C17 Commission on Quantum Electronics
R. E Slusher
Nanometer scale features are becoming increasingly important for both new optical materials and light guiding structures. Recent material advances include semiconductor quantum dots and electro-optic polymers. Semiconductor quantum dots range in size from 1 to 10 nm. The luminescent emission wavelength emitted from quantum dots depends on the dot size because the electron of holes are confined to a volume smaller than their natural (exciton) binding volume in bulk material. This allows tuning diode lasers and LEDs based on quantum dot emission. The interaction between light and the quantum dots is enhanced due to the increased overlap of the electron and hole wavefunctions in the confined volume and the higher density of states in the zero dimensional dots. Examples of quantum dot materials include InAs, PbTe, CdSe and InGaAs. Silicon quantum dots efficiently emit radiation near 900nm wavelengths and may provide enough gain for optical amplifiers and laser sources that could be fabricated using CMOS compatible processing. Electro-optic polymers are similar to semiconductor quantum dots. An organic chromophore, used as a dopant in the polymer, with high emission efficiency and or large electro-optic coefficient plays the role of the semiconductor quantum dot.
A number of interesting phenomena remain to be explored in quantum dots. For example, electromagnetically induced transparency and slow light propagation should be possible in quantum dots where the emission line broadening is dominated by the fundamental spontaneous emission rates. Quantum dots in semiconductor micro-resoantors should exhibit many of quantum electrodynamic phenomena that have been demonstrated for single atoms.
High index contrast photonic crystals and total internal reflection structures also require attention to spatial scales in the nanometer regime. Dimensions for Bragg gratings, photonic crystals, optical waveguides and micro-resonators are in the range from 200 nm to 5 microns. The edge roughness of these high index contrast structures must be controlled to the level of a few nanometers in order to avoid scattering losses that ruin the resonator Q values and cause large propagation losses.
Optical fibers are being developed with a wide variety of micro-structured cores and claddings. As with the micro-resonators the dimensions of the micro-features must be controlled at the nanometer level. New composite structures and nanostructured materials will play an important role in he future of optical fiber.
Interesting new physics remains to be explored in nonlinear photonic crystals. These nonlinear studies require very large optical nonlinearities, hopefully much larger than those available today. One interesting possibility for enhancing nonlinear interactions is to introduce nanoscale resonant structures into nonlinear materials. For example, metallic plasmon resonances can be coupled to optical modes in a Kerr nonlinear material by introducing a periodicity of the order of a few hundred nanometers in the metal surface or by using periodic metallic nano-dots or nanowires.
Applications for nanophotonics are increasingly interesting and important. They promise chip level integration of thousands of optical devices along with high-speed electronics. This next generation of opto-electronic chips may play a major role in integrating the advantages of optical transport with the processing and storage capabilities of electronics for applications in the optical interconnect field. For example, one application may be an optical packet router chip with a throughput of 2 Tb/s.
Quantum dot lasers are already being fabricated that have the potential to displace quantum well lasers since they can be electrically modulated without the frequency chirp that is inherent in quantum well lasers.
Polymer materials doped with nanostrucutred semiconductors or organic chromophores have potential for fabrication on silicon-based chips where they could serve as optical sources, electro-optic modulators or optical switches. The low cost and simplicity of fabrication using spin on techniques is a major advantage for polymer-based nanophotonics.