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 in the pass-band 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 loss ripple. We also derive the OSNR penalty resulting from the loss ripple in both on-off-keyed (OOK) and differential phase-shift keyed (DPSK) transmissions. Furthermore, a special kind of loss ripple 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 a loss ripple generator.