CN114964328A - All-fiber angular momentum interference sensing measurement system and method based on spiral grating - Google Patents

All-fiber angular momentum interference sensing measurement system and method based on spiral grating Download PDF

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CN114964328A
CN114964328A CN202210508065.1A CN202210508065A CN114964328A CN 114964328 A CN114964328 A CN 114964328A CN 202210508065 A CN202210508065 A CN 202210508065A CN 114964328 A CN114964328 A CN 114964328A
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CN114964328B (en
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赵华
郭晨吉
郝媛媛
陆华丽
黄训华
王鹏
郝辉
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Nanjing Normal University
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    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
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    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/161—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by interferometric means
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Abstract

The invention discloses a helical grating-based all-fiber angular momentum interference sensing measurement system and a helical grating-based all-fiber angular momentum interference sensing measurement method.A single-wavelength laser emits a fundamental mode Gaussian beam to a first fiber coupler, then the fundamental mode Gaussian beam passes through a first orbit angular momentum beam conversion transmission module and a second orbit angular momentum beam conversion transmission module respectively, then the fundamental mode Gaussian beam is combined and passes through a second fiber coupler, then an interference beam I is emitted through a collimating mirror, a beam rotation angle detection module receives the interference beam I and detects a rotation angle delta alpha of the interference beam I; the sensing optical fiber module is arranged on the surface of the first or second orbital angular momentum light beam conversion and transmission module and is used for providing a sensing quantity gamma to be measured. According to the method, a first spiral grating and a second spiral grating which generate p-order and q-order orbital angular momentum mode light beams are manufactured according to the setting requirement of a grating period, then petal-shaped interference light beams with the number of petals p-q are obtained, the rotation angle delta alpha of the interference light beams is measured, and a relation function delta alpha is calibrated to g (gamma) according to the relation between the rotation angle delta alpha and a measured sensing quantity gamma; and calculating the sensing quantity gamma to be measured according to the relation delta alpha between the delta alpha and the measured sensing quantity gamma, namely g (gamma).

Description

All-fiber angular momentum interference sensing measurement system and method based on spiral grating
Technical Field
The invention mainly relates to the technical field of optical fiber sensors, in particular to a system and a method for measuring full-optical-fiber angular momentum interference sensing based on a spiral grating.
Background
Orbital angular momentum is a novel photonic property, demonstrated by Allen et al, 1992, a vortex beam carrying orbital angular momentum: an orbital angular momentum beam of
Figure BDA0003636868710000011
A particular spiral phase wavefront is shown, where j is in imaginary units,
Figure BDA0003636868710000012
and l is the topological charge number, and the orbital angular momentum beams with different topological charge numbers are mutually orthogonal. These characteristics make vortex light beam have wide application prospect in optical sensing and optical communication.
Recent studies have shown that optical fibers such as few-mode, ring core and photonic crystal can effectively transmit orbital angular momentum modes over long distances, so the development of optical fiber sensors based on optical fiber orbital angular momentum beams becomes feasible. The orbit angular momentum mode has spiral phase distribution, and a spiral interference beam pattern can be obtained when the orbit angular momentum mode interferes with the Gaussian beam; when orbital angular momentum beams with different topological charge numbers interfere, a petal-shaped interference beam pattern is generated. A change in the phase of one of the beams participating in the interference causes a corresponding rotation of the interference beam pattern. Because the phase of the light beam passing through the sensing quantity measuring area can be changed due to the change of various sensing quantities, the corresponding sensing quantities can be measured with high precision and high sensitivity by detecting the rotation angle of the interference pattern.
The spiral fiber grating has spiral refractive index distribution, and researches in recent years prove that the generation and the conversion of optical fiber orbital angular momentum modes with different topological charge numbers can be realized, and the fundamental mode in the optical fiber can be converted into the optical fiber orbital angular momentum mode with the appointed topological charge number at a specific wavelength position by accurately controlling the grating period of the spiral fiber grating. Compared with other optical fiber devices generating optical fiber orbital angular momentum modes, the spiral optical fiber grating has the unique characteristics of low loss and independence of polarization.
A large number of patents and papers research various optical fiber sensors at home and abroad, but most of the optical fiber sensors are not based on the principle of optical fiber orbital angular momentum mode interference. In recent years, optical fiber sensors based on optical fiber orbital angular momentum interference have appeared, but some optical fiber orbital angular momentum modes are generated by using a spatial light modulator, and other optical fiber orbital angular momentum modes are generated by combining optical fiber dislocation and optical fiber torsion, and the orbital angular momentum modes generated by the methods are related to polarization, are relatively large in environmental interference and not stable enough, and are difficult to be widely applied. In addition, most papers and patents adopt a method of interference of orbital angular momentum beams and gaussian beams, the method has small degree of rotation angle discrimination of generated spiral interference beam patterns, and an area array photoelectric detection unit such as a Charge Coupled Device (CCD) which has to realize high-precision detection and has high resolution is high in cost and high in detection complexity.
Disclosure of Invention
The invention aims to: the orbital angular momentum generation method of the all-fiber spiral fiber grating which is irrelevant to polarization can overcome the defects.
In order to achieve the purpose, the invention provides the following technical scheme: the all-fiber angular momentum interference sensing measurement system based on the spiral grating comprises a single-wavelength laser, a first fiber coupler, a first orbital angular momentum beam conversion and transmission module, a second orbital angular momentum beam conversion and transmission module, a sensing fiber module, a second fiber coupler, a beam rotation angle detection module and a collimating mirror;
the first orbital angular momentum beam conversion and transmission module comprises a first transmission optical fiber and a first spiral fiber grating manufactured on the first transmission optical fiber; one end of the first transmission optical fiber forms an input end of the first orbital angular momentum light beam conversion transmission module, and the other end of the first transmission optical fiber forms an output end of the first orbital angular momentum light beam conversion transmission module;
the second orbital angular momentum beam conversion and transmission module comprises a second transmission optical fiber and a second spiral fiber grating manufactured on the second transmission optical fiber; one end of the second transmission optical fiber forms an input end of the second orbital angular momentum light beam conversion transmission module, and the other end of the second transmission optical fiber forms an output end of the second orbital angular momentum light beam conversion transmission module;
the single-wavelength laser emits a fundamental mode Gaussian beam with the wavelength of lambda to the input end of a first optical fiber coupler through a transmission optical fiber, the first optical fiber coupler receives the fundamental mode Gaussian beam with the wavelength of lambda, and the fundamental mode Gaussian beam with the wavelength of lambda is divided into a fundamental mode Gaussian beam A with the wavelength of lambda and a fundamental mode Gaussian beam B with the wavelength of lambda according to a preset proportion;
the first optical fiber coupler outputs a fundamental mode Gaussian beam A with a wavelength lambda to a first orbital angular momentum beam conversion transmission module, one end of the first transmission optical fiber receives the fundamental mode Gaussian beam A with a preset wavelength lambda, and the first spiral optical fiber grating manufactured on the first transmission optical fiber converts the fundamental mode Gaussian beam A with the preset wavelength lambda into an orbital angular momentum beam P with the same wavelength and topological charge number of P;
meanwhile, the first optical fiber coupler outputs a fundamental mode Gaussian beam B with the wavelength lambda to a second orbital angular momentum beam conversion transmission module, and one end of the second transmission optical fiber receives the fundamental mode Gaussian beam B with the preset wavelength lambda; the second spiral fiber grating manufactured on the second transmission fiber converts the fundamental mode Gaussian beam B with the preset wavelength lambda into an orbital angular momentum beam Q with the same wavelength and the topological charge number of Q;
the other end of the first transmission optical fiber outputs an orbital angular momentum light beam P with equal wavelength and topological charge number P, the other end of the second transmission optical fiber outputs an orbital angular momentum light beam Q with equal wavelength and topological charge number Q, the other end of the first transmission optical fiber and the other end of the second transmission optical fiber are respectively connected with a second optical fiber coupler, the second optical fiber coupler combines the orbital angular momentum light beam P with equal wavelength and topological charge number P with equal wavelength and the orbital angular momentum light beam Q with equal wavelength and topological charge number Q to generate an interference light beam I, the output end of the second optical fiber coupler is connected with the light incident end of a collimating mirror, and the light incident end of the collimating mirror receives the interference light beam I; the light emitting end of the collimating mirror faces the input end of the light beam rotation angle detection module and emits the interference light beam I to the input end of the light beam rotation angle detection module, the input end of the light beam rotation angle detection module receives the interference light beam I, and the light beam rotation angle detection module is used for detecting the rotation angle delta alpha of the interference light beam I;
the sensing optical fiber module is arranged on the surface of the first transmission optical fiber or the surface of the second transmission optical fiber and is used for providing a sensing quantity gamma to be measured of the transmission optical fiber arranged on the sensing optical fiber module;
further, the first transmission fiber and the second transmission fiber are any one of few-mode fibers, ring-core fibers or photonic crystal fibers.
