Reflective Plate for Substrate Guided HUD Grating Efficiency
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Solution Overview
Problem
Substrate guided Head Up Displays (HUDs) face issues with optical efficiency due to diffracted light being transmitted in the opposite direction, fragility of diffraction gratings, and the need for a compact, cost-effective solution with improved protection and wider field of view.
Innovation Solution
A substrate waveguide with input and output diffraction gratings, where the output grating is protected by a plate to reflect transmitted orders of light back into the HUD, increasing optical efficiency and using surface relief gratings in high refractive index materials for wider field of view and luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a substrate guided HUD uses transparent diffraction gratings for out-coupling light, then the HUD can provide pupil expansion and compact design, but a considerable amount of diffracted light is transmitted through the grating in the opposite direction which lowers optical efficiency
Solution Approach 1:
The patent converts the harmful transmitted light (which was previously lost in the opposite direction) into a beneficial resource by using a reflective layer to redirect it back through the waveguide toward the pilot's eye. This transforms the waste light into useful illumination, thereby improving optical efficiency without requiring additional light sources.
Solution Approach 2:
The patent recovers the transmitted light that would otherwise be discarded by the out-coupling diffraction grating. The reflective layer positioned behind the grating captures this transmitted light and redirects it back through the waveguide, effectively recovering energy that would have been lost and improving overall system efficiency.
2Adaptability or versatility
If substrate guided HUDs use diffraction gratings, then pupil expansion is achieved, but the diffraction gratings are fragile and delicate and can be damaged by debris or improper handling
Solution Approach 1:
The patent employs a protective cover glass that acts as a robust shell over the fragile diffraction grating. This cover glass is transparent to maintain optical performance while providing mechanical protection against debris and improper handling, thus preserving the reliability of the fragile grating structure.
Solution Approach 2:
The protective cover glass serves as an intermediary element between the external environment (debris, handling) and the fragile diffraction grating. It mediates the interaction by providing a protective barrier that prevents direct contact between harmful external factors and the sensitive optical component.
3Reliability
If the HUD is designed to be compact with protected diffraction gratings, then reliability and protection are improved, but device complexity increases
Solution Approach 1:
The patent merges the protective function with the existing HUD structure by integrating the protective cover glass as part of the waveguide assembly. Rather than adding a separate protective component, the cover glass is incorporated into the overall structural design, thereby providing protection while minimizing increases in device complexity.
Solution Approach 2:
The protective cover glass serves multiple functions: it protects the diffraction grating from damage, maintains the structural integrity of the waveguide, and preserves optical transparency. This multi-functionality reduces the need for additional specialized components, thereby limiting the increase in device complexity while achieving reliable protection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances optical efficiency, protects the diffraction grating, and provides a compact, lightweight HUD with improved field of view and luminance, while being cost-effective.
Implementation Method 1
Collimated light travels from the input to the output within the substrate waveguide by total internal reflection
Implementation Method 2
The light directed toward the pilot is diffracted in a reflective manner by the out-coupling diffraction grating
Data Source
AI summary
A display (for example, a head up display (HUD)) includes a substrate waveguide. The substrate waveguide can act as a combiner. The substrate waveguide receives collimated light an input and provides the collimated light to an output. The collimated light travels from the input to the output within the substrate waveguide by total internal reflection. An input diffraction grating is disposed in the first area at the input and an output diffraction grating is disposed in the second area at the output. A plate covers at least a portion of the second area. The plate can protect the diffraction grating and reflect transmitted order light from the diffraction grating to improve efficiency.