Compensation of nonlinear effects in optical communication systems through phase-conjugation

摘要

In recent years the world-wide transmission bandwidth demand has shown a continuous increase. 40-Gb/s transmission systems have reached the level of commercial maturity and research attention is being focused on the realization of links with a single-channel capacity exceeding 80 Gb/s. Although most of the operating optical-fiber communication links are based on amplitude modulation formats (on-off-keying: OOK), there are several reasons suggesting that future systems operating at extremely high bit rates should rely on phase modulation techniques, such as differential-phase-shift keying (DPSK) [1] .Moreover, the phase-modulation approach lends itself to the implementation of multi-level formats (like DQPSK: differential-quadrature-phase-shift-keying), which allow transmitting 2 or more bits encoded in each signal “symbol”, hence doubling the actual data rate.