Functional materials and dielectric buffer embedded layered metamaterials as nanophotonic active devices

Abstract

Plasmonic phenomena provide unique advantages in controlling light at the nanoscale. The unprecedented optical behaviours of passive metamaterials have been reported, exploiting the plasmonic composites in a wide spectral range of microwave to visible wavelengths. Yet, the electromagnetic response of the passive elements relies on structural characteristics. Avenues for active plasmonic device research have emerged to control the electromagnetic response (of the device) due to external stimuli. The possibility of dynamic control of optical properties will vastly expand the potential applications in sensing, imaging, beam streaming, etc. This thesis describes the studies of active layered metamaterials incorporated with functional materials in the context of applications in the terahertz (THz), infrared (IR), and visible wavelengths. The optical response of such metamaterials has been deduced by exploiting the transfer matrix method and effective medium theory. The in-house algorithm, which is developed in MATLAB, provides a fast and accurate approach to extract the optical response of the subwavelength structures compared to the commercial solvers. Besides, the impact of external stimuli on the optical properties of the embedded functional materials is imported into the algorithm and the associated variations of the optical response of the structure have been obtained. In this stream, the realization of an electrically tuneable filter in the THz wavelength has been investigated by utilizing the graphene-overdielectric schema. The results reveal tuneable transmission as a function of the applied chemical potential of graphene sheets and the incidence angle of the radiated waves. The thesis also focuses on the investigation of reconfigurable absorbers. The tuneable dual-band absorber has been conceptualized by exploiting the Ge2Sb2Te5 phase-change medium and SiO2 thin films where the absorption spectrum can be widely tuned in the visible light and c-telecommunication band by applying the electrical pulses to the embedded graphene micro-heaters. Moreover, it has been shown that the subwavelength layers of stibnite and silver exhibit hyperbolic metamaterial (HMM) – a scalable, non-resonant structure comprising an extreme anisotropic permittivity – the behaviour contributing to a perfect absorption tuneable from 1310 to 1570 nm in a wide range of incidence angle and polarization state of the incoming radiation. It has been also noticed that the HMM-based structure comprising halide metal perovskite and gold yields over 99% absorption regardless of the impinging polarization state of light in the near-IR and visible regimes. These HMM-based structures are of great use for solar energy harvesting and IR cloaking applications. The Brewster modulator can be developed by HMM-based structures as the intensity and phase modulators – indispensable active elements of varieties of optical systems. As natural materials are unable to exhibit proper light-matter interactions in the THz regime, it is technically difficult to realize active components in this regime. Interestingly, it has been shown in this work that a structure comprising strontium titanate, indium tin oxide and SiO2 layers demonstrates a broadband intensity and phase modulation with 99.8% modulation depth at 2.28 THz frequency. Investigations have also been carried out considering thin films of stibnite and silver to design a thermally programmable reflection modulator in the visible regime. It becomes evident that the amplitude and phase of the reflected wave can be thermally modulated with a high contrast of 3.29×107 at 538 nm wavelength and an incidence angle of 62°.