High-power ultrashort external cavity modelocked semiconductor lasers.

摘要

The objective of this thesis is to generate high power ultrashort optical pulses using external cavity modelocked semiconductor lasers for commercial applications including high speed telecommunications, the large scale printing, 3-D display, confocal microscopy, low coherence optical tomography, nonlinear spectroscopy and femtosecond time-resolved spectroscopy.; The ultrafast dynamics of each individual optical element in the cavity are measured to study their contribution to modelocking. The key physical processes involved with the modelocked operation of external cavity semiconductor lasers are self phase modulation (SPM) and gain saturation of the semiconductor optical amplifier (SOA), the absorption saturation of a saturable absorber and the group velocity dispersion (GVD) caused by linear elements in cavity. In this thesis, it is experimentally proved that the integrating SPM of the SOA leads to a parabolically chirped asymmetric temporal pulse shape, while the linearization of the chirp is obtained by the combined effects of the GVD and the saturable absorption. By using these experimental results, a theoretical model is developed to predict the pulse shaping effects of external cavity modelocked semiconductor lasers. Finally, this theoretical model is supported by a computer simulation.; To address the technical and physical issues associated with high power generation, a novel semiconductor optical amplifier design using the inverse bow-tie shaped geometry was introduced to realize a high power modelocked laser system. The salient feature of employing this structure is that one can achieve the high output powers characteristic of tapered structures while maintaining a small amount of astigmatism. With the development of these devices, an external cavity laser was designed, built and experimentally characterized for CW and modelocked operation. Hybrid modelocked operation produced optical pulses with an average output power of 400 mW and temporal width of ∼6 ps.; Finally, novel intracavity spectral shaping techniques were introduced in an effort to generate ultra short optical pulses. Pulses with a substantially broad optical spectrum were generated as a result of the spectral shaping technique. The spectral phase of these pulses were characterized and compensated through various techniques. As a result, optical pulses with a temporal duration of 250 fs were generated, which is only 10% exceeding the transform limit.