Optical Design of Generalised Gradient-Index Lenses

Abstract

Within the optics industry, there is a continuous drive to reduce the size, weight, power consumption and cost of optical systems (known as SWAP-C). A new generation of fabrication technologies for GRadient-INdex (GRIN) materials promise the capability to manufacture GRIN media of arbitrary refractive index distribution (within index variation and spatial resolution limits). This represents an opportunity to further optimise the SWAP-C of lens systems, yet also presents challenges for the optical designer. The necessary optical design tools for arbitary GRINs are not widely implemented, and the potential applications where arbitrary GRINs provide a benefit are not widely explored.

This work addresses these design challenges via two routes. In the first body of work we explore the necessary design tools for generalised GRIN lenses, including efficient mathematical representations for GRIN distributions and tools for the generation of starting points for further optimisation. A powerful new tool is devised that can convert conventional homogeneous lens constructions to generalised GRIN media, which allows the GRIN lens designer to leverage the vast archive available of homogeneous lens solutions as starting points. We also address the aberration correction potential of GRIN lenses with planar surfaces.

In the second body of work we explore the applications that directly benefit from GRIN optics. We demonstrate that layered polymer GRIN lenses of spherical distribution enabled by new extrusion-based manufacture technologies can show comparable performance to conventional cemented doublets and hybrid refractive-diffractive lenses. We also explore the application of a freeform-GRIN distribution to the design of a head-mounted display (HMD), showing that GRIN can significantly reduce the optical complexity of a baseline homogeneous HMD design. Finally, we demonstrate that GRIN can be a powerful tool in the optical design of optical systems with very wide, multispectral infrared wavebands. A short-wave to long-wave (SWIR-LWIR) infrared design study shows a GRIN-based solution can dramatically reduce lens count, size and mass while reducing sensitivity to manufacturing tolerances.

We conclude that the required design infrastructure for arbitrary GRIN lenses is feasible and emerging, and that there are technological challenges in modern optical design that justify ongoing research into GRIN optics. Progress in the optical design of generalised GRINs must be accompanied by refinement in manufacture, metrology, and environmental qualification to enable widespread adoption and deployment.