Ultrafast all optical beam steering

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EPSRC : Justus Bohn : EP/L015331/1Nonlinear optics is the study of the interaction of intense laser light with matter. Nonlinear optical phenomena enable a broad range of applications, such as telecommunications, beamshaping and all-optical data processing. However, most materials exhibit only an extremely weak optical nonlinearity, even under intense illumination. Consequently, long interaction lengths are needed for the build-up of nonlinear optical phenomena, and these interaction paths are usually obtained by using bulky material structures that are difficult to scale up and to integrate into nanophotonics systems. As a result, a long standing goal in the field of nonlinear optics has been the development of materials with very large nonlinear responses, whose optical properties can be dramatically changed with a low-power optical field. In addition, it is highly desirable that these materials possess a sub-picosecond time response to reach THz rates and are suitable for nanoscale integration through existing complementary metal- oxide-semiconductor (CMOS) fabrication technologies long established in industry.Current interest is motivated by the observation that degenerate semiconductors such as tin-doped indium oxide (ITO) exhibit a huge enhancement of the non-linear optical response at telecoms wavelengths. Since these initial discoveries, it has been shown that the effect can be even further increased by utilising gold antennas on an ITO layer. This has opened the door to ultrathin nonlinear systems, with greatly reduced interaction lengths allowing for better integration into nanophotonic architectures. One of the most important applications currently being addressed with ITO is all-optical beam steering. Considering the sub-picosecond response time of the material, all-optical steering has the potential to be very fast, and if workable, could provide drastic improvements to the speed of location scanning systems. Here, ITO with properly designed nano-antenna array, offer the prospect of an ultra thin, highly efficient, all-optical beam steering platform. In this joint research project we aim to design, manufacture and characterize all optically switched beam steering samples. We will develop, optimise and fabricate nonlinear devices during my stay in Ottawa, and carry out a first characterisation in air which will allow us to establish the basic nonlinear behaviour. On returning to Exeter, we will fully characterise the angular response of the switching. We hope this will be the starting point of more complex metasurface designs that enable full beam shape control.