3,150 research outputs found
All-optical membrane InP switch on silicon for access applications
Using an integrated membrane switch on SOI, optical clock distribution is achieved while all-optical switching of datapackets is maintained. Transmission through 25km SMF is demonstrated with 1.5dB penalty, limited by signal OSNR and pump extinction
InP membrane based broadband regenerator for silicon-based optical interconnect applications
We demonstrate the use of a Membrane-InP-Switch(MIPS) on-silicon as a signal regenerator. A receiver sensitivity enhancement >2.5dB across the entire C-band and a tripling of Extinction Ratio(ER) for low ER signals at 1Gb/sec is demonstrated
Passive InP regenerator integrated on SOI for the support of broadband silicon modulators
Passive signal regeneration based on the Membrane InP Switch (MIPS) is demonstrated. Because of the high confinement of light in the active region of the MIPS, the device acts as a saturable absorber with a highly non-linear response. Using this effect, the extinction ratio (ER) of low-ER signals can be tripled and a receiver sensitivity enhancement of 4.5dB is demonstrated using an input signal at 1Gb/s with an ER of 2dB. Regenerator operation up to 5Gb/s is demonstrated and using a device simulator a strategy to reach higher bitrate operation is propose
Thermally induced magnetic switching in bit-patterned media
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 122, 043907 (2017) and may be found at https://doi.org/10.1063/1.4992808.We have studied the thermal variation of the switching field of magnetic islands at room temperature. A model bit-pattern media composed of an assembly of islands with 80 nm width was fabricated by sputter deposition onto a pre-patterned substrate. Using direct magnetic-contrast imaging of the islands under applied field, we extract the switching probabilities of individual islands. Based on an analytical model for the thermally activated switching of the islands, we are able to determine the intrinsic magnetic anisotropy of each island and, consequentially, a distribution of anisotropies for the island ensemble investigated. In the distribution, we identify a separated group of islands with a particularly small anisotropy. We attribute this group to islands containing misaligned grains triggering the magnetic reversal. At room temperature and slow field sweep rates, the observed thermal broadening of the switching-field distribution is small compared to the intrinsic broadening. However, we illustrate that thermal fluctuations play a crucial role at high sweep rates by extrapolating our results to technological relevant regimes
Membrane InP saturable absorbers on silicon as building blocks for transparent optical networks
As silicon photonics continues to gain research and industrial relevance, some of the building blocks in this technology such as modulators and switches still suffer from limitation when it comes to insertion losses and/or extinction ratio. In the past two years we have been investigating a promising new building block for silicon on insulator (SOI) circuits which is based on ultra-thin narrow stripes of InP bonded on top of SOI, which operate as saturable absorbers at very low optical power levels. The unique properties of these membrane InP switches (MIPS) make them ideally suitable as complementary components to SOI devices. By controlling the band gap of the active layers in the membrane as well as the confinement of light critical properties of such MIPS can be determined and tailored to specific applications.
In this talk we will highlight two exciting applications of MIPS on SOI. First we will show how they enhance the performance of silicon based modulators by regenerating the signal through their non-linear response. Secondly we will show how they may solve a unique engineering challenge for next generation access networks by operating as optically controlled switches with high extinction ratio and no electrical power supply
A 2D pixelated stilbene scintillator detector array for simultaneous radiography with fast neutrons and gammas
For radiography applications using fast neutrons simultaneously with gammas
we have developed a detector with 16 stilbene crystals in a 44 2D array
with a 5~mm pitch and a depth of 25~mm. The crystal array is read out by
Silicon photomultipliers and custom signal processing electronics. The detector
prototype was tested using a custom D-D fast neutron generator at the Paul
Scherrer Institute. By applying a pulse shape discrimination algorithm the
detector is able to detect and distinguish fast neutrons and gammas
simultaneously. Various attenuating samples placed between the source and
detector with different materials and thicknesses were tested and the measured
macroscopic fast neutron cross sections were compared to what was expected.
