CN108562980B - A kind of production method of the fiber transverse plane coupler for microstrip probe - Google Patents

Abstract

A manufacturing method of an optical fiber end-face coupler for a microstrip probe, comprising the following steps: (1) generating an oxide layer on a silicon wafer by a thermal oxidation method; (2) on the oxide layer in step (1) depositing a layer of sacrificial layer; (3) using a vacuum evaporation coating method, a metal film is plated on the sacrificial layer in step (2) to form a metal screen; (4) spin coating photolithography on the metal screen in step (3) (5) UV exposure and development of the photoresist to form a slot; (6) Insert the optical fiber into the slot and fix it; (7) Remove the sacrificial layer, and separate the optical fiber end-face coupler from the silicon wafer; (8) Use Focused ion beam etching technology produces mounting holes on the metal screen for the assembly of microstrip probes. The invention enables the microstrip probe to be coupled and connected to the transmission optical fiber, improves the excitation energy efficiency of the plasmon, greatly reduces the difficulty of system adjustment, and promotes the practical application of the microstrip probe.

Description

A kind of manufacturing method of optical fiber end-face coupler for microstrip probe

technical field

The invention belongs to the field of photoelectric detection based on micro-probes, and in particular relates to a manufacturing method of an optical fiber end-face coupler for micro-strip probes.

Background technique

Microprobes mostly refer to optical microstructure probes used in the field of high-precision photoelectric detection, such as the commonly used optical fiber probes. The fiber probe is directly processed at the end of the fiber, directly connected to the fiber, or even a part of the fiber. It is very convenient to form a system by using a mature diode laser system and a fiber laser to generate the required Gaussian beam. , detection of micro-area size and many other deficiencies. The microstrip probe based on the metal-insulator-metal waveguide structure is a recently proposed new type of microprobe, which is essentially a surface plasmon-based nanostructure with high local excitation energy efficiency, small size, and low loss. Etc. Microstrip probes can achieve resolution beyond the diffraction limit, so they have good application prospects in the fields of super-resolution imaging, optical communication, and ultra-high-density data storage. Once the microstrip probe was proposed, it aroused the interest of many researchers, and they carried out theoretical and experimental studies to verify its superiority (S. Kawata, Y. Inouye, P. Verma, Plasmonics for near-field nanometers) -imaging and superlensing, 2009, Nat. Photonics 3, 388–394), which has the advantage of short metallization in the metal-insulator-metal waveguide structure, so the losses are very low; in addition, the energy efficiency of the plasmonic excitation is high. The biggest disadvantage is that it is very difficult to connect with the transmission channel of light energy and cannot achieve practical purposes. Therefore, it is very important to invent a novel coupling device that can couple and connect the microstrip probe to the transmission fiber, and has high optical energy coupling efficiency, simple structure and easy implementation, which can effectively promote the practical application of the microstrip probe. Super-resolution optical systems, biological detection, optical communication and other fields play a role.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies in the prior art that the optical system used to excite plasmons by direct laser irradiation is very complicated to adjust, has poor versatility, and has low optical energy coupling efficiency and cannot be practically applied, the present invention provides an optical system for The manufacturing method of the optical fiber end-face coupler of the microstrip probe enables the microstrip probe to be coupled and connected to the transmission optical fiber, improves the excitation energy efficiency of the plasmon, greatly reduces the difficulty of system adjustment, and promotes the practical application of the microstrip probe .

The technical scheme adopted by the present invention to solve its technical problems is:

A manufacturing method of an optical fiber end-face coupler for a microstrip probe, the manufacturing method comprising the following steps:

(1) generating an oxide layer on a silicon wafer by thermal oxidation;

(2) depositing a sacrificial layer on the oxide layer of step (1);

(3) using vacuum evaporation coating method, on the sacrificial layer of step (2), a metal film is plated to form a metal face screen;

(4) spin coating photoresist on the metal face screen of step (3);

(5) UV exposure and development are carried out to the photoresist to form a slot, the shape of the slot is a cylindrical shape, and the diameter of the slot is the same as the outer diameter of the optical fiber to be inserted;

(6) Insert the optical fiber into the slot and fix it;

(7) Remove the sacrificial layer, and separate the optical fiber end-face coupler from the silicon wafer;

(8) Using the focused ion beam etching technology to process the mounting holes for the microstrip probe assembly on the metal screen.

