Showing papers on "Birefringence published in 2004"
TL;DR: In this article, a model describing the temperature effect of liquid crystal refractive indices is derived and confirmed by experiment Two single liquid crystal compounds (5CB, 5PCH) and two mixtures (MLC-6241-000 and UCF-35) with different birefringence values were used to validate the model.
Abstract: A model describing the temperature effect of liquid crystal (LC) refractive indices is derived and confirmed by experiment Two single LC compounds (5CB, 5PCH) and two mixtures (MLC-6241-000 and UCF-35) with different birefringence values were used to validate the model This model fits all the experimental data well For a low-birefringence LC mixture, if the operating temperature is far below its clearing point, the temperature-dependent refractive indices can be approximated as a parabolic form This prediction is also experimentally validated In addition, a linear relationship between 〈n2〉 and temperature is found
300 citations
TL;DR: An analysis for polarization-sensitive optical coherence tomography that facilitates the unrestricted use of fiber and fiber-optic components throughout an interferometer and yields sample birefringence, diattenuation, and relative optic axis orientation is presented.
Abstract: We present an analysis for polarization-sensitive optical coherence tomography that facilitates the unrestricted use of fiber and fiber-optic components throughout an interferometer and yields sample birefringence, diattenuation, and relative optic axis orientation. We use a novel Jones matrix approach that compares the polarization states of light reflected from the sample surface with those reflected from within a biological sample for pairs of depth scans. The incident polarization alternated between two states that are perpendicular in a Poincare sphere representation to ensure proper detection of tissue birefringence regardless of optical fiber contributions. The method was validated by comparing the calculated diattenuation of a polarizing sheet, chicken tendon, and muscle with that obtained by independent measurement. The relative importance of diattenuation versus birefringence to angular displacement of Stokes vectors on a Poincare sphere was quantified.
279 citations
TL;DR: A swept source based polarization-sensitive Fourier domain optical coherence tomography (FDOCT) system was developed that can acquire the Stokes vectors, polarization diversity intensity and birefringence images in biological tissue by reconstruction of both the amplitude and phase terms of the interference signal.
Abstract: A swept source based polarization-sensitive Fourier domain optical coherence tomography (FDOCT) system was developed that can acquire the Stokes vectors, polarization diversity intensity and birefringence images in biological tissue by reconstruction of both the amplitude and phase terms of the interference signal. The Stokes vectors of the reflected and backscattered light from the sample were determined by processing the analytical complex fringe signals from two perpendicular polarizationdetection channels. Conventional time domain OCT (TDOCT) and spectrometer based FDOCT systems are limited by the fact that the input polarization states are wavelength dependent. The swept source based FDOCT system overcomes this limitation and allows accurate setting of the input polarization states. From the Stokes vectors for two different input polarization states, the polarization diversity intensity and birefringence images were obtained.
246 citations
TL;DR: This work observed that in the intermediate regime there is a correlation among the negative sign of the effective index change, the presence of anisotropic reflection, and birefringence, and proposes a model that can explain all three principal characteristics.
Abstract: Although femtosecond lasers have proved to be of great utility for micromachining within bulk transparent materials, little is known about the fundamental physics that drive the process. Depending on the laser intensity delivered to the sample, any of three types of feature can be written into the glass. We observed that in the intermediate regime there is a correlation among the negative sign of the effective index change, the presence of anisotropic reflection, and birefringence. We propose a model that can explain all three principal characteristics. Results show that the local index change can be as high as 10-1.
246 citations
TL;DR: P polarization-sensitive optical coherence tomography (OCT) images of human skin in vivo are presented, demonstrating the ability of the technique to visualize and quantify the birefringent properties of skin.
