Multi-section mode-locked semiconductor lasers

When the microwave community discusses broadband electrical amplifiers, they speak of devices with tens of GHz of bandwidth using MESFET or HEMT transistors. When the optical community discusses broadband optical amplifiers, they speak of semiconductor laser diode devices with thousands of GHz of bandwidth. This dissertation describes new methods to take advantage of the THz bandwidth in semiconductor laser amplifiers by mode-locking techniques. Mode-locked semiconductor lasers are devices that produce short optical pulses in which the pulsewidth is limited only by the tremendous bandwidth of the laser amplifiers.;This Dissertation focusses on advancements in the field of mode-locked semiconductor lasers that are the result of using laser diodes which use multiple pumping contacts instead of the single contact devices which were commonly used in previous research. With a multiple contact process, the functions of gain, gain modulation, saturable absorption, repetition rate tuning, and photodetection can be integrated together on a single monolithic chip. For repetition rates above 5 GHz (limited by fabrication technology), the entire optical cavity can be monolithically integrated together on a single chip forming a very compact source of optical pulses. The most important component in multiple segment mode-locked lasers is the saturable aborber. A large section of this dissertation is devoted to the study of the optimization of this component.;As a result of this work and that of others, the pulsewidths that are directly achievable from mode-locked lasers have dropped from 5-10 ps down to the 1-3 ps range. This will soon drop into the subpicosecond range as researchers develop phase compensation filters in the optical cavity. Mode-locked semiconductor lasers are becoming increasingly important for optical and optoelectronic applications. They will see widespread use in high-speed telecommunications systems, optoelectronic measurement systems, microwave signal generation, and distribution applications.;This dissertation takes a very practical approach to the analysis and design of mode-locked lasers. The approach is to identify those characteristics which would be important to a designer who wants to incorporate a mode-locked laser into his system. The characteristics of amplitude noise, phase noise, pulsewidth, pulse energy, optical spectral width, and repetition rate tunability of the pulse streams are measured. These characteristics are then connected to the device design parameters of segment lengths, active region design, electrical parasitics, and waveguiding characteristics so that the optimal design can be obtained.