RBS MEASUREMENT OF DEPTH PROFILES OF ERBIUM INCORPORATED INTO LITHIUM-NIOBATE FOR OPTICAL AMPLIFIER APPLICATIONS

Rutherford Backscattering Spectrometry (RBS) was used for the determin ation of Er3+ concentration profiles in locally doped lithium niobate. The doped layers are the basic substrates for the fabrication of opti cal waveguiding structures which may be utilized as planar optical amp lifiers and waveguiding lasers making use of the I-4(13/2) --> I-4(15/ 2) transition in Er3+ which falls into the third low loss telecommunic ation window (1.5 mu m). We present a new aproach of fabrication of lo cally doped lithium niobate single crystal wafers. The doping occurs u nder moderate temperature (similar to 350 degrees C) from reaction mel ts containing ca. 10 wt% of erbium nitrate, The erbium content in part icular cuts varies dramatically between ca. 3 at.% in the Y- and Z-cut up to 20 at.% in the X-cuts. Erbium ions are localized in a 50 nm thi ck layer, but they can be diffused deeper into the substrate by subseq uent annealing at 350 degrees C. The Er concentrations of the samples doped at moderated temperature are compared with the Er concentrations of the samples doped by a standard high-temperature diffusion (> 1000 degrees C) from evaporated metal layers. To utilize the Er doped subs trates in integrated optic circuits high quality waveguides must be su bsequently fabricated. For that we used the Annealed Proton Exchange ( APE) method with adipic acid. For the actual fabrication of the wavegu ides the following order of operation should be kept: the erbium dopin g should be done before the APE because the substantially changed stru cture of APE layers prevents the doping process. The APE process is ch ecked by measurements of lithium depth profiles by Neutron Depth Profi ling (NDP). (C) 1998 Elsevier Science B.V.