2026 Theses Doctoral

Metasurface-Enhance Biomedical Imaging

Therien, Aidan M.

Biomedical optical imaging requires optical systems that can deliver, shape, and collect light within constrained tissue-facing geometries. This dissertation develops optical and computational methods for compact biomedical imaging probes, with emphasis on optical coherence tomography (OCT), metasurface-enabled wavefront engineering, and fiber-tip device assembly. The dissertation first establishes OCT as the principal imaging modality and presents a forward-viewing M-mode OCT system for large-field imaging under constrained acquisition conditions. By combining electromagnetic tracking with compressed-sensing-inspired reconstruction, this work demonstrates a method for generating OCT-derived parametric maps from sparsely sampled measurements. The dissertation then develops the wave-optical foundation for metasurface probe design, including angular spectrum propagation, phase-only hologram synthesis, and simulation of single-mode-fiber illumination.

The central contribution is the design, fabrication, assembly, and characterization of a metasurface-packaged single-mode fiber probe for extended-depth-of-focus OCT. A silicon metasurface phase mask was designed to transform the diverging field from a single-mode fiber into a needle-like beam suitable for compact OCT imaging. The resulting probe was fabricated, assembled, beam-profiled, and evaluated in phantom, ex vivo, and human-tissue imaging experiments. To enable this work, the dissertation introduces Optical Assembly Scheme with In-Situ Sensing (OASIS), an OCT-guided packaging method that provides volumetric feedback during alignment of transparent, micron-scale optical components. OASIS addresses a practical bottleneck in translating metasurface optics from planar chips into functional fiber-tip devices and provides a pathway toward future lab-on-fiber sensors, distal beam-shaping elements, and compact multimodal probes.

The dissertation also includes ongoing work on metasurface-enabled Fourier-domain temporal scattering sensing, which extends the probe concept from structural imaging toward measurements of photon migration and scattering dynamics. Earlier first-author work in hyperspectral imaging, inverse Monte Carlo modeling, and OCT-based deep learning classification provides complementary context by addressing a related question: how optical measurements can be converted into physically meaningful and clinically relevant tissue information. Together, this work shows that metasurfaces can be integrated into fiber-based biomedical probes in a practical and experimentally validated way, and contributes a simulation framework for fiber-illuminated phase-mask design, a demonstrated metalensed OCT probe, and an OCT-guided assembly strategy for high-precision fiber-tip photonic devices.