Simulation and micro-fabrication of optically switchable split ring resonators

Abstract

The effect of conductivity variation as a proposed method for the investigation of photoconductive switching properties of split ring resonators (SRRs) is simulated. Three different systems that are applicable under certain fabrication and/or optical excitation conditions are described. The simulated transmission spectrum indicates that for a large range of dark conductivity values, complete switching of the SRR resonance is possible. One of the simulated systems, involving split ring resonators on Si substrate, was fabricated and characterized. The transmission spectrum of that system was measured, with the Si in its high-resistivity state, and a À60 dB dip between 108 and 115 GHz, due to SRRs magnetic resonance, was observed. . These materials exhibit the unique physical property of having both negative electrical permittivity (e) and negative magnetic permeability (m) over a common frequency band. Left handed metamaterials generated a great interest, partly due to the properties of these materials which are not observed in naturally occurring materials. These include negative refractive index, artificial magnetism, super focusing, and reduced lens aberrations [1][2][3][4][5]. Since the first demonstration of LH metamaterials [4], different structures that exhibit equivalent properties have been proposed [6]; however the initial structure consisting of the periodic arrangement of split ring-resonators (SRRs) and metallic wires remains the mostly studied. The wires provide the negative electric permittivity, (e), [7] whereas the SRRelements generate the negative magnetic permeability (m) response [2]. The SRR consists of metallic rings with gaps that act like a capacitor-inductor (LC) circuit when a magnetic field component is perpendicular to their plane. Due to the resonant circular currents in the rings they exhibit a resonance at v m = 1/(LC) 1/2 associated with resonant circular currents in the SRR rings [8][9][10]. It was also demonstrated that besides for a magnetic field that is perpendicular to the SRR plane, the existence of an electric field parallel to the gaps of the SRR can couple to the magnetic resonance and excite an oscillating resonant current around the rings. This phenomenon is described as

Metamaterials for microwave frequencies

“…SRR's are mainly used to focus point sources, increasing the distance of near field waves [10]. In the application realm, they have been used recently as photoconductive switches and reflectors [32]. …”

The science of negative index materials

“…To obtain a negative refractive index n we need simultaneously negative values of the effective permeability μ(ω) and permittivity ε(ω); hence a simultaneous negative magnetic and electric response is needed. In the microwave region a negative permittivity is usually achieved by combining the SRRs with an array of thin continuous wires, which provide a plasmonic ε(ω) with effective plasma frequencies in the microwave region [6][7][8][9][10][11][36][37][38][39]. This approach is not well suited for THz frequencies because of dimensional problems and the absence of good conductors [32].…”

Electric and magnetic excitations in anisotropic broadside-coupled triangular-split-ring resonators

“…Besides, numerous types of different SRRs and/or SRRlike configurations have been suggested to achieve a negative permeability over a certain frequency band [4,[13][14][15][16][17][18][19]. In most cases, the simulations and experimental studies of such structures were performed for a negative permeability when the external magnetic field is perpendicular to the SRR plane with the direction of propagation parallel to SRRs.…”