Optical access networks, including Fiber To The Home /Curb / Node (FTTX), has long been considered a definite solution to the problem of upgrading current congested access networks to ones capable of delivering future broadband integrated services. Time Division Multiplexing Passive Optical Networks (TDM-PONs) have been developed to address this issue.
In a few years, once TDM-PONs are deployed, upgrading these optical access networks will be a challenge when user demand outgrows the existing access network capacities. Wavelength Division Multiplexing (WDM) technology has been considered an ideal solution to extend the capacity of TDM-PONs without drastically changing the fiber infrastructure.
Novel line codes combined with WDM techniques allow simple and cost-effective overlay of higher bit-rate services in existing fiber optical access networks.
A new spectral shaping LCO code has been developed which shifts all the new users data to a higher frequency so that the data is filtered out by the Low pass Filters of the existing setup and received only by the wavelength selective filters of the new users. The shift in frequencies is achieved by introducing extra bits in the data sequence to decrease power content in the lower frequencies.