CN108507490B - Bending sensing method based on double-core optical fiber - Google Patents
Bending sensing method based on double-core optical fiber Download PDFInfo
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- CN108507490B CN108507490B CN201810224050.6A CN201810224050A CN108507490B CN 108507490 B CN108507490 B CN 108507490B CN 201810224050 A CN201810224050 A CN 201810224050A CN 108507490 B CN108507490 B CN 108507490B
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- 239000000835 fiber Substances 0.000 claims description 26
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
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Abstract
The invention discloses a bending sensing method based on a double-core optical fiber. According to the theory of double-hole interference, when two beams of light with the same frequency, stable phase difference and mutually parallel vibration components pass through the double holes, coherent superposition can be generated in space, so that the energy of the light is redistributed in space to form a series of interference fringes with staggered brightness, the double cores in the double-core optical fiber just imitate the double-hole structure, and when a single-frequency laser light source passes through the double-core optical fiber, the interference fringes can be generated on a receiving screen. When the dual-core optical fiber is bent, the optical path difference changes compared with that when the dual-core optical fiber is not bent, so that the position of the highest point of the interference fringe shifts, and an offset is formed. The offset is thus read from the receiving screen and the radius of curvature can be deduced back. The invention has the advantages of simple structure, convenient measurement, low cost, high sensing precision and the like.
Description
Technical Field
The invention relates to the research field of optics and optical fiber sensing, and provides a novel bending sensing method based on a double-core optical fiber interference theory based on a double-hole interference theory combined with the excellent bending characteristic of a double-core optical fiber and a precision linear array CCD (charge coupled device) for data receiving.
Background
Fiber optic sensors have evolved over decades, with significant advances in research, design, and manufacturing. Optical fiber sensors have many advantages, such as low manufacturing cost, compact structure, high sensitivity, electromagnetic interference resistance, chemical corrosion resistance, ability to be embedded in an engineering structure, and convenience for cascading, and thus optical fiber sensing technology is receiving more and more attention.
The optical fiber sensor converts the physical characteristic parameter of the optical signal to be measured into the change of the physical characteristic parameter by using the light transmission property of the optical fiber, and obtains the change of the external variable by detecting the optical characteristic. The existing commonly used optical fiber bending sensor is based on the principle of the optical fiber Bragg grating, the optical fiber Bragg grating is fixed on a tested device or is arranged in an engineering device, the optical fiber Bragg grating is stretched or extruded by bending the tested device, and the reflected wavelength drift is obtained, so that the bending sensing is carried out. Later improvements made it possible to implement fiber bend sensing methods that measure both the bend radius of curvature and the bend direction. However, most of the methods are based on the theories of Bragg grating, coupling effect and the like, and the writing of the grating needs a precise laser with high manufacturing cost, so that the technical difficulty is higher and the cost is higher.
Disclosure of Invention
The invention provides a bending sensing method based on a double-core optical fiber interference theory on the basis of the existing optical fiber bending sensor technology by a new method and by utilizing the basic theory of double-hole interference.
The technical scheme adopted by the invention for solving the technical problem is as follows:
two fiber cores in the double-core optical fiber are symmetrically distributed in the double-core optical fiber, the distance between each fiber core and the central point of the double-core optical fiber is set to be L, and the length of the double-core optical fiber is set to be S. According to the theory of double-hole interference, when two bundles of light with the same frequency, stable phase difference and mutually parallel vibration components pass through the double holes, coherent superposition can be generated in the space, so that the energy of the light is redistributed in the space to form a series of interference fringes with staggered brightness, the double cores in the double-core optical fiber just imitate the double-hole structure, and when a single-frequency laser light source passes through the double-core optical fiber, the interference fringes can be generated on a receiving screen. When the two-core optical fiber is bent, the optical path difference changes compared with the unbent optical fiber, so that the position of the highest point of the interference fringe is shifted to form a shift amount Y, wherein Y is SL/R. The offset Y is thus read from the receiving screen and the radius of curvature R can be deduced back.
