Great efforts and vast investments have been put into the research and development of widely tunable lasers in the last
25 years. Tunable lasers have become critical components in the implementation of next generation telecommunication
networks and systems, to provide dynamic wavelength provision for channel restoration, reconfiguration and protection.
Some stringent requirements have been imposed on tunable lasers by telecommunication applications. Consequently,
ultra-high optical output power (⩾100 mW), wide tunability (tuning range ~ 40nm), narrow linewidth (< 2MHz), and
side-mode suppression ratio (SMSR > 40dB) have become the main objectives for the development of the future
telecommunication tunable lasers. Facet output power is the fundamental decisive factor among these targets. Original
design ideas and novel approaches to the design of ultra-high power InGaAsP/InP based multisection widely-tunable
laser gain section have been reported by the authors previously, mainly including: firstly, a bulk balance layer structure
is placed above the InP buffer layer and below the MQWs stack, which enables a large reduction of free-carrier
absorption loss by greatly shifting the optical field distribution to the intrinsic and n-doped sides. Secondly, an InP
spacer layer is placed below the ridge and above the multiple quantum wells (MQWs) stack, so as to introduce extra
freedom in the control of widening the single mode ridge width. This paper will focus on the optimization on the
implementation of the above design ideas and approaches, regarding single mode ridge width, optical confinement in
the MQWs, optical overlap with the p-doped epilayers, output power, threshold current, and slope efficiency.