Further, the sensing quantity gamma to be measured provided by the sensing optical fiber module is temperature data, magnetic field data, stretching data or torsion data.
Further, the topological charge number P of the orbital angular momentum light beam P generated by the first spiral fiber grating is not equal to the topological charge number Q of the orbital angular momentum light beam Q generated by the second spiral fiber grating, and the number of lobes of the interference light beam I generated by the second fiber coupler is | P-Q |.
Further, the light beam rotation angle detection module is a charge coupled device, a photodetection array or a photodetector.
On the other hand, the invention provides a method of an all-fiber angular momentum interference sensing measurement system based on a spiral grating, when a sensing fiber module is arranged on the surface of a second transmission fiber, steps A to B are executed, and then step C1 is executed to obtain the sensing quantity gamma to be measured between the first transmission fiber and the second transmission fiber q Induced transmission phase difference
Figure BDA0003636868710000031
Then, step D is executed to obtain the transmission phase difference delta beta of the orbital angular momentum light beam Q with the topological charge number Q transmitted by the first transmission optical fiber and the orbital angular momentum light beam P with the topological charge number P transmitted by the second transmission optical fiber; and executing the steps E1 to G1 to obtain the electric field amplitude E 'of the orbital angular momentum light beam Q with the topological charge number Q generated by the second spiral fiber grating' q (r, theta) and the received transmission phase difference
Figure BDA0003636868710000032
Intensity I of petal-shaped interference light beam I with the number of lobes P-Q | generated by combining the orbital angular momentum light beam P with the number of topological charges P generated by the first spiral fiber grating and the orbital angular momentum light beam Q with the number of topological charges Q generated by the second spiral fiber grating, which are influenced by the transmission phase difference delta beta q (r, θ), and then obtaining a rotation angle Δ α of the petal-shaped interference beam by a rotation angle detection method q And according to the rotation angle Delta alpha q A transmission phase difference between the first transmission fiber and the second transmission fiber
Figure BDA0003636868710000041
Through step H1, the sensing quantity gamma to be measured of the sensing measurement optical fiber module is obtained q ；
When the sensing measurement optical fiber module is arranged on the surface of the first transmission optical fiber, steps A to B are executed, and then step C2 is executed to obtain the sensing quantity gamma to be measured between the first transmission optical fiber and the second transmission optical fiber p Induced transmission phase difference
Figure BDA0003636868710000042
Then, step D is executed to obtain the transmission phase difference delta beta of the orbital angular momentum light beam Q with the topological charge number Q transmitted by the first transmission optical fiber and the orbital angular momentum light beam P with the topological charge number P transmitted by the second transmission optical fiber; and executing the steps E2 to G2 to obtain the electric field amplitude E 'of the orbital angular momentum light beam P with the topological charge number P generated by the first spiral fiber grating' p (r, theta) and the received transmission phase difference
Figure BDA0003636868710000043
Intensity I of petal-shaped interference light beam I with the number of lobes P-Q | generated by combining the orbital angular momentum light beam P with the number of topological charges P generated by the first spiral fiber grating and the orbital angular momentum light beam Q with the number of topological charges Q generated by the second spiral fiber grating, which are influenced by the transmission phase difference delta beta p (r, θ), and then obtaining the rotation angle Δ α of the petal-shaped interference beam I by a rotation angle detection method p And according to the rotation angle Delta alpha p A transmission phase difference between the first transmission fiber and the second transmission fiber
Figure BDA0003636868710000044
Through step H2, the sensing quantity gamma to be measured of the sensing optical fiber module (5) is obtained p ；
Step A: based on the effective refractive index of a fundamental mode Gaussian beam in a preset transmission fiber, the effective refractive index of an orbital angular momentum beam P with the topological charge number P generated by a first spiral fiber grating and the effective refractive index of an orbital angular momentum beam Q with the topological charge number Q generated by a second spiral fiber grating, wherein n is respectively the effective refractive index of the fundamental mode Gaussian beam, n is the effective refractive index of the orbital angular momentum beam P, and Q is the effective refractive index of the orbital angular momentum beam Q 0 、n p 、n q (ii) a According to the following formulas respectively:
Λ p ＝p·λ/(n 0 -n p )，
Λ q ＝q·λ/(n 0 -n q )，
calculating the period Lambda of the first spiral fiber grating p And a second spiral fiber grating period Λ q (ii) a Wherein λ is the wavelength; then entering step B;
and B: according to the following formula:
E p (r,θ)＝R p (r)exp(jpθ)exp(j2πn p z/λ)，
E q (r,θ)＝R q (r)exp(jqθ)exp(j2πn q z/λ)，
respectively calculating the electric field amplitude E of the orbital angular momentum light beam P with the topological charge number P generated by the first spiral fiber bragg grating p (r, theta), electric field amplitude E of orbital angular momentum beam Q with topological charge number Q generated by second spiral fiber grating q (R, θ) wherein R p (R, θ) represents the transverse field distribution of the orbital angular momentum beam P with topological charge number P, R q (r, θ) represents the transverse field distribution of an orbital angular momentum beam with topological charge number q, z is the propagation direction, λ is the wavelength, r is the distance from the pole on polar coordinates, θ is the angle from the polar axis in the counterclockwise direction, and j is the imaginary unit;
step C1: the length of an optical fiber of a sensing part of a sensing optical fiber module (5) on a second transmission optical fiber is preset to be L m The refractive index of the optical fiber of the sensing part of the sensing optical fiber module (5) on the second transmission optical fiber is n eff When the sensing optical fiber module (5) is used for sensing the sensing quantity gamma to be measured q When the change occurs, the following formula is adopted:
Figure BDA0003636868710000051
calculating the sensing quantity gamma to be measured between the first transmission optical fiber and the second transmission optical fiber q Induced transmission phase difference
Figure BDA0003636868710000052
Wherein, Δ n eff (γ q ) For the sensed quantity gamma to be measured q Induced length of L m Of the transmission fiber, Δ L m (γ q ) Is the change in length of the transmission fiber caused by the sensed quantity to be measured;
