An optical fiber and air pressure sensor with F-P cavity structure

Abstract

The application provides an optical fiber and air pressure sensor with F-P cavity structure, comprising: a front single-mode optical fiber, an F-P cavity and a rear single-mode optical fiber; the F-P cavity comprises a cladding, a center hole is arranged in the center of the cladding along an axial direction, the center hole is filled with air as a core, and a plurality of cladding holes along the axial direction are arranged in the cladding; the F-P cavity is arranged between the front single-mode optical fiber and the rear single-mode optical fiber, the cross-sectional size of the core is greater than the cross-sectional size of the core of the single-mode optical fiber and is less than the cross-sectional size of the single-mode optical fiber; the cross-sectional size of the F-P cavity is greater than the cross-sectional size of the single-mode optical fiber, and the cladding hole is in communication with external air; when the air pressure of the external air changes, the effective refractive index of the core changes. The F-P cavity structure can be formed with the step-type single-mode optical fiber, has high sensitivity to external air pressure, and can be used for high-resolution detection of high pressure and low pressure.

Description

Technical Field

[0001] This application belongs to the field of fiber optic sensing, and particularly relates to a fiber optic and barometric pressure sensor with an FP cavity structure. Background Technology

[0002] A photonic cavity (FP) is a beam interference device. Two beams of light reflected from the end face of an FP cavity will produce interference. The phase of the interference light determines the intensity of the light, while the phase difference is determined by the cavity length of the FP cavity, the effective refractive index of the FP cavity, and the wavelength of the light wave.

[0003] Broadband light is used as the light source to generate FP interference fringes. Changing the cavity length or effective refractive index can cause the interference fringes to shift. Therefore, this principle can be used to measure external environmental factors such as air pressure, temperature, and vibration.

[0004] In the literature "Jin L,Guan BO,Wei H.Sensitivity Characteristics of Fabry-Perot Pressure Sensors Based on Hollow-Core Microstructured Fibers[J].Journal of Lightwave Technology,2013,31(15):2526-2532.", anti-resonant fiber was used as an FP cavity for air pressure sensing. When the fiber length was 12mm, the sensitivity to air pressure was -17.3pm / Mpa.

[0005] It has low sensitivity to air pressure and is not sufficient for detecting low-pressure areas. Summary of the Invention

[0006] This invention proposes an optical fiber and barometric pressure sensor with an FP cavity structure, which can be combined with a step-index single-mode optical fiber to form an FP cavity structure. It has high sensitivity to external barometric pressure and can perform high-resolution detection of both high and low pressure.

[0007] The first aspect of the present invention provides an optical fiber with an FP cavity structure, comprising: a front single-mode fiber, an FP cavity, and a back single-mode fiber;

[0008] The FP cavity includes a cladding, a central hole is provided in the center of the cladding along the axial direction, the central hole is filled with air as the fiber core, and multiple cladding holes are arranged in the cladding along the axial direction.

[0009] The FP cavity is positioned between the front single-mode fiber and the rear single-mode fiber. The cross-sectional size of the fiber core is larger than that of the single-mode fiber core, but smaller than that of the single-mode fiber.

[0010] The cross-sectional size of the FP cavity is larger than that of the single-mode fiber, and the cladding hole is connected to the outside air. When the outside air pressure changes, it causes a change in the effective refractive index of the fiber core.

[0011] Optionally, the cross-section of the central hole is a flattened hexagon.

[0012] Optionally, the number of cladding pores is 6.

[0013] Optionally, each side of the hexagon corresponds to a sector-shaped cladding hole.

[0014] Optionally, the flattening degree of the fiber core can be set to 3 / 8;

[0015] Wherein, the flattening degree of the fiber core is f=(ba) / b, where a is the length of the four short sides of the hexagon and b is the length of the two opposite long sides of the hexagon.

[0016] Optionally, the wall thickness between the cladding pores and the fiber core is 0.2um-0.5um.

[0017] Optionally, the length of the FP cavity is 10-15mm.

[0018] A second aspect of the present invention provides a barometric pressure sensor employing an optical fiber with an FP cavity structure as described in any one of the first aspects.

[0019] The beneficial technical effects of this application are as follows:

[0020] This invention proposes a fiber optic FP cavity structure and pressure sensor with high sensitivity to air pressure. It overcomes the shortcomings of commonly used fiber optic FP cavity pressure sensors, such as low sensitivity and low resolution. This invention enlarges the cladding aperture size so that the air pressure in the cladding aperture is equal to the changing external air pressure value in real time, increasing the effect of air pressure on the fiber core wall. The radius of the cladding aperture is made larger than the radius of the step-index single-mode fiber that serves as the FP cavity wall. Furthermore, the hexagonal fiber core structure is flattened to make the stress on each fiber core wall unequal, increasing the change in effective refractive index within the fiber core. This improves the sensitivity of this FP cavity structure to air pressure by 140 times. When the fiber length is 12mm, the sensitivity to air pressure is -2.4nm / MPa. Attached Figure Description

[0021] Figure 1 A schematic diagram of the optical fiber with an FP cavity structure provided by the present invention. Figure 1 ;

[0022] Figure 2 A schematic diagram of the fiber core wall thickness provided by the present invention;

[0023] Figure 3 A schematic diagram of the optical fiber with an FP cavity structure provided by the present invention. Figure 2 ;

[0024] Figure 4 Variation of effective refractive index of fiber core with core radius and wall thickness in novel optical fiber

[0025] Figure 5 The flattening law of the effective refractive index of the fiber core with the flattening degree of the fiber core. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.

[0028] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0030] Please see Figure 1-5 The present invention provides an optical fiber with an FP cavity structure and a pressure sensor using the structure.

