CN110823411B - High-precision optical fiber temperature measuring device and method based on spectrum Fourier transform demodulation - Google Patents
High-precision optical fiber temperature measuring device and method based on spectrum Fourier transform demodulation Download PDFInfo
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- CN110823411B CN110823411B CN201911165679.9A CN201911165679A CN110823411B CN 110823411 B CN110823411 B CN 110823411B CN 201911165679 A CN201911165679 A CN 201911165679A CN 110823411 B CN110823411 B CN 110823411B
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- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
Abstract
The invention provides a high-precision optical fiber temperature measuring device and method based on spectrum Fourier transform demodulation, wherein the measuring device comprises a wide-spectrum light source, a first optical fiber coupler, an optical fiber temperature measuring module, a polarization controller, a second optical fiber coupler, a long-period optical fiber grating, a spectrum analyzer and a computer, the optical fiber temperature measuring module comprises an input single-mode optical fiber, an output single-mode optical fiber, a panda polarization maintaining optical fiber welded between the input single-mode optical fiber and the output single-mode optical fiber, a tubular heating furnace and a temperature controller, the panda polarization maintaining optical fiber is placed in the tubular heating furnace, and the temperature in the tubular heating furnace is controlled by the temperature controller. The invention realizes the detection effect of high precision, large dynamic range, accuracy and reliability to the temperature signal.
Description
Technical Field
The invention relates to the technical field of optical fiber temperature sensing, in particular to a high-precision optical fiber temperature measuring device and method based on spectrum Fourier transform demodulation.
Background
The accurate optical fiber temperature measurement has wide application in industrial production and many aspects of people's life, and has very important significance.
In recent years, as one of the most common sensors, an optical fiber temperature sensor is widely used in the fields of medical treatment, industry, aviation, and the like. The optical fiber temperature sensors which are researched more at present are of a grating type, a special optical fiber, a microstructure, an interference type and the like. The demodulation methods can be roughly classified into wavelength demodulation, intensity demodulation, and phase demodulation. Wavelength-based demodulation methods typically require complex phase mask writing techniques; the intensity demodulation method is often affected by the jitter of the light source, thereby reducing the measurement accuracy; the phase demodulation method affects the measurement accuracy and sensing range due to the interference phase shift. Therefore, how to obtain an optical fiber temperature sensor with high precision, large dynamic range, stability, reliability and insensitivity to external interference is a great technical problem at present.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides the high-precision optical fiber temperature measuring device and method based on spectrum Fourier transform demodulation, so that the high-precision, large-dynamic-range, accurate and reliable detection effect on the temperature signal is realized.
A high-precision optical fiber temperature measuring device based on spectrum Fourier transform demodulation comprises a wide-spectrum light source, a first optical fiber coupler, an optical fiber temperature measuring module, a polarization controller, a second optical fiber coupler, a long-period optical fiber grating, a spectrum analyzer and a computer, wherein the wide-spectrum light source is connected to an input port of the first optical fiber coupler, an upper output port and a lower output port of the first optical fiber coupler are respectively connected to two input ports of the second optical fiber coupler through the optical fiber temperature measuring module and the polarization controller, an output port of the second optical fiber coupler is connected to the spectrum analyzer through the long-period optical fiber grating, and spectrum data output by the spectrum analyzer are transmitted to the computer for data processing; the fiber temperature measuring module comprises an input single-mode fiber, a panda polarization maintaining fiber, an output single-mode fiber, a tubular heating furnace and a temperature controller, one end of the input single-mode fiber is connected with one output port of the first fiber coupler, the other end of the input single-mode fiber is in fusion joint with one end of the panda polarization maintaining fiber, the other end of the panda polarization maintaining fiber is connected with one end of the output single-mode fiber, the other end of the output single-mode fiber is connected with one input port of the second fiber coupler, the panda polarization maintaining fiber is placed in the tubular heating furnace, and the temperature in the tubular heating furnace is controlled by the temperature controller.
Further, the first optical fiber coupler and the second optical fiber coupler are both 1 × 2 optical fiber couplers, and the splitting ratio is 50: 50.
