Nano-optical waveguide modes in gaps embedded in left-handed metamaterial

We explored backward waves propagating predominantly in a regular dielectric or even a vacuum. These modes emerge when a dielectric gap is made in a left-handed material, also known as a negative index material. As the gap becomes nanometric in size, the modal pattern conforms with surface waves distribution and can exhibit either (or both) right-handed or left-handed characteristics. Interestingly, the details of the modal field in the gap is reminiscent of the plasmon polariton solutions of either a gap in metals (forward propagating) or a metal slab in a dielectric bulk (backward propagating). Subsequently, we examined a specific metamaterial realization of the left-handed optical medium by use of elongated nanometallic inclusions to generate positive-negative waveguide anisotropy. We used this metamaterial embedded between dielectric layers as the cladding layer of a gap and verified that the important results predicted above, namely nanometric-size backward waves, are obtained for this specific implementation.