High-power high-reliability and narrow linewidth Al-free DFB laser diode for Cs pumping (852nm)

摘要

Precise gyroscopes and atomic clocks are in high demand for positioning and flight navigation systems or measurement of fundamental constants. The development of techniques such as atom optical pumping (Cs or Rb) requires laser diodes with high power and excellent spectral (narrow linewidth) and beam qualities. For spatial applications a high reliability is required (mission lifetime is around 15 years). We have realized different studies of reliability on our Al-free DFB lasers: Catastrophically Optical Mirror Damage (COMD) evaluation, lifetest, optical and spectral measurements before and after ageing. We obtained high COMD densities (respectively 13MW/cm~2 in continuous wave CW and 19MW/cm~2 in pulsed mode. Furthermore, we have realized ageing test on these DFB laser diodes emitting at 852.12nm (D2 line of Cs). We used five different ageing conditions (power and temperature) to determine ageing properties. The extrapolated lifetimes of our DFB laser (for operating current variation equal to 100%) are higher than 140000 hours (about 15 years) for an ageing at T= 25℃ and P= 40mW. This confirms the excellent potential of this Al-free technology for long life spatial mission. The Side Mode Suppression Ration (SMSR) of the aged D2 line DFB lasers remains very high with a measured change of-1.4dB ± 8dB. There are no significant drifts of the DFB laser wavelength after aging (average ～0.03 nm). We also measured the linewidth of our aged DFB lasers by the self-heterodyne technique and obtained narrow beating linewidths of around 900kHz.