Optical filters are crucial elements in optical communications. The influence of cascaded filters in the optical signal will
affect the communications quality seriously. In this paper we will study and simulate the optical signal impairment
caused by different kinds of filters which include Butterworth, Bessel, Fiber Bragg Grating (FBG) and Fabry-Perot (FP).
Optical signal impairment is analyzed from an Eye Opening Penalty (EOP) and optical spectrum point of view. The
simulation results show that when the center frequency of all filters aligns with the laser’s frequency, the Butterworth
has the smallest influence to the signal while the F-P has the biggest. With a -1dB EOP, the amount of cascaded
Butterworth optical filters with a bandwidth of 50 GHz is 18 in 40 Gbps NRZ-DQPSK systems and 12 in 100 Gbps PMNRZ-
DQPSK systems. The value is reduced to 9 and 6 respectively for Febry-Perot optical filters. In the situation of
frequency misalignment, the impairment caused by filters is more serious. Our research shows that with a frequency
deviation of 5 GHz, only 12 and 9 Butterworth optical filters can be cascaded in 40 Gbps NRZ-DQPSK and 100 Gbps
PM-NRZ-DQPSK systems respectively. We also study the signal impairment caused by different orders of the
Butterworth filter model. Our study shows that although the higher-order has a smaller clipping effect in the
transmission spectrum, it will introduce a more serious phase ripple which seriously affects the signal. Simulation result
shows that the 2nd order Butterworth filter has the best performance.