step C2: the optical fiber length of a sensing part of a sensing optical fiber module (5) on the first transmission optical fiber is preset to be L' m Sensing optical fiber mode on second transmission optical fiberThe refractive index of the optical fiber of the block (5) sensing part is n' eff When the sensing optical fiber module (5) is used for sensing the sensing quantity gamma to be measured p When the change occurs, the following formula is adopted:
Figure BDA0003636868710000053
calculating the sensing quantity gamma to be measured between the first transmission optical fiber and the second transmission optical fiber p Induced transmission phase difference
Figure BDA0003636868710000054
Wherein, delta n' eff (γ p ) For the sensed quantity gamma to be measured p Length of origin is L' m Of the transmission fiber of (1), Δ L' m (γ p ) Is the change of the length of the transmission fiber caused by the sensing quantity to be measured;
step D: according to the following formula:
Δβ＝2π(n q L q -n p L p )/λ，
calculating the transmission phase difference Delta beta, L of the orbital angular momentum light beam Q with the topological charge number Q transmitted by the first transmission optical fiber and the orbital angular momentum light beam P with the topological charge number P transmitted by the second transmission optical fiber q Is the second transmission fiber length, L p Is a first transmission fiber length;
step E1: according to the following formula:
Figure BDA0003636868710000061
calculating the electric field amplitude E 'of orbital angular momentum light beam Q with topological charge number Q generated by the second spiral fiber grating when the sensing fiber module (5) is positioned on the surface of the second sensing fiber' q (r,θ)；
Step E2: according to the following formula:
Figure BDA0003636868710000062
calculating the electric field amplitude E 'of the orbital angular momentum light beam P with topological charge number P generated by the first spiral fiber grating when the sensing fiber module (5) is arranged on the surface of the first sensing fiber' p (r,θ)；
Step F1: according to the following formula:
E I (r,θ)＝E p (r,θ)+E' q (r,θ)，
calculating the electric field amplitude E of the interference light beam I when the sensing optical fiber module (5) is arranged on the surface of the second sensing optical fiber I (r, θ); step F2: according to the following formula:
E′ I (r,θ)＝E' p (r,θ)+E q (r,θ)，
calculating the electric field amplitude E 'of interference light beam I when sensing measurement fiber module (5) is placed on first orbital angular momentum light beam conversion transmission module (3)' I (r,θ)；
Step G1: according to the following formula:
Figure BDA0003636868710000063
calculating the intensity I (r, theta) of the interference light beam I, and determining the interference light beam I to be a petal-shaped interference light beam with the number of petals p-q |; wherein, I DC (r, theta) and I AC (r, θ) respectively represent the direct current intensity and alternating current intensity of the petal-shaped interference light beam I with the number of petals | p-q |;
step G2: according to the following formula:
Figure BDA0003636868710000071
calculating the intensity I' (r, theta) of the interference light beam I, and determining the interference light beam I to be a petal-shaped interference light beam with the number of petals p-q |; wherein, I' DC (r, theta) and I' AC (r, θ) respectively represent the direct current intensity and the alternating current intensity of the petal-shaped interference beam I with the number of petals | p-q |;
step H1: the rotation angle detection method is based on the number of lobes being | p-q |Rotation angle delta alpha of petal-shaped interference light beam I q By
Figure BDA0003636868710000072
Is determined, i.e. is
Figure BDA0003636868710000073
And is
Figure BDA0003636868710000074
Further obtaining the rotation angle delta alpha of the interference beam I q And measuring the sensed quantity gamma q In relation to (2)
Figure BDA0003636868710000075
Finally obtaining the sensing quantity gamma to be measured when the sensing measurement optical fiber module (5) is arranged on the second transmission optical fiber q 。
Step H2: the rotation angle detection method is based on the rotation angle delta alpha of the petal-shaped interference light beam I with the number of petals p-q | p By
Figure BDA0003636868710000076
Is determined, i.e.
Figure BDA0003636868710000077
And is
Figure BDA0003636868710000078
Further obtaining the rotation angle delta alpha of the interference beam I p And measuring the sensed quantity gamma p The relationship of (1):
Figure BDA0003636868710000079
finally obtaining the sensing quantity gamma to be measured when the sensing optical fiber module (5) is arranged on the first transmission optical fiber p 。
Further, the rotation angle measurement method is any one of a cross-correlation method, a four-step phase shift method and a centroid phase shift measurement method.
The structure and the manufacturing method are simple, and the spiral fiber grating can stably generate a orbital angular momentum mode and has the characteristics of polarization independence and electromagnetic interference resistance; the adopted orbital angular momentum interferometry has the advantages of high precision and sensitivity. The all-fiber measurement structure has the characteristics of electromagnetic interference resistance and stability.
Drawings
FIG. 1 is a schematic experimental block diagram of a helical grating-based all-fiber angular momentum interferometric sensing measurement system and method;
FIG. 2 is a transmission spectrum of a spiral fiber grating fabricated to produce a beam of orbital angular momentum mode with a topological charge number of + 1;
FIG. 3 is the transmission spectrum of a spiral fiber grating for writing an orbital angular momentum mode light beam with a topological charge number of-1;
FIG. 4 is a schematic experimental block diagram of a temperature sensing measurement system and method based on helical grating full-fiber angular momentum interference;
FIG. 5 is a diagram of the interference pattern of the conjugate orbital angular momentum beams obtained from the experiment of the present invention;
FIG. 6 is a schematic experimental block diagram of a strain sensing measurement system and method based on helical grating full-fiber angular momentum interference;
FIG. 7 shows the interference pattern of the light beams with the angular momentum of the conjugated orbitals obtained by the experiment of the present invention.
Detailed Description
In order to better understand the technical content of the present invention, specific embodiments are described below with reference to the accompanying drawings.
Aspects of the invention are described herein with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. Embodiments of the invention are not limited to those illustrated in the drawings. It is to be understood that the invention is capable of implementation in any of the numerous concepts and embodiments described hereinabove or described in the following detailed description, since the disclosed concepts and embodiments are not limited to any embodiment. In addition, some aspects of the present disclosure may be used alone, or in any suitable combination with other aspects of the present disclosure.