Abstract: Optical coherence tomography enables cross-sectional imaging of tissue structure to depths of around 1.5 mm, at high-resolution and in real time. Incorporation of polarization sensitivity (PS) provides an additional contrast mechanism which is complementary to images mapping backscattered intensity only. We present here polarization-sensitive optical coherence tomography (OCT) images of human skin in vivo, demonstrating the ability of the technique to visualize and quantify the birefringent properties of skin. Variation in normal skin birefringence according to anatomical location is demonstrated, and discussed in relation to collagen distribution at each location. From measurements on a sample of five human volunteers, mean double-pass phase retardation rates of 0.340+/-0.143, 0.250+/-0.076, and 0.592+/-0.142 deg/microm were obtained for the dorsal hand, temple, and lower back regions, respectively. We demonstrate how averaging the Stokes parameters of backscattered light over a range of axial and lateral dimensions results in a reduction of speckle-induced noise. Examples of PS-OCT images from skin sites following wound healing and repair are also presented and discussed.
235 citations
TL;DR: Although free-space coupling experiments emphasize the similarity of these spicules to commercial optical fibers, the absence of any birefringence, the presence of technologically inaccessible dopants in the fibers, and their improved mechanical properties highlight the advantages of the low-temperature synthesis used by biology to construct these remarkable structures.
Abstract: Biological systems have, through the course of time, evolved unique solutions for complex optical problems. These solutions are often achieved through a sophisticated control of fine structural features. Here we present a detailed study of the optical properties of basalia spicules from the glass sponge Euplectella aspergillum and reconcile them with structural characteristics. We show these biosilica fibers to have a distinctive layered design with specific compositional variations in the glass/organic composite and a corresponding nonuniform refractive index profile with a high-index core and a low-index cladding. The spicules can function as single-mode, few-mode, or multimode fibers, with spines serving as illumination points along the spicule shaft. The presence of a lens-like structure at the end of the fiber increases its light-collecting efficiency. Although free-space coupling experiments emphasize the similarity of these spicules to commercial optical fibers, the absence of any birefringence, the presence of technologically inaccessible dopants in the fibers, and their improved mechanical properties highlight the advantages of the low-temperature synthesis used by biology to construct these remarkable structures.
229 citations
TL;DR: The fabrication of what is believed to be the first microstructured optical fibers with uniformly oriented elliptical holes with a high degree of hole ellipticity is reported with a simple technique that relies on hole deformation during fiber draw.
Abstract: We report the fabrication of what are believed to be the first microstructured optical fibers with uniformly oriented elliptical holes. A high degree of hole ellipticity is achieved with a simple technique that relies on hole deformation during fiber draw. Both form and stress-optic birefringence are characterized over a broad wavelength range. These measurements are in excellent agreement with numerical modeling and demonstrate a birefringence as high as 1.0×10-4 at a wavelength of 850 nm.
215 citations
TL;DR: In this article, a temperature-insensitive interferometer made from a HiBi-PCF fiber loop mirror (FLM) is achieved for the wavelength spacing of 0.43 nm, a wavelength spacing variation with temperature of only 0.05 pm/spl deg/C, and a transmission peak shift of
Abstract: Utilizing the high birefringence and the low-temperature coefficient of birefringence of the highly birefringent photonic crystal fiber (HiBi-PCF), a temperature-insensitive interferometer made from a HiBi-PCF fiber loop mirror (FLM) is achieved. For the wavelength spacing of 0.43 nm, a wavelength spacing variation with temperature of only 0.05 pm//spl deg/C, and a transmission peak shift of 0.3 pm//spl deg/C is demonstrated. The stability of the FLM is improved dramatically when it uses a HiBi-PCF, as compared to FLMs using conventional HiBi fibers.
211 citations
TL;DR: This work presents polarization sensitive B-scan images and to the best of the knowledge, the first 3D-data sets of retardation and fast axis orientation of fovea and optic nerve head region in vivo and the polarizing and birefringence properties of different retinal layers are studied.
