Service availability objectives for "fiber in the loop" telecommunication systems place limits on maximum component failure rates. For example, an optical network unit (ONU) located at or near the customer's location should have a maximum average downtime of
26 mm/yr/line, which translates to a failure rate of about 8250 FITs (8.25 ONU failures per million unit-hours). Laser modules used in this network element, therefore, need to be less than ~5000 FITs. Estimates of component failure rates, however, often have large uncertainty. For example, laser module reliability cannot be predicted more accurately than a possible range of 3000 to 12,000 FITs; the reliability of the fiber pigtail and its alignment to the laser are a major source of this uncertainty. More information is required about the laser module and other fiber optic components to increase the confidence in failure rate projections.