CN104180921B - Temperature-Stress two parameter measurement device based on orthogonal double polarizing light fibre laser - Google Patents

Abstract

The invention relates to a temperature-stress dual-parameter measuring device based on an orthogonal dual-polarization fiber laser, which is used to detect two signals of stress and temperature, including a DBR fiber laser sensor whose central wavelength of the output laser signal is near the 1550nm band, and wavelength division multiplexing Use device, 980nm laser, narrow linewidth laser, 3dB coupler, photoelectric converter, two polarization controllers, spectrum analyzer, wherein, the laser generated by the 980nm laser enters the DBR fiber laser sensor after passing through the wavelength division multiplexer, The temperature-stress dual-parameter signal acts on the DBR fiber laser sensor, and the optical signal with the temperature-stress dual-parameter modulation information generated by the energy conversion of the DBR fiber laser sensor returns to the wavelength division multiplexer and then passes through the optical isolator Isolated output. The energy-adjustable narrow-linewidth laser signal output by the narrow-linewidth laser is energy-adjusted by the second polarization controller, and the two sets of two sets of modulation information carrying the temperature-stress dual-parameter signal to be measured are output after being adjusted by the first polarization controller. Orthogonal polarization mode optical signals enter the 3dB coupler. The invention can simultaneously detect two signals of temperature and stress.

Description

Temperature-stress dual-parameter measurement device based on orthogonal dual-polarization fiber laser

Technical field

The invention belongs to the field of optical fiber sensing, and in particular relates to a sensing device capable of simultaneously detecting temperature signals and stress signals based on orthogonal double-polarized fiber lasers.

Background technique

In the field of practical application of optical fiber sensing technology, temperature and stress are two very important physical parameters in sensing and detection. Especially in the field of safety monitoring and process control of large bridges, tunnels, dams, etc., the two basic physical parameters of temperature and stress must be monitored. However, since most of the optical fibers themselves are sensitive to temperature and stress at the same time, it is often impossible to clearly separate the specific effects of the two, which severely restricts the application of optical fiber sensing technology in the temperature-stress dual-parameter differential measurement to a certain extent. development of.

Patent CN102607621A discloses a distributed optical fiber Brillouin sensing device and method for simultaneously detecting temperature and stress. Two different types of sensing optical fibers are used to form a composite sensing optical fiber combined with self-published Brillouin scattering to correspond to two measured Two-parameter measurement can be realized by changing the frequency shift. Patent CN103344277A discloses a Fabry-Perot sensor and its detection device that can detect two parameters at the same time. Two different lengths of Fab cavities are made at the joint of the mode fiber, and the two sets of sensors make the Fap sensor have the characteristics of detecting two parameters at the same time. Patent CN102261967A discloses a temperature and stress sensor based on coaxial optical fiber, wherein the resonance spectra with different wavelengths inside the No. 1 sensing unit and No. 2 sensing unit have different sensitivities to the two parameters of temperature and stress, thereby realizing Dual-parameter fiber optic sensing. Although the optical fiber sensing technology mentioned above can achieve temperature-strain dual-parameter differential measurement, it is inevitable to use some complex optical fiber sensing head processing technologies in the production process, such as chemical corrosion, mechanical polishing, and sensor head coating. Overlay and other processes. At the same time, in the demodulation process, at least one set of equipment is often required to realize the demodulation output, and it involves analyzing the output data of different types of signals (such as wavelength, beat frequency, etc.), which greatly reduces the demodulation accuracy and improves the system performance. cost and complexity.

Contents of the invention

The present invention aims to overcome the above-mentioned shortcomings of the prior art, and provides a temperature-stress dual-parameter measuring device with simple preparation process, high measurement stability and precision, and simple structure. The present invention selects a relatively mature single sensing optical fiber without complex process treatment. Under the condition that the dual parameters of temperature and stress change at the same time, the structure of the optical fiber is affected according to the change of the external parameter, thereby causing the transmission characteristics of the optical signal inside the optical fiber to change. Using only one set of sensing and demodulation equipment to distinguish the temperature parameter and the stress parameter can effectively overcome the shortcomings of the above-mentioned dual-parameter measurement scheme of temperature and stress based on the principle of optical fiber sensing, and has the advantages of simple preparation process, measurement stability and High precision, simple structure and so on. Technical scheme of the present invention is as follows:

A temperature-stress dual-parameter measurement device based on an orthogonal dual-polarization fiber laser, used to detect both stress and temperature signals, including a DBR fiber laser sensor with an output laser signal center wavelength near 1550nm, a wavelength division multiplexer, 980nm laser, a narrow linewidth laser with a center wavelength of 1550nm, a 3dB coupler, a photoelectric converter, two polarization controllers, and a spectrum analyzer, among which,

