An alternative method to develop fibre grating temperature sensors using the fibre loop ringdown scheme

We present a new method to develop fibre Bragg grating (FBG)-based temperature sensors using the fibre grating loop ringdown (FGLRD) technique. With this novel approach, temperature is sensed by measuring the wavelength-dependent optical loss resulting from the temperature variations incurred in the FBG. The sensor incorporates a standard telecommunications diode laser and an inexpensive photodetector and achieves rapid temperature measurements in a time domain (measuring the ringdown time). Apparent advantages of this method over the current FBG-OSA approach include the high measurement resolution and low instrument costs. A temperature sensor (type I) using a standard off-the-shelf single-mode bare FBG as the sensing element has been developed and it achieved an absolute measurement resolution of 0.18 °C (based on 3-σ) limited by the precision of the temperature calibration source used in the experiment. To the best of our knowledge, this is the highest measurement resolution of an FBG-based temperature sensor using a standard bare FBG. Additionally, the general applicability of the method has also been evaluated by constructing a temperature sensor (type II) using a long period grating. Discussions on the advantages and limitations of the FGLRD method as compared with the current FBG-OSA scheme are presented.