Furthermore, the long-period fiber grating is a transmission type filter device.
Furthermore, the Mach Zehnder arm length difference is 3-6 mm, the panda polarization maintaining optical fiber birefringence is about 6 multiplied by 10 < -4 >, and the panda polarization maintaining optical fiber length is 4-12 cm.
A high-precision optical fiber temperature measurement method based on spectrum Fourier transform demodulation is characterized by comprising the following steps: the method is carried out by adopting the measuring device, and the measuring method comprises the following steps:
firstly, digitally controlling temperature change in a tubular heating furnace by using a temperature controller, wherein internal birefringence of a panda polarization maintaining optical fiber is changed under the influence of a thermal expansion effect and a thermo-optic effect, so that an output envelope spectrum is shifted;
secondly, frequency spectrum amplitude change information after FFT conversion of the envelope spectrum in a certain small section of range is monitored, temperature change information is obtained through demodulation, an amplitude-temperature change curve is formed by drawing with computer software, namely a standard scale mark of the optical fiber temperature sensor is formed, and the change of the external temperature corresponds to the FFT amplitude information;
and step three, corresponding the detected FFT amplitude value with a standard scale mark of the optical fiber temperature sensor, and obtaining an external temperature value corresponding to the FFT amplitude value.
The invention has at least the following technical effects or advantages:
the invention embeds a section of panda polarization maintaining fiber in a sensing arm of a common fiber Mach Zehnder interferometer through a light path structure to form a composite interferometer structure, and the spectral output of the composite interferometer consists of two parts: the method for measuring the temperature of the optical fiber is novel and wonderful, the sensing precision is greatly improved, and the dynamic range is large; in addition, the sensing interferometer structure is insensitive to interference factors such as light source power jitter, spectrometer wavelength drift and reference arm phase shift, and detection is more accurate and reliable.
Drawings
FIG. 1 is a schematic structural diagram of one embodiment of a high-precision optical fiber temperature measuring device based on spectral Fourier transform demodulation according to the present invention;
FIG. 2 is a schematic diagram of the internal structure of the optical fiber temperature measuring module according to the present invention;
FIG. 3 is a graph of the spectrum of the output spectrum of the spectrum analyzer at different temperatures obtained by a computer using Fourier transform FFT calculations over a specified range of wavelengths;
FIG. 4 is an amplitude-temperature variation curve plotted with substantially linear variation in spectral amplitude and substantially constant frequency values at different temperatures.
In the figure: 1-wide spectrum light source, 2-first optical fiber coupler, 3-optical fiber temperature measuring module, 4-polarization controller, 5-second optical fiber coupler, 6-long period optical fiber grating, 7-spectrum analyzer, 8-computer, 9-input single-mode optical fiber, 10-panda polarization maintaining optical fiber, 11-output single-mode optical fiber, 12-tubular heating furnace and 13-temperature controller.
Detailed Description
The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings.
Referring to fig. 1, one embodiment of a high-precision optical fiber temperature measuring device based on spectral fourier transform demodulation according to the present invention includes a wide-spectrum light source 1, a first optical fiber coupler 2, an optical fiber temperature measuring module 3, a polarization controller 4, a second optical fiber coupler 5, a long-period fiber grating, a spectrum analyzer 7, and a computer 8.
The wide-spectrum light source 1 is connected to an input port of a first optical fiber coupler 2, an upper output port and a lower output port of the first optical fiber coupler 2 are respectively connected to two input ports of a second optical fiber coupler 5 through an optical fiber temperature measuring module 3 and a polarization controller 4, an output port of the second optical fiber coupler 5 is connected to a spectrum analyzer 7 through a long-period optical fiber grating 6, the spectrum analyzer 7 is used for monitoring an output spectrum, and spectrum data output by the spectrum analyzer 7 is transmitted to a computer 7 for data processing.
