Orthogonal double-shaft aspheric optical fiber micro lens
阅读说明：本技术 一种正交双轴非球面光纤微透镜 (Orthogonal double-shaft aspheric optical fiber micro lens ) 是由 苑立波 孟令知 陈宫傣 于 2020-05-10 设计创作，主要内容包括：本发明提供的是一种正交双轴非球面光纤微透镜。其特征是：它由椭圆芯光纤经热扩散制备而成。正交双轴非球面光纤微透镜是在恒温场中,经热扩散制备而成,精细设计的椭圆芯光纤的椭圆芯掺杂剂扩散后,折射率分布变为非圆周对称的准高斯分布,可以等效为微透镜。本发明提供了一种纤维集成的正交双轴非球面光纤微透镜,同时具有制作简单、成本低的优点。本发明可用于纤维集成的微透镜的制备,可广泛应用于基于纤维集成的正交双轴非球面光纤微透镜的微型内窥镜、细胞生物光纤成像系统、光纤光镊系统、微型无人机等领域。(The invention provides an orthogonal biaxial aspheric optical fiber micro lens. The method is characterized in that: it is prepared by thermal diffusion of an elliptical core optical fiber. The orthogonal biaxial aspheric optical fiber micro lens is prepared by thermal diffusion in a constant temperature field, and after the elliptical core dopant of the finely designed elliptical core optical fiber is diffused, the refractive index distribution is changed into non-circumferential symmetric quasi-Gaussian distribution which can be equivalent to a micro lens. The invention provides a fiber-integrated orthogonal biaxial aspheric optical fiber micro lens, which has the advantages of simple manufacture and low cost. The preparation method can be used for preparing the fiber-integrated microlens, and can be widely applied to the fields of miniature endoscopes, cell biology optical fiber imaging systems, optical fiber optical tweezers systems, miniature unmanned aerial vehicles and the like of the orthogonal biaxial aspheric optical fiber microlens based on the fiber integration.)
1. An orthogonal biaxial aspheric optical fiber microlens. The method is characterized in that: it is prepared by thermal diffusion of an elliptical core optical fiber. The orthogonal biaxial aspheric optical fiber micro lens is prepared by thermal diffusion in a constant temperature field, and after the elliptical core dopant of the finely designed elliptical core optical fiber is diffused, the refractive index distribution is changed into non-circumferential symmetric quasi-Gaussian distribution which can be equivalent to a micro lens.
2. The orthogonal biaxial aspheric optical fiber microlens as claimed in claim 1, which is prepared by thermal diffusion in a constant temperature field. The temperature of the constant temperature field is above 1000 ℃.
3. The orthogonal biaxial aspheric optical fiber microlens as claimed in claim 1, wherein the orthogonal biaxial aspheric optical fiber microlens with different sizes can be prepared by cutting the elliptical core fiber after heat diffusion in a constant temperature field for a certain length after heating diffusion.
4. The orthogonal biaxial aspheric optical fiber microlens as claimed in claim 1, wherein the elliptical core fiber can be finely designed, and the elliptical core fiber can have different geometric sizes of elliptical core, dopant species, numerical aperture, etc.
5. The orthogonal biaxial aspheric optical fiber microlens as claimed in claim 1, comprising the steps of:
1) the elliptic core optical fiber is finely designed
The geometric dimension, the dopant species and the numerical aperture of the elliptical core are designed.
2) Performing thermal diffusion treatment on the elliptic core optical fiber
The elliptical core optical fiber is placed in a constant temperature field for thermal diffusion treatment, and after heating for a certain time, the refractive index distribution of the elliptical core optical fiber is gradually changed into stable non-circumferentially symmetrical quasi-Gaussian distribution.
3) Cutting the optical fiber with elliptical core
The oval core optical fiber after thermal diffusion is cut in a fixed length, and orthogonal biaxial aspheric optical fiber micro lenses with different sizes can be prepared.
(I) technical field
The invention relates to an orthogonal biaxial aspheric optical fiber micro lens, which can be used for preparing a fiber integrated micro lens and can be widely applied to the fields of miniature endoscopes, cell biological optical fiber imaging systems, optical fiber optical tweezers systems, miniature unmanned aerial vehicles and the like of the orthogonal biaxial aspheric optical fiber micro lens based on fiber integration.
