Showing papers on "Birefringence published in 1980"

Bending-induced birefringence in single-mode fibers

Abstract: In a bent optical fiber, lateral internal stress induces a birefringence, betab. At lambda = 0.633 microm in a silica fiber, betab = 7.7 X 10(7) r2 /R2 deg/m, where r is the fiber radius and R is the bending radius.

Single-mode fibre fractional wave devices and polarisation controllers

Abstract: We describe new single-mode fibre optic devices which are completely equivalent to fractional wave plates of classical optics. They employ a very simple configuration which uses the stress birefringence induced by bending the fibre. Several devices can be combined to control the polarisation inside any single-mode fibre.

Liquid crystal display with improved angle of view and response times

Abstract: A nematic liquid crystal light shutter with improved angle of view by the incorporation of retardation plate means disposed in front of the liquid crystal cell to compensate for the off-axis performance of the device due to the birefringent nature of the liquid crystal material. When the transparent plates of the liquid crystal display are rubbed or otherwise aligned at right angles to each other to effect a twisted-nematic structure, two retardation plates are employed, the net retardation of each being less than or equal to the net retardation of the liquid crystal material itself. On the other hand, when the plates are rubbed or otherwise aligned parallel to each other, three retardation plates can be employed. The retardation plates can be incorporated into the front polarizer which is to be used on the display. Also disclosed is a liquid crystal display device having an exceedingly high speed of response.

The origin of magnetic birefringence and dichroism in magnetic fluids

Abstract: The optical birefringence and dichroism observed in magnetic fluids when subjected to a magnetic field are generally ascribed to orientation of the particles, to anisotropic spatial ordering, or to string formation. Magnitude, concentration- and time dependence of the anisotropies predicted by these mechanisms are compared with the available experimental data. This leads to the conclusion that orientation of small aggregates and secondary aggregation of large aggregates into strings are the most likely cause of the large anisotropies. Orientation of single particles can be responsible for small anisotropies only. Field-induced spatial ordering has, at least optically, not (yet) been observed.

Ferroelastic phase transition in BiVO4 I. Birefringence measurements using the rotating-analyser method

Abstract: A brief review of methods of measuring birefringence is given. Apparatus for the accurate measurement of optical birefringence at high temperatures using a modulation (rotating-analyser) method is described in detail, together with suggestions for further applications of the equipment. The technique is applied to the particular case of the ferroelastic monoclinic–tetragonal phase transition in BiVO4. The birefringence was found to show mean-field behaviour over a wide temperature range with a mean-field transition temperature of 519.9 (3) K.

Three-stage birefringent filter tuning smoothly over the visible region: theoretical treatment and experimental design.

Abstract: The Jones transformation matrix, which describes the arbitrary incidence of polarized light on a thin uniaxial birefringent plate, is determined. With the optic axis presumed to lie in the plane of the plate, digital solutions to the resulting formulas are presented for several different quartz plates to depict the tuning characteristics of a birefringent plate functioning as a single-stage birefringent filter. A simplified model is used to generalize these results to describe a multistage birefringent filter. This theoretical study forms the basis for the design and construction of a three stage, quartz, birefringent filter to be used as the coarse tuning element in a visible cw dye laser. A relatively simple and straightforward procedure for the assembly of the three-stage filter is given. The performance of this newly constructed filter is found to be superior to currently available commercial models, tuning smoothly over the 4400-6600-A wavelength region.

High birefringence in tension-coiled single-mode fibers.

Abstract: Coiling a single-mode fiber of radius r under tension onto a cylinder of radius R produces a linear birefringence of βtc ≃ 28 × 107∊2r/R deg/m in the fiber at λ = 0.63 μm, where ∊z is the relative fiber elongation. Polarization beat lengths down to 2.5 cm have been realized this way, providing excellent polarization holding.

Polarization mode coupling in long single-mode fibres

Abstract: In this paper we look at the polarization state evolution of light propagating in long, birefringent, single-mode fibres in the presence of mode coupling. We show first that there always exist two orthogonal linear input polarizations which lead to linear output polarization for monochromatic light. The applicability of the coupled power equations is discussed and it is shown that they cannot be used with only two propagating modes. A more detailed analysis is then carried out for a uniform coupling and the effect of the spectral width of the source is investigated. Some insight into the time-dependent propagation is also given. Experimental results illustrate the theoretical considerations.

Single-polarisation single-mode optical fibre with refractive-index pits on both sides of core

Abstract: A new refractive-index distribution for realising a single-polarisation single-mode optical fibre is proposed. This distribution features two pits, on either side of the core. The propagation characteristics are calculated by the two-dimensional finite-element method. The relative birefringence δβ/βav is 1 ∼ 2.5 × 10−4 when core/cladding index difference is 1%.

Faraday rotation in highly birefringent optical fibers

Abstract: Faraday rotation is obtained in highly birefringent single-mode fibers by using alternating or periodically spaced regions of magnetic field. This approach has potential applications in isolators, circulators, combination tuning and unidirectional elements, and for studying fiber birefringence.

