Showing papers on "Birefringence published in 1979"

Polarization optics of twisted single-mode fibers

Abstract: In twisted single-mode optical fibers the polarization of light is affected by an elastooptically induced optical activity and by a modification of any linear birefringence present. These effects are discussed theoretically and demonstrated experimentally. The activity/twist ratio is α/τ ≃ 0.13 … 0.16 universally in weakly guiding silica fibers. Twisted fibers may be used as polarization rotators. A fiber with a ±68° double twist operates as a fast/slow mode interchanger, suitable for delay equalization.

An organic crystal with an exceptionally large optical second‐harmonic coefficient: 2‐methyl‐4‐nitroaniline

Abstract: We have grown and measured the optical second‐harmonic coefficient dijk of the new nonlinear crystal 2‐methyl‐4‐nitroaniline (MNA). We find that the dijk are very large with d12 being 5.8 times larger than d31 of LiNbO3 giving a birefringence phase‐matching figure of merit d2/n3 which is 45 times larger than LiNbO3. The other coefficient d11 is 40 times larger than LiNbO3, giving a huge figure of merit which is 2000 larger than LiNbO3.

Electroclinic effect at the A-C phase change in a chiral smectic liquid crystal

Abstract: When a smectic-$A$ phase is composed of chiral molecules, it exhibits an electroclinic effect, i.e., a direct coupling of molecular tilt to applied field. The pretransitional behavior of the electroclinic effect in the $A$ phase is used to study the critical behavior near the second-order, smectic-$A$---smectic-$C$ phase transition. This behavior is measured by monitoring the change in birefringence of a sample as the electroclinic effect causes a tilt of the molecules. A large pretransitional effect is measured, and constants describing the critical behavior are determined.

Matrix Theory of Photoelasticity

Abstract: 1. Introduction.- 2. Electromagnetic Theory of Light.- 3. Description of Polarized Light.- 4. Passage of Polarized Light Through Optical Elements.- 5. Measurement of Elliptically Polarized Light.- 6. The Photoelastic Phenomenon.- 7. Two-Dimensional Photoelasticity.- 8. Three-Dimensional Photoelasticity.- 9. Scattered-Light Photoelasticity.- 10. Interferometric Photoelasticity.- 11. Holographic Photoelasticity.- 12. The Method of Birefringent Coatings.- 13. Graphical and Numerical Methods in Polarization Optics, Based on the Poincare Sphere and the Jones Calculus.- Author Index.

Magneto‐optic current sensing with birefringent fibers

Abstract: To measure currents on high‐voltage lines, the Faraday rotation is used in a single‐mode optical fiber encircling the conductor. Disturbing linear birefringence is suppressed by twisting the fiber. With ∼10 m of fiber, coiled with a 3‐cm radius, we obtain 0.25 mrad/A polarization rotation, permitting measurement of currents of 0.2–2000 A.

Wall-induced pretransitional birefringence: A new tool to study boundary aligning forces in liquid crystals

Abstract: A wall-induced birefringence in a nematic liquid crystal above the nematic-isotopic phase transition point has been observed for the first time. It is expected that this phenomenon will provide a useful tool to study the nature of aligning forces at liquid-crystal--solid interfaces.

Fiber-ring interferometer: polarization analysis.

Abstract: In a rotation-sensing fiber-optical Sagnac interferometer, temperature fluctuations and mechanical vibrations affect the birefringence of the fiber and may cause phase shifts like those resulting from rotation. Insertion of polarizing elements, acting at both ends of the fiber, yields a stable phase.

Lattice parameters and birefringence in PbTiO3 single crystals

Abstract: Measurements of lattice parameters and birefringence of PbTiO3 single crystals are described as a function of temperature. The anomalous rise in birefringence with temperature is interpreted in terms of lattice strain and dielectric polarization.

The origin of the optical anisotropy of solvent cast polymeric films

Abstract: The optical mode structures of solvent cast films of different polymers have been measured with a single prism film coupler. The allowed modes define the index of refraction for light polarized in and perpendicular to the plane of the film. It is shown that the solvent coating process preferentially aligns the polymeric chain backbone in the plane of the film and that this biaxial orientation may produce birefringent films in optically anisotropic resins. The sign of this birefringence depends upon the orientation of the dominating polarizable group relative to the chain backbone in the plasticized melt. The magnitude of this effect reflects both the optical anisotropy of the group and the steric constraints to its free rotation.

A new approach to the continuum theory of birefringence of oriented polymers

Abstract: The internal field in a transparent anisotropic dielectric is described with the aid of the classical electromagnetic theory by the introduction of the internal field or Lorentz-factor tensor. On the basis of the internal field equation generalized Lorentz-Lorenz relations are derived. A virtual refractive index in lieu of the mean refractive index is defined by the trace of the inverse susceptibility tensor. By the same token the harmonic mean replaces the arithmetic mean specific refractivity. The relation between birefringence, polarizability and structural anisotropy of the medium is formulated.

