Silicon photonics foundry fabricated high-speed slow-light mach-zehnder modulators for digital communication and photonic computing
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Authors
Begovic, Amir
Issue Date
2025-12
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Electrical engineering
Alternative Title
Abstract
A key challenge in silicon photonics is the development of high-speed electro-optic modulators (EOMs), a type of modulator that can manipulate the polarization or refractive index of light using an external electric field or applied voltage. EOMs are particularly useful in data centers which rely on high-speed optical communication links to transfer large amounts of data between servers and storage devices. Si EOMs allow for dense integration, CMOS compatibility with microelectronics, and low-cost mass fabrication compared to other materials such as indium phosphide or lithium niobate. Two common forms of Si EOMs are Mach-Zehnder Modulators (MZMs) and micro-ring modulators. Although micro-ring modulators tend to have more compact footprints as compared to MZMs, they suffer from temperature instability. The sharp resonance peak characteristic of micro-ring modulators tends to shift in response to environmental changes, impacting their performance. Additionally, due to their high Q, their optical bandwidth tends to be narrower than for MZM-based EOMs. Silicon based MZMs still face obstacles in reducing power consumption, increasing bandwidth, reducing loss, and achieving compact device footprints while maintaining compatibility with foundry fabrication processes. One approach to address these challenges is the integration of slow-light structures, such as photonic crystal waveguides or Bragg gratings. These resonant structures increase light-matter interaction, thereby increasing modulation efficiency and enabling smaller footprint MZMs. Improved modulation efficiency helps reduce power consumption, while a smaller footprint tends to reduce loss. With careful design of electrodes and phase matching of electrical and optical signals within the device, slow-light enhanced MZMs can achieve high bandwidths (theoretically around 40--50 GHz per channel). This thesis develops foundry-compatible silicon MZMs that embed slow-light Bragg-grating phase shifters to increase light–matter interaction, reducing drive energy and footprint while maintaining practical bandwidths. Devices are fabricated on the AIM Photonics platform and evaluated end-to-end. The design flow combines optical and electrical co-simulation (Lumerical, HFSS, Tidy3D), and characterization including DC/C–V, S-parameters, eye diagrams, and bit-resolution measurements. The work also presents coupling and packaging enablers, misalignment-tolerant laser-to-Si/SiN edge couplers, with designs and characterizations of passive building blocks (splitters, photonic crystals) that support integration. Compact slow-light MZMs with short phase shifters and low-voltage differential drive achieve mid-tens of fJ/bit energy (e.g., 45 fJ/bit), high modulation efficiencies (e.g., 0.33 V$\cdot$cm), and open eyes up to 10 Gbps are demonstrated. Bandwidth is ultimately limited by test-fixture impedance and photon-lifetime/RC trade-offs inherent to short slow-light devices. The thesis further connects these MZMs to photonic tensor-core style computing: 4–8-bit MZM links with on-chip Ge photodetectors are analyzed for error metrics versus clock frequency (200 MHz–3.2 GHz), and energy-per-switch/bit models demonstrate low-power operation at useful compute precisions for both communication and analog photonic-compute contexts.
Description
December2025
School of Engineering
School of Engineering
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY