An interleaving combiner (ILC) that may be used to implement hybrid
amplification in a bidirectional interleaved wavelength-division
multiplexing (WDM) system. The ILC implements a composite pump/signal
combining and interleaving filtering function in a single topology
characterized by relatively low insertion losses. In a preferred form, the
ILC is a four-port device that is configured to (i) route bidirectional
optical signals corresponding to different communication channels to and
from unidirectional lumped optical amplifiers and (ii) combine those
signals with a pump signal for distributed amplification in a fiber span
between different lumped amplifiers. The ILC provides relatively high
rejection for the pump signal along optical paths different from the
intended one and relatively low in- and out-of-band crosstalk for the
communication channels. The ILC may be implemented using a Gires-Tournois
interferometer.