The blue phase, which emerges between cholesteric and isotropic phases within a three-dimensional periodical superstructure, is of great significance in display and photonic applications. The crystalline orientation plays an important role in the macroscopic performance of the blue phase, where the single crystal shows higher uniformity over the polydomain and monodomain, resulting in higher Bragg reflection intensity, lower hysteresis, and lower driving voltage. However, currently reported methods of forming a single-crystal blue phase based on thermal controlling or e-beam lithography are quite time-consuming or expensive for large-scale fabrication, especially in the centimeter range, thus hindering the broad practical applications of single-crystal blue-phase-based photonic devices. Herein, a strategy to fabricate a large scale single crystalline blue-phase domain using holography lithography is proposed. Defect-free single-crystal domains both in blue phase I and blue phase II with a desired orientation of over 1 cm2 are fabricated based on a nanopatterned grating with periodic homeotropic and degenerate parallel anchoring, with colors from red and green to blue. This holography lithography-assisted strategy for fabrication of a large-scale single-crystal blue phase provides a time-saving and low-cost method for a defect-free single crystalline structure, leading to broad applications in liquid crystal displays, laser devices, adaptive optics elements, and electro-optical devices.
We propose liquid-crystal-based reconfigurable chiral metasurface absorbers and numerically investigate their chiro-optical properties. The chiral metasurface absorber is based on a metal-insulator-metal structure on the substrate, which can strongly absorb a circularly polarized wave of one spin state and reflects that of the opposite spin, resulting a strong circular dichroism. A birefringent liquid crystal (LC) is exploited to serve as the insulator layer in the metal-insulator-metal structure. We could then vary the circular state of the incident light by controlling the alignment of the LC molecules, hence inversing the circular dichroism. The simulation results show that the sign of the circular dichroism can be effectively changed by externally controlling the alignment of the LC molecules in between the homogenous and homeotropic states. The absorption efficiency for the specific circularly polarized wave can be larger than 80% and the CD is nearly 70%. The simple and compact design of our proposed chiral metasurface absorber is especially favorable for integration, and such reconfigurable chiral metasurface absorber could find many potential applications in biological detection/sensing, polarimetric imaging, and optical communications.
Chiral plasmonic nanostructures offer the ability to achieve strong optical circular dichroism (CD) activity over a broad spectral range, which has been challenging for chiral molecules. Chiral plasmonic nanostructures have been extensively studied based on top-down and bottom-up fabrication techniques. Particularly, in the top-down electron-beam lithography, 3D plasmonic nanostructure fabrication involves layer-by-layer patterning and complex alignment, which is time-consuming and causes many defects in the structures. Here, we present a free-standing 3D chiral plamonic nanostructures using the electron-beam lithography technique with much simplified fabrication processes. The 3D chiral plasmonic nanostructures consist of a free-standing ultrathin silicon nitride membrane with well-aligned L-shape metal nanostructures on one side and disk-shape ones on the other side. The free-standing membrane provides an ultra-smooth metal/dielectric interface and uniformly defines the gap between the upper and lower layers in an array of chiral nanostructures. Such free-standing chiral plasmonic nanostructures exhibit strong CD at optical frequencies, which can be engineered by simply changing the disk size on one side of the membrane. Experimental results are in good agreement with the finite-difference time-domain simulations. Such free-standing chiral plasmonics holds great potential for chirality analysis of biomolecules, drugs, and chemicals.
In this paper, we design layered composite meta-structures to investigate its’ effect on the optical activity and circular
dichroism (CD). The layered composite meta-structures consist of thin gammadion nanostructure with thickness λ/10,
where λ is the incident wavelength. The layered meta-structures are alternate between a dielectric and gold (AU)
material. Each layered composite meta-gammadion is arranged together in an array of pitch 700 nm. In the first case, 3
layers of meta-gammadion, with metal-insulator-metal (MIM) and insulator-metal-insulator (IMI) configuration are
simulated with material properties from optical hand book. There are 3 modes in the CD spectrum, which can be
characterized into Bloch CD mode and hybrid CD modes. Compared with the CD spectrum of whole structure of
gammadion in gold with same total height, the CD of the MIM layered composite are larger. When the number layer
increase to 5, it is observed that the CD is reduced by 30% and there is a red shift in the Bloch CD mode and a slight blue
shift in the hybrid CD modes. By further increasing the number of layers to 7, we observed further CD increment and
larger wavelength shift in the CD modes. The layered composite meta-gammadion is fabricated using template stripping
method. Experimental results also show excellent agreement with the simulation results for CD and wavelength shift. We
submerge the layered meta-gammadion into a solution of chiral molecules. The CD spectrum of the meta-gammadion
shows a larger wavelength shift compared to pure metal structures. This indicate a more sensitive and robust detection of
chiral molecules.
