Microwave Photonics Filtering Interrogation Technique Under Coherent Regime For Hot Spot Detection on a Weak FBGs Array

Abstract

An interrogation technique of cascaded FBGs sensors based on a Microwave Photonics filtering technique under coherent regime is presented. The sensing information of a 5m fiber coil containing 500 weak FBGs with a similar central wavelength is retrieved. The FBGs are 9mm long and the spatial separation between consecutive FBGs is 1mm. The principle of operation is based on the calculation of the impulse response by recording the electrical frequency response of the system. Hot spot detection, location and temperature measurement are demonstrated by experimental measurements with a temperature sensitivity of 0.6dB/ºC in a 10ºC range. Fifteen measurements are recorded in order to average them to reduce noise and smooth the saw tooth appearance typical of coherent measurements. The resolution of the proposed interrogation technique is related to the bandwidth of the electrical measurement. We have obtained a resolution of 20 cm for an electrical bandwidth of 1 GHz. The SNR was larger than 16dB despite the fact that no amplification was used within the system.

FBG Arrays for Quasi-Distributed Sensing: A Review

“…The sensor principle is based on the evaluation of the reflection peak at the Bragg wavelength. Compared with the distributed sensing based on backscattered light, FBG-based sensing exhibits much higher SNR [23,24] while providing the exact temperature information. In addition, FBG arrays have been introduced into distributed vibration sensing.…”

Sub-cm Temperature Monitoring of 500 Weak Gratings Array Through Chirped Ultra-Short Light Pulses

“…Different techniques were implemented and presented in literature to perform multi-points and quasi-distributed sensing using FBGs arrays and long FBGs: wavelength division multiplexing (WDM) techniques and arrays of FBGs fabricated at different wavelength [1]; interferometry on array of near-identical weak gratings [2]; microwave filtering photonic techniques used to interrogate a weak gratings array [3] and long weak grating [4].…”

Thermal Profile Detection Through High-Sensitivity Fiber Optic Chirped Bragg Grating on Microstructured PMMA Fiber

“…OFDR system can further reduce the spatial resolution below the millimeter while maintaining a measurement time close to 1 Hz. However, distributed sensing system based on OFDR [13], [14] are built on interferometers with a reference trigger, that constitute a bulky optical hardware, that requires a swept-laser interferometer [13] or a microwave photonic circuit [14]. In addition, distributed systems do not have a specific active (or sensing) region in which the change of reflectivity is detected and encoded into a change of spectrum, but rather the entire fiber acts as a sensor along its entire length.…”