Strain compensated GaInAs/AlInAs tunnelling barrier MQW structure for polarisation independent optical switching

Large electro-optic modulation is available in InP based photonic devices for communication systems working in the 1.55 /spl mu/m window. This is because the quantum confined Stark effect (QCSE) can be exploited to switch and modulate the light wave. But signal processing in the receiver front end often has to be polarisation independent. However, the QCSE proves to be inherently polarisation dependent. In the present work this problem was tackled by applying a tunnelling barrier QW (TBQW) structure. This concept was reported recently for the GaAs material system and is transferred here to InP based devices for the first time. Its realisation necessitates to optimise the electrical, optical and structural material quality in order to make it suitable for device applications. First the investigations concerning the epitaxial growth conditions are described. Then the experimental results for TBQW structures are reported, including the polarisation independent electro-absorption characteristics of Mach-Zehnder interferometers (MZI) incorporating strained TBQWs. Such a MZI switch is the basic building block of a high speed time division demultiplexer (DEMUX). The development of the DEMUX is a part of the European ACTS HIGHWAY project.