1,720,968 research outputs found
Sensing Opportunities in Integrated Photonics (invited tutorial)
No full textGreen 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.Dynamics of Micro and Nano System
Silicon photonic micro-ring resonators to sense strain and ultrasound
No full textWe demonstrated that photonic micro-ring resonators can be used in micro-machined ultrasound microphones. This might cause a breakthrough in array transducers for ultrasonography; first because optical multiplexing allows array interrogation via one optical fiber and second because the silicon-on-insulator technology allows cost-effective fabrication. To understand this microphone, all of its components were studied: fundamental theory of the photonic resonators, experimental characteristics of the resonators, and the effect of a static deformation of the resonator. The most familiar use of ultrasound is observing unborn children but ultrasonography is widely used in medical and industrial applications. Today's clear ultrasonic images are made by digital focusing which requires an array of transducers that records the sound at a number of positions spaced less than a wavelength. Typical sound frequencies are 1-40 MHz with corresponding wavelengths of 0.04-1.5 mm in water. Conventional ultrasound transducers employ piezo-electric material to convert sound pressure to an electronic signal. An array requires individual fabrication, placement and wiring of these transducers. Last decades, micro-machined ultrasound transducers (MUTs) have received large interest. Array MUTs are fabricated and wired directly as a single silicon "chip". This micro-machining technology leverages the cost-effective wafer-scale CMOS technology that was developed by the semiconductor industry. A MUT consists of a flexible membrane that is sensitive to ultrasonic pressure waves, like a drumhead. The membrane deformation is most commonly measured by recording the electrical capacitance between the membrane and a fixed bottom plate. Unfortunately, these MUTs do not meet the sensitivity of piezo-electric transducers. Moreover, electrical transducers normally require a coaxial wire for each array element. The size of this wire bundle is, for example, problematic in medical intravascular ultrasonography (IVUS), where atherosclerosis is diagnosed from a high-resolution ultrasonograph of the artery wall that is obtained by catheter which is brought inside the blood vessel. We propose a new type of ultrasound microphone that consists of a silicon photonic micro-ring resonator integrated in the membrane of a MUT. Incident ultrasonic pressure waves deform the membrane and thus deform the resonator, thereby shifting its optical resonance frequencies. This shift is accurately recorded by an external interrogation system. Next to the resonators, it is possible to integrate tiny optical multiplexers on the same chip so that many resonators can be simultaneously interrogated via a single optical fiber. Moreover, the all-optical sensor can be used in MRI scanners. We proved the operation principle of this new ultrasound microphone. The designed, fabricated and characterized microphone consists of a photonic racetrack-shaped resonator (footprint 50 ?m by 10 ?m, height 0.220 ?m) that is integrated in an acoustically resonant silicon-dioxide membrane (diameter 0.124 mm, height 2.5 ?m). Fabrication of the microphone demonstrated successful integration of silicon photonic circuits in silicon micro-mechanical systems. First the photonic circuit was fabricated in a semi-industrial CMOS line. Second the membrane was fabricated by etching a hole from the back-side of the wafer using a Bosch etch process. The photonic micro-ring resonator was interrogated using a laser and a photo-receiver, providing a minimal detectable wavelength shift of 36 fm. We measured an ultrasonic minimal detection level (noise equivalent pressure) below 1 Pa which is on the same order of magnitude as the state-of-the-art of PZT piezo-electric based transducers. The microphone showed an acoustical resonance around 0.75 MHz with a -6 dB bandwidth of 20%. We only studied the most simple configuration of this microphone and there is a lot of room for improvement. The relation between a deformation of the micro-ring resonator and the shift in the resonance wavelengths was studied in a well-defined static mechanical setup. Depending on the width of the waveguide and the orientation of the silicon crystal, the linear wavelength shift per applied strain varies between 0.5 and 0.75 pm/microstrain for infrared light around 1550 nm wavelength. The influence of the increasing ring circumference is about three times larger than the influence of the change in the propagation speed of the light through the waveguide (effective index), and the two effects oppose each other. The strong dispersion in silicon sub-wavelength waveguides (400 nm by 220 nm) accounts for a decrease in sensitivity of about a factor two. The optical characteristics of the micro-ring resonators and their components were extensively studied. Different methods