Alphawave’s CTO, Tony Chan Carusone, continues his technical talks on high-speed communications discussing fundamental benefits of optical links. Compared to electrical links, optical fibre waveguides are inherently crosstalk free, channel loss is low, and the response is relatively flat, so they require less equalization. There are two fiber types, single-mode and multimode, and two types of material, glass and plastic, that are used to transmit optical signals. IMDD (intensity modulation direct detection) is modulation which detects the intensity of light to represent logic levels; another modulation scheme is waveform division multiplexing (WDM). Optical applications, their specifications and various impairments are described further in this last installment of high speed communications, including extinction ratio and transmitter and dispersion eye closure quaternary, or TDECQ. Optical receiver front-end design can also be co-optimized and is critical in getting the right signal to noise ratio out of your design.