1,721,635 research outputs found
Second-harmonic generation in AlGaAs-on-insulator waveguides
No full textSecond-harmonic generation is demonstrated in AlGaAs-on-insulator waveguides at telecom wavelengths. Using this material platform, a maximum internal normalized efficiency of 1202 55% W −1 cm −2 is achieved for a 100 fs pulsed excitation wavelength at 1560 nm. This finding is important towards enabling new chip-scale devices for sensing, metrology, and quantum optics
Supercontinuum generation in dispersion engineered AlGaAs-on-insulator waveguides
No full textThe effect of engineering the dispersion of AlGaAs-on-insulator (AlGaAs-OI) waveguides on supercontinuum generation is investigated at telecom wavelengths. The pronounced effect the waveguide width has on the nonlinear dynamics governing the supercontinua is systematically analyzed and the coherence of the spectra verified with numerical simulations. Using dispersion engineered AlGaAs-OI waveguides, broadband supercontinua were readily obtained for pulse energies of ∼ 3 pJ and a device length of only 3 mm. The results presented here, further understanding of the design and fabrication of this novel platform and describe the soliton and dispersive wave dynamics responsible for supercontinuum generation. This study showcases the potential of AlGaAs-OI for exploring fundamental physics and realizing highly efficient, compact, nonlinear devices
Correlation Between Intensity and Phase in Speckle Pattern Interferometry
No full textWe simulate the field distribution of a fully developed speckle pattern (SP) due to diffusion of laser light from a remote rough surface. We show that, under some circumstances, the phase fluctuation and the logarithm of intensity are linked by Hilbert transform, excluding deep intensity minima. To overcome the problems arising from deep intensity minima., we propose the integration of the SP field over the finite detector area. We compute the autocorrelation function of the SP along the longitudinal axis z as a function of the detector area; we find a rapid increase of the correlation length with the detector area, up to a nearly complete correlation for integration just over a few transversal speckles. We conclude that the Hilbert transform method could open the way to compensation of SP phase errors in interferometric measurements
Design of chirped-coupling sidewall Bragg gratings for narrow linewidth distributed feedback lasers
Full text linkA chirped-coupling sidewall Bragg grating is proposed to mitigate the nonlinear effects that deteriorate the linewidth in DFB lasers operating at a high power and current regime. This novel grating geometry is analyzed and simulated to extract the optimal design parameters in terms of intra-cavity field distribution. Compared to lasers with uniform Bragg gratings, devices fabricated with a chirped-coupling grating are shown to operate in stable single mode operation over a wider current and power range and exhibit linewidth as narrow as 100 kHz
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
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
Broadband and High-Capacity Silicon Photonics Single-Sideband Modulator
No full textWe propose a novel photonic-integrated single-sideband (SSB) modulator realized in silicon on insulator technology operating either in suppressed-carrier or full-carrier mode with continuously tunable carrier-to-sideband ratio (CSBR). Large rejection levels of the spurious sidebands and residual carrier in excess of 40 and 30 dB, respectively, with a CSBR tunability over a sim 50 dB range, are demonstrated. By employing a single silicon photonics (SiP) phase modulator and a compact and high-performance filtering element, the proposed architecture exhibits a compact layout and tolerates high driving voltage levels, leading to large OSNR values of the modulated sideband in excess of 50 dB. The device supports broadband RF data signals and its operation is tested with an up to 5 Gbps ASK-modulated carrier at 16.5 GHz, limited by available RF equipment. Furthermore, the technique allows to implement a frequency-multiplication mechanism for the input RF carrier, and up to threefold effective bandwidth enhancement of the SiP modulator is obtained by generating an optical SSB signal with a modulated spectral component spaced by 49.5 GHz from the optical carrier. Such features are promising for implementing cost-effective optical distribution of millimeter-wave wireless data signals supporting the evolution of next-generation radio access networks
Flexible Millimeter-Wave Carrier Generation up to the Sub-THz with Silicon Photonics Filters
No full textWe report on the characterization of a photonic integrated circuit (PIC) for the generation of a RF carrier wave in the millimeter-wave band up to the sub-THz region. The circuit has been implemented in silicon waveguides through a standard multi project wafer service, and exploits an innovative filtering technique for effectively selecting two tones out of an input optical frequency comb (OFC) driven by a local oscillator at a sub-multiple frequency of the system output RF signal. Experimental results confirm a large suppression ratio of RF spurious tones up to more than 30 dB for generated carrier frequencies ranging from 20 GHz to 126 GHz with input OFC frequency spacing between 10 GHz and 20 GHz. Additionally, the unfiltered input OFC tones are recovered in the scheme with negligible loss, enabling efficient comb reuse for minimizing optical and RF equipment in PIC-based future wireless communications and sensing networks systems. Design strategies for further improving the circuit performances are finally presented
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