Birefringent Core Research Articles

Sagnac Interferometer Based on a Highly-Birefringent Two-Core PCF: Theory, Experiment, and Sensing Characteristics

In this article, we present comparative study on the transmission and the sensing characteristics of an all-fiber Sagnac loop interferometer (SLI) made by different kinds of the highly-birefringent (HB) two-core photonic crystal fiber (TCPCF), respectively for strain, torsion, and temperature sensing. The fiber device is analyzed theoretically and experimentally. Transmission spectrum of the SLI using the HB TCPCF shows six spatial frequencies due to superposition of multiple two-beam interferences originating from the intra-core and the inter-core interactions between the fundamental polarization modes propagating in the two birefringent cores. Our results reveal that the transmission characteristics of the fiber device and the sensing features of its multiplexed interferences are strongly dependent on the optical and the structural properties of the two birefringent cores such as their intrinsic birefringences, the effective index contrast between them, and the relative orientation between the (slow) birefringence axes. Finally, the application of the SLI made by the specific HB TCPCF is discussed in the simultaneous measurement of three parameters.

Geochemistry of major and rare earth elements in garnet of the Kal-e Kafi skarn, Anarak Area, Central Iran: Constraints on processes in a hydrothermal system

Grossular-andradite (grandite) garnets, precipitated from hydrothermal solutions is associated with contact metamorphism in the Kal-e Kafi skarn show complex oscillatory chemical zonation. These skarn garnets preserve the records of the temporal evolution of contact metasomatism. According to microscopic studies and microprobe analysis profiles, the studied garnet has two distinct parts: the intermediate (granditic) composition birefringent core that its andradite content based on microprobe analysis varies between 0.68–0.7. This part is superimposed with more andraditic composition, and the isotropic rim which its andradite content regarding microprobe analysis ranges between 0.83–0.99. Garnets in the studied sample are small (0.5–2 mm in diameter) and show complex oscillatory zoning. Electron microprobe analyses of the oscillatory zoning in grandite garnet of the Kal-e Kafi area showed a fluctuation in chemical composition. The grandite garnets normally display core with intermediate composition with oscillatory Fe-rich zones at the rim. Detailed study of oscillatory zoning in grandite garnet from Kal-e Kafi area suggests that the garnet has developed during early metasomatism involving monzonite to monzodiorite granitoid body intrusion into the Anarak schist- marble interlayers. During this metasomatic event, Al, Fe, and Si in the fluid have reacted with Ca in carbonate rocks to form grandite garnet. The first step of garnet growth has been coeval with intrusion of the Kal-e Kafi granitoid into the Anarak schist- marble interlayers. In this period of garnet growth, change in fluid composition may cause the garnet to stop growing temporarily or keep growing but in a much slower rate allowing Al to precipitate rather than Fe. The next step consists of pervasive infiltration of Fe rich fluids and Fe rich grandite garnets formation as the rim of previously formed more Al rich garnets. Oscillatory zoning in the garnet probably reflects an oscillatory change in the fluid composition which may be internally and/or externally controlled. The rare earth elements study of these garnets revealed enrichment in light REEs (LREE) with a maximum at Pr and Nd and a negative to no Eu anomaly. This pattern is resulted from the uptake of REE out of hydrothermal fluids by growing crystals of calcsilicate minerals principally andradite with amounts of LREE controlled by the difference in ionic radius between Ca++ and REE3+ in garnet x site.

Circular and elliptical birefringence in spun microstructured optical fibres

We investigate circular birefringence induced by spinning microstructured optical fibres during their fabrication to produce helical-shaped holes. Designs with an offset core which results in a helical path for the light and exhibit only circular birefringence and designs with a linearly birefringent core that result in elliptical birefringence are both investigated.

Self‐Assembled Cylindrical Lipid Tubules with a Birefringent Core

Optical anisotropic fibers with straight, zigzag, and loop shapes were fabricated by filling hollow cylindrical lipid tubules with nematic liquid crystals (see Figure). The optical anisotropy of the filled lipid tubules was examined by a polarizing optical microscope. Due to the tunable refractive index of nematic liquid crystals, tubules with liquid-crystal cores have potential application in sensors, photonic devices, and optical communications.

