3.3 Design and calibration of strain-insensitive FBG
temperature sensor
While designing an FBG temperature sensor, the first
consideration is how to reduce the strain effect. In this
experiment, a 10 mm-long bare FBG is inserted into a 50-
mm-long glass tube (with an inner diameter of 3 mm). The
bare FBG is pre-curled inside the tube, and both ends of the
tube are encapsulated with some potting resin/epoxy (as shown in Fig. 7). The sensor is placed in an oven for
calibration; the results show that the Bragg wavelength is
increased in a linear manner when the temperature
increased from room temperature to around 140°C (as
depicted in Fig. 8). It is observed that with every degree
Celsius change in temperature, the wavelength will shift
10 pm. The temperature resolution of this sensor is mainly
dependent on that of the FBG interrogator. For example, if
the resolution of the FBG interrogator is 1 pm (e.g.,
Micron-Optics SM325 series), with such FBG temperature
sensor, we can achieve a temperature resolution of 0.1°C.
This should be good enough for body temperature
measurement. However, further study on which body
part to attach the sensor will need to be carried out, and
necessary calibration is required to obtain accurate
absolute body temperature readings.