A photonic bandgap (PBG) silicon structure confines light to within a small volume by scattering from a periodic array of scattering centers. Developed first for microwave radiation, the PBG structure has been extended to infrared (IR) light by researchers at the Massachusetts Institute of Technology (Cambridge, MA). They created a strip of silicon 0.47 µm wide, with 0.10-µm-radius holes 0.42 µm apart, that blocks light from about 1.3 to 1.7 µm. By introducing a defect into the PBG structure, such as a break in the periodicity of the holes in the silicon strip, a break can be formed in this wavelength range. A single hole gap of 0.63 µm produced a wavelength gap of about 400 nm, with a resonance wavelength of 1.56 µm, a quality factor Q (l/Dl) of 265, and a modal volume of 0.055 µm3, that is, the photonic crystal acts as a filter allowing the transmission of light at 1.56 µm—an important wavelength for fiberoptics—but eliminating light at nearby wavelengths.
The PBG waveguide microcavity might be used in spontaneous-emission-enhancement devices such as resonant-cavity light-emitting diodes and could, according to the researchers, lead to development of zero-threshold laser devices and efficient erbium-doped-silicon light emitters.