PCF-based polarization splitters with simplified structures

We propose novel polarization splitters based on photonic crystal fibers (PCFs), in which the cores of the splitters are nearly nonbirefringent. Different from conventional fiber-based polarization splitters, the birefringence in the new splitters results mainly from narrow silica regions physically connecting the two cores. This means that polarization splitting can be achieved without employing highly birefringent cores, which provides a possibility to greatly simplify the structures of the PCF-based polarization splitters and make them more practical. A 5-mm-long splitter with an extinction ratio of 20 dB has been obtained. We also discuss how the silica regions influence coupling characteristics of the dual-core PCFs and present a design guidance for the polarization splitters based on polarization-dependent coupling.

A Novel Polarization Splitter Based on the Photonic Crystal Fiber With Nonidentical Dual Cores

A novel polarization splitter based on photonic crystal fibers (PCFs) with two nonidentical cores is proposed. The two highly birefringent cores are vertically arranged to obtain polarization selective coupling. The horizontal polarization exchanges its energy between the two cores. However, the vertical polarization shows little coupling between the two cores. This is achieved in single-material glass waveguides for the first time to our knowledge. The PCF-based polarization splitter exhibits many advantages such as shorter length, high extinction ratio, and wide bandwidth over its counterparts.

Swelling-Induced Birefringence of a Polyelectrolyte Gel Strongly Interacting with Metal Ions

The swelling behavior of a polyelectrolyte gel in aqueous salt solutions is studied in the case where metal ions are binding with polyions, forming insoluble compounds. The hydrogel swelling and contraction in such solutions and the metal ion penetration inside the network are monitored by polarizing optical microscopy. The growth of an insoluble layer on the surface of the gel particle is accompanied by the formation of a birefringent core. Changes of the thickness of the birefringent layer with time and the dependence of the birefringence on salt concentration are discussed.

Genesis of subsurface horizons of a soil catena in a humid tropical climate (Yaounde, Cameroon)

Summary A soil catena situated between the summit and the footslope of an inselberg in the South-Cameroon has been studied. The b-fabric of the B-horizons of the catena is dominantly circular striated. This is due to the packing of micropeds consisting of a non or weakly birefringent core and a birefringent wall. Clay and Fe oxyhydroxides are the main constituents of the micropeds. The birefringent microped wall consists of easily dispersible (E.D.) clay. The micropeds, mainly those of the upper soil horizons ( As a result of microstructurolysis on the one hand and the formation of zoogeneous micropeds close to the soil surface on the other a so-called consistency horizon develops in the transition zone between the A- and the B-horizons. In sloping positions in the landscape a lateral water flow develops on top of the consistency horizon and less water prcolates through the profile. E.D. clay is transported in the lateral water flow causing “appauvrissement” (impoverishment). Depending on the amount of percolation water and in this way, depending on the slope gradient and on the position in the landscape a color B-(cambic) horizon, a textural B-(argillic) horizon or a ferrallitic B-(oxic) horizon may be formed.

Studies on the microtubules in heliozoa. II. The effect of low temperature on these structures in the formation and maintenance of the axopodia.

When specimens of Actinosphaerium nucleofilum are placed at 4 degrees C, the axopodia retract and the birefringent core (axoneme) of each axopodium disappears. In fixed specimens, it has been shown that this structure consists of a highly patterned bundle of microtubules, each 220 A in diameter; during cold treatment these microtubules disappear and do not reform until the organisms are removed to room temperature. Within a few minutes after returning the specimens to room temperature, the axonemes reappear and the axopodia begin to reform reaching normal length 30-45 min later. In thin sections of cells fixed during the early stages of this recovery period, microtubules, organized in the pattern of the untreated specimens, are found in each reforming axopodium. Reforming axopodia without birefringent axonemes (and thus without microtubules) are never encountered. From these observations we conclude that the microtubules may be instrumental not only in the maintenance of the axopodia but also in their growth. Thus, if the microtubules are destroyed, the axopodia should retract and not reform until these tubular units are reassembled. During the cold treatment short segments of a 340-A tubule appeared; when the organisms were removed from the cold, these tubular segments disappeared. It seems probable that they are one of the disintegration products of the microtubules. A model is presented of our interpretation of how a 220-A microtubule transforms into a 340-A tubule and what this means in terms of the substructure of the untreated microtubules.