Optical fiber polarimetric chemical sensor with modulated injection of sample fluid

A chemical sensor for analyzing a sample fluid containing a carrier fluid and at least one analyte, said sensor comprising:

• a pump for pressurizing the sample fluid at a predetermined pressure;
• a modulator receiving the pressurized sample fluid and varying periodically the concentration of the sample fluid according to an injection frequency, thus giving a modulated sample fluid;
• a light source emitting linearly-polarized light;
• an optical waveguide having a birefringence B, said birefringence defining a polarization beat length for any given wavelength of said light, said optical waveguide having:
• a propagation volume having an input end and an output end, said input end receiving said linearly-polarized light, said light propagating in said propagation volume toward said output end,
• a passage located adjacent to the propagation volume and receiving the modulated sampled fluid, the sample fluid then flowing through in the passage;
• a partitioning material covering an inner surface of said passage and exposed to said flowing 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 and thereby affecting a polarization state of the light;
• an optical polarizer receiving light from the output end of said propagation volume, said optical polarizer transmitting a part of the received light that is polarized parallel to a predetermined direction, and
• an optical detector receiving light from said optical polarizer, said optical detector detecting periodical variations of the polarization state of the light at an oscillation frequency, said variations being caused by the sample fluid flowing through the passage and containing at least one analyte.