A novel class of fluid sensors is proposed based on monitoring the optical
properties of multi-section chiral sculptured thin films (STFs) that functi
on as spectral reflection holes. Using a nominal model that treats a chiral
STF as a two-phase composite material with locally biaxial dielectric prop
erties, we predict that the presence of a fluid in the porous film results
in a red-shift of the spectral holes. Several device operation modes are pr
oposed, and their relative merits are compared. Proof-of-concept experiment
s with both circularly polarized and unpolarized incident light confirm the
red-shift of the spectral holes, and demonstrate operation in a practical
situation. (C) 2001 Elsevier Science B.V. All rights reserved.