The invention has the advantages of simple structure, convenient measurement, low cost, high sensing precision and the like.
Drawings
FIG. 1a is a schematic diagram of an apparatus used in the present invention.
FIG. 1b is a schematic cross-sectional view of a dual-core optical fiber used in the present invention.
Fig. 2a is a schematic view of light passing through a straight fiber.
Fig. 2b is a schematic view of light passing through a bent optical fiber.
FIG. 3 is a schematic view of a bend magnification of a dual core fiber.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
As shown in fig. 1a, the apparatus used in the present invention comprises: a single-frequency laser light source 1 (visible light), a beam expander 2 (multimode fiber), a double-core fiber 3 with the length of 0.4m and a linear array CCD 4. Wherein, the double-core fiber (the cross section is shown in figure 1b), two fiber cores are symmetrically distributed in the double-core fiber, the distance between each fiber core and the central point of the double-core fiber is L, and the diameter of the two fiber cores is D. According to the theory of double-hole interference, when two beams of light with the same frequency, stable phase difference and mutually parallel vibration components pass through the double holes, coherent superposition can be generated in space, so that the energy of the light is redistributed in the space, and a series of interference fringes with staggered light and shade are formed. And the double core in the double-core optical fiber just imitates the double-hole structure, and when a single-frequency laser light source passes through the double-core optical fiber, interference fringes can be generated on a receiving screen. In addition, in order to prevent the coupling phenomenon, the inner core of the double-core optical fiber is 3-5 μm, and the distance between the central points of the two fiber cores is 10-15 μm. When the dual-core optical fiber is bent, the optical path difference changes compared with a straight optical fiber, and the position of the highest point of the interference fringe shifts.
Single-frequency light output by the single-frequency laser light source is injected into the straight double-core optical fiber through the multimode optical fiber, the core diameter of the multimode optical fiber is 50-105 mu m, and the multimode optical fiber covers two fiber cores of the double-core optical fiber. The output end of the double-core optical fiber is fixed by a support, so that the optical fiber is vertical to the linear array CCD. Interference fringes are observed in a line CCD, as shown in FIG. 2a, where P is1Is the position of the highest point of the interference fringe, S1Is the Core1 output end and P1Optical path between, S2Is the Core2 output end and P1And S is the original length of the straight double-core optical fiber. When Y is equal to S1-S2And Y is an offset amount, 0.
When the two-core fiber is bent at a certain angle, other incident conditions are not changed, as shown in fig. 2 b. Wherein P is2Is the position of the highest point of the interference fringe, S11For light at two ends of the bent double-Core optical fiber Core1Procedure, S22Is the optical path, S, across the bent dual Core fiber Core21Is the Core1 output end and P2Optical path between, S2Is the Core2 output end and P2Optical path length between, R1Radius of curvature, R, of Core2 after bending2Is the radius of curvature of Core1 after bending. Has S1+S11＝S22+S2Transformed to obtain S2-S1＝S11-S22. For S2-S1As shown in fig. 2b, since the distance between the two cores of the dual-core fiber is very small, there are:
for S11-S22As shown in fig. 3, there are:
simultaneous formula (1) and (2) are
Namely, it is
It can be derived that the offset is proportional to the inverse of the radius of curvature, with a scaling factor SL. The value of the offset is read out from the linear array CCD, and the curvature radius can be reversely deduced.
Example (b):
the single-frequency laser light source emits light with wavelength of 632.8nm, the light passes through a multimode fiber (core diameter is 62.5 μm, length is 5mm), a straight double-core fiber is driven into the single-frequency laser light source, the light passing through the double-core fiber is input into a linear array CCD, the distance from the tail end of the double-core fiber to the CCD is 0.2m, and the highest point X of interference fringes is selected on an image1；
Bending the double-core optical fiber with a certain curvature radius R, inputting the output light into the linear array CCD to obtain a new interference pattern, and taking the highest point X of the interference fringe2Record X2Point to X1Distance of points, | X2-X1I is the offset when the curvature radius is R, and the offset obtained from the CCD is 0.008 m;
from the derived formula, a radius of curvature of 10m can be calculated.
