CN109470163B - High-capacity ultrahigh-speed optical fiber sensing device for strain monitoring of spacecraft - Google Patents
High-capacity ultrahigh-speed optical fiber sensing device for strain monitoring of spacecraft Download PDFInfo
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- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
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Abstract
The invention discloses a high-capacity ultra-high-speed optical fiber sensing device for strain monitoring of a spacecraft, which solves the technical problems of more single optical fiber sensors and ultra-fast demodulation rate; the capacity of the sensors on a single optical fiber is improved by adopting an intensive wave division technology and a low-reflectivity grating alternative use technology, and the number of the single optical fiber sensors is thousands, so that the requirement of large-capacity optical fiber sensing large-area array detection of a spacecraft is met; the method realizes the ultra-high speed demodulation of the spacecraft optical fiber sensing by a non-mechanical strength adjusting principle, and related researches realize the upgrading and updating of the existing products, thereby bringing huge market value.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a high-capacity ultrahigh-speed optical fiber sensing device for strain monitoring of a spacecraft.
Background
In the process of the on-orbit flight of the spacecraft, garbage fragments, particles and the like in the space collide with the spacecraft at a high speed, and the collisions generate strain on the surface of a spacecraft cabin body to form damage accumulation. Meanwhile, the cabin body can also deform in the processes of pressure charging and releasing and rendezvous and docking of the spacecraft. Therefore, the strain of the spacecraft cabin needs to be monitored in real time, which provides guarantee for the reliability and safety of the spacecraft.
At present, two methods, namely a piezoelectric sensor and a fiber bragg grating sensor, are mainly adopted to monitor the strain of the spacecraft cabin body.
(1) A piezoelectric type sensor. Because the frequency of the collision stress wave is relatively high, a piezoelectric sensor with the frequency measurement range of 0.1Hz to hundreds of kHz is often adopted for monitoring, and the bandwidth is large. However, for the spacecraft, the piezoelectric sensor has large volume, weight and power consumption, a detection system is complex, and the anti-electromagnetic interference capability of the piezoelectric sensor is poor, so that the piezoelectric sensor is slowly replaced by a novel sensor.
(2) Fiber grating type sensors. The fiber grating sensor belongs to a novel sensor on a spacecraft, has a series of advantages of small size, light weight, high sensitivity, wide dynamic range, electromagnetic interference resistance, corrosion resistance, capability of being applied to high-temperature/high-pressure environments and the like, and has attracted high attention and application in domestic and foreign space systems.
However, the best technical state of the fiber grating sensing technology in China on a spacecraft is that the number of single fiber sensors is less than 10, and the demodulation rate is less than 5 kHz. Particularly, the two advantages of the 'high sensor number of a single optical fiber' and the 'ultra-fast demodulation rate' are combined with the key technology and are not solved all the time, which brings great influence on the subsequent function expansion application.
On one hand, the requirement of large-capacity optical fiber sensing arrangement of the spacecraft in a large area is difficult to meet. If the optical fiber sensors need to be arranged in a large range, dozens of optical fibers or more than hundreds of optical fibers are needed, the circuit is complex, the failure rate is increased, and the weight cost is greatly increased.
On the other hand, the demodulation speed is low, and high-frequency strain and vibration signals higher than 5kHz cannot be monitored, for example, high-frequency signals generated in a fragment impact process cannot be monitored, so that the functional expansion and the wide application of the optical fiber sensing on the spacecraft are severely limited.
Disclosure of Invention
In view of this, the present invention provides a high-capacity and ultra-high-speed optical fiber sensing device for spacecraft strain monitoring, which can improve the capacity of a sensor on a single optical fiber and realize ultra-high-speed demodulation of optical fiber sensing.
