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

Abstract

The development of techniques such as atom optical pumping, for atomics clocks or precise gyroscopes, requires laser diodes with high power and excellent spectral (narrow linewidth) and spatial qualities together with high reliability. We have realized a six months ageing test on Al-free DFB lasers emitting at 852nm for Cs pumping. Ten DFB lasers were aged at 40°C and 20mW. The extrapolated lifetimes at 40°C, based on 20mW operating current, of our DFB lasers are higher than 500000 hours which confirms the excellent potential of this Al-free technology for long life spatial mission. Furthermore, the evolution of the operating current (initially around 70mA), after six months, is less than 5% (corresponding to 3mA). We obtain a very good stability of optical spectra: an average variation of the Side Mode Suppression Ratio (SMSR) of less than 2dB and a variation of the wavelength of less than 0.12 nm. We also measured the linewidth of our DFB lasers with the delayed self-heterodyne method after the six months ageing: we obtain a very narrow linewidth at 25°C (measurement temperature) around 215kHz (lorentzian fit, white noise) or 330kHz (gaussian fit, 1/f noise).