The growing need for cost-effective renewable energy sources is hampered by the stagnation in solar cell technology, thus preventing a substantial reduction in the module and energy-production price. Lowering the energy-production cost could be achieved by using modules with efficiency. One of the possible means for increasing the module efficiency is concentrated photovoltaics (CPV). CPV, however, requires complex and accurate active tracking of the sun that reduces much of its cost-effectiveness. Here, we propose a passive tracking scheme based on a reactive optical device. The optical reaction is achieved by a new kind of light activated mechanical force that acts on micron-sized particles. This optical force allows the formation of granular disordered optical media that can be switched from being opaque to become transparent based on the intensity of light it interacts with. Such media gives rise to an efficient passive tracking scheme that when combined with an external optical cavity forms a new solar power conversion approach. Being external to the cell itself, this approach is indifferent to the type of semiconducting material that is used, as well as to other aspects of the cell design. This, in turn, liberates the cell layout from its optical constraints thus paving the way to higher efficiencies at lower module price.
The spin-Hall effect - the influence of the intrinsic spin on the electron trajectory, which produces transverse
deflection of the electrons, is a central tenet in the field of spintronics. Apparently, the handedness of the light's
polarization (optical spin up/down) may provide an additional degree of freedom in nanoscale photonics. The direct
observation of optical spin-Hall effect that appears when a wave carrying spin angular momentum interacts with
plasmonic nanostructures is presented. The measurements verify the unified geometric phase, demonstrated by the
observed spin-dependent deflection of the surface waves as well as spin-dependent enhanced transmission through
coaxial nanoapertures even in rotationally symmetric structures. Moreover, spin-orbit interaction is demonstrated by
use of inhomogeneous and anisotropic subwavelength dielectric structures. The observed effects inspire one to
investigate other spin-based plasmonic effects and to propose a new generation of optical elements for nanophotonic
An extraordinary coherent thermal emission from an anisotropic microstructure is experimentally and theoretically
presented. The enhanced coherency is due to coherent coupling between resonant cavities obtained by surface standing
waves, where each cavity supports a localized field that is attributed to coupled surface phonon-polaritons. We show that
it is possible to obtain a polarized quasi-monochromatic thermal source from a SiC microstructure with a high quality
factor Q ~ 600 at the resonant frequency of the cavity, and a spatial coherence length 760λ which corresponds to angular
divergence of 1.3mrad.
Surface waves have been shown to play a key role in spontaneous thermal emission in the near-field as well as the
coherence and the polarization properties of the nonradiative field. The near-field coherence of the delocalized
nonradiative surface waves can be transferred into radiative fields by introducing a shallow grating on the surface. We
show that the coherency of the thermal radiation can be enhanced by an order of magnitude compared with the
coherency imposed by the delocalized surface waves. The enhanced coherency is due to coherent coupling between
resonant cavities obtained by surface standing waves, where each cavity supports localized field that is attributed to
coupled surface waves. We realized coupled resonant cavity structure on amorphous SiO2 and crystalline SiC, both
support surface phonon-polaritons, to demonstrate extraordinary coherent thermal emission with a high quality factor of
600 and a spatial coherence length of 760λ (8.8mm).
The Pancharatnam-Berry phase is a geometric phase associated with the polarization of light. We present novel optical
phase elements based on the space-domain Pancharatnam-Berry phase. Such elements can be realized using
inhomogeneous anisotropic micro and nanostructures, where the geometric phase is induced by spin-to orbital angular
momentum transfer. The elements are polarization dependent, thereby enabling multipurpose optical elements. Vectorial
vortices, and vectorial vortex mode transformation for a hollow waveguide are demonstrated. Manipulating of thermal
radiation by use of anisotropic micro and nanostructures is also investigated. We demonstrate an extraordinary coherent
thermal radiation from coupled resonant cavities; each of them supports standing wave surface polaritons.
