Design and recording methods for holographic waveguide displays

Abstract

Waveguide displays are a prominent optical architecture for near-eye displays because exit-pupil expansion enables a large field of view and a large eyebox within a compact form factor. However, embedding conventional planar waveguides into prescription lenses with convex base curves increases lens thickness and weight. Spherically curved holographic waveguides could avoid these penalties, enabling lightweight display glasses with the form factor of conventional eyewear. To the author's knowledge, this thesis presents the first exact geometric design framework for spherical holographic waveguide displays. It is shown that the exact eigenmodes underlying previous planar and cylindrical waveguide display designs do not exist in spherical waveguides. Instead, closed geometric mode families for planar, cylindrical, and spherical waveguides are constructed using exact jump maps that recover previously known eigenmodes in the planar and cylindrical limit. These modes make overlapping generations of guided beams single-valued and turn incoupler and expander gratings into analytic translations in mode space. Residual geometric aberrations arise only during image extraction at the outcoupler. For spherical curvatures below 3 D, non-sequential ray tracing predicts angular errors below 1 arcmin for monochromatic imaging to an 8 mm pupil across a 22$^\circ$ diagonal field of view, approaching the visual-acuity limit. The thesis then addresses the fabrication of holographic waveguides. Conventional recording schemes rely on edge-lit exposure with immersion contact, which complicates both prototyping and fabrication. Shifts in recording wavelength and recording configuration are investigated as potential means of fabricating waveguide displays without immersion contact. Analytical bounds on immersion-free recordability are derived for planar holographic gratings and remain approximately valid for gratings formed on weakly curved substrates. The results show that the considered red, green, and blue incouplers and outcouplers for typical reflective photopolymer waveguides can be recorded without immersion contact. By contrast, the expander gratings required for practically relevant planar and spherical photopolymer waveguides lie outside the range of immersion-free recordability. Automated edge-lit waveguide recording requires both a wide range of beam angles and centimeter-scale beam apertures to record the incoupler, expander, and outcoupler gratings. To the author's knowledge, this thesis reports the first automated recording platform for holographic waveguide displays. The system combines two collimators mounted on six-axis robots with a custom edge-lit prism assembly. Exposure poses are computed from the prescribed gratings using inverse ray tracing and robot kinematics, with compensation for material shrinkage and alignment of the recording-beam polarization. Calibration yields a mean absolute angular error below \SI{0.1}{\degree}, while interferometric measurements demonstrate relative optical-path stability of order $\pm\lambda/20$ over typical exposure times. The complete workflow is validated through the fabrication of a planar waveguide that transmits readable text. Its modulation transfer function is evaluated, and pupil-sampling-induced intensity modulation in the laser-scanned image is explained analytically. Together, these results establish the optical feasibility of lightweight, prescription-compatible spherical holographic waveguide displays and identify fabrication as the principal remaining challenge. The developed design framework, recordability analysis, and automated exposure platform for planar waveguides provide a foundation for the future development of spherical waveguide displays.