Magnetophotonic crystals: nonreciprocity, birefringence and confinement

Photonic crystals in magnetic materials open up a number of interesting possibilities for the study of nonreciprocal effects in confined geometries, including enhanced Faraday rotation and optical unidirectionality. The development of integrated devices based on nonreciprocal magneto-optic phenomena requires understanding the effects of geometrical confinement on light propagation and magnetization in these systems. This article introduces a model for controlling the band gap by exploiting the birefringence in film-based planar magneto-optic structures. It also presents a study of magnetic remanence control through magnetization confinement in the resonant microcavity of one-dimensional planar magnetophotonic crystals.     

Anisotropy of the nonreciprocal linear birefringence in crystals

Results are presented of an experimental investigation of nonreciprocal linear birefringence (a difference between the phase velocities of counterpropagating waves having the same linear polarization) in lithium iodate and potassium dihydrophosphate crystals in a magnetic field. An original double-pass optical measuring system using two linear quarter-wave phase plates (Fresnel rhombs) is used to demonstrate a new method of studying the effect which can give a fairly high sensitivity and avoid accompanying effects. Pis’ma Zh. Tekh. Fiz. 24, 13–18 (February 26, 1998)     

一种高双折射低限制性损耗光子晶体光纤设计

本文设计了一种适用于长距离光纤通信的新型光子晶体光纤。该光纤包层内椭圆形和圆形空气孔呈交错排列,纤芯两侧为两个小椭圆空气孔。利用有限元分析方法对所设计光纤的传输特性进行分析并对其结构进行了优化,确定了最佳结构。结果表明,波长为1550 nm时,此新型光子晶体光纤在最佳结构下可提供高达3.51×10^-2的高双折射和低至1.5×10^-9 dB/m的限制性损耗。与现存的引入椭圆形空气孔的光子晶体光纤相比,本文中的光子晶体光纤的双折射系数有较大提高,限制性损耗系数降低了5个数量级。另外,本文还详细研究了光子晶体光纤的色散随光子晶体光纤结构的变化以及其布里渊增益特性,并分析了其可制造性。基于其高双折射和低限制性损耗特性,此种光纤可应用于长距离光纤通信系统。     

Analysis on the birefringence property of lyotropic liquid crystals below Krafft temperature

The effect of lyotropic liquid crystalline material, below Krafft temperature, in changing the polarization of the optical beam has been demonstrated. It is found that the lamella structures formed in the material below Krafft temperature are birefringent and this birefringence can be controlled by flowing it in rectangular channel under a suitable flow rate.     

Analyzing combinations of circular birefringence,linear birefringence,and elliptical dichroism in magneto-optical rotators

We derive analytic expressions for the polarization characteristics of light emerging from a magneto-optical medium possessing arbitrary contributions from linear and circular birefringence as well as magnetic circular dichroism. The medium is placed inside a static magnetic field. The rotation of the plane of polarization and the ellipticity of the resultant light exhibit interesting characteristics that can be a useful guide in the design and analysis of new photonic devices. Furthermore, the Jones matrices are derived in all cases, including for elliptical dichroism, indicating the role of hyperbolic trigonometric functions in modeling the effects of dichroism. Finally, implications for experimental detection of the polarization state and the limits on the performance of optical isolators are discussed.     

The birefringence spectroscopic studies on ferroelectric glycine phosphite (GPI) single crystals

The ferroelectric glycine phosphite single crystals have been grown from aqueous solution by both conventional and Sankaranarayanan-Ramasamy methods. The modified channelled spectrum method has been adopted for spectral dependence of optical birefringence studies over the wavelength range of 480–620 nm, which show that both the crystals exhibit relatively high birefringence values. The photoluminescence excitation studies were carried out for the grown crystals in a wide wavelength range between 300 nm and 600 nm at 224 K. The crystals were also subjected to scanning electron microscopy analysis in order to determine the ferroelectric domain pattern configuration.     

Numerical investigation of birefringence and confinement loss formed by rectangular/elliptical/circular air holes photonic crystal fibers

In this paper, high birefringence and low confinement loss of rectangular air holes photonic crystal fibers (PCFs) are numerically investigated and compared with elliptical and circular patterns using the finite element method. The mode birefringence of the proposed PCFs with rectangular air holes at λ?=?1.55?µm reaches 8.1?×?10^?2 and the confinement loss is less than 5?×?10^?3?dB/km. Besides, a high birefringence up to 2.76?×?10^?2 is also achieved from the proposed circular air holes PCF, which is the highest value compared to conventional circular air holes PCF.     

