Selective Reflection of Chiral Ferroelectric Nematic Liquid Crystals Tuned by Electric Field Along the Helix Axis

By lunching the beam into the chiral nematic liquid crystals it is possible to achieve a non-diffractive beam similar to a soliton. This effect is caused by the molecular reorientation i.e. nonlinear response of the material forming the areas of higher refractive index. Diffraction is suppressed by the focusing effect. For appropriate launching conditions it is also possible to achieve a beam which splits into two or more separate beams. Such phenomenon is discussed in this article and analyzed theoretical. To model this effect Fully Vectorial Beam Propagation Method coupled with the Frank-Oseen elastic theory is used. Simulations are performed for various input beam powers, widths, polarization angles and launching positions. Full Text: PDF ReferencesG. Assanto and M. A. Karpierz, "Nematicons: self-localised beams in nematic liquid crystals", Liq. Cryst. 36, 1161–1172 (2009) CrossRef G. Assanto, Nematicons: Spatial Optical Solitons in Nematic Liquid Crystals, John Wiley & Sons Inc. Hoboken, New Jersey (2013) DirectLink A. Piccardi, A. Alberucci, U. Bortolozzo, S. Residori, and G. Assanto, "Soliton gating and switching in liquid crystal light valve", Appl. Phys. Lett. 96, 071104 (2010). CrossRef D. Melo, I. Fernandes, F. Moraes, S. Fumeron, and E. Pereira, "Thermal diode made by nematic liquid crystal", Phys. Lett. A 380, 3121 – 3127 (2016). CrossRef U. Laudyn, M. Kwaśny, F. A. Sala, M. A. Karpierz, N. F. Smyth, G. Assanto, "Curved optical solitons subject to transverse acceleration in reorientational soft matter", Sci. Rep. 7, 12385 (2017) CrossRef M. Kwaśny, U. A. Laudyn, F. A. Sala, A. Alberucci, M. A. Karpierz, G. Assanto, "Self-guided beams in low-birefringence nematic liquid crystals", Phys. Rev. A 86, 013824 (2012) CrossRef F. A. Sala, M. M. Sala-Tefelska, "Optical steering of mutual capacitance in a nematic liquid crystal cell", J. Opt. Soc. Am. B. 35, 133-139 (2018) CrossRef U. A. Laudyn, A. Piccardi, M. Kwasny, M. A. Karpierz, G. Assanto, "Thermo-optic soliton routing in nematic liquid crystals", Opt. Lett. 43, 2296-2299 (2018) CrossRef F. A. Sala, M. M. Sala-Tefelska, M. J. Bujok, J. "Influence of temperature diffusion on molecular reorientation in nematic liquid crystals", Nonlinear Opt. Phys. Mater. 27, 1850011 (2018) CrossRef I-C Khoo Liquid crystals John Wiley & Sons, Inc (2007) DirectLink P. G. de Gennes, J. Prost, The Physics of Liquid Crystals, Clarendon Press (1995) DirectLink U. A. Laudyn, P. S. Jung, M. A. Karpierz, G. Assanto, "Quasi two-dimensional astigmatic solitons in soft chiral metastructures", Sci. Rep. 6, 22923 (2016) CrossRef J. Beeckman, A. Madani, P. J. M. Vanbrabant, P. Henneaux, S-P. Gorza, M. Haelterman, "Switching and intrinsic position bistability of soliton beams in chiral nematic liquid crystals", Phys. Rev. A 83, 033832 (2011) CrossRef A. Madani, J. Beeckman, K. Neyts, "An experimental observation of a spatial optical soliton beam and self splitting of beam into two soliton beams in chiral nematic liquid crystal", Opt. Commun. 298–299, 222-226, (2013) CrossRef G. D. Ziogos, E. E. Kriezis, "Modeling light propagation in liquid crystal devices with a 3-D full-vector finite-element beam propagation method", Opt. Quant. Electron 40, 10 (2008) CrossRef F. A. Sala, M. A. Karpierz, "Chiral and nonchiral nematic liquid-crystal reorientation induced by inhomogeneous electric fields", J. Opt. Soc. Am. B 29, 1465-1472 (2012) CrossRef F. A. Sala, M. A. Karpierz, "Modeling of molecular reorientation and beam propagation in chiral and non-chiral nematic liquid crystals", Opt. Express 20, 13923-13938 (2012) CrossRef F. A. Sala, "Design of false color palettes for grayscale reproduction", Displays, 46, 9-15 (2017) CrossRef

Orientationally ordered soft matter is exceptionally responsive to a variety of excitations. That’s the basis for its great range of applications.

