研究目的
To propose and realize a high spatial resolution demodulation method for Ultra-weak FBGs based on incoherent optical frequency domain reflection and chaotic laser.
研究成果
The proposed method can realize the position and wavelength demodulation of Ultra-weak FBGs with 10cm spatial interval. The accuracy of demodulation system is within 16 pm. The method reduces the requirements for light sources and sampling rate by using spectrum shifting and improves the spatial resolution of demodulation system to 10cm and realized the feasibility of long-distance demodulation.
研究不足
The spatial resolution of the sensing system only depends on the frequency bandwidth and effective index of the sensing fiber. The maximum time delay, generated by the last FBG, should be smaller than the sweep cycle to prevent frequency aliasing.
1：Experimental Design and Method Selection:
The method involves modulating a single longitudinal mode, narrow linewidth light output from a DFB laser with a frequency swept microwave, then entering the FBGs and reflecting. The reflected optical signal is transformed into an electric signal by a photodiode, and then mixes with the original microwave to produce the beat frequency. Fast Fourier transformation is used to analyze the beat frequency to modulate the location information. The wavelength of the DFB laser is controlled to sweep in a specific range to obtain the wavelength information of FBGs. Chaotic signals from DFB laser with optical feedback are generated to broaden the linewidth of laser to eliminate the influence of interference between light reflected from the FBGs.
2：Sample Selection and Data Sources:
The samples are ultra-weak FBGs. The data sources are the reflected signals from the FBGs.
3：List of Experimental Equipment and Materials:
DFB laser, optical coupler, circulator, polarization controller, variable optical attenuator, erbium-doped fiber amplifier, bandpass filter, microwave signal source, electro-optical modulator, photodetector, low-pass filter, data acquisition card.
4：Experimental Procedures and Operational Workflow:
The chaotic output is amplified by an EDFA, modulated by a frequency-sweeping microwave signal, directed to the FBG sensing array, and the reflected signal is detected by a photodetector. The generated beat signal is filtered, collected by a DAQ, and post-processed to recover the position of the FBGs. The wavelength of the chaotic source is scanned to achieve interrogation of the gratings.
5：Data Analysis Methods:
Fast Fourier transformation is used to analyze the beat frequency to modulate the location information of the FBGs.
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DFB laser
Used as the chaotic source.
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optical coupler
Directs the laser output to the sensing system and back to the laser.
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circulator
Used to direct the optical signal.
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polarization controller
Aligns the polarization of the light with that of the DFB laser.
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variable optical attenuator
Controls the feedback strength.
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erbium-doped fiber amplifier
Amplifies the chaotic output.
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bandpass filter
Rejects the amplified spontaneous emission noise from the EDFA.
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microwave signal source
Generates a frequency-sweeping microwave signal.
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electro-optical modulator
Modulates the amplified chaotic output.
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photodetector
1.6-GHz
Detects the reflected signal.
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low-pass filter
Filters the generated beat signal.
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data acquisition card
DAQ
Collects the filtered beat signals.
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