Showing papers on "Birefringence published in 1998"
TL;DR: In this article, an optical torque can be induced on microscopic birefringent particles of calcite held by optical tweezers, which can be held in three-dimensional optical traps at very high power without heating.
Abstract: Light-induced rotation of absorbing microscopic particles by transfer of angular momentum from light to the material raises the possibility of optically driven micromachines. The phenomenon has been observed using elliptically polarized laser beams1 or beams with helical phase structure2,3. But it is difficult to develop high power in such experiments because of overheating and unwanted axial forces, limiting the achievable rotation rates to a few hertz. This problem can in principle be overcome by using transparent particles, transferring angular momentum by a mechanism first observed by Beth in 19364, when he reported a tiny torque developed in a quartz ‘wave-plate’ owing to the change in polarization of transmitted light. Here we show that an optical torque can be induced on microscopic birefringent particles of calcite held by optical tweezers5. Depending on the polarization of the incident beam, the particles either become aligned with the plane of polarization (and thus can be rotated through specified angles) or spin with constant rotation frequency. Because these microscopic particles are transparent, they can be held in three-dimensional optical traps at very high power without heating, leading to rotation rates of over 350 Hz.
913 citations
TL;DR: An improved polarization-sensitive optical coherence tomography (OCT) system is developed and used to measure birefringence in porcine myocardium tissue and produce two-dimensional bireFringence mapping of the tissue.
Abstract: An improved polarization-sensitive optical coherence tomography (OCT) system is developed and used to measure birefringence in porcine myocardium tissue and produce two-dimensional birefringence mapping of the tissue. Signal-to-noise issues that cause systematic measurement errors are analyzed to determine the regime in which such measurements are accurate. The advantage of polarization-sensitive OCT systems over standard OCT systems in avoiding image artifacts caused by birefringence is also demonstrated.
399 citations
TL;DR: Polarization Sensitive Optical Coherence Tomography (PS- OCT) was used to image the reduction of birefringence in biological tissue due to thermal damage and demonstrates the potential of PS-OCT for burn depth assessment.
Abstract: Polarization Sensitive Optical Coherence Tomography (PS-OCT) was used to image the reduction of birefringence in biological tissue due to thermal damage. Through simultaneous detection of the amplitude of signal fringes in orthogonal polarization states formed by interference of light backscattered from turbid media and a mirror in the reference arm of a Michelson interferometer, changes in the polarization due to the optical phase delay between light propagating along the fast and slow axes of birefringent media were measured. Inasmuch as fibrous structures in many biological tissues influence the polarization state of light backscattered, PS-OCT is a potentially useful technique to image the structural properties of turbid biological materials. Birefringence of collagen, a constituent of many biological tissues, is reduced by denaturation that takes place at a temperature between 56-65 °C, thus providing an “optical marker” for thermal damage. Images showing reduction of birefringence due to thermal damage in porcine tendon and skin are presented and demonstrate the potential of PS-OCT for burn depth assessment.
353 citations
TL;DR: In this paper, a quasi-phase matching scheme was proposed to compensate for optical dispersion, which results in different phase velocities for light of different frequencies in anisotropic birefringent crystals.
Abstract: Frequency conversion in nonlinear optical crystals1,2 is an effective means of generating coherent light at frequencies where lasers perform poorly or are unavailable. For efficient conversion, it is necessary to compensate for optical dispersion, which results in different phase velocities for light of different frequencies. In anisotropic birefringent crystals such as LiNbO3 or KH2PO4 (‘KDP’), phase matching can be achieved between electromagnetic waves having different polarizations. But this is not possible for optically isotropic materials, and as a result, cubic materials such as GaAs (which otherwise have attractive nonlinear optical properties) have been little exploited for frequency conversion applications. Quasi-phase-matching schemes1,3, which have achieved considerable success in LiNbO3 (ref. 4), provide a route to circumventing this problem5,6, but the difficulty of producing the required pattern of nonlinear properties in isotropic materials, particularly semiconductors, has limited the practical utility of such approaches. Here we demonstrate a different route to phase matching — based on a concept proposed by Van der Ziel 22 years ago7 — which exploits the artificial birefringence of multilayer composites of GaAs and oxidised AlAs. As GaAs is the material of choice for semiconductor lasers, such optical sources could be integrated in the core of frequency converters based on these composite structures.
