Design & analysis of Optical Ring Resonator with Circular Cavity as Add-drop Multiplexer Prasenjeet Damodar Patil 1 Department of Computer Science and Engineering MIT Art, Design & Technology University Pune, Maharashtra, India prasenjeet.patil@mituniversity.edu.in Nilesh Bhaskarrao Bahadure 2 Department of Computer Science and Engineering GSFC University Vadodara, Gujarat, India nbahadure@gmail.com Pradip Ram Selokar 3 Department of Electronics and Communication Engineering Ramdeobaba University Nagpur, Maharashtra, India selokarpr@rknec.edu Gajanan Govind Sarate 4 Department of Electronics Engineering Government Polytechnic Amaravati, Maharashtra, India ggsanshu@gmail.com Abstract—From the last decade, there has been immense in- terest in development of optical components. Optical components can be broadly classified into two types viz. active and passive components. These components are used for purpose of splitting, multiplexing, filtering etc. In order to investigate performance of these components, computationally complex Maxwell’s equations are solved either in time or frequency domain. Numerous mathematical methods are developed to solve these equations for analysis of wave propagation inside optical components. The effectiveness of these method depends on the dimensions of the component, wavelength and step size used in the problem. Optical ring resonators are passive components, which are used as channel dropping filters in dense wavelength division multiplexing(DWDM). Filtering performance of ring resonators depends upon various parameters such as size and shape of cavity, coupling length, separation gap from adjacent waveguides etc. In this paper, finite difference beam propagation method(FD- BPM) is used to analyze the filtering performance of optical ring resonator with circular cavity. The filtering performance is determined by selecting circular cavities with different diameters and its separation distance for adjacent parallel waveguide. Simulation results shows that maximum optical power can be dropped for circular cavity with smaller diameters with lesser separation gaps, which are consistent with theoretical results. This paper also investigates effect of negative separation gap on filtering performance of ring resonator. Index Terms—DWDM, FDTD, BPM, FD-BPM, evanescence coupling. I. I NTRODUCTION Optical components are used in light wave communi- cation for various purpose viz. splitting, combining, filter- ing, light detection and generation. Types of optical com- ponents include lenses, diffraction gratings, optical multi- plexers, splitters, filters, y-branch etc. The design of these components requires proper selection of physical dimensions, refractive index profile and propagation wavelength. Lithium niobate(LiNbO 3 ) is one of the most promising material used in design of such components, as it provides good con- trast in refractive index profile, having low loss coefficients and supports light modification by electric control. In or- der to perform analysis of these components, the first step is to prepare mathematical model and then check the ef- fect of wave propagation through it. Maxwell’s equations in either time or frequency domain are effectively demon- strated in earlier work [1] as a good solution to this prob- lem. Numerical methods available includes, Effective Index Method, Finite Difference Time Domain(FDTD) [2], Finite El- ement Analysis(FEM), Full Wave Analysis, Beam Propagation Method(BPM) [3], Eigen Value Expansion Method, Method of Lines(MoL) etc. Selection of a method depends upon complexity of the problem and other parameters like com- putational time, efficiency, accuracy, hardware requirements etc. Commercially available software’s for waveguide analysis are either expensive or limited to use of specific method. Finite difference time domain method(FDTD) is one of the widely used method for analysis of optical components. In this method, to find the solution of E & H field components for small step change, the problem is discretized into small grids and central limit approximations are used for computing values of field components.The computational time increases with decrease in step size, which further increases memory require- ments. Beam Propagation Method [4] is oldest, well demon- strated and easiest to implement method used for analysis of 2D and 3D structures. It is used for analysis of complex struc- tures extending longitudinally along the propagation direction. In this paper, we present Finite Difference Beam Propaga- tion Method (FD-BPM) [5]–[7]for analysis of filtering per- formance of ring resonator with circular cavity with different diameters. II. FINITE DIFFERENCE BEAM PROPAGATION METHOD For linear, isotropic and homogeneous medium, the wave equation can be reduced to scalar Helmholtz equation repre- 2024 IEEE Pune Section International Conference (PuneCon) Pune, India. Dec 13-15, 2024 979-8-3315-2782-2/24/$31.00 ©2024 IEEE 1 2024 IEEE Pune Section International Conference (PuneCon) | 979-8-3315-2782-2/24/$31.00 ©2024 IEEE | DOI: 10.1109/PuneCon63413.2024.10895152 Authorized licensed use limited to: INDIAN INSTITUTE OF TECHNOLOGY MADRAS. Downloaded on March 02,2025 at 15:05:06 UTC from IEEE Xplore. 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