Chapter 5 - Optical System Performance Measurements

Abstract

This chapter discusses techniques to measure the performance of digital fiber-optic systems and subsystems. It provides an overview of digital optical transmission systems and their performance specifications, such as bit error rate (BER), the quality factor (Q), and techniques to measure them. In a fiber-optic transmission system, the receiver has to correctly recover the data carried by the optical carrier; receiver sensitivity and receiver OSNR tolerance are two useful receiver specifications. In practical applications, receiver sensitivity is useful for receiver noise-dominated optical systems, whereas required optical signal-to-noise ratio (R-OSNR) is often used in systems with inline optical amplifiers in which performance is mainly determined by the OSNR of the optical signal. In fiber-optic transmission systems, performance degradation can be caused by random noise and deterministic waveform distortion. Time jitter has always been an issue affecting the performance of digital communication systems and networks. There are a number of techniques to detect time jitter; among them the most widely used techniques are sampling oscilloscope measurement, phase detection measurement, and BER-scan measurement. A number of in situ performance-monitoring techniques for optical transmission systems are available, where data traffic carried in the system is used as probing signal for measurement. Physical parameters of the fiber system, such as chromatic dispersion, PMD, and PDL, can be extracted from these measurements without interrupting system operation. Furthermore, the chapter discusses the aspects of nonlinear crosstalk between wavelength channels, modulation instability, transmission performance measurements, and fiber-optic recirculating loops.