An optical fiber sensing device comprises a C-waveband + L-waveband continuous broadband light source, an electro-optic modulator EOM, a circulator, 40 groups of optical fiber sensors, an intensive wave splitter, a voltage proportion module, a wavelength reduction module and a strain acquisition module;
the wavelength range of the C-band and L-band continuous broadband light source is 1520nm-1610 nm;
the electro-optical modulator EOM modulates continuous optical signals emitted by the C-band and L-band continuous broadband light source into pulse optical signals with the period of 10 mus and the pulse width of 10 ns;
each of the 40 groups of optical fiber sensors comprises 25 gratings with different central wavelengths; the groups of the 40 groups of optical fiber sensors are connected by delay optical fibers of 50 meters;
pulse optical signals emitted by the electro-optical modulator EOM pass through the circulator and are incident into each group of optical fiber sensors; the optical signals reflected by the optical fiber sensors are sent to the dense wavelength division device through the circulator;
the time delay optical fibers among the groups are used for delaying the time of the pulse optical signals entering the optical fiber sensors of the groups;
the dense wavelength division device divides the reflected light of the optical fiber sensor into 25 wave bands according to the 25 different central wavelengths;
25 voltage proportion modules are provided, and the voltage proportion modules respectively correspond to 25 wave bands obtained by dividing grating reflected light by the dense wavelength division device; each voltage proportion module comprises a coupler, a first photodetector PD1-1, an F-P light intensity filter, a second photodetector PD1-2 and a divider; the passband bandwidth of each F-P light intensity filter corresponds to the wave band output by the dense wave division device and received by the voltage proportion module;
the coupler divides one path of optical signal 1:1 received by the voltage proportion module from the dense wavelength division device into two paths of light; the first photodetector PD1-1 converts one path of light into a voltage signal VG1Then sending the data to the divider;
after the F-P optical intensity filter filters the other path of optical signal branched by the coupler, the second photodetector PD1-2 converts the other path of optical signal into a voltage signal VF1Then sending the data to the divider;
the divider receives a voltage signal VG1Sum voltage signal VF1To V pairG1And VF1Division is carried out to obtain a ratio VF1/VG1；
The wavelength reduction module is stored with a ratio VF established in advance through a calibration test1/VG1A database in one-to-one correspondence with the wavelengths; by receiving the ratio VF of the outputs of the dividers1/VG1After comparison in the database, the ratio VF is obtained1/VG1Corresponding wavelength, thereby obtaining a corresponding wavelength value;
and the strain acquisition module receives the wavelength value information sent by each voltage proportion module to obtain a strain value.
Preferably, the power of the C-band + L-band continuous broadband light source is not lower than 20dBm, and the spectral flatness is lower than 2 dB.
Preferably, each band of the dense wavelength division device occupies a bandwidth of 3nm, and the adjacent optical path buffer protection bandwidth is 0.6 nm.
Preferably, the optical fiber sensor adopts a fiber Bragg grating.
Preferably, the optical fiber sensor adopts a grating with the reflectivity of 1%.
Preferably, the dense wave separator has an inter-channel isolation greater than 40 dB.
The invention has the following beneficial effects:
aiming at the technical problem that the existing optical fiber sensor high point number and high demodulation rate cannot be compatible, the invention firstly provides a high-capacity and ultra-high-speed optical fiber sensing device for strain monitoring of a spacecraft, and solves the technical problem that the single optical fiber sensor has more number and the ultra-fast demodulation rate is simultaneously provided; the capacity of the sensors on a single optical fiber is improved by adopting an intensive wave division technology and a low-reflectivity grating alternative use technology, and the number of the single optical fiber sensors is thousands, so that the requirement of large-capacity optical fiber sensing large-area array detection of a spacecraft is met; the method realizes the ultra-high speed demodulation of the spacecraft optical fiber sensing by a non-mechanical strength adjusting principle, and related researches realize the upgrading and updating of the existing products, thereby bringing huge market value.
Drawings
FIG. 1 is a schematic construction diagram of a high-capacity ultra-high-speed optical fiber sensing device according to the present invention.
FIG. 2 is a schematic diagram of a 90nm broadband light source incident fiber grating used in the present invention.
Fig. 3 is a graph of the crosstalk signal specific gravity when 40 gratings with low reflectivity and wavelength are used alternately.
FIG. 4 is an insertion loss diagram of the dense wavelength splitter of the present invention for 25 channels in 1520-1610 bands.
Detailed Description
The invention is described in detail below by way of example with reference to the accompanying drawings.
As shown in fig. 1, the high-capacity ultra-high-speed optical fiber sensing device of the invention comprises a C-band + L-band continuous broadband light source, an electro-optical modulator EOM, a circulator, 40 groups of optical fiber sensors, a dense wavelength divider, a voltage proportion module, a wavelength reduction module and a strain acquisition module;
the wavelength range of the C-band + L-band continuous broadband light source is 1520-1610nm, the bandwidth is 90nm, the power is not lower than 20dBm, and the spectral flatness is lower than 2 dB.
The electro-optical modulator EOM is subjected to light path on-off operation by a driving circuit, the driving circuit obtains signals from a function generator, the period of pulse signals given by the function generator is 10 mu s, and the pulse width is 10 ns. Therefore, the pulse light signal period of the continuous broadband light source after passing through the electro-optical modulator EOM is 10 mus, and the pulse width is 10 ns.
Each of the 40 groups of optical fiber sensors comprises 25 gratings with different central wavelengths; lambda [ alpha ]1，λ2 ……λ 2525 gratings with wavelength between 40 groups are in one-to-one correspondence, namely lambda1，λ2……λ25The grating of the center wavelength is repeated 40 times; the groups of the 40 groups of optical fiber sensors are connected by delay optical fibers of 50 meters;
pulse optical signals emitted by the electro-optical modulator EOM pass through the circulator and are incident to 1000 fiber bragg grating sensing arrays; the optical signals reflected by each grating are sent to the dense wavelength division device through the circulator;
the time delay optical fibers among the groups are used for delaying the time of the pulse optical signals entering the optical fiber sensors of the groups, so that the optical fiber sensors of different groups reflect signals to enter the dense wavelength division device in sequence.
