Transmissive Optically Addressed Spatial Light Modulator for Full-Color Display
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Solution Overview
Problem
Existing optically addressed spatial light modulators (SLMs) operating in reflection mode absorb significant portions of visible light, limiting their ability to produce full-color images with fine gray scales and high brightness, as they are not capable of modulating the entire visible spectrum effectively, especially in transmissive modes.
Innovation Solution
The development of transmissive-mode optically addressed spatial light modulators (OASLMs) that use a nematic liquid crystal and a photoconductive structure to modulate a wide spectrum of visible light, allowing for energy-efficient, high-brightness, and high-definition displays without the need for electrode arrays, and enabling the use of inexpensive ultraviolet write light sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If prior art optically addressed SLMs use photoconductive layers that absorb light in the visible spectrum, then they can achieve spatial light modulation, but they cannot transmit full-color visible light effectively
Solution Approach 1:
The device segments the optical spectrum by using a photoconductive layer that selectively absorbs only ultraviolet write light while transmitting visible read light. This spectral segmentation allows simultaneous UV absorption for modulation and visible transmission for full-color display without interference between write and read operations.
Solution Approach 2:
The patent introduces an intermediary photoconductive layer with specific spectral properties that mediates between the UV write light source and the visible read light. This intermediary layer converts UV optical energy to electrical signals for liquid crystal modulation while remaining transparent to visible wavelengths, enabling optically addressed control without blocking the display spectrum.
2Stability of the object's composition
If ferroelectric liquid crystals are used in transmissive mode, then bistability is achieved, but fine gray scale and large intensity range are difficult to attain
Solution Approach 1:
The patent changes the material parameter from ferroelectric to nematic liquid crystal, which fundamentally alters the switching characteristics. Nematic liquid crystals provide continuous analog control of optical properties, enabling fine gray scale (256 or more levels) and large intensity modulation ranges, while the optically addressed photoconductive mechanism provides sufficient switching speed and stability.
3Reliability
If reflection mode is used in prior art SLMs, then photoconductive absorption is effective, but the readout light cannot reach the photoconductive layer for full color imaging
Solution Approach 1:
The patent inverts the conventional reflection mode architecture by implementing transmissive mode operation. Instead of reflecting read light back through the photoconductive layer, the system transmits read light through the photoconductive layer to the liquid crystal modulator. The photoconductive layer is positioned and spectrally engineered to absorb UV write light from one side while transmitting visible read light from the opposite side, enabling full-color transmissive display.
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
These OASLMs achieve fine gray scale and full-color capabilities with reduced energy consumption, avoiding image lag and ghosting, and allowing for flexible pixilation formats without hardware changes, while maintaining long service life and low manufacturing costs.
Implementation Method 1
a photoconductive structure (12) tuned to absorb the write light
Implementation Method 2
a liquid crystal light modulating structure (14) positioned between a pair of electrode structures (16, 18)
Data Source
AI summary
An optically addressed, photoconductive spatial light modulator (SLM) operates in a transmissive mode and is capable of modulating a wide spectrum of visible light. There is no pixel structure or native pixel resolution in the SLM. The SLM has no photodiodes and does not rectify. A light projection system (100) in which one or more SLMs (128, 130, 132) are placed includes a write (image definition) UV light path (102) and a read (illumination) visible light path (104) to form a color image projection display. The write UV light propagates from an image display pattern source (120) and either sequentially or continuously writes image patterns on the photoconductive SLMs. The read visible light propagates through the SLM and is modulated by an electro-optical material, the optical properties of which change in response to the image structure carried by the write light. The result is a high efficiency display system that delivers high resolution color images through a projection lens (190) onto a display screen.