CN216132474U - Fiber grating center wavelength demodulation system and demodulation instrument - Google Patents
Fiber grating center wavelength demodulation system and demodulation instrument Download PDFInfo
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- CN216132474U CN216132474U CN202121664058.8U CN202121664058U CN216132474U CN 216132474 U CN216132474 U CN 216132474U CN 202121664058 U CN202121664058 U CN 202121664058U CN 216132474 U CN216132474 U CN 216132474U
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Abstract
The utility model provides a fiber grating center wavelength demodulation system and a demodulation instrument, which relate to the technical field of fiber demodulation instruments and comprise: the device comprises an optical path unit, a photoelectric conversion unit, a signal conditioning unit, an A/D sampling unit and an upper computer; the fiber grating central wavelength demodulation system is simple in structure, the light intensity and the wavelength of reflected light of the fiber grating sensor correspond to each other through the filter slope, the flatness requirement on a light source is low, the system can be simultaneously suitable for application environments with high frequency and low frequency demodulation as long as the operation speed of a CPU (central processing unit) of an upper computer is enough, and the problems that the cost is high, the requirement on the flatness of the light source is high, the high frequency demodulation and low frequency demodulation application environments are difficult to meet simultaneously and the like in the existing demodulation system are solved.
Description
Technical Field
The utility model relates to the technical field of fiber-optic demodulators, in particular to a fiber grating central wavelength demodulating system.
Background
The fiber grating sensor reflects the change of an external physical parameter through the change of a central wavelength, so that the most important part in a fiber grating sensing system is a method for demodulating the wavelength of the fiber grating sensor.
(1) And (3) detection by a spectrometer: the center wavelength and its shift can be detected directly with a spectrometer or monochromator. The method has simple structure and is suitable for laboratories. However, the resolution of the conventional spectrometer based on a dispersion prism or a diffraction grating is low, and the conventional spectrometer cannot meet the requirements. Although high resolution spectrometers are adequate, these spectrometers are expensive and bulky, and the resulting systems lack the necessary compactness and robustness, and the detection of wavelengths by this method is impractical in sensor systems for practical engineering applications.
(2) And (3) matched filtering method: the matched filtering method is to utilize a reference grating or a band-pass filter device, track the wavelength change of the sensing grating by means of heterodyne carrier technology under the action of a driving element, and acquire external physical parameters such as measured stress or temperature and the like by tracking and scanning of a driving signal, so as to realize the demodulation of the reference grating to the sensing grating signal. This approach can be divided into reflective and transmissive types. Light reflected by the sensing grating enters the reference grating through the coupler, the reference grating is driven by the driving element to scan, when the reflection center wavelength of the reference grating is matched with the reflection wavelength of the sensing grating, the output of the detector is the largest, and the size of the driving signal at the moment is recorded according to the output of the detector, so that the size of the measured object can be obtained. The method has the advantages that the precision is greatly influenced by the stability of the light source and external interference, and the requirement on the detector is high.
(3) Tunable narrowband light source demodulation method: the method demodulates the sensing grating array through the calibrated adjustable narrow linewidth laser light source, thereby determining the central wavelength of the Bragg fiber grating.
A distributed bragg reflector laser (DBR) is fixed to a piezoelectric body (PZT), and when the PZT is driven by a sawtooth wave or sine wave voltage, the laser wavelength is scanned within a range, and when the wavelength just satisfies a certain bragg grating wavelength, light incident on the sensing grating array is reflected by the response grating. The reflected light signal is sent to a detector after passing through a 3dB circulator, and a function relation curve of the Bragg grating reflectivity and the wavelength can be obtained by connecting a digital oscilloscope. In order to improve the measurement accuracy, a small disturbance signal can be added to the scanning voltage, and a feedback closed loop is formed by locking the peak wavelength when the disturbance frequency of the detection electric signal is zero. The signal light power of the system is high, noise can be suppressed, and therefore the system has high signal-to-noise ratio and resolution. The minimum wavelength resolution obtained by the experiment is about 2.3pm, but the stability and the tunable range of the existing optical fiber laser are not ideal enough, and the number and the application range of the sensing Bragg grating are limited to a certain extent.