The invention adopts the double-core optical fiber as the core sensing device, and adopts the visible light laser light source and the linear array CCD with lower cost as the main devices, thereby having the advantages of simple operation, low cost and the like.
The above description is only an embodiment of the present invention, but the technical features of the present invention are not limited thereto, and any changes or modifications within the field of the present embodiment by those skilled in the art are covered by the present invention.
Claims (1)
1. A bending sensing method based on a double-core optical fiber is characterized in that: two fiber cores in the double-core optical fiber are symmetrically distributed in the double-core optical fiber, the distance between each fiber core and the central point of the double-core optical fiber is set to be L, and the length of the double-core optical fiber is set to be S; according to the theory of double-hole interference, when two beams of light with the same frequency, stable phase difference and mutually parallel vibration components pass through double holes, coherent superposition can be generated in space, so that the energy of the light is redistributed in space to form a series of interference fringes with staggered brightness, the double cores in the double-core optical fiber just imitate the double-hole structure, and when a single-frequency laser light source passes through the double-core optical fiber, the interference fringes can be generated on a receiving screen; when the double-core optical fiber is bent, the optical path difference changes compared with the unbent optical fiber, so that the position of the highest point of the interference fringe shifts, and an offset is formed
To do so
(ii) a Thereby reading the offset from the receiving screen
The curvature radius R can be reversely deduced; the single-frequency laser light source firstly passes throughAnd the multimode optical fiber passes through the double-core optical fiber, and the core diameter of the multimode optical fiber covers two fiber cores of the double-core optical fiber.
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| CN110109246A (en) * | 2019-05-13 | 2019-08-09 | 武汉理工大学 | A kind of optical time delay line based on core shift optical fiber |
| CN113188468B (en) * | 2021-04-15 | 2022-07-05 | 广东工业大学 | Vector bending sensing system and method based on double-core few-mode fiber tilt grating |
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| CN2441116Y (en) * | 2000-08-24 | 2001-08-01 | 中国科学院长春光学精密机械与物理研究所 | Device for measuring moderate and long radius of curves with high accuracy |
| WO2009023801A1 (en) * | 2007-08-14 | 2009-02-19 | Hansen Medical, Inc. | Robotic instrument systems and methods utilizing optical fiber sensor |
| CN102128600A (en) * | 2010-12-10 | 2011-07-20 | 西安科技大学 | Method and device for measuring curvature radius of lens by use of laser |
| CN103411542A (en) * | 2013-07-29 | 2013-11-27 | 宁波大学 | Optical fiber micrometric displacement sensor based on Mach-Zehnder interference and manufacturing method of optical micrometric displacement sensor |
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| TWI266635B (en) * | 2004-12-27 | 2006-11-21 | Univ Nat Taiwan | Fiber-optic sensing system for measuring curvature |
| CN103123254B (en) * | 2013-02-07 | 2015-05-27 | 南开大学 | Two-dimensional bending vector sensor based on fiber grating interference structure |
| CN106959077A (en) * | 2017-03-06 | 2017-07-18 | 哈尔滨工程大学 | A kind of universal bend sensor of multi-core fiber grating |
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| CN2441116Y (en) * | 2000-08-24 | 2001-08-01 | 中国科学院长春光学精密机械与物理研究所 | Device for measuring moderate and long radius of curves with high accuracy |
| WO2009023801A1 (en) * | 2007-08-14 | 2009-02-19 | Hansen Medical, Inc. | Robotic instrument systems and methods utilizing optical fiber sensor |
| CN102128600A (en) * | 2010-12-10 | 2011-07-20 | 西安科技大学 | Method and device for measuring curvature radius of lens by use of laser |
| CN103411542A (en) * | 2013-07-29 | 2013-11-27 | 宁波大学 | Optical fiber micrometric displacement sensor based on Mach-Zehnder interference and manufacturing method of optical micrometric displacement sensor |
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