Folded Projection System Using Prism and Diffractive Beam Splitter
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Solution Overview
Problem
The challenge is to develop a compact projection system suitable for small, mobile multipurpose devices like smartphones and tablets, where the limited Z-space constrains the size of imaging components, requiring a solution that reduces the Z-height of the projection system while maintaining or enhancing the field of view.
Innovation Solution
A compact folded projection system incorporating a laser light source, a folded lens system with refractive lenses and a light folding element, and a diffractive beam splitter, which redirects and replicates light rays to achieve a larger field of view while minimizing the system's Z-height, using a prism as the light folding element and a diffractive beam splitter with active surfaces to optimize optical axis folding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a conventional projection system is used, then the field of view is adequate, but the Z-height is too large for thin mobile devices
Solution Approach 1:
The patent folds the optical axis by 90 degrees using a light folding element (prism), transforming the optical path from a linear Z-axis arrangement to a folded configuration. This allows the projection system to achieve an adequate field of view while reducing the Z-height to fit within thin mobile devices (4mm or less), directly resolving the contradiction between compact size and field of view capability
2Length of moving object
If the Z-height is reduced to fit thin devices, then the system becomes compact, but the field of view is reduced
Solution Approach 1:
By folding the optical axis 90 degrees through the prism, the system extends the effective field of view in the X-Y plane while maintaining a compact Z-height. The folded optical path allows light to traverse a longer optical distance within a shorter physical Z-dimension, thus achieving both compactness and adequate field of view
Solution Approach 2:
The light folding element (prism) acts as an intermediary that redirects the optical path without absorbing or significantly altering the light. This intermediary enables the optical axis to be folded, effectively decoupling the field of view size from the physical Z-height of the device
3Length of moving object
If a folded optical path is used to reduce Z-height, then the system becomes compact, but the optical complexity increases
Solution Approach 1:
The patent employs a single light folding element (prism) as the intermediary to achieve the optical axis fold. This single component performs the folding function without requiring multiple complex optical elements, thus minimizing the increase in optical complexity while successfully reducing the Z-height
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 effectively reduces the Z-height of the projection system, enabling it to fit within the constrained space of mobile devices while providing a larger field of view, suitable for applications in thin devices where Z-space is limited, and maintains image quality across the field of view.
Implementation Method 1
a light folding element (e.g., a prism)... redirects the ray bundles
Implementation Method 2
a diffractive beam splitter that includes at least one diffractive surface... replicates the ray bundles into N×M duplications
Implementation Method 3
a lens stack including two or more refractive lenses or lens groups... refracted by the lenses in the lens stack
Data Source
AI summary
A compact folded projection system is described that includes a laser light source, a folded lens system comprising a lens stack including two or more refractive lenses and a light folding element (e.g., a prism), and a diffractive beam splitter that includes at least one diffractive surface. The light folding element provides a “folded” optical axis for the lens system to reduce the Z-height of the projection system, for example to within a range of 1.7 to 4 millimeters (e.g., 2 millimeters in some implementations). The laser light source emits light that is refracted by the lens stack to the folding element. The folding element redirects the light to the beam splitter which replicates the light into N×M duplications or tiles to thus generate a larger field of view (FOV) than the internal FOV of the lens system.