Fiber optic transponders are devices that receive, amplify, and retransmit optical signals on different wavelength channels. They are used to convert optical and electrical signals, for serialization and de-serialization, and for monitoring and control. Often, fiber optic transponders are used to for testing interoperability and compatibility. Typical tests and measurements include jitter performance, receiver sensitivity as a function of bit error rate (BER), and transmission performance based on path penalty. Some fiber optic transponders are also used to perform transmitter eye measurements. Selecting fiber optic transponders requires an understanding of jitter measurements and BER measurements. There are three types of jitter measurement: jitter generation, jitter tolerance, and jitter transfer. Jitter analyzers are used with fiber optic transponders and test boards. Jitter generation data includes current and maximum values for jitter peak - peak, jitter + peak, jitter - peak, and jitter RMS (root mean squared). Jitter tolerance and jitter performance are scaled values. For BER measurements, test boards with fiber optic transponders are used with pulse pattern generators, error detectors, reference lasers, and reference receivers. Case temperature is an important variable. Specific test setups are required for measuring transmission performance based on path penalty, and for transmitter eye measurements. For path-penalty testing, test boards with fiber optic transponders are used with pulse pattern generators, reference lasers, reference receivers, and fiber spools. Original chirp and optimal chirp are important parameters to consider. For transmitter eye measurements, fiber optic transponders are used with pulse pattern generators, reference lasers, and high-speed oscilloscopes. There are significant differences between the filtered eye and the unfiltered eye. Eye measurements vary by distance and, because of the error rate (ER), may require optical modulation amplitude (OMA) instead. Fiber optic transponders carry product specifications for local channels, remote channel, system performance, power, operating environment, and regulatory compliance. Local channel parameters include data rates for low-speed and mid-speed modules, protocols such as Ethernet and fiber distributed date interface (FDDI), and single-mode wavelength. For both low-speed modules and mid-speed modules, transmitter output and receiver sensitivity are important to consider. Suppliers of fiber optic transponders also specific remote-channel values such as transmitter output, wavelength, and clock recovery. Bit error rate (BER) is critical for system performance.