Imaging through optical multimode fiber: towards ultra-thin endoscopy
Optical imaging in biomedicine provides pathophysiological information with high resolution, high speed, and minimal invasiveness. Endoscopy in particular has revolutionized healthcare diagnosis and treatment as well as biological research by offering visual access to otherwise unreachable remote ti...
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| Format: | Thesis |
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Massachusetts Institute of Technology
2022
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| Online Access: | https://hdl.handle.net/1721.1/146703 https://orcid.org/ 0000-0002-9381-3849 |
| Summary: | Optical imaging in biomedicine provides pathophysiological information with high resolution, high speed, and minimal invasiveness. Endoscopy in particular has revolutionized healthcare diagnosis and treatment as well as biological research by offering visual access to otherwise unreachable remote tissues. However, existing endoscopic modalities face fundamental limitations in their designs that prohibit miniaturization to below a few millimeters in diameter, which would enable imaging through any natural or artificial lumen and thus unprecedented opportunities. This predicament and unmet medical needs such as deep-brain imaging, imaging-guided needle biopsy, and imaging-guided micro-surgery for new and scalable endoscope designs have motivated the concept of utilizing a single optical multimode fiber (MMF) as a stand-alone image conduit. MMF is fascinating as an optical waveguide attributed to its ultra-small footprint, high data throughput, low cost, and flexibility. Nevertheless, the mode mixing and dispersion effects inherent to MMF are technical barriers to its ability to relay clear images; optical propagation through a short length of MMF scrambles an image completely. The focus of this dissertation research is therefore to study waveguide physics of MMF and to innovate powerful computational methods as compensatory strategies that enable high fidelity imaging and sensing through the fiber: We developed numerical simulation toolboxes and experimental measurement systems to characterize bi-directional light transport through MMF; By modeling the light transmission through MMF and sample interaction with matrix operations, we demonstrated three-dimensional (3D) label-free multi-modal imaging based on computational reconstruction; To facilitate multi-spectral and broadband operations with MMF, we established a parametric dispersion model for efficient fiber calibration across a broad spectrum; The spatio-temporal modes within the MMF can be conveniently leveraged for depth sensing, where we created a high-resolution and long-range axial profiling system using MMF; Finally, we showed a proximal MMF calibration method for implementing flexible MMF-based endoscopes by exploiting the waveguide physics and numerical optimization. |
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