Publications by authors named "Marcus Dahlem"

16 Publications

  • Page 1 of 1

[Postoperative dumping-syndrome with relevant impairment of glucose homeostasis - relief by continuous glucose monitoring and individual therapy with GLP-1 receptor agonists].

Z Gastroenterol 2021 Jun 15;59(6):556-559. Epub 2021 Jun 15.

Innere Medizin, Krankenhaus St. Marienwörth, Bad Kreuznach, Germany.

Dumping syndromes are a common side effect after partial or total gastric resection. The symptoms may be diverse, with vasomotoric reactions, collapse tendencies and digestive disorders (early dumping) as well as blood sugar derailment as a result of too fast absorption of glucose (late dumping).Entrenched therapy concepts, including personalized nutritional concepts and the use of medication as octreotide or diazoxide, will not always lead to the desired results. It is then, that individual therapy concepts have to be found to restore the patient's quality of life, as shown in this case study.
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http://dx.doi.org/10.1055/a-1324-4136DOI Listing
June 2021

Beam shaping for ultra-compact waveguide crossings on monolithic silicon photonics platform.

Opt Lett 2020 Nov;45(22):6230-6233

A beam shaping approach has been implemented to realize high-performance waveguide crossings based on cosine tapers. Devices with a compact footprint of 4.7µ×4.7µ were fabricated on the GLOBALFOUNDRIES 45 nm monolithic silicon photonics platform (45 CLO technology). Fabricated devices are found to be nearly wavelength independent (±0.035 for 1260≤≤1360) with low insertion loss (∼0.2) and crosstalk (-35). The measured response of the devices is consistent with the three-dimensional finite-difference time-domain simulation results. The design stability is validated by measuring the device insertion loss on eight chips, which is found to be 0.197±0.017 at the designed center wavelength of 1310 nm.
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http://dx.doi.org/10.1364/OL.402446DOI Listing
November 2020

High-extinction ratio polarization splitter based on an asymmetric directional coupler and on-chip polarizers on a silicon photonics platform.

Opt Express 2020 Jul;28(15):22899-22907

A high performance compact silicon photonics polarization splitter is proposed and demonstrated. The splitter is based on an asymmetric directional coupler. High extinction ratios at the through and drop ports of the polarization splitter are achieved by using an on-chip TE-pass polarizer and a TM-pass polarizer, respectively. The splitter, implemented on a silicon-on-insulator platform with a 220 nm-thick silicon device layer, has a measured insertion loss lower than 1 dB (for both TE and TM modes) and extinction ratio greater than 25 dB (for TM mode) and greater than 36 dB (for TE mode), in the wavelength range from 1.5 µm to 1.6 µm. The footprint of the device is 12 µm × 15 µm.
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http://dx.doi.org/10.1364/OE.396505DOI Listing
July 2020

Compact silicon TE-pass polarizer using adiabatically-bent fully-etched waveguides.

Opt Express 2018 Nov;26(24):31850-31860

A high-performance integrated silicon TE-pass polarizer is proposed and demonstrated. The polarizer uses a series of adiabatic waveguide bends that yield high extinction ratio for the TM polarization and low insertion loss for the TE polarization, and does not require special materials or complex fabrication steps. The polarizer, implemented on a silicon-on-insulator platform with a 220 nm silicon thickness, is measured to have insertion loss ≤ 0.37 dB (average 0.12 dB) and extinction ratio ≥ 27.6 dB (average 36.0 dB) over a 1.5 μm to 1.6 μm wavelength range, with a footprint of 63 μm × 9.5 μm. The trade-off between the footprint of the polarizer and its performance is established. While the analysis was done for a silicon-on-insulator platform, the concept is applicable to other waveguide geometries and integrated photonic platforms.
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http://dx.doi.org/10.1364/OE.26.031850DOI Listing
November 2018

Discerning the Contribution of Morphology and Chemistry in Wettability Studies.

J Phys Chem A 2018 Sep 27;122(38):7768-7773. Epub 2018 Jul 27.

Laboratory for Energy and Nano-Sciences , Khalifa University of Science and Technology , Abu Dhabi , United Arab Emirates.

