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Artificial Metamaterials, Metasurfaces, and Their Applications
Published in Song Sun, Wei Tan, Su-Huai Wei, Emergent Micro- and Nanomaterials for Optical, Infrared, and Terahertz Applications, 2023
Polarization state represents one of the most fundamental properties of electromagnetic waves, which conveys valuable information for many photonic applications, such as communication, sensing and imaging. Conventional methods to control polarization rely on birefringent materials with bulky sizes and limited performance. Metasurfaces have garnered intense research attentions in recent years for polarization control owing to their great capabilities and flexibilities in electromagnetic wave control. In this section, we mainly focus on the progress of metasurface-based polarization conversion, including linear-to-circular polarization conversion and polarization rotation.
Fiber Optics
Published in Lazo M. Manojlović, Fiber-Optic-Based Sensing Systems, 2022
The polarization state of the propagating wave cannot be maintained along the standard fiber. Therefore, to maintain the polarization state, one can try to reduce the birefringence. However, this can be hard to achieve, even if the built-in tension can be suppressed during the manufacturing process, there is still no control over bending the fiber by the users. As it is not possible to suppress the birefringence to the negligible levels, one can try to do quite opposite by making the fibers intentionally with large birefringence. One can make such fibers by introducing an asymmetric core structure such as elliptic core or insert additional structural elements that break the fiber circular symmetry. By inserting elements with a slightly different thermal expansion coefficient, where during the cooling of the glass of the fiber, a mechanical stress has been built into the fiber, the symmetry of the fiber is broken. Typical structures of such polarization-maintaining fibers are presented in Figure 5.14.
Properties of Starch and Modified Starches
Published in Jean-Luc Wertz, Bénédicte Goffin, Starch in the Bioeconomy, 2020
Jean-Luc Wertz, Bénédicte Goffin
Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light.5 Birefringence is responsible for the phenomenon of double refraction whereby a ray of light, when incident upon a birefringent material, is split by polarization into two rays taking slightly different paths.6 Hence, birefringence is the ability to doubly refract polarized light.2, 7
Design of a Terahertz Alcohol Sensor Using a Steering-Wheel Microstructured Photonic Crystal Fiber
Published in IETE Journal of Research, 2023
In the previous sections, we have discussed the important physical parameters for determining the relative sensitivity and robustness of the proposed sensor. Now, in this section, we turn to compute the birefringence exhibited by the proposed SW PCF. It is well known that the birefringence is an optical property that depends on the polarization and propagation of light in an optical fiber [30]. Birefringence can be calculated from the refractive index differences between the two orthogonal polarization modes. We find that there are two basic orthogonal polarization modes (HEx and HEy) during the propagation. The degree of modal birefringence can be calculated using the following expression [30]: Here, the physical parameter B(λ), , represent the modal birefringence and the effective refractive indices of the x(horizontal) and y(vertical) polarization modes, respectively. Figure 7 shows the variation of birefringence against frequency for water, ethanol and benzene. From Figure 7, it is clear that the induced birefringence increases with operating frequency. Here, the birefringence is 0.00265, 0.00208 and 0.00179 for water, ethanol and benzene, respectively at 2.1 THz frequency. However, the maximum birefringence can be achieved for frequencies other than optimized one.
Optical characterisation of dyed liquid crystal cells
Published in Liquid Crystals, 2022
Obeng Appiagyei Addai, Ruilin Xiao, Xiaoyu Zheng, Peter Palffy-Muhoray
Liquid crystals are typically birefringent, as are oriented dichroic dyes. When the transmittance of a mixture is measured with the polarisation of incident light either parallel or perpendicular to the LC director, only one principal refractive index contributes to the transmittance. The alignment of LCs and dye mixtures was confirmed by applying a voltage across the cell. Since the LC has a negative dielectric anisotropy at low frequency, no change in orientation is expected, and none was observed.
Temperature dependence of 2V angle in biaxial negative and positive nematic lyotropic phases
Published in Phase Transitions, 2019
D. D. Luders, W. S. Braga, O. R. Santos, A. R. Sampaio, N. M. Kimura, M. Simões, A. J. Palangana
We remember that the anisotropic part of the optical susceptibility of these lyotropic nematic materials may be expressed as a function of the optical birefringence () which has been considered as an important macroscopic order parameter [14, 40]. The laboratory frame axes are defined with the boundary surfaces parallel to the 1−2 plane and 3 is the axis normal to the biggest surface of the sample cell, with axis parallel to the length (width) of the cells [14, 30, 41]. Optical birefringence () is positive in an phase and () is negative in an phase, where () is the extraordinary (ordinary) refractive index defined for plane wave traveling in a uniaxial nematic medium with the polarization parallel () or perpendicular (⊥) to the optic axis of the nematic sample. The change of sign of optical birefringence, determined in these uniaxial nematic lyotropic phases, is related to the fact that the hydrocarbon chains of the amphiphile molecules in the phase are oriented parallel to the director; whereas, in the phase, the hydrocarbon chains of the amphiphile molecules are oriented perpendicular to the director [42, 43]. In addition, the () phase presents negative (positive) anisotropy of diamagnetic susceptibility [2–5]. This means that homeotropic (planar) alignment of the () phase can be obtained via magnetic field interaction.