The dense wavelength division device divides the reflected light of the grating into 25 wave bands, each wave band occupies the bandwidth of 3nm, and the adjacent light path buffering protection bandwidth is 0.6 nm.
25 voltage proportion modules are provided, and the voltage proportion modules respectively receive 25 wave bands into which grating reflected light is divided by the dense wavelength division device; each comprising a coupler, a first photodetector PD1-1, a first amplifier 1-1, an F-P optical intensity filter, a second photodetector PD1-2, a second amplifier 1-2, and a divider; the two amplifiers are used for amplifying the voltage signal to be within the working voltage range of the divider. The passband bandwidth of each F-P optical intensity filter corresponds to the band of the dense wavelength division device output received by the voltage proportion module, the effective filtering range of each group of F-P optical intensity filters is different, see table 1 for details, the insertion loss of light with different wavelengths entering the F-P optical intensity filters is different, and therefore the voltage values measured by the detector are different.
The coupler divides one path of optical signal 1:1 received by the voltage proportion module from the dense wavelength division device into two paths of light; the first photoelectric detector PD1-1 converts one path of light into a voltage signal, and the voltage signal is amplified by the first amplifier 1-1 to obtain a voltage signal VG1Then the signal is sent to a divider;
after the F-P optical intensity filter filters the other path of optical signal split by the coupler, the second photodetector PD1-2 converts the other path of optical signal into a voltage signal, and the voltage signal is amplified by a second amplifier 1-2 to obtain a voltage signal VF1；
Divider receiving voltage signal VG1Sum voltage signal VF1To V pairG1And VF1Division is carried out to obtain a ratio VF1/VG1；
Due to the ratio VF1/VG1Has one-to-one correspondence with the wavelength, so the ratio VF established by calibration test in advance is stored in the wavelength reduction module1/VG1A database in one-to-one correspondence with the wavelengths; by receiving the ratio VF of the outputs of the dividers1/VG1After comparison in the database, the ratio VF is obtained1/VG1The corresponding wavelength, and therefore the corresponding wavelength value, can be obtained. Similarly, the other 24 segments of the optical path are also processed in the same wayAnd (5) processing.
The strain acquisition module receives wavelength information sent by each voltage proportion module to obtain the variation of the wavelength, and the variation of the wavelength is divided by the sensitivity coefficient of the grating to obtain a strain value. Over 10 mus, strain values measured by 1000 sensors of 40 groups can be obtained.
Figure 2 is a schematic diagram of a 90nm broadband light source incident fiber grating. When 90nm broadband light is transmitted in an optical fiber, the characteristic parameter wavelength of the 90nm broadband light is modulated by external factors such as strain, temperature and the like to change. A Fiber Bragg Grating (FBG) sensor using FBG technology belongs to a wavelength modulation type sensor, when broadband light is incident to the FBG, light with specific wavelength is emitted back, the change of reflected light wavelength is related to the strain and temperature to be measured, and the return wavelength lambda of the reflected light is obtained by acquiring the gratingiThe strain and the temperature are measured by the change of the temperature.
FIG. 3 is a graph of the reliability of a 40-wavelength identical low-reflectivity grating. For gratings with different reflectivities, the multiplexing number of the gratings is limited due to the influence of other optical path interference effects, so that the influence of other optical path interference effects is considered under the aim of continuously increasing the multiplexing number of the system.
The light source emits light pulses, a small part of energy can be reflected after the light pulses pass through the sensor group, the energy of transmitted light pulse signals is gradually attenuated along with the increase of the transmission number, and therefore the reflected signals of the sensors at the tail end group are the weakest. Let I0Is the intensity of incident light, INThe reflection light intensity of the Nth same-wavelength sensor, R is the reflectivity of the grating, and then:
IN＝I0×R(1-R)2(N-1)(formula 1)
In the detection, the detector can simultaneously detect a plurality of reflected signals under paths with the same distance to form interference signals, wherein only one-order reflected interference signals are considered, other signals are very weak, and the intensity of the first-order reflected crosstalk is as high as
IN'＝I0×R3(1-R)2(N-2)(formula 2)
The larger the number of the gratings with the same wavelength is, the larger the light intensity of the first-order reflected crosstalk is.
