Techniques to expand the exit pupil of Maxwellian display: A review

The near-eye display (NED) devices are required to provide visual instructions in the fields of education, navigation, military operations, construction, healthcare, etc. The issues with conventional NEDs are the vergence-accommodation conflict (VAC) and form factor. The Maxwellian display alleviates the VAC in NEDs by providing always-focused images to the viewer regardless of the depth of focus of the human eye. The main limitation of the Maxwellian display has a limited exit pupil size. Due to misalignment of the device or eyeball rotation, the user may miss the eye box, and the image will become lost. To mitigate this limitation, exit pupil expansion can be obtained either statically or dynamically. This paper reviews the various techniques employed to expand the exit pupil. The review includes the principle, advantages, and drawbacks of various techniques for expanding the exit pupil of the Maxwellian display. The structure of the paper starts with an introduction and the principle of the Maxwellian display, followed by a discussion of the main limitations that arise with various techniques, along with potential solutions.