Referring to fig. 1, the optical fiber temperature measuring module 3 includes an input single-mode fiber 9, a panda polarization maintaining fiber 10, an output single-mode fiber 11, a tubular heating furnace 12, and a temperature controller 13, where one end of the input single-mode fiber 9 is connected to one of the output ports of the first optical fiber coupler 2, the other end of the input single-mode fiber 9 is welded to one end of the panda polarization maintaining fiber 10, the other end of the panda polarization maintaining fiber 10 is connected to one end of the output single-mode fiber 11, and the other end of the output single-mode fiber 11 is connected to one input port of the second optical fiber coupler 5. The panda polarization maintaining fiber 10 is placed in a tubular heating furnace 12, and the temperature in the tubular heating furnace 12 is controlled by a temperature controller 13.
The first optical fiber coupler 2 and the second optical fiber coupler 5 are both 1 × 2 optical fiber couplers, and the splitting ratio is about 50: 50; the polarization controller 4 is used for controlling the polarization state of the interferometer to keep better interference contrast; the long-period fiber grating 6 is a transmission filter device and is used for distinguishing contrast variation series so as to expand the measurement range.
The Mach Zehnder arm length difference (namely the length difference of two optical fibers where the optical fiber temperature measuring module 3 and the polarization controller 4 are located) is 3-6 mm, the birefringence of the panda polarization-maintaining optical fiber 10 is about 6 multiplied by 10 < -4 >, and the length of the polarization-maintaining optical fiber is 4-12 cm.
The optical fiber temperature measuring module 3 can directly sense temperature information around the optical fiber. The working principle of the optical fiber temperature measuring module 3 is as follows: the temperature controller 13 is used for digitally controlling the temperature change in the tubular heating furnace 12, and because the panda polarization maintaining fiber 10 in the tubular heating furnace 12 is influenced by the thermal expansion effect and the thermo-optic effect, the internal birefringence thereof will be changed, which will cause the relative intensity change of the spectrum of the composite interferometer, and the temperature change information will be obtained by demodulating through monitoring the amplitude change of the FFT (fast fourier transform) transformation.
The optical path structure of the invention is a composite interferometer structure formed by embedding a panda polarization maintaining fiber 10 in a sensing arm of a common fiber Mach-Zehnder interferometer. The spectral output of the composite interferometer consists of two parts: fine spectra due to mach zehnder arm length differences and envelope spectra due to polarization maintaining fiber birefringence. The external temperature change can cause the birefringence change of the polarization maintaining fiber to cause the envelope spectrum to drift, the information of the temperature change can be demodulated by monitoring the spectrum amplitude change information of the envelope spectrum after Fourier transform in a certain small segment range, and the approximate effect is shown in fig. 3 and 4.
Fig. 3 is a spectrogram obtained by taking fourier transform FFT calculation through the computer 8 in a specified wavelength range of the spectrum output from the spectrum analyzer 7 under different temperature conditions, which shows that the amplitude of the spectrum at different temperatures changes substantially linearly, and the frequency value remains substantially unchanged. According to the change rule, an amplitude-temperature change curve shown in fig. 4 can be formed by drawing by computer software, namely, the amplitude-temperature change curve is equal to a standard scale line for describing the optical fiber temperature sensor, so that the change of the external temperature corresponds to FFT amplitude information, when the temperature is measured, the external temperature value corresponding to the FFT amplitude can be obtained by corresponding the detected FFT amplitude to the standard scale line of the optical fiber temperature sensor, and the optical fiber temperature sensor can be used for detecting the external temperature information.
The embodiment of the invention also provides a high-precision optical fiber temperature measuring method based on spectrum Fourier transform demodulation, which is carried out by adopting the measuring device, and the measuring method comprises the following steps:
firstly, a temperature controller 13 is used for digitally controlling the temperature change in a tubular heating furnace 12, and the internal birefringence of the panda polarization maintaining fiber 10 is changed under the influence of a thermal expansion effect and a thermo-optic effect, so that the output envelope spectrum is shifted;
secondly, frequency spectrum amplitude change information after FFT conversion of the envelope spectrum in a certain small section of range is monitored, temperature change information is obtained through demodulation, an amplitude-temperature change curve is formed by drawing with computer software, namely a standard scale mark of the optical fiber temperature sensor is formed, and the change of the external temperature corresponds to the FFT amplitude information;
and step three, corresponding the detected FFT amplitude value with a standard scale mark of the optical fiber temperature sensor, and obtaining an external temperature value corresponding to the FFT amplitude value.