Fiber optic polarization controller

Abstract: Fiber optic device for controlling the state of polarization of light. In one embodiment, a strand of fiber optic material is bent into a generally planar coil of relatively tight radius to stress the material and form a birefringent medium having principal axes which are rotated to control the polarization of light passing through the strand. In a second embodiment, one portion of a fiber optic strand is twisted about its axis to change the polarization, and a second portion of the strand is formed into a coil which is free to change in radius without additional twisting as the first portion is twisted.

A Contribution to the Study of Optical Properties of Fibers with Irregular Transverse Sections

Abstract: A new method is suggested by the complementary use of the interference and scanning electron microscopy to measure the mean refractive indices and birefringence of fibers having irregular trans verse section. '

Birefringence in single-mode optical fiber due to elliptical core deformation and stress anisotropy

Abstract: A formula for the difference between propagation constants of two polarization modes caused by elliptical core deformation and stress anisotropy is given for single-mode optical fibers. Birefringence in circular and elliptical core fibers subject to an externally applied uniaxial pressure are measured. Birefringence caused by elliptical core deformation and stress anisotropy are experimentally separated by measuring their wavelength dependences. A value of 3.36 \times 10^{-10} cm2/gram weight (gw) (= 3.43 \times 10^{-12} m2/N) is obtained for the stress-optical constant of silica fibers. Residual stress corresponding to external pressure of 240 gw/cm is observed for a fiber with 0.35 core ellipticity.

Rheo-optics of shear and elongational flow of liquid cystalline polymer solutions: hydroxypropyl cellulose/water and poly-p-phenylene terephthalamide/sulfuric acid

Abstract: An experimental study is reported of the quiescent and flow birefringent characteristics of two liquid crystalline polymer solution systems, poly-p-phenylene terephthalamide (PPD-T) in sulfuric acid and hydroxypropyl cellulose (HPC) in water over a range of concentrations. It is shown that for the quiescent state the dilute solutions are optically isotropic while the concentrated solutions consists of negatively birefringent domains. During flow at low deformation rates, moving domains are still seen. At higher deformation rates, a homogeneous highly birefringet fluid is obtained. The birefringence increases with concentration at constant deformation rate and exhibits a major increase as the liquid crystalline state is formed. The source of the birefringence is due to (1) anisotropy of polarizability of oriented macromolecules, and (2) difference in refractive index of solvent and oriented macromolecules (form birefringence). The results are interpreted in terms of the level of polymer orientation which may be developed in flow for liquid crystalline polymer solutions as compared to solutions of flexible macromolecules.

Optical fibres for current measurement applications

Abstract: The polarization properties of optical fibres are of interest in several different communications and measurement applications. This paper indicates the properties ideally required of a fibre for use in current measurement systems and describes an extremely low birefringence fibre which meets many of these requirements. Measurements of the polarization properties of this fibre are given and a laboratory prototype current measurement system using the fibre is described.

Radial birefringent element and its application to laser resonator design.

Abstract: We have invented a quasi-Gaussian profile-transmittance filter based on radially varying the phase retardation in a birefringent element. The radial birefringent element has been applied to resonator design and has demonstrated its usefulness in generating an improved resonator spatial-mode profile.

Stress-acoustic relations for stress measurement by ultrasonic technique

Abstract: New equations are proposed for stress measurements in orthotropic materials by ultrasonic birefringence technique. Intensity of stress-induced anisotropy and its principal direction are related to the applied stress through three coefficients, in contrast to only one coefficient required for isotropic materials. Experiments of ultrasonic birefringence were carried out to determine the three coefficients in a plate of aluminum alloy with a slight orthotropy originated from roll working. Anisotropy induced by uniaxial stress and rotation of the principal axis were observed in several specimens with different directions of rolling. The results are in good agreement with the curves theoretically predicted by the equations proposed here, showing the validity and usefulness of these equations for stress measurements in materials conventionally used.

Improvements in birefringent filters. 6: Analog birefringent elements

Abstract: A 100-mA analog birefringent element has been built from a polarizing wide field solid Michelson interferometer. The analog element behaves on-axis identically to a crystal element but has the field characteristics of a wide field Michelson. It is demonstrated that by proper choice of glasses for the arms of the Michelson the wide field condition can hold over a large spectral and large temperature range. Most important, proper choice of arm materials allows minimization of the wavelength sensitivity to temperature. A reduction of a factor of 10(2)-10(3) compared to birefringent crystals can be achieved.

Surface‐induced ordering of a liquid crystal in the isotropic phase. II. 4‐methoxybenzylidene‐4′‐n‐butylaniline (MBBA)

Abstract: The boundary order parameter of the liquid crystal 4‐methoxybenzylidene‐4′‐n‐butylaniline (MBBA) in the isotropic phase has been deduced for several surface treatments by measuring the surface‐induced pretransitional birefringence. Results for the silane surface coupling agent, methyl‐3‐aminopropyltrimethoxy‐silane (MAP) were particularly interesting, indicating a negative surface order parameter. An analytic expression for the temperature‐dependent birefringence is derived from Landau’s expanison in the order parameter. This expression shows that the value of the boundary order parameter determines the absolute minimum isotroic phase temperature.

