Abstract
Optical beam deflectors based on the combination of cholesteric liquid crystals and polymer micro gratings are reported. Dual frequency cholesteric liquid crystal (DFCh-LC) is adopted to accelerate the switching from the homeotropic state back to the planar state. Polarization independent beam steering components are realized whose transmission versus the polarizing angle only varies 4.4% and 2.6% for the planar state and the homeotropic state, respectively. A response time of 451 ms is achieved for DFCh-LC-grating beam deflectors, which is fast compared to other nematic LC beam steerers with similar LC thickness.
Highlights
Nowadays, more and more tunable beam steering or deflecting components are employed in newly emerging photonic and optical products, such as revolving mirrors for lighting or scanners[1], adaptive concentrators for solar cell panels[2], zoom lenses for digital cameras[3], highly directional backlight systems for autostereoscopic displays[4, 5] and so forth
Based on the above idea and working mechanism, Ch-liquid crystal (LC) materials are combined with polymer micro grating substrates to assemble the polarization independent beam steering devices
Since the operating voltage of cholesteric liquid crystals (Ch-LCs) is inherently higher than that of the NLCs20, to reduce the driving voltage of the Ch-LC beam deflector, the conductive layer is deposited on top of the micro grating structure instead of underneath
Summary
More and more tunable beam steering or deflecting components are employed in newly emerging photonic and optical products, such as revolving mirrors for lighting or scanners[1], adaptive concentrators for solar cell panels[2], zoom lenses for digital cameras[3], highly directional backlight systems for autostereoscopic displays[4, 5] and so forth Those applications are based on either electro-mechanical movements or micro-electro-mechanical systems (MEMS). A saw tooth like distribution of the optical path difference (OPD) is achieved by applying different voltage signals on the addressing electrodes[6] One drawback of this type of device is that the deflection efficiency gets lower as the steering angle increases, largely due to the invalid flattened area on the phase profile caused by the intrinsic fringe field between two adjacent grating units[7, 8]. Putting the conductive layers on top of the micro structures can reduce the operating voltage to some extent[15], but this approach is difficult to implement and still needs higher driving voltages than the aforementioned LC grating with a gradient refractive index
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