Porous silicon optical microcavities

Porous silicon optical microcavities are 1D photonic bandgap structures that reflect light at specific frequencies. The color of reflected light depends in part on the refractive index (n) of substances that fill the porous volume. This principle is exploited in designing biosensor and drug delivery devices. The figure shows an SEM image of a porous silicon surface superimposed on a baseline and shifted optical spectrum. Porous silicon optical microcavity sensors exhibit a large color change when exposed to ethanol (n= 1.3614) displacing air (n= 1.0000) from the pores.