Fabrication and analysis of enhanced thermal stability and high-sensitivity turnaround point long-period fiber grating

This paper presents a what we believe is a novel method to fabricate turnaround point long-period gratings (TAP-LPGs) possessing enhanced thermal stability and high sensitivity. It is shown by analysis and by experiment that LPG resonance in photosensitive fibers can be controlled partially by UV fluence and thermal annealing. TAP-LPGs with enhanced thermal stability were fabricated by following three steps: (I) finding grating period versus writing UV fluence for TAP operation; (II) writing gratings at a relatively higher period with higher fluence, in which case the resonance is out of phase; (III) controlled annealing so that the postannealed LPG operates at/near TAP. The thermal stability is enhanced. The average temperature sensitivity of dual peak resonance measured for a typical TAP-LPG in the temperature interval of 70°C-240°C is about 2.3 nm/°C. This study will be useful for the development of high temperature TAP-LPG sensors.