Broadband III-V on silicon hybrid superluminescent LEDs by quantum well intermixing and multiple die bonding

Combining quantum well intermixing and multiple die bonding a broadband superluminescent III-V on silicon LED was realized. Balancing four LEDs with different band gaps resulted in 292nm 3dB bandwidth and an on-chip power of -8dBm

High temperature thermoreflectance imaging and transient Harman characterization of thermoelectric energy conversion devices

Advances in thin film growth technology have enabled the selective engineering of material properties to improve the thermoelectric figure of merit and thus the efficiency of energy conversion devices. Precise characterization at the operational temperature of novel thermoelectric materials is crucial to evaluate their performance and optimize their behavior. However, measurements on thin film devices are subject to complications from the growth substrate, non-ideal contacts, and other thermal and electrical parasitic effects. In this manuscript, we determine the cross-plane thermoelectric material properties in a single measurement of a 25 mu m InGaAs thin film with embedded ErAs (0.2%) nanoparticles using the bipolar transient Harman method in conjunction with thermoreflectance thermal imaging at temperatures up to 550K. This approach eliminates discrepancies and potential device degradation from the multiple measurements necessary to obtain individual material parameters. In addition, we present a strategy for optimizing device geometry to mitigate the effect of both electrical and thermal parasitics during the measurement. Finite element method simulations are utilized to analyze non-uniform current and temperature distributions over the device area as well as the three dimensional current path for accurate extraction of material properties from the thermal images. Results are compared with independent in-plane and 3 omega measurements of thermoelectric material properties for the same material composition and are found to match reasonably well; the obtained figure of merit matches within 15% at room and elevated temperatures. (C) 2014 AIP Publishing LLC

An integrated magneto-optic modulator for cryogenic applications

Superconducting circuits can operate at higher energy efficiencies than their room-temperature counterparts and have the potential to enable large-scale control and readout of quantum computers. However, the required interface with room-temperature electronics creates difficulties in scaling up such cryogenic systems. One option is to use optical fibres as a medium in conjunction with fast optical modulators that can be efficiently driven by electrical signals at low temperatures. However, as superconducting circuits are current operated with low impedances, they interface poorly with conventional electro-optical modulators. Here we report an integrated current-driven modulator that is based on the magneto-optic effect and can operate at temperatures as low as 4 K. The device combines a magneto-optic garnet crystal with a silicon waveguide resonator and integrates an electromagnet to modulate the refractive index of the garnet. The modulator offers data rates of up to 2 Gbps with an energy consumption below 4 pJ per bit of transferred information, which could be reduced to less than 50 fJ per bit by replacing dissipative electrodes with superconductors and optimizing the geometric parameters

Right sizes of nano- and microstructures for high-performance and rigid bulk thermoelectrics

In this paper, we systematically investigate three different routes of synthesizing 2% Na-doped PbTe after melting the elements: (i) quenching followed by hot-pressing (QH), (ii) annealing followed by hot-pressing, and (iii) quenching and annealing followed by hot-pressing. We found that the thermoelectric figure of merit, zT, strongly depends on the synthesis condition and that its value can be enhanced to similar to 2.0 at 773 K by optimizing the size distribution of the nanostructures in the material. Based on our theoretical analysis on both electron and thermal transport, this zT enhancement is attributed to the reduction of both the lattice and electronic thermal conductivities; the smallest sizes (2 similar to 6 nm) of nanostructures in the QH sample are responsible for effectively scattering the wide range of phonon wavelengths to minimize the lattice thermal conductivity to similar to 0.5 W/m K. The reduced electronic thermal conductivity associated with the suppressed electrical conductivity by nanostructures also helped reduce the total thermal conductivity. In addition to the high zT of the QH sample, the mechanical hardness is higher than the other samples by a factor of around 2 due to the smaller grain sizes. Overall, this paper suggests a guideline on how to achieve high zT and mechanical strength of a thermoelectric material by controlling nano-and microstructures of the material

Methylating mushrooms

Peptide N-methylation is an important strategy used by medicinal chemists to improve cell permeability, oral bioavailability, and target affinity of peptide-based inhibitors. Correspondingly, N-methyl amides appear extensively in bioactive natural products. In the case of the immunosuppressant cyclosporine, for example, specific N-methylation of seven out of ten backbone amide nitrogens in the cyclic decapeptide is thought to allow a conformational ‘shapeshifting’ that hides polar N–H moieties and facilitates passive diffusion across cell membranes. Until now, N-methylation has primarily been the mark of peptide natural products from complex nonribosomal peptide synthetase (NRPS) assembly lines, and has not previously been found among their cousins, the ribosomally synthesized and post-translationally modified peptide (RiPP) natural products. In this issue, van der Velden et al. uncover the biosynthetic origins of the omphalotins, peptide natural products from the bioluminescent fungus O. olearius (Fig. 1a), and bring peptide backbone N-methylation into the realm of peptide post-translational modifications

Roadmap of optical communications

© 2016 IOP Publishing Ltd. Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications