Laser Backlight Speckle Suppression via Beam Segmentation
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Solution Overview
Problem
Coherent light sources, such as lasers, generate speckles due to high coherency, leading to brightness unevenness and physiological adverse effects in illumination systems, particularly in backlight apparatuses for liquid crystal panels, where speckle suppression techniques are inadequate.
Innovation Solution
A plane illumination apparatus and backlight apparatus utilizing a hologram recording medium that diffracts coherent light beams to create diffused light, scanning the light guide plate with a scanning device to minimize speckle formation and ensure uniform brightness by diffusing light across a specific zone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a laser beam is used as a light source, then light incidence efficiency is improved, but speckles are generated causing brightness unevenness
Solution Approach 1:
The patent divides the laser beam into multiple separate beams using a beam splitting element (such as a diffraction grating or beam splitter array). Each divided beam is then directed to illuminate different regions of the light guide plate, preventing the formation of speckle patterns while maintaining high light incidence efficiency. The multiple divided beams interfere with each other to create a more uniform illumination pattern.
Solution Approach 2:
The patent employs a multi-layered optical structure where beam dividing elements, scanning mechanisms, and light guide components are nested within each other. The beam splitting element is positioned within the optical path of the laser source, and the resulting divided beams are scanned across the light guide plate surface, creating a compact integrated system that achieves both high efficiency and speckle suppression.
2Length of stationary object
If LED is used as a light source, then backlight apparatus can be made thin, but light incidence efficiency is reduced due to uniform diffusion illumination
Solution Approach 1:
The patent introduces a beam splitting element as an intermediary component between the laser source and the light guide plate. This intermediary device divides the single laser beam into multiple beams, which then scan across the light guide plate surface, achieving both thin profile and high light incidence efficiency that neither LED nor conventional laser systems could achieve alone.
3Illumination intensity
If coherent light beams are used, then straightness and energy density are improved, but speckles are generated causing physiological adverse effects
Solution Approach 1:
The patent segments the coherent laser beam into multiple incoherent or partially coherent beams through beam division. This segmentation reduces the temporal and spatial coherence that causes speckle formation, thereby eliminating physiological adverse effects while preserving the high energy density advantage of laser illumination.
Solution Approach 2:
The patent implements a scanning mechanism that dynamically moves the divided laser beams across different positions on the light guide plate. This dynamic scanning approach ensures that no single location receives continuous coherent illumination, reducing speckle visibility and physiological impacts while maintaining overall high energy delivery to the illumination area.
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 speckle visibility and brightness unevenness, achieving uniform illumination with a speckle contrast of less than 4, superior to traditional LED-based systems, and enhances light utilization efficiency while minimizing the complexity of the optical module.
Implementation Method 1
an optical device having a plurality of recording areas on which interference fringes are formed; when coherent light beams are emitted to respective positions of the optical device, the coherent light beams are diffused by the optical device
Implementation Method 2
light is incident on an edge of a light guide plate, repeatedly reflected between two opposing surfaces by total reflection
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
A plane illumination apparatus has an optical device, an irradiation unit to irradiate the coherent light beams to the optical device. The irradiation unit makes the coherent light beams scan the surface of the optical device by changing propagation directions of the coherent light beams, the light guide plate comprises a light take-out portion specific zone to take out coherent light beams to outside while making coherent light beams propagate between a first end face on which coherent light beams from the optical device are incident and a second end face that is provided to face the first end face, and the specific zone is provided inside the light take-out portion or along the first end face, or along the second end face.