Analysis of cascaded chirp characteristics in fiber Bragg gratings for spectral sensor applications

Abstract

Chirped Fiber Bragg Gratings (CFBGs) offer broadened reflection bandwidths, making them attractive for wavelength-based spectral sensing applications. In this study, the spectral characteristics of a cascade CFBG system were analyzed using OptiGrating 4.2.2 and OptiSystem software with eight total chirp variations of 0.3 nm, 0.5 nm, 1.0 nm, 1.5 nm, 2.0 nm, 2.5 nm, 3.0 nm, and 3.5 nm. The parameters analyzed included reflection bandwidth (FWHM), maximum reflectivity, spectral distribution, channel spacing, and output power. Simulation results indicate that increasing the total chirp significantly broadens the reflection bandwidth until 1.24 nm at a chirp value of 0.3 nm to 9.78 nm at 3.5 nm. Meanwhile, the maximum reflectivity tends to decrease from 100% to approximately 80% as the chirp value increases. The cascade configuration consisting of eight CFBGs successfully generated eight spectral channels within the wavelength range of 1550.4720– 1556.0000 nm, producing a total spectral span of 5.5280 nm. The highest output power was 39,198 dBm at CFBG 2, while the lowest was 12,203 dBm at CFBG 5. These findings demonstrate that total chirp variation significantly influences the spectral characteristics of cascade CFBG systems and provides a basis for optimizing fiber-optic spectral sensor designs.