Recent progress in data transmission systems requires high output power single transverse mode laser diodes for Raman and Erbium-Doped Fiber Amplifier pump sources. Several approaches have shown high output power emission up to 1 Watt for 14xx-nm InGaAsP/InP pump lasers. In these works, the design rules were mainly related to the active volume increase, through large or flared waveguides or through the use of MMI. Such designs lead to electrical and thermal resistance decrease. MMI waveguide have already demonstrated better behavior in comparison with straight active waveguide, but neither experimental comparison nor modelisations between different active MMI structures have been reported.
In this work, we report on 2D-BPM simulations and experimental results between different active MMI 1x1 structures for 14xx-nm pump laser. The MMI 1x1 is a large multimode waveguide connected in both sides center by one single transverse mode waveguide. Several parameters such as p order, wavelength emission, MMI width and MMI length have been studied in order to carry out simple design rules for active MMI waveguide based lasers. Moreover, to achieve high level output power, long lasers are necessary. In this case, we also compare long laser, typically 1.2mm, formed by one long MMI waveguide or formed by several short MMI waveguide.
Simulations show a better behavior for short MMI length (LMMI<250μm) and small MMI width (WMMI<10μm). As expected, experimental results are in good agreement with simulations, and the output power figure is improved using the long laser formed by several short MMI waveguide.
Observation of spatial hole burning reduction is reported for the first time to our knowledge on flared 1480nm high power InGaAsP/InP buried ridge lasers. We determined the longitudinal carrier density profile by spatially resolved spontaneous emission measurements for slightly tapered and straight active waveguides. The tapered stripe shows spatial hole burning reduction leading to 25% output power enhancement.