The invention discloses a sensing measurement system and a sensing measurement method for realizing + 1-order and-1-order orbital angular momentum interference by taking two spiral fiber gratings with topology charge number p being 1 and topology charge number q being-1 as an example. The structure of the all-fiber angular momentum interference sensing measurement system based on the spiral grating is shown in figure 1 and comprises a single-wavelength laser (1), a first fiber coupler (2), a first orbital angular momentum beam conversion and transmission module (3), a second orbital angular momentum beam conversion and transmission module (4), a sensing fiber module (5), a second fiber coupler (6), a beam rotation angle detection module (7) and a collimating mirror (8);
the first orbital angular momentum beam conversion and transmission module (3) comprises a first transmission optical fiber and a first spiral fiber grating manufactured on the first transmission optical fiber; one end of the first transmission optical fiber forms an input end of the first orbital angular momentum light beam conversion and transmission module (3), and the other end of the first transmission optical fiber forms an output end of the first orbital angular momentum light beam conversion and transmission module (3);
the second orbital angular momentum beam conversion and transmission module (4) comprises a second transmission optical fiber and a second spiral fiber grating manufactured on the second transmission optical fiber; one end of the second transmission optical fiber forms an input end of the second orbital angular momentum light beam conversion and transmission module (4), and the other end of the second transmission optical fiber forms an output end of the second orbital angular momentum light beam conversion and transmission module (4); the first transmission optical fiber and a first spiral fiber grating manufactured on the first transmission optical fiber, and the second transmission optical fiber and a second spiral fiber grating manufactured on the second transmission optical fiber are manufactured by heating and twisting a carbon dioxide laser;
the left-handed and right-handed spiral fiber gratings are respectively inscribed on the spiral fiber grating to generate an orbital angular momentum mode with the topological charge number p being 1 and the topological charge number q being-1. Referring to fig. 2, the first spiral fiber grating and the first transmission fiber generate an orbital angular momentum mode with a topological charge number p equal to 1, and the resonant wavelength thereof is around 1550 nm; referring to fig. 3, the second spiral fiber grating and the second transmission fiber generate an orbital angular momentum mode with topological charge number q-1, and the resonant wavelength thereof is around 1550 nm.
The single-wavelength laser (1) emits a fundamental mode Gaussian beam with the wavelength of 1550nm to the input end of a first optical fiber coupler (2) through a transmission optical fiber, the first optical fiber coupler (2) receives the fundamental mode Gaussian beam with the wavelength of 1550nm, and the ratio of the fundamental mode Gaussian beam to the fundamental mode Gaussian beam with the wavelength of 1550nm is determined according to the following steps of 50: dividing the fundamental mode Gaussian beam with the wavelength of 1550nm into a fundamental mode Gaussian beam A with the wavelength of 1550nm and a fundamental mode Gaussian beam B with the wavelength of 1550nm according to the power ratio of 50;
the first optical fiber coupler (2) outputs a fundamental mode Gaussian beam A with the wavelength of 1550nm to a first orbital angular momentum beam conversion and transmission module (3), one end of the first transmission optical fiber receives the fundamental mode Gaussian beam A with the wavelength of 1550nm, and the first spiral optical fiber grating manufactured on the first transmission optical fiber converts the fundamental mode Gaussian beam A with the wavelength of 1550nm into an orbital angular momentum beam P with the same wavelength and the topological charge number P equal to 1;
meanwhile, the first optical fiber coupler (2) outputs a fundamental mode Gaussian beam B with the wavelength of 1550nm to the second orbital angular momentum beam conversion and transmission module (4), and one end of the second transmission optical fiber receives the fundamental mode Gaussian beam B with the preset wavelength of 1550 nm; the second spiral fiber grating manufactured on the second transmission fiber converts the fundamental mode Gaussian beam B with the wavelength of 1550nm into a track angular momentum beam Q with the same wavelength and the topological charge number Q-1;
the other end of the first transmission optical fiber outputs an orbital angular momentum light beam P with equal wavelength and topological charge number P equal to 1, the other end of the second transmission optical fiber outputs an orbital angular momentum light beam Q with equal wavelength and topological charge number Q equal to 1, the other end of the first transmission optical fiber and the other end of the second transmission optical fiber are respectively connected with a second optical fiber coupler (6), the second optical fiber coupler combines the orbital angular momentum light beam P with equal wavelength and topological charge number P equal to 1 with the orbital angular momentum light beam Q with equal wavelength and topological charge number Q equal to 1 to generate an interference light beam I, the output end of the second optical fiber coupler (6) is connected with the light incident end of a collimating mirror (8), and the light incident end of the collimating mirror (8) receives the interference light beam I; the light emitting end of the collimating mirror (8) faces the input end of the light beam rotation angle detection module (7) and emits the interference light beam I to the input end of the light beam rotation angle detection module (7), the input end of the light beam rotation angle detection module (7) receives the interference light beam I, and the light beam rotation angle detection module (7) is used for detecting the rotation angle delta alpha of the interference light beam I;
the sensing optical fiber module (5) is arranged on the surface of the first transmission optical fiber or the surface of the second transmission optical fiber and is used for providing a sensing quantity gamma to be measured of the transmission optical fiber; the sensing optical fiber module (5) is used for providing and detecting sensing quantities which can cause the optical path length change of the light beam in the optical fiber where the sensing optical fiber module is located, and the measured sensing quantities include but are not limited to temperature, stretching, magnetic fields, torsion and the like. The second optical fiber coupler (6) is used for interfering the two generated orbital angular momentum beams, and when the two generated orbital angular momentum beams with the topological charge number p of 1 and the topological charge number q of-1 interfere, a petal-shaped interference pattern with the lobe number of 2 is generated. The light beam rotation angle detection module (7) is used for detecting the rotation angle of the petal-shaped interference light beam, collecting image data of the petal-shaped interference light beam by adopting a CCD (charge coupled device), and then calculating the rotation angle by a centroid phase shift measurement method to obtain sensing variation.
Centroid phase shift measurement method: smoothing and denoising the received image, calculating a global threshold value, carrying out binarization processing on the image according to the calculated threshold value, and searching the mass center (x) of two light spots in the binarized image 0 ,y 0 )，(x 1 ,y 1 ) Using α ═ arctan (x) 1 -x 0 )/(y 1 -y 0 ) Obtaining the angle value alpha of the initial interference image 1 Obtaining the angle value alpha of the interference image after rotation by the same method 2 The angle of rotation of the petal interference pattern is delta alpha-alpha 2 -α 1 . And calculating the to-be-measured sensing quantity gamma according to the relation delta alpha between the measured rotation angle delta alpha and the measured sensing quantity gamma, namely g (gamma).
