Ohtsu Reserch Group, Department of Electrical Engineering and Information Systems, Graduate School of Engineering, The University of Tokyo

Ohtsu Reserch Group, Department of Electronics Engineering, Graduate School of Engineering, The University of Tokyo

Nanophotonics Team
Solution Oriented Research for Science and Technology (SORST)
Japan Science and Technology Agency    

Research Director

Professor Motoichi Ohtsu

Research Term

 October 2003 - September 2008

1. Background

A novel optical nano-technology that exceeds the diffraction limit is required to support future optical technology. To meet this requirement, the Ohtsu Localized Photon Project, ERATO (Oct. 1998 ~ Sep. 2003), has studied nanophotonics (a technology to fabricate and operate nanometric photonic devices that utilize local electromagnetic interactions between a small nanometric element and an optical near-field) and atom-photonics (a technology that manipulates atoms using an optical near-field), together with the nature of optical near-fields theoretically. We have developed the following:

  1. A quantum mechanics theory of optical near-fields that describes the localized electromagnetic interaction between an optical near-field and nano-materials in a nanometric system embedded within a macroscopic system.
  2. Nanofabrication techniques and the operation of nanophotonic devices.
  3. Atom control techniques that use optical near-fields, including atom deflection and a single-atom trap.

Based on the results, the Nanophotonic Team (SORST) hopes to fabricate prototype nanophotonic devices. To realize this, we plan to study near-field optical chemical vapor deposition and near-field induced photochemical etching. Furthermore, we will develop a new information processing system using nanophotonic devices.

Optical near-fields are widely used in optical microscopy and spectroscopy and have also been applied in biotechnology. Our project aims to develop a new concept of nano-scale photonic devices, i.e., nanophotonic devices, and to develop new fabrication methods using optical near-fields. Research groups in Europe or the United States have not yet proposed this concept. Our basic concept and the originality of our work is in the use of optical near-fields as a carrier and for controlling the optical near-field energy transfer among the resonant energy states of quantum dots. Furthermore, since the use of optical near-field energy makes it possible to transfer the optical energy between dipole forbidden energy states, nanophotonic devices can be operated only under optical near-field excitation.

The requirements for advanced communications and improvements in public welfare in the near future necessitate improved information processing and optical telecommunication systems, high-density optical memory, high-resolution displays, and optical input-output interfaces. To realize these requirements, the development of nanophotonic devices is an essential research area, which industry has recently recognized. For example, the Japanese government predicted that the data transmission rates in optical fiber transmission systems must reach as high as 400 Tb/s by the year 2015. To support this increase, it is estimated that the size of photonic matrix switching devices should be reduced to a sub-100-nm scale, with an ultra-small power supply, to integrate more than 10,000 ? 10,000 input/output channels on a substrate. However, the reduction of the scale of photonic devices is limited by the diffraction limit of light. In other words, the use of propagating far-field light as a signal carrier does not permit the reduction of the scale of devices below the diffraction of light. In order to overcome this limitation, a paradigm shift in optics is necessary. Although conventional photolithography has enabled the fabrication of sub-100-nm-scale devices by using an extreme ultra violet light source, the total system of photolithography costs more than $10 million. Furthermore, future society will require small production runs of large items. Therefore, the most important task for the realization of nanophotonic devices is the development of new techniques that are inexpensive, yet have high throughput.

The achievement of nanophotonic devices in this project will enable data transmission rates as high as 400 Tb/s, as required by global fiber optical transmission systems by the year 2015, and produce a market that is anticipated to be as large as $90 billion in 2015. In addition, since heat generation during the operation of a nanophotonic device is extremely small, such devices will not only be applicable to optical communication, as described above, but also to micro-processing devices in computers, which presently generate large amounts of heat. In addition, they will be applicable to high-density optical storage media and ultra-high-resolution and brightness displays. Furthermore, near-field lithography should become a key technology, replacing photolithography, and be worth more than $10 billion in 2015.

2. Research Strategy

The Nanophotonics Team plans to develop a nanophotonic device that uses an optical near-field light as the carrier and a new fabrication technique using optical near-fields. Another area of study is a new information processing system using nanophotonic devices. The major research topics are as follows.

(1) Nanophotonic device

The fabrication of nanophotonic devices using optical near-field energy transfer among the resonant energy states in quantum dots.

(1-1) The nanophotonic switch (prototype nanophotonic device): A nano-scale optical switch using optical near-field energy transfer between the resonant energy states of quantum dots.
(1-2) Logical operation devices: AND, XOR, and delay circuits, and buffer memory.

CuCl quantum dots are one possibility for constructing these devices, because of their large potential depth. In addition, owing to their large exciton binding energy, GaN and ZnO quantum dots are being tested to realize room-temperature operation of a nanophotonic switch. Si nanodots, which are suitable for extant electronic integrated circuits, are also being explored for future nanophotonic devices.

In order to realize a nano-scale optical waveguide as an input/output terminal between a nanophotonic device and an external photonic device, the following devices are also being developed:

(1-3) Nanophotonic waveguide: A nanodot coupler consisting of a chain of metal nanodots.
(1-4) Nanophotonic condenser: A plasmon-polariton focusing device using metallic nanoparticles and a nanophotonic fountain using near-field energy transfer among quantum dots.

(2) Nanophotonic fabrication

(2-1) The development of a fabrication method with nano-scale controllability in size and position: Nonresonant near-field optical chemical vapor deposition. Near-field photochemical etching.
(2-2) Self-assembly for mass production: Size- and position-controlled nanoparticle alignment using near-field desorption.
(2-3) Near-field lithography: The fabrication of a template on the scale of several tens of nanometers using an optical near-field. The fabrication of a prototype nanophotonic switching array.

(3) Nanophotonic system

The Nanophotonics Team aims to develop a new system for information processing, i.e., an ultra-fast Optical Time Division Multiplexing (OTDM) communication system and a nanophotonic router system.

3. Members

Official position Name elonging
Research Director Motoichi Ohtsu The University of Tokyo
Researcher Takashi Yatsui Japan Science and Technology Agency
Tadashi Kawazoe Japan Science and Technology Agency
Akiyoshi Oride Japan Science and Technology Agency
Makoto Naruse National Institute of Information and Communications Technology

Project Office

4th Floor, Tenko Building No.17, 687-1 Tsuruma, Machida, Tokyo 194-0004, Japan

Tel: +81-42-788-6030

Fax: +81-42-788-6031