A novel short-cavity-based narrow linewidth random fiber laser (RFL) is proposed. The random distributed feedback mechanism of RFL is assumed by a set of arbitrarily distributed weak reflection fiber Bragg grating arrays (FBGs). A π-phase-shifted FBG with a narrow transmission window is used in the RFL to further limit the number of random subcavity modes and suppress the output linewidth. High gain erbium-doped fibers and half-open cavity designs are used to maintain low lasing thresholds. A stable single-mode lasing operation with 3-dB linewidth of 211 Hz and 58 dB sidemode-suppression-ratio is established.
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.
We proposed an high-resolution broadband phase interrogation technique for an interferometric fiber optic sensor which is designed as an unbalance michelson interference structure. The frequency stabilization technique based on PoundDrever-Hall (PDH) method is used for reducing low-frequency phase noise of the laser. An (Piezoelectric Transition) PZT, acting on one arm of the interferometer, is used to generate additional phase modulation. A phase generation carrier (PGC) algorithm is proposed for phase demodulation. The experiment results show that the proposed system has a very wide wavelength detection capability (from 0.1 Hz to 500 Hz) with an ultrahigh resolution of 2 × 10-4 email@example.com Hz, and better than 10-5 rad in the frequency range from 1 Hz - 500 Hz.
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.