During last decade, the fast-growing communication need has promoted the development of 1.3 £gm~1.6 £gm laser light source. The Cr4+ doped YAG solid-state laser has potential to meet this broadband demand. In addition, diode-laser-pumped solid state laser has the merits of high laser beam quality, long lifetime, compact, and simple structure. In this thesis, crystal fiber was used as the laser gain medium, and coated with optical thin film at its end facets as the laser cavity. Using this configuration, the volume and cost of the laser can be appreciatively reduced, and the heat dissipation can be improved. The laser-heated-pedestal-growth method was used to grow crystal fiber, which can obtain small diameter at very fast rate. Outside the glass clad Cr4+:YAG crystal fiber, Al-Cu alloy was employed as the heat sink to improve heat dissipation. After grinding, polishing, and coating of this device, the Cr4+:YAG crystal fiber laser was fabricated. Some characteristics of Cr4+:YAG crystal fiber, such as the distribution of Cr2O3 and CaO doping concentration, fluorescence intensity, refraction index, propagation loss, and absorption coefficient were measured and analyzed. A record-low threshold of 0.75 mW was achieved. It is more than 500 times lower than any previously reported Cr4+:YAG lasers, and a slope efficiency of 6.9% was obtained. The ultralow-threshold lasing is made possible by the low propagation loss of 0.08 dB/cm and the high pump intensity of the core. Such a low-threshold operation makes the double-clad crystal fiber laser be compatible to present optical communication systems. In the meanwhile, some simulations of the laser output power have been developed to predict the experimental results.

In this thesis, we demonstrate a new type of resonant, nonlinear, light-matter interaction facilitated by the unique electromagnetic vacuum density-of-state (DOS) structure of Photonic Band Gap (PBG) materials. Strong light localization inside PBG waveguides allows extremely strong coupling between laser fields and embedded two-level quantum dots (QD). The resulting Mollow splitting is large enough to traverse the precipitous DOS jump created by a waveguide mode cutoff. This allows the QD Bloch vector to sense the non-smoothness of the vacuum structure and evolve in novel ways that are forbidden in free space. These unusual strong-coupling effects are described using a "vacuum structure term" of the Bloch equation, combined with field-dependent relaxation rates experienced by the QD Bloch vector. This leads to alternation between coherent evolution and enhanced relaxation. As a result, dynamic high-contrast switching of QD populations can be realized with a single beam of picosecond pulses. During enhanced relaxation to a slightly inverted steady state at the pulse peak, the Bloch vector rapidly switches from anti-parallel to parallel alignment with the pulse torque vector. This then leads to a highly inverted state through subsequent coherent "adiabatic following" near the pulse tail, providing a robust mechanism for picosecond, femto-Joule all-optical switching. The simultaneous input of a second, weaker (signal) driving beam at a different frequency on top of the stronger (holding) beam enables rich modulation effects and unprecedented coherent control over the QD population. This occurs through resonant coupling of the signal pulse with the Mollow sideband transitions created by the holding pulse, leading to either augmentation or negation of the final QD population achieved by the holding pulse alone. This effect is applied to ultrafast all-optical logic AND, OR and NOT gates in the presence of significant (0.1 THz) nonradiative dephasing and (about 1%) inhomogeneous broadening. Further numerical studies of pulse evolutions inside the proposed devices demonstrate satisfactory population contrast within a PBG waveguide length of about 10 micro meter. These results provide the building blocks for low-power, ultrafast, multi-wavelength channel, on-chip, all-optical computing.

In this thesis, we demonstrate a new type of resonant, nonlinear, light-matter interaction facilitated by the unique electromagnetic vacuum density-of-state (DOS) structure of Photonic Band Gap (PBG) materials. Strong light localization inside PBG waveguides allows extremely strong coupling between laser fields and embedded two-level quantum dots (QD). The resulting Mollow splitting is large enough to traverse the precipitous DOS jump created by a waveguide mode cutoff. This allows the QD Bloch vector to sense the non-smoothness of the vacuum structure and evolve in novel ways that are forbidden in free space. These unusual strong-coupling effects are described using a "vacuum structure term" of the Bloch equation, combined with field-dependent relaxation rates experienced by the QD Bloch vector. This leads to alternation between coherent evolution and enhanced relaxation. As a result, dynamic high-contrast switching of QD populations can be realized with a single beam of picosecond pulses. During enhanced relaxation to a slightly inverted steady state at the pulse peak, the Bloch vector rapidly switches from anti-parallel to parallel alignment with the pulse torque vector. This then leads to a highly inverted state through subsequent coherent "adiabatic following" near the pulse tail, providing a robust mechanism for picosecond, femto-Joule all-optical switching. The simultaneous input of a second, weaker (signal) driving beam at a different frequency on top of the stronger (holding) beam enables rich modulation effects and unprecedented coherent control over the QD population. This occurs through resonant coupling of the signal pulse with the Mollow sideband transitions created by the holding pulse, leading to either augmentation or negation of the final QD population achieved by the holding pulse alone. This effect is applied to ultrafast all-optical logic AND, OR and NOT gates in the presence of significant (0.1 THz) nonradiative dephasing and (about 1%) inhomogeneous broadening. Further numerical studies of pulse evolutions inside the proposed devices demonstrate satisfactory population contrast within a PBG waveguide length of about 10 micro meter. These results provide the building blocks for low-power, ultrafast, multi-wavelength channel, on-chip, all-optical computing.

