Publication # 358

The use of optics to make connections within and between electronic chips has been the subject of research for over 20 years because it could solve many of the problems experienced in electrical systems.1-3 A critical challenge for the convergence of optics and electronics is that the micrometre scale of optics is significantly larger than the nanometre scale of modern electronic devices. In the conversion from photons to electrons by photodetectors, this size incompatibility often leads to substantial penalties in power dissipation, area, latency and noise.4 A photodetector can be made smaller by using a subwavelength active region which, however, could result in very low responsivity because of the diffraction limit of the light. Here we exploit the idea of a dipole antenna from radio waves, but at near infrared wavelengths (~ 1.3 µm), to concentrate radiation into a nanometre-scale Ge photodetector. Despite the small antenna size (~ 380 nm long) and the different properties of metals at such high frequencies (~ 230 THz), the antenna has qualitatively similar behavior to the common radio-frequency half-wave (i.e., half wavelength long) Hertz dipole. It gives a polarization contrast of 20 times in the resulting photocurrent in the subwavelength Ge detector element, which has an active volume of 0.00072 μm3, two orders of magnitude smaller than previously demonstrated detectors at such wavelengths.

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