Design and Simulation of an Efficient Hybrid Plasmonic-Photonic Waveguide

Abstract

Hybrid Plasmonic Waveguiding (HPW) is emerging as a tool which has the potential to realize low modal propagation loss with larger propagation length at nanoscale mode confinement. In this work, a detailed analysis is carried for the HPW for the low loss with deep subwavelength confinement. The improvement in the propagation length with low loss and mode coupling character of the hybrid plasmonic mode is obtained with various designs. The mode character for the hybrid mode and effect of high index layer on the waveguiding performance is also analyzed. The HPW with their deep-subwavelength mode sizes and long propagation lengths can be promising for applications in on-chip nano-scale devices such as nanolasers, biosensing and signal modulation for optical communication and optical interconnects. In this work some of the novel designs of HPW are proposed one of which is hollow HPW. In our hollow design, long range propagation length obtained by optimizing the width and height of the air slice, sandwiched between metal and silicon leads to the confinement of Hybrid Plasmonic (HP) mode in the air. It is found that the introduction of air to confine the HP mode in the nanoscale can increase the propagation distance and can reduce the mode area, which done to reduce the effective index and the lateral optical spread. The analysis of optical mode confinement and propagation characteristic provides us low loss with nano scale confinement in the Hollow HPW. The hybrid plasmonic mode is formed by the mode coupling between plasmonic and optical mode is shown. Mode hybridization of photonic and plasmonic modes in HP waveguide is proposed to achieve low-loss sub-wavelength (nano-scale) optical-confinement with variable optical nonlinearity. The coupled -mode-theory is used to calculate the coupling between the SPP and photonic- mode for the estimation of mode character. The high-index region under the (confinement) dielectric layer also plays a significant role in controlling the mode hybridization across the dielectric layer. It is found that beyond a certain thickness of high-index region evanescent filed into dielectric begins to lose its coupling with SPP mode which disables the mode hybridization; the guided mode now becomes leaky photonic mode with larger field in the high-index region. Further, some engineered structures of HPW by introducing the periodicity in HPW are proposed. Effect of different grating parameters like, (grating period, duty cycle, width, depth, grating length) on the waveguide characteristics is also studied. The garting shows the significant improvement on the propagation length with low loss and high nonlinearity. A nanophotonic coupler based on HPW is proposed which shows long propagation length with high-speed coupling because of ultra-short coupling length. The introduction of a Lateral Subwavelength Grating (LSG) into the high-index layer in the HPW results in efficient coupling characteristics. The lateral resonances in the LSG modify the vertical coupling of HP modes providing us an ultra-short coupling length resulting from large phase difference between even and odd HP modes. Further the proposed coupler exhibits acceptably large propagation lengths for odd and even modes. In addition, the broadband nature of the LSG pushes the proposed coupler to show broadband coupling where coupling length remains acceptably small and the coupling performance remains high over a broad range of wavelength. The proposed work on the design, analysis and simulation of the HPW can be used to realize a nanophotonic platform with long range propagation with acceptably low-loss and nanoscale confinement.