Selectively erbium (Er) doped titanium (Ti) in-diffused optical waveguide amplifiers on lithium niobate (LiNbO3) substrate have been fabricated and characterized in the wavelength regime around ? = 1.53um using counter-directional pumping at ?P = 1.48um. LiNbO3 waveguide amplifiers are desirable for providing gain in optical circuit chips through integration with other optical elements on a single substrate. A prerequisite for achieving useful gain rests on the optimization of overlap between the incident guided optical signal mode distribution and the evolving emission from excited Er ions. The extent of overlap can be controlled by adjusting fabrication parameters. Fabrication parameters for Er-doped Ti in-diffused waveguide amplifiers of useful optical gain have been optimized by diffusing selective patterns of vacuum-deposited 17nm-thick erbium film at 1100?C for 100 hours into LiNbO3, and integrating with 7um-wide single mode straight channel waveguides formed by diffusing 1070A thick titanium film into the LiNbO3. Small-signal gain characterization was carried out with a -30 dBm of transmitted input signal power at ?S=1531nm with counter-directionally launched pump power ranging between 0 to 119mW at ?P=1488nm, using TM polarization for both the signal and pump beams. At a maximum launched pump power of 119mW, a signal enhancement of 8.8dBm for 25mm-long erbium doped region, and 11.6dBm for 35mm-long erbium doped region were obtained. The corresponding calculated net gain values are 1.8dB and 2.8dB, for the 25mm-long and 35mm-long Er-doped regions, respectively.
