NANOFABRICATED 3-DIMENSIONAL PHOTONIC CRYSTALS OPERATING AT OPTICAL WAVELENGTHS

We describe the nanofabrication of the first three-dimensional (3-d) p hotonic crystals with a forbidden photonic bandgap lying in the near i nfrared region of the electromagnetic spectrum, 1.1 mu m < lambda < 1. 5 mu m, just beyond the electronic band-edge of GaAs. We fabricated th ese structures by chemically assisted ion beam etching through a trian gular hole array mask, defined by electron beam lithography on GaAs. T he 3-d forbidden photonic bandgap was spectrally tuned by 2-d lithogra phic control of the 3-d spatial periodicity. Optical transmission spec tra were generally in good agreement with microwave frequency transmis sion on centimeter scale models. Nevertheless, we find that the mid-ga p optical reflectivity is surprisingly sensitive to structural errors in the photonic crystal degrading the optical rejection from an expect ed 95% to an observed 80%. We suggest that mid-gap attenuation in the most vulnerable k-space directions, rather than overall thickness, is the relevant Figure-of-Merit for nano-scale photonic crystals.