ABSTRACT
In this chapter, the authors provide humidity measurement-related parameters and the advantages of the fiber sensor for humidity sensing over the conventional electronic sensors. Optical fiber sensors (OFS) is suitable for use as the sensing instrument for applications in extraordinary and harsh environments, such as in civil engineering structures, high-voltage and biomedical instrumentation, mining environments, and agriculture ecosystems. Humidity sensors are among the applications of OFS that have been intensively studied by many researchers to cater to the high specific demand of the sensing industry. The authors introduce a simple sealed-void photonic crystal fiber interferometric humidity sensor that operates in reflection mode and is insensitive to temperature condition. The electronic humidity sensors are typically available for less than $10, which are the most low-cost sensors in the market. This low-cost fiber-optic humidity sensor uses a silica film as a coating through a solgel process and enhances the sensitivity of the sensor by doping the silica film with a methylene blue.
