Noise analysis of subcarrier-multiplexed coherent optical video transmission systems using direct frequency modulation of semiconductor lasers

The authors present a noise analysis of an analog subcarrier-multiplexing coherent optical system for video transmission using direct frequency modulation of semiconductor lasers. Receiver sensitivity using the FM subcarrier modulation format is analyzed for realistic values of receiver thermal noise (3.31*10/sup -22/ A/sup 2//Hz), laser linewidth (up to 100 MHz), relative intensity noise (RIN) (-130 to -170 dB/Hz), and optical bandwidth (20 GHz). Linewidth-induced performance degradation is negligible for up to 50 channels, and RIN-induced performance degradation becomes dominant as RIN increases above -140 dB/Hz. A sensitivity floor of about -40 dBm (for RIN=-160 dB/Hz) exists for small numbers of channels (up to 50) due to the FM threshold effect at the IF demodulator.<
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