Modeling and fabrication of tuned circuits for optical meta-materials

Recently there has been a drive to create artificial optical materials, or meta-materials, with a specified electrical permittivity and magnetic permeability at optical frequencies. Control over these properties can give rise to new physical phenomena, such as a negative refractive index and "super lensing", with potential applications in nanophotonic systems and nanolithography. Because most materials do not exhibit magnetic behaviour at optical frequencies, control over the effective magnetic permeability is achieved using patterned metal structures much smaller than the wavelength of light. The electric currents induced in the structures produce magnetic fields that may be in phase or may oppose the magnetic field of the incident light. When combined with dielectric materials, these structures form coupled inductor-capacitor (LC) circuits that can resonate at frequencies in the optical spectrum. Since the resonant properties of the LC circuits control the properties of the meta-material, it is important to understand how changes in shape, size and the position of the subwavelength components affect the resonances. Using the Finite Difference Time Domain (FDTD) method, we study a number of different inductor-capacitor configurations. By applying the concepts of lumped impedance to the electromagnetic fields, the resonant frequencies and Q factors of the tuned optical circuits are determined from the FDTD data. Our in-house electron beam lithography system has been used to fabricate some of the structures. Results of the simulations, the nano-fabrication process and experiments on the meta-materials will be presented.