CN111650689A - Fiber integrated micro lens set - Google Patents
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- CN111650689A CN111650689A CN202010389632.7A CN202010389632A CN111650689A CN 111650689 A CN111650689 A CN 111650689A CN 202010389632 A CN202010389632 A CN 202010389632A CN 111650689 A CN111650689 A CN 111650689A
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- 239000000835 fiber Substances 0.000 title claims abstract description 117
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- 239000002019 doping agent Substances 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims abstract description 21
- 238000010438 heat treatment Methods 0.000 claims description 29
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- 238000003384 imaging method Methods 0.000 abstract description 3
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- 229910052732 germanium Inorganic materials 0.000 description 2
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 2
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
Abstract
The invention provides a fiber integrated micro-lens group. The method is characterized in that: it is formed by connecting two sections of optical fibers which are prepared by thermal diffusion and have refractive index distribution of circular symmetric quasi-Gaussian distribution and circular symmetric reverse quasi-Gaussian distribution respectively. The fiber integrated micro-lens group is formed by placing optical fibers in a constant temperature field, preparing and connecting the optical fibers through thermal diffusion, and after the fiber core dopant of the optical fibers is diffused, the refractive index distribution is changed into quasi-Gaussian distribution with symmetrical circumference, so that the fiber integrated micro-lens group can be equivalent to a micro-convex lens; the refractive index distribution becomes a circumferentially symmetric reverse quasi-Gaussian distribution, and can be equivalent to a micro-concave lens. The invention mainly provides a construction method of an optical fiber micro lens, and a fiber integrated micro lens group is constructed in an optical fiber. The invention can be used for preparing the fiber integrated micro lens, and can be widely applied to the fields of micro endoscopes, cell biological optical fiber imaging systems, optical fiber optical tweezers systems, micro unmanned aerial vehicles and the like based on the fiber integrated micro lens group.
Description
(I) technical field
The invention relates to a fiber integrated micro-lens group, which can be used for preparing fiber integrated micro-lenses, can be widely applied to the fields of micro endoscopes, cell biology optical fiber imaging systems, optical fiber optical tweezers systems, micro unmanned aerial vehicles and the like based on the fiber integrated micro-lens group, and belongs to the technical field of fiber integration.
(II) background of the invention
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.
In general, the optical fiber micro-lenses are divided into three types, and the optical fiber micro-lenses which are originally appeared and are most easily conceived are like the traditional geometric lenses, and the change of the curvature of the end face of the optical fiber is realized by polishing and grinding of the end face of the optical fiber, corrosion, surface tension forming in a high-temperature molten state and the like. The second is to realize the micro-lens effect by the modulation of the refractive index inside the optical fiber, such as the welding or adhering of a segment of self-focusing optical fiber or self-focusing lens on the end of the common optical fiber. The third is the recent production of fiber microlenses by printing polymer lenses directly on the end faces of optical fibers using high precision 3D printing technology, which enables the production of microlenses and microlens arrays with high precision and high freedom of design, but the required equipment is very expensive and difficult to obtain, and the polymer materials have limited application range.
In recent decades, the position of microlenses in photonic integrated devices and optical fibers has become more and more important. Current lens systems are limited in size, shape, and dimensions by the manufacturing process. Since the conventional lens geometry lens only changes the trajectory of light at the input and output surfaces, while the inside of the lens travels straight, it is difficult to construct an ideal fiber-integrated microlens set as desired.
Graded index (GRIN) lenses represent another approach to lens design, and instead of relying on a uniform material surface to manipulate light, the refractive index can be varied throughout the lens body to enable greater manipulation of the light ray trajectory. Although GRIN lenses have significant potential advantages over conventional lenses, they are far from common in practical applications because the process of achieving large refractive index gradients in a controlled manner makes it quite difficult to fabricate the lenses.
The thermal diffusion technology provides a potential gradient refractive index design scheme for people, on one hand, the difficulty in the preparation process of the gradient refractive index material is avoided, on the other hand, the refractive index distribution in the material can be reshaped in a flexible mode, and finally smooth gradient refractive index change is presented, even a three-dimensional gradient refractive index structure is constructed.
