Uniform Birefringence Research Articles

Large birefringence in the quasi-one-dimensional material Sb2Se3: A DFT investigation of electronic and optical anisotropy

Investigation of the optical and electronic properties of the quasi-one-dimensional semiconductor Sb2Se3 is performed with density functional theory, which takes into consideration the spin–orbit coupling and the on-site Coulomb self-interaction. Sb2Se3 has an orthorhombic crystal structure and belongs to the Pnma space group. The pronounced dispersion along the R−U, Z−Γ, Γ−Y, and S−X high-symmetry directions and low dispersion along the U−Z and Y−S directions confirm the layered structure, with strong bonding interactions along the [001] direction, as well as along the [010] direction, along which the SbSe6 and SbSe7 chains are aligned, and weak van der Waals interactions along the [100] direction. The material is a semiconductor with an indirect bandgap of 1.2 eV. Sb2Se3 exhibits appreciable carrier mobility and low carrier recombination rates in the plane of the layers, indicating its applicability in solar and photovoltaic devices. Simulated X-ray photoelectron spectra show that the photoelectron emission occurs from the Se p, Sb s, and Se s atomic orbitals, while for high-energy X-rays, photoelectron emission is mainly from Sb s orbital. Sb2Se3 possesses appreciable anisotropy in its refractive index, absorption coefficient, reflectivity, extinction coefficient, and optical conductivity. Sb2Se3 is a negative biaxial crystal, in which the principal optical axis X→a, Y→b, and Z→c. It possesses uniform birefringence in the IR region until the optical cutoff edge at 1030 nm. The material shows strong unidirectional linear dichroism in the wavelength range from 300 nm to 620 nm, with linear dichroism conversion at 275 nm. The energy loss is isotropic for slow electrons below 4.0 eV, but for highly energetic electrons it varies along different crystal directions. Sb2Se3 is a promising material for optoelectronic and polarimetric applications because of its desirable bandgap of 1.2 eV, linear dichroism conversion, and large optical anisotropy, refractive index, dielectric constant, and absorption coefficient.

Highly birefringent microstructured optical fiber for distributed hydrostatic pressure sensing with sub-bar resolution.

We demonstrate distributed optical fiber-based pressure measurements with sub-bar pressure resolution and 1 m spatial resolution over a ∼100 m distance using a phase-sensitive optical time-domain reflectometry technique. To do so, we have designed a novel highly birefringent microstructured optical fiber that features a high pressure to temperature sensitivity ratio, a high birefringence and a mode field diameter that is comparable to that of conventional step-index single mode fibers. Our experiments with two fibers fabricated according to the design confirm the high polarimetric pressure sensitivities (-62.4 rad×MPa-1×m-1 and -40.1 rad×MPa-1×m-1) and simultaneously low polarimetric temperature sensitivities (0.09 rad×K-1×m-1 and 0.2 rad×K-1×m-1), at a wavelength of 1550 nm. The fiber features a sufficiently uniform birefringence over its entire length (2.17×10-4 ± 7.65×10-6) and low propagation loss (∼3 dB/km), which allows envisaging pressure measurements along distances up to several kilometers.

Diamond-rich crystalline nanosheets seeded with a Langmuir monolayer of arachidic acid on water.

The enigmatic self-assembling ability of nanodiamond (ND) particles has been discovered herein. Diamond-rich crystalline nanosheets with thickness of approximately ∼25 nm were grown from a Langmuir monolayer of arachidic acid (AA) at the interface between air and a dilute aqueous ND solution. Their fine rectangular shapes with uniform uniaxial birefringence indicate appreciable crystallinity, thus supporting that they are hydrated colloidal crystals of homogeneous ND particles.

Folding-induced in-plane birefringence in homeotropically aligned graphene-oxide liquid crystal films formed by solution shear

ABSTRACT Graphene-oxide (GO) has been widely explored as a functional two-dimensional (2D) material. The GO-flakes self-assemble into colossal sheets of 2D aggregates with extreme flexibility and the GO-dispersion in water forms an alternately layered phase with nematic order. Highly ordered supramolecular anisotropic GO films can be fabricated by a hydraulic shear. For a uniform in-plane shear, it is generally known that GO aligns tangential to the shear plane, resulting in homeotropic orientation of the optic axis with no in-plane birefringence. However, it surprisingly results in uniform in-plane birefringence with the optic axis (Δn < 0) aligned perpendicular to the shear direction. The in-plane birefringence originates from the folding deformation of homeotropically aligned GO layers, rather than reorientation of pristine GO flakes. 2D GO aggregates are very large and flexible so that prone to be deformed by external force, rather than reorientation. For the alternately layered GO-LC phase, drying is a directional process so that major compression occurs predominantly along the layer-normal. As a result, both folding width and film thickness are reduced considerably and the folded band protrudes during a drying process. This folding-induced in-plane birefringence of GO-LCs provides useful insights for processing anisotropic 2D materials, beneficial for various electrical, optical, and mechanical applications.