Further, in the step (1), the process of thermal oxidation preparation is as follows: removing the natural oxide layer on the surface of the silicon wafer, using HF/H etching solution, immersing the cleaned wafer in the etching solution for about 1 minute and taking out, using Rinse the surface of the wafer with deionized water and blow it dry; put it into the tube vacuum furnace and set the temperature parameters; put the silicon wafer into the center of the tube furnace, fasten the connecting flanges on both sides of the furnace tube, and open the oxygen cylinder; start the tube Type furnace, start thermal oxidation growth of silicon dioxide film; after the growth is completed, take out.

Still further, the sacrificial layer of the step (2) adopts an electrochemical deposition process.

Further, in the step (3), a vacuum coating method is used to grow a metal face screen, and the shape of the metal face screen is a circle.

The metal face screen is an aluminum face screen, and the melting point of the aluminum sheet is relatively low, and is heated by a resistance heating method.

In the step (4), the photoresist is SU-8 photoresist, and a slot is prepared on the SU-8 photoresist by means of ultraviolet lithography, so that the central area of the cylindrical SU-8 photoresist is formed. It is hollowed out but not penetrated. At this time, the slot is connected to the optical fiber, the outer side of the cup bottom is connected to the metal screen, and the metal screen is connected to the silicon substrate through the sacrificial layer and the silicon dioxide oxide layer; when the sacrificial layer is dissolved, the coupler is connected. Separated from the silicon wafer.

In the step (8), the installation hole is a square hole, and a square hole is machined on the metal screen by using the focused ion beam etching technology. The square hole must pass through the aluminum screen, and its size is determined by the microstrip probe. size is determined.

In the step (5), the slot is a cup-shaped slot, the outer surface of the cup bottom of the cup-shaped slot is a smooth plane, and a layer of metal film is grown on the smooth plane to form the metal face screen.

The technical idea of the present invention is as follows: firstly, an aluminum panel is formed on a silicon wafer by thermal oxidation and vacuum evaporation; Further, use UV glue to fix the optical fiber inserted into the cup-shaped slot, remove the sacrificial layer, and separate the optical fiber end-face coupler from the silicon wafer; finally, a square hole of the designed size is processed in the aluminum screen.

The beneficial effects of the invention are mainly manifested in: (1) the microstrip probe is directly coupled and connected to the optical fiber through a coupler like a common optical fiber probe, the structure is simple, and the use is convenient; (2) the local excitation energy efficiency of the plasmon (3) The metallization size of the microstrip probe is short, so the loss is very low; (4) It is convenient to combine with the existing commercial semiconductor lasers to form a high-power Gaussian beam, so as to realize its practical application and meet the requirements of the microstrip probe. Applications in super-resolution optical systems, biological detection and other fields.

Description of drawings

Figure 1 is a schematic diagram of the three-dimensional structure of an optical fiber end-face coupler, wherein 1 represents an optical fiber, 2 represents a cup-shaped slot, 3 represents a metal screen, and 4 represents a square hole on the metal screen.

Figure 2 is a schematic diagram of the structural design of the optical fiber end-face coupler, wherein (a) is a view on the side where the optical fiber is inserted, (b) is a view on the side where the microstrip probe is inserted, (c) is a top view of the optical fiber end-face coupler, and d ₁ represents The inner diameter of the cup-shaped slot, d ₂ represents the outer diameter of the cup-shaped slot; a represents the length of the square hole on the metal panel, u represents the width of the square hole on the metal panel; L ₁ represents the optical fiber embedded in the cup-shaped slot Length, L ₂ represents the total length of the cup body of the cup slot, L ₃ represents the thickness of the metal face screen, L ₄ represents the cup bottom thickness of the cup slot, L ₅ , t and b represent the length of the microstrip probe respectively , the thickness of the metal layer and the thickness of the insulator.

FIG. 3 is a schematic diagram of the aluminum panel deposited in the manufacturing step (3), wherein 5 represents a silicon substrate, and 6 represents an oxide layer and a sacrificial layer.

