Passive modelocking of low gain soliton lasers with a saturable Bragg reflector

Solid state Cr4+:YAG and Erbium/Ytterbium doped fiber lasers are passively modelocked with a novel semiconductor saturable Bragg reflector; the first implementations of this modelocking device within these lasers and the 1550 nm spectral region. In these lasers, this device produces self-starting and extremely robust modelocked performance and delivers a considerable stability improvement relative to traditional passive modelocking methods. Compact high repetition rate cavities of both lasers are designed and. produce pulses at fundamental repetition rates as high as 1 GHz and, with the employment of soliton harmonic modelocking, as high as 5 GHz. For the Cr4+:YAG laser, this development marks the highest achieved repetition rate, both fundamental and harmonic, to date. The perturbations to the pulse within these lasers are sufficiently low that the pulse behaves as a transform-limited fundamental soliton of the average cavity parameters. This combination of low perturbation and strong soliton behavior enables the initial observation and understanding of several interesting effects that are indiscernible within most lasers. Most significantly, a stable balance between the linear birefringence and (Kerr) nonlinear birefringence of an intracavity soliton causes the polarization state of that pulse to remain fixed despite the birefringent environment. This is the initial experimental observation and characterization of this previously theoretically predicted temporal polarization "vector soliton" pulse. This low perturbation nature also facilitates the most lucid experimental observation to date of the Kerr nonlinearity induced instability of light polarized along a principal axis of a birefringence fiber. Finally, the interaction of multiple intracavity soliton pulses with the small and slow dynamics of the gain medium causes passive and stable alignment of the pulses during harmonic modelocking. An analytical model describing this interaction is devised and its predictions are compared with the observed experimental behavior.