Achieving over 500% Improvement in Optical Efficiency for VHOE-Lightguide Near-Eye Glasses with Exit Pupil Expansion

Abstract

This paper proposes an optimized spectrum distribution of the input image to significantly enhance the optical efficiency of volume holographic optical element (VHOE)-based lightguides with exit pupil expansion (EPE). VHOEs-based lightguides can suppress the eye-glow effect and use multiplexing to expand field of view (FOV) with good color performance. Along with the demonstration of good image quality, it makes VHOEs one of the best choices for couplers of EPE lightguide. This method utilizes the Model named “Volume Hologram being an Integrator of the Lights Emitted from Elementary Light Sources (VOHIL)” to derive an analytical solution for the wavelength-angular degeneracy properties of VHOEs, enabling the authors to calculate the peak wavelength distribution that passes through the lightguide. To prove the concept, by meticulously controlling the wavelength distribution and the full width at half maximum of the input light spectrum with a dispersion holographic optical element, a remarkable increase in efficiency is achieved. This approach yields an optical efficiency of 9% for the lightguide with a 30° FOV, representing a 5.63-fold improvement over conventional VHOE-based EPE lightguides. It is three times better than the best record of published efficiency in SRG-based EPE lightguides. This breakthrough has significant potential for advancing the development of high-performance, user-friendly near-eye glasses.