312 citations
TL;DR: It is reported here that the birefringence of a small drop of peptide solution can supply information related to the cooperative packing of amyloid fibers and their capacity for magnetic orientation.
261 citations
Book•
11 Feb 1998
TL;DR: In this article, the propagation equations of biaxial media are discussed, including basis vectors, transfer matrices, reflection and transmission guided waves, anisotropic scatter fluid transport metal films and linear polarizers phase retarders birefringent filters.
Abstract: Part 1 Propagation in biaxial media: propagation equations basis vectors transfer matrices reflection and transmission guided waves. Part 2 Characterization of biaxial films: deposition form birefringence effective media anisotropic scatter fluid transport metal films. Part 3 Applications of biaxial media: linear polarizers phase retarders birefringent filters.
256 citations
TL;DR: In this paper, a birefringent α-BaB 2 O 4 crystal, 40mm in diameter, 35mm in height has been grown successfully in a laboratory by Czochralski method.
221 citations
TL;DR: Cross-sectional birefringence- and polarization-independent backscatter imaging of laser-induced thermal damage in porcine myocardium in vitro is demonstrated using a polarization-sensitive optical coherence tomography system and it is demonstrated that bireFringence is a more sensitive indicator of thermal damage than is backscattered light.
Abstract: We demonstrate cross-sectional birefringence- and polarization-independent backscatter imaging of laser-induced thermal damage in porcine myocardium in vitro, using a polarization-sensitive optical coherence tomography system. We compare the generated images with histological sections of the tissue and demonstrate that birefringence is a more sensitive indicator of thermal damage than is backscattered light. Loss of birefringence in thermally damaged regions is quantified and shown to have significant contrast with undamaged sections of the tissue. A detailed theoretical analysis of the birefringence measurements is provided, including a calculation of the systematic errors associated with background noise, system imperfections, and tissue dichroism.
221 citations
TL;DR: Photorefractive polymers with high diffraction efficiency in the visible and near-infrared regions of the electromagnetic spectrum have been developed and have enabled demonstrations of imaging through scattering media, using a holographic time-gating technique at a wavelength that is compatible with the transparency of biological tissues and with the emission of low-cost semiconductor laser diodes.
Abstract: Photorefractive polymers with high diffraction efficiency in the visible and near-infrared regions of the electromagnetic spectrum have been developed. These polymers, which have a large dynamic range because of their high orientational birefringence, incorporate a dye designed to have a large dipole moment and a high linear polarizability anisotropy. Such polymers have enabled demonstrations of imaging through scattering media, using a holographic time-gating technique at a wavelength that is compatible with the transparency of biological tissues and with the emission of low-cost semiconductor laser diodes.
214 citations
TL;DR: This work has observed extraordinarily large optical nonlinearity in Methyl Red-doped nematic liquid-crystal film, attributed to formation of an optically induced dc space-charge field and to the resulting reorientation of the highly birefringent nematic director axis.
Abstract: We have observed extraordinarily large optical nonlinearity in Methyl Red–doped nematic liquid-crystal film. Grating diffraction can be generated with an optical intensity as low as 40 µW/cm2, and a refractive-index change coefficient of more than 6 cm2/W is obtained. The effect is attributed to formation of an optically induced dc space-charge field and to the resulting reorientation of the highly birefringent nematic director axis.
208 citations
Patent•
11 Jun 1998
TL;DR: In this paper, two dimensional images of optical birefringence in turbid samples as a function of depth are measured using a low coherence Michelson interferometer.
