Generation of Broadband Optical Frequency Comb by Interfering Dual Lasers in Electro-Optic Modulators

Abstract

In this article, we proposed two schemes for generating a broadband optical frequency comb (OFC) source using dual laser sources. In the first proposed technique, the OFC is generated using a cascaded single-drive Mach-Zehnder modulator (MZM) and dual-drive Mach-Zehnder modulator (DD-MZM). Here, the two CW light sources are modulated by each of the MZM, respectively. The first single-drive MZM generates the subcarriers, while The second DD-MZM carries out intensity modulation on the output spectrum generated by the MZM, ensuring that the power fluctuations of both even and odd sidebands are adjusted to an equal level. The second approach involves replacing the single-drive MZM with a phase modulator (PM). The center frequencies of laser 1 and laser 2 must be carefully set to achieve a non-overlapping or gap-free comb spectrum. The frequency of the RF signal driving the modulators determines the spacing between the laser frequencies. In order to illustrate this aspect, we have utilized three distinct RF signal frequencies: 10 GHz, 16 GHz, and 20 GHz. Furthermore, we have examined the constraints that impact the estimation of the center frequency of laser 2, aiming for a non-overlapping and gap-free comb spectrum. By considering these constraints, we can ensure the successful generation of a uniform and stable comb spectrum with the desired characteristics in our proposed approach. The theoretical and primary analysis of cascaded single-drive MZM and DD-MZM, as well as cascaded PM and DD-MZM, is also investigated, and simulation results confirm the findings. By employing our proposed approach, OFC achieves a significant number of comb lines while exhibiting a power deviation of $\sim $ 2 dB in comparison to single laser configurations.