The laser light generated by the 980nm laser passes through the wavelength division multiplexer and enters the DBR fiber laser sensor. The DBR fiber laser sensor includes a pair of identical FBG sub-gratings and a resonator in between. The temperature-stress dual parameter signal acts on the DBR fiber laser sensor. The optical fiber laser sensor makes its internal structure change indefinitely, thereby changing its internal birefringence characteristics. The optical signal with the temperature-stress dual-parameter modulation information generated by the DBR optical fiber laser sensor through energy conversion is returned to the wavelength division multiplexing device, and then through the optical isolator to isolate the output. The energy-adjustable narrow-linewidth laser signal output by the narrow-linewidth laser is energy-adjusted by the second polarization controller, and the two sets of modulation information carrying the temperature-stress dual-parameter signal output after adjustment by the first polarization controller The orthogonal polarization mode optical signal enters the 3dB coupler. At this time, the narrow linewidth laser signal with a central wavelength of 1550nm output by the narrow linewidth laser and two sets of orthogonal polarization mode optical signals carrying the measured information are adjusted by adjusting the polarizer The direction of energy distribution and mutual beat frequency, the optical path output from the polarizer contains 3 sets of new optical beat frequency signals that can reflect the temperature-stress information. Output the electrical signal that is easy to identify in the radio frequency field, so as to realize the differential measurement of temperature-stress dual parameters.

The invention uses a DBR fiber optic laser sensor based on orthogonal dual polarization heterodyne as a sensing unit without other chemical processes or mechanical treatments. The sensing unit has a single longitudinal mode dual polarization (dual wavelength) laser output characteristic, can output a beat frequency signal with a stable frequency, and is sensitive to both temperature and stress, but the sensitivity to stress is much greater than that to temperature degree. In addition to the sensing unit, the whole system also includes a signal processing unit and a signal demodulation unit. The beneficial effects of the present invention are:

Compared with the existing optical fiber sensor that can simultaneously measure temperature-stress dual parameters, the present invention has the following obvious substantive advantages: (1) The optical fiber sensor has a mature and simple manufacturing process, high sensitivity and good stability. (2) Only one optical fiber and a set of demodulation equipment can realize the simultaneous differential measurement of two parameters. (3) Simultaneous measurement of temperature-stress dual parameters does not require complex technology to compensate the influence of temperature changes on birefringence, and has the characteristics of miniaturization and light weight.

Description of drawings

Figure 1. Schematic diagram of the optical fiber sensor structure.

Figure 2. Schematic diagram of temperature-stress dual-parameter measurement scheme based on orthogonal dual-polarization fiber laser

Figure 3. Temperature-stress dual-parameter measurement output spectrum

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

The invention includes three parts: an optical fiber sensing unit, a signal processing unit and a signal demodulation unit. The optical fiber sensing unit is a single longitudinal mode dual polarization DBR fiber laser sensor; the signal processing unit includes a 980nm laser, a 980/1550 nm wavelength division multiplexer, an optical isolator, a polarization controller, a narrow linewidth laser, and 3dB A coupler, a polarizer and a photoelectric converter; the signal demodulation unit is a spectrum analyzer. The sensing unit is a DBR (Distributed Bragg Reflection) fiber laser, which is composed of a pair of FBG gratings and a resonant cavity, as shown in Figure 1. Since the pair of FBG sub-gratings have the same temperature sensitivity and different stress sensitivity, the two groups of gratings have the same temperature sensitivity under the action of external temperature changes in a single temperature change measurement, and the two groups of resonance peaks change separately , the wavelength shifts in the same direction and equal in magnitude, but the spacing between the two groups of resonance peaks does not change significantly. When external stress changes act on the fiber optic sensor, due to the stress action angle and the characteristics of the different positions of the resonant cavity, the fiber structure is no longer symmetrical, so the two orthogonal directions of the fiber laser are under unequal pressure, and the two groups of resonance peaks cause easily distinguishable effects. The device is sequentially connected by an optical fiber sensing unit, a signal processing unit and a signal demodulation unit. When the dual parameters of temperature and stress act at the same time, the influence of temperature on the two sub-gratings is similar, and the stress has an asymmetric effect on the fiber structure, which leads to the inconsistent amplitude and direction of the wavelength shift of the two groups of resonance peaks under the stress, so that Realize the differential measurement of temperature-stress dual parameters.

