Broadband upgrade of an operating narrowband single-fiber passive optical network using coarse wavelength division multiplexing and subcarrier multiple access

We demonstrate an overlay of a broadband passive optical network (PON) on the same fiber network as an operating baseband digital system. The baseband system is modeled after current-generation narrowband PONs, and the two PONs can be operated simultaneously. The broadband PON incorporates coarse wavelength division multiplexing to increase the downstream bit rate, and subcarrier multiple access for the upstream upgrade. We examine the RF interference between baseband and subcarrier signals, and provide guidelines on channel spacing and means for accommodating differing power levels for the two signals. The broadband architecture described here provides a graceful upgrade path for providing advanced digital services on a PON without having to modify the network or terminal equipment used for providing narrowband services.