Optical Stack Reflective Polarizers Wavelength Optimization
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Solution Overview
Problem
Current polarizing beam splitters face challenges in achieving high transmission and reflection efficiency for polarized light within specific wavelength ranges while maintaining a narrow angle between pass axes, which affects their performance in applications like display systems and head-mounted displays.
Innovation Solution
The use of an optical stack comprising two reflective polarizers with polymeric interference layers, where one polarizer has a lower block state leakage and the other has a lower color separation, adhered together with a specific thickness profile and angle alignment, to achieve high transmission and reflection efficiency for normally incident light across a predetermined wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single reflective polarizer is used, then the device complexity is low, but the transmission and reflection efficiency cannot simultaneously achieve high performance across the wavelength range
Solution Approach 1:
The single polarizer is segmented into two separate reflective polarizers with different optical characteristics. The first polarizer (P1) has a smaller separation distance between extreme interference layers for reduced color separation, while the second polarizer (P2) has a larger separation distance for reduced block state leakage. This segmentation allows each polarizer to be optimized for a specific function, achieving high transmission and reflection efficiency simultaneously.
Solution Approach 2:
Different regions of the optical system are assigned different polarizer types with locally optimized properties. The first polarizer is positioned to handle wavelengths where color separation is critical, while the second polarizer handles wavelengths where block state leakage is the dominant issue. This local quality approach ensures optimal performance at each stage of light processing.
2Ease of manufacture
If the separation distance between interference layers is increased, then the color separation is reduced, but the block state leakage increases
Solution Approach 1:
The optical stack segments the polarizing function into two distinct polarizers with different separation distances. The first polarizer uses a smaller separation distance (d1) to minimize color separation, while the second polarizer uses a larger separation distance (d2) to minimize block state leakage. This segmentation resolves the trade-off by assigning different separation distance optimizations to different functional components.
Solution Approach 2:
The invention changes the separation distance parameter differently for each polarizer. By setting d1 < d2, the system optimizes color separation for the first polarizer and block state leakage for the second polarizer. This parameter differentiation allows both performance metrics to be improved simultaneously through coordinated design of multiple components.
3Reliability
If the separation distance between interference layers is decreased, then the block state leakage is reduced, but the color separation increases
Solution Approach 1:
The system segments the polarizing function across two polarizers where the first polarizer (with smaller d1) handles color separation optimization and the second polarizer (with larger d2) handles block state leakage optimization. This segmentation allows each parameter optimization to be applied where it is most effective without compromising overall performance.
4Length of moving object
If the angle between pass axes is reduced, then the lateral separation of exiting light rays is reduced, but the alignment precision requirements increase
Solution Approach 1:
The invention optimizes the angle between pass axes to be less than 10 degrees, which reduces the lateral separation distance between exiting light rays of different wavelengths. This parameter optimization minimizes the distance over which spectral components separate, improving image quality in applications like head-mounted displays.
Solution Approach 2:
The optical stack is designed with local quality optimization where the first and second polarizers have specifically engineered interference layer configurations that compensate for the small angle between pass axes. This ensures that despite the tight angular alignment, each polarizer maintains its optimal performance characteristics for its designated wavelength range.
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 configuration ensures at least 80% transmission and 90% reflection of light polarized along specific axes, with a narrow lateral separation of exiting light rays, enhancing the performance of polarizing beam splitters in various display and imaging applications.
Implementation Method 1
Each reflective polarizer includes a plurality of polymeric interference layers reflecting and transmitting light primarily by optical interference in the predetermined wavelength range
Data Source
AI summary
An optical stack including a first reflective polarizer adhered to a second reflective polarizer is described. For normally incident light and each wavelength in a same predetermined wavelength range, each reflective polarizer transmits at least 80% of light polarized along a pass axis of the reflective polarizer and reflects at least 90% of light polarized along an orthogonal block axis of the reflective polarizer. Each reflective polarizer includes a plurality of polymeric interference layers reflecting and transmitting light primarily by optical interference in the predetermined wavelength range. A separation between the two polymeric interference layers in the plurality of polymeric interference layers farthest from each other are d1 and d2 for the respective first and second reflective polarizers, d1 is at least 20% less than d2. Polarizing beam splitters including the optical stack and optical systems including the polarizing beam splitter are described.