Showing papers on "Birefringence published in 1983"

Submicrometer periodicity gratings as artificial anisotropic dielectrics

Abstract: Gratings of dielectric material can act as homogeneous birefringent materials if the wavelength of the incident radiation is greater than twice the period of the grating. For the case of square profile gratings, simple equations predict the birefringence versus linewidth‐to‐period ratio of the gratings. By using x‐ray lithography and reactive ion etching, 240‐nm period gratings of polymethylmethacrylate and silicon nitride were fabricated with various linewidths. The birefringence of these was measured at 632.8 nm and found to agree closely with the theory. Silicon nitride gratings which act as half‐wave and quarter‐wave plates in the visible were made.

Optical elements with ultrahigh spatial-frequency surface corrugations.

Abstract: In this paper we discuss the properties of optical elements fabricated by holographically recording an ultrahigh spatial-frequency pattern in a photoresist mask followed by reactive ion etching to transfer this pattern into the surface of a quartz substrate. Such optical elements are environmentally durable, potentially easy to replicate, and exhibit diffraction efficiencies in excess of 85%. In addition, two other properties are reported for the first time. Such elements at normal (0°) incidence are antireflective, with broadband reflection coefficients as low as 0.035%. Also, the elements exhibit artificially produced birefringence making them useful as wave plates. These results may be particularly significant in the UV and IR, where damage-resistant antireflection coatings and transparent birefringent materials may not exist.

A new optical method and apparatus `HAUP' for measuring simultaneously optical activity and birefringence of crystals. I. Principles and construction

Abstract: A new and accurate method has been developed by which all the components of the anisotropy of the optical susceptibilities can be determined. The apparatus based on this method has been constructed, and named as HAUP (High-Accuracy Universal Polarimeter). The basic principle is to measure the intensity of the light beam, which is propagated successively through a polarizer, a specimen, and an analyser, as functions of azimuth and deflecting angle from the crossed-Nicols condition. Thus the method is characterized by its extreme simplicity, which prevents systematic errors. Considerations and tests of inevitable systematic errors are made. The systematic errors originating in the parasitic ellipticities of the polarizer and analyser are found to be serious for the measurements of optical activity; appropriate solutions to remove them are devised here. Sensitivities of measurements of optical activity and birefringence by the HAUP method reach 4.8 × 10−8 and 2.2 × 10−6 respectively, the accuracy being 4.2 × 10−3 and 2.2 × 10−3 respectively. By using HAUP it has become possible to measure simultaneously all the components of optical activity, birefringence and rotation of optical indicatrix of any crystals, including those belonging to the monoclinic and triclinic systems. These measurements can be made from about 400 K down to 10 K. Also, simultaneous determinations of electrogyration and electrooptic coefficients have become feasible by applying electric fields to crystals.

Electric field-gradient-induced birefringence in N2, C2H6, C3H6, Cl2, N2O and CH3F

Abstract: The optical birefringence induced by an electric field-gradient has been measured in the four non-polar gases nitrogen, ethane, cyclopropane and chlorine, and in the two polar gases nitrous oxide and methyl fluoride Together with known values of the anisotropy in molecular polarizability, the measurements on the non-polar molecules yield the electric quadrupole moments Θ = -4·90 ± 0·3 × 10-40 C m2 for nitrogen, -3·34 ± 0·13 × 10-40 C m2 for ethane, 5·3 ± 0·7 × 10-40 C m2 for cyclopropane and 10·79 ± 0·54 × 10-40 C m2 for chlorine In polar molecules the measured birefringence arises not only from the quadrupole moment, but also from the higher polarizabilities describing the electric dipole induced by an electric field-gradient and a time-varying magnetic field This additional contribution is shown to be small in the case of nitrous oxide, but in methyl fluoride it predominates

Single-polarisation operation of highly birefringent bow-tie optical fibres

Abstract: Experimental results show that bow-tie fibres with high levels of stress-induced birefringence can be operated such that they support only a single linearly polarised mode. Under these conditions the loss of the fibre is 5 dB/km for the guided mode and 55 dB/km for the suppressed mode For short-length operation as a polariser, extinction ratios as high as 50 dB/m have been obtained.

Performance of Lyot depolarizers with birefringent single-mode fibers

Abstract: Fiber-optic Lyot depolarizers which are attractive for fiber-optic gyros have been studied theoretically and experimentally. It is shown that the amount of residual polarization at the depolarizer output is proportional to the square root of the polarization-maintaining parameter h , yielding a residual polarization of about 1 percent for a fiber-optic depolarizer with h = 1.1 \cdot 10^{-4} /m and a superluminescent diode.

