X-Cube Prism Segmentation for Compact DMD Projection
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Solution Overview
Problem
Conventional multi-chip DMD projection systems with corner-Manhattan array layouts suffer from long optical path lengths and increased costs due to the use of large Philips-type prisms, which result in larger, more complex, and costly projection lenses, and suffer from color fidelity issues due to polarization-induced leakage across color filters.
Innovation Solution
The use of two-axis tilt pixel modulators and an X-cube color prism with individual TIR or RTIR prisms between each DMD and the color combining prism reduces optical path lengths and eliminates polarization-induced leakage, enabling clean-up color filtering and improved thermal management, while allowing bottom illumination to fold light paths across the shortest DMD dimension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Philips-type color separation prism is used to split white light into RGB components and recombine them, then color separation and combination is achieved, but the optical path length becomes significantly longer and the prism size increases
Solution Approach 1:
The patent divides the single large Philips-type prism into multiple smaller prisms (typically three separate prisms for red, green, and blue channels). Each prism handles a specific color channel, allowing the optical path to be optimized independently for each channel. This segmentation reduces the overall optical path length while maintaining effective color separation and recombination functionality.
2Manufacturing precision
If the green path is extended to match the longer red and blue paths in the Philips prism, then equal path length for all colors is achieved, but the green path becomes excessively long and the prism size increases
Solution Approach 1:
By separating the color handling into individual prisms, each prism can be optimized for its specific color channel's path length requirements. The green channel prism can be compact without needing to accommodate the extended paths required by the red and blue channels in a unified Philips prism structure.
Solution Approach 2:
The patent introduces additional spatial dimensions and folding mechanisms in the optical path design, allowing light to travel through compact prism volumes while achieving the necessary effective path lengths through folded configurations rather than straight-line extensions.
3Ease of operation
If a single large TIR prism is used to inject light at 45 degrees to the DMD, then correct orientation is maintained, but the prism size increases significantly to prevent vignetting of expanded light cones
Solution Approach 1:
The single large TIR prism is divided into multiple smaller TIR prisms, each serving a specific color channel. This segmentation allows each smaller prism to handle a narrower light cone without vignetting, eliminating the need for an excessively large single prism while maintaining correct light orientation and direction.
4Measurement precision
If higher cost dichroic coatings are used to minimize s- and p-polarization separation, then color fidelity is improved, but system cost increases
Solution Approach 1:
By separating the color channels into individual prisms and using targeted dichroic coatings only where absolutely necessary, the system reduces the total surface area requiring high-cost polarization-minimizing coatings. The segmentation allows for more selective and efficient use of expensive optical coatings.
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 results in a more compact, lower-cost projection system with improved contrast and color fidelity by reducing prism sizes and eliminating the need for even numbers of reflections, thus shortening the back working distance of the projection lens and preventing color gamut desaturation.
Implementation Method 1
A single total internal reflection (TIR) prism is used between the projection lens and the Phillips prism to inject the light at a 45-degree orientation to the DMD's
Implementation Method 2
an X-cube color prism for a white light source application
Implementation Method 3
to split white light from an illumination source into constituent RGB color components
Implementation Method 4
use a Philips-type color separation prism (Philips prism) to split white light from an illumination source into constituent RGB color components to respective DMDs, and to recombine the separately modulated colors into a composite complete RGB image
Data Source
AI summary
A multi-DMD projection system uses an extended X-cube color splitting/recombining prism to implement splitting and recombining functions at different sections of the cube. Light directed from a white light source is split into red, green and blue components in a lower section of the cube. The components are directed to respective first, second and third DMDs for separate modulations and reentered into the X-cube prism by TIR prism for recombining at an upper section of the cube.