Double channel side-coupled micro ring resonators for optical filtering

Abstract

Recent developments in the materials technology have made possible the fabrication in dimensions of optical wavelengths. The progress in microfabrication techniques have resulted in increasing the requirement of more accurate models for understanding the behaviour of electromagnetic radiation in such small structures. Numerical simulations provide a low-cost feasibility study enabling one to optimize the design before actual device fabrication. Accurate simulations based on reliable models provide deep insight into complex phenomena related with optical microstructures. Micro ring resonators (MRR) are key micro-components for powerful communication and computation systems. Free Spectral Range (FSR), full width half maximum (FWHM), quality factor (Q) and finesse (F) are significant properties that characterize the performance of MRR. This thesis presents the modelling of multi-stage ring resonators, Side Coupled Integrated Spaced Sequence of Resonators (SCISSORs). The influence of design parameters including number of rings, ring radii, center wavelength and coupling coefficients is investigated over FSR and FWHM of the output signal in a proposed designed system based on SCISSORs. Computational investigations are performed using OptiFDTD (Finite- Difference Time-Domain), Matlab (2009a) and OptiWave Software V8.0. Double Channel SCISSORs is designed for optical filter application and power at input and output ports and circulated optical field within the ring resonator is simulated. The 2D model structure of SiO2 wafer is designed with refractive index equal to air’s refractive index (i.e. 1.00). Design of the system consists of 4 micro-rings and a waveguide. The refractive index of waveguide is set to isotropic constant real value of 1.54 and no imaginary part. Validity of the model is extensively discussed and the transfer function of proposed micro ring resonator system is derived by using analytical treatment. The performance of SCISSORs is tested at input amplitudes of 1 V/m, 5 V/m, 10 V/m and 15 V/m. Power propagation is studied at input wavelengths of 1 μm, 1.25 μm, 1.55 μm, 2.9 μm and 4.25 μm which reveals a higher signal at Through port than Input port. A symmetric trend in 0.9-1.1 μm range with a higher gain was achieved by amplifying the input signal through SCISSORs. Investigations have shown the promise of SCISSORs as an optical filter that can be extremely useful in optical communication systems from transmission and security point of view.