Glossary entry

Burn-in

Operation of semiconductor lasers at elevated bias and temperature to accelerate early-life failures, screening out devices likely to fail during their service life. The standard reliability-screening step in qualified laser production.

Burn-in is a controlled stress test performed on semiconductor lasers (and other active optoelectronic components) shortly after fabrication to accelerate latent failure mechanisms. Devices that survive burn-in are statistically much less likely to fail in subsequent service. Devices that fail burn-in are screened out before reaching the customer.

Physical motivation. Semiconductor laser failure rates follow a bathtub curve: a high early-failure period during the first hours to weeks of operation (driven by manufacturing defects, latent dislocations, mirror contamination), a long flat random-failure middle period (driven by random events such as electrostatic discharge or external mechanical shock), and a final wear-out period (driven by dislocation growth, oxidation, metal migration). Burn-in stresses the device hard enough that early-failure-mode defects manifest within a tractable test duration.

Standard burn-in conditions for a telecom InP DFB laser:

Parameter	Setting
Temperature	85 °C (sometimes 100 °C for aggressive screen)
Drive current	$1.5 - 2 \times$ rated operating current
Duration	96 – 168 hours (4 – 7 days)
Monitoring	Periodic LIV (every 24 hours) to identify drift
Pass criterion	$I_\text{th}$ shift $< 5\%$ , slope efficiency drop $< 5\%$ , no sudden failure

The acceleration factor relative to room-temperature operation is set by the activation energy $E_a$ of the dominant failure mechanism, typically 0.5 – 0.8 eV:

A \;=\; \exp\!\left[ \frac{E_a}{k} \left( \frac{1}{T_\text{op}} - \frac{1}{T_\text{stress}} \right) \right].

For $E_a = 0.7$ eV, $T_\text{op} = 25$ °C, $T_\text{stress} = 85$ °C: acceleration factor $\approx 50$ — one week of burn-in tests $\approx$ one year of room-temperature operation. Combined with the higher drive current factor (typically $\sim 5\times$ ), the equivalent accelerated lifetime in 168 hours can reach $\sim 5$ years of nominal operation.

Failure modes screened by burn-in:

Dislocation propagation in active region: visible as gradual $I_\text{th}$ rise; classical early-life failure mode in III–V epitaxy
Mirror facet oxidation / contamination: appears as slope efficiency loss
Solder fatigue between submount and heatsink: shows as thermal resistance rise, $T_0$ degradation
Catastrophic optical damage (COD): sudden output power drop; identifies devices with marginal mirror passivation
Wire bond degradation: $V_\text{on}$ rise, sometimes intermittent at first
Contact metallization issues: series resistance rise

Quality-control statistics. Standard production yield rates:

Population	Typical pass rate
Mature InGaAsP/InP DFB process	$> 99\%$ pass burn-in
New or aggressive design	$80 - 95\%$ pass burn-in
Engineering samples	varies widely; 50 – 95%

A burn-in pass rate substantially below the mature process baseline is a flag for a fabrication problem and triggers root-cause investigation.

Burn-in vs Telcordia qualification. Burn-in is a 100% screen — every device in the production lot undergoes burn-in. Telcordia GR-468 qualification testing is a destructive sample-based test (typically $\sim 50$ devices) that demonstrates the design's intrinsic 20-year reliability and is performed once per design qualification, not per lot.

Burn-in is one of the major contributors to packaged laser cost — equipment, time, and yield loss combine to add $2 – $50 per device depending on the product class.

References: Telcordia GR-468 Issue 2 (qualification requirements for optoelectronic devices); JEDEC JESD22 series for thermal/electrical stress test specifications.