Abstract: Recently, we developed a phase resolved polarization sensitive OCT system based on transversal scanning. This system was now improved and adapted for retinal imaging in vivo. We accelerated the image acquisition speed by a factor of 10 and adapted the system for light sources emitting at 820nm. The improved instrument records 1000 transversal lines per second. Two different scanning modes enable either the acquisition of high resolution B-scan images containing 1600×500 pixels in 500ms or the recording of 3D data sets by C-scan mode imaging. This allows acquiring a 3D-data set containing 1000×100×100 pixels in 10 seconds. We present polarization sensitive B-scan images and to the best of our knowledge, the first 3D-data sets of retardation and fast axis orientation of fovea and optic nerve head region in vivo. The polarizing and birefringence properties of different retinal layers: retinal pigment epithelium, Henle’s fiber layer, and retinal nerve fiber layer are studied.
210 citations
TL;DR: Knowing of the retardation and the slow axis distribution of the cornea might improve nerve fiber polarimetry for glaucoma diagnostics and could be useful for diagnosing different types of pathologies of the Cornea.
Abstract: Optical coherence tomography (OCT) is an emerging technology for high-resolution, noncontact imaging of transparent and scattering media. Polarization-sensitive optical coherence tomography (PS-OCT) is a functional extension of OCT that can image birefringent properties of a biological sample. PS-OCT was used to measure and image retardation and birefringent axis orientation of in vitro human cornea. We used a two-channel PS-OCT system employing a phase-sensitive recording of the interferometric signals in two orthogonal polarization channels. Using an algorithm based on a Hilbert transform, it is possible to calculate the retardation and the slow axis orientation of the sample with only a single A-scan per transversal measurement location. While the retardation information is encoded in the amplitude ratio of the two interferometric signals, the axis orientation is encoded entirely in their phase difference. We present maps of retardation and the distribution of slow axis orientation of the human cornea in longitudinal cross-sections and en face images obtained at the back surface of the cornea. The retardation increases in a radial direction and with depth; the slow axis varies in the transversal direction. Knowledge of the retardation and the slow axis distribution of the cornea might improve nerve fiber polarimetry for glaucoma diagnostics and could be useful for diagnosing different types of pathologies of the cornea.
200 citations
TL;DR: A fiber-based PS-OCT setup that produces real-time images of the human retina in vivo, coregistered with retinal video images of a healthy volunteer's location, shows that the nerve fiber layer located inferior and superior to the optic nerve head is more birefringent than the thinner layer of nerve fiber tissue in the temporal and nasal regions.
Abstract: Glaucoma causes damage of the nerve fiber layer, which may cause loss of retinal birefringence. Therefore, PS-OCT is a poten- tially useful technique for the early detection of glaucoma. We built a fiber-based PS-OCT setup that produces real-time images of the hu- man retina in vivo, coregistered with retinal video images of the lo- cation of PS-OCT scans. Preliminary measurements of a healthy vol- unteer show that the double-pass phase retardation per unit of depth of the RNFL is not constant and varies with location, with values between 0.18 and 0.37 deg/mm. A trend in the preliminary measure- ments shows that the nerve fiber layer located inferior and superior to the optic nerve head is more birefringent than the thinner layer of nerve fiber tissue in the temporal and nasal regions. © 2004 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1627774)
TL;DR: A novel optical coherence tomography method to measure backscattered intensity and birefringence properties (retardation and fast axis orientation) and apply it to imaging of human ocular tissue is presented and the first OCT images of retardation andFast axis orientation of the anterior chamber angle region in vivo are presented.
Abstract: We present a novel optical coherence tomography (OCT) method to measure backscattered intensity and birefringence properties (retardation and fast axis orientation) and apply it to imaging of human ocular tissue. The method is based on a Mach Zehnder interferometer, on transversal scanning, and on a polarization sensitive two-channel detection. A highly stable carrier frequency is generated by acousto-optic modulators (AOMs). This allows a phase sensitive demodulation by the lock-in technique. Since the recording of individual interference fringes is avoided by this method the amount of data to be recorded and processed is considerably reduced. We demonstrate this method on human cornea and anterior chamber angle and present, to the best of our knowledge, the first OCT images of retardation and fast axis orientation of the anterior chamber angle region in vivo.
