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.;
May2023; School of Engineering
Dept. of Electrical, Computer, and Systems Engineering;
Rensselaer Polytechnic Institute, Troy, NY
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