Optical fiber with F-P cavity structure and air pressure sensor

Abstract

The invention provides an optical fiber with an F-P cavity structure and an air pressure sensor. The optical fiber with the F-P cavity structure comprises 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 formed in the center of the cladding in the axial direction, the center hole is filled with air to serve as a fiber core, and a plurality of cladding holes in the axial direction are formed in the cladding; the F-P cavity is arranged between the front single-mode optical fiber and the rear single-mode optical fiber, and the sectional dimension of the fiber core is larger than that of the single-mode optical fiber and smaller than that of the single-mode optical fiber; the section size of the F-P cavity is larger than that of the single-mode fiber, the cladding hole is communicated with outside air, and when the pressure of the outside air changes, the effective refractive index of the fiber core changes. The optical fiber can form an F-P cavity structure with a 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 an optical fiber and a pressure sensor with an F-P cavity structure. Background Art

[0002] An F-P cavity is a beam interference device. Two beams of light reflected from the end faces of the F-P cavity respectively will produce an interference phenomenon. Its phase determines the interference light intensity, and the phase difference is jointly determined by the cavity length of the F-P cavity, the effective refractive index in the F-P cavity, and the wavelength of the light wave.

[0003] Using broadband light as the light source to generate F-P interference fringes, changing the cavity length or the effective refractive index can cause the interference fringes to shift. Therefore, this principle can be used to measure external environments such as air pressure, temperature, and vibration.

[0004] In the literature "Jin L, Guan B O, 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.", an anti-resonant fiber is used as the F-P cavity for air pressure sensing. When the fiber length is 12 mm, the sensitivity to air pressure is -17.3 pm / Mpa.

[0005] The sensitivity to air pressure is relatively low, and it is not sufficient to detect small air pressure ranges such as low air pressure. Summary of the Invention

[0006] The present invention provides an optical fiber and a pressure sensor with an F-P cavity structure, which can form an F-P cavity structure with a step-type single-mode optical fiber, has high sensitivity to external air pressure, and can perform high-resolution detection of high pressure and low pressure.

[0007] The first aspect of the present invention provides an optical fiber with an F-P cavity structure, including: a front single-mode optical fiber, an F-P cavity, and a rear single-mode optical fiber;

[0008] The F-P cavity includes a cladding. A central hole is axially arranged in the center of the cladding, and air is filled in the central hole as the core. A plurality of axially arranged cladding holes are arranged in the cladding;

[0009] 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 larger than the cross-sectional size of the core of the single-mode optical fiber and smaller than the cross-sectional size of the single-mode optical fiber;

[0010] The cross-sectional size of the F-P cavity is larger than that of the single-mode optical fiber, and the cladding holes communicate with the outside air. When the air pressure outside changes, it causes a change in the effective refractive index of the core.

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

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

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

[0014] Optionally, the value of the flattening degree of the core is 3 / 8;

[0015] Among them, the flattening degree f of the core = (b - a) / 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 hole and the core is 0.2 μm - 0.5 μm.

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

[0018] In the second aspect of the present invention, a pressure sensor is provided, which uses the optical fiber with the F-P cavity structure described in any one of the first aspects.

[0019] The beneficial technical effects of this application:

[0020] The present invention proposes an optical fiber F-P cavity structure and a pressure sensor with high sensitivity to air pressure, which overcomes the disadvantages of low sensitivity and low resolution of the commonly used optical fiber F-P cavity air pressure sensing. The present invention enlarges the size of the cladding holes, so that the air pressure in the cladding holes is equal to the external changing air pressure value in real time, increases the effect of air pressure on the core wall, makes the radius of the cladding hole larger than the radius of the step-type single-mode optical fiber as the F-P cavity wall, and performs flattening treatment on the regular hexagon core structure, so that the force on each core wall is unequal, increases the change in the effective refractive index in the core, and improves the sensitivity of this F-P cavity structure to air pressure by 140 times. When the length of the optical fiber is 12 mm, the sensitivity to air pressure is -2.4 nm / Mpa. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the structure of the optical fiber with the F-P cavity structure provided by the present invention Figure 1 ;

[0022] Figure 2 It is a schematic diagram of the wall thickness of the core provided by the present invention;

[0023] Figure 3 It is a schematic diagram of the structure of the optical fiber with the F-P cavity structure provided by the present invention Figure 2 ;

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

[0025] Figure 5 Flattening law of the effective refractive index of the core of a novel optical fiber with the core flattening degree. Specific implementation manners

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

[0027] The features and illustrative embodiments in various aspects of the present invention will be described in detail below. In the following detailed description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be practiced without some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by showing examples of the present invention. The present invention is in no way limited to any specific arrangements and methods set forth below, but covers any improvements, substitutions and modifications of structures, methods, and devices without departing from the spirit of the present invention. Well-known structures and technologies are not shown in the drawings and the following description to avoid unnecessarily obscuring the present invention.

[0028] It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other, and the various embodiments can refer to and cite each other. The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

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

[0030] Please refer to Figures 1-5 , the present invention provides an optical fiber with an F-P cavity structure and a pressure sensor adopting this structure.

