CN110057479B - Coating type double-layer sensitive film for FP cavity optical fiber pressure sensor and preparation method - Google Patents

Abstract

The invention relates to a coating type double-layer sensitive film for an FP cavity optical fiber pressure sensor and a preparation method thereof, and belongs to the technical field of pressure sensors. The FP cavity optical fiber pressure sensor comprises a capillary glass tube, a single-mode optical fiber and a sensitive film, wherein the single-mode optical fiber is inserted from one annular end face of the capillary glass tube, the other annular end face is fixedly connected with a coated double-layer sensitive film which covers the single-mode optical fiber, and an air cavity is formed between the single-mode optical fiber and the coated double-layer sensitive film and used as an FP cavity; the coating type double-layer sensitive film comprises a soft film and a metal hard film coated on the outer surface of the soft film, wherein the metal hard film is arranged opposite to the fiber core cross section of the single-mode fiber, the diameter of the metal hard film is equal to the diameter of the fiber core cross section of the single-mode fiber, and the diameter of the soft film is equal to the outer diameter of the annular end face of the capillary glass tube. The invention coats the metal hard film with larger elastic modulus and large reflectivity on the outer surface of the soft film with small elastic modulus to form the sensitive film with an outer coated double-layer structure, and has good deformability and reflectivity.

Description

Coated double-layer sensitive film for FP cavity optical fiber pressure sensor and preparation method

Technical field

The present invention relates to the technical field of pressure sensors, and in particular to a coated double-layer sensitive film used for FP cavity optical fiber pressure sensors and a preparation method.

Background technique

Fiber optic sensors can be used to measure many physical quantities such as pressure, strain, displacement, temperature, humidity, current, magnetic field, etc. The fiber optic pressure sensor based on FP cavity has the characteristics of high reliability, high sensitivity, resistance to harsh environments, resistance to electromagnetic interference, etc., and is widely used in aviation It has been widely used in aerospace, bridge construction, high-temperature oil wells, acoustic intraoral detection and biomedicine. Compared with traditional FP fiber optic pressure sensors, the extrinsic diaphragm FP fiber optic pressure sensor has higher sensitivity and stronger anti-interference ability. It is used in aspects such as component health monitoring, medical ultrasonic testing, and biological in vivo detection that require high-precision measurement. Has great application potential.

Most of the extrinsic diaphragm FP optical fiber sensors are composed of two mirrors of the FP cavity formed by the cut fiber end face and the sensitive diaphragm. The membrane vibrates under the action of external force, resulting in changes in the interference of the FP cavity. Through detection Interference changes can obtain changes in external pressure. Therefore, the design and processing of the sensitive diaphragm have an important impact on the overall performance of the sensor.

FP cavity optical fiber sensors based on sensitive films made of different materials and structures have been reported many times: for example, (1) Dai et al. used a single-layer graphene film as the sensitive film, combined with a single-mode optical fiber covered with a capillary tube to form an FP cavity , and then made a FP cavity fiber sensor; the sensitive film made of a single-layer graphene film has a low elastic modulus, but has a low refractive index, high cost and is easily damaged. (2) Majun et al. used multi-layer graphene as a sensitive film. The sensitive film made of multi-layer graphene has a high response between 0.2-22Khz. At the same time, as the thickness of graphene increases, the refractive index of the sensitive film increases, but Its elastic modulus increases. (3) Using photonic crystal reflectors as sensitive films has high response between 10-50Khz. The sensitive films made of photonic crystal reflectors have the characteristics of high reflectivity and high elastic modulus.

Existing sensitive films only have a single characteristic of high reflectivity or low elastic modulus, which cannot meet the requirements for actual FP cavity optical fiber pressure sensors.

Contents of the invention

In view of this, the present invention provides a coated double-layer sensitive film for FP cavity optical fiber pressure sensor and a preparation method. The sensitive film is coated with a layer of high reflectivity on the outer surface of a soft film with a small elastic modulus. Metal hard film has the characteristics of small elastic modulus and high reflectivity.

