Pure optical phase modulation is essential for various applications, including holograms, adaptive optics, wavelength selective switches (WSS), etc.[1-11] Currently, nematic liquid crystals are used for phase modulation that usually suffers from fringing field effect (FFE) and slow response time, and therefore the modulated light shows various artifacts. Despite several efforts, it is difficult to suppress the FFE for conventional nematic liquid crystals. The problems become multiple-fold difficult for the phase modulation in the C-band or L-band of the light. In this talk, I will discuss our recent finding for the vertically aligned ferroelectric liquid crystals that eliminate the FFE and show significantly fast switching speed. The orientational Kerr effect in vertically aligned ferroelectric liquid crystals offers a fast, hysteresis-free, fringe field effect (FFE)-free, continuous modulation with 96% reflectance. [3-6] The FLC material with sub-wavelength helical pitch and enormous spontaneous polarization is the key to achieving FFE-free, fast pure phase modulation. We did not observe FFE in these light modulators, even for the excellent pixel pitch. We achieved a Kerr constant (240 nm/V2, see figure 1) at the communication. These new findings pave the way for large-capacity intelligent optical telecommunication systems and next-generation phase modulators for ultra-high-pixel density display and photonic applications.
Prof. Abhishek Kumar Srivastava is an Assistant Professor at Hong Kong University of Science and Technology, Hong Kong. His current research interest includes Photo-alignment, Ferroelectric liquid crystals, field sequential color displays (received best I-Zone display prototype of the year in 2018, SID Display Week, USA), Alignment of Nano Materials (Received LG Bronze Award, IMID-2018, South Korea), photo luminescence type color filters (Received silver award IMID, 2021, South Korea) and their application in Displays and Photonic. To date, he has published 212 articles and holds 44 patents/patent applications patents/patent applications. In 2014, he received the ILCS Early-Career Award: The Michi Nakata Prize for his early career efforts in the field of ferroelectric liquid crystals and photo alignment. He is a Senior Member of the Society for Information Displays and Editor-in-Chief of the Journal of the Society for Information Display.