Let’s start with the basics. We know that light can behave like a wave or a particle, and this behavior can be manipulated. The term “optics” refers to the study of light and often is used to talk about the light that is visible to the human eye (e.g., the light from a headlamp, light reflecting from a lens such as a magnifying glass, etc.). The term “photonics” means systems where light is being reflected or manipulated at a much smaller scale (think smaller than a few micrometers). Integrated photonics is when the photonic system is manufactured using semiconductor technology with wafers that are processed in a cleanroom facility. And if the manufacturing process that is used is very much like CMOS fabrication, that is when it is referred to as silicon photonics.
In other words, silicon photonics is a material platform from which photonic integrated circuits (PICs) can be made using silicon on insulator (SOI) wafers as the semiconductor substrate material. The technology is becoming much more popular and feasible than ever before, and there is an important reason why.
Initially, integrated photonics started using materials like doped silica glass, lithium niobate, or indium phosphide as the material surface, especially for telecom and long-haul datacom applications. However, the vast majority of the semiconductor industry uses silicon as the primary material to create integrated CMOS circuits, achieving very high yield and low cost. The physics of photonics makes it perfectly suitable to pattern and fabricate photonic devices and circuits using CMOS processes used on older silicon nodes. Using mature manufacturing processes has opened an economically viable path to mass production, and, consequently, integrated silicon photonics has taken off.
Today, silicon photonics has leveraged the mature CMOS manufacturing and design ecosystem that has proven to be very cost-effective at scale to start building integrated photonics systems.