Multistage, codoped fiber amplifiers generate high-power signals
Investigators from AT&T Bell Laboratories (Murray Hill, NJ), SDL (San Jose, CA), and Polaroid (Cambridge, MA) have demonstrated a three-stage configuration of diode-pumped 1.5-mm erbium/ytterbium (Er/Yb) fiber amplifiers with up to 4-W output. Cladding-pumped neodymium-doped fiber lasers--producing up to 5 W at 1.064 µm--were used as pump sources. The ytterbium codopant absorbs the 1.064-µm pump light in the Er/Yb-fiber-amplifier gain medium. A single-stage amplifier, pumped by a fiber laser operating in a counterpropagating configuration, produced 1.5 W of 1.56-µm light from a pump power of 3.8 W. Adding a second counterpumped amplifier stage, with a pump reflector copumping the first stage, produced 2.5-W output from 7.8 W of pump power. This arrangement was used for a digital systems test of 2.5-Gbit/s free-space optical-link transmission and resulted in only a 0.3-dB penalty in power at the receiver from the amplifier.
In a third stage, pumped by a counterpropagating fiber laser, 4.04 W of output power was achieved when the total pump power was 12.6 W. Optical conversion efficiency from 1.06 to 1.5 µm was 47% for the third stage and 33% overall. No saturation of the amplifier output was noted up to the 4-W level. High-power amplifiers at this wavelength have applications including long-distance repeaterless communication and satellite links, split-fiber architectures and nonlinear optical switching, laser radar, and lidar-based remote sensing.