The effect of having a finite number of layers on the design of omnidirectional reflectors was investigated. It was shown that the structure should be finished with a low-index layer having a thickness larger than a quarter-wave to increase reflectivity, whereas layers below may remain of quarter-wave optical thickness at normal incidence angle. This general trend has been used for designing and realizing two a-Si–SiO<sub>2</sub> (amorphous silicon and silicon dioxide) omnidirectional reflectors in the near-infrared range on a silicon and a silica substrate, respectively. Owing to the decrease of absorption of recrystallized silicon as compared with a-Si in the visible range, the transmissivity of the structure realized on silica substrate was dramatically increased in the visible range upon annealing, whereas the high reflectivity and the omnidirectional effect were maintained in the near-infrared range.
© 2001 Optical Society of America
(080.2740) Geometric optics : Geometric optical design
(230.1480) Optical devices : Bragg reflectors
(230.4170) Optical devices : Multilayers
(260.2130) Physical optics : Ellipsometry and polarimetry
(310.1860) Thin films : Deposition and fabrication
Bruno Gallas, Serge Fisson, Eric Charron, Aline Brunet-Bruneau, Gérard Vuye, and Josette Rivory, "Making an Omnidirectional Reflector," Appl. Opt. 40, 5056-5063 (2001)