The outstanding properties of Liquid Crystalline Elastomers (LCEs) make them ideal candidates to address challenges in different research areas, from photonics to unsolved tissue engineering issues. This talk will present a brief explanation on the material nature, its preparation and possible 3D structuration at different length scale, along with some applications in photonics and tissue engineering.

Blue phase liquid crystals (BPLCs) are chiral liquid crystals with unique cubic structures that have optical isotropy and very fast response times to electrical fields, making them attractive for photonic and electro-optical applications. Inorganic nanoparticles have been added to improve the BPLC stability and opto-electric properties. Gold nanoparticles (NPs) and nanorods (GNRs) stabilized with low molecular weight polymer ligands were added to a wide range BPLC and characterized by optical microscopy and UV-Vis spectroscopy to determine the effect of the particle size and shape without variation of the NP core and ligand shell composition.

Optoelectronic nanocrystals are of enormous interest for material science and applications including solar cells and light-emitting diodes due to precise tunability of their properties via size and shape. Accordingly, various synthetic methods have been proposed, but achieving monodispersed nanocrystals remains a key challenge leading to the present lack of their commercial value and real-world applications. In this presentation, I will present that unique features of liquid crystals can be leveraged to synthesize nanocrystals with an unprecedented level of control over size and shape. The approach is a simple, rapid, and room-temperature process, yet it enables access to highly homogeneous nanocrystals with substantially reduced surface defects resulting in significantly improved optoelectronic features. The results offer a versatile and generalizable strategy to be broadly compatible with a range of nanomaterials and other synthetic methods. This work was supported by NRF funded by the Korea government (RS-2023-00212739, RS-2023-00302586).

Multicolor emission exhibited by complex organic systems is interesting and desired phenomenon for many optical applications. Laser devices capable to emit the light in the spectral range of three fundamental colors (red, green and blue) can revolutionize the modern display and lightening technologies. White lasers are becoming increasingly relevant in various fields, since they exhibit unprecedented properties in terms of beam brightness and intensity modulation. Here we demonstrate a multicolor stimulated emission phenomenon obtained in dye doped, liquid crystalline systems or in a multifunctional phase-separation system based on polymer matrix encompassing liquid crystals and multiple organic chromophores, where the precise color adjustment can be provided by applying the external electric DC fields, or pumping energy density.

Albeit, the first observations of lasing from liquid-crystal media were recorded forty years ago, still the engineering of materials and microstructures providing laser light on-demand, generated in-situ, seems to be one of the most important fields of photonic materials engineering. Here we give a snapshot of the research done on laser emission from different liquid-crystal media and structures. An extended study of the lasing induced in various periodic, self-assembled LC structures and artificial resonant structures tuned with liquid crystals is presented. We show observations of lasing obtained in dual-frequency-based, near defect-less, cholesteric structures, exhibiting a relatively big Q-factor. We report newly observed, topologically protected lasing from 3D, dye-doped, highly ordered macroscopic (of the diameter of several millimeters) monodomain samples of blue phase structures BFI and BFII. The unique lasing with two coherent beams with an opposite circular polarization, emitted from the custom-made microcavity formed between two, distributed Bragg reflectors is shown. An emission from a similar cavity with a perovskite emitter is also discussed.

Computational spectral imaging systems have been gaining momentum in recent years thanks to their ability to acquire information using a smaller number of measurements alongside emerging powerful Deep Learning algorithms. Recently [1] we developed a multispectral imaging system based on 25um liquid crystal retarder; however, its relatively large thickness limits the speed. In this work, we will present a multispectral imaging system based on a 2um thick Fabry-Perot spectral modulator filled with nematic liquid crystal combined with a deep learning algorithm. The system combined with a novel deep learning algorithm, designed to operate at 9 narrow spectral bands covering the VIS and NIR, holds a fast response and provides reliable spectral information, which makes it a potential candidate for various applications. [1] Doron Pasha, Marwan J. Abuleil, Isaac August, Ibrahim Abdulhalim, Faster multispectral imager based on thin liquid crystal modulator and 3D neural network lattice, Lasers&Photonics Review 2200913(8p) (2023).

