Recent advancements in design, manufacturing, and metrology have enabled broader use of freeform components for high-performing optical systems. Freeform optics, which lack rotational symmetry, provide additional design freedoms that can enable compact systems with enhanced functionality. As one example, freeform optics have the potential to reduce the cost and number of required parts for Extended Depth of Field (EDoF) imaging through Point Spread Function (PSF) engineering. Imaging systems with high Numerical Aperture (NA) have shallow depth of field, meaning they create clear images only along a small longitudinal distance. Prior work has demonstrated the use of freeform components for extended depth of field imaging, but each optical system typically requires a custom phase plate. As a result, methods that can enable variable EDoF for multiple imaging systems are of particular interest.The primary goals of this dissertation are to explore and characterize methods that leverage pairs of freeform phase plates for variable EDoF imaging. Results are addressed through three articles. The first article addresses the design and simulation of a pair of 4th order polynomial freeform surfaces to enable variable EDoF for commercial lenses with a range of NA values. The second article presents an alternate design method and enhanced performance results for a pair of logarithmic freeform surfaces for the same commercial lenses. The third article presents the fabrication and experimental performance characterization of the 4th order freeform phase plate pair. These three articles showcase the advantages freeform optics can offer in PSF engineering for EDoF imaging and methods used to design, manufacture, and characterize their performance.