TL;DR: Two novel devices for converting a linear polarization state to radial or azimuthal polarization states are realized by use of space-variant inhomogeneous media on a subwavelength scale, demonstrating high conversion efficiency.
Abstract: Novel devices for converting a linear polarization state to radial or azimuthal polarization states are realized by use of space-variant inhomogeneous media on a subwavelength scale. The two designs presented use form birefringence to locally transform the polarization state. The devices are fabricated in a GaAs substrate for operation in the far-infrared wavelength range. The experimental characterization is in good agreement with the designs, demonstrating high conversion efficiency.
TL;DR: This work reports on a polarization maintaining large mode area photonic crystal fiber, which is both single mode at any wavelength and have a practically constant birefringence for any wavelength.
Abstract: We report on a polarization maintaining large mode area photonic crystal fiber Unlike, previous work on polarization maintaining photonic crystal fibers, birefringence is introduced using stress applying parts This has allowed us to realize fibers, which are both single mode at any wavelength and have a practically constant birefringence for any wavelength The fibers presented in this work have mode field diameters from about 4 to 65 micron, and exhibit a typical birefringence of 15·10-4
TL;DR: In this paper, a polarization-sensitive Fourier domain optical coherence tomography (PS-FD-OCT) system is demonstrated, which is based on a spectral interferometer and enables phase information to be used in an OCT image.
Abstract: A polarization-sensitive Fourier domain optical coherence tomography (PS-FD-OCT) system is demonstrated. This OCT system is based on a spectral interferometer, does not require mechanical axial scanning, and enables phase information to be used in an OCT image. Owing to this phase information, the system requires only two measurements for determining the Jones matrix images and Muller images of biological samples. This system reveals the birefringence properties of the inner surface of a porcine esophagus.
TL;DR: In this paper, a planar waveguide echelle grating demultiplexers with 48 channels and 256 channels are described and demonstrated, which have a measured crosstalk of -35 dB, an insertion loss better than 4 dB, and a uniformity of 1 dB across the C-band.
Abstract: Silica planar waveguide echelle grating demultiplexers with 48 channels and 256 channels are described and demonstrated. Polarization effects due to stress birefringence and polarization-dependent grating efficiency have been eliminated using a modified polarization compensator and grating design. The devices have a polarization-dependent wavelength shift of less than 10 pm, and a polarization-dependent loss below 0.2 dB. The 48-channel device has a measured crosstalk of -35 dB, an insertion loss better than 4 dB, and a uniformity of 1 dB across the C-band.
TL;DR: Experimental results with beef tendon and rabbit tendon and muscle show that this technique has promising potential for imaging the birefringent structure of multiple-layer samples with varying optical axes.
Abstract: Conventional polarization-sensitive optical coherence tomography (PS-OCT) can provide depth-resolved Stokes parameter measurements of light reflected from turbid media. A new algorithm that takes into account changes in the optical axis is introduced to provide depth-resolved birefringence and differential optical axis orientation images by use of fiber-based PS-OCT. Quaternion, a convenient mathematical tool, is used to represent an optical element and simplify the algorithm. Experimental results with beef tendon and rabbit tendon and muscle show that this technique has promising potential for imaging the birefringent structure of multiple-layer samples with varying optical axes.
TL;DR: It is shown that phase-matching is achieved in properly engineered waveguides where birefringence compensates for material dispersion and the sensitivity of the phase mismatch to fabrication-induced errors in waveguide dimensions is quantified.
Abstract: The efficiency of four-wave-mixing arising from Raman and non-resonant nonlinear susceptibilities in silicon waveguides is studied in the 1.3–1.8µm regime. The wavelength conversion efficiency is dominated by the Raman contribution to the nonlinear susceptibility, and high conversion efficiencies can be achieved under the phase-matching condition. In this context, dispersion in silicon waveguides is analyzed and it is shown that phase-matching is achieved in properly engineered waveguides where birefringence compensates for material dispersion. Finally the sensitivity of the phase mismatch to fabrication-induced errors in waveguide dimensions is quantified.
