Abstract
We present an ultrafast nanoscale light source utilizing a shifted-core coaxial nano-cavity, with a footprint of merely one-third of its emission wavelength in all three dimensions at telecommunication wavelengths. We show that, by shifting the metallic core off center of the coaxial structure, the effective mode volume of the cavity can be as small as 0.0078 × (λ0/na)3, resulting in a Purcell factor over 390 and a modulation bandwidth exceeding 60GHz. We further show that the evolution trend of the cavity Q factor as a function of core-shifting distance can be engineered by choosing proper substrate material. Compared to its symmetric counterpart, this shifted-core coaxial nano-cavity features not only higher Q factor, Purcell factor, and modulation bandwidth but also an improved emission directivity that is essential in its coupling with other on-chip components. The proposed nano-emitter also features robust single mode operation over the entire core-shifting range, resulting in a near-unity spontaneous emission factor. Therefore, this device can be a good candidate for low power optical interconnect applications.
Highlights
Because of the urging demand for high-speed intrachip and chip-to-chip communication, the research of replacing the narrow band electronic communication link with optical link has been very active over the last decade [1]
The first challenge can be addressed by using metallic cavities, which offer extraordinary mode confinement; the second challenge can be addressed by using a cut-off free coaxial cavity design that supports the transverse electromagnetic (TEM) mode
We have demonstrated high Purcell factor and broad modulation bandwidth up to 394 and 62GHz, respectively
Summary
Because of the urging demand for high-speed intrachip and chip-to-chip communication, the research of replacing the narrow band electronic communication link with optical link has been very active over the last decade [1]. We design a shifted-core coaxial nano-emitter supporting the cut-off free quasi-TEM mode [6], for applications in high density photonic integration. By carefully choosing the cavity geometrical parameters, single mode operation can be enforced over the entire core shifting range for typical III-V materials This feature of single mode operation grants near-unity spontaneous emission factor β for energy efficient operation; the deep sub-wavelength cavity size is maintained. We believe this ultra-compact and ultrafast nano-emitter is a promising light-source candidate for photonic integrated circuits, and paves the way towards the development of fully on-chip optical communication systems
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