Modeling birefringence in SiO2 glass fiber using surface stress relaxation

AbstractThe retardance of silica glass fibers was evaluated using photoelastic techniques. Here, surface birefringence in glass fibers is shown to be a consequence of surface stress relaxation for as‐received fibers drawn from Suprasil II. The surface features of the birefringent fibers were compared to a model of the residual axial stress profile resulting from a diffusion‐controlled surface stress relaxation. Additionally, a uniform birefringence in the fiber equivalent to a constant tensile stress was recognized and attributed to structural anisotropy produced during fiber drawing. The contribution of structural anisotropy to the observed birefringence remained constant as the surface features were successively etched away. Surface compressive stress generation was also observed, as retardance corresponding to a surface compressive stress was found to increase with applied tensile stress during short heat treatments. Significant features of the retardance profile in as‐received silica glass fibers, with a thin surface compressive stress layer and compensating interior tensile stress, agreed with the residual stress profiles predicted by the surface stress relaxation model after correcting for this observed structural anisotropy.

Robust Chiral Organization of Cellulose Nanocrystals in Capillary Confinement.

We showed large area uniformly aligned chiral photonic bioderived films from a liquid crystal phase formed by a cellulose nanocrystal (CNC) suspension placed in a thin capillary. As a result of the spatial confinement of the drying process, the interface between coexisting isotropic and chiral phases aligns perpendicular to the long axis of the capillary. This orientation facilitates a fast homogeneous growth of chiral pseudolayers parallel to the interface. Overall, the formation of organized solids takes hours vs weeks in contrast to the slow and heterogeneous process of drying from the traditional dish-cast approach. The saturation of water vapor in one end of the capillary causes anisotropic drying and promotes unidirectional propagation of the anisotropic phase in large regions that results in chiral CNC solid films with a uniformly oriented layered morphology. Corresponding ordering processes were monitored in situ at a nanoscale, mesoscale, and microscopic scale with complementary scattering and microscopic techniques. The resulting films show high orientation order at a multilength scale over large regions and preserved chiral handedness causing a narrower optical reflectance band and uniform birefringence over macroscopic regions in contrast to traditional dish-cast CNC films and those assembled in a magnetic field and on porous substrates. These thin films with a controllable and well-identified uniform morphology, structural colors, and handedness open up interesting possibilities for broad applications in bioderived photonic nanomaterials.

Terahertz birefringence and absorption of a chalcopyrite CdSiP2 crystal

The terahertz (THz) birefringence and absorption of a chalcopyrite CdSiP2 (CSP) crystal are studied at frequencies between 0.5 and 2.9 THz. Time-domain spectroscopy measurements are used to record the phonon-polariton dispersion and reststrahlen band absorption (centered at 2.03 THz) of CSP's lowest-frequency E mode. The ordinary and extraordinary refractive indices of this material, along with the extinction coefficients, are determined over the investigated frequency range. The uniform CSP birefringence (∼0.08) and the low extinction coefficient values (≤0.008) at frequencies between 0.5 and 1.9 THz suggest the potential for waveplate applications.

Dispersion compensating photonic crystal fiber using double-hole assisted core for high and uniform birefringence

A novel photonic crystal fiber design is presented. The design provides broadband high and uniform birefringence, large negative dispersion and low confinement loss. The fiber is based on double-hole assisted core in the conventional square lattice cladding. For the proposed PCF, high and uniform birefringence of 7.5×10−3, the negative dispersion of −150ps/(nmkm) and an extremely low confinement loss can be obtained over E+ S+C+L+U (1380∼1780nm) wavelength bands.

All-optical flip-flops based on dynamic Brillouin gratings in fibers.

A method to generate an all-optical flip-flop is proposed and experimentally demonstrated based on dynamic Brillouin gratings (DBGs) in polarization maintaining fibers. In a fiber with sufficiently uniform birefringence, this flip-flop can provide extremely long storage times and ultra-wide bandwidth. The experimental results demonstrate an all-optical flip-flop operation using phase-modulated pulses of 300ps and a 1m long DBG. This has led to a time-bandwidth product of ∼30, being in this proof-of-concept setup mainly limited by the relatively low bandwidth of the used pulses and the short fiber length.

