Features of APE waveguides in different Er:LiNbO3 and (Er + Yb):LiNbO3 cuts: electrooptical coefficient r33

Abstract Our contribution represents a systematic study of optical layers fabricated by the annealed proton exchange (APE) method in various cuts ( X , Y , Z ) of lithium niobate that was doped in bulk with erbium (500 ppm) and mixture of erbium and ytterbium in weight portion 1:9 (1000 ppm). Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA) and neutron depth profiling (NDP) methods have been used for monitoring a composition of fabricated optical layers, i.e. changes of the concentration of the rare earths (RE), hydrogen and lithium. We have used mode spectroscopy and a Mach–Zehnder interferometer to monitor the relevant properties, i.e. changes in the effective refractive index and the electrooptical coefficient r 33 . The obtained results show that during the APE process, there is no loss of the rare earths from the substrate and that during the treatment of the as-exchanged samples the hydrogen concentration increases while the lithium concentration decreases. Waveguiding properties and composition of the RE doped waveguides were not substantially changed compared with those fabricated in pristine lithium niobate. The presence of the doping ions decreases the r 33 , however, a carefully designed APE technology can increase the r 33 almost to the value of the pristine LiNbO 3 . A correlation between the uniform distribution of lithium and high values of the electrooptic coefficient r 33 was found. According to our results the proton exchange not necessarily lowers the efficiency of the 1.5 μm emission and certainly does not lower the concentration of the RE.