A molecular theory of the helical twisting in chiral liquid crystals is developed, which provides an explanation for the experimentally observed helical sense inversion induced by a change of concentration in binary mixtures of chiral and nonchiral nematic liquid crystals. The theory also describes the sense inversion induced by a change of temperature observed in some single component nematics. The theory present is based on a simple model of a chiral rigid molecule, composed of several equivalent nonchiral sites, which are arranged in the molecule to form a chiral configuration. The macroscopic helical pitch in the chiral nematic phase, twist elastic constant, and nematic order parameters are calculated using the same molecular model. It is shown that the helical sense inversion can be determined by a large biaxiality of chiral molecules. It is also demonstrated that the biaxiality is important in determining the variation of the helical pitch with temperature and concentration.

We investigate nonlinear self-focusing and nematicon generation in low birefringencenematic liquid crystals (NLCs), where n=0.04. are obtained for larger optical powers but they are more than in NLCs with standard birefringence, of the order of n=0.2 Moreover, in low-birefringent NLCs, polarization components exchange energy in a nonlinear regime. Such behaviour is not observed in typical NLCs, where ordinary and extraordinary waves tend to propagate independently due to large walk off.The results of our experimental rest are also compared with numerical simulations, using a fully vectorial BPM. Calculations and experimental results are in good qualitative and quantitative agreement. Full Text: PDF References G. Assanto and M. A. Karpierz, Nematicons: self-localised beams in nematic liquid crystals, Liq. Cryst. 36, 1161 (2009). CrossRef M. Peccianti and G. Assanto, Nematicons, Phys. Rep. 516, 147(2012). CrossRef M. Peccianti, G. Assanto, A. De Luca, C. Umeton and I. C. Khoo, Electrically assisted self-confinement and waveguiding in planar nematic liquid crystal cells, Appl. Phys. Lett. 77, 7 (2000). CrossRef M. A. Karpierz, M. Sierakowski, M. Swillo and T. Wolinski, Self Focusing in Crystalline Waveguides, Mol. Cryst. Liq. Cryst. 320, 157 (1998). CrossRef U. A. Laudyn, M. Kwasny, M. A. Karpierz, Nematicons in chiral nematic liquid crystals, Appl. Phys. Lett. 94, 091110 (2009). CrossRef U. A. Laudyn, M. Kwasny, K. Jaworowicz, K. A. Rutkowska, M. A. Karpierz and G. Assanto, Properties of spatial solitons in chiral nematic liquid crystal cells, Photon. Lett. Poland 1, 7 (2009). CrossRef I. C. Khoo, Liquid Crystals, Second Edition, Wiley & Sons, New Jersey (2007). CrossRef A. Piccardi, A. Alberucci, G. Assanto, Soliton self-deflection via power-dependent walk-off, Appl. Phys. Lett.96, 061105 (2010). CrossRef F. A. Sala and M. A. Karpierz, Modeling of molecular reorientation and beam propagation in chiral and non-chiral nematic liquid crystals, Opt. Express 20, 13923 (2012). CrossRef A. Piccardi, M. Trotta, M. Kwasny, A. Alberucci, R. Asquini, M. Karpierz, A. D'Alessandro and G. Assanto, Trends and trade-offs in nematicon propagation, Appl. Phys. B 104, 805 (2011). CrossRef R. Dąbrowski, J. Dziaduszek and T. Szczucinski, Mesomorphic Characteristics of Some New Homologous Series with the Isothiocyanato Terminal Group, Mol. Cyst. Liq. Cryst. 124, 241 (1985). CrossRef

