| A semiconductor laser is a diode device that emits light via stimulated emission. Conventionally, light emitted from a semiconductor laser is spatially coherent or narrowband. The fundamental mechanism of stimulated emission process in general leads only to a single wavelength emission. However, there are some lasers emit light with a broad spectrum or different distinct wavelength subjected to various operating conditions such as external grating configuration with semiconductor laser, diode-pumped self-Q-switch fiber laser, ultrashort pulse excitation, photonic crystal fiber, ultrabroadband solid-state lasers, semiconductor optical amplifier-based multiwavelength tunable fiber lasers, nonlinear crystal, broadband semiconductor laser etc. This type of broadband laser is vital in many practical applications such as optical telecommunications, spectroscopy measurement, imaging technology, etc.Recently, an ultra-broadband semiconductor laser that utilizes intersubband optical transitions via quantum cascade configuration has been realized. Laser action with a Fabry-Perot spectrum covering all wavelengths from 6 to 8 microm simultaneously is demonstrated with this approach. More recently, broadband emission results from interband optical transitions via quantum-dot/dash nanostructures have been demonstrated in a simple p-i-n laser diode structure. To date, this latest approach offers the simplest design by proper engineering of quantized energy states as well as utilizing the high inhomogeneity of the dot/dash nanostructures, which is inherent from self-assembled growth technology.In this dissertation, modeling of semiconductor InGaAs/GaAs quantum-dot broadband laser utilizing the properties of inhomogeneous and homogeneous broadening effects on lasing spectral will be discussed, followed by a detail analysis of another type of broad interband semiconductor laser, which is InAs/InGaAlAs quantum-dash broadband laser. Based on the device characterization results, broad interband laser emission is found to be originated from multiple families of quantum-dash ensembles in addition to multiple orders of subband energy levels within a single quantum-dash ensemble. Therefore, a novel technique is proposed and implemented successfully to enhance the lasing bandwidth of the quantum-dash broadband laser at postgrowth condition. Moreover, the design, growth and measurements of quantum-dash partial laser structures utilizing different epitaxial parameters are initiated to study the origins of unique lasing mechanism in broadband quantum-dash lasers. The measurement results support the postulation of the presence of multiple families of quantum-dash ensembles with different sizes across multiple stacking layers of quantum-dash/quantum-well/barrier and depict the importance of barrier width in controlling the stimulated emission bandwidth. These results lead to an important approach for future development to realize a single semiconductor laser diode that emits light in broad and continuous spectrum profile over more than 150 nm bandwidth. |
