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.
Self-assembled periodic micro-nanostructures triggered by responses to external influences often occur in anisotropic self-assembled supramolecular soft-matter systems (such as liquid crystal (LC) systems). However, these structures are often not easily to control or even change, e.g., orderliness of the structures. A pre-built 1D periodic microgroove structure on the planar cholesteric LC cell is used to study whether it can effectively improve the large-area order of the electro-induced 2D deformation structure. Experimental results show that the 2D microgrid structure caused by the Helfrich deformation of the CLC can be effectively controlled to be ordered macroscopically by the pre-built 1D periodic microgroove structure. Furthermore, the uniformity of the microgrid size is also improved. The findings enhance the potential applicability of the well-known Helfrich deformation phenomenon and provide an example for further control of periodic micro-nanostructures in self-assembled supramolecular systems.
In this study, the bent dimers were added in the azobenzene chiral doped cholesteric liquid crystals. The photoisomerization of azo-chiral material can induce a change in pitch and eventually lead to the occurrence of Helfrich deformation. Experimental results show that the photoinduced microgrid structure can be significantly stabilized by adding bent dimers and simultaneously applying a low voltage below the threshold of electric-induced Helfrich deformation. Furthermore, the spacing of the resulting meshed microgrids can be tuned by dimer concentration or applied voltage, revealing its potential for multiparameter controllable optical diffraction devices.
With the flourish development of artificial intelligence, lasing with tailored features generated by photonic crystal lasers play a more important part in the field of optics and in potential applications such as self-control, LiDAR, telecommunications, and, holography imaging. Here, a self-steering lasing emission from a defect-mode sandwich-like structure consisting of photomechanical deformed azobenzene cholesteric liquid crystal elastomer is demonstrated. The output single-mode lasing emission can be fast steered by UV irradiation to a widely angular tuning range of approximately ±60° with an excitation threshold of Eth = 7.9 ± 0.5 μJ cm−2 per pulse. We envision that this flexible, portable and durable sandwich-like laser system with controllable lasing beam steering and mechanical robustness will open a gate for self-driving vehicle, self-sustained machines and optical devices with the core feature of photomechanical transduction.
The self-organized periodic micro/nano structure caused by the deformation of the stimulus responsive structure often occurs in anisotropic self-assembled supramolecular systems (such as cholesteric liquid crystal (CLC) systems). However, the long-distance ordering of these structures is often not easy to control. This investigation first demonstrates the manipulation ability of a 1D interference field on the macroscopic orderliness of the resulting 2D microgrid chiral structure via the firstly discovered photopolymerization-induced Helfrich deformation. A pre-built polymer layer in the early stage of photopolymerization continuously thicken to compress the helical pitch of the CLC–monomer region and then induce an internal longitudinal strain, leading to the 2D disordered microgrid structure of Helfrich deformation. A 1D laser interference field can effectively control the post-formed 2D grid microstructure to be arranged in an orderly manner in a macro-exposure area.
In this work, the thermal- and photo-reversible symmetrical deformation and structural color changed actuators based on fully-polymerized cholesteric liquid crystal (CLC) polymer beads are demonstrated. A jack-inspired soft microdevice comprising durable fully-polymerized CLC beads by the stand-alone and free of extraction technique is demonstrated to have the unique photo-responsive capabilities of lifting substantially heavy objects and photochromatism via light-triggered symmetric volume expansion of the CLC beads. The desired symmetrical volume expansion with photochromatic property is realized by decreasing the degree of the order parameter, which is caused by the reorientation of the LC director. Such dynamic manipulation of anisotropic geometric deformation of soft materials offer promising infinite possibilities for the applications of smart devices.
This Conference Presentation, Bio-inspired photo-actuation based on cholesteric liquid-crystal elastomers with photosensitive derivatives was recorded at Photonics West 2020 held in San Francisco, California, United States.
This study investigated a polyethylene terephthalate (PET) substrate and the effect of indium tin oxide (ITO) thin-film interference on the electromagnetic resonance of distorted metamaterials. The photoresist was developed on a PET substrate and swollen using isopropyl alcohol. The SRRs had various total lengths, gaps, and line widths. In addition, each of these three dimensions varied greatly and thus the distorted SRRs exhibited a broadband resonance spectrum. An ITO thin film was coated on the back of the PET substrate with a distorted metamaterials sample, and the terahertz spectrum was measured. The experimental results revealed that the ITO thin film can flatten the spectrum of the SRR sample. To determine the underlying reason, we varied the sheet resistance of the ITO film and observed the differences among the corresponding spectra. The flattened spectrum of the ITO films enhanced the thin-film interference effect of the PET substrate; consequently, the distorted metamaterials exhibited a flattened spectrum. These distorted metamaterials can be applied in terahertz imaging, terahertz communication systems, and optoelectronic integrated circuits.
