Experimental Evaluation of Low-Cost Interrogation Techniques for FBG Sensors

In this paper, the experimental investigation of two simple, cost-effective interrogation techniques based on optical power measurement for fiber Bragg gratings (FBG) sensors are presented. The first technique proposed employs each channel of a coarse wavelength division multiplexing (CWDM) demultiplexer as an edge filter to modulate the optical power reflected by each sensing FBG, allowing for an array of FBG sensors to be interrogated simultaneously, sharing the same broadband light source (BLS) and interrogation system. In the second technique, the optical power reflected by a single sensing FBG is modulated directly by the transmission spectrum of the BLS, allowing for a simpler interrogation system. Both techniques rely on a compact, low-cost optoelectronic circuit developed for the acquisition and measurement of the optical signals. With resolutions of up to 1.26 pm for a mechanical strain sensor, or an equivalent 0.09 degrees C for a temperature sensor, experimental results show that both techniques are accurate, reliable, and suitable for applications where the only requirement is the monitoring of the spectral position of the Bragg wavelength ( lambda(B)) of the FBG sensors, replacing more expensive, generalpurpose FBG interrogators available in the market. Since FBGs are passive, lightweight, and provide dielectric insulation, the proposed techniques are suitable for temperature or mechanical strain measurements in hostile environments in which the use of conventional sensors must be avoided, such as in high voltage power lines and cables, and explosive atmospheres.