A multi-focal focusing optical device based on a fiber facet and a method for manufacturing the same

Abstract

The application discloses a kind of multi-focal focusing light devices based on optical fiber end face and preparation method thereof, and multi-focal focusing light device includes optical fiber and focusing unit array on optical fiber end face substrate, the focusing unit array includes several densely arranged focusing units, each focusing unit includes several two-dimensional plane phase elements, each phase element is filled by a circular column, the diameter of circular column in the same focusing unit is same, height is different, the diameter of circular column in different focusing units can be different, the circular column is densely arranged, the phase element is used to independently regulate and control incident light beam, and the thickness of the focusing unit is nanometer order of magnitude.The application is implemented in optical fiber end face to realize multi-focal focusing, reduces process difficulty, and can be widely applied in optical device technical field.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, and in particular to a multifocal focusing optical device based on an optical fiber end face and its fabrication method. Background Technology

[0002] Fiber optic end-face devices refer to miniature devices with specific optical functions fabricated on the end face of optical fibers. These devices achieve certain optical functions and utilize optical fibers as the medium for light transmission and collection, reducing signal loss during transmission. Numerous applications based on optical field manipulation have already been implemented on fiber optic end-face platforms, such as typical endoscopes, particle trapping, and optical imaging. Their advantage lies in their greater flexibility in application scenarios compared to traditional optical components. Leveraging the unique properties of optical fibers—light weight, small size, strong optical confinement, and high-efficiency long-distance transmission—application scenarios can be expanded to more complex areas. Achieving beam focusing by fabricating structures on the fiber end face that control the phase and amplitude of the light beam, and creating a focused light field with a large divergence angle, is key to realizing fiber optic tweezers technology.

[0003] However, single-focus fiber optic end-face focusing devices have limited functionality and low efficiency, only capable of endoscopy at a single location or capture within a single focal point. In the traditional field of fiber optic end-face focusing, achieving simultaneous operation of multiple focal points requires more complex designs and fabrication processes; if not effectively combined, this can negatively impact focusing performance. In recent years, various design schemes have been proposed to achieve multifocal focusing in the field of beam focusing. For example, maskless ultraviolet lithography is used to fabricate superlens arrays; inkjet printing technology is used to realize microlens focusing arrays, and so on. However, these microlens arrays are on the order of micrometers in size, and the fabrication processes are numerous and complex. Achieving multifocal focusing functionality at fiber optic end-faces using existing multifocal focusing design principles remains challenging, hindering further improvements in the functionality and performance of fiber optic end-face multifocal focusing devices. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a multi-focus optical device based on the fiber end face and its fabrication method, so as to achieve multi-focus focusing on the fiber end face and reduce the difficulty of the process.

[0005] On one hand, embodiments of the present invention provide a multi-focus optical device based on an optical fiber end face, including an optical fiber and a focusing unit array located on a substrate of the optical fiber end face. The focusing unit array includes a plurality of densely arranged focusing units, each focusing unit including a plurality of two-dimensional planar phase elements, each phase element being filled by a circular pillar. The circular pillars in the same focusing unit have the same diameter but different heights, while the diameters of the circular pillars in different focusing units may be different. The circular pillars are densely arranged, and the phase elements are used to independently control the incident beam. The thickness of the focusing unit is on the nanometer scale.

[0006] Optionally, the phase of the phase element satisfies the following formula:

[0007] in, The phase of the phase element is represented. Denotes the order of the Taber fraction. Indicates the conversion factor. and Indicates the position of the phase element.

[0008] Optionally, the height of the circular pillar in the phase element satisfies the following formula:

[0009] in, It is the height of the circular column. It is the phase of the phase element. It is the refractive index of the cylindrical material. The wavelength of the incident beam is denoted as λ.

[0010] Optionally, the material of the focusing unit includes photoresist, which comprises a photoinitiating material with visible light absorption spectral characteristics and monomer materials constituting the polymer.

[0011] Optionally, the optical fiber includes a fusion-spliced ​​single-mode fiber and a beam expander fiber, with one end of the beam expander fiber connected to the single-mode fiber and the other end of the beam expander fiber serving as the fiber end face substrate.

[0012] Optionally, the beam expanding fiber includes multimode fiber or hollow fiber.

