This PDF file contains the front matter associated with SPIE Proceedings Volume 10941, including the Title Page, Copyright information, Table of Contents, Introduction, Author and Conference Committee lists

Magnetic fluids or ferrofuids (FF) are colloidal suspension of magnetic nanoparticles in a liquid carrier. When a material is illuminated with a high-intensity light, typically nanosecond, picosecond and femtosecond pulsed laser beam, its refractive index n2 and absorption coefficient β depend on the light intensity I. The Z-Scan (ZS) nonlinear optical and the Small-Angle X-Ray Scattering (SAXS) techniques are used to investigate the structure and nonlinear optical properties of magnetite nanoparticles dispersed in a colloid and trapped in thin films. n2 and β were measured as a function of the intensity of an external applied magnetic field H. Different relative orientations of the field with respect to the light-polarization direction were investigated. When the external magnetic field is applied to the colloidal sample (H parallel to the light-polarization direction), β increases with the field, ranging from 1.5 cm/GW (without field) to 2.4 cm/GW (2700 Oe). For the field direction perpendicular to the light polarization direction, β decreases to 1.0 cm/GW (2700 Oe) and after remains stable. These values allowed us to evaluate some elements of the third-order nonlinear optical susceptibility tensor χ^((3)). The SAXS experiments revealed that when the eld is applied, small linear aggregates are formed in the direction of H. Considering that the nanoparticles rotate to align their magnetic moment parallel to the applied field direction, and the particle's magnetic moment is aligned along the ⟨111⟩ lattice direction of the nanoparticle’s crystalline structure, our results indicate an optical anisotropy in magnetite. The calculated third-order nonlinear optical susceptibility, along the ⟨111⟩ direction, is Imχ_xxxx^((3))=2.0(3)×〖10〗^(-20) m^2/V^2, while its average along the other two orthogonal directions is 1/2 (Imχ_yyyy^((3))+Imχ_zzzz^((3)) )=0.9(3)×〖10〗^(-20) m^2/V^2. For the thin-film sample, however, the n2 and β values do not change when the field of 1600 Oe is applied. Within the experimental error, n_2 does not seem to change with field for the colloidal samples. CNPq, FAPESP, CAPES, INCT-FCx and NAP-FCx.

A calamitic liquid crystal composed of 1,3-dioxane and fluorinated aryl units exhibits a highly polar and fluid mesophase (MP phase). In the MP phase, anomalously large dielectric permittivity (ca. 10⁴), ferroelectric-like polarization switching, and second harmonic generation (SHG) are observed. SHG interferometry also indicates the polarization inversion by reversing the applied electric field in the MP phase. These experimental data clearly show that in the MP phase, a unidirectional ferroelectric-like polar order exists along the director.

We have invented the new principle to produce the slippery interfaces on the glass plates. Slippery interfaces are created by the localized disorder effect near the substrates. We designed and realized several proto types of the model for self-organized slippery interfaces. In the conventional LC display, switching dynamics is only defined by the motion of bulk director, because the director on the glass substrate is completely fixed due to the strong anchoring condition. By introducing the slippery interface, the motion of the surface director play key role for the switching dynamics as a new hydrodynamic variable. The reduction of the driving voltage and enhancement of mode efficiency can be achieved by the rotation of surface director. Furthermore, even the response time can be accelerated by the lubrication for the motion of surface director. We characterize the slippery interface by measuring the dynamics of surface director ns after switching on/off or under the rotating the external magnetic field. The anchoring energy and the viscosity of the surface director can be evaluated directly from the dynamics of ns. On the other hand, the gliding phenomena, which is the movement of so-called easy axis nh, is investigated from the dynamics of ns after switching off the magnetic field. The gliding feature can be represented by the viscosity of the movement of the easy axis. It should be important to distinguish the dynamics of ns and nh independently. This work was supported by JST-CREST (JPMJCR1424).

A chiral liquid crystal sandwiched by two parallel plates has been shown to exhibit various exotic structures including a hexagonal lattice of Skyrmion excitations. Here we focus on the optical properties of a hexagonal Skyrmion lattice and present our theoretical studies based on direct numerical solving of Maxwell equations for light waves. Specifically, we discuss Kossel diagrams and optical microscope images of a hexagonal Skyrmion lattice and other structures resembling a thin slice of a bulk blue phase structure.

