CN211234711U - Double-core photonic crystal fiber sensing structure - Google Patents
Double-core photonic crystal fiber sensing structure Download PDFInfo
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- CN211234711U CN211234711U CN201921832745.9U CN201921832745U CN211234711U CN 211234711 U CN211234711 U CN 211234711U CN 201921832745 U CN201921832745 U CN 201921832745U CN 211234711 U CN211234711 U CN 211234711U
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Abstract
The utility model relates to a double-core photonic crystal fiber sensing structure, which comprises a background material area, six hexagonal layers of air hole arrangement structures, a first circular fiber core structure and a second circular fiber core structure; polymethyl methacrylate is doped in the first circular fiber core structure; a plurality of small-bore air holes are arranged around the first circular fiber core structure; the photonic crystal fiber is introduced, a dual-core structure is arranged in the PCF, the dual-interference arm is arranged in one optical fiber, and a single optical fiber realizes transmission and interference of two modes, so that the photonic crystal fiber has a simple structure and a small size and is easy to process and integrate; the photonic crystal is introduced as a sensitive element of the sensor, and the cladding air hole of the photonic crystal can reduce the equivalent Young modulus of a cladding region, increase the elastic coefficient of the material and improve the deformation amount; in a dual-core structure designed by PCF, polymethyl methacrylate with better elastic property is doped into a single core, internal stress is generated under the action of pressure on the dual-core, the difference of the effective mode refractive indexes of the dual-core is in a linear relation, and the sensitivity is improved.
Description
Technical Field
The utility model belongs to the technical field of photonic crystal fiber, concretely relates to twin-core photonic crystal fiber sensing structure.
Background
The fiber optic hydrophone provides a plurality of technical approaches for solving the underwater sound research, and provides an ideal solution for solving a plurality of problems of the underwater sound research and application of shallow sea low frequency. The most widely applied core shaft type structure of the traditional optical fiber hydrophone in the acoustic pressure hydrophone generally adopts a Michelson interferometer or a Mach-Zehnder interferometer as a sensitive element, and the technical principle of realizing sensing is as follows:
(1) one arm or two arms of the interferometer made of the optical fiber material are wound on the elastic structure of the mandrel in a differential mode;
(2) the sound pressure acts on the elastic structure to cause the refractive index of the optical fiber to change;
(3) the sound pressure is sensed by detecting the phase difference caused by the change of the refractive index.
The optical fiber hydrophone has the advantages of high sensitivity, light and handy structure, easiness in large-scale formation, strong anti-electromagnetic interference capability and the like, and the manufacturing process is mature.
However, in a water area environment, the conventional optical fiber hydrophone is difficult to meet the requirement of weak signal detection due to the limitation of materials and structure, and the structure is complex, so that the trend development of the sound pressure sensor towards miniaturization and integration is hindered.
Because the traditional optical fiber hydrophone adopts the Mach-Zehnder interferometer as a sensitive element, the reference arm and the measuring arm can not be integrated in the same element, namely the two arms are separated, the structure is relatively complex, and the miniaturization of the sensor is limited to a certain extent; so that further reductions in the size of the structures encounter bottlenecks.
Because two arms of the traditional hydrophone interferometer are made of quartz materials, the Young modulus and Poisson coefficient of the traditional hydrophone interferometer are large, the photoelastic coefficient is small, and the traditional hydrophone interferometer has no flexible structural design characteristics and is directly insensitive to pressure; the materials of the two areas of the layer and the fiber core are different, the thermal expansion coefficients are different, and temperature compensation cannot be carried out; the optical fiber has small deformation under the action of large pressure, and is cross-sensitive to temperature and pressure and low in sensitivity.
Therefore, a core photonic crystal fiber sensing structure is needed to solve the above problems.
Disclosure of Invention
The objective of the present invention is to provide a dual-core photonic crystal fiber sensing structure for solving the above problems.
The utility model discloses a following technical scheme realizes above-mentioned purpose:
the double-core photonic crystal fiber sensing structure comprises a background material region and a hexagonal six-layer air hole arrangement structure, wherein the hexagonal six-layer air hole arrangement structure is arranged in the background material region;
a first circular fiber core structure and a second circular fiber core structure are distributed on two sides of the center line of the six-layer hexagonal air hole arrangement structure of the fiber core layer;
the first circular fiber core structure is arranged inside the first hexagonal air hole arrangement structure; the second circular fiber core structure comprises a second hexagonal air hole arrangement structure and a base material; the first hexagonal air hole arrangement structure and the second hexagonal air hole arrangement structure are symmetrically distributed on two sides of the central line of the six-layer hexagonal air hole arrangement structure of the fiber core layer;
polymethyl methacrylate is doped in the first circular fiber core structure;
a plurality of small-bore air holes are arranged around the first circular fiber core structure; the air holes formed in the hexagonal six-layer air hole arrangement structure, the first hexagonal air hole arrangement structure and the second hexagonal air hole arrangement structure are all large-aperture air holes.
Specifically, the hexagonal six-layer air hole arrangement structure, the first hexagonal air hole arrangement structure and the second hexagonal air hole arrangement structure are all regular hexagons.
Specifically, six small-aperture air holes are provided; the small-aperture air holes are arranged in a regular hexagon around the center of the first circular core structure.
Specifically, the small-aperture air holes are disposed inside the first hexagonal air hole arrangement structure.
Preferably, the distance between the centers of any two nearest large-aperture air holes is 5.5 um;
the diameter of the large-aperture air hole is 2.5 um;
the distance between the centers of the first circular fiber core structure and the second circular fiber core structure is 11 um;
the diameter of the undoped region in the second circular core structure is 5 um;
the diameter of the small-aperture air hole is 1.4 um;
the diameter of the region doped with the polymethyl methacrylate in the first circular fiber core structure is 2.2 um;
the distance between the center of the first circular fiber core structure and the center of any small-aperture air hole is 2 microns.
The beneficial effects of the utility model reside in that:
the utility model discloses a twin-core photonic crystal fiber sensing structure;
1. the structure is miniaturized; the photonic crystal fiber is introduced, a dual-core structure is arranged in the PCF, the dual-interference arm is arranged in one optical fiber, the transmission and interference of two modes are realized by a single optical fiber, and the reference arm is not required to be subpackaged and packaged. Simple structure, the size is little, easily processes and integrates.
2. The precision and the sensitivity are improved; based on the characteristic that the photonic crystal is insensitive to temperature, the photonic crystal is introduced to serve as a sensitive element of the sensor, and the cladding air hole of the photonic crystal can reduce the equivalent Young modulus of a cladding region, increase the elastic coefficient of the material and improve the deformation quantity.
In a dual-core structure designed by PCF, polymethyl methacrylate with better elastic property is doped into a single core, internal stress is generated under the action of pressure on the dual-core, the difference of the effective mode refractive indexes of the dual-core is in a linear relation, and the sensitivity is improved.
Drawings
FIG. 1 is a schematic diagram of a conventional optical fiber sensor structure;
FIG. 2 is a schematic cross-sectional structure of the present application;
FIG. 3 is an enlarged view of the doped core region of the present application;
FIG. 4 is a graph showing the variation of transmission spectra at different sound pressures;
FIG. 5 is a schematic diagram of a first hexagonal arrangement of air holes and a second hexagonal arrangement of air holes according to the present application;
description of reference numerals:
11-a fiber coupler; 12-an elastic cylinder; 13-a reference arm; 14-a sensing arm; 21-background material area; 22-hexagonal six-layer air hole arrangement structure; 23-a first circular core structure; 24-a second circular core structure; 25-a first hexagonal arrangement of air holes; 26-second hexagonal air hole arrangement.
