Comb-Shifted Skew Mirrors for Flexible Reflective Axis
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Solution Overview
Problem
Conventional dielectric mirrors and grating structures have limitations, such as a reflective axis constrained to the surface normal, making them suboptimal for applications requiring a flexible reflective axis, and being either too heavy or limited in wavelength and incidence angle range, which is not suitable for head-mounted display devices.
Innovation Solution
The development of an optical device with a grating medium containing comb-shifted skew mirrors, featuring overlapping holograms with different grating frequencies, allowing for a reflective axis not constrained to the surface normal and maintaining constant angle of reflection across a range of incidence angles and wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional dielectric mirrors are used, then high reflectivity is achieved, but the reflective axis is constrained to surface normal
Solution Approach 1:
The patent changes the fundamental parameter of the reflective surface from a planar dielectric coating to a volumetric holographic grating with specific spatial frequency and orientation. This allows the reflective axis to be decoupled from the surface normal, enabling flexible beam steering while maintaining high reflectivity through Bragg diffraction conditions.
Solution Approach 2:
The patent replaces the mechanical constraint of planar mirror geometry with an optical solution using volumetric holographic gratings. The reflective properties are encoded in the three-dimensional refractive index modulation rather than being dictated by surface orientation, allowing independent control of reflective axis and surface normal.
2Adaptability or versatility
If conventional grating structures are used to achieve non-normal reflective axis, then reflective axis flexibility is improved, but wavelength and incidence angle range is limited
Solution Approach 1:
The patent segments the volumetric grating into multiple holographic recordings with different spatial frequencies and orientations. Each hologram records a specific wavelength-angle combination, and the superposition of multiple such holograms creates a grating that reflects across a broad wavelength and angle range while maintaining the non-normal reflective axis property.
Solution Approach 2:
The patent creates a composite volumetric grating structure by superimposing multiple holographic patterns within the same medium. This composite structure combines the properties of individual holograms to achieve broad spectral and angular bandwidth while maintaining controlled diffraction geometry, effectively creating a multi-functional optical element.
3Weight of moving object
If glass dielectric mirrors are used, then high reflectivity is achieved, but weight increases
Solution Approach 1:
The patent replaces heavy glass substrates with thin holographic gratings that can be implemented in lightweight media such as photopolymers or thin glass coatings. The reflective function is achieved through volumetric refractive index modulation within a thin layer rather than requiring thick glass mirrors, dramatically reducing weight while maintaining optical performance.
Solution Approach 2:
The patent substitutes the mechanical mass of glass mirrors with an optical solution using volumetric holographic gratings in lightweight media. The reflective functionality is achieved through interference-based diffraction rather than bulk material reflection, enabling weight reduction suitable for head-mounted displays and other portable applications.
4Productivity
If overlapping holograms with different grating frequencies are used, then diffraction efficiency across multiple wavelengths is improved, but manufacturing complexity increases
Solution Approach 1:
The patent employs preliminary hologram recording steps where multiple holographic patterns are sequentially recorded within the same volumetric medium. Each hologram is recorded with specific spatial frequency and orientation parameters tailored to target particular wavelength ranges, and the cumulative effect achieves high diffraction efficiency across the entire spectral band with a single integrated grating structure.
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
This solution enables a lightweight, flexible reflective device that can efficiently reflect light about a constant axis, improving image quality and reducing bulkiness in head-mounted display devices by allowing for pupil equalization and enhanced diffraction efficiency across multiple wavelengths and angles.
Implementation Method 1
an optical device with a grating medium containing comb-shifted skew mirrors, featuring overlapping holograms with different grating frequencies, allowing for a reflective axis not constrained to the surface normal and maintaining constant angle of reflection across a range of incidence angles and wavelengths
Implementation Method 2
Each of the holograms in the first set at least partially overlaps each of the other holograms in the first set. Each of the holograms in the first set has a different respective grating frequency from a first set of grating frequencies
Data Source
Figure 1
Figure 2A~2B
Figure 3A
AI summary
Optical systems having comb-shifted sets of holograms across different regions of a grating medium are disclosed. A first set of holograms may be formed in a first region of the grating medium and a second set of holograms may be formed in a second region of the grating medium. Each of the holograms in the first set may have a different respective grating frequency from a first set of grating frequencies. Each of the holograms in the second set may have a different respective grating frequency from a second set of grating frequencies. The second set of grating frequencies may be located within adjacent frequency gaps between the grating frequencies in the first set of grating frequencies. Comb-shifted sets of holograms may be used to perform pupil equalization, output coupling, input coupling, cross coupling, or other operations.