The Detect Theme is dedicated to the integration of metasurfaces into photodetectors to expand their functionality and develop the next generation of imaging systems from the visible to the LWIR regions. Electromagnetic waves carry a wealth of information in the form of spectral content, polarisation and phase that cannot be directly accessed with current detection technologies that sense only intensity. This ‘hidden’ knowledge is central to applications in areas as diverse as LIDAR, remote sensing, in-vivo imaging of biological tissue, optical communications, microscopy of living cells and the identification of objects for machine vision. The filters and other optical components required to tap this extensive information add to the size, complexity and cost of optical systems and increasing attractive computational methods also require energy and compromise speed.
Furthermore, although silicon-based photosensors are inexpensive and widely available, these sense only short-wavelength visible light and access to longer wavelengths in the near, short-wave, mid-wave and longwave infrared regions of the spectrum requires expensive, bulky and noisy detectors. Yet this region of the spectrum is an enabler for major applications in Industry 4.0 such as night vision, passive thermal imaging, and imaging through objects opaque to visible light.
Detect comprises sub-programs of work that will develop meta-optical devices for advanced multi-modal detection and their integration into non-imaging detectors and meta-optical enhanced imaging harnessing the visible and infrared spectral radiation bands. Metasurfaces will revolutionise access to hitherto unavailable optical information and deliver ultra-compact optical components. This will result in savings in cost, materials and energy in manufacturing and expand access to state-of-the-art devices.
Recent achievements
- Demonstration of dual (visible and NIR) GaAsSb Nanowire Array multiwavelength photodetectors along with their application to RGB colour imaging.
- Demonstration of a InGaAs/InP multi-QW photoconductive photodetector with high room temperature responsivity (14.5 A/W @1550 nm).
- Demonstration of highly uniform multiple QW nanowire growth which is critical for NW-QWIP fabrication.
- Demonstration of a device that can discriminate between different angles of incidence on a metasurface and its application to phase contrast imaging of optical wavefields and microscopy of biological cells.
Subprogram 3A – Advanced Infrared Imaging
The relative inefficiency of existing infrared detectors at room temperatures, however, is a major roadblock to miniaturisation and precludes their use in drones and space applications where weight is critical. New approaches to infrared detection using semiconductor nanowires and the integration of subwavelength elements into mercury cadmium telluride detectors will enable the miniaturisation and lowering of cost of portable electronic devices for applications such as astronomy, security & surveillance, agriculture, night vision, remote sensing and medical imaging.
We aim to increase the resolution/sensitivity of infrared imaging devices, along with reducing the size, weight and power (SWaP) by combining imaging arrays with meta-materials, micro-lenses, and engineering the material properties. We are exploring novel materials and smart engineering of the detectors to create novel devices.
Our recent plasmonic research is aimed at enhancing mid-infrared nanophotonics by fabricating emerging nanostructures such as III-V nanowire quantum well detectors. We have combined experimental methods and computer simulations to demonstrate enhanced infrared absorption at shortwave spectral band employing such structures.
We have also developed tiny infrared resonators for remote thermal sensing and imaging utilising metamaterials. These are fixed or electrically tunable structures which will only pass a specific wavelength of light just before entering the photodetector or imaging array. The aim is to achieve Mercury-Cadmium-Telluride (MCT) imaging arrays with lower cross-talk, improved modulation transfer function (MTF), and higher operating temperature (HOT). Both design and simulation have been completed for an on-pixel aligned metalens array that is compatible with MCT mid-wave infrared (MWIR) imaging array technology.
Our aim for 2023 is to finalise designs for hybridisation of metalens array with MCT imaging array. Simultaneously, we will have our initial fabrication and technology development of metalens array, and optical characterization of them, which is essential for the success of the project. We will develop an initial fabrication technology for integrating metalens array with MCT imaging array which has been never done before.
Action Items for 2023
- Design and validation of metamaterial-based lens for extending field of view of infrared focal plane array
- Integration of metamaterial-based lens with infrared detector or focal plane array
- Demonstration of single pixel polarisation sensitive nanowire array for NIR imaging
- Demonstration of multi-pixel nanowire array for NIR to SWIR imaging
- Develop MBE process for growing suitable MCT layers that meet the required specifications
- Preliminary development of fabrication process for ultra-high QE SWIR detectors and initial device testing and characterisation
- Enhanced photodetection with plasmonic nanoparticles on ultrathin films
- Develop flexible nanowire array SWIR photodetectors
Subprogram 3B – Seeing the Invisible with Nanotechnology
The second Detect subtheme focuses on research that uses nanotechnology to extract information from light. Light carries a vast amount of ‘hidden’ information that is crucial for applications such as agriculture, pharmaceutical production, medical diagnostics, environmental monitoring and machine vision. We create meta-optical systems that permit accessing and measuring these properties of light.
Our work towards nanotechnology-enabled light detection application includes identifying chemicals based on the way they interact with light by engineering a micrometer-sized device able to perform this analysis by leveraging nanotechnology and artificial intelligence algorithms. These ‘micro spectrometers’ could enable low-cost and mobile chemical detection in future handheld devices.
We are also developing highly compact photodetectors that can efficiently determine the polarisation of light in an image in the infrared spectral region are challenging to create. We have numerically demonstrated that nanometer sized sheets of InAs semiconductor can successfully achieve this task. We are currently working on the experimental implementation of these structures.
Action Items for 2023
- Using bound-states in the continuum (BIC’s) to demonstrate enhanced chemical detection with micro spectrometers
- Demonstrate quantum ghost imaging using photon pairs generated by nonlinear-metasurfaces
- Demonstrate electrically tunable, graphene based infrared sensing and image processing devices
- Investigate and develop polarisation sensitive quantum well nanowire mid-infrared photodetectors