CN112432655B - Optical fiber sensing system based on free-form surface off-axis reflection and measuring method - Google Patents
Optical fiber sensing system based on free-form surface off-axis reflection and measuring method Download PDFInfo
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- 230000008859 change Effects 0.000 claims abstract description 12
- 150000004770 chalcogenides Chemical group 0.000 claims abstract description 10
- 239000004038 photonic crystal Substances 0.000 claims abstract description 10
- 230000003321 amplification Effects 0.000 claims description 11
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 11
- 239000000463 material Substances 0.000 claims description 6
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- 239000004332 silver Substances 0.000 claims description 6
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims description 5
- 238000001228 spectrum Methods 0.000 claims description 5
- 230000000694 effects Effects 0.000 claims description 4
- 238000000691 measurement method Methods 0.000 claims 2
- 230000035945 sensitivity Effects 0.000 abstract description 7
- 238000001514 detection method Methods 0.000 abstract description 6
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- 230000004075 alteration Effects 0.000 description 3
- 238000009529 body temperature measurement Methods 0.000 description 3
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- 101100064323 Arabidopsis thaliana DTX47 gene Proteins 0.000 description 2
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- 238000005259 measurement Methods 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- 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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Abstract
The invention provides an optical fiber sensing system and a measuring method based on free-form surface off-axis reflection, wherein the sensing system comprises: the system comprises a continuous laser, an off-axis two-mirror optical system based on a free-form surface, an optical fiber sensor, a spectrometer connected with the output end of the optical fiber sensor and an upper computer connected with the spectrometer; laser emitted by the continuous laser is coupled to the optical fiber sensor after being reflected and focused by the off-axis two-mirror optical system based on the free-form surface, the optical fiber sensor is a chalcogenide photonic crystal optical fiber sensor, a plurality of air holes are arranged in a cladding of the optical fiber sensor, and the air holes are uniformly distributed by taking a fiber core of the sensor as a center. The off-axis free-form surface is applied to a four-wave mixing optical fiber sensing system, the traditional coaxial-based optical fiber detection device is changed, and the coupling efficiency is improved; the sensing mechanism is based on the change of the four-wave mixing parameter gain bandwidth, and the practicability and the sensing sensitivity of the optical fiber sensing system are improved.
Description
Technical Field
The invention relates to the technical field of optical design, in particular to an optical fiber sensing system and a measuring method based on free-form surface off-axis reflection.
Background
With the rapid development of industrial production, the requirements on an optical fiber sensing system with high sensitivity, miniaturization and strong practicability are higher and higher. The traditional optical fiber sensing system is based on a coaxial optical path, and effective measurement cannot be carried out on scenes with optical path turning requirements, such as oil well detection, ocean detection, tunnel detection and the like. Off-axis reflective optical systems are now gaining attention from researchers. Such systems typically consist of multiple off-axis mirrors, and do not have global rotational symmetry and a uniform optical axis. However, non-rotationally symmetric off-axis reflective optical systems naturally suffer from a series of asymmetric aberrations that do not allow a perfect focus of the rays at one point, and these aberrations are usually not corrected by conventional spherical or aspherical surfaces.
The free-form surface is a non-traditional optical surface with non-rotational symmetry, which is beneficial to realizing the high-performance system design with advanced index, compact structure and small volume, and has the capability of correcting the asymmetric aberration of an off-axis system; the four-wave mixing process originates from the nonlinear response of bound electrons in a medium to an external electromagnetic field, a phenomenon of light wave inter-modulation in nonlinear optics. In a traditional optical fiber sensing system based on the four-wave mixing effect, external parameters are detected by analyzing the movement of the central wavelengths of Stokes and anti-Stokes waves, but the higher requirements of the Stokes and anti-Stokes waves on the pump wavelength are obviously and effectively observed.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide an optical fiber sensing system and a measuring method based on off-axis reflection of a free-form surface, in which the free-form surface is introduced into an off-axis reflection system to improve the optical performance of the off-axis reflection system, and external parameters are detected by the change of parameter gain bandwidth in the measuring method.
In order to achieve the purpose, the invention adopts the following technical scheme:
a free-form off-axis reflection based fiber optic sensing system comprising: the device comprises a continuous laser, an off-axis two-mirror optical system based on a free-form surface, an optical fiber sensor, a spectrometer connected with the output end of the optical fiber sensor, and an upper computer connected with the spectrometer; the laser emitted by the continuous laser is coupled to the optical fiber sensor after being reflected and focused by the off-axis two-mirror optical system based on the free-form surface, the optical fiber sensor is a chalcogenide photonic crystal optical fiber sensor, a plurality of air holes are arranged in the cladding of the optical fiber sensor, and the air holes are uniformly distributed by taking the fiber core of the sensor as the center.
