This reviews the current status and its prediction in 2020 of power consumption of ICT, followed the two
methodologies of analysis of power consumption of optical network and optical transport; top-down and
bottom-up approaches. Next, technologies for the power saving in optical network and optical transport
will be discussed. Finally, some of promising optical signal processings in the future are reviewed, and
the advantages over the electronic counterpart are discussed.
Developing ultra-small optical devices and integrating them are quite useful for realizing energy effi cient
optical devices and also constructing ICT systems with newly introducing such optical devices. For this
purpose, silicon photonics is quite promising. In this report, we briefl y review recent silicon photonics
technology trends and then focus on optical switching devices based on silicon photonics. A silicon
thermo-optical switch element is driven with low heating power. To integrate many elements and
construct functional devices with energy effi ciency, we need to establish several points, such as high
uniformity, polarization independence, and ambient temperature independence. We demonstrate high
extinction ratio switching of the 1 × 8 optical switch with meeting above-mentioned points for energy
efficiency. Such optical switches can be applied to R-OADMs in photonic networks, which provide
fl exible optical path setup and thus contribute to energy effi cient systems.
With the continuous growth of data traffi c in the communication networks and datacenters, the energy
consumption at the electric packet switches and routers is becoming the bottleneck in scaling up the data
capacity. Optical switching has been considered as the key technology to achieve drastic energy saving
by bypassing the power-consuming electric packet forwarding. In this article, we review the present
status of the high-speed, large-scale photonic integrated switches using InP-based compound
semiconductor materials. Recent trends and progresses in the wavelength-converting switches and
semiconductor optical amplifi er switches are presented. We then review our work on integrated phasedarray
switches and discuss their potentials as well as challenges.
The power consumption of network devices will continue to increase due to the increase in transmission
speed and reach 97 GW by 2020. This paper introduces urgently needed network power reduction
methods. First, the paper focuses on the optical access network architectures that use active devices such
as high-speed optical switches or variable wavelength lasers to achieve significant energy savings.
These new architectures are expected to dramatically reduce the Optical Network Unit (ONU)’s power
consumption by introducing an effective sleep mode. Second, this paper introduces an extremely energy
efficient future-Internet architecture that uses a large optical aggregation network. It combines the
centralized Service Cloud with the Cloud Router and application servers and the Optical Aggregation
Network. The optical aggregation network can be realized with just simple optical circuit switches,
wavelength-converters, and wavelength-multiplexers/demultiplexers; the complicated layer-3 function is
realized only at the center Cloud Router. The optical aggregation network realizes a network structure
well suited to today’s traffic centralization. According to our evaluation, total network power
consumption can be reduced to just 1/1000 compare to the electrical based network architecture.
This article will review dynamic optical path network (DOPN), recently proposed by AIST, that is a
promising technology to dramatically reduce the energy consumption allowing the sustainable growth of
the network traffic in the forthcoming ultra-high definition video era. Then, some of the enabling
photonic technologies being developed at AIST will be introduced: they are intersubband quantum well
waveguide devices; silicon photonics optical switches; and all-optical signal processing through highly
Photonic crystal nanocavities have enabled ultrasmall and largely-integratable optical memories and
random access memories (RAMs) that consume extremely little power. Here we show the characteristics
of our photonic crystal memories and RAM, and discuss their impact on information and communication
technology (ICT) and chip-scale many-core processors, especially for network routing functions.
This paper overviews the current status of bistable semiconductor lasers and their applications to
photonic switching as well as the recent results of our research on polarization bistable VCSELs. Many
kinds of bistable semiconductor lasers such as VCSELs and ring-lasers with low power consumption
have been developed so far. In our experiments with 980-nm polarization-bistable VCSELs, we
successfully demonstrated the following results. All-optical fl ip-fl op operation was achieved at a record
low bias current of 0.85 mA using an oxidation confi nement structure. 1-bit data signals were arbitrarily
sampled and memorized from 20 Gb/s PRBS RZ and 40 Gb/s NRZ signals.
We demonstrate photo-detection at 1.55-μm wavelength light using a photonic crystal nanocavity with
an integrated p-i-n junction. The device is made from silicon and integrated on a chip. Our results
showed that it has an extremely low dark current of 15 pA and can operate at high sensitivity. The
detectable smallest input light was 0.9 nW, which outperformed other detectors such as a germanium
detector on silicon due to the strong confi nement of the light by ultrahigh-Q photonic crystal nanocavity.
We also performed detailed theoretical and numerical analysis and showed that quantum effi ciency of
12.5% is possible using two-photon absorption. Higher effi ciency is possible if we can increase the onephoton
absorption or the cavity’s Q. Based on our analysis, the sensitivity can be reduced to 1.8 pW due
to the low dark current.