Silicon Photonics Enables Low-power AI Accelerator Platform

Context: Recently, scientists have created the first miniaturised laser directly on a silicon chip, marking a significant breakthrough in silicon photonics.

What is Silicon Photonics?

• Silicon photonics is a technology that uses light (photons) instead of electricity (electrons) to carry and process information on silicon-based microchips.
• It combines optical components with traditional silicon electronics, allowing faster and more energy-efficient communication between and within chips.

Advantages of Photons over Electrons

• Photons move faster and can carry much more data at once (high bandwidth).
• They generate less heat and lose less energy during transmission.
• This makes photonic chips ideal for high-speed data transmission, especially over short distances like between servers or chips.

Challenge in using Photons

• A key challenge was integrating a light source (laser) directly into the silicon chip, as silicon does not naturally emit light.
  • Silicon has an indirect bandgap, meaning electrons in silicon need assistance (like vibration energy) to drop energy levels and emit light.
• The ideal solution is to build the laser directly on the silicon chip, but this is difficult because:
  • Materials like gallium arsenide and silicon have different crystal structures
  • This causes defects when one is grown on the other, reducing efficiency.
• Recently, researchers solved this integration problem:
  • They used nanometre-wide trenches in a 300 mm silicon wafer & grew gallium arsenide at the bottom of these trenches, trapping defects there.
  • This allowed high-quality laser material to grow on top.
  • Direct integration reduces costs, making the technology scalable for mass production.

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