Chiral Photonic Bandgap Research Articles

Thermoregulated CPL‐Active Flexible Polymer/Perovskite Hybrid Materials with High Luminescence Dissymmetry Factor

AbstractCPL‐active flexible materials with high luminescence dissymmetry factor (glum) and luminescent quantum yield are indispensable for 3D displays, wearable devices and so on. Perovskite has drawn much attention due to its fascinating photoelectric properties as well as its abundant applications. However, the existing strategies are inefficient in acquiring perovskite NCs with high glum. In this work, thermoregulated CPL‐active flexible polymer/perovskite hybrid materials with high glum by the creation of chiral photonic bandgap in polymer film with cholesteric domains using toluene as the dielectric media is reported. Based on selective CPL reflection, a satisfied CPL with a maximum glum of 0.6 is achieved. Importantly, the chiral photonic bandgap center of the polymer film can be easily tuned by thermal annealing at different temperatures to adapt various perovskite NCs with full‐spectral emission. The handedness of CPL of hybrid materials can be regulated with and without dielectric media. The presence of the flexible polymer makes hybrid materials a candidate to achieve patterned display applications. Additionally, the polymer/perovskite hybrid materials show excellent stability thanks to the encapsulation effect from polymers. This work provides a facile and general approach to induce adjustable CPL in the whole visible spectrum with high glum and photoluminescence quantum yield (PLQY).

Dynamically Selective and Simultaneous Detection of Spin and Orbital Angular Momenta of Light with Thermoresponsive Self-Assembled Chiral Superstructures

Featuring a self-assembled helical nanostructure and external stimuli-responsive chiral photonic band gap, cholesteric liquid crystals (CLCs) create more opportunities in harnessing multiple degrees of freedom of light, especially the spin and orbital angular momenta (SAM/OAM). Here, we propose and demonstrate an innovative method for a dynamically selective and simultaneous detection of SAM and OAM of light via two cascaded CLC superstructures with thermal controllability and opposite chirality. By independently regulating their temperatures, on-demand selective detection for the intended wavelength and spin eigenstate is achieved with high efficiency and broadband tunability. The information of the desired angular momenta is vividly identified by the reflected diffraction patterns from cascaded chiral superstructures, while the nondetected components are preserved in the transmitted light. This indicates an in situ and nondestructive manner and may facilitate advanced optical manipulation, imaging, and information (de)multiplexing. This work brings important insights into the design, construction, and application of self-assembled chiral nanostructures, promoting multiple and active functionalities in diverse intelligent devices.

Photonic Signatures of Spin-Driven Ferroelectricity in Multiferroic Dielectric Oxides.

We study the dispersion and scattering properties of electromagnetic modes coupled to a helically ordered spin lattice hosted by a dielectric oxide with a ferroelectric polarization driven by vector spin chirality. Quasianalytical approaches and full-fledged numerics evidence the formation of a chiral magnonic photonic band gap and the presence of gate-voltage dependent circular dichroism in the scattering of electromagnetic waves from the lattice. Gating couples to the emergent ferroelectric polarization and hence, to the underlying vector-spin chirality. The theory relies on solving simultaneously Maxwell's equations coupled to the driven localized spins taking into account their spatial topology and spatial anisotropic interactions. The developed approach is applicable to various settings involving noncollinear spins and multiferroic systems with potential applications in noncollinear magnetophotonics.

Liquid crystal nose based on chiral photonic bandgap materials: principles of selective response

Novel liquid crystalline (LC) compositions are suggested and studied as elements of LC-nose. This allows for optical detection of several volatile organic compounds (VOCs). Ethanol, toluene, pyridine and acetic acid were detected by means of colorimetric and spectroscopic techniques during their diffusion inside chiral elements of LC-nose. Selectivity to different VOCs is enhanced by means of components of liquid crystal matrix with different viscosity, affinities to the solvents, and abilities to form hydrogen bonding.

