Application of Nonlinear Fitting for Etalon-Type Gain-Flattening Filter Design

We describe a method. of designing an etalon-type gain-flattening filter. The method is based on nonlinear fitting of transmission spectra of combined etalons, and it enables us to design gain-flattening filters that exhibit better compensation of any spectra than conventional methods. By manufacturing a typical filter module, we demonstrate excellent gain-flattening behavior applicable to the C-band optical amplifier for metro transmission systems.