Infrared Radiation Detection With Matched Fiber Bragg Gratings

In this letter, a novel infrared (IR) radiation detector is proposed for early fire detection. It consists of two matched apodized fiber Bragg gratings (FBGs) cascaded in a single optical fiber and separated by a few centimeters. One of the gratings is covered with an IR-absorbing layer that converts the radiation into heat while the second FBG provides a temperature reference. To obtain a fast and cost-effective detector, the demodulation technique consists in measuring the total reflected power, which monotonically evolves in a range of flux that depends on the FBGs spectral characteristics. With the 24-mm-long Gaussian apodized FBGs used in this work, we report a mean sensitivity of 7 nW/(W/m²) in the range 0-3000 W/m².