Dyson spheres

I review the origins and development of the idea of Dyson spheres, their purpose, their engineering, and their detectability. I explicate the ways in which the popular imagining of them as monolithic objects would make them dynamically unstable under gravity and radiation pressure, and mechanically unstable to buckling. I develop a model for the radiative coupling between a star and large amounts of material orbiting it, and connect the observational features of a star plus Dyson sphere system to the gross radiative properties of the sphere itself. I discuss the still-unexplored problem of the effects of radiative feedback on the central star's structure and luminosity. Finally, I discuss the optimal sizes of Dyson spheres under various assumptions about their purpose as sources of low-entropy emission, dissipative work, or computation.

Transparent multispectral photodetectors mimicking the human visual system

Compact and lightweight photodetection elements play a critical role in the newly emerging augmented reality, wearable and sensing technologies. In these technologies, devices are preferred to be transparent to form an optical interface between a viewer and the outside world. For this reason, it is of great value to create detection platforms that are imperceptible to the human eye directly onto transparent substrates. Semiconductor nanowires (NWs) make ideal photodetectors as their optical resonances enable parsing of the multi-dimensional information carried by light. Unfortunately, these optical resonances also give rise to strong, undesired light scattering. In this work, we illustrate how a new optical resonance arising from the radiative coupling between arrayed silicon NWs can be harnessed to remove reflections from dielectric interfaces while affording spectro-polarimetric detection. The demonstrated transparent photodetector concept opens up promising platforms for transparent substrates as the base for opto-electronic devices and in situ optical measurement systems.

Dynamically Tunable Plasmon-Induced Transparency Based on Radiative–Radiative-Coupling in a Terahertz Metal–Graphene Metamaterial

New technologies and materials with superior characteristics impel great development of functional devices in the terahertz field. The dynamically tunable plasmon-induced transparency (PIT) based on radiative–radiative-coupling in terahertz hybrid metal–graphene metamaterial is numerically investigated in this paper. For the active manipulation of the PIT device, the single-layer graphene is integrated into the proposed structure consisting of the split-ring-resonator (SRR) and the closed-ring-resonator (CRR). Dynamically adjusting Fermi energy in graphene leads to modulation of the PIT window, allowing for the active control of the group delay. From the simulated electrical field distributions and effective circuit model to analyze, the transmission spectrum modulation can be attributed to the altering in the energy loss of the dark mode resonator through the conduction effect of the graphene layer. Our work offers theoretical references for the development of slow light terahertz devices in the future.