THERMAL INVESTIGATION ON HIGH POWER DFB BROAD AREA LASERS AT 975nm, WITH 60 EFFICIENCY.

摘要

The high power diode laser plays a key role for the pump source of fiber. Our knowledge on performances, robustness and failure analysis, allow us to implement the design for reliability rules from the fabrication of the diode laser since this last takes positive feedback from characterization to epitaxial process improvement. The external efficiency (dP/dI) of 1 WA~(-1) combined with low threshold current I_(th) (450mA) and low series resistance R_S (36mΩ), for a 4 mm cavity laser allows a high value of WPE with a maximum above 60% and remains stable until 8A, at least. The optical spectrum (SMSR＞30dB and spectral width ＜1nm) and the internal parameters place the laser among the best reported works in literature. The thermal management in the high power laser is crucial, for this reason we put in place a new method for thermal resistance measurements and a FEM simulation. The intrinsically multimode nature of such diode laser, combined with low value of R_(th) ≈ 2K/W , makes hard the measurements of thermal resistance with the well-known classical method. Hence we used the T3STER© methods that directly measure the dissipated power. We established a protocol of measurements for the T3STER© and to our knowledge this is the first time such measure is done with high power diode laser at 975nm. We obtain the best value of R_(th) in literature. The measure of R_(th) with T3STER© gives information not only regarding the R_(th) but moreover regarding the heat flux in all interfaces. The simulation has a good value of accordance (maximum error ＜ 10%) between simulation and experimental results. Moreover, we found the optimum etching depth, a good compromise between the optical and electrical confinement. This etching depth allows the diode laser to remain vertically mono mode, his gain is well confined in the central ridge and the thermal management is optimized. The more the etching is deeper and more the current density in the LOC structure will increase, and the Joule effect associated will raise the temperature inside of the laser.rnIn future, we plan to simulate the optical power, in order to untie the thermal simulation from the experimental measurement. This situation will allow us to foresee eventual bottleneck for the optical power (at high current level).