Inherent Birefringence Research Articles

Birefringence Properties of Polymeric Substrate Materials

Depending upon the nature of the application, three materials currently dominate the optical substrate market today. Polycarbonate (PC), the most commonly used material, is typically used in disks with diameters up to 120 mm. For larger diameters, the inherent birefringence exhibited by PC interacts with the read laser and results in errors in the read-back signal. For 200 mm and greater, both polymethylmethacrylate (PMMA) and glass are used. Because PMMA is low in inherent birefringence, it is widely used for 200 mm video disks, an application which takes advantage of the manufacturing economies of the injection molding process. For larger diameter data storage disks, however, glass is used because it does not have the disadvantage of relatively high moisture absorption or the low heat resistance of PMMA.This article will deal with the state-of-the-art in materials used for polymeric substrates. It will focus primarily on polycarbonate and the most significant substrate property currently confronting the field, namely birefringence. Other constraints placed by optical storage technology on the substrate material will be discussed along with new materials and research activities aimed at circumventing some of the current limitations.

Stress-optic effects, birefringence, and reduction of birefringence by annealing in fiber Fabry-Perot interferometers

The effects of inherent fiber birefringence, packaging stresses, and stress tuning on the behavior of a fiber Fabry-Perot interferometer are examined. A polarization doublet due to birefringence is observed. For birefringence of 1 ps/km, the doublet spacing is 40 MHz, at 1.5- mu m wavelength, independent of the FFP finesse or free spectral range, and is due mainly to the inherent fiber birefringence. It was found that annealing depressed-cladding single-mode fiber reduced the fiber birefringence, for example, from 40-80 MHz to 15-25 MHz. Where the bandpass of the FFP is greater than the birefringence doublet, this device should be polarization insensitive for most applications. >

Linear dichroism of molecules with cubic symmetry

Linear dichroism (LD) of chromophores which belong to the cubic point group of symmetry has been observed. The molecules CrO 2− 4, Fe(CN) 3− 6 and Mo(CO) 6 were dissolved in several lyotropic liquid crystals. These systems can be macroscopically aligned which is a prerequisite in LD spectroscopy. The observed LD is ascribed to distortions of the cubic symmetry caused by the uniaxial constraints in the liquid crystals. Contributions to the LD due to the inherent optical birefringence of the systems were taken into account. Furthermore, NMR of CrO 2− 4 and ESR of Mn 2+ in various lyotropic liquid crystals strongly support that the symmetry is distorted.

Optical Artifacts in Circularly Polarized Luminescence Spectroscopy

The source of optical artifacts in circularly polarized luminescence is examined by application of the method of Mueller matrices. Expressions for the circularly polarized luminescence intensity are developed that illustrate that the source of the artifact in most cases is due to the small inherent birefringence in the photoelastic modulator employed in the experimental measurement. Experimental results are presented that are consistent with this conclusion.

Thin-film waveguide magneto-optic isolator

A thin-film waveguide Faraday rotator which provides nonreciprocal polarization rotation of ±45° for light of wavelength 1.45 μm with an extinction ratio of 500:1 has been demonstrated. This isolator structure makes use of laser annealing to reverse the sublattice magnetization and hence the sign of the Faraday effect in localized regions of a (Bi, Ga) yttrium iron garnet film. A novel geometrical pattern was designed for these regions to overcome the effects of the inherent thin-film birefringence.

Influence of orientation on polyester fibres

AbstractThe technological applications and the associated molecular mechanisms of various levels of orientation in polyester fibres are discussed. The inherent birefringence of these fibres is high and therefore the orientation is easily measurable, while their behaviour is very sensitive to small changes in orientation. In particular, practical properties such as strength, productivity and ease of bulking are very dependent on the spun yarn orientation before the drawing operation takes place, but for completely different reasons. Polyester fibres can be pretreated in terms of orientation in such a way that an extremely high spontaneous extension can be obtained, a property which can be used for bulking. It is shown that variations in low levels of orientation can have profound industrial implications.

Simultaneous changes in fluorescence and optical retardation in single muscle fibres during activity.

WHEN a skeletal muscle is stimulated to twitch, small changes in the optical properties of the fibres can be detected which may give information about excitation–contraction coupling. An example is provided by the experiments of Bezanilla and Horowicz1,2. After treatment of muscles with Nile Blue A, fluorescence changes were found which, it was suggested, arise from changes in potential across the membranes of the sarcoplasmic reticulum (SR). Such potential changes might reflect the movement of calcium ions from inside the SR into the myoplasm, a step in the normal activation of contraction. Baylor and Oetliker3,4 measured changes in optical retardation, which rely on the inherent birefringence of a muscle fibre rather than the addition of an extrinsic probe. The large second component of the signal was suggested to arise from a change in SR membrane potential. These explanations are plausible since small changes in both extrinsic fluorescence and optical retardation are known to accompany voltage changes across neuronal membranes5–8. An important test of these hypotheses is to compare the fluorescence and retardation signals from the same fibre, to see if they follow the same time course.