In this paper, we rotate an array of asymmetrical double layer of 4-strips windmill structure to investigate its effect on
the chirality and sensitivity detection of biomolecular structures. The structure is made up of silver material with 300nm
pitch and 10nm separation between layers. The spectrum shows two resonance modes on 600THz and 900THz with
linear polarized light normally incident on the structure. We investigate the CD by rotating one of the layers with respect
to the horizontal axis of the other layer by the angle θ. It is observed that the CD spectra at different angles are different.
The rotation resulted in larger wavelength shift of the CD spectra. In addition, the CD also increases with the rotating
angle given a larger absorption difference between the left and right handed circular polarized light.
In this paper, the effect of tapered asymmetrical gammadion on the optical rotational properties and sensitivity detection
of biomolecular structures is presented. The asymmetrical structure is made up of gold material on a glass structure and
immersed in water. The chirality of the un-rotated array is first determined by measuring the circular dichroism (CD)
spectrum. Three modes, arising from Bloch periodic theory and surface resonance mode are observed. Then each
asymmetrical gammadion structure is tapered at the arms. Tapering fraction, which define the ratio of tapered end to the untapered end is used for defining the new design. The designs are then fabricated using e-beam lithography and tested using the polarimeter for CD spectra. The spectra show that the three CD modes changes in degree amplitude and wavelength, especially for smaller tapering fractions.
The concept of fractal, such as Cantor set, has been combined with the Fresnel zone plates (ZPs) to improve its imaging
capability and introduce additional freedom for optimizing. In this letter, Fibonacci zone plates (FiZPs), which is
generated by means of Fibonacci fractals, was proposed. The FiZPs can be constructed by the generating rules of the
Fibonacci sequences similar with the Cantor set zone plate published. Numerical simulation based on Fresnel diffraction
is performed to verify the on-axis intensity distribution of the FiZPs. According to the simulated results, the FiZPs can
focus the incident beam as conventional zone plates as well but with fractal on-axis intensity profile. The theoretical
results are also verified by the experiment by means of phase-only spatial light modulator (pSLM).
Furthermore, the spiral Fibonacci zone plate (sFiZPs) was designed by overlapping the spiral phase on the FiZPs. Both
numerical simulations and experiments are performed and the results are coincident well with each other.
Photopolymerization offers a single-step and rapid formation of different kinds of structures in polymer-dispersed liquid
crystals (PDLCs) for various applications. Here we investigate the fabrication of a computer-generated hologram in PDLCs to generate an electrically switchable optical vortex. First, a computer-generated hologram was numerically designed and then transferred to a transparency as a photomask. The photomask has an effective area of 1 × 1 cm2 with a resolution of 25 μm and a pattern containing almost parallel lines with a fork-like bifurcation at the vortex core. Then the photomask was clipped onto a cell filled with PDLC materials, and subjected to a collimated Ar+ laser (514.5 nm) beam. The intensity impinged on the photomask was about 12 mW/cm2. The optimal exposure time was 2 min in our experiment judged from the fading of the photoinitiator (rose bengal) color. Due to the photopolymerization induced phase separation between polymer and liquid crystal, an index modulation was formed between the polymer-rich and liquid crystal-rich regions. The structures inside the cell were examined under an optical microscope. A good optical vortex beam with high fidelity was reconstructed using a collimated He-Ne laser beam (543 nm). The diffraction efficiency was estimated to be about 13 - 17%. With a suitable voltage applied, the reconstructed optical vortex beam can be switched due to the index change between the polymer and liquid crystal. The experimental results show promising applications of PDLC materials in optical trapping.
Optimize the working model of LCoS (Liquid Crystal on Silicon) in parameter space by simulation. Two models are selected, which is suitable for phase modulating. One is the RTN-52° model, the other is parallel alignment ECB model. Phase changing is measured when various voltage are applied to Lcos. Show some results when the Lcos is used as a Fresnel lens.
Several modes are simulated in parameter space to find profitable mode for amp SLM design and RTN52° with high reflectance, high dDn and low phase shift is used for experiment. The reflectance and contrast are measured on a RTN52° LCOS device.
Holographic polymer dispersed liquid crystal (HPDLC) is a kind of novel photoelectronic information materials. The diffraction efficiency (DE) can be modulated by the application of electric field. HPDLC devices are potentially useful for optical communication, panel dipslay, information storage and integrated optics. The diffraction efficiency plays an important role in application of HPDLC. Based on the phase separation process of HPDLC and the morphology observed by the scanning electronic microscope (SEM), the diffractive character was studied. We investigated the dependence of diffraction efficiency on different monomers, exposure intensity, liquid crystal loading and curing temperature. The best conditions were founded to make the diffraction properites optimized and the highest diffraction efficiency 80.2 percent was gotten.
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