Bragg Polarization Grating

The future of augmented reality

  • A Bragg polarization grating (BPG) is an optically “thick” grating that follows (2-4um)
  • Bragg PGs are analogous to Volume Phase Holograms and Volume Bragg Gratings

Image of BPG equation

How It Works

BPGs are a special case of polarization gratings that operate in the Bragg regime or Q>1. It has several unique properties that make it ideal for several applications including augmented and virtual reality. When operating in the Bragg regime, a polarization grating will diffract only a single polarization (+1st order) and leave the orthogonal polarization un-diffracted. With a circularly polarized input, the efficiency can reach up to 99%. For very wide field of views, the efficiency can be as high as 90%.

bragg polarization

Traditional Grating

  • 20 Degree Field of View
  • 40% Grating Efficiency
  • > 100um Thickness

ImagineOptix BPG

  • 60 Degree Field of View
  • 99% Grating Efficiency
  • 2um Thickness

Technical Details

Specifications

AR/VR Gratings

  • Diffraction of single order only (+1st order, RHC)
    • 0th order (LHC) is undiffracted
    • Diffracted order is always orthogonal to input
    • RHC -> LHC
  • Efficiency:  Up to 90% diffraction efficiency through a waveguide
  • Max Efficiency for single grating: Near 99%
  • Field of View: >60°
    • Requires very high index waveguide
  • Subwavelength Grating Periods for VIS and IR
  • Minimum Grating Period: <300nm
  • Grating Thickness: ~2um
  • Can be tuned for Narrow or Wideband use
  • Size: up to 120 x 120mm sq; round samples custom

Telecom Blazed Gratings

  • >90% Efficiency
  • Transmissive
  • Can be made reflective with reflective substrate

Benefits

AR/VR

BPGs are the only technology for holographic waveguides that give unparalleled efficiency, coupled with single order and single polarization diffraction, that operates over an extraordinary wide field of view (FOV). These gratings can also be implemented with an efficiency gradient that helps with color and brightness uniformity. These aspects make the BPG ideal for use in augmented reality. One polarization can be used with high efficiency over a large FOV to convey the overlayed information and the other polarization (external view from the outside world) can come through without distortion.

Telecom

  • Thinner
  • Higher efficiency
  • Large angle of operation
  • Can be tuned to operate over full band with high efficiency
  • Additional Information

    Any desired angle of incidence (e.g., in=0۠) can be waveguided by selecting the proper slant angle G and period Λ.

    Diffraction angle Θ1 must follow grating equation, where nin and nout are refractive

    BPG Efficiency

     

Let’s make something impossible come to vision