Photonic Integrated Circuits

- Photonic Integrated Circuits

Photonic integrated circuits (PICs) or integrated optical circuits are microchips that contain two or more photonic components that form a functional circuit. The technology detects, generates, transmits and processes light. Photonic integrated circuits use photons (or particles of light) instead of electrons, which are used by electronic integrated circuits. The main difference between the two is that photonic integrated circuits provide functionality for information signals applied at wavelengths of light typically in the visible spectrum or near-infrared (850-1650 nm). 

Compared to optical components, integrated optics offer the following advantages: greatly reduced size depending on the footprint of the optical waveguide, more robust optical alignment, i.e. optical alignment performed by the manufacturing process itself, and massive parallelism that reduces costs Reduced surface processing is possible. 

The most commercially used material platform for photonic integrated circuits is indium phosphide (InP), which allows the integration of various optically active and passive functions on the same chip. The initial example of a photonic integrated circuit is a simple 2-section distributed Bragg reflector (DBR) laser, consisting of two independently controlled device sections - a gain section and a DBR mirror section. Therefore, all modern monolithic tunable lasers, broad-spectrum tunable lasers, externally modulated lasers and transmitters, integrated receivers, etc. are examples of photonic integrated circuits. 

As of 2012, devices integrate hundreds of functions onto a single chip. Pioneering work in this area was carried out at Bell Labs. The most famous academic centers of excellence for photonic integrated circuits in the InP field are the University of California, Santa Barbara, Eindhoven University of Technology, and the University of Twente, the Netherlands. 

A development in 2005 showed that although silicon is an indirect bandgap material, it can still be used for lasing via Raman nonlinearity. Such lasers are not electrically driven but optically driven, so an additional optically pumped laser source is still required.