Depolarization of a randomly distributed plasmonic meander metasurface characterized by Mueller matrix spectroscopic ellipsometry

Electronically Controlled Time-Domain Integral Average Depolarizer Based on a Barium Titanate (BTO) Metasurface

A depolarizer, a kind of optical element that converts polarized light to unpolarized light, has been found massive applications in classical optics. However, depolarizers based on metasurface which can be applied in integrated optics have rarely been proposed. In this paper, an electronically controlled metasurface depolarizer is demonstrated based on the time-domain integral average method and nano-material barium titanate. It obtains emergent light with a degree of polarization reduced to 2.5% when hit by linearly polarized light at 633 nm, and has a transmission efficiency greater than 72%. This depolarizing metasurface can be designed on-demand, immunizing the degree of the emergent light from its size, and has the simple electronic control with high-speed response.

Perfect depolarization in single scattering of light from uncorrelated surface and volume disorder

We demonstrate that single scattering of p-polarized waves from uncorrelated surface and volume disorder can lead to perfect depolarization. The degree of polarization vanishes in specific scattering directions that can be characterized based on simple geometric arguments. Depolarization results from a different polarization response of each source of disorder, which provides a clear physical interpretation of the depolarization mechanism.

Ultra-compact visible light depolarizer based on dielectric metasurface

With rapid development towards shrinking the size of traditional photonic systems such as cameras, spectrometers, displays and illumination systems, there is an urgent need for high performance and ultra-compact functional optical elements. The large footprint of traditional bulky optical elements, their monofunctional response and the inability for direct integration into nanophotonic devices have severely limited progress in this area. Metasurfaces, consisting of an array of subwavelength nanoscatterers with spatially varying geometries, have shown remarkable performance as ultrathin multifunctional optical elements. Here, based on an all-dielectric metasurface, we propose and experimentally demonstrate a spatial domain optical depolarizer capable of efficiently depolarizing linearly polarized light in the visible spectral band from 450 nm to 670 nm, with a degree of polarization of less than 10 %. Remarkably, it is capable of depolarizing light beam with a diameter down to several micrometers, about two orders of magnitude smaller than commercial liquid crystal depolarizers. Furthermore, the long response time, bulky footprint, tight optical alignment tolerance and large pixel size severely limit the performance and system integration of commercial depolarizers. We envision the metasurface depolarizer to find applications in next generation ultra-compact grating spectrometers and illumination systems.

Cascaded plasmonic superlens for far-field imaging with magnification at visible wavelength

We experimentally demonstrate a novel design of a cascaded plasmonic superlens, which can directly image subwavelength objects with magnification in the far field at visible wavelengths. The lens consists of two cascaded plasmonic slabs. One is a plasmonic metasurface used for near field coupling, and the other one is a planar plasmonic lens used for phase compensation and thus image magnification. First, we show numerical calculations about the performance of the lens. Based on these results we then describe the fabrication of both sub-structures and their combination. Finally, we demonstrate imaging performance of the lens for a subwavelength double-slit object as an example. The fabricated superlens exhibits a lateral resolution down to 180 nm at a wavelength of 640 nm, as predicted by numerical calculations. This might be the first experimental demonstration in which a planar plasmonic lens is employed for near-field image magnification. Our results could open a way for designing and fabricating novel miniaturized plasmonic superlenses in the future.

Physical interpretation of Mueller matrix spectra: a versatile method applied to gold gratings

The interaction of nanostructures, periodic or random, with polarized light creates very rich physics where scattering, diffraction and absorbance are linked to a variety of dispersive modes and coupling effects. Each of these excitations depends strongly on polarization, angle of incidence, azimuthal orientation of the sample and wavelength. The entire optical response can be obtained, independently from any model, by measuring the Mueller matrices at various k-vectors over a broad frequency range. This results in complex data hiding the underlying physics. Here we present a simple but versatile method to identify the physical properties present in the Mueller matrices. This method is applicable to a wide variety of photonic and plasmonic samples. Based on the simple example of a one-dimensional gold grating where the optical response is characterized not only by diffraction but also by a complex mixing of polarization, we present a very general procedure to analyze the Mueller matrix data using simple analytical tools. The calculated Mueller matrix contour plots obtained from an effective anisotropic layer model are completed by the presence of plasmonic modes, Rayleigh-Woods anomalies and the interband transition absorbance. A comparison of the so-constructed contour plots with the measured ones satisfactorily connects the optical properties of the grating to their physical origin. This straightforward procedure is very general and will be powerful for the analysis of complex optical nanostructures.