Widely tunable ultra-high power monolithic multi-section tunable lasers have been a sought after dream for more than two decades. In recent years, tunable lasers have become critical components in the development of the next generation telecommunication networks and systems, due to their unique attributes and flexible functionalities. However, some stringent requirements have been imposed on tunable lasers by telecommunication applications regarding their tuning range, optical output power, side-mode suppression ratio (SMSR), linewidth, chirp, tuning speed, reliability, and so on. In addition, monolithic tunable lasers, requiring a regrowth process, suffer from butt-joint reflections from the regrowth interfaces of these multi-section devices, which have seriously affected their tunability, and greatly reduced their facet output power. Butt-joint reflection losses between active-passive interfaces are therefore the crucial and decisive factors in multi-section tunable laser operation. In this paper, original design ideas and novel approaches to the design of ultra-high power InGaAsP-InP based multi-section widely-tunable lasers are introduced. Simulation results show that the facet output power in the proposed new design can be greatly increased compared with a conventional design. The optimized butt-joint angles and the arrangements of these angles at the active-passive interfaces in a multi-section tunable laser can largely reduce the total adverse interface reflection in the device, and tremendously improve the operation performance of the multi-section tunable laser. Finally, an integrated curved semiconductor optical amplifier with an angled facet is introduced that would futher increase the total optical output power of the device and reduce the backward optical reflection into the device.