Nanocrystal fluorescence in photonic bandgap microcavities and plasmonic nanoantennas

Results are presented here towards robust room-temperature single-photon sources based on fluorescence in nanocrystals: colloidal quantum dots, color-center diamonds and doped with trivalent rare-earth ions (TR3+). We used cholesteric chiral photonic bandgap and Bragg-reflector microcavities for single emitter fluorescence enhancement. We also developed plasmonic bowtie nanoantennas and 2D-Si-photonic bandgap microcavities.

Resonance in quantum dot fluorescence in a photonic bandgap liquid crystal host

Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a one-dimensional (1D) chiral photonic bandgap cholesteric-liquid crystal host under cw excitation. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stop band, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular-polarization dissymmetry factor g(e) of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric-laser research, in which so far only dyes were used, as well as for room-temperature single-photon source applications.

Bistability, multistability, and nonreciprocity in a chiral photonic bandgap structure with nonlinear defect

The effects of the bistability, multistability, and nonreciprocity in a finite photonic bandgap structure of chiral and achiral layers with an asymmetrically placed nonlinear defect are investigated. The effect of the chirality parameter and angle of incidence on the wave multistable transmission and reflection is studied.

Polarization properties of symmetrical and asymmetrical nonreciprocal chiral photonic bandgap structure with defect

The polarization properties of perfectly periodical and defective one-dimensional photonic bandgap structures with nonreciprocal chiral (bi-isotropic) layers are studied. The method of solution is based on the 2×2 block-representation transfer-matrix formulation. Numerical simulations are carried out for different types of structures (symmetrical or asymmetrical) in order to reveal the dependence of the reflection and transmission coefficients on frequency, chirality, nonreciprocity parameters, and angle of wave incidence.

Organic photonic bandgap microcavities doped with semiconductor nanocrystals for room-temperature on-demand single-photon sources

We report the first experimental observation of fluorescence from single semiconductor nanocrystals (colloidal quantum dots) in microcavities. In these room-temperature experiments we observed photon antibunching from single CdSe nanocrystals doped into a chiral one-dimensional photonic bandgap liquid-crystal microcavity. The chirality resulted in high-purity, circular polarization of definite handedness of the emitted single photons. We also report the fabrication of chiral microcavities for telecom wavelengths doped with PbSe nanocrystals as well as a solution-processed-polymer microcavity with a defect layer doped with CdSe nanocrystals between two distributed Bragg reflectors. These systems with their low host fluorescence background are attractive for on-demand single-photon sources for quantum information and communication.

Polarization-dependent optical switch and its application for integrated optical circuit devices

An optical switching mechanism that uses chiral photonic band-gap structures is proposed. The switching is carried out by shifting the band-gap of the configuration. The component employs selective reflection in cholesteric layers and phase-shifting variance in retardation plates. The prototype has been designed and its parameters have been investigated. The spectral response of the component is calculated with respect to the input of orthogonal linear polarizations which are shown to be either efficiently transported to the forward and the backward directions within different photonic band-gaps. Two designs for stop-band tuning can be considered in the modulation functionalities, and thus a tunable dual-state polarization switching for mutually orthogonal polarized lights could be realized. Related applications of this component as a variable in-line polarization router and combiner for optical communication systems are emphasized.

Control of photonic bandgaps in chiral liquid crystals for distributed feedback effect

This paper describes two strategies to control the photonic bandgap (PBG) in chiral liquid crystals (CLCs) to generate laser action through the distributed feedback effect. First, we demonstrated the electrical control of supramolecular helical structure and lasing action from the CLCs, which were comprised of an optically active agent and an achiral nematic liquid crystal, doped with a small amount of a fluorescent dye. When the dye-doped CLC cell was optically pumped with linearly polarized laser beam, the laser action took place at the edge(s) of the CLC reflection bands. The threshold pumping energy to induce laser action was dependent on the PBG position of LC hosts. Subsequently, applying voltages to the optically pumped CLC cells over 20 V brought about immediate disappearance of the laser emission due to the supramolecular structural changes of CLCs from planar to focal conic texture. The laser emission could be observed again by reconstruction of the initial planar structure as high voltages over 75 V were switched off. Secondly, the photoinduced tunability of PBG band in CLC and laser oscillation wavelength was explored by using a photoreactive mixture of cholesteryl derivatives. Photoirradiation of the dye-doped CLC cell with 254 nm light brought about continuous changes in the chiral PBG as a result of the predominant photolysis of cholesteryl iodide in the CLC host, leading to the phototunable laser oscillation in a wavelength ranging from 560 to 620 nm. The present report opens promising ways to design novel active mirrorless laser devices by electro- and photo-modulation of the self-organized chiral PBG structures.