Meanwhile, 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 initial parameters of the optical fiber are reasonably selected, and the optical fiber is subjected to thermal diffusion processing, so that the micro-lenses with different focal lengths can be prepared. When the refractive index distribution of the optical fiber after the thermal diffusion treatment is circularly symmetric quasi-Gaussian distribution, the optical fiber can be equivalent to a micro convex lens, and when the refractive index distribution is circularly symmetric reverse quasi-Gaussian distribution, the optical fiber can be equivalent to a micro concave lens, the prepared micro convex lenses and micro concave lenses with different focal lengths are connected, and a fiber integrated micro lens group can be constructed in the optical fiber.
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 the graded index fiber cannot be obtained at low cost and is designed according to the requirement.
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 connecting a single mode fiber with large mode area.
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 CN201910359143.4 discloses a method for manufacturing a microlens, which is characterized in that a pressure-controlled micro nozzle is used to form a raised ultraviolet curing glue drop shape, and then the drop is transferred to the end face of an optical fiber or the surface of other substrate by contact, and the drop on the end face of the optical fiber or the surface of other substrate naturally forms a spherical lens shape due to the action of surface tension, and then the microlens is obtained by curing, which has substantial difference with the method of the invention.
Patent CN200420023915.6 discloses a thermal expansion core diameter micro-lens multimode optical fiber, which is characterized in that the end part of the multimode optical fiber is provided with a thermal expansion core diameter, and the end of the thermal expansion core diameter part is provided with a wedge-shaped optical fiber end face and a cylindrical optical fiber micro-lens with an arc surface tangent to the wedge-shaped optical fiber end face. The fiber end cannot be effectively used for constructing a fiber integrated micro-lens group in an optical fiber after being ground.
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 of manufacturing a microlens at an optical fiber end is disclosed, but the method is complicated in manufacturing process.
Patent US7013678B2 discloses a method for manufacturing a graded index fiber lens, which is an important component in a fiber optic communication system and can be used as a lens, but the method is relatively complex in process and high in 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 is complex in process and high in production cost.
The invention discloses a fiber integrated micro lens group, mainly provides a preparation method of a fiber micro lens, and simultaneously constructs the fiber integrated micro lens group in an optical fiber, can be used for preparing the fiber integrated micro lens, and can be widely applied to the fields of a micro endoscope, a cell biology optical fiber imaging system, an optical fiber tweezers system, a micro unmanned aerial vehicle and the like based on the fiber integrated micro lens group. The fiber integrated micro-lens group can be constructed by adopting a thermal diffusion technology, carrying out thermal diffusion treatment on the fiber in a constant temperature field, forming a refractive index gradient region with circularly symmetric quasi-Gaussian distribution or circularly symmetric reverse quasi-Gaussian distribution in the thermal diffusion region, cutting the thermally diffused fiber in a fixed length, thus preparing fiber micro-lenses with different focal lengths, and connecting two sections of fiber micro-convex lenses and micro-concave lenses. Compared with the prior art, the fiber integrated micro-lens group can be constructed in the optical fiber due to the adoption of the thermal diffusion technology, and the fiber integrated micro-lens group can be prepared in batch at low cost and high efficiency.
Disclosure of the invention
The invention aims to provide a fiber integrated microlens set which is simple to manufacture, low in cost and capable of being produced in batches.
The purpose of the invention is realized as follows:
the fiber integrated micro-lens group is formed by connecting two sections of optical fibers which are prepared by thermal diffusion and have refractive index distribution of circular symmetric quasi-Gaussian distribution and circular symmetric reverse quasi-Gaussian distribution respectively. The fiber integrated micro-lens group is formed by placing optical fibers in a constant temperature field, preparing and connecting the optical fibers through thermal diffusion, and after the fiber core dopant of the optical fibers is diffused, the refractive index distribution is changed into quasi-Gaussian distribution with symmetrical circumference, so that the fiber integrated micro-lens group can be equivalent to a micro-convex lens; the refractive index distribution becomes a circumferentially symmetric reverse quasi-Gaussian distribution, and can be equivalent to a micro-concave 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, circumferentially symmetric quasi-gaussian profile or a circumferentially symmetric reverse quasi-gaussian profile. The optical fiber is placed in a constant temperature field for heating, the dopant distribution in the optical fiber is gradually changed into stable quasi-Gaussian distribution, and the normalization frequency of the optical fiber is not changed in the heating process. The quasi-Gaussian distribution of the dopant makes the initial refractive index distribution of the optical fiber gradually change into the quasi-Gaussian distribution, and the optical fiber is bent towards a region with higher refractive index in the process of light beam propagation, so that the optical fiber after thermal diffusion can be equivalent to a 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 core, respectively. The refractive index profile of the fiber changes with heating time t at a heating temperature field of 1600 c, as shown in fig. 2. FIG. 2a shows the refractive index profile of a step-index multimode optical fiber having a core diameter of 62.5 μm, as a function of heating time t, where curves 21, 22, and 23 are the refractive index profiles of the step-index multimode optical fiber in the radial direction of the optical fiber after heating for 0h, 1h, and 1.7h, respectively; after 1.7h of thermal diffusion treatment, the refractive index profile of the step-multimode fiber tended to be a more stable quasi-gaussian profile, as shown in fig. 2 b. FIG. 2c shows the refractive index profile of an annular core fiber with a cladding diameter of 62.5 μm as a function of heating time t, where curves 24, 25, and 26 show the refractive index profile of the annular core fiber in the radial direction of the fiber after heating for 0h, 1h, and 1.7h, respectively; after 1.7h of thermal diffusion treatment, the refractive index profile of the ring core fiber tended to be a more stable inverted quasi-gaussian profile, as shown in fig. 2 d.
