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ABSTRACT: The distributed optical fiber temperature sensor system based on Raman scattering has developed rapidly since it was invented
in 1970s. The optical wavelengths used in most of the distributed temperature optical fiber sensor system based on the Raman
scattering are around from 840 to 1330 nm, and the system operates with multimode optical fibers. However, this wavelength
range is not suitable for long-distance transmission due to the high attenuation and dispersion of the transmission optical
fiber. A novel distributed optical fiber Raman temperature sensor system based on standard single-mode optical fiber is proposed.
The system employs the wavelength of 1550 nm as the probe light and the standard communication optical fiber as the sensing
medium to increase the sensing distance. This system mainly includes three modules: the probe light transmitting module, the
light magnifying and transmission module, and the signal acquisition module.
Frontiers of Optoelectronics in China 04/2012; 2(2):215-218.
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ABSTRACT: In this paper, a high-power erbium-doped fiber amplifier (EDFA) for the temperature sensor system is theoretically designed
and experimentally demonstrated. It consists of an erbium-doped fiber that is pumped bidirectionally with two 980-nm high-power
laser diodes (LDs). At the EDFA input, an optical isolator (ISO) is used to ensure that the signal pulse transmits forward
only. After that, a wavelength division multiplexer (WDM) is employed to combine the forward pump laser (980 nm) and incident
optical pulse (1550 nm) into the erbium-doped fiber for direct amplification in the optical domain. At the EDFA output, another
WDM couples the backward pump laser (980 nm) into the erbium-doped fiber and outputs the amplified optical pulse (1550 nm)
with an ISO followed to isolate the backscattering light. According to this structure, we carried out the experiment in the
condition as follows. For 980 nm pump LD, the operating current is 590 mA, and the setting temperature is 25°C. For EDFA,
the length of erbium-doped fiber is 12.5 m, and the power of 1550 nm input signal is 1.5mW. As a result, the power of pump
LD is 330mW, and the power uncertainty is 0.5%. The power of EDFA output at 1550 nm is 300mW, and the power uncertainty is
± 3mW.
Frontiers of Optoelectronics in China 04/2012; 2(2):210-214.
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ABSTRACT: A novel distributed optical fiber vibrationsensing system based on Mach-Zehnder interferometer has been designed and experimentally
demonstrated. Firstly, the principle of Mach-Zehnder optical path interferometer technique is clarified. The output of the
Mach-Zehnder interferometer is proportional to the phase shift induced by the perturbation. Secondly, the system consists
of the laser diode (LD) as the light source, fiber, Mach-Zehnder optical interferometers as the sensing units, a 1×N star fiber-optic coupler, an N×1 fiber-optic coupler, a photodiode (PD) detector, and a computer used in signal processing. The entire monitoring region
of this system is divided into several small zones, and each small monitoring zone is independent from each other. All of
the small monitoring zones have their own sensing unit, which is defined by Mach-Zehnder optical interferometer. A series
of sensing units are connected by the star fiber-optic couplers to form a whole sensing net. Thirdly, signal-processing techniques
are subsequently used to calculate the phase shift to estimate whether intruders appear. The sensing system is able to locate
the vibration signal simultaneously, including multiple vibrations at different positions, by employing the time-division
multiplexed (TDM) technique. Finally, the operation performance of the proposed system is tested in the experiment lab with
the conditions as follows: the number of the sensing units is 3, the length of the sensing fiber is 50 m, and the wavelength
of the light diode is 1550 nm. Based on these investigations, the fiber surrounding alert system is achieved. We have experimentally
demonstrated that the sensing system can measure both the frequency and position of the vibration in real time, with a spatial
positional resolution better than 50 m in an area of 1 km2.
Frontiers of Optoelectronics in China 04/2012; 2(2):229-232.
