CN110057479A - Plating laminar double-layer sensitive film and preparation method for FP chamber fibre optic compression sensor - 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, and belongs to the technical field of pressure sensors. The FP cavity optical fiber pressure sensor of the present invention includes a capillary glass tube, a single-mode optical fiber and a sensitive film. The single-mode optical fiber is inserted from one annular end face of the capillary glass tube, and the other annular end face is fixedly connected with the coating-type double-layer sensitive film covering it. , an air cavity is formed between the single-mode fiber and the coated double-layer sensitive film as the FP cavity; the coated double-layer sensitive film includes a soft film and a metal hard film coated on the outer surface of the soft film, and the metal hard film and the single-mode fiber The cross-sections of the cores are arranged opposite, the diameter of the metal hard film is equal to the diameter of the cross-section of the single-mode fiber core, and the diameter of the soft film is equal to the outer diameter of the annular end face of the capillary glass tube. In the invention, the metal hard film with large elastic modulus and high reflectivity is coated on the outer surface of the soft film with small elastic modulus to form an externally plated double-layer structure sensitive film, which has good deformability and reflectivity at the same time.

Description

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

technical field

The invention relates to the technical field of pressure sensors, in particular to a coating type double-layer sensitive film for an FP cavity optical fiber pressure sensor and a preparation method thereof.

Background technique

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

Most of the extrinsic diaphragm FP fiber sensors are two mirrors of the FP cavity composed of the cut fiber end face and the sensitive diaphragm. The film vibrates under the action of external force, which causes the interference of the FP cavity to change. 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 membranes made of different materials have been reported many times: for example, (1) Dai et al. used a single-layer graphene film as a sensitive membrane, combined with a single-mode optical fiber sheathed with a capillary tube to form an FP cavity , and then make an FP cavity optical fiber sensor; wherein the sensitive film made of single-layer graphene film has low elastic modulus, but has low refractive index, high cost and easy damage. (2) Majun et al. used multi-layer graphene as the sensitive film. The sensitive film made of multi-layer graphene has a high response between 0.2 and 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) The photonic crystal mirror is used as the sensitive film, which has a high response between 10-50Khz. The sensitive film made of the photonic crystal mirror has the characteristics of high reflectivity and high elastic modulus.

The existing sensitive films only have a single feature of high reflectivity or low elastic modulus, which cannot meet the requirements of practical FP cavity optical fiber pressure sensors.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a coating type double-layer sensitive film for an FP cavity optical fiber pressure sensor and a preparation method. The metal hard film has the characteristics of small elastic mode and high reflectivity at the same time.

The invention provides a coating type 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, wherein the single-mode optical fiber is formed from a capillary glass tube. The annular end face is inserted, the other annular end face of the capillary glass tube is fixed with the coated double-layer sensitive film covering it, and an air cavity is formed between the single-mode optical fiber and the coated double-layer sensitive film as the FP cavity, and the capillary glass tube The inner diameter of the annular end face is equal to the diameter of the single-mode fiber; the center of the cross-section of the single-mode fiber and the center of the sensitive film are both on the axis of the capillary glass tube, and the cross-section of the core of the single-mode fiber and the sensitive film serve as two parts of the FP cavity. A cavity mirror, which is 90° to the axial direction of the capillary glass tube, forms an FP cavity interference structure.

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

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

Further, the metal hard coat 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 present invention also provides a preparation method of the above-mentioned coating type double-layer sensitive film, comprising the following steps:

S1. An oxide layer is deposited on the substrate as a sacrificial layer, a layer of photoresist is spin-coated on the oxide layer, high-energy radiation is exposed to the photoresist through a specific pattern on a mask, and the exposed photoresist is removed with a developing solution. The photoresist whose properties have changed, obtains an empty groove in the shape of the pattern corresponding to the mask, and then the remaining photoresist is used as a mask, and ICP is used to etch the entire surface, and the corresponding pattern marks are obtained on the oxide layer. , which is convenient for the positioning of subsequent engraving steps;

S2. Coat the photoresist again, and use another mask with the same marking pattern at the same position as the mask in step S1 for positioning. In step S2, the mask is also provided with a circular pattern; In the steps of exposing and dissolving, a cylindrical hollow groove is formed in the photoresist, and the soft film solution is filled in the cylindrical hollow groove to obtain a soft film;

S3. Coat the photoresist on the soft film again, and use another mask with the same marking pattern at the same position as the mask in step S1 for positioning. In step S3, the mask is also provided with a circular pattern, the center of which is Coinciding with the center of the circular pattern opened by the mask in step S2; through the same exposure and dissolving steps as in step 1, a cylindrical hollow groove is formed in the photoresist, and the outer surface of the soft film is formed by electron beam evaporation technology. Coated with a layer of metal hard film;

S4, removing the photoresist and the substrate to obtain 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 clean.