The first order reflected interference light intensity is expressed as
The first order reflection on the N gratings with the same wavelength interferes with the total light intensity
In order to make the system not interfered by the first-order reflection, it must satisfy
IN＞10IN' (formula 5)
Through simulation design, the maximum capacity of usable gratings with the same wavelength under different reflectivities (0.6% -6%) is shown in fig. 3.
In the experiment, the grating with 1 percent of reflectivity is selected to satisfy IN＞10IN' the number theoretically reusable reaches 46, and to leave a margin, we choose the number of multiplexes 40. The advantages of this design are: on the premise of ensuring the multiplexing number, the reflectivity of the optical fiber is highest, the energy which can be detected by the photoelectric detector is the largest, and the signal-to-noise ratio can be realized to the greatest extent.
FIG. 4 shows an insertion loss diagram of a dense type splitter at 25 channels in the 1520-1610 band. The dense wave splitter splits the reflected light with the bandwidth of 90nm into 25 paths, and the bandwidth information occupied by each path of light is shown in table 1.
Table 1 table of bandwidth information occupied by wavelength division 25 channels of light
The wavelength ranges of 25 wave bands in the table 1 are designed, so that the effective wavelength range of each wave band is 3nm, the sensitivity of the grating is 0.6 pm/mu, and the corresponding strain range is 0-5000 mu, thereby meeting the strain measurement requirement in engineering (the general strain requirement range in engineering is 0-2500 mu).
For the multi-channel dense wave separator, the isolation between channels is greater than 40dB, so that signal crosstalk among different channels can be avoided, and the application requirements are met.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (6)
1. An optical fiber sensing device is characterized by comprising a C-waveband + L-waveband continuous broadband light source, an electro-optic modulator EOM, a circulator, 40 groups of optical fiber sensors, an intensive wavelength divider, a voltage proportion module, a wavelength reduction module and a strain acquisition module;
the wavelength range of the C-band and L-band continuous broadband light source is 1520nm-1610 nm;
the electro-optical modulator EOM modulates continuous optical signals emitted by the C-band and L-band continuous broadband light source into pulse optical signals with the period of 10 mus and the pulse width of 10 ns;
each of the 40 groups of optical fiber sensors comprises 25 gratings with different central wavelengths; the groups of the 40 groups of optical fiber sensors are connected by delay optical fibers of 50 meters;
pulse optical signals emitted by the electro-optical modulator EOM pass through the circulator and are incident into each group of optical fiber sensors; the optical signals reflected by the optical fiber sensors are sent to the dense wavelength division device through the circulator;
the time delay optical fibers among the groups are used for delaying the time of the pulse optical signals entering the optical fiber sensors of the groups;
the dense wavelength division device divides the reflected light of the optical fiber sensor into 25 wave bands according to the 25 different central wavelengths;
25 voltage proportion modules are provided, and the voltage proportion modules respectively correspond to 25 wave bands obtained by dividing grating reflected light by the dense wavelength division device; each voltage proportion module comprises a coupler, a first photodetector PD1-1, an F-P light intensity filter, a second photodetector PD1-2 and a divider; the passband bandwidth of each F-P light intensity filter corresponds to the wave band output by the dense wave division device and received by the voltage proportion module;
the coupler divides one path of optical signal 1:1 received by the voltage proportion module from the dense wavelength division device into two paths of light; the first photodetector PD1-1 converts one path of light into a voltage signal VG1Then sending the data to the divider;
after the F-P optical intensity filter filters the other path of optical signal branched by the coupler, the second photodetector PD1-2 converts the other path of optical signal into a voltage signal VF1Then sending the data to the divider;
the divider receives a voltage signal VG1Sum voltage signal VF1To V pairG1And VF1Division is carried out to obtain a ratio VF1/VG1；
The wavelength reduction module is stored with a ratio VF established in advance through a calibration test1/VG1A database in one-to-one correspondence with the wavelengths; by receiving the ratio VF of the outputs of the dividers1/VG1After comparison in the database, the ratio VF is obtained1/VG1Corresponding wavelength, thereby obtaining a corresponding wavelength value;
and the strain acquisition module receives the wavelength value information sent by each voltage proportion module to obtain a strain value.
2. The fiber optic sensing device of claim 1, wherein the C-band + L-band continuous broadband light source has a power of no less than 20dBm and a spectral flatness of less than 2 dB.
3. The optical fiber sensing device according to claim 1, wherein each wavelength band of said dense wavelength division device occupies a bandwidth of 3nm and an adjacent optical path buffer protection bandwidth is 0.6 nm.
4. The optical fiber sensing device according to claim 1, wherein said optical fiber sensor employs a fiber bragg grating.
5. An optical fiber sensing device according to claim 4, wherein said optical fiber sensor employs a grating having a reflectivity of 1%.
6. An optical fiber sensing device according to claim 1, wherein the dense splitter has an interchannel isolation greater than 40 dB.
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