(II) background of the invention
With the development of modern industry and scientific technology, people have gradually entered the information-based era. 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, which requires that devices for realizing various functions be as small as possible, and the development is directed toward miniaturization and miniaturization.
The fiber-integrated micro-optical element has the advantages of small volume, light weight, flexible design and manufacture, low manufacturing cost, easy realization of arraying and batch production and the like, can realize the function which is difficult to realize by a common optical element, and has important application value in the fields of optical fiber communication, information processing, aerospace, biomedicine, laser technology, optical calculation and the like.
With the continuous and deep research, many methods for manufacturing micro-optical elements are proposed, mainly including semiconductor lithography, single-point diamond turning, electron beam etching, femtosecond laser direct writing, and the like. The semiconductor photoetching process needs to use a mask plate, and the microstructure is transferred onto the photoresist through development by utilizing ultraviolet light exposure. The method has mature process, is suitable for mass production and has low average cost. The defects that the processed structure only can be planar, multiple times of alignment are needed when a multi-stage structure is processed, the requirement on alignment precision is high, and the cost is increased sharply. The surface roughness of single-point diamond turning is small, the surface roughness is generally below 10nm, and the method is suitable for processing structures with any rotary appearance. The machining precision depends on the tool bit and the machine tool, the precision requirement on the machine tool is high, the machined material is limited, and the size of a machined structure cannot be too small. The electron beam etching is divided into a scanning type and a projection type, a mask plate is not needed in the scanning type, the alignment and the splicing are automatically controlled by a computer, and the processing precision is extremely high. The disadvantages are complex equipment, high cost, small single exposure area and too long time for manufacturing large-size structures. The projection type processing speed is fast, but the mask preparation is difficult. Both methods need to be carried out in vacuum, which greatly limits the application range. The femtosecond laser processing is a processing method of a non-contact high-precision micro-nano photoelectric device, and has strong universality on applicable materials. The defects are high equipment cost, complex processing technology and low processing efficiency.
Current lens systems are limited in shape and size due to manufacturing process concerns. Fabrication techniques for fiber integration of optical fibers with micro-optical elements have recently been proposed for fabrication of micro-optical elements directly on the end face of an optical fiber using different methods of fabrication techniques such as focused ion beam milling, interference lithography, nanoimprint techniques, lithography, polishing techniques, etc. However, they have the disadvantages of difficult processing, complicated manufacturing device, etc.
The thermal diffusion processing technology has the advantages of easiness in implementation, low cost, simplicity in operation and the like, and has great application potential in micro-electro-mechanical systems, optical integrated devices, optical communication and optical fiber sensing. The optical fiber is subjected to thermal diffusion treatment, so that smooth gradual change of the refractive index can be formed in a thermal diffusion processing area, and the smooth gradual change refractive index area has the effect of a micro lens. The finely designed elliptic core optical fiber is processed by thermal diffusion, and the fiber integrated orthogonal biaxial aspheric optical fiber micro lens can be prepared.
Patent CN01144937.3 discloses an optical fiber having a lens function and a method for manufacturing the same, which is effective for an optical fiber having an abrupt refractive index by using a graded-index optical fiber having a period length indicating lens function. The method can collimate a single-mode fiber, but does not have the function of an orthogonal biaxial aspheric fiber microlens.
Patent CN201210011571.6 discloses a single mode fiber connector with large mode area and a manufacturing method thereof, which is to perform thermal diffusion of core doping elements on a step multimode fiber to form a graded index lens with a refractive index decreasing outward in the radial direction, and is mainly used for the connection of the single mode fiber with large mode area, and does not have the function of an orthogonal biaxial aspheric fiber microlens.
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. Since the light beam is collimated by using the microlens, the case of inserting connection or the like cannot be applied, the range of use is limited, and the manufacturing is difficult.
Patent US4269648A discloses a method of mounting a microsphere coupling lens onto an optical fiber, where the microsphere coupling lens can be mounted onto the end of the optical fiber using an adhesive. A method for manufacturing a microlens at an optical fiber end is disclosed, but the method is complex in manufacturing process and does not have the function of an orthogonal biaxial aspheric optical fiber microlens.
