Semiconductor optical amplifier-fiber ring laser for FBG dynamic strain sensing with an adaptive two-wave mixing demodulator

In this paper, we propose a semiconductor optical amplifier (SOA)-fiber ring laser (FRL) for fiber Bragg grating (FBG) dynamic strain sensing system with an adaptive demodulator based on two-wave mixing (TWM) photorefractive interferometry. Any strain in the FBG is encoded as a wavelength shift of the light reflected by the FBG. The wavelength modulation is perfectly converted to intensity modulation by splitting the light into signal and pump beams and interfering the beams in an photorefractive InP:Fe crystal. The classical beam-combiner was replaced by a dynamic hologram continuously recorded in the InP:Fe crystal. The results demonstrate that TWM interferometer has the characteristics of adaptability and multiplexing. To investigate multiplexability, a three-channel SOA-fiber ring laser sensor system is presented to detect dynamic strain signals from three FBG sensors simultaneously. Experimental results prove that true multiplexing of several FBG dynamic strain sensors with a single adaptive source is feasible. This technique is expected to be suitable for the monitoring of external impact as well as acoustic emission in structures.