Simulation and fabrication of thin film notch filter

Abstract

Optical filters are used for altering the optical properties of surfaces. They work on a specific range of the electromagnetic spectrum, and they are divided into two as interference and absorptive filters. Interference filters are composed of multilayer periodic thin films and they based on the interference principle of electromagnetic waves. In interference filters, desired transmission and reflection ratios can be achieved by controlling film thickness and refractive index of film material and substrate. There are many parameters of the refractive index, but the wavelength is the most outstanding one for optical filters. The wavelength-dependent refractive index is named dispersion and it can be expressed semi-empirical or empirical models. There are many types of interference filters, so they are categorized according to filtering shape and their location on the electromagnetic spectrum. Notch filters are a type of interference filter. Notch filters block a narrow band between the cut-off frequencies and they transmit other parts of the spectrum. They are the most complex interference filter type because of having two cut-off frequencies and a narrow non-transmitting band. In this thesis, the main purpose is to create an open-source and free thin film notch filter simulation and fabricate various thin film notch filters using unused material combinations according to outputs of the simulation. Also, produced thin film notch filters are suitable for different applications. The thin film notch filter simulation has been created using Python software. The physical principles of the thin films are also in the scope of this thesis.