Analysis of loss ripple and its application to the mitigation of optical filtering penalty

An analytical expression for the signal distortion that results from the loss ripple (LR) in the passband of an optical component is derived. The expression, when simplified to its first-order form, provides a clear physical picture of how the signal is affected by the ripple period, magnitude, and the signal center frequency location with respect to the LR. We also derive the optical signal-to-noise ratio penalty resulting from the LR in both on-off keyed and differential phase-shift keyed (DPSK) transmissions. Furthermore, a special kind of LR can be applied to mitigate the penalty associated with tight optical filtering, which is experimentally verified with a 42.7-Gb/s DPSK signal passing through two filters having a 3-dB bandwidth of 43 GHz and an LR generator.