1,720,963 research outputs found
Tapered silicon core fibres for supercontinuum generation
No full textA series of silicon-core fibre tapers are designed that allow for longitudinal variation of their nonlinear and dispersion parameters with length. A supercontinuum (SC) is generated in the waist region of the taper due to the increased nonlinearity there. The long-wavelength edge of the SC is then boosted by up-tapering to a specific core diameter which is chosen to optimise the phase-matching conditions for four-wave mixing. This means that the bulk of the initially-generated SC can be used as pump sources for transferring power to the long-wavelength edge. Each design targets a specific wavelength range with a 0.25 µm bandwidth. The design work is driven by simulations of mid-infrared laser pulse propagation through the fibres, which work by solving the generalised nonlinear Schrödinger equation (GNLSE). This incorporates numerous nonlinear effects in silicon affecting SC generation, including two-photon absorption (TPA), three-photon absorption and free-carrier effects. The wavelength-dependence of linear loss and the effective area of the fundamental mode is incorporated into the GNLSE, which is extended to also incorporate the wavelength-dependence of TPA. The possibility of using these taper design principles is also explored for silicon on-insulator waveguides
Dataset for: Designing silicon-core fiber tapers for efficient supercontinuum generation in the greenhouse has absorption region
No full textDataset supports: Campling, J, Horak, P. & Peacock, A.C. (2020).Designing silicon-core fiber tapers for efficient supercontinuum generation in the greenhouse gas absorption region. Journal of the Optical Society of America B</span
Designing silicon-core fiber tapers for efficient supercontinuum generation in the greenhouse gas absorption region
No full textWe propose a tapered silicon-core optical fiber design for extending the long-wavelength edge of supercontinuum generation to obtain a high spectral density source across the 3-4.5 µm regime. The taper works by generating sufficient spectral broadening of the driving laser pulse to produce a series of pumps for nondegenerate four-wave mixing, and then opening up new phase-matching conditions to transfer the power from these pumps to a target region of mid-infrared wavelengths. We show, by simulation, that this taper design works effectively when pumped with a conventional 2.1 µm femtosecond fiber laser, significantly improving the spectral coverage obtained with a fixed-diameter fiber. Thus, these tapered silicon-core fibers offer a potential platform for an efficient all-fiber spectroscopy solution to measure greenhouse gases
Designing silicon-core fiber tapers for efficient mid-IR supercontinuum generation
No full textWe propose a taper design for a silicon-core fiber for the purpose of
generating a supercontinuum (SC) from a 2.1μm pulsed fiber laser. The
design is tailored to maximise the conversion efficiency (CE) to the
3-4μm region, which is important for environmental sensing as it
includes several key greenhouse gas absorption lines.
There is a need for compact, low-power and efficient solutions.
Aluminium nitride photonic-chip waveguides have been shown to generate
0.3mW in the 3-4μm region with an 80mW input. Although this is
sufficient power for some applications, the system only offers a 0.4%
CE. More recently a silicon nitride planar waveguide was used to
transfer energy from a commercial 2.1μm femtosecond laser to targeted
wavelengths in the 3-4μm region through dispersive wave generation. To
cover the entire region, it is estimated that an input of 40mW would be
needed to generate ~1mW (CE of 2.5%).
Compared to these materials silicon has a higher nonlinearity and,
despite multi-photon absorption, is highly efficient at transferring
energy to different wavelengths with modest input powers. Moreover,
silicon-core fibers can be tapered using established post-processing
procedures, which can be used to control the phase-matching conditions
to concentrate energy in a required wavelength range.
We have designed a silicon-core fiber taper that can take the input from
a 2.1μm fiber laser and efficiently transfer the energy to cover the
entire 3-4μm range.
We simulated SC generation using the generalised nonlinear Schrödinger
equation including wavelength-dependent loss terms (linear, TPA and
3PA). From these simulations we estimate that ~0.8mW average power can
be generated covering the entire 3-4μm region, with only 15mW input
power, a CE of 5%
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Net optical parametric gain in a submicron silicon core fiber pumped in the telecom band
No full textA silicon core fiber (SCF) has been designed and fabricated with a dispersion engineered profile to support broadband optical parametric amplification across the telecom window. The combination of low optical transmission losses and high coupling efficiency of the SCF platform have allowed for an on-off optical parametric gain up to 9dB, without experiencing gain saturation due to nonlinear absorption, resulting in a net off-waveguide gain of 2dB. The ability to splice the SCFs with conventional silica fiber systems opens a route to compact and robust all-fiber integrated optical parametric amplifiers and oscillators that could find use in telecoms systems
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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