The optical fiber temperature measuring method designed by the invention is novel and wonderful, is limited by the resolution of a spectrometer compared with the traditional spectrum drift demodulation method, greatly improves the final sensing precision due to higher resolution of the intensity amplitude, and increases the dynamic range due to the fact that the measuring range is free from the constraint of the free spectrum range in the spectrum shift method; in addition, the core of the invention lies in the relative intensity change of the spectrum of the composite interferometer, so that the structure of the sensing interferometer is insensitive to interference factors such as the absolute power jitter of a light source, the wavelength drift of a spectrometer, the phase shift of a reference arm and the like, and the detection can be more accurate and reliable.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (3)
1. A high-precision optical fiber temperature measurement method based on spectrum Fourier transform demodulation is characterized by comprising the following steps: the high-precision optical fiber temperature measuring device based on spectrum Fourier transform demodulation is adopted and comprises a wide spectrum light source (1), a first optical fiber coupler (2), an optical fiber temperature measuring module (3), a polarization controller (4), a second optical fiber coupler (5), a long-period optical fiber grating (6), a spectrum analyzer (7) and a computer (8), wherein the wide spectrum light source (1) is connected to an input port of the first optical fiber coupler (2), an upper output port and a lower output port of the first optical fiber coupler (2) are respectively connected to two input ports of the second optical fiber coupler (5) through the optical fiber temperature measuring module (3) and the polarization controller (4), an output port of the second optical fiber coupler (5) is connected to the spectrum analyzer (7) through the long-period optical fiber grating (6), the spectral data output by the spectrum analyzer (7) is transmitted to a computer (8) for data processing; the optical fiber temperature measuring module (3) comprises an input single-mode optical fiber (9), a panda polarization maintaining optical fiber (10), an output single-mode optical fiber (11), a tubular heating furnace (12) and a temperature controller (13), one end of the input single-mode optical fiber (9) is connected with one output port of the first optical fiber coupler (2), the other end of the input single-mode optical fiber (9) is welded with one end of the panda polarization maintaining optical fiber (10), the other end of the panda polarization maintaining optical fiber (10) is connected with one end of the output single-mode optical fiber (11), the other end of the output single-mode optical fiber (11) is connected with one input port of the second optical fiber coupler (5), the panda polarization maintaining optical fiber (10) is placed in the tubular heating furnace (12), the temperature in the tubular heating furnace (12) is controlled by the temperature controller (13), and the long-period optical fiber grating (6) is a transmission type filter device, the length difference of the two optical fibers where the optical fiber temperature measuring module (3) and the polarization controller (4) are located is the Mach Zehnder arm length difference, and the measuring method comprises the following steps:
firstly, a temperature controller (13) is used for digitally controlling the temperature change in a tubular heating furnace (12), and the internal birefringence of the panda polarization maintaining optical fiber (10) is changed under the influence of a thermal expansion effect and a thermo-optic effect, so that the output envelope spectrum is shifted;
secondly, frequency spectrum amplitude change information after FFT conversion of the envelope spectrum in a certain small section of range is monitored, temperature change information is obtained through demodulation, an amplitude-temperature change curve is formed by drawing with computer software, namely a standard scale mark of the optical fiber temperature sensor is formed, and the change of the external temperature corresponds to the FFT amplitude information;
and step three, corresponding the detected FFT amplitude value with a standard scale mark of the optical fiber temperature sensor, and obtaining an external temperature value corresponding to the FFT amplitude value.
2. The method of claim 1 for high precision fiber temperature measurement based on spectral fourier transform demodulation, wherein: the first optical fiber coupler (2) and the second optical fiber coupler (5) are both 1 x 2 optical fiber couplers, and the light splitting ratio is 50: 50.
3. The method of claim 1 for high precision fiber temperature measurement based on spectral fourier transform demodulation, wherein: the Mach Zehnder arm length difference is 3-6 mm, and the birefringence of the panda polarization maintaining fiber (10) is 6 multiplied by 10-4The length of the panda polarization maintaining fiber (10) is 4-12 cm.
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