Analytic solution for the birefringence produced by thermal stress in polarization-maintaining optical fibers

Abstract: Polarization-maintaining optical fibers are usually made by inducing a large anisotropic thermal stress in the core so that it appears highly birefringent. A simple analytic solution has been found for the birefringence in terms of the cross-sectional distribution of the high-expansion material used to create the thermal stress. The analysis is able to predict optimal structures which efficiently utilize the available stress and thus maximize the birefringence. It is shown that the optimum structure has a cross-sectional geometry resembling a bow-tie. Design rules are given whereby the dimensions may be chosen and these are verified in a simple experiment.

Polarimetric strain gauges using high birefringence fibre

Abstract: When a highly-birefringent fibre is stretched, the birefringence changes. The phenomenon is shown to result from a difference in Poisson's ratio of the two glasses from which the fibre is constructed. Experimental verification is given and a simple polarimetric strain gauge made from bow-tie fibre is demonstrated.

Optical pulse reshaping based on the nonlinear birefringence of single-mode optical fibers

Abstract: We report the observation of strong reshaping of 3-psec dye-laser pulses by nonlinear birefringence during passage through a 150-cm-long, single-mode optical fiber and a crossed polarizer. For lower-intensity input pulses to the fiber, the transmitted pulses were observed to be proportional to the cube of the input pulses. With increased intensity, more-complicated pulse shapes were obtained. Our experimental results agree well with the predicted intensity dependence of the reshaping action.

Determination of the anisotropic potential at the nematic liquid crystal-to-wall interface

Abstract: The integrated birefringence of a surfactant (C16H33NH2)‐aligned methoxybenzylidene butylaniline cell as a function of applied magnetic field (up to 100 kG) has been measured. The Oseen and Frank elastic continuum theory and a generalized torque balance equation at the interface have been utilized for the calculation to fit the measured data. A very good fit to the data was obtained using an anisotropic liquid crystal‐to‐wall interfacial potential of the form C cos2 θ+C4 cos4 θ for the calculation. It was found that C4/C=−0.38.

Wavelength-sweeping technique for measuring the beat length of linearly birefringent optical fibers

Abstract: In this Letter a new method is proposed for measuring the beat length of linearly birefringent optical fibers. In this method the beat length is determined from the wavelength dependence of the phase difference between two orthogonally polarized HE(11) modes at the output end of a sample fiber. The important feature of this method is the wide range of the measurable beat length (0.4 mm-1 m:) The principle, the experimental setup, and the result of the experiment are described.

Orientation development in the injection molding of amorphous polymers

Abstract: Frozen-in orientation in the injection-molding of amorphous polymers has been considered in terms of flow- and cooling-induced birefringence. In particular, measurements of the frozen-in orientation distribution in polystyrene (PS) molded strips and circular runners have been performed. Three birefringence components, Δn, n22 − n33, and n11 − n33, have been measured for strips, and two components, Δn and nrr − nθθ, for runners. The effects of various processing conditions, of strip thickness, and of runner diameter on orientation development have been analyzed and compared with those predicted by our previously developed viscoelastic theory. In addition to injection-molding experiments, free and constrained quenching experiments for PS and poly(methyl methacrylate) (PMMA) strips have been carried out and the gapwise distribution of cooling-induced (thermal) birefringence has been measured. Relaxation of thermal birefringence following quenching has been observed for PMMA. The effects of flow- and cooling-induced orientation on various components of birefringence in molded parts have been elucidated and limitations on the applicability of the stress-optical law to the injection-molding of amorphous polymers have been discussed.

Pulsed gain and thermal lensing of Nd:LiYF 4

Abstract: Measurements show that a 1 cm diameter Nd:YLF rod amplifier produces extremely weak thermal lensing when pulse pumped at 3 Hz to a gain of 13 at 1053 nm. Direct comparison with Nd:YAG indicates much weaker thermal lensing effects for both ordinary and extraordinary polarizations in Nd:YLF.

Low birefringence encapsulated liquid crystal and optical shutter using same

Abstract: Briefly, a liquid crystal material composition has a low, preferably zero or near zero, birefringence characteristic. Such material is mixed with a quantity of pleochroic dye to form a solution therewith to increase absorption characteristics and is encapsulated; and such encapsulated material may be used as an optical light control device or optical shutter in which light intensity may be controlled without distorting or at least without substantially distorting the optical image transmitted therethrough.

