Tunable Radio Frequency Generation Using a Graphene-Based Single Longitudinal Mode Fiber Laser

A novel, simple, and short cavity design of single longitudinal mode (SLM) tunable erbium-doped fiber ring laser using a graphene-based saturable absorber is proposed and demonstrated as a tunable signal source. The SLM output is then mixed with another output signal from a tunable laser source (TLS) to generate tunable radio frequency (RF) signals. The tunable SLM fiber ring laser uses a short length of 1 m highly doped erbium-doped fiber as the gain medium. Graphene is used as a saturable absorber to generate the SLM operation, as opposed to the commonly used unpumped erbium-doped fiber. The tuning range of the fiber ring laser is determined by a tunable fiber Bragg grating, which can be tuned from 1547.88 to 1559.88 nm. A continuous wavelength spacing tuning range of 0.020–0.050 nm is obtained between the output of the SLM fiber ring laser and the TLS which is then mixed in a 6 GHz bandwidth optical-to-electrical convertor. This generates a corresponding RF signal of between 2.4 and 5.9 GHz with a low variation in output power. The current RF signal generation is limited by the frequency bandwidth of the optical-to-electrical convertor.