We present in this article a comparison of 1.3 mu m InAs0.45P0.55/In0.81Ga0.19P strain-compensated multiple quantum well (SC-MQW) modulators with and without an InP insertion layer. Material quality was evaluated by cross-sectional transmission electron microscope analysis, x-ray rocking curves with dynamical simulations, and photoluminescence measurements. Devices were fabricated and device performance criteria such as contrast ratio (C.R.) and uniformity were also compared. It was found that higher C.R. and highly uniform InAsP/InGaP SC-MQW modulators can be achieved by inserting thin InP layers at the heterointerfaces between InAsP and InGaP.