Abstract
High-speed optical communication systems rely on careful receiver filter design to preserve timing margin and sensitivity in intensity-modulation/direct-detection (IM/DD) links. This thesis investigates how receiver low-pass filter architecture affects 25 Gb/s non-return-tozero and return-to-zero systems through dual-domain validation: optical simulations in ANSYS Lumerical and baseband analysis in MATLAB. Six receiver filters are examined—Bessel, Butterworth, Chebyshev Type I, Gaussian, Rectangular, and RC—with performance evaluated using Q-factor, eye diagrams, bit-error-rate, and minimum required optical signal-to-noise ratio at BER = 10⁻⁹. Results demonstrate that Bessel filters provide optimal performance for both NRZ and RZ modulation due to their maximally flat group delay, achieving the highest baseband Q-factors (3.808 NRZ, 3.848 RZ) and the lowest relative OSNR. Butterworth ranks second, while Chebyshev underperforms despite its sharp roll-off due to 1.5 dB passband ripple. Strong cross-domain agreement confirms that phase linearity dominates performance for both modulation formats, providing practical guidance for 25 Gb/s IM/DD receiver design.