Photothermal induced variations in the optical transmission of a photonic band gap structure

We consider an application of the photothermal effect for the realization of an optical limiter with a photonic band gap (PBG) structure. By means of a pump–probe setup, we investigate the optical transmission of 12 periods of a ZnSe/MgF 2 PBG structure under different heating conditions. The investigated spectral range (600–700 nm) corresponds to a band edge in the transmission spectrum. The induced temperature increase is responsible for both thermal expansion of the layers and refractive index changes, thus redshifting the transmission curve by several nanometers. The initial transmission of the probe beam is restored after pump laser removal, thus indicating the reversible nature of the observed changes. The maximum transmission variation we obtained is 40% of signal at 660 nm. A theoretical reconstruction of the transmission spectra was calculated for different temperatures in order to evaluate the temperature increase ΔT corresponding to the observed shift. In order to have a confirmation, ΔT has also been measured by means of an interferometric technique. The obtained value has been found to be consistent with the theoretical predictions.