Design and simulation of a chirped Fiber Bragg Grating based demultiplexer for ultra dense Wavelength Division Multiplexing based Passive Optical Networks

Wavelength Division Multiplexing (WDM) based Passive Optical Networks (PONs) give higher capacity than standard Time Division Multiplexed (TDM) PONs. Ultra Dense WDM (UDWDM) scheme greatly increases the capacity of these networks and is needed to meet the ever increasing demand for high capacity optical links. This paper discusses the application of a Fiber Bragg Grating (FBG) based Demultiplexer (DEMUX) in Ultra Dense WDM PONs. The theoretical design and simulation of a chirped FBG DEMUX is described. Each wavelength channel is demultiplexed using the reflection spectrum of a single FBG. The proposed design is simpler, compact and more cost effective than previously proposed FBG DEMUX designs. Quadratic chirped, Gaussian apodized FBGs are used to simulate Ultra Dense Wavelength Division Multiplexing based PONs for a wavelength spacing of 25GHz at data rates of 1.25Gbps and 2.5Gbps for 10km, 15km and 20km lengths of optical fiber. A comparison between Gaussian and Tanh apodization functions is shown. The spectral responses and Quality factors (Q-factors) of the DEMUX ports are presented and discussed. The maximum and minimum Q-factors are tabulated for different cases. Certain anomalies observed in the spectral responses of certain DEMUX ports are described in detail. All simulations were performed in Optisystem 7.0.