A silicon-based fibre-optic temperature sensor

A temperature sensor based on the absorption properties of an indirect semiconductor has potentially superior properties to one based on a direct semiconductor such as GaAs or CdTe. Preliminary results are reported on a simple pointwise, single-ended, fibre-optic sensor utilising a 10 mu m layer of single-crystal silicon as the temperature-sensitive material. Measurements in the range 20-180 degrees C indicate that with a single wavelength (GaAs LED centred at 950 nm) the discrimination of the device is +or-0.2 degrees C with an accuracy of about 4 degrees C. Errors are believed to arise from thermal strains in the sensor-head materials. With an antireflection coating on the Si layer a discrimination of +or-0.12 degrees C was achieved. Specific methods of improving the measurement range, accuracy and resolution are pointed out.