Constraints on parity violation from ACTpol and forecasts for forthcoming CMB experiments

We use the ACTpol published cosmic microwave background (CMB) polarization data to constrain cosmological birefringence, a tracer of parity violation beyond the standard model of particle physics. To this purpose, we employ all the polarized ACTpol spectra, including the cross-correlations between temperature anisotropy and B mode polarization (TB) and between E mode and B mode (EB), which are most sensitive to the effect. We build specific, so-called D-estimators for birefringence and assess their performances and error budgets by using realistic Monte Carlo simulations based on the experimental characteristics provided by the ACTpol collaboration. We determine the optimal multipole range for our analysis to be 250<ℓ<3025 over which we find a null result for the uniform birefringence angle α=0.29°±0.28° (stat.) ±0.5° (syst.), the latter uncertainty being the estimate published by the ACTpol team on their global systematic error budget. We show that this result holds consistently when other multipole ranges are considered. Finally, we forecast the capability of several forthcoming ground based, balloon and space borne CMB experiments to constrain the birefringence angle, showing, e.g., that the proposed post-Planck COrE satellite mission could in principle constrain α at a level of 10 arcsec, provided that all systematics are under control. Under the same circumstances, we find the COrE constraints to be at least 2 or 3 times better than what could ideally be achieved by the other experiments considered.

다수 개 빼기 성형에서 일반사출성형과 사출압축성형의 성형특성 비교

일반사출성형은 공정 중 보압단계에서 캐비티에 높은 압력이 작용하여 성형품에 큰 잔류응력이 남게 된다. 또한 캐비티 내 위치 별로 압력분포가 달라 균일한 물성의 제품을 얻는데 한계가 있다. 다수 개 빼기 일반사출성형에서는 캐비티간 충전 불균형이 일어나 캐비티간 품질의 편차를 일으킨다. 이와 같은 한계를 극복하기 위해 사출압축성형 공정을 사용하는 경우가 많다. 본 연구에서는 다수 개 캐비티를 갖는 금형을 이용하여 일반사출성형과 사출압축성형을 비교 분석하였다. 실험과 해석을 통하여 연구를 수행하였으며 투명한 수지인 PC와 PS를 이용하여 시편에 나타나는 복굴절을 관찰하여 일반사출성형과 사출압축성형에서 나타나는 성형특성을 비교하였다. 연구결과, 사출 압축성형으로 제작된 시편에서 캐비티 내의 압력이 균일하여 복굴절과 성형수축률이 낮고 균일하게 나타났다. 그리고 일반사출성형에서 나타나는 캐비티간 충전 불균형에 의한 캐비티간 물성의 편차가 사출압축성형에서는 크게 줄어들었다. 본 연구를 통하여 사출압축성형은 다수 개 빼기 사출성형에서 캐비티 내 균일한 물성확보뿐만 아니라 캐비티간 품질 불균형을 해소하는데 유용함을 확인할 수 있었다. Large residual stresses are remained in the conventional injection molded products because of the high cavity pressure in packing phase during injection molding process. Conventional injection molding (CIM) invokes distribution of cavity pressure and it has a limitation to obtain product with uniform physical property. Multi-cavity conventional injection molding contains quality deviation among the cavities since flow imbalance occurs during filling phase. Injection compression molding (ICM) is adopted to overcome these limitations of CIM. In this study, molding characteristics of CIM and ICM have been investigated using multi-cavity injection mold. Researches were performed by both experiment and computer simulation through observations of birefringence for transparent resins, polycarbonate and polystyrene in CIM and ICM. As a result, low and uniform birefringence and mold shrinkage were showed in the specimens by ICM that could give a uniform cavity pressure. Deviation of physical property among the specimens in multi-cavity mold shown in CIM was significantly reduced in the specimens by ICM. Through this study it was concluded that the ICM in multi-cavity molding was valid for molding products with uniform property in an individual cavity and also reduced property deviation among the cavities.

