A QED emitter is a coherent quantum-dot light source: a quantum dot held in an optical cavity and driven so that the amplitude and phase of its output are modulated in the time domain, rather than radiating at the fixed lines of an incoherent source. Its spectrum is therefore whatever its drive waveform specifies. Arrayed at a pitch finer than a wavelength of visible light, QED emitters control the optical field completely, in space and in time: an array can produce any pattern of light that physics permits a surface to produce, including the full reconstruction of an optical wavefront. The largest deployments are the holographic skies of the gyrealms.

Name#

The name descends from the cavity-quantum-electrodynamics laboratories where coherent dot emission was first engineered, and displaced QLED, the incoherent quantum-dot diode of pre-gyrealm displays. The collision with the initialism of quantum electrodynamics is counted apt rather than unfortunate — the device is applied quantum electrodynamics — and the further echo of quod erat demonstrandum was relished from the beginning.

Wavefront reconstruction#

Because an array commands phase as well as amplitude, it can reproduce the wavefront that light from a real scene would deliver to its surface. A reconstructed object is visually indistinguishable from a real one, with true depth and parallax, and — where the scene calls for it — true glare: reconstructing a bright source at effectively infinite distance sends the full intensity along exactly the bundle of rays the real source would deliver to an observer’s eye, while the total power emitted stays modest.

Physical limits#

Reconstructions are ordinary light. They are visible only within the line of sight of the emitters that generate them, cannot be projected into space away from a generating surface, and carry no mass or force.

Applications#

The sky is the largest array a resident stands under, but not the most numerous: the same emitters underlie domestic and vehicle displays — programmable windows, holographic telepresence, and the stadium and ballroom skies that render live views of Earth and Moon as a habitat’s rotation carries them across the field of view. Because the spectrum is set per emitter and per direction, an array also serves as directed lighting plant; the sky’s use of that capability is described under holographic sky.