Impact analysis of optical filter parameters on the flatness of optical frequency comb lines

Abstract

This paper introduces an innovative approach for generating flat optical frequency combs (OFCs) through the use of M-ary quadrature amplitude modulation (M-QAM) combined with Mach-Zehnder modulation (MZM). Unlike traditional methods that rely on a conventional radio frequency (RF) signal, our technique employs a digital signal (DS) to activate electro-optic modulators (EOMs). The study meticulously examines the influence of various parameters of optical filters on their output characteristics. We conducted evaluations using two distinct types of filters: the Gaussian filter (GF) and the Butterworth filter (BWF). This work not only delves into the mathematical modeling of the OFC generator system but also provides a comprehensive simulation using OptiSystem software, showcasing the sophisticated setup involved. Our findings reveal that each parameter distinctly shapes the spectral output, with specific operational ranges identified as optimal for achieving peak performance, favorable outcomes, and enhanced flatness. Both types of filters contribute effectively to flattening the comb lines (CLs); however, the GF demonstrates slightly superior results compared to its BWF counterpart. Additionally, the convenience of adjusting the comb spacing of the OFCs by simply manipulating the bit rate of the DS streamlines operational efficiency.