Designing Optical Waveguides: Myth and Reality
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GENERAL AND APPLIED PHYSICS
Designing Optical Waveguides: Myth and Reality Muddassir Iqbal1
· Delin Zhao1 · YouQiao Ma1 · Kun Zhong1
Received: 3 January 2020 © Sociedade Brasileira de F´ısica 2020
Abstract In this paper, a review of numerical methods for design and analysis of nano/micro-sized optical waveguides is carried out. Besides discussing various types of optical waveguides, design of few structures is also presented using FDTD, BPM, and FEM algorithms. Subsequently, few optical devices based upon integration of more than one optical waveguide have also been revealed. Modal effective index analysis and its impact on waveguide designing/signal propagation has also been brought into consideration. Optical waveguides characterization has been carried out by computing second-order and higher order dispersion characteristics, which is vital for information interchange and other nonlinear phenomena. It is anticipated that this effort will help readers in understanding the requirement (subsequently selection) of tools for the design and analysis of optical waveguides. Keywords Optical waveguide · Modal effective index · Slot waveguide · Dispersion · Finite element analysis
1 Introduction An optical waveguide is a crucial element of any sizeable optical circuit, which can guide, couple, switch, split and, multiplex/de-multiplex the optical signal [1, 2]. Commonly, the name, optical waveguide, includes optical fiber, and micro/nano-optical waveguides. Most of the optical waveguides comprise a high R.I. (refractive index) layer of the dielectric channel, deposited with low refractive index cladding material. Wave optics comprehension following Snell’s law (n1 sin θ1 = n2 sin θ2 ) [3] helps in understanding the transmission of an electric field within the optical guiding structure. Core and cladding refractive indices are n1 and n2 , respectively. For θ2 = 90◦ , total internal reflection (TIR) is experienced, due to incident light striking the boundary (between both mediums) returns to the originating medium. Relation governing critical angle calculation is as follows: θc = arcsin(n2 /n1 ). In waveguides, reflection at the boundaries occurs at an angle greater than θc ; subsequently, the light ray will theoretically stay in the core area for an indefinite time. Muddassir Iqbal
[email protected] 1
School of Physics and Optoelectronic Engineering, Nanjing University of Information Sciences and Technology, Nanjing 210044, China
Optical waveguides with sizeable effective areas (Aeff ) require a large turning radius, making it problematic to form an integrated optical circuit. Vice versa, waveguides with small effective area experience losses at the interface; however, tiny size helps in easy incorporation of photonic integrated circuits. Planar optical waveguides exist in various types of configurations such as the following: slab (Fig. 1a), ridge (Fig. 1b), channel (Fig. 2a), and rib waveguide. The dielectric ridge waveguide (often termed as rib waveguide) develops a high effective index area immediately und
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