Fibre Bragg gratings with micro-engineered temperature coefficients

Abstract

Fibre Bragg gratings (FBGs) are ubiquitous as sensors for a range of parameters and also as optical components in telecommunications systems. However, their temperature dependence of around + 10 pm/°C is a limiting factor, making it challenging for sensors to discriminate strain from temperature, while telecommunications components require additional thermal stabilization. We microfabricate low loss FBGs in standard single-mode fibre, with wide control over their temperature coefficient between + 10 pm/°C and − 55 pm/°C. We also show a temperature insensitive FBG which is stable to ± 12.5 pm over a 17 to 45°C range, which is an order of magnitude reduction in sensitivity. It has only ± 3.5% reflectivity variation over this range and only 1.29 dB transmission loss. The large negative coefficient FBGs would find application in separating strain and temperature effects, as well as for thermally tunable components. Separately, the temperature insensitive FBG would have applications for strain sensing with low temperature cross-sensitivity as well as for low-cost temperature stable optical components. Moreover, the microfabrication process developed has significant potential for new classes of sensor and tunable optical devices.