Polymeric electro-optic digital optical switches with low switching voltage - Electronics Letters

Introduction: High-speed and high-performance optical switches are vital for optical communication networks and optical signal-processing systems. Among these, optical switches based on the electro-optic (EO) effect are promising for applications that require high-speed switching, such as: optical burst switching or optical packet switching. Mach–Zehnder interferometer (MZI) switches and directional coupler (DC) switches have been under intensive investigation for a long time, but they both have very limited fabrication tolerance. Furthermore, bias control networks and precise switching voltages are needed in MZI switches and DC switches to achieve high performance. Digital optical switches (DOSs) were first proposed in 1987 [1] based on the principle of mode evolution (or, equivalently, adiabatic propagation). These kinds of devices are known for their tolerance of fabrication errors and wavelength=polarisation insensitivity. Also, there is no need of bias control for DOSs and their output has been shown to have a step-like response to the applied driving voltage, which is desirable for simplification of the control electronics of large-scale optical crossconnections. Since the optical signal is switched between the output ports of the DOS, it is a spatial optical switch. So it is well suited for applications that route signals through different paths, such as the delay network in an optically controlled phase-array radar system. Electro-optic polymers are particularly interesting for new device design and high-speed operation [2]. Because of the large electro-optic coefficient of polymer material, a certain amount of refractive index change can be realised by lower driving voltage than in other EO materials. Since there is better optical=RF velocity matching inside the EO polymer, high-speed switching can be achieved easily. Hence EO polymers are excellent materials to realise high-speed DOS devices.