Upgrade of passive optical subscriber network

An upgrade method is described for a two-way broadband service transmission of a previously proposed passive optical subscriber network (PASS-NET) PASS-NET uses optical frequency division multiplex/time-division multiplex (OFDM/TDM) techniques for downstream transmission and time division multiple access (TDMA) for upstream. Fundamental experiments for downstream transmission to two subscribers are executed to demonstrate the possibility of the upgrade method. Two wavelengths emitted by a distributed Bragg reflector-laser diode (DBR-LD) tunable laser with a 5-GHz (0.04-nm) space between them are directly intensity modulated at 32 Mb/s. Each wave transmits narrowband service to each subscriber. The third wavelength emitted by another DBR-LD tunable laser with an 11-nm separation from the two wavelengths is directly intensity modulated at 100 Mb/s and overlaid