In this letter, we propose all-dielectric Huygens' metasurface structures to construct high numerical aperture flat lenses and beam deflecting devices. The designed metasurface consists of two-dimensional array of all dielectric nanodisk resonators with spatially varying radii, thereby introducing judiciously designed phase shift to the propagating light. Owing to the overlap of Mie-type magnetic and electric resonances, high transmission was achieved with rigorous design analysis. The designed flat lenses have numerical aperture value of 0.85 and transmission values around 80%. It also offers easy fabrication and compatibility with available semiconductor technology. This spectrally and physically scalable, versatile design could implement efficient wavefront manipulation or beam shaping for high power laser beams, as well as various optical microscopy applications without requiring plasmonic structures that are susceptible to ohmic loss of metals and sensitive to the polarization of light.

<div>Aperiodic structures offer new functionalities for control, manipulation, and sensing that can benefit applications in all frequency ranges. We present a study of the influence of the degrees of freedom from a binary aperiodic nanostructure in free space, where each pixel is either the scatterer or the background, that uses a multivariate statistical analysis to examine the covariance matrix of the output field distributions. The total variance of the output fields and the rank can be evaluated to provide quantitative measurements of control. In addition, the field statistics provide an improved understanding of the scattering properties of aperiodic structures.</div><div><br></div><div><br></div><div><div>It has been proposed that structuring a metal surface can substantially increase the optical pressure over that possible with a planar interface. Based upon the forces on the mirrors of a one-dimensional asymmetric Fabry-Perot cavity, we show that the sum of the pressures on both mirrors increases through asymmetry and with quality factor. Using cavity quality factor as a measure, we present the physical basis of the enhanced pressure on a nanostructured metallic surface as being due to an array of asymmetric resonant cavities.</div></div><div><br></div><div><div>With use of optimized, aperiodic structures, more control and higher pressure should be possible. We present a design method by which the electromagnetic pressure on a nanostructured binary material can be controlled in terms of both the enhancement and the direction. This analysis offers new avenues for optomechanics.</div></div>

A metallic hole array of a rectangular converging-diverging channel (RCDC) shape exhibits extraordinary transmission for wavelengths larger than the periodicity of the holes. We use a three-dimensional (3D) finite element method to analyze the transmission characteristics of two-dimensional metallic hole arrays (2D-MHA) with RCDC. For a straight channel MHA, when the aperture size is reduced, the transmission peaks have a blue-shift. The same result is observed for a smaller gap throat for the RCDC structure. For the rectangular holes with a high length-width ratio, a similar blue-shift in the transmission peaks as well as a narrower full width at half maximum (FWHM) are observed. The asymmetry from the rectangular shape gives this structure high selectivity for light with different polarizations. Furthermore, the RCDC shape gives extra degrees of geometrical variables to 2D-MHA for tuning the location of the transmission peak and the FWHM. Tunable extraordinary transmission via changing temperature of a porous metallic layer on top of a thin layer of dielectric strontium titanate (STO) is then studied. The metallic layer has a through-hole array and each hole has a circular converging-diverging channel (CDC) shape, which induces the excitation of surface plasmon polaritons (SPPs) and then results in a controllable extraordinary optical transmission in the terahertz (THz) frequency range. We use a three-dimensional (3D) finite element method to analyze the transmission characteristics of the structure. Location and magnitude of the transmission peaks can be adjusted by the hole size, converging angle, and thicknesses of metal and STO layers. Remarkably, the suggested structure presents a strong transmission dependency on temperature, which offers a new approach to actively and externally tune the transmission. Currently, the performances of thin film solar cells are limited by poor light absorption and carrier collection. In this research, large, broadband, and polarization-insensitive light absorption enhancement is realized via integrating with unique metallic nanogratings. Through simulation, three possible mechanisms are identified to be responsible for such an enormous enhancement. A test for totaling the absorption over the solar spectrum shows an up to ~30% broadband absorption enhancement when comparing to bare thin film cells. Overall performance of a thin film solar cell is determined by the efficiency of conversing photons to electrons that include light absorption, carrier generation and carrier collection processes. Photon management via hybrid designing has been emerging as a powerful means to further boost the conversion efficiency. Here a new nanograting solar cell design, which can be universal and a new solar cell platform technology, is proposed with goals to achieve large enhancement on broadband light absorption and carrier generation, most importantly, under the much reduced usage of active and non-earth-abundant materials. A test for the short circuit current density in CuIn[subscript x]Ga([subscript 1-x])Se₂ (CIGS) thin film solar cells shows an up to ~250% enhancement when comparing to the corresponding bare thin film cells. Besides that, by placing metal strips on top of the nanograting, which act as the top electrode, this design is able to reduce the use of non-earth-abundant materials such as indium that is normally used in both active and transparent conducting materials. / text

