refractive index distribution along the b-axis of the elliptical core fiber with the heating time t in a temperature field of 1600 °C, and Figure 2d is the elliptical core fiber after heating for 0.4h The refraction along the b-axis Schematic diagram of the rate distribution.

Figure 3 is the cross-sectional refractive index distribution of the elliptical core fiber after heating for 0.4h.

Figure 4 is a three-dimensional display of the cross-sectional refractive index distribution of the elliptical core fiber after heating for 0.4 h.

5 is a schematic cross-sectional view of an elliptical core optical fiber in an embodiment. 51 is the cladding of the elliptical core fiber, and 52 is the elliptical core of the elliptical core fiber.

FIG. 6 is a schematic structural diagram of a single-mode fiber + an orthogonal biaxial aspherical fiber microlens in an embodiment. 61 is a single-mode fiber, and 62 is a fiber-integrated orthogonal biaxial aspherical fiber microlens prepared from an elliptical core fiber.

Fig. 7a is the refractive index distribution of the single-mode fiber+orthogonal biaxial aspherical fiber microlens along the a-axis in the embodiment, and Fig. 7b is the single-mode fiber+orthogonal biaxial aspherical fiber microlens along the a-axis in the embodiment The three-dimensional display of the refractive index distribution in the direction, FIG. 7c is the refractive index distribution of the single-mode fiber + orthogonal biaxial aspherical fiber microlens along the b-axis direction in the embodiment, and FIG. 7d is the single-mode fiber + orthogonal double in the embodiment. Three-dimensional display of the refractive index profile of an aspherical fiber microlens along the b-axis.

Fig. 8a is the light field distribution of the single-mode fiber exiting the fiber end in the embodiment, Fig. 8b is the light field distribution of the single-mode fiber+orthogonal biaxial aspherical fiber microlens exiting the fiber end along the a-axis direction in the embodiment, Fig. 8c is the light field distribution of the single-mode fiber + orthogonal biaxial aspherical fiber microlens along the b-axis direction of the light field output in the embodiment, and Fig. 8d is the light intensity of the light field output from the fiber end of the single-mode fiber in the embodiment Distribution, Figure 8e is the light intensity distribution of the light field output from the fiber end along the a-axis direction of the single-mode fiber+orthogonal biaxial aspherical fiber microlens in the embodiment, and Figure 8f is the single-mode fiber+orthogonal biaxial in the embodiment The light intensity distribution of the outgoing light field from the fiber end of the aspherical fiber microlens along the b-axis direction.

Figures 9a-g respectively show the light field distribution of the cross-section when the light beam propagates in a single-mode fiber + an orthogonal biaxial aspherical fiber microlens at 0 μm, 80 μm, 180 μm, 280 μm, 380 μm, 480 μm, and 580 μm in the embodiment.

(5) Specific implementation methods

The present invention will be further described below in conjunction with specific embodiments.

Example 1:

A schematic cross-sectional view of the elliptical core optical fiber in this embodiment is shown in FIG. 5 . 51 is the cladding of the elliptical core fiber, and 52 is the elliptical core of the elliptical core fiber.

The preparation steps of the fiber-integrated orthogonal biaxial aspherical optical fiber microlens of the present embodiment are as follows:

The first step is to finely design the elliptical core fiber, including the design of the geometric size of the elliptical core, the types of dopants, and the numerical aperture. The parameters of the finely designed elliptical core fiber in this embodiment are that the cladding radius is 62.5 μm, the a-axis radius of the elliptical core is 17.5 μm, the b-axis radius is 10 μm, and the numerical aperture is 0.14. The dopant species of the elliptical core fiber is germanium.

In the second step, thermal diffusion treatment is performed on the elliptical core fiber. A section of elliptical core fiber was placed in a constant temperature field for thermal diffusion treatment. The temperature of the constant temperature field was 1600 °C. After heating for 0.4 h, the refractive index distribution of the elliptical core fiber gradually changed to a stable non-circumferentially symmetric quasi-Gaussian distribution.

In the third step, the elliptical core optical fiber is cut, and the thermally diffused elliptical core optical fiber is cut to a fixed length to prepare orthogonal biaxial aspherical optical fiber microlenses of different sizes.

First take a piece of single-mode fiber, weld the thermally diffused elliptical core fiber to the single-mode fiber, and cut the thermally diffused elliptical core fiber side to a fixed length to use it as a fiber-integrated orthogonal biaxial aspherical fiber microlens , the structure of single-mode fiber + orthogonal biaxial aspheric fiber microlens is formed, as shown in Figure 6. 61 is a single-mode fiber; 62 is a heat-diffused elliptical core fiber cut to a fixed length, which is welded to the fiber end of the single-mode fiber 61 as a microlens.

