Publications

@article{LightSwitching,

title = {Light Switching with a Metal-Free Chiral-Sensitive Metasurface at Telecommunication Wavelengths},

author = {Chih-Zong Deng and Ya-Lun Ho and J. Kenji Clark and Takashi Yatsui and Jean-Jacques Delaunay},

doi = {10.1021/acsphotonics.0c01377},

year  = {2020},

date = {2020-10-12},

urldate = {2020-10-12},

journal = {ACS Photonics},

volume = {7},

number = {10},

pages = {2915–2922},

abstract = {Controlling the direction of light propagation, or light switching, enables the addressing of individual optical elements in high-density and complex photonic integrated devices. Light switching is therefore crucial to the development of photonic/plasmonic integrated circuits. Chiral-sensitive metasurfaces using metallic nanostructures have been used to realize light switching by coupling incident light of different spins to surface plasmon polaritons propagating in different directions. However, surface plasmon polaritons-based devices suffer from short propagation lengths and narrow resonance wavelength ranges resulting from ohmic losses in their metal layers. Bloch surface waves can be seen as a metal-free analogy to surface plasmon polaritons with superior properties such as low propagation losses and wide operating wavelength ranges. Here, we demonstrate a metal-free chiral-sensitive Bloch-surface-wave switching circuit consisting of a carefully arranged array of U-shaped apertures, guiding slabs, and grating couplers. By engineering the amplitude and phase of the Bloch surface wave to achieve spin-controlled unidirectional coupling, control of the propagation direction of the Bloch surface waves is realized. Very high directional selectivity is reported at the telecommunications wavelength of 1550 nm, both theoretically at 23 dB and experimentally at 13.5 dB. The ability to realize spin-controlled light switching on a chip at telecommunications wavelengths using metal-free chiral-sensitive metasurfaces should benefit the development of low-loss on-chip photonic integrated devices.},

keywords = {Nanophotonic device, Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{2014NomuraY,

title = {Demonstration of Controlling the Spatiotemporal Dynamics of Optical Near-Field Excitation Transfer in Y-Junction Structure Consisting of Randomly Distributed Quantum Dots},

author = {Wataru Nomura and Makoto Naruse and Masashi Aono and Song-Ju Kim and Tadashi Kawazoe and Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1155/2014/569684},

year  = {2014},

date = {2014-02-01},

urldate = {2014-02-01},

journal = {Advances in Optical Technologies},

volume = {2014},

pages = {569684},

abstract = {Solution searching devices that operate on the basis of controlling the spatiotemporal dynamics of excitation transfer via dressed photon interactions between quantum dots have been proposed. Long-range excitation transfer based on dressed photon interactions between randomly distributed quantum dots is considered to be effective in realizing such devices. Here, we successfully controlled the spatiotemporal dynamics of excitation transfer using a Y-junction structure consisting of randomly dispersed CdSe/ZnS core-shell quantum dots. This Y-junction structure has two “output ends” and one “tap end.” By exciting one output end with control light, we observed increased excitation transfer to the other output end via a state-filling effect. Conversely, we observed reduced excitation transfer to the output ends by irradiating the tap end with control light, due to excitation of defect levels in the tap end. These results show the possibility of controlling the optical excitation transfer dynamics between multiple quantum dots.},

keywords = {Nanophotonic device, Near-field effect, QD},

pubstate = {published},

tppubtype = {article}

}

@article{2012nomuraAPB,

title = {Direct observation of optical excitation transfer based on resonant optical near-field interaction},

author = {Wataru Nomura and Takashi Yatsui and Tadashi Kawazoe and Makoto Naruse and Erich Runge and Christoph Lienau and Motoichi Ohtsu},

doi = {10.1007/s00340-012-5009-6},

year  = {2012},

date = {2012-04-01},

journal = {Applied Physics B},

volume = {107},

number = {2},

pages = {257-262},

publisher = {Springer Nature},

abstract = {This article reports the direct observation of long-distance optical excitation transfer based on resonant optical near-field interactions in randomly distributed quantum dots (QDs). We fabricated optical excitation transfer paths based on randomly distributed QDs by using CdSe/ZnS core-shell QDs and succeeded for the first time in obtaining output signals resulting from a unidirectional optical excitation transfer length of 2.4 ƒÊm. Furthermore, we demonstrate that the optical excitation transfer occurs via the resonant excited levels of the QDs with a comparative experiment using non-resonant QDs. This excitation-transfer mechanism allows for intersecting, non-interacting nano-optical wires.},