Example 1: the temperature sensing measurement system and method based on the spiral grating full-fiber angular momentum interference is realized by referring to the structure of FIG. 4. The sensing optical fiber module (5) utilizes a heating controller to adjust the temperature change of a sensing measuring areaAnd the length of the optical fiber in the temperature sensing and measuring area is 8 cm. Temperature of the heating controller from T 0 The change to T can cause the refractive indexes of the optical fibers in the sensing measurement area of the first spiral fiber grating and the first transmission optical fiber to change, and the relation n is satisfied T ＝n T0 [η(T-T 0 )]Where η is the thermo-optic coefficient and the thermal expansion coefficient of the fiber. The temperature-induced refractive index change causes the corresponding refractive index change deltan of the optical fiber in the section of the sensing measurement area in the orbital angular momentum mode eff And cause corresponding transmission phase changes
Figure BDA0003636868710000101
Wherein L is m λ is the wavelength for the fiber sensing length. The transmission phase difference eventually appears to interfere with the rotation of the petal-like pattern.
As shown in fig. 5, the phase difference between the two orbital angular momentum beams changes with the temperature change of the heating controller, and the petal interference pattern rotates, (a) the interference pattern at a heating controller temperature of 30 ℃, (b) the interference pattern at a heating controller temperature of 35 ℃, (c) the interference pattern at a heating controller temperature of 40 ℃, and (d) the interference pattern at a heating controller temperature of 45 ℃. The initial temperature of the heating controller is 30 ℃, and the temperature sensor sensitivity can reach 230.706 degrees/DEG C when the temperature is increased by 5 ℃ each time until the temperature reaches 80 ℃. Assuming that the detection precision of the rotation phase can reach 0.01 ℃, the temperature sensing precision can reach 0.000043 ℃.
Example 2: the structure of figure 6 is used for realizing a strain sensing measurement system and a strain sensing measurement method based on the all-fiber angular momentum interference of the spiral grating. The sensing optical fiber module (5) utilizes a strain controller to adjust the strain of a sensing measurement area, the length of an optical fiber of the temperature sensing measurement area is 5 cm, the length and the refractive index of a first spiral optical fiber grating and a first transmission optical fiber can be changed under the action of the strain controller, and a length difference and a refractive index difference are generated between the first spiral optical fiber grating and a second transmission optical fiber, so that a conjugated orbit angular momentum light beam generates a transmission phase difference
Figure BDA0003636868710000111
The strain induced phase change can be expressed as
Figure BDA0003636868710000112
Wherein n is the refractive index of the spiral fiber grating, L m Is the optical fiber sensing length, λ is the wavelength, u is the Poisson's ratio, P 11 And P 12 Is the elasto-optic coefficient. The transmission phase difference eventually appears to interfere with the rotation of the petal-like pattern.
As shown in fig. 7, as the strain controller starts to stretch, the optical fiber is strained, the phase difference between the two orbital angular momentum beams changes, and the petal interference pattern rotates, (a) the pattern corresponds to the interference pattern when the strain becomes 0 μ ∈, (b) the pattern corresponds to the interference pattern when the strain becomes 1 μ ∈, (c) the pattern corresponds to the interference pattern when the strain becomes 2 μ ∈, and (d) the pattern corresponds to the interference pattern when the strain becomes 3 μ ∈. The initial strain is 0 mu epsilon, each time stretching is 1 mu epsilon, and the sensitivity of stretching sensing can reach 13.4028 DEG/. mu.epsilon when the strain is 10 mu epsilon. If the detection precision of the rotation phase can reach 0.01 degrees, the stretching sensing precision can reach 0.00075 mu epsilon.
The invention provides a method of an all-fiber angular momentum interference sensing measurement system based on a spiral grating, which comprises the steps of A to B when a sensing fiber module (5) is arranged on the surface of a second transmission fiber, and then C1 is executed to obtain the sensing quantity gamma to be measured between the first transmission fiber and the second transmission fiber q Induced transmission phase difference
Figure BDA0003636868710000113
Then, step D is executed to obtain the transmission phase difference delta beta of the orbital angular momentum light beam Q with the topological charge number Q transmitted by the first transmission optical fiber and the orbital angular momentum light beam P with the topological charge number P transmitted by the second transmission optical fiber; and executing the steps E1 to G1 to obtain the electric field amplitude E 'of the orbital angular momentum light beam Q with the topological charge number Q generated by the second spiral fiber grating' q (r, theta) and the received transmission phase difference
Figure BDA0003636868710000114
And a transmission phase difference ΔThe intensity I of a petal-shaped interference beam I with the number of lobes P-Q | generated by combining a track angular momentum beam P with the number of topological charges P generated by a first spiral fiber grating and a track angular momentum beam Q with the number of topological charges Q generated by a second spiral fiber grating under the influence of beta q (r, θ), and then obtaining a rotation angle Δ α of the petal-shaped interference beam by a rotation angle detection method q And according to the rotation angle Delta alpha q A transmission phase difference between the first transmission fiber and the second transmission fiber
Figure BDA0003636868710000121
Through the step H1, the sensing quantity gamma to be measured of the sensing measurement optical fiber module (5) is obtained q ；
When the sensing measurement optical fiber module (5) is arranged on the surface of the first transmission optical fiber, the steps A to B are executed, and then the step C2 is executed to obtain the sensing quantity gamma to be measured between the first transmission optical fiber and the second transmission optical fiber p Induced transmission phase difference
Figure BDA0003636868710000122
Then, step D is executed to obtain the transmission phase difference delta beta of the orbital angular momentum light beam Q with the topological charge number Q transmitted by the first transmission optical fiber and the orbital angular momentum light beam P with the topological charge number P transmitted by the second transmission optical fiber; and executing the steps E2 to G2 to obtain the electric field amplitude E 'of the orbital angular momentum light beam P with the topological charge number P generated by the first spiral fiber grating' p (r, theta) and the received transmission phase difference
Figure BDA0003636868710000123
Intensity I of petal-shaped interference light beam I with the number of lobes P-Q | generated by combining the orbital angular momentum light beam P with the number of topological charges P generated by the first spiral fiber grating and the orbital angular momentum light beam Q with the number of topological charges Q generated by the second spiral fiber grating, which are influenced by the transmission phase difference delta beta p (r, θ), and then obtaining the rotation angle Δ α of the petal-shaped interference beam I by a rotation angle detection method p And according to the rotation angle Delta alpha p A transmission phase difference between the first transmission fiber and the second transmission fiber
Figure BDA0003636868710000124
Through the step H2, the sensing quantity gamma to be measured of the sensing measurement optical fiber module (5) is obtained p ；
