Dynamic, Tunable and Multi-Functional Liquid Crystalline Geometric Phase Optics

Artificial materials composed of engineered subwavelength structures with a designer optical response, known as metamaterials, have a rich scientific history. Initial experimental work in this field was limited primarily to longer wavelengths (e.g., radiofrequencies) due to fabrication challenges associated with producing 3D nanostructured materials [1]. Advances in foundry-based planar nanofabrication techniques in combination with novel design approaches has given rise to a rich and vast field of research concerning 2D nanostructured surfaces, known as metasurfaces [1–3]. Over the past few decades research concerning metasurfaces has spanned from studies of fundamental light-matter interactions with dielectric and plasmonic nanostructures [4,5], to demonstrations of planar optical components capable of focusing, beam deflection and holography [1–3,6,7]. Even more recently the field has expanded to include demonstrations of non-linear metasurfaces with exceptional effective non-linear properties [8] and multi-functional metasurfaces capable of simultaneous control of the different degrees of freedom of light [9]. Despite these extensive efforts, several fundamental research challenges remain concerning optical metasurfaces, including the low efficiency of optical metasurfaces, particularly those that target broadband, achromatic optical functionalities and challenges producing high-efficiency dynamic metasurfaces which can be modulated in a repeatable and fast-manner [1,7,10].<br/><br/>An alternative and potentially complimentary approach towards the design and fabrication of artificial 2D and 3D optical materials with engineered optical response involves spatial patterning of the optical birefringence axis in a liquid crystal (LC) material, which modulate the phase of light leveraging the well-known geometric phase. This class of 2D or 3D patterned optical material are known as geo-phase materials and LC-based implementations can achieve ultra-high optical efficiencies [11] due to reliance on molecular scale self-assembly, which alleviates traditional losses in conventional optical metasurfaces (e.g., scattering and absorption). Another benefit of LC-based geo-phase materials is the intrinsic tunability and active nature of LCs. In this talk we will present recent work on LC based geo-phase optics, including demonstrations of dynamic, tunable optical functionality and of polarization insensitive, broadband optical functionality based on multilayered structures where the optical birefringence pattern is controlled in three-dimensions [12]. Finally, we will discuss tradeoffs between LC geo-phase optics and conventional metasurfaces and highlight, when possible, potential means for these two different approaches towards the design and fabrication of artificial optical materials to be used complimentarily.<br/><br/>References<br/><br/>[1] Kuznetsov, Arseniy I., et al. <i>ACS Photonics</i> 11.3 (2024).<br/>[2] Yu, Nanfang, et al. <i>Science</i> 334, 333-337 (2011).<br/>[3] Ni, Xingjie, et al. <i>Science</i> 335.6067 (2012).<br/>[4] Giannini, Vincenzo, et al. <i>Chemical Reviews</i> 111.6 (2011).<br/>[5] Koshelev, Kirill, and Yuri Kivshar. <i>ACS Photonics</i> 8.1 (2020).<br/>[6] Balthasar Mueller, J. P., et al. <i>Physical Review Letters</i> 118.11 (2017).<br/>[7] Chen, Wei Ting, et al. <i>Nature Nanotechnology</i> 13.3 (2018).<br/>[8] Mann, Sander A., et al. <i>ACS Photonics</i> 10.4 (2023).<br/>[9] Overvig, Adam C., et al. <i>Physical Review Letters</i> 125.1 (2020).<br/>[10] Lalanne, Philippe, and Pierre Chavel. <i>Laser & Photonics Reviews</i> 11.3 (2017).<br/>[11] Tabiryan, Nelson V., et al. <i>Advanced Optical Materials</i> 9.5 (2021).<br/>[12] Moran, Mark J., et al. <i>Polymer</i> 283 (2023).