A micro-lens array based fiber core diameter parabolic transformation structure

Abstract

This invention belongs to the field of optical technology, specifically relating to a fiber core diameter-preserving focal ratio conversion structure based on a microlens array, comprising a large-core-diameter fiber, a microlens array, and several small-core-diameter fibers. The large-core-diameter fiber, the microlens array, and the several small-core-diameter fibers are connected sequentially from left to right. The light emitted from the large-core-diameter fiber is refracted by the microlens array and enters each small-core-diameter fiber. The microlens array is composed of several microlens units, the number of which corresponds to the number of small-core-diameter fibers. Each microlens unit has an equilateral hexagonal cross-sectional shape. The circumcircle diameter of each microlens unit is... d 3 is smaller than the output beam diameter of a large-core fiber. d 1. The diameter of the inscribed circle of the microlens array d 2 is greater than the output beam diameter of a large-core fiber. d 1. This invention enables a method for optical field transformation using microlens arrays, achieving low-loss, focus-preserving coupling transmission between large and small core diameter optical fibers.

Description

Technical Field

[0001] This invention belongs to the field of optical technology, specifically relating to an optical fiber core diameter-preserving focal ratio transformation structure based on a microlens array. Background Technology

[0002] Since its invention, optical fiber has rapidly transformed information transmission, becoming a crucial medium for humanity's entry into the information society. Optical fibers are categorized into many types, including single-mode fiber, multimode fiber, and large-core fiber, each with its own distinct applications.

[0003] Since fiber optic technology was first applied to astronomical observation in the late 1970s, its applications have become increasingly widespread, especially in the field of astronomical spectroscopic observation. Performance optimization of astronomical spectroscopic observation systems involves multi-parameter coordinated control, with each key element having a systematic impact on spectral quality: the telescope aperture determines the diffraction spot size, thus limiting fiber coupling efficiency; in multi-target observation, the focal plane positioning device must employ high-precision measurement techniques to ensure alignment between the fiber and the star image; when observing extended-source targets, the integrating field of view unit needs to optimize the matching relationship between the fiber core diameter and the aperture stop; the transmission performance of large-scale optical fibers is constrained by the cable design and manufacturing process, requiring control of focal ratio degradation and transmission loss; core influencing factors at the spectrometer end include the matching degree between the entrance slit width and the fiber arrangement accuracy, diffraction grating parameters (determining spectral range and resolution), and performance indicators such as the pixel size of the CCD detector.

[0004] With advancements in technology and the deepening of scientific research, spectroscopic observation (or imaging) is receiving increasing attention from astronomers. Many astronomical spectroscopic systems use optical fibers as the transmission medium, but the choice of fiber core diameter presents a dilemma: a desire to use large-diameter fibers at the telescope end to improve energy coupling efficiency, while a desire to use small-diameter fibers at the spectrometer end to improve spectral resolution.

[0005] In large-scale spectroscopic surveys, hundreds or even thousands of large-core optical fibers are placed on the focal plane of a telescope to simultaneously receive the spectra of a large number of target stars, greatly improving the efficiency of spectroscopic observation. To meet the seeing requirements at the telescope's focal length, these fibers often have relatively large core diameters; however, when these fibers transmit starlight to the spectrometer, the excessively large core diameter reduces the spectrometer's spectral resolution. To ensure spectral resolution, it is sometimes necessary to sacrifice light intensity by adding slits at the fiber optic exit ends. This approach significantly reduces the signal-to-noise ratio when the target star is weak. Summary of the Invention

[0006] The purpose of this invention is to provide a fiber core diameter-preserving focal ratio transformation structure based on a microlens array, which can realize optical field transformation by using a microlens array to achieve low-loss, focal ratio-preserving coupling transmission between large and small core diameter fibers.

[0007] The specific technical solution adopted by this invention is as follows: A fiber core diameter-preserving focal ratio conversion structure based on a microlens array includes a large-core fiber, a microlens array, and several small-core fibers. The large-core fiber, the microlens array, and the several small-core fibers are connected sequentially from left to right. The light emitted from the large-core fiber is refracted by the microlens array and enters each small-core fiber. The microlens array is composed of several microlens units, the number of which corresponds to the number of small-core optical fibers, and the cross-sectional shape of each microlens unit is an equilateral hexagon.

