Application of thermo-optic beam control in GaAs-based edge emitters

Edge-emitting GaAs-based diode lasers and amplifiers are a fundamental technological concept for manufacturing efficient, high-power, coherent light sources. Their emission wavelength spans from 620 nm to 1180 nm and is tuneable via the integrated quantum well configurations within the emitter. With these features, they are used in numerous applications ranging from metrological to direct material processing scenarios. While their capabilities in the matter of light generation and amplification are undisputed, other technological approaches deliver the possibilities of an increased functional density on a chip level. In the context of photonic integrated circuits, other platforms such as silicon or glass have shown great advances in the recent decade. The motivation of this work is to increase the capabilities of GaAs-based emitters by utilizing the already existing vertical structures and implementing additional adaptive optical elements. An enhanced functional scope enables direct access to applications previously reserved for other technological platforms or complex macroscopic optical setups. Many mechanisms are well established to alter the optical landscape within a semiconductor device dynamically. In this work, the impact of temperature changes on an optical medium's refractive index is used to actively control light within a device. Known as the thermo-optical effect, it allows a large amplitude of refractive index modulation with moderate power input, making it suitable for adaptive on-chip applications. To gain a thorough understanding of the thermal impact on light propagation on the one hand and explore possible applications on the other hand, this work is separated into two main parts. 1. The basic behavior of light propagation under localized heat impact within edge emitters is the subject of the first part. For localized heat sources, metallized areas, described as heater stripes, are processed on top of the devices and in the vicinity of the vertical waveguide. A passive vertical structure is designed to assess the optical capabilities of the created thermal profile. It preserves the typical optical properties of an active vertical structure with its optical slab waveguide properties but dispenses the use of quantum wells. Hence, the thermal impact on the horizontal waveguiding can be studied without unintended side effects, such as elevated light absorption. In this part, straight and bent heater stripes are investigated. Based on straight heater stripes, thermal waveguiding is demonstrated for the first time in GaAs-based devices. The experimental results are supported by multi-physical simulations addressing the microscopic behavior of the created thermal waveguides and evaluating their transversal modal properties. Bend heater stripes are utilized to investigate the limits of thermal waveguiding and study bend losses under variations of bend offset and heat input. 2.The key findings of the first part are applied to part two. Here, an established vertical structure for high-power applications emitting light at1120 nm is combined with top-side heater stripes. Two use cases are investigated in detail to demonstrate the capabilities of thermo-optical elements. First, heater stripes are used to alter the propagation direction of light as it emerges from a semiconductor device. Referred to as beam steering, a parametric study supported by simulations is conducted and demonstrates steering angles over \SI{14}{\degree} per direction in the horizontal plane while maintaining near diffraction limited beam quality. The achieved steering angle, together with modulation frequencies greater than 0.6 kHz, demonstrate unmatched performance in optical on-chip steering solutions opening applications in LIDAR or other scanning tasks. Second, the developed heater elements are introduced to tapered edge-emitting amplifiers (TPAs). Here, the thermal-induced refractive index profile is used to counteract the TPA intrinsic, variable astigmatism of the emerging beam, a feature that, when unattended, limits the use cases of tapered devices. The underlying microscopic mechanisms are evaluated by experiment and simulation. In a preferable device layout, an astigmatism compensation was realized for the majority of the typical TPA operation range. While the adaptive optical element shows significant optical capabilities, the beam quality and power output of the amplifier reveal low alteration compared to standard TPAs without adaptive thermal elements. The enhanced TPAs are thereby suitable for former unconsidered applications, where power variations in later applications are intended. For example, fiber coupling scenarios or direct pumping of nonlinear crystals can profit now from the adaptive thermal lensing concept. With the results of this thesis, the benefit of precise thermal input to edge emitters becomes evident. With careful device design, a multitude of functions can be integrated into GaAs-based edge emitters. Both in-depth investigated layouts, supporting beam steering and working as a tunable lens, demonstrate two possible use cases. However, studies on purely thermal waveguiding especially show the limitations of the proposed concept and stress the need to apply thermo-optical elements within suitable circumstances. The knowledge gained within this work gives the fundamentals for future advanced light-emitting laser diodes and amplifiers on a GaAs basis.