Step A: based on the effective refractive index of a fundamental mode Gaussian beam in a preset transmission fiber, the effective refractive index of an orbital angular momentum beam P with the topological charge number P generated by a first spiral fiber grating and the effective refractive index of an orbital angular momentum beam Q with the topological charge number Q generated by a second spiral fiber grating, wherein n is respectively the effective refractive index of the fundamental mode Gaussian beam, n is the effective refractive index of the orbital angular momentum beam P, and Q is the effective refractive index of the orbital angular momentum beam Q 0 、n p 、n q (ii) a According to the following formulas respectively:
Λ p ＝p·λ/(n 0 -n p )，
Λ q ＝q·λ/(n 0 -n q )，
calculating the period Λ of the first spiral fiber grating p And a second spiral fiber grating period Λ q (ii) a Wherein λ is the wavelength; then entering step B;
and B: according to the following formula:
E p (r,θ)＝R p (r)exp(jpθ)exp(j2πn p z/λ)，
E q (r,θ)＝R q (r)exp(jqθ)exp(j2πn q z/λ)，
respectively calculating the electric field amplitude E of the orbital angular momentum light beam P with the topological charge number P generated by the first spiral fiber bragg grating p (r, theta), electric field amplitude E of orbital angular momentum beam Q with topological charge number Q generated by second spiral fiber grating q (R, θ) wherein R p (R, θ) represents the transverse field distribution of the orbital angular momentum beam P with topological charge number P, R q (r, θ) represents the transverse field distribution of an orbital angular momentum beam with topological charge number q, z is the propagation direction, λ is the wavelength, r is the distance from the pole on polar coordinates, θ is the angle from the polar axis in the counterclockwise direction, and j is the imaginary unit;
step C1: the length of an optical fiber of a sensing part of a sensing optical fiber module (5) on a second transmission optical fiber is preset to be L m The sensing optical fiber module (5) on the second transmission optical fiberThe refractive index of the optical fiber of the sensing part is n eff When the sensing optical fiber module (5) is used for sensing the sensing quantity gamma to be measured q When the change occurs, the following formula is adopted:
Figure BDA0003636868710000131
calculating the sensing quantity gamma to be measured between the first transmission optical fiber and the second transmission optical fiber q Induced transmission phase difference
Figure BDA0003636868710000132
Wherein, Δ n eff (γ q ) For the sensed quantity gamma to be measured q Induced length of L m Of the transmission fiber, Δ L m (γ q ) Is the change in length of the transmission fiber caused by the sensed quantity to be measured;
step C2: the optical fiber length of a sensing part of a sensing optical fiber module (5) on the first transmission optical fiber is preset to be L' m The refractive index of the optical fiber of the sensing part of the sensing fiber module (5) on the second transmission fiber is n' eff When the sensing optical fiber module (5) is used for sensing the sensing quantity gamma to be measured p When the change occurs, the following formula is adopted:
Figure BDA0003636868710000133
calculating the sensing quantity gamma to be measured between the first transmission optical fiber and the second transmission optical fiber p Induced transmission phase difference
Figure BDA0003636868710000134
Wherein, delta n' eff (γ p ) For the sensed quantity gamma to be measured p Length of origin is L' m Of the transmission fiber of (1), Δ L' m (γ p ) Is the change in length of the transmission fiber caused by the sensed quantity to be measured;
step D: according to the following formula:
Δβ＝2π(n q L q -n p L p )/λ，
calculating the transmission phase difference Delta beta, L of the orbital angular momentum light beam Q with the topological charge number Q transmitted by the first transmission optical fiber and the orbital angular momentum light beam P with the topological charge number P transmitted by the second transmission optical fiber q Is the length of the second transmission fiber, L p Is a first transmission fiber length;
step E1: according to the following formula:
Figure BDA0003636868710000141
calculating the electric field amplitude E 'of orbital angular momentum light beam Q with topological charge number Q generated by the second spiral fiber grating when the sensing fiber module (5) is positioned on the surface of the second sensing fiber' q (r,θ)；
Step E2: according to the following formula:
Figure BDA0003636868710000142
calculating the electric field amplitude E 'of orbital angular momentum light beam P with topological charge number P generated by the first spiral fiber grating when the sensing fiber module (5) is arranged on the surface of the first sensing fiber' p (r,θ)；
Step F1: according to the following formula:
E I (r,θ)＝E p (r,θ)+E' q (r,θ)，
calculating the electric field amplitude E of the interference light beam I when the sensing optical fiber module (5) is arranged on the surface of the second sensing optical fiber I (r, θ); step F2: according to the following formula:
E′ I (r,θ)＝E' p (r,θ)+E q (r,θ)，
calculating the electric field amplitude E 'of interference light beam I when sensing measurement fiber module (5) is placed on first orbital angular momentum light beam conversion transmission module (3)' I (r,θ)；
Step G1: according to the following formula:
Figure BDA0003636868710000143
calculating the intensity I (r, theta) of the interference light beam I, and determining the interference light beam I to be a petal-shaped interference light beam with the number of petals p-q |; wherein, I DC (r, theta) and I AC (r, θ) respectively represent the direct current intensity and alternating current intensity of the petal-shaped interference light beam I with the number of petals | p-q |;
step G2: according to the following formula:
Figure BDA0003636868710000151
calculating the intensity I' (r, theta) of the interference light beam I, and determining the interference light beam I to be a petal-shaped interference light beam with the number of petals p-q |; wherein, I' DC (r, θ) and I' AC (r, θ) respectively represent the direct current intensity and alternating current intensity of the petal-shaped interference light beam I with the number of petals | p-q |;
step H1: the rotation angle detection method is based on the rotation angle delta alpha of the petal-shaped interference light beam I with the number of petals p-q | q By
Figure BDA0003636868710000152
Is determined, i.e. is
Figure BDA0003636868710000153
And is
Figure BDA0003636868710000154
Further obtaining the rotation angle delta alpha of the interference beam I q And measuring the sensed quantity gamma q In relation to (2)
Figure BDA0003636868710000155
Finally obtaining the sensing quantity gamma to be measured when the sensing measurement optical fiber module (5) is arranged on the second transmission optical fiber q ；
Step H2: the rotation angle detection method is based on the rotation angle delta alpha of the petal-shaped interference light beam I with the number of petals p-q | p By
Figure BDA0003636868710000156
Is determined, i.e. is
Figure BDA0003636868710000157
And is
Figure BDA0003636868710000158
Further obtaining the rotation angle delta alpha of the interference beam I p And measuring the sensed quantity gamma p In relation to (2)
Figure BDA0003636868710000159
Finally obtaining the sensing quantity gamma to be measured when the sensing optical fiber module (5) is arranged on the first transmission optical fiber p 。
In summary, the present invention utilizes the spiral fiber grating to generate the orbital angular momentum mode, and has the characteristic of polarization independence; the interference method of orbital angular momentum beams with different topological charge numbers is easy to realize high-precision measurement; the all-fiber measurement structure has the characteristics of electromagnetic interference resistance and stability.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be determined by the appended claims.

