KEYWORDS: Sensors, Fiber lasers, Fiber Bragg gratings, Fiber optics sensors, Signal to noise ratio, Laser resonators, Modes of laser operation, Reflectors, Signal detection, Signal generators
A multilongitudinal mode fiber ring laser sensor is proposed and experimentally demonstrated by measuring the strain applied on the laser sensor head. The ring cavity of the laser is formed by a 3-dB coupler, a section of erbium-doped fiber, and one fiber Bragg grating. Photonic generation of beat signals and strain measurement theory are discussed in detail. The strain applied on the fiber ring cavity is obtained by measuring the beat frequency shift. The selection way of the optimal beat signal for strain measurement is obtained by experimental research and discussion. The root-mean-square deviation of the strain and the response of beat frequency to the strain are 2.7 μɛ and 1.5 kHz/μɛ at 1993 MHz, respectively. The proposed sensor scheme offers a cost-effective and high-stability device for strain measurement.
A special sampling structure based on the double exposure technology is proposed to achieve dual-wavelength lasing in
the distributed feedback (DFB) fiber laser. This structure is composed of two grating pitches in one sampling period,
which could be realized by changing the fiber's length in the fabrication. And through employing an equivalent phase
shift, only a submicrometer-level precision is required for precise phase control. Then a stable dual-wavelength laser
with the spacing of 400pm is obtained in the experiment successfully. The output power is 30.46uW and the SMSR is
46dB under a pumped power of 146mw.
A multi-longitudinal-mode fiber laser sensor is proposed and experimentally
demonstrated base on beat frequency demodulation method. A novel laser cavity is formed by a
FBG, a section of erbium-doped fiber and a broadband reflector. The proposed laser sensor has
ultra-stable frequency information due to self-phase matching of FBG, and high signal to noise
ratio.
We propose and experimentally demonstrate a novel FBG dual-wavelength fiber laser sensor based on the beat
frequency demodulation technology. The dual-wavelength beat frequency sensing signal of about 5.224 GHz has been
obtained in a photodetector and observed by a radio-frequency spectrum analyzer (RFSA). Furthermore, by employing a
LiNbO3 modulator, the high-frequency beating signal can be tuned arbitrarily to tens or hundreds of MHz without
distortions. Thus a very cheap and low-frequency RF spectrum analyzer can be used in frequency signal detection. When
a strain is applied on the sensor, the beating signal will shift with a stain sensitivity of about (-3.92) kHz/με.
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