Pulse position modulation for optically amplified passive optical networks

The implications of using pulse position modulation over a passive optical network (PON) are considered. PONs employing optical power amplifiers are likely to become standard so the placement of an erbium doped fibre amplifier (EDFA) at the head end is assumed. We consider the possibility of reaching the maximum number of subscribers at a given bit-rate (STM-1) in the downstream direction while not concerning ourselves overmuch with the services to be provided. For the purposes of the analysis presented we consider the single wavelength case only. We present mathematical analysis for such systems employing an on-off keyed non-return to zero (OOK NRZ) binary modulation regime and a PPM regime, and thus demonstrate that PPM holds a significant advantage over OOK NRZ in terms of the reachable number of customers when the same average source laser power is employed