Pancharatnam–Berry phase reversal via opposite-chirality-coexisted superstructures

In modern photonic applications, such as the optical communications and AR/VR displays, on-demand multi-dimensional light control plays a crucial rule, including the modulation of wavelength, amplitude, phase, and polarization. Along with the miniaturization and integration of photonic technology, ultra-compact and multifunctional optical devices are highly desired. In terms of cost-efficient large-scale fabrication, high optical efficiency, and reliable dynamic light control, liquid crystal (LC) becomes a famous and strong “candidate”, whose success has been well verified in the display industry. As a typical LC mesophase, CLC is very attractive due to its self-assembled chiral superstructures, and has been found to possess reflective PB phase in 2016. Thus, it supplies a versatile platform for multi-functional and active light control. However, the single-handed chiral structure of CLC determines that it cannot manipulate light with opposite circular polarization simultaneously, let alone getting the conjugated PB phase.

In a new paper published in Light: Science & Applications, a team of scientists, led by Associate Professor Peng Chen and Professor Yan-Qing Lu from National Laboratory of Solid State Microstructures, and College of Engineering and Applied Sciences, Nanjing University, Nanjing, China, and co-workers have developed an innovative scheme based on opposite-chirality-coexisted superstructures. These scientists summarize the principle of their device:

“It comes to us whether it is possible to break the intrinsic single chirality of common CLCs. If somehow chiral superstructures with contrary handedness could be integrated into a single layer to form a uniformly-distributed and sub-wavelength local chirality heterogeneity, namely, the opposite-chirality-coexisted superstructures, light beams with orthogonal circular polarization and conjugated PB phase should be simultaneously reflected and superposed.” mentioned by Prof. Chen.

“Luckily, the CLC polymer networks reported in prior arts are compatible of media with different properties, and further guide our way. Practice makes perfect. To be honest, we were surprised to see that it worked so well in the light control. It is a powerful tool!” he added.

They have simultaneously modulated the orthogonal circular polarization and get PB phase reversal. Through refilling CLC into a washed-out polymer network with opposite chirality and delicate photo-patterned structures, reflective optical vortex (OV) with opposite topological charges and vector beams with conjugated spiral PB phases are efficiently generated depending on the incident polarization. Furthermore, they encoded OV holograms to reconstruct polarization-selective OV arrays.

It stands out for some important merits of ultra-compact configuration, exemption from careful alignment, and higher efficiency without multiple interfaces. This device breaks the limitation of traditional CLC devices and brings an important insight into the understanding of PB phase and polarization optics. “We believe it will facilitate the architectures and functionalities of soft chiral superstructures towards versatile elegant photonic devices.” Prof. Lu forecast.