[0013] Optionally, the cross-section of the phase element comprises a regular polygon, wherein the regular polygon comprises a regular hexagon.

[0014] Optionally, the focal length of the multifocal focusing optical device satisfies the following formula:

[0015]

[0016] in, Indicates focal length. Denotes the order of the Taber fraction. Indicates the diameter of the circular cylinder. The wavelength of the incident beam is denoted as λ.

[0017] On the other hand, embodiments of the present invention provide a method for fabricating a multi-focus focusing optical device based on an optical fiber endface, comprising: Photoresist was coated onto the fiber end face substrate and then covered with a cover glass plate. The photoresist-coated fiber end face substrate is fixed to the fiber controller, the three-dimensional coordinate information of each circular pillar in all two-dimensional planar phase elements in the focusing unit array is determined, and the three-dimensional coordinate information is imported into the three-dimensional micro-translation stage. The pre-processed laser beam is controlled to be focused onto the photoresist on the fiber end face substrate by a two-dimensional galvanometer and an objective lens at preset time intervals. The three-dimensional micro-translation stage is controlled to move according to the three-dimensional coordinate information, while the two-dimensional galvanometer is controlled to vibrate according to preset requirements so that the laser beam rotates in a circle according to a preset radius.

[0018] Optionally, the fiber end face substrate is prepared by the following method: One end of the single-mode fiber and one end of the beam expander fiber are fused together. The other end of the beam expanding fiber is cut to make the beam expanding fiber reach a preset length, and the other end of the cut beam expanding fiber is used as the fiber end face substrate.

[0019] The implementation of this invention provides the following advantages: In this invention, the multi-focus optical device based on the fiber end face includes an optical fiber and a focusing unit array located on the fiber end face substrate. The focusing unit array includes several densely arranged focusing units, each focusing unit including several two-dimensional planar phase elements, each phase element being filled by a circular pillar. The circular pillars in the same focusing unit have the same diameter but different heights, while the diameters of the circular pillars in different focusing units can be different. The thickness of the focusing unit is on the nanometer scale. The phase is adjusted by adjusting the height of the circular pillars in the same focusing unit, and multiple different focal lengths are adjusted by adjusting the Talbot fractional parameter and the diameter of the circular pillars in different focusing units, thereby achieving multi-focus focusing at the fiber end face. In addition, based on two-photon polymerization processing technology, the size of the multi-focus optical device is precisely controlled by a processing method combining two-dimensional galvanometers and three-dimensional micro-translation stages, allowing direct processing of the multi-focus optical device structure on the fiber end face, thus reducing the difficulty of the process. Attached Figure Description

[0020] Figure 1This is a schematic diagram of the structure of a multifocal focusing optical device and focusing unit provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a multifocal focusing optical device and optical fiber provided in an embodiment of the present invention; Figure 3 These are cross-sectional and perspective views of a single focusing unit provided in an embodiment of the present invention; Figure 4 This is a characterization optical path diagram of a multifocal focusing optical device provided in an embodiment of the present invention; Figure 5 This is a focus pattern and parameter statistics chart provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of a stepped focusing structure and a test result diagram provided by an embodiment of the present invention; Figure 7 This is a schematic diagram of a multi-focus deflection focusing array provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the fabrication system for a multifocal focusing optical device provided in an embodiment of the present invention; Figure 9 This is a schematic flowchart of a method for fabricating a multi-focus focusing optical device according to an embodiment of the present invention; Figure 10 This is a schematic diagram of the structure of a multi-focal focusing optical device provided in an embodiment of the present invention; Figure 11 These are SEM images of a single focusing unit and cross-sectional views of a multifocal focusing optical device provided in embodiments of the present invention. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only for ease of explanation and do not limit the order of the steps. The execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.

[0022] like Figure 1 As shown, Figure 1 (a) shows a top view of a multifocal focusing optical device. Figure 1(b) represents a three-dimensional view of a single focusing unit. An embodiment of the present invention provides a multi-focus focusing optical device based on an optical fiber end face, including an optical fiber and a focusing unit array 1-2 located on the substrate of the optical fiber end face. The focusing unit array includes a plurality of densely arranged focusing units 1-1. Each focusing unit includes a plurality of two-dimensional planar phase elements. Each phase element is filled by a circular pillar. The circular pillars in the same focusing unit have the same diameter but different heights. The diameters of the circular pillars in different focusing units may be different. The circular pillars are densely arranged. The phase elements are used to independently control the incident beam. The thickness of the focusing unit is on the nanometer scale.

