Thermal Management Characterization of Microassemblied High Power Distributed-Feedback Broad Area Lasers Emitting at 975nm

This paper reports on thermal performances characterization of a new high power Distributed Feedback (DFB) laser diode technology for Yb, Er and Yb/Er doped fiber lasers demanding a very narrow and stable absorption line close to 975nm. In order to overcome these limitations in terms of spectral linewidth and wavelength stabilization, an integrated distributed feedback structure is proposed. The pump Laser diode has a 90μm × 4mm cavity including a patterned 2nd order grating layer and the Large Optical Cavity (LOC) consists in an Al-free active area. Performances are pointed out in terms of electro-optical and spectral responses and compared with free-running Fabry-Perot (FP) laser diodes. For a 4mm cavity length DFB Laser diode, a typical optical power of 5.5W at 8A, a maximum wall plug efficiency of 45% near 4A, a threshold current equal to 660mA and a spectral linewidth lower than 1nm with a SMSR over 30dB have been demonstrated. Additionally, a central wavelength drift versus temperature of 0.08nm/K is highlighted that is largely reduced in comparison of the free-running FP structure. Thermal resistance of the DFB device is also extracted using a dedicated equipment namely T3STER© allowing to characterize the thermal contribution of each part of the microassemblied device. Thermal resistance of the whole microassemblied device (≈ 2.5K/W) agrees with the state-of-the-art published values. These results have been compared with those given by the well-established technique achieved from the spectral measurements of the Laser diode giving the central wavelength drift versus temperature that is more difficult to apply for multimodal Laser diodes even for a DFB configuration. Finally, the interest to use diamond-copper composite as thermo-compensators submount is also investigated and compared to the typical CuW material.