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Edge Emitting LED: Structure, Working, Advantages, and Disadvantages

edge emitting led optical fiber communication system semiconductor

This article explores the edge-emitting LED, covering its structure, operation, along with its pros and cons.

Edge Emitting LED Structure and Working Operation

  • 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.

  • 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.

Edge Emitting LED Structure

  • Modern epitaxial growth techniques, like MBE (Molecular Beam Epitaxy) and MOCVD (Metal-Organic Chemical Vapor Deposition), are used to create these complex LED structures.

  • 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.

  • 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.

  • 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:

  • Superior Beam Collimation: Provides greater coupling efficiency with fiber optic cables compared to surface-emitting LEDs.

  • Higher Efficiency: Offers good efficiency with low to high radiance. Suitable for high-brightness LED lighting applications.

  • Reduced Power Loss: Radiates less power to the air compared to surface-emitting LEDs due to reduced reabsorption and interfacial recombination.

  • Better Modulation Bandwidth: Exhibits a better modulation bandwidth and a more directional emission pattern.

  • 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.

  • 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:

  • Complex Structure: The design and fabrication are intricate.

  • Difficult Heat Sink Design: Designing an effective heat sink can be challenging.

  • Higher Cost: They are more expensive compared to other LED types.

  • Installation Issues: Mechanical mounting and installation can be problematic.