US Patent 7440163 Compact passive module for erbium and other fiber amplifiers

Techniques for designing optical devices with passive components for erbium and other doped fiber amplifiers are disclosed. In one aspect, all passive components needed to construct optical amplifiers of both single and multiple-stage forward or backward pumps are integrated without extensively using optical fiber splicing joints. One of the features is to use free-space optics for inter-function cascades among various necessary functions, such as one or more tap couplings, WDM filtering to multiplex (Mux) or de-multiplex (Demux) pump and signal lights, gain-flattening, pump isolation and even performing Mux and Demux of different polarizations.