For a square index distributed radial Graded Index Fiber (GIF), the light ray transmission track inside the core is sinusoidal periodic, and is therefore also referred to as a self-focusing fiber. Light rays emanating from a point will be periodically focused along the fiber, so the GIF can be imaged like a lens. This is the fundamental principle of a gradient index lens rod or a self-focusing lens rod. The function of the radial gradient index of refraction n of the square-rate distribution with respect to the radial position r is generally given by:
n in formula (8)0Is the index of refraction at the center of the fiber, r is the radial distance from the central axis, and g is the gradient constant. When the minus sign is (8), the refractive index at the center of the optical fiber is the highest, and the axial length is LFocal length of the group being
Corresponding, back focal length fb(distance of focus from second surface) is defined as:
when a plus sign appears in the formula (8), indicating that the refractive index at the center of the optical fiber is the lowest, the focal length of the fiber-integrated microlens group having an axial length L is
Accordingly, the back focal length is:
the section refractive index of the prepared microlens after the step-multimode fiber with the diameter of 62.5 mu m is thermally diffused for 1.7h is shown in figure 3 a; FIG. 3b is a three-dimensional representation of its cross-sectional refractive index. The refractive index of the section of the prepared microlens after the 62.5 μm ring-core optical fiber is thermally diffused for 1.7h is shown in FIG. 3 c; fig. 3d is a three-dimensional representation of its cross-sectional refractive index. As can be seen, the refractive index of the microlenses is circumferentially symmetric, quasi-gaussian, with the center refractive index being highest and decreasing as the radial distance from the central axis increases. The refractive index of the microlens is a circumferentially symmetric reverse quasi-gaussian distribution with the central refractive index being the lowest and becoming larger as the radial distance from the central axis increases.
When the fiber integrated micro lens group is prepared, optical fibers with different parameters can be selected, wherein the optical fibers comprise initial refractive index distribution, dopant types, numerical aperture and the like. After the selected optical fiber is prepared by thermal diffusion, the refractive index distribution of the optical fiber is in a circumferentially symmetrical quasi-Gaussian distribution or a circumferentially symmetrical reverse quasi-Gaussian distribution.
When the fiber integrated micro lens group is prepared, the optical fiber is placed in a constant temperature field, and is prepared and connected through thermal diffusion. The temperature of the constant temperature field is above 1000 ℃. The thermal diffusivity of optical fibers with different core dopants is different.
When the fiber integrated micro-lens group is prepared, the fiber after thermal diffusion is cut in a fixed length after being heated and diffused for a certain time in a constant temperature field, and micro convex lenses and micro concave lenses with different focal lengths can be prepared.
When the fiber integrated micro lens group is prepared, two micro lenses with the same focal length are connected, and the sum of the back focal lengths (the distance between the focal points and the second surface) of the two micro lenses is equal to zero, so that the fiber integrated Galileo telescope is formed.
When the fiber integrated micro-lens group is prepared, the micro-lenses with two focal lengths are connected, and the sum of the back focal lengths (the distance between the focal points and the second surface) of the two micro-lenses is not equal to zero, so that the fiber integrated micro-lens group with the equivalent focal length can be formed.
