Reliability Investigations for High-Power Laser Diodes and Bars
Qualification of laser diode design and technology
- Determination of Degradation Rates ≥ 10-5/h in aging tests at 15°C ≤ T ≤ 80°C and t > 1000 h
- Test Equipment:
- Current control for CW and QCW operation
- 10 places - CW up to an optical power of 100 W (bars)
- 130 places - CW up to an optical power of 40 W
- 150 places - QCW – duty cycle smaller 10%, peak current 300 A
- 10 places - dual contact for tapered lasers up to 40 W
- 10 places - four contacts for hybrid laser systems
- 45 places - BA and RW laser up to optical power of 4 W
- 120 places - burn-in up to 10 A
- Relative power measurement with 1% accuracy within 1000 h
Nondestructive failure analysis
- Electroluminescence
- Facet microscopy
- Spectra analysis below threshold
Example 1: Reliability tests of lasers for medical applications
- Lifetimes larger than 1,000 h necessary
- 630 nm - 760 nm requested for photodynamic therapy
- Shown example: 650 nm devices with 100 μm x 1.5 mm
- Test conditions: constant optical power 1.2 W at T = 15°C
Example 2: Lifetime test under hard pulse conditions
- Reliability test of diode lasers and bars with full thermal cycling
- Maximal current - 10 x 100 A, 130 x 45 A
- Switching frequency below 1 Hz
- Shown example: 980 nm broad area lasers 90 μm x 4 mm
- Test conditions: 15 A current pulses, 0.5 Hz at T = 25°C
Example 3: Determination of acceleration parameters
- Accelerated life test of laser diodes over 20,000 h
- Three lots of different stress conditions (1 - 1.5 W, 45 - 60°C)
- observed failures are plotted in log-normal scale
- Model of accelerated ageing: life time ∝ P-β exp(EA/kT)
- Evaluation of acceleration parameters by maximum likelihood method: EA = 0.28 eV, β = 2.33
