In this paper, we will analyze the effect accumulated jitter has on the decision making process inside the

th fiber optic regenerator of a long chain of fiber optic regenerators. The criteria for a correct bit decision in the presence of receiver noise, static phase offset, and accumulated input jitter will be derived, and calculations of the bit error rate penalties caused by the presence of known distributions of accumulated input jitter will be made. We will then define the jitter tolerance of a fiber optic regenerator as an effective measure of the regenerator\´s capability to tolerate incoming accumulated jitter. We will show that excessive bit error rate penalties will not occur if the accumulated input jitter does not exceed the regenerator\´s measured jitter tolerance template. Finally, the jitter tolerance measurement technique will be used to find the optimum sampling time inside a fiber optic regenerator resulting in a regenerator that is optimized for use in long-haul systems.