The wetting behavior of homogeneous systems is now well understood at the macroscopic scale. However, this understanding offers little predictive power regarding wettability when mesoscopic chemical and morphological heterogeneities come into play. The fundamental interest in the effect of heterogeneity on wettability is derived from its high technological relevance in several industries, including the petroleum industry where wettability is recognized as a key determinant of the overall efficiency of the water-flooding-based enhanced oil recovery process. Here, we demonstrate the use of the atomic force microscopy force curve measurements to distinguish the roles of chemistry and morphology in the wetting properties of rock formations, thus providing a clear interpretation and deeper insight into the wetting behavior of heterogeneous formations. Density functional theory calculations further prove the versatility of our approach by establishing benchmarks on ideal surfaces that differ in chemistry and morphology in a predefined manner.
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http://dx.doi.org/10.1021/acs.jpca.8b04197DOI Listing
September 2018

Gradient-index optical fiber lens for efficient fiber-to-chip coupling.

Opt Express 2017 Jun;25(12):13035-13045

A gradient-index optical fiber lens is proposed and fabricated on the tip of a single-mode fiber using focused ion beam milling. Second-order effective medium theory is used to design a gradual change in the fill factor, which ensures a parabolic effective refractive index distribution. The proposed fiber lens design is simulated via the three-dimensional finite-difference time-domain method, and demonstrated through confocal optical measurements. At a wavelength of 1550 nm, the fabricated lenses focus a 10.4 μm mode field diameter exiting the fiber into spot sizes between 3-5 μm, located 4-6 μm away from the fiber tip. Direct coupling into a silicon-on-insulator chip is also demonstrated, where the fabricated gradient-index lens has a coupling efficiency comparable to a commercial lensed fiber.
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http://dx.doi.org/10.1364/OE.25.013035DOI Listing
June 2017

Gradient-index optofluidic waveguide in polydimethylsiloxane.

Appl Opt 2017 Feb;56(4):1202-1206

We demonstrate a gradient-index (GRIN) optofluidic waveguide using polydimethylsiloxane cured with a radial variation of temperature. The waveguide wraps the microfluidic channel and the GRIN profile localizes the light around it, making the device suitable for evanescent sensing applications. The fabricated waveguide shows good light confinement, with a propagation loss of 1.47 dB/cm at a wavelength of 632.8 nm.
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http://dx.doi.org/10.1364/AO.56.001202DOI Listing
February 2017

Silicon photonic time-wavelength pulse interleaver for photonic analog-to-digital converters.

Opt Express 2016 Jun;24(12):13489-99

A 4-channel time-wavelength optical pulse interleaver is implemented on a silicon chip. The interleaver forms a train of pulses with periodically changing wavelengths by demultiplexing the input pulse train into several wavelength components, delaying these components with respect to each other, and multiplexing them back into a single path. The interleaver is integrated on a silicon chip, with two arrays of microring resonator filters performing multiplexing and demultiplexing, and long sections of silicon waveguides acting as delay lines. The 4-channel interleaver is designed for an input pulse train with 1 GHz repetition rate, and is measured to have 0.35% RMS pulse timing error, insertion loss between 1.6 dB and 5.8 dB in different channels, crosstalk below -24 dB, and 52 nm free spectral range achieved using the Vernier effect.
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http://dx.doi.org/10.1364/OE.24.013489DOI Listing
June 2016

Absence of Structural Impact of Noble Nanoparticles on P3HT:PCBM Blends for Plasmon-Enhanced Bulk-Heterojunction Organic Solar Cells Probed by Synchrotron GI-XRD.

Sci Rep 2015 Jun 1;5:10633. Epub 2015 Jun 1.

Masdar Institute of Science and Technology, PO Box 54224, Abu Dhabi, United Arab Emirates.

The incorporation of noble metal nanoparticles, displaying localized surface plasmon resonance, in the active area of donor-acceptor bulk-heterojunction organic photovoltaic devices is an industrially compatible light trapping strategy, able to guarantee better absorption of the incident photons and give an efficiency improvement between 12% and 38%. In the present work, we investigate the effect of Au and Ag nanoparticles blended with P3HT: PCBM on the P3HT crystallization dynamics by synchrotron grazing incidence X-ray diffraction. We conclude that the presence of (1) 80 nm Au, (2) mix of 5 nm, 50 nm, 80 nm Au, (3) 40 nm Ag, and (4) 10 nm, 40 nm, 60 nm Ag colloidal nanoparticles, at different concentrations below 0.3 wt% for Au and below 0.1% for Ag in P3HT: PCBM blends, does not affect the behaviour of the blends themselves.
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http://dx.doi.org/10.1038/srep10633DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4450591PMC
June 2015

Photonic ADC: overcoming the bottleneck of electronic jitter.