When the fiber integrated micro-lens group is prepared, after the fiber integrated micro-lens group is heated and diffused in a constant temperature field for a certain time, the step multimode fiber after thermal diffusion is cut in a fixed length, the optical fiber micro-convex lenses with different focal lengths can be prepared by a formula (9), and the optical fiber micro-concave lenses with different focal lengths can be prepared by a formula (11).
The invention discloses a preparation method of a fiber integrated microlens set, which is characterized by comprising the following steps:
first, initial parameters of the fiber are selected. The optical fiber is prepared by thermal diffusion, and the refractive index distribution of the optical fiber is circularly symmetric quasi-Gaussian distribution or circularly symmetric reverse quasi-Gaussian distribution.
And secondly, carrying out thermal diffusion treatment on the optical fiber. And (3) putting the 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 optical fiber into stable circularly symmetric quasi-Gaussian distribution or circularly symmetric reverse quasi-Gaussian distribution.
And thirdly, cutting the optical fiber subjected to thermal diffusion. The optical fiber after thermal diffusion is cut in a fixed length, and optical fiber micro convex lenses or micro concave lenses with different focal lengths can be prepared.
And fourthly, welding the two sections of optical fibers subjected to thermal diffusion. And welding the two sections of the optical fiber micro convex lenses and the micro concave lenses after cutting with fixed length to form the fiber integrated micro lens group.
When the fiber integrated micro lens group is prepared, after a certain time of thermal diffusion treatment, the initial refractive index distribution of the selected optical fiber tends to be more stable quasi-Gaussian distribution with circumferential symmetry, the refractive index at the center is highest, and the initial refractive index distribution is reduced along with the increase of the distance from the radial distance to the central axis. After the optical fiber is subjected to thermal diffusion treatment, the dopant forms smooth quasi-Gaussian distribution in a thermal diffusion processing area. The distribution of the dopant is quasi-Gaussian distribution, the refractive index distribution of the optical fiber is also quasi-Gaussian distribution, and the optical fiber is bent towards a region with higher refractive index in the process of light beam propagation, so that the optical fiber after thermal diffusion can be equivalent to a micro convex lens. Similarly, when the refractive index distribution of the optical fiber is in a circumferentially symmetric reverse quasi-gaussian distribution, the refractive index at the center is the lowest, and becomes larger as the distance from the radial direction to the central axis increases, which is equivalent to a micro-concave lens.
In the micro-convex lens of the present invention, as shown in fig. 4a, the light rays travel along a sinusoidal curve and can be periodically converged and diverged until reaching the rear surface of the micro-convex lens, and the light beam exits from the fiber end. Therefore, when the lens is cut to have different lengths L, the lens can be used as a convex lens or a concave lens. The length of the light ray that completes a sinusoidal periodic propagation is expressed as a pitch (P). As shown in fig. 4b, in the micro-concave lens of the present invention, the light is gradually diverged, and thus, it can be used only as a concave lens.
In the invention, the thermal diffusion optical fiber is cut in a fixed length, optical fiber micro lenses with different focal lengths are prepared, and two sections of optical fiber micro convex lenses and two sections of optical fiber micro concave lenses are connected, so that the fiber integrated micro lens group with different equivalent focal lengths can be constructed.
When the optical fiber is selected by the invention, the dopant of the fiber core can be one or more different doped dopants according to the requirement. When the optical fiber is selected to prepare the optical fiber micro lens, the optical fiber micro lens with larger mode field diameter can be prepared by designing larger fiber core and cladding diameter or increasing heating time and heating temperature. The use of one or more different dopants doped does not affect the performance of the fiber microlens function. The initial refractive index profile, the numerical aperture of the initial fiber, and the heating temperature and heating time of the thermal diffusion all affect the gradient constant g and ultimately the focal length of the microlens.
The invention discloses a fiber integrated micro lens group, mainly provides a preparation method of an optical fiber micro lens, and simultaneously constructs the fiber integrated micro lens group in an optical fiber. Compared with the prior art, the fiber integrated micro-lens group can be constructed in the optical fiber due to the adoption of the thermal diffusion technology, and the fiber integrated micro-lens group can be prepared in batch at low cost and high efficiency.
(IV) description of the drawings
Fig. 1 is a schematic structural view of a fiber-integrated microlens assembly. 1 is a micro convex lens, and 2 is a micro concave lens.
