Performance enhancement of optical communication system with cascaded FBGs of varying lengths

Abstract

In this paper, an optical communication system constructed with cascaded fiber Bragg gratings or FBGs of varying lengths capable of operating in the C-band is presented. Here, initially, a passive optical device formed with four cascaded FBGs of varying lengths is proposed and analysed. Subsequently, the proposed device is kept in the optical communication system to reduce the spectral width
of the source, thereby enhancing the system's performance. Analytical formulation based on the transfer matrix method (TMM) of an optical device is incorporated. The effect of such a device on the system performance at various operating distances is discussed. Further, the system performance is studied with the apodized FBGs in the passive optical device. At the end, we investigated the effect of incorporating the cascaded FBG structure in the system utilizing four-level pulse amplitude modulation or PAM-4 modulation . As per the simulation results, the proposed device has given a maximum reflectivity of 98.39% and a minimum FWHM of 0.175 nm for uniform FBGs. But with the apodized FBGs, an FWHM of 0.07 nm with a reflectivity of 59.81% has been achieved. Simulation results reveal that the system formed with the proposed device has given better performance up to a distance of 105 km compared to the absence of the device. At the maximum operating distance of the system with apodized FBGs, the Q-factor and bit error rate (BER) are recorded as 6.712 and 9.5321×10-12, respectively. Apart from the Q-factor and BER estimation, eye height is also used to estimate the system performance at various operating distances.