keywords = {Nanophotonic device, Near-field effect, QD},

pubstate = {published},

tppubtype = {article}

}

@article{Akahane_2011,

title = {Energy Transfer in Multi-Stacked InAs Quantum Dots},

author = {Kouichi Akahane and Naokatsu Yamamoto and Makoto Naruse and Tadashi Kawazoe and Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1143/jjap.50.04dh05},

year  = {2011},

date = {2011-04-01},

journal = {Japanese Journal of Applied Physics},

volume = {50},

number = {4},

pages = {04DH05},

publisher = {IOP Publishing},

abstract = {We fabricated a modulated stacked quantum dot (QD) structure to investigate energy transfer among QDs using a strain compensation technique that allowed us to fabricate a vertically aligned, highly stacked structure without any degradation in crystal quality. Enhanced photoluminescence (PL) intensity for the ground state of large QDs was clearly observed in a sample where the ground state of small QDs was resonant to the first excited state of large QDs, indicating energy transfer from small QDs to large QDs. Long-range energy transfer reached approximately 200 nm and can be considered from the measurement of N dependence of PL intensity.},

keywords = {Energy-transfer, Nanophotonic device, QD},

pubstate = {published},

tppubtype = {article}

}

@article{2010nomuraAPB,

title = {Structural dependency of optical excitation transfer via optical near-field interactions between semiconductor quantum dots},

author = {Wataru Nomura and Takashi Yatsui and Tadashi Kawazoe and Makoto Naruse and Motoichi Ohtsu},

doi = {10.1007/s00340-010-3977-y},

year  = {2010},

date = {2010-07-01},

journal = {Applied Physics B},

volume = {100},

number = {1},

pages = {181-187},

publisher = {Springer Nature},

abstract = {The distribution dependency of quantum dots was theoretically and experimentally investigated with respect to the basic properties optical excitation transfer via optical near-field interactions between quantum dots. The effects of three-dimensional structure and arraying precision of quantum dots on the signal transfer performance were analyzed. In addition, the quantum dot distribution dependency of the signal transfer performance was experimentally evaluated by using stacked CdSe quantum dots and an optical near-field fiber probe tip laminated with quantum dots serving as an output terminal, showing good agreement with theory. These results demonstrate the basic properties of signal transfer via optical near-field interactions and serve as guidelines for a nanostructure design optimized to attain the desired signal transfer performances.},

keywords = {Energy-transfer, Nanophotonic device, QD},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.3372639,

title = {Self-assembly method of linearly aligning ZnO quantum dots for a nanophotonic signal transmission device},

author = {Takashi Yatsui and Yang Ryu and Tetsu Morishima and Wataru Nomura and Tadashi Kawazoe and Tetsu Yonezawa and Masao Washizu and Hiroyuki Fujita and Motoichi Ohtsu},

url = {https://doi.org/10.1063/1.3372639},

doi = {10.1063/1.3372639},

year  = {2010},

date = {2010-01-01},

urldate = {2010-01-01},

journal = {Applied Physics Letters},

volume = {96},

number = {13},

pages = {133106},

abstract = {We report a self-assembly method that aligns nanometer-sized quantum dots (QDs) into a straight line along which photonic signals can be transmitted by optically near-field effects. ZnO QDs were bound electrostatically to DNA to form a one-dimensional QD chain. The photoluminescence intensity under parallel polarization excitation along the QDs chain was much greater than under perpendicular polarization excitation, indicating an efficient signal transmission along the QD chain. As optical near-field energy can transmit through the resonant energy level, nanophotonic signal transmission devices have a number of potential applications, such as wavelength division multiplexing using QDs of different sizes.},

keywords = {First, Nanophotonic device, QD, Self-assembly, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{10.1117/1.2817657,

title = {Observation of dissipated optical energy transfer between CdSe quantum dots},

author = {Wataru Nomura and Takashi Yatsui and Tadashi Kawazoe and Motoichi Ohtsu},

doi = {10.1117/1.2817657},

year  = {2007},

date = {2007-11-01},

journal = {Journal of Nanophotonics},

volume = {1},

number = {1},

pages = {011591},

publisher = {SPIE},

abstract = {Exciton energy transfer between quantum dots via an optical near-field and subsequent dissipation was observed. Two sizes of CdSe/ZnS quantum dots with resonant energy levels were mixed to confirm the energy transfer and dissipation using time-resolved photoluminescence spectroscopy. It was estimated that the energy transfer time was 135 ps, which is shorter than the exciton lifetime of 2.10 ns. This indicates that CdSe quantum dots are promising material for nanophotonic devices.},

