Effective Refractive-Index Approximation: A Link between Structural and Optical Disorder of Planar Resonant Optical Structures Article Swipe
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· 2018
· Open Access
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· DOI: https://doi.org/10.1103/physrevapplied.9.064041
· OA: W2811266944
We provide detailed insights into a link between structural and optical\ndisorder of resonant optical structures, in particular, distributed Bragg\nreflectors (DBRs) and resonant microcavities. The standard (targeted) DBR\nstructures have periodic square wave like refractive-index profiles, and their\noptical performance is determined by the refractive index ratio of the two\napplied materials and the number of DBR periods. It is well known that its\nstructural disorder strongly affects its optical properties, but, despite that,\nthis influence has not been quantitatively addressed in the literature. We\npropose a precise quantitative definition for a structural disorder of a single\nDBR unit cell (disorder factor), completing the set of DBR fundamental\nparameters. Then we expose the basis for the effective refractive index\napproximation (ERIA), showing that, as long as DBR optical properties are\nconcerned, the influence of increasing structural disorder is virtually\nidentical to the influence of decreasing refractive index ratio, with the\nlatter influence being easily quantified. Making use of the ERIA method, simple\nanalytical formulas, which enable rapid insights into the reflectivity and stop\nband width of DBRs with different types of transient layers at the\nheterointerfaces, are derived and the results validated, via both transfer\nmatrix simulations and direct experimental measurements of imperfect DBRs. The\ninsights of the ERIA method are then further applied on resonant\nmicrocavitities, providing a comprehensive link between their structural\ndisorder and subsequent deterioration of their quality (Q) factor.\n