The finite element method was used to establish a model for the thermal diffusion process of the optical fiber, and the change of the refractive index distribution after the thermal diffusion treatment was simulated. As shown in Figure 7a, it is the refractive index distribution of the single-mode fiber + orthogonal biaxial aspherical fiber microlens along the a-axis direction, and Figure 7c shows the single-mode fiber + orthogonal biaxial aspherical fiber microlens along the b-axis direction. Refractive index distribution. In the established simulation model, the length of the single-mode fiber 61 is 5 μm, the numerical aperture is 0.14, the core diameter is 9 μm, and the cladding diameter is 125 μm; the length of the fiber-integrated orthogonal biaxial aspherical fiber microlens 62 is 380 μm. . Fig. 7b is a three-dimensional display of the refractive index distribution of the single-mode fiber+orthogonal biaxial aspherical fiber microlens along the a-axis direction in the embodiment, and Fig. 7d is the single-mode fiber+orthogonal biaxial aspherical fiber microlens in the embodiment Three-dimensional display of the refractive index profile along the b-axis.

The fiber-integrated orthogonal biaxial aspherical optical fiber microlens 62 has a smooth and gradual transition of the refractive index distribution, and the refractive index distribution is elliptical, that is, a stable non-circumferentially symmetric quasi-Gaussian distribution, the central refractive index is the highest, and increases with It decreases with increasing radial distance from the central axis.

In this embodiment, the refractive index distribution of the orthogonal biaxial aspherical optical fiber microlens is elliptical, and modeling and simulation are performed along the tangent planes passing through the center line of the a-axis and the b-axis respectively. The outgoing light field of single-mode fiber and the outgoing light field of single-mode fiber + orthogonal biaxial aspherical fiber microlens were simulated by finite element method. In the established simulation model of the single-mode optical fiber 61 , the length of the single-mode optical fiber 61 is 20 μm, and the length of the vacuum 63 is 200 μm. In the established single-mode fiber + orthogonal biaxial aspheric fiber microlens simulation model, the length of the single-mode fiber 61 is 5 μm, the length of the fiber-integrated orthogonal biaxial aspheric fiber microlens 62 is 380 μm, and the vacuum 63 The length is 200 μm. The simulation results are shown in Figure 8. Fig. 8a shows the light field distribution of the single-mode fiber 61 exiting from the fiber end, Fig. 8b shows the light field distribution of the single-mode fiber 61+orthogonal biaxial aspherical fiber microlens 62 exiting the fiber end along the a-axis direction, Fig. 8c is the light field distribution of the single-mode fiber + orthogonal biaxial aspherical fiber microlens along the b-axis direction of the fiber end. Fig. 8d is the light intensity distribution of the light field of the single-mode fiber 61. The light intensity distribution of the outgoing light field at the fiber end along the a-axis direction of the single-mode fiber 61+orthogonal biaxial aspherical fiber microlens 62, Figure 8f shows the single-mode fiber 61+orthogonal biaxial aspherical fiber microlens 62 along the b The light intensity distribution of the outgoing light field at the fiber end in the axial direction.

Comparing Figures 8a, 8b and 8c, single-mode fiber 61, single-mode fiber 61 + orthogonal biaxial aspherical fiber microlens 62 along the a-axis direction and single-mode fiber 61 + orthogonal biaxial aspherical fiber microlens 62 The light field distribution along the b-axis direction exiting the fiber end. When the light beam propagates in the fiber-integrated orthogonal biaxial aspheric fiber microlens 62, the light along the a-axis direction and along the b-axis direction is gradually bent to the region with high refractive index, that is, the single-mode fiber 61 + orthogonal biaxial The divergence angle of the outgoing beam from the aspherical fiber microlens 62 is smaller than that of the outgoing beam from the single-mode fiber 61 . However, the refractive index along the b-axis direction is higher, the bending ability of light along the b-axis direction is stronger, and the beam divergence along the b-axis direction is smaller than that along the a-axis direction, and the orthogonal biaxial aspherical fiber microlens 62 is equivalent to on aspherical microlenses. Therefore, after the light beam travels for a certain distance in the orthogonal biaxial aspherical optical fiber microlens 62, the light beam will become an elliptical light field distribution. Comparing the light field distribution of the single-mode fiber 61 and the single-mode fiber 61 + the orthogonal biaxial aspherical fiber microlens 62 at the fiber end, the orthogonal biaxial aspherical fiber microlens 62 provided by the present invention has the function of beam shaping.

