OPTICAL DATA FORMAT CONVERTER WITH EXTINCTION RATIO ENHANCEMENT AND OPTICAL COINVERTING SYSTEM USING THE SAME

摘要

PURPOSE: An apparatus for enhancing an extinction ratio in an optical NRZ(non-return to zero)-to-RZ conversion system and an optical modulation system therefor are to enhance the extinction ratio by using an optical loop mirror together with an optical amplifier. CONSTITUTION: A variable coupling unit(30) receives external optical signals and splits them to respective terminals of a loop mirror with a predetermined coupling ratio. A variable optical delaying unit(31) delays phases of the optical signals split by the variable coupling unit. An optical amplification unit(32) amplifies an optical intensity and varies a refractive index. The optical amplification unit is positioned asymmetrically so as to cause a phase delay of a counterclockwise pulse with respect to a clockwise pulse. The phase delay is smaller than a bit time of an RZ signal pattern inputted slightly departed from a center of the loop mirror. A polarization adjusting unit(33) adjusts a polarization of optical signals splitted by the variable coupling unit. An optical band pass filter(34) removes noises from signals output from the loop mirror.