FIG. 2a is a graph showing the change of the refractive index profile of a step-mode optical fiber having a core diameter of 62.5 μm according to the change of heating time t in a temperature field of 1600 ℃ and FIG. 2b is a graph showing the refractive index profile after heating for 1.7 h. Fig. 2c is a graph showing the change of the refractive index profile of the annular core optical fiber having a cladding diameter of 62.5 μm with the change of heating time t in a temperature field of 1600 c, and fig. 2d is a graph showing the refractive index profile thereof after heating for 1.7 h.
FIG. 3a is a cross-sectional refractive index profile of a step-multimode optical fiber having a core diameter of 62.5 μm after heating for 1.7h, and FIG. 3b is a three-dimensional representation of the cross-sectional refractive index profile. FIG. 3c is a cross-sectional refractive index profile of a ring-core optical fiber having a cladding diameter of 62.5 μm after heating for 1.7h, and FIG. 3d is a three-dimensional display of the cross-sectional refractive index profile
Fig. 4a is a schematic diagram of light propagating along a sinusoidal curve in a fiber optic lenticular lens. FIG. 4b is a schematic view of the ray divergence in a fiber optic micro-concave lens.
FIG. 5a is a schematic cross-sectional view of a step-mode optical fiber according to an embodiment. 51 is the cladding of the step-index fiber and 52 is the core of the step-index fiber. FIG. 5b is a schematic cross-sectional view of a ring core optical fiber according to the embodiment. 53 is the cladding of the ring core fiber and 54 is the core of the ring core fiber.
FIG. 6 is a schematic structural diagram of a fiber-integrated microlens assembly according to an embodiment. 61 is a micro convex lens prepared by different lengths or focal lengths in the embodiment of the invention; reference numeral 62 denotes a concave lens manufactured with different lengths or focal lengths according to an embodiment of the present invention.
Fig. 7a shows the light transmission trace of the micro-convex lens 61 in the embodiment. Fig. 7b shows the light transmission trace of the micro-concave lens 62 in the embodiment.
Fig. 8a-d show the light transmission traces of the fiber-integrated microlens assembly constructed by the micro-convex lens 61 and the micro-concave lens 62 in the embodiment.
(V) detailed description of the preferred embodiments
The invention is further illustrated below with reference to specific examples.
Example 1:
a schematic cross-sectional view of a selected step-mode optical fiber in this embodiment is shown in fig. 5 a. 51 is the cladding of the step-index fiber and 52 is the core of the step-index fiber. A cross-sectional view of a selected ring core fiber in this embodiment is shown in fig. 5 b. 53 is the cladding of the ring core fiber and 54 is the core of the ring core fiber.
The preparation steps of the fiber integrated microlens set in this embodiment are as follows:
first, initial parameters of the fiber are selected. Including the initial refractive index profile of the fiber, dopant species, numerical aperture, etc. In this embodiment, a step multimode fiber is selected, and the parameters of the micro-convex lens 61 are that the diameter of the cladding is 125 μm, the diameter of the fiber core is 62.5 μm, and the numerical aperture is 0.14; the parameters of the optical fiber of the micro-concave lens 62 are that the diameter of the cladding is 62.5 μm, the diameter of the core is 125 μm, and the numerical aperture is 0.14. The dopant species is germanium. After the selected step multimode optical fiber is prepared by thermal diffusion, the refractive index distribution of the optical fiber is in a quasi-Gaussian distribution with circumferential symmetry. After the selected annular core optical fiber is prepared by thermal diffusion, the refractive index distribution of the optical fiber is reverse quasi-Gaussian distribution with circumferential symmetry.
And secondly, carrying out thermal diffusion treatment on the optical fiber. And placing the initial optical fibers of the convex micro-lens 61 and the concave micro-lens 62 in a constant temperature field for thermal diffusion treatment, wherein the temperature of the constant temperature field is 1600 ℃, the convex micro-lens 61 and the concave micro-lens 62 are heated for 1.7h, and the refractive index distribution is gradually changed into stable quasi-Gaussian distribution with circumferential symmetry and reverse quasi-Gaussian distribution with circumferential symmetry respectively.
And thirdly, cutting the optical fiber subjected to thermal diffusion. The micro convex lens 61 and the micro concave lens 62 after thermal diffusion are cut in a fixed length, and optical fiber micro convex/concave lenses with different focal lengths can be prepared.
And fourthly, welding the two sections of optical fibers subjected to thermal diffusion. And welding the micro convex lens 61 and the micro concave lens 62 which are cut to be in fixed length to form the fiber integrated micro lens group.