Controllable compression of the temporal duration of light pulses takes place in a liquid crystal medium via self-action processes of beam mixing, namely, a dynamic Bragg grating formation by incoming light waves with their consequent self-diffraction on the same recorded grating. Wherein, the laser pulse duration should be comparable with the time relaxation constant of the medium while the extent of the temporal compression is controlled by the variation of the input pulse durations and the value of nonlocal response. Full Text: PDF ReferencesU. Bortolozzo, S. Residori and J. P. Huignard, "Beam coupling in photorefractive liquid crystal light valves", J. Phys. D: Appl. Phys. 41, 224007 (2008). CrossRef P. Guner and J.P. Huignard, Photorefractive Matrials and their Applications, 1, 2, and 3 (New York Springer) and references therein (2006). CrossRef S. Bugaychuk and E. Tobisch, "Single evolution equation in a light-matter pairing system", J. Phys. A: Math. Theor., 51 (12), 125201 (2018). CrossRef S. Bugaychuk and R. Conte, "Nonlinear amplification of coherent waves in media with soliton-type refractive index pattern", Phys. Rev. E 86, 026603 (2012). CrossRef A. Iljin, "Light-induced order modification – The way to speed up", Journal of Molecular Liquids 267, 38 (2018). CrossRef A. Iljin, "Transient Modulation of Order Parameter and Optical Non-Linearity in a Chiral Nematic Liquid Crystal", Mol. Cryst. Liq. Cryst. 543, 143 (2011). CrossRef D. Wei, A. Iljin, Z. Cai, S. Residori, and U. Bortolozzo, "Two-wave mixing in chiral dye-doped nematic liquid crystals", Opt. Lett. 37, 734 (2012). CrossRef S. Bugayhuk, A. Iljin, O. Lytvynenko, L. Tarakhan and L. Karachevtseva, Nanoscale Res. Lett., 12, 449 (2017). CrossRef

Evaporation induced self-assembly of silica nanoparticles on ITO substrates in a confined cell for vertical alignment of liquid crystals and performance analysis

Study on laser action from UV-curable chiral nematic liquid crystals

Chiral liquid crystal (LC) materials are indispensable functional components of advanced optoelectronic devices. In this study, we fabricated chiral nematic liquid crystal (N*‐LC) devices by introducing perylene and its N,N ‐di‐ n ‐octyl‐3,4,9,10‐perylenetetracarboxylic diimide (OPDI) derivative, as achiral luminophores, into an N*‐LC host composed of the achiral 4'‐pentyl‐4‐cyanobiphenyl (5CB) LC and the planar‐chiral 4,12‐dihydroxy[2.2]paracyclophane ([2.2]‐PCP) dopant. Remarkably, both perylene and OPDI exhibited pronounced circularly polarized luminescence (CPL) within the planar‐chiral‐dopant‐induced N*‐LC environment, despite the use of achiral luminophores. Furthermore, the handedness of the CPL can be controlled by the planar chirality of the [2.2]‐PCP dopant. In addition, the resulting N*‐LC materials exhibited rapid and reversible inversion of CPL handedness when a direct‐current (DC) electric field was applied and then removed. This reversible behavior is ascribable to the electric‐field‐induced phase transition between the helical N*‐LC structure of 5CB and another ordered phase. These findings provide a new material design principle in which a planar‐chiral dopant induces the N*‐LC phase in 5CB, thereby enabling high‐speed, reversible CPL modulation based on the application of an electric field.

