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Variable pitch hydrodynamic electro-optic gratings utilising bent liquid crystal dimers
R Morris1, J C Jones, M Nagaraj
1School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK. m.nagaraj@leeds.ac.uk.
Soft Matter
|October 15, 2020
Summary
Electrohydrodynamic instabilities in liquid crystals create tunable gratings for light steering. By altering elastic constants, researchers achieved narrower pitch lengths, enabling wider angle beam steering for optical devices.
Area of Science:
- Materials Science
- Optics
- Physics
Background:
- Electrohydrodynamic instabilities (EHDI) in liquid crystals (LCs) can form tunable diffractive structures.
- These structures, like 1D gratings, allow continuous angular modulation of optical beams.
- Previous limitations included a restricted angular range due to the grating pitch.
Purpose of the Study:
- To investigate the influence of elastic constants on EHDI grating pitch.
- To develop LC mixtures enabling narrower pitch lengths than previously achievable.
- To enhance the angular steering range for diffractive optical devices.
Main Methods:
- Forming EHDI gratings in a novel LC mixture.
- Doping a host nematic LC with CB7CB to significantly increase the splay to bend elastic constant ratio (k11/k33).
- Characterizing the pitch length of the formed gratings and comparing them to theoretical limits.
Main Results:
- The lower pitch limit of EHDI gratings is significantly influenced by the LC's elastic constant ratio (k11/k33).
- The new LC mixture achieved k11/k33 > 5, resulting in grating pitches well below half the cell gap.
- This enabled a continuous steering range up to 50% wider than previously reported.
Conclusions:
- Altering the elastic properties of LCs is a viable strategy to control EHDI grating pitch.
- Achieving significantly reduced pitch lengths enhances the performance of LC-based beamsteering devices.
- This work expands the potential applications of EHDI in tunable diffractive optics.
