Abstract
An improved phase-locked loop (PLL) for versatile synchronization of a sampling pulse train to an optical data
stream is presented. It enables optical sampling of the true waveform of repetitive high bit-rate optical time
division multiplexed (OTDM) data words such as pseudorandom bit sequences. Visualization of the true waveform can
reveal details, which cause systematic bit errors. Such errors cannot be inferred from eye diagrams and require
word-synchronous sampling. The programmable direct-digital-synthesis circuit used in our novel PLL approach allows
flexible adaption of virtually any problem-specific synchronization scenario, including those required for waveform
sampling, for jitter measurements by slope detection, and for classical eye-diagrams. Phase comparison of the PLL is
performed at 10-GHz OTDM base clock rate, leading to a residual synchronization jitter of less than 70 fs.
© 2007 IEEE
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