Novel technique for measuring dispersion and detuning of a UV written silica-on-silicon waveguide

We shall present a new method of measuring the dispersive properties of UV written waveguides in the silica-on-silicon platform used to fabricate planar Bragg gratings. The technique involves direct measurement of the modal refractive index of a waveguide produced in the material. The data obtained also provides additional information about the spectral range of Bragg grating inscription. This direct writing technique reported previously differs from fibre Bragg grating fabrication by the small spot size of the writing beam and permits detuning of the Bragg wavelength from 1250nm to 1625nm. The fabrication technique provides the exact period of the grating and thus interrogation of the gratings produces information on the effective index of the mode. A series of integrated gratings were fabricated in a direct UV written waveguide via the direct grating writing technique in order to measure the wavelength dependence of the refractive index of the material. The Sellmeier curve obtained is shown

Seismic Evidence of Shallow Permafrost Beneath Islands in the Beaufort Sea, Alaska

Shallow ice-bonded permafrost has been shown by seismic refraction methods to exist beneath several islands in the Beaufort Sea. The marked contrast of seismic velocities in bonded materials (>2500 m/sec) and unbonded materials (<2100 m/sec) was used to determine the location of permafrost. In many cases these data were confirmed by shallow probing and drill holes. Several general conclusions are made about the distribution of shallow bonded permafrost beneath islands in the Beaufort Sea. Shallow permafrost occurs under areas where remnants of tundra still exist. These conditions exist on the larger islands that have not been eroded away by the ocean. Islands which have been eroded by the ocean, leaving only accumulation of sand and gravel, are generally moving westward and landward and for the most part are not underlain by shallow permafrost. However, the oldest and most persistent parts of these islands are in some cases underlain by shallow permafrost. This is believed to be a consequence of repeated freezings and thawings causing a reduction of salt brine in the sediments and allowing the materials to freeze

An integrated reconfigurable Bragg grating utilising a photoresponsive co-polymer

Reconfigurable Bragg grating devices are of significant interest for telecomm applications. Such devices can be fabricated by combining a UV-written silica Bragg grating with an azobenzene-based polymer - a photoresponsive material that undergoes reversible refractive index change on exposure to ultraviolet light. The preliminary 17 GHz tuning response suggests future applicability

Facet machining of silica waveguides with nanoscale roughness without polishing or lapping

To achieve low-loss free space coupling for integrated optics, device facets need to be smooth, free of chips and flat. The typical route for accomplishing these requirements is by traditional lapping and polishing. We report that high quality optical quality facets with a Sa = 4.9 nm can be machined using a simple dicing technique. In order to directly measure the scatter loss a device with a series of Bragg gratings is used to characterise the average interface loss per facet

Ultra-wide detuning planar Bragg grating fabrication technique based on direct UV grating writing with electro-optic phase modulation

A direct UV grating writing technique based on phase-controlled interferometry is proposed and demonstrated in a silica-on-silicon platform, with a wider wavelength detuning range than any previously reported UV writing technology. Electro-optic phase modulation of one beam in the interferometer is used to manipulate the fringe pattern and thus control the parameters of the Bragg gratings and waveguides. Various grating structures with refractive index apodization, phase shifts and index contrasts of up to 0.8×10-3 have been demonstrated. The method offers significant time/energy efficiency as well as simplified optical layout and fabrication process. We have shown Bragg gratings can be made from 1200 nm to 1900 nm exclusively under software control and the maximum peak grating reflectivity only decreases by 3dB over a 250 nm (~32THz) bandwidth

Simple planar Bragg grating devices for photonic Hilbert transform

Hilbert transformers are important devices widely used in information processing and signal analysis in the electronic domain. For example, for spectral efficiency improvement, it is used to construct the analytic signal for single sideband (SSB) modulation from a real signal. Photonic Hilbert transformers (PHTs) are proposed for a similar range of applications and would allow the direct processing of optical signals at bandwidths far beyond current electronic technologies

Realisation of photonic Hilbert transformer with a simple planar Bragg grating

Photonic Hilbert transformers (PHTs) are desirable for the direct processing of optical signals at high speeds and operation bandwidths, allowing optical networks to outperform current electronic technologies. We practically demonstrate a photonic Hilbert transformer in planar geometry; utilising a pi-phase shift planar Bragg grating with proper apodization profile. The device is fabricated by direct UV grating writing technology in silica-on-silicon [1]. The PHT has a pi-phase shift at the zero point of the frequency response, whereas the amplitude remains constant. The pi-phase shift in PHT is simply induced by placing a pi-phase shift in the refractive index modulation. The constant amplitude is achieved by precise apodization of the grating coupling strength, while the apodization profile is given by [2]. With our current direct UV writing technology, the proposed grating can be fabricated in a much higher accuracy then the conventional fibre Bragg grating manufacturing technique. We will present our latest work on more complex apodized gratings to obtain the ideal realisable frequency and temporal responses for PHTs

The impact of language factors on learner achievement in Science

South African learner achievement remains poor, despite large investment in schooling over the last two decades. Literature and research findings offer no single explanation or solution. In this article, the authors explored the relative contribution of specific language factors such as the role of home- and school-language equivalence, cultural and economic capital, and other school and classroom factors to Science achievement. The analysis identified specific language and/or contextual factors having the biggest influence on learner achievement. This was achieved through secondary analysis of South African Grade Nine (N = 12,000) data from the Trends in International Mathematics and Science Study (TIMSS) 2011. Multiple-regression modelling using contextual and achievement data suggested that home- and school-language equivalence and how frequently learners used the school language at home were strongly associated with the Science achievement results of Grade Nine learners in South Africa. Several other language factors that could be seen as cultural capital, beyond broader economic capital, some classroom-related contextual conditions and selected school-level factors, also showed strong influences. It is concluded that language, teacher training, and broader economic policy changes and their thorough implementation are required to address these concerns.Keywords: cultural capital; economic capital; home language; language factors; language of assessment; language of learning; language of teaching; Science achievement; Trends in International Mathematics and Science Study (TIMSS

Gas chromatographic studies of the relative retention of the sulfur isotopes in carbonyl sulfide, carbon disulfide, and sulfur dioxide

A precision gas chromatograph, coupled to a quadrupole mass spectrometer and an on-line computer, was used to study the fractionation on Porasil A of the /sup 32/S//sup 34/S isotopic pair in a variety of sulfur-containing molecules. Carbonyl sulfide (COS) yielded an average ..cap alpha.. value of 1.00074 +- 0.00017 (standard deviation) for the temperature range 25/sup 0/C to 75/sup 0/C. The carbon disulfide (CS/sub 2/) value was 1.00069 +- 0.00023 for the range 53/sup 0/C to 103/sup 0/C, and that for sulfur dioxide (SO/sub 2/) was 1.00090 +- 0.00018 for the range 62/sup 0/C to 112/sup 0/C. Differential thermodynamic data have been reported. A Porapak Q column showed no fractionation of this isotopic pair in these three molecules

Travelling Randomly on the Poincar\'e Half-Plane with a Pythagorean Compass

A random motion on the Poincar\'e half-plane is studied. A particle runs on the geodesic lines changing direction at Poisson-paced times. The hyperbolic distance is analyzed, also in the case where returns to the starting point are admitted. The main results concern the mean hyperbolic distance (and also the conditional mean distance) in all versions of the motion envisaged. Also an analogous motion on orthogonal circles of the sphere is examined and the evolution of the mean distance from the starting point is investigated