DYNAMIC-RANGE OF COHERENT ANALOG FIBEROPTIC LINKS

We investigate the performance of coherent analog optical links employ ing amplitude modulation (AM), phase modulation (PM), and frequency mo dulation (FM). The performance of these coherent links is compared to that of AM direct-detection (DD) links. The signal-to-noise ratios, no nlinearities, and spurious-free dynamic ranges (SFDR's) of the foregoi ng links are evaluated. We calculate the SFDR for links using DFB and Nd:YAG lasers with typical linewidths of 10 MHz and 5 kHz, respectivel y. The performance of PM and FM links is dominated by phase noise abov e a critical value of received optical power. For a linewidth of 10 MH z, and SFDR's of PM and FM links are 30 and 31 dB, respectively, for a received optical power above -27 dBm in a 1 GHz bandwidth. For a line width of 5 kHz, the corresponding SFDR's above a received power level of 0 dBm are 51 and 53 dB. The performance of DD and AM links is domin ated by RIN above a critical value of received optical power. For a RI N level of -155 dB/Hz, the SFDR's of DD and AM links are 49 and 47 dB, respectively, for a received optical power of 10 dBm in a 1 GHz bandw idth. The SFDR's of the DD and coherent links used for transmission of subcarrier-multiplexed (SCM) signals are also derived. We evaluate ta rget laser parameters needed by a number of different applications. Fo r AM video and antenna remoting applications, linewidths of < 1 and < 3 kHz are required to use PM and FM links, respectively. For FM video, linewidths of < 150 and < 350 MHz are required to use PM and FM links . For SCM digital applications, linewidths of < 80 and < 200 MHz are r equired to use PM and FM links. The paper concludes with a discussion of system implementation issues, including linearization, optical freq uency modulation, balanced receivers and IF issues.