Refractive index profile for (a) gradient index film with central spacing layer of thickness and (b) a gradient index film with phase shift . Both index profiles are centered around an average index and have a peak-to-peak amplitude of .
A GLAD equipped electron beam evaporation system. Two computer controlled motors independently set the deposition angle and substrate rotation angle . A crystal thickness monitor (CTM) measures the deposition rate and is used to provide feedback for the computer.
A model of a columnar film where the diameter of the columns varies periodically in the direction of the substrate normal. The cross sections show the film at the density extremes illustrating the origin of the refractive index variation seen in such a film.
SEM images of (a) a 19 period thick film with a central spacing layer, and (b) a 20 period thick film with phase shift defect. Both defects are located in the center of the film.
Normal incidence optical transmittance measurements (circles) and simulations (dotted line) for (a) a 19 period thick film with a central spacing layer, and (b) a 20 period thick film with phase shift defect.
Normal incidence transmittance spectra (normalized to the center wavelength of the stopband) for a set of gradient index films with phase shift defects. Each spectrum corresponds to a film with a different phase shift, ranging from π/2 to 3π/2.
Simulated (circles) spectral location (normalized to the center wavelength of the stop band) of the transmittance peaks for gradient index films with different phase shifts. The line is included as a guide for the eyes. The spectral locations of the transmittance peak agree with the measured (triangles) peak locations.
(a) A vertical postdefect is optically isotropic in the plane of the substrate resulting in polarization insensitive optical properties. (b) A slanted columnar defect on the other hand is optically anisotropic in the planar cross section and will exhibit polarization dependant optical properties. The index ellipsoid is shown for both defect layers.
SEM image of a gradient index film with a biaxial spacing layer. (a) Shows the entire 21 period film, while (b) is a closeup image of the slanted columnar film in the spacing layer.
Transmittance spectra for a gradient index film with biaxial spacing layer, open circles denoting -polarized light and filled circles denoting and filled circles denoting -polarized light. The location of the transmittance peak differs depending on the polarization state, while the spectrum is otherwise polarization insensitive.
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