Vapor sensor realized in an ultracompact polarization interferometer built of a freestanding porous-silicon form birefringent film

A novel vapor sensor that uses polarization interferometry in a form birefringent porous-silicon film is introduced, analyzed, and experimentally characterized. Simulations and analysis of accuracy, versatility, stability, and control of dynamic range of the device are provided. The simulation accurately predicts the polarization interference signal, which is used to estimate the effective refractive indexes characterizing the form birefringence of a porous-silicon film with 0.001 accuracy. The device was tested for the detection of heptane concentration in a range of 342-20 000 ppm (=2.0%).