High sensitivity temperature and humidity sensing based on physically deformed long-period fiber grating

In this paper, we proposed a highly sensitive temperature and humidity sensors based on two types of physically deformed long-period fiber gratings (LPFGs) which was fabricated by periodically twisting and micro-tapering single- mode fiber, also known as chiral long-period fiber grating (CLPG) and microtapered long-period fiber grating (MTLPFG), respectively. Meanwhile, the superior sensing characteristics of graphene-enhanced CLPG sensor for temperature and polyvinyl alcohol (PVA) coated MTLPFG sensor for humidity are successfully demonstrated. In the temperature experiment, due to the excellent thermal conductivity of graphene, the CLPG transmission spectrum has excellent responsiveness and linearity, and the measured temperature sensitivity is 115 pm/℃. Compared with the traditional fiber gratings, the temperature sensitivity has been significantly improved. Unfortunately, as a humidity measure, fiber grating is insensitive to humidity. Therefore, the MTLPG coated with PVA nanofilms is proposed to realize humidity sensing measurement. Due to the perfect combination of the special micro-nano structure and humidity sensitive film, this humidity sensor obtained excellent sensing sensitivity and linearity. Note that the humidity sensitivity of the PVA-coated MTLPFG has a humidity sensitivity of up to 13.27 pm/%RH. This physically deformed LPFGs are non-degradable, stable and higher sensitive, we believe that it will providing a key role in high-precision temperature and humidity sensing fields.