Modelocking pulse dynamics in fiber lasers

Abstract

Erbium-doped fibers are ideal as the basic components for lasers and amplifiers operating near 1550 nm. Consequently, considerable interest and research in the past few years has focused on the use of Erbium-doped fibers in actively and passively modelocked fiber lasers operating in both the normal and anomalous dispersion regimes. This paper presents a variety of analytic and numerical techniques which can be used to quantitatively describe the dynamic pulse formation in a passive laser cavity which includes dispersion, nonlinearity, loss, and bandwidth limited gain-saturation. The mechanisms for modelocking (e.g. quantum-well semiconductor structures, APM action, etc.) are incorporated into the modelocking models via various appropriate approximations. The models capture the fundamental intensity-dependent loss required to achieve stable modelocked operation. This generic feature of modelocked lasers will be discussed in detail and illustrated in various modelocking devices and configurations. Additionally, the characteristic differences between modelocking in the normal dispersion regime, for which highly chirped pulses are observed, and the anomalous dispersion regime, for which soliton pulses can be achieved, will be discussed. Finally, stability of the modelocked pulses will be investigated. Here we will emphasize the range of stable one-pulse per round trip operation and the instability to multi-pulse operation. For multi-pulse operation, mechanisms for harmonic modelocking such as gain- relaxation, dispersive radiation, and the acoustic effect will be discussed. In most instances, analytic methods can be utilized to gain significant insight into the laser operation and stability.