(4) Tunable fiber F-P filter method: the Fabry-Perot (F-P) cavity is equivalent to a narrow-band filter, if parallel light enters the Fabry-Perot (F-P) cavity in a certain wavelength range, only light with certain specific wavelength meeting the coherence condition can interfere to generate extremely high coherence, and the reflection wavelength of the optical fiber sensor array can be demodulated by utilizing the characteristic of the Fabry-Perot (F-P) cavity. When the Fabry-Perot (F-P) filter is fixed on the piezoelectric ceramic, if the transmission wavelength of the Fabry-Perot (F-P) cavity is coincident with the reflection wavelength of the fiber Bragg grating, the detector can detect the optimal light intensity, and the voltage applied to the piezoelectric ceramic corresponds to the reflection wavelength of the fiber Bragg grating, so that the measured light intensity is obtained. However, since the transmission spectrum is a convolution of the reflection spectrum and the transmission spectrum of the Fabry-Perot (F-P) filter, the bandwidth is increased and the resolution is reduced. Therefore, a small jitter voltage is added to the scanning voltage, the output is passed through a mixer and a low-pass filter, the jitter frequency is measured, and when the signal is zero, the measured signal is the central wavelength, so that the resolution of the system can be greatly improved. Due to the wide FFP tuning range, demodulation of multiple sensors can be achieved. The higher finesse FFP is too costly and the filtering loss is large.
SUMMERY OF THE UTILITY MODEL
Technical problem to be solved
Aiming at the defects of the prior art, the utility model provides a fiber grating center wavelength demodulation system to solve the problems that the prior demodulation system proposed in the background art has high cost and high requirement on light source flatness, and is difficult to simultaneously meet the application environments of high-frequency demodulation and low-frequency demodulation, and the like.
(II) technical scheme
In order to achieve the purpose, the utility model is realized by the following technical scheme: a fiber grating center wavelength demodulation system comprising:
the device comprises an optical path unit, a photoelectric conversion unit, a signal conditioning unit, an A/D sampling unit and an upper computer 1-18; the optical path unit, the photoelectric conversion unit, the signal conditioning unit, the A/D sampling unit and each device and chip in the upper computer are electrically connected with each other to form the fiber bragg grating central wavelength demodulation system;
the optical path unit includes: 1-1 of ASE light source, 1-2 of three-port circulator, 1-3 of fiber Bragg grating sensor, 1-4 of fiber coupler and 1-5 of edge filter;
the photoelectric conversion unit includes: a first photoelectric conversion circuit 1-6, a second photoelectric conversion circuit 1-7;
the signal conditioning unit comprises: a first current-voltage conversion circuit 1-8, a second current-voltage conversion circuit 1-9, a first linear amplification circuit 1-10, a second linear amplification circuit 1-11, a first low-pass filter 1-12, a second low-pass filter 1-13, a first dark current compensation circuit 1-14, a second dark current compensation circuit 1-15;
the A/D sampling unit comprises: first A/D sampling circuits 1-16, second A/D sampling circuits 1-17.
Preferably, the three-port circulator 1-2 includes: one port, two ports, three ports; near-infrared light emitted by the ASE light source 1-1 enters through one port of the three-port circulator 1-2, and after the near-infrared light exits from the two ports and enters the optical fiber Bragg grating sensor 1-3, reflected light of the near-infrared light exits to the optical fiber coupler 1-4 through the three ports of the three-port circulator 1-2.
Preferably, the optical fiber coupler 1-4 is 1: 1, and the optical fiber coupler 1-4 splits reflected light of the optical fiber Bragg grating sensor 1-3 into a measuring optical path and a reference optical path in an average manner.
Preferably, the edge filter 1-5 uses a chirped grating to linearly filter the measurement light path; the measuring optical path is filtered by an edge filter 1-5 and then transmitted to a first photoelectric conversion circuit 1-6.
Preferably, the reference optical path is directly input into the second photoelectric conversion circuit 1 to 7.
Preferably, the method further comprises the following steps: and inputting the filtered measuring light path and the filtered reference light path into the signal conditioning unit to obtain effective voltage values corresponding to the measuring light path and the reference light path, sampling the effective voltage values by the A/D sampling unit, and converting the effective voltage values into digital signals which can be directly processed by the upper computer 1-18.
Preferably, the first photoelectric conversion circuit 1-6 and the second photoelectric conversion circuit 1-7 are PIN photodiodes.
