High relative humidity sensing using gelatin-coated long period grating

Khay Ming Tan; Swee Chuan Tjin; Chi Chiu Chan; Lipi Mohanty; Chia Meng Tay

doi:10.1117/12.623607

23 May 2005 High relative humidity sensing using gelatin-coated long period grating

Khay Ming Tan, Swee Chuan Tjin, Chi Chiu Chan, Lipi Mohanty, Chia Meng Tay

Proceedings Volume 5855, 17th International Conference on Optical Fibre Sensors; (2005) https://doi.org/10.1117/12.623607
Event: 17th International Conference on Optical Fibre Sensors, 2005, Bruges, Belgium

Abstract

A long-period grating (LPG) coated with gelatin was developed as a high relative humidity (RH) sensor. The resonance dip or coupling intensity of the LPG spectrum varies with humidity while the resonance wavelength remains constant. The principle of operation of the sensor is based on the effect of an external medium, with higher refractive index than that of silica or cladding, on the LPG spectrum. Experimental investigations on the sensor yield a sensitivity of 1.2dB/%RH with an accuracy of ±0.25%RH, and a resolution of ±0.00833%RH. The LPG RH sensor also offers repeatability, hysteresis and stability errors of less than ±0.877%RH, ±0.203%RH and ±0.04%RH respectively. In addition to the characterization of the LPG RH sensor, further studies were conducted to determine the effect of grating periodicities on the sensitivity. Results show that higher-order cladding modes from smaller grating periods enable the sensor to achieve higher sensitivity to humidity. This method is proposed to be more cost effective as compared to more complex spectroscopic methods based on wavelength detection. This sensor can also help to solve problems in measuring high humidity with existing relative humidity measurement systems.

Citation Download Citation

Khay Ming Tan, Swee Chuan Tjin, Chi Chiu Chan, Lipi Mohanty, and Chia Meng Tay "High relative humidity sensing using gelatin-coated long period grating", Proc. SPIE 5855, 17th International Conference on Optical Fibre Sensors, (23 May 2005); https://doi.org/10.1117/12.623607

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