Microwave frequency comb generation through optical double-locked semiconductor lasers.

A microwave frequency comb (MFC) consists of equally spaced discrete microwave frequency components that have small magnitude variations across its bandwidth. In this work, a scheme comprising of a slave laser that is optically injected by a strongly intensity-modulated master laser is proposed and numerically investigated to generate MFCs. Based on the double-locking characteristics of the periodic oscillations induced by strong intensity-modulated optical injection, locked comb structures are invoked when the modulation frequency is at a submultiple frequency of the period-one oscillation frequency. Furthermore, broad microwave frequency comb bandwidths are achieved through the bandwidth enhancement effect of optically injected lasers at appropriate operating conditions. The demonstrated MFC source has a continuously tunable comb-line spacing between 1–10 GHz reaching bandwidths that are six times the relaxation resonance frequency of the free-running semiconductor laser. [ABSTRACT FROM AUTHOR]