Integration of edge emitting quantum dot laser onto silicon photonics platforms by transfer printing
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Full Text E-thesis
Date
2024
Authors
Uzun, Ali
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Publisher
University College Cork
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Abstract
Photonic integrated circuits (PICs) enable the implementation of complex optical systems with a small footprint, opening up new applications and minimising energy consumption. Similar to electronic circuits, PICs can be manufactured in foundries at decreasing costs with increased volume, following the successful trend observed in the electronics industry. Currently, the primary applications for PICs are in transceivers for the data communications industry, driven by the growing demand for higher bandwidths. This demand necessitates increased bandwidth density for server-to-server interconnects while reducing energy dissipation and costs per Gbps. However, the absence of an integrated light source imposes limitations on silicon-based photonic integrated circuits. The development of on-chip lasers that can operate at high ambient temperature with low-loss coupling to PICs is crucial. This research focusses on the development of transfer-printable InAs/GaAs quantum dot (QD) based edge-emitting lasers and their integration onto various silicon photonics platforms by micro transfer-printing (MTP). Firstly, the fabrication process flow to realise transferable QD lasers on native GaAs substrate has been developed and standardised to enable low-threshold, high-efficiency QD lasers. We deal with the development and optimisation of various processes including plasma etching of facets to obtain a smooth and vertical mirror, stress management of laser coupons, design of tethering system, and release etch process based on HCl for the AlGaAs sacrificial layer with varying Al content ranging from 90 to 95 % to release the devices from the native substrate with high selectivity. Receiver waveguides are then designed and simulated on various platforms including 220 nm SOI, 3 μm SOI and 300 nm SiN with an SU-8 spot size converter (SSC). These waveguides are optimised to achieve effective light edge coupling from the laser into the waveguides with relaxed alignment tolerance. Here, transfer printed laser diodes on Si substrate with 70 nm BCB exhibit a threshold current of 15 mA and provide an output power of more than 60 mW at an injection current of 160 mA. This implies that there is no degradation in device performance after transfer printing. The same device delivered an output power of 43 mW at 70°C in continuous-wave (CW) mode. In addition, integration of 4.5 μm thick 65 μm wide QD laser devices up to 2.4 mm long is demonstrated on the above platforms with a >95% yield. At 100 mA, waveguide coupled powers of 7.7 mW, 2.0 mW, and 1.2 mW are measured after out-coupling from the 220 nm SOI, 3 μm SOI and 300 nm SiN waveguides, respectively. The integration and optical coupling challenges and proposed solutions are discussed. This works presents a potential path for achievement of integrated light sources for silicon photonics by demonstrating the versatility of the technology with the same lasers integrated onto different waveguide platforms.
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Keywords
Silicon photonics , Heterogeneous integration , Data centers , Si waveguide , SiN waveguide , III-V semiconductor laser , Micro transfer printing , Quantum dot lasers , Edge-emitting lasers , Edge coupling
Citation
Uzun, A. 2024. Integration of edge emitting quantum dot laser onto silicon photonics platforms by transfer printing. PhD Thesis, University College Cork.