The micro convex lens 61 and the micro concave lens 62 which are subjected to thermal diffusion and cut to a fixed length are welded, and the fiber integrated micro lens group can be constructed, and the structure is shown in fig. 6. 61 is a convex microlens made of a step-multimode fiber having a core diameter of 62.5 μm, and 62 is a concave microlens made of a ring-core fiber having a cladding diameter of 62.5 μm.
The finite element method is used for modeling the optical fiber thermal diffusion treatment process, and the change of the refractive index distribution after the thermal diffusion treatment is simulated, as shown in fig. 3. The refractive index of the cross section of the prepared micro convex lens after the step multimode fiber is thermally diffused for 1.7h is shown in figure 3 a; FIG. 3b is a three-dimensional representation of its cross-sectional refractive index. The refractive index of the cross section of the prepared micro-concave lens after the annular core is thermally diffused for 1.7h is shown in FIG. 3 c; fig. 3d is a three-dimensional representation of its cross-sectional refractive index.
As can be seen from the figure, the fiber-integrated microlens sets have smoothly graded refractive index profile transitions. The refractive index of the convex microlens 61 is circumferentially symmetric and quasi-gaussian distributed, the central refractive index is the highest, and decreases as the distance from the central axis in the radial direction increases; the refractive index of the micro-concave lens 62 is circumferentially symmetric, inversely quasi-gaussian with the center refractive index being lowest and becoming larger as the radial distance from the central axis increases.
The fiber integrated microlens set was analyzed by a ray tracing method, and the simulation results are shown in fig. 7 and 8. Fig. 7a shows the light transmission trace of the micro-convex lens 61 in the embodiment. Fig. 7b shows the light transmission trace of the micro-concave lens 62 in the embodiment. Fig. 8a-d show the light transmission traces of the fiber-integrated microlens assembly constructed by the micro-convex lens 61 and the micro-concave lens 62 in the embodiment. The incident end face is a plane wave normal incidence light source, the size of the plane wave is 30 mu m x 30 mu m, and the light source is abstracted into a plurality of hexapole distributed light rays.
In fig. 7a, when the micro-convex lens 61 transmits 690 μm, the light spot is the smallest, i.e. the focal length of the micro-convex lens 61 is 690 μm. In fig. 7b, the micro-concave lens 62 diverges in the free space 63.
In FIG. 8a, 61-1 is a convex microlens 61 with a length of 279.83 μm and a focal length of 691.5 μm; 62-1 is a micro-concave lens 62 with a length of 411.67 μm and a focal length of-411.67 μm. 63 is a free space with a length of 500. mu.m. The incident plane wave propagates in the fiber-integrated microlens set, is collimated out at the rear end face of the microlens 62-1, and stably propagates in the free space 63. The sum of the back focal lengths of the microlens 61-1 and the microlens 62-1 is equal to zero, i.e., a fiber-integrated Galilean telescope is formed.
In FIG. 8b, 61-2 is a 238 μm long convex microlens 61 with a focal length of 494.7 μm; 62-2 is a micro-concave lens 62 with a length of 310.3 μm and a focal length of-494.72 μm. 63 is a free space with a length of 500. mu.m. The incident plane wave propagates in the fiber-integrated microlens set, is collimated out at the rear end face of the microlens 62-2, and stably propagates in the free space 63. The sum of the back focal lengths of the microlens 61-2 and the microlens 62-2 is equal to zero, i.e., a fiber-integrated Galilean telescope is formed.
In FIG. 8c, 61-3 is a convex lenticule 61 with a length of 250 μm and a focal length of 465.59 μm; 62-3 is a micro-concave lens 62 with a length of 200 μm and a focal length of-706.48 μm. 63 is a free space with a length of 500. mu.m. The incident plane wave propagates in the fiber-integrated microlens set, converges and exits at the rear end face of the microlens 62-3, and propagates in the free space 63. The sum of the back focal lengths of the micro lens 61-3 and the micro lens 62-3 is not equal to zero, so that the fiber integrated micro lens group with the equivalent focal length is formed.
