Differential QPSK transmission system for 80 compressed digital video channels
C. R. Joyce, R. Olshansky · 1993
Video signals have commonly been transmitted by means of subcarrier multiplexed optical carriers in an amplitude-modu- lated-vestigial-sideband (AM-VSB)1 format with 6-MHz channel spacing in the 100-550-MHz range and requiring carrier-to- noise ratios (CNR’s) of ≥45 dB and highly linear DFB lasers.2 Alternatively, SCM digital transmission of compressed digital video permits the use of low-cost Fabry-Perot lasers and CNR's of ≈20 dB (improving the system power budget),3 New digital- compression standards being developed by the Moving Picture Experts Group (MPEG) are expected to convey VHS quality video at 1.5 Mbit/s (MPEG1) and high-quality NTSC video signals at 4-5 Mbit/s (MPEG2) .4 We demonstrate a 20-subcarrier differential quadrature-phase-shift-keyed modulated (DQPSK)5 system, for up to 80 digital video channels, that uses an inexpensive Fabry-Perot (F-P) laser with 18 km of single-mode Fiber and a simple delay-line demodulator.