Low-cost RF photonics [for HFC CATV systems]

CATV systems have evolved from coaxial architectures providing approximately fifty AM-VSB television channels to two-way hybrid-fiber coax (HFC) communication systems providing over 100 channels of video (both analog and digital) as well as data and telephony. It is well-known that transmitting large numbers of analog channels requires high performance optical links. The National Association of Broadcasters requires a carrier-to-noise ratio (CNR) of 46 dB on standard NTSC video channels. The requirements for transmission of digital signals on analog subcarriers are considerably relaxed. To achieve a bit-error-rate of 10/sup -9/ 64-QAM requires a CNR of only 30 dB; if QPSK is used than the required CNR is only 16 dB. These relaxed requirements open the possibility of using lower-cost optical components.