Type of Test

Lifetime.

Goal of Test

Find laser lifetime in harsh conditions. Use it to predict lifetime in regular conditions.

Glossary

• Optical power = output power = light output (L) = amount of energy laser emits per second.
• Forward current = current (I). Current determines voltage & power.
• Forward voltage = voltage (V).
• Constant power mode = testing mode where you send in whatever current is needed to maintain power. Need to send in more and more current as laser diode ages.
• Median time to failure (MTTF) = median time in a batch of lasers before failure condition is met (ex. current is 30% higher than normal)

Testing Procedure, Length, and Frequency

• Dozens of lasers are monitored for at least 1,000 hours. Use high temperatures to accelerate ageing (ex. 75°C).
• Often use constant power mode and track current change over time.

Sample of 16 lasers being tested at 75°C. You track how long it takes before 20% increase in current. This is realistic data representing uncertainties, power outages,

• In the first hundred hours, there is rapid (curvy) degradation of the device. After that, there is a linear pattern to which you can extrapolate a line of best fit to.
• You find median time to failure across all lasers. Then, use the Arrhenius model $Life=A^{(\frac{E_a}{kT})}$ to estimate what the lifetime would've been like at a normal temperature with a specific activation energy.

Activation energies are known for different ypes of lasers. Or, if you test different batches at different temps, you can calculate the activation energy.

Key Variables Being Measured

• Time until current you need to input to get the rated power of diode is X% higher than normal. Ex. After 10,000 hours, the current you input to get 500 mW is 20% higher than normal. So lifetime = 10,000 hours.

Constant power mode is used for telecom lasers.

Regulations/Restrictions/Requirements

• Define sample size and length of testing time required.
• No standard temp. because different lasers have different use temps. Most lasers stop functioning at 100°C anyways.