Claims (7)

1. The all-fiber angular momentum interference sensing measurement system based on the spiral grating is characterized by comprising a single-wavelength laser (1), a first fiber coupler (2), a first orbital angular momentum light beam conversion and transmission module (3), a second orbital angular momentum light beam conversion and transmission module (4), a sensing fiber module (5), a second fiber coupler (6), a light beam rotation angle detection module (7) and a collimating mirror (8);
the first orbital angular momentum beam conversion and transmission module (3) comprises a first transmission optical fiber and a first spiral fiber grating manufactured on the first transmission optical fiber; one end of the first transmission optical fiber forms an input end of the first orbital angular momentum light beam conversion and transmission module (3), and the other end of the first transmission optical fiber forms an output end of the first orbital angular momentum light beam conversion and transmission module (3);
the second orbital angular momentum light beam conversion and transmission module (4) comprises a second transmission optical fiber and a second spiral fiber grating manufactured on the second transmission optical fiber; one end of the second transmission optical fiber forms an input end of the second orbital angular momentum light beam conversion and transmission module (4), and the other end of the second transmission optical fiber forms an output end of the second orbital angular momentum light beam conversion and transmission module (4);
the single-wavelength laser (1) emits a fundamental mode Gaussian beam with the wavelength of lambda to the input end of a first optical fiber coupler (2) through a transmission optical fiber, the first optical fiber coupler (2) receives the fundamental mode Gaussian beam with the wavelength of lambda, and the fundamental mode Gaussian beam with the wavelength of lambda is divided into a fundamental mode Gaussian beam A with the wavelength of lambda and a fundamental mode Gaussian beam B with the wavelength of lambda according to a preset proportion;
the first optical fiber coupler (2) outputs a fundamental mode Gaussian beam A with a wavelength lambda to a first orbital angular momentum beam conversion and transmission module (3), one end of the first transmission optical fiber receives the fundamental mode Gaussian beam A with a preset wavelength lambda, and the first spiral optical fiber grating manufactured on the first transmission optical fiber converts the fundamental mode Gaussian beam A with the preset wavelength lambda into an orbital angular momentum beam P with the same wavelength and topological charge number P;
meanwhile, the first optical fiber coupler (2) outputs a fundamental mode Gaussian beam B with the wavelength lambda to a second orbital angular momentum beam conversion and transmission module (4), and one end of the second transmission optical fiber receives the fundamental mode Gaussian beam B with the preset wavelength lambda; the second spiral fiber grating manufactured on the second transmission fiber converts the fundamental mode Gaussian beam B with the preset wavelength lambda into an orbital angular momentum beam Q with the same wavelength and the topological charge number of Q;
the other end of the first transmission optical fiber outputs an orbital angular momentum light beam P with equal wavelength and topological charge number of P, the other end of the second transmission optical fiber outputs an orbital angular momentum light beam Q with equal wavelength and topological charge number of Q, the other end of the first transmission optical fiber and the other end of the second transmission optical fiber are respectively connected with a second optical fiber coupler (6), the second optical fiber coupler combines the orbital angular momentum light beam P with equal wavelength and topological charge number of P with equal wavelength and the orbital angular momentum light beam Q with equal wavelength and topological charge number of Q to generate an interference light beam I, the output end of the second optical fiber coupler (6) is connected with the light incident end of a collimating mirror (8), and the light incident end of the collimating mirror (8) receives the interference light beam I; a light emitting end of the collimating mirror (8) faces an input end of the beam rotation angle detection module (7) and emits the interference beam I to the input end of the beam rotation angle detection module (7), the input end of the beam rotation angle detection module (7) receives the interference beam I, and the beam rotation angle detection module (7) is used for detecting a rotation angle delta alpha of the interference beam I;
the sensing optical fiber module (5) is arranged on the surface of the first transmission optical fiber or the surface of the second transmission optical fiber and is used for providing a sensing quantity gamma to be measured of the transmission optical fiber.
2. The helical grating-based all-fiber angular momentum interferometry system of claim 1, wherein the first transmission fiber and the second transmission fiber are any one of a few-mode fiber, a ring-core fiber, or a photonic crystal fiber.
3. The helical grating-based all-fiber angular momentum interferometry system according to claim 1, wherein the sensing quantity γ to be measured provided by the sensing fiber module (5) is temperature data, magnetic field data, tension data or torsion data.
4. The spiral-grating-based all-fiber angular momentum interferometric sensing system of claim 1, wherein the topological charge number P of the orbital angular momentum beam P generated by the first spiral fiber grating is not equal to the topological charge number Q of the orbital angular momentum beam Q generated by the second spiral fiber grating, and the lobe number of the interference beam I generated by the second fiber coupler is | P-Q |.
5. The helical grating-based all-fiber angular momentum interferometry system according to claim 1, wherein the beam rotation angle detection module (7) is a charge-coupled device, a photo-detection array, or a photo-detector.
6. The method for the helical grating-based all-fiber angular momentum interferometry system according to any of claims 1-5, wherein steps A-B are performed when the sensing fiber module (5) is disposed on the surface of the second transmission fiber, and then step C1 is performed to obtain the measured sensing quantity γ between the first transmission fiber and the second transmission fiber q Induced transmission phase difference
Figure FDA0003636868700000021
Then, step D is executed to obtain the transmission phase difference delta beta of the orbital angular momentum light beam Q with the topological charge number Q transmitted by the first transmission optical fiber and the orbital angular momentum light beam P with the topological charge number P transmitted by the second transmission optical fiber; and executing the steps E1 to G1 to obtain the electric field amplitude E 'of the orbital angular momentum light beam Q with the topological charge number Q generated by the second spiral fiber grating' q (r, theta) and the received transmission phase difference
Figure FDA0003636868700000022
Intensity I of petal-shaped interference light beam I with the number of lobes P-Q | generated by combining the orbital angular momentum light beam P with the number of topological charges P generated by the first spiral fiber grating and the orbital angular momentum light beam Q with the number of topological charges Q generated by the second spiral fiber grating, which are influenced by the transmission phase difference delta beta q (r, θ), and then obtaining a rotation angle Δ α of the petal-shaped interference beam by a rotation angle detection method q And according to the rotation angle Delta alpha q A transmission phase difference between the first transmission fiber and the second transmission fiber
Figure FDA0003636868700000031
Through step H1, the to-be-measured sensing quantity gamma of the sensing measurement optical fiber module (5) is obtained q ；
When sensing measurementsWhen the optical fiber module (5) is arranged on the surface of the first transmission optical fiber, the steps A to B are executed, and then the step C2 is executed to obtain the sensing quantity gamma to be measured between the first transmission optical fiber and the second transmission optical fiber p Induced transmission phase difference
Figure FDA0003636868700000032
Then, step D is executed to obtain the transmission phase difference delta beta of the orbital angular momentum light beam Q with the topological charge number Q transmitted by the first transmission optical fiber and the orbital angular momentum light beam P with the topological charge number P transmitted by the second transmission optical fiber; and executing the steps E2 to G2 to obtain the electric field amplitude E 'of the orbital angular momentum light beam P with the topological charge number P generated by the first spiral fiber grating' p (r, θ) and the received transmission phase difference
