Design Of Optical Bandpass Filter Based On Interference On Thin Films

Abstract

Three different wavelengths (656.3 nm, 486.1 nm and 464.7 newlinenm) are of significance in controlled thermonuclear fusion reactors. newlineDesign of these filters with dielectric materials is a major challenge newlinefaced by the researchers. Though various filter designs are available, newlinedeveloping filters with nearly 100% transmittance at the desired newlinewavelength and 100% at the undesired wavelengths is yet to be newlinematerialized. In this research work, successful attempts have been made newlineto design these three filters with two combinations of dielectric newlinematerials. Also, the impact of number of layers on the performance of newlinethe filters is studied. In order to enhance the performance i.e. fine tuning newlinethe transmittance at the desired central wavelength, three different newlineoptimization techniques were proposed. Initially, the work began with newlinedeveloping iterative techniques for determining the desired thickness of newlinechosen pair of dielectric materials (one with high refractive index and newlinethe other with low refractive index). Here the choice of the thickness is newlinelimited as the thickness can lie within the desired band as decided by the newlineprogrammer. Also, the performance of these filters is depicted in the newlineform of transmittance and reflectance. Having identified the thickness, newlinefilter is fabricated and the performance is experimentally verified. It was newlinefound that transmittance is much less than expected. Hence the research newlineis shifted to developing suitable optimization techniques for identifying newlinethe number of dielectric materials for the same pairs of dielectrics in the newlinedesign of three different filters. Performance is studied in terms of newlinetransmittance at central wavelength and Full Width Half Maximum. newlineModified Grasshopper Optimization Algorithm (GOA) and Bald Eagle newlineSearch (BES) Optimization techniques are developed. newlinevi newlineIn both these algorithms, the thickness for each layer and the newlinenumber of layers is determined for the given stack configuration. newlineScalability of the proposed technique is verified for the second set of newlinedielectric pairs.