An apparatus for transferring monitor signals, which apparatus receives a primary
signal, and a secondary signal for monitoring a wavelength, and outputs the primary
signal and the modulated secondary signal. The apparatus includes an optical coupler
to which the primary signal is input, a first optical branching filter optically
connected to a signal output terminal, a first optical amplifier optically connected
in series between the optical coupler and the first optical branching filter, and
a first optical band-pass filter optically connected in series between the optical
coupler and the first optical branching filter, but optically connected in parallel
with the first optical amplifier. The primary signal is input into the optical
coupler and output from the signal output terminal through the first optical amplifier
and the first optical branching filter. The primary signal is divided into two
parts by the first optical branching filter, and one of the two parts is input
again into the first optical amplifier through the first optical band-pass filter
and the optical coupler. The apparatus makes it possible to generate a monitor
signal without employing a laser module.
