Random Fiber Grating Characterization Based on OFDR and Transfer Matrix Method

Abstract

Random fiber gratings (RFGs) have shown great potential applications in fiber sensing and random fiber lasers. However, a quantitative relationship between the degree of randomness of the RFG and its spectral response has never been analyzed. In this paper, two RFGs with different degrees of randomness are first characterized experimentally by optical frequency domain reflectometry (OFDR). Experimental results show that the high degree of randomness leads to low backscattering strength of the grating and strong strength fluctuations in the spatial domain. The local spectral response of the grating exhibits multiple peaks and a large peak wavelength variation range when its degree of randomness is high. The linewidth of its fine spectrum structures shows scaling behavior with the grating length. In order to find a quantitative relationship between the degree of randomness and spectrum property of RFG, entropy was introduced to describe the degree of randomness induced by period variation of the sub-grating. Simulation results showed that the average reflectivity of the RFG in dB scale decreased linearly with increased sub-grating entropy, when the measured wavelength range was smaller than the peak wavelength variation range of the sub-grating. The peak reflectivity of the RFG was determined by κ2LΔP (where κ is the coupling coefficient, L is the grating length, ΔP is period variation range of the sub-grating) rather than κL when ΔP is larger than 8 nm in the spatial domain. The experimental results agree well with the simulation results, which helps to optimize the RFG manufacturing processes for future applications in random fiber lasers and sensors.

Enhanced Strain Measurement Sensitivity with Gold Nanoparticle‐Doped Distributed Optical Fibre Sensing

“…Te intensity and phase of the scattered light spectra within the gauge length can be obtained by square windowing the positions within the gauge length and using an inverse Fourier transform. Ten, the spectral shift can be obtained using cross-correlation between the reference spectrum and the spectrum after the strain is applied [42].…”

Narrow Linewidth Half-Open-Cavity Random Laser Assisted by a Three-Grating Ring Resonator for Strain Detection

“…A narrow linewidth is beneficial to suppress frequency noise levels of fiber lasers and can further improve resolution in optical dynamic strain-sensing systems [ 1 , 2 , 3 ]. Random fiber lasers (RFLs) have a simple cavity configuration, low threshold, and good temporal coherence, and they are a promising alternative for narrow linewidth and low frequency noise fiber lasers [ 4 , 5 , 6 ]. Recently, RFLs have attracted considerable interest due to their unique emission characteristic and potential sensing application prospects [ 4 , 7 ].…”

Supplementary document for Stabilizing Brillouin random laser with photon localization by feedback of distributed random fiber grating array - 5855685.pdf

“…The reflection spectrum of the random fiber grating array (RFGA) is calculated by the transfer matrix method [1][2][3]. The amplitude of the reflected and transmitted waves before and after the n th uniform region of the random fiber grating (RFG) is represented in a matrix M n , which is given by…”