An experimental study on the effects of injection-molding types for the birefringence distribution in polycarbonate discs

Even though injection molding technology has been developed for many years, it is still needed to study the effect of processing conditions on the final properties of injection-molded parts for producing precision products in optical field. The optical anisotropy, i.e., birefringence, is a significant factor which affects the function of many optical components. In the present study, we have focused on the effects of packing and compression processes on the birefringence structure remaining in the disc by examining the gap-wise distribution of birefringence and extinction angle. As a result, two extra birefringence and extinction peaks near the center in thickness direction showed the effect of packing pressure, which came from the extra flow during packing stage. Furthermore, more uniform birefringence distribution was found in injection/compression case than in conventional injection-molded case. Depending on the process condition, even the reversal flow was found from the distribution of extinction angle in injection/compression case. Finally, graphical representation technique of optical refractive indicatrix was suggested to show the difference of final birefringence structure for different process types.

Evaluation of zona pellucida birefringence intensity during in vitro maturation of oocytes from stimulated cycles

BackgroundThis study evaluated whether there is a relationship between the zona pellucida birefringence (ZP-BF) intensity and the nuclear (NM) and cytoplasmic (CM) in vitro maturation of human oocytes from stimulated cycles.ResultsThe ZP-BF was evaluated under an inverted microscope with a polarizing optical system and was scored as high/positive (when the ZP image presented a uniform and intense birefringence) or low/negative (when the image presented moderate and heterogeneous birefringence). CM was analyzed by evaluating the distribution of cortical granules (CGs) throughout the ooplasm by immunofluorescence staining. CM was classified as: complete, when CG was localized in the periphery; incomplete, when oocytes presented a cluster of CGs in the center; or in transition, when oocytes had both in clusters throughout cytoplasm and distributed in a layer in the cytoplasm periphery Nuclear maturation: From a total of 83 germinal vesicle (GV) stage oocytes, 58 of oocytes (69.9%) reached NM at the metaphase II stage. From these 58 oocytes matured in vitro, the high/positively scoring ZP-BF was presented in 82.7% of oocytes at the GV stage, in 75.8% of oocytes when at the metaphase I, and in 82.7% when oocytes reached MII. No relationship was observed between NM and ZP-BF positive/negative scores (P = 0.55). These variables had a low Pearson's correlation coefficient (r = 0.081). Cytoplasmic maturation: A total of 85 in vitro-matured MII oocytes were fixed for CM evaluation. Forty-nine oocytes of them (57.6%) showed the complete CM, 30 (61.2%) presented a high/positively scoring ZP-BF and 19 (38.8%) had a low/negatively scoring ZP-BF. From 36 oocytes (42.3%) with incomplete CM, 18 (50%) presented a high/positively scoring ZPBF and 18 (50%) had a low/negatively scoring ZP-BF. No relationship was observed between CM and ZP-BF positive/negative scores (P = 0.42). These variables had a low Pearson's correlation coefficient (r = 0.11).ConclusionsThe current study demonstrated an absence of relationship between ZP-BF high/positive or low/negative score and nuclear and cytoplasmic in vitro maturation of oocytes from stimulation cycles.

사출 및 사출/압축 성형품 내에서의 복굴절 구조 변화에 관한 연구

It is still needed to study the effect of process conditions on the final properties of injection-molded parts for producing precision optical products. Especially, the optical anisotropy, i.e., birefringence, is a significant factor to affect the function of many optical components. In the present study we have focused on the effect of holding and compression processes on the birefringence remaining in the transparent disc by examining the gap-wise distribution of birefringence and extinction angle. As a result, two extra birefringence and extinction peaks near the center in thickness direction showed the effect of holding pressure, which came from the flow in packing stage. However, more uniform birefringence distribution than injection-only cases could be found in injection/compression cases. Depends on the process condition even the flow reversal could be found from the distribution of extinction angle. Finally, graphical representation of optical indicatrix was added for better understanding the final structure of injection-only and injection/compression cases.

OPTICAL PROPERTIES OF PHOTONIC CRYSTAL FIBERS WITH A FIBER CORE OF ARRAYS OF SUBWAVELENGTH CIRCULAR AIR HOLES: BIREFRINGENCE AND DISPERSION

We propose a kind of novel photonic crystal flbers (PCFs) based on a flber core with arrays of subwavelength circular air holes, achieving the ∞exible control of the birefringence or the dispersion property of the PCFs. A highly birefringent (HB) PCF is achieved by employing arrays of subwavelength circular air hole pairs in the flber core, which are arranged as a conventional hexagonal lattice structure with a subwavelength lattice constant. The HB-PCF is with uniform and ultrahigh birefringence (up to the order of 0.01) in a wavelength region from 1.25m to 1.75m or even a larger region, which, to the best of our knowledge, is the best birefringence property of the PCFs. A dispersion-∞attened (DF) PCF with near-zero dispersion is achieved by employing arrays of subwavelength circular air holes in the flber core arranged as a conventional hexagonal lattice structure with a subwavelength lattice constant, which contributes negative waveguide dispersion to the PCF. The proposed design of the DF-PCF provides an alternate approach for the dispersion control of the PCF. Besides the high birefringence and the ∞attened near-zero dispersion, the proposed PCFs with a flber core of arrays of subwavelength circular air holes have the potential to achieve a large mode area single mode PCF.

