Flat frequency comb generation employing cascaded single-drive Mach–Zehnder modulators with a simple analogue driving signal
Mahmoud Muhanad Fadhel, Haroon Rashid, Abdulwahhab Essa Hamzah, Mohd Saiful Dzulkefly Zan, Norazreen Abd Aziz, Norhana Arsad
Abstract
A scheme, using two-single drive Mach–Zehnder modulators (SD-MZMs) to generate flat optical frequency comb (OFC) by an analogue driving signal, is experimentally demonstrated. The modulator is used to add equidistant sidebands to an injected carrier continuous-wave laser centred at 1550 nm. The flatness of the comb lines is achieved by tuning the DC bias voltages supplied to both modulators. Five comb lines are tested for different frequency spacing of 8.5, 10, 11.5, and 12 GHz and show good frequency tunability. Also, the effect of increasing the radio frequency (RF) modulation signal power on the number of comb lines is investigated. A total of 5 comb lines are obtained with a repetition rate of 10 GHz and 0.77 dB flatness. The proposed system is simple and cost-effective due to the utilization of a simple Mach–Zehnder modulator structure driven by one RF signal generator.