A hybrid plasmonic waveguide is an

optical waveguide An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber waveguides, transparent dielectric waveguides made of plastic and glass, liquid light ...

that achieves strong light confinement by coupling the light guided by a

dielectric waveguide An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber waveguides, transparent dielectric waveguides made of plastic and glass, liquid light ...

and a

plasmonic In physics, a plasmon is a quantum of plasma oscillation. Just as light (an optical oscillation) consists of photons, the plasma oscillation consists of plasmons. The plasmon can be considered as a quasiparticle since it arises from the quan ...

waveguide. It is formed by separating a medium of high

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

(usually

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...

) from a metal surface (usually

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...

silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...

) by a small gap.

History

Dielectric waveguides use

total internal reflection Total internal reflection (TIR) is the optical phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflect ...

to confine light in a high index region. They can guide light over a long distance with very low loss, but their light confinement ability is limited by diffraction. Plasmonic waveguides, on the other hand, use

surface plasmon Surface plasmons (SPs) are coherent delocalized electron oscillations that exist at the interface between any two materials where the real part of the dielectric function changes sign across the interface (e.g. a metal-dielectric interface, such ...

to confine light near a metal surface. The light confinement ability of plasmonic waveguides is not limited by diffraction, and, as a result, they can confine light to very small volumes. However, these guides suffer significant propagation loss because of the presence of metal as part of the guiding structure. The aim of designing the hybrid plasmonic waveguide was to combine these two different wave guiding schemes and achieve high light confinement without suffering large loss. Many different variations of this structure have been proposed. Many other types of hybrid plasmonic waveguides have been proposed since then to improve light confinement ability or to reduce fabrication complexity.

Principle of operation

The operation of the hybrid plasmonic waveguides can be explained using the concept of

mode coupling In the term mode coupling, as used in physics and electrical engineering, the word "mode" refers to eigenmodes of an idealized, "unperturbed", linear system. The superposition principle says that eigenmodes of linear systems are independent of each ...

. The most commonly used hybrid plasmonic waveguide consists of a silicon nanowire placed very near a metal surface and separated by a low index region. The silicon waveguide supports dielectric waveguide mode, which is mostly confined in silicon. The metal surface supports

, which is confined near the metal surface. When these two structures are brought close to each other, the dielectric waveguide mode supported by the silicon nanowire couples to the surface plasmon mode supported by the metal surface. As a result of this mode coupling, light becomes highly confined in the region between the metal and the high index region (silicon nanowire).

Applications

Hybrid plasmonic waveguide provides large confinement of light at a lower loss compared to many previously reported plasmonic waveguides. It is also compatible with silicon photonics technology, and can be integrated with silicon waveguides on the same chip. Similar to a slot-waveguide, it can also confine light in the low index medium. Combination of these attractive features has stimulated worldwide research activity on the application of this new guiding scheme. Some notable examples of such applications are compact lasers, electro optic modulators, biosensors, polarization control devices, and thermo-optic switches.{{cite journal, authors=F. Lou, L. Thylen, L. Wosinski, editor3-first=Iñigo, editor3-last=Molina-Fernandez, editor2-first=Jiří, editor2-last=Čtyroký, editor1-first=Pavel, editor1-last=Cheben, title=Hybrid plasmonic microdisk resonators for optical interconnect applications, journal=Proc. SPIE, volume=8781, page=87810X, date=2013, doi=10.1117/12.2017108, series=Integrated Optics: Physics and Simulations, bibcode=2013SPIE.8781E..0XL , s2cid=119802655

References

Photonics Plasmonics