Preferably, after the filtered measurement optical path and the filtered reference optical path are input into the signal conditioning unit, the current signal is logarithmically amplified and then converted into a voltage signal by the first current-voltage conversion circuit 1-8 and the second current-voltage conversion circuit 1-9, the converted voltage is secondarily amplified by the first linear amplification circuit 1-10 and the second linear amplification circuit 1-11, the high-frequency noise is filtered by the first low-pass filter 1-12 and the second low-pass filter 1-13, and the first dark current compensation circuit 1-14 and the second dark current compensation circuit 1-15 are used for canceling an error generated by a dark current possessed by a PIN photodiode of the photoelectric conversion unit.
The utility model also provides a fiber grating center wavelength demodulator, which adopts any fiber grating center wavelength demodulating system as described above to build the demodulator hardware.
(III) advantageous effects
The utility model provides a fiber grating center wavelength demodulation system and a demodulation instrument. The method has the following beneficial effects:
the fiber grating central wavelength demodulation system is simple in structure, the light intensity and the wavelength of reflected light of the fiber grating sensor correspond to each other through the filter slope, the flatness requirement on a light source is low, the system can be simultaneously suitable for application environments with high frequency and low frequency demodulation as long as the operation speed of a CPU (central processing unit) of an upper computer is enough, and the problems that the cost is high, the requirement on the flatness of the light source is high, the high frequency demodulation and low frequency demodulation application environments are difficult to meet simultaneously and the like in the existing demodulation system are solved.
Drawings
FIG. 1 is a schematic diagram of a central wavelength demodulation system of a fiber grating according to the present invention;
FIG. 2 is a schematic structural diagram of a fiber grating center wavelength demodulator according to the present invention;
in the figure: the optical fiber Bragg grating sensor comprises an ASE light source 1-1, a three-port circulator 1-2, an optical fiber Bragg grating sensor 1-3, an optical fiber coupler 1-4, an edge filter 1-5, a first photoelectric conversion circuit 1-6 and a second photoelectric conversion circuit 1-7; the optical fiber Bragg grating sensor comprises a first current-voltage conversion circuit 1-8, a second current-voltage conversion circuit 1-9, a first linear amplification circuit 1-10, a second linear amplification circuit 1-11, a first low-pass filter 1-12, a second low-pass filter 1-13, a first dark current compensation circuit 1-14, a second dark current compensation circuit 1-15, a first A/D sampling circuit 1-16, a second A/D sampling circuit 1-17, an upper computer 1-18, an ASE light source 1, a three-port circulator 2, an optical fiber Bragg grating sensor 3, an optical fiber coupler 4, an edge filter 5, a first photoelectric converter 6, a second photoelectric converter 7, a signal conditioning circuit 8, an A/D sampling circuit 9 and an upper computer 10.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
An embodiment of the present invention provides a fiber grating center wavelength demodulation system, as shown in fig. 1, including:
the device comprises an optical path unit, a photoelectric conversion unit, a signal conditioning unit, an A/D sampling unit and an upper computer 1-18; the optical path unit, the photoelectric conversion unit, the signal conditioning unit, the A/D sampling unit and each device and chip in the upper computer are electrically connected with each other to form the fiber bragg grating central wavelength demodulation system;
the optical path unit includes: 1-1 of ASE light source, 1-2 of three-port circulator, 1-3 of fiber Bragg grating sensor, 1-4 of fiber coupler and 1-5 of edge filter;
in the embodiment, the CS-ASE light source 1 provided by shenzhenjiki science and technology limited is selected, and the ASE light source has the advantages of good flatness, 10mw of output power, high stability, low noise and low polarization.
The photoelectric conversion unit includes: a first photoelectric conversion circuit 1-6, a second photoelectric conversion circuit 1-7;
in this embodiment, the photoelectric conversion circuit is an LSIPD-UL0.3-PIN indium gallium arsenide photodiode provided by beijing optical technology ltd, and the diode is packaged by optical fiber single-mode transmission and has an interface of an FC-APC interface.
