Bio-inspired Slim Polymer Films With Wide Fields Of View And Multiple Imaging Capabilities
Inspired by the behaviour of light-harvesting ommatidia – biological waveguides composed of a lens, crystalline cone and rhabdom – found in the compound eyes of arthropods, the Saravanamuttu Research Group at McMaster University has developed a fundamentally new class of intelligent thin films: Waveguide Encoded Lattices (WELs) possess enhanced panoramic fields of view (FOV) as well as powerful optical properties such as excellent panoramic imaging resolution and range, infinite depth of field and operability at all visible wavelengths including the broad spectra of incandescent light (such as sunlight) and discrete spectral ranges emitted by lasers and LEDs.
Light beams naturally diverge and weaken in intensity as they travel through boundless, homogeneous media but when confined to a waveguide, propagate over long distances (>> Rayleigh range) as optical modes that retain their original spatial profiles. When packed into a hemisphere, the discrete light-collection ranges of individual ommatidia impart a cumulative FOV of ~180º. Despite their near-hemispherical FOVs, compound eyes often possess limited imaging range and resolution due to the small number of light-collecting elements – ommatidia – that can be packed into their characteristically curved geometry. Elegant replicas of compound eyes, which aim to transcribe arthropodal vision to imaging devices have been fabricated; these range from a curved circuit board aligned with a micro-lens array (Floreano et al., PNAS 2013), hemispheres densely patterned with micro-lenses (Deng et al. Adv. Funct. Mater. 2016) to a lens-patterned polymer hemisphere interfaced to Si photodetectors (Song et al., Nature 2013).
The WELs developed by the Saravanamuttu Research Group are unprecedented in the field. Unlike the predominantly curved architectures of artificial and biological compound eyes, WELs are optically flat, slim (3 mm-thick) and flexible polymer films encoded with an exceptionally high density of light-harvesting, multimode, multiwavelength waveguides (> 5 x 15, 000 cm-2). These impart a significantly enhanced panoramic FOV – an increase of 66 % relative to a film without waveguides. Whereas the vast majority of artificial compound eyes rely on hemispherical assemblies of micro-lenses, the properties of the WEL originate from a carefully designed lattice of intersecting, pentadirectional and lens-free cylindrical waveguides. The design rationale and fabrication of WEL – which would be impossible to construct through conventional lithographic techniques – is achieved by launching and eliciting collisions between nonlinear white light waves in a single, room-temperature step involving only incandescent bulbs and epoxide photoresist.
In addition to possessing a large FOV, WELs are also capable of sophisticated imaging operations. These include the ability to transmit (without divergence), focus and invert images without the need for bulky optics. Also different from curved constructs, WELs possess discrete translation symmetry, which would allow them to be limitlessly extended over large areas – through roll-to-roll processing for example – without loss of optical functionality. This coupled with their flexibility would enable WELs to be integrated with ease into light-based technologies such as LCDs, solar cells, cameras, and smartphones. WELs also promise entirely new avenues for introducing imaging functionality into miniaturized optics and photonics devices.
These findings are described in the article entitled “Waveguide Encoded Lattices (WELs): Slim Polymer Films with Panoramic Fields of View (FOV) and Multiple Imaging Functionality”, Adv. Funct. Mater. 2017, 27, 1702242.