Optical fiber repeatered transmission systems utilizing SAW filters

Baseband digital transmission-line systems capable of signaling rates of several hundred to several thousand Mbit/s are presently being developed around the world. The pulse regeneration process is gated by a timing wave which is synchronous with the symbol rate of the arriving pulse stream. Synchronization is achieved by extracting a timing wave from the arriving pulse stream, itself. To date, surface acoustic-wave (SAW) filters have been widely adopted for timing recovery in the in-line regenerators of high-bit-rate systems. The present investigation has the objective to acquaint the SAW community in general, and SAW filter suppliers in particular, with the requirements for timing recovery filters in repeatered digital transmission systems. Attention is given to the system structure, the timing loop function, the system requirements affecting the timing-recovery filter, the decision process, timing jitter accumulation, the filter 'ringing' requirement, and aspects of reliability.