Patent US7013678B2 discloses a method for manufacturing a graded index fiber lens, which 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 the function of an orthogonal biaxial aspheric fiber micro lens, and the method has complicated process and high production cost.
Patent US7228033B2 discloses an optical waveguide lens and method of making the same by fusion splicing a uniform glass lens blank to the distal end of an optical fiber, heating and stretching the lens blank to separate it into two segments, and attaching the segments to the optical fiber defining a tapered end, and then heating the lens blank above its softening point to form a spherical lens. The optical waveguide lens can be used for collimating or focusing light beams, but the lens manufactured by the method does not have the function of an orthorhombic biaxial aspheric optical fiber micro lens.
The invention discloses an orthogonal biaxial aspheric optical fiber micro lens, which can be used for preparing a fiber integrated micro lens and can be widely applied to the fields of miniature endoscopes, cell biological optical fiber imaging systems, optical fiber optical tweezers systems, miniature unmanned aerial vehicles and the like of the orthogonal biaxial aspheric optical fiber micro lens based on the fiber integration. The method adopts a thermal diffusion technology to carry out thermal diffusion treatment on a finely designed elliptical core optical fiber in a constant temperature field, forms a non-circumferential symmetric refractive index gradient region with quasi-Gaussian distribution in the thermal diffusion region, and cuts the elliptical core optical fiber subjected to thermal diffusion in a fixed length manner to prepare the orthogonal biaxial aspheric optical fiber micro-lenses with different sizes. Compared with the prior art, the optical fiber micro lens has the advantages that the micro lens can be integrated on the optical fiber due to the adoption of the thermal diffusion technology and the finely designed elliptical core optical fiber, the function of the fiber-integrated aspheric lens can be realized on the optical fiber, and the fiber-integrated orthogonal biaxial aspheric optical fiber micro lens can be prepared in batches at low cost and high efficiency.
Disclosure of the invention
The invention aims to provide an orthogonal biaxial aspheric optical fiber micro lens which is simple to manufacture, low in cost and capable of being produced in batch.
The purpose of the invention is realized as follows:
the orthogonal biaxial aspheric optical fiber micro lens is prepared by thermal diffusion of an elliptical core optical fiber. The orthogonal biaxial aspheric optical fiber micro lens is prepared by thermal diffusion in a constant temperature field, and after the elliptical core dopant of the finely designed elliptical core optical fiber is diffused, the refractive index distribution is changed into non-circumferential symmetric quasi-Gaussian distribution which can be equivalent to a micro lens.
Thermal diffusion techniques are commonly used for expansion of the fundamental mode field, which enables the dopant profile in the fiber to be graded into a stable quasi-gaussian profile. The finely designed elliptical core optical fiber is placed in a constant temperature field for heating, the dopant distribution in the elliptical core is gradually changed into stable non-circumferential symmetric quasi-Gaussian distribution, and the normalized frequency of the optical fiber is not changed in the heating process. The non-circular symmetrical quasi-Gaussian distribution of the dopant gradually changes the refractive index distribution of the elliptical core fiber into the non-circular symmetrical quasi-Gaussian distribution, and the light beam is bent towards a region with higher refractive index in the propagation process, so that the elliptical core fiber after heat diffusion has the function of an aspheric micro lens.
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. Consider the initial boundary conditions:
where a is a constant and represents the diameter of the optical fiber.
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 αnIs the root of it
J0(aαn)＝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 ncoThe refractive indices of the fiber cladding and the intermediate core, respectively. When the heating temperature field is 1600 ℃, the refractive index distribution of the elliptical core optical fiber changes along with the heating time t. The
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 an orthogonal biaxial aspheric fiber microlens with a radially graded index of refraction, the central index of refraction of the fiber is highest and decreases as the radial distance from the central axis increases.
