Selection of a Laser Reliability Assurance Strategy for a Long-Life Application

Abstract

We are concerned with assuring the reliability of semiconductor lasers intended for an application in which the design lifetime is long, replacement or redundancy is impossible or impractical, and the failure of even a few lasers could be disastrous. In the search for a reliability assurance strategy that will meet our objectives, we have carefully examined the well-known and widely used bathtub and lognormal approaches. Based upon our understanding of the expected aging behavior of lasers, we propose an alternative reliability assur ance strategy that we believe to be an improvement over the traditional approaches. The object is not how to make reliable lasers, but rather how to confidently predict, in a timely fashion, which lasers in a given population will endure beyond the intended system lifetime. Particular emphasis is placed upon initially imposed overstress regimes that address the anticipated presence of transient modes of degradation and infant failure modes with low thermal activation energies that may be invulnerable to detection during accelerated thermal aging. Since lasers degrade gradually rather than fail suddenly, comparable emphasis is placed upon monitoring the stabilized long-term degradation rates of the survivors of the overstress regimes so as to permit lifetime predictions of individual lasers.

Methodology of Accelerated Aging

“…For example, the device or its bond may melt at T a , or a strongly temperaturedependent degradation mechanism, 5,18 which is of secondary signifi cance at T s , may become dominant at T a . Then temperature, or at least the value T a , is simply not a valid accelerating stress because it does not induce the same, or even approximately the same, physical degradation process as aging at T".…”

“…Another truncation strategy, which is incorporated, for example, in the purge [4][5][6] and the tailored-accelerating-screen 2 procedures, is prem ised on the following physical model: All components eventually fail because all possess a common wear-out mechanism. In addition, certain flawed components are also afflicted with a second failure mechanism having a shorter life under normal operating conditions.…”

Implementation of the Proposed Reliability Assurance Strategy for an InGaAsP/InP, Planar Mesa, Buried Heterostructure Laser Operating at 1.3 μm for Use in a Submarine Cable

“…Potential low thermal activation energy modes of failure may not, however, be identified in this kind of screening test. 8,9 We shall show that due to the existence of an initially occurring saturable mode of degradation, which exists in some degree in virtually all lasers, and which typically can escape detection in burn-in tests because it has an incubation period, the conventional elevated temperature burn-in was found to be inadequate to assure reliability of its survivors. The purge (understood, hereinaf ter, to mean the overstress regimes) that was imposed on the burn-in survivors was essential to the success of the undertaking.…”

“…Discussions of screening strategies 8,9 have emphasized the concepts of the harshness, selectivity, and tailoring of the accelerants used to detect the presence of premature non-wear-out failure and transient modes. Initial device characterization and an understanding of how the device operates is crucial in giving specificity to these concepts.…”

A Statistical Approach to Laser Certification

“…If aging for a time ii at ΤΊ causes the same degradation as aging for a time f s at T s , and if the Arrhenius relation is applicable, then tl/ts = e < ? V -™ ( 2 ) where E is a parameter called the activation energy and K is Boltzmann's constant. In the following, two cases are considered according to whether E varies significantly from laser to laser (as determined from step stressing), or whether a common value for E may be used for all lasers.…”