to characterize directional couplers (direct and in ring-resonators) gave similar results. An interesting observation was that directional couplers introduce a large coupling-induced phase delay when nearly all light couples from one waveguide to the other. Most properties of silicon ring resonators and their components can be computed using approximate analytical theories. Many theories on integrated optics were originally derived for low-index-contrast waveguides like optical fibers (?n < 0.1). We reviewed and revised those theories for application to silicon-on-insulator waveguides which have a very high index contrast (?n ~ 2). This work is formulated such that it can be used in a university course with only basic theory of electrodynamics as prerequisite. Analytical theories provide insight and allow fast computation of the behavior of photonic devices and circuits. In conclusion, we studied silicon photonic micro-ring resonators and their application in mechanical sensing. Application of these sensors in micro-machined ultrasound transducers opens new opportunities for ultrasonic array technology.Department of Imaging PhysicsApplied Science
Exploring Silicon Photonics to Sense Two-Dimensional Membrane Mechanics
No full textSilicon photonics have received more attention in recent years due to further development in CMOS manufacturing methods. The development allows silicon photonics to be smaller than ever before. This leads to smaller silicon photonic devices that can transceive light, which is typically done at a wavelength of 1550nm for silicon photonics. A silicon photonic device that benefits from this wavelength is the silicon waveguide, which can transceive light by being coupled to other waveguides. When the second guide is later coupled back with the main waveguide, a resonance can form between the guides. This can turn the silicon waveguide in to a sensor that relies on interference from the recoupled signal. The design used for this study has the waveguides in a relatively deep trench, which means that a membrane can be suspended above the waveguides. In theory the membrane should reflect some of the light that escapes from the waveguide back. In this work membranes made from graphene and molybdenum disulfide are suspended over a silicon waveguide in hopes to detect the motion of the membrane. A proof of concept by experimenting with membranes integrated on silicon photonics can give way for a new type of sensor, which is both microscopic and has a high signal-to-noise ratio. The experiments are conducted by propagating light through the waveguide, the light should then interact with the suspended membrane on top. The first indication that the concept was possible was when a transmission graph that swept the light’s wavelength around 1550nm changed after introducing a suspended membrane over the waveguide. The change showed that waveguides react to membranes over them without eliminating the transmission altogether. This is a great step when it comes to a proof for the concept. However, it is still needed to take a frequency measurement before the concept has been fully proofed.Mechanical Engineering | Micro-optics and Optomechatronic
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
Automatic Differentiation based Multi-Mode Ptychography: A flexible and highly efficient lensless imaging algorithm
No full textThe scientific community recognizes the critical role played by ptychography in nanoscale imaging. Compared with the conventional imaging, which has high requirements on the manufacturing of optical elements, ptychography, as a computational imaging technique, uses a set of measured intensities of the diffraction patterns to reconstruct the image of the object and hence no imaging system is needed. This technique is especially useful in the short wavelength, e.g. EUV, regime, where manufacturing high quality optical elements such as mirrors is extremely expensive. Most of the present ptychographic algorithms require the illumination of the object to be both spatially and temporally coherent so that the diffraction pattern can be interpreted as the intensity of the Fourier transform of the field exiting the object. However, the coherence of the sources that produce the EUV radiation often cannot be guaranteed. Therefore, it is crucial to extend the ptychography method to consider partial coherence effects. This requires the use of a flexible propagator which depends on the wavelength to deal with the temporal partial coherence and a modal representation for the spatially partially coherent field. Also, the ambiguity of the reconstructed modes of the probe will be solved by an orthogonalization approach, which could enhance the reproducibility of the results. These methods will be implemented on an existing ptychography platform based on automatic-differentiation and will be validated using both simulation data and experimental data.Mechanical Engineering | Precision and Microsystems Engineerin
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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