Abstract: Employing a low coherence Michelson interferometer, two dimensional images of optical birefringence in turbid samples as a function of depth are measured Polarization sensitive detection of the signal formed by interference of backscattered light from the sample and a mirror or reference plane in the reference arm which defines a reference optical path length, give the optical phase delay between light propagating along the fast and slow axes of the birefringence sample Images showing the change in birefringence in response to irradiation of the sample are produced as an example of the detection apparatus and methodology The technique allow rapid, noncontact investigation of tissue or sample diagnostic imaging for various medical or materials procedures
TL;DR: In this article, the intrinsic and induced birefringence of optical fibers were measured at 1550 nm using the optical frequency-domain reflectometry technique, which confirmed the theoretical analysis, which predicts the appearance of oscillations on the detected Rayleigh backscattering intensity, with periods equal to the polarization beat length.
Abstract: Measurements of intrinsic and induced birefringence of optical fibers are performed at 1550 nm using the optical frequency-domain reflectometry technique. The experiment confirms the theoretical analysis, which predicts the appearance of oscillations on the detected Rayleigh backscattering intensity, with periods equal to the polarization beat length L/sub b/ and to L/sub b//2. Polarization mode-coupling length values are obtained from local birefringence and polarization mode dispersion measurements.
TL;DR: In this paper, the authors derived closed-form expressions for the effective index of subwavelength gratings up to the fourth and the second order for TE and TM polarization, respectively, for arbitrary grating structures and are a generalization of previous results obtained for lamellar gratings with one groove per period.
Abstract: We derive closed-form expressions for the effective index of subwavelength gratings up to the fourth and the second order for TE and TM polarization, respectively. These expressions are valid for arbitrary grating structures and are a generalization of previous results obtained for lamellar gratings with one groove per period (a structure often called a two-component layered medium). The effective-medium-theory predictions are carefully validated with exact electromagnetic theories for slanted and unslanted sinusoidally modulated volume gratings and for classical mounting. It is shown that, even for large period-to-wavelength ratios near the cutoff value, the form birefringence is accurately predicted at any angle of incidence.
TL;DR: In this paper, the effect of the rotation of the principal states of polarization (PSP) is shown to generate power overshoots on the "1" and "0" bit sequences.
Abstract: The time-space varying birefringence in single-mode optical fibers causes the polarization mode dispersion (PMD) to be a serious problem in high bit-rate transmissions. The PMD first- and second-order statistics are well known in the literature, but second-order PMD-induced pulse distortions have still to be clarified for sequences of pulses of arbitrary shape. We give, for the first time, the exact PMD time impulse response, up to second order. We show, both numerically and experimentally, that the effect of the rotation of the principal states of polarization (PSP) is to generate power overshoots on the "1" and "0" bit sequences.
TL;DR: It is shown that superior phase-only operation can be obtained over a given operating range for the LCD compared with other approaches and that the eigenvectors are elliptically polarized.
Abstract: We derive theoretical expressions for the eigenvalues and the eigenvectors for a twisted-nematic liquid-crystal display (LCD) as a function of the twist angle and the birefringence by use of the Jones-matrix formalism. These polarization eigenvectors are of particular interest for phase-only transmission because they propagate unchanged through the display. We find that the eigenvectors are elliptically polarized and that the ellipticity changes as a function of the birefringence of the LCD (which is proportional to the external voltage applied to the display). We can define an average eigenvector over a desired range for the applied voltage. We show, using Jones matrices, how this average eigenvector can be generated using a quarter-wave plate and a linear polarizer having appropriate orientation angles. Using this average eigenvector, we show that superior phase-only operation can be obtained over a given operating range for the LCD compared with other approaches.
TL;DR: The birefringence of microtubules (MTs) and of MT-based macromolecular assemblies in vitro and in living cells is measured by using the new Pol-Scope and the theoretical concept is based on Wiener's theory of mixed dielectrics, which is well established for nonimaging applications.
