Large scale integrated slow-light silicon photonic devices for rf-photonic applications

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Anderson, Stephen, Raymond
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Electronic thesis
Electrical engineering
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The integrated circuit (IC) has come to occupy a ubiquitous space in our daily lives, as thekey component of our cellphones and global telecommunications infrastructure. Less visible to the public are the fiber-optic components which enable long-haul communications and inter-connectivity within data centers. Recent decades have seen the emergence of photonic integrated circuits (PICs), which combine the benefits of fiber-optics into conventional ICs using high-index contrast materials. In turn, there has been a large research effort to produce integrated photonic components to manipulate light on-chip in useful ways. This dissertation focuses on silicon metastructure waveguides, and the slow-light effect they support, which can be applied to a variety of radio-frequency photonic (RF-Photonic) applications. Slow-light gratings are analyzed using plane-wave expansion, transfer-matrix, and finite-difference time domain methods. Coupling methods to improve transmission into the slow-light grating, through apodization, mode-transition gratings, and inverse-design techniques, are explored. Slow-light gratings are fabricated at the Specialty Electronic Materials and Sensors cleanroom at the Army Research Laboratory, and through a foundry service provided by the American Institute of Manufacturing Integrated Photonics (AIM Photonics). The slow-light phenomenon allows for an enhanced light-matter interaction, which further reduces device footprint on-chip, improves modulation efficiency, and can lead to densely integrated, low driving voltage modulators for data center applications. The theory and characterization of foundry-fabricable slow-light enhanced silicon Mach-Zehnder modulators (SLMs) are presented, with a focus on analog performance assessed by the spur-free dynamic range (SFDR). The modified transfer function of a slow-light grating phase-shifter allows for device linearization when other methods, such as doping optimization, are limited through a foundry fabrication process. A 5th-order accurate MZM model is derived. A SLM with a slope-efficiency enhancement of 2.18 and an SFDR of 113.2 dB/Hz2/3 is demonstrated. Thermo-optic splitters provide power balancing to optimize the extinction ratio under slow-light and low driving voltage conditions. Additionally, a selection of slow-light true-time delay-lines have been fabricated to perform beamforming for a future optically controlled phased array antenna and Radar system, producing up to 175 ps of tunable delay. The delay is characterized using realtime pulse delay and lock-in phase measurement techniques. An evanescent-field-coupled delay-line architecture is presented to eliminate coupled-cavity effects.
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Rensselaer Polytechnic Institute, Troy, NY
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