A study of tunable optical filters based on micro-ring structures

A tunable optical filter based on micro-ring structure is studied in the paper. The normalized energy expression is derived at the output port of the filter. Some factors, such as losses and coupling coefficient, are given to valuate the performance of the filter. The change of waveguide´s effective refractive index is calculated to implement the tuning characteristics of the filter. The influence of refractive index´s change on the free spectrum range (FSR) and the full width at half maximum (FWHM) of the filter is small, so the tuning method of changing refraction index is feasible. Structures using electrode thermal pad and p-i-n respectively are brought forwards to realize the tuning characteristics of the filter.