Narrow silicon nanowires host a rich set of physical phenomena. Understanding these phenomena will open new opportunities for applications of silicon nanowires in optoelectronic devices and adds more functionality to silicon especially in those realms that bulk silicon may not operate remarkably. Compatibility of silicon nanowires with the mainstream fabrication technology is also advantageous. The main theme of this thesis is finding the possibility of using silicon nanowires in light sources; laser and light emitting diodes. Using Tight Binding (TB) and ab-initio Density Functional Theory (DFT) methods it was shown that axial strain can induce significant changes in the effective mass, density of states and bandgap of silicon nanowires. Generality of the observed effects was proven by investigating nanowires of different crystallography, diameter and material (e.g. germanium nanowires). The observed direct to indirect bandgap conversion suggests that strain is able to modulate the light emission properties of silicon nanowires. To investigate this possibility, spontaneous emission time was formulated using perturbation theory including Longitudinal Optical (LO) and Acoustic (LA) phonons. It was observed that corresponding to bandgap conversion, the spontaneous emission time can be modulated by more than one order of magnitude. This emanates from bandgap conversion and symmetry change of wave function in response to strain. A mechanism for population inversion was proposed in the thesis which is based on the Ensemble Monte Carlo (EMC) study of carrier statistics in direct and indirect conduction sub bands. By calculating all possible electron-phonon scattering mechanisms which may deplete the already populated indirect subband, it was shown that at different temperatures and under different electric fields there is a factor of 10 difference between the population of indirect and direct sub bands. This suggests that population inversion can be achieved by biasing an already strained nanowire in its indirect bandgap state. The light emission is possible then by releasing or inverting the strain direction. A few ideas of implementing this experiment were proposed as a patent application. Furthermore the photo absorption of silicon nanowires was calculated using TB method and the role of diameter, optical anisotropy and strain were investigated on band-edge absorption.

Narrow silicon nanowires host a rich set of physical phenomena. Understanding these phenomena will open new opportunities for applications of silicon nanowires in optoelectronic devices and adds more functionality to silicon especially in those realms that bulk silicon may not operate remarkably. Compatibility of silicon nanowires with the mainstream fabrication technology is also advantageous. The main theme of this thesis is finding the possibility of using silicon nanowires in light sources; laser and light emitting diodes. Using Tight Binding (TB) and ab-initio Density Functional Theory (DFT) methods it was shown that axial strain can induce significant changes in the effective mass, density of states and bandgap of silicon nanowires. Generality of the observed effects was proven by investigating nanowires of different crystallography, diameter and material (e.g. germanium nanowires). The observed direct to indirect bandgap conversion suggests that strain is able to modulate the light emission properties of silicon nanowires. To investigate this possibility, spontaneous emission time was formulated using perturbation theory including Longitudinal Optical (LO) and Acoustic (LA) phonons. It was observed that corresponding to bandgap conversion, the spontaneous emission time can be modulated by more than one order of magnitude. This emanates from bandgap conversion and symmetry change of wave function in response to strain. A mechanism for population inversion was proposed in the thesis which is based on the Ensemble Monte Carlo (EMC) study of carrier statistics in direct and indirect conduction sub bands. By calculating all possible electron-phonon scattering mechanisms which may deplete the already populated indirect subband, it was shown that at different temperatures and under different electric fields there is a factor of 10 difference between the population of indirect and direct sub bands. This suggests that population inversion can be achieved by biasing an already strained nanowire in its indirect bandgap state. The light emission is possible then by releasing or inverting the strain direction. A few ideas of implementing this experiment were proposed as a patent application. Furthermore the photo absorption of silicon nanowires was calculated using TB method and the role of diameter, optical anisotropy and strain were investigated on band-edge absorption.