Utilizing and overcoming nature's randomness for optical imaging through scattering media

• Main Author: Zhu, Xiangwen
• Other Authors: Cuong Dang
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: https://hdl.handle.net/10356/172290
• Institution: Nanyang Technological University

Scattering media such as frosted glass, diffusers and biological tissue are complex optical components that scatter light everywhere because of their natural inhomogeneous structures, affecting human's understanding of imaging through it. Based on the "memory effect" phenomenon, the research focuses on utilizing and overcoming nature's randomness of scattering media. For utilization of scattering media’s randomness, we demonstrates the feasibility of a single-shot multi-view imaging technique using a "scattering lens". The "scattering lens" consists of scattering media to multiplex multi-view signals and a condenser lens to collect signals in the imaging system. The signals demultiplexing are computed by scattering media's uncorrelation. Stereo imaging with significant disparity and up to seven-view imaging of a 3D object can be reconstructed from only one speckle pattern. For overcoming of scattering media’s randomness, firstly, the work focuses on non-invasive super-resolution imaging through scattering media. Two super-resolution approaches (SOSLI and NISSFI) suitable for different scenarios are presented. SOSLI uses the blinking object status to pinpoint emitters from speckle patterns. Simulations and experiments are performed to prove the feasibility of breaking the diffraction-limit and achieving 100 nm resolution. NISSFI exploits a series of speckles from object fluctuation, breaking the diffraction limit and achieving 200 nm resolution by analyzing the speckle's higher-order cumulants. Three cases are demonstrated: fluctuating emitters, non-labeling samples, and dynamics scattering media. Second, a high-quality imaging approach using coherent light is presented compared to incoherent light. It has a similar computational pipeline. However, a more robust reconstruction method is proposed by decomposing the incoherent light into coherent light in the scattering imaging system. Theoretical and experimental demonstrate that incoherent light is a special case (mean) of coherent light, in which the coherent interference is canceling out. On the contrary, the variance of coherent interference is dominated and thus is suitable for low SNR and suppressing artifacts. Both utilizing and overcoming nature's randomness for optical imaging paves a better understanding of scattering media, especially its reaction to the light phase at propagating.