TL;DR: In this paper, the authors describe the applicability of SiON for optical filtering in a new architecture for wavelength multiplexing, modulation, polarization splitting and second-harmonic generation.
Abstract: The refractive index of silicon oxynitride (SiON), a widely used material for integrated optics devices, can be chosen in a wide range between 1.45-2.0. We describe how the consequent large design freedom can be exploited on the one hand for a "standard" polarization independent optical channel waveguide having a favorable tradeoff between efficient fiberchip coupling and small bend radii (compact devices) and on the other hand for special-purpose and hybrid components where the refractive index should be finely adjusted for obtaining the desired functionality. We illustrate the applicability of SiON by describing a few devices for optical filtering in a new architecture for wavelength multiplexing, modulation, polarization splitting and second-harmonic generation.
TL;DR: In this article, the polarization properties of holographic gratings in side-chain azobenzene polyesters were investigated, where an anisotropic grating that is due to photoinduced linear and circular birefringence is recorded in the volume of the material and a relief grating appears on the surface.
Abstract: We investigate the polarization properties of holographic gratings in side-chain azobenzene polyesters in which an anisotropic grating that is due to photoinduced linear and circular birefringence is recorded in the volume of the material and a relief grating appears on the surface. A theoretical model is proposed to explain the experimental results, making it possible to understand the influence of the different photoinduced effects. It is shown that at low intensity the polarization properties of the diffraction at these gratings are determined by the interaction of the linear and circular photobirefringences, and at larger intensity the influence of the surface relief dominates the effect of the circular anisotropy. Owing to the high recording efficiency of the polyesters, the ±1-order diffracted waves change the polarization interference pattern during the holographic recording, resulting in the appearance of a surface relief with doubled frequency.
TL;DR: In this paper, a dynamical experimental study on the diffraction efficiencies and the formation of birefringence grating and surface relief grating on doped and/or covalently bonded azobenzene derivatives containing polymer films were carried out using laser beams with different polarizations.
Abstract: Dynamical experimental studies on the diffraction efficiencies and the formation of birefringence grating and surface relief grating on doped and/or covalently bonded azobenzene derivatives containing polymer films were carried out using laser beams with different polarizations. From polarization analyses of the first-order (±1) diffracted beams, the contributions to the diffraction efficiency are separated into an anisotropic (or birefringence) part and a surface relief part. During the growth of the gratings the dynamical responses of both contributions appear to be quite distinct, and estimates of the time variations of the anisotropic phase shift, Δφ, due to the induced birefringence and of the surface relief height, 2Δd, due to the polymer mass transport are obtained. Calculations and simulations of the theoretical expressions allow us to confirm the experimental findings and to reproduce all the observed polarized first-order diffraction curves with good agreement, even when the surface relief is im...
TL;DR: In this paper, the results of the dichroic ratio measurement of liquid-crystal cells, UV absorption spectra, birefringence, and PI conformation calculations using molecular mechanics suggest that the photodecomposition of PI by UV exposure produces anisotropic van der Waals forces, which align LC along its optical axis.
Abstract: Unidirectional liquid-crystal (LC) alignment by a linearly polarized ultraviolet light (UV) exposure was examined using two types of polyimide (PI). PI with a fluorene unit incorporated in a side chain showed LC alignment perpendicular to those of conventional PIs, i.e., perpendicular to the rubbing direction and parallel to the exposure polarization of UV. The results of the dichroic ratio measurement of LC cells, UV absorption spectra, birefringence, infrared absorption spectra, and PI conformation calculations using molecular mechanics suggest that the photodecomposition of PI by UV exposure produces anisotropic van der Waals forces, which align LC along its optical axis.
TL;DR: The effect of several parameters known to affect the microtubule assembly are investigated with respect to their effect on the final degree of alignment and comparisons with earlier fiber diffraction work and small-angle x-ray solution scattering experiments are made.
