Nano-photodiodes with a subwavelength active area using the optical near-field enhanced by surface plasmon resonance are proposed. We fabricated a Si Schottky photodiode that consists of an active area of 300 nm in diameter and a surface plasmon antenna to generate the carrier within the active area efficiently. The fabricated photodiode shows an increase of the photocurrent by several tenfold compared to that without a surface plasmon antenna. This result suggests an enhanced photogeneration of carriers in a semiconductor via surface plasmon resonance. Such a Si nano-photodiode is a potential high-speed optical signal detector because the opto-electronic conversion process occurs within a subwavelength scale.

We describe a cost-effective and low-power-consumption approach for on-chip optical interconnection. This approach includes an investigation into architectures, devices, and materials. We have proposed and fabricated a bonded structure of an Si-based optical layer on a large-scale integration (LSI) chip. The fabricated optical layer contains Si nanophotodiodes for optical detectors, which are coupled with SiON waveguides using surface-plasmon antennas. Optical signals were introduced to the optical layer and distributed to the Si nanophotodiodes. The output signals from the photodiodes were sent electrically to the transimpedance-amplifier circuitries in the LSI. The signals from the photodiodes triggered of the circuitries at 5 GHz. Since electrooptical modulators consume the most power in on-chip optical interconnect systems and require a large footprint, they are critical to establish on-chip optical interconnection. Two approaches are investigated: 1) an architecture using a fewer number of modulators and 2) high electrooptical coefficient materials.

Engineers are currently facing some technical issues in support of the exponential performance growths in information industries. One of the most serious issues is a bottleneck of inter-chip interconnects. We propose a new “Photonics-Electronics Convergence System” concept. High density optical interconnects integrated with a 13-channel arrayed laser diode, silicon optical modulators, germanium photodetectors, and silicon optical waveguides on single silicon substrate were demonstrated for the first time using this system. A 5-Gbps error free data transmission and a 3.5-Tbps/cm² transmission density were achieved. We believe that this technology will solve the bandwidth bottleneck problem among LSI chips in the future.

Silicon optical interposers for inter-chip interconnects, integrated with an arrayed laser diode, an optical splitter, silicon optical modulators and germanium photodetectors on a single silicon substrate were demonstrated. A 12.5-Gbps error-free data transmission and 6.6-Tbps/cm² transmission density were achieved.

We previously proposed a photonics-electronics convergence system to solve bandwidth bottleneck problems among large-scale integrations (LSIs) and demonstrated a high bandwidth density with silicon optical interposers at room temperature. For practical applications, the interposers should be usable under high-temperature conditions or rapid temperature changes so that they can cope with the heat generated by the mounted LSIs. We designed and fabricated athermal silicon optical interposers integrated with temperature-insensitive components on a silicon substrate. An arrayed laser diode (LD) chip was a flip-chip bonded to the substrate. Each LD had multiple quantum dot layers with a 1.3-μm lasing wavelength. The output power was higher than 10 mW per channel up to 100 °C. Silicon optical modulator and germanium photodetector (PD) arrays were monolithically integrated on the substrate. The modulators were structured as symmetric Mach-Zehnder interferometers, which were inherently insensitive to temperature and wavelength. The phase shifters composed of p-i-n diodes were stable against temperature change under a constant bias-current condition. The PD photocurrent was also temperature insensitive, and the photo-to-dark current ratio was higher than 30 dB up to 100 °C. We achieved error-free data links at 20 Gbps and a high bandwidth density of 19 Tbps/cm ² operating up to 125 °C without adjusting the LDs, modulators, or PDs. The interposers are tolerant of the heat generated by the mounted LSIs and usable over the extended industrial temperature range without complex monitoring or feedback controls. The bandwidth density is sufficient for the needs of the late 2010s.