  We report fabrication of THz fiber Bragg gratings (TFBG) using CO2 laser
inscription on subwavelength step-index polymer fibers. A fiber Bragg grating
with 48 periods features a ~4 GHz-wide stop band and ~15 dB transmission loss
in the middle of a stop band. The potential of such gratings in design of
resonant sensor for monitoring of paper quality is demonstrated. Experimental
spectral sensitivity of the TFBG-based paper thickness sensor was found to be ~
-0.67 GHz / 10 um. A 3D electromagnetic model of a Bragg grating was used to
explain experimental findings.
