Resonant THz sensor for paper quality monitoring using THz fiber Bragg gratings

TL;DR

This paper demonstrates the fabrication of THz fiber Bragg gratings on polymer fibers and explores their potential as resonant sensors for monitoring paper quality, specifically paper thickness.

Contribution

It introduces a novel fabrication method for THz fiber Bragg gratings and demonstrates their application as sensitive paper thickness sensors.

Findings

Fabricated TFBGs exhibit a ~4 GHz stop band and 15 dB transmission loss.

Spectral sensitivity of the sensor is approximately -0.67 GHz per 10 micrometers of paper thickness.

A 3D electromagnetic model explains the experimental spectral sensitivity results.

Abstract

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.