Detailed Description
Hereinafter, example embodiments according to the present application will be described in detail with reference to the accompanying drawings. It should be understood that the described embodiments are only some embodiments of the present application and not all embodiments of the present application, and that the present application is not limited by the example embodiments described herein.
Summary of the application
As shown in fig. 1, a schematic diagram of a conventional optical fiber sensing head structure is shown, which includes an optical fiber coupler 11, an elastic tube 12, a reference arm 13 and a sensing arm 14, and this structure winds one sensing arm of an interferometer around the outside of the elastic tube, and the reference arm is fixed outside a sound field or is subjected to a sound pressure shielding treatment. The two interference arms interfere with each other, the interference fringes move under the action of pressure, and the change of the physical quantity in the environment to be measured can be measured by monitoring the movement quantity of the fringes.
However, the optical fiber structure is made of the traditional optical fiber quartz material, the Young modulus is up to the 79GPa level, and therefore the sensing unit cannot detect information under the condition of small pressure. And the sensitivity and the precision of the traditional optical fiber hydrophone are difficult to improve due to the limitation of materials and structures. And two arms of the optical fiber are separately packaged, so that the optical fiber can not be integrated in a single optical fiber, the structure is relatively complex, and the miniaturization is difficult to further realize. This application is based on traditional optic fibre hydrophone interferometer structure principle preparation doping type two-core photonic crystal fiber sensor, and two-core photonic crystal fiber has two leaded light fibre cores, can replace traditional optic fibre hydrophone's sensing fiber arm and reference fiber arm ideally, accomplishes an optic fibre with two interference arms, and single optic fibre realizes the transmission and the interference of two kinds of modes, and this structure is easily the miniaturization of sensor. The dual cores have a certain difference, namely, an effective refraction difference is formed. After the pressure acts on the photonic crystal fiber, the effective refractive index difference of the double cores with the same polarization changes along with the pressure, the phase difference of the two fiber cores at the emergent end changes, and an interference transmission spectrum with certain characteristics is formed at the emergent port. If the sound pressure further enlarges the difference of the double cores, the interference transmission spectrum is changed along with the sound pressure, and the sensing characteristic can be obtained according to the movement of the analysis transmission peak. The photonic crystal fiber introduces air holes into the cladding to obtain large refractive index difference which cannot be realized by the traditional fiber, and the optical characteristics of the photonic crystal fiber can be controlled by changing the size and the distribution of the air holes, so that the application carries out innovative design on the structure of the double-core photonic crystal fiber.
The present invention will be further explained with reference to the accompanying drawings:
as shown in figures 2, 3 and 5,
the double-core photonic crystal fiber sensing structure comprises a background material region 21 and six hexagonal layers of air hole arrangement structures 22, wherein the six hexagonal layers of air hole arrangement structures 22 are arranged in the background material region 21;
a first circular fiber core structure 23 and a second circular fiber core structure 24 are distributed on two sides of the center line of the six-layer air hole arrangement structure 22 of the fiber core layer hexagon;
the first circular core structure 23 is disposed inside the first hexagonal air hole arrangement structure 25; the second circular core structure 24 comprises a second hexagonal arrangement of air holes 26 and a base material; the first hexagonal air hole arrangement structure 25 and the second hexagonal air hole arrangement structure 26 are symmetrically distributed on two sides of the center line of the core layer hexagonal six-layer air hole arrangement structure 22;
in order to obtain higher sound pressure sensitivity, the first circular core structure 23 is doped with a pressure-sensitive material polymethyl methacrylate;
the plurality of small-aperture air holes are arranged around the first circular fiber core structure 23, so that the effective refractive index of the first circular fiber core structure 23 area is reduced; the air holes formed in the hexagonal six-layer air hole arrangement structure 22, the first hexagonal air hole arrangement structure 25 and the second hexagonal air hole arrangement structure 26 are all large-aperture air holes.
As shown in figures 2 and 5 of the drawings,
the hexagonal six-layer air hole arrangement structure 22, the first hexagonal air hole arrangement structure 25, and the second hexagonal air hole arrangement structure 26 are all regular hexagons.