TL;DR: In this article, the horizontal gradient-freeze (HGF) growth technique has been used to control stoichiometry by minimizing vapor transport as well as to eliminate cracking due to anisotropic thermal expansion.
Abstract: ZnGeP2 and CdGeAs2 have long been recognized as promising crystals for infrared frequency generation. They exhibit the highest nonlinear optical coefficients (d36 equals 75 pm/V and 236 pm/V for ZnGeP2 and CdGeAs2, respectively) among all known compounds that possess adequate birefringence for phase matching. ZnGeP2's transparency range (0.62−13 μm) makes it the optimum material for shifting the wavelength of 2-μm pump lasers into the 3–5-μm range via optical parametric oscillation (OPO), whereas that of CdGeAs2 (2.3–18 μm) is better suited for doubling the frequency of CO2 lasers (9–11 μm) into the same range via second-harmonic generation. In both cases however, the application of these materials has been hindered by great difficulty in achieving crack-free single crystals, and by large defect-related absorption losses.The horizontal-gradient-freeze (HGF) growth technique has been instrumental in overcoming these difficulties. “Ultralow” axial gradients (1–3°C/cm) have been used to control stoichiometry by minimizing vapor transport as well as to eliminate cracking due to anisotropic thermal expansion. (The a-axis and c-axis thermal-expansion coefficients of ZnGeP2 differ by a factor of two, whereas those of CdGeAs2 differ by a factor of 15.) In addition, oriented seeds were used to ensure monocrystalline nucleation (because even a small degree of polycrystallinity can lead to cracking even in low gradients) and growth along preferred directions to facilitate fabrication of device crystals. Finally growth was performed in a two-zone, transparent furnace in order to monitor and control the seeding-and-growth process.
Patent•
29 Jun 1998
TL;DR: In this article, a passive polarisation modulating optical element comprises a layer of birefringent material, which consists of retarder regions forming a regular pattern, for instance to act as a parallax barrier for a 3D display.
Abstract: A passive polarisation modulating optical element comprises a layer of birefringent material. The layer has substantially fixed birefringence and comprises retarder regions forming a regular pattern, for instance to act as a parallax barrier for a 3D display. The retarders have optic axes aligned in different directions from each other. The element may be associated with a polariser, for instance an output polariser of a liquid crystal device, with the polarising direction of the polariser being parallel to the optic axis of the retarders. Thus, the retarders have no effect on the intensity of light passing through the element whereas the retarders act as half waveplates and rotate the polarisation vector of light passing therethrough, for instance by 90°.
TL;DR: Magnetic birefringence experiments under static eld are performed on ionic ferrofluid samples based on Fe2O3. A colloidal size-sorting of the particles allows to obtain narrow size distributions as discussed by the authors.
Abstract: Magnetic birefringence experiments under static eld are performed on ionic ferrofluid samples based on Fe2O3 . A colloidal size-sorting of the particles allows to obtain narrow size distributions. The optical birefringence of the solutions is found positive and can be described by a Langevin formalism. It scales as H 2 in the low eld limit. In the high eld limit the particles size dependence of the saturation birefringence is compatible with a surface anisotropy constant KS =2 : 810 2 erg cm 2 associated with a particle elongation of 1.25 both coherent with N eel predictions of surface anisotropy in small grains.
TL;DR: In this paper, the magnetochiral birefringence of two optically active organic liquids, 3-(trifluoroacetyl)-camphor and carvone, at a wavelength of 633 nm in a static magnetic field of 5 T was measured.
TL;DR: In this article, a deuterated polyfluoromethacrylate was synthesized for use as optical waveguide materials, and both single-mode and multimode optical waveguides were fabricated using the polymer.