Opt Express 2012 Feb;20(4):4454-69

Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.

Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical imaging, and communication systems. Aperture jitter has been a major bottleneck on the way towards higher speeds and better accuracy. Photonic ADCs, which perform sampling using ultra-stable optical pulse trains generated by mode-locked lasers, have been investigated for many years as a promising approach to overcome the jitter problem and bring ADC performance to new levels. This work demonstrates that the photonic approach can deliver on its promise by digitizing a 41 GHz signal with 7.0 effective bits using a photonic ADC built from discrete components. This accuracy corresponds to a timing jitter of 15 fs - a 4-5 times improvement over the performance of the best electronic ADCs which exist today. On the way towards an integrated photonic ADC, a silicon photonic chip with core photonic components was fabricated and used to digitize a 10 GHz signal with 3.5 effective bits. In these experiments, two wavelength channels were implemented, providing the overall sampling rate of 2.1 GSa/s. To show that photonic ADCs with larger channel counts are possible, a dual 20-channel silicon filter bank has been demonstrated.
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http://dx.doi.org/10.1364/OE.20.004454DOI Listing
February 2012

Reconfigurable multi-channel second-order silicon microring-resonator filterbanks for on-chip WDM systems.

Opt Express 2011 Jan;19(1):306-16

Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

We report the fabrication of a reconfigurable wide-band twenty-channel second-order dual filterbank, defined on a silicon-on-insulator (SOI) platform, with tunable channel spacing and 20 GHz single-channel bandwidth. We demonstrate the precise tuning of eleven (out of the twenty) channels, with a channel spacing of 124 GHz (~1 nm) and crosstalk between channels of about -45 dB. The effective thermo-optic tuning efficiency is about 27 μW/GHz/ring. A single channel of a twenty-channel counter-propagating filterbank is also demonstrated, showing that both propagating modes exhibit identical filter responses. Considerations about thermal crosstalk are also presented. These filterbanks are suitable for on-chip wavelength-division-multiplexing applications, and have the largest-to-date reported number of channels built on an SOI platform.
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http://dx.doi.org/10.1364/OE.19.000306DOI Listing
January 2011

Ultrafast all-optical modulator with femtojoule absorbed switching energy in silicon-on-insulator.

Opt Express 2010 Oct;18(21):22485-96

IBM Research GmbH, Zurich Research Laboratory, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

We demonstrate an all-optical switch based on a waveguide-embedded 1D photonic crystal cavity fabricated in silicon-on-insulator technology. Light at the telecom wavelength is modulated at high-speed by control pulses in the near infrared, harnessing the plasma dispersion effect. The actual absorbed switching power required for a 3 dB modulation depth is measured to be as low as 6 fJ. While the switch-on time is on the order of a few picoseconds, the relaxation time is almost 500 ps and limited by the lifetime of the charge carriers.
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http://dx.doi.org/10.1364/OE.18.022485DOI Listing
October 2010

Device architecture and precision nanofabrication of microring-resonator filter banks for integrated photonic systems.

J Nanosci Nanotechnol 2010 Mar;10(3):2044-52

Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 36-285, Cambridge, MA 02139, USA.

To achieve the maximum benefit of electronic-photonic integrated circuits wavelength-division multiplexing must be used. This requires the design and fabrication of a highly integratable photonic device, capable of performing multiplexing/demultiplexing operations with low loss and minimal crosstalk. A filter bank consisting of high-index-contrast microring-resonator filters, with accurately spaced resonant frequencies can meet these requirements. This paper describes the basic architecture of microring-resonator filter banks, and how to maximize performance while keeping fabrication challenges reasonable. The greatest challenge in fabricating such devices is achieving the dimensional precision, on the scale of tens of picometers, needed to attain accurately spaced resonant frequencies. To do this, a fabrication method based on varying the electron-beam dose during scanning-electron beam lithography is used. This approach is used to create a dual twenty-channel filter bank, comprised of second-order silicon-rich silicon nitride microring resonators. The average resonant frequency spacing is off from the target spacing by only 3 GHz, corresponding to a dimensional precision of 75 pm. This approach is also shown to be compatible with the fabrication process for silicon microring resonators. Furthermore, it is shown that any remaining resonant frequency errors can be corrected with postfabrication thermal tuning. Also, a method of using the contra-propagating mode of a microring-resonator filter is demonstrated, enabling a single filter bank to multiplex/demultiplex two signals at the same time.
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http://dx.doi.org/10.1166/jnn.2010.2035DOI Listing
March 2010

Accurate frequency alignment in fabrication of high-order microring-resonator filters.

