Blue LED Optical Coupling to Light Guide Plate
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Solution Overview
Problem
Current blue LED designs suffer from poor blue light extraction efficiency due to reflection from the encapsulation-polymer/air interface, leading to significant absorption of blue light by the LED die, which reduces the optical power output of liquid crystal display (LCD) backlights.
Innovation Solution
Optically coupling the blue LED to a light guide plate using a tape or adhesive, or via an encapsulant protruding from the LED, with a composition of phosphors such as YAG, silicate, or luminescent nanocrystals like CdSe or ZnS, to enhance light coupling and reduce reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If blue LED emits light directly into air, then light extraction is simple, but reflection from encapsulation-polymer/air interface causes poor blue light extraction efficiency
Solution Approach 1:
The patent introduces a light guide plate as an intermediary medium between the blue LED and the display. The light guide plate has a refractive index matching the encapsulation polymer, eliminating the air interface that causes reflection. This mediator allows blue light to be coupled efficiently into the light guide plate without the harmful reflection losses that occur at polymer/air interfaces.
2Power
If optical coupling is implemented to improve blue light extraction, then optical power output increases, but device structure becomes more complex
Solution Approach 1:
The light guide plate serves multiple functions simultaneously: it acts as an optical coupling medium to improve blue light extraction efficiency, functions as a light distribution element to deliver light to the display, and provides a structural platform for mounting the LED. By combining these functions into a single component, the patent increases optical power output without proportionally increasing device complexity.
3Reliability
If blue light is reflected back to LED die, then extraction efficiency is reduced, but die temperature increases reducing reliability
Solution Approach 1:
The patent applies preliminary anti-action by preventing blue light from reflecting back toward the LED die in the first place. The light guide plate is optically coupled to the LED encapsulation before light extraction occurs, creating a refractive index-matched interface that prevents the formation of reflective boundaries. This proactive prevention eliminates the harmful feedback loop of reflection and re-absorption that would otherwise increase die temperature and reduce reliability.
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 approach increases the optical power output of blue LED-based display systems by at least 10% compared to systems without optical coupling, improving luminous output and extending LED package lifetime by reducing blue light absorption and die temperature.
Implementation Method 1
Optically coupling the blue LED to a light guide plate using a tape or adhesive, or via an encapsulant protruding from the LED
Implementation Method 2
LCD backlights often utilize phosphors, such as YAG phosphors. Traditionally, these phosphors have been situated inside the LED package itself.
Implementation Method 3
Blue light extraction efficiency is poor in current blue LED designs. This is most likely a result of the reflection from the encapsulation-polymer/air interface.
Data Source
AI summary
Disclosed herein are display systems comprising light-emitting, diodes (LEDs), suitably blue light LEDs, which demonstrate increased optical power output. In embodiments, the display systems include compositions comprising phosphors, including luminescent nanocrystals.