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Study of frequency noise in spectral lineshape of 780nm GaAsP/GaInP quantum well lasers for inertial sensor applications

Ultra precise and stable gravimeters and gyrometers are highly demanded for various applications like fundamental physics, geophysics, navigation systems. Interferometry of Rubidium cold atoms requires high power, narrow linewidth, low frequency noise and highly reliable optical sources emitting at 780 nm. In this context, we developed basic bricks for realization of a distributed feedback (DFB) laser. On one hand, 100 μm broad area devices achieve at 20°C a continuous wave (CW) output power of more than 4 W per facet. On the other hand, we demonstrated excellent performances on Fabry-Perot ridge-waveguide lasers with a threshold current of 35 mA, emitting up to 120 mW per facet, in single lateral mode at 780 nm. We already achieved an output power of 20 mW with a small spectral linewidth of less than 1 MHz on a DFB laser. We present here the results on a new and systematic investigation of the low frequency noise of such laser structures, in order to better understand and improve their performances. By using an appropriate current source and very low noise voltage amplifier (10-19 V2/Hz at 10 Hz), we can measure the intrinsic Terminal Electrical Noise (TEN), due to the fluctuations of the laser voltage. The measurements have been performed at low frequency (1Hz < f <100 kHz) and different laser currents (around the threshold current, above and at high laser current). On broad band area lasers, we obtained very low 1/f level noise (10-13 V2/Hz at 1 Hz) due to optical gain fluctuations. The white noise(shot and thermal noise) level is about 10-18 V2/Hz. The corner frequency between 1/f and white noise is about 3 kHz, which is a good result for this kind of structures. Electrical noise measurements will be interpreted by using lasers noise theory.