[0023] It should be noted that the number, size, and arrangement of focusing units on the fiber end face substrate are determined based on the actual application, as are the diameter and height of the circular cylinders. For example, the cross-sectional size of a single focusing unit is tens of micrometers, and the maximum height of the cylinder is 1.2 μm.

[0024] Phase is controlled by adjusting the height and Talbo fraction order of the circular pillars in the same focusing unit; multiple different focal lengths are adjusted by adjusting the diameter and Talbo fraction parameters of the circular pillars in different focusing units; and angle deflection is achieved by superimposing deflection phases in different focusing units.

[0025] Optionally, the optical fiber includes a fusion-spliced ​​single-mode fiber and a beam expander fiber, with one end of the beam expander fiber connected to the single-mode fiber and the other end of the beam expander fiber serving as the fiber end face substrate.

[0026] Optionally, the beam expanding fiber includes multimode fiber or hollow fiber.

[0027] Specifically, the propagation formula of the light beam in the expanded fiber is as follows: (1) in, It is the mode field diameter, and z is the longitudinal distance with the fusion splice point between the single-mode fiber and the beam expander fiber as the zero point. It is the beam waist radius of the incident light. , This is the Rayleigh criterion, where n is the refractive index of the medium (fiber core). In this embodiment, the mode field diameter is chosen to be 2. It is 75µm. According to the above formula, the length of the expanded fiber cut is 700µm. Figure 2 (a) is a cross-sectional view of the fiber end face. Figure 2 (b) is a cross-sectional view of a multi-focusing array based on an all-dielectric fiber endface. Figure 2The image shows an array of 19 focusing units arranged in a dense pattern. Multiple focusing units are densely arranged on the fiber end face, and the number of focusing units can be increased or decreased at will according to actual application requirements.

[0028] Optionally, the phase of the phase element satisfies the following formula: (2) (3) in, The phase of the phase element is represented. Denotes the order of the Taber fraction. Indicates the conversion factor. and Represents the position coordinates of the phase primitive.

[0029] See Figure 3 The entire focusing unit is hexagonal, and within the focusing unit plane, it is "split" laterally into several two-dimensional planar phase element points. The position of each phase element point is determined by (u... n v n Once the position is determined, the phase of the primitive is also determined by the above formula. Figure 3 The phase diagram of the focusing unit is shown in (a). =15, the shade of color represents the phase size of each phase element.

[0030] Optionally, the height of the circular pillar in the phase element satisfies the following formula: (4) in, It is the height of the circular column. It is the phase of the phase element. It is the refractive index of the cylindrical material. The wavelength of the incident beam is denoted as λ.

[0031] Figure 3 Figure (b) is a three-dimensional structural diagram of the focusing unit. Each phase element is filled with a fully dielectric circular pillar. The phase of the phase element is adjusted by the optical path difference of the circular pillars; the diameters of these circular pillars are the same and are determined by the lateral dimensions of the phase element.

[0032] In one specific embodiment, wavelength =600nm, photoresist refractive index 1.5, cylinder diameter 350nm, according to the phase information obtained in phase formula (2)-(3), and according to the above formula (4), the height of the cylinder required for each primitive point is calculated.

[0033] Optionally, the material of the focusing unit includes photoresist, which comprises a photoinitiating material with visible light absorption spectral characteristics and monomer materials constituting the polymer.

[0034] The thickness of the focusing unit array and the diameter of the cylinder are both on the nanometer scale. Because photoresist has low absorption and high light transmittance in the visible light region, photoresist is selected as the material for the focusing unit. The focusing unit structure is obtained by femtosecond laser processing, and the entire focusing array optical element is placed on the end face of the optical fiber.

[0035] Optionally, the cross-section of the phase element comprises a regular polygon, wherein the regular polygon comprises a regular hexagon.

