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.
Ring resonators and Mach-Zehnder interference structures are promising candidates for compact optical filters and electro-optic modulators in the field of integrated photonics. Two types of ring-loaded Mach-Zehnder interferometers (MZIs) based on 3D direct laser writing are designed by finite-element simulation software. The model is composed of two Y-waveguides, Mach-Zehnder waveguide arm, and a micro-ring coupled with Mach-Zehnder waveguide arm side. The optimal radius of curvature of the two models and the spectral characteristics of the two models are calculated by numerical analysis. The optimal radii of curvature for the bend of Y-waveguides are 385 μm, the average free spectral ranges (FSRs) of are about 18 nm, and the average full widths at half maximum (FWHM) are about 1.4 nm and 3.2 nm, respectively, for the two MZI models. The numerical analysis results have practical reference value for the fabrication of resonator coupled Mach-Zehnder interferometer using 3D direct laser writing technology.
Fiber Bragg grating (FBG) sensors are popular sensing elements and have a wide application of strain monitoring in the area of structural health monitoring, medical and aerospace due to the features of electromagnetic interference resistance, high sensitivity and simplicity. Here, a simple intensity demodulation configuration based on a semiconductor ring laser is proposed for FBG dynamic strain sensing system. Due to the characteristics of semiconductor optical amplifier, it can act as the gain medium as well as light source. An arrayed waveguide grating module is adapted to be the wavelength demodulator. It is feasible for this configuration to respond when FBG is subjected to dynamic strains at a high frequency. Additionally, a simultaneous dual-channel interrogation system is in detail discussed. This interrogation scheme can be widely utilized in structure health monitoring because of its low insertion loss, high stability and low cost.
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