Timing jitter control of an add/drop optical module in a convergent network

Summary form only given. Timing jitter is the deviation of a signal from its "should be" position in time and it is one of the major sources of errors in communication networks especially for high data-rate systems. Two factors that make jitter control more important and more difficult than ever before in a convergent network are the ever-increasing data rates and the natural disparities of various applications. As the data rate increases, the timing window for data capture becomes smaller and smaller and therefore the difficulty of correctly capturing the data increases. Timing jitters further reduce the window and thereby increase the probability of data-sampling or data-recovery errors. With more and more applications are being converged to the network, the timing variations among these applications increase and therefore impose more technical challenges for recovering the clock and the data. Sources of timing jitters in general can be categorized as random or deterministic. The former comes from the random nature of electronic components such as thermal noise and shock noise while the latter is normally attributed to the design. Three measurements are typical for modules - jitter tolerance, jitter transfer, and jitter generation. Since jitter cannot be eliminated completely, a module should be able to tolerate the maximum amount of jitters that could possible exist in a system without making any error. The measurement of jitter tolerance of a module is to ensure this capacity. The measurement of jitter transfer is to find out how much jitter that a module adds to that of an incoming signal. The measurement of jitter generation is the measurement of the jitter that a module generates. Technology advancement has made the measurements of jitter much easier. Instruments are now available for these measurements. However, differences among the various instruments as well as accuracies of measurements are some of the major concerns. Although jitters cannot be eliminated completely, they can be reduced or controlled by good design and proper operation. From the operational point of view, the temperature and the power supplies should be controlled to reduce noise and the module should be kept away from strong electromagnetic interference. Common practices in a goo- d design include selection of the right components for the desired frequency and temperature ranges, proper component placement and signal routing in the physical layout of the printed circuit board, and good thermal management with proper mechanical design. This presentation cover the basics of current jitter measurement and design techniques for an optical module.