A study of fibre bragg gratings

Abstract

This thesis concerns the fabrication, characterization, and application of fibre Bragg gratings (FBGs). Being in-fibre wavelength-selective reflectors, FBGs have wide applications in optical communication and sensing systems. Compared with conventional bulk-optic gratings, FBGs offer the advantages of low loss, polarisation independence, compatibility with fibres, ease of fabrication, small size, and low cost. For the fabrication of FBGs, the phase-mask method with a pulsed excimer laser (emitting at 24811x11)a s the UV source was implemented. Several methods for tuning the Bragg wavelengths of FBGs were studied, which included temperature tuning, mechanical tuning by stretching or bending, and tuning with a piezoelectric or magnetostrictive material. The results obtained from these studies form the basis of the applications described in the thesis. As to the applications, a band-pass filter with tunable characteristics by using two concatenated FGBs was designed and demonstrated. It was shown experimentally that a FBG could be used as a simple measurement tool to characterize the hysteresis properties of a piezoelectric cylinder. An inexpensive technique based on matching gratings for interrogation of FBG-based sensors and a temperature-compensated FBG-based vibration sensor were also demonstrated. As an extension of the study, some long-period gratings (LPGs) were fabricated and their spectral characteristics measured.