CN112179537A - Fabry-Perot interferometer optical fiber sensor based on optical fiber surface waveguide - Google Patents
Fabry-Perot interferometer optical fiber sensor based on optical fiber surface waveguide Download PDFInfo
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- CN112179537A CN112179537A CN202011075532.3A CN202011075532A CN112179537A CN 112179537 A CN112179537 A CN 112179537A CN 202011075532 A CN202011075532 A CN 202011075532A CN 112179537 A CN112179537 A CN 112179537A
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 84
- 239000000835 fiber Substances 0.000 claims abstract description 27
- 238000000034 method Methods 0.000 claims abstract description 9
- 230000008569 process Effects 0.000 claims abstract description 9
- 238000005530 etching Methods 0.000 claims description 15
- 238000012545 processing Methods 0.000 claims description 7
- 238000001228 spectrum Methods 0.000 claims description 3
- 238000010329 laser etching Methods 0.000 claims description 2
- 230000005540 biological transmission Effects 0.000 claims 1
- 230000008878 coupling Effects 0.000 claims 1
- 238000010168 coupling process Methods 0.000 claims 1
- 238000005859 coupling reaction Methods 0.000 claims 1
- 230000001902 propagating effect Effects 0.000 claims 1
- 238000005259 measurement Methods 0.000 abstract description 12
- 230000035945 sensitivity Effects 0.000 abstract description 9
- 230000000694 effects Effects 0.000 abstract description 5
- 238000012360 testing method Methods 0.000 description 10
- 230000008901 benefit Effects 0.000 description 5
- 230000003595 spectral effect Effects 0.000 description 5
- 238000013461 design Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 238000005253 cladding Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000005459 micromachining Methods 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 230000003321 amplification Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000003292 glue Substances 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 238000002310 reflectometry Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
- G01N2021/458—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods using interferential sensor, e.g. sensor fibre, possibly on optical waveguide
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Abstract
The invention discloses a Fabry-Perot interferometer (FPI) optical fiber sensor based on optical fiber surface waveguide. The device consists of an X-type coupler processed by femtosecond laser, an optical fiber surface waveguide and two FPIs with parallel structures. And the FP cavity on the optical fiber surface waveguide is used as a sensing cavity, and the FP cavity on the fiber core is used as a reference cavity. The X-type coupler couples the light in the fiber core to the optical fiber surface waveguide, and the optical fiber surface waveguide has a strong evanescent field in the process of transmitting the light and can interact with surrounding media, so that the refractive index sensing outside the optical fiber can be carried out. Meanwhile, the sensor uses the principle of vernier effect, so that the measurement sensitivity of the device is greatly improved, and the refractive index or stress can be measured with high sensitivity.
Description
Technical Field
The invention belongs to the field of optical fiber sensing and measurement, and particularly relates to a Fabry-Perot interferometer optical fiber sensor based on optical fiber surface waveguide and preparation thereof.
Background
In recent years, optical fiber stress and refractive index measurement sensors have been widely used in fields such as environmental measurement, industrial manufacturing, and biosensing. For example, FBG and FPI based fiber optic strain measurement sensors, which have the advantages of compact structure and convenient measurement, but generally have the disadvantage of low sensitivity, on the order of several pm. For example, a refractive index sensor in which a fiber grating is written in a micro-nano optical fiber having a diameter close to the wavelength of incident light or a refractive index sensor in which sensing is performed on the surface of a D-type optical fiber has an advantage of high measurement sensitivity, but has a defect in design because the structure is fragile and unstable in performance.
Based on the current situation, the invention designs a Fabry-Perot interferometer optical fiber sensor based on optical fiber surface waveguide, which can be applied to refractive index and high-sensitivity sensing; the optical fiber sensor can achieve the purpose, meanwhile, the structural design ensures that the sensor is insensitive to temperature change, and the interference degree of temperature to the measurement process is reduced. In addition, the device does not damage the complete structure of the single-mode optical fiber in the processing process, so that the characteristics of firm and durable structure and stable performance are ensured.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a Fabry-Perot interferometer optical fiber sensor based on optical fiber surface waveguide and a preparation method thereof; the purpose is to realize high-sensitivity measurement of stress and refractive index through a novel structure, and to ensure the structure firmness and stable performance by adopting a nondestructive micromachining process.
