1,721,094 research outputs found
rac-N-{6-[Bromo(hydroxy)methyl]-2-pyridyl}pivalamide
No full textThe title compound, C(11)H(15)BrN(2)O(2), contains an amide group which is close to coplanar with the adjacent pyridine ring, the dihedral angle between the planes being 9.0 (5)degrees. The molecular packing reveals a mutual hydrogen-bond interaction between centrosymmetrically related hydroxyl O atoms. Further hydrogen bonding involving O-H center dot center dot center dot Br and N-H center dot center dot center dot Br interactions also appears to consolidate the packing
Pure silica single-mode fibre with hexagonal photonic crystal cladding
No full textPure silica fibres supporting guided modes were first investigated in the 1970's, the aim being to achieve low transmission losses. The huge success of chemical vapour deposition in producing extremely low loss fibre has largely superseded this early technology. We have recently revisited it in the context of photonic crystals, and report here the realisation of a new kind of pure silica microstructured optical fibre which supports a robust single mode. Photonic crystals are periodically microstructured materials with a pitch on the scale of the optical wavelength. They have recently been the subject of much interest because of their unusual optical properties, including their ability to support a full photonic band gap. Several research teams have reported fabricating two-dimensional photonic crystal material out of glasses using selective etching processes. However, such a fabrication process results in samples of at most a few millimetres in the third dimension. The photonic crystal fibre described here is formed by creating a hexagonal silica/air preform (including a deliberate defect to guide light) on a macroscopic scale and then reducing its size by several orders of magnitude by pulling it into an optical fibre (see Fig 1)
All-silica single-mode optical fiber with photonic crystal cladding
No full textWe report the fabrication of a new type of optical waveguide: the photonic crystal fiber. It consists of a pure silica core surrounded by a silica-air photonic crystal material with a hexagonal symmetry. The fiber supports a single robust low-loss guided mode over a very broad spectral range of at least 458-1550 nm. Also see errata - http://eprints.soton.ac.uk/78010
Properties of photonic crystal fiber and the effective index model
No full textWe report on the waveguiding properties of a new type of low-loss optical waveguide. The photonic crystal fiber can be engineered to support only the fundamental guided mode at every wavelength within the transparency window of silica. Experimentally, a robust single mode has been observed over a wavelength range from 337nm to beyond 1550nm (restricted only by available wavelength sources). By studying the number of guided modes for fibers with different parameters and the use of an effective index model we are able to quantify the requirements for monomode operation. The requirements are independent of the scale of the fiber for sufficiently short wavelengths. Further support for the predictions of the effective index model is given by the variation of the spot size with wavelength
Guided modes in a photonic crystal fibre
No full textPhotonic crystal fibre (PCF) is a unique form of low-loss optical waveguide, which works by trapping light in a defect within a two-dimensional silica/air photonic crystal material (see figure 1)[1]. The photonic crystal material is formed by a 2 dimensional array of small closely-spaced (1-5µm) air holes which run down the length of the silica fibre. The defect is a region of pure silica embedded in the holey material. Although it works by total internal reflection, as do conventional fibres, we have found that PCF has properties which are fundamentally different to those displayed by other fibres. These properties are determined by the design of the unit cell of the crystal cladding material - the shape, the pitch and the air-filling fraction - as well as by the size of the defect core. The photonic crystal is a new type of optical material, so there is considerable scope to fabricate fibre with novel properties. For example, we have demonstrated a fibre with a simple hexagonal array of air holes in the cladding which is single-moded over an extraordinary bandwidth range, extending from 337nm to beyond 1.55µm, a result which is supported by theoretical considerations. Figure 1 Optical micrograph of a photonic crystal fibre, of diameter 80µm. Figure 2 Higher-order mode in the core of a photonic crystal fibre. By increasing the size of the air holes in the structure one increases the effective index difference between the silica core and the silica/air cladding, increasing the number of guided modes. Likewise, the use of more complex unit cell structures as illustrated here can result in more guided modes (figure 2). This paper describes more fully the dependence of the number of guided modes on the design of the photonic crystal cladding
Reduced repetition rate Yb<sup>3+</sup> mode-locked picosecond fiber laser with hollow core fiber
No full textAnti-resonant guiding negative curvature hollow core fiber operating at a
wavelength of 1064 nm is used in the cavity of an ytterbium (Yb3+)
mode-locked fiber laser to increase cavity length without increasing
the nonlinear phase shift. Repetition rates from 37 to 5.4 MHz are
demonstrated using lengths of hollow core fiber up to 48 m in length.
