Patent ID: 7190851

Claim:
A method for sensing chemical species based on measuring a phase difference between two orthogonally polarized modes propagating in a waveguide, comprising: (a) propagating two orthogonally polarized modes of laser light differing in wavelength through a waveguide having thereon a layer of host reagent that forms inclusion complexes with a chemical species; (b) contacting the layer of host reagent with a gas to be tested for the presence of a selected chemical species; (c) transmitting a portion of each of the two modes of laser light through a polarizing analyzer after their emergence from the waveguide; (d) detecting a beat frequency of the two orthogonally polarized modes of laser light from the polarizing analyzer; (e) measuring a relative phase difference, comprising measuring a phase of the detected beat frequency relative to a phase of a beat frequency of a reference signal, the beat frequency of the reference signal comprising a difference in frequency between the two orthogonally polarized modes of laser light; and (f) detecting a chemical species by correlating the relative phase difference with a change in effective refractive index caused by inclusion of the selected chemical species in the host reagent.