Integrated passively modelocked fiber lasers and method for constructing the same

摘要

Stable operation of an ultra-compact modelocked fiber laser generating short optical pulses generally without use of any non-fiber, intra-cavity polarization-manipulating elements is obtained by employing a saturable absorber coupled to one end of a highly-birefringent fiber serving as the laser cavity. Once the laser is modelocked in one of the polarization axes of the highly-birefringent fiber, the degeneracy of the polarization axis is eliminated and cw oscillation along the other polarization axis is also prevented. Without a polarization-dependent loss in the cavity, the modelocked polarization axis is indeterminate, i. e., modelocking can occur on either of the polarization axes. However, the introduction of only a small polarization dependent loss is sufficient to ensure the reliable start-up of modelocking on only the low- loss axis. Such a small polarization dependent loss can be introduced by tightly coiling the highly-birefringent fiber, which generates a higher loss along the fast axis; thus, reliable modelocked operation along the slow axis is obtained. Alternatively, single polarization operation is obtained by employing a saturable absorber with a polarization-dependent loss or by introducing polarization- manipulating elements external to the laser cavity.