Compact Collimated Image Projector Using Dual PBS Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Compact image projectors using dielectric coated polarizing beam splitters suffer from light leakage due to off-angle skew rays, leading to image degradation, especially in configurations with a single optical element between the spatial light modulator and collimating optics.
Innovation Solution
A collimated image projector design employing two parallel homogeneous dielectric polarizing beam splitters (PBSs) along the light path, with one acting as an entrance pre-polarizer to filter skew rays, and optionally using a compound polarizing beam splitter apparatus with a structural polarizer and compensating plate to minimize optical aberrations and leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single optical element is placed between the SLM and collimating optics to reduce device complexity, then the projector achieves a shorter effective focal length and more compact design, but off-angle skew rays leak through the polarizing beam splitter causing image degradation
Solution Approach 1:
The single optical element is segmented into two separate polarizing beam splitters: a first PBS positioned before the SLM to pre-polarize incoming light and filter skew rays, and a second PBS positioned after the SLM to collimate the reflected light. This segmentation allows each PBS to perform a specific function, preventing skew ray leakage while maintaining a compact design without requiring additional optical elements.
Solution Approach 2:
The first polarizing beam splitter performs a preliminary action by pre-polarizing the incoming light before it reaches the SLM. This preliminary polarization filtering removes off-angle skew rays that would otherwise leak through the second PBS and degrade image quality, ensuring that only properly aligned polarized light proceeds through the system.
2Productivity
If dielectric coated polarizing beam splitters are used to illuminate the LCOS and collimate light, then the system achieves efficient light distribution and collimation, but off-angle skew rays leak through the PBS towards the exit pupil causing image degradation
Solution Approach 1:
The light path is segmented into two stages with separate PBSs: the first PBS handles illumination and pre-polarization before the SLM, while the second PBS handles collimation after the SLM. This segmentation ensures that skew rays are filtered at the first PBS and cannot reach the exit pupil through the second PBS, eliminating the harmful light leakage while maintaining efficient light distribution.
Solution Approach 2:
The design converts the potential harm of skew ray leakage into a benefit by using the first PBS to pre-polarize the light. The skew rays that would otherwise be harmful are blocked at the first PBS, and the polarized light that passes through is then efficiently collimated by the second PBS, turning the polarization filtering action into a protective measure that improves image quality.
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 eliminates light leakage from skew rays onto the exit pupil, maintaining image quality and contrast, even in short effective focal length configurations, by ensuring optimal polarization alignment and reducing optical aberrations.
Implementation Method 1
a first homogeneous dielectric polarizing beam splitter (PBS) deployed along the light path and defining a first transition from a first light path segment to a second light path segment
Implementation Method 2
a first substantially transparent compensating plate having a third RI different than each of the first and second RI and a thickness so as to at least partially compensate for optical aberrations introduced by the polarizer
Data Source
AI summary
A collimated image projector that receives light from an illuminating source and propagates the light along a light path towards an exit pupil, the projector comprising: a first homogeneous dielectric polarizing beam splitter (PBS) deployed along the light path and defining a first transition from a first light path segment to a second light path segment; a second homogeneous dielectric PBS deployed parallel to the first PBS along the second light path segment and defining a second transition from the second light path segment to a third light path segment; and collimating optics deployed along the light path after the second PBS so as to direct a collimated image towards the exit pupil; wherein the first and second PBSs are deployed such that either the first and second transitions are both performed via transmission, or the first and second transitions are both performed via reflection.