Femtosecond Laser Inscribed Excessively Tilted Fiber Grating for Humidity Sensing

• Published in: Sensors (Basel, Switzerland) Vol. 24; no. 2; p. 342
• Main Authors: Jing, Liqing, Liu, Bonan, Liu, Dejun, Liu, Dan, Wang, Famei, Guan, Chunying, Wang, Yiping, Liao, Changrui
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.01.2024; MDPI
• Subjects: agarose sensors; Asymmetry; Biocompatibility; Communication; Environmental monitoring; excessively tilted fiber grating sensing; femtosecond laser processing; Fiber optics; Humidity; humidity sensing; Hydrogels; Inscriptions; Lasers; Polyvinyl alcohol; Sensors; Symmetry; humidity sensing; excessively tilted fiber grating sensing; agarose sensors; femtosecond laser processing
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s24020342

We propose a humidity sensor using an excessively tilted fiber grating (Ex-TFG) coated with agarose fabricated using femtosecond laser processing. The processed grating showcases remarkable differentiation between TE and TM modes, achieving an exceptionally narrow bandwidth of approximately 1.5 nm and an impressive modulation depth of up to 15 dB for both modes. We exposed the agarose-coated TFG sensor to various relative humidity levels and monitored the resonance wavelength to test its humidity sensing capability. Our findings demonstrated that the sensor exhibited a rapid response time (2-4 s) and showed a high response sensitivity (18.5 pm/%RH) between the humidity changes and the resonant wavelength shifts. The high sensitivity, linearity, repeatability, low hysteresis, and excellent long-term stability of the TFG humidity sensor, as demonstrated in our experimental results, make it an attractive option for environmental monitoring or biomedical diagnosis.