Referring to Fig. 2, the working principle of the present invention is roughly as follows: 980nm laser is used as the pump light source, enters the wavelength division multiplexer by the 980nm port of the wavelength division multiplexer, and then enters the DBR fiber optic laser sensor by the common port of the wavelength division multiplexer . Under the simultaneous action of temperature-stress dual parameters, the structure of a pair of fiber gratings inside the DBR fiber laser sensor is changed, thereby changing the optical properties (polarization state) of the internal transmitted light. The DBR fiber laser emits two sets of orthogonal polarization states And the optical signal with the external dual-parameter signal, these two groups of optical signals enter the wavelength division multiplexer from the input port of the DBR fiber laser through the common port of the wavelength division multiplexer, and the optical signal output by the wavelength division multiplexer passes through The optical isolator realizes the one-way transmission of the laser signal. The laser signal output by the narrow linewidth laser, and the two sets of orthogonal polarization signals output by the DBR fiber laser sensor after being subjected to the action of double parameters pass through the polarization controller 1 (the first polarization unit) and the polarization controller 2 (the second polarization unit) respectively. Perform energy adjustments to avoid excessive energy differences. The three groups of optical signals enter the same optical path after passing through the 3dB coupler, and the two groups of orthogonally polarized signals are adjusted to the same direction by adjusting the polarizer to avoid excessive energy difference. When the external temperature and stress change at the same time, two sets of orthogonally polarized signals with dual-parameter information to be measured and optical frequency signals introduced by narrow linewidth lasers, two beat frequencies between the three sets of signals generate three new sets that can reflect the temperature -Comparative optical signal of stress information, after the conversion of optical signal to electrical signal is completed by photoelectric conversion device, an electrical signal that is easy to identify in the radio frequency field is output on the spectrum analyzer.

In terms of spectrum analyzer display, the reflection spectrum will be broadened and split into two groups of resonance peaks under the simultaneous action of temperature-stress (temperature T1, stress P1), and contain wavelength change (offset) information of two groups of orthogonal polarization modes, And display accordingly on the spectrum analyzer. Since the selected DBR fiber laser sensor has two sets of polarization modes, X mode and Y mode. The temperature T1 causes the same wavelength shift to the two groups of modes, and the difference caused by the different directions and positions of the stress P1 causes the internal stress distribution of the originally symmetrical fiber structure to be asymmetrical, which is converted into unequal pressure on the two groups of orthogonal directions of the fiber laser, Therefore, the stress P1 causes different wavelength shifts for the two groups of modes, so that the refractive index of the fiber laser changes so that the two groups of polarization modes can be used to achieve temperature-stress differential measurements. One group of polarization modes (X mode) has the same sensitivity to temperature and corresponds to the known action angle θ, and has different stress sensitivity characteristics from the other group of polarization modes (Y mode), which can be converted by the photodetector device. The signal is used to restore the dual-wavelength shift characteristics of the two sets of polarization modes, and then to detect the parameters. When the temperature and stress act simultaneously, the reflection spectrum of the fiber grating will shift and the overall shape will also change accordingly. By detecting the two groups of frequency changes, the simultaneous measurement of temperature and stress change information can be realized, see the formula ( 1).

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; co</span>}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\\ \mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; the\; si</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Claims (1)

1. a Temperature-Stress two parameter measurement device based on orthogonal double polarizing light fibre laser, is used for detecting stress and two kinds of signals of temperature, bag Include Output of laser signal center wavelength DBR fiber laser sensor near 1550nm wave band, wavelength division multiplexer, 980nm laser instrument, center Wavelength is the narrow linewidth laser of 1550nm, three-dB coupler, two Polarization Controllers, optical-electrical converter, spectrum analyzer, wherein,

The laser produced by 980nm laser instrument is by entering DBR fiber laser sensor after wavelength division multiplexer, described DBR optical-fiber laser senses Device includes a pair of identical FBG sub-gratings and therebetween resonator, and Temperature-Stress Radix Triplostegiae Grandiflorae amount signal function senses at DBR optical-fiber laser Device so that it is internal structure occurs indefinite change, thus changes its internal birefringence characteristic, is carried out energy conversion by DBR fiber laser sensor and produces The raw optical signal with Temperature-Stress Radix Triplostegiae Grandiflorae amount modulation intelligence to be measured, after close echo division multiplexer, output is to optoisolator, then via optoisolator After isolation, it is input to the first Polarization Controller and carries out energy adjusting；The energy adjustable narrow-linewidth laser signal of narrow linewidth laser output is through second After Polarization Controller energy adjusting, with adjust via the first Polarization Controller after output carry Temperature-Stress to be measured double parameter signals modulation intelligence Two groups of orthogonal polarization mode optical signallings enter in three-dB coupler, now via the narrow line that centre wavelength is 1550nm of narrow linewidth laser output Wide laser signal and the two groups of orthogonal polarization mode optical signallings carrying information measured, carried out energy distribution by regulation polaroid direction and clapped mutually Frequently, comprising 3 groups of new optical beat signals that can reflect Temperature-Stress information from the light path of polaroid output, this signal is through optical-electrical converter After being converted into the signal of telecommunication, spectrum analyzer exports the signal of telecommunication that RF application is readily identified, thus realizes the differentiation to Temperature-Stress Radix Triplostegiae Grandiflorae amount Measure.