Reflective Microdisplay Head-Mounted Projection Display
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Head-mounted projection displays (HMPDs) face limitations in image brightness and contrast due to low efficiency and resolution, making them unsuitable for outdoor or well-lit indoor environments, particularly with transmissive AMLCDs which have low transmission efficiency and pixel fill factor.
Innovation Solution
A compact, telecentric projection lens and optical illumination system using a reflective microdisplay with a light engine that includes a polarized beamsplitter, quarter-wave retarder, and concave spherical reflector to enhance luminance and contrast, combined with a telecentric projection lens made of plastic components with aspheric surfaces and a diffractive optical element for improved efficiency and compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If transmissive AMLCDs are used as image sources, then the display can be implemented, but the transmission efficiency and pixel fill factor are low resulting in reduced image brightness
Solution Approach 1:
The patent inverts the conventional transmissive display approach by using a reflective microdisplay instead. The microdisplay reflects light back through the beamsplitter to the user's eye, achieving higher light efficiency and image brightness compared to transmissive AMLCDs which lose significant light through absorption and low transmission efficiency.
2Adaptability or versatility
If multiple beamsplitting is used in the optical path, then the head-mounted display function is achieved, but the overall efficiency drops to around 4%
Solution Approach 1:
The patent introduces a polarized beamsplitter as an intermediary component that selectively transmits or reflects light based on polarization state. This allows the system to achieve the necessary optical path folding for head-mounted display while minimizing energy loss by directing light efficiently through polarization-controlled routing rather than conventional non-polarizing beamsplitters.
3Ease of operation
If the image luminance is low at 4 cd/m2, then the display can operate, but it appears washed out in well-lit environments with luminance over 100 cd/m2
Solution Approach 1:
The patent changes the key parameter of light efficiency in the optical system by using a reflective microdisplay combined with a polarized beamsplitter configuration. This parameter change increases the image luminance from 4 cd/m2 to potentially 12 cd/m2 or higher, making the display visible and usable in well-lit environments without appearing washed out.
4Weight of moving object
If a compact projection lens is used, then the device becomes more ergonomic, but the lens design complexity increases with aspheric surfaces and diffractive elements
Solution Approach 1:
The patent employs composite optical design by combining aspheric surfaces with diffractive optical elements in the projection lens. This composite approach allows the lens to achieve compact form factor and reduced weight while maintaining optical performance, as the diffractive elements add corrective functionality without requiring additional separate lens components.
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 significantly increases the luminance and maintains high contrast of the projected image, making it more suitable for use in well-lit environments while being compact and lightweight for ergonomic use.
Implementation Method 1
a polarized head-mounted projection display (p-HMPD) was proposed
Implementation Method 2
a quarter-wave retarder is placed between the PBS and the retroreflective screen. By passing through the quarter wave retarder twice, the incident S-polarized light is converted to P-polarization
Implementation Method 3
the projected light is reflected by the PBS, it is retroreflected back to the same PBS by a retroreflective screen
Implementation Method 4
a compact, telecentric projection lens and optical illumination system using a reflective microdisplay with a light engine that includes a polarized beamsplitter, quarter-wave retarder, and concave spherical reflector
Implementation Method 5
The image on the LCD display is projected through the projection lens, forming a real intermediate image
Data Source
AI summary
The present invention relates generally to a head-mounted projection display, and more particularly, but not exclusively to a polarized head-mounted projection display including a light engine and a compact, high-performance projection lens for use with reflective microdisplays.