Advanced all-optical signal processing using quadratic nonlinearities

With the advent of the Internet data traffic has rapidly over taken voice to become the dominant type of information transported by today's high speed optical communication networks. Moreover traffic is predicted to continue to grow at a phenomenal pace for the foreseeable future, driven by existing applications such as e-mail, e-commerce and video conferencing along with emerging applications such as telemedicine, virtual reality games and video-on-demand. In order to increase the capability and flexibility of optical networks to allow for new services and the next generation Internet, it will become increasingly more attractive, if not essential, to process the data signals within the optical layer. The nodes of these advanced telecom networks will thus require highly functional optical devices capable of seamlessly processing multiple signals in parallel at extremely high speeds (40 Gbit/s and beyond). The optical analogues of the modulators, switches and mixers used in electrical systems are thus required, dictating the need to use nonlinear optical effects.To date the majority of research into nonlinear optical devices has focussed on the use of optical fibre which posseses an ultrafast but unfortunately inherently low nonlinearity, or semiconductor materials which suffer from relatively low switching speeds. In this project we propose to investigate a different approach, based on the use of quadratic nonlinearities, which despite their many attractive properties, still remain the least explored option in the telecom area. To prove and leverage the full potential of quadratic nonlinearities in this field, we want to design and develop several compact, quadratic all-optical processing modules capable of operating at modest optical power levels and that are able to meet the stringent requirements of ultrahigh capacity telecom systems. To achieve this we will exploit the use of cascaded nonlinear effects in periodically poled lithium niobate waveguides. We shall also look to exploit various pulse shaping techniques, and the use of novel apodised nonlinear grating designs. It is to be appreciated that although telecoms is the main target-application to be considered within this project several of the device concepts developed should also be of use for other all-optical processing applications in fields such as metrology, spectroscopy, sensing, biology and medicine.