Subwavelength Focusing using Radiationless Inteference at Optical Wavelengths

In this work, I propose two methods for extending radiationless intereference to achieve an extreme subwavelength focus in the visible part of the optical spectrum. These methods are based on metal-insulator-metal (MIM) waveguide structures. The first uses the transverse evanescent field from a slit-coupled MIM waveguide. The second uses the highest order mode of a MIM waveguide array. Subwavelength focusing to a tenth of the optical wavelength is demonstrated numerically. Considering recent experiments, the proposed structures are practically viable. Methods to overcome other technical issues associated with this proposal are discussed.