Negative Refraction By Nonlinear Optical Methods And Its Applications

A perfect lens with unlimited resolution has always posed a challenge to both theoretical and experimental physicists.Recent developments in optical meta-materials promise an attractive approach towards perfect lenses using negative refraction to overcome the diffraction limit,improving resolution.However,those artificially engineered meta-materials are usually accompanied by high losses from metals and are extremely difficult to fabricate.An alternative proposal using negative refraction by four-wave mixing has attracted much interest recently,though most existing experiments still require metals and none of them have been implemented for an optical lens.Here,we experimentally demonstrate a metal-free flat lens for the first time using negative refraction by degenerate four-wave mixing with a thin glass slide.We realize an optical lensing effect utilizing a nonlinear refraction law,which may have potential applications in microscopy.A simple optical lens plays an important role for exploring the microscopic world in science and technology by refracting light with tailored spatially varying refractive indices.Recent advancements in nanotechnology enable novel lenses,such as,superlens and hyperlens,with sub-wavelength resolution capabilities by specially designed materials' refractive indices with meta-materials and transformation optics.However,these artificially nano-or micro-engineered lenses usually suffer high losses from metals and are highly demanding in fabrication.Here,we experimentally demonstrate,for the first time,a nonlinear dielectric magnifying lens using negative refraction by degenerate four wave mixing in a plano-concave glass slide,obtaining magnified images.Moreover,we transform a nonlinear flat lens into a magnifying lens by introducing transformation optics into the nonlinear regime,achieving an all-optical controllable lensing effect through nonlinear wave mixing,which may have many potential applications in microscopy and imaging science.Alternative nonlinear negative refraction approaches like phase conjugation and four wave mixing have shown advantages of low-loss and easy-to-implement,but associated problems like narrow accepting angles can still halt their practical applications.Here we demonstrate theoretically and experimentally a new scheme to realize negative refraction by nonlinear difference frequency generation with wide tunability,where a thin BBO slice serves as a negative refraction layer bending the input signal beam to the idler beam at a negative angle.Furthermore,we realize optical focusing effect using such nonlinear negative refraction,which may enable many potential applications in imaging science.Graphene surface plasmon polaritons(graphene plasmons)can not be excited by freepropagating waves at IR and THz frequencies,because its wave vector is orders of magnitude larger than that of the free space.Here,we propose to use optical four-wave mixing to overcome the large mismatch between the wave vectors.Simulation results show that propagating plasmonic wave is excited when wavevector matching condition is achieved.The spatial localization and field enhancement effect are also analyzed.The generated propagating graphene plasmons can be a unique source for plasmonic devices.