[0036] Figure 4 This is a representation of the optical path of a fiber optic end-face multifocal focusing array. The optical path includes: a pulsed laser 4-1, a three-dimensional fiber optic controller 4-2, an optical fiber 4-3, an end-face multifocal focusing array 4-4, an objective lens 4-5, a lens 4-6, and an image sensor 4-7. In a specific embodiment, the pulsed laser 1 is a 500-680 nm wavelength continuous-wave laser, and the continuous-wave laser 4-1 can be replaced by a picosecond laser or a nanosecond laser under certain conditions. The incident beam emitted by the pulsed laser 4-1 couples into the optical fiber 4-3, propagates within the fiber 4-3, and then passes through the end-face multifocal focusing array 4-4 fabricated on the end face of the fiber, generating a multifocal array pattern. This pattern is collected by the image sensor 4-7. The three-dimensional fiber optic controller 4-2 is used to fix the optical fiber 4-3, and the objective lens 4-5 and lens 4-6 are used to focus the light beam.

[0037] Figure 5 (a) is a schematic diagram of the obtained multifocal array. Figure 5 (b) is a Figure 5 Statistical results of intensity and full width at half maximum (FWHM) for each focal point in (a). Figure 5 The intensity of the focal spot in (b) is uniform, and the full width at half maximum (FWHM) of each focal spot is close to the diameter of the column, 350 nm, and is stable within a very small range.

[0038] Optionally, the focal length of the multifocal focusing optical device satisfies the following formula:

[0039]

[0040] in, Indicates focal length. Denotes the order of the Taber fraction. Indicates the diameter of the circular cylinder. The wavelength of the incident beam is denoted as λ.

[0041] Figure 6 Figure (a) is a schematic diagram of a specific implementation of stepped focusing, where the focal length of each focusing unit is independently adjusted by changing the fractional order of the fractional Talbot effect and the diameter of the circular cylinder. Figure 6 In (a), the parameters of the focusing elements located at the center, inner ring, and outer ring are as follows: Center: β=18, D=293nm Inner ring: β=15, D=350nm Outer ring: β=12, D=434nm Their fractional orders are 18, 15, and 12, respectively. Considering the need for dense arrangement, it is necessary to ensure that the total size of each focusing unit is equal. Therefore, after calculation, the diameters of the corresponding cylinders are 293nm, 350nm, and 434nm, respectively.

[0042] Figure 6 A schematic diagram of the multifocal array with stepped focal lengths obtained in (b). The focal length of focusing plane i is 2.91 μm, the focal length of focusing plane ii is 3.45 μm, and the focal length of focusing plane iii is 4.24 μm.

[0043] Figure 6 (c) shows the measured full width at half maximum (FWHM) of the focal points on the three planes. The FWHM of each focal point in the realized multi-focus array is related to the diameter of the cylindrical cylinder. The FWHM of the focal point in plane i is 290 nm, the FWHM of the focal point in plane ii is 336 nm, and the FWHM of the focal point in plane iii is 429 nm. The results show that the FWHM of the focal point is approximately equal to the diameter of the cylinder; changing the diameter of the cylinder changes the FWHM of the focal point.

[0044] Figure 7 It is a deflection focusing array in a specific embodiment, which superimposes a deflection phase on the original focusing phase to achieve a deflection focusing point at a specific angle. Figure 7 (a) is the phase diagram of the deflection focusing array. Figure 7 In (a), seven focusing units are arranged closely together. In the outer ring, a 20° outward deflection phase along the axis is superimposed on the focusing phase of each focusing unit. Figure 7 (b) is a three-dimensional schematic diagram of the obtained fiber end face multi-focus deflection focusing array. Figure 7 Image (c) is an optical characterization diagram of a fiber optic endface multifocal device with deflection and focusing capabilities. Figure 7 As can be seen in (c), each focal point of the outer ring is not at the exact center, but rather offset outwards. Due to the difference in focal plane between the exact center and the outer ring, and because the equivalent numerical aperture of oblique focusing is larger than that of normal focusing, the focusing intensity is weaker, and the focal width (FWHM) is wider.

