Gradient-index nanophotonics

Abstract

It is demonstrated that a new kind of low-loss surface electromagnetic wave may propagate along a planar surface inside a lossy medium if the medium permittivity changes continuously across such surface. Similar to surface plasmons, the wavelength of this wave may be considerably shorter than the light wavelength in free space, which may enable its applications in super-resolution microscopy and nanolithography techniques. However, unlike plasmonics-based nanophotonic devices, which are typically built using a very limited number of low loss optical materials, the newly found class of surface waves may be supported by a much broader range of lossy media. Such materials as graphite seems to be ideal in UV nanophotonics applications. On the opposite side of the electromagnetic spectrum, similar long-range surface electromagnetic radio waves are capable of propagating underwater along a sandy seabed, which may enable efficient underwater radio communication and imaging.

Electromagnetic Wave Propagation Through Stratified Lossy Conductive Media

“…1(b)) and these rocks and soils typically have ε ′′ ≫ ε ′ at radio frequencies, using our theoretical results it may become possible to greatly improve spatial resolution and ground penetrating performance of the ground penetrating radar (GPR) techniques. Our findings may also enable novel super-resolution microscopy techniques and lower-loss electromagnetic metamaterial designs working across such previously inaccessible frequency ranges as deep UV, in which all the conventional optical materials suffer from very large losses [12]. Compared to the earlier results reported in [3,12] where the propagation length of the surface waves remained similar (or even below) the skin depth, the findings reported here are quite novel and striking, since several analytically solvable model distributions of ε(z) have been found which give rise to electromagnetic waves propagating in highly lossy media over distances which greatly exceed the conventional skin depth.…”

Roadmap on Label‐Free Super‐Resolution Imaging

“…However, consideration of a "more physical" situation in which the electric permittivity (or conductivity) of a material changes continuously across some gradual interface, leads to appearance of a new class of deeply subwavelength surface waves. [582,583] It appears that low-loss surface electromagnetic waves may exist at planar gradual interfaces between lossy media, even if the dielectric losses are very high on both sides of the interface. This very recent and highly unexpected result seems to be applicable to most any electromagnetic frequency range from the very low frequencies (VLF) of radio waves all the way up to the UV light.…”

“…We anticipate that this may be accomplished by using the newly discovered class of surface electromagnetic waves which propagate along gradual interfaces of lossy optical media. [582,583]…”

Surface electromagnetic waves in lossy media for environmental sensing applications

“…1b, which is mostly affected by the gradient terms, will look essentially similar. The only necessary condition for such modes to exist is that the loss tangent should not change considerably across the interface [8]. Therefore, TM polarized SEW solutions must also exist in the highly lossy dielectric cases in the UV range, which is quite typical for almost all known optical materials.…”