Generation and Modulation of a Millimeter-Wave Subcarrier on an Optical Frequency Generated via Optical Injection

A highly tunable millimeter-wave subcarrier signal is generated by optically injecting a Fabry-Perot semiconductor laser. The optically injected light, which enables microwave subcarrier frequencies well beyond the injected laser´s free-running relaxation-oscillation frequency, is then on-off keyed by direct-current (dc) modulation of the injected slave laser. Adjustment of the subcarrier frequency is easily accomplished by changing either the dc bias current and/or junction temperature of the injected slave or the injecting master laser. In this paper, we theoretically and experimentally investigate the purity of the modulated microwave subcarrier. The generated microwave signal was then transmitted over 50 km of single-mode fiber, demonstrating the applicability of a directly modulated slave laser optically injected into the period-one state for radio-over-fiber applications.