Metasurface for ultrathin planar optical devices with unusual functionalities

Miniaturization and integration are two continuing trends in the production of photonic devices. The functionality of a traditional photonic device is usually realized by reshaping the wavefront of the light that relies on gradual phase changes along the optical paths, which are accomplished by either controlling the surface topography or varying the spatial profile of the refractive index. The thickness of photonic devices usually remains comparable to the wavelength of the light. However, further reduction in the thickness of the corresponding element is hindered by the design theory since it is based on phase accumulation along the optical path. Metamaterials can usually be engineered to exhibit electromagnetic properties that may not be found in nature or its constituent components, thus providing an unconventional alternative to optical design. Metasurfaces, the emerging field of metamaterials, which consist of a single layer of artificial "atoms", have recently captured the attention of the scientific community since they do not require complicated three-dimensional nano-fabrication techniques but can control light propagation in equally dramatic ways. Unlike the phase change by the accumulated optical path in traditional optical elements, the abrupt phase change takes place at the metasurfaces, meaning that a new freedom for controlling light propagation is introduced. Metasurfaces promise a whole variety of amazing applications, e.g. ultrathin metalens, spin-hall effect of light and spin controlled photonics. Recently, the PI and his collaborators have experimentally observed several new interesting phenomena connected with the phase discontinuities occurring at the metasurfaces: i) 3D optical holography ii) broadband vortex beam generator iii) dual-polarity ultrathin metalenses and iv) polarization dependent unidirectional surface plasmon polariton excitation. These findings are still under investigation and promise new exciting applications: such as simultaneous multiplane imaging, 3D optical holography with switchable reconstructed images and a waveguide based optical switch.

The proposal aims to expand our initial findings into a research programme based on my current competitive advantage in exploration of phase discontinuities at metasurfaces. I will design and fabricate plasmonic nanoantennas and elucidate phase discontinuities on the metasurfaces. The main focus of this research will be 1) to design and construct a state-of-the-art optical measurement system to characterize metasurface devices, 2) to elucidate the nature of phase discontinuities and tailor metaurfaces with unusual functionalities, 3) to engineer and fabricate plasmonic metasurfaces and 4) to experimentally demonstrate the prototype devices for simultaneous multiplane imaging, 3D optical holography with switchable reconstructed images and waveguide based optical switch. I plan not only to fabricate new plasmonic metasurfaces and study their extraordinary optical properties but also to assess their applications, which I believe are the most promising and within my expertise. It is the PI's expertise in nanofabrication, plasmonic metasurface and proof-of-concept demonstration which forms the basis of this proposal. It represents a timely and challenging adventure as this proposal is a synergetic integration of fundamental science, nano material/structure design, and prototype device development, which will impact a wide range of fields such as imaging, communication, encryption, information handling and data storage.

The technology output from this research could develop beyond and extend across a wide range of areas: from physics to engineering. Outcomes from the programme outlined here will considerably impact plasmonics, nanophotonics, information optics and optical communications and serve to further integrate them. This wide spectrum of interest highlights the importance of the work proposed here. My results will be important first and foremost for the academic community. The theory of the phase discontinuities at the plasmonic metasurfaces will be useful for nanooptics and photonics. The new metamaterials based on nanoantennas will be stimulating and important for metamaterial community. Moreover, the phase discontinuity based plasmonic devices could useful for optoelectronics. We hope to widen understanding of the relevant physics, clarify the mechanisms of the studied effects and to check them by direct experiments.

To date the majority of metamaterial research has been conducted from a fundamental science perspective, but it is now at the crucial point where the knowledge accumulated over last decade has reached the critical mass that would generate a host of future high-impact technological applications. Successful completion of this research project would lead to the invention and development of exciting new ultrathin devices with novel functionalities which will be interesting for industry and technology. One of the important areas that this project can impact is biomedicine. The metadevices for simultaneous multiplane imaging is able to image simultaneously several layers within an object field, which is desirable for biomedical imaging. By collaborating with Prof. A.H. Greenaway from the Institute of Biological chemistry, Biophysics & Bioengineering, this unique imaging technique can attract the attention of biomedical companies. Also, a new freedom, circular polarization is introduced to realize the switchable reconstructed images, which can have an immediate impact in security and anti-counterfeiting. Prof. M.R. Taghizadeh (diffractive optics) has established links with industry on optical holographic techniques, any progress in this work will attract the attention of these companies through collaboration. Finally, the waveguide based optical switch is very useful for optical communications. In principle, the suggested research can result in more compact optical system due to high-level integration. By working closely with Research and Enterprise Services in Heriot-Watt University, research findings will be evaluated for commercialization potential. The economic and societal impact will be apparent within 10 years.

Plasmonic metasurface is a multidisciplinary research area, which can lead to training highly qualified scientific workforce and future researchers who will preserve and enhance UK's international technological competitiveness. The broader impact of this project goes far beyond what we can envisage today, which will surely benefit UK on a variety of fields such as imaging, communication, encryption, information handling and data storage.