As shown in figure 3 of the drawings,
six small-aperture air holes are formed; the small-aperture air holes are arranged in a regular hexagon around the center of the first circular core structure 23.
As shown in figure 3 of the drawings,
the small-bore air holes are disposed inside the first hexagonal air hole arrangement structure 25.
As shown in figures 2 and 3 of the drawings,
d6 for the distance between the centers of any two nearest large-aperture air holes is 5.5 um; according to the interference principle, the sound pressure sensitivity can be improved by improving the difference of the effective refractive index of the double cores, and the effective refractive index of the undoped fiber core (the second circular fiber core structure 24) can be stabilized to be near 1.439 by setting the air hole spacing d6 to be 5.5 um;
the diameter d4 of the large-aperture air hole is 2.5 um;
the distance d7 between the centers of the first and second circular core structures 23, 24 is 11 um; the thickness of the fiber core is close to 10um of the fiber core of the single-mode fiber, and certain operation difficulty can be reduced in the fusion process. The areas of the double-core mode fields are approximately the same, so that the insertion loss in the welding process can be reduced, and the extinction ratio can be improved.
The diameter d5 of the undoped region in the second circular core structure 24 is 5 um;
the diameter d3 of the small-aperture air hole is 1.4 um;
the diameter d2 of the polymethylmethacrylate-doped region in the first circular core structure 23 is 2.2 um; and enlarging the hole diameter d2 of the doped core region (the first circular core structure 23) significantly increases the effective refractive index of the doped core region (the first circular core structure 23).
The center-to-center distance d8 between the center of the first circular core structure 23 and any one of the small-aperture air holes is 2 um.
In some embodiments, the dual core fiber diameter d1 is 125 um;
in some embodiments, a basic photonic crystal fiber structure with a hexagonal six-layer air hole arrangement is established using a quartz material as the background material region 21 of the photonic crystal fiber.
The structure of the present application was tested and the change of the transmission spectrum at different sound pressures is shown in fig. 4. Therein is shown
The wave valley wavelength of the transmission spectrum has obvious displacement, the moving wavelength interval and the applied uniform radial sound pressure (31 under the action of 20MPa sound pressure, 32 under the action of 30MPa sound pressure, 33 under the action of 40MPa sound pressure, 34 under the action of 50MPa sound pressure and 35 under the action of 60MPa sound pressure) basically change linearly, and the pressure sensitivity effect is good. The sensing structure transmits at a free space wavelength of 1.55 mu m, the sensing length is 6cm, and under uniform radial pressure, the sensitivity of X-polarization sound pressure can reach 0.15942nm/KPa, which is one order of magnitude higher than the existing level. Under the action of KPa-magnitude sound pressure, the free spectrum width is about 1 nm; under the action of 40MPa sound pressure, the free spectral width is about 2.5465 nm. In the measuring range, the linearity is high, the insertion loss is low, and the wavelength multiplexing is easy.
And (3) comparative analysis: the key technical parameter pairs of the traditional hydrophone and the hydrophone designed by the patent are as follows:
to summarize the above data:
(1) the design improves the difference value of the Young modulus of the left and right double cores, thereby increasing the effective refractive index difference of the double cores;
(2) the polymethyl methacrylate is doped, the photoelastic coefficient of the polymethyl methacrylate is far greater than that of the traditional quartz optical fiber, and the pressure sensitivity is enhanced.
(3) The channel width of a DWDM system can reach 1nm, and the reusability of the hydrophone is improved;
in the present application, it is preferred that,
1. introducing 6 layers of air hole layers on the photonic crystal fiber, designing a symmetrical double-core structure, wherein the small core structure is small, the large core structure is adopted, polymethyl methacrylate with a smaller Young modulus is doped in the small core, and a circle of small-aperture air holes are surrounded by a doped fiber core; therefore, the effective refractive index difference is increased, and the sound pressure sensitivity is improved.
