Efficient Er³⁺-doped optical fiber amplifier pumped by a 1.48-μm high-power laser diode

Efficient gain characteristics of the Er³⁺ -doped single-mode fiber amplifier pumped by a high-power laser diode at a wavelength of 1.48 μm are reported. The core diameter, refractive-index difference, and cutoff wavelength of the Er³⁺ -doped fiber were 6.09 μm, 0.85%, and 1.41 μm, respectively. The fiber absorption loss at 1.535 μm was approx.19.4 dB/m, and the doping concentration was approx.1370 ppm. A CW distributed feedback laser at a wavelength of 1.535 μm was used as a signal source and a high-power laser diode at 1.48 μm as a pumping source. When the absorbed pump power reaches 4.2 mW, the gain is equal to the intrinsic absorption loss for 1.8-m-long fiber. With an increase in the pump power, the gain is as high as 9.1 dB with a 1.8-m-long Er³⁺-doped fiber for an absorbed pump power of 13 mW. It is clearly shown that the Er³⁺ ions can be efficiently pumped by a high-power laser diode at 1.48 μm. The gain change is shown as a function of fiber length, where input power power is 32 mW. The absorption loss at 1.535 μm is so large that a gain longer than 1.9 m in length could not be measured. The gain in the 1.0-m-long fiber is 5.0 dB and increases to 9.5 dB in 1.9-m-long fiber. The gain is linearly proportional to the fiber length.