Polarisation insensitive electroabsorption modulator with record power saturation using strained InGaAsP/InGaAsP/InAsP MQW structure

Polarisation insensitive multi-quantum wells electroabsorption modulators becomes very attractive for optical communications, in particular for in line applications where the incident light polarisation is random. One key issue of the modulators remains their power saturation. The phenomenon cited as limiting power saturation is the accumulation of holes, in the quantum wells, which creates screening of applied field. To overcome this problem a low height barrier for holes is necessary to decrease the escape time of holes. In the InGaAsP system the relatively large valance band offset prevents a fast holes evacuation. Consequently the quaternary compositions range for wells and barriers which satisfied the two requirements, high power saturation and polarisation insensitivity, is very narrow. In this study we report a innovative design with strain multiquantum well structure InGaAsP/InGaAsP/InAsP giving high power saturation together with polarisation insensitivity. A careful analysis of the structure in terms of band gap engineering has been performed to fulfil the requirements. The growth has been performed by MOCVD at atmospheric pressure. The quality material assessed by photocurrent, DDX, TEM and photoluminescence measurements are presented