A Fundamental Limit on Subwavelength Guided Waves

Abstract

Abstract-A fundamental relation between the cross sectional confinement of an arbitrary mode of a general waveguide and its propagation length is found. It is shown that due to material loss of the waveguide, the propagation length shrinks as the confinement of the mode increases. Normalized second central moment of magnetic energy density in the cross section plane of the waveguide is used as a measure of mode size and it is found that for a given mode size, there is a limit for the waveguide propagation length. This limit depends solely on permittivity of the waveguide material and its surrounding medium. As an application, this result provides a lower bound for propagation loss in subwavelength optical confinement in plasmonic waveguides which are of special interest for their nano-meter mode dimensions.

Fundamental limits on the losses of phase and amplitude optical actuators

“…For instance, plasmonic waveguides systematically suffer from large losses, especially in the visible and near‐infrared spectral ranges, which are of interest for communications . This does not occur by chance, since the field confinement and the propagation losses are connected by a fundamental relation involving solely the properties of the plasmonic material, and hence of noble metal optical constants . The presence of fundamental limits in optics, however, does not only concern guiding elements: considering intensity modulators, it has been recently highlighted that, when graphene is the active material, the insertion loss of the overall device is substantially governed by the graphene conductivity tensor, according to an inequality proved for planar, multilayered devices embedding conducting sheets .…”

Transparent Dielectric Metasurfaces for Spatial Mode Multiplexing

“…Many designs and functionalities of metasurfaces suggested so far are based largely on plasmonic planar structures; [13] however, most of these metasurfaces demonstrate low efficiencies in transmission due to losses in their metallic components. In contrast, all-dielectric metasurfaces are based on lattices of subwavelength resonant dielectric elements [14] that allow avoiding absorption losses, enhancing substantially the overall efficiency of planar metaoptics [15][16][17][18][19][20] making all-dielectric metasurfaces a promising platform for diverse applications in optical communications.…”

“…Indeed, in the past we have seen demonstrations of metasurfaces combining functionalities of a lens and a beam deflector, or a lens and a polarization converter. [16] Thus, a single metasurface can combine functionalities of beam collimator, mode converter, and beam deflector if necessary. In addition, provided that metasurfaces can be directly fabricated on optical fiber facets, [22] they allow for ultimate miniaturization and integration of the spatial mode multiplexing/demultiplexing setups.…”

Paper-based plasmonic nanosensor monitors environmental lead pollution in real field

“…28 Here, we calibrated our device from 0 to 600 ppm, which covers a sufficiently good range for Pb monitoring in the air as well as areas where much higher amounts of Pb (up to 1000 ppm) can be found, such as sediments and industrial waste. 29 Herein, we have chosen AgNPs as plasmonic nanosensors due to their tuneable LSPR properties even if dropcast on a paper substrate. The nanosensor embedded in the paper substrate showed a significant selective colorimetric response to Pb in its ionic form.…”