TL;DR: In this article, the physical properties of high birefringence isothiocyanato biphenyl-bistolane liquid crystals were evaluated and a eutectic mixture based on those compounds was formulated and its physical properties evaluated.
Abstract: We have designed, synthesized, and evaluated the physical properties of some high birefringence (Δn) isothiocyanato biphenyl-bistolane liquid crystals. These compounds exhibit Δn~0.7–0.8 at room temperature and wavelength λ=633 nm. Laterally substituted short alkyl chains and fluorine atom eliminate smectic phase and lower the melting temperature. The moderate melting temperature and very high clearing temperature make those compounds attractive for eutectic mixture formulation. A eutectic mixture based on those compounds was formulated and its physical properties evaluated. The simulated absorption spectra agree reasonably well with the measured results.
TL;DR: Tunable phase shift up to 360 degrees at 1 THz is achieved with a liquid crystal (LC) device using a nematic LC, E7, which exhibits a birefringence of ~ 0.17.
Abstract: Tunable phase shift up to 360° at 1 THz is achieved with a liquid crystal (LC) device. The key to this design is (1) the use of a nematic LC, E7, which exhibits a birefringence of ~0.17 (0.2–1.2 THz); (2) a LC cell (3-mm in thickness) with sandwiched structure to increase the interaction length while minimizing interface Fresnel losses; and (3) the use of magnetic field to align the thick LC cell and achieve continuous tuning of phase from 0 to 360°. This device can be operated over a broad range near room temperature.
TL;DR: Two exemplary liquid crystal mixtures are formulated, designated as UCF-1 andUCF-2, and their physical properties are compared with a commonly used commercial liquid crystal compound 5CB, showing high birefringence and low clearing temperature play crucial roles.
Abstract: We have analyzed the physical origins of the temperature gradient of the ordinary refractive index ( dn(o) /dT) of liquid crystals. To achieve a large dn(o) /dT , high birefringence and low clearing temperature play crucial roles. Based on these simple guidelines, we formulated two exemplary liquid crystal mixtures, designated as UCF-1 and UCF-2, and compared their physical properties with a commonly used commercial liquid crystal compound 5CB. The dn(o) /dT of UCF-1 is ~4X higher than that of 5CB at room temperature.
TL;DR: Frozen-in viscoelasticity was only recently found to be an important draw-induced inelastic strain that can significantly perturb the refractive index profile and hence the waveguiding properties of optical fibers as mentioned in this paper.
Abstract: Frozen-in stresses and strains can significantly impact both the optical and mechanical performance of optical fibers, enabling unique functionalities or leading to serious impairments. Frozen-in strains can be grouped into two general categories: those directly inducing strong birefringence, which are associated with residual elastic stresses; and those inducing a substantially isotropic index perturbation, which can be described as inelastic frozen-in strains. Both types of frozen-in strains can be simultaneously present in the same optical fiber. Frozen-in viscoelasticity was only recently found to be an important draw-induced inelastic strain that can significantly perturb the refractive index profile and hence the waveguiding properties of optical fibers. The optical and mechanical effects of both types of frozen-in stresses and strains are reviewed. Both practical applications as well as impairments are discussed.
TL;DR: A highly birefringent photonic crystal fibre has been characterised as a function of temperature and has been found to be independent of temperature from -25 to 800 degrees C.
Abstract: A highly birefringent photonic crystal fibre has been characterised as a function of temperature. The modal birefringence has been found to be independent of temperature from -25 to 800 °C.
TL;DR: In this article, a hollow core photonic band-gap fiber with very high group birefringence was fabricated and characterized, and two independent methods, wavelength scanning and direct measurement of differential group delay (DGD), were used to obtain the group beatlength and group bilinearity.
Abstract: A hollow-core photonic band-gap fiber with very high group birefringence is fabricated and characterized. Two independent methods, wavelength scanning and direct measurement of differential group delay (DGD), are used to obtain the group beatlength and group birefringence. The fiber illustrates a very high group birefringence of 0.025 at 1550 nm. The wavelength dependence of the group beatlength and group birefringence are also analyzed.