Reliability and sensitive information protection are critical aspects of integrated circuits. A novel technique using near-field evanescent wave coupling from two subwavelength gratings (SWGs), with the input laser source delivered through an optical fiber is presented for tamper evidence of electronic components. The first grating of the pair of coupled subwavelength gratings (CSWGs) was milled directly on the output facet of the silica fiber using focused ion beam (FIB) etching. The second grating was patterned using e-beam lithography and etched into a glass substrate using reactive ion etching (RIE). The slightest intrusion attempt would separate the CSWGs and eliminate near-field coupling between the gratings. Tampering, therefore, would become evident. Computer simulations guided the design for optimal operation of the security solution. The physical dimensions of the SWGs, i.e. period and thickness, were optimized, for a 650 nm illuminating wavelength. The optimal dimensions resulted in a 560 nm grating period for the first grating etched in the silica optical fiber and 420 nm for the second grating etched in borosilicate glass. The incident light beam had a half-width at half-maximum (HWHM) of at least 7 µm to allow discernible higher transmission orders, and a HWHM of 28 µm for minimum noise. The minimum number of individual grating lines present on the optical fiber facet was identified as 15 lines. Grating rotation due to the cylindrical geometry of the fiber resulted in a rotation of the far-field pattern, corresponding to the rotation angle of moiré fringes. With the goal of later adding authentication to tamper evidence, the concept of CSWGs signature was also modeled by introducing random and planned variations in the glass grating. The fiber was placed on a stage supported by a nanomanipulator, which permitted three-dimensional displacement while maintaining the fiber tip normal to the surface of the glass substrate. A 650 nm diode laser was fixed to a translation mount that transmitted the light source through the optical fiber, and the output intensity was measured using a silicon photodiode. The evanescent wave coupling output results for the CSWGs were measured and compared to the simulation results.

De nouveaux concepts d’imagerie permettent aux systèmes optiques d’être plus compacts et plus performants. Parmi ces nouvelles techniques, les systèmes d’imagerie hybrides par codage de pupille allient un système optique comprenant un masque de phase et un traitement numérique. La fonction de phase implantée sur le masque rend l’image insensible à un défaut du système optique, qui peut être une aberration ou de la défocalisation. Cet avantage est obtenu au prix d’une déformation connue de l’image qui est ensuite corrigée par un traitement numérique.L’étude des propriétés de ces systèmes a été effectuée en cherchant à augmenter la profondeur de champ d’un système d’imagerie. Un gain sur ce paramètre permet déjà d’envisager le relâchement de contraintes de conception optique telles que la courbure de champ, la défocalisation thermique, le chromatisme… Dans ces techniques d’imagerie, la prise en compte du bruit du capteur constitue l’un des paramètres critiques pour le choix et l’utilisation de méthodes de traitement d’image.Les travaux menés durant cette thèse ont permis de proposer une approche originale de conception conjointe de la fonction de phase du masque et de l’algorithme de restauration d’image. Celle-ci est basée sur un critère de rapport signal à bruit de l’image finale. Contrairement aux approches connues, ce critère montre qu’il n’est pas nécessaire d’obtenir une stricte invariance de la fonction de transfert du système optique. Les paramètres des fonctions de phase optimisés grâce à ce critère sont sensiblement différents de ceux usuellement proposés et conduisent à une amélioration significative de la qualité de l’image.Cette approche de conception optique a été validée expérimentalement sur une caméra thermique non refroidie. Un masque de phase binaire qui a été mis en œuvre en association avec un traitement numérique temps réel implémenté sur une carte GPU a permis d’augmenter la profondeur de champ de cette caméra d’un facteur 3. Compte-tenu du niveau de bruit important introduit par l’utilisation d’un capteur bolométrique, la bonne qualité des images obtenues après traitement démontre l’intérêt de l’approche de conception conjointe appliquée à l’imagerie hybride par codage de pupille. / New imaging techniques allow better and smaller systems. Among these new techniques, hybrid imaging systems with wavefront coding includes an optical system with a phase mask and a processing step. The phase function of the mask makes the system insensitive to a fault of the optical system, such as an aberration or a defocus. The price of this advantage is a deformation of the image acquired by a sensor, which is then processed. The study of the properties of these hybrid imaging systems has been completed by increasing the depth of field of an imaging system, which allows to relax some design constraints such as field curvature, thermal defocus, chromaticism… In these imaging techniques, the consideration the noise of the sensor is one the critical parameters when choosing the image processing method.The work performed during this thesis allowed to proposed an original approach for the cross-conception of the phase function of the mask and the processing step. This approach is based on a signal-to-noise criterion. Unlike known approaches, this criterion shows that a strict insensitivity of the modulation transfer function of the optics is not required. The parameters of the phase functions optimized thanks to this criterion are noticeably different from those usually proposed and lead to a significant increase of the image quality.This cross-conception approach has been validated experimentally on an uncooled thermal camera. A binary phase mask associated with a real-time processing implemented on a GPU allowed to increase the depth of field of this camera by a factor 3. Considering the important level of noise introduced by the use of a bolometric sensor, the good quality of the processed image shows the interest of the cross-conception for hybrid imaging system with wavefront coding.