Design considerations for a fibre Bragg grating interrogation system utilizing an arrayed waveguide grating for dynamic strain measurement

Abstract

Dynamic strain signals are important for many structural monitoring applications, but the high-speed interrogation of strain sensors based on fibre Bragg gratings (FBGs) remains a challenge. Arrayed waveguide grating (AWG) interrogation schemes have been proposed, and by using modelling and validation experiments several design considerations are investigated and their relationship to system performance indicators determined. The Bragg grating length has an impact on the ability of the grating to ‘observe’ the transient strain field, while the spectral widths of both the FBG and AWG influence the recovered strain resolution. The system performance was examined for both high frequency noise as well as the long-term drifts over an hour, with a strain resolution of 1.4 µε observed and drift of less than 3.1 µε h−1. The noise dependence on the relative overlap of the AWG and FBG spectra was found to be significant and the inclusion of a semiconductor optical amplifier to boost light intensity at the detectors was found to significantly improve performance with an improvement in the signal-to-noise ratio up to 200%.

A New Interrogation System for FBG Sensors based on Midband Filter with Correction

“…These values reduce in a huge way the cost of the system of interrogation. The proposed filter serves to eliminate the problems mentioned above and make a challenge with the arrayed waveguide grating [18] and the Fabry Perot cavity [19]. In addition, the edge filter for the interrogation system must be accordable and provide for each channel of FBG sensors an individually filter with a midband bandwidth.…”

High-Precision Continuous FBG Interrogator based on an AWG

“…Yuan et al demonstrated an AWG system that increases the channel spacing to 3 nm, and the dynamic range was 1.2 nm with a 1.3 nm bandwidth at 3 dB 18 . In the above studies, the dynamic range is still limited by the bandwidth of a single channel in the AWG and the small wavelength interval between two intersecting AWG channels 21 , so the dynamic range of previous demodulation methods was not large. Considering the correlation between the dynamic range and the relative spectral width of the FBG and AWG channels, a scheme for measuring the power of multiple channels is proposed to improve the dynamic range and remove the constraint of channel spacing 22,23 , but the peak of the FBG must overlap with several AWG channels.…”

High-Resolution AWG-Based Fiber Bragg Grating Interrogator

“…The typical static resolution of such sensors is in the order of 2-4 microstrain (2.5-5 pm) [1], and the best value reported is 0.04-0.05 pm [3], [4]. Recently several approaches to use photonic integration to reduce the size and cost of the units were made [5]. The achieved resolution expressed as an RMS wavelength measurement noise σ λrms ranges from half a picometer [6] to a few picometers [7].…”