MULTIBAND PHOTONIC INTEGRATED CIRCUITS USING PLASMONIC MIM WAVEGUIDE

Abstract

Plasmonics is a rapidly evolving subfield of nanophotonics that deals with the interaction of light with surface plasmons, which are collective oscillations that occur at the interface between metal and insulator. Plasmonics meet a demand for optical interconnects which are small enough to coexist with nanoscale electronic circuits. This thesis mainly focused on the process of developing dual band plasmonic devices from the concept of nanoscale wireless links, with specific emphasis on synthesizing data from numerical simulation into an accurate, predictive understanding of nanoscale optical phenomena. The realization of nanoscale wireless links require miniaturized transmitter and receivers. A wireless link operating at single band have limited applications in future due the increased demand of multiple functions using the same system. Thus, we require multiband wireless links to accommodate more than one standards and functions. When multiple functions have to be performed; the single band system will become very complex and power hungry. Multi-band systems can be implemented by parallel, switchable or concurrent configurations. The parallel or switchable configuration suffers from the drawback of bulky circuitry and switching delay in the operation. The concurrent multiband front end provides different standard compatibility with a single circuitry only; hence reduces the circuit size and the power consumption. So far there is no attempt by researchers across the globe to implement this concept in photonic integrated circuits. Probably due to the fact that most of the photonic integrated circuits are developed by using optical waveguides. These optical waveguides operate in transverse electric (TE) or transverse magnetic (TM) modes and have a limited single mode operational bandwidths. In order to obtain multiband operation, we require large single mode operational bandwidth of the waveguide so that no higher order mode can start propagating in the desired two or more than two frequency bands. This can easily be achieved, if waveguide operates in transverse electromagnetic (TEM) or Quasi TEM mode. Plasmonic MIM waveguide supports TM modes and it has been shown by researchers that surface plasmon polariton (SPP) wave (fundamental TM mode) has field lines similar to the Quasi TEM mode. Thus, the Quasi TEM nature of SPP mode supported by metal-insulator-metal (MIM) waveguide fulfills the requirement for the designing of multiband photonic integrated circuits. This waveguide can be modeled with the help of a two wire transmission line operating in quasi TEM mode. viii Although, nanoscale wireless link concept was proposed in 2010; realization of this concept requires individual building blocks and their systematic design methodology. This portion is still not available in the literature. Therefore, there is a strong need to address this issue i.e. design of building blocks for nanoscale wireless links so that in future this concept can be realized. Keeping this research gap in mind, the research work reported in this Ph. D dissertation has been devoted to design and analysis of MIM plasmonic waveguide based integrated circuits for future multifunctional photonic systems. This thesis consists of six chapters. The first chapter of thesis gives a brief review of the existing technology of photonics along with the motivation and discusses the importance of the present dissertation work. A detailed literature review has been given to construct the problem statement along with the thesis composition. Chapter 2 gives a brief discussion on transmission line theory and characteristics of MIM slot waveguide, such as normalized propagation constant, characteristic impedance and propagation length, are obtained through full wave simulation software (CST-Microwave Studio). Chapter 3 of this dissertation describes the MIM waveguide based resonators such as ring resonator, uniform width resonators and stepped width resonators. Further, dual pass band and dual stop band photonic circuits have been designed using band pass filters and band stop filters. The full wave simulations have been carried of using commercial software tool CST microwave studio. Chapter 4 describes the design of a filter based dualband diplexer and directional coupler for concurrent dual band photonic networks. The diplexer design involves two dualband band pass filter (BPF) designed using plasmonic MIM stepped width resonator and a broadband chamfered T-junction. This diplexer can simultaneously multiplex two signals at two different wavelengths or one can treat it as a multiplexer where signals at four different bands can be multiplexed. The simulated results of the diplexer demonstrate a promising concurrent behavior over the desired band of operation. The design of the coupler also uses the concept of the SWR; hence only one structure is required for concurrent operation in both optical bands. The diplexer and coupler designs can be used in the development of photonic integrated circuits and it can be combined with existing silicon photonic integrated circuits. ix Chapter 5 explains the design and analysis of a dual band antenna at THz frequencies. The antenna is designed with two MIMSWRs connected with a gap. The proposed structure simultaneously operates at 1309-nm and 1604-nm bands with a wide stop band in between. A better response for achieving concurrent dual band operation is provided by the gap width of the two resonators. The performance of the proposed antenna agrees fairly with the theory and simulation. The concept can be extended to design several other components such as Tri and Quad-band antennas. Finally, the conclusions and future scope for further research work have been presented in Chapter 6 of this dissertation.