The cross-sectional refractive index of the prepared fiber-integrated orthogonal biaxial aspheric optical fiber microlens after the elliptical core optical fiber is subjected to thermal diffusion for 0.4h is shown in fig. 3. FIG. 4 is a three-dimensional representation of the cross-sectional refractive indices of a fiber-integrated orthogonal biaxial aspheric fiber microlens. As can be seen from the figure, the refractive index profile of the orthorhombic biaxial aspheric fiber microlens is elliptical, i.e., a quasi-gaussian profile with non-circumferential symmetry, the central refractive index is the highest and decreases as the radial distance from the central axis increases.
When the fiber-integrated orthogonal biaxial aspheric optical fiber micro-lens is prepared, the elliptical core optical fiber can be finely designed, including the design of the geometric dimension, the dopant type, the numerical aperture and the like of the elliptical core.
The invention is prepared by thermal diffusion in a constant temperature field when preparing the fiber integrated orthogonal biaxial aspheric optical fiber micro lens. The temperature of the constant temperature field is above 1000 ℃. Elliptical core fibers with different elliptical core dopants have different thermal diffusivity.
When the fiber-integrated orthogonal biaxial aspheric optical fiber micro-lens is prepared, after the fiber-integrated orthogonal biaxial aspheric optical fiber micro-lens is heated and diffused in a constant temperature field for a certain time, the elliptical core optical fiber subjected to thermal diffusion is cut in a fixed length, and then the orthogonal biaxial aspheric optical fiber micro-lens with different sizes can be prepared.
The invention discloses a method for preparing a fiber-integrated orthogonal biaxial aspheric optical fiber micro lens, which is characterized by comprising the following steps of:
the first step is to carry out fine design on the elliptical core optical fiber, including the design on the geometric dimension, the dopant species, the numerical aperture and the like of the elliptical core.
And secondly, performing thermal diffusion treatment on the elliptical core optical fiber, placing the elliptical core optical fiber in a constant temperature field for thermal diffusion treatment, and after heating for a certain time, gradually changing the refractive index distribution of the elliptical core optical fiber into stable quasi-Gaussian distribution which is not circularly symmetrical.
And thirdly, cutting the elliptical core optical fiber, and cutting the elliptical core optical fiber subjected to thermal diffusion in a fixed length manner to prepare the orthogonal biaxial aspheric optical fiber micro-lenses with different sizes.
When the fiber-integrated orthogonal biaxial aspheric optical fiber micro-lens is prepared, after a certain period of thermal diffusion treatment, the refractive index distribution of the elliptical core optical fiber tends to stable non-circumferentially symmetrical quasi-Gaussian distribution, the central refractive index of the optical fiber is highest, and the central refractive index of the optical fiber is reduced along with the increase of the radial distance from the central axis. After the elliptical core optical fiber is subjected to thermal diffusion treatment, the dopant forms smooth non-circumferentially symmetrical quasi-Gaussian distribution in a thermal diffusion processing area. The distribution of the dopant is non-circumferential symmetric quasi-Gaussian distribution, the refractive index distribution of the elliptical core optical fiber is also non-circumferential symmetric quasi-Gaussian distribution, and the elliptical core optical fiber is bent towards a region with higher refractive index in the process of light beam propagation, so that the elliptical core optical fiber after thermal diffusion has the function of a micro lens.
As shown in fig. 3, the cross-sectional refractive index profile of the fiber-integrated orthogonal biaxial aspheric optical fiber microlens is elliptical, i.e., a quasi-gaussian profile that is not circumferentially symmetrical, and the central refractive index of the optical fiber is the highest and decreases as the radial distance from the central axis increases. When the incident light beam passes through the micro lens, the central and edge light rays are gradually bent towards the area with high refractive index, and the capability of bending the light rays by the a axis and the b axis is different, which is equivalent to an aspheric micro lens. Therefore, after the optical fiber is transmitted in the orthogonal biaxial aspheric optical fiber micro lens for a certain distance, the light beam can become an elliptic optical field distribution.
The fiber-integrated orthogonal biaxial aspheric optical fiber micro-lens prepared by the invention can realize the function of shaping light beams, so that Gaussian light beams and the like are shaped into elliptical light field distribution. The fiber-integrated orthogonal biaxial aspheric optical fiber micro-lens is cut in a fixed length, so that orthogonal biaxial aspheric optical fiber micro-lenses with different sizes can be prepared, and the function of beam shaping of different requirements is realized.
