Eye diagrams visualize signal quality; wider "eye openings" mean better integrity. Bit Error Ratio (BER) measures error rates but requires downtime and may overlook error bursts. Advanced in-service monitoring enhances system evaluation without disrupting operations. This paper provides an introduction to the BER Contour measurement - what it is, how it is constructed, and why it is a valuable way of viewing parametric performance at gigabit speeds. It shows all possible transitions (0-to-1, 1-to-0, 0-to-0, and 1-to-1) on top of each other. Eye diagram are more relevant for wireline communication systems like USB, PCIe. This lecture introduces the concepts of bit error rate (BER) and eye diagrams in high-speed photodetectors. It begins with the definition of BER as the probability of incorrectly identifying bits during transmission. The resulting image takes on a distinct eye-like shape, from which engineers can discern important signal characteristics.
[PDF Version]