Electrodes and alignment layers are major components of practically any liquid crystal device. Typically, indium-tin oxide films serve as electrodes (to apply an external voltage across the liquid crystal layer) whereas polyimide-based polymers (alignment layers) provide the required alignment of liquid crystals. Conducting polymers can combine the afore-mentioned two functions thus serving as both electrodes and alignment layers. In the majority of the reported studies, highly conducting polymers were used. On the contrary, in this paper, we report on electro-optics of liquid crystal cells utilizing weakly conducting polymers. Both static and time electro-optical response are analyzed. The designed cells are characterized by some interesting electro-optical features including the dependence of the effective threshold voltage on the frequency (0-1000 Hz) of the applied electric field. The model of this frequency dependence of the effective threshold voltage is discussed. Our results suggest that weakly conducting polymers are very promising materials for the development of flexible and wearable liquid crystal devices.

We demonstrate non-contact temperature measurement with 0.1 K precision at distances of several meters using omnidirectional laser emission from dye-doped cholesteric liquid crystal droplets freely floating in a fluid medium. Upon the excitation with a pulsed laser the liquid crystal droplet emits laser light due to 3D Bragg lasing in all directions. The spectral position of the lasing is highly dependent on temperature, which enables remote and contact-less temperature measurement with high precision. Both laser excitation and collection of light emitted by microlasers is performed through a 20 cm aperture optics at a distance of up to several meters. The optical excitation volume, where the droplets are excited and emit the laser light, is approx. 10 cubic millimeters. The measurement is performed with sub-second speed when several droplets pass through the excitation volume due to their thermal motion. Since the method is based solely on measuring the spectral position of a single and strong laser line, it is quite insensitive to scattering, absorption and background signals, such as auto-fluorescence. This enables a wide use in science and industry, with a detection range exceeding tens of meters.

Liquid Crystal (LC) devices with photosensitive elements have incredible scope for creating unique photo-induced optical devices. The use of azobenzene based materials, which undergo a trans-cis isomerisation when irradiated with light of a specific wavelength, is firmly established in LC research. The trans conformation is an elongated rod-like shape, similar to LC mesogens, whilst the cis conformation is closer to a spherical (bent) shape, disrupting to the LC order. When these materials are doped into LC materials they are able to produce light induced responses, and therefore their application to photo-switchable optics and devices is undeniable. In this research paper the light induced order modification, rather than light induced reorientation, is utilized to produce an all-optical switchable laser protection device. Upon irradiation of an azo-doped LC system with a continuous, low power (0.5 mW), laser threat (λ=405 nm) the transcis photoisomerisation process is triggered. This results in the trans-cis conformal shape change, lowering of the LC order, and causing the system to switch from the LC nematic phase (transmitting between crossed polarisers) to the isotropic liquid phase (blocking/dark between crossed polarisers). The optical properties of the azo-doped LC materials have been characterized and the response time dependence on azo-dopant concentration, system temperature, and laser threat intensity is thoroughly investigated.

Liquid crystals (LCs) have very attractive properties that the response can be controlled by the external stimulus such as electric field and temperature. Terahertz (THz) devices based on LC have wide applications. But the development of high-performance LC THz functional devices is still in its infancy. We firstly develop a large birefringence LC material in THz range. Then broadband tunable transmissive driven with porous graphene and reflective THz waveplates based on this LC are proposed. Furthermore, graphene-assisted high efficiency tunable THz metamaterial absorber is demonstrated. A magnetically and electrically polarization-tunable THz emitter that integrates a ferromagnetic heterostructure and the large-birefringence LC is also demonstrated. Last but not least, we use a temperaturesupersensitive cholesteric liquid crystal (CLC) to not only measure the beam profiles but also detect the powers of THz waves generated from a nonlinear crystal pumped by a table-top laser, which is visible, cost-effective, portable and robust at room temperature. These LC based THz devices can be used in applications such as THz imaging, biological sensing, and inspection.

There are many important applications for phase-only liquid crystal on Silicon-based spatial light modulators (LCOS SLMs). Among the applications, the diffractive beam splitting, beam shaping and beam steering with LCOS SLM are finding more and more use in telecommunication applications (e.g. wavelength selective switch for ROADM, space and mode division multiplexing). However, many effects of LCOS device have to be considered if we want to get high quality output light field. For example, the ideal phase, intensity and polarization distribution in far field are usually deteriorated by the pixelated metal structure and fringing field effects. Thus, the total efficiency is decreased. By using electro-optical and electromagnetic simulation methods, we can properly incorporate the effects that influence the optical performance of LCOS and optimize the design. Furthermore we report the implementation of the high-performance high-resolution LCOS SLM for the telecommunication C- and L-band with the average insertion loss (IL) of less than 0.2 dB, achieved by the reflectivity-enhancement coating on the LCOS backplane. The experimental results on reflectivity, diffraction efficiency, crosstalk and other important parameters are compared with the theoretical predictions.