[0045] In one specific embodiment, the processing equipment for multifocal focusing optical devices based on fiber endfaces, such as... Figure 8 As shown, 8-1 represents the laser, 8-2 represents the half-wave plate, 8-3 represents the optical switch, 8-4 represents the 4f lens group, 8-5 represents the spatial filter aperture, 8-6 represents the first reflecting mirror, 8-7 represents the second reflecting mirror, 8-8 represents the two-dimensional galvanometer, 8-9 represents the semi-reflective lens, 8-10 represents the objective lens, 8-11 represents the three-dimensional micro-displacement platform, 8-12 represents the end face of the optical fiber to be processed, 8-13 represents the optical fiber controller, 8-14 represents the optical fiber, 8-15 represents the third reflecting mirror, 8-16 represents the filter, 8-17 represents the convex lens, 8-18 represents the image sensor, and 8-19 represents the computer equipment. Photoresist is applied to the end face of the expanding fiber and covered with a cover glass. The photoresist-coated fiber is then fixed to the fiber optic controller, which is in turn fixed to the three-dimensional micro-translation stage. After the laser beam is emitted from the laser, it passes through a half-wave plate used to adjust the light intensity, then through an optical switch and a 4f lens group for beam expansion. During this process, the beam is filtered at a spatial filter aperture. After passing through the first and second reflecting mirrors, the laser beam reaches the two-dimensional galvanometer. After passing through the two-dimensional galvanometer, it is then focused onto the end face of the sample to be processed, which is placed on the three-dimensional micro-translation platform, by adjusting the longitudinal height of the three-dimensional micro-translation platform and the light controller. The laser beam is then focused to the designated position on the end face of the sample to be processed.

[0046] Under the action of a focused laser beam, the end face of the sample to be processed is excited with a fluorescence signal. The fluorescence signal is emitted through a cover glass and then passes sequentially through a semi-reflective lens, a third reflecting mirror, a filter 16 (which retains the fluorescence), and a convex lens 17 (which focuses the light) before entering the image sensor 18. The filter is used to filter stray light and transmit fluorescence, while the convex lens is used to focus the filtered fluorescence.

[0047] It should be noted that the computer equipment connects to an optical switch, a two-dimensional galvanometer, a three-dimensional micro-displacement platform, and an image sensor. The computer equipment is used to control the on / off state of the optical switch, the vibration of the two-dimensional galvanometer, and the movement of the three-dimensional micro-displacement platform. The computer equipment is also used to store and analyze images.

[0048] This invention provides a method for fabricating a multifocal focusing optical device based on an optical fiber end face, wherein the optical fiber end face substrate is fabricated by the following method: S010. Fusion splice one end of the single-mode fiber and one end of the beam expander fiber. S020. Cut the other end of the beam expanding fiber to make the beam expanding fiber reach a preset length, and use the cut other end of the beam expanding fiber as the fiber end face substrate.

[0049] Specifically, a fiber optic fusion splicer is used to fuse one end of a single-mode fiber with a beam expander fiber, and the other end of the beam expander fiber is cut to the desired length. In one specific embodiment, the length of the beam expander fiber after cutting is 700 μm.

[0050] It should be noted that the optical fiber used for beam expansion can be multimode fiber or hollow fiber.

[0051] This invention provides a method for fabricating a multifocal focusing optical device based on an optical fiber endface, comprising: S100. Coat the fiber end face substrate with photoresist and cover it with a cover glass.

[0052] Specifically, the end face of the expanded fiber is used as a substrate, and photoresist is directly dropped onto the end face of the expanded fiber and covered with a cover glass.

[0053] S200. Fix the photoresist-coated fiber end face substrate to the fiber controller, determine the three-dimensional coordinate information of each circular pillar in all two-dimensional planar phase elements in the focusing unit array, and import the three-dimensional coordinate information into the three-dimensional micro-translation stage.

[0054] Specifically, the optical fiber is fixed on the optical fiber controller, and the optical fiber controller is fixed on the three-dimensional micro-movement platform; the multi-focus three-dimensional structure formula model to be processed is divided into several cylinders along the horizontal plane, each cylinder consisting of a starting point and an ending point; the spatial coordinate information of all the points that are combined into the three-dimensional model structure is imported into the control system of the three-dimensional micro-movement platform.