In order to achieve the above object, in one aspect of the present invention, there is provided a fabry-perot interferometer fiber sensor based on fiber surface waveguides, including four parts, a first part being an X-type coupler, a second part being a fiber surface waveguide, a third part being a reference FP cavity, and a fourth part being a sensing FP cavity; wherein the inclined etching line which forms an included angle theta with the axial direction of the optical fiber is used as an X-shaped coupler, and the inclined etching line is changed into an etching line which is parallel to the axial direction of the optical fiber and is used as an optical fiber surface waveguide after extending to the surface of the optical fiber for a certain distance; both FP cavities are formed by mirrors with identical sides.
The axial included angle theta between the X-type coupler and the optical fiber is 0-10 degrees; and the distance between the surface wave of the optical fiber and the surface of the optical fiber is 0 to 5 mu m.
The length of a single-sided reflecting mirror forming the sensing FP cavity is 1 to 5 mu m, and the total length of two-sided reflecting mirrors is 100 to 1000 mu m; the distance between a reflector forming the reference FP cavity and the center of the fiber core is 0-5 mu m; the length of a single reflector is usually 1 to 5 μm; the total length of the two-sided mirror is 100 to 1000 [ mu ] m.
The principle of the invention is that the X-type coupler couples the light in the fiber core to the optical fiber surface waveguide, and the optical fiber surface waveguide has a strong evanescent field in the process of transmitting the light and can interact with the surrounding medium, so that the external refractive index sensing of the optical fiber can be carried out. Meanwhile, when the sensing cavity is acted by external force, the cavity length can be changed, stress sensing can be carried out through corresponding change, and in addition, the sensor uses the principle of vernier effect, so that the measuring sensitivity of the refractive index and the stress is greatly improved.
According to an aspect of the present invention, there is provided a fabry-perot interferometer optical fiber sensor based on an optical fiber surface waveguide, comprising the steps of:
(1) firstly, fixing the single mode fiber without the coating layer on a three-dimensional micromachining platform;
(2) processing an etching line (X-type coupler) which forms an angle of 0-10 degrees with the axis of the optical fiber at the position of 0-5 mu m of the center of the optical fiber core in the step (1) by using femtosecond laser, wherein the etching line is changed into an etching line (optical fiber surface waveguide) which is axially parallel to the optical fiber when extending to the surface of the optical fiber by 0-5 mu m, and the total length of two sections of etching lines is set according to requirements;
(3) processing a reflecting mirror with two completely same parameters on the parallel etching line (optical fiber surface waveguide) in the step (2) to serve as a sensing FP cavity, wherein the total length of the single-sided reflecting mirror is 1 to 5 mu m, the thickness of the single-sided reflecting mirror is 1 to 3 mu m, and the total length of the single-sided reflecting mirror is 100 to 1000 mu m;
(4) on the basis of the step (3), two reflectors with completely same parameters are processed at the left fiber core of the sensing FP cavity to serve as a reference FP cavity, a second reflector of the reference FP cavity and a first reflector of the sensing cavity are in the same vertical optical fiber axial plane, the total length of the single reflector is 1 mu m to 5 mu m, the thickness of the single reflector is 1 mu m to 3 mu m, and the total length of the single reflector is 100 mu m to 1000 mu m.
In general, compared with the prior art, the invention can achieve the following beneficial effects:
1. the sensing head adopts the common single-mode optical fiber with low price, and has the advantages of simple manufacture and low cost;
2. the sensor is based on the vernier effect principle, and can obtain a larger sensitivity amplification factor and correspondingly obtain a larger test sensitivity by adjusting the cavity length difference of the two FP cavities;
3. the sensor can be used for independently detecting two parameters of the refractive index or the strain in design, the test sensitivity is very high, and the common sensor is difficult to simultaneously detect the parameters;
4. the second surface reflector of the reference FP cavity and the first surface reflector of the sensing FP cavity are in the same vertical optical fiber axial plane, so the sensor has compact structure height and small volume;
5. the distance between the two cavities is close, when the temperature changes, the temperatures of the two cavities change simultaneously, and the necessary condition of vernier effect cannot be met (the reference cavity to be measured is kept constant), so that the temperature sensitivity of the invention is not amplified compared with a single-cavity FP optical fiber sensor, and the influence degree of the temperature is very small when the refractive index or strain is measured;
6. the sensor does not damage the complete appearance of the optical fiber in the processing process, and compared with the same type of optical fiber sensor which takes a cavity structure or a tapered structure as a sensing head, the optical fiber sensor has firmer structure, more stable testing performance and higher repeatability.