Deviations were studied with the help of detailed Geant4 simulations. The
detection efficiency for D-D fast neutrons was measured to be around 10\%.Comment: Prepared for submission to JINST. Changes compared to previous
version: article was edited due to JINST referee feedback (minor revision
requested). Figure 3 was updated. Formulations were improved, some
explanations were given in more detail. Reference list was updated (reference
15 was exchanged
Magnetic ground state and 2D behavior in pseudo-Kagome layered system Cu3Bi(SeO3)2O2Br
Anisotropic magnetic properties of a layered kagome-like system
Cu3Bi(SeO3)2O2Br have been studied by bulk magnetization and magnetic
susceptibility measurements as well as powder and single-crystal neutron
diffraction. At T_N = 27.4 K the system develops an alternating
antiferromagnetic order of (ab) layers, which individually exhibit canted
ferrimagnetic moment arrangement, resulting from the competing ferro- and
antiferro-magnetic intralayer exchange interactions. A magnetic field B_C ~ 0.8
T applied along the c axis (perpendicular to the layers) triggers a
metamagnetic transition, when every second layer flips, i.e., resulting in a
ferrimagnetic structure. Significantly higher fields are required to rotate the
ferromagnetic component towards the b axis (~7 T) or towards the a axis (~15
T). The estimates of the exchange coupling constants and features indicative of
an XY character of this quasi-2D system are presented.Comment: 7 pages, 6 figures, final versio
Magnetism of PdNi alloys near the critical concentration for ferromagnetism
We report results of a muon spin rotation and relaxation (SR) study of
dilute PdNi alloys, with emphasis on Ni concentrations 0.0243
and 0.025. These are close to the critical value for the onset
of ferromagnetic long-range order (LRO), which is a candidate for a quantum
critical point. The 2.43 and 2.5 at.% Ni alloys exhibit similar SR
properties. Both samples are fully magnetic, with average muon local fields
2.0 and 3.8 mT and Curie temperatures
1.0 and 2.03 K for 2.43 and 2.5 at.% Ni, respectively, at . The
temperature dependence of suggests ordering of
Ni spin clusters rather than isolated spins. Just above a two-phase
region is found with separate volume fractions of quasistatic short-range order
(SRO) and paramagnetism. The SRO fraction decreases to zero with increasing
temperature a few kelvin above . This mixture of SRO and paramagnetism is
consistent with the notion of an inhomogeneous alloy with Ni clustering. The
measured values of extrapolate to = 0.0236 0.0027.
The dynamic muon spin relaxation in the vicinity of differs for the two
samples: a relaxation-rate maximum at is observed for = 0.0243,
reminiscent of critical slowing down, whereas for 0.025 no dynamic
relaxation is observed within the SR time window. The data suggest a
mean-field-like transition in this alloy.Comment: 15 pages, 15 figures, to be published in Phys. Rev.
Hantavirus-driven PD-L1/PD-L2 upregulation: An imperfect viral immune evasion mechanism
Viruses often subvert antiviral immune responses by taking advantage of inhibitory immune signaling. We investigated if hantaviruses use this strategy. Hantaviruses cause viral hemorrhagic fever (VHF) which is associated with strong immune activation resulting in vigorous CD8+ T cell responses. Surprisingly, we observed that hantaviruses strongly upregulate PD-L1 and PD-L2, the ligands of checkpoint inhibitor programmed death-1 (PD-1). We detected high amounts of soluble PD-L1 (sPD-L1) and soluble PD-L2 (sPD-L2) in sera from hantavirus-infected patients. In addition, we observed hantavirus-induced PD-L1 upregulation in mice with a humanized immune system. The two major target cells of hantaviruses, endothelial cells and monocyte-derived dendritic cells, strongly increased PD-L1 and PD-L2 surface expression upon hantavirus infection in vitro. As an underlying mechanism, we found increased transcript levels whereas membrane trafficking of PD-L1 was not affected. Further analysis revealed that hantavirus-associated inflammatory signals and hantaviral nucleocapsid (N) protein enhance PD-L1 and PD-L2 expression. Cell numbers were strongly reduced when hantavirus-infected endothelial cells were mixed with T cells in the presence of an exogenous proliferation signal compared to uninfected cells. This is compatible with the concept that virus-induced PD-L1 and PD-L2 upregulation contributes to viral immune escape. Intriguingly, however, we observed hantavirus-induced CD8+ T cell bystander activation despite strongly upregulated PD-L1 and PD-L2. This result indicates that hantavirus-induced CD8+ T cell bystander activation bypasses checkpoint inhibition allowing an early antiviral immune response upon virus infection
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