Adiabatic frequency conversion in epsilon near zero materials – it is all about group velocity

We investigate adiabatic frequency conversion using epsilon near zero (ENZ) materials. We show that, while the maximum frequency conversion for a given change of permittivity does not exhibit an increase in the vicinity of the Re[εr]=0 condition, the change in permittivity can be achieved in a shorter length and, if the pump is also in the ENZ region, at a lower pump intensity. This slow propagation effect makes the conversion efficiency in the ENZ material comparable to that in micro-resonators and other structured slow light schemes, but unlike the latter, no nanofabrication is required for ENZ materials which constitutes their major advantage over alternative frequency conversion approaches. Our results, supported by experimental measurements, indicate that transparent metal oxides operating near the ENZ point are good candidates for future frequency conversion schemes.