Design and Simulation of a High Index Contrast Grating Based Hollow Optical Waveguide

Abstract

A new era in sub-wavelength grating study was opened after the first High index Contrast Grating broadband mirror was designed. The extraordinarily broad band and the high reflectivity from the High index Contrast Gratings was achieved by the arrangement of gratings which is unique as the low-index medium surrounds entirely the high-index region. The distributed Bragg reflectors (thick and multilayer)can be replaced by HCGs. There are many uses of high index contrast gratings in the fields of optoelectronic devices such as hollow-core waveguides with low loss, vertical-cavity surface-emitting lasers, tunable devices etc. Hollow Waveguides remain an attractive choice in photonic technology because even in very low refractive index materials and many such other applications, they enable light guiding capabilities. In this work, we have studied and optimized High index contrast gratings and thus achieving maximum reflectivity. Some important HCG design parameters include grating duty cycle and grating period along with thickness of grating and that of our underlying low index layer which are deeply studied and optimized to achieve the desired results. One dimensional high index contrast grating has been optimized so that it can be used in the design of grating based hollow optical waveguide. In the area of integrated photonics, due to design flexibility and low cost fabrication of hollow optical waveguides, they are finding applications in the numerous tunable optical functions. The Broadband high reflectivity of HCG is taken as a base to propose an on chip hollow optical waveguide. A low loss providing HCG based hollow optical waveguide is thus designed and proposed. In parallel, low loss is further attained by optimizing the grating period at an air core thickness which is narrow. We have studied the wavelength spectrum with the optimized grating period to get broadband narrow core low loss hollow optical waveguide. Recently, slow light has come up as a new research area in field of photonic crystal waveguides. There is a compromise with the slow light benefits because of the propagation loss and dispersion. We have studied the slow light characteristics of proposed design of grating based hollow optical waveguide with narrow core and low loss.Bragg reflectors are used in broad range of applications in optical fiber communications including lasers and sensing. To achieve high reflectivity, a two-dimensional HCG is further optimized for both TE and TM mode. Also a design of an on chip two-dimensional HCG reflector at Bragg incidence with low polarization dependence been proposed. The proposed reflector provides high reflectivity more than 99.99% with polarization independence at 1.55µm. The polarization insensitivity of the proposed reflector has the potential to innovate optoelectronic devices foe various applications in high end optical network. Next proposition was of a two-dimensional HCG based two-way on chip reflector. The design, which is a two-way reflector, reflects efficiently at Bragg incidence and also at vertical incidence. The results of the proposed design are simulated using improved Fourier modal method. The dependence of grating period, grating thickness on reflectivity at Bragg and vertical incidence is obtained for the proposed structure for TE mode. The results are also obtained for angular dependence of proposed reflector with optimized design parameters using FMM. It is also validated using FDTD. The wavelength spectrum of proposed Reflector has been obtained at Bragg and vertical incidence.