Reliability of high-power 1030 nm DBR tapered diode lasers with different lateral layouts

Reliability step tests of two batches of 1030 nm DBR tapered diode lasers are presented. All 6 mm long devices are based on a previously published structure with a triple quantum well embedded in an asymmetric super large optical cavity. Layout variations include devices with straight waveguides and gratings, tapered waveguides and straight gratings, and straight waveguides and tapered gratings. The latter two enable enhanced DBR diffraction efficiencies, improving the spatial mode filtering within the device. Step tests are carried out with 1 W power increases every 1,000 h. In the first batch step test, devices with the all-straight design were operated at output powers from 5 W to 10 W, using a previously applied current density in the straight ridge waveguide of 75 A/mm(2). Here a demonstrated lifetime up to 5,700 h was measured, resulting in an estimated mean time to failure (MTTF) of 20,000 h at 5 W and 3,000 h at 8 W, respectively. The second batch step test contained devices with tapered waveguides or gratings. In these experiments, the ridge waveguide (RW) injection current densities were selected for highest spatial quality. The step tests were performed from 7 W to 9 W. Devices with tapered RWs had to be operated at 150 A/mm(2), three times higher compared to devices with straight waveguides in this test, and failed after 2,000-2,500 h. This is a shorter lifetime compared to the demonstrated 2,600 h for devices with tapered gratings. The overall estimated MTTF of 2,800 h at 8 W was comparable to the first batch, indicating the reliability of the vertical layer structure. Intermediate measurements before failure show more or less comparable stable electro-optical, spectral and spatial performances. After failure, corresponding to a 20% current increase required for the selected optical output power, near field measurements as well as electroluminescence and front facet images indicated that internal damages in the vicinity of the front facet might have occurred. Based on changes in the spectral behavior, damages and subsequent device failures are potentially linked to damaged intersections between waveguides and amplifiers. Nevertheless, these results show the robustness of the layer structure and processed devices and indicate that straight waveguide designs, requiring low RW injection currents to achieve excellent beam quality, are to be preferred.