Light Recycling in Micromirror Projection Displays
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Solution Overview
Problem
Micromirror-based projection display systems face inefficiencies in light usage due to the reflection of 'off' pixel light away from the display screen, leading to reduced contrast and increased scattering, which complicates the separation of 'on' and 'off' pixel light, thereby degrading image quality and requiring larger, more costly projection lenses.
Innovation Solution
A system where 'off' pixel light is efficiently recycled back into the illumination engine using a reflective surface and fast projection lenses, minimizing the distance between the micromirror spatial light modulator and projection lenses, and eliminating the need for a TIR prism to separate 'on' and 'off' pixel light, allowing for a more compact and cost-effective design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional light recycling techniques are used in micromirror-based projection displays, then light usage efficiency is improved, but contrast is reduced due to scattering of off-pixel light
Solution Approach 1:
The patent segments the light recycling function into two distinct optical paths: one for on-pixel light that maintains contrast, and another for off-pixel light that enables recycling. The beam splitter divides the reflected light from the micromirror array, directing on-pixel light to the projection lens while routing off-pixel light to the light recycling system, thus resolving the contradiction between light efficiency and contrast.
Solution Approach 2:
The patent extracts off-pixel light from the main optical path using a beam splitter and recycling optics, separating it from on-pixel light. This extracted off-pixel light is then redirected back to the illumination source through dedicated recycling mirrors and lenses, allowing efficient light recovery without contaminating the on-pixel light path that determines image contrast.
2Difficulty of detecting and measuring
If TIR prism is used to separate on and off pixel light, then light separation is achieved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the Total Internal Reflection (TIR) prism with a beam splitter based on partial reflection and transmission principles. This substitution maintains the light separation functionality while reducing optical path complexity and eliminating the need for precise TIR angle calculations, thereby simplifying the overall optical system design and reducing component cost.
3Loss of energy
If larger projection lenses are used to accommodate scattered off-pixel light, then light collection is improved, but system size and cost increase
Solution Approach 1:
The patent extracts off-pixel light from the main optical path before it reaches the projection lens, using a beam splitter and dedicated recycling optics. By removing this scattered light component, the projection lens only needs to handle the concentrated on-pixel light, allowing for smaller, more compact lens design while maintaining high light collection efficiency for the useful image-forming light.
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 approach enhances light recycling efficiency without reducing contrast, allows for a competitive form factor with non-micromirror-based displays, and reduces the size and cost of projection lenses while maintaining high optical quality.
Implementation Method 1
a reflective surface directs incident sequential-color light to the spatial light modulator, and off-pixel light reflected by the spatial light modulator is directed along substantially the same path back to the reflective surface
Data Source
AI summary
A digital micromirror projection display system is disclosed in which “off” pixel light is recaptured and recycled. In the disclosed system, a digital micromirror device directs incident light for “on” pixels in the image to be displayed through projection lenses to a projection screen. The digital micromirror device directs incident light for “off” pixels back toward the light source for recapture by a light integrator. Both the incident and projected light can pass through a rear group of projection lenses, with the first projection lens being disposed near the digital micromirror device. A mirror directs the incident light toward the digital micromirror device, and the “off” pixel light from the digital micromirror device toward the light integrator. As a result, “off” pixel light can be recycled without degrading image contrast, in a manner that can place fast projection lenses close to the digital micromirror device to save cost.