[0055] S300 controls the pre-processed laser beam to be focused onto the photoresist on the fiber end face substrate by passing through a two-dimensional galvanometer and objective lens at preset time intervals. It controls the three-dimensional micro-translation stage to move according to the three-dimensional coordinate information, and at the same time controls the two-dimensional galvanometer to vibrate according to preset requirements so that the laser beam rotates in a circle according to a preset radius.

[0056] The laser beam is expanded, collimated, and its intensity is adjusted. The adjusted laser beam first passes through a two-dimensional galvanometer and then through an objective lens to be focused onto the photoresist at the end face of the optical fiber. The three-dimensional micro-moving platform moves along a preset motion trajectory of the control system, and the photoresist is exposed according to the preset platform motion trajectory under the illumination of the focused laser beam. While the micro-moving platform moves along the preset trajectory, the two-dimensional galvanometer vibrates in a circular motion mode. That is, the exposure trajectory of the light spot focused in the photoresist is composed of the superposition of the vibration trajectory of the two-dimensional galvanometer and the movement trajectory of the three-dimensional micro-nano micro-moving platform.

[0057] An optical switch is placed in front of the galvanometer to control the time it takes for the light beam to pass through the shutter, enter the objective lens, and focus on the processed material. The opening and closing time of this switch is determined by the time it takes for the micro-moving platform to move between two points. In the optical path, the optical shutter is either a level-triggered high-speed mechanical switch or an acousto-optic modulator.

[0058] In one specific embodiment, the laser source is a femtosecond pulsed laser with a wavelength in the visible light band. The femtosecond pulsed laser emitted by the laser source is adjusted in front of the two-dimensional galvanometer through an optical path. The objective lens is placed vertically below or above the three-dimensional micro-moving platform, and the laser beam passes through the objective lens from bottom to top or from top to bottom and is focused on a designated position in the photoresist placed on the micro-moving platform.

[0059] In one specific embodiment, the formula for the structure to be processed is generated using calculation software, and the phase represented in the formula is "split" into several two-dimensional plane phase units along the horizontal direction. Then, each phase unit in the two-dimensional plane is transformed into a cylinder of different heights, and the starting and ending coordinates (x, y, z) of the cylinder are extracted.

[0060] In one specific embodiment, after data processing, the spatial coordinate information of all points of the 3D structure to be processed is obtained and stored in the form of a txt text file. This txt text file is then loaded into the control system of the 3D micro-moving platform. The txt text file imported into the control system of the 3D micro-moving platform contains not only the coordinate information of each point of the structure to be processed, but also the on / off state of the shutter at each point, i.e., whether it is exposed or not. The coordinates of all points form a motion trajectory in sequence, and the platform moves according to the motion trajectory. The photoresist is exposed according to the on / off state at the focal point. The data processing software is MATLAB, and the control system of the processing platform is programmed using LabVIEW.

[0061] In one specific embodiment, the single focused 3D structure being processed is arranged in a hexagonal pattern, and the multi-focused 3D array structure to be processed can be arbitrarily densely arranged using multiple single-focus 3D structures.

[0062] See Figure 10 , Figure 10 In diagram (a), the galvanometer undergoes two-dimensional planar circular vibration (represented by dashed lines), while the vertically upward solid lines represent the movement trajectory of the micro-movement platform. During the processing, the galvanometer and the micro-movement platform move simultaneously, and their superimposed motion trajectories determine the exposure trajectory of the photoresist. The rotation radius r of the galvanometer determines the diameter of the processed cylinder, and the starting point of the platform's movement path (…). , , and the endpoint ( , , Determine the height of the cylinder to be machined. Figure 10Image (b) shows an array of cylinders with different cylinder heights and radii processed using the method of this invention. In practical applications, the processing parameters can be adjusted according to actual processing requirements to obtain the desired structural dimensions.

[0063] In one specific embodiment, see Figure 11 , Figure 11 (a) shows the structure diagram of a single focusing unit. Figure 11 (b) shows a cross-sectional view of a multifocal focusing optical device. Figure 11 In (a) the Talbot fractional order of the multifocal focusing optical device is 15, the pillar diameter requirement is 350 nm, the processing parameters are laser power 2.5 mw, platform moving speed 50 μm / s, and galvanometer vibration radius 65 nm. Figure 11 In the middle (b), 19 focusing lenses are arranged in a hexagonal honeycomb pattern.

