KEYWORDS: Demodulation, Digital signal processing, Fiber optics sensors, Interferometers, Sensors, Signal detection, Signal processing, Mach-Zehnder interferometers, Phase shifts, Acoustics
A phase demodulation scheme of interferometic distributed optic fiber sensor (DOFS) for strain and vibrations
measurement is proposed in this paper. We discuss the principles of interferometic DOFS based on long-length
MZI, and present the preliminary results on the application of distributed optic fiber sensor for the measurements
of distributed signals in long-distance region. And illustrate important points in regard to the phase demodulation.
The system is all fiber and uses a 3×3 coupler for phase demodulation. Parameters such as strain sensitivity,
transverse strain sensitivity, failure strain, and frequency response are discussed. In addition, this technique can
yield a large dynamic range with phase amplitudes for its symmetry. The high speed digital processing (DSP)
technology is used in the sensor system, which can carry out all operations in real time and promote the resolution
of localization. The hardware design of phase demodulation scheme of the sensor is completed and the
experimental results are obtained. The new scheme greatly reduces the complexity of practical fiber
interferometers and an experimental setup has been implemented to demonstrate its expected merits.
The interferometic DOFS has better sensitivity and resolution than the others. In theoretic, it allows fully
distributed strain, vibration and acoustic wave measurement over a sensing length of tens of kilometer. At the time
of writing, the system is only partially completed; therefore the content of this paper will focus on the principle of
distributed optical fiber sensor. The results mainly are presented in laboratory.
This paper demonstrates the recent achievements in the field of distributed optical fiber sensor (DOFS). A novel type
of distributed optic fiber vibration sensor is presented to detect and locate a time-varying disturbance along the whole
fiber length. It measures the first simultaneous information by using Mach-Zehnder Interferometer(MZI). The sensor
consists of a MZI where two directional optical signals are simultaneously traveling. We discuss the principles of
distributed optic fiber vibration sensor based on long-length MZI, and present the preliminary results on the application
of distributed optic fiber sensor for the measurements of distributed signals in long-distance region. The sensor is
illuminated by one continuous-wave laser, which is different from the conventional scheme. The phase shift caused by
any disturbance around the fiber is detected and converted to the information on the perturbation position and amplitude,
which can be determined by combining two phase signals from the above device. In addition, we adopt a new technique
by using optical delay effect to improve the spatial resolution of distributed optic fiber sensor. It is completely different
from the spatial-resolution technique of optical time-domain reflectometry (OTDR). The system has capability for cross-correlation
algorithm and fast Fourier transform (FFT) analysis of the detected disturbance signals. For the sake of
determining the disturbance position and type, high speed digital processing (DSP) technology is used in the sensor
system, which can carry out all operations in real time and promote the resolution of localization. The hardware design
of the sensor is completed and the experimental results are obtained. This type of optic fiber sensor has better sensitivity
and resolution than the others. It achieves a 100Hz-20KHz frequency of vibration resolution, with 100-m practical
spatial resolution, over a sensing length of 8 km. At the time of writing, the system is only partially completed; therefore
the content of this paper will focus on the principle of distributed optical fiber sensor. The results mainly are presented in
laboratory.
A novel type of distributed fiber optic sensor is presented to detect and locate a time-varying disturbance along the whole fiber length. The sensor consists of a Mach-Zehnder interferometer (MZI) where two directional optical signals are simultaneously traveling. This is achieved by a fiber-loop in the configuration, causing one MZI to operate as two co- and counter- propagating interferometers. The sensor is illuminated by only one continuous-wave laser, which is different from the conventional scheme. The phase shift caused by any disturbance around the fiber is detected and converted to the information on the perturbation position and amplitude, which can be determined by combining two phase signals from the above device. In addition, passive homodyne demodulation with application of a 3×3 fiber optical coupler for recovering a signal of interest from the MZI is also described. This technique can yield a large dynamic range with phase amplitudes for its symmetry. Also, high speed digital processing (DSP) technology is used in the sensor system, which can carry out all operations in real time and promote the resolution of localization. The system has capability for cross-correlation algorithm and fast Fourier transform (FFT) analysis of the detected disturbance signals, for the sake of determining the disturbance position and type. Finally, a positional resolution better than 100 m has been theoretically discussed and experimentally demonstrated in a system over 6.8 km fiber length.
A new distributed interferometic optical fiber sensor (IOFS) for strain and vibrations measurement is proposed in the paper. It measures the first simultaneous information by using Mach-Zehnder Interferometer. The important points in regard to phase demodulation are explained. The system is all fiber and uses a 3×3 coupler for phase demodulation. Parameters such as strain sensitivity, transverse strain sensitivity, failure strain, and frequency response are discussed. The new scheme greatly reduces the complexity of practical fiber interferometer. An experimental setup has been implemented to demonstrate its expected merits. This type of IOFS has better sensitivity and resolution than others. At the time of writing, the system is only partially completed; therefore the content of this paper will focus on the principle of distributed optical fiber sensor. The results mainly are presented in laboratory.
A new distributed interferometic sensor for strain and vibrations measurement is proposed in this paper. It measures the first simultaneous information by using Mach-Zehnder Interferometer. We illustrate important points in regard to the proposed distributed signals measurement, and present the preliminary results on the application of optical fiber interferometic sensor (OFIS) for the measurements of distributed signals in long-distance region, and discuss the principles of distributed OFIS based on long-length Mach-Zehnder interferometic technique. We also adopt a new technique by using optical delay effect to improve the spatial resolution of distributed interferometic sensor. It is completely different from the spatial-resolution technique of optical time-domain reflectometry (OTDR). This type of OFIS has better sensitivity and resolution than the others. In addition, this paper describes a form of passive phase demodulation for recovering a signal of interest from a Mach-Zender optical fiber interferometric sensor. It achieves a 100Hz-2KHz frequency of vibrations resolution, with 100-m practical spatial resolution, over a sensing length of 6.8 km. At the time of writing, the system is only partially completed; therefore the content of this paper will focus on the principle of distributed sensor. The results mainly are presented in laboratory.
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