Motoichi Ohtsu

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Motoichi Ohtsu
Native name	大津 元一
Born	(1950-10-01) October 1, 1950 Yokohama, Japan
🏳️ Citizenship	Japanese
🎓 Alma mater	Tokyo Institute of Technology
💼 Occupation
Known for	Nanophotonics, "Dressed Photon" (DP) theory, Dressed-Photon-Phonon (DPP) interactions
🏅 Awards	Medal with Purple Ribbon (2004), Julius Springer Prize for Applied Physics (2009), Isaac Koga Gold Medal (1984)

Motoichi Ohtsu (Japanese: 大津 元一, Ōtsu Motoichi, born October 1950) is a Japanese electrical engineer, physicist, and professor emeritus at the University of Tokyo and Tokyo Institute of Technology. He is a pioneer in the field of nanophotonics and near-field optics, widely recognized for proposing the foundational principles of optical near-field technology to transcend the optical diffraction limit. His research focuses extensively on the concept of the "dressed photon"—a localized light-matter quasiparticle state generated within nanometric spatial boundaries.

Early life and education

Ohtsu was born in Yokohama, Japan, in October 1950. He attended the Tokyo Institute of Technology, earning his Bachelor of Engineering in Electronics Engineering in 1973. He completed his graduate studies at the same institution, receiving a Master of Engineering in 1975 and a Doctor of Engineering in 1978.

Academic career

Following his doctorate in 1978, Ohtsu was appointed a Research Associate at the Tokyo Institute of Technology, advancing to associate professor in 1982. From 1986 to 1987, he went on leave to join the Crawford Hill Laboratory at AT&T Bell Laboratories in Holmdel, New Jersey, where he conducted research in semiconductor laser frequency stabilization.

In 1991, he was promoted to full Professor at the Tokyo Institute of Technology. In 2004, he moved to the University of Tokyo as a professor in the Department of Electrical Engineering and Information Systems, where he spent the remainder of his primary academic teaching career. He has since served as a professor and researcher at the Tokyo University of Social Welfare.

Major research initiatives

Throughout his career, Ohtsu directed several major state-sponsored research initiatives in Japan aimed at bridging fundamental quantum electrodynamics with commercial engineering applications:

• Photon Control Project (1993–1998): Director at the Kanagawa Academy of Science and Technology.
• Localized Photon Project (1998–2003): Research Director under the prestigious ERATO (Exploratory Research for Advanced Technology) program of the Japan Science and Technology Agency (JST).
• Terabyte Optical Storage Technology Project (2002–2006): Led under the New Energy and Industrial Technology Development Organization (NEDO).

Scientific contributions

Foundations of nanophotonics

In 1993, Ohtsu formally proposed "nanophotonics" as an engineering discipline dedicated to manipulating light-matter interactions at scales far smaller than the wavelength of propagating light. While contemporary optical frameworks (such as photonic crystals and metamaterials) operate within traditional wave optics and are fundamentally constrained by the Rayleigh diffraction limit, Ohtsu's work leveraged the non-propagating properties of the optical near-field.

The Dressed Photon and Off-Shell Science

Ohtsu's most notable theoretical contribution is the formulation and application of the Dressed Photon (DP) and the Dressed-Photon-Phonon (DPP) interaction. Under Ohtsu's framework, when an electromagnetic wave is injected into an unconstrained sub-wavelength space (such as the tip of a fiber probe or a nanometric atomic cluster), it cannot propagate as a free photon. Instead, the localized energy field couples with the material's electron and phonon oscillations, entering a transient, virtual state known as a "dressed photon."

Under Ohtsu's theoretical framework, dressed photons are localized quasiparticle states arising from interactions among photons, electrons, and phonons in nanometric structures.

• Nanophotonic logic gates and optical switches operating via dipole-forbidden energy transfers between quantum cubes.
• DPP-assisted annealing methods, enabling wide-bandgap semiconductors (like silicon carbide and silicon) to behave as high-efficiency light-emitting diodes and infrared lasers, bypassing their native indirect bandgap restrictions.
• Near-field optical fiber probes fabricated through selective chemical etching, achieving a 1-nanometer tip radius for precision scanning tunneling microscopy.

Awards and honors

Ohtsu has authored hundreds of scientific publications and holds numerous patents.

• 1988: Japan IBM Science Award
• 2003: Elected Fellow of the Optical Society of America (now Optica)
• 2004: Awarded the Medal with Purple Ribbon by the Government of Japan.
• 2007: Distinguished Achievement Award from the Institute of Electronics, Information and Communication Engineers (IEICE)
• 2009: Julius Springer Prize for Applied Physics

Selected bibliography

• Ohtsu, M. (1991). Highly Coherent Semiconductor Lasers. Artech House. ISBN 978-0890064627. Search this book on
• Ohtsu, M. (1996). Frequency Control of Semiconductor Lasers. Wiley-Interscience. ISBN 978-0471013419. Search this book on
• Ohtsu, M.; Hori, H. (1999). Near-Field Nano-Optics: From Basic Principles to Nano-Fabrication and Nano-Photonics. Springer. ISBN 978-0306460098. Search this book on
• Ohtsu, M.; Kobayashi, K.; Kawazoe, T.; Sangu, S.; Yatsui, T. (2008). Principles of Nanophotonics. CRC Press. ISBN 978-1584889731. Search this book on
• Ohtsu, M., ed. (2009). Nanophotonics and Nanofabrication. Wiley-VCH. ISBN 978-3527321216. Search this book on

External links

• Motoichi Ohtsu publications indexed by Google Scholar

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