Wideband two-process frequency conversion under stimulated Raman adiabatic passage via a continuum of dark intermediate states

In this paper, we propose a novel hybrid planar-channel waveguide configuration in which the channel waveguide is submerged within the planar region, with an aim to study two simultaneous three-wave mixing processes under stimulated Raman adiabatic passage. In our study, an input frequency is converted to an output frequency lying very close to or very far from the input frequency via an intermediate frequency. This frequency is in the form of a continuum of modes in the planar region, while all other frequencies propagate as guided modes of the channel waveguide. The continuum of modes at the intermediate frequency allows the simultaneous phase matching to be satisfied over a wide range of wavelengths. As a consequence, this leads to a wideband and efficient conversion from the input to the output frequency without any significant power accumulation at the intermediate stage, which is ensured through the counterintuitive and adiabatic variation in the nonlinear coupling strengths.