Edge Emitting LED: Structure, Working, Advantages, and Disadvantages
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This article explores the edge-emitting LED, covering its structure, operation, along with its pros and cons.
Edge Emitting LED Structure and Working Operation
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Edge-emitting LEDs are commonly used in optical fiber communication systems. Here, collimated light from the LED needs to be efficiently coupled into the fiber.
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Figure 1 shows the multilayer structure of an InP-based edge-emitting LED. These are often used for long-wavelength optical communication, roughly between 1.33 and 1.55 µm.
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Modern epitaxial growth techniques, like MBE (Molecular Beam Epitaxy) and MOCVD (Metal-Organic Chemical Vapor Deposition), are used to create these complex LED structures.
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The central active layer is made of InGaAs, which has a narrow bandgap. It’s surrounded by wide bandgap layers, such as p+ InGaAsP and n+ InP cladding layers.
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These cladding layers confine injected electrons and holes to the middle layer. They also help the emitted photons travel along the LED axis due to their optical properties.
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As a result, light is emitted from the edge of the LED, hence the name “edge-emitting LED.”
Advantages of Edge Emitting LEDs
Here are the benefits of using edge-emitting LEDs:
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Superior Beam Collimation: Provides greater coupling efficiency with fiber optic cables compared to surface-emitting LEDs.
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Higher Efficiency: Offers good efficiency with low to high radiance. Suitable for high-brightness LED lighting applications.
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Reduced Power Loss: Radiates less power to the air compared to surface-emitting LEDs due to reduced reabsorption and interfacial recombination.
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Better Modulation Bandwidth: Exhibits a better modulation bandwidth and a more directional emission pattern.
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Increased Coupled Power: Delivers 5-6 times more coupled power into the NA (Numerical Aperture) of step/graded index fibers, thanks to small beam divergence.
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High Data Rates: Supports higher data rates (> 20 Mbps) compared to surface-emitting LEDs.
Disadvantages of Edge Emitting LEDs
The drawbacks of using edge-emitting LEDs include:
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Complex Structure: The design and fabrication are intricate.
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Difficult Heat Sink Design: Designing an effective heat sink can be challenging.
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Higher Cost: They are more expensive compared to other LED types.
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Installation Issues: Mechanical mounting and installation can be problematic.