Circularly-Symmetric Grating, Surface-Emitting SemiconductorLaser

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The research team will investigate the fabrication and performance of circularly-symmetric-grating, surface-emitting (CSGSE) semiconductor lasers. The objective of the research is the development and demonstration of an AlGaAs-GaAs semiconductor laser that emits a beam with a circular cross-section. Such a laser has the potential to improve the efficiency with which light can be coupled into an optical fiber, to reduce the divergence of the emitted beam, and to serve as the basic element in a two- dimensional phase-locked array. Circular grating will be fabricated in AlGaAs-GaAs semiconductor laser structures, grown my molecular beam epitaxy, using electron-beam writing and chemically-assisted ion-beam etching. Quantum-well laser structures grown on misoriented GaAs substrates will be used to obtain the highest quality material and the lowest threshold current density possible, and to minimize the possibility of filamentary lasing. The circular grating will operate to produce oscillating laser modes in the waveguide that are radially inward- and outward-going circular waves. The use of a second-order grating will allow a circularly- symmetric beam to be coupled out of the laser through the surface. The fabrication and experimental evaluation of the laser will be accompanied and guided by theoretical analysis.