Photonic summation and memory devices for photonic digital-to-analog conversion, neuromorphic photonics on-chip, and flat-optical beam forming.
Open AccessThis dissertation presents a comprehensive study on the development and optimization of Integrated Photonic Digital-to-Analog Converters (DAC), Photonic Random-Access Memories (P-RAM), highly integrated photonic tensor cores, and reconfigurable focusing and defocusing meta lenses, with a focus on their applications in efficient data processing and imaging[1].The first part of the research introduces a novel coherent parallel photonic DAC concept along with a 4-bit experimental prototype capable of performing this DAC without optic–electric–optic domain crossing. This new paradigm guarantees a linear intensity weighting among bits when operating at high sampling rates (50 GHz), featuring an exceptional sampling efficiency (> 100 GS) and small footprint (≈1 mm2) in an 8-bit implementation. Importantly, this photonic DAC enables seamless interfaces of next-generation data processing hardware with high relevance in data centers, task-specific compute accelerators such as neuromorphic engines, and network edge processing applications. The second part of the research explores the design and implementation of a multi-state electrically programmed low-loss non-volatile photonic memory based on a broadband transparent phase change material (Ge2Sb2Se5, GSSe). The memory, demonstrated on a silicon-on-insulator platform, features efficient amplitude modulation and an ultra-low insertion loss, showing a 100x improved signal to loss ratio compared to other phase-change-materials based photonic memories. The robustness of this material and device is validated through a half-a million cyclability test. This low-loss photonic retention-of-state adds a key feature for photonic functional and programmable circuits impacting many applications including neural networks, LiDAR, and sensors. The final part of the research demonstrates an electrically driven tunable meta lens in the telecom range by exploring the full potential of a low absorption loss and high refractive index contrast PCM alloy, Sb2Se3, to realize non-volatile, reversible, fast focusing and defocusing meta lens in the 1550 telecom spectral range. With a fixed geometric design, the phase change material of Sb2Se3 switches the focusing length of a silicon photonic meta lens between two different values nonviolently. This unique functionality of the hybrid meta surface is attributed to the fact that the silicon’s refractive index is in the middle of the two convertible states in the optical phase change material. The transparency of Sb2Se3 in both states enables near phase-only meta surface structures. This work represents a critical advance towards the development of integrable dynamic meta lens and their potential for beamforming applications. The dissertation concludes with a discussion on the potential future directions of this research, including the exploration of other phase change materials for photonic memories, the optimization of the integrated photonic tensor core architecture for more complex image processing tasks, and the further development and application of photonic DACs and reconfigurable meta lenses.
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