Optical properties of micro- and nanostructures ,
Nonlinear and active metamaterials ,
Nonlinear plasmonics ,
Quantum optics in composite media ,
Optical communications ,
Photonic devices
Publications (9)
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We experimentally analyze the simultaneous processes of difference frequency generation (DFG) and second harmonic (SH) generation in multilayer structures exhibiting an effective epsilon-near-zero (ENZ) response and ENZ properties in one of their layers. The structures consist of subwavelength-thin tri-layer periods of 75% ITO, 12.5% Al2O3, and 12.5% BaTiO3, with the total thickness kept near 120 nm. The number of periods and ITO layer thickness (3-30 nm) vary between samples, allowing to tune the effective ENZ wavelength over 1000 nm. We demonstrate that the level of DFG and SH enhancement can be increased by over two orders of magnitude with multilayer composition, with the highest enhancement in samples having 12-15 nm thick ITO layers. The peak enhancement wavelength follows the effective ENZ wavelength, while the relative enhancement levels of DFG and SH depend on sample composition. Our findings are supported by COMSOL simulations, TEM analysis, and ellipsometry data.
We discuss control of thermally-induced focal shifts via engineering the metalens construction and show that metalenses offer additional degree of freedom in controlling the thermal stability of optical systems, compared to standard refractive and diffractive lenses.
Metasurfaces offer flexibility for expanding functionality and reducing the size of optical systems by providing optical functionality from a flat surface. Previous work has demonstrated a rapid fabrication and testing process for wafers containing multiple 1-centimeter diameter metalenses that can be applied towards mass manufacturing. However, quality feedback was limited to analyzing imaging performance parameters such as the modulation transfer function and focal length. These techniques do not give direct feedback about specific manufacturing errors. Currently, getting this feedback still requires expensive, time-intensive processes such as scanning electron microscope (SEM) measurements or local area interferometry, which tend to have a small field of view. Theoretical investigation suggests that phase errors in the metasurface phase profile result in a shift in diffraction efficiency away from the first order and into the other diffraction orders, zero order, second, third, etc. We exploit this concept to comprehensively characterize metalens performance, including the analysis of standard image quality parameters and extending the study to multiple diffraction orders. An extensive set of measurements of the relative efficiency of the diffraction orders is presented for a set of fabricated metalenses alongside SEM measurements to cross-validate the presence of manufacturing defects. This will establish the extent to which current conventional CMOS processing and manufacturing techniques can be applied to metasurface optics by indicating uniformity and yield characteristics across positions and wafers.
KEYWORDS: Sum frequency generation, Plasmonics, Deep learning, Upconversion, Nonlinear metamaterials, Photons, Second harmonic generation, Nonlinear optics
Photonic upconversion from the infrared regime to the visible spectrum can occur through sum-frequency generation (SFG). A second-order nonlinear optical response, such as SFG, can be produced from a nonlinear material, in this case an ABC nanolaminate. Optimization of a metamaterial consisting of a plasmonic nanolaminate device can maximize the SFG from incident wavelengths. Utilization of a deep learning framework removes the need for traditional guess and check methods and creates new possibilities for plasmonic geometries. Applications of this research include low-cost night vision or low light imaging systems for defense, autonomous vehicles, and other commercial uses.
Traditional processes for the design of metamaterial structures are often computational heavy, time-consuming, and occasionally does not lead to the desired optical response. Deep learning can quickly optimize structures through inverse design, and create new geometries for devices. This research uses a deep learning framework for the inverse design of an optimal plasmonic structure to maximize the second-order nonlinear response from a nonlinear metamaterial. The thinfilm nonlinear metamaterial employed is a nanolaminate, and the optimal plasmonic structure is fabricated to establish the validity of the deep learning algorithm.
Incorporating planar optics such as metalenses or metacorrectors into optical designs can drastically improve the performance of imaging systems with additional benefits such as cost, size and weight improvements. However, modeling of such hybrid lenses is challenging because of the multi-scale nature of the simulation. We demonstrate that one can combine ray optic simulations with full wave electromagnetic simulations and Fourier optics approaches to model a whole compound/hybrid lens considering all metasurface unit cell interactions and to study the effect of possible fabrication errors.
Optical metasurfaces are designed to control light similarly to conventional refractive optics, but with considerably less size and weight. They manipulate light based on the designed scattering from subwavelength resonant nanostructures within the surface. Such devices have only recently been fabricated. We characterized the performance of a 4-cm-focallength infrared dielectric metasurface lens using a scanning InSb detector array to record the intensity field behind the lens through its focal point and an optical scatterometer to measure its scatter. For the scatter measurements, a 5-mm-diameter beam illuminated a subsection of the metasurface at ten locations across the 40-mm extent of the lens to evaluate scattering in each subsection. The affected beam was steered through the lens’ focal point and expanded beyond it due to the 50-cm length of the scatterometer’s measurement arm. In general, the metasurface had scattering “shoulders” at angles outside the intended focal area about 2 orders of magnitude in transmission distribution space (Sr-1) higher than those of either a comparable infrared refractive optic or a flat polished silicon substrate; an additional forward-scattering lobe and a colinear peak caused by light travelling through the metasurface unaffected, which are not typically observed in a refractive lens, were also observed.
We engineer the nonlinear response of multilayered hyperbolic metamaterials systems by employing the optical response of Arsenide semiconductor materials. The photoexcited carriers lead to spectral, temporal, and polarization dependent optical response that is described in this talk. The response is suggestive of generating a transient hyperbolic materials response in this system. Exploration of this response and the use of these materials as a basis for nonlinear metasurfaces will be discussed.
We present the operation of a one-way nonlinear mirror, where the image is formed by the process of difference frequency generation on one and the same side of the metasurface, independently of the object location on the left or right. The imaging principle is based on the generalized law of refraction. Regularly, an image of a source, produced by such a deeply subwavelength layer of a nonlinear material, is expected to form on both sides of the surface with a nearly equal efficiency. This symmetric two-side generation is a consequence of the lack of phase-matching constraints within the subwavelength-thin medium. The use of a nanostructured medium allows for control of the generation directionality via interference of the multipolar partial waves produced by the nonlinear response of nanoelements comprising the metasurface. Such interference can result in suppression of the generated field on one side of the metasurface. The approach proposed here allows for a nonreciprocal directionality where this side, additionally, remains unchanged independently of the source location. The approach does not require asymmetry of the nanoelement geometry. Rather, it relies on the existence of shared pathways inducing electric and magnetic multipolar moments in the nanoelement via a nonlinear interaction These pathways allow controlling the phase of both electric and magnetic, nonlinearly produced, multipolar modes by a single (electric or magnetic) vector of the fundamental field of a given frequency. Reversing the direction of that fundamental field thus results in a simultaneous phase switch of both electric and magnetic, nonlinearly produced, multipolar modes, preserving the generation direction.
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