Liquid crystals are known for their well-controlled molecular organization which is used to the benefit of liquid crystal displays, diffractive optics, soft robotics, and active surfaces. When chirality is introduced to the liquid crystal, the molecular organization becomes more complex as the director field becomes nonuniform. In our work we combine these chiral liquid crystals with motor molecules that change conformation or orientation upon activation by an external trigger, usually light or electricity. In the presentation we will discuss the principles and place them in the perspective of applications such as information windows, haptic surfaces, pick-and-place elements, soft robotics and surface effects for lubrication and debris removal.

Advanced multi-functional integrated photonic and cryptographic hardware demands for nonlinear and reconfigurable materials that can efficiently modulate light propagation. By tailoring the chemical formulation of liquid crystalline networks and polymer dispersed and polymer stabilized liquid crystals, we achieved tunable 4D printed photonic structures [1-4] and all-optical multi-level cryptographic functions [5]. References [1] Nocentini, S., Parmeggiani, C., Martella, D., Zanotto, S., Wiersma, D.S., Adv. Opt. Mater. 2018, 1800207. [2] Nocentini, S., Riboli, F., Burresi, M., Martella, D., Parmeggiani, C., Wiersma, D.S., ACS Photonics 2018, 5, 3222. [3] De Bellis, I., Nocentini, S., Delli Santi, M.G., Martella, D., Parmeggiani, C., Zanotto, S. and Wiersma, D.S., Laser Phot. Rev. 2021, 15(8), 2100090 [4] De Bellis, I., Martella, D., Parmeggiani, C., Wiersma, D.S. and Nocentini, S., 2023. Adv Funct Mater, p.2213162. [5] Nocentini, S., Ruhrmair, U., Barni, M., Wiersma, D.S., Riboli, F., arXiv preprint arXiv:2301.02147 (2022). Accepted.

In the recent decade, liquid crystals (LCs) have been a fascinating class of materials that exhibit unique electro-optic properties, which have found wide-ranging applications in various technologies. In this talk, an overview of various LC-based optical devices will be discussed that we have designed and fabricated in our laboratory. We have developed an LC-based all-electrically controlled multidirectional laser beam steering device, an active and bistable polarization beam splitter, a free-standing optical diffuser, and a laser speckle contrast suppressor. These devices offer several advantages over existing technologies and exhibit fascinating features such as excellent control with tunability, low voltage control, quick response times, and also offer flexibility. We have recently explored the LC in energy harvesting systems to develop a thermoelectric and flexoelectric generator. These findings will be discussed in detail during the talk.

Our prior studies have garnered significant interest due to our novel insights into the heating effect caused by pseudo-dielectric relaxation, also known as pseudo-dielectric heating (PDH). This phenomenon has frequently been confused with misrecognized as dielectric heating (DH), which is a result of orientational relaxation in liquid crystal (LC). In this presentation, we aim to clarify the pseudo-dielectric heating effect originating seemingly from dielectric relaxation and compare the two intrinsically distinct electro-thermal effects. Some examples are given to demonstrate how PDH can be applied in LC photonic devices.

Cellulose, the main constituent of plants, plays a significant role in forming helical structures observed across different scales. These structures play a crucial role in creating structural coloration. This work focuses on molecular and nanoscale helical photonic arrangements in cellulose-based systems. Emphasis is given to cellulose nanocrystals, their interactions with water, and the formation of colorful structures in cellulose-based out-of-equilibrium systems. Specific systems with varying helicities and adaptive behaviors will be shown. The current findings suggest that significant work remains in out-of-equilibrium cellulosic colourful systems. Furthermore, there is much to be learned from nature's designs to create innovative helical functional materials featuring unique photonic properties.

Counterfeit products have become more accurate with technology development, and deterrent anti-counterfeiting solutions are in constant demand. Structural-color-generating films from cellulose nanocrystals (CNC) nanocomposites present good properties to be used as anti-counterfeiting systems. Derived from liquid crystalline suspensions, these photonic materials present selective left-handed circular reflection that acts as a covert anti-counterfeiting feature, while the structural coloration that can act as an overt feature, flexibility, and response to multiple stimuli (can act as additional covert features). [1-4] Tunning optical properties and flexibility of solid films of CNC with other cellulosic derivatives was explored by the addition of hydroxypropylcellulose (HPC) [3] and hydroxypropylmethylcellulose (HPMC) [5] in home-made and commercial cellulose nanocrystals in liquid crystalline colloidal suspension, within the biphasic regime. HPC and HPMC content allows modulation of the reflected pitch value within all composite systems and induces flexibility. These new photonic cellulose-based nanomaterials are excellent candidates as anti-counterfeiting optical variable devices.