Liquid crystal spatial light modulators (LC-SLMs) are usually polarization sensitive optical elements. In this paper, we propose a polarization-independent beam steering system to overcome the polarization problem of conventional liquid crystal devices by employing two polarization-dependent LC-SLMs, a polarizing beam splitter and a half-wave plate. In this system, two one-dimensional LC-SLMs are aligned orthogonally to deflect the beam in azimuthal and elevation, respectively. This system enables LC-SLMs to work in any polarization state of incident light, and can realize continuous two-dimensional laser beam pointing. Properties of polarization-independence as well as two-dimensional beam steering were mathematically and experimentally verified with a good agreement. Using the well aligned beam steering system, linearly polarized beams in different polarization angle are deflected with high accuracy and efficiency. The measured angular deviations are less than 5 micro-radians to show a high-accuracy beam steering of the system. This polarization-independent beam steering scheme is useful in the applications of nonmechanical laser communication, Lidar, and other LC-based devices.

The hyper-Rayleigh scattering technique was used to determine the first order hyperpolarizability β of magnetic nanoparticles dispersed on colloidal solutions. Pulse trains of mode-locked pulses of 100 ps on an a Q-switcher envelope of 150 ns emitted by a Nd:YAG laser, centered on 1064 nm, were used since this method allows measurements as a function of the incident beam intensity without the need of external elements. In order to determine the procedure to measure second-order optical nonlinearities on magnetic nanoparticles and avoid cumulative effects during the measurements, that lasts between to consecutive pulse trains, the results were studied for different values of the Q-switcher repetition rate, from 5 Hz to 800 Hz. Since cumulative effects were verified for higher values of repetition rates, all measurements were performed at the rate of 30 Hz. Therefore, the first-order hyperpolarizability β was measured in the presence and absence of external magnetic field of magnitude H = 800 G. The linear attenuation spectrum was determined and didn't change with the appliance of magnetic field since large aggregates of nanoparticles were not formed. Nonlinear scattering measurements were performed in the case were the laser light polarization was parallel and perpendicular to the external field lines, employing a half-wave plate to change the light polarization state. In the absence of magnetic field, β_H=0 = 8:5(1)×10^-28 cm⁵/esu, while in their presence of magnetic field, β = 9:8(2)×10^-28 cm⁵/esu and β⊥ = 8:1(1)×10^-28 cm⁵/esu, showing an anisotropy β-β⊥/β of about 17%.

A liquid crystal on silicon spatial light modulator (LCoS-SLM), operating in phase only modulation mode, was used to dynamically control the aperture diameter in an adaptive optics system. The LCoS-SLM was optically conjugated to the Fourier plane of the collimator lens focused on the stimulus. A projector was used to produce stimulus in white light. A dedicated phase profile, resembling an axicon lens, but with a constant phase within the diameter of the intended aperture, was programmed on the LCoS-SLM. The portion of the wavefront passing through the central zone with constant phase remained non-modulated, while the wavefront passing through the axicon lens was propagated away from the optical axis. A field-stop was included in an additional plane to further filter the diverging light. The phase mask acted as a low-pass spatial filter, simulating the virtual effect of a physical aperture. To evaluate the performance of the method, a motorized iris was placed into a plane optically conjugated to the LCoS-SLM. The experimental modulation transfer functions of the system were compared when obtained through the physical aperture and with the phase mask production the virtual pupil. It was found that the phase mask generated by the LCoS-SLM performs similarly to the real aperture, although the field of view had to be limited to filter out the wavefront coming from the axicon lens. This method allows, under certain conditions, to use a single LCoS-SLM to control both intensity and phase simultaneously in a system.

Controlled shape changes of polymerized liquid crystalline coatings is often achieved via prepatterning the molecular orientation of liquid crystal (LC) monomers at the stage of preparation. In this work, using the so-called hybrid alignment of the LC, we produce surface structures of positive Gaussian curvature of coatings without complex techniques such as photoalignment. A mixture of LC monomers coated onto a glass plate with planar alignment of the director is exposed to air, which promotes vertical alignment. The competing planar and homeotropic boundary conditions result in a) thickness dependent director and b) spontaneous formation of spindle-like regions, limited by disclination loops, that are called the reverse tilt domains (RTDs). The disclination separates different director configurations inside and outside the RTD. The RTDs produce relatively big protrusions (100 − 600 nm) of the LC network coating. Actuation of the coating by heat increases the amplitude of RTD protrusions.

