Simultaneous measurements of the thermal optical and linear thermal expansion coefficients of a thin film etalon from the reflection spectra of a super-luminescent diode

An experimental determination technique for simultaneous measurements of the thermal optical and linear thermal expansion coefficients of tantalum pentoxide thin films in the infrared wavelength region is described. A tantalum pentoxide thin film deposited directly onto the end face of a single mode optical fibre is illuminated by a super-luminescent diode source and its spectrum on reflection, between 1460 and 1620 nm, is monitored at various temperatures using an optical spectrum analyser. Temperature induced change in the index of refraction and the film thickness are determined from the reflection spectrum to calculate the thermal optical and linear thermal expansion coefficients simultaneously