[0031] The F-P cavity structure designed by the present invention based on a large-core anti-resonant optical fiber is as Figure 1As shown in the figure, the influence of air pressure on the phase of the fundamental mode in the optical fiber mainly changes the length of the optical fiber and the effective refractive index of the fundamental mode. Since the F-P cavity used for sensing in the optical fiber generally has a short length, it is necessary to improve the sensitivity of the effective refractive index of the fundamental mode to air pressure. When the cladding holes are enlarged so that the radius of the cladding holes is greater than the radius of the optical fiber fused with the F-P cavity, the external gas can enter the cladding holes of the optical fiber, thereby making the core more sensitive to the outside world.

[0032] Exemplarily, as Figure 1 and 2 shown, the present invention provides an optical fiber with an F-P cavity structure, including: a front single-mode optical fiber, an F-P cavity, and a rear single-mode optical fiber;

[0033] The F-P cavity includes a cladding. A central hole is axially arranged in the center of the cladding. Air is filled in the central hole as the core. A plurality of axial cladding holes are arranged in the cladding;

[0034] 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 larger than the cross-sectional size of the core of the single-mode optical fiber and smaller than the cross-sectional size of the single-mode optical fiber;

[0035] The cross-sectional size of the F-P cavity is larger than the cross-sectional size of the single-mode optical fiber, and the cladding holes communicate with the outside air. When the outside air pressure changes, the effective refractive index of the core changes.

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

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

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

[0039] The optical fiber structure parameters that have a greater influence on the air pressure sensitivity are mainly the core radius r1 and the wall thickness c. Therefore, these two parameters are mainly adjusted to optimize the optical fiber performance. As a sensing element for air pressure, the change in air pressure and the change in the effective refractive index should be a linear relationship. When the core diameter is in the range of 18um - 23um and the wall thickness is in the range of 0.2um - 0.5um, there is a good linear relationship.

[0040] Within this linear region, the relationship between the effective refractive index of the fundamental mode and the core radius and the wall thickness is as Figure 4 shown. The air pressure sensitivity increases with the increase of the core and the decrease of the wall thickness, and the factor of the wall thickness has a greater influence on it.

[0041] The core of the optical fiber is flattened. For the optical fiber structure with r1 = 22um and c = 0.25um, the four short sides of the core are marked as a, and the two long sides are marked as b. The degree of flattening is characterized by the value of f = (b - a) / b. Figure 3The relationship between the effective refractive index of the fundamental mode and the external air pressure at different flattening degrees is shown. When f is smaller, the change of the effective refractive index of the fundamental mode with the air pressure is larger.

[0042] Considering the actual processing difficulty and the size of the single-mode fiber, in summary, the core radius r1 = 22um, the cladding radius r2 = 80um, the fiber radius r3 = 100um, the wall thickness c = 400nm, and the flattening degree f = 3 / 8 are taken. Then the air pressure sensitivity is S = -0.001367ppm / Pa. Taking a 12mm fiber as the F-P cavity, the air pressure sensitivity is 2.4nm / Mpa.

[0043] It is found by comparison that, compared with the literature "Jin L, Guan B O, 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.", the fiber structure is 140 times higher. According to this rule, better parameters are taken, and the air pressure sensitivity is higher.

[0044] The designed novel fiber structure with high sensitivity to air pressure, its parameters include Figure 1 , Figure 2 all the core radii, wall thicknesses, and flattening degrees listed.

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

[0046] As mentioned above, it is only a further embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the scope disclosed by the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, all belong to the protection scope of the present invention.

Claims

1. An optical fiber with an F-P cavity structure, characterized in that, It includes: A front single-mode optical fiber, an F-P cavity, and a rear single-mode optical fiber; The F-P cavity includes a cladding. Along the axial direction, a central hole is arranged in the center of the cladding, and air is filled in the central hole as the core. A plurality of axial cladding holes 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 dimension of the core is larger than the cross-sectional dimension of the core of the single-mode optical fiber and smaller than the cross-sectional dimension of the single-mode optical fiber; The cross-sectional dimension of the F-P cavity is larger than the cross-sectional dimension of the single-mode optical fiber, and the cladding holes communicate with the outside air. When the air pressure outside changes, the effective refractive index of the core changes.

2. The optical fiber with an F-P cavity structure according to claim 1, wherein The cross-section of the central hole is a flattened hexagon.

3. The optical fiber with an F-P cavity structure according to claim 2, characterized in that, The number of the cladding holes is six.

4. The optical fiber with an F-P cavity structure according to claim 3, wherein Each side of the hexagon corresponds to a sector-shaped cladding hole.

5. The optical fiber with an F-P cavity structure according to claim 2, wherein, The flattening degree value of the core is 3 / 8; Wherein, the flattening degree f of the core = (b - a) / b, 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 F-P cavity structure according to claim 2, wherein, The wall thickness between the cladding hole and the core is 0.2 um - 0.5 um.

7. The optical fiber with an F-P cavity structure according to claim 1, wherein, The length of the F-P cavity is 10 - 15 mm.

8. A barometric pressure sensor, characterized in that, An optical fiber having an F-P cavity structure as described in any one of claims 1 - 7 is adopted.

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