Optical fiber sensor for humidity monitoring based on thermal lens detection technique

This paper proposes the construction of an optical fiber (OF) humidity sensor based on a thermal lens (TL) detection technique. The sensing head is comprised of two spherical lensed fibers (SLFs) that are assembled across from each other. A 1.48 μm wavelength multimode oscillation laser diode (fiber-out power: 100 mW) was used as the pumping laser beam to excite the TL because there is a peek for optical absorption of water in the vicinity of this wavelength. Accordingly, it was demonstrated that our TL sensor functions as a hygrometer.