Compared to single-mode VCSELs, multimode VCSELs have not received much attention in models and characterizations for functional parameters, despite making up the majority of commercially available VCSELs [1]. In particular, the extraction of the linewidth enhancement factor for multimode VCSELs has been overlooked, likely due to difficulties in measurement. Additionally, multimode models for VCSELs have, until recently, omitted spectral characteristics such as linewidth [2]. This is the first work to report a measured linewidth enhancement factor value (lower bound) for a multimode VCSEL. A characterization for the functional parameters of a red multimode vertical-cavity surface-emitting laser (VCSEL) is shown herein. The extracted values form a complete working set of parameters for the laser rate equations. The techniques employed for extracting values include frequency responses, power versus current fittings, and optical spectral measurements. From the frequency responses at various bias currents, the relaxation oscillation frequency and damping factor are found. The power versus current curve is fitted to find parameters including the modal spontaneous emission rate and carrier density at threshold. The spectral measurements are used for evaluating the linewidth enhancement factor (LEF) also known as the alpha factor or Henry factor. These 5 methods have been applied previously to characterizing single-mode VCSELs [3]–[5]. The experimentally extracted parameters herein are important for creating accurate models and simulations for multimode VCSELs. Improved multimode VCSEL models are necessary for improving optical communication, especially for short-range optical interconnects [2]. The measured parameters for the characterized VCSEL are comparable to similar single-mode VCSELs characterized in other works. This is promising because multi-mode VCSELs have higher output power than their single-mode counterparts, thus these results may aid in improving short-range optical interconnects.

This thesis reports an experimental characterization of the ultrafast gain and refractive index dynamics of a novel InAs/InGaAsP/InP quantum-dot (QD) semiconductor optical amplifier (SOA) operating near 1.55-µm wavelengths, assessing its high-speed performance characteristics for the first time. The thesis also studies the influence of the degree of quantum confinement on the dynamics of SOAs by comparing the zero-dimensional (0-D) QD's dynamics to those in 1-D InAs/InAlGaAs/InP quantum-dash (QDash), and 2-D InGaAsP/InGaAsP/InP quantum-well (QW) SOAs, both of which also operate near 1.55-µm wavelengths, and are made with matching or similar materials and structures. The ultrafast (around 1 ps) and long-lived (up to 2 ns) amplitude and phase dynamics of the SOAs are characterized via advanced heterodyne pump-probe measurements with 150-femtosecond resolution. It is found that the QD SOA has an 80-picosecond amplitude, and 110-picosecond phase recovery lifetime in the gain regime, 4-6 times faster than the QDash and QW recovery lifetimes, as well as reduced ultrafast transients, giving it the best properties for high-speed (> 100 Gb/s) all-optical signal processing in the important telecommunications wavelength bands. An impulse response model is developed and used to analyze the dynamics, facilitating a comparison of the gain compression factors, time-resolved linewidth enhancement factors (alpha-factors), and instantaneous dynamic coefficients (two-photon absorption and nonlinear refractive-index coefficients) amongst the three structures. The quantum-dot device is found to have the lowest effective alpha-factor, 2-10, compared to 8-16 in the QW, as well as time-resolved alpha-factors lower than in the QW—promising for reduced-phase-transient operation at high bitrates. Significant differences in the alpha-factors of lasers with the same structure are found, due to the differences between gain changes that are induced optically or through the electrical bias. The relative contributions of stimulated transitions and free-carrier absorption to the total carrier heating dynamics in SOAs of varying dimensionality are also reported for the first time. Examining the QD electroluminescence and linear gain spectra in combination with the carrier dynamics also brings about conclusions on the nature of the quantum confinement, dot energy-level structure, and density of states—aspects of the material that have not been previously well understood.

This thesis reports an experimental characterization of the ultrafast gain and refractive index dynamics of a novel InAs/InGaAsP/InP quantum-dot (QD) semiconductor optical amplifier (SOA) operating near 1.55-µm wavelengths, assessing its high-speed performance characteristics for the first time. The thesis also studies the influence of the degree of quantum confinement on the dynamics of SOAs by comparing the zero-dimensional (0-D) QD's dynamics to those in 1-D InAs/InAlGaAs/InP quantum-dash (QDash), and 2-D InGaAsP/InGaAsP/InP quantum-well (QW) SOAs, both of which also operate near 1.55-µm wavelengths, and are made with matching or similar materials and structures. The ultrafast (around 1 ps) and long-lived (up to 2 ns) amplitude and phase dynamics of the SOAs are characterized via advanced heterodyne pump-probe measurements with 150-femtosecond resolution. It is found that the QD SOA has an 80-picosecond amplitude, and 110-picosecond phase recovery lifetime in the gain regime, 4-6 times faster than the QDash and QW recovery lifetimes, as well as reduced ultrafast transients, giving it the best properties for high-speed (> 100 Gb/s) all-optical signal processing in the important telecommunications wavelength bands. An impulse response model is developed and used to analyze the dynamics, facilitating a comparison of the gain compression factors, time-resolved linewidth enhancement factors (alpha-factors), and instantaneous dynamic coefficients (two-photon absorption and nonlinear refractive-index coefficients) amongst the three structures. The quantum-dot device is found to have the lowest effective alpha-factor, 2-10, compared to 8-16 in the QW, as well as time-resolved alpha-factors lower than in the QW—promising for reduced-phase-transient operation at high bitrates. Significant differences in the alpha-factors of lasers with the same structure are found, due to the differences between gain changes that are induced optically or through the electrical bias. The relative contributions of stimulated transitions and free-carrier absorption to the total carrier heating dynamics in SOAs of varying dimensionality are also reported for the first time. Examining the QD electroluminescence and linear gain spectra in combination with the carrier dynamics also brings about conclusions on the nature of the quantum confinement, dot energy-level structure, and density of states—aspects of the material that have not been previously well understood.