Each constructed cavity produced coherent 4-ps 1/e2 duration
soliton-like pulses, with no degradation of the pulse peak power or
pulse shape at lower repetition rates. Both the spectral distributions
and the autocorrelations of output pulses are compared along with the
mode-locking and multi-pulse power thresholds
Hybrid Photonic Crystal Fiber
No full textWe present a hybrid photonic crystal fiber in which a guided mode is confined simultaneously by modified total internal reflection from an array of air holes and antiresonant reflection from a line of high-index inclusions. Experimental results demonstrate that this fiber shares properties of both index-guided and photonic bandgap structures. © 2006 Optical Society of America.142926931Knight, J.C., Photonic crystal fibres (2003) Nature, 424, pp. 847-851Birks, T.A., Knight, J.C., Russell, P.S.J., Endlessly single-mode photonic crystal fiber (1997) Opt. Lett., 22, pp. 961-963Ortigosa-Blanch, Knight, J.C., Wadsworth, W.J., Arriaga, J., Mangam, B.J., Birks, T.A., Russell, P.S.J., Highly birefringent photonic crystal fibers (2000) Opt. Lett., 25, pp. 1325-1327Wadsworth, W.J., Ortigosa-Blanch, A., Knight, J.C., Birks, T.A., Man, T.-P.M., Russell, P.St.J., Supercontinuum generation in photonic crystal fibers and optical fiber tapers: A novel light source (2002) J. Opt. Soc. Am. B, 19, pp. 2148-2155Knight, J.C., Birks, T.A., Cregan, R.F., Russell, P.S.J., De Sandro, P.D., Large mode area photonic crystal fibre (1998) Electron. Lett., 34, pp. 1347-1348Reeves, W.H., Knight, J.C., Russell, P.St.J., Roberts, P.J., Demonstration of ultra-flattened dispersion in photonic crystal fibers (2002) Opt. Express, 10, pp. 609-613Knight, J.C., Arriaga, J., Birks, T.A., Ortigosa-Blanch, Wadsworth, W.J., Russell, P.S.J., Anomalous dispersion in photonic crystal fibers (2000) IEEE Photon. Technol. Lett., 12, pp. 807-809Luan, F., George, A.K., Hedley, T.D., Pearce, G.J., Bird, D.M., Knight, J.C., Russell, P.St.J., All-solid photonic bandgap fiber (2004) Opt. Lett., 29, pp. 1-4Argyros, A., Birks, T.A., Leon-Saval, S.G., Cordeiro, C.M.B., Luan, F., Russell, P.St.J., Photonic bandgap with an index step of one percent (2004) Opt. Express, 13, pp. 1540-1550Bouwmans, G., Bigot, L., Quiquempois, Y., Lopez, F., Provino, L., Douay, M., Fabrication and characterization of an all-solid 2D photonic bandgap fiber with a low-loss region (<20dB/km) around 1550 nm (2005) Opt. Express, 13, pp. 8452-8459Litchinitser, N.M., Dunn, S.C., Steinvurzel, P.E., Eggleton, B.J., White, T.P., McPhedran, R.C., De Sterke, C.M., Application of an ARROW model for designing tunable photonic devices (2004) Opt. Express, 12, pp. 1540-1550Litchinitser, N.M., Abeeluck, A.K., Headley, C., Eggleton, B.J., Antiresonant reflecting photonic crystal optical waveguides (2002) Opt. Lett., 27, pp. 1592-1594Litchinitser, N.M., Dunn, S.C., Usner, B., Eggleton, B.J., White, T.P., McPhedran, R.C., De Sterke, C.M., Resonances in microstructured optical waveguides (2003) Opt. Express, 11, pp. 1243-1251Arismar Cerqueira Jr., S., Nobrega, K.Z., Hernandez-Figueroa, H.E., Di Pasquale, F., A powerful tool based on finite element method for designing photonic crystal devices (2004) Proceedings of International Conference on Telecommunications, pp. 287-295Clarricoats, P.J.B., Chan, K.B., Electromagnetic-wave propagation along radially inhomogeneous dielectric cylinders (1970) Electron. Lett., 6, pp. 694-695Cregan, R.F., Mangan, B.J., Knight, J.C., Birks, T.A., Russell, P.St.J., Roberts, P.J., Allan, D.C., Single-mode photonic band gap guidance of light in air (1999) Science, 285, pp. 1537-1539Jasapara, J., Her, T.H., Bise, R., Windeler, R., Di Giovanni, D.J., Group-velocity measurements in a photonic bandgap fiber (2003) J. Opt. Soc. Am. B, 20, pp. 1611-161
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Two-dimensional photonic crystal material in fibre form
No full textPhotonic crystals are formed of periodically structured dielectric material, the pitch or period of the structure being of the order of the optical wavelength. A novel property of photonic crystal materials is they can be designed so as to exhibit photonic bandgaps, i.e. frequency ranges in which there are no propagating modes in the material. Some interesting consequences of such photonic band gaps occur for waves propagating out-of-plane in two-dimensionally materials. One possibility is to fabricate low-loss waveguides which guide soley by Bragg reflection. This could be done by using a 2-D structure which is effectively infinite in the third dimension, and which exhibits a bandgap in its transmission characteristics for waves which have a certain wavevector component beta =k along the structure. By purposefully introducing some kind of defect which is embedded in the crystal structure we can create a spatially localized region where such a wave can exist - a "defect state" appears in the band structure of the material. Light in this defect state would be unable to leak away from the defect through the crystal material, but would travel along the defect with propagation constant beta
- …
