Patent ID: 8574920

Claim:
A method of analyzing a sample fluid containing a carrier fluid and at least one analyte, said method comprising the steps of: (a) injecting linearly-polarized light in a propagation volume of an optical waveguide having a birefringence B, said birefringence defining a polarization beat length for any given wavelength of the injected light; (b) injecting the sample fluid in a passage located adjacent to the propagation volume, the passage having a partitioning material covering an inner surface of said passage and exposed to said sample fluid, said partitioning material absorbing a part of the at least one analyte contained in said flowing sample fluid, said absorbed part interacting with an evanescent wave of the light propagating in the propagation volume, thereby affecting a polarization state of the light; (c) determining an oscillation frequency associated to a given one of the at least one analyte flowing with a characteristic migration speed over a distance corresponding to a plurality of beat lengths along the passage; (d) modulating the injection of the sample fluid periodically at the determined oscillation frequency in a manner that a plurality of zones of higher concentration of the sample fluid is created along the passage, said zones of higher concentration being spaced from each other by an integer multiple of the beat length; (e) detecting a presence of periodical variations in the polarization state of the light exiting from the propagation volume, the detection of said periodical variations at the determined oscillation frequency being indicative of a presence of the given one of the at least one analyte in the sample fluid.