Figure FDA0003636868700000033
Intensity I of petal-shaped interference light beam I with the number of lobes P-Q | generated by combining the orbital angular momentum light beam P with the number of topological charges P generated by the first spiral fiber grating and the orbital angular momentum light beam Q with the number of topological charges Q generated by the second spiral fiber grating, which are influenced by the transmission phase difference delta beta p (r, θ), and then obtaining the rotation angle Δ α of the petal-shaped interference beam I by a rotation angle detection method p And according to the rotation angle Delta alpha p A transmission phase difference between the first transmission fiber and the second transmission fiber
Figure FDA0003636868700000034
Through the step H2, the sensing quantity gamma to be measured of the sensing measurement optical fiber module (5) is obtained p ；
Step A: based on the effective refractive index of a fundamental mode Gaussian beam in a preset transmission fiber, the effective refractive index of an orbital angular momentum beam P with the topological charge number P generated by a first spiral fiber grating and the effective refractive index of an orbital angular momentum beam Q with the topological charge number Q generated by a second spiral fiber grating, wherein n is respectively the effective refractive index of the fundamental mode Gaussian beam, n is the effective refractive index of the orbital angular momentum beam P, and Q is the effective refractive index of the orbital angular momentum beam Q 0 、n p 、n q (ii) a According to the following formulas respectively:
Λ p ＝p·λ/(n 0 -n p )，
Λ q ＝q·λ/(n 0 -n q )，
calculating the period Lambda of the first spiral fiber grating p And a second spiral fiber grating period Λ q (ii) a Wherein λ is the wavelength;
then entering step B;
and B: according to the following formula:
E p (r,θ)＝R p (r)exp(jpθ)exp(j2πn p z/λ)，
E q (r,θ)＝R q (r)exp(jqθ)exp(j2πn q z/λ)，
respectively calculating the electric field amplitude E of the orbital angular momentum light beam P with the topological charge number P generated by the first spiral fiber bragg grating p (r, theta), electric field amplitude E of orbital angular momentum beam Q with topological charge number Q generated by second spiral fiber grating q (R, θ) wherein R p (R, θ) represents the transverse field distribution of the orbital angular momentum beam P with topological charge number P, R q (r, θ) represents the transverse field distribution of an orbital angular momentum beam with topological charge number q, z is the propagation direction, λ is the wavelength, r is the distance from the pole on polar coordinates, θ is the angle from the polar axis in the counterclockwise direction, and j is the imaginary unit;
step C1: the length of an optical fiber of a sensing part of a sensing optical fiber module (5) on a second transmission optical fiber is preset to be L m The refractive index of the optical fiber of the sensing part of the sensing optical fiber module (5) on the second transmission optical fiber is n eff When the sensing optical fiber module (5) is used for sensing the sensing quantity gamma to be measured q When the change occurs, the following formula is adopted:
Figure FDA0003636868700000041
calculating the sensing quantity gamma to be measured between the first transmission optical fiber and the second transmission optical fiber q Induced transmission phase difference
Figure FDA0003636868700000042
Wherein, Δ n eff (γ q ) For the sensed quantity gamma to be measured q Induced length of L m Of the transmission fiber, Δ L m (γ q ) Is the change in length of the transmission fiber caused by the sensed quantity to be measured;
step C2: the optical fiber length of a sensing part of a sensing optical fiber module (5) on the first transmission optical fiber is preset to be L' m The refractive index of the optical fiber of the sensing part of the sensing fiber module (5) on the second transmission fiber is n' eff When the sensing optical fiber module (5) is used for sensing the sensing quantity gamma to be measured p When the change occurs, the following formula is adopted:
Figure FDA0003636868700000043
calculating the sensing quantity gamma to be measured between the first transmission optical fiber and the second transmission optical fiber p Induced transmission phase difference
Figure FDA0003636868700000044
Wherein, delta n' eff (γ p ) For the sensed quantity gamma to be measured p Length of origin is L' m Of the transmission fiber of (1), Δ L' m (γ p ) Is the change in length of the transmission fiber caused by the sensed quantity to be measured;
step D: according to the following formula:
Δβ＝2π(n q L q -n p L p )/λ，
calculating the transmission phase difference Delta beta, L of the orbital angular momentum light beam Q with the topological charge number Q transmitted by the first transmission optical fiber and the orbital angular momentum light beam P with the topological charge number P transmitted by the second transmission optical fiber q Is the length of the second transmission fiber, L p Is a first transmission fiber length;
step E1: according to the following formula:
Figure FDA0003636868700000051
calculating sensing optical fiber modeWhen the block (5) is positioned on the surface of the second sensing optical fiber, the second spiral fiber grating generates the electric field amplitude E 'of the orbital angular momentum light beam Q with topological charge number Q' q (r,θ)；
Step E2: according to the following formula:
Figure FDA0003636868700000052
calculating the electric field amplitude E 'of orbital angular momentum light beam P with topological charge number P generated by the first spiral fiber grating when the sensing fiber module (5) is arranged on the surface of the first sensing fiber' p (r,θ)；
Step F1: according to the following formula:
E I (r,θ)＝E p (r,θ)+E' q (r,θ)，
calculating the electric field amplitude E of the interference light beam I when the sensing optical fiber module (5) is arranged on the surface of the second sensing optical fiber I (r,θ)；
Step F2: according to the following formula:
E′ I (r,θ)＝E' p (r,θ)+E q (r,θ)，
calculating the electric field amplitude E 'of interference light beam I when sensing measurement fiber module (5) is placed on first orbital angular momentum light beam conversion transmission module (3)' I (r,θ)；
Step G1: according to the following formula:
Figure FDA0003636868700000053
calculating the intensity I (r, theta) of the interference light beam I, and determining the interference light beam I to be a petal-shaped interference light beam with the number of petals p-q |;
wherein, I DC (r, theta) and I AC (r, θ) respectively represent the direct current intensity and alternating current intensity of the petal-shaped interference light beam I with the number of petals | p-q |;
step G2: according to the following formula:
Figure FDA0003636868700000061
calculating the intensity I' (r, theta) of the interference light beam I, and determining the interference light beam I to be a petal-shaped interference light beam with the number of petals p-q |; wherein, I' DC (r, theta) and I' AC (r, θ) respectively represent the direct current intensity and alternating current intensity of the petal-shaped interference light beam I with the number of petals | p-q |;
step H1: the rotation angle detection method is based on the rotation angle delta alpha of the petal-shaped interference light beam I with the number of petals p-q | q By
Figure FDA0003636868700000062
Is determined, i.e. is
Figure FDA0003636868700000063
And is
Figure FDA0003636868700000064
Further obtaining the rotation angle delta alpha of the interference beam I q And measuring the sensed quantity gamma q The relationship of (1):
Figure FDA0003636868700000065
finally obtaining the sensing quantity gamma to be measured when the sensing measurement optical fiber module (5) is arranged on the second transmission optical fiber q 。
Step H2: the rotation angle detection method is based on the rotation angle delta alpha of the petal-shaped interference light beam I with the number of petals p-q | p By
Figure FDA0003636868700000066
Is determined, i.e. is
Figure FDA0003636868700000067
And is
Figure FDA0003636868700000068
Further obtaining the rotation angle delta alpha of the interference beam I p And measuring the sensed quantity gamma p In relation to (2)
Figure FDA0003636868700000069
Finally obtaining the sensing quantity gamma to be measured when the sensing optical fiber module (5) is arranged on the first transmission optical fiber p 。
7. The method of claim 6, wherein the rotation angle measurement method is any one of a cross-correlation method, a four-step phase shift method, or a centroid phase shift measurement method.
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