[0008] Furthermore, the circumcircle diameter of the microlens unit d 3 is smaller than the output beam diameter of a large-core fiber. d 1. The diameter of the inscribed circle of the microlens array d 2 is greater than the output beam diameter of a large-core fiber. d 1.

[0009] Furthermore, several small-core optical fibers are positioned by any method such as stacking, insertion, or capillary positioning. The position of each small-core optical fiber corresponds to a microlens unit, and the assembly of all small-core optical fibers is aligned and fixed at the rear end of the microlens array.

[0010] Furthermore, several of the small-core optical fibers are fixed in a capillary glass tube and bonded to the rear end of the microlens array.

[0011] Furthermore, the diameter of the surface coating layer on each of the small-core optical fibers... D 2 is smaller than the inscribed circle diameter of the microlens array d 2. The numerical aperture of each small-core fiber is not less than the numerical aperture of the large-core fiber.

[0012] Furthermore, the end face of the microlens unit near the large-core fiber is an eccentric refractive spherical structure.

[0013] Furthermore, the core diameter of the small-core optical fiber... D 1 is greater than the diameter of the exit pupil spot that converges at the rear end face of the microlens array.

[0014] Furthermore, the end face of the microlens array is coated with an antireflective film for the working band.

[0015] The technical effects achieved by this invention are as follows: The fiber core diameter-preserving focal ratio conversion structure based on microlens array of the present invention uses microlenses to divide the emitted light spot of a large core diameter fiber into many parts. The required fiber core diameter is smaller than the diameter of the emitted light spot of the large core diameter fiber, thereby reducing the fiber core diameter at the incident end of the spectrometer and improving the spectral resolution.

[0016] The fiber core diameter focal ratio conversion structure based on microlens array of the present invention can design microlens units at each position individually, so that the light spot emitted from the large core diameter fiber is coupled into the small core diameter fiber with the same incident focal ratio after being converged by the microlens array. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a cross-sectional schematic diagram of the microlens array of the present invention; Figure 3 This is a schematic diagram of the cross-section of the small-core-diameter optical fiber of the present invention; Figure 4 This is a schematic diagram of the beam of the large-core fiber emitted by the present invention propagating in the cross-section of the core diameter conversion device; Figure 5 This is a schematic diagram of the object-image relationship corresponding to the microlens unit of the present invention; Figure 6 This is a schematic diagram of the imaging surface calculation model of the outermost ring microlens unit of the present invention.

[0018] The attached diagram lists the components represented by each number as follows: 1. Large-core fiber; 2. Microlens array; 3. Small-core fiber; 4. Microlens at the center of the microlens array; 5. Fiber at the center of the small-core fiber; 6. Outermost fiber of the small-core fiber. Detailed Implementation

[0019] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0020] like Figures 1-6 As shown, a fiber core diameter-preserving focal ratio conversion structure based on microlens array includes a large core diameter fiber 1, a microlens array 2 and several small core diameter fibers 3. The large core diameter fiber 1, the microlens array 2 and the several small core diameter fibers 3 are connected sequentially from left to right. The light emitted from the large core diameter fiber 1 is refracted by the microlens array 2 and enters each small core diameter fiber 3. The microlens array 2 is composed of several microlens units, the number of which corresponds to the number of small-core optical fibers 3, and the cross-sectional shape of each microlens unit is an equilateral hexagon.

[0021] like Figure 2 As shown, the side length of the microlens unit m The output beam diameter of large-core fiber 1 d 1. Related to the circumcircle diameter of the microlens unit. d3 is smaller than the output spot diameter of a large-core fiber. d 1. Diameter of the inscribed circle of the microlens array 2 d 2 is larger than the output beam diameter of a large-core fiber. d 1.

[0022] The mathematical relationship is as follows: ; Several small-core optical fibers 3 are positioned by any method such as stacking, insertion, or capillary positioning. The position of each small-core optical fiber 3 corresponds to a microlens unit, and the assembly of all small-core optical fibers 3 is aligned and fixed at the rear end of the microlens array 2.

[0023] Several small-core optical fibers 3 are fixed in a capillary glass tube and bonded to the rear end of the microlens array 2.

[0024] In astronomical applications, the distribution of the light field emitted from the large-core fiber 1 will vary depending on the alignment between the large-core fiber 1 and the star image. Consequently, the energy coupled to the different small-core fibers 3 will differ. By comparing the energy of each small-core fiber 3, information can be provided to some extent regarding the alignment effect between the large-core fiber 1 and the star image.

