An optical modulation apparatus is provided which implements a stable
amplifying function by reducing the effect of reflected light rays from
end faces of a bidirectional optical amplifier by imposing a numerical
limitation on the relationship between the gain of the bidirectional
optical amplifier and the loss of the optical modulator, or by inserting
a polarization rotation section in a reflection type optical modulator
including the bidirectional optical amplifier or in a multi-wavelength
collective optical modulation system combining the multiple optical
modulators. An optical modulation apparatus is provided which implements
a stable amplifying function and cost reduction by reducing the effect of
reflected light rays by interposing optical isolators at every alternate
SOAs in a transmission-type optical modulation apparatus including a
plurality of semiconductor optical amplifiers (SOAs) connected in a
multistage fashion.