Band-Limited Filters and Bragg Reflectors in Perturbed Defect Nanostructures of Chiral Sculptured Thin Films

Abstract

Sculptured thin films (STFs) are engineered films having tailored morphology and high porosity. Henceforth, we can elicit desired optical responses upon light excitation in these films. The oblique deposition of the nanocolumns and the resulting anisotropic properties have been discovered over the past decade. Their discovery has lead to unique and predictable optical, mechanical, electrical, magnetic, thermal, and biological properties. To study the optical response of such STFs, we introduced a central defect in a perturbed chiral STF (CSTF), which transmits light of one circular polarization state and reflects the other in a spectral Bragg regime. The perturbed CSTF reflects light of both circular polarization states in the Bragg regime if the amplitude of modulation of vapor incident angle increases. A structurally chiral layer defect or either central twist defect in a perturbed matched CSTF fabricated a narrow bandpass (ultranarrow bandstop filter) and Bragg reflectors depending upon the thickness and periods of these nanostructures. However, both the ultranarrow bandstop filter and Bragg reflectors have become polarization insensitive by the appropriate modulation of the tilt nanohelixes of perturbed CSTFs. Moreover, simulation revealed that the polarization-insensitive Bragg mirrors, laser mirror, and Bragg reflector were fabricated using such CSTF structures having structural defect. These structural nanomaterials are very tolerant when the amplitude of modulation of vapor incident angle is sufficiently large. It has been also examined that different STFs structures of different refractive indices and porosity are fabricated by changing deposition angle and angle of inclination through modulation and glancing angle deposition.