scope:

This Recommendation describes a method of transmitting multi-channel television signals over optical access networks through the use of Sub-Carrier Multiplexing (SCM).

In the SCM technique, the main carrier is the optical frequency signal carrier; the sub-carriers transfer the electrically multiplexed FDM video signals in the optical sideband. The format of the signals output by the Photo Detector (PD) of the Optical Network Terminal (ONT) is the same as that of the signals input to the modulator of the optical transmitter. The SCM method is used in the trunk line of Hybrid Fibre-Coax (HFC) systems.

The system described in this Recommendation transmits FDM analogue AM-VSB and digital video signals by SCM technology. The optical modulation format is Intensity Modulation (IM).

Optical amplifiers are used to compensate the losses of the optical transmission/splitters used to create the access network. Dispersion compensation fibres (DCF) are used to compensate the chromatic dispersion of access network fibres. DCF imposes the reverse chromatic dispersion in advance in order to offset the degradation due to CSO created by the transmission of 1.55 μm optical signals over 1.3 μm zero-dispersion access fibres.

SCM technology is simple, and is based on an electrical/optical (E/O) converter and optical amplifiers in the transmitter side, and an optical/electrical (O/E) converter in the receiver side. However, the allowable optical transmission/splitter loss is smaller than that in the FM converted system. Moreover, optical reflections in the transmission lines may degrade video quality.

This system can be integrated with the G.983 series B-PON system by using G.983.3 WDM technology, with the G.984 series G-PON system by using G.984.5 WDM technology, and with the IEEE 802.3ah EPON systems. This allows the PON system to offer broadcast services and also data and voice communication services over the same optical access network. By using the bidirectional data PON system, upstream signals, e.g., control functionality and data to indicate user requirements, can be transmitted as well.

NOTE - The structure and content of this Recommendation have been organized for ease of use by those familiar with the original source material; as such, the usual style of ITU-T recommendations has not been applied.