Concentric-Circle Grating, Surface-Emitting Semiconductor Waveguides and Distributed Feedback Lasers: Properties and Propagation of Highly Directional, Azimuthally Polarized Radiation.
This thesis explores, both theoretically and experimentally, the radiation properties of concentric-circle grating, surface-emitting optical waveguides and semiconductor lasers. The concentric-circle grating, through a distributed feedback process, defines a circular, two-dimensional resonant cavity, couples together the circular resonator modes, and diffracts these modes to the radiation field. A laser employing this type of circular grating should emit a well-confined, circularly symmetric beam. Two types of electrically pumped, concentric-circle grating, surface-emitting, semiconductor lasers were fabricated and tested. Results indicate that a buried, full (extending from the origin outward) circular grating, distributed feedback structure has greater potential for producing a well-confined, symmetric laser beam, than does a surface-located, annular grating, distributed Bragg reflector design. Optically pumped concentric-circle grating lasers were fabricated, and shown to produce slowly diverging (<1^circ),^ectrally narrow (<1 A), azimuthally polarized radiation that is circularly symmetric in cross-section. Two perturbative approaches, the field expansion method and the volume current method, are used to predict the directionality, polarization, and shape of the radiation emitted by concentric -circle grating structures, to relate these properties to grating and material parameters, and to define the relationship between the radiation field and the guided modes. These investigations showed that a second-order grating, matched to the lowest transverse electric mode supported by the structure, produces a highly directional, azimuthally polarized, circularly symmetric, surface-emitted beam. A desire to describe the free-space propagation of symmetric, azimuthally polarized beams led to the formulation of the azimuthal paraxial scalar wave equation. The solution to this equation is comprised of a plane wave propagation factor, multiplied by a Bessel function of the first kind, order one, and a Gaussian factor, and is named the azimuthal Bessel-Gauss beam. The device-specific perturbative approaches and the azimuthal Bessel-Gauss beam predict radiation patterns which show good qualitative agreement with far-field patterns emitted by a concentric-circle grating, surface-emitting semiconductor laser.
- Pub Date:
- January 1995
- Physics: Optics; Engineering: Electronics and Electrical