Furthermore, the off-axis two-mirror optical system based on the free-form surface comprises a main mirror and a secondary mirror, wherein the main mirror is a hyperboloid, and the secondary mirror is an XY polynomial free-form surface.
Furthermore, the off-axis two-mirror optical system based on the free-form surface has a working waveband of 3000nm to 5000nm, an effective focal length range of 5mm to 10mm, and the optical system is symmetrical about a YOZ plane.
Furthermore, the radius range of the main reflector is-20 mm to-70 mm, and the range of aspheric coefficients is-2 to-8; the radius range of the secondary reflector is 10 mm-20 mm, and the range of the aspheric surface coefficient is-5-10.
Furthermore, the fiber core and the cladding of the optical fiber sensor are made of the same material, and the molar ratio of the elements in the material is Ge, Sb and S is 23, 12 and 65.
Further, from inside to outside has set gradually first, two, three layers of air hole in the optical fiber sensor cladding, and every layer of air hole all uses the fibre core to be regular hexagon as the center and distributes, the aperture of every layer of air hole of optical fiber sensor is different, and wherein the aperture range of first layer air hole is 1.0~1.2um, and the aperture range of second layer air hole is 1.3~1.5um, and the aperture range of third layer air hole is 1.4um ~1.9 um.
Furthermore, the diameter range of the fiber core of the optical fiber sensor is 3.5 um-4.5 um; the diameter range of the cladding outside the fiber core is 28 um-32 um; the length range of the optical fiber sensor is 1 m-3 m.
Furthermore, one side end face of the optical fiber sensor is plated with a layer of reflection film, and the reflection film is a silver film with the thickness range of 0.5 cm-1 cm.
Further, the off-axis two-mirror optical system based on the free-form surface has an effective focal length of 8.8mm, a radius of the primary mirror of-60.7 mm, an aspheric coefficient of-6.084, a radius of the secondary mirror of 20mm, an aspheric coefficient of-8.399 and a secondary mirror of 6-order free-form surfaces.
Furthermore, the length of the optical fiber sensor is 1m, the diameter of the fiber core is 4um, the diameter of the cladding is 30um, and the end surface is plated with a silver film with the thickness of 1 cm; the aperture of the first layer of air holes in the middle cladding layer is 1.2um, the aperture of the second layer of air holes is 1.3um, and the aperture of the third layer of air holes is 1.4 um.
The invention also provides a measuring method of the optical fiber sensing system based on the free-form surface off-axis reflection, which comprises the following steps:
the continuous laser emits laser pulses with the central wavelength of 3200nm and 5W, outputs parallel light, is coupled to a fiber core of the optical fiber sensor after being reflected and focused by an off-axis two-mirror optical system based on a free-form surface, excites a four-wave mixing effect to generate parametric amplification pulses and transmits the parametric amplification pulses along the optical fiber, the parametric amplification pulses are reflected and transmitted to the spectrometer through a reflecting film on the end face of the optical fiber sensor, and the spectrometer displays the change of the spectrum on an upper computer.
Furthermore, in the measuring method, the parametric gain bandwidth of the parametric amplification pulse changes along with the external change to be measured, and the external change to be measured can be reversely deduced by observing the change of a map in an upper computer connected with the spectrometer.
Compared with the prior art, the invention has the following beneficial effects:
(1) compared with the traditional quartz optical fiber sensor, the chalcogenide photonic crystal optical fiber sensor has high nonlinear characteristic, wide transmission bandwidth and wide wavelength range, and compared with visible light, the chalcogenide photonic crystal optical fiber sensor has high detection sensitivity, strong stability, simple preparation process and low cost;
(2) the optical fiber sensing system and the measuring method based on the off-axis reflection of the free-form surface effectively solve the problem that the traditional optical fiber sensing system cannot effectively carry out detection on an application scene with a light path turning requirement based on a coaxial light path, and simultaneously introduce the free-form surface into the design of the off-axis reflection system to improve the optical performance of the off-axis reflection system;
(3) the optical fiber sensing system and the measuring method based on the off-axis reflection of the free-form surface measure the object to be measured by changing the parameter gain bandwidth, are easy to observe and improve the sensing measurement sensitivity.