Drawings
In order to more clearly illustrate the embodiments or technical solutions of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments;
FIG. 1 is a schematic view of a sensor head according to the present invention;
FIG. 2 is a schematic cross-sectional view of a sensor head according to the present invention;
FIG. 3 is a schematic diagram of a test system according to the present invention;
FIG. 4 is a stress measurement fixture for a sensor head according to the present invention.
In the figure, 1-single mode fiber core, 2-X type coupler, 3-fiber surface waveguide, 4-sensing FP cavity, 5-reference FP cavity, 6-single mode fiber cladding, 7-single mode fiber core center point, 8-fiber surface waveguide cross section, 9-reflector cross section, 10-single mode fiber core, 11-single mode fiber cladding, 12-sensing head, 13-circulator, 14-spectrometer 15-broadband light source, 16-reference FP cavity, 17-fixing clamp, 18-sensing FP cavity and 19-moving clamp.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments; it should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; in addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a Fabry-Perot interferometer optical fiber sensor based on an optical fiber surface waveguide, which comprises an X-type coupler, an optical fiber surface waveguide and two FP cavities; the invention is further described with reference to the following drawings and examples.
The structure schematic diagram of the sensing head of the invention is shown in fig. 1, and an X-type coupler 2 and an optical fiber surface waveguide 3 in the implementation are formed by etching a femtosecond laser in a single-mode optical fiber; an axial included angle theta between the X-type coupler 2 and the optical fiber is usually 0-10 degrees, the X-type coupler 2 extends to the position of 0-5 mu m on the surface of the optical fiber and becomes the optical fiber surface waveguide 3 which is parallel to the axial direction of the optical fiber, and the specific lengths of the X-type coupler 2 and the optical fiber surface waveguide 3 are changed along with the degree of theta and actual requirements, and no specific requirement exists.
The reference FP cavity 5 on the single-mode fiber core 1 is formed by two femtosecond laser etching lines serving as reflectors, two reflectors are parallel to each other, the length of a single-sided reflector is usually 1 to 5 mu m, and the thickness of the single-sided reflector is 1 to 3 mu m; the distance between the reflecting mirrors is 100 to 1000 mu m; the sensing FP cavity 4 on the optical fiber surface waveguide 3 is composed of reflectors with two parallel surfaces, light reflected by the reflectors formed by single etching lines on the waveguide is insufficient to form a vernier effect with the whole, and in order to increase the reflectivity of the reflectors, the single-surface reflector is composed of 4 parallel etching lines with the interval of 0.3 mu m; the length of a single reflector is usually 1 to 5 μm; the spacing between the reflectors is 100 to 1000 μm.
The schematic diagram of the cross section structure of the sensing head is shown in FIG. 2, and the etching position of the optical fiber surface waveguide 8 is 0 mu m to 5 mu m away from the optical fiber surface; the distance between the etching position of the reflector cross section 9 and the fiber core central point 7 is 0 mu m to 5 mu m, the processing speed of the femtosecond laser is 0 mu m/s to 10 mu m/s, and the processing power is 100nJ to 400 nJ.
The refractive index testing system is schematically shown in FIG. 3, and comprises a sensing head 12, a circulator 13, a spectrometer 14 and a broadband light source 15; immersing sensor head 12 in a series of standard index matching fluids, the index of refraction of which increases sequentially from 1.410 to 1.460 at 0.01 intervals; after each test, the test piece is cleaned by alcohol until the spectrum recovers to the original spectrum position, and then the next operation is carried out.
Light from a broadband light source 15 passes through the circulator 13 to the sensor head 12, and the spectrometer 14 records spectral information; the X-type coupler 2 couples light in the fiber core to the optical fiber surface waveguide 3, the optical fiber surface waveguide 3 has a strong evanescent field in the process of transmitting light, the evanescent field can interact with surrounding media, when the external refractive index changes, the whole spectral line shifts, and the refractive index parameter of the external environment is reflected through the spectral line shift; compared with the traditional application test system of the optical fiber refractive index sensor, the system is simple, the loss of the optical signal intensity is small, and the system is not influenced by the temperature.
