3D Printed Fresnel Lenses for Sensing Applications

Abstract

The discovery and synthesis of functional optical devices have been the subject of ongoing research and paving pathways to the industrial revolution of optical systems in the past decades. Numerous industries, including optics, electromagnetics, soft electronics, and biomedicine, have extensively used structures, patterns, and devices made of inexpensive polymer materials. Polymer-based optically active materials have been widely used for manufacturing optical lenses and arrays including Fresnel lenses, optical waveguides, optical fibers, and micro-nano optical devices due to their excellent optical transmission properties, high flexibility, and superior mechanical properties along with the capacity of integration with other smart materials (stimuli responsive). However, several issues need to be resolved regarding the production and processing of complex optical devices as well as identifying the process of unique characteristics of polymer-based functional devices for optical sensing applications.

A Fresnel lens consists of concentric annular rings capable of converging or diverging incident light. Fresnel lenses can be employed in various optical, acoustic, microwave, and millimeter-wave devices/sensors applications. Moreover, such lenses can be utilized in imaging and non-imaging target-specific applications. Methods for fabricating these lenses are typically etching and layer deposition of optically active materials. For instance, conventionally manufactured glass and silicon-based Fresnel lenses have been reported for their utilization in photovoltaics and space applications. Other fabrication techniques, such as casting, injection molding, and compression molding, have also been reported in the literature. However, the major limitations of these conventional fabrication techniques are related to high cost, low throughput, limited design freedom, and process flexibility.

In comparison, polymer-based 3D printing fabrication techniques provide solutions to these limitations by rapidly manufacturing components and devices with more complex designs and shapes. Thus, the rapid advancements in 3D printing enables the fabrication of many optical components, such as optical fiber, waveguides, optical tweezers, interactive optical devices, and Fresnel lenses using computer-assisted design (CAD) modeling. This thesis investigates the design and fabrication of polymer-based 3D printed Fresnel lenses for various optical sensing applications such as light filtering, thermal sensing, holographic sensing, and alcohol sensing. Resin 3D printing processes such as digital light processing (DLP) and masked stereolithography (MSLA), known for their rapid production and precision, were employed for the fabrication of Fresnel lenses. 3D Printing process integrity was ensured with specific formulation by mixing an optimized ratio of the resin matrix and incorporating smart materials (e.g., colored inks and thermochromic powders) to avoid any adverse impact on optical properties. The structural integrity of printed lenses was based on optimized printing parameters for each intended application. The surface roughness of photocured lenses achieved is within the acceptable range of λ/4 to λ/10 (where λ is the curing wavelength) for optical devices without post-processing, which led to less than 8 mm deviation in focal length measurements. Using polyvinyl chloride (PVC) film on the print head during fabrication resulted in about 10% improvement in the optical transmission properties. This work provides an in-depth analysis of the processing-property relationship of 3D printed Fresnel lenses and their composites through optical, physical, microscopic, and spectroscopic studies, revealing their optical performance in transmission spectra variations, focusing functionality, and light intensity variations. The advancements in AM techniques and the ability to design intricate optical structures will enable the fabrication of new optical systems with unprecedented properties.

Date of Award	Apr 2023
Original language	American English
Supervisor	Haider Butt (Supervisor)