Drawings
FIG. 1 is a schematic diagram of the overall structure of a free-form off-axis reflection-based optical fiber sensing system according to the present invention;
FIG. 2 is a cross-sectional view of a chalcogenide photonic crystal fiber sensor in accordance with the present invention;
FIG. 3 is a free-form surface XY polynomial coefficient of the free-form surface based off-axis two-mirror optical system of the present invention;
FIG. 4 is a schematic view of the ray propagation of the free-form surface based off-axis two-mirror optical system of the present invention;
FIG. 5 is a schematic view of the free-form surface based off-axis two-mirror optical system for focusing light rays according to the present invention;
FIG. 6 is a bottom hole temperature measurement spectrum curve of chalcogenide photonic crystal fiber sensor according to an embodiment of the present invention;
FIG. 7 is a graph of the bottom hole temperature measurement sensitivity of a chalcogenide photonic crystal fiber sensor in accordance with an embodiment of the present invention;
reference numerals: 1-a continuous laser; 2-off-axis two-mirror optical system based on free-form surface; 3-a fiber optic sensor; 4-a spectrometer; 5-an upper computer; 6-a fiber core; 7-a cladding; 8-first layer air holes; 9-second layer air holes; 10-third layer air holes; 11-silver film; 12-a primary mirror; 13-secondary mirror.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further 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.
Examples
A free-form surface based four-wave mixing optical fiber sensing system, as shown in fig. 1, comprising: the device comprises a continuous laser 1, an off-axis two-mirror optical system 2 based on a free-form surface, an optical fiber sensor 3, a spectrometer 4 connected with the output end of the optical fiber sensor, and an upper computer 5 connected with the spectrometer; the laser emitted by the continuous laser is coupled to the optical fiber sensor after being reflected and focused by the off-axis two-mirror optical system based on the free-form surface.
The off-axis two-reflector optical system based on the free-form surface comprises a main reflector and a secondary reflector, wherein the main reflector 12 is a hyperboloid, the radius is-60.7 mm, the aspheric coefficient is-6.084, the secondary reflector 13 is an XY polynomial free-form surface and is a 6-order free-form surface, the radius is 20mm, the aspheric coefficient is-8.399, the XY polynomial coefficient is shown in figure 3, the optical system is symmetrical about a YOZ plane, the working waveband is 3000 nm-5000 nm, the effective focal length is 8.8mm, and the working distance of the main reflector and the secondary reflector is 5.385 mm.
The optical fiber sensor is a chalcogenide photonic crystal optical fiber sensor, the schematic cross section of the optical fiber sensor is shown in fig. 2, the length of the optical fiber sensor is 1m, the materials of a fiber core and a cladding of the optical fiber sensor are the same, the molar ratio of elements in the materials is Ge, Sb and S is 23:12:65, the diameter of the fiber core 6 is 4um, the diameter of the cladding 7 is 30um, and the end face of the sensor is plated with a silver film 11 with the thickness of 1 cm; the cladding is internally and sequentially provided with a first air hole, a second air hole and a third air hole (8, 9 and 10) from inside to outside, each air hole is distributed in a regular hexagon by taking the fiber core as the center, the aperture of each air hole of the optical fiber sensor is unequal, the aperture of the first air hole in the cladding is 1.2um, the aperture of the second air hole is 1.3um, and the aperture of the third air hole is 1.4 um.
The continuous laser adopts a TITAN SID1 laser; the spectrometer used a YOKOGAWA AQ6375B spectrometer.
The method for measuring the bottom hole temperature by adopting the optical fiber sensing system based on the free-form surface off-axis reflection comprises the following steps:
(1) the TITAN SID1 laser emits laser pulse with central wavelength of 3200nm and 5W, outputs parallel light, is reflected and focused by an off-axis two-mirror optical system based on a free-form surface, and is coupled to a fiber core of an optical fiber sensor, and a light propagation schematic diagram is shown in FIG. 4;
(2) the laser pulse is focused on the fiber core of the optical fiber sensor, the four-wave mixing effect is excited to generate parametric amplification pulse and the parametric amplification pulse is transmitted along the optical fiber sensor, the schematic diagram of light focusing is shown in fig. 5, the diameter of a focusing light spot is 0.03um and is far smaller than the diameter of the fiber core, the focusing light spot can be well coupled into the optical fiber sensor, and the coupling efficiency is improved;
(3) the parametric amplification pulse is reflected by a silver film on the end face of the optical fiber sensor and transmitted to a YOKOGAWA AQ6375B spectrometer; the spectrometer displays the change of the map on the upper computer.
