For low cost passive optical access networks (PON), we have studied the downstream delivery of an additional > 1 Gb/s in the passband above the 155 Mb/s baseband services. Both signals are transmitted on the same fiber using a single transmitter and a single receiver within the power budgets of ITU-T G983. Although our study has used broadcast DSS digital video services for the passband that delivers about 1.2 Gb/s, the passband bandwidth can be used for any broadcast or switched multimedia services, i.e., digital video, data, and audio. For switched services, the baseband upstream will be the return path. Furthermore, the passband can be used to provide a dedicated bandwidth to any subscriber. The passband approach offers a graceful upgrade of a 155 Mb/s baseband system, and is compatible with baseband only optical network unit (ONU). We multiplexed a 155.52 Mb/s baseband signal with quadrature phase shift keying (QPSK) modulated passband digital video channels in the 270-1450 MHz range with minimal degradation. We used an additional 860 MHz carrier modulated with 8 Mb/s using QPSK as a passband test-signal. An optical-to-electrical (O/E) receiver using a PIN diode satisfies the need for class B operation as defined in ITU-T G983 (-28 dBm receiver sensitivity for a 10-10 bit error rate) with 1.5 dBo1 margin if we consider the proposed technique as an upgrade of the baseband 155 Mb/s to 622 Mb/s. Otherwise it only meets the specifications of class B (-30 dBm receiver sensitivity). However, an APD based receiver satisfies the power budget needs of ITU-T G983 class C operation (-33 dBm receiver sensitivity) with 5.5 dBo margin for both baseband and passband with forward error correction (7/8 convolution and (96, 110) Reed-Solomon coding). The available optical power margin with an APD receiver may be large enough that it can also allow use of 16-QAM in place of QPSK in class C mode or 64 QAM in class B mode.
Naresh Chand, Peter D. Magill, Swami V. Swaminathan, and Thomas H. Daugherty, "Delivery of Digital Video and Other Multimedia Services ( >1 Gb/s Bandwidth) in Passband above the 155 Mb/s Baseband Services on a FTTx Full Service Access Network," J. Lightwave Technol. 17, 2449- (1999)