4 is a schematic diagram of the structure of the SU-8 photoresist produced by spin coating in the manufacturing step (4), wherein 5 represents a silicon substrate, and 6 represents an oxide layer and a sacrificial layer.

FIG. 5 is a schematic diagram of a cup-shaped socket formed after ultraviolet photolithography in the manufacturing step (5), wherein 5 represents a silicon substrate, and 6 represents an oxide layer and a sacrificial layer.

FIG. 6 is a schematic view of the structure after the optical fiber is fixed by UV glue in the manufacturing step (6), wherein 5 represents a silicon substrate, and 6 represents an oxide layer and a sacrificial layer.

FIG. 7 is a schematic diagram of the separation of the optical fiber end-face coupler from the silicon wafer in the manufacturing step (7), wherein 5 represents the silicon substrate, and 6 represents the oxide layer and the sacrificial layer.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

1 to 7 , a method for manufacturing an optical fiber end-face coupler for a microstrip probe, the material of the cup-shaped slot is photoplastic epoxy type SU-8 photoresist, and the material of the metal film is Aluminum material, the manufacturing method includes the following steps:

(1) generating an oxide layer on a silicon wafer by thermal oxidation;

(2) depositing a sacrificial layer on the oxide layer of step (1);

(3) using vacuum evaporation coating method, on the sacrificial layer of step (2), aluminized film is formed to form an aluminum face screen;

(4) spin coating SU-8 photoresist on the aluminum face screen of step (3);

(5) SU-8 photoresist is subjected to ultraviolet exposure and development to form a slot, the shape of the slot is a cylindrical shape, and the diameter of the slot is the same as the outer diameter of the optical fiber to be inserted;

(6) Insert the optical fiber into the slot and fix it with UV glue;

(7) Remove the sacrificial layer, and separate the optical fiber end-face coupler from the silicon wafer;

(8) Using the focused ion beam etching technology, the designed size of the mounting hole for the microstrip probe to be assembled is machined on the aluminum panel.

In the step (1), the silicon dioxide thin film prepared by the thermal oxidation method has a compact structure, good uniformity and repeatability. Specific steps: remove the natural oxide layer on the surface of the silicon wafer, use HF/H etching solution, immerse the cleaned wafer in the etching solution for about 1 minute, take it out, rinse the wafer surface with deionized water and blow dry; Vacuum furnace and set temperature parameters. Put the silicon wafer into the center of the tube furnace, fasten the connecting flanges on both sides of the furnace tube, and open the oxygen cylinder. Start the tube furnace and start the thermal oxidation growth of the silicon dioxide film; after the growth is completed, take it out.

The sacrificial layer in the step (2) adopts an electrochemical deposition process.

In the step (3), a vacuum coating method is used to grow the aluminum face screen, the shape of the aluminum face screen is a circle, the melting point of the aluminum sheet is relatively low, and the resistance heating method is used for heating.

In the step (4), a method of ultraviolet photolithography is used to prepare a cup-shaped slot on the SU-8 photoresist, so that the central area of the cylindrical SU-8 photoresist is hollowed out but not penetrated, similar to the shape of a cup. The purpose of the cup-shaped slot is to allow the optical fiber to be inserted into it and held in place with UV glue. At this time, the cup-shaped slot is connected to the optical fiber, the outer side of the cup bottom is connected to the aluminum panel, and the aluminum panel is connected to the silicon substrate through the sacrificial layer and the silicon dioxide oxide layer. Dissolving the sacrificial layer separates the coupler from the silicon wafer.

In the step (8), the installation hole is a square hole, and a square hole is processed on the aluminum panel by using the focused ion beam etching technology. The square hole must pass through the aluminum panel, and its size is determined by the microstrip probe. The size of the microstrip probe is determined so that the microstrip probe can be inserted directly into the square hole.

In the step (5), the slot is a cup-shaped slot, the outer surface of the cup bottom of the cup-shaped slot is a smooth plane, and a layer of metal film is grown on the smooth plane to form the metal face screen.