Vectorial vortices obtained with quantized Pancharatnam-Berry phase optical elements (PBOEs) are presented. A vectorial vortex occurs around a point where a scalar vortex is centered in at least one of the scalar components of the vectorial wave field. PBOEs utilize the geometric phase that accompanies space-variant polarization manipulations to achieve a desired phase modification. The geometric phase is formed through the use of discrete computer-generated space-variant subwavelength dielectric gratings. By discretely controlling the local grating orientation, we could form complex vectorial fields. Propagation-invariant vectorial Bessel beams with linearly polarized axial symmetry were experimentally demonstrated. Moreover, a new class of vectorial vortices based on coherent addition of two orthogonal circular polarized Bessel beams of identical order, but with different propagation constant is presented. The transversely
space-variant axially symmetric polarization distributions of these vectorial fields rotate as they propagate while still maintaining a propagation-invariant Bessel intensity distribution. The polarization properties were verified by both full space-variant polarization analysis and measurements. Rotating intensity patterns were also demonstrated by transmitting the vectorial vortices through a linear polarizer.
Space-variant polarization manipulation of enhanced omnidirectional thermal emission in a narrow spectral peak is
presented. The emission is attributed to surface phonon-polariton excitation from space-variant subwavelength SiO2
gratings. Polarization manipulation was obtained by discretely controlling the local orientation of the grating. We
experimentally demonstrated thermal emission in an axially symmetric polarization distribution. We show that by
coupling surface phonon-polaritons to a propagating field, large anisotropy of the emissivity is obtained within a narrow
spectral range. We experimentally demonstrate this effect by fabricating a space-variant subwavelength grating on a SiO2
substrate to encrypt an image in the polarization state of a thermal radiation field. Theoretical calculations based on
rigorous coupled-wave analysis are presented along with experimental results.
We present a unique method for real-time polarization measurement by use of a discrete space-variant subwavelength grating. The formation of the grating is done by discrete orientation of the local subwavelength grooves. The complete polarization analysis of the incident beam is determined by spatial Fourier transform of the near-field intensity distribution transmitted through the discrete subwavelength dielectric grating followed by a subwavelength metal polarizer. We discuss a theoretical analysis based on Stokes-Muller formalism and experimentally demonstrate our approach with polarization measurements of infrared radiation at a wavelength of 10.6um. Moreover, a new far-field polarimetry approach is presented along with preliminary experimental results.
Space-variant Pancharatnam-Berry phase optical elements based on computer-generated subwavelength gratings are presented. By continuously controlling the local orientation and period of the grating we can achieve any desired phase element. Unlike diffractive and refractive elements, the phase is not introduced through optical path differences, but results from the geometrical phase that accompanies space-variant polarization manipulation. We introduce and experimentally demonstrate Pancharatnam-Berry phase optical elements (PBOEs) such as polarization beam-splitters, optical switches and spiral phase. We also introduce and experimentally demonstrate quanitized pancharatnam-Berry phase diffractive optics. We realized quantized geometrical blazed polarization diffraction gratings, as well as a polarization dependent focusing lens for CO2 laser radiation at a wavelength of 10.6 micron on GaAs substrates. We also demonstrate the formation of propagation-invariant linearly polarized axial symmetric beams by use of quantized Pancharatnam-Berry optical elements. Finally a novel method for real time polarimetry and infrared polarization scrambler by use of quasi-periodic subwavelength structures is presented.
Novel methods for space-variant polarization-state manipulation using subwavelength metal and dielectric gratings are presented. By locally controlling the period and direction of the grating, we show that any desired polarization can be achieved. The methods presented in this paper are generic to any portion of the spectrum, and we present experimental demonstrations of our theory using CO2 laser radiation at a wavelength of 10.6μm. Moreover, we exploited our computer-generated subwavelength gratings to demonstrate a polarization Talbot self-imaging, as well as nondiffracting periodically space-variant polarization beams, and a unique method for real-time polarization measurement. We also present novel optical phase elements based on the space-domain Pancharatnam-Berry phase. Unlike diffractive and refractive elements, the phase is not introduced through optical path differences, but results from the geometrical phase that accompanies space-variant polarization manipulation. We intoduce and experimentally demonstrate Pancharatnam-Berry phase optical elements (PBOEs) based on computer-generated subwavelength gratings such as polarization beam-splitters, optical switches and spiral phase.