Date of Award
Doctor of Philosophy (PhD)
Electrical and Computer Engineering
Photonic integrated circuits (PICs) are devices that integrate multiple photonic functions on a small chip and allow for accurate dimension control and massive production. Similar to electronic integrated circuits, PICs can significantly reduce the system cost, size, weight, and operation power (CSWaP). Recently, the PIC technology has transformed many optical technologies which traditionally rely on tabletop systems and bulky components, such as optical interconnects, nonlinear optics, and quantum photonics, into a chip-scale platform. This device and system miniaturization has successfully led to a wide range of practical applications in computing, sensing, spectroscopy, and communication. However, the traditional passive PIC platform lacks efficient gain media or source components.
Hybrid integration, which combines different material systems on a single chip, is a promising candidate to overcome the limitation of the traditional passive PIC platform. By integrating III-V semiconductor chips with passive PICs, it is possible to enhance the functionality of PICs and create novel miniaturized laser systems. III-V semiconductor gain chips are generally favored for hybrid photonic integration due to their small footprint, low cost, and high electrical-to-optical conversion efficiency. There are various approaches to obtain hybrid integration, including direct epitaxy growth, edge coupling, and wafer/die bonding. Hybrid integration by edge coupling provides a simple solution that avoids the material lattice mismatch problem presented by the direct epitaxy approach because the active chips and passive chips can be fabricated, optimized, and thermal controlled independently. In addition, by using silicon nitride material in this hybrid platform, the transparency window can be extended below 1 um, which makes it possible to combine visible and near infrared laser sources through the III-V/Si3N4 hybrid integration.
Laser combining systems have many emerging applications, such as integrated nonlinear optics, remote sensing, free space communication, infrared countermeasure, and light detection and ranging (LIDAR). The traditional approaches of laser combining include coherent beam combining (CBC) and wavelength beam combining (WBC). CBC is phase sensitive, which is suited to applications that require single wavelength operation. The difficulty of this technique is that the relative phase of all lasers needs to be operated within a small fraction of a wavelength. On the contrary, WBC usually relies on diffraction gratings or spectral filters to spatially overlap beams from different lasers which operate at different wavelengths. The main advantage of WBC is that it does not require accurate phase control and can scale to many array elements. These laser beam combining techniques (CBC or WBC) usually require free space or fiber optical components, leading to bulky and complex systems. In this thesis, we provide a chip-scale WBC system based on the hybrid integration of Reflective Semiconductor Optical Amplifiers (RSOA) and Arrayed Waveguide Grating (AWG), which demonstrated a four-channel combining system with watt-level output.
To explore the gain component for the passive PIC, we provide a Hook-Shape Semiconductor Optical Amplifiers (HSSOA) design to overcome the alignment challenge introduced by the traditional Traveling-wave Semiconductor Optical Amplifiers (TSOA), which requires two-sides edge-coupling and accurate thickness control to avoid vertical mode mismatch. The flip chip bonding of these two-facet TSOAs require extra markers and well-designed submounts to obtain good alignment between multiple components in a high-density integration. The proposed HSSOA design can be easily extended with multiple gain sections in one chip, which is convenient for high-density photonic integration. The Euler bend design used in the HSSOA cavity helps decrease the coupling loss between the bending waveguide and straight waveguide. By applying multiple etch depths inside the HSSOA cavity, we can maintain a small footprint for the whole device and avoid high-order modes in the straight waveguide region. We realize an unidirectional ring laser through the integration of the hook-shape SOA and the Taiji ring resonator.
Multiple gain components in a single chip might be one option for future work, which provides additional gain/power for the III-V/Si3N4 hybrid integration platform.
Zeng, Siwei, "Hybridly Integrated Semiconductor Lasers and Amplifiers on III-V/SI3N4 Platform for Beam Combining and Other Advanced Applications" (2023). All Dissertations. 3454.
Author ORCID Identifier