An evanescent filed based sensor uses a detector for sensing variations in properties
of a fluid flowing in a boundary layer adjacent to the detector. The detector comprises
an optical waveguide in the form of an optical fiber having a core layer covered
by a cladding layer and having a substantially D-shaped cross section defining
a planar surface with an optical grating pattern thereon. When a beam of laser
light is directed through the detector as an input, variations in an output of
the beam of laser light are indicative of changes in fluid pressure or density
in the boundary layer or immediate region adjacent to the grating of the optical waveguide.