Time‐dependent birefringence, linear dichroism, and optical rotation resulting from rigid‐body rotational diffusion

Abstract: Expressions are derived for the time‐dependent relaxation behavior of a monodisperse suspension of arbitrarily shaped rigid bodies, after initial alignment by an externally applied field. We show that five exponential terms are necessary for a complete description of birefringence, linear dichroism, and optical rotation decay phenomena in a force‐free rotational diffusion process. The explicit form for the multiplicative coefficients of the exponential relaxation terms are presented; they are expressed in terms of the optical anisotropy tensor and a tensor characteristic of the initial alignment conditions. Symmetry constraints that involve special relationships between the optical anisotropy tensor, the alignment tensor, and the diffusion tensor or that involve the initial orientational distribution conditions, are shown to lead to a reduction in the number of required exponential relaxation terms. We concern ourselves mainly with alignment by means of an electric field in a Kerr cell, but other alignmen...

Birefringence in elliptically clad borosilicate single-mode fibers.

Abstract: Experimental results indicate that the stress-induced strain birefringence in borosilicate elliptically clad fibers arises from the expansion coefficient mismatch between the borosilicate elliptical cladding and the pure silica outer jacket. This strain birefringence cannot be annealed even after repeated thermal cycling. It is shown that, for a given dopant concentration, the birefringence depends primarily on the cladding ellipticity ∊ and increases linearly with increasing ellipticity and expansion coefficient mismatch.

Surface‐induced ordering of a liquid crystal in the isotropic phase

Abstract: A detailed account of a measurement of order parameter of a liquid crystal at the boundary by means of the wall‐induced pretransitional birefringence is given. Several surface treatments were studied including surfactants and evaporated films. Although all treatments produced good alignment in the nematic phase, the boundary order parameter (hence the strength of the aligning force) in the isotropic phase differed very much depending on the treatment, indicating the diverse nature of the alignment process.

Single‐polarization optical fibers: Slab model

Abstract: Calculations for a simple three‐layer slab model show that sufficient anisotropic strain birefringence can be introduced into germanosilicate, phosphosilicate, and borosilicate single‐mode fibers to reduce the coupling between orthogonally polarized modes to a level of practical interest for single‐mode single‐polarization propagation.

Fabrication of single-mode fibres exhibiting extremely low polarisation birefringence

Abstract: An investigation of the relative effects of core ellipticity and stress-induced birefringence on fibre polarisation properties is described. It is found that a reduction in core stress levels is necessary to obtain low-birefringence fibres. A fibre having a retardation of only 2.6°/m is reported.

Birefringence in elliptically deformed optical fibres

Abstract: The phase difference between the two polarisation states of the fundamental mode on a slightly elliptical, weakly guiding fibre is derived using both an exact analysis and perturbation theory. Deficiences in some earlier calculations are also discussed.

Polarization-preserving optical fiber

Abstract: A method of making a polarization-preserving optical fiber is disclosed having a first step of fabricating a substrate tube to have a wall of nonuniform thickness, the nonuniformity in thickness being arranged about the wall of the substrate tube so that maxima and minima in wall thickness lie in planes which are substantially orthogonal. This first step is followed by deposition of cladding layers and a core layer within the substrate tube. The substrate is then collapsed and the fiber drawn therefrom. The nonuniform wall thickness of the substrate tube operates together with differential thermal contraction of the layers to produce stress-induced birefringence in the fiber, which birefringence provides a polarization-preserving optical fiber.

Polarization effects on single‐mode optical fiber sensors

Abstract: In a conventional circular cross‐section single‐mode fiber, built‐in and induced birefringences remove the degeneracy and make the fiber a two‐Eigenmode system. We have constructed the first all‐fiber interferometric sensor system and have performed preliminary studies on the effects of birefringence in these interferometers. Theoretical analysis and experimental data supporting this analysis are presented for the 3‐dB coupler and all‐fiber interferometer sensor.

Modes of a symmetric slab optical waveguide in birefringent media - Part II: Slab with coplanar optical axis

Abstract: We study the modes of a symmetric thin-film slab waveguide composed of birefringent crystalline material in the film and in the equivalent substrate and superstrate. In addition we assume that the optical axes of the uniaxial materials of film and substrate are parallel to each other and also parallel (coplanar) to the plane of the film. This simple anisotropic waveguide has interesting properties. It supports only hybrid modes but in the limit of propagation along the optical axis and at right angles to it the modes become almost of the TE and TM type. Moreover, some of the modes become leaky waves as they propagate at increasingly larger angles relative to the optical axis of the dielectric material. For guides made of materials whose ordinary refractive index n o is larger than the extraordinary index n e , the extraordinary wave modes, which approximate TE modes, become leaky; and for n_{e} > n_{o} , the ordinary wave modes, which approximate TM modes, become leaky. The leakage losses are large near a "critical angle," where leakage begins to appear but may be insignificant at larger angles, measured between the optical axis and the direction of propagation.