The strain test system and refractive index measurement system are shown in fig. 3, and a sensor stress measurement fixing diagram is shown in fig. 4 and comprises a reference FP cavity 16, a fixing clamp 17, a sensing FP cavity 18 and a moving clamp 19;
in the test process, the reference FP cavity 5 is fixed on a fixing clamp 17 by glue, so that the stress is prevented from interfering the reference FP cavity 5; when the moving fixture 19 applies 0 to 240 mu axial stress at 40 mu intervals to the sensing FP cavity 4, the length of the sensing FP cavity changes, and the strain value is obtained by the amount of spectral shift along with the spectral shift.
The above-mentioned embodiments, which further illustrate the objects, technical solutions and advantages of the present invention, should be understood that the above-mentioned embodiments are only examples of the present invention, and should not be construed as limiting the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A Fabry-Perot interferometer optical fiber sensor based on optical fiber surface waveguide is characterized in that: the fiber surface waveguide type optical fiber coupler consists of an X-type coupler formed by processing femtosecond laser in an optical fiber, an optical fiber surface waveguide, a reference FP cavity on a fiber core and a sensing FP cavity on the optical fiber surface waveguide.
2. According to claim 1, the invention is characterized in that: the optical fiber used in the sensor of claim 1 is a single mode optical fiber.
3. According to claims 1 to 2, the present invention is characterized in that: the X-type coupler is used for coupling light in the fiber core to the optical fiber surface waveguide, and the optical fiber surface waveguide has a strong evanescent field in the process of transmitting light and can interact with surrounding media, so that the refractive index sensing outside the optical fiber can be carried out; the axial included angle between the X-type coupler and the optical fiber is 0-10 degrees, and the distance from the starting point to the fiber core is 0-5 mu m; the distance between the optical fiber surface waveguide and the optical fiber surface is 0 mu m to 5 mu m.
4. According to claims 1 to 3, the present invention is characterized in that: the two FP cavities are both formed by two parallel femtosecond laser etching lines; the femtosecond laser is used for etching the inside of the optical fiber along the direction vertical to the axial direction of the optical fiber without damaging the surface of the optical fiber, and the formed etching line can reflect, absorb and transmit the transmission light in the optical fiber and can be used as a reflector.
5. According to claims 1 to 4, the present invention is characterized in that: the FP cavity on the fiber core is a reference cavity; the FP cavity on the optical fiber surface waveguide is a sensing cavity; the second mirror of the reference cavity is in the same vertical fiber optic axial plane as the first mirror of the sensing cavity.
6. According to claims 1 to 5, the present invention is characterized in that: the lengths of the sensing cavity and the reference cavity are respectively 100 mu m to 1000 mu m, the length of the reflecting mirror is 1 mu m to 5 mu m, and the thickness is 1 mu m to 3 mu m.
7. The invention according to claims 1-6 is characterized in that: light propagating in the optical fiber surface waveguide is reflected by the sensing FP cavity, the refractive index of a medium around the sensing cavity is changed or stress is exerted on the sensing cavity independently, and the refractive index or the stress value is determined by measuring the drift amount of the reflection spectrum of the light.
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| CN202011075532.3A CN112179537A (en) | 2020-10-10 | 2020-10-10 | Fabry-Perot interferometer optical fiber sensor based on optical fiber surface waveguide |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113091970A (en) * | 2021-04-07 | 2021-07-09 | 西京学院 | Self-healing intelligent all-optical flexible diaphragm |
| CN114858052A (en) * | 2022-04-26 | 2022-08-05 | 厦门大学 | High-sensitivity large-range interferometry method based on virtual reference cavity and vernier effect |
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| CN109974759A (en) * | 2019-04-23 | 2019-07-05 | 中国计量大学 | With cascade Fabry-Perot-type cavity sensor in optical fiber cable of the femtosecond laser induction based on cursor effect |
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2020
- 2020-10-10 CN CN202011075532.3A patent/CN112179537A/en active Pending
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113091970A (en) * | 2021-04-07 | 2021-07-09 | 西京学院 | Self-healing intelligent all-optical flexible diaphragm |
| CN114858052A (en) * | 2022-04-26 | 2022-08-05 | 厦门大学 | High-sensitivity large-range interferometry method based on virtual reference cavity and vernier effect |
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Application publication date: 20210105 |