Liquid Crystal Polarization Controller for Laser Projectors
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Solution Overview
Problem
Conventional optical devices using laser diodes suffer from speckle patterns due to coherent light interference, leading to deteriorated image quality, and existing polarization controllers increase device size and have wavelength dependency, causing extinction ratio drops.
Innovation Solution
An optical device incorporating a liquid crystal cell and wave plates that cyclically shift the polarization direction of laser light, allowing control of the polarization state through a single wideband device without wavelength dependency, reducing device size and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polarization controller is provided for each beam of primary color light, then the polarization state of each beam can be controlled, but the device size increases
Solution Approach 1:
The patent merges multiple polarization control functions into a single polarization controller that handles all primary color light beams simultaneously. This is achieved by using a liquid crystal variable retarder that can control the polarization state of multiple wavelengths through a single optical path, thereby reducing device size while maintaining control precision.
Solution Approach 2:
The polarization controller is designed with multi-functionality to handle different wavelengths (primary colors) through a single device. The liquid crystal variable retarder can adjust its retardation to control polarization states for red, green, and blue light beams sequentially or simultaneously, eliminating the need for separate controllers for each wavelength.
2Area of stationary object
If a single polarization controller is used for multiple beams of primary color light, then device size is reduced, but wavelength dependency causes extinction ratio drop
Solution Approach 1:
The patent employs a liquid crystal variable retarder that can dynamically adjust its retardation value to compensate for wavelength dependency. By cycling through different retardation settings corresponding to different primary color wavelengths, the system maintains high extinction ratios for all colors despite using a single static polarization controller structure.
Solution Approach 2:
The polarization controller cycles through different retardation states periodically, with each state optimized for a specific primary color wavelength. This periodic adjustment of the liquid crystal retarder ensures that each wavelength receives appropriate polarization control, maintaining high extinction ratios across all colors while using a single device.
3Area of stationary object
If laser light is used to reduce lighting device size, then projector size is reduced, but speckle patterns develop due to coherent light interference
Solution Approach 1:
The patent introduces periodic modulation of the polarization state of laser light by cycling the liquid crystal variable retarder through different retardation values. This periodic change in polarization state causes the speckle pattern to fluctuate over time, and when averaged by the human eye or camera, the speckle noise is significantly reduced while maintaining the compact projector design.
Solution Approach 2:
The patent converts the harmful coherent nature of laser light that causes speckle into a beneficial feature by utilizing polarization modulation. By rapidly switching polarization states, the system creates temporal variations in the speckle pattern that average out to reduce noise, while the coherent properties of laser light are still exploited for efficient coupling into optical fibers and compact beam delivery.
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 enables high-speed polarization direction shifting, reducing speckle noise and enabling 3D display functions while minimizing device size and maintaining image quality.
Implementation Method 1
a liquid crystal cell that transmits laser light that is in a state of polarization of a given direction and of a given wavelength, the liquid crystal cell being capable of shifting a direction of a director with respect to the given direction by rotating the direction of the director parallel to a substrate surface
Implementation Method 2
a wave plate that transmits laser light emitted from the liquid crystal cell, the wave plate having a phase delay axis set in an arbitrary direction
Data Source
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AI summary
A light source unit (110) emits linearly polarized laser light of a given wavelength. A wave plate (121) transmits the laser light emitted from the light source unit (110) and has a phase delay axis of which the direction is adjusted to about 0 degrees with respect to the polarization direction (101) of the laser light. A liquid crystal cell (123) transmits laser light that has passed through the wave plate (121) and by a switchable rotation amount, rotates the polarization direction (101) of the laser light transmitted through the liquid crystal cell (123). A wave plate (125) transmits laser light that has passed through the liquid crystal cell (123); and further has a phase delay axis of which the direction is adjusted to about 0 degrees with respect to the polarization direction (101) of the laser light.