Design & Optimization of Nanophotonic Devices for IR Band Applications

Abstract

Nanophotonic devices have emerged as promising tools for various applications, particularly in the infrared (IR) band, owing to their unique properties at the nanoscale. This thesis explores the design, optimization, and applications of nanophotonic devices tailored specifically for the IR wavelength range. Leveraging the principles of nanophotonics, these devices offer unprecedented control over light-matter interactions, enabling enhanced performance in diverse IR applications. The thesis begins by providing an overview of the fundamental principles of nanophotonics relevant to the IR band, highlighting the importance of controlling light at subwavelength scales. It then delves into the design methodologies employed in creating nanophotonic structures optimized for IR applications. Various materials, including plasmonic and dielectric nanostructures, are discussed in the context of their suitability for IR manipulation. The primary objective is to develop various nanophotonic switches and sensors for diverse applications in the telecommunication wavelength range by employing a hybrid plasmonic waveguide (HPWG) configuration. The work is divided into two significant research areas. The first part of the thesis deals with the design and simulation of nanophotonic switches followed by the ultra-sensitive HPWG sensors. Initially, through numerical simulations, we illustrated a CMOS-compatible all-optical switching mechanism using the metal-insulator-semiconductor-insulator-metal (MISIM) configuration, operating in the wavelength ranges from 1.473 to 1.502 μm (extinction ratio (ER) = 5.5 dB) and 1.512 to 1.5306 μm (ER =3.079 dB). However, due to the direct coupling of the light signal into the primary waveguide, we observed a degradation in ER for the initial switching scheme. Later, we addressed this issue by employing the Franz-Keldysh effect (FKE) induced absorption coefficient and tuning Si0.15Ge0.85 as the control port material. In the next part, we have developed an innovative all-optical switch based on a hybrid plasmonic waveguide (HPWG) structure utilizing the transparent conductive oxide (TCO) material zinc-doped cadmium oxide (ZnCdO) as the switching material. This ZnCdO can be transitioned from the metallic to the dielectric phase through electrical manipulation of the refractive vi index. The mobility of free carrier concentration is significantly enhanced by a nonlinear optical effect induced by the epsilon-near-zero (ENZ) material near the operating wavelength. Our simulated switch achieves an insertion loss (IL) of 0.5 dB, an ER of 13.75 dB, and a figure of merit (FoM) of 27.5 at 1.55 μm. Additionally, we conducted a reliability study by varying the height and width of the waveguide to assess their impact on the performance of the on-chip switch design. In the latter part of this report, we have modeled and simulated a nanoscale V-shaped hybrid plasmonic waveguide (HPWG) sensor to monitor changes in refractive index and temperature. The aqueous analyte (benzene C6H6) is to be sensed using the wavelength interrogation method, which involves monitoring a shift in the resonance peak of propagation loss within the wavelength range of 1.18 to 2.2 μm. The sensor design incorporates a titanium oxide (TiO2) layer deposited over the silicon oxide to maximize the sensor's overall sensitivity. Through numerical simulation, the device exhibits a sensitivity of 1022.75 nm/RIU, a figure of merit of 15.88 RIU-1, and 2.95 nm/0C. Subsequently, we have developed and examined theoretically a highly sensitive nanoscale plasmonic biosensor for detecting human blood groups in the visible and near-infrared (NIR) spectrum. A metal-insulator-metal (MIM) waveguide featuring an array of elliptical nanoholes serves as the basis of the suggested sensor structure. These nanoholes serve as the sensing surface and exhibit significant optical features, including extraordinary optical transmission (EOT) and nanoscale light confinement. A comparison between the two potential designs of the sensor reveals that design 1 (D1) attains sensitivity values of 64.26 nm/RIU, 101.16 nm/RIU, and 82.1 nm/RIU, respectively.