The signal conditioning unit comprises: a first current-voltage conversion circuit 1-8, a second current-voltage conversion circuit 1-9, a first linear amplification circuit 1-10, a second linear amplification circuit 1-11, a first low-pass filter 1-12, a second low-pass filter 1-13, a first dark current compensation circuit 1-14, a second dark current compensation circuit 1-15;
in this embodiment, an AD825 chip is used as a current-voltage conversion circuit to convert a current signal into a voltage signal that can be sampled;
because the voltage converted by the current-voltage conversion circuit is only about a few millivolts to a few tens of millivolts generally, and the voltage value is too small, the bit number of A/D sampling is limited, therefore, the NE5532 is adopted to design a linear amplification circuit, and the amplification factor can be adjusted by 100 times under the condition of small signals. For the voltage signal after amplification, high-frequency noise may be amplified at the same time, the occurrence of the high-frequency noise only affects the experimental result, and is a potential threat for the sampling interface, so a second-order butterworth low-pass filter circuit is designed by adopting MAX275ACWP to process the amplified signal, and the interference of the high-frequency noise is eliminated. Finally, a dark current compensation circuit is designed by using NE5532, and errors generated by dark current of the photodiode are offset by adding bias voltage. And finally, voltage values respectively corresponding to the reference light and the measured light are obtained.
The A/D sampling unit comprises: first A/D sampling circuits 1-16, second A/D sampling circuits 1-17.
Preferably, the three-port circulator 1-2 includes: one port, two ports, three ports; near-infrared light emitted by the ASE light source 1-1 enters through one port of the three-port circulator 1-2, and after the near-infrared light exits from the two ports and enters the optical fiber Bragg grating sensor 1-3, reflected light of the near-infrared light exits to the optical fiber coupler 1-4 through the three ports of the three-port circulator 1-2.
Preferably, the optical fiber coupler 1-4 is 1: 1, and the optical fiber coupler 1-4 splits reflected light of the optical fiber Bragg grating sensor 1-3 into a measuring optical path and a reference optical path in an average manner.
Preferably, the edge filter 1-5 uses a chirped grating to linearly filter the measurement light path; the measuring optical path is filtered by an edge filter 1-5 and then transmitted to a first photoelectric conversion circuit 1-6;
the optical fiber devices which can be used as linear filter devices in the market at present mainly comprise three filter devices, namely a wavelength division multiplexer, a chirped grating and a Fabry-Perot (F-P) filter. However, the fabry-perot filter is difficult to satisfy the condition of linear filtering and to realize demodulation in an application environment with high precision, and the existing coarse wavelength division multiplexer and the existing dense wavelength division multiplexer cannot satisfy the filtering range of a single channel of 3 nm.
The chirp grating filter is mainly suitable for application environments with higher frequency and low frequency demodulation, and the chirp grating filter range can reach 11nm to the maximum extent, so that the chirp grating filter has the basis of large-range linear filtering. Therefore, the chirped grating is selected as the edge filter in this embodiment.
Preferably, the reference optical path is directly input into the second photoelectric conversion circuit 1 to 7.
Preferably, the method further comprises the following steps: and inputting the filtered measuring light path and the filtered reference light path into the signal conditioning unit to obtain effective voltage values corresponding to the measuring light path and the reference light path, sampling the effective voltage values by the A/D sampling unit, and converting the effective voltage values into digital signals which can be directly processed by the upper computer 1-18.
Preferably, the first photoelectric conversion circuit 1-6 and the second photoelectric conversion circuit 1-7 are PIN photodiodes.
Preferably, after the filtered measurement optical path and the filtered reference optical path are input into the signal conditioning unit, the current signal is logarithmically amplified and then converted into a voltage signal by the first current-voltage conversion circuit 1-8 and the second current-voltage conversion circuit 1-9, the converted voltage is secondarily amplified by the first linear amplification circuit 1-10 and the second linear amplification circuit 1-11, the high-frequency noise is filtered by the first low-pass filter 1-12 and the second low-pass filter 1-13, and the first dark current compensation circuit 1-14 and the second dark current compensation circuit 1-15 are used for canceling an error generated by a dark current possessed by a PIN photodiode of the photoelectric conversion unit.
As shown in fig. 2, the present invention further provides a fiber grating center wavelength demodulator, which is constructed by using any one of the fiber grating center wavelength demodulation systems as described above.