[0064] The implementation of this invention provides the following advantages: In this invention, the multifocal focusing optical device based on the fiber end face includes an optical fiber and a focusing unit array located on the fiber end face substrate. The focusing unit array includes several densely arranged focusing units, each focusing unit including several two-dimensional planar phase elements, each phase element being filled by a circular pillar. The circular pillars in the same focusing unit have the same diameter but different heights, while the diameters of the circular pillars in different focusing units can be different. The thickness of the focusing unit is on the nanometer scale. The phase is adjusted by adjusting the height of the circular pillars in the same focusing unit, and multiple different focal lengths are adjusted by adjusting the diameter and Talbot fractional order of the circular pillars in different focusing units, thereby achieving multifocal focusing at the fiber end face. In addition, based on two-photon polymerization processing technology, the size of the multifocal focusing optical device is precisely controlled by combining a two-dimensional galvanometer and a three-dimensional micro-translation stage, allowing the multifocal focusing optical device structure to be directly processed on the fiber end face, reducing the manufacturing difficulty.

[0065] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A multifocal focusing optical device based on an optical fiber endface, characterized in that, The device includes an optical fiber and a focusing unit array located on the substrate at the end face of the optical fiber. The focusing unit array includes several densely arranged focusing units. Each focusing unit includes several two-dimensional planar phase elements. Each phase element is filled by a circular pillar. The circular pillars in the same focusing unit have the same diameter but different heights. The diameters of the circular pillars in different focusing units may be different. The circular pillars are densely arranged. The phase elements are used to independently control the incident beam. The thickness of the focusing unit is on the nanometer scale. The phase of the phase element satisfies the following formula: in, The phase of the phase element is represented. Denotes the order of the Taber fraction. Indicates the conversion factor. and Indicates the position of the phase element; The height of the circular pillar in the phase element satisfies the following formula: in, It is the height of the circular column. It is the phase of the phase element. It is the refractive index of the cylindrical material. The wavelength of the incident beam is denoted as λ.

2. The multifocal focusing optical device according to claim 1, characterized in that, The material of the focusing unit includes photoresist, which comprises a photoinitiating material with visible light absorption spectral characteristics and monomer materials constituting the polymer.

3. The multifocal focusing optical device according to claim 1, characterized in that, The optical fiber includes a fused single-mode fiber and a beam expander fiber, one end of which is connected to the single-mode fiber, and the other end of which serves as the fiber end face substrate.

4. The multifocal focusing optical device according to claim 3, characterized in that, The beam expander fiber includes multimode fiber or hollow fiber.

5. The multifocal focusing optical device according to claim 1, characterized in that, The cross-section of the phase element comprises a regular polygon, which includes a regular hexagon.

6. The multifocal focusing optical device according to claim 1, characterized in that, The focal length of the multifocal focusing optical device satisfies the following formula: in, Indicates focal length. Denotes the order of the Taber fraction. Indicates the diameter of the circular cylinder. The wavelength of the incident beam is denoted as λ.

7. A method for fabricating a multifocal focusing optical device based on an optical fiber endface, characterized in that, The multifocal focusing optical device according to any one of claims 1-6 comprises: Photoresist was coated onto the fiber end face substrate and then covered with a cover glass plate. The photoresist-coated fiber end face substrate is fixed to the fiber controller, the three-dimensional coordinate information of each circular pillar in all two-dimensional planar phase elements in the focusing unit array is determined, and the three-dimensional coordinate information is imported into the three-dimensional micro-translation stage. The pre-processed laser beam is controlled to be focused onto the photoresist on the fiber end face substrate by a two-dimensional galvanometer and an objective lens at preset time intervals. The three-dimensional micro-translation stage is controlled to move according to the three-dimensional coordinate information, while the two-dimensional galvanometer is controlled to vibrate according to preset requirements so that the laser beam rotates in a circle according to a preset radius.

8. The preparation method according to claim 7, characterized in that, The fiber end face substrate is prepared by the following method: One end of the single-mode fiber and one end of the beam expander fiber are fused together. The other end of the beam expanding fiber is cut to make the beam expanding fiber reach a preset length, and the other end of the cut beam expanding fiber is used as the fiber end face substrate.

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