Modulational instability in a silicon-on-insulator directional coupler: Role of the coupling-induced group velocity dispersion

We report frequency conversion experiments in silicon-on-insulator (SOI) directional couplers. We demonstrate that the evanescent coupling between two subwavelength SOI waveguides is strongly dispersive and significantly modifies modulational instability (MI) spectra through the coupling induced group velocity dispersion (GVD). As the separation between two 380-nm-wide silicon photonic wires decreases, the increasing dispersion of the coupling makes the GVD in the symmetric supermode more normal and suppresses the bandwidth of the MI gain observed for larger separations

Revolution and Diavolution: What is the Difference?

Whereas revolution has been often viewed as contrary to organization, it in fact requires the overcoming of a present organization in the promise of achieving another superior organization. The revolutionaries of every age have always harboured a dream of organization. In an attempt to achieve better understanding of the relationship between organization and revolution, the article conducts a theoretical, rather than historical, reflection on the interplay among three concepts: organization, revolution, and diavolution. By exploring the modernist conception of revolution and its religious substratum, the idea is advanced that the relationship can be framed as follows: organization is the katéchon of revolution, whereas revolution is the éschaton of organization. The last part of the article introduces and discusses the concept of diavolution as an attempt to overcome the dichotomy between the subjectivist and the structuralist view both at the theoretical and the practical level. Diavolution is a style of inhabiting organizations that differs from the revolutionary one; a style of resistance that, although much more elusive and difficult to capture, may prove to be at the same time more human

Evanescent coupling assisted four-wave mixing in a silicon-on-insulator directional coupler

Four-wave mixing (FWM) has been extensively explored in optical fibers and more recently in on-chip silicon-oninsulator (SOI) waveguides. A phase-matched FWM with a pair of degenerate pump photons generating and amplifying signal and idler photons is referred as modulational instability (MI). Following theory of FWM in waveguide arrays, we utilize evanescent couplings between neighboring waveguides to control the phase-matching condition in FWM. In experiments, a set of single-channel SOI nanowaveguides with the waveguide width decreasing from 380nm to 340nm demonstrate that changing the waveguide group velocity dispersion (GVD) at the pump wavelength from being anomalous to being normal makes MI gain gradually disappear. We also perform the same experiment with an array of two 380nm-wide SOI waveguide, and demonstrate that for the large separation of 900nm and 800nm, MI gain is present as for the single waveguide; while for the small separation of 400nm, the MI gain disappears. This transformation of phase-matching in FWM is attributed to the fact that the coupling induced dispersion changes the net GVD of the symmetric supermode from being anomalous for large separation to being normal for small separation. Our observation illustrates that the coupling-induced GVD can compete and exceed in value the GVD of a single SOI nanowaveguide. This creates a new previously unexplored degree of freedom to control FWM on chips

Pregnancy in women with a mechanical heart valve: Data of the European Society of Cardiology Registry of Pregnancy and Cardiac Disease (ROPAC)

Background - Pregnant women with a mechanical heart valve (MHV) are at a heightened risk of a thrombotic event, and their absolute need for adequate anticoagulation puts them at considerable risk of bleeding and, with some anticoagulants, fetotoxicity. Methods and Results - Within the prospective, observational, contemporary, worldwide Registry of Pregnancy and Cardiac disease (ROPAC), we describe the pregnancy outcome of 212 patients with an MHV. We compare them with 134 patients with a tissue heart valve and 2620 other patients without a prosthetic valve. Maternal mortality occurred in 1.4% of the patients with an MHV, in 1.5% of patients with a tissue heart valve (P=1.000), and in 0.2% of patients without a prosthetic valve (P=0.025). Mechanical valve thrombosis complicated pregnancy in 10 patients with an MHV (4.7%). In 5 of these patients, the valve thrombosis occurred in the first trimester, and all 5 patients had been switched to some form of heparin. Hemorrhagic events occurred in 23.1% of patients with an MHV, in 5.1% of patients with a tissue heart valve (P<0.001), and in 4.9% of patients without a prosthetic valve (P<0.001). Only 58% of the patients with an MHV had a pregnancy free of serious adverse events compared with 79% of patients with a tissue heart valve (P<0.001) and 78% of patients without a prosthetic valve (P<0.001). Vitamin K antagonist use in the first trimester compared with heparin was associated with a higher rate of miscarriage (28.6% versus 9.2%; P<0.001) and late fetal death (7.1% versus 0.7%; P=0.016). Conclusions - Women with an MHV have only a 58% chance of experiencing an uncomplicated pregnancy with a live birth. The markedly increased mortality and morbidity warrant extensive prepregnancy counseling and centralization of care.</p