Research Projects

Below is a summary of our core research themes. For more information about the research please contact either Dr Stephen Morris (stephen.morris@eng.ox.ac.uk) or Professor Steve Elston () directly.

1. Aberration-corrected Direct Laser Writing in Liquid Crystals & Polymers

We are working closely with the Dynamic Optics and Photonics group of Professor Martin Booth and Dr Patrick Salter to develop new electro-optic effects and photonics technologies by writing micron-sized polymer features into polymerizable liquid crystal materials and devices. Two-photon polymerization direct laser writing (TPP-DLW) is a technique for creating micro- and nanoscale polymer objects and is a key advanced additive manufacturing or 3D printing technique. The capabilities of TPP-DLW go well beyond that offered by traditional lithographic processes, as it provides true 3D structuring rather than 2D layer-by-layer fabrication. It allows rapid prototyping and flexible, direct conversion from 3D design to 3D microstructure as well as the remarkable ability to create sub-diffraction limited polymer features, making it a true nanoprinting technique. By translating a photopolymerizable sample (a resin) in a controlled manner relative to the laser focus, 3D structures can be built-up from polymerized voxels (the 3D analogy of pixels) formed via free-radical polymerization.

 

Figure 1. Direct laser writing of polymer pillars in liquid crystals.

Figure 2. Laser-written polymer bicycle in a liquid crystal device.

 Figure 3. Laser written QR code.

 A key challenge for emerging nanoprinting techniques is to increase the functionality and capabilities of the resin materials. We are directly addressing this by developing tunable resins using stimuli-responsive liquid crystal materials that change their optical and physical properties in response to external fields. Developing such bespoke resins that incorporate polymerizable liquid crystal molecules has allowed us to lock-in different alignments of the liquid crystal director (the average pointing direction of the molecules). Thus from a single resin, we are able to engineer polymer structures with different material properties in a single-step fabrication process, leading to new electro-optic capabilities and practical applications.

 Research Highlights:

 

Relevant publications

 

2. Inkjet Printing of Liquid Crystals & Polymers

 

3. Optoelectronic Devices

 

a. Laser Speckle Reducers


b. Phase Modulators


c. Thin-Film Lasers

Our research on organic laser devices involves using a combination of liquid crystals and polymer materials to create hybrid lasers that are wavelength tuneable (Figure 4). We are interested in developing new laser sources based upon these organic materials in an attempt to create low-threshold lasers that are potentially compatible with low-cost manufacturing techniques. The research includes both fundamental studies of the emission characteristics such as coherence properties as well as the design and fabrication of new device architectures.

We are working in collaboration with the research groups of Professors Henry Snaith FRS and Moritz Reade in the Department of Physics (University of Oxford) to develop new thin-film lasers that combine the absorption and emission properties of perovskite structures with the feedback and reflection properties of chiral liquid crystalline materials. The aim of this work is to develop new, low threshold laser sources that are photostable and can be tuned using external stimuli. We have recently developed an amplified spontaneous emission source based upon a thin layer of perovskite material sandwiched between a chiral nematic (cholesteric) liquid crystal reflector and a gold layer (see publication below). Further work on combining the perovskites with tuneable liquid crystalline polymer reflectors for laser devices is currently in progress. This work was also carried out in collaboration with Professor Albert Schenning's group at the Eindhoven University of Technology and the Optoelectronics Research Group in the Cavendish Laboratory at the University of Cambridge.

Figure 6. ASE from a perovskite structure using a chiral nematic (cholesteric) reflector and a gold reflector.

Emission on flexible chiral nematic liquid crystal substrates.

 

LC Perovskite 

Figure 7. ASE from a perovskite structure using a flexible chiral nematic (cholesteric) reflector.

 

Distributed feedback structures for laser emission.

 

 

Figure 8. Illustration of a distributed feedback perovskite laser.

Clustomesogens

Figure 9. Clustomesogen structures synthesised by the team of Dr. Yann Molard (University of Rennes 1)

 

Clustomesogens 2

Figure 10. Emission characteristics of Molybdenum-based clustomesogens in chiral nematic liquid crystals.


Relevant publications:

  • Wavelength-tuneable laser emission from stretchable chiral nematic liquid crystal gels via in situ photopolymerization  RSC Advances6, 31919-31924 (2016)
  • Enhanced Amplified Spontaneous Emission in Perovskites using a Flexible Cholesteric Liquid Crystal Reflector  Nano Letters 15, 4935-4941 (2015)
  • Structured Organic–Inorganic Perovskite toward a Distributed Feedback Laser Advanced Materials, 28, 923-929 (2016)
  • Polarized Phosphorescence of Isotropic and Metal-Based Clustomesogens Dispersed into Chiral Nematic Liquid Crystalline Films Advanced Optical Materials, 3, 1368-1372, (2015)


4. New Measurement Techniques & Processes


a. Time-resolved measurements


b. Solvent-induced alignment


5. Smart Materials

 a. Chiral Polymer Scaffolds 

Our research in this area involves the fabrication and characterisation on new photonic and meta-materials based upon chiral nematic and blue phase liquid crystals that have been ‘templated’ using a polymer scaffold that has been created by a cross-linked polymer network. The aim of this work is to harness the self-organising feature of liquid crystalline phases that naturally assemble to form a structure with a periodic modulation of the refractive index that is on the order of the wavelength of visible light. Furthermore, depending upon the liquid crystal phase, this periodicity can exist in either 1-dimension (chiral nematic) or 3-dimensions (blue phase). By forming a template of these structures with a polymer network it is then possible to impart this macroscopic structure onto other materials. An example of the 'templating' process of a blue phase is shown in Figure 1. This work is carried out in collaboration with Dr Flynn Castles in the Department of Materials at the University of Oxford and also previously with the Centre of Molecular Materials for Photonics and Electronics at the University of Cambridge.

 

Blue phase template

Figure 1. A Blue phase template (a self-assembled 3D photonic crystal). 

b. Stretchable Photonic Crystal-like Gels

In addition, we are also studying the mechanochromic and electro-optic properties of chiral nematic blue phase liquid crystalline gels, which have recently been demonstrated as a result of research carried out at the Departments of Engineering at both Oxford and Cambridge. Examples of free-standing blue phase gels from a recent publication in Nature Materials are shown in Figure 2.

Stretchable liquid crystalline blue phase gels

Figure 2. Stretchable liquid crystalline blue phase gels.

We are also working on stretchable laser gels based upon chiral nematic and blue phase liquid crystals. An example of wavelength tuning of the laser emission from a liquid crystal laser gel is shown in Figure 3. 

 

Figure 3. Stretchable cholesteric liquid crystalline gels

Figure 4. Stretchable cholesteric liquid crystalline gels 

Relevant publications:

  • Wavelength-tuneable laser emission from stretchable chiral nematic liquid crystal gels via in situ photopolymerization  RSC Advances, 6, 31919-31924 (2016)
  • Stretchable liquid-crystal blue-phase gels Nature Materials, 13, 817-821(2014)
  • Blue-phase templated fabrication of three-dimensional nanostructures for photonic applications Nature Materials 11, 599 (2012)
  • Simultaneous red-green-blue reflection and wavelength tuning from an achiral liquid crystal and a polymer template Adv. Mater., 22, 53-56, (2010)