Joint supervisors: Prof C David Wright and Dr Isaac Luxmoore
In recent years, electromagnetic metasurfaces have generated huge interest due to their ability for precise control of the amplitude, phase and polarisation of waves, from the microwave region right through to the optical part of the spectrum. Indeed, optical metasurfaces can mimic the wavefront manipulation capabilities of conventional optics, without the need for bulky optical components or any moving parts. A variety of optical and photonic metadevices for wavefront shaping, such as flat lenses, hologram generators and beam steerers have been reported. However, in such approaches device operation is essentially fixed-by-design, making them unsuitable for applications where light needs to be controlled dynamically. However, by combining metasurface concepts with active materials whose refractive index can be selectively (user) controlled, we can provide hitherto un-realised and real-time dynamic control of the metasurface properties, leading to the provision of new and enhanced functionality.
One class of suitable active materials is the chalcogenide phase-change alloys (PCMs), the development and application of which Exeter is internationally leading (see e.g. [1-3]). PCMs possess the ability to be switched quickly (nanoseconds or less) and repeatedly (billions of times) between amorphous and crystalline states (or indeed to an intermediate state between the two) by an appropriate thermal, optical or electrical stimulus – with the different phase-states possessing strikingly different optical properties (very large contrast in real and imaginary parts of the refractive index). Thus, by integrating PCMs with optical metasurfaces we can provide a form of continuously tuneable dielectric whose refractive index can be user-controlled via appropriate (electrical, thermal or optical) excitation. This opens-up exciting new possibilities for provision of active, dynamic and re-configurable photonic devices including – one focus of this PhD project – compact, low-power, high-efficiency optical beam steering devices with moving parts. The development of such devices would open up a new route to a variety of exciting applications, such as imaging and detection systems for security and defence, LIDAR scanning systems for autonomous vehicles, robotics and sensing, free space and surface wave optical signal coupling.
 Hosseini P, Wright CD, Bhaskaran H. (2014) An optoelectronic framework enabled by low-dimensional phase-change films, Nature, volume 511, no. 7508, pages 206-211, DOI:10.1038/nature13487
 Cheng Z, Ríos C, Youngblood N, Wright CD, Pernice WHP, Bhaskaran H. (2018) Device-Level Photonic Memories and Logic Applications Using Phase-Change Materials, Adv Mater, volume 30, DOI:10.1002/adma.201802435
 C R De Galarreta et al., Nonvolatile Reconfigurable Phase-Change Metadevices for Beam Steering in the Near Infrared, Adv Func Mater, DOI:10.1002/adfm.201704993 (2018)
See all project and application process details: http://www.exeter.ac.uk/studying/funding/award/?id=3449
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