SUPPRESSION OF RF NOISE TONES CAUSED BY RAYLEIGH BACKSCATTER IN TO ANUNISOLATED LASER USING AUDIO-FREQUENCY EXTERNAL OPTICAL-PHASE MODULATION

When Fabry-Perot lasers are subject to Rayleigh backscatter, dramatic line-narrowing and frequency hopping up to 500 MHz, evidenced by radio -frequency (RF) tones, are observed, These RF tones Rill severely degr ade the system performance of a subcarrier multiplexed transmission sy stem, such as quadrature phase-shift keying. In this letter, it is dem onstrated that audio-frequency external optical-phase modulation can s uppress the noise tones and restore the laser linewidth. This scheme m ay offer an inexpensive alternative to optical isolators to recover th e system performance and thus is very important for cost-effective cus tomer access networks.