SiPh involves data that is transferred between computer chips by using optical rays. Although this might sound simple, it can be difficult to understand. It might therefore help to compare it to electrical circuits.
The first electrical circuits used discrete components e.g. resistors, capacitors and transistors that were interconnected with tracks on a printed circuit board. Discrete components were later formed adjacently on a single silicon substrate and interconnected to reduce cost and size. This was the start of integrated circuits (ICs or chips). The type of components that could be manufactured this way expanded while their power consumption and size shrank exponentially. Billions of components can now be built into a single IC, each at a trifling cost.
Silicon photonics aims at achieving the same cost effectiveness by integrating components in the optical field. Optical components, including combiners, modulators, splitters and lasers, are interconnected with transparent paths or waveguides that light travels through, similar to electricity running through tracks on a circuit board. The industry is focusing on leveraging the investments made by the electrical chip industry in silicon whenever possible.
Although SiPh solutions' technical capability has made progress, two challenges still keep the cost relatively high:
- The waveguides used by SiPh are small and this makes interconnections to and from chips expensive and difficult. The waveguide's diameter is less than half a micron, about 1/20th the diameter of a single mode fiber. Although alignment techniques are available, these are costly.
- Lasers can't be formed directly in silicon. Lasers are made from other materials and the light from them is coupled into waveguides.
Significant market impact is made by replacing pure silicon substrate with silicon dioxide (glass). The ensuing circuit is called a Photonic Light Circuit (PLC). A limited number of components can be formed on PLCs, although the use of a glass substrates produces waveguides that are six times bigger. This reduces the challenge of aligning to components such as lasers. This technological combination helps solve challenges and reduces the cost of high speed photonics. It also changes the industry's definition from "silicon photonics" to "integrated photonics (InPh)".
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