High power distributed feedback and Fabry-Perot Al-free laser diodes at 780nm for rubidium pumping

Abstract

Development of techniques such as atom optical pumping, for atomic clocks and matter-wave interferometers (gyrometer, accelerometer, gravimeter and gradiometer), requires laser diodes with high power and excellent spectral (narrow linewidth) and spatial qualities together with high reliability. We have developed high power Fabry-Perot and distributed Feedback lasers diodes (DFB) emitting at 780nm corresponding to the D 2 line of Rubidium. We have realized a Fabry-Perot laser diode, without aluminium in the active region, with a cavity length and a waveguide width of respectively 1mm and 4μm and an AR/HR coating on the facets. We obtain a low threshold current around 40mA and a high slope efficiency of 1W/A at 20°C. We obtain a good beam quality M² of 2 at 200mW. These lasers diodes are very interesting to be inserted in an external cavity. For DFB lasers, we used a second order diffraction grating in a GaInP/GaAsP/GaInP waveguide. We calculated the coupling coefficient KL of 1.5 for a length of 2mm, for a width of 4μm. These lasers show a low threshold current (around 65mA) with a slope efficiency around 0.37W/A. We have obtained at 25°C, 145mA an optical power of 25mW at the D 2 line of Rubidium with a side mode suppression ratio around 44dB. By the selfheterodyne method, we measured a low linewidth of our DFB laser at 780nm around 1.25MHz (lorentzian fit).