Abstract
In today’s networked world and the ever-increasing global demands in data bandwidth, optical communication systems are evolving towards employing higher channel data-rates at 10 Gb/s, 40 Gb/s and beyond. At such bit-rates, the dispersion or group-delay properties of not only the transmission fibers, but also of each optical components used, are important parameters for system designers and component vendors. Various methods have been proposed for group-delay or dispersion measurement. The most commonly adopted “industrial” standard for group-delay measurement is mainly based on the modulation phase-shift (MPS) technique. Typically, a tunable external-cavity laser (ECL) is used as an optical source and the output being intensity-modulated at a known radio-frequency (RF) signal. The modulated signal is launched through the device- under-test (DUT) and detected through a photo-detector and lock-in RF phase-discriminator. The optical group-delays at each wavelength can then be calculated from the measured RF phase differences. The measurement is usually performed with an RF network analyzer and a tunable ECL which steps each measuring wavelength point-by-point, at a rate which take seconds per point, due to ECL wavelength settling time. Additionally, a wavelength meter may also be essential due to the poor wavelength accuracy of an ECL, which further increases the measurement time.
© 2002 Optical Society of America
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