The optical fiber end-face coupler for the microstrip probe in this embodiment is composed of a metal screen 3 and a cup-shaped slot 2 . The shape of the cup-shaped slot 2 is cylindrical, and its diameter is the same as the outer diameter of the optical fiber 1 . The outer surface of the cup bottom of the cup-shaped slot 2 is a smooth plane, and a layer of metal film is grown on the smooth plane to form the metal screen 3 . A square hole 4 is opened in the center of the metal face screen, and the square hole 4 penetrates the entire metal film. The optical fiber 1, the metal screen 3, the cup-shaped slot 2, and the microstrip probe must be on the same optical axis.

The material of the cup-shaped socket 2 is preferably a photoplastic epoxy type SU-8 photoresist.

The material of the metal thin film is preferably an aluminum material.

The square hole 4 on the metal screen 3 is for fixing the microstrip probe. The metal screen is used to suppress the background radiation, and the purpose of suppressing the background radiation is to reduce the interference of the background radiation during the scanning detection of the microstrip probe and increase the detection accuracy.

The size of the square hole 4 is determined by the size of the microstrip probe, and at the same time, the size of the square hole on the metal faceplate is such that only the TE ₁₀ mode can propagate in the square hole.

The size of the cup-shaped slot 1 is determined by the size of the optical fiber coupled with the microstrip probe, so that the cup-shaped slot can just fix the optical fiber, and the outer plane of the cup bottom of the cup-shaped slot is in line with the tape. Metal face screens with square holes are connected, and the square holes fix the microstrip probe, and the overall effect is to couple and connect the microstrip probe to the optical fiber.

The structure size of the microstrip probe, the thickness of the metal film, and the size of the square hole 4 on the metal screen are calculated by the following formulas:

in:

w=b/2, u=b/2+t

Among them, γ is the complex propagation constant, ω is the angular frequency of the electromagnetic wave, ε _d represents the dielectric constant of silicon dioxide material, ε _m represents the dielectric constant of aluminum material, ε _a represents the dielectric constant of air, b represents the microstrip The thickness of the insulator in the probe, t is the thickness of the metal layer in the microstrip probe, h is the magnetic field strength function, c _{eff_1 is} the energy transfer function, and P and P ₀ are the radiant energy flow before and after the metal screen, respectively.

Further, the optical energy is transmitted into the optical fiber end-face coupler through the optical fiber, and the plasma of the microstrip probe structure is excited by the method of end-face coupling.

The optical fiber end-face coupler used for the microstrip probe in this embodiment is composed of an aluminum screen and a cup-shaped slot made of photoplastic SU-8 photoresist material. The shape of the cup-shaped slot is cylindrical, the diameter d ₁ of which is the same as the outer diameter of the optical fiber, and the optical fiber is inserted into the cup-shaped slot so that it is just inserted into the cup-shaped slot. The outer surface of the cup bottom of the cup-shaped slot is a smooth plane, and a layer of metal aluminum film is grown on the smooth plane to form the aluminum surface screen. The outer diameter _d2 of the photoplastic SU-8 photoresist cup-shaped slot is equal to the diameter of the aluminum face screen, so the bottom surface of the SU-8 photoresist cup-shaped slot coincides with the aluminum face screen. There is a square hole running through the center of the aluminum screen. The square hole on the aluminum screen is for fixing the microstrip probe. The length a of the square hole is equal to the width of the microstrip probe, and the width u of the square hole is equal to The thickness b of the insulator in the microstrip probe, the microstrip probe can be directly inserted into the aluminum screen in actual use. Optical fiber, aluminum screen, SU-8 material cup-shaped slot, and microstrip probe must be on the same optical axis to ensure that the optical fiber is directly connected to the microstrip probe through the end-face coupler. At the same time, the laser incident from the fiber excites the plasma on the microstrip probe by means of end-face coupling.