keywords = {dissipation, Excitons, Nanophotonic device, Near-field effect, QD},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.2743949,

title = {Nanophotonic switch using ZnO nanorod double-quantum-well structures},

author = {Takashi Yatsui and Suguru Sangu and Tadashi Kawazoe and Motoichi Ohtsu and Sung Jin An and Jinkyoung Yoo and Gyu-Chul Yi},

doi = {10.1063/1.2743949},

year  = {2007},

date = {2007-01-01},

urldate = {2007-01-01},

journal = {Applied Physics Letters},

volume = {90},

number = {22},

pages = {223110},

abstract = {The authors report on time-resolved near-field spectroscopy of ZnO∕ZnMgO nanorod double-quantum-well structures (DQWs) for a nanometer-scale photonic device. They observed nutation of the population between the resonantly coupled exciton states of DQWs. Furthermore, they demonstrated switching dynamics by controlling the exciton excitation in the dipole-inactive state via an optical near field. The results of time-resolved near-field spectroscopy of isolated DQWs described here are a promising step toward designing a nanometer-scale photonic switch and related devices.},

keywords = {First, Nanophotonic device, Selected, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{2008IEEEb,

title = {Nanophotonics: design, fabrication, and operation of nanometric devices using optical near fields},

author = {Motoichi Ohtsu and Kiyoshi Kobayashi and Tadashi Kawazoe and Suguru Sangu and Takashi Yatsui},

doi = {10.1109/JSTQE.2002.801738},

year  = {2002},

date = {2002-07-01},

journal = {IEEE Journal of Selected Topics in Quantum Electronics},

volume = {8},

number = {4},

pages = {839-862},

publisher = {IEEE},

abstract = {This paper reviews progress in nanophotonics, a novel optical nanotechnology, utilizing local electromagnetic interactions between a few nanometric elements and an optical near field. A prototype of a nanophotonic integrated circuit (IC) is presented, in which the optical near field is used as a carrier to transmit a signal from one nanometric dot to another. Each section of this paper reviews theoretical and experimental studies carried out to assess the possibility of designing, fabricating, and operating each nanophotonic IC device. A key device, the nanophotonic switch, is proposed based on optical near-field energy transfer between quantum dots (QDs). The optical near-field interaction is expressed as the sum of the Yukawa function, and the oscillation period of the nutation of cubic CuCl QDs is estimated to be less than 100 ps. To guarantee one-directional (i.e., irreversible) energy transfer between two resonant levels of QDs, intrasublevel transitions due to phonon coupling are examined by considering a simple two-QD plus phonon heat bath system. As a result, the state-filling time is estimated as 22 ps for CuCl QDs. This time is almost independent of the temperature in the Born-Markov approximation. Using cubic CuCl QDs in a NaCl matrix as a test sample, the optical near-field energy transfer was experimentally verified by near-field optical spectroscopy with a spatial resolution smaller than 50 nm in the near-UV region at 15 K. This transfer occurs from the lowest state of excitons in 4.6-nm QDs to the first dipole-forbidden excited state of excitons in 6.3-nm QDs. To fabricate nanophotonic devices and ICs, chemical vapor deposition using an optical near field is proposed; this is sufficiently precise in controlling the size and position of the deposited material. A novel deposition scheme under nonresonant conditions is also demonstrated and its origin is discussed. In order to confirm the possibility of using a nanometric ZnO dot as a light emitter in a nanophotonic IC, spatially and spectrally resolved photoluminescence imaging of individual ZnO nanocrystallites was carried out with a spatial resolution as high as 55 nm, using a UV fiber probe, and the spectral shift due to the quantum size effect was found. To connect the nanophotonic IC to external photonic devices, a nanometer-scale waveguide was developed using a metal-coated silicon wedge structure. Illumination (wavelength: 830 nm) of the metal-coated silicon wedge (width: 150 nm) excites a TM plasmon mode with a beam width of 150 nm and propagation length of 2.5 /spl mu/m. A key device for nanophotonics, an optical near-field probe with an extremely high throughput, was developed by introducing a pyramidal silicon structure with localized surface plasmon resonance at the metallized probe tip. A throughput as high as 2.3% was achieved. Finally, as an application of nanophotonics to, a high-density, high-speed optical memory system, a novel contact slider with a pyramidal silicon probe array was developed. This slider was used for phase-change recording and reading, and a mark length as short as 110 nm was demonstrated.},

note = {review article},

keywords = {Nanophotonic device, Nanophotonic fabrication, Review, Selected},

pubstate = {published},

tppubtype = {article}

}