Novel form birefringence modeling for an ultracompact sensor in porous silicon films using polarization interferometry

The optical form birefringence in porous silicon films is measured by analyzing the transmitted interference intensity of a polarization interferometer. A novel form birefringence model called "boundary condition (BC) model" for porous materials is introduced and evaluated experimentally against samples of porous silicon films. The variation of optical indexes of refraction vs the porosity in silicon films agrees with the calculated values of n_o/n_e within 1% error using the BC model, in contrast to the ∼15% error using effective medium approximation model.