When the elliptical core optical fiber is finely designed, the dopant of the elliptical core can be one or more different doped dopants according to the requirement. When the elliptic core optical fiber is used for preparing the orthogonal biaxial aspheric optical fiber micro lens, the orthogonal biaxial aspheric optical fiber micro lens with larger mode field diameter can be prepared by designing larger elliptic core diameter or increasing heating time and heating temperature. One or more doped different dopants are used, and the implementation of the beam shaping function of the orthogonal biaxial aspheric optical fiber micro lens is not influenced.
The fiber-integrated orthogonal biaxial aspheric optical fiber micro lens provided by the invention is prepared by thermal diffusion of an elliptical core optical fiber. Compared with the prior art, the optical fiber micro lens has the advantages that the micro lens can be integrated on the optical fiber due to the adoption of the thermal diffusion technology and the finely designed elliptical core optical fiber, the function of the fiber-integrated aspheric lens can be realized on the optical fiber, and the fiber-integrated orthogonal biaxial aspheric optical fiber micro lens can be prepared in batches at low cost and high efficiency.
(IV) description of the drawings
FIG. 1 is a schematic representation of the refractive index profile of a fiber-integrated orthogonal biaxial aspheric optical fiber microlens before and after thermal diffusion fabrication.
Fig. 2a is a graph showing the change of the refractive index profile along the a-axis of an elliptical core optical fiber in a temperature field of 1600 c with the change of the heating time t, fig. 2b is a graph showing the refractive index profile along the a-axis of the elliptical core optical fiber after being heated for 0.4h, fig. 2c is a graph showing the change of the refractive index profile along the b-axis of the elliptical core optical fiber in a temperature field of 1600 c with the change of the heating time t, and fig. 2d is a graph showing the refractive index profile along the b-axis of the elliptical core optical fiber after being heated for 0.4 h.
FIG. 3 is a cross-sectional refractive index profile of an elliptical core fiber heated for 0.4 h.
FIG. 4 is a three-dimensional representation of the cross-sectional refractive index profile of an elliptical core fiber after heating for 0.4 h.
FIG. 5 is a schematic cross-sectional view of an elliptical core optical fiber according to 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 + orthogonal biaxial aspheric fiber microlens in an embodiment. 61 is a single mode fiber and 62 is a fiber-integrated orthogonal biaxial aspheric fiber microlens made from an elliptical core fiber.
Fig. 7a is a refractive index profile of a single-mode fiber + orthogonal biaxial aspheric fiber microlens in an example along the a-axis direction, fig. 7b is a three-dimensional display of a refractive index profile of a single-mode fiber + orthogonal biaxial aspheric fiber microlens in an example along the a-axis direction, fig. 7c is a refractive index profile of a single-mode fiber + orthogonal biaxial aspheric fiber microlens in an example along the b-axis direction, and fig. 7d is a three-dimensional display of a refractive index profile of a single-mode fiber + orthogonal biaxial aspheric fiber microlens in an example along the b-axis direction.
Fig. 8a is a light field distribution of a fiber end outgoing light field of a single-mode fiber in an embodiment, fig. 8b is a light field distribution of a fiber end outgoing light field of a single-mode fiber + orthogonal biaxial aspheric fiber microlens in an a-axis direction in an embodiment, fig. 8c is a light field distribution of a fiber end outgoing light field of a single-mode fiber + orthogonal biaxial aspheric fiber microlens in a b-axis direction in an embodiment, fig. 8d is a light intensity distribution of a fiber end outgoing light field of a single-mode fiber in an embodiment, fig. 8e is a light intensity distribution of a fiber end outgoing light field of a single-mode fiber + orthogonal biaxial aspheric fiber microlens in an a-axis direction in an embodiment, and fig. 8f is a light intensity distribution of a fiber end outgoing light field of a single-mode.
FIGS. 9 a-g are the optical field distributions of the section when the light beam propagates in the single mode fiber + orthogonal biaxial aspheric fiber microlens of the embodiment by 0 μm, 80 μm, 180 μm, 280 μm, 380 μm, 480 μm, and 580 μm, respectively.
(V) detailed description of the preferred embodiments
The invention is further illustrated below with reference to specific examples.
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