CN-116989923-B - Optical fiber pressure sensing method based on orbital angular momentum mode

CN116989923BCN 116989923 BCN116989923 BCN 116989923BCN-116989923-B

Abstract

The invention discloses an optical fiber pressure sensing method based on an orbital angular momentum mode, which is characterized in that the relation between the 10ps walk-off distance and a pressure value is established by measuring the 10ps walk-off distance and utilizing the elliptical eccentricity or the concave angle as an intermediate quantity, so that the measurement of the pressure is realized, and a feasible scheme is provided for the application of an OAM mode in optical fiber pressure sensing.

Inventors

WANG XIAOHUI
HE XIAOFENG
ZHU TIEZHU
WANG CHAO
YANG YUDONG
JU YONGFENG
YU YONGZE
DENG DONGDONG
WANG YANG
Mao shuai
Gu Haoyu
ZHUANG LIYUN
JI RENDONG
YANG SONG

Assignees

淮阴工学院

Dates

Publication Date: 20260508
Application Date: 20230804

Claims (10)

1. An optical fiber pressure sensing method based on an orbital angular momentum mode, comprising: (1) Determining an optical fiber and an OAM mode in the optical fiber, wherein the optical fiber adopts a hollow optical fiber with a central atmospheric hole; (2) Applying uniform pressure on the optical fiber by utilizing a square pressing block to enable the optical fiber to generate elliptical deformation, and taking elliptical eccentricity as an intermediate quantity to obtain a plurality of groups of elliptical eccentricities, corresponding pressure values and 10ps walk-away distances; (3) Fitting the elliptical eccentricity and the 10ps walk-off distance to obtain a first fitting formula, and fitting the elliptical eccentricity and the pressure value to obtain a second fitting formula; (4) And measuring a 10ps walk-off distance, obtaining a corresponding elliptical eccentricity according to a first fitting formula, and obtaining a corresponding pressure value according to a second fitting formula.
2. The optical fiber pressure sensing method according to claim 1, wherein a plurality of air hole layers are arranged outside the central atmospheric hole in the optical fiber structure, and each air hole layer is composed of a plurality of small air holes which are annularly arranged.
3. The optical fiber pressure sensing method according to claim 1, wherein the OAM mode in the optical fiber is formed by superposition of parity components of vector modes HE or EH as shown in formula (1): wherein l is topological charge, j is pi/2 phase difference between an even mode and an odd mode of the same vector mode, m is a radial index, the superscript + -indicates a circular polarization direction of a left hand or a right hand, the subscript + -indicates a right-hand or left-hand direction of a phase wavefront, even indicates an even component, and odd indicates an odd component; the OAM mode selects a vector mode of order 4 or more.
4. The optical fiber pressure sensing method according to claim 3, wherein the calculation formula of the 10ps walk-off distance L 10ps is: Where c is the speed of light in vacuum, 10ps is time, Is the effective refractive index of the even mode, Is the effective refractive index of the odd mode.
5. The method of claim 1, wherein the first and second fitting formulas are each fitted using a cftool tool in matlab.
6. An optical fiber pressure sensing method based on an orbital angular momentum mode, comprising: (1) Determining an optical fiber and an OAM mode in the optical fiber, wherein the optical fiber adopts a hollow optical fiber with a central atmospheric hole; (2) Applying non-uniform pressure on the optical fiber by using a cylindrical pressing block to enable the optical fiber to change the inner concave angle, and taking the inner concave angle as an intermediate quantity to obtain a plurality of groups of inner concave angles and corresponding pressure values and 10ps walk-off distances; (3) Fitting the concave angle and the 10ps walk-off distance to obtain a first fitting formula, and fitting the concave angle and the pressure value to obtain a second fitting formula; (4) And measuring a 10ps walk-off distance, obtaining a corresponding concave angle according to a first fitting formula, and obtaining a corresponding pressure value according to a second fitting formula.
7. The method of claim 6, wherein the fiber structure has a plurality of air hole layers outside the central air hole, and the air hole layers are formed by a plurality of small air holes arranged in a ring shape.
8. The optical fiber pressure sensing method according to claim 6, wherein the OAM mode in the optical fiber is formed by superposition of odd-even components of the vector mode HE or EH as shown in formula (1): Wherein l is topological charge, j is pi/2 phase difference between an even mode and an odd mode of the same vector mode, m is a radial index, the superscript + -indicates a circular polarization direction of a left hand or a right hand, the subscript + -indicates a right hand or a left hand direction of a phase wavefront, even indicates an even component, odd indicates an odd component, and an OAM mode selects a vector mode of 4 th order or more.
9. The optical fiber pressure sensing method according to claim 8, wherein the calculation formula of the 10ps walk-off distance L 10ps is: Where c is the speed of light in vacuum, 10ps is time, Is the effective refractive index of the even mode, Is the effective refractive index of the odd mode.
10. The method of claim 6, wherein the first and second fitting formulas are each fitted using a cftool tool in matlab.

