Towards plasmonic lasers for optical interconnects

A plasmonic laser structure coupled to a dielectric waveguide is proposed and investigated by rigorous simulations. Modal characteristics, such as propagation loss and confinement factor were obtained for a wavelength of 1.55 µm. In addition, FDTD (Finite-Difference Time-Domain) simulations were used to calculate the reflectivity from the end facets of the laser structure and also to calculate the coupling between the laser and a dielectric waveguide. Simulations show that a threshold gain of 1796 cm-1 is required to compensate the total loss in a 200 nm wide and 50 µm long laser, which can be achievable at room temperature

Towards a circular economy: insights based on the development of the global ENGAGE-materials model and evidence for the iron and steel industry

A number of recent economic modelling studies have attempted to analyse resource efficiency and the circular economy. However, modelling analysis in this area is relatively underdeveloped. In particular, many CGE models are unable to provide significant insight given their aggregated sectoral coverage. Here we describe the development of the Environmental Global Applied General Equilibrium (ENGAGEmaterials) model created to consider the economic and sectoral effects of potential policies on a circular economy and resource efficiency, which affect materials and resources at the stages of extraction, production and recycling. Our policy scope is global with a special emphasis on China and Europe, as both regions have dedicated policies in place and indicate their willingness to take the lead. The case of steel is relevant as it is a key material for all economies across the world and offers a range of interesting features for circularity and sustainability. ENGAGE-materials models iron ore mining, primary production of iron and steel, secondary production of iron and steel, and steel scrap recycling at the global level. We utilise this technology rich framework to provide preliminary results on scenarios comprising economic insights into a saturation effect and straightforward policy such as doubling the availability of secondary steel

Waveguide-coupled nanolasers in III-V membranes on silicon

Semiconductor nanolasers provide an attractive route towards high density photonic integrated circuits in low power applications such as optical interconnects. In this paper we present the concept of a waveguide-coupled nanolaser for integration in a CMOS compatible photonic platform. We exploit metallic and dielectric confinement to provide high quality factors exceeding 500 in a wavelength-scale cavity, that provides efficient cooling and cross-talk immunity due to the metal coverage. We present simulations detailing the design considerations for high quality factors and efficient waveguide coupling. Optical and electrical simulations predict room temperature operation at 1.55 µm with a threshold current of 120 µA and a differential quantum efficiency of 0.16. We also discuss briefly the challenges of fabricating these devices and integrating them in the photonic platform

Fabrication of an efficient metal grating coupler for membrane-based integrated photonics

This paper reports the progress on the fabrication process of highly efficient metal grating couplers for membrane-based integrated circuits, using double side processing technology on bonded samples. This type of gratings comprises a buried SiO2/Ag grating of 125nm thickness with a silver layer as metal mirror, and has several advantages over dielectric gratings as metallic gratings are independent from the buffer thickness. We predict a theoretical chip-to-fiber coupling efficiency of 74% and 89% for uniform and apodized gratings respectively, at a wavelength of 1550 nm. Furthermore, the fabrication process can be used for both, SOI and III-V based platforms

Economy-wide rebound makes UK's electric car subsidy fall short of expectations

Environmental policies often underperform due to so-called rebound effects, namely behavioural and systemic responses to technical change leading to additional consumption and environmental damage. While evidence of rebound is abundant, studies generally focus on technical changes that are neither associated with specific technologies nor their production costs, making it difficult to connect these changes with the policies governing them. To overcome this limitation, this study proposes to combine a technology-rich model based on life cycle assessment and a behaviour-optimising model for the global economy based on computable general equilibrium modelling. This approach allows to quantify policy-induced economy-wide rebound effects for four relevant environmental impacts: climate change, acidification, photochemical ozone formation, and particulate matter. We apply this approach to evaluate the effectiveness of the United Kingdom's subsidy on electric cars. The results show notable economy-wide rebound effects associated with this subsidy: over or close to 100% (no environmental benefits) for acidification and particulate matter impacts, and a lower, yet notable, magnitude for climate change (~20–50%) and photochemical ozone formation (~30–80%) impacts. The results also show the important role of macro-economic effects from price changes, particularly how the shift from petrol to electricity triggered additional demand for cheaper petrol

Low-optical-loss, low-resistance Ag/Ge based ohmic contacts to n-type InP for membrane based waveguide devices

We present the development of Ag/Ge based ohmic contacts to n-type InP with both low contact resistances and relatively low optical losses. A specific contact resistance as low as 1.5×10-6 O cm2 is achieved by optimizing the Ge layer thickness and annealing conditions. The use of Ge instead of metal as the first deposited layer results in a low optical absorption loss in the telecommunication wavelength range. Compared to Au based contacts, the Ag based metallization also shows considerably reduced spiking effects after annealing. Contacts with different lengths are deposited on top of InP membrane waveguides to characterize the optical loss before and after annealing. A factor of 5 reduction of the propagation loss compared to the conventional Au/Ge/Ni contact is demonstrated. This allows for much more optimized designs for membrane photonic devices

Steel in a circular economy: global implications of a green shift in China

China is increasingly known for its ambitions towards an ‘ecological civilisation’ and a circular economy. Our article assesses the implications of an accelerated shift towards steel recycling in China. Given the relevance of steel for development worldwide as well as its environmental intensity, any such shift is likely to have implications for competitiveness in China and beyond. Recent findings suggest that China could take advantage of an increasing availability of obsolete steel scrap in the coming decades, moving towards more circular, and potentially greener, steel production. We assess such industrial restructuring from an economic perspective and address the competitiveness of China relative to other developing and industrialised regions. The analysis uses a novel global economy-wide modelling framework (ENGAGE-materials) to assess the aggregate and sector-level impacts of different scrap use options in China in the 2019–2030 time frame. The results show moderate GDP gains for China of cumulated USD 589 billion in GDP gains by 2030 despite a replacement of primary steel capacity. A more comprehensive industrial policy mix aimed at improved recycling practices and more adaptive downstream sectors could increase gains to USD 819 billion. The international implications are mixed, with losses for iron ore producers (Australia, Brazil and India) and gains for most developing countries benefiting from lower steel prices. Another result is an increasing demand for coal in electricity production if such a shift wouldn’t be aligned with an accelerated energy transition towards low carbon pathways. We discuss policy implications of such alignment, potential co-benefits, and a need for green international partnerships