CN100417961C - Microlens and Optical Fiber Integration Method Based on Focused Ion Beam Technology - Google Patents

Abstract

The method for realizing integration of the micro lens and the optical fiber by the focused ion beam technology directly inputs the geometric parameters of the designed micro lens into a computer to control and focus the ion beam spot of 10 nanometers to be written into and processed or added with materials layer by layer point according to a certain track, belongs to a one-step manufacturing method, avoids the graph transfer procedure from photoresist to a substrate, which is necessary in the laser direct writing method, the electron beam scanning direct writing method and the optical scribing method reported in the past, and reduces the accumulated manufacturing error, thereby greatly improving the control precision in the manufacturing process of the micro optical element. The invention can be made into an integrated lens optical fiber in one step, and has important application value for developing and developing a micro-photoelectric system and analyzing and monitoring instruments to be miniaturized and compact.

Description

Microlens and Optical Fiber Integration Method Based on Focused Ion Beam Technology

technical field

The invention relates to a new method for integrating a microlens and an optical fiber by adopting a one-step manufacturing technology of a focused ion beam, that is, a method for integrating a microlens and an optical fiber based on a focused ion beam technology.

Background technique

"Fiber optic lens" has been widely used in optical measurement, environmental monitoring, biochemical analysis and other fields, especially in the development and development of micro-optical systems that have been favored in recent years. As early as the early 1980s, G. Eisenstein of the Crawford Hill Laboratory in the United States used chemical etching to produce micro-axicons at the core of the single-film fiber end (G. Eisenstein, and D. Vitello, "Chemically etched conical microlenses for coupling single-mode lasers into single-mode fibers." Applied Optics 21(19), 3470-3474(1982)). In the nearly 30 years before and after, methods such as arc melting, laser processing, and photopolymerization have come out one after another (D. Kato, "Light coupling from asstrip-geometry GaAs diode laser into an optical fiber with a spherical end." J.Appl.Phys.44, 2756-2758(1973)), H.M.Presby, A.F.Benner, and C.A.Edwards, "laser micromachining of efficient fiber microlenses," Appl.Opt.29, 2692-2695(1990), Renaud Bachelot, Carole Ecoffet, etc. "Integration of micrometer-sized polymer elements at the end of optical fibers by free-radical photopolymerization," Appl. Opt. 40(32), 5860-5871(2001)).

The Center for Precision Engineering and Nanotechnology, Nanyang Technological University, Singapore, and the State Key Laboratory of Microfabrication Optical Technology, Institute of Optoelectronic Technology, Chinese Academy of Sciences, have jointly developed a new method of integrating microlenses and optical fibers. The application prospects brought by the microlens-fiber integration method for precise control have led many famous universities and research institutes to carry out exploratory research in this area. But so far, there have been no reports at home and abroad on the one-step fabrication technology of focused ion beams to achieve precise control of microlenses and optical fiber integration methods, and there are few related technical details.

There are two common deficiencies in the reported traditional integration methods: one is that it is difficult to achieve precise control of the micro-lens surface, and the other is that it is impossible to achieve the integration of micro-diffraction structures. Although Italy's M.Prasciolu et al. reported in 2003 that the electron beam etching method was used to make a diffractive structure at the end of the fiber (M.Prasciolu, D.Cojoc, S.Cabrini, etc. "Design and fabrication of on-fiber diffractive elements for fiber-waeguide coupling by means of e-beamlithography," Microelectronic Engineering, 67-68, 169-174 (2003)), but a pattern transfer process is still required to transfer the photoresist pattern to the end of the optical fiber.

Contents of the invention

The technical problem of the present invention is: to overcome the deficiencies of the prior art, and to propose a microlens and optical fiber integration method based on focused ion beam technology that can realize one-step fabrication and precise control.

The technical solution of the present invention is: the integrated method of microlens and optical fiber based on focused ion beam technology is completed through the following steps:

(1) First select the microlens material and perform calibration;

(2) Design microlenses for integration according to system requirements, such as spherical, aspheric, ellipsoidal, cylindrical, diffractive lens, blazing light, sinusoidal grating, etc.;

(3) Select the optical fiber, and strip the outer plastic cladding of the optical fiber to a distance of about 5mm from the end face;

(4) discretize the data of the microlens continuous curved surface designed in step (2), and write out the control program for machine automatic operation according to the discretized data, calibration data, and production process parameters;

(5) polishing the end of the optical fiber cut in step (3) with a special polishing machine until the surface roughness is below 2 nanometers;

(6) Fix the processed optical fiber in a special fixture, put it into the focused ion beam vacuum chamber, and keep the optical fiber perpendicular to the worktable;

(7) Use the focused ion beam to observe the optical fiber imaging and adjust the core and verticality;

(8) Set the initial parameters of the machine operation and the operating mode (etching mode or deposition mode), and run the design program in step (4), to complete one-step etching production or deposition production;

(9) adopt interferometer to measure the geometric parameter of microlens;

(10) Performance testing of microlens-fiber integration (focusing characteristics, collimating characteristics, and coupling efficiency).

The continuous curved surface of the microlens of the design is approximated by discrete multi-steps, and different steps correspond to different etching depths or deposition heights, and the discrete step distance depends on the specific lens design size, such as annulus The width is 3-10 microns, and the discrete step is 0.5 microns; if the ring width is 1-3 microns, the discrete step is 0.15 microns; if the ring width is 10-20 microns, the discrete step is 0.8 microns; Band width > 20 microns, discrete step is 1 micron. The whole production process is controlled by computer programming, and the initial parameters of machine operation are set, such as ion beam energy, beam current density, worktable height, worktable tilt angle, field of view, ion residence time, and beam spot overlap in X and Y directions etc., then call the design program and start the machining process. Since the optical fiber material is quartz, which is a non-metallic insulator, a positive charge neutralizer (called Flood Gun in the Micrion 9500EX machine) must be used during processing. Some commercial focused ion beam machines do not have this configuration, such as FEI Quanta 2003D. Due to the particularity of the position of the end of the optical fiber, the geometric size of the lens cannot be measured with an atomic force microscope, and a non-contact optical interferometer is a more suitable measurement tool, such as the WYKO NT2000 interferometer. The optical performance test of the integrated microlens can be realized by lapping devices such as a beam profiler, a light source, a coupling between a microscopic objective lens and an integrated optical fiber, and a precision three-dimensional moving stage.

Compared with the prior art, the present invention has the advantages that the designed microlens geometric parameters are directly input into the computer to control the 4 spots of the focused ion beam (which can be focused to a minimum of 10 nanometers) and are processed point by point according to a certain trajectory. It is a one-step production method (see Figure 1), which avoids the necessary pattern transfer process from photoresist to substrate in the previously reported laser direct writing method, electron beam scanning direct writing method and optical scribing method , reducing the cumulative manufacturing error, thereby greatly improving the control precision in the microlens production process; in addition, the high deflection scanning control precision of the focused ion beam can be used to realize the precise control of the microlens surface. The integration of various conventional microlenses (spherical, aspheric, ellipsoidal, cylindrical, diffractive lens, blazed grating, sinusoidal grating, etc.) 3-1, Figure 3-2, and Figure 5). The ion beam direct assisted deposition technology of the present invention is a one-step manufacturing method based on the principle of material addition, and deposits layer by layer according to the selected deposition thickness of the optimized design, and the deposition material is usually selected as silicon dioxide (see Fig. 4, Fig. 6, and Fig. 7). The whole process can be programmed or manually controlled. This method successfully realizes the direct single-step fabrication of refractive micro-spherical, cylindrical, and ellipsoidal lenses. Using this method, micro-optical sensors, micro-spectrometers, micro-biochemical analyzers, and micro-sensors for small satellite payloads can be made, which provides an important basis for the research and development of micro-optical systems, as well as the miniaturization and compactness of analytical monitoring instruments. and effective means.

Description of drawings

Fig. 1 is the schematic diagram of the direct writing method of the focused ion beam of the present invention;

Figure 2-1 and Figure 2-2 are schematic diagrams of the focused ion beam directly written into the diffractive lens of the present invention;

Fig. 3-1 and Fig. 3-2 are the principle diagrams of integrating the miniature refracting lens 8 and the diffractive lens 3 at the fiber end 2 by the direct writing method of the focused ion beam 4 of the present invention;

Fig. 4 is the schematic diagram of the integrated miniature refracting lens 9 at the fiber end 2 by the direct deposition method of the focused ion beam 4 of the present invention;

Fig. 5 is a flow chart of making a diffractive optical element of the present invention;

Fig. 6 is the production flowchart of microlens deposition method of the present invention;

Fig. 7 is a principle diagram of the layer-by-layer deposition of the direct deposition method of the present invention.

Detailed ways

Example 1

As shown in Figure 5, the production flow chart of diffractive optical elements,

The integration of the miniature diffractive lens made by the method of the present invention and the multimode optical fiber is as follows:

(1) Use fused silica material for calibration, that is, find out the linear relationship between the ion dose and the corresponding etching depth;

(2) Strip the outer plastic cladding 1 of the optical fiber 2 to a distance of about 5 mm from the end face, and design a miniature diffractive optical element 3 with a continuous relief structure (see Figure 1, Figure 2-1, 2-2 and Figure 3-2 ) surface two-dimensional profile discretization, such as designing a micro-diffraction lens with a diameter of 67 microns, its discrete step distance is 0.5 microns, and according to discretized data, such as diameter and corresponding depth, calibration data of step (1), and Etching process parameters, such as ion beam energy, beam current density, processing field of view, ion dose, etc. Write computer 6 operation control program;

(3) Polish the end of the cut multimode fiber 2 (see Figure 1 and Figure 3) with a special polishing machine until the surface roughness is below 2 nanometers (Ra value), and the surface at this time can be measured with a WYKO interferometer roughness;

(4) Fix the processed optical fiber in a special fixture and put it into the focused ion beam vacuum chamber. The optical fiber should be kept perpendicular to the worktable (for the convenience of processing, multiple optical fibers can be clamped at one time);

(5) Use the focused ion beam 4 (see Fig. 1, Fig. 3-1 and 3-2) to observe the image of the optical fiber 2 and adjust the core and verticality (which can be realized by tilting the workbench);

(6) Set the working mode of the machine to etching mode, and set the initial parameters of the machine operation, such as ion beam energy, beam density, table height, table tilt angle, field of view, ion residence time, and X and Y beam spot overlap in the direction, etc.;

(7) Start the positive charge neutralizer (not shown in the figure), call and run the design program, and complete one-step etching production;

(8) Take out the optical fiber, and use the WYKO interferometer to measure the depth of the three-dimensional profile, the relief width and its symmetry, the surface roughness of the relief structure, etc.;

(9) Testing the focusing or collimating characteristics of the integrated lens fiber.

Example 2

Refer to Figure 4 for direct principle of microlens, process flow chart 6 for deposition method, and Figure 7 for layer-by-layer deposition principle of direct deposition method.

The integration of the micro-refractive lens (spherical lens) and the multimode optical fiber made by the method of the present invention (material addition method for direct deposition of focused ion beams) is as follows:

(1) Use silicon dioxide (SiO ₂ ) material for calibration, that is, to find out the linear relationship between the ion dose and the corresponding deposition thickness;

(2) Strip the distance from the outer plastic cladding 1 of the optical fiber 2 to the end face by about 5 millimeters, and discretize the surface two-dimensional profile of the designed micro-spherical lens 8 (see FIG. 4 ), such as designing a micro-refractive lens with a diameter of 65 microns. The discrete step is 0.5 micron, and according to the discretized data, the diameter and the height of the corresponding spherical cap, the calibration data in step (1), and the etching process parameters, such as ion beam 4 energy, beam current density, processing field of view, Write computer operation control program for ion dose, etc.;