When the bottom hole temperature is different, the gain bandwidths of the parameter pulses are different, and the bottom hole temperature is reversely deduced by observing the change of a gain bandwidth map curve in an upper computer connected with a YOKOGAWA AQ6375B spectrometer. When the bottom hole temperature is 10 ℃, 20 ℃, 30 ℃ and 40 ℃ respectively, the central gain bandwidth spectrum curve displayed by the YOKOGAWA AQ6375B spectrometer on the upper computer is shown in figure 6, the bottom hole temperature measurement sensitivity curve of the chalcogenide photonic crystal fiber sensor is shown in figure 7, and the bottom hole temperature sensing sensitivity is 1.34428 nm/DEG C.
The technical idea of the present invention is described in the above technical solutions, and the protection scope of the present invention is not limited thereto, and any changes and modifications made to the above technical solutions according to the technical essence of the present invention belong to the protection scope of the technical solutions of the present invention.
Claims (6)
1. An optical fiber sensing system based on free-form surface off-axis reflection, comprising: the device comprises a continuous laser, an off-axis two-mirror optical system based on a free-form surface, an optical fiber sensor, a spectrometer connected with the output end of the optical fiber sensor, and an upper computer connected with the spectrometer; the laser emitted by the continuous laser is coupled to an optical fiber sensor after being reflected and focused by an off-axis two-mirror optical system based on a free-form surface, the optical fiber sensor is a chalcogenide photonic crystal optical fiber sensor, a first layer of air holes, a second layer of air holes and a third layer of air holes are sequentially arranged in a cladding of the optical fiber sensor from inside to outside, each layer of air holes is distributed in a regular hexagon shape by taking a fiber core as a center, and the aperture of each layer of air holes of the optical fiber sensor is different;
the off-axis two-mirror optical system based on the free-form surface has a working waveband of 3000-5000 nm and an effective focal length range of 5-10 mm, and is symmetrical about a YOZ plane; the off-axis two-reflector optical system based on the free-form surface comprises a main reflector and a secondary reflector, wherein the main reflector is a hyperboloid, and the secondary reflector is an XY polynomial free-form surface; the radius range of the main reflector is-20 mm to-70 mm, and the range of the aspheric surface coefficient is-2 to-8; the radius range of the secondary reflector is 10 mm-20 mm, and the range of the aspheric surface coefficient is-5 to-10; the fiber core and the cladding of the optical fiber sensor are made of the same material, and the molar ratio of elements in the material is Ge: Sb: S =23:12: 65.
2. The optical fiber sensing system based on free-form surface off-axis reflection according to claim 1, wherein the aperture range of the first layer of air holes in the optical fiber sensor cladding is 1.0-1.2 um, the aperture range of the second layer of air holes is 1.3-1.5 um, and the aperture range of the third layer of air holes is 1.4-1.9 um.
3. The optical fiber sensing system based on free-form surface off-axis reflection according to claim 1, wherein the fiber core diameter of the optical fiber sensor ranges from 3.5um to 4.5 um; the diameter range of the cladding outside the fiber core is 28-32 um; the length range of the optical fiber sensor is 1 m-3 m.
4. The optical fiber sensing system based on free-form surface off-axis reflection according to claim 1, wherein a side end face of the optical fiber sensor is coated with a reflective film, and the reflective film is a silver film with a thickness ranging from 0.5cm to 1 cm.
5. A measurement method using the optical fiber sensing system of claim 1, comprising the steps of: the continuous laser emits laser pulses with the central wavelength of 3200nm and 5W, outputs parallel light, is coupled to a fiber core of the optical fiber sensor after being reflected and focused by an off-axis two-mirror optical system based on a free-form surface, excites a four-wave mixing effect to generate parametric amplification pulses and transmits the parametric amplification pulses along the optical fiber, the parametric amplification pulses are reflected and transmitted to the spectrometer through a reflecting film on the end face of the optical fiber sensor, and the spectrometer displays the change of the spectrum on an upper computer.
6. The measurement method according to claim 5, wherein the parametric gain bandwidth of the parametric amplification pulse changes with the external change to be measured, and the external change to be measured can be reversely deduced by observing the change of the spectrum in the upper computer connected with the spectrometer.
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