Direct Detection of Digital Optical Receiver

Direct detection is the simplest form of optical signal recovery. The transmitter modulates the intensity of the optical carrier, and the receiver uses a photodetector (PIN diode or avalanche photodiode) that responds only to the optical power envelope. 100 Gb/s links (and higher) are now common between regional data centers, often stretching tens of kilometers. The receiver implements strong dispersion and delay lines on a compact chip. For much of the past fifteen years, the boundary between these two approaches was relatively clear. [pdf]