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Closed Light Paths in Equiangular Spiral Disks  [PDF]
Eckhard Hitzer
Physics , 2013, DOI: 10.1007/s00006-000-0005-z
Abstract: A new type of deformation for microscopic laser disks, the \textit{equiangular spiral deformation} is proposed. First a short review of the geometry of light paths in equiangular spirals in the language of real two-dimensional geometric calculus is given. Second, the constituting equations for \textit{closed paths} inside equiangular spirals are derived. Third, their numerical solution is performed and found to yield two generic types of closed light paths. \textit{Degenerate} closed paths that exist over large intervals of the deformation parameter, and \textit{nondegenerate} closed paths which only exist over relatively small deformation parameter intervals spanning less than 1% of the nondegenerate intervals. Fourth, amongst the nondegenerate paths a \textit{stable asymmetric bow-tie} shaped light trajectory was found.
Wideband Measurement in a Small Shielded Box Using Equiangular Spiral Antennas
T. Korinek,P. Piksa,M. Mazanek
Radioengineering , 2006,
Abstract: Small shielded boxes are nowadays widely used for measurement of EMS, EMI and sensitivity properties of different devices. This paper deals with an improvement of commercial small shielded box parameters for a measurement of sensitivity of small mobile devices in 650 MHz to 4 GHz frequency band. Optimization of shielded box parameters is obtained by an inner area modification. Suitable wideband equiangular spiral antenna was designed for this measurement. Parameters of antenna inside the box, such as gain, impedance, directivity etc. are discussed in the paper. Effects of antenna positions in the box for a transmission are shown and the best configuration of antennas placing for the transmission in the shielded box is chosen.
The Geometry of Light Paths for Equiangular Spirals  [PDF]
Eckhard Hitzer
Physics , 2013, DOI: 10.1007/BF03042381
Abstract: First geometric calculus alongside its description of equiangular spirals, reflections and rotations is introduced briefly. Then single and double reflections at such a spiral are investigated. It proves suitable to distinguish incidence from the \textit{right} and \textit{left} relative to the radial direction. The properties of geometric light propagation inside the equiangular spiral are discussed, as well as escape conditions and characteristics. Finally the dependence of right and left incidence from the source locations are examined, revealing a well defined inner \textit{critical} curve, which delimits the area of purely right incident propagation. This critical curve is self similar to the original equiangular spiral.
Highly Nonlinear and Birefringent Spiral Photonic Crystal Fiber  [PDF]
S. Revathi,Srinivasa Rao Inbathini,Rizwan Ali Saifudeen
Advances in OptoElectronics , 2014, DOI: 10.1155/2014/464391
Abstract: We propose and design a spiral photonic crystal fiber with elliptical air holes for achieving high birefringence, large nonlinearity, and negative dispersion. The structure is designed using chalcogenide glass (As2S3) for different ellipticity ratios of air holes in the cladding and the effect on various properties is observed. The proposed structure has birefringence of the order 10?2, nonlinearity of 26739.42?W?1?m?1, and dispersion of ?1136.69 at 0.85?μm. An accurate numerical approach based on finite element method is used for the design and simulation of the structure. Due to high birefringence and negative dispersion, the proposed structure can be used for polarization control and dispersion compensation, respectively. 1. Introduction Photonic crystal fiber is a class of optical fiber which is based on the properties of photonic crystal. Due to its unique properties photonic crystal fiber finds a lot of applications in optical fiber communication [1]. In standard fiber, the guiding mechanism is by a region with higher refractive index than the surrounding cladding. In case of PCFs, the microstructure of core and air holes surrounding it provide the required index difference. The basic principle of operation of a PCF is based either on modified total internal reflection in which light is guided in solid core which depends on the relative refractive index difference between the core and the microstructure cladding or on photonic band gap effect in which light is confined by a photonic band gap that is created by the microstructure cladding [2–4]. Such fiber allows the propagation of light through lower index core or even through hollow core. Compared to conventional fiber, PCFs provide large freedom in the design which allows the flexibility in various properties including birefringence, flattened and negative dispersion, effective area, and nonlinearity. Apart from the conventional hexagonal lattice, different types of air hole arrangements are proposed for achieving many useful properties [5–7]. In equiangular spiral photonic crystal fiber, the air holes are distributed around the solid core so that the arrangement gives a spiral pattern. The design parameters for spiral PCF include number of spiral arms, number of air holes in each spiral arm, and core diameter. Various useful properties can be obtained by tailoring these parameters to the PCF design. Equiangular spiral PCF (ES-PCF) with small effective area and large nonlinearity has been reported [8]. Spiral PCF with elliptical core is designed [9] which has large birefringence and
Terahertz Waveguiding in Silicon-Core Fibers  [PDF]
Derek A. Bas,Scott K. Cushing,John Ballato,Alan D. Bristow
Physics , 2013,
Abstract: We propose the use of a silicon-core optical fiber for terahertz (THz) waveguide applications. Finite-difference time-domain simulations have been performed based on a cylindrical waveguide with a silicon core and silica cladding. High-resistivity silicon has a flat dispersion over a 0.1 - 3 THz range, making it viable for propagation of tunable narrowband CW THz and possibly broadband picosecond pules of THz radiation. Simulations show the propagation dynamics and the integrated intensity, from which transverse mode profiles and absorption lengths are extraced. It is found that for 140 - 250 micron core diameters the mode is primarily confined to the core, such that the overall absorbance is only slightly less than in bulk polycrystalline silicon.