Description

Optical fiber pressure sensing method based on orbital angular momentum mode Technical Field The invention relates to an optical fiber pressure sensing method, in particular to an optical fiber pressure sensing method based on an orbital angular momentum mode. Background One of the advantages of OAM (orbital angular momentum) based sensing is its multiplexing capability, where different OAM modes can be used as independent sensing channels, multiplexing multiple pressure sensors in the same fiber. Each OAM mode represents a different sensing channel and pressure measurements can be made simultaneously at different points along the fiber. Furthermore, OAM modes are not susceptible to certain common disturbances, such as temperature variations and bending, which may affect other types of fiber sensors because OAM modes are based on the spatial phase distribution of light, rather than the intensity or polarization of light, and are therefore less sensitive to certain environmental disturbances. OAM-based sensing can also be implemented in a non-invasive manner, which is particularly useful in applications where direct contact with the object under test is not desired or possible, as the fiber itself is the sensor. The optical fiber pressure sensor adopting the OAM mode has compact structure and light weight, and is suitable for remote and distributed sensing application. The ability to multiplex multiple sensors in one fiber makes it advantageous to monitor pressure changes over a long distance, allowing pressure changes at different points to be monitored simultaneously. Such distributed sensing capability is very valuable in structural health monitoring and oil and gas pipeline monitoring applications. Although the application of the OAM mode in the optical fiber pressure sensing is a promising research field, at present, the early development stage is still in progress, and how to realize the pressure measurement is still a problem to be solved. Disclosure of Invention The invention aims to provide an optical fiber pressure sensing method based on an orbital angular momentum mode, which firstly provides that a 10ps walk-off distance of an OAM mode in an optical fiber is used as a sensing measurement value, the optical fiber deforms due to pressure, the walk-off distance of the OAM mode is obviously changed due to the deformation, and the deformation degree of the optical fiber is analyzed by measuring the characteristic distance, so that the measurement of the pressure is realized. The optical fiber pressure sensing method based on the orbital angular momentum mode comprises the following steps: (1) Determining an optical fiber and an OAM mode in the optical fiber, wherein the optical fiber adopts a hollow optical fiber with a central atmospheric hole; (2) Applying uniform pressure on the optical fiber by utilizing a square pressing block to enable the optical fiber to generate elliptical deformation, and taking elliptical eccentricity as an intermediate quantity to obtain a plurality of groups of elliptical eccentricities, corresponding pressure values and 10ps walk-away distances; (3) Fitting the elliptical eccentricity and the 10ps walk-off distance to obtain a first fitting formula, and fitting the elliptical eccentricity and the pressure value to obtain a second fitting formula; (4) And measuring a 10ps walk-off distance, obtaining a corresponding elliptical eccentricity according to a first fitting formula, and obtaining a corresponding pressure value according to a second fitting formula. Further, a plurality of air hole layers are arranged outside the central atmospheric hole in the optical fiber structure, and each air hole layer is composed of a plurality of small air holes which are annularly arranged. Further, the OAM mode in the optical fiber is formed by superposition of parity components of the vector mode HE or EH, as shown in equation (1): wherein l is topological charge, j is pi/2 phase difference between an even mode and an odd mode of the same vector mode, m is a radial index, the superscript + -indicates a circular polarization direction of a left hand or a right hand, the subscript + -indicates a right-hand or left-hand direction of a phase wavefront, even indicates an even component, and odd indicates an odd component; the OAM mode selects a vector mode of order 4 or more. Further, the calculation formula of the 10ps walk-off distance L 10ps is: Where c is the speed of light in vacuum, 10ps is time, Is the effective refractive index of the even mode,Is the effective refractive index of the odd mode. Further, the first fitting formula and the second fitting formula are both fitted by using cftool tools in matlab. As an alternative, the optical fiber pressure sensing method based on the orbital angular momentum mode according to the invention comprises the following steps: (1) Determining an optical fiber and an OAM mode in the optical fiber, wherein the optical fiber adopts a hollow op