Improving of high birefringence photonic crystal fiber with low confinement loss using small elliptical air holes in the core region

In this paper, a novel design double lattice photonic crystal fiber is proposed for achieving both high birefringence and low confinement loss. In this structure, circular air holes are arranged as octagonal lattice in the cladding and elliptical as rectangular lattice in the core region. Numerical results illustrate that the birefringence in such fibers is determined not only by the double lattice but also the changing of the shape and the arrangement of the air hole in the first inner rings of the cladding. The birefringence property and confinement loss are studied by employing the finite difference time domain method with transparent boundary condition. The numerical results demonstrate that the maximal birefringence and lowest confinement loss of our optimized structure PCF at the excitation wavelength of λ = 1550 nm can be achieved at 5.16 × 10^?2 and 0.003 dB/km, respectively.     

Rayleigh scattering, absorption, and birefringence of large-size bulk single-crystal sapphire

While the thermomechanical properties of sapphire make it an excellent candidate of test mass for advanced laser interferometers, its optical quality is not well understood or well controlled. We have studied the results from high-resolution measurements of scattering, absorption, and birefringence in test-mass samples to better understand issues of quality. Samples show large-scale scattering structures clearly linked to the crystal-growth process. Samples characterized by the presence of point defects have significantly lower scattering (except at the point defects). In general on a large scale, high scattering also correlates with higher absorption and higher average birefringence inhomogeneity. However, on a smaller scale there is not a clear point-to-point correlation between scattering and absorption. Often a large-scale scattering structure is spatially displaced by tens of millimeters from a similar absorption structure, indicating that quite separate microscopic mechanisms give rise to scattering and absorption. The spatial displacements indicate that absorption centers and scattering centers are laid down during crystal growth at different distances from the solid-liquid interface. We suggest that absorption may be linked to F centers, while scattering may be linked to impurities such as iron.     

Random conjugated polybenzazole copolymers: Synthesis, characterization, and exciton confinement effects in photophysical properties

New conjugated random copolymers of poly(p-phenylene benzobisoxazole) (PBO) and poly(2,5-benzoxazole) (ABPBO) with various compositions have been synthesized and characterized by Fourier transform infrared (FTIR), wide-angle X-ray diffraction (WAXD), UV-absorption, and photoluminescence spectra. The side-to-side distance between two neighboring PBO-ABPBO chains can be modulated by the composition ratio. The absorption, excitation, and emission peaks for the copolymers in methanesulfonic acid can also be regulated by the copolymer composition from the homopolymer ABPBO solution to homopolymer PBO solution. However, the emission peaks of copolymers in solid state are quite different from those of their homopolymers. The copolymers showed blue shifted, structured emission spectra centered with higher quantum efficiency at 470 nm compared with the parent homopolymer PBO, indicating the effects of exciton confinement in the random copolymers. The relationship between the structure and properties for the random copolymers can be interpreted roughly by the sequence length distribution of the different segments estimated from the copolymerization statistics.     

FRP confinement of masonry: analytical modeling

International and National Building Codes provide requirements for design and construction of new masonry structures, but design provisions for the repair, retrofitting, and rehabilitation of masonry structures are not always available and included in the same documents. Due to the extremely large variability in masonry performances, equations of general validity cannot often be provided, namely relationships suitable for every masonry type. Despite the great research effort in the experimental field, considerable theoretical work is still needed to fully outline a definitive analytical model to predict the behavior of FRP confined masonry. Most of the available models, empirical in nature, have been calibrated against their own sets of experimental data, or they are simply derived from concrete. Even if large amount of results obtained for concrete led to consolidated design guidelines, they cannot be simply extended to masonry. In this study, a mechanically based confinement model is proposed based on mechanical parameters able to differentiate similar masonry types and to highlight that they present different confinement performance. Crucial aspects of masonry confinement will be also discussed, namely: lateral dilation; confinement effectiveness; lateral pressure also in non-circular shapes; effective strain of FRP.     

Perovskite single crystals: Dimensional control,optoelectronic properties,and applications

Lead halide perovskite single crystals have emerged as promising candidates for high-performance optoelectronic devices because of their superior optoelectronic properties. To date, much literature has reported the fabrication of various perovskite single-crystal structures. However, it still lacks effective rationalization and a comprehensive understanding of the relationship between the structural characteristics and functional properties of the perovskite single crystals, which is of great significance for fabricating perovskite single crystals-based high-performance optoelectronic devices. In this review, we give a comprehensive overview of the synthesis of perovskite single crystals with diverse dimensions, including 0D perovskite quantum dots (QDs), 1D micro/nanowires, 2D micro/nanoplates and single-crystal thin films (SCTFs), and 3D micro/nanoscale single-crystal structures. The relationship between the dimensional structure and properties of the perovskite single crystals is discussed in detail. Dimensional requirements for different optoelectronic applications are systematically summarized. Finally, perspectives on remaining challenges and future opportunities are highlighted.     