Energy saving, as important as energy harvesting and storage in sustainable energy endeavor, would greatly decrease the energy production and will help in alleviating the increasing pressure on nonrenewable energy sources, which will not only lengthen their exhaustion but also would provide sufficient time to explore alternative potential sources of sustainable energy. Hitherto, extensive efforts have been devoted to developing energy saving technology to meet environmental and economic restrictions. In this context, liquid crystal (LC) based energy-saving devices employing chiral LC phases as the active materials have been demonstrated. As unique LCs, chiral LC phases possess many excellent characteristics on molecular arrangement and optical properties due to their periodic modulated structure, which enables their promising applications in energy-saving devices. Here we discuss different approaches adopted to develop LC devices with energy saving characteristics. The devices are based on the chiral LCs, i.e., chiral nematic LCs and blue phase LCs, however the use of chiral nematic LCs is highlighted in this chapter. The bistable states of chiral nematic LCs present different optical properties in absence of external field for potential applications in low energy consumption displays, image storage, and light shutters. Furthermore, their selective reflection exhibits the high efficiency on solar energy tuning as a smart window or adaptor of photovoltaic devices. By doping photosensitive chiral switches or motors into the LC, light tunability on reflection band of chiral LCs has been achieved. In this sense, recent developments of delicate light driven energy-saving photonic devices will be also discussed.

Chiral nematic liquid crystals have attracted substantial interest. They spontaneously self-organize to form a helical structure with no complex fabrication procedure required and exhibit a reflection band for a certain wavelength interval. Since the photonic band gap can be tuned by applying external factors (heat, voltage, light, elasticity) chiral nematic liquid crystals are potentially interesting for large area optical filters and shutters, reflective displays and tunable lasers. In this work, a device which consists of a mixture of photo-polymerizable liquid crystal, non-reactive nematic liquid crystal and a chiral dopant is fabricated. By selecting the appropriate chiral dopant concentration, it is possible to make devices for different operation wavelengths. The influence of UV illumination on a partially polymerized chiral liquid crystal is investigated. A blue-wavelength shift of the photonic band gap is obtained as a function of power, duration time of UV illumination and the thickness of the cells. Interestingly the width and depth of the photonic band gap is unaffected by the change in UV curing conditions, which indicates that there is no degradation by the UV light.

A series of crown ether type binaphthyl derivatives (CEBDs) were synthesized and used as chiral dopants to induce chiral nematic (N*) liquid crystals (LCs). The twisting powers of the CEBDs for phenylcyclohexane (PCH)-derived nematic LCs were evaluated. It was found that the twisting powers of the CEBDs increased with decreasing ring size of the crown ether. Helical polyacetylenes were synthesized in the N*-LCs induced by the CEBDs. The relationship between the morphology of the helical polyacetylene and the helical structure of the N*-LC was investigated. The result showed that the interdistance between the fibril bundles of the helical polyacetylene was equal to a half-helical pitch of the N*-LC and the screw direction of the polyacetylene fibrils was opposite to that of the N*-LC.

Summary form only given. We investigate the optical phase conjugation phenomenon in chiral nematic liquid crystal. Nematic chiral liquid crystals exhibit Bragg like reflection - or light stop band - for left or right circular polarization. We use the mixture of chiral liquid crystal cholesteryloleate and nematic E7 mixture in volume proportion 2:1. The photonic band gap of such a chiral mixture can be tuned by changes of temperature and shifts over the whole visible light spectrum (cf. Fig.1a). We enhanced the nonlinear optical properties of liquid crystal mixture by addition of photochromic azo-dye Disperse Red 1.In proposed novel optical configuration shown in Fig. 1b for degenerated four-wave mixing we used only two incident beams: a pump beam and a signal one. The pump light beam propagates parallel to the long axis of a chiral structure. The counter propagating, second pump beam results from a Bragg reflection of the pump beam on the chiral structure with a suitable pitch. The signal beam illuminates the sample at small angle with respect to the pump beam. Both incident beams came from the same cw Nd:YAG laser doubled in frequency (λ = 532 nm) and are coherent. Due to Bragg condition the phase conjugate to the signal beam is observed only in the small temperature interval. The intensity of phase conjugate beam strongly depends on pump and signal beams polarization states, being maximal for left circular polarization and vanishing for right circular polarization states of both beams. The signals of the optical self-pumped phase conjugation and self-diffraction are observed at low laser light intensities (P <; 1 mW) due to resonant enhancement. This enhancement is due to the matching of the light wavelength and natural material photonic band gap which 'slow downs' the light and thus can amplify light - matter interaction. The role of azo-dye is crucial for creating of suitable diffraction gratings which arise in a material. We estimated a value of third order optical susceptibility χ(3) =2.8 x 10-17 m2/V2 and we attribute it to enhancement of azo-dye induced molecular reorientation process of liquid crystal molecules.