Dynamical behaviour of drag-reducing polymer solutions☆

Abstract: Related to the problem of the drag-reduction mechanism due to the elastic properties of macromolecular additives, we study theoretically and experimentally the dynamically behaviour of the molecules and the corresponding flow field. Optical properties, orientation, configuration or change of shape are studied by flow birefringence in classical or original, elongational flow devices. The dependence of the birefringence threshold on the molecular weight, nature, ionic character, concentration and level of degradation of the polymer is studied. The flow field is determined experimentally and by computation using a simple rheological model. A correlation with drag-reduction measurement in capillaries is tried.

Coupling of optical and mechanical properties in crystalline polymers

Abstract: The modules and birefringence of oriented polymers are known to couple through the structural and intrinsic properties of the polymer. Recent developments in both optical and mechanical theories have allowed this coupling to be expanded so that it includes predictions of modulus and refractive indices of uniaxially-oriented polymer films at various angles to the draw direction. The validity of these theories has been tested in this study by predicting the angular dependence of the optical and mechanical properties of seven uniaxiallyoriented films of isotactic polypropylene. The present study also provides intrinsic material properties associated with the crystalline and noncrystalline components of the polymer, and consequently allows the identification of the structural parameters that control the properties of ultra-high oriented isotactic polypropylene.

Liquid crystal tuned birefringent filter

Abstract: Moderately narrow band, tunable, birefringent filters are disclosed using zero-twist liquid crystal cells as variable retarders in a Lyot-type birefringent filter. These filters can achieve analytically useful levels of resolution and stray-light ratios for costs that are competitive with prism and grating monochromators. These birefringent filters can be tuned and/or rendered opaque by the application of a suitable voltage to the cells. Thus, a variety of different optical instruments can be constructed with no moving parts. Power requirements are negligible. A useful filter can be designed to occupy a volume less than one cubic inch. These properties render such a filter ideally suited to microprocessor control.

Electro-optics and dielectrics of macromolecules and colloids

Abstract: Theoretical Advances.- Specific Kerr Constants of Rigid, Ellipsoidal Macromolecules in Conducting Solution at Very Low Ionic Strength.- Transient Electric Birefringence of Macromolecular Solutions at Reversing Fields of Arbitrary Strength and Duration.- The Limit of the Numerical Method of Inverting the Laplace Transformation and the Uniqueness of Relaxation Distribution Function Obtained by the Method.- Low Angle Approximations to the Theory of Alternating Electric Field Light Scattering.- A Theory of Dynamic Light-Scattering by Flexible Macromolecules in a Fluctuating Electric Field.- Electro-Optical Responses of Chiral Substances.- Absorption Phenomena.- An Instrument for the Measurement of Electric Dichroism.- Simultaneous Measurement of Dichroism and Birefringence on Suspensions of Absorbing Particles.- Electric Dichroism of Purple Membrane.- Electrochromism of Organic Dyes in Polymer Matrices.- Electrically Induced Fluorescence Changes from Solutions of Dye Tagged Polyribonucleotides.- Polarized Fluorescence in an Electric Field: Theoretical Calculation at Arbitrary Fields. Experimental Comparison with Other Electrooptical Effects. Saturation of the Induced Dipole Moment in Polyelectrolytes.- Nucleic Acids and Polynucleotides.- Dielectric Properties of Low-Molecular Weight DNA in Aqueous Solutions at Low Ionic Strength.- Electro-Optic Measurement of ?-ray Induced Damage in DNA.- Physical Studies of Hg(ll) and Ag(l) DNA Complexes - Theory.- Electric-Field Induced Orientation of Polynucleotides.- The Stabilized Induced Dipole in Solutions of Polynucleotides.- Biological Systems.- Electro-Optical Properties of Nucleosomes and Nucleosomal DNA.- Polarisability Anisotropy as an Indicator of the Effects of Aminoglycoside Antibiotics on Sensitive, Dependent and Resistant Strains of E. coli.- Rotational Diffusion Coefficients of Complex Macromolecules.- Determination of Rotational Diffusion Coefficients of the Bacteriophages T4B and T7 by Depolarized Dynamic Light Scattering. The Influence of Double Scattering.- Effects of Calcium and ATP on the Conformation of F-Actin in Vivo and In Vitro.- Electric Birefringence of Cartilage Proteoglycan and its Association with Hyaluronic Acid.- An Electrical Birefringence Study of the Contribution of Permanent and Induced Dipole Moments to Acid-Soluble Collagen Polarization.- Polyelectrolytes and Polymers.- Electro-Optical Changes in Biopolymers - Chemical and Rotational Contributions.- Reversal of Birefringence Sign of Natural and Synthetic Polyelectrolytes in the Presence of Metal Cations and Coordination Complexes.- Electro-Optic Study of the Conformational Changes Induced in Partially Charged Poly-4-Vinylpyridine by Ions of Heavy Metals.- Kerr Constants of Naturally-Occurring ?-Amino Acids in Aqueous Solution.- A Bridge Method for Measuring the Dielectric Relaxation of Conducting Solutions.- Photoconductivity and Dielectric Properties of Polyhexamethylene Adipamide.- Colloidal Systems.- Electro-Optic Studies of Colloids and their Stability.- Size Distributions of Rigid Colloids from Transient Birefringence Data.- Length Dependence of the Ionic Contribution to the Anisotropy of the Electrical Polarisability for Rigid Rods.- Flow Alignment of a Colloidal Solution Which Can Undergo a Transition from the Isotropic to the Nematic Phase (Liquid Crystal).- Quasi-Crystals Produced By Colloidal Photochrome Dyes in an Applied Electric Field.- Effect of CTAB on Colloidal Suspensions of Sepiolite - A Study by Light Scattering, Electric Birefringence, Laser Line Broadening and Electrophoretic Light Scattering.- Laser and High Field Effects.- Some Evidences for a Conformational Change of Polypeptide Induced by Strong Electric Fields.- Nonlinear Dielectric Effect of PBLG in Nonpolar Medium.- Laser and Electric Field Induced Kerr Effect Studies on Nematic Liquid Crystals.- Slow Non-Critical Molecular Reorientation in the Isotropic Phases of Nematogens.- A Comparison of Optico-Optical Scattering and Birefringence Measurements on Wyoming Sodium Bentonite Suspensions.- Laser Photoinduced Changes in the High Frequency Dielectric Constant of Chloroplasts and Dyes.- Relation Between Electric Field-Induced Optical Rectification and Electro-Optic Kerr Effect in Macromolecular Solutions.

