We propose a design method of an achromatic waveplate that comprises anisotropic thin films as a multi-cell layered system. Each cell is a symmetrical three-layered ABA structure with equivalent refractive indices and phase thicknesses. A merit function defined as the rate of change of the phase retardation with respect to wavelength is introduced to control the variation of phase retardation by selecting proper birefringence and thickness for each film. The allowed thickness of each birefringent film is investigated for different requirement about the uniformity of phase retardation. An achromatic waveplate with a smaller number of cells is demonstrated by arranging the two composed films made of different materials with high contrast of refractive index between them. The arrangement of a matching layer, which is associated with the performance of the achromatic waveplate, is also discussed.
In this work, the birefringence of bideposited symmetric nanorod array is investigated. The Ta2O5 nanorod arrays
composed of several subdeposits are fabricated by serial bideposition (SBD) technique. Each nanorod consists of several
identical units and each unit consists of symmetrical sections ABA. From the lateral view of the structure, the nanorod
array is a symmetrical multilayered. The deposition planes for layer A and layer B are perpendicular to each other. For
normal incident ray, the polarization-dependent refractive indices and phase thicknesses of the film are presented as
functions of wavelength and optical constants of each layer. The transmittance spectra of symmetrical sections have a
pass band property as the equivalent refractive indices are real. The principal indices of the Ta2O5 nanorod arrays with
each subideposition thickness of 3 nm associated with the two orthogonal polarizations are measured by ellipsometer
when the deposition angle is changed from 70° to 80°. According to principal indices database, a uniform phase
retardation between the two orthogonal polarization directions can be designed for a specific wavelength range.
In this work, we investigate magnetic responses in various Ag-SiO2-Ag nanosandwich structures at
visible wavelengths. The two electric resonant modes corresponding to the in-phase (symmetric) and
anti-phase (asymmetric) electric dipole on the top and the bottom nanopillars are observed by the finite
difference time domain (FDTD) simulation. In the asymmetric resonant mode, the phases of electric
fields oscillating in the top and bottom pillars have opposite directions, leading to a virtual current loop
that induces the magnetic field reversal. The nanosandwich structure produces a large enhancement of
the magnetic field as the thickness of SiO2 nanopillar is much smaller than wavelength. By increasing
the diameter of nanopillars from 150 nm to 250 nm, the inverse magnetic response wavelength shifts
from 532 nm to 690 nm. On account of the magnetic field reversal caused by the anti-phase electric
dipole coupling, the real part of the equivalent permeability of the film is negative. Therefore, the
wavelength range associated with the intensity of inverse magnetic response is tunable by varying the
size of Ag-SiO2-Ag nanosandwich structure. The equivalent electromagnetic parameters of the
Ag-SiO2-Ag nanosandwich thin film prepared by glancing angle deposition are derived from the
transmission and the reflection coefficients measured by walk-off interferometers. The measured
results indicate that film exhibit double negative properties and lead to negative values of the real parts
of equivalent refractive indices -0.854, -1.179, and -1.492 for λ = 532 nm, 639 nm, and 690 nm,
respectively. Furthermore, the real part of permeability is negatively enhanced to be -4.771 and the
maximum value of figures of merit (FOM) recorded being 6.543 for p-polarized light at λ = 690 nm.
Finally, we analyze the admittance loci for our nanosandwich thin film. This analysis can be applied to
interpret extraordinary optical properties such as negative index of refraction from Ag-SiO2-Ag
One symmetric and two asymmetric chevron thin films of silver were fabricated by bidepositing oppositely tilted nanorods sequentially via oblique angle deposition. The equivalent electromagnetic parameters of the films for s and p polarizations were retrieved at a wavelength of 639 nm for normal incidence using walk-off and polarization interferometers. Experimental results indicate that the symmetric chevron thin film has the strongest magnetic field reversal among the three different shapes. The coupling of the transverse magnetic field between two separate rods makes the equivalent permeability negative real.
In this work, the chevronic films composed of silver nanorods are fabricated using glancing angle deposition (GLAD).
The chevronic structure is grown by bidepositing opposite nanorods sequentially: the substrate is oriented at the polar
angle Φ=0 deg (about the substrate's normal) for the bottom rods and Φ180 deg for the top rods. When the applied
electric field is parallel to the plane Φ= deg, the induced magnetic dipole moment between nanorods leads to a negative
real part of the equivalent permeability. The equivalent refractive indices, the equivalent permittivities and the equivalent
permeabilities of chevronic films with thickness 230 ± 5 nm for p-polarized light are measured by walk-off
interferometer. The equivalent permeabilities of chevronic films with lengths of top rods 291 nm, 409 and 509 nm and
bottom rods 512 nm, 378 nm and 301 nm are measured to be -2.406+0.443 i, -3.870+2.109 i and -2.126+0.904 i at the
wavelength of 639 nm, respectively. The shape affects the real part of the equivalent permeability significantly. When
the length of the top rods is longer than that of the bottom rods, the magnetic dipole moment between nanorods is
suppressed and the quantity of the equivalent permeability becomes small. The real part of equivalent permeability of the
chevronic film is related to the lengths of top and bottom nanorods.
In this work, we use glancing angle deposition (GLAD) to fabricate a silver nanorod array. The average tilt angle and
diameter of the silver nanorod are 65° ± 5 and 323 nm, respectively. When the array is illuminated by normal incident
light, oscillating electric field parallel to the rod and perpendicular to the rod would induce the transverse and
longitudinal plasmon resonant modes. As the longitudinal plasmon mode occurs, the absorption of the array with
thickness 323nm is enhanced and the TM mode transmittance is reduced to be 0.3 percentages. The transmitted
ellipsometric parameters are measured and the phase difference between TE mode and TM mode transmission
coefficients is detected. The absolute transmission coefficient is measured by walk-off interferometer. Compared with
the relative phase, the phase of TM mode transmission coefficient becomes a negative value. It is proposed here that a
wave propagates through the "effective thin film" and acts like a backward wave in the film.
The ability of a weakly anisotropic thin film to modulate the polarization state of light was considered. We found that, in a configuration for enhanced polarization conversion, most polarization states can be generated by tuning the direction of incident linear polarization and the aspect of the anisotropic thin film. The modulation for omniform polarization state can be extended to a broad wavelength range by adding an isotropic thin film in the system.
In this work, we use oblique incident deposition technique to fabricate silver nanorod arrays (NRA). It is found that the
orientation of nanorod growth does not obey the traditional tangent rule (empirical relation between the deposition angle
and column growth angle). The maximum Ag nanorods tilt angle with respect to the substrate normal can reach to 76
deg. The Ag nanorods almost lie on the substrate and the array behaves as a polarizer. The transmittance versus the
polarization direction of normal incident ray is presented in this paper. For a Ag nanorod array with thickness 220 nm
and nanorod tilt angle 76 deg, the extinction ratio at wavelength 632.8 nm becomes 0.12 that is better than previous
work. The extinction ratio of the polarizer would be further reduced to be less than 0.05 by arranging an isotropic Ag
film between the Ag nanorod array and the substrate. On the other hand, it is interesting to show that Ag nanorod array is
isotropic for normal incident ray with any polarization direction at a certain critical wavelength λc. In the wavelength
range λ>λc, the maximum absorption occurs when the polarization is TM mode (electric field direction parallel to the
deposition plane). In the wavelength range λ<λc, the maximum absorption occurs when the polarization is TE mode
(electric field direction perpendicular to the deposition plane). The critical wavelengths for Ag nanorod arrays fabricated
by different deposition angles are measured and analyzed in this paper.