Unwound chiral nematics controlled by confining surface anchoring and geometry are frustrated systems that exhibit a variety of metastable topological solitonic structures. On top of that, their intrinsic chirality reduces the laser power needed for the propagation of bouncing optical solitons, whereas nonlinear chiral nematic media periodically compensate for the diffraction spreading of light beams more effectively than in conventional nematicons. Unwound chiral nematics thus provide an excellent playground for studying the interactions of topological and optical solitons. Modeling and simulations first developed for linear light interaction are here extended to nonlinear situations experimentally studied by Smalyukh's group. The delicate balance of the light-to-matter transfer of momentum and the force due to the nonlocal orientational elasticity of chiral liquid crystals enables the tractor effect and spatial localization of topological solitons. These simple examples show that the optomechanical interplay of both kinds of solitons has potential for use in soft photonics.

Efficient, reliable and low power optical phase shifters are required in many applications of photonic integrated circuits. Thanks to their large birefringence, liquid crystals are an interesting material for obtaining large phase shifts with low voltages. Due to the high index difference between liquid crystal and silicon, the mode overlap is often small and the tuning effect limited. It is important to consider configurations in which there is a large mode overlap or periodic configurations that can enhance the electro-optic effect. We review a number of interesting configurations and discuss the need for accurate simulations of the liquid crystal behavior, both in two dimensional and three dimensional geometries. Next to maximising the tuning efficiency, it is important to keep the losses introduced by the liquid crystal minimal. We present accurate measurements of the scattering induced by liquid crystal and discuss theoretical models to estimate the amount of light scattering as a function of applied voltages.

We experimentally report on nonvolatile and rewritable binary optical memory where the photon spin state controls the polarity of optically recorded localized orientational distortions in liquid crystals, which behave as elastic quasiparticles having long-term storage capabilities. The memory effect is made possible by the chiral nature of the liquid crystal mesophase, while the supramolecular polarity of the recorded ‘spinbits’ results from the chiral light-matter interaction involving spin-angular momentum transfer from light to matter.

This study presents an innovative approach to create a tunable multifocal LC microlens array (TMLCMA) that can switch between convex and concave modes. The TMLCMA is constructed using nematics and a triple-electrode structure comprising a top large-hole electrode, a middle small-hole array, and a bottom planar ITO electrode. A ZTO modal film is applied to the large-hole electrode on the top substrate to aid in distributing the electric field across the large-hole area. Various voltage control methods can manipulate the TMLCMA. Under the influence of voltage, the axially symmetric fringing electric field generated by the top large-hole electrode leads to a gradual and radial adjustment of the microlens's focal length from the TMLCMA's periphery to its center. This electrically tunable gradient in focal length is achieved. Practical demonstrations of the imaging functions of the TMLCMA are provided.

In this talk, we’ll discuss our latest findings on cascaded spiral diffractive lenses (cSDL) based on liquid crystal (LC) technology. Our lenses are notable for their low voltage requirements (less than 10Vrms), direct addressing capabilities, and wide aperture (greater than 25mm OD). They also boast high fill factors (over 98%) and a broad tunable focal range (over 4 Diopters). Each of the two cascaded devices are standard LC cells, created using a single direct laser writing lithographical process on a conventional transparent ITO covered glass substrate. We’ll also share our recent work with dual frequency materials and the application of these lenses in zoom systems and dynamic achromatic image capture, highlighting our progress in reducing the haze often present in diffractive liquid crystal lenses, and other high resolution devices. We’ll showcase implementations with both 24 and 72 electrodes, which allow for quasi analogue tuning across the entire tuning range. Keywords: Liquid Crystal, flat lens, adaptive optics, diffractive optics, optical vortex, orbital angular momentum