Topological birefringence and combined Rytov-Magnus effect

It is shown that the symmetry properties of the locally isotropic inhomogeneous medium of an optical fiber cause circular and linear topological birefringence. The circular birefringence δn _C in graded-index fibers is ∼(λ/ρ)² (where λ is the wavelength and ρ is the core radius), while the linear birefringence is δn _L ∼(λ/ρ)³. This topological birefringence is characterized not only by the polarization basis (as in crystals for example) but also by the magnitude and sign of the topological charge of the guided vortex. This topological birefringence forms the basis of the instability of the fiber IV vortex and is observed experimentally as the combined Rytov-Magnus effect. Pis’ma Zh. Tekh. Fiz. 25, 41–46 (March 12, 1999)     

Thermally induced birefringence in Nd:YAG slab lasers

We study thermally induced birefringence in crystalline Nd:YAG zigzag slab lasers and the associated depolarization losses. The optimum crystallographic orientation of the zigzag slab within the Nd:YAG boule and photoelastic effects in crystalline Nd:YAG slabs are briefly discussed. The depolarization is evaluated using the temperature and stress distributions, calculated using a finite element model, for realistically pumped and cooled slabs of finite dimensions. Jones matrices are then used to calculate the depolarization of the zigzag laser mode. We compare the predictions with measurements of depolarization, and suggest useful criteria for the design of the gain media for such lasers.     

Photonic crystals,amorphous materials,and quasicrystals

Photonic crystals consist of artificial periodic structures of dielectrics, which have attracted much attention because of their wide range of potential applications in the field of optics. We may also fabricate artificial amorphous or quasicrystalline structures of dielectrics, i.e. photonic amorphous materials or photonic quasicrystals. So far, both theoretical and experimental studies have been conducted to reveal the characteristic features of their optical properties, as compared with those of conventional photonic crystals. In this article, we review these studies and discuss various aspects of photonic amorphous materials and photonic quasicrystals, including photonic band gap formation, light propagation properties, and characteristic photonic states.     

Circular dichroism and birefringence in unconventional superconductors

We present a theoretical analysis of circular dichroism and birefringe in unconventional BCS superconductors with appropriate broken symmetries. We show that for the effect to exist, that in addition to broken time-reversal and two-dimensional parity symmetries, it is necessary to take into account the weak particle-hole asymmetry of the low-energy excitations of the metallic state. Circular dichroism and birefringence are shown to arise from the order parameter collective mode response of the superconductor; in the clean limit the contribution to the current response from the single-particle excitations does not give rise to circular dichroism or birefringence, even with particle-hole asymmetry. The magnitude of the circular dichroism is found to be small for the classes of superconductors which are thought to be likely candidates to exhibit the requisite broken symmetries, namely the heavy fermions and oxide superconductors. The order of magnitude of the elliptical polarization of a linearly polarized incident wave is V_f/c(/_L) (/E_f) ln(E_f/), which is roughly 10^–7–10^–8 rad at frequencies of order the gap, and decreases at least as fast as (2/)² at higher frequencies.     

Quark confinement and the renormalization group

Recent approaches to quark confinement are reviewed, with an emphasis on their connection to renormalization group (RG) methods. Basic concepts related to confinement are introduced: the string tension, Wilson loops and Polyakov lines, string breaking, string tension scaling laws, centre symmetry breaking and the deconfinement transition at non-zero temperature. Current topics discussed include confinement on R(3)×S(1), the real-space RG, the functional RG and the Schwinger-Dyson equation approach to confinement.     

Measurement of birefringence of low-loss, high-reflectance coating of m-axis sapphire

The birefringence of a low-loss, high-reflectance coating applied to an 8-cm-diameter sapphire crystal grown in the m-axis direction has been mapped. By monitoring the transmission of a high-finesse Fabry-Perot cavity as a function of the polarization of the input light, we find an upper limit for the magnitude of the birefringence of 2.5 x 10(-4) rad and an upper limit in the variation in direction of the birefringence of 10 deg. These values are sufficiently small to allow consideration of m-axis sapphire as a substrate material for the optics of the advanced detector at the Laser Interferometer Gravitational Wave Observatory.     

Multicomponent crystals of gliclazide and tromethamine: preparation,physico-chemical,and pharmaceutical characterization*

Objective: To improve the pharmaceutical behavior of the oral antidiabetic agent gliclazide through the synthesis of multicomponent crystals with tromethamine.

Methods: Multicomponent crystals were prepared by solvent evaporation method, kneading, and combining mechanical and thermal activation. DSC, FT-IR spectroscopy, X-ray diffraction, SEM-EDS, and SSNMR were used to investigate their formation. Measurements of solubility and dissolution rate were carried out for the pharmaceutical characterization.

Results: The formation of multicomponent crystals of gliclazide and tromethamine was confirmed by all the techniques. In particular, FT-IR and NMR measurements revealed that the interaction between drug and coformer leads to significant changes of the hydrogen bond scheme, and that almost all the functional groups of the two molecules are involved. The dissolution profile of the new phase is significantly better than that of both pure gliclazide and of the reference commercial product Diabrezide^®.

Conclusions: The new system shows an improved pharmaceutical behavior and could be formulated in a dosage form to obtain a rapid and complete release of the drug available for absorption.