In FIG. 8d, 61-4 is a convex lenticule 61 with a length of 250 μm and a focal length of 465.59 μm; 62-4 is a micro-concave lens 62 with a length of 500 μm and a focal length of-375.34 μm. 63 is a free space with a length of 500. mu.m. The incident plane wave propagates in the fiber-integrated microlens set, diverges and exits at the rear end face of the microlens 62-4, and propagates in the free space 63. The sum of the back focal lengths of the micro lens 61-4 and the micro lens 62-4 is not equal to zero, so that the fiber integrated micro lens group with the equivalent focal length is formed.
The invention discloses a fiber integrated micro lens group, mainly provides a preparation method of an optical fiber micro lens, and simultaneously constructs the fiber integrated micro lens group in an optical fiber. Compared with the prior art, the fiber integrated micro-lens group can be constructed in the optical fiber due to the adoption of the thermal diffusion technology, and the fiber integrated micro-lens group can be prepared in batch at low cost and high efficiency.
The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto. Various modifications and alterations of this invention will occur to those skilled in the art in view of the spirit and scope of this invention and are intended to be encompassed by the following claims.
Claims (7)
1. A fiber integrated microlens assembly. The method is characterized in that: it is formed by connecting two sections of optical fibers which are prepared by thermal diffusion and have refractive index distribution of circular symmetric quasi-Gaussian distribution and circular symmetric reverse quasi-Gaussian distribution respectively. The fiber integrated micro-lens group is formed by placing optical fibers in a constant temperature field, preparing and connecting the optical fibers through thermal diffusion, and after the fiber core dopant of the optical fibers is diffused, the refractive index distribution is changed into quasi-Gaussian distribution with symmetrical circumference, so that the fiber integrated micro-lens group can be equivalent to a micro-convex lens; the refractive index distribution becomes a circumferentially symmetric reverse quasi-Gaussian distribution, and can be equivalent to a micro-concave lens.
2. The fiber-integrated microlens assembly of claim 1, which is prepared and bonded by placing the optical fiber in a constant temperature field, and performing thermal diffusion. The temperature of the constant temperature field is above 1000 ℃.
3. The fiber-integrated microlens set according to claim 1, wherein the length of the thermally diffused optical fiber is cut after heating and diffusing in a constant temperature field for a certain time, so that the micro convex lenses and the micro concave lenses with different focal lengths can be prepared.
4. The fiber-integrated microlens set of claim 1, wherein the optical fiber with different parameters can be selected, including initial refractive index profile, dopant species, numerical aperture, etc. of the optical fiber. After the selected optical fiber is prepared by thermal diffusion, the refractive index distribution of the optical fiber is in a circumferentially symmetrical quasi-Gaussian distribution or a circumferentially symmetrical reverse quasi-Gaussian distribution.
5. The fiber-integrated microlens assembly as claimed in claim 1, wherein the two microlenses with the same focal length are connected, and the sum of the back focal lengths (the distance from the focal point to the second surface) of the two microlenses is equal to zero, thereby forming the fiber-integrated Galilean telescope.
6. The fiber integrated microlens assembly as claimed in claim 1, wherein the two microlenses with different focal lengths are connected such that the sum of the back focal lengths (the distance from the focal point to the second surface) of the two microlenses is not equal to zero, thereby forming the fiber integrated microlens assembly with an equivalent focal length.
7. The method for manufacturing a fiber-integrated microlens assembly according to claim 1, comprising the steps of:
1) selecting initial parameters of the optical fiber
The optical fiber is prepared by thermal diffusion, and the refractive index distribution of the optical fiber is circularly symmetric quasi-Gaussian distribution or circularly symmetric reverse quasi-Gaussian distribution.
2) Performing thermal diffusion treatment on the optical fiber
And (3) putting the 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 optical fiber into stable circularly symmetric quasi-Gaussian distribution or circularly symmetric reverse quasi-Gaussian distribution.
3) Cutting the optical fiber after thermal diffusion
The optical fiber after thermal diffusion is cut in a fixed length, and optical fiber micro convex lenses or micro concave lenses with different focal lengths can be prepared.
4) And welding the two sections of optical fibers after thermal diffusion
And welding the two sections of the optical fiber micro convex lenses and the micro concave lenses after cutting with fixed length to form the fiber integrated micro lens group.
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Application publication date: 20200911 Assignee: Jianuo (Tianjin) Technology Development Co.,Ltd. Assignor: GUILIN University OF ELECTRONIC TECHNOLOGY Contract record no.: X2023980045809 Denomination of invention: A Fiber Integrated Microlens Group Granted publication date: 20220325 License type: Common License Record date: 20231107 |