On the Jones birefringence

Abstract: The possibility that a physical system may possess simultaneously two independent linear birefringences is a consequence of the Jones calculus formulated in 1948. Before this only one linear birefringence was known. The new one is characterized by a pair of orthogonal fast and slow axes that bisect those of the traditional linear birefringence. Apparently over­looked since it was initially postulated, the Jones birefringence is the subject of the present investigation. Pictorial symmetry arguments and a Mueller matrix method are used to identify systems in which both linear birefringences may exist. They are found to occur naturally in certain magnetic and non-magnetic crystals, for which the relevant uniaxial classes are listed. In addition, it is shown that the Jones birefringence may be induced in a fluid by the application of uniform electric and magnetic fields E and B , parallel to each other and transverse to the light path, the dependence being linear in EB . A quantitative theory relates both birefringences to physical property tensors and confirms the symmetry predictions. From the theory an assessment is made of the magnitude of the effect in a crystal and a gas, and although very much smaller than known linear birefringences, it should be capable of measurement.

Measurement of fiber birefringence by wavelength scanning: effect of dispersion

Abstract: Scanning the wavelength in high-birefringence fibers inherently measures the group delay difference, and not the phase delay difference, between the two polarization modes. Dispersion of the birefringence will result in a 10–20% error in fiber beat lengths interpolated from such measurements, even if only stress birefringence is present. Geometrical dispersion can introduce even larger errors in some fibers.

A new optical method and apparatus `HAUP' for measuring simultaneously optical activity and birefringence of crystals. II. Application to triglycine–sulphuric acid (NH2CH2CO2H)3.H2SO4

Abstract: As the test for the utility of HAUP, simultaneous determinations of birefringence, optical activity, and rotation of the indicatrix, and electrooptic, and electrogyration coefficients were made for both paraelectric and ferroelectric states of triglycine-sulfuric acid, 3C2H5NO2.H2SO4. In the ferroelectric state, the hysteresis loop of the gyration tensor g22 was clearly observed. Electrooptic and electrogyration coefficients referred to polarization are found to be nearly independent of temperature over the paraelectric and ferroelectric states. It is important to note that gyration is more largely induced than birefringence under lower electric fields. This fact, contrary to the previous belief, indicates that simultaneous determinations of gyration and birefringence are indispensable for the correct evaluations of the optical properties of crystals.

Single-mode, single-polarization fibers made of birefringent material

Abstract: Optical fibers composed of highly birefringent material are studied. One of the two fundamental modes can be made leaky when the birefringence is sufficiently large. This suggests a novel single-mode, single-polarization fiber design that can be realized by stress-induced birefringence. The leakage rate is calculated by a perturbation method, which accounts for degeneracy between a bound mode and a packet of radiation modes.

Reduced thermal focusing and birefringence in zig-zag slab geometry crystalline lasers

Abstract: Replacing the rod in a Nd:YAG laser with a zig-zag slab resulted in a very substantial reduction of the thermally induced optical distortion without sacrifice of output power or efficiency This reduction was possible after simple measures were taken to eliminate end and edge effects

Acousto-optic frequency shifter for single-mode fibres

Abstract: A fibre-optic frequency shifter has been constructed using a birefringent single-mode fibre positioned asymmetrically within two acoustic resonators driven 90° out of phase. The incident wave in one polarisation state is coupled to a frequency-shifted wave in the orthogonal state. Sideband suppression of better than 20 dB is achieved.

Organization of collagen fibers in the intestine.

Abstract: The characteristic extinction pattern which is observed when the submucosa is viewed in the optical polarizing microscope has been analyzed in terms of the configuration and orientation of the 4 μm diameter collagen fibers. It is shown that the observed polarization effects are produced by periodic variations in orientation of fully birefringent fibers. The fiber configuration required to produce the observed polarization effects is a tilted wave configuration with a crimp period of approximately 20 μm. In the model, the tilted waveform fibers are crimped in register and form parallel arrays. The arrays are oriented in layers at approximately + 30° and -30° to the longitudinal direction and are mirror images of each other. Analysis of the extinction pattern shows that the model satisfactorily accounts for the observed polarization effects at several different angles of the crossed polaroids. The calculated strain necessary to straighten the wavy fibers of the model correlates well with the observed strain...