Magnetic birefringence of ferrofluids. II. Pulsed field measurements

Abstract: For pt.I see ibid., vol.12, p.311 (1979). A method is described for measuring the rotary diffusion coefficient of ferrofluid particles, and hence their hydrodynamic size, by observing the decay of their birefringence after a magnetic field pulse. Details of the pulse amplifier used to produce field pulses of from 8*10-3 to 8*10-2 T with decay times of 3.6 to 36 mu s are given. The origin of the birefringence in ferrofluids is discussed and it is concluded that it is predominantly due to the shape anisotropy of the particles: particles in which Neel rotation occurs do not contribute to the birefringence. The existence of Faraday rotation in Co and Fe3O4 ferrofluids is also reported.

Birefringence in optical fibres with elliptical cross-section

Abstract: A comparison is made between various approximations for the phase delay between orthogonally polarised modes in elliptical optical fibres. A more accurate analysis is presented which gives a lower value for the birefringence produced by a given ellipticity. The effect on fibre bandwidth is shown to be small compared with that resulting from stress birefringence.

An electro‐optic tunable filter

Abstract: This letter describes a tunable optical filter that couples light energy between ordinary and extraordinary polarizations in a birefringent electro‐optic crystal at the phase‐matched wavelength by means of a spatially periodic dc electric field. The specific embodiment described here is a LiTaO3 platelet operating with transverse electric field and located between cross polarizers. Analogies to both the Solc birefringent filter and the Harris acousto‐optic filter are cited. The electro‐optic filter is tuned by varying the spatial period of the electric field via an array of separately addressable finger electrodes. We have demonstrated tunability from 4700 A to 4.5 μm. Experimental results of transmittance versus applied voltage and of bandwidth versus pass wavelength agree well with theory. The flexibility of this type of electronic filter in allowing synthesis of arbitrary transfer functions through nonperiodic voltage distributions is emphasized.

Magnetic birefringence of ferrofluids. I. Estimation of particle size

Abstract: The magnetic birefringence of various samples of Fe3O4 ferrofluids with particle sizes in the range of approximately 8.5-18.5 nm has been measured in field strengths of 5*10-4 to 5*10-1 T. For all the samples it has been found that in low fields the birefringence varies as the square of the field strength, indicating a classical behaviour of the particles. The size of the particles and the width of the particle size distribution curve have been estimated from an analysis of the variation of the birefringence with the applied magnetic field; the results obtained are in good agreement with results obtained from electron microscope and magnetic susceptibility measurements.