Multidimensional manipulation of light properties such as wavelength, polarization, spin and orbital angular momenta plays an important role in expanding the information capacity of photon-based communications. Among recently proposed ideas, stimulus-responsive self-organizing helical superstructures offer a promising avenue for development of future chiro-optics-based photonic devices. This study explores a photolithographic-like photoalignment system to fabricate spatially-micropatterned cholesteric liquid crystals (CLCs) formed by chiral molecular motors (CMM). The geometric phase provides an integrated strategy for laser beam shaping. Several specific chiro-optical elements with different geometric phase patterns. Additionally, by finely controlling the dynamic balance between the concentrations of CMM molecules with opposite handedness in the CLC devices with different optical functions, the spectral position and handedness of the photonic bandgap can be continuously, bidirectionally, and reversibly tuned in the ultra-broadband spectral region. This work demonstrates a promising approach to replace conventional photonic devices that are bulky and only serve static functions.

Surface alignment of liquid crystals (LCs) is key for optimizing their performance. Effective LC alignment strongly depends on the substrate used, which should promote strong local anchoring of the director field. Our work introduces a novel method using nanolithography to control the alignment of thermotropic LCs. Key to the approach is the use of 3D nanoprinting to create customized parallel nanogrooves on a glass substrate. These grooves yield azimuthal anchoring energies ranging from 10^-6 J/m² to 10^-5 J/m², partially surpassing values from other photopolymers. This approach offers high spatial resolution (~2µm) and allows for electro-optical switching, thus providing a flexible substrate platform for LC applications.

Photovoltaic spatial light modulators (PSLM) are self-activated optical devices that can be used as dynamic glazing or as optically addressable spatial light modulator. The range of potential applications of this new kind of optical device is highly dependent on its clear-state transmittance, spectral distribution of transmittance modulation, as well as on its response time, stability, and spatial resolution. These features are in turn mainly determined by the materials used for the various parts making up a PSLM, namely the photovoltaic unit, the liquid crystal layer, the liquid crystal alignment layers, and the polarizers. This contribution will focus on the multiple links between material properties and device performance and present our recent results on the design and processing of organic semiconductor materials designed to broaden the field of applications of PSLMs.

Augmented/Mixed reality devices require dynamic light management to create the necessary contrast ratio between the displayed information and ambient lighting. Over the past few years, guest-host liquid crystals have emerged as a leading technology to address this need. Here we present AlphaMicron’s electronic tint-on-demand technology, e-Tint, and discuss its electro-optic and mechanical properties that make it suitable for adoption into AR/MR applications.

A spectrometer performs two optical functions: chromatic dispersion and imaging onto a sensor. These two optical functionalities can be combined in a single device consisting of chiral nematic liquid crystals (CLC) deposited onto a curved substrate. To anchor the liquid crystal, we use the photo-alignment technique which involves interference of two beams onto a photosensitive layer. The resulting interference pattern generates a linear diffraction grating. Through ray-tracing simulations, the layout of the spectrometry setup is optimised for minimum astigmatism. We experimentally demonstrate the prototyping of a compact spectrometer based on holographically aligned chiral liquid crystals onto a curved substrate.

Flat diffractive optics utilizing chiral liquid crystal (CLC) has gained a lot of interest as a potential in- and out-coupling technology for applications such as augmented reality and head-up display systems. The unique properties of CLC together with a photoalignment technique capable of inducing controlled variation of the optical axis within a thin liquid crystal layer make it possible to obtain a range of efficient optical components. These components typically operate in reflection mode and can possess a variety of optical functionalities. In this study, we investigate 2D diffraction gratings and holographic lenses that combine diffraction grating and lens functionalities.

Cellulose ribbons, when produced from liquid crystalline solutions, exhibit a remarkable responsiveness to moisture. Cellulose-based Nature inspired materials have significant potential for opening up new routes for the production of novel mobile soft materials with tremendous impact on intelligent textiles, energy generation, drug delivery, bio-medical and bio-sensing devices, and micro soft robotics. This work focuses on the development and evaluation of stimuli-responsive cellulose-based liquid crystalline films, using for example, shear-casting techniques employing a multi-layered design. The applicability of these films as flexible humidity and temperature sensors will offer a significant contribution to the LC field.