Deep Surface Relief Gratings for High-Efficiency Waveguide Displays
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Solution Overview
Problem
Existing waveguide manufacturing methods are inefficient and costly for producing high-efficiency gratings, particularly for waveguide displays using unpolarized light sources like OLEDs, leading to significant polarization efficiency loss.
Innovation Solution
A method for fabricating deep surface relief gratings (SRGs) by forming a holographic polymer dispersed liquid crystal (HPDLC) grating and removing liquid crystal to create polymer-rich regions, followed by applying a protective layer, which enhances S-polarized and P-polarized light diffraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional waveguide manufacturing methods are used, then production cost is reduced, but diffraction efficiency for S-polarized and P-polarized light deteriorates
Solution Approach 1:
The manufacturing process is segmented into distinct stages: forming the HPDLC grating structure, selectively removing liquid crystal from specific regions, and applying protective layers. This segmentation allows each step to be optimized independently, achieving high diffraction efficiency while maintaining manufacturing feasibility through systematic process breakdown.
Solution Approach 2:
The invention changes the physical and chemical parameters of the grating structure by controlling the phase separation between polymer and liquid crystal, adjusting the refractive index modulation, and optimizing the depth and profile of the surface relief features. These parameter changes enable high diffraction efficiency for both S and P polarizations.
2Loss of energy
If deep surface relief gratings are fabricated using HPDLC method, then diffraction efficiency for both S-polarized and P-polarized light is improved, but manufacturing process complexity increases
Solution Approach 1:
The invention extracts the liquid crystal from specific regions of the HPDLC grating to create air gaps or voids in the polymer matrix. This extraction process is achieved through selective solvent treatment or thermal processing, which removes LC from certain areas while preserving it in others, thereby creating the desired deep surface relief structure with high polarization efficiency.
Solution Approach 2:
The invention uses composite materials consisting of polymer matrices combined with liquid crystal phases, and subsequently polymer-air or polymer-liquid crystal hybrid structures. This composite approach allows tuning of optical properties to achieve high diffraction efficiency for both polarizations while managing manufacturing complexity through material design.
3Shape
If liquid crystal is removed to form polymer-rich regions, then surface relief depth is increased, but manufacturing time increases
Solution Approach 1:
The invention performs preliminary actions by pre-forming the HPDLC grating structure with embedded liquid crystal regions before the liquid crystal removal step. This preliminary structuring allows the subsequent removal process to be more efficient and targeted, reducing the overall manufacturing cycle time while achieving the required surface relief depth.
Solution Approach 2:
The invention accelerates the liquid crystal removal process by using optimized solvent treatments, elevated temperatures, or enhanced diffusion methods that rapidly extract LC from the polymer matrix. This rushing through of the removal step minimizes manufacturing time while still achieving complete or near-complete liquid crystal extraction for maximum surface relief depth.
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
The method achieves high diffraction efficiency for both S-polarized and P-polarized light, improving waveguide display performance and reducing manufacturing costs.
Implementation Method 1
During the recording process, the monomers polymerize, and the mixture undergoes a photopolymerization-induced phase separation
Implementation Method 2
a polymer grating structure for diffracting light propagating in total internal reflection in said waveguide
Implementation Method 3
light propagating in total internal reflection in said waveguide
Data Source
Figure 1A~1D
Figure 2
Figure 3
AI summary
Improvements to gratings for use in waveguides and methods of producing them are described herein. Deep surface relief gratings (SRGs) may offer many advantages over conventional SRGs and Bragg gratings, an important one being a higher S -diffraction efficiency. In one embodiment, deep SRGs can be implemented as polymer surface relief gratings or evacuated Bragg gratings (EBGs). EBGs can be formed by first recording a holographic polymer dispersed liquid crystal (HPDLC) grating. Removing the liquid crystal from the cured grating provides a polymer surface relief grating. Polymer surface relief gratings have many applications including for use in waveguide-based displays.