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 prior art, 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, which is used as a cavity mirror of the fiber FP cavity. When under pressure, the deformation mainly occurs on the outer soft film layer, and the metal hard film layer within the diameter of the fiber mode field. The deformation is small and the reflectivity is high, which 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 drawings

The drawings are for the purpose of illustrating specific embodiments only and are not to be considered limiting of the invention, and like reference numerals refer to like parts throughout the drawings.

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

Fig. 2 is the structural representation of the coating type double-layer sensitive film in Fig. 1;

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

Reference number:

1-capillary glass tube; 2-single-mode fiber; 3-sensitive film; 31-soft film; 32-metal hard film; 4-air cavity; 5-silicon bottom; 6-silicon dioxide layer; 7-photoresist .

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to 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 is composed of a capillary glass tube 1, a single-mode optical fiber 2 and a sensitive film 3. The optical fiber 2 is inserted from an annular end face of the capillary glass tube 1, and the other annular end face of the capillary glass tube 1 is fixedly connected with the coated double-layer sensitive film 3 covering it. An air cavity 4 is formed between them as the FP cavity. The inner diameter of the annular end face of the capillary glass tube 1 is equal to the diameter of the single-mode optical fiber 2; Above, the core cross-section of the single-mode fiber 2 and the sensitive film 3 are used as the two cavity mirrors of the FP cavity, which are 90° to the axial direction of the capillary glass tube 1, forming the 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, and the metal hard film 32 is opposite to the cross section of the core of the single-mode optical fiber 2 The diameter of the metal hard film 32 is equal to the diameter of the cross section of the core 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 face of the capillary glass tube 1 .

As shown in FIG. 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 prepared plated 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 The diameter of the hard coat 32 is equal to the diameter of the cross-section of the core of the single-mode optical fiber 2, and is 10 μm.

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

(1) A layer of silicon dioxide layer 6 with a thickness of 1-3um is plated on the silicon substrate 5 as a sacrificial layer, and then a thin layer of photoresist is spin-coated on the silicon dioxide layer 6, and a mask is covered on the On the thin-layer photoresist, the edge of the mask is provided with a triangular mark pattern; use ultraviolet light to pass through the triangular mark pattern on the mask to expose the photoresist, and use the developer to melt away the changed properties after exposure. Photoresist; remove the mask, use ICP technology to directly etch the surface of the device, then remove the thin layer of photoresist, and obtain a triangular mark (not shown in the figure) on the silicon dioxide layer 6, which is convenient for subsequent process steps The positioning and engraving are shown in Figure 3(a).

(2) In the area other than the triangular mark of the silicon dioxide layer 6, spin-coat a layer of photoresist 7 with a thickness of 2.5 μm on the silicon dioxide layer 6 by using a glue spinner, as shown in FIG. 3( b ).

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

In step (3), a circular hole with a diameter of 250 μm is also opened on the mask plate, and the photoresist 7 is exposed by ultraviolet light through the circular hole on the mask plate, and the photolithography of the middle exposure part is melted by the developing solution. 7, and a cylindrical groove with a diameter of 250 μm is obtained in the photoresist 7, as shown in FIG. 3(c).

(4) The prepared PDMS solution was dried in a vacuum oven to remove air bubbles, and then spin-coated on the silicon dioxide layer 6 and the photoresist 7 using a glue spinner to fill the PDMS solution with the diameter of 250 μm in step (3). Cylinder slot, as shown in Fig. 3(d).

(5) Scrape across the surface of the PDMS substrate with a flat and smooth rubber blade until the blade and the top surface of the photoresist 7 are in contact, remove the excess PDMS solution, and only keep the 250 μm diameter cylindrical groove in the photoresist. The PDMS solution is then heated to prepare the PDMS soft film 31, as shown in Figure 3(e).

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

(7) A layer of photoresist 7 is spin-coated on the silicon dioxide layer 6 and the PDMS soft film 31 in step (6) again using a glue spinner, as shown in FIG. 3(g).

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

Use ultraviolet light to expose the photoresist 7 through the circular hole on the mask, and 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 3(h).

