Converting 4Gb/s IM data onto tunable 60GHz RF optical carrier using four wave-mixing in semiconductor ring laser

RF signals for radio over fibre systems (RoF) can be generated optically by mode-locking (ML) in semiconductor lasers. External optical injection at non-lasing cavity modes of semiconductor ring laser (SRL) generates strong cavity enhanced four-wave mixing(FWM), that result in generation of optical waves modulated by high purity RF frequencies as a result of the mode-locking by way of such FWM. This makes the SRL very attractive for the generation of RF or millimetre wave modulated optical signals that may be used in RoF systems. We report, for the first time, the generation and wideband modulation of RF optical signals using a combination of optical injection locking (OIL) and FWM in the SRL. We demonstrate that ordinary intensity modulated optical data up to 4 Gb/s can be converted onto RoF carrier, with the RF frequency widely tunable up to hundreds of GHz, with excellent data quality. We further demonstrate that this scheme is versatile in generating various modulation formats by simple filtering.