Ultrafast Shifted-Core Coaxial Nano-Emitter
We present an ultrafast nanoscale light source utilizing a shifted- core coaxial nanocavity, 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 x (λ₀/n_a)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.