Opt Express 2008 Sep;16(20):15958-63

Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.

Frequency mismatch in high-order microring-resonator filters is investigated. We demonstrate that this frequency mismatch is caused mainly by the intrafield distortion of scanning-electron-beam-lithography (SEBL) used in fabrication. The intrafield distortion of an SEBL system is measured, and a simple method is also proposed to correct this distortion. By applying this correction method, the average frequency mismatch in second-order microring-resonator filters was reduced from -8.6 GHz to 0.28 GHz.
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http://dx.doi.org/10.1364/oe.16.015958DOI Listing
September 2008

Achieving centimetre-scale supercollimation in a large-area two-dimensional photonic crystal.

Nat Mater 2006 Feb 15;5(2):93-6. Epub 2006 Jan 15.

Diffraction, a fundamental process in wave physics, leads to spreading of the optical beams as they propagate. However, new photonic crystal (PhC) meta-materials can be nano-engineered to generate extreme anisotropy, resulting in apparent propagation of light without diffraction. This surprising phenomenon, called supercollimation, effectively freezes the spatial width of a light beam inside a PhC, observed over a few isotropic diffraction-lengths. However, using such experiments to predict the behaviour for longer propagation lengths is difficult, as a tiny error in a measured width can extrapolate to order unity uncertainty in the width at distances over hundreds of diffraction-lengths. Here, supercollimation is demonstrated in a macroscopic PhC system over centimetre-scale distances, retaining spatial width confinement without the need for waveguides or nonlinearities. Through quantitative studies of the beam evolution in a two-dimensional PhC, we find that supercollimation possesses unexpected but inherent robustness with respect to short-scale disorder such as fabrication roughness, enabling supercollimation over 600 isotropic diffraction-lengths. The effects of disorder are identified through experiments and understood through rigorous simulations. In addition, a supercollimation steering capability is proposed.
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http://dx.doi.org/10.1038/nmat1568DOI Listing
February 2006

A novel activation process of protein kinase C in the remote, non-ischemic area of an infarcted heart is mediated by angiotensin-AT1 receptors.

J Mol Cell Cardiol 2003 Nov;35(11):1349-58

Department of Cardiology, Technical University of Dresden, Fetscherstreet 76, D-01307 Dresden, Germany.

Background: Translocation and activation of protein kinase C (PKC) has been shown to occur in the ischemic heart. It is, however, controversial if this activation process occurs also in the non-ischemic, remote area of an infarcted heart early after infarction. Furthermore, the mechanisms contributing to the translocation process induced by acute myocardial ischemia in both areas are not fully elucidated.

Methods: Regional myocardial infarction was induced by left anterior descending coronary artery (LAD-) ligation in situ for 2.5 min in rats or in pigs. To evaluate the influence of angiotensin and bradykinin signaling, ramiprilat, candesartan, or the bradykinin-receptor antagonist HOE 140 was given. In biopsies from the ischemic and the non-ischemic remote area, PKC activity and intracellular isozyme distribution were determined.

Results: Translocation and activation of PKC could be demonstrated for the first time in the myocardium remote from the infarcted area. This activation was conserved both in pigs and in rats. All major cardiac isozymes of PKC were involved. Whereas bradykinin-receptor blockade had no effect, both angiotensin-converting enzyme inhibition (ACEI) and angiotensin receptor could effectively block this activation process of PKC.

Conclusion: In the area remote from a myocardial infarction, the activation of PKC could be detected for the first time as early as 2.5 min after LAD ligation. This newly characterized activation in the non-infarcted area can be prevented by ACEI via an angiotensin-AT1-receptor-dependent mechanism. It is supposed that this newly characterized activation process of PKC plays an important role in the signal transduction in the remote myocardium in acute myocardial infarction as a trigger for the late development of hypertrophy and heart failure.
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http://dx.doi.org/10.1016/s0022-2828(03)00250-5DOI Listing
November 2003
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