Optical Domain PON Technologies

This chapter focuses on the optical domain PON technologies. The OLT provides the optical carrier signals to each ONU. The ONU then reflects and modulates this signal to create the upstream signal. There are two basic methods for the OLT to provide the upstream carrier signal to the ONU. One method is for the OLT send a continuous wave signal to the ONU at the upstream wavelength in addition to the downstream signal on its own wavelength. The second approach is for the ONU to modulate the downstream data signal that it receives in order to create the upstream signal. The concept behind Code‐division multiple access (CDMA) is to carry multiple client signals with their transmission spectrum spread over the same channel. The most promising subcarrier multiplexing approach for providing ultra‐high bandwidth makes use of orthogonal frequency division multiplexing (OFDM) techniques.