Broad Stopband Characteristic of Dielectric Chiral Photonic Crystals

In this paper, a novel chiral photonic crystal structure is presented. The formula of reflection coefficient of multi-layer chiral media is applied to dielectric-chiral photonic crystal structure, which is composed of thin chiral layers sandwiched by conventional media. To compare with previous literature, we consider the dielectric structure with alternate glass and GaAs layers. The power reflectance as a function of wavelength for this photonic crystal structure has been calculated. The results are in good agreement with that of Reference. However, our method is simpler. From these graphs, it is found that 100% reflectance is only in finite wavelength ranges, and reflection bandwidth is also small for conventional photonic crystal structure. For chiral photonic crystal, the results show that the chiral photonic band gap (PBG) structure gives nearly 100% reflections in the near-infrared region in addition to some parts of the visible region of the wavelengths. Therefore, it can be used as a broadband reflector and filter.

One-dimensional chiral photonic band gap structure analyzed by non-symmetric transmission-line method

In this paper, the formula of reflection coefficient of multi-layer chiral media is derived by non-symmetric transmission-line method. Then, it is applied to one-dimensional (1-D) chiral photonic crystal structure, which is composed of thin chiral layers sandwiched by air. The results show that it is difficult to obtain photonic band gap for general dielectric when the contrast of two media refractive indices is not large, and the reflection coefficient is small. However, for chiral photonic crystal, although the refractive index of chiral layer is small, the wave spectrum contains forbidden zones and the reflection coefficient from such a structure is found to be almost equal to 1, i.e., the wave is almost totally reflected through adjusting chiral parameter. Therefore it is easier to obtain an ideal photonic band gap.

Phototunable photonic bandgap in a chiral liquid crystal laser device

This letter describes the phototunable photonic bandgap of cholesteric liquid crystal (CLC) doped with a fluorescent dye to generate the distributed feedback effect. Photoirradiation of the dye-doped CLC cell under UV light at 254 nm resulted in continuous changes in the chiral photonic bandgap from 550 to 720 nm due to photolysis reaction of the cholesteryl iodide embedded in the CLC host. We showed that the laser oscillation wavelength could be controlled in a wide wavelength range from 610 to 700 nm by photoassisted adjustment of CLC photonic bandgaps.

Lasing from chiral photonic band gap materials based on cholesteric glasses

Glass-forming cholesteric liquid crystals were studied as promising dye-doped lasing materials at different pumping energies and temperatures. Cholesteric samples doped with laser dye pyrromethane 597 were pumped by Nd:YAG laser. Lasing was found to depend strongly on the vitrification rate of cholesteric samples, their temperature and multidomain structure. The lasing threshold and intensity as a function of thickness of cholesteric resonator are determined by two competing factors: narrowing of the band edge modes and increasing disorder.

Electrical control of the structure and lasing in chiral photonic band-gap liquid crystals

This letter describes the electrical control of structure and lasing in the photonic bandgaps of cholesteric liquid crystals (CLCs). Photoexcitation of dye-doped CLC cells with a linearly polarized laser gives rise to laser emission at the edge(s) of the chiral photonic band gap. Applying voltages to the optically pumped CLC cells enables reversible switching of the laser action as a result of the structural changes in the chiral photonic band gap.

All-optical switching with a nonlinear chiral photonic bandgap structure

A pump–probe optical switching mechanism that uses a nonlinear chiral photonic bandgap structure is proposed. The switching is achieved by shifting the bandgap of the structure; the chirality permits the use of the same frequency for the pump and the probe beam. The pump beam is never transmitted, so there is no discrimination problem. A new extension of the finite-difference time-domain technique is developed to simulate the propagation of an electromagnetic wave in a Kerr nonlinear chiral medium.