Browsing by Author "Manda, Ramesh"

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Helical pitch-dependent electro-optics of optically high transparent nano-phase separated liquid crystals
(2018-10-15)
Pagidi, Srinivas
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Manda, Ramesh
;
Lim, Young Jin
;
Song, Seong Min
;
Yoo, Hyesun
Feeble light leakage in a dark state of conventional optically isotropic liquid crystal (OILC) device has a strong impact on the contrast ratio of a liquid crystal (LC) device. In order to overcome such intrinsic problem, we proposed an OILC in which the LC directors inside droplets are twisted by introducing chirality. The light leakage is effectively suppressed by matching the refractive indices between LC and polymer matrix; consequently, we achieved a high contrast ratio, 1:1401. Interestingly, the on-state transmittance is enhanced by similar to 49% compared to conventional OILC. The response time was also improved and the hysteresis was suppressed to be negligible. The improved electro-optic performances of the proposed OILC device would give diverse applications in upcoming flexible display and various photonic devices. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Origins of Kerr Phase and Orientational Phase in Polymer-Dispersed Liquid Crystal
(2017-01-01)
Chang, Chia-Ming
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Lin, Yi-Hsin
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Reshetnyak, Victor
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Park, Chui Ho
;
Manda, Ramesh
The anisotropic properties of nematic liquid crystals result in polarization dependency which leads to requirement of at least a polarizer in liquid crystal photonic devices. To develop polarizer free phase modulation, Kerr effect is one of the path. The phase modulation in polymer dispersed liquid crystals (PDLCs) is shown to have two parts: Kerr phase, which is the optical phase modulation linearly proportional to a square of electric field, and orientational phase. However, many puzzles are still under investigation: the origins of Kerr phase, the relation between Kerr phase and orientational phase, and how two-steps of electro-optical (EO) response relates to Kerr phase and orientational phase. We investigated the origins of Kerr phase and orientational phase in PDLC and their connection to two-step EO response. In our study, the Kerr phase is a result of LC orientation in the center of LC droplets. The orientational phase attribute to orientation of LC molecules near LC-polymer interfaces. The two phase in PDLC samples are adjustable depending on droplet size. We also found that two-steps EO response existing in small droplet (<333 nm) is related to Kerr phase and orientational phase. A modified PDLC model related to the Kerr phase and orientational phase is also proposed. Besides the conventional features of PDLC, such as polarization independent optical phase shift and response time independent of cell gap, we believe the Kerr phase and orientational phase with different response times (similar to msec) in PDLC pave a way for designing versatile photonic devices with pure optical phase modulation.
Origins of Kerr phase and orientational phase in polymer-dispersed liquid crystals
(2017-08-21)
Chang, Chia-Ming
;
Lin, Yi-Hsin
;
Reshetnyak, Victor
;
Park, Chui Ho
;
Manda, Ramesh
Polymer-dispersed liquid crystals (PDLCs) modulate the amplitude and optical phase of light. The optical phase modulation of PDLC can be dissected into two parts: Kerr phase and orientational phase according to the electro-optical (EO) response. We investigated the origins of the Kerr and orientational phases in PDLCs and their connection with the two-step EO response. The Kerr phase is attributed to LC orientation in the center of LC droplets. The orientational phase results from orientation of LC molecules near LC-polymer interfaces. Both phases can be adjusted by varying the droplet size. The two-step EO response in small droplets (<333 nm) is related to the Kerr and orientational phases, and possibly to rotation of point defects. A modified PDLC model considering the Kerr and orientational phases is proposed. Our findings suggest the possibility of versatile photonic devices using pure optical phase modulation. (C) 2017 Optical Society of America