Transmission systems employing passively retimed regenerators require a bandpass timing filter to extract the timing wave from the data stream. Typically, filters with Q exceeding 100 are necessary in long-haul fiber-optic systems. The fabrication of a microstrip filter with a loaded Q of over 500 and an insertion loss of 8 dB, is reported. The midband return loss in 4.8 dB. The filter is fabricated on a 1-in*1-in*1-in Ba/sub 2/Ti/sub 9/O/sub 20/ substrate. This material has a dielectric constant of about 39 and can be formulated with temperature coefficients of resonant frequency from -2 to +6 p.p.m./ degrees C. The fabricated device has a temperature coefficient of +2 p.p.m./ degrees C. This combination of material properties facilitates high Q and small filter size and has the potential to compensate for temperature-induced electronic phase shifts between signal and clock recovery paths to the bit-decision circuit.>

The new lightwave long-haul transmission systems typically use surface-acoustic-wave (SAW) filters for timing recovery, in place of the phase-locked loops favored in slower systems. We report here analytical studies of jitter phenomena allowed by two kinds of filter ripple. The ripple is capable of causing jitter to accumulate exponentially with the number of regeneratorsNin a repeatered line. Such behavior is well known in the case of phase-locked-loop retiming, where the "jitter peaking" that usually appears in the loop response must be carefully limited to avoid exponential jitter growth. We show that equivalent phenomena can appear when the SAW filters exhibit passband ripple, or, as previously reported in condensed form, When ripple-free filters are detuned by approximately one-half the full 3 dB bandwidth. Furthermore, in the case of ripply filters, exponential jitter accumulation is found to be much more pronounced for random jitter than for systematic jitter. In addition, the alignment jitter within each regenerator can grow exponentially along the chain of regenerators. Neither of these statements is true in the case of the ripple-free filters previously treated in the literature.

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 technology is ready and reliable, filter size is consistent with the severe space limitations of undersea repeater housings, and cost is reasonable, especially for the transversal (tapped-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.