[0025] The surface coating diameter of each small-core optical fiber 3 D 2 is smaller than the inscribed circle diameter of the microlens array 2 d 2. The numerical aperture of each small-core fiber 3 is not less than the numerical aperture of the large-core fiber 1.

[0026] The end face of the microlens unit near the large-core fiber 1 is an eccentric refractive spherical structure.

[0027] In this system, the microlens unit images the emitting end of the large-core fiber 1, with the imaging position located on the rear surface of the microlens array 2. Maintaining a constant fiber focal ratio does not mean that the emission angle of the large-core fiber 1 and the incident angle of the small-core fiber 3 are the same, but rather that the maximum refraction angle within the fiber is the corresponding angle. Figure 4 The beam angles inside the medium-to-large core diameter fiber 1 and the small core diameter fiber 3 should be the same. To achieve a constant focal ratio, each microlens surface needs to be designed individually.

[0028] A series of eccentric refractive spherical surfaces can be used, such as Figure 4 As shown, to achieve the desired focal ratio data, taking the outermost microlens unit as an example, the line connecting the optical axes from the large-core fiber 1 to the small-core fiber 3 is the dashed line in the figure, and the corresponding refracting sphere corresponds to the black curve on the outer unit of the microlens array 2. In order to achieve the best refraction effect, we can choose to realize the ideal fourth-order aspherical equation corresponding to the equal optical path between the center of the large-core fiber 1 and the center of the small-core fiber 3.

[0029] The core diameter of small-diameter optical fiber 3 D 1 is greater than the diameter of the exit pupil spot that converges at the rear end face of the microlens array 2.

[0030] like Figures 4-5 As shown, the imaging process of the central microlens in microlens array 2: Will Figure 4 The fiber associated with the central microlens is marked separately. Analyzing the object-image relationship corresponding to this microlens, we can choose a microlens and a small-core fiber 3 made of the same or similar materials, thus ignoring light refraction and reflection at their interface. Figure 5 It can be seen that, in order to maintain the focal ratio, the maximum refraction angle of light in the large-core fiber 1 should be the same as that in the small-core fiber 3, which is... u '.

[0031] Based on the imaging formula of a microlens single-refractive sphere and lateral magnification β The formula: ; ; In the formula, and These are the focal lengths of the microlens units in the image side (which can be quartz) and the object side (usually air), respectively. and These are the image distance and the object distance, respectively. and These are the refractive indices on the image side and the object side, respectively.

[0032] Therefore, the core diameter of small-core fiber 3 D 1 can be larger than the diameter of the image spot formed by the microlens unit of the large core diameter fiber 1.

[0033] like Figure 6 As shown, for the microlens of the outer ring, in order to ensure that the incident focal ratio of the small-core fiber 3 does not degrade, the central axis of the incident cone of each fiber should be perpendicular to the surface of the small-core fiber 3. Figure 4 The first in i Taking a microlens with an outer ring as an example, a microlens surface with a hexagonal outer frame but an aspherical shape is required. The left side of this surface can be air (refractive index...). n =1), the right side can be quartz (refractive index =1), To ensure that the emitting end of the large-core fiber 1 can be better imaged onto the core of the small-core fiber 3, we first analyze the light rays emitted from the center of the core of the large-core fiber 1, the origin O, which travel to a point P on the refractive surface and then refracts towards the refracting point. i Small-core optical fiber 3 centers The coordinates of each point are given in the diagram. Therefore, according to Fermat's principle, the corresponding optical path length is... A constant value can achieve equal optical path imaging.

[0034] ; This is based on O and The rotationally symmetric aspherical surface of the Cartesian oval line with the base point is then intercepted as follows: Figure 6 The hexagonal part in the equation can satisfy the condition from O to... Equal optical path imaging.

[0035] The same method can be used to derive the morphology equations of all microlenses (different small-core fiber 3 corresponds to different optical axes and different Cartesian ovoids), thereby achieving low-loss, focus-preserving imaging.

[0036] The end face of the microlens array 2 is coated with an anti-reflection film for the working band to reduce light energy loss caused by reflection from the component surface.

