Plasmonics
[11] While gate lengths of CMOS nodes used for electrical circuits are ever decreasing, the size of conventional PICs is limited by diffraction, thus constituting a barrier for further integration.
Researchers are attempting to reduce losses in surface plasmon propagation by examining a variety of materials, geometries, the frequency and their respective properties.
[19] Finally, emerging applications of plasmonics for thermal emission manipulation [20] and heat-assisted magnetic recording [21] leverage Ohmic losses in metals to obtain devices with new enhanced functionalities.
[30][31] Dissipation losses accompanying SPP propagation in metals can be mitigated by gain amplification or by combining them into hybrid networks with photonic elements such as fibers and coupled-resonator waveguides.
[30][31] This design can result in the previously mentioned hybrid plasmonic waveguide, which exhibits subwavelength mode on a scale of one-tenth of the diffraction limit of light, along with an acceptable propagation length.
In one instance, the interaction of two light beams of different wavelengths was demonstrated by converting them into co-propagating surface plasmons via cadmium selenide quantum dots.
Specifically, electro-optic modulators have been designed using evanescently coupled resonant metal gratings and nanowires that rely on long-range surface plasmons (LRSP).
[39] Likewise, thermo-optic devices, which contain a dielectric material whose refractive index changes with variation in temperature, have also been used as interferometric modulators of SPP signals in addition to directional-coupler switches.
Some thermo-optic devices have been shown to utilize LRSP waveguiding along gold stripes that are embedded in a polymer and heated by electrical signals as a means for modulation and directional-coupler switches.
Many passive elements such as prisms, lenses, and beam splitters can be implemented in a plasmonic circuit, however fabrication at the nano scale has proven difficult and has adverse effects.
[11] Another method used to create compact photonic components relies on CPP waveguides as they have displayed strong confinement with acceptable losses less than 3 dB within telecommunication wavelengths.
