| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 96 === The refractive index is the most important property for optical devices. For optical devices, i.e. telescopes and eyeglasses, optical coatings, i.e. Distributed Bragg Reflector (DBR) and Anti-Reflection (AR) coating, the designs of the refractive index matches are dominating the performance of those optical applications. In reality, some desires of specific refractive index values are often needed for specific optical device designs. However, the effective refractive index can be used to redeem these refractive indices desires. E-beam oblique-angle deposition is a technique to fabricate the tunable and ultra-low-refractive-index nanoporous thin films. In my experiments, the nanoporous thin films deposited by SiO2, TiO2 and Si evaporation sources are discussed with the structure analysis, refractive indices change, reduction thickness and porosity of nanoporous thin films. The lowest refractive index of these nanoporous thin film is as low as 1.08.
In my application experiments, the single and double pair DBRs on silicon substrate deposited by only TiO2 evaporation source were successfully fabricated and enhancing the reflectivity above 74%. The reflectivity at central wavelength of single layer AR coating on glass slider substrate is eliminated from R= 7% to R=0.1%. The gradient-index 4-layer modified quintic AR coating on silicon substrate also diminish the reflectivity R< 5% from 527 nm to 1279 nm and reflectivity R< 1% from 618 nm to 972 nm. It provides a broad-band very low reflection region.
Oxidation phenomena of silicon nanoporous thin film were discussed before. Discussion for oxidation degree of different nanoporous thin film with different incident flux angles is made in my experiment. Moreover, the effect of degradation of silicon nanoporous thin film for optical AR coating is demonstrated and I provide a simple way to solve this kind of problem.
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