A dye-doped LC/polymer light shutter with a polymer structure that is formed using the thermally-induced phase separation (TIPS) method is demonstrated. The TIPS method relies on the difference in solubility between thermoplastic polymer and solvent, and thus there is no degradation of the dye during the fabrication process. The light shutter can be fabricated quickly because the optical properties are not affected by the cooling time. The fabricated TIPS cell shows a superior black color with excellent optical properties, such as a low haze value of 0.5% in the transparent state, and a high haze value of 99.1% in the opaque state. This result can be applied for the high image quality of see-through displays using organic light-emitting diodes.

A wide spectra color-reflective device based on polymer-sustained conical helix (PSCH) of cholesteric liquid crystal (CLC) is demonstrated. The phase-separated three-dimensional polymer network transcribes the helicoidal structure of a CLC and sustains the deformation of helices by the external electric field for wide spectrum turning. Besides the selective reflection of light, the device also demonstrates light-scattering focal conic texture in off-state and transparent homeotropic state at high electric field. The new electro-chromic devices with PSCH that can reversibly change of wide-range colors in response to ascending and descending of electric field are promising in various fields including smart windows, sensors, displays, and camouflage applications.

In this talk, we will report a study of using electric power to trigger programmed shape changes and motions of a liquid crystal polymer network (LCN). The used LCN is a photocrosslinkable main-chain liquid crystal polymer (Tg and clearing temperature near room temperature and 60 oC respectively) that, upon stretching, can undergo large plastic elongation to form monodomain of uniaxial LC orientation before photocrosslinking. By sandwiching thin and flexible conducting wires between a LCN strip and Kapton tape (polyimide film), the resistive heating effect is used to activate the LC-isotropic (order-disorder) phase transition of the LCN and produce reversible bending of the strip at voltage-on and unbending at voltage-off state. The robust, electric field-induced deformation can be repeated for thousands of times without fatigue; and the deformation amplitude and speed are dependent upon the applied voltage. By taking advantage of the great processability of the LCN, complex shapes of the polymer actuator can be prepared at the field-off state. We show that by depositing the conducting wire with Kapton tape in selected areas of the LCN strip (either side or “pattering” on one surface), upon application of a programmed square-wave electric field, versatile shape changes and motions, including locomotion and periodic twisting/unwinding, can be achieved. In certain cases, the electric power is transformed into physical work through the LCN actuation. Possible applications will be discussed.

Due to the presence of a polarization-sensitive photonic band gap, cholesteric liquid crystals (CLCs) strongly modify the emission of fluorescent guest molecules, which makes them promising candidates for coherent or incoherent light sources with unique polarization properties. We present a systematic study of the angular dependent spontaneous emission properties of CLC films doped with a fluorescent dye. Our main findings are: (1) wavelength intervals of almost complete emission suppression due to the emergence of a polarizationinsensitive band gap at large detection angles; (2) additional band-edge resonance peaks almost completely dominating emission in certain angular ranges; and (3) striking angular and wavelength dependent polarization variations.

Computational accommodation-invariant (AI) display attempts to mitigate vergence-accommodation conflict (VAC) by showing a constant imagery no matter where the observer focuses on. However, due to the usage of an electrically focus-tunable lens, the contrast of imagery is degraded as point-spread functions of multiple foci are integrated. In this paper, we introduce the content-adaptive approach to improve the contrast at the depth of highly salient region in the image. The position of focal plane is dynamically determined considering the zone of comfort and the mean focal distance of salient region. The contrast enhancement compared to conventional accommodation-invariant display is shown through simulation results using USAF resolution target image. We demonstrate our proof-of-concept prototype and its optical feasibility is verified with experimental results.

Liquid crystals are well known for their display applications (LCDs), but they are known much less for their use in practical (real) optical imaging or vision systems. In reality, those materials have been explored during several decades to develop electrically variable lenses. Their performance optimization requires particular trade-offs that depend upon the specific application. In some cases, (such as mobile phone miniature cameras or ophthalmic), they perform rather well by providing low power consumption and miniature alternatives for mechanical systems. Our presentation will describe recent results obtained by one of the lens designs. In this design, the peripheral electrode segmentation is used to dynamically obtain various wavefront profiles, without any electrode pixel within the clear aperture of the lens. Potential applications of this approach will be presented, for example, in the field of adaptive endoscopy. Thus, the focus tuning and correction of wavefront asymmetry will be demonstrated. In addition, those lenses may provide unique capability of dynamic adjustment of the wavefront’s shape by creating prism like and other complex profiles, generating various non diffracting beams.