Electrical tuning of photonic bandgap (PBG) of cholesteric liquid crystal (CLC) without deformation within the entire visible region at low voltages is not easy to achieve. This study demonstrates low-voltage-tunable PBG in full visible region with less deformation of the PBG based on smart materials of ferroelectric liquid crystal doped CLC (FLC-CLC) integrating with electrothermal film heaters. Experimental results show that the reflective color of the FLC-CLC can be low-voltage-tuned through entire visible region. The induced temperature change is induced by electrically heating the electrothermal film heaters at low voltages at near the smectic-CLC transition temperature. Coaxial electrospinning can be used to develop smart fibrous devices with FLC/CLC-core and polymer-shell which color is tunable in full visible region at low voltages.
The scientists in the field of liquid crystal (LC) have paid significant attention in the exploration of novel cholesteric LC (CLC) polymer template (simply called template) in recent years. The self-assembling nanostructural template with chirality can effectively overcome the limitation in the optical features of traditional CLCs, such as enhancement of reflectivity over 50%, multiple photonic bandgaps (PBGs), and changeable optical characteristics by flexibly replacing the refilling LC materials, and so on. This work fabricates two gradient-pitched CLC templates with two opposite handednesses, which are then merged as a spatially tunable and highly reflective CLC template sample. This sample can simultaneously reflect right- and left-circularly polarized lights and the tunable spectral range includes the entire visible region. By increasing the temperature of the template sample exceeding the clearing point of the refilling LC, the light scattering significantly decreases and the reflectance effectively increase to exceed 50% in the entire visible region. This device has a maximum reflectance over 85% and a wide-band spatial tunability in PBG between 400 nm and 800 nm which covers the entire visible region. Not only the sample can be employed as a wide-band spatially tunable filter, but also the system doping with two suitable laser dyes which emitted fluorescence can cover entire visible region can develop a low-threshold, mirror-less laser with a spatial tunability at spectral regions including blue to red region (from 484 nm to 634 nm) and simultaneous lasing emission of left- and right-circular polarizations.
This study elucidates electrically and all-optically controllable random lasers in dye-doped liquid crystals with adding a
photoisomerizable dye. The lasing intensities and the energy thresholds of the random lasers can be electrically
controlled below the Fréedericksz transition threshold or all-optically controlled sequentially with a two-step exposure of
UV and green beams. The below-threshold-electric- and all-optical controllabilities of the random lasers are attributable
to the effective change of the spatial fluctuation of the orientational order and thus of the dielectric tensor of LCs by
changing the electric-field-aligned order of LCs below the threshold and via the isothermal nematic-isotropic phase
transition of LCs, respectively; thereby changing the diffusion constant and thus the scattering strength of the
fluorescence photons in their recurrent multiple scattering. This can result in the change in the lasing intensity and thus
the energy threshold of the random lasers.
This investigation reports for the first time a novel phenomenon, called band-tunable color cone lasing emission (CCLE),
based on a single-pitched one-dimensional photonic crystal-like dye-doped cholesteric liquid crystal (DDCLC) cell. The
lasing wavelength in the CCLE pattern is distributed continuously at 676.7-595.6 nm as the oblique angle increases
continuously from 0° to 50° relative to the helical axis. The variation of the lasing wavelength in the CCLE with the
oblique angle is consistent with that of the wavelength at the long-wavelength edge (LWE) of the CLC reflection band
(CLCRB) with the oblique angle. Simulation results obtained utilizing Berreman's 4×4 matrix method show that, at each
oblique angle, the associated group velocity and density of photonic state (DOS) are near zero and large at the shortwavelength
edge (SWE) and LWE of the CLCRB, respectively, and are in good agreement with experimental results.
The particularly strong lasing ring emission at a cone angle of ~35° can be explained to be likely due to a special effect
that, under the condition of overlap between the LWE of the CLCRB measured at 35° and the SWE of the CLCRB
measured at 0°, the LWE and SWE fluorescence propagating along 35° and 0°, respectively, may indirectly enhance
each other due to individual enhanced rate of spontaneous emission. Furthermore, the lasing band of the CCLE can be
tuned from long-wavelength (deep red~orange) to short-wavelength (orange~green) regions by changing the
concentration of the chiral or by the photo-irradiation on a DDCLC cell with a photoisoemerizable chiral dopant.
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