Role of Surfactant in the Stability of Liquid Crystal-Based Nanocolloids

We examine the dependence of liquid crystalline nanocolloid formation and stability on surfactant. Nanocolloids composed of polymerizable liquid crystal mesogens and cross-linking agents and capped with either ionic or nonionic surfactants are prepared via the miniemulsion technique. Colloids synthesized with anionic surfactant were stable and displayed 2D hexagonal packing when deposited via slow vertical pulling of the silicon substrate from an aqueous suspension. Liquid crystal nanocolloids stabilized with the nonionic, polar polymer polyvinyl alcohol (PVA) were stable in aqueous environments but coalesced upon drying to form relatively large, well-defined crystal-like structures with uniform birefringence. SEM images reveal that the coalesced structures have mesalike features. Polarized light, atomic force, and polarized Raman microscopy of these structures indicate that the liquid crystal molecules are arranged with their long molecular axis slightly tilted with respect to the surface normal. A mechanism is proposed to explain the formation of the mesalike structures from the nanocolloids. These studies provide fundamental insight into the incorporation and stabilization of polymerizable liquid crystal molecules into nanovolumes and open up opportunities for the incorporation of functionality and anisotropy into isotropically shaped nanocolloids.

Effects of osmotic force and torque on microtubule bundling and pattern formation

We report effects of polyethylene glycol (PEG, molecular weight of 35 kDa ) on microtubule (MT) bundling and pattern formation. Without PEG, polymerizing tubulin solutions of a few mg/ml that are initially subjected to a field that aligns MTs can spontaneously form striated birefringence patterns. These patterns form through MT alignment, bundling, and coordinated bundle buckling. With increasing PEG concentrations, solutions form progressively weaker patterns. At a sufficiently high PEG concentration ( approximately 0.5% by weight), the samples maintain a nearly uniform birefringence (i.e., no pattern) and laterally contract at a later stage. Concomitantly, on a microscopic level, the network of dispersed MTs that accompany the bundles in pure solutions disappear and the bundles become more distinct. We attribute the weakening of the pattern to the loss of the dispersed MT network, which is required to mediate the coordination of bundle buckling. We propose that the loss of the dispersed network and the enhanced bundling result from PEG associated osmotic forces that drive MTs together and osmotic torques that facilitate their bundling. Similarly, we attribute the lateral contraction of the samples to osmotic torques that tend to align crossing bundles in the network.

Evolution of the polarization state in material media with uniform linear birefringence and an applied nonhomogeneous external magnetic field: application to bulk-type Faraday current sensors

In this work we find the exact solution for the evolution of the polarization state of a light wave that propagates in a material medium with uniform linear birefringence and a nonuniform external magnetic field. The obtained results could be used to improve the precision of existing Faraday current sensors.

Finite Element Analysis of Photonic Crystal Rods With Inhomogeneous Anisotropic Refractive Index Tensor

A procedure for incorporating inhomogeneous anisotropic variations in the refractive index tensor into two-dimensional finite element calculations of the guided mode characteristics of photonic crystal rods is presented. The stress tensor distribution is assumed to be known. Photonic crystal rod designs incorporating stress applying parts are analyzed using this procedure. The predicted guided mode structure is compared to the simplified case described by uniform birefringence revealing differences in the effective indexes of the guided modes, the effective area and eccentricity of the fundamental mode, the modal birefringence, and the overlap with the gain region of active devices. The method is applicable to all dielectric waveguide structures.

Achievement of broadband uniform modal birefrigence in an index-guiding holey fibre using a novel circular hollow ring defect structure

A novel silica index-guiding holey fibre (IGHF) design is proposed utilizing a new defect structure that is composed of a three-layered defect with a central air hole germanosilicate ring and silica clad, based on a hollow optical fibre (HOF). Effects of these parameters on birefringence were numerically analysed using the plane wave expansion method. The proposed IGHF showed unique modal properties such as uniform birefringence and differential group delay in 1.55 µm optical communication windows that have not been achieved in prior arts.