Vector representation of behavior of polarized light in a weakly inhomogeneous medium with birefringence and dichroism

Abstract: An investigation is made of the vectorial and geometrical representation of the polarization of light propagating through a weakly inhomogeneous absorbing anisotropic and optically active medium. When the approximations of geometrical optics are used, Maxwell’s equations lead to the equation ∂G/∂x3 = (i/2)(Ω + iT)G, governing the behavior of polarized light propagating along the x3 axis in the medium, where x3 is the propagation distance along a light path, G is the complex amplitude of the electric vector, the vectors Ω = (0, Ω1, Ω2, Ω3) and T = (T0, T1, T2, T3), whose basis vectors are the unit matrix and the Pauli spin matrices, represent the optical properties of the medium. The two successive transformations of the resulting equation by the Stokes vector and the normalized polarization vector s yield a simple vector equation ∂s/∂x3=Ω^×s+(T^×s)×s, where Ω^ = (Ω1, Ω2, Ω3) and T^ = (T1, T2, T3) are defined as the birefringent vector and the dichroic vector, respectively, representing the birefringence and the dichroism of the absorbing medium. The component Ω1 (or T1) shows the linear birefringence (or the dichroism) along the x1 and x2 axes, Ω2 (or T2) shows the linear birefringence (or dichroism) along the bisectors of the x1 and x2 axes, and Ω3 (or T3) shows the circular birefringence (or dichroism). The vector equation can represent clearly the geometrical behavior of the polarization of light in the inhomogeneous absorbing medium with the help of the Poincare sphere.

Birefringent-fiber polarization coupler.

Abstract: Periodically stressing a birefringent fiber once per beat length can cause coherent coupling to occur between polarization modes. Such a birefringent-fiber polarization coupler is described here. More than 30 dB of power transfer between polarizations has been achieved. The device has been used as the output coupler of an in-line Mach-Zehnder interferometer, and better than 25-dB on/off extinction has been measured. The device is wavelength selective and can be used as a multiplexer or as a notch filter. A notch of 9-nm full width at half-maximum has been achieved with a 60-period comb structure.

Light-induced nonreciprocity, field invariants, and nonlinear eigenpolarizations.

Abstract: It is shown that the magnitude of nonlinear nonreciprocity, self-induced by counterpropagating laser beams, is related to the anisotropic properties of the nonlinear third-order susceptibility (resulting in the light-induced birefringence and gyrotropy) and therefore is sensitive to the mutual arrangement of polarization of both of the beams. The invariants of nonlinear wave equations suggest an existence of mutual eigenarrangements of polarization with different relevant eigennonreciprocities. By using this effect, a nonreciprocal spectroscopy of the anisotropic nonlinear susceptibility may be developed.

Thermal properties of highly birefringent optical fibers and preforms.

Abstract: Temperature cycling of highly birefringent optical fibers and preforms has been used to investigate the thermal properties of bow-tie and elliptically clad structures. The thermal hysteresis of the birefringence is shown to be a direct consequence of the thermal history of the fiber or preform and has been related to volume changes in the stress-producing borosilicate sections. Annealing increases the axial stress as well as the stress anisotropy and hence the birefringence. Increases of up to a factor of 2 in the birefringence on suitable thermal treatment indicate a new method for further improvement of high birefringence fibers. The implications of the results in the design, fabrication, and use of such fibers are discussed.

Polarization independent beam splitter

Abstract: A new type of beam splitter is described, which is capable of producing a division of light in a polarization independent manner. Typical beam splitters (used off-axis) have a pronounced polarization dependence. The device is a thin plate of suitably oriented, birefringent material having a thickness chosen to interchange the characteristic polarizations of the beam between the faces of the plate. The reflection/refraction ratio at the two boundaries are then complementary and the combined effect is insensitive to the polarization of the incident beam.

New design for a photoelastic modulator

Abstract: Modulation of the polarization of light can be achieved by a periodical birefringence. A new photoelastic modulator is described in this paper. In comparison with previously described apparatus, the originality of our mounting consists in the production of longitudinal resonance vibrations caused by shear stresses. These are generated by thin ceramics glued to one side of the material, birefringence modulation being thus achieved. Thanks to the use of ceramics, this modulator is much easier to construct than were the previous ones. The stray birefringence is kept very low in this instrument.

Polarization rotation compensator and optical isolator using the same

Abstract: A polarization rotation compensator and an optical isolator using the same are described. The optical isolator comprises a first birefringent wedge plate; a polarization rotation compensator composed of a combination of a half-wave plate whose principal axis is inclined at an angle of θ/2 with respect to the plane of polarization of the incident light and a quarter-wave plate whose principal axis is inclined at an angle of θ with respect to the plane of polarization of the incident light; a Faraday rotator; and a second birefringent wedge plate; wherein the Faraday rotator, quarter wavelength plate, and half-wavelength plate are respectively arranged in the order of propagation of the backward light or of the forward light.