High brightness, frequency stabilized diode laser at 1530nm

We report on high brightness diode laser at 1.5 m with wavelength stabilized output. 22W are delivered from a uncoated 100m fiber with 0.15 NA at 1532nm with a bandwidth of 2 nm. InP diode lasers emitting at 1.5 m show much lower power than GaAs based diodes emitting around 900 nm due to the low electro-optical efficiency of 1.5 m diodes of about 35%, compared to about 65% of GaAs diodes. Single emitters allow the highest power from given size broad area emitter due to optimized cooling. Up to 6W (15W) are available from a 95 m broad area single emitter at 1.5 m (9xx nm). At 1.5 m the maximum power is typically limited by thermal roll over and efficient heat dissipation from the diode is essential for power scaling. Optical stacking is deployed for power scaling thus symmetrizing the beam quality in fast and slow axis for efficient fiber coupling. Typically, 65% efficiency for optical stacking and fiber coupling are achieved resulting in more than 22W from a 100 m fiber of 0.15 NA. Resonant pumping of Er lasers requires a 2nm linewidth centered at 1530nm. The free running diodes show about 10nm linewidth (96% power content) and about 2.5nm/A tuning coefficient with varying drive current depending on heatsinking. Frequency stabilization is achieved with external Volume Bragg Gratings. More than 85% power is confined within a 2nm bandwidth up to 8A drive current resulting in 17W from the uncoated 100 m fiber. The diodes are emitting at 1546nm at 8A without VBG and 20W from the fiber are possible with the proper lower wavelength diode.