Field test unit for windscreen optical evaluation

Abstract: An apparatus for analyzing the deleterious characteristics of optically transparent bodies, including distortion, multiple imaging and birefringence. A beam of light is projected along an optical axis onto a beam splitter. The reflected segment passes through the transparent body and is then reflected back along nearly the same path toward the beam splitter by a retro-reflective screen lying at the image plane of the beam. The portion of the reflected beam passing directly through the beam splitter is detected by an optical sensor in substantial orientation with the axis of the beam reaching it. Distortions and multiple imaging are detected by shape changes and images, respectively, in a pattern of opaque areas superimposed on the originating beam. Birefringence is analyzed by polarizing the originating beam and observing the color pattern and intensity reaching the sensor.

Polarisation-maintaining single-mode fibre cable design

Abstract: Guidelines for the design of a circular-polarisation-maintaining single-mode fibre cable are given. The use of circular polarisation allows use of low birefringence fibres and there is no need for orienting the fibres at splices. Quarter-wave plates at input and output of the fibres achieve the desired linear-circular polarisation conversion, and vice versa.

Stress-induced birefringent single mode optical fiber and a method of fabricating the same

Abstract: The stress-induced birefringent single mode optical fiber includes an optical core having a high refractive index and a high thermal expansion coefficient. An arrangement formed from an optical material having a low refractive index and a low thermal expansion coefficient is disposed to engage the outer surface of the core tangentially at opposite ends of a diameter of the core to establish a stress therein. Air encompasses the remainder of the outer surface of the core to provide a light guiding cladding for the core and, hence, the fiber itself. The arrangement to establish the stress may include a pair of flat plates engaging the outer surface of the core tangentially which are entrapped in a circular tube which is concentric with the core such that air is entrapped between the plates and the circular tube to provide the light guiding cladding. Alternatively, an elliptical tube is provided to engage the outer surface of the core at the minor axis of the elliptical tube to provide the desired stress in the fiber. In this case air is enclosed in the elliptical tube to provide the light guiding cladding.

Single-mode-fiber birefringent filters.

Abstract: It is proposed to utilize optical birefringence in single-mode fibers for construction of wavelength-dependent filters. The birefringence may be natural (a consequence of the drawing process) or induced through external stresses. In the latter case, simple variation of these stresses may be used to tune the filter transfer function.

Anomalous dispersion of birefringence of sapphire and magnesium fluoride in the vacuum ultraviolet

Abstract: Previous measurements of the birefringence of sapphire and magnesium fluoride have been extended to their respective limits of transparency, revealing anomalous dispersion effects at short wavelengths, which are qualitatively discussed. Possible practical applications to Lyot filters and quarter-wave plates for Lyman-alpha are indicated.

The influence of thermal history on internal stress distributions in sheets of PMMA and polycarbonate

Abstract: The through-thickness birefringent patterns (nx – nz) of PMMA and polycarbonate (PC) are measured as a function of thickness, cooling rate, and annealing time. A method is demonstrated for separating the elastic stress from the residual birefringence. The residual birefringence is explained as the residual orientation induced when cooling through the galss transition. The shape of the elastic (tempering) stress distribution is apparently independent of the cooling rate and annealing time, the choice of polymer, and the sheet thickness. The magnitude of the tempering stres is dependent on cooling rate but nearly independent of choice of polymer and sheet thickness. The decays of both the tempering stress and the residual orientation are measured as a function of annealing time at 120°C for polycarbonate. The measured birefringence decays only slightly; however, the elastic tempering stress reverts, on annealing, to permanent (anelastic) orientational strain. The tempering stress at the sheet surface is not an adequate criterion for defining toughness in polycarbonate.

Ferroelastic phase transition in BiVO4 II. Birefringence at simultaneous high pressure and temperature

Abstract: The accurate measurement of optical birefringence at simultaneous high pressures and temperatures using a diamond-anvil pressure cell is described Data are presented for BiVO4 which show that the optical birefringence may be described by mean-field behaviour An applied hydrostatic pressure of only 8 × 108 Pa reduces the mean-field temperature of the ferroelastic monoclinic tetragonal phase transition from 5197 to 393 K A birefringence–pressure–temperature phase diagram is presented

Reflection of plane-polarized light by the retina.

Abstract: Experiments are described in which retinal reflectance was measured as a function of wavelength for three subjects. Two components of the reflected light were studied: that which retained polarization and that which was depolarized. Both components were found to be present at all visible wavelengths and to have magnitudes which rose at the red end of the spectrum, although the fraction of the reflected light which retained polarization was then lower. The results are compared with those of earlier studies. While there is qualitative agreement on the form of the wavelength-dependence of retinal reflectance, the magnitudes of the values deduced by different authors vary considerably. The influence of ocular birefringence on polarized-light studies of the retina is discussed, together with possible locations from the structures responsible for the observed reflectances.