We proposed a novel structure of short-cavity random fiber laser (RFL) with a stable narrow linewidth output. A random-spaced Bragg grating array is used for random feedback. A ring optical path and the grating array form a short half-open cavity, and a high-precision π-phase-shifted grating (π-FBG) is placed in the ring path for filtering and modelocking to ensure a stable single-mode random laser operation. The linewidth of the laser is 257 Hz with 50 dB sidemode-suppression-ratio (SMSR). The laser wavelength drift measured in the laboratory is less than 1 pm within 20 min. The RFL has a simple structure and can achieve a stable narrow linewidth single mode output, which provides a new choice for high resolution optical fiber sensing.
In the experiment, a fiber Bragg grating embedded in a hollow glass bead/epoxy resin composite was used to monitor the strain changes at different stages of curing, while two free fiber gratings were placed in the oven to realize temperature compensation. At the end of the cooling stage, the minimum strain monitored is - 6123 με. In addition, the study shows that the variation of internal strain in the sample is delayed relative to the temperature change in the oven. This test verifies the feasibility of using FBG to monitor the curing cycle of buoyancy materials.
In the paper, the Long period fiber gratings (LPFG) were fabricated in a single-mode fiber using a high frequency CO2
laser system with the point-to-point technique. The experimental setup consists of a CO2 laser controlling system, a
focusing system located at a motorized linear stage, a fiber alignment stage, and an optical spectrum analyzer to monitor
the transmission spectrum of the LPFG. The period of the LPFG is precisely inscribed by periodically turning on/off the
laser shutter while the motorized linear stage is driven to move at a constant speed. The efficiency of fiber writing
process is improved.
Compared with Fiber Bragg grating (FBG), Distributed Feedback fiber laser (DFB-FL) sensors has the advantages of ultra-narrow line-width, high output power, and low noise level, which will result in a better performance in ultra-slight acoustic emission (AE) detection. In this paper, we demonstrate a DFB fiber laser acoustic sensor. The intensity response of DFB-FL to external acoustic waves has been investigated. The frequency response of the DFB fiber laser based AE sensor is measured in aluminum plate. The experiment results show that the intensity modulated DFB fiber laser acoustic sensor can accurately record the continuous acoustic emission signal and the pencil lead-broken acoustic emission waves.