Photodetector Using Surface-Plasmon Antenna for Optical Interconnect
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1145-MM01-05
Photodetector Using Surface-Plasmon Antenna for Optical Interconnect Keishi Ohashi1,2 and Junichi Fujikata1,2 1 Nano Electronics Research Labs, NEC Corporation, Tsukuba, Ibaraki 305-8501, Japan. 2 MIRAI-Selete, Tsukuba, Ibaraki 305-8501, Japan.
ABSTRACT We used a surface-plasmon antenna to obtain small photodetectors for LSI on-chip optical interconnection by using near-field light generated by the antenna. Such near-field devices are not constrained by the diffraction limit and they offer an approach to integrated nanoscale photonic devices. A small semiconductor structure is located near the antenna to absorb the nearfield light. This structure can be made as small as the Schottky depletion layer, so the separation between electrodes can be reduced to almost the size of the near-field region. We have demonstrated a “Si nano-photodiode” or plasmon photodiode that uses the near-field localized in a subwavelength region, which is usually relatively large in size because of the long absorption length for Si (~10 µm at a wavelength of ~800 nm). The Si nano-photodiode has a fast impulse response with a full-width at half-maximum of ~20 ps even when the bias voltage is small (~1 V or less). We demonstrated an on-chip optical interconnect chip to operate circuitry in an LSI chip by using waveguide-coupled Si nano-photodiodes. INTRODUCTION Optical components are fairly large compared with electronic ones. Integrated photonic circuits have been investigated from the early 1970s: nevertheless, their integration level is still at a low level, i.e., only a few photonic components on a chip. The fundamental difference in size between photonic and electronic components comes from the fact that the wavelength of light (~1 µm) is longer than the de Broglie wavelength of the electron (~10 nm). There are two approaches to closing this gap in size difference. One is to slow down the group velocity of light in photonic components. An example of this approach is to use structures with a high effective refractive index, including artificial structures such as photonic crystals. The other approach is to use the near-field, which is not constrained by the diffraction limit [1]. A strong near-field can be created by using surface plasmons, which are the surface charge density oscillations sustained by the free electron gas in a metal naturally coupled with the electromagnetic field [2,3,4]. One of the main targets of these approaches is to make micrometer-sized photonic devices for on-chip interconnects. Optics is expected to offer high-data-rate transmission with low energy loss. On-chip optical interconnects have the potential to provide a larger data capacity than electronic interconnects. A critical technology for the development of optical interconnects is reduction of the overhead with electro-optical and optoelectronic signal conversions, including the power consumption, footprint, and cost [5]. One of the reasons for the difficulty of achieving highly integrated photonic components comes from the diffraction limit, w
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