Abstract: A nibble inversion and block inversion code coding and decoding method and a coding and decoding apparatus for the same.

Abstract: An apparatus for enhancing the extinction ratio in an optical NRZ-to-RZ converting system, and an optical modulation system, are disclosed. The extinction ratio is improved by using an optical fiber loop mirror together with optical amplifiers. The apparatus for enhancing the extinction ratio includes a variable coupling means for receiving external signals to split them to respective terminals of a loop mirror. A variable optical delaying means delays the phases of the signals after their dispersion by the variable coupling means. An optical amplifying means positioned asymmetrically smaller than a bit time of an RZ signal pattern inputted slightly departed from the center of the loop mirror amplifies the optical intensity, and varies the refractive index so as to cause a phase delay. A polarization adjusting means adjusts the polarization of the optical signals, and an optical band pass filtering means removes noises from signals outputted from the loop mirror.