2. The photonic crystal fiber material is adopted to replace the traditional quartz material, and the cladding and the fiber core have the same thermal expansion coefficient, so that the temperature is compensated; thereby reducing temperature sensitivity.
3. The double cores are integrated in one optical fiber, and the sensor has larger numerical aperture and very low bending loss, namely the sensor can be miniaturized; in this way, the structural size of the sensor unit is reduced.
4. The low twin core spacing and comparable mode field area will help control extinction ratio and insertion loss during fusion; thereby increasing extinction ratio and reducing insertion loss.
5. The structure shows large-difference free spectral width under different sound pressure effects, and can be properly adjusted in length when applied to the fields of different stress levels; facilitating wavelength division multiplexing.
The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the above embodiments, and that the foregoing embodiments and descriptions are provided only to illustrate the principles of the present invention without departing from the spirit and scope of the present invention. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (5)
1. The double-core photonic crystal fiber sensing structure comprises a background material region and a hexagonal six-layer air hole arrangement structure, wherein the hexagonal six-layer air hole arrangement structure is arranged in the background material region;
the method is characterized in that: a first circular fiber core structure and a second circular fiber core structure are distributed on two sides of the center line of the six-layer hexagonal air hole arrangement structure of the fiber core layer;
the first circular fiber core structure is arranged inside the first hexagonal air hole arrangement structure; the second circular fiber core structure comprises a second hexagonal air hole arrangement structure and a base material; the first hexagonal air hole arrangement structure and the second hexagonal air hole arrangement structure are symmetrically distributed on two sides of the central line of the six-layer hexagonal air hole arrangement structure of the fiber core layer;
polymethyl methacrylate is doped in the first circular fiber core structure;
a plurality of small-bore air holes are arranged around the first circular fiber core structure; the air holes formed in the hexagonal six-layer air hole arrangement structure, the first hexagonal air hole arrangement structure and the second hexagonal air hole arrangement structure are all large-aperture air holes.
2. The dual core photonic crystal fiber sensing structure of claim 1, wherein: the hexagonal six-layer air hole arrangement structure, the first hexagonal air hole arrangement structure and the second hexagonal air hole arrangement structure are all regular hexagons.
3. The dual core photonic crystal fiber sensing structure of claim 1, wherein: six small-aperture air holes are formed; the small-aperture air holes are arranged in a regular hexagon around the center of the first circular core structure.
4. The dual core photonic crystal fiber sensing structure of claim 1, wherein: the small-aperture air holes are arranged inside the first hexagonal air hole arrangement structure.
5. The dual core photonic crystal fiber sensing structure of any of claims 1 to 4, wherein:
the distance between the centers of any two nearest large-aperture air holes is 5.5 um;
the diameter of the large-aperture air hole is 2.5 um;
the distance between the centers of the first circular fiber core structure and the second circular fiber core structure is 11 um;
the diameter of the undoped region in the second circular core structure is 5 um;
the diameter of the small-aperture air hole is 1.4 um;
the diameter of the region doped with the polymethyl methacrylate in the first circular fiber core structure is 2.2 um;
the distance between the center of the first circular fiber core structure and the center of any small-aperture air hole is 2 microns.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115128728A (en) * | 2022-06-01 | 2022-09-30 | 长飞光纤光缆股份有限公司 | Distributed acoustic vibration sensing optical fiber and acoustic vibration monitoring system |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115128728A (en) * | 2022-06-01 | 2022-09-30 | 长飞光纤光缆股份有限公司 | Distributed acoustic vibration sensing optical fiber and acoustic vibration monitoring system |
| CN115128728B (en) * | 2022-06-01 | 2023-09-26 | 长飞光纤光缆股份有限公司 | Distributed acoustic vibration sensing optical fiber and acoustic vibration monitoring system |
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Granted publication date: 20200811 Termination date: 20211029 |