Novel Ferroelectric Photonic Band-Gap Structures: a Feasibility Study

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A photonic band gap is created when a material is patterned in a periodic fashion, typically by drilling in a periodic pattern of holes on a scale of microns. The properties of light in this periodically-patterned medium are vastly changed, with interactions at some specific wavelengths becoming very much stronger. The adventure and innovation in this pilot study is in the combination of photonic band gap patterning with highly nonlinear epitaxial single-crystal ferroelectric materials in a waveguiding format, thus adding vertical confinement of light to the lateral patterning. With such a combination,we can conceive of making massive gains in optical device efficiency which, in turn, will allow faster speeds of data transfer and processing in optical communications in miniaturised device formats. A key question to answer in this feasibility study is whether ferroelectric waveguiding layers can be grown with sufficiently high optical quality and sufficiently low optical loss to demonstrate the enhancements in nonlinear optical effects predicted by theory. With proof of concept in mind, we have chosen to demonstrate a number of simple key devices in the well-known lithium niobate/lithium tantalate nonlinear optical system. We seek to show that custom-designed and dedicated epitaxial growth of high-quality films by both liquid phase epitaxy and epitaxial growth by melting will yield material of the necessary quality for subsequent photonic band-gap patterning and novel device demonstration. This will set the platform for a full programme involving a wider range of more exotic materials and more elaborate device formats at the end of this one-year study. To our knowledge, this is the first time that such a programme to combine the exciting new advances in photonic band-gap engineering with highly nonlinear ferroelectric epitaxial layers has been undertaken. We are uniquely placed to achieve the aims of this one-year programme because of the collaboration between groups at Warwick and Bristol, which combines their respective expertise in materials growth and characterisation and optical device design, fabrication and testing.