Timing Recovery with SAW Transversal Filters in the Regenerators of Undersea Long-Haul Fiber Transmission Systems

Surface-acoustic-wave (SAW) filters have been generally accepted as the best available choice for timing recovery in repeatered transoceanic fiber transmission systems operating in the range of 300 Mbit/s as well as in other digital transmission systems operating from approximately 0.1 to 1 or 2 Gbit/s. The SAW tqhnology is ready and reliable, filter sue is consistent with the severe space limitations of undersea repeater housings, and cost is reasonable, especially for the transversal (tipped-delay-line) filter type. This paper updates the relationship between system performance and the characteristics of transversal SAW filters, which have a finite impulse response and non-minimum-phase behavior. New results relate to passband ripple (typical in these filters), thermal characteristics, and the impact of the delay-line structure on filter " ringing " time.