Amplification and transmission at 1.53-1.55 μm with Er³⁺-doped fibers

Efficient optical amplification in an Er³⁺-doped fiber pumped with an InGaAsP laser diode at 1.48 μm is discussed. Er amplifiers can be used not only as low-noise preamplifiers but also as power amplifiers. Optical solitons can thus be amplified. Pump wavelength dependences on the gain coefficient of the Er amplifier using 1.48- and 0.98-μm band tunable sources are discussed. The Er³⁺-doped fiber amplifier can be used in soliton communication. It is shown that it is possible to amplify picosecond and subpicosecond soliton pulses with Er fiber since the gain recovery time of the amplifier is on the order of milliseconds, which means that the saturation is determined by the average input power, not the soliton peak power. Therefore, there is none of the patterning effect, which occurs when a laser amplifier diode is used. The major results for soliton amplification and transmission are reviewed. The amplification of a 20-GHz soliton train and wavelength-division multiplexing (WDM) solitons are also considered. The preemphasis technique for soliton transmission with an Er amplifier over long distances is discussed. An N = 1 soliton with relatively high amplitudes (1.2 < A < 1.4), which is used as an input soliton, plays an important role in a lumped gain soliton amplification system. The initial soliton pulse width can be preserved after propagation over long distances despite fiber loss.