Cavity-Enhanced Four-Wave Mixing in Semiconductor Ring Lasers

We report on cavity-enhanced four-wave mixing (FWM) in 1.55-
mu
m semiconductor ring lasers (SRLs). External optical injection into one of the cavity modes of the ring laser induces a FWM signal up to detuning frequencies of 1.5 THz. Mode-locked signals at 34.5 GHz with a linewidth as small as 5 kHz were measured. Initial results show similar characteristics with a distributed feedback laser monolithically integrated next to the SRL.