A duobinary optical transmission device provides duobinary optical
transmission with improved quality by a technique that does not require
an electrical low pass filter LPF.A duobinary optical transmission device
includes at least one semiconductor optical amplifier (SOA). A light
source outputs a carrier wave as an optical signal. A precoder encodes an
input of a non-return-to-zero (NRZ) electrical signal. An interferometer
type semiconductor optical amplification unit modulates the carrier wave
according to a change of an applied bias current coupled to the encoded
signal. An optical band pass filter (OBPF) receives the phase-modulated
optical signal from the semiconductor optical amplification unit, filters
the received phase-modulated optical signal according to a designated
band, and outputs an optical duobinary signal.