Photonic Integrated Circuit

Every day, you use dozens of devices containing microchips (integrated circuits; ICs). These mini electronic assemblies consist of tiny transistors, resistors, and amplifiers, all carefully installed on a semiconductor wafer. But electricity is not an ideal medium when it comes to ICs: bandwidth and speed are limited, electron-to-electron interference slows things down, and energy is lost over time. For optimal performance, forward-thinkers are looking to substitute photons for electrons and use photonic integrated circuits instead of standard ICs. 

An optical IC is typically composed of laser diodes, waveguides, filters, and gain media. Waveguides are the analogy to metallic wires, and using optical principles such as total internal reflection they guide the light in whatever direction desired. All the components of a PIC are installed on a flat base; perhaps a silicon wafer. Inside of this PIC, photons move at the speed of light, and they aren’t slowed down by other photons. Impressive speed and the fact that there’s almost no energy loss make a photonic integrated circuit incredibly powerful and efficient. 

So why weren’t all electronic ICs replaced by optical ICs yesterday? PICs are still in development, and although they are now available commercially they are more expensive and harder to find than your standard IC. They are also bigger than electron-based ICs, although ‘big’ here is relative. Electronic components may be extremely small, and a hundred million transistors can be installed on 1 mm of IC space. The elements of a PIC are significantly larger, leading to optical integrated circuits that are measured on the micron scale.  However, when additional micro-optics are included on the PIC the size differential goes the other direction, and the use of optical ICS enables lower-weight, compact systems that are easy to install.