Grating Based Lasers for Photonic Integration and Surface Emission
Abstract: This thesis deals with the fabrication and characterization of grating-based integration-compatible semiconductor lasers. Waveguide gratings provide feedback for the laser resonators, and are used to diffract the laser output out of the waveguide for surface-emission. Beam-shaping functions, such as focusing and spot-array generation, are incorporated in the outcoupler gratings, which eliminates the need for external optics. Such lasers can be tested on wafer and monolithically integrated with other active and passive optical elements to form highly functional optoelectronic components.Two different laser geometries have been investigated. Both are designed to produce a broad, diverging, and spatially coherent output necessary for integration with high resolution beam-shaping outcouplers. The first device is a short-cavity laser with curved deep-etched distributed Bragg reflectors as feedback elements. The curvature is intended to increase the spatial mode selectivity and to reduce the lateral diffraction losses. The laser is, with its diverging output, intended for integration with an optical amplifier and a grating outcoupler for a broad-area high power output. The second device is an unstable-resonator laser which is integrated with focusing and more advanced beam-shaping outcouplers. The laser produces well defined beams which are stable with increasing drive current. A new type of multifunctional grating coupler, with simultaneously optimized feedback and outcoupling characteristics has also been integrated with the unstable-resonator laser for improved performance. Both laser designs have undergone extensive numerical simulations in order to better understand the characteristics and to improve the designs.
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