Nanostructure of Technology for Making Photonic Crystals

California Institute Of Technology, Pasadena CA

Investigators

Abstract

The past rapid emergence of optical microcavity devices, such as Vertical Cavity Surface Emitting Lasers (VCSELs) [1] can be largely attributed to the high precision over the layer thickness control available during semiconductor crystal growth. High reflectivity mirrors can be grown with sub-nanometer accuracy to define high=Q cavities in the vertical dimension. Recently, it has also become possible to microfabricate high reflecti-vity mirrors by creating two- and three-dimensional periodic structures. These periodic "photonic crystals" can be designed to open up frequency bands within which the propagation of electromagnetic waves is forbidden irrespective of the propagation direction in space and define photonic bandgaps [2,3]. When combined with high index contrast slabs in which light can be efficiently guided, microfaricated two-dimensional photonic badgap mirrors provide us wit the geometries needed to confine light into extremely small volumes [4,5]. 2-D Fabry-Perot resonators wit hmicrofabricated mirrors are formed when defects are introduced into the photonic bandgap structure. It is then possible to tune these cavities lithographically by changing the precise geometry of the microstructures surrounding the defects. Surprisingly, we have found that small cavities consisting of single defects in a two-dimensional photonic bandgap crystal can still exhibit high Q values, and we have calculated, by finite-difference time-domain (FDTD) modeling, Qs in the range of 25,000 [6]. When real cavities are measured in absorbing semiconductor material, Q values ain excell of 1500 are measured. We have shown, as part of our previous NSF contract, that these high Qs make it now possible to define microcavity lasers [7] which functio at room temperature [8], with mode volumes as small as 2.5 (l/2nslab)3, or 0.03 um3 in InGaAsP emitting at 1.55 um.