Geometric phase diffractive optics technology is rapidly advancing including patterned liquid crystal and polymer liquid crystal elements and devices. The need exists for a set of design methods and tools to engineer optical components and systems. Numerical and analytical design methods are discussed with an emphasis on optical systems. Multilevel simulation methods are used incorporating full numerical electromagnetic solutions, diffraction theory, and ray tracing. Additionally, iterative algorithms are used to design the local anisotropic axis orientation of various regions in order to produce the desired diffraction effects. Elements are optimized for both amplitude and phase. Examples are presented including an optical system based on geometric phase elements that sorts the orbital and spin angular momentum states of an optical beam. Designs are demonstrated in polymer liquid crystal diffractive waveplate thin film elements fabricated through photo-alignment with a spatial light polarization modulator. The array of numerical design technique presented allow the rapid design of optical phase patterns, integration with real optical systems, and evaluation of physical materials and device properties.

A two-dimensional (2D) liquid-crystal (LC) grating consisting of three LC molecular orientation domains is fabricated by a microrubbing process, with the aim of application to the Stokes polarimetry. It was found that the in-plane orientation direction, retardation, and twist angle in the obtained LC molecular orientation state varied in space. The fabricated LC grating was applied to the Stokes polarimetry to ensure the viability of the proposed measurement scheme. As a result, the measured Stokes parameter of the incident light agreed with that of the incident light. Furthermore, we point out the possibility of performance adjustability by an applied voltage, which can be a great advantage of the LCgrating Stokes polarimetry.

Liquid crystals in the twist bend modulated nematic phase spontaneously form gratings when filled in planar cells. Such gratings transform the polarization properties of the incident light and as such can be used as low cost switchers because no surface patterning is required to obtain the grating. In addition, the polarization properties of the second order diffraction peak, combined with a theoretical modelling, can be used to determine the spatial variation of the optical axis in the cell. In this paper, we report on a generalized behavior of the polarization of the diffracted light in cells of various thicknesses and for different twist bend nematic materials.

In this paper, we propose a new type of liquid-crystal cylindrical microlens arrays (LCCMAs) with nonuniform microcoil electrodes (NMEs). The key functional microstructure of the LCCMAs includes two ~500-μm-thick glass substrates with indium-tin-oxide (ITO) films for shaping the top and the bottom electrodes and a thin LC layer with a typical thickness of 20μm. The ITO film of the upper substrate is etched into the shape of nonuniform microcoil by traditional lithography process and inductively coupled plasma etching (ICP etching). By simply adjusting voltage signal applied on the NMEs, the LCCMAs exhibit relatively sharp point spread functions (PSFs) at the focal plane of different spectral beams including red (635-671nm), green (501-561nm) and blue (430-473nm) lasers at relatively low signal voltages (even less than 3Vrms).

Infrared reflectance tuning or controlling based on functioned nanostructure has become a research hotspot. Via designing particular surface nanostructure, special infrared optical devices can be devised. However, once these functioned structures are fabricated, their optical characteristics are also determined, so as to limit their application. Here, we theoretically and experimentally demonstrated a signal voltage tunability of a dynamic infrared reflectance device by using an aluminum 2-dimension grating with a birefringence nematic liquid-crystal (LC). The hybrid microstructure allows electrically controlled reflectance at infrared wavelength by only applying a voltage signal with relatively low RMS amplitude. Besides the rubbed polyimide film fabricated for shaping initial LC direction contacted directly with nanostructures, the aluminum 2-dimension grating itself serves as an alignment layer to form a twisted LC cell. And the nanostructured aluminum also serves as an electrode. The working principle of our device is based on the fact that LC is polarization tunability. When applied a small electric field on the aluminum electrode and another electrode, the LC molecule can be reoriented and thus lead to a remarkable change of the dielectric constant surrounding the metallic nanostructure, and also excite relatively strong surface plasmon polaritons (SPP) modes on the LC-metal interface so as to provide a possibility of adjusting the reflectance. The aluminum metasurfaces is prepared by electron-beam lithography (EBL). The Fourier Transform Infrared Spectrometer (FT-IR) is used to observe the reflectance of the device at infrared wavelengths. A significant spectral tunability at 3μm to 4μm of such a device has been demonstrated by applying the voltage from 0 to 20 V_rms.