Sub-diffraction negative and positive index modes in mid-infrared waveguides

We characterize a strongly anisotropic waveguide consisting of alternating 80 nm layers of n(+)-InGaAs and i-AlInAs on InP substrate. A strong increase in the transverse magnetic (TM) reflection at lambda = 8.4 mu m corresponds to a characteristic low- order mode cutoff for the left-handed waveguide. The subsequent decrease of TM reflection at lambda = 11.5 mu m represents the onset of right-handed no-cutoff light guiding. Good qualitative agreement is found when the experimental results are compared to finite element and transfer-matrix frequency domain simulations. (c) 2008 Optical Society of America