High-sensitivity temperature-independent force sensor based on PS-LPFG formed by inserting a microbend

A unique phase-shifted long period grating (PS-LPFG) is proposed and demonstrated by means of fabricating a microbend in the center of LPFG written by CO₂ laser. Experiments demonstrate that this PS-LPFG can be used to develop a promising high sensitive force sensor by measuring the wavelength separation between the two resonance loss dips. Moreover, the wavelength separation is insensitive to the external temperature. The force sensitivity of the PS-LPFG with a bending radius 2.62 mm is measured to be up to -186.74 nm N^-1, which is enhanced two orders compared to the LPFG without a microbend.