Uniformity improvement of two-dimensional surface relief grating waveguide display using particle swarm optimization

Area of Science:

• Optics
• Display Technology
• Nanophotonics

Background:

• Diffractive waveguides are crucial for near-eye displays in augmented reality head-mounted displays (AR-HMDs).
• Achieving high exit pupil size and uniform image illuminance are key challenges in diffractive waveguide design.
• Current designs often struggle with consistent illumination across the display.

Purpose of the Study:

• To propose and validate a novel method for optimizing the illuminance uniformity of two-dimensional (2D) diffractive waveguides.
• To enhance the display performance of AR-HMDs by addressing critical factors like exit pupil size and illuminance consistency.
• To achieve high uniformity in both exit pupil and angular illuminance.

Main Methods:

• Design of a straight-line 2D surface relief grating (SRG) waveguide with divided grating regions.
• Establishment of an illuminance uniformity evaluation model based on energy propagation.
• Utilization of non-sequential ray tracing to optimize multi-region grating diffraction efficiency.
• Combination of particle swarm optimization (PSO) and rigorous couple wave analysis (RCWA) to optimize grating structural parameters for uniform diffraction efficiency across different fields of view (FOVs).

Main Results:

• The optimized waveguide achieved an exit pupil size of 16 mm × 14 mm with an eye relief (ERF) of 20 mm.
• Demonstrated a high exit pupil illuminance uniformity of 91%.
• Achieved an angular illuminance uniformity of 64%.

Conclusions:

• The proposed novel method effectively optimizes 2D diffractive waveguides for high illuminance uniformity.
• The optimized waveguide design significantly enhances display performance for AR-HMDs.
• This approach provides a pathway to improved visual quality in near-eye display applications.