The aluminum surface screen is used to suppress background radiation, and the purpose of suppressing background radiation is to reduce the interference of background radiation during scanning and detection of the microstrip probe and increase the detection accuracy. The size of the square hole is determined by the size of the microstrip probe, while the size of the square hole on the aluminum faceplate is such that only the TE ₁₀ mode can propagate in the square hole. The structure size of the microstrip probe, the thickness of the aluminum face screen, and the size of the square hole on the aluminum face screen are calculated by the following formulas:

in:

w=b/2, u=b/2+t

Among them, γ is the complex propagation constant, ω is the angular frequency of the electromagnetic wave, ε _d represents the dielectric constant of silicon dioxide material, ε _m represents the dielectric constant of aluminum material, ε _a represents the dielectric constant of air, b represents the microstrip The thickness of the insulator in the probe, t is the thickness of the metal layer in the microstrip probe, h is the magnetic field strength function, c _{eff_1 is} the energy transfer function, and P and P ₀ are the radiant energy flow before and after the aluminum screen, respectively.

Claims (8)

1. a method for making an optical fiber end-face coupler for a microstrip probe, characterized in that: the method for making comprises the following steps: (1) generating an oxide layer on a silicon wafer by thermal oxidation; (2) depositing a sacrificial layer on the oxide layer of step (1); (3) using vacuum evaporation coating method, on the sacrificial layer of step (2), a metal film is plated to form a metal face screen; (4) spin coating photoresist on the metal face screen of step (3); (5) UV exposure and development are carried out to the photoresist to form a slot, the shape of the slot is a cylindrical shape, and the diameter of the slot is the same as the outer diameter of the optical fiber to be inserted; (6) Insert the optical fiber into the slot and fix it; (7) Remove the sacrificial layer, and separate the optical fiber end-face coupler from the silicon wafer; (8) Using the focused ion beam etching technology to process the mounting holes for the microstrip probe assembly on the metal screen. 2. The manufacturing method of an optical fiber end-face coupler for a microstrip probe as claimed in claim 1, characterized in that: in the step (1), the process of preparing by thermal oxidation is: removing the natural oxidation on the surface of the silicon wafer layer, using HF/H etching solution, immerse the cleaned wafer in the etching solution for about 1 minute, take it out, rinse the wafer surface with deionized water and blow dry; put it in a tube vacuum furnace and set the temperature parameters; put the silicon wafer Put it into the center of the tube furnace, fasten the connecting flanges on both sides of the furnace tube, and open the oxygen cylinder; start the tube furnace, and start the thermal oxidation growth of the silicon dioxide film; after the growth, take it out. 3 . The manufacturing method of an optical fiber end-face coupler for a microstrip probe according to claim 1 or 2 , wherein the sacrificial layer in the step (2) adopts an electrochemical deposition process. 4 . 4. The manufacturing method of an optical fiber end-face coupler for a microstrip probe as claimed in claim 1 or 2, characterized in that: in the step (3), a vacuum coating method is used to grow a metal panel, and the metal panel is The shape is round. 5 . The method for manufacturing an optical fiber end-face coupler for a microstrip probe according to claim 4 , wherein the metal panel is an aluminum panel, and the aluminum sheet has a relatively low melting point and is heated by a resistance heating method. 6 . 6. The method for making an optical fiber end-face coupler for a microstrip probe according to claim 1 or 2, wherein in the step (4), the photoresist is SU-8 photoresist, and ultraviolet light is used. The method of photolithography is to prepare a slot on the SU-8 photoresist, so that the central area of the cylindrical SU-8 photoresist is hollowed out but not penetrated. At this time, the slot is connected to the optical fiber, and the outer side of the cup bottom is connected to the metal surface screen, and the metal face screen is connected to the silicon substrate through a sacrificial layer and a silicon dioxide oxide layer; dissolving the sacrificial layer separates the coupler from the silicon wafer. 7. The manufacturing method of an optical fiber end-face coupler for a microstrip probe according to claim 1 or 2, characterized in that: in the step (8), the mounting hole is a square hole, which is engraved by a focused ion beam The etching technique produces square holes in the metal faceplate, the square holes must penetrate the aluminum faceplate, and the size of the square holes is determined by the size of the microstrip probe. 8. The manufacturing method of an optical fiber end-face coupler for a microstrip probe according to claim 1 or 2, wherein in the step (5), the slot is a cup-shaped slot, and the cup The outer surface of the cup bottom of the slot-shaped slot is a smooth plane, and a layer of metal film is grown on the smooth plane to form the metal surface screen.