PVG
Three-dimensional liquid crystal orientation provides polarization-selective volume diffraction for AR waveguide input and output coupling.
PRODUCT TERMINOLOGY
Liquid Crystal Polarization Volume Grating
Related names: PVG, Polarization Volume Grating, Polarization Volume Holographic Grating
| Name / abbreviation | English expansion | Meaning & scope |
|---|---|---|
| PVG | Polarization Volume Grating | The liquid crystal volume grating described here is designed for polarization-selective volume diffraction. |
| Volume holographic grating | Polarization Volume Holographic Grating | A fuller name emphasizing the volume-holographic structure; it refers to the same product family in this context. |
| PVH | Polarization Volume Hologram | A broader class that can include gratings, lenses and other wavefront functions, rather than PVG alone. |
PVG and PVL are polarization volume elements with different target wavefronts. Specify coupling or focusing requirements when selecting an element.
01 / HOW IT WORKS
A polarization volume grating encodes an anisotropic dielectric structure through periodic liquid crystal orientation in the plane and through the thickness. The reflective PVG discussed here uses a cholesteric liquid crystal polymer. Its helix, in-plane period and slant jointly determine diffraction geometry and polarization selectivity; a scalar surface-relief model alone does not describe this structure.
Incident and diffracted waves couple under the volume grating phase-matching condition. Period and orientation determine the grating vector. Wavelength, angle and polarization changes affect efficiency and output direction, so spectral and angular response, polarization conversion and parasitic orders must be evaluated together.
kd = ki + K
k_i and k_d are wave vectors inside the device medium; K is the relevant grating vector. This specifies phase matching. Efficiency requires an anisotropic coupled-wave or electromagnetic model.
For AR waveguides, an input grating couples external light into a direction that satisfies total internal reflection in the substrate; an output grating couples guided light toward the viewing region. Substrate index, propagation angles, coupling regions, pupil geometry and energy distribution across fields and wavelengths must be co-designed. Grating efficiency is different from total display-system efficiency.
LC-layer thickness, grating slant, period and birefringence jointly influence volume diffraction and polarization conversion. Single- or multilayer optimization can tailor coupling efficiency across RGB wavelengths and fields to control color balance and brightness. Output regions also require spatial coupling-strength design for pupil energy distribution. Validation includes spectral–angular scans, polarization-resolved measurements, leakage and spatial uniformity.
Background: LC polarization holography, geometric phase and volume diffraction ↗
02 / TECHNICAL BENEFITS
Reflective PVGs use polarization-selective volume diffraction to direct light in the designed channel toward the intended propagation direction, helping reduce unwanted forward leakage. Co-designing LC layer thickness, polarization evolution and waveguide propagation geometry can further suppress leakage and stray light caused by repeated coupling.
Under matched wavelength, angle and polarization conditions, PVGs can achieve high diffraction efficiency and concentrate energy in the intended diffraction channel. Co-designing input and output gratings with the propagation path can improve useful optical-energy utilization; individual grating efficiency and the complete waveguide efficiency to the eye must be assessed separately.
LC layer thickness, grating slant, period and multilayer structures provide joint design variables for coupling efficiency across RGB bands and fields of view. Together with spatial efficiency profiles across the output region, these variables can optimize color balance, brightness uniformity and energy distribution within the eye box.
Photoalignment, LC film fabrication and curing form the grating structure with less reliance on complex micro- and nanoscale etching, supporting large-area batch fabrication and lower unit costs at production scale. Actual cost depends on the process, layer count, yield and production volume.
Orientation within the LC polymer carries the optical function, allowing custom coupling regions on planar substrates with reduced coupling-element thickness. The film and waveguide substrate can be co-designed for integration in thin, lightweight optical modules.
03 / DESIGN INPUTS
These are the inputs for a design assessment, not fixed product specifications. Numerical performance, test conditions and delivery scope are confirmed for the agreed design.
| Parameter | Requirements to discuss |
|---|---|
| Spectrum / angular response | Define wavelengths, incidence angles and diffraction targets. |
| Coupling geometry | Assess in-coupling / out-coupling with the waveguide design. |
| Efficiency / uniformity | Define measurement conditions and spatial requirements. |
| Substrate / usable area | Evaluate substrate, grating area and integration method. |
04 / APPLICATIONS
01
Connect external display optics to the guided path by coupling light into the required substrate propagation direction.
Design conditionsMatch substrate index, total-internal-reflection conditions, input field, spectrum and polarization.
02
Couple guided light toward the viewing region and design the spatial energy distribution across the output pupil.
Design conditionsAssess field of view, eye box, uniformity, utilization and repeated coupling.
03
Develop and validate coupling elements for specified wavelength, angle and polarization channels.
Design conditionsBroadband or broad-angle operation requires joint design and validation.
Suitability depends on the complete optical system and must be assessed against your operating conditions.
05 / COMMON QUESTIONS
They use different grating architectures and have different spectral and angular behavior. Selection depends on the optical function and system constraints.
This page describes optical grating and coupling-element development. Contact us to define the required component and the scope of waveguide integration.
TECHNICAL REQUIREMENTS
Share the target optical function, spectrum, aperture, polarization and system-integration conditions.