The invention provides a coated double-layer sensitive film for an FP cavity optical fiber pressure sensor. The FP cavity optical fiber pressure sensor is composed of a capillary glass tube, a single-mode optical fiber and a sensitive film. The single-mode optical fiber is formed from one end of the capillary glass tube. The annular end face is inserted, and the other annular end face of the capillary glass tube is firmly connected to the coated double-layer sensitive film covering it. An air cavity is formed between the single-mode optical fiber and the coated double-layer sensitive film as the FP cavity. The capillary glass tube The inner diameter of the annular end face is equal to the diameter of the single-mode optical fiber; the cross-sectional center of the single-mode optical fiber and the center of the sensitive membrane are both on the axis of the capillary glass tube. The core cross-section of the single-mode optical fiber and the sensitive membrane serve as two parts of the FP cavity. A cavity mirror is 90° to the axis of the capillary glass tube, forming an FP cavity interference structure.

The coated double-layer sensitive film in the present invention includes a soft film and a metal hard film plated on the outer surface of the soft film. The two form an inverted T-shaped structure. The metal hard film is opposite to the core cross-section of the single-mode optical fiber. The diameter of the membrane is equal to the diameter of the single-mode optical fiber core cross-section, and the diameter of the soft membrane is equal to the outer diameter of the annular end surface of the capillary glass tube.

Furthermore, the soft film is a rubber mold or silicone film with a smooth and smooth surface, and the soft film is preferably made of PDMS.

Further, the metal dura mater is made of gold or silver.

Further, the thickness of the soft film is 0.5-10 μm, and the thickness of the metal hard film is 10-1000 nm.

The invention also provides a method for preparing the above-mentioned plated double-layer sensitive film, which includes the following steps:

S1. Deposit an oxide layer on the substrate as a sacrificial layer, spin-coat a layer of photoresist on the oxide layer, expose the photoresist to high-energy radiation through a specific pattern on a mask, and use a developer to remove the exposed The properties of the photoresist have been changed to obtain empty grooves with a pattern corresponding to the mask. Then the remaining photoresist is used as a mask, and ICP is used to etch the entire surface, and a mark corresponding to the pattern is obtained on the oxide layer. , to facilitate the positioning of subsequent overlay steps;

S2. Apply photoresist again, and use another mask with the same mark pattern at the same position as the mask in step S1 for positioning. The mask in step S2 also has a circular pattern; go through the same process as in step 1. In the exposure and dissolution steps, a cylindrical hollow groove is formed in the photoresist, and the soft film solution is filled in the cylindrical hollow groove to prepare a soft film;

S3. Apply photoresist on the soft film again, and use another mask with the same mark pattern at the same position as the mask in step S1 for positioning. In step S3, the mask also has a circular pattern with the center of the circle. It coincides with the center of the circular pattern created on the mask in step S2; after the same exposure and dissolution steps as in step 1, a cylindrical hollow groove is formed in the photoresist, and the outer surface of the soft film is formed using electron beam evaporation technology. Coated with a metal hard coating;

S4. Remove the photoresist and substrate to prepare a plated double-layer sensitive film.

Further, in step S2, the soft film is made of PDMS, the thickness of the soft film is 0.5-10 μm, and the surface is smooth and smooth.

Further, in step S3, the metal hard film is made of gold or silver, and the thickness of the metal hard film is 10-1000 nm.

Compared with the existing technology, the technical solution of the present invention has the following beneficial effects: the coated double-layer sensitive film of the present invention coats a metal hard film with a large elastic modulus and a high reflectivity on a soft film with a small elastic modulus. The outer surface forms a double-layer composite film. This film is used as a cavity mirror of the optical fiber FP cavity. When under pressure, deformation mainly occurs on the outer soft film layer and the metal hard film layer within the diameter range of the fiber mode field. The small deformation and high reflectivity will effectively increase the number of round trips of the beam in the cavity, improve the Q value of the FP cavity and the sharpness of the reflection spectrum, thereby improving the sensitivity of the sensor.

