Compact microscopy systems with non-conventional optical techniques

Abstract

This work has been motivated by global efforts to decentralize high performance imaging systems through frugal engineering and expansion of 3D fabrication technologies. Typically, high resolution imaging systems are confined in clinical or laboratory environment due to the limited means of producing optical lenses on the demand. The use of lenses is an essential mean to achieve high resolution imaging, but conventional optical lenses are made using either polished glass or molded plastics. Both are suited for highly skilled craftsmen or factory level production. In the first part of this work, alternative low-cost lens-making process for generating high quality optical lenses with minimal operator training have been discussed. We evoked the use of liquid droplets to make lenses. This unconventional method relies on interfacial forces to generate curved droplets that if solidified can become convex-shaped lenses. To achieve this, we studied the droplet behaviour (Rayleigh-Plateau phenomenon) before creating a set of 3D printed tools to generate droplets. We measured and characterized the fabrication techniques to ensure reliability in lens fabrication on- demand at high throughput. Compact imaging requires a compact optical system and computing unit. So, in the next part of this work, we engineered a deconstructed microscope system for field-portable imaging. Still a core limitation of all optical lenses is the physical size of lens aperture – which limits their resolution performance, and optical aberrations – that limit their imaging quality performance. In the next part of this work, we investigated use of computational optics-based optimization approaches to conduct in situ characterization

of aberrations that can be digitally removed. The computational approach we have used in this work is known as Fourier Ptychography (FP). It is an emerging computational microscopic technique that combines the use of synthetic aperture and iterative optimization algorithms, offering increased resolution, at full field-of-view (FOV) and aberration-removal. In using FP techniques, we have shown measurements of optical distortions from different lenses made from droplets only. We also, investigated the limitations of FP in aberration recovery on moldless lenses. In conclusion, this work presents new opportunities to engineer high resolution imaging system using modern 3D printing approaches. Our successful demonstration of FP techniques on moldless lenses will usher new additional applications in digital pathology or low-cost mobile health.