semiconductor lasers, and hollow-core fibers.30,31,32,33 Higher-dimensional metamaterials or custom nanophotonic structures provide extra design “knobs” to turn to modify optical characteristics and design devices with no precedent in conventional optics. Whereas one-dimensional photonic nanostructures have long been used in commercial products in the form of Bragg reflectors, dielectric interference filters, or antireflection coatings, higher-dimensional photonic nanostructures are not easy to fabricate and require more research on process technology.

TECHNOLOGY CHALLENGES OF NANOSTRUCTURED MATERIALS

Nanostructured materials became a subject of great interest because of the promise to “tailor” materials’ innate physical properties when they are made small enough for the wave functions of electrons, phonons, or photons to be significantly confined by the structured boundaries. Control of matter on nanometer scales would allow manipulation of absorption, emission, transmission, refraction, transport, and energy conversion and storage in innovative ways that could have profound implications for many applications.

The applications of nanostructures for optoelectronic devices started when one-dimensional confinement structures, quantum wells, were demonstrated in 1974.34 Double heterostructured material with a thickness under 20 nm was shown to provide quantum confinement of electrons to alter the material’s effective bandgap energy. Today, most semiconductor diode lasers and integrated optoelectronics use quantum wells as a means to control wavelength, reduce threshold, and provide modulation. In the near future, it will be possible to extend this quantum confinement to two-dimensional (quantum wires) and three-dimensional (quantum dots, QDs) to achieve temperature-independent, ultra-low-threshold laser diodes and ultra-broadband semiconductor optical amplifiers.

In addition to changing the effective bandgap due to the quantization effect, nanostructures may enable monolithic integration of lattice-mismatched materials

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30 Block, I.D., L.L. Chan, and B.T. Cunningham. 2006. Photonic crystal optical biosensor incorporating structured low-index porous dielectric. Sensors and Actuators B: Chemical 120:187-193.

31 Park, H.G., S.H. Kim, S.H. Kwon, Y.G. Ju, J.K. Yang, J.H. Baek, S.B. Kim, and Y.H. Lee. 2004. Electrically driven single-cell photonic crystal laser. Science 305:1444-1447.

32 Allan, D.C., N.F. Borrelli, J.C. Fajardo, D.W. Hawtof, and J.A. West. 2001. Photonic Crystal Fiber. U.S. Patent 6 243 522.

33 Temelkuran, B., S.D. Hart, G. Benoit, J.D. Joannopoulos, and Y. Fink. 2002. Wavelength-scalable hollow optical fibres with large photonic bandgaps for CO2 laser transmission. Nature 420:650-653.

34 Dingle, R., W. Wiegmann, and C.H. Henry. 1974. Quantum states of confined carriers in very thin Al{x}Ga{1-x}As-GaAs-Al{x}Ga{1-x}As heterostructures. Physical Review Letters 33:827-829.



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