In conclusion, the fiber grating central wavelength demodulation system is simple in structure, the light intensity and the wavelength of reflected light of the fiber grating sensor are corresponding through the filter slope, the flatness requirement on a light source is low, the fiber grating central wavelength demodulation system can be simultaneously suitable for application environments with high frequency and low frequency demodulation as long as the operation speed of a CPU (central processing unit) of an upper computer is enough, and the problems that the cost is high, the requirement on the flatness of the light source is high, the high frequency demodulation application environment and the low frequency demodulation application environment are difficult to simultaneously meet and the like in the conventional demodulation system are solved.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the utility model, the scope of which is defined in the appended claims and their equivalents.
Claims (9)
1. A fiber grating center wavelength demodulation system is characterized in that: the method comprises the following steps:
the device comprises a light path unit, a photoelectric conversion unit, a signal conditioning unit, an A/D sampling unit and an upper computer (1-18); the optical path unit, the photoelectric conversion unit, the signal conditioning unit, the A/D sampling unit and each device and chip in the upper computer are electrically connected with each other to form the fiber bragg grating central wavelength demodulation system;
the optical path unit includes: the optical fiber sensor comprises an ASE light source (1-1), a three-port circulator (1-2), an optical fiber Bragg grating sensor (1-3), an optical fiber coupler (1-4) and an edge filter (1-5);
the photoelectric conversion unit includes: a first photoelectric conversion circuit (1-6) and a second photoelectric conversion circuit (1-7);
the signal conditioning unit comprises: a first current-voltage conversion circuit (1-8), a second current-voltage conversion circuit (1-9), a first linear amplification circuit (1-10), a second linear amplification circuit (1-11), a first low-pass filter (1-12), a second low-pass filter (1-13), a first dark current compensation circuit (1-14), a second dark current compensation circuit (1-15);
the A/D sampling unit comprises: a first A/D sampling circuit (1-16) and a second A/D sampling circuit (1-17).
2. The fiber grating center wavelength demodulation system of claim 1, wherein: the three-port circulator (1-2) includes: one port, two ports, three ports; near-infrared light emitted by the ASE light source (1-1) enters through one port of the three-port circulator (1-2), and after the near-infrared light enters the fiber Bragg grating sensor (1-3) through the two ports, reflected light of the near-infrared light is emitted to the fiber coupler (1-4) through the three ports of the three-port circulator (1-2).
3. The fiber grating center wavelength demodulation system of claim 1, wherein: the optical fiber coupler (1-4) is 1: the optical fiber Bragg grating sensor comprises an optical fiber coupler (1), wherein the optical fiber coupler (1-4) splits reflected light of the optical fiber Bragg grating sensor (1-3) into a measuring optical path and a reference optical path in an average way.
4. The fiber grating center wavelength demodulation system of claim 3, wherein: the edge filter (1-5) selects a chirped grating and linearly filters the measuring light path; the measuring optical path is filtered by an edge filter (1-5) and then transmitted to a first photoelectric conversion circuit (1-6).
5. The fiber grating center wavelength demodulation system of claim 4, wherein: the reference optical path is directly input into the second photoelectric conversion circuit (1-7).
6. The fiber grating center wavelength demodulation system of claim 5, wherein: further comprising: and inputting the filtered measuring light path and the filtered reference light path into the signal conditioning unit to obtain effective voltage values corresponding to the measuring light path and the reference light path, sampling the effective voltage values by the A/D sampling unit, and converting the effective voltage values into digital signals which can be directly processed by an upper computer (1-18).
7. The fiber grating center wavelength demodulation system of claim 6, wherein: the first photoelectric conversion circuit (1-6) and the second photoelectric conversion circuit (1-7) are selected from PIN photodiodes.
8. The fiber grating center wavelength demodulation system of claim 7, wherein: after the filtered measurement light path and the filtered reference light path are input into the signal conditioning unit, the current signals are logarithmically amplified and then converted into voltage signals through the first current-voltage conversion circuit (1-8) and the second current-voltage conversion circuit (1-9), the converted voltages are secondarily amplified through the first linear amplification circuit (1-10) and the second linear amplification circuit (1-11), the first low-pass filter (1-12) and the second low-pass filter (1-13) filter high-frequency noise, and the dark current compensation circuit is used for offsetting errors generated by dark current of a PIN photodiode of the photoelectric conversion unit.
9. A fiber grating center wavelength demodulator is characterized in that: the fiber bragg grating central wavelength demodulation system of any one of claims 1 to 8 is adopted for the hardware construction of the demodulator.
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