A wavelength-switchable and tunable fiber ring laser has been proposed to implement an optical source of a fiber Bragg grating (FBG) vibration sensor array based on intensity modulation technique. The laser consists of an erbium-doped fiber amplifier (EDFA) and an optical switch with tuning FBGs, in which the lasing output is coupled out from a selected tuning FBG and serves as an optical source of one of the multiplexed FBG vibration sensor elements. By changing the channel of the optical switch, the lasing wavelength can be chosen for the sensing FBG of the respective sensor element. In addition, the temperature effects on the sensor outputs due to environmental temperature can be eliminated when the temperature changes are applied commonly to both the tuning and sensing FBGs. In the experiment, multipoint vibration detection with a temperature-insensitive operation is successfully demonstrated by constructing two sensor elements arranged in parallel.
A novel erbium-doped fiber laser (EDFL) has been proposed to implement an optical source of a fiber Bragg grating (FBG) vibration sensor array based on intensity modulation technique. The laser consists of an erbium-doped fiber amplifier (EDFA), an optical coupler and an optical switch with tuning FBGs, in which the lasing wavelength is determined by the Bragg wavelength of the selected tuning FBG to serve as an optical source of one of the arrayed FBG sensors. In addition, the temperature effects on the sensor outputs due to environmental temperature can be compensated when the temperature changes are applied commonly to both the tuning and sensing FBGs. In the experiment, multipoint vibration detection with a temperature-insensitive operation is successfully demonstrated by constructing two sensor elements arranged in tandem.Keywords fiber laser, tunable laser, fiber optic sensor, fiber Bragg grating, vibration sensor
INTRODUCTIONRecently, fiber Bragg grating (FBG) sensors have been paid much attention because of their practical characteristics such as ease in multiplexed operation, simple structure, compactness, and semi-point sensing capability. The principle of operation of such sensors is based on the change in the Bragg wavelength of the FBG when an FBG is under the influence of various parameters to be measured [1-3]: static stress and strain, hydro pressure, vibration, acoustic wave, temperature and so on. The interrogation scheme of such FBG sensors is the essential technology and mainly classified into two methods: one is based on direct measurement of transmission (or reflection) spectrum of the FBG, and the other is based on intensity modulation converting wavelength shift to the optical intensity. The latter method is a very attractive approach in the fabrication of a simple FBG vibration sensor with wide dynamic range [3]. In such sensors, the FBG modulates the intensity of transmitted (or reflected) light with a wavelength tuned to the slope of the FBG transmission (or reflection) spectrum curve if the vibration is applied to the FBG. This technique is successfully applied to the detection of mechanical vibration of solid and acoustic wave in water, but such sensors have a drawback in which it is likely to suffer from environmental temperature variation. Since the temperature variation causes the sensor sensitivity to vary considerably, the FBG vibration sensor based on intensity modulation
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