Perfect absorption in ultra-thin uniform and nanostructured media

© OSA 2015. We show that perfect absorption can be achieved in ultra-thin gratings composed of weakly absorbing dielectric materials combined with a mirror. The structures can be fabricated using standard processing techniques

Mode-based analysis of silicon nanohole arrays for photovoltaic applications

We investigate the optical properties of silicon nanohole arrays for application in photovoltaic cells in terms of the modes within the structure. We highlight three types of modes: fundamental modes, important at long wavelengths; guided resonance modes, which enhance absorption for wavelengths where the intrinsic absorption of silicon is low; and channeling modes, which suppress front-surface reflection. We use this understanding to explain why the parameters of optimized nanohole arrays occur in specific ranges even as the thickness is varied. © 2014 Optical Society of America

Total absorption of visible light in ultrathin weakly absorbing semiconductor gratings

© 2016 Optical Society of America. The perfect absorption of light in subwavelength thickness layers generally relies on exotic materials, metamaterials or thick metallic gratings. Here we demonstrate that total light absorption can be achieved in ultra-thin gratings composed of conventional materials, including relatively weakly-absorbing semiconductors, which are compatible with optoelectronic applications such as photodetectors and optical modulators. We fabricate a 41 nm thick antimony sulphide grating structure that has a measured absorptance of A = 99.3% at a visible wavelength of 591 nm, in excellent agreement with theory. We infer that the absorption within the grating is A = 98.7%, with only A = 0.6% within the silver mirror. A planar reference sample absorbs A = 7.7% at this wavelength

Finite Element Analysis of Stimulated Brillouin Scattering in Integrated Photonic Waveguides

© 2019 IEEE. We describe a finite element algorithm for modeling stimulated Brillouin scattering in optical waveguides of arbitrary cross-section. The method allows rapid calculation of optical and elastic dispersion relations, field profiles, and gain. Additionally, we provide an open and extensible set of standard problems and reference materials to facilitate the bench-marking of our solver against subsequent tools. Such a resource is needed to help settle discrepancies between existing formulations and implementations, and to facilitate comparison between results in the literature. The resulting standardized testing framework will allow the community to gain confidence in new algorithms and will provide a common tool for the comparison of experimental designs of opto-acoustic waveguides

Perfect absorption in uniform and nanostructured media

© 2015 IEEE. We consider the conditions for perfect absorption in uniform thin-films and in thin gratings. We find that perfect absorption of TE polarized light can occur in gratings composed of weakly absorbing materials

Positional disorder in nanowire array photovoltaics

Nanowire arrays are the focus of considerable research for incorporation into next generation solar cells. For these structures to be economically viable they must be designed to achieve high efficiencies in the presence of fabrication variations. Here we report on a systematic study of arrays of clustered nanowires, which reveals how the underlying physics of absorption enhancement in nanowire arrays is altered by the introduction of positional disorder. We find that positional disorder in fact enhances absorption efficiency over the majority of the parameter space due to the formation of additional modes in the structure and subsequently broadened absorption peaks. © 2013 IEEE

Absorption enhancement using dielectric gratings for thin film solar cells

© OSA 2014. We investigate how a dielectric grating positioned on top of a thin absorber can enhance the absorption of the photovoltaic cell. We observe absorption peaks from electric field enhancement within the absorber due to Fabry-Perot resonances

Modal formulation for diffraction by absorbing photonic crystal slabs

A finite element-based modal formulation of diffraction of a plane wave by an absorbing photonic crystal slab of arbitrary geometry is developed for photovoltaic applications. The semianalytic approach allows efficient and accurate calculation of the absorption of an array with a complex unit cell. This approach gives direct physical insight into the absorption mechanism in such structures, which can be used to enhance the absorption. The verification and validation of this approach is applied to a silicon nanowire array, and the efficiency and accuracy of the method is demonstrated. The method is ideally suited to studying the manner in which spectral properties (e.g., absorption) vary with the thickness of the array, and we demonstrate this with efficient calculations that can identify an optimal geometry. © 2012 Optical Society of America

Nanowire array photovoltaics: Radial disorder versus design for optimal efficiency

Solar cell designs based on disordered nanostructures tend to have higher efficiencies than structures with uniform absorbers, though the reason is poorly understood. To resolve this, we use a semi-analytic approach to determine the physical mechanism leading to enhanced efficiency in arrays containing nanowires with a variety of radii. We use our findings to systematically design arrays that outperform randomly composed structures. An ultimate efficiency of 23.75 is achieved with an array containing 30 silicon, an increase of almost 10 over a homogeneous film of equal thickness. © 2012 American Institute of Physics