Marco Clementi

The Stability of the US Hegemony in Times of Regional Divergence

This chapter focuses on the relationship between the possible US decline and the growing divergence of political dynamics at the regional level. It investigates contemporary US strategic discourse in order to understand whether it has theorized the decline-regionalism nexus and, if so, with what policy implications. To this aim, the chapter develops a theoretical framework to classify the different conceptions of decline and sketches the different causal paths by which declinism and regionalism could influence one another. The chapter maintains that, short of Bush Junior’s Global War on Terror, the decline-regionalism nexus has steadily influenced US contemporary foreign policy. In particular, it maintains that the regional policies adopted by the US to answer the perception of national decline, and thus keep its global influence, contributed to the overall process of regionalization. However, the kind of decline the US perceived did change and revealed the decline-regionalism nexus differently related to the hegemonic role of the country.

Ultrahigh-Q photonic crystal cavities in silicon rich nitride

Ultrahigh-Q Photonic Crystal cavities were realized in a suspended Silicon Rich Nitride (SiNx) platform for applications at telecom wavelengths. Using a line width modulated cavity design we achieved a simulated Q of 520,000 with a modal volume of 0.77(λ/n)3. The fabricated cavities were measured using the resonance scattering technique and we demonstrated a measured Q of 120,000. The experimental spectra at different input power also indicate that the non-linear losses are negligible in this material platform.

On-Chip Nonlinear Optics in Silicon Rich Nitride Photonic Crystal Cavities

Photonic crystal (PhC) nanocavities allow to confine light with ultra high quality (Q) factors to wavelength-sized mode volumes, with a strong enhancement of light-matter interaction. Although these features make PhC cavities a promising platform for integrated nonlinear optical components, the usual materials of photonic fabrication (specifically silicon and gallium arsenide) suffer from parasitic effects such as two-photon absorption (TPA) and free-carrier absorption (FCA), which limit the benefits of integration. In this work we show how a novel material, silicon rich nitride [1], can be successfully employed for the fabrication of air membraned PhC cavities reaching ultra high Q factor at telecom wavelength. We fabricated samples with line-width modulated geometry, approaching a theoretical value (from FDTD simulations) of Qth = 520, 000. We then measured the cavities with resonant scattering technique [2], determining a maximum experimental value Qexp = 122, 000. We later studied the spectral behaviour of the cavity at a regime of optical bistability [3]. The resulting analysis of the thermo-optic resonance shift as a function of input power suggests the absence of TPA and TPA-related FCA. In order to confirm the suitability of this material for nonlinear optical signal processing, we designed and fabricated far-field optimized samples [4] with heterostructure geometry. Far-field optimization allows to dramatically increase the coupling of the cavity to focused laser beams, thus increasing the available intracavity optical power. In this experimental configuration we observed second (SHG) and third (THG) harmonic generation even at low CW input power (as low as a fraction of milliwatt). These results confirm the suitability of silicon rich nitride as a potential platform for efficient integrated nonlinear optical devices based upon PhC nanocavities in a fully CMOS compatible approach.

Domestic Constraints, Governmental Instability and Italian Foreign Policy

This chapter provides an analysis of how Italy’s policymakers adjusted Italys foreign and security policies to an evolving international political and security environment in the mid-2000s. A particular focus will be laid on Italy’s foreign policy choices of the centre-left government led by Prime Minister Romano Prodi in 2007 when domestic controversies on foreign policy caused a government crisis. The chapter concludes that Italy is today more active and involved in international politics and security and has had to come to terms with the use of force when contributing to international military operations. However, the events that occurred during the Prodiled government suggest that Italy’s political institutions have been able to safeguard the coherence and commitments of Italian foreign policies despite obstacles and contradictions in domestic politics.