[0031] The FP cavity structure based on large-aperture anti-resonant fiber designed in this invention is as follows: Figure 1As shown, the effect of air pressure on the fundamental mode phase in optical fiber mainly changes the fiber length and the effective refractive index of the fundamental mode. Since the FP cavity used for sensing is generally short, it is necessary to increase the sensitivity of the effective refractive index of the fundamental mode to air pressure. Enlarging the cladding aperture, making its radius larger than the radius of the fiber fused to the FP cavity, allows external gas to enter the cladding aperture, thus making the fiber core more sensitive to external stimuli.

[0032] For example, such as Figure 1 and 2 As shown, the present invention provides an optical fiber with an FP cavity structure, comprising: a front single-mode fiber, an FP cavity, and a back single-mode fiber;

[0033] The FP cavity includes a cladding, a central hole is provided in the center of the cladding along the axial direction, the central hole is filled with air as the fiber core, and multiple cladding holes are arranged in the cladding along the axial direction.

[0034] The FP cavity is positioned between the front single-mode fiber and the rear single-mode fiber. The cross-sectional size of the fiber core is larger than that of the single-mode fiber core, but smaller than that of the single-mode fiber.

[0035] The cross-sectional size of the FP cavity is larger than that of the single-mode fiber, and the cladding hole is connected to the outside air. When the outside air pressure changes, it causes a change in the effective refractive index of the fiber core.

[0036] Optionally, the cross-section of the central hole is a flattened hexagon.

[0037] Optionally, the number of cladding pores is 6.

[0038] Optionally, each side of the hexagon corresponds to a sector-shaped cladding hole.

[0039] The fiber structure parameters that significantly affect pressure sensitivity are the core radius r1 and the wall thickness c. Therefore, these two parameters are mainly adjusted to optimize fiber performance. As a pressure sensor, the change in pressure should have a linear relationship with the change in effective refractive index. A good linear relationship exists within the range of 18µm-23µm core diameter and 0.2µm-0.5µm wall thickness.

[0040] Within this linear region, the relationship between the effective refractive index of the fundamental mode and the core radius and wall thickness is as follows: Figure 4 As shown, the air pressure sensitivity increases with increasing fiber core thickness and decreasing wall thickness, with wall thickness having a significant impact.

[0041] The fiber core is flattened. The fiber structure is r1 = 22 μm and c = 0.25 μm. The four short sides of the fiber core are labeled a and the two long sides are labeled b. The degree of flattening is represented by the value of f = (ba) / b. Figure 3The figure shows the relationship between the effective refractive index of the fundamental mode and the external air pressure for different flattening degrees. The smaller the value of f, the greater the change in the effective refractive index of the fundamental mode with air pressure.

[0042] Considering the actual processing difficulty and the size of single-mode fiber, based on the above, we take the core radius r1 = 22 μm, cladding radius r2 = 80 μm, fiber radius r3 = 100 μm, wall thickness c = 400 nm, and flattening degree f = 3 / 8. Then the pressure sensitivity is S = -0.001367 ppm / Pa. Taking 12 mm fiber as the FP cavity, the pressure sensitivity is 2.4 nm / MPa.

[0043] Comparison revealed that this fiber optic structure is 140 times more efficient than the one described in the literature "Jin L, Guan BO, Wei H. Sensitivity Characteristics of Fabry-Perot Pressure Sensors Based on Hollow-Core Microstructured Fibers[J]. Journal of Lightwave Technology, 2013, 31(15): 2526-2532." Following this pattern, selecting even better parameters would result in even higher pressure sensitivity.

[0044] The designed novel optical fiber structure with high sensitivity to air pressure has the following parameters: Figure 1 , Figure 2 All core radii, wall thicknesses, and flatness are listed.

[0045] For example, such as Figure 3 As shown, the cross-section of the central hole is a regular octagon, and the number of cladding holes can also be 8.

[0046] The above description is merely a further embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope disclosed in the present invention, based on the technical solution and concept of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. An optical fiber with an FP cavity structure, characterized in that, include: Front-end single-mode fiber, FP cavity, and back-end single-mode fiber; The FP cavity includes a cladding, with a central hole arranged along the axial direction at the center of the cladding. The central hole is filled with air as the fiber core, and multiple cladding holes are arranged along the axial direction within the cladding. The FP cavity is positioned between the front single-mode fiber and the rear single-mode fiber. The cross-sectional size of the fiber core is larger than that of the single-mode fiber core, but smaller than the overall cross-sectional size of the single-mode fiber. The cross-sectional size of the FP cavity is larger than that of the single-mode fiber, and the cladding hole is connected to the outside air. When the outside air pressure changes, it causes a change in the effective refractive index of the fiber core. The central hole has been flattened.

2. The optical fiber with an FP cavity structure according to claim 1, characterized in that, The cross-section of the central hole is a flattened hexagon.

3. The optical fiber with an FP cavity structure according to claim 2, characterized in that, The number of cladding pores is 6.

4. The optical fiber with an FP cavity structure according to claim 3, characterized in that, Each side of the hexagon corresponds to a sector-shaped cladding hole.

5. The optical fiber with an FP cavity structure according to claim 2, characterized in that, The flattening degree of the fiber core is 3 / 8; Wherein, the flattening degree of the fiber core is f=(ba) / b, where a is the length of the four short sides of the hexagon and b is the length of the two opposite long sides of the hexagon.

6. The optical fiber with an FP cavity structure according to claim 2, characterized in that, The wall thickness between the cladding pores and the fiber core is 0.2um-0.5um.

7. The optical fiber with an FP cavity structure according to claim 1, characterized in that, The length of the FP cavity is 10-15mm.

8. A barometric pressure sensor, characterized in that, The optical fiber with an FP cavity structure as described in any one of claims 1-7 is used.

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