We have d eveloped a technology to integrate a thin layer of liquid crystal (LC) on top of a Vertical -Cavity Surface -Emitting Laser (VCSEL). Based on this technology, we demonstrate VCSELs with a chiral liquid crystal (CLC) layer , which acts as a tuneable mirror. Th e reflection properties of the CLC layer are controlled by temperature. Next we demonstrate VCSEL devices with tuneable external cavity using a nematic LC layer incorporated with an additional dielectric mirror (SiO 2 /Ta 2 O 5 ). The VCSEL and the LC layer can be electrically driven independently and the optical length in the external cavity can be tuned by the applied voltage on the LC layer. In both configurations we show that the emission properties of the VCSEL can be changed, in terms of emission wavelength , polarization state and/or lasing threshold. Keywords: Vertical Cavity Surface Emitting Laser , external cavity , ch iral liquid crystal 1. INTRODUCTION Because of its high emission efficiency and low operation power consumption, VCSELs ( Vertical -Cavity Sur face -Emitting Lasers) have been broadly used as light sources in optoelectronic devices in the past decade in optical interconnects and sensing applications [1-4]. The emission properties of VCSELs can be further improved to realize tunable polarization and wavelength [5-7]. In our previous publication, a technology to inte grate a VCSEL chip into a standard liquid crystal (LC) cell is developed [8]. Based on this technology, a new type of device is developed for a broader range of functionalities. The basic idea is to introduce reflection of light back into the VCSEL cavity . It is realized by using chiral liquid crystals (CLCs) or nematic LCs incorporated wit h an extra reflector. In the first case the extra reflection arises from the photonic band gap of the LC material itself. In this work, we fabricate and characterize electrically driven VCSEL devices , in which the emitting area of the VCSEL is covered with a thin LC layer. Two different device structures are demonstrated : VCSEL with CLC overlay (CLC -VCSEL) and VCSEL with nematic LC combined with a dielectric mirror (DE -LC -VCSEL) . For the first structure, the C LC layer has a photonic reflection band which co vers the VCSEL emission wavelength, so that one circular ly polarized mode of the laser emission which has the same handedness with the CLC helix is reflected and used as feedback into the VCSEL [9, 10 ]. For the second structure, the dielectric mirror provides strong refle ction and forms an external cavity, in which nematic LC can be filled. It is observed that the polarization state and the wavelength of the laser emission can be controlled by the applied voltage across the nematic LC overlay .

Helical polyacetylene was synthesized under an asymmetric reaction field consisting of chiral nematic (N*) liquid crystals (LCs). The chiral nematic LC was prepared by adding a chiroptical binaphthol derivative as a chiral dopant to a mixture of two nematic LCs. Acetylene polymerizations were carried out using the catalyst titanium tetra-n-butoxide-triethylaluminum dissolved in the chiral nematic LC solvent. The polyacetylene film was shown by scanning electron microscopy to consist of clockwise or counterclockwise helical structure of fibrils. A Cotton effect was observed in the region of the pi --> pi* transition of the polyacetylene chain in circular dichroism spectra. The high electrical conductivities of approximately 1500 to 1800 siemens per centimeter after iodine doping and the chiral helicity of these films may be exploited in electromagnetic and optical applications.

Helical polyacetylene was synthesized under asymmetric reaction field constructed with chiral nematic liquid crystal (LC). The chiral nematic LC was prepared by adding a chiral phenylcyclohexyl (PCH) derivative, (R)- or (S)-PCH308*, as a dopant, into an equi-weighted mixture of two kinds of nematic LCs. Acetylene polymerization was carried out with Ti(O-n-Bu)4 - Et3Al catalyst dissolved in the chiral nematic LC. It is found from SEM measurements that the polyacetylene films is composed of helical fibrils that are bundles of polyene chains. CD spectrum of the polyacetylene film showed positive or negative Cotton effect, depending on the helicity of the chiral nematic LC.