Active and nonreciprocal Nanophotonics

Abstract

Recently, the field of nanophotonics has seen rapid developments in the area of dielectric metasurfaces governed by Mie scattering. The dielectric metasurfaces have shown remarkable versatility of their functionalities. Ranging from Huygens metasurfaces controlling directionality and phase of light scattering to sharp Fano-resonators to quasi-BICs and nonlinear metasurfaces supporting higher order nonlinear effects. However, active and nonreciprocal nanophotonics with metasurfaces has been facing challenges like miniaturization to the nanoscale and extreme suppression of Mie scattering by active media. Active and nonreciprocal metasurfaces acting as light sources and switches were difficult to realise. The last seven years several different strategies for the harmonious combination of optically active media and dielectric metasurfaces have been developed and demonstrated. However, the scope of fundamental approaches, detailed methodology and experimental demonstration of functional active nanophotonic devices remained a challenge. This hindered the development of active and nonreciprocal metasurfaces from fundamental to applicaitons as prospective nano-optical devices.

In my Thesis, I focus on the design, development and demonstration of working active and nonreciprocal nanophotonic devices and their practical applicability as prospective nano-optical devices. I developed a general framework for design and demonstrated both light generation, active light modulation and directional control capabilities in the near infrared wavelength range. Amongst light sources, I demonstrated the capability to generate polarized luminescence at the nanoscale as well as nanolasing. And in case of light modulation, I demonstrated amplitude modulation and spectral modulation. The directional control is shown in nonreciprocal transmitters. Ultimately, I addressed the design and development challenges in the realization of nano-optical devices and their role in emergence of nanophotonics as a major player in upcoming industry.

In, Chapter 1 I describe the overall motivation behind this work and the concept of active and nonreciprocal nanophotonics in detail.

Chapter 2 delves into the methods used (both theoretical and experimental) throughout this research.

Chapter 3 and 4 elaborate on the design of active metasurfaces as light sources. Specifically, Chapter 3 talks about active metasurfaces which can produce polarized photoluminescence. These metasurfaces rely on coupling of polarized scattering from dielectric nanoparticles to the nanoparticles of rare earth doped nanoparticles. Our work is one of the first approaches that demonstrate polarization control in fluorescence emission from rare earth nanoparticles. In Chapter 4, highly confined fields are generated in membrane based dielectric nanostructures which have thin layers of quantum wells sandwiched within them leading to the earliest demonstration of topological and anapole nanolasing at room temperatures.

In Chapter 5, I elaborate on the maiden demonstrations of nanophotonic nonreciprocal light control devices. The light control is achieved by the deployment of a layer of phase change or highly nonlinear materials in the structure of the metasurface. First, I demonstrate amplitude and spectral modulation using vanadium dioxide based metasurafes. Next, I show nonreciprocal transmission using ITO based metasurfaces.

In the final chapter, I summarise my findings and outline the future scope.