14 April 2006 Al-free active region (λ = 852nm) DFB laser diodes for atomic clocks and interferometry applications
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Atomic clocks will be used in the future European positioning system Galileo. Among them, the optically pumped clocks provide a better alternative with comparable accuracy for a more compact system. For these systems, diode lasers emitting at 852nm are strategic components. The laser in a conventional bench for atomic clocks presents disadvantages for spatial applications. A better approach would be to realise a system based on a distributed-feedback laser (DFB). We have developed the technological foundations of such lasers operating at 852nm. These include an Al-free active region, a single spatial mode waveguide and a DFB structure. The device is a separate confinement heterostructure with a GaInP large optical cavity and a single compressive-strained GaInAsP quantum well. The broad-area laser diodes are characterised by low internal losses (<3 cm-1), a high internal efficiency (94%) and a low transparency current density (100A/cm2). For an AR/HR coated 2mm long around 4μm wide ridge diode, we obtain a low threshold current (40mA) and a high slope efficiency (0.90W/A). With the Fabry-Perot laser structure we obtain 852nm wavelength at 145mW (I=200mA, 15°C). We measure an optical power of 230mW (I=280mA) in a single spatial mode with the beam quality parameter M2=1.3. With the DFB laser structure, we have obtained single frequency (side-mode-suppression ratio : SMSR over 30dB) and single mode lasers (M2<1.5) with a high optical power. An optical power of 150mW was obtained at 854nm wavelength and 20°C for AR-HR coated 2mm long, ~ 4μm wide devices. At this power, both near and far fields in the slow axis are gaussian-shaped with respective full widths at 1/e2 of 8μm and 9.2° respectively, corresponding to a single spatial mode emission with a beam quality parameter M2=1.29. The SMSR is over 30dB. Furthermore, the preliminary results of the linewidth obtained with a Fabry-Perot interferometer give a value of less than 2MHz.
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V. Ligeret, V. Ligeret, F.-J. Vermersch, F.-J. Vermersch, S. Bansropun, S. Bansropun, M. Lecomte, M. Lecomte, M. Calligaro, M. Calligaro, O. Parillaud, O. Parillaud, M. Krakowski, M. Krakowski, } "Al-free active region (λ = 852nm) DFB laser diodes for atomic clocks and interferometry applications", Proc. SPIE 6184, Semiconductor Lasers and Laser Dynamics II, 61840A (14 April 2006); doi: 10.1117/12.662723; https://doi.org/10.1117/12.662723


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