LED Light Emitting Device Reflective Layer
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Solution Overview
Problem
Light emitting diode (LED) print heads in image forming apparatuses suffer from lower light intensity compared to laser scanning units, with light being absorbed by the substrate, and face efficiency issues due to increased temperature, affecting light generation and extraction efficiency.
Innovation Solution
A light emitting device is designed to prevent light absorption by the substrate, utilizing a reflective layer to reflect light back and improve light extraction efficiency, even at elevated temperatures, by employing a Bragg reflector and varying refractive indices in the AlGaAs semiconductor structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a light emitting diode (LED) print head is used to reduce the size of the exposure module, then the size of the exposure module is reduced, but the light intensity is lower compared to laser scanning units
Solution Approach 1:
The patent introduces a reflective layer beneath the LED array to reflect light that would otherwise be absorbed by the substrate back through the LED structure. This adds a spatial dimension (bottom reflection path) to light generation, effectively increasing light intensity without increasing the horizontal footprint of the exposure module.
Solution Approach 2:
The patent converts the harmful effect of substrate light absorption into a beneficial reflection path. By placing a reflective layer at the substrate interface, light that would be lost to absorption is instead reflected back to generate additional useful light output, improving overall light intensity and efficiency.
2Power
If the LED operates at elevated temperatures, then the device can maintain operation under high power conditions, but light generation and extraction efficiency decrease
Solution Approach 1:
The patent converts the harmful thermal effects and substrate absorption into beneficial reflections. The reflective layer captures light that would be absorbed (whether due to temperature-related efficiency loss or direct substrate absorption) and redirects it back through the LED structure, recovering energy that would otherwise be lost.
Solution Approach 2:
The patent modifies the optical parameters of the system by introducing a reflective layer with specific reflectivity characteristics. This changes the light extraction pathway and improves the overall light generation efficiency by recovering light that would otherwise be lost to substrate absorption, particularly under elevated temperature operating conditions.
3Use of energy by moving object
If a reflective layer is added to prevent light absorption by the substrate, then light extraction efficiency is improved, but device complexity increases
Solution Approach 1:
The reflective layer serves multiple functions: it reflects light back to improve light extraction efficiency, it can act as a thermal management interface, and it provides structural support at the substrate interface. By combining multiple functions into a single layer, the patent minimizes the increase in device complexity while achieving significant improvements in light extraction efficiency.
4Use of energy by moving object
If a Bragg reflector with varying refractive indices is used to improve light extraction, then light extraction efficiency is enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent employs a Bragg reflector structure with varying refractive indices to create constructive interference and enhance light reflection at specific wavelengths. This parameter-based approach (controlling refractive index gradients) provides a systematic method for improving light extraction that can be implemented through standard semiconductor fabrication techniques, balancing manufacturing feasibility with performance enhancement.
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
Enhances light generation and extraction efficiency, maintaining performance despite temperature increases, and reduces substrate absorption, thereby improving the overall efficiency of the image forming apparatus.
Implementation Method 1
employing a Bragg reflector and varying refractive indices in the AlGaAs semiconductor structure
Implementation Method 2
varying refractive indices in the AlGaAs semiconductor structure
Implementation Method 3
a light emitting diode (LED) print head (LPH), in which a plurality of LEDs are arranged in a scanning direction
Data Source
AI summary
An image forming device comprises: an exposer having a plurality of light emitting devices, a light emitting device among the plurality of light emitting devices to transmit light toward a photosensitive drum; and a developer to develop an electrostatic latent image formed on a surface of the photosensitive drum by the light, wherein the light emitting device among the plurality of light emitting devices includes: a light emitting layer to generate the light; and a reflective layer to reflect at least a portion of the generated light. The reflective layer can include a plurality of sub-reflective layers, in which a thickness of a sub-reflective layer among the plurality of sub-reflective layers is different from a thickness of another sub-reflective layer among the plurality of sub-reflective layers, and/or a refractive index of a sub-reflective layer among the plurality of sub-reflective layers is different from a refractive index of another sub-reflective layer among the plurality of sub-reflective layers.