A method to modulate the local optical properties of porous silicon photonic crystals is reported. The porous silicon
photonic crystals are fabricated by electrochemical etching in a hydrofluoric acid-based electrolyte. Local oxidation was
performed using either a UV lamp or 532 nm laser to irradiate selective regions of the photonic crystal. The sample was
then soaked in an alcohol solution. Unmasked regions of the porous silicon photonic crystal exhibited significant
spectral degradation and loss of the microcavity resonance. The region of the porous silicon photonic crystal protected
by the oxide exhibited no significant changes in the reflectance spectrum. This simple photolithographic technique can
be used to fabricate a variety of spatially localized silicon-based structures such as photonic bandgap mirrors, optical
filters, waveguides and optical switches.