Differential precoder IC modules for 20-and 40-Gbit/s optical duobinary transmission systems

This paper reports on 20- and 40-Gbit/s differential precoder modules for optical duobinary transmission systems. These precoder modules overcome the speed limit of a conventional preceder by parallel processing. The proposed precoders handle two or four parallel signals before multiplexing with data rates of one-half or one-quarter the transmission bit rate, and the final preceded signal is obtained by multiplexing the preceder output bit by bit, Production-level 0.2-mu m gate-length GaAs MESFET's were used to fabricate the precoders,The precoders are mounted in an RF package. They successfully performed 20- and 40-Gbit/s preceding for the first time, and the 20-Gbit/s preceder achieved a maximum preceding rate of 22 Gbit/s, which is 76% faster than that of the conventional circuit using the same MESFET's. The 40-Gbit/s preceder performs 40-Gbit/s preceding when combined with a 40-Gbit/s multiplexer unit. Twenty-Gbit/s optical duobinary transmitter and receiver circuits using the 20-Gbit/s preceder module successfully generate fully encoded optical duobinary signal at this tate for the first time. These circuits show a receiver sensitivity of -28.6 dBm for a bit error rate of 1 x 10(-9).