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UBC Theses and Dissertations

Computational imaging with diffractive optics Peng, Yifan


Diffractive optical elements (DOEs) have been studied extensively in optics for decades, but have recently received a lot of renewed interests in the context of computational imaging and computational display because they can drastically reduce the size and weight of devices. However, the inherent strong dispersion is an obstacle that limits the use of DOEs in full spectrum imaging, causing unacceptable color fidelity loss in the captured or reconstructed images. Despite the benefits of facilitating compact form factors, DOEs have sufficient degrees of freedom that one can manipulate to encode the desirable light modulation functionality. In this dissertation we theoretically and experimentally investigate the practicability of introducing numerical optimization into the design procedure of optics, to enable a variety of diffractive optics subject to different application scenarios. Regarding imaging applications, we first validate the practicality of introducing diffractive-refractive hybrid elements as simplified optics in conventional computational imaging. We re-implement a cross-channel based deconvolution to correct the chromatic aberration. The full fabrication cycle of photolithography technique is developed, serving as the basis for all designs. Then, the desirable focal powers in both spectral and spatial domain are encoded onto the DOEs. Precisely, we develop the diffractive achromat that balances the focusing contributions in full visible spectrum. The color fidelity can thus be well preserved. Meanwhile, we develop the encoded lenses that provide focus tunable imaging ability and multi-focal sweep imaging compromise. The trade-off light loss and residual aberrations are tackled by a deconvolution step. In addition, we extend the design paradigm from image capture to image display, where the holograms of visualization of multiple narrowband spectra are encoded onto a pair of ultrathin diffractive phase plates. The mix-and-match scheme of designing high degree-of-freedom diffractive optics is exploited via the complex matrix factorization. The essential random appearance of holograms in fact benefits to enabling a wide range of visualization applications. We envision the work on computational imaging, involving both capture and display end, provide new insights on incorporating optics and computation algorithms to better record, understand and deliver desirable visual information under the constraint of current data bandwidth of hardware.

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