Design of ultra-high power multisection tunable lasers

Monolithic tunable lasers have been a sought-after dream for more than 20 years, due to their unique attributes and potential applications. They are expected to have significant applications in many areas, from fiber optics to medical applications, especially in fiber optical telecommunications, driven by the huge demand for telecommunication bandwidth. This paper introduces novel approaches on how to achieve ultra-high power in the designs of practical InGaAsP-InP-based multisection widely tunable lasers. The inventive ideas basically are comprised of three parts. First, to increase the facet optical output power by the inclusion of an InP spacer layer below the ridge and above the multiple quantum wells (MQWs) stack, in order to have extra freedom in the control of widening the single-mode ridge width. Second, to reduce the free-carrier absorption loss by the inclusion of a graded-index separate-confinement heterostructure (GRIN-SCH) structure below the MQWs stack and above the buffer layer, so as to largely shift the optical power distribution to the intrinsic and n-doped sides of the epilayer structure where the free-carrier absorption losses are lower than that of the p-doped side. Third, optimized butt-joint angles are designed to tackle the butt-joint reflection problems and optimize the operation performance of multisection tunable laser devices. As a result, the facet output power can be increased by up to 83% compared with conventional designs, and the reflectivity across butt-joints in multisection devices can be greatly reduced.