Optical Unit Prism Asymmetry Reduces Thickness
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Solution Overview
Problem
Conventional optical units with biaxial-control digital micromirror devices face challenges in size reduction due to the increased thickness of the second prism, which leads to larger optical units and potential issues like ghost light and temperature rise causing lower contrast and imaging performance degradation.
Innovation Solution
The optical unit design includes a second prism with an OFF-light reflecting surface that reflects OFF light away from the optical axis of ON light, allowing for a thinner profile by forming the first area longer along the line normal to the projection-optical-axis plane, and using specific refractive index conditions to ensure proper separation and transmission of light rays, thus reducing the overall size of the optical unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a biaxial-control digital micromirror device is mounted to the optical unit, then the brightness of the projection image is improved, but the thickness of the second prism increases and the optical unit is increased in size
Solution Approach 1:
The second prism is designed with asymmetric dimensions where the first area (along the line normal to the projection-optical-axis plane) is formed longer than the second area. This asymmetric configuration allows the prism to effectively reflect OFF light away from the optical axis while maintaining a compact thickness, resolving the contradiction between improving brightness and reducing prism thickness
Solution Approach 2:
The patent utilizes the spatial arrangement of light paths in different dimensions by directing OFF light reflection away from the projection-optical-axis plane. This dimensional separation allows the second prism to be thinner while still effectively managing OFF light, thus improving brightness without increasing thickness
2Productivity
If OFF light is incident on the projection lens, then the projection image can be formed, but ghost light is caused and local temperature rise occurs degrading imaging performance
Solution Approach 1:
The second prism is designed to extract and redirect OFF light away from the optical axis and projection lens. By taking out OFF light from the main optical path through the OFF-light reflecting surface, the system prevents ghost light and temperature rise while maintaining projection image formation
Solution Approach 2:
The OFF light, which would otherwise cause harmful effects (ghost light and heat), is converted into a beneficial design feature by using it to define the asymmetric geometry of the second prism. The prism utilizes the OFF light's path to create an asymmetric structure that improves overall optical performance while eliminating harmful effects
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 design effectively separates OFF light from ON light, preventing ghost light and temperature rises, leading to improved imaging performance and a reduced size of the optical unit and projector.
Implementation Method 1
The second prism has a total reflection surface that transmits ON light reflected from the ON-state micro-mirrors while totally reflecting OFF light reflected from the OFF-state micro-mirrors
Implementation Method 2
The digital micromirror device forms an image by illumination light intensity modulation in which a surface of each of the micro-mirrors is tilted by ON/OFF control
Data Source
AI summary
An optical unit includes a digital micromirror device in which each of micro-mirrors is driven biaxially in ON/OFF control, a first prism directs illumination light to the digital micromirror device, a second prism including an OFF-light reflecting surface reflects OFF light reflected from the micro-mirrors in an OFF state and transmits ON light reflected from the micro-mirrors in an ON state, and a third prism emits the ON light incident from the second prism toward a projection side. The micro-mirrors reflect the OFF light so that an optical axis of the OFF light is directed away from a projection-optical-axis plane including an optical axis of the ON light and an optical axis of the illumination light.