An efficient tapered coupling mechanism for monolithic integration of active and passive devices on InGaAsP/InP quantum well (QW) structures is theoretically analyzed and experimentally demonstrated. An easier fabrication technique using \(ZrO_2\) impurity-free QW-intermixing is used to achieve vertical tapering, while photolithography is used to optimize horizontal tapering. The importance of designing the epitaxial layer specifically for this fabrication technique and the device combination to be used is demonstrated. First, on a regular InGaAsP/InP waveguide photodiode structure and then redesigning the same for optimization and experimental verification. The improvement is achieved by introducing an InGaAs/InP superlattice (SL)—graded index (GRIN) with a single QW absorption layer in the waveguide core. Asymmetrical InGaAs/InP SL cladding layers are used for lower optical losses and higher index contrast. While the regular structure shows a reduction in coupling and insertion loss of 1 and 3 dB, respectively, a redesign of the epitaxial structure brought down the same by 7.5 and 9.0 dB, respectively.
