Experimental verification of an optical negative-index material

摘要

Artificially designed materials (metamaterials) with a negative refractive index allow the achievement of new functionality unattainable with naturally-existing media [1], including the feasibility of imaging with subwavelength resolution limited by only the material quality [2]. In these negative-index materials (NIMs) the phase velocity is an-tiparallel to the energy flow leading to the unusual effect of negative refraction at the interface with a conventional, positive refractive index medium. The seminal paper defining a method toward a negative refractive index was published in the 1960s [3]. In media characterized by dielectric permittivity ε = ε' + iε'' and magnetic permeability μ = μ' + μ'' the condition ε' < 0 and μ < 0 is sufficient for negative refraction [3]. Under the necessary condition ε''μ' + μ''ε' < 0 [4], the real part (n') of the complex refractive index (n = n' + in" = εμ{sup}(1/2)) becomes negative in a passive medium. Recently a design of such metamaterials for the microwave spectral range, using metal split ring resonators and thin metal wires, was proposed theoretically [5,6] and realized in microwave experiments [7]. In this letter we demonstrate an optical NIM based on coupled metal rods that was previously predicted theoretically [8,9]. The negative refractive index is verified by direct phase and amplitude measurements near the communication wavelength of 1.5μm aling with 3D finite difference time domain simulations [10].