Uni-directional Beam Splitter Coating for HMDs
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Solution Overview
Problem
Conventional beam-splitting components in optical systems, such as head-mounted displays, suffer from unwanted light emission that interferes with the 'see-through' function, requiring selective wavelength or polarization filtering, which degrades the natural viewing capability.
Innovation Solution
A spatially variant one-way mirror coating is applied to the beam splitter surface, comprising a multilayer optical coating with an optically reflective and absorptive layer, patterned to allow light to pass in one direction while absorbing in the other, effectively suppressing stray radiation without impacting the 'see-through' capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If an absorptive coating is applied to suppress unwanted light emission, then the unwanted emission is reduced, but the see-through function is degraded
Solution Approach 1:
The coating is applied selectively to specific regions of the beam splitter surface rather than uniformly across the entire surface. This allows the coating to suppress unwanted light emission from the display source while leaving other regions uncoated to maintain the see-through function for environmental light.
Solution Approach 2:
Instead of using a conventional absorptive coating that blocks light, the invention uses a reflective coating that redirects unwanted light. This inverse approach achieves suppression of unwanted emission without the same degree of light loss, preserving the see-through capability better than absorptive coatings.
2Object-generated harmful factors
If a polarization filter is used to suppress unwanted emissions, then the emission suppression is achieved, but the see-through function is interfered with
Solution Approach 1:
The reflective coating is applied only to specific regions of the beam splitter where it is needed to suppress display source emission, while other regions remain uncoated to allow environmental light to pass through without polarization filtering effects.
3Ease of operation
If a conventional beam splitter is used, then light separation is achieved, but unwanted light emission exits the front face
Solution Approach 1:
The invention inverts the conventional approach by using a reflective coating instead of an absorptive or polarizing filter. This reflective coating redirects the unwanted light back toward the display source or into the optical system, preventing it from exiting the front face while maintaining the beam splitting function.
Solution Approach 2:
The unwanted light that would otherwise exit the front face is reflected back into the optical system where it can be redirected or reused. This converts the harmful unwanted emission into a beneficial element that can be managed within the system.
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 solution effectively suppresses unwanted light emissions while maintaining the natural 'see-through' function, being insensitive to incident angles and suitable for robust integration between prism halves, enhancing the performance of optical devices like head-mounted displays and camera viewfinders.
Implementation Method 1
a first, optically reflective coating layer is applied to an optically transparent substrate
Implementation Method 2
a second, optically absorbent coating layer is applied over the first layer
Data Source
AI summary
A beam splitter optical surface comprises a transparent substrate and a multilayer optical coating applied in a pattern onto the transparent substrate. The multilayer optical coating has at least an optically reflective layer and an optically absorbent layer.