Specialty Fibers for Terahertz Generation and Transmission: A Review  [PDF]
Ajanta Barh,B. P. Pal,G. P. Agrawal,R. K. Varshney,B. M. A. Rahman
Physics , 2015,
Abstract: Terahertz (THz) frequency range, lying between the optical and microwave range covers a significant portion of the electro-magnetic spectrum. Though its initial usage started in the 1960s, active research in the THz field started only in the 1990s by researchers from both optics and microwaves disciplines. The use of optical fibers for THz application has attracted considerable attention in recent years. In this article, we review the progress and current status of optical fiber-based techniques for THz generation and transmission. The first part of this review focuses on THz sources. After a review on various types of THz sources, we discuss how specialty optical fibers can be used for THz generation. The second part of this review focuses on the guided wave propagation of THz waves for their transmission. After discussing various wave guiding schemes, we consider new fiber designs for THz transmission.
Probing Terahertz Metamaterials with Subwavelength Optical Fibers  [PDF]
Martin Girard,Maksim Skorobogatiy
Physics , 2013, DOI: 10.1364/OE.21.017195
Abstract: Transmission through a subwavelength terahertz fiber, which is positioned in parallel to a frequency selective surface, is studied using several finite element tools. Both the band diagram technique and the port-based scattering matrix technique are used to explain the nature of various resonances in the fiber transmission spectrum. First, we observe that spectral positions of most of the transmission peaks in the port-based simulation can be related to the positions of Van Hove singularities in the band diagram of a corresponding infinite periodic system. Moreover, spectral shape of most of the features in the fiber transmission spectrum can be explained by superposition of several Fano-type resonances. We also show that center frequencies and bandwidths of these resonances and, as a consequence, spectral shape of the resulting transmission features can be tuned by varying the fiber-metamaterial separation.
Equiangular Frames and Signature Sets  [PDF]
Preeti Singh
Mathematics , 2009,
Abstract: We will present a relation between real equiangular frames and certain special sets in groups which we call signature sets and show that many equiangular frames arise in this manner. Then we will define quasi-signature sets and will examine equiangular frames associated to these subsets of groups. We will extend these results to complex equiangular frames where the inner product between any pair of vectors is a common multiple of a cube root of unity and exhibit equiangular frames that arise from groups in this manner.
Low loss, low dispersion and highly birefringent terahertz porous fibers  [PDF]
Shaghik Atakaramians,Shahraam Afshar V.,Bernd M. Fischer,Derek Abbott,Tanya M. Monro
Physics , 2008, DOI: 10.1016/j.optcom.2008.09.058
Abstract: We demonstrate that porous fibers have low effective material loss over an extended frequency range, 4.5 times larger bandwidth than that can be achieved in sub-wavelength solid core fibers. We also show that these new fibers can be designed to have near zero dispersion for 0.5-1 THz resulting to overall less terahertz signal degradation. In addition, it is demonstrated that the use of asymmetrical sub-wavelength air-holes within the core leads to high birefringence ~0.026. This opens up the potential for realization of novel polarization preserving fibers in the terahertz regime.
Graded Index Microstructured Polymer Optical Fibers for Terahertz Applications  [PDF]
Tian Ma,Andrey Markov,Lili Wang,Maksim Skorobogatiy
Physics , 2014,
Abstract: Graded index microstructured polymer optical fiber incorporating a specially designed air-hole array featuring variable air-hole diameters and inter-hole separation is proposed, fabricated and characterized in view of the fiber potential applications in low-loss, low-dispersion terahertz guidance. The proposed fiber features simultaneously low chromatic and intermodal dispersions, as well as low loss in the terahertz spectral range. We then experimentally demonstrate that proposed fibers exhibit smaller pulse distortion, larger bandwidth and more reliable excitation when compared to the porous fibers of comparable geometry.
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