Event
Ph.D. Research Proposal: Daniel Pimbi
Monday, December 15, 2025
1:00 p.m.
PSC 2136
Sarah Pham
301 473 2449
spham124@umd.edu
ANNOUNCEMENT: Ph.D. Research Proposal Exam
Name: Daniel Pimbi
Committee:
Professor Thomas Murphy (Chair)
Professor Yanne Chembo
Professor Mohammad Hafezi
Date/time: Monday, December 15th, 2025 at 1:00PM
Location: PSC 2136
Title: Thermally stable frequency splitting in photonic crystal microrings for on-chip microwave
reference sources
Abstract:
Low-phase-noise microwave signals are essential for modern communication, navigation,
quantum information processing, radar sensing, and precision metrology. Integrated photonics
offers a compelling route to compact, scalable microwave generation; yet its performance
remains fundamentally limited by the strong thermal sensitivity of dielectric microresonators
used as frequency-division elements or reference cavities. Existing stabilization techniques,
ranging from active methods such as dual-mode thermometry, resistive sensing, and electronic
feedback to passive approaches including large mode volumes, undercuts, and thermal-isolation
structures, either introduce significant system complexity or provide only partial mitigation of
thermorefractive and thermoelastic fluctuations, while increasing fabrication cost and design
constraints. Critically, most existing systems generate microwave signals by stabilizing two
individual absolute optical frequencies and then using optical frequency division components to
extract their difference as a microwave signal. However, direct stabilization of the frequency
difference itself remains largely unexplored, though it could pave the way for thermally robust,
fully integrated on-chip microwave sources. Here, we propose a fully passive, design-driven
approach that targets the frequency difference itself. Our preliminary results using finite-
element-method simulations demonstrate that bandgap engineering in a photonic crystal
microring resonator (PhCR) can introduce a grating-induced frequency splitting that is
intrinsically temperature-insensitive while simultaneously generating a microwave-rate interval.
By embedding thermal robustness directly into the photonic band structure, this method
addresses thermal instability at its physical origin and eliminates the need for optical frequency-
division components or active thermal control. Our approach aims to establish a pathway toward
compact, monolithic, and thermally stable microwave reference sources, thereby enabling a new
class of chip-scale oscillators with long-term stability suitable for field-deployable integrated
photonic systems.
