This design note describes why the SMPTE serial digital interface (SDI) form of digital video is difficult to transmit over fiber optic links, and how the MAX3656 laser driver can be used to successfully overcome this problem. Early digital fiber-optic transmission systems were designed to deliver digitized audio (voice) over large telecommunication networks. For example, Synchronous Optical Network (SONET) is an optical transmission standard that uses scrambling to make clock and data recovery easier. Scrambling can help randomize the data to make it easier for the receiver to recover the clock without increasing overhead data. Uncompressed digital video also uses scrambling to help randomize the data being transmitted. However, the problem with digital video is that it can be created artificially by color generators, and digital color generators can create video with no noise. In particular, two colors do not always get adequately randomized by the scrambler and can result in repeating patterns that have either a large DC offset or a low transition density. These difficult-totransmit patterns are called “pathological patterns.” The pathological pattern containing the large DC offset is very troublesome for fiber optic transmitters. Overcoming problems with pathological patterns is the focus of this application note.