1,720,959 research outputs found
Integrating Photonics into Fab Labs
No full textAn ambitious project teams up local photonics organizations with creative facilities to promote European photonics innovation.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ImPhys/Optic
Review of Near-Field Terahertz Measurement Methods and Their Applications: How to Achieve Sub-Wavelength Resolution at THz Frequencies
No full textIn the last decades, many research teams working at Terahertz frequencies focused their efforts on surpassing the diffraction limit. Numerous techniques have been investigated, combining methods existing at optic wavelength with THz system such as Time Domain Spectroscopy. The actual development led on one side to a resolution as high as ?/3000 and one the other side to a video-rate recording. The purpose of this paper is to give an overview of the history of the field, to describe the different approaches, to give examples of existing applications and to draw the perspective for this research area.Imaging Science and TechnologyApplied Science
An exact solution for dipole fields inside optical multilayer structures
No full textIn this report, we derive some tools that can be used to construct semi-analytical solution for the electromagnetic field of a dipole in an arbitrary multilayer system. The proposed methods consist of a recursive determination of electric fields -- using the mathematical principle behind a Fabry-Perot interferometer -- and two different derivations for the decomposition of the electric field of a resonating dipole into plane waves -- using dyadic Green functions and two dimensional Fourier transforms respectively. These decomposition methods are not analytic, since the resulting integrals can only be computed numerically. The results of these tools are compared to known results from other literature and seem to nicely match, making them useful tools for the combination into a method for computing the dipole field in the multilayer. This merge is not completed in this project. However, some suggestions on how to perform this combination are done.Applied SciencesApplied MathematicsApplied Physics and Applied Mathematic
Designing interactive demonstrations of optics phenomena
No full textThe United Nations and Unesco have declared 2015 to be the international year of light. The Optics department of the faculty of Applied Physics from the TU Delft has decided to contribute to this effort by designing optics experiments to be displayed at the Science Center Delft. The goal of this project was to manage first year students that helped design and explain these experiments. Another part was to design an experiment involving lithography. The students were split into three groups, each with a different subject, polarization, cloaking and light emitting diodes. The management part of the subject went well; ten experiments were designed and the principle behind them were explained on posters. I have learned that communication is very important in teamwork and that the group members need to be motivated in order get the proper results.OpticsImaging Science & TechnologyApplied Science
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
Limits of realizing irradiance distributions with shift-invariant illumination systems and finite etendue sources
No full textWhen redistributing the light emitted by a source into a prescribed irradiance distribution, it is not guaranteed that, given the source and optical constraints, the desired irradiance distribution can be achieved.We analyze the problem by assuming an optical black box that is shift-invariant, meaning that a change in source position does not change the shape of the irradiance distribution, only its position. The irradiance distribution we can obtain is then governed by deconvolution. Using positive-definite functions and Bochner s theorem, we provide conditions such that the irradiance distribution can be realized for finite etendue sources.We also analyze the problem using optimization, showing that the result heavily depends on the chosen source distribution.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ImPhys/Adam groupImPhys/Urbach grou
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
The Fourier transform interrogator
No full textPhotonic sensors have recently attracted much attention in both industry and academia. High accuracy, low weight and the possibility of building a large sensor network are key benefits of photonic sensors. Another benefit is installing optical sensors in harsh environments where electronic sensors' usage is not plausible: aerospace applications where ionizing radiation is present or gas and oil pipes are some examples.Integrated photonics brings new challenges to the interrogation of multiplexed sensors in WDM. Unlike FBG sensors, whose resonance wavelength can be chosen to an accuracy better than 1.0 nm, the resonance wavelength of integrated micro-ring resonators cannot be chosen during the design stage. The main reason is the imperfections of the manufacturing process. The fact that the resonance wavelength is unpredictable is a problem for interrogators based on interferometry. Such interrogators perform the demultiplexing and demodulation in different stages: first, a spectrometer separates the optical channels; subsequently, outputs of the spectrometer are conveyed to interferometers. From the photo-receiver voltages connected to MZI outputs, the signal from the sensors can be demodulated. As the resonance value of sensors cannot be determined during design, two sensors may have their resonances in the same spectrometer's channel. As a result, the demultiplexing step fails, compromising the interrogator's operation. In Chapter 4 of this thesis, a new interrogation method is proposed. Much of the effort of interferometric interrogators is to separate the spectrum of the sensors correctly. In the Fourier Transform Interrogator, the spectrum of all sensors is sent to an array of Mach-Zehnder interferometers (MZI) with different OPDs. Using the output voltages from the photo-receivers attached to the MZIs, we derive a system of non-linear equations, whose solution provides the signal from each sensor. The demodulation and demultiplexing steps are performed simultaneously for the Fourier interrogator, which guarantees the interrogator's unique flexibility. On the other hand, the computational cost is high since the system of non-linear equations is solved using Newton's method. For each set of voltages sampled over time, a different system of equations is obtained. Chapter 4 leaves some unanswered questions: Does the system of non-linear equations have a unique solution? How many solutions are there? What is the physical meaning of each of the solutions? Is it possible to solve non-linear systems of equations for fast sensors in real-time? All these questions are answered in Chapter 5. As a consequence of the new algebraic formulation, it is possible to solve about 1 000 000 algebraic systems of equations in about 10 ns, i.e., allowing the real-time interrogation of high-speed sensors. The interrogator is a candidate for interrogating arrays of ultrasound ring resonator sensors in the tens of MHz range.ImPhys/Optic
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