Low Cost TWDM by Wavelength-Set Division Multiplexing

After extensive comparison of candidate technologies, FSAN (Full Service Access Network) in early 2012 took the decision to define TWDM (Time/Wavelength Division Multiplexing) as primary solution for NG-PON2 (Next Generation PON 2). For down- and upstream, a minimum of 4 wavelengths are foreseen providing a total capacity per feeder line of 40Gbit/s and 10Gbit/s or more. Conventional WDM lasers from core or metro networks are too expensive for FTTH (Fiber-to-the-Home) systems, because every ONU will need a tunable laser for the upstream. In this paper we will compare different technical solutions and present WSDM (Wavelength-set Division Multiplexing) as the preferred solution for cost reasons, a scheme that was developed by Bell Labs. It is using a laser that can be tuned by an on-chip heater stripe. To exploit this partial wavelength tunability, we do not use contiguous wavelength bands, but wavelength-sets consisting of cyclic interleaved wavelength slots on a fine grid. This wavelength plan can be implemented e.g. by a cyclic AWG with a small Free Spectral Range. We will describe the concept in detail and report on its experimental validation.