VO(2) based waveguide-mode plasmonic nano-gratings for optical switching.

Abstract

In this paper, we present one dimensional plasmonic narrow groove nano-gratings, covered with a thin film of VO(2) (Vanadium Dioxide), as novel optical switches. These narrow groove gratings couple the incident optical radiation to plasmonic waveguide modes leading to high electromagnetic fields in the gaps between the nano-gratings. Since VO(2) changes from its semiconductor to its metallic phase on heating, on exposure to infra-red light, or on application of voltage, the optical properties of the underlying plasmonic grating also get altered during this phase transition, thereby resulting in significant switchability of the reflectance spectra. Moreover, as the phase transition in VO(2) can occur at femto-second time-scales, the VO(2)-coated plasmonic optical switch described in this paper can potentially be employed for ultrafast optical switching. We aim at maximizing this switchability, i.e., maximizing the differential reflectance (DR) between the two states (metallic and semiconductor) of this VO(2) coated nano-grating. Rigorous Coupled Wave Analysis (RCWA) reveals that the switching wavelengths - i.e., the wavelengths at which the values of the differential reflectance between VO(2) (S) and VO(2) (M) phases are maximum - can be tuned over a large spectral regime by varying the nano-grating parameters such as groove width, depth of the narrow groove, grating width, and thickness of the VO(2) layer. A comparison of the proposed ideal nano-gratings with various types of non-ideal nano-gratings - i.e., nano-gratings with non-parallel sidewalls - has also been carried out. It is found that significant switchability is also present for these non-ideal gratings that are easy to fabricate. Thus, we propose highly switchable and wide-spectra VO(2) based narrow groove nano-gratings that do not have a complex structure and can be easily fabricated.