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

(10) Then the whole device was immersed in acetone solution upside down, the excess photoresist 7 and the silver metal layer on the photoresist 7 were removed, and the PDMS soft film 31 was left on the silicon dioxide layer 6 and plated on it. The silver metal layer 7 is shown in Figure 3(j).

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

In summary, the present invention provides a coated double-layer sensitive film for an FP cavity optical fiber pressure sensor and a preparation method. The coated double-layer sensitive film coats a metal hard film with a large elastic modulus and a high reflectivity. On the outer surface of the soft film with small elastic modulus, a double-layer composite film is formed, and the film is used as a cavity mirror of the optical fiber FP cavity. When under pressure, the 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 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 of the embodiments herein may be combined with each other without conflict.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, 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 (8)

1. a kind of plating laminar double-layer sensitive film for FP chamber fibre optic compression sensor, the FP chamber fibre optic compression sensor is by capillary Glass tube, single mode optical fiber and sensitive membrane composition, wherein single mode optical fiber is inserted into from an annular end face of glass capillary, capillary glass Another annular end face of pipe is connected with the plating laminar double-layer sensitive film covered, single mode optical fiber and plating laminar double-layer sensitive film Between form an air chamber as FP cavity, the internal diameter of glass capillary annular end face and the diameter of single mode optical fiber are equal；Single mode The cross-section center of optical fiber and the center of sensitive membrane are on the axis of glass capillary, the fiber core cross section of single mode optical fiber and quick Feel two hysteroscopes of the film as FP cavity, it is in 90 ° with the axial direction of glass capillary, form FP chamber interference structure；It is characterized in that, The plating laminar double-layer sensitive film includes mantle and the metal dura mater for being plated in mantle outer surface, and the two forms inverted T-shaped structure, metallic hard The fiber core cross section of film and single mode optical fiber is oppositely arranged, the diameter phase of the diameter and single mode optical fiber fiber core cross section of metal dura mater Deng the diameter of mantle is equal with the outer diameter of glass capillary annular end face.

2. a kind of plating laminar double-layer sensitive film for FP chamber fibre optic compression sensor, feature exist according to claim 1 In the mantle is the bright and clean rubber pattern or pellosil of surfacing.

3. a kind of plating laminar double-layer sensitive film for FP chamber fibre optic compression sensor, feature exist according to claim 2 In the mantle is made of PDMS.

4. a kind of plating laminar double-layer sensitive film for FP chamber fibre optic compression sensor, feature exist according to claim 1 In the metal dura mater is made of gold or silver.

5. a kind of plating laminar double-layer sensitive film for FP chamber fibre optic compression sensor, feature exist according to claim 1 In, the mantle with a thickness of 0.5-10 μm, metal dura mater with a thickness of 10-1000nm.

6. a kind of method for preparing plating laminar double-layer sensitive film, which comprises the following steps:

S1, layer of oxide layer is deposited in substrate as sacrificial layer, one layer photoresist of spin coating in oxide layer, high-energy radiation penetrates Special pattern exposes photoresist on one mask plate, with the photoresist that changes of property after developer solution removal exposure, obtain with The empty slot of the corresponding graphics shape of mask plate, then remaining photoresist carves whole surface using ICP as exposure mask Erosion obtains the label of corresponding figure, in oxide layer convenient for the positioning of subsequent alignment step；

S2, photoresist is coated again, offer same tag figure with mask plate same position in step S1 using another Mask plate is positioned, and mask plate is also provided with circular pattern in step S2；By exposure identical with step 1, dissolving step, A cylindrical body empty slot is formed in the photoresist, mantle solution is filled in cylindrical body empty slot, and mantle is made；

S3, photoresist is coated on mantle again, offers identical mark with mask plate same position in step S1 using another The mask plate of note figure is positioned, and mask plate is also provided with circular pattern, the center of circle and mask plate in step S2 in step S3 The center of circle of the circular pattern opened up is overlapped；By exposure identical with step 1, dissolving step, a cylinder is formed in the photoresist Body empty slot plates one layer of metal dura mater in the outer surface of mantle by electron beam evaporation technique；

Plating laminar double-layer sensitive film is made in S4, removal photoresist and substrate.

7. a kind of method for preparing plating laminar double-layer sensitive film according to claim 6, which is characterized in that in step S2 In, the mantle is made of PDMS, mantle with a thickness of 0.5-10 μm, surfacing is bright and clean.

8. a kind of method for preparing plating laminar double-layer sensitive film according to claim 6, which is characterized in that in step S3 In, the metal dura mater by gold or silver be made, metal dura mater with a thickness of 10-1000nm.