[OPTICAL REVIEW Vol. 7, No. 3 (2000) 205-208]

A Fiber Optic Wavelength Modulation Sensor Based on Tantalum Pentoxide Coatings for Absolute Temperature Measurements

M. Naci INCI* and Toshihiko YOSHINO

Department of Electronic Engineering, Faculty of Engineering, Gunma University, 1-5-1, Tenjin-cho, Kiryu, Gunma, 376-8515 Japan

(Received October 23, 1999; Accepted March 3, 2000)

A fiber optic low-coherence sensor based on the spectral shift of tantalum pentoxide thin films for absolute temperature sensing up to 650°C is described. A tantalum pentoxide single layer was deposited directly onto the cleaved end-face of a single mode optical fibre and was illuminated with an super luminescence diode (SLD) source through a directional coupler. Interference fringes of the film on reflection were obtained within the optical bandwidth of the SLD using an optical spectrum analyser. The spectral shift versus temperature rise showed no turning points and the output was unambiguous, linear, monotonic and gave about 0.016 nm wavelength shift in the spectrum per °C. A semi-empirical calibration procedure based on the refractive index (n) and thickness (l) of the tantalum pentoxide film for absolute thermometric measurements is described.

Key words : optical fibres, temperature, sensors, tantalum pentoxide, thermal optic, thermal expansion