Highly reliable and high power 980 nm pump laser diode module for undersea cable systems

Highly reliable and high power weakly index guided buried-stripe type 980 nm pump laser diodes developed for undersea applications are reviewed. The 10,000-hour large scale reliability tests of the first generation LD chips shows that 16.7 FIT for the random failure was confirmed at 10°C with 60% confidence level at 120mW output power. We also fabricated a FBG locked co-axial type module using a can-sealed LD with a two-lens system, which showed a stable FBG locked mode oscillation at 980 nm under the temperature range from 5°C to 45°C. The 5,000-hour heat cycle test of the modules reveals that the cumulative failure rate after 27 years at 10°C is expected to be 0.023%. These first generation LD modules were employed in the transoceanic commercial systems such as Pacific Crossing-1 and the Japan-US cable system projects. We have also succeeded in developing the 980 nm LD for higher output operation with optimizing waveguide design. The 1000 μm long LD showed CW kink-free operation up to 545mW optical output and a maximum output power of over 650 mW, which was limited by thermal rollover. In addition, a preliminary aging test at 350 mW optical output power at 50°C has shown stable operation up to 2,300 h. We also confirmed 300 mW kink-free fiber output power with a co-axial type module with the improved coupling efficiency of approximately 78%. These figures are the highest reported operation levels for 980-nm co-axial type modules.