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J.G.FLEMING, SHAWN-Yu LIN Sandia National Laboratories, Albuquerque NM 87185, [email protected]

ABSTRACT Three-dimensional photonic lattices have been fabricated in the infrared using a combination of advanced silicon processes. The structures display bandgaps centered at 12j. and 1.551i. INTRODUCTION The drive for miniature photonic devices has been hindered by our inability to tightly control and manipulate light. Moreover, photonics technologies are typically not based on silicon and, up till now, only indirectly benefited from the rapid advances being made in silicon processing technology. In this work, we overcome some of the disadvantages of silicon inherent in its electronic structure through the use of a 3-D silicon photonic lattice. This advance has been made possible through a combination of integrated circuit fabrication technologies and may enable the development of entirely new Si photonic devices. The ability to confine and control light in three dimensions would have important implications for quantum optics and quantum-optical devices: the modification of blackbody radiation, the localization of light to a fraction of a cubic wavelength, and thus the realization of single-mode light-emitting diodes, are but a few examples [1-3]. Photonic crystals- the optical analogues of semiconducting crystals- provide a means of achieving these goals. The photonic band structure results when light encounters a well-controlled

repeating arrangement of materials with differing refractive indexes. This behavior is entirely independent of the electronic properties of the material making up the lattice, as long as it does not strongly adsorb. When correctly designed and fabricated, such structures can exhibit the property that photons with the bandgap energy may not penetrate the lattice, regardless of their angle of incidence. The existence of photonic bandgaps was proposed over a decade ago by Yablonovitch (currently of UCLA) and was quickly demonstrated at millimeter wavelengths using macroscopic repeating structures made of alumina rods [1-2]. However, since the critical dimensions of the lattice scale with the wavelength of the light, a reduction in wavelength to the infrared requires structures with minimum feature sizes on the order of a micron. As a result, fabrication difficulties have stymied research in this area. DESIGN

The first ever silicon 3-D photonic crystal yielding a photonic bandgap at infrared wavelengths, 10-15p, has been created at Sandia [4]. The design that we have fabricated was proposed by researchers at Iowa State University [5-8] and consists of a series of dielectric rods all aligned parallel to each other with a pitch equal to roughly half the

615 Mat. Res. Soc. Symp. Proc. Vol. 557 © 1999 Materials Research Society

wavelength of the mid point of the bandgap. The next layer is laid on top of, and orthogonal to, the first. The third level is aligned parallel with the first, but translated by a distance equal to half the pitch. The fourth level is parallel to the second, but is aga