Respiratory monitoring via a nanoporous film-coated tilted fiber Bragg grating humidity sensor

A humidity sensor for respiratory monitoring based on a tilted fiber Bragg grating (TFBG) functionalized with a nanoporous coating consisting of titanium carbide (Ti₂C) and fullerene (C₆₀) is proposed. By incorporating the C₆₀ into Ti₂C, a nanocomposite film with abundant three-dimensional porousness is coated on the TFBG surface. The nanocomposite film with strong hygroscopicity and desorption properties is highly sensitive to environmental humidity variations, where the induced refractive index changes of the coating result in the spectral responses of TFBG multi-resonances. Experimental results show that the sensitivity of the sensor is as high as 0.055 dB/%RH in the relative humidity range of 10-90%RH with the response and recovery time of 0.59 and 0.91 s, respectively. Furthermore, the humidity sensor was successfully used to perform in vivo respiratory monitoring of the humans.