Manipulating light has been the essence of optics, from shaping glasses to make lenses and telescopes to using pinhole cameras to capture images. Traditional optical components have curves and edges making them thick, limiting miniaturisation. With meta-optics, one can go beyond traditional optics by employing nanotechnology to create ultra-thin and flat structures to achieve the same functions and even extend performance. To manipulate light with meta-optics, we focus on optical metasurfaces and holography.

Metasurfaces enable much stronger tunability and reconfigurability than any natural non-structured material. This makes meta-optics a promising candidate for future flat devices that will dynamically control the wavelength, amplitude, phase, and polarisation of light. To create futuristic optical devices for holography and remote imaging, these capabilities are essential.

Our research aims to enhance the sensitivity of optical properties of metasurfaces to an external stimulus. The results will benefit not only the manipulation of light but also the development of metasurfaces for interaction with materials to create efficient light sources and for optical sensing applications.

Optical holograms can be created by simultaneous manipulation of both amplitude and phase of a light beam to reconstruct objects in three dimensions (3D). It permits the visualisation of 3D objects and offers extensive applications that include optical microscopy and imaging, three-dimensional displays, and metrology.

The Manipulate Theme will develop novel ultra-thin holographic elements that will enable the next generation of flexible and transparent augmented reality displays as well as neuromorphic holographic networks for optical image recognition and processing.

Recent achievements

  • Demonstrated tunability of metasurfaces with liquid crystals through applied magnetic field
  • Initiated the studies of vanadium dioxide use in tunable metasurfaces
  • Demonstrated phase-only tuning of Huygens metasurfaces
  • Studied properties of electro-optic metasurfaces
  • Reviewed surface functionalisation and texturing of optical metasurfaces for sensing applications
  • Developed nanowire array gas sensor for dynamic NO2 monitoring

This research program aims to create tunable metadevices where the properties of light can be controlled and programmed dynamically in real time for image processing applications. Action items for 2022 were achieved by using a variety of approaches for making tunable metasurfaces and achieving their practical functionality. We have further investigated phase-change materials to realise tunable metasurfaces.

Alongside using pure vanadium dioxide that undergoes insulator-to-metal transition, we have demonstrated that tailored nanostructuring of vanadium dioxide can dramatically enhance optical transmission modulation, which is two times larger than the previous modulation achieved. Continuing to explore liquid crystal as tunable material, we have developed a new type of dynamic control of metasurfaces infiltrated with liquid crystal by applying an external magnetic field. This method opens novel opportunities for realising switchable metadevices without the usual limitations imposed by boundary conditions of liquid crystal cells and external voltage.

Furthermore, a new method for realising 2π-dynamic phase tuning in transmissive dielectric metasurfaces has been proposed, which can be implemented by controlling the bias voltage and changing the temperature of the surrounding liquid crystal. We are also continuing to investigate and design liquid crystal metalens with adjustable focal lengths to replace bulky, curved traditional lenses. We have designed electro-optic metadevices based on lithium niobate and studied their amplitude and phase tunability.

We also have proposed metadevices with the possibility of controlling light polarisation. Electrically tunable metasurfaces were developed for beamshaping applications. It was designed and fabricated with four individual metasurface pixels that can be controlled separately. By applying an asymmetric driving voltage, flash heating was achieved, leading to 90% transmission modulation depth and switching time

Action Items for 2023

  • Fabricate and demonstrate a neuromorphic optical diffractive neural network for chemical classification
  • Characterise phase change material-sb 2se 3 and demonstrate its applications
  • Integrate nanoscale light sources/detectors with optical sensing platforms
  • Integrate focusing lenses and metasurface designs with off-shelf light sources/ detectors
  • Develop technology to scale nanowire array sensor fabrication and develop new nanowire sensors including gas and multiplexed sensors with integrated functionalities
  • Continue to explore phase change materials for optical and sensor applications
  • Fabricate and characterise electro-optic metasurface devices based on lithium niobate and expand their functionality
  • Design and develop tunable metadevices using liquid crystal through the dynamic molecular realignment
  • Explore a fully controllable tunable metasurfaces in full 3D
  • Continue towards development of tunable metadevices using MEMS
  • Development of parametric metadevices for electromagnetic wave amplification