Abstract: Deuterated polyfluoromethacrylate which has high transparency, low birefringence and good processability was newly synthesized for use as optical waveguide materials, and both single-mode and multimode optical waveguides were fabricated using the polymer. The propagation loss and waveguide birefringence of the single-mode waveguides were as low as 0.10 dB/cm and -5.5/spl times/10/sup -6/ at 1.31 /spl mu/m, respectively. The propagation losses of the multimode waveguides were less than 0.02 dB/cm at both 0.68 and 0.83 /spl mu/m, and 0.07 dB/cm at 1.31 /spl mu/m.
08 Mar 1998
TL;DR: Polarization sensitive optical coherence tomography (PS-OCT) was used to obtain images of optical birefringence in biological tissues in this article, where simultaneous detection of two orthogonal polarization states of the signal formed by interference of light backscattered from the biological sample and a mirror in the reference arm of a Michelson interferometer was measured.
Abstract: Polarization sensitive optical coherence tomography (PS-OCT) was used to obtain images of optical birefringence in biological tissues. Through simultaneous detection of two orthogonal polarization states of the signal formed by interference of light backscattered from the biological sample and a mirror in the reference arm of a Michelson interferometer, the optical phase delay between light propagating along the fast and slow axes of birefringence was measured. Simultaneous detection of both polarizations also permits reconstruction of the electro-magnetic wave backscattered from the sample. Inasmuch as any fibrous structure will influence the polarization of light, PS-OCT is a potentially powerful technique in the field of biomedical imaging. It allows rapid non-contact investigation of tissue structural properties through spatially resolved imaging of birefringence.
Patent•
02 Jul 1998TL;DR: A fiber optic pressure transducer having enhanced resolution and dynamic range is described in this article. But, it is not shown how to use it in conjunction with a light source and a spectral demodulation system in order to detect pressure ambient.
Abstract: A fiber optic pressure transducer having enhanced resolution and dynamic range includes a fiber optic core having one or more gratings written onto it, a birefringence structure for enhancing the birefringence of the core, and a structure for converting isotropic pressure forces to anisotropic forces on the fiber core. Several different embodiments of prestressing structure are disclosed (both extrinsic and intrinsic). Several different embodiments of structure (both extrinsic and intrinsic) for converting isotropi c pressure to anisotropic pressure are also disclosed. The fiber optic pressure transducer according to the invention is advantageously used in conjunction with a light source and a spectral demodulation system in order to detect pressure ambient to the fiber optic pressure transducer based on the wavelength and shift of spectral peaks.
TL;DR: A novel device that acts as a quarter-wave plate at normal incidence and as a polarizing beam splitter at an angle of incidence of ~40 deg is fabricated by direct-write electron-beam lithography and reactive ion etching.
Abstract: We have fabricated a novel device that acts as a quarter-wave plate at normal incidence and as a polarizing beam splitter at an angle of incidence of ?40 deg. The device is made from a multilayer SiO2/Si3N4 surface-relief zeroth-order one-dimensional grating with a period of 0.3 µm. The device is designed for an operating wavelength of 632.8??nm. We designed the device by using rigorous coupled-wave analysis and fabricated it by direct-write electron-beam lithography and reactive ion etching. Measurements confirmed the performance of the device as a wave plate and as a polarizing beam splitter.
TL;DR: In this paper, the authors presented a completely new method able to characterize polarization mode dispersion (PMD) properties of randomly birefringent single-mode fibers, using polarization sensitive backscattering technique.
Abstract: This paper presents a completely new method able to characterize polarization mode dispersion (PMD) properties of randomly birefringent single-mode fibers, using polarization sensitive backscattering technique. We show analytical relationships between evolution of polarization state of backscattered signal with respect to state of polarization of forward one. Our technique allows one to measure differential group delay, beat length, and correlation length at the same time over long single-mode fibers using only one fiber end. Experimental data fit very well with numerical results, confirming the capability of our technique for fast routine characterization of PMD during cabling, before and after installation.