“Confining the Enemy”—Halford Mackinder’s Theory of Containment and the Conflict in Ukraine

Before George Kennan outlined his vision of containment, Halford Mackinder articulated a vision of maritime geostrategic logic that prioritized some geographic locations over others. Because Mackinder’s writings have been marshaled to assess the ongoing U.S. commitment to Ukraine, it is important to appreciate how his theory applies to the current crisis

All-Optical Modulation in a Silicon Waveguide Based on a Single-Photon Process

All-optical, low-power modulation is a major goal in photonics. Because of their high mode-field concentration and ease of manufacturing, nanoscale silicon waveguides offer an intriguing platform for photonics. So far, all-optical modulators built with silicon photonic circuits have relied on either two-photon absorption or the Kerr effect. Both effects are weak in silicon, and require extremely high (~5 W) peak optical power levels to achieve modulation. Here, we describe an all-optical Mach-Zehnder modulator based on a single-photon absorption (SPA) process, fabricated entirely in silicon. Our SPA modulator is based on a process by which a single photon at 1.55 mum is absorbed and an apparently free-carrier-mediated process causes an index shift in silicon, even though the photon energy does not exceed that of silicon's bandgap. We demonstrate all-optical modulation with a gate response of 1deg/mW at 0.5 Gb/s. This is over an order of magnitude more responsive than typical previously demonstrated devices. Even without resonant enhancement, further engineering may enable all optical modulation with less than 10 mW of gate power required for complete extinction, and speeds of 5 Gb/s or higher

High quality factors and room-temperature lasing in a modified single-defect photonic crystal cavity

We propose and analyze a new photonic crystal cavity design that supports a dipole mode with a quality factor greater than 20,000. Such a high quality factor is obtained by precise tuning of the cavity length with minimal disruption of the surrounding photonic crystal. A fabrication procedure based on dry etching of InGaAsP material in HI/H2/Ar is used to demonstrate photonic crystal lasers with smooth and straight sidewalls. These room-temperature lasers concentrate optical energy in air and are suitable for use as tunable lasers and chemical sensors

High-Q optical resonators in silicon-on-insulator-based slot waveguides

This letter describes the design, fabrication and characterization of high-Q oval resonators based on slot waveguide geometries in thin silicon-on-insulator material. Optical quality factors of up to 27 000 were measured in such filters, and we estimate losses of –10 dB/cm in the slotted waveguides on the basis of our resonator measurements. Such waveguides enable the concentration of light to very high optical fields within nanoscale dimensions, and show promise for the confinement of light in low-index material with potential applications for optical modulation, nonlinear optics and optical sensing

High-Q ring resonators in thin silicon-on-insulator

We have fabricated high-Q microrings from thin silicon-on-insulater SOI layers and measured Q values of 45 000 in these rings, which were then improved to 57 000 by adding a PMMA cladding. The optimal waveguide designs were calculated, and the waveguide losses were analyzed. These high-Q resonators are expected to lead to interesting devices for telecommunication filters and sources as well as optical refractive index sensing

Integrated plasmon and dielectric waveguides

We have designed, fabricated and characterized surface plasmon waveguides for near infrared light in the telecommunications spectrum. These waveguides exhibit losses of -1.2dB/μm and can guide light around 0.5 μm bends. Light can also be efficiently coupled between more conventional silicon waveguides and these plasmon waveguides with compact couplers, and we demonstrate that surface plasmon optical devices can be constructed by using planar circuit fabrication techniques. The large optical field enhancements of metallic surface plasmon devices are expected to lead to a new class of plasmonic optical devices, which will take advantage of the large field enhancements at the surfaces of the plasmon waveguides for nonlinear or sensing functionality, while utilizing the low losses available in silicon waveguides to move light longer distances on chip