Event
Ph.D. Research Proposal: Masoud Heidari Khouzani
Friday, January 23, 2026
2:00 p.m.
AVW 1146
Sarah Pham
301 473 2449
spham124@umd.edu
ANNOUNCEMENT: Ph.D. Research Proposal Exam
Name: Masoud Heidari Khouzani
Committee:
Professor Mario Dagenais (Chair)
Professor Yanne K. Chembo
Professor Avik Dutt
Date/time: Friday, January 23 2026 at 2:00 pm
Location: AVW 1146
Title: Integrated Fabry-Perot Bragg Gratings on Silicon Nitride Platform for Advanced Photonic Applications
Abstract:
Silicon nitride (Si₃N₄) has emerged as one of the most promising platforms for photonic integrated circuits due to its low optical loss and compatibility with standard CMOS fabrication. These characteristics make it ideal for developing low-loss waveguides and high-Q resonators. In particular, Fabry–Pérot Bragg gratings (FPBGs) on Si₃N₄ can leverage its excellent film quality and ultralow propagation loss to achieve precise bandwidth control and narrow-linewidth optical resonances.
Dispersion compensation is a critical challenge in optical resonators, as both material and geometric dispersion can degrade device performance. In this work, a novel dispersion compensation approach using FPBGs on the Si₃N₄ platform is proposed. Compared to ring resonators, grating-based structures offer greater flexibility in dispersion engineering since their geometry and refractive index profile can be readily tuned through the grating’s effective index step, period, or duty cycle. This tunability enables precise dispersion control while maintaining high reflectivity and compact device footprints.
To further enhance FPBG performance, an Advanced Tapered Grating (ATG) design that minimizes mode mismatch between the waveguide and Bragg mirrors is introduced, enabling record-high intrinsic quality factors (Qint) of up to 121 million and 58 million on 100-nm and 300-nm Si₃N₄ platforms, respectively, with propagation losses as low as 0.19 and 0.45 dB/m. These results represent a significant advance toward compact, ultrahigh-Q photonic resonators for nonlinear and precision photonics.
An extended Advanced Tapered Grating Plus (ATG⁺) design further implemented in the Grating Transition Region (GTR), the interface between two Bragg gratings with distinct central wavelengths. The ATG⁺ structure gradually adapts the optical mode across the transition, minimizing reflection and scattering losses to enable low loss coupling between spectrally distinct gratings.
Another way to design gratings is through complex waveguide Bragg grating (CWBG) structures, which can be synthesized using layer-adding/layer-peeling (LA/LP) algorithms. These grating structures enable precise control over the stopband reflectivity at each wavelength. This capability allows escape-efficiency engineering, an important factor for optimizing squeezed-light generation by tailoring the photon leakage and cavity-grating coupling strength. However, since CWBGs have weak local effective refractive index modulation, achieving comparable reflectivity requires much longer gratings, making them more suitable for applications where a small free spectral range (FSR) is acceptable.
Building upon this high-Q FPBG platform, a nanophotonic cavity system for atom trapping and strong atom–photon coupling is developing. Targeting Yb atoms near the 1539 nm transition, the system employs a waveguide-integrated cavity designed to achieve an internal cooperativity (Cin) of approximately 100, sufficient for entering the strong-coupling regime. By engineering a small effective mode area and optimizing cavity geometry and quality factor, efficient coupling between single atoms and guided photons can be realized. This platform establishes a scalable foundation for hybrid quantum photonic systems, enabling deterministic light–matter interfaces for quantum networking, single-photon generation, and squeezed-light applications.