Description of the drawings

The drawings are for the purpose of illustrating specific embodiments only and are not to be construed as limitations of the invention. Throughout the drawings, the same reference characters represent the same components.

Figure 1 is a schematic three-dimensional cross-sectional view of a FP cavity optical fiber pressure sensor based on a coated double-layer sensitive film in an embodiment of the present invention;

Figure 2 is a schematic structural diagram of the coated double-layer sensitive film in Figure 1;

3(a) to 3(k) are schematic diagrams of the manufacturing process for preparing a plated double-layer sensitive film in an embodiment of the present invention.

Reference signs:

1-Capillary glass tube; 2-Single mode optical fiber; 3-sensitive film; 31-soft film; 32-metal hard film; 4-air cavity; 5-silicon bottom; 6-silica layer; 7-photoresist .

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

The present invention provides a coated double-layer sensitive film for an FP cavity optical fiber pressure sensor. It should be noted that the FP cavity optical fiber pressure sensor is composed of a capillary glass tube 1, a single-mode optical fiber 2 and a sensitive film 3, wherein the single-mode optical fiber pressure sensor The optical fiber 2 is inserted from one annular end face of the capillary glass tube 1, and the other annular end face of the capillary glass tube 1 is firmly connected to the coated double-layer sensitive film 3 covering it, between the single-mode optical fiber 2 and the coated double-layer sensitive film 3 An air cavity 4 is formed as the FP cavity. The inner diameter of the annular end surface of the capillary glass tube 1 is equal to the diameter of the single-mode optical fiber 2; the cross-sectional center of the single-mode optical fiber 2 and the center of the sensitive film 3 are both on the axis of the capillary glass tube 1 On the top, the core cross-section of the single-mode optical fiber 2 and the sensitive film 3 serve as two cavity mirrors of the FP cavity, and are 90° with the axial direction of the capillary glass tube 1, forming an FP cavity interference structure.

The sensitive film 3 in the embodiment of the present invention is a plated double-layer sensitive film, including a soft film 31 and a metal hard film 32 plated on the outer surface of the soft mode 31. The metal hard film 32 is opposite to the core cross-section of the single-mode optical fiber 2. It is set that the diameter of the metal hard film 32 is equal to the diameter of the core cross-section of the single-mode optical fiber 2, and the diameter of the soft film 31 is equal to the outer diameter of the annular end surface of the capillary glass tube 1.

As shown in Figure 2, in a specific embodiment, the soft film 31 in the plated double-layer sensitive film 3 is made of PDMS, the metal hard film 32 is made of silver, and the surface of the PDMS soft film 31 is smooth and smooth; finally The thickness of the soft film 31 in the manufactured coated double-layer sensitive film 3 is 2.5 μm, and the thickness of the silver metal hard film 32 is 400 nm; the diameter of the PDMS soft film 31 is equal to the inner diameter of the annular end face of the capillary glass tube 1, which is 250 μm; the silver metal hard film 31 has a thickness of 2.5 μm. The diameter of the hard coat 32 is equal to the diameter of the core cross-section of the single-mode optical fiber 2, which is 10 μm.

As shown in Figure 3(a)-Figure 3(k), the preparation method of the plated double-layer sensitive film in the embodiment of the present invention is as follows:

(1) Plate a 1-3um thick silicon dioxide layer 6 on the silicon substrate 5 as a sacrificial layer, then spin-coat a thin layer of photoresist on the silicon dioxide layer 6, and cover a mask on the silicon substrate 5 On the thin layer of photoresist, a triangular marking pattern is set on the edge of the mask; UV light is used to expose the photoresist through the triangular marking pattern on the mask, and the developer is used to melt away the properties that have changed after exposure. Photoresist; remove the mask, use ICP technology to directly etch the device surface, and then remove the thin layer of photoresist to obtain a triangular mark (not shown in the figure) on the silicon dioxide layer 6 to facilitate subsequent process steps The positioning and overlaying are shown in Figure 3(a).