[0037] Furthermore, in practical applications, a multi-ring hexagonal microlens array 2 can be selected, for example, 3 rings with 19 microlenses (such as...). Figure 1 , 2 (As shown). If the core diameter of the incident large-core fiber 1 is 250 micrometers, the output focal ratio is... F / 5, the spacing between the large-core fiber 1 and the microlens array is Millimeters, with air in between. n =1. The microlenses are made of selectively fused silica with a refractive index of 1. The core diameter of the small-core fiber 3 connected to the rear end of the microlens is 100 micrometers, resulting in an imaging magnification of -0.4. To ensure that the microlens array 2 can cover the diameter of the emitted light spot... The diameter of the inscribed circle of the microlens array 2 is at least millimeters. d 2= d 1 = 0.2 mm, from which the minimum side length of the hexagonal microlens unit can be calculated. Millimeters. To ensure that the (equivalent from air) incident focal ratio of the small-core fiber 3 is also... F / 5, and since this structure conforms to paraxial optics, the required length of the quartz microlens unit is Millimeters. Furthermore, the surface profile of each microlens unit can be calculated using a formula where the optical path is constant, thus achieving focus ratio transformation.

[0038] Another application is where the incident large-core fiber 1 is a few-mode fiber, while the corresponding small-core fiber 3 is a single-mode fiber, thus achieving mode decomposition. This structure can be used in various single-mode fiber spectral demodulators, including integrated spectral demodulators. Of course, this structure can also be used in space-to-space and space-to-terrestrial laser communications, allowing a larger laser spot to enter several single-mode fibers, thereby increasing the intensity of the received signal and suppressing noise.

[0039] Since the large-core fiber 1 and the star image (or laser communication image) may not be perfectly aligned, more higher-order modes are excited. As a result, the energy distribution of the subsequent small-core fibers 3 will show a higher proportion in the outer ring. This can also be fed back as a reference signal to adjust the position of the telescope end of the large-core fiber 1.

[0040] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A fiber core diameter-preserving focal ratio conversion structure based on a microlens array, characterized in that: It includes a large-core fiber (1), a microlens array (2) and several small-core fibers (3), which are connected sequentially from left to right. The light emitted from the large-core fiber (1) is refracted by the microlens array (2) and enters each small-core fiber (3). The microlens array (2) is composed of several microlens units, the number of microlens units corresponds to the number of small core optical fibers (3), and the cross-sectional shape of each microlens unit is an equilateral hexagon.

2. The fiber core diameter-preserving focal ratio conversion structure based on a microlens array according to claim 1, characterized in that: The circumcircle diameter of the microlens unit d 3. The diameter of the emitted light spot is smaller than that of a large core diameter optical fiber (1). d 1. The diameter of the inscribed circle of the microlens array (2) d 2. Larger core diameter fiber (1) output spot diameter d 1.

3. The fiber core diameter-preserving focal ratio conversion structure based on a microlens array according to claim 1, characterized in that: Several small-core optical fibers (3) are positioned by any method such as stacking, insertion, or capillary positioning. The position of each small-core optical fiber (3) corresponds to a microlens unit. The assembly of all small-core optical fibers (3) is aligned and fixed at the rear end of the microlens array (2).

4. The fiber core diameter-preserving focal ratio conversion structure based on a microlens array according to claim 3, characterized in that: Several small-core optical fibers (3) are fixed in a capillary glass tube and bonded to the rear end of the microlens array (2).

5. The fiber core diameter-preserving focal ratio conversion structure based on a microlens array according to claim 1, characterized in that: The surface coating diameter of each of the small-core optical fibers (3) D 2 is smaller than the inscribed circle diameter of the microlens array (2). d 2. The numerical aperture of each small-core fiber (3) is not less than the numerical aperture of the large-core fiber (1).

6. The fiber core diameter-preserving focal ratio conversion structure based on a microlens array according to claim 1, characterized in that: The end face of the microlens unit near the large-core fiber (1) is an eccentric refractive spherical structure.

7. The fiber core diameter-preserving focal ratio conversion structure based on a microlens array according to claim 1, characterized in that: The core diameter of the small-diameter optical fiber (3) D 1 is greater than the diameter of the exit pupil spot that converges at the rear end face of the microlens array (2).

8. The fiber core diameter preserving focal ratio transformation structure based on a microlens array according to claim 1, characterized in that: The end face of the microlens array (2) is coated with an anti-reflection film for the working band.

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