External Retarder LCD Optics Without PBS for High Contrast
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Solution Overview
Problem
Conventional liquid crystal spatial light modulators (SLMs) using polarizing beam splitters (PBS) face challenges in achieving compact designs, high contrast ratios, and efficient image brightness due to large volume and dynamic switching time issues, especially in AR and VR applications.
Innovation Solution
An optical design for SLMs that utilizes external retarders to achieve phase retardation greater or less than 0.25 for specific illumination wavelengths, eliminating the need for PBS and enhancing contrast ratios by exploiting near-zero throughput minimums in electro-optic curves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polarizing beam splitters (PBS) are used in conventional optical designs, then high-contrast images can be achieved, but the device volume increases and compact design becomes difficult
Solution Approach 1:
The patent removes the polarizing beam splitter (PBS) from the optical system entirely, replacing it with a different configuration involving a linear polarizer and quarter-wave plate. This extraction of the problematic component directly reduces device volume while maintaining the ability to achieve high-contrast images through the alternative optical path design.
Solution Approach 2:
The patent employs a single linear polarizer that serves multiple functions: it defines the initial polarization state for the liquid crystal layer and works in conjunction with the quarter-wave plate to create the necessary polarization transformations. This multi-functional approach eliminates the need for separate PBS components, reducing overall device volume.
2Reliability
If polarizing beam splitters (PBS) are used in conventional optical designs, then high-contrast images can be achieved, but image brightness decreases
Solution Approach 1:
The patent replaces the PBS-based polarization separation mechanism with a transmission-based system using a linear polarizer and quarter-wave plate. This substitution changes the optical interaction from reflection/separation to transmission/modulation, reducing light loss and improving image brightness while maintaining contrast through precise polarization control.
3Reliability
If polarizing beam splitters (PBS) are used in conventional optical designs, then high-contrast images can be achieved, but dynamic switching time increases
Solution Approach 1:
By removing the PBS component entirely, the patent eliminates the associated dynamic limitations. The alternative configuration with linear polarizer and quarter-wave plate enables faster polarization switching, directly reducing dynamic switching time while maintaining high-contrast image capability.
4Reliability
If polarizing beam splitters (PBS) are used in conventional optical designs, then high-contrast images can be achieved, but fringing field effects between neighboring pixels become more visible
Solution Approach 1:
The patent replaces the PBS-based system with a transmission optics approach using linear polarizer and quarter-wave plate. This substitution fundamentally changes the electromagnetic field interaction, reducing the generation and visibility of fringing field effects between adjacent pixels while preserving image contrast through controlled polarization states.
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 achieves high contrast ratios exceeding 2000 for all illumination wavelengths, maintaining compact designs and efficient switching times, while overcoming the limitations of PBS-based SLMs.
Implementation Method 1
The retarder modifies a phase difference between two orthogonal polarization components of light such that the retarder produces a phase retardation value that is either greater than 0.25 for all illumination wavelengths in a set of illumination wavelengths or less than 0.25 for all illumination wavelengths in the set of illumination wavelengths
Implementation Method 2
SLMs using liquid crystals with a negative dielectric anisotropy use electro-optic modes which include the Vertically Aligned Nematic (VAN) display mode and the Twisted Vertically Aligned Nematic (TVAN) display mode
Implementation Method 3
The linear polarizer transforms incident light into linearly polarized light with a polarization axis that is oriented at a predetermined angle with respect to a slow axis of the retarder
Data Source
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AI summary
A system includes a spatial light modulator comprising a first substrate, a second substrate, and a liquid crystal layer between the first substrate and the second substrate. The spatial light modulator is characterized by a first retardation and a first phase retardation and has a first slow axis for light propagation. A voltage source is configured to apply a drive voltage to the spatial light modulator and the first retardation of the spatial light modulator is a function of the drive voltage. A retarder is positioned external to the spatial light modulator and is characterized by a second retardation and a second phase retardation. The retarder includes a second slow axis for light propagation. The second retardation has a value such that all illumination wavelengths in a set of illumination wavelengths are above or below a phase retardation value of 0.25. The set of illumination wavelengths includes at least on illumination wavelength in each of at least three different color spectrums.