Omnidirectional reflection from nanocolumnar TiO2 films

Abstract

Anisotropic properties of columnar nanoporous thin films were utilized to design and fabricate interference mirrors with lossless omnidirectional reflection in the visible spectral range. Index graded columnar films with distributed Bragg reflector (DBR), sinusoidal, and Gaussian refractive index profiles were studied using finite-difference frequency-domain and finite-difference time-domain methods, with an emphasis on maximizing the omnidirectional reflection bandwidth. Titanium dioxide columnar films with sixteen period sinusoidal refractive index profile were fabricated using the glancing angle deposition technique and characterized by angle resolved transmittance measurements. Simulations and experimental measurements have shown the presence of the omnidirectional reflection band up to 5% wide for a film with a maximum refractive index nmax=2.3 and refractive index contrast Δn=0.8. Simulations further showed that with the optimal choice of the refractive index variation range, the omnidirectional reflection band can reach 10.5% width in TiO2 films with a sinusoidal index profile, 14.5% with a DBR index profile, and 12% with a Gaussian profile. Due to the optical anisotropy of the columnar films, the reflection bandwidth exceeded the corresponding value, observed in isotropic analogs, by a factor of three to four depending on the choice of the refractive index profile.

Optical properties of nanostructured WO3 thin films by GLancing Angle Deposition: Comparison between experiment and simulation

“…They showed that it was possible to tune selective transmission of linearly polarized light for thin films with S-shape structures nano-designed by GLAD. In 2012, this method was used to simulate optical reflection of thin films composed of columns grown with a squared spiral shape [27] in order to model interference mirrors [28]. Among the panel of metal oxides deposited by GLAD, some studies have been focused on stoichiometric tungsten oxide WO 3 thin films [29][30][31] because this dielectric material has a high refractive index (n WO3 = 2.5 [32]).…”

Vapor and liquid optical monitoring with sculptured Bragg microcavities

“…One of the most interesting effects of GLAD is the capability to grow strongly birefringent or dichroic coatings because of the possibility to control the anisotropic microstructure of the deposited materials. Thus porous columnar thin films (CTF) or more sophisticated sculptured thin films (STF) can be manufactured to work as retarders [7], mirrors showing circular Bragg phenomenon [8,9], omnidirectional reflection mirrors [10], or tunable circular polarizers [11].…”

Facile Deposition of YSZ-Inverse Photonic Glass Films

“…However, the strong scattering of light in the disordered structure and resulting high diffuse reflectance over a broad wavelength range also make photonic glasses highly suitable for broadband reflectors, as can be observed in this study. Broadband reflectors have applications as optical filters, , high-efficiency omnidirectional reflectors, − and thermal barrier coatings. , …”