Fibre Bragg grating gas temperature sensor with fast response

Abstract

We investigated the use of a fibre Bragg grating as a gas temperature sensor under dynamic conditions. Simulations indicated that the time response of the device is determined by heat conduction from the surface of the cladding to the fibre core where the grating is located, and from the core to the cladding if the outside temperature is lowered. These calculations also indicated that the response could be improved by an order of magnitude through thinning of the cladding by chemical etching. The transient stresses induced in the fibre due to the temperature distribution in the fibre are supportive to improving the temperature response of the sensor. The sensor was tested experimentally by oscillating it at variable frequency from stationary ambient air across a column of heated air flowing vertically upwards. It was confirmed experimentally that the response of this sensor improved monotonically with decrease in cladding diameter to better than 10 Hz for a 14 µm cladding diameter.