Comparing Figures 8d, 8e and 8f, single-mode fiber 61, single-mode fiber 61 + orthogonal biaxial aspherical fiber microlens 62 along the a-axis direction and single-mode fiber 61 + orthogonal biaxial aspherical fiber microlens 62 The light intensity distribution of the light field outgoing from the fiber end along the b-axis direction. The light intensity distribution of the light field outgoing from the fiber end is taken as 1/2e of the maximum energy distribution of the light field when the light beam is outgoing. It can be seen from the comparison that when the light beam propagates in the fiber-integrated orthogonal biaxial aspherical fiber microlens 62, the light along the a-axis direction and along the b-axis direction gradually bends to the region with high refractive index, that is, the single-mode fiber 61+ The energy of the light field of the outgoing beam in the orthogonal biaxial aspherical fiber microlens 62 is more concentrated than the energy of the light field of the outgoing light beam from the single-mode fiber 61, and the propagation distance is longer. However, the refractive index along the b-axis direction is higher, and the bending ability of light along the b-axis direction is stronger, so the energy of the light field along the b-axis direction is more concentrated than that along the a-axis direction, and it is stable in vacuum 63 spread. The orthogonal biaxial aspherical optical fiber microlens 62 provided by the present invention has the function of shaping and collimating the light beam.

The simulation model is established by the beam propagation method. Figures 9a to g respectively show that the beam propagates 0μm, 80μm, 180μm, 280μm, 380μm, 480μm, 580μm in the single-mode fiber 61 + the orthogonal biaxial aspherical fiber microlens 62 in the embodiment. The light field distribution of the time slice. When the beam propagates in the axial direction, the diameter of the beam gradually increases along the a-axis and the b-axis due to the circularly symmetrical Gaussian distribution light field in the single-mode fiber 61, and the beam diameter of the b-axis is smaller than that of the a-axis. Therefore, when propagating in the fiber-integrated orthogonal biaxial aspherical fiber microlens 62 , the circularly symmetric Gaussian distribution light beam gradually changes into a circularly symmetrical elliptical distribution light beam, and propagates stably in the vacuum 63 .

The fiber-integrated orthogonal biaxial aspherical optical fiber microlens provided by the embodiments of the present invention can integrate the microlens into the optical fiber, and can realize the function of the fiber-integrated aspherical microlens on the optical fiber. Compared with the prior art, the fiber-integrated orthogonal biaxial aspherical fiber microlenses can be fabricated in a low-cost, batch and high-efficiency manner due to the adoption of thermal diffusion technology and finely designed elliptical core fibers.

The above descriptions are only preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can make various modifications and changes to the present invention according to the spirit and scope of the present invention, which shall be included in the protection scope of the claims of the present invention.

Claims (5)

1. An orthogonal biaxial aspheric optical fiber microlens. It is characterized in that it is prepared by thermal diffusion of elliptical core optical fiber. Orthogonal biaxial aspheric fiber microlenses are prepared by thermal diffusion in a constant temperature field. After the elliptical core dopant of the finely designed elliptical core fiber is diffused, the refractive index distribution becomes a non-circumferentially symmetric quasi-Gaussian distribution. Can be equivalent to a microlens. 2 . The orthogonal biaxial aspherical optical fiber microlens according to claim 1 , which is prepared by thermal diffusion in a constant temperature field. 3 . The temperature of the constant temperature field is above 1000°C. 3. The orthogonal biaxial aspherical optical fiber microlens according to claim 1, after heating and diffusing in a constant temperature field for a certain period of time, the elliptical core fiber after thermal diffusion is cut to a fixed length, and orthogonal biaxial optical fibers of different sizes can be prepared. Axial Aspheric Fiber Microlenses. 4 . The orthogonal biaxial aspherical optical fiber microlens according to claim 1 , which can finely design an elliptical core fiber, and the elliptical core fiber can have different elliptical core geometric dimensions, dopant types, numerical apertures, and the like. 5 . 5. Orthogonal biaxial aspherical optical fiber microlens according to claim 1, is characterized in that comprising the following steps: 1) Fine design of elliptical core fiber The geometry, dopant species, and numerical aperture of the elliptical core were designed. 2), thermal diffusion treatment of elliptical core fiber The elliptical core fiber is placed in a constant temperature field for thermal diffusion treatment. After heating for a certain period of time, the refractive index distribution of the elliptical core fiber gradually changes into a stable non-circumferential quasi-Gaussian distribution. 3) Cutting the elliptical core fiber The thermally diffused elliptical core fiber is cut to a certain length to prepare orthogonal biaxial aspherical fiber microlenses of different sizes.

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