(2) In the area outside the triangular mark of the silicon dioxide layer 6, use a glue leveler to spin-coat a layer of 2.5 μm thick photoresist 7 on the silicon dioxide layer 6, as shown in Figure 3(b).

(3) Cover another mask on the photoresist 7. The mask in step (3) is provided with a triangular mark pattern at the same position as the mask in step (1). The triangular mark pattern of the stencil is aligned with the triangular mark pattern of the silicon dioxide layer 6 .

In step (3), a round hole with a diameter of 250 μm is also opened on the mask. UV light is used to expose the photoresist 7 through the round hole on the mask, and the developer is used to melt away the photoresist in the middle exposed part. Resistor 7, a cylindrical groove with a diameter of 250 μm is obtained in the photoresist 7, as shown in Figure 3(c).

(4) Dry the prepared PDMS solution in a vacuum oven to remove bubbles, and then use a glue leveler to spin-coat it on the silicon dioxide layer 6 and photoresist 7 so that the PDMS solution fills the 250 μm diameter in step (3). Cylindrical groove, as shown in Figure 3(d).

(5) Use a flat and smooth rubber blade to scrape the surface of the PDMS substrate laterally until the blade is in contact with the top surface of the photoresist 7. Remove the excess PDMS solution, leaving only the 250 μm diameter cylindrical groove in the photoresist. The PDMS solution is then heated to obtain a PDMS soft film 31, as shown in Figure 3(e).

(6) After the heating is completed, there is a thin solid layer on the silicon dioxide layer 6, which is etched using ICP technology, as shown in Figure 3(f).

(7) Use the glue leveler again to spin-coat a layer of photoresist 7 on the silicon dioxide layer 6 and PDMS soft film 31 in step (6), as shown in Figure 3(g).

(8) Cover another mask on the photoresist 7. The mask in step (8) is provided with a triangular mark pattern at the same position as the mask in step (1). The triangular mark pattern of the mask is aligned with the triangular mark of the silicon dioxide layer 6. In step (8), a round hole with a diameter of 10 μm is also opened on the mask. The round hole in step (8) is the same as that in step (3). The centers of the circular holes coincide.

Use ultraviolet light to pass through the round hole on the mask to expose the photoresist 7, use the developer to melt the photoresist 7 in the middle exposed part, and obtain a cylindrical groove with a diameter of 10 μm in the photoresist 7, as shown in the figure As shown in 3(h).

(9) Using electron beam evaporation technology, a layer of silver metal is plated on the PDMS soft film 31 inside the 10 μm diameter cylindrical groove and on the photoresist 7 outside the 10 μm diameter cylindrical groove. The silver metal layer serves as the metal hard film 32. The thickness is 400nm, as shown in Figure 3(i).

(10) Then turn the entire device upside down and soak it in the acetone solution, remove the excess photoresist 7 and the silver metal layer on the photoresist 7, leaving the PDMS soft film 31 on the silicon dioxide layer 6 and plated on it. The silver metal layer 7 is as shown in Figure 3(j).

(11) Use hydrofluoric acid to dissolve the silicon dioxide layer 6 to prepare a plated double-layer sensitive film, as shown in Figure 3(k).

In summary, the present invention provides a coated double-layer sensitive film for FP cavity optical fiber pressure sensor and a preparation method. The coated double-layer sensitive film coats a metal hard film with large elastic modulus and high reflectivity. A double-layer composite film is formed on the outer surface of the soft film with a small elastic modulus. This film is used as a cavity mirror of the optical fiber FP cavity. When under pressure, deformation mainly occurs on the outer soft film layer, which is in the fiber mode field. The metal hard coating layer within the diameter range has small deformation and high reflectivity, which will effectively increase the number of round trips of the light beam in the cavity, improve the Q value of the FP cavity and the sharpness of the reflection spectrum, thereby improving the sensitivity of the sensor.

The above-described embodiments and features in the embodiments herein may be combined with each other if there is no conflict.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (6)

1. A coated double-layer sensitive film for an FP cavity optical fiber pressure sensor. The FP cavity optical fiber pressure sensor is composed of a capillary glass tube, a single-mode optical fiber and a sensitive film. The single-mode optical fiber is formed from an annular end face of the capillary glass tube. Insert, the other annular end face of the capillary glass tube is firmly connected to the coated double-layer sensitive film covering it, an air cavity is formed between the single-mode optical fiber and the coated double-layer sensitive film as the FP cavity, and the annular end face of the capillary glass tube The inner diameter of the single-mode fiber is equal to the diameter of the single-mode fiber; the cross-sectional center of the single-mode fiber and the center of the sensitive film are both on the axis of the capillary glass tube. The core cross-section and sensitive film of the single-mode fiber serve as the two cavities of the FP cavity. The mirror is 90° to the axial direction of the capillary glass tube, forming an FP cavity interference structure; it is characterized in that the coated double-layer sensitive film includes a soft film and a metal hard film plated on the outer surface of the soft film, and the two form an inverted T -shaped structure, the metal hard film is arranged opposite to the core cross-section of the single-mode optical fiber, the diameter of the metal hard film is equal to the diameter of the single-mode optical fiber core cross-section, and the diameter of the soft film is equal to the outer diameter of the annular end surface of the capillary glass tube. Wherein, the soft film is a rubber mold or silicone film with a smooth and smooth surface, and the metal hard film is made of gold or silver. 2. A coated double-layer sensitive film for FP cavity optical fiber pressure sensor according to claim 1, characterized in that the soft film is made of PDMS. 3. A coated double-layer sensitive film for FP cavity optical fiber pressure sensor according to claim 1, characterized in that the thickness of the soft film is 0.5-10 μm, and the thickness of the metal hard film is 10-1000 nm. 4. A method for preparing a coated double-layer sensitive film, which is characterized in that it includes the following steps: S1. Deposit an oxide layer on the substrate as a sacrificial layer, spin-coat a layer of photoresist on the oxide layer, expose the photoresist to high-energy radiation through a specific pattern on a mask, and use a developer to remove the exposed The properties of the photoresist have been changed to obtain empty grooves with a pattern corresponding to the mask. Then the remaining photoresist is used as a mask, and ICP is used to etch the entire surface, and a mark corresponding to the pattern is obtained on the oxide layer. , to facilitate the positioning of subsequent overlay steps; S2. Apply photoresist again, and use another mask with the same mark pattern at the same position as the mask in step S1 for positioning. The mask in step S2 also has a circular pattern; go through the same process as in step 1. In the exposure and dissolution steps, a cylindrical hollow groove is formed in the photoresist, and the soft film solution is filled in the cylindrical hollow groove to prepare a soft film; S3. Apply photoresist on the soft film again, and use another mask with the same mark pattern at the same position as the mask in step S1 for positioning. In step S3, the mask also has a circular pattern with the center of the circle. It coincides with the center of the circular pattern created on the mask in step S2; after the same exposure and dissolution steps as in step 1, a cylindrical hollow groove is formed in the photoresist, and the outer surface of the soft film is formed using electron beam evaporation technology. Coated with a metal hard coating; S4. Remove the photoresist and substrate to prepare a plated double-layer sensitive film. 5. A method for preparing a coated double-layer sensitive film according to claim 4, characterized in that, in step S2, the soft film is made of PDMS, the thickness of the soft film is 0.5-10 μm, and the surface is smooth. Smooth and clean. 6. A method for preparing a coated double-layer sensitive film according to claim 4, characterized in that, in step S3, the metal hard film is made of gold or silver, and the thickness of the metal hard film is 10- 1000nm.