Stacking the Equiangular Spiral

We present an algorithm that adapts the mature Stack and Draw (SaD) methodology for fabricating the exotic Equiangular Spiral Photonic Crystal Fiber. (ES-PCF) The principle of Steiner chains and circle packing is exploited to obtain a non-hexagonal design using a stacking procedure based on Hexagonal Close Packing. The optical properties of the proposed structure are promising for SuperContinuum Generation. This approach could make accessible not only the equiangular spiral but also other quasi-crystal PCF through SaD

Tailoring light-sound interactions in a single mode fiber for the high-power transmission or sensing applications

A full-vectorial numerically efficient Finite Element Method (FEM) based computer code is developed to study complex light-sound interactions in a single mode fiber (SMF). The SBS gain or SBS threshold in a fiber is highly related to the overlap between the optical and acoustic modes. For a typical SMF the acoustic-optic overlap strongly depends on the optical and acoustic mode profiles and it is observed that the acoustic mode is more confined in the core than the optical mode and reported overlap is around 94 % between these fundamental optical and acoustic modes. However, it is shown here that selective co-doping of Aluminum and Germanium in core reduces the acoustic index while keeping the optical index of the same value and thus results in increased acoustic- optic overlap of 99.7%. On the other hand, a design of acoustic anti-guide fiber for high-power transmission systems is also proposed, where the overlap between acoustic and optical modes is reduced. Here, we show that by keeping the optical properties same as a standard SMF and introducing a Boron doped 2ndlayer in the cladding, a very low value of 2.7% overlap is achieved. Boron doping in cladding 2ndlayer results in a high acoustic index and acoustic modes shifts in the cladding from the core, allowing much high power delivery through this SMF

Soft Glass Equiangular Spiral Photonic Crystal Fiber for Supercontinuum Generation

An equiangular spiral photonic crystal fiber (ES-PCF) design in soft glass is presented that has high nonlinearity ( gamma > 5250 W-1 middot km-1 at 1064 nm and gamma > 2150 W-1 middot km-1 at 1550 nm) with a low and flat dispersion (D ~ 0.8 ps/kmmiddotnm and dispersion slope ~ -0.7 ps/km middot nm2 at 1060 nm). The design inspired by nature is characterized by a full-vectorial finite element method. The ES-PCF presented improves over the mode confinement of triangular core designs and dispersion control of conventional hexagonal PCF, combining the advantages of both designs; it can be an excellent candidate for generating supercontinuum pumped at 1.06 mum

Implications of a Quantum Mechanical Treatment of the Universe

We attempt to treat the very early Universe according to quantum mechanics. Identifying the scale factor of the Universe with the width of the wave packet associated with it, we show that there cannot be an initial singularity and that the Universe expands. Invoking the correspondence principle, we obtain the scale factor of the Universe and demonstrate that the causality problem of the standard model is solved.Comment: LaTex, 5 pages, 1 figure, to be published in Mod. Phys. Lett.

Ultra low bending loss equiangular spiral photonic crystal fibers in the terahertz regime

An Equiangular Spiral Photonic Crystal Fiber (ES-PCF) design in Topas® for use in the Terahertz regime is presented. The design shows ultra low bending loss and very low confinement loss compared to conventional Hexagonal PCF (H-PCF). The ES-PCF has excellent modal confinement properties, together with several parameters to allow the optimization of the performance over a range of important characteristics. A full vector Finite Element simulation has been used to characterize the design which can be fabricated by a range of techniques including extrusion and drilling

Design and Characterization Low-loss modes in Dielectric-Coated Hollow-core waveguides at THz Frequency

Designs of hollow-core rectangular, circular, and elliptical waveguides with inner coating of silver and polystyrene (PS) are presented for low-loss terahertz guidance. The PS thickness deposited over silver is optimized to achieve the lowest possible loss for each waveguide at the frequency of 2.5 THz. The mode also tends to be a near-Gaussian in shape, easy for coupling to transmitter and receiver. The lowest propagation loss of 0.13 dB/m is obtained for the mode in a circular waveguide with 2200 μm bore diameter by using a full-vectorial finite element method. It is also shown here that rectangular and elliptical waveguides with a similar core area offer a lower loss value for the Hp21 mode and the LP02 mode, respectively, compared to a circular waveguide. Besides this optimized rectangular waveguide not only shows a minimum loss of 0.09 dB/m but with 4 times higher loss for the other polarization, hence the polarization state of the signal can also be maintained in this waveguide

Metal-Coated Defect-Core Photonic Crystal Fiber for THz Propagation

Modal solutions for metal-coated defect-core photonic crystal fiber (PCF) with a central air-hole have been obtained by using a full-vectorial finite element method to model the guidance of THz waves. It has been shown that the surface plasmon modes can couple with the defect-core PCF mode to form supermodes, with potential for sensing applications

Growth and Metabolic Responses of Saccharum Species in Relation to Flooding.

Some growth and metabolic responses of different clones of Saccharum in relation to their flood-tolerance were examined. Clones grown in soil subjected to flooding demonstrated their ability to produce water roots as a means of morphological adaptation to flooding. Significant differences were observed among the clones with respect to the quantities of water roots produced, but all the clones were visually tolerant to flooding. Clones representing Saccharum spontaneum followed by the commercial hybrid produced the maximum quantities of water root under the flooded condition. The clones of Saccharum barberi and Saccharum robustum produced the least quantities of water root. Artificially imposed anoxia under nutrient culture provided a basic screening technique for the tolerant and intolerant clones. The tolerant clones suffered only a minimal reduction in root growth ((LESSTHEQ) 40%) and stalk elongation (41-53%) whereas the intolerant clones suffered greater reductions in root growth (\u3e 50%) and stalk elongation (80-98%) under anoxia. Intolerant clones tended to cease stalk elongation and root growth beyond 20 days of anoxic treatment while the tolerant clones continued to grow throughout the experimental period. Both inter- and intraspecific differences in growth parameters were observed with the clones tested. Among the metabolic parameters, the activity of the enzyme alcohol dehydrogenase (ADH) appeared to hold some merit for identifying the intolerant clones. Although two different trends of responses were obtained with the tolerant clones viz., Coimbatore, CP 65-357, and NG 77-59, this enzyme showed a consistently high level of activity in the intolerant clones viz., NG 77-160, Cavengerie and D-74. The activity of the enzymes, malate dehydrogenase, lactate dehydrogenase and peroxidase did not show any metabolic significance in relation to flooding tolerance of the clones tested. A low level of pyruvate decarboxylase activity was detected only at 3 days of anoxia. Of the metabolites, the concentration of ethanol appeared to complement the response characteristics due to ADH. Other metabolites viz., malate, sucrose, glucose and fructose, did not show any consistent changes that could be correlated with tolerance or intolerance of the different clones tested; however, there were consistently higher levels of ethanol, malate and sugars under anoxic conditions