Temperature and strain insensitive long period gratings (LPGs) in W fibre with post-annealing

LPGs with ultra-low strain and temperature sensitivities are reported in germanosilicate fibre with a W-shaped index profile. Through low temperature annealing, the temperature and strain coefficients are dramatically reduced to dλ/dT ~ - (8.75×10 -2 ) pm/K and dλ/d epsilon ~ (2.21×10 -2 ) pm/μepsilon respectively. As a control reference, LPGs in standard SMF-28 fibre were inscribed but were not found to exhibit similar reductions in sensitivity; this illustrates that the design of the W-shaped, with its inner cladding, plays a key role in altering the LPG performance.