Refraction

About: Refraction is a research topic. Over the lifetime, 9712 publications have been published within this topic receiving 141743 citations.

Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction

Abstract: Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat’s principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces.

Optical and retinal factors affecting visual resolution.

Abstract: If a scene containing fine spatial detail is viewed at constant high photopic luminance, there are two main factors which limit the perception of the fine detail-the quality of the optics of the eye forming the image on the retina and the ability of the retina (coupled to the brain) to resolve the details of that image. In the past there have been many theoretical studies of the potential resolving power of the optics based on consideration of diffraction and the chromatic and spherical aberrations of the eye. It is only recently that objective measurements of the quality of the optics of man in vivo have been obtained (Flamant, 1955; Westheimer & Campbell, 1962; Krauskopf 1962; R6hler, 1962). As will be demonstrated, it is not possible to use these findings to determine the relative weighting that should be given to the optics and the retina in determining a given threshold. This paper reports the results of experiments using an improved version of the well-known interference fringe technique (Le Grand, 1937; Byram 1944; Westheimer, 1960; Arnulf & Dupuy, 1960) which theoretically allows a sinusoidal pattern of very high contrast to be formed directly on the retina. The practical difficulty in using this technique is to obtain a light source of high intrinsic brightness and coherence with which to form high-luminance interference fringes on the retina; this has been solved by using a neon-helium gas laser. By decreasing the contrast (Fig. 1) of the interference fringes with another source of light it was possible to determine the contrasts on the retina at which the fringes are just detected. Thus a measure of the resolving power of the retina-brain is obtained without prior modification by the optics of the eye. Measurements have also been made of the visual resolution of external gratings whose intensity varied sinusoidally with distance across the gratings and which were imaged on to the retina by the optical components of the eye. By comparing the threshold contrasts of these external sinusoidal gratings with thresholds for sinusoidal fringes of the same spatial frequency formed through interference, the quality of the

Gradient-index meta-surfaces as a bridge linking propagating waves and surface waves

Abstract: The arbitrary control of electromagnetic waves is a key aim of photonic research. Although, for example, the control of freely propagating waves (PWs) and surface waves (SWs) has separately become possible using transformation optics and metamaterials, a bridge linking both propagation types has not yet been found. Such a device has particular relevance given the many schemes of controlling electromagnetic waves at surfaces and interfaces, leading to trapped rainbows, lensing, beam bending, deflection, and even anomalous reflection/refraction. Here, we demonstrate theoretically and experimentally that a specific gradient-index meta-surface can convert a PW to a SW with nearly 100% efficiency. Distinct from conventional devices such as prism or grating couplers, the momentum mismatch between PW and SW is compensated by the reflection-phase gradient of the meta-surface, and a nearly perfect PW-SW conversion can happen for any incidence angle larger than a critical value. Experiments in the microwave region, including both far-field and near-field characterizations, are in excellent agreement with full-wave simulations. Our findings may pave the way for many applications, including high-efficiency surface plasmon couplers, anti-reflection surfaces, light absorbers, and so on.

Broadband Light Bending with Plasmonic Nanoantennas

Abstract: The precise manipulation of a propagating wave using phase control is a fundamental building block of optical systems. The wavefront of a light beam propagating across an interface can be modified arbitrarily by introducing abrupt phase changes. We experimentally demonstrated unparalleled wavefront control in a broadband optical wavelength range from 1.0 to 1.9 micrometers. This is accomplished by using an extremely thin plasmonic layer (~λ/50) consisting of an optical nanoantenna array that provides subwavelength phase manipulation on light propagating across the interface. Anomalous light-bending phenomena, including negative angles of refraction and reflection, are observed in the operational wavelength range.