Raman lasers in silicon photonic wires: unidirectional ring lasing versus Fabry-Perot lasing

Integrated-optical silicon Raman lasers based on a ring cavity can potentially operate unidirectionally owing to the strong non-reciprocity of the Raman gain in submicron photonic wires. This makes the ring-cavity structure significantly more efficient than the alternative Fabry-Perot structure, in which the less efficient of the two propagation directions is unavoidably involved.