Patent•
18 Nov 2004TL;DR: In this article, a source of light having a variable frequency with a polarization state which varies linearly with frequency is provided as an input to the device under test, and the combined light for the frequencies of interest is split into two orthogonal polarizations which are then detected in a spectral acquisition apparatus and supplied to a microprocessor.
Abstract: In order to characterize the optical characteristics of a device, a source of light having a variable frequency with a polarization state which varies linearly with frequency is provided as an input to the device under test. The input light is also passed through a known reference path and is added to the light output from the device under test in a beam combiner. The combined light for the frequencies of interest is split into two orthogonal polarizations which are then detected in a spectral acquisition apparatus and supplied to a microprocessor. The spectral measurements are digitized and curve-fitted to provide optical power versus optical frequency curves. Fourier transforms of each of the curves are calculated by the microprocessor. From the Fourier transforms, the four arrays of constants are calculated for the Jones matrix characterizing the device under test.
TL;DR: Numerical simulations with a full vectorial beam propagation method demonstrate that it is possible to obtain a 1.9-mm-long splitter with the extinction ratio better than -20 dB and a bandwidth of 37nm.
Abstract: A novel design of polarization splitter in three-core photonic crystal fibers (PCFs) has been proposed. The three-core PCF consists of two given identical cores with two-fold symmetry separated by a core with high birefringence. The polarization splitter is based on the phenomenon of resonant tunneling. Numerical simulations with a full vectorial beam propagation method demonstrate that it is possible to obtain a 1.9-mm-long splitter with the extinction ratio better than -20 dB and a bandwidth of 37 nm.
TL;DR: In this tutorial review, recent developments in the measurement of the principal crystallo-optical quantities including linear birefringence, linear dichroism, circular bire furringence, and circular dichROism are reviewed.
Abstract: Classical crystal optics has recently undergone a renaissance as developments in optical microscopy and polarimetry, enabled in part by sensitive imaging CCD cameras and personal computers, now permit the analytical separation of various optical effects that are otherwise convolved in polarized light micrographs. In this tutorial review, we review recent developments in the measurement of the principal crystallo-optical quantities including linear birefringence, linear dichroism, circular birefringence, and circular dichroism, as well as new effects in crystal optics encountered in unusual mixed crystals. The new microscopies and polarimetries are applied to problems of crystallographic twinning, phase transformations, stress birefringence, symmetry reduction, and the design of new crystalline materials.
TL;DR: By annealing the sample, this work reduces the losses by approximately 30% (at 633 nm) and decreases the birefringence by a factor of 4 in fused silica.
Abstract: We identify two states of stress induced in waveguides fabricated by femtosecond lasers in fused silica and show how they can be relieved by annealing. In-plane stress and stress concentration are revealed through birefringence and loss measurements. Another kind of laser-induced stress appears in the form of swelling of the glass surface when waveguides are written near the surface and is a manifestation of confined rapid material quenching. By annealing the sample we reduce the losses by ∼30% (at 633 nm) and decrease the birefringence by a factor of 4 in fused silica.
Patent•
05 Apr 2004TL;DR: An organic EL cell is formed to satisfy the expression (1): B 0
Abstract: An organic EL cell is formed to satisfy the expression (1): B 0
TL;DR: In this article, a numerical study of the polarization properties of the broadband supercontinuum (SC) generated in birefringent photonic crystal fibers (PCFs) is presented.
Abstract: We present a numerical study of the polarization properties of the broadband supercontinuum (SC) generated in birefringent photonic crystal fibers (PCFs). The simulations are based on generalized coupled nonlinear Schrodinger equations with quantum noise taken into account. The simulations illustrate the complicated polarization behavior in the SC spectra and show that the pulse-to-pulse polarization state of SC spectra fluctuates because of vector modulation instability. We investigate the polarization stability and uniformity of SC spectra under several simulation conditions and discuss generation of the SC in birefringent PCFs for applications with various polarization requirements.