Dissertation/Thesis Abstract

Concept and Designs of Nonlinear All-Optical Switch Using Subwavelength ITO Gratings
by Parikh, Aayush A., M.S., California State University, Long Beach, 2018, 53; 10978066
Abstract (Summary)

Switches are devices that turn ON and OFF when externally excited. The fundamental property of switches is to block and unblock the transmission of the input signal. The mechanism of switches, to be either in ON state or OFF state, is dependent on the type of excitation provided and this excitation regulates the output. The excitations could be mechanical, electrical, thermal or optical. The excitation causes the structure of the device to change its physical properties and resultant output is calibrated to show either logical 0 or 1.

The most widely used switches in the industries of microelectronics and integrated circuits, relies on the electrical excitation of semiconductors such as Silicon. These are referred as transistor switches or electronic switches. Electronic switches showcase the characteristics of Resistor-Capacitor (RC) delay, which is the propagation delay of the signal caused due to the resistance and capacitance of the device. The RC delay effects the performance, efficiency and speed of switches. Billions of nanoscale transistor switches are interconnected together to obtain overall fast operating speeds for manufacturing integrated circuits. However, since the demand of high speed communication, data transmission, and high speed signal coupling is increasing, a new switching technique is introduced which does not showcase any RC delays limits.

An all-optical switch can be defined as a structure that shows the ON/OFF transition using light as the excitation medium. The change in refractive index of an optically nonlinear material is intensity dependent. This intensity dependent change blocks and unblocks the incident light, which proves optimal for demonstrating the switching action, similar to a semiconductor transistor. Due to absence of any electrical signals, the RC delay is eliminated, and only the electromagnetic spectrum of light causes a change in optical properties.

This thesis demonstrates the switching action using Coupled Mode Theory (CMT) and Finite Difference Time Domain (FDTD) analysis methods. CMT is applied on subwavelength gratings modeled with a dispersive material, and FDTD simulations result in asymmetric line-shapes, similar to Fano Resonance.

A change in the transmission spectra shows ultra-fast sharp responses of the line-shapes in Terahertz frequency range with femtosecond response times. The response times are devoid of time delays and electromagnetic susceptibility; this provides enough transmission and reflection spectra for ultra-fast control of the input and output signal. The ultra-fast responses are studied for five configurations models, which are designed on the basis of deposition techniques. The responses are then compared to decide the most suitable model that demonstrate the switching action. The model with an optimal response could be fabricated for applications in Phonic Integrated Circuits and optical waveguides such as fiber-optic cables. Signal routing is done electronically using transistor switches; all-optical switching could be applied for fast and reliable routing through fiber-optic cables.

Indexing (document details)
Advisor: Ahmed, Aftab
Commitee: Kwon, Seok-Chul (Sean), Mozumdar, Mohammad
School: California State University, Long Beach
Department: Electrical Engineering
School Location: United States -- California
Source: MAI 58/05M(E), Masters Abstracts International
Subjects: Engineering, Electrical engineering
Keywords: Coupled mode theory, Finite-difference time domain, Nonlinear switching, Photonics
Publication Number: 10978066
ISBN: 9781392073803
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