(3) Polish the end of the cut multimode optical fiber 2 (see FIG. 4 ) with a special polishing machine, and the straight surface roughness is below 2 nanometers (Ra value), and the surface roughness at this time can be measured by a WYKO interferometer;

(4) Fix the processed optical fiber 2 in a special fixture, and then put it into a focused ion beam vacuum chamber. The optical fiber should be kept perpendicular to the worktable (for the convenience of processing, multiple optical fibers can be installed at one time);

(5) Use the focused ion beam 4 (see FIG. 4 ) to observe the image of the optical fiber 2 and adjust the core and verticality (which can be realized by tilting the workbench);

(6) The working mode of the machine is set to the deposition mode, silicon dioxide (SiO ₂ ) is selected as the deposition material, the height of the workbench is set to the deposition position (32 mm from the emission surface of the ion chamber 5), and the initial parameters of the machine operation are set, Such as ion energy, beam current density, table tilt angle, field of view, ion residence time, and beam spot overlap in X and Y directions, etc. (the overlap is 0, and the beam spot spacing is 10 times that of the etching mode);

(7) Start the gas source injection device 9 (see Figure 4) to call and run the design program, the chemical gas 10 (TMCTS+H ₂ O) is decomposed and deposited on the end of the optical fiber under the action of the ion beam, and completes the step of the microlens 8 Deposition production. The post-processing procedure (included in the operation program) here is the key of the whole deposition process, as shown in Figure 7 (covering layer 12, the size is identical with the bottom first layer 11), it determines the final profile of deposition lens 8 and Surface roughness;

(8) Take out the optical fiber, and use the WYKO interferometer to measure the diameter of the three-dimensional profile, the height of the spherical cap, the surface roughness of the spherical cap, and the symmetry of the spherical cap;

(9) Testing the focusing or collimating characteristics of the integrated lens fiber.

Claims (5)

1. The microlens and optical fiber integration method based on focused ion beam technology can be realized through the following main steps: (1) First select the microlens material and perform calibration; (2) Design microlenses for integration according to system requirements; (3) Select the optical fiber, and strip the outer plastic cladding of the optical fiber to a distance of about 5mm from the end face; (4) Discretize the data of the continuous curved surface of the microlens designed in step (2), and write out the control program for the automatic operation of the machine according to the discretized data, calibration data, and production process parameters; (5) polishing the end of the optical fiber cut in step (3) with a special polishing machine until the surface roughness is below 2 nanometers; (6) Fix the processed optical fiber in a special fixture, put it into the focused ion beam vacuum chamber, and keep the optical fiber perpendicular to the worktable; (7) Use the focused ion beam to observe the optical fiber imaging and adjust the core and verticality; (8) Set the initial parameters and operation mode of machine operation, the operation mode here is etching mode or deposition mode, and run the design program in step (4), complete one-step etching production or deposition production; (9) Measure the geometric parameters of the microlens by using an interferometer; (10) Finally, the performance test of the microlens-fiber integration. 2. The microlens and optical fiber integration method based on focused ion beam technology according to claim 1, characterized in that: the material in the step (1) is fused silica. 3. The microlens and optical fiber integration method based on focused ion beam technology according to claim 1, characterized in that: the material in the step (1) is silicon dioxide. 4. The microlens and optical fiber integration method based on focused ion beam technology according to claim 1, characterized in that: the continuous curved surface of the designed microlens in the step (4) is formed by discrete multi-step approximation of. 5. the microlens and optical fiber integration method based on focused ion beam technology according to claim 1, is characterized in that: in described step (10), performance test comprises the optical performance to focusing characteristic, collimating characteristic and coupling efficiency test.

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