Sliding-block line codes to increase dispersion-limited distance of optical fiber channels

We investigate the use of a run-length-limited (RLL) sliding-block line code to reduce the effects of intersymbol interference in high-speed (multi-Gb/s) data transmission over the direct-detection single-mode optical fiber channel. In addition to their well-known use for synchronization purposes, line codes can be designed to eliminate certain worst-case patterns that would otherwise preclude reliable data transmission at high rates and very long fiber lengths. The code considered here prohibits isolated “one´s” (the 010 pattern) from appearing in the transmitted sequence. Simulation results indicate that this code, coupled with a simple compensation scheme at the receiver, can significantly increase dispersion-limited data rates and/or fiber lengths for both externally modulated and directly modulated systems. While our emphasis is on one particular line code, we discuss sliding block coding for the optical fiber channel in a general context