980-nm-pumped Er-doped LiNbO3 waveguide amplifiers: a comparison with 1484-nm pumping

We have investigated by numerical modeling the relative efficacy of 980-nm and 1484-nm-pumped guided-wave optical amplifiers in Er-doped LiNbO₃. The shorter wavelength produces a larger differential gain, but the waveguide amplifier suffers from the photorefractive effect if no precautions are taken. Model calculations show that an optical gain of 2.5 dB/cm can be achieved at 80-mW 980-nm pump power, compared to 1.3 dB/cm when pumped at 1484 nm. Experimental results using 80 mW 980 nm give a gain of ~2.2 dB/cm (minus propagation loss). This gain, however, is degraded by photorefractive damage, which we find is not only due to the 980-nm pump light, but also to the green up-converted light, the latter having the larger effect. Several techniques were shown to reduce the photorefractive damage. ZnO indiffused waveguides in MgO-doped LiNbO₃ substrates proves to be the most effective. In bulk-doped Er:Mg:LiNbO₃ samples with ZnO waveguides, an optical gain of 1.6 dB/cm (minus propagation loss) was observed with 54 mW of out-coupled pump power