Faculty Profiles - Fujiwara Masazumi

Papers - Fujiwara Masazumi

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Observation of 1.2-GHz linewidth of zero-phonon-line in photoluminescence spectra of nitrogen vacancy centers in nanodiamonds using a Fabry-Perot interferometer Reviewed

Hong-Quan Zhao, Masazumi Fujiwara, Masayuki Okano, Shigeki Takeuchi

OPTICS EXPRESS 21 ( 24 ) 29679 - 29686 2013.12

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

Photoluminescence (PL) spectra of single nitrogen vacancy (NV) centers in 50-nm diamond nanocrystals at the zero-phonon line (ZPL) were directly observed using a Fabry-Perot interferometer at cryogenic temperatures. The narrowest linewidth of ZPL was 1.2 GHz (1.9 +/- 0.7 GHz on average), comparable to ZPL linewidths in PL spectra reported for NV centers in pure bulk diamond. This observation is important to the application of NV centers for use in quantum communication and computation devices, and in nano-sensing. (C) 2013 Optical Society of America

DOI： 10.1364/OE.21.029679

Observation of 1.2-GHz linewidth of zero-phonon-line in photoluminescence spectra of nitrogen vacancy centers in nanodiamonds using a Fabry-Perot interferometer Reviewed

Hong-Quan Zhao, Masazumi Fujiwara, Masayuki Okano, Shigeki Takeuchi

OPTICS EXPRESS 21 ( 24 ) 29679 - 29686 2013.12

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

Photoluminescence (PL) spectra of single nitrogen vacancy (NV) centers in 50-nm diamond nanocrystals at the zero-phonon line (ZPL) were directly observed using a Fabry-Perot interferometer at cryogenic temperatures. The narrowest linewidth of ZPL was 1.2 GHz (1.9 +/- 0.7 GHz on average), comparable to ZPL linewidths in PL spectra reported for NV centers in pure bulk diamond. This observation is important to the application of NV centers for use in quantum communication and computation devices, and in nano-sensing. (C) 2013 Optical Society of America

DOI： 10.1364/OE.21.029679

Embedded TiO2 waveguides for sensing nanofluorophores in a microfluidic channel Reviewed

Masayuki Furuhashi, Masazumi Fujiwara, Takahito Ohshiro, Kazuki Matsubara, Makusu Tsutsui, Masateru Taniguchi, Shigeki Takeuchi, Tomoji Kawai

APPLIED PHYSICS LETTERS 101 ( 15 ) 2012.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Crossed structure of a microfluidic channel and an optical channel waveguide is simple and promising to realize detection of weak fluorescence on an integrated device. Usage of TiO2 waveguides is suitable for the device because of the high numerical aperture. In this study, we developed fabrication processes for the TiO2 channel waveguides traversed by microfluidic channels of 0.5-6 mu m widths and investigated the effect of the microfluidic channel to the transmittances. The results elucidated that the photointensity at the microfluidic channel was enough to excite fluorophores. Furthermore, we demonstrated detection of fluorescence from 350 quantum dots. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757759]

DOI： 10.1063/1.4757759

Embedded TiO2 waveguides for sensing nanofluorophores in a microfluidic channel Reviewed

Masayuki Furuhashi, Masazumi Fujiwara, Takahito Ohshiro, Kazuki Matsubara, Makusu Tsutsui, Masateru Taniguchi, Shigeki Takeuchi, Tomoji Kawai

APPLIED PHYSICS LETTERS 101 ( 15 ) 2012.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Crossed structure of a microfluidic channel and an optical channel waveguide is simple and promising to realize detection of weak fluorescence on an integrated device. Usage of TiO2 waveguides is suitable for the device because of the high numerical aperture. In this study, we developed fabrication processes for the TiO2 channel waveguides traversed by microfluidic channels of 0.5-6 mu m widths and investigated the effect of the microfluidic channel to the transmittances. The results elucidated that the photointensity at the microfluidic channel was enough to excite fluorophores. Furthermore, we demonstrated detection of fluorescence from 350 quantum dots. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757759]

DOI： 10.1063/1.4757759

ナノテーパ光ファイバを駆使した光量子デバイス

藤原正澄, 竹内繁樹

化学工業 63 ( 9 ) 25 - 30 2012.9

Effect of Substrates on the Temperature Dependence of Fluorescence Spectra of Nitrogen Vacancy Centers in Diamond Nanocrystals Reviewed

Hong-Quan Zhao, Masazumi Fujiwara, Shigeki Takeuchi

JAPANESE JOURNAL OF APPLIED PHYSICS 51 ( 9 ) 2012.9

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

The temperature dependence of fluorescence spectra of nitrogen vacancy (NV) centers in diamond nanocrystals is investigated in terms of the ability of the substrate to suppress the fluorescence phonon sideband of negatively charged NV (NV-) centers. Three substrates were used: a glass coverslip, undoped silicon (Si), and thermally oxidized silicon (SiO2/Si). Nanocrystals were distributed on these substrates and the temperature dependence of fluorescence spectra of NV- centers of individual nanocrystals were measured in the temperature range 3.5-230 K. We found that the zero-phonon line (ZPL) of NV- centers in nanocrystals on the SiO2/Si substrate remained intense as the temperature was increased from 3.5 to 160 K, whereas it monotonically decreased for the Si substrate. Diamond nanocrystals dispersed on a glass coverslip did not exhibit prominent ZPLs of NV- centers, even at 3.5 K. The temperature dependencies of the peak intensities of NV- centers were quantitatively analyzed by determining the Debye-Waller factors of the three substrates. As the temperature was increased from 3.5 to 230 K, the Debye- Waller factor decreased almost linearly from 10 to 1.7% for the SiO2/Si substrate, decreased from 6.1 to 1.6% for the Si substrate, and decreased from 0.9 to 0.62% for the glass coverslip. These results will be useful for nanophotonic device applications of nanodiamond NV centers in quantum information science and sensing. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.090110

Effect of Substrates on the Temperature Dependence of Fluorescence Spectra of Nitrogen Vacancy Centers in Diamond Nanocrystals Reviewed

Hong-Quan Zhao, Masazumi Fujiwara, Shigeki Takeuchi

JAPANESE JOURNAL OF APPLIED PHYSICS 51 ( 9 ) 2012.9

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

The temperature dependence of fluorescence spectra of nitrogen vacancy (NV) centers in diamond nanocrystals is investigated in terms of the ability of the substrate to suppress the fluorescence phonon sideband of negatively charged NV (NV-) centers. Three substrates were used: a glass coverslip, undoped silicon (Si), and thermally oxidized silicon (SiO2/Si). Nanocrystals were distributed on these substrates and the temperature dependence of fluorescence spectra of NV- centers of individual nanocrystals were measured in the temperature range 3.5-230 K. We found that the zero-phonon line (ZPL) of NV- centers in nanocrystals on the SiO2/Si substrate remained intense as the temperature was increased from 3.5 to 160 K, whereas it monotonically decreased for the Si substrate. Diamond nanocrystals dispersed on a glass coverslip did not exhibit prominent ZPLs of NV- centers, even at 3.5 K. The temperature dependencies of the peak intensities of NV- centers were quantitatively analyzed by determining the Debye-Waller factors of the three substrates. As the temperature was increased from 3.5 to 230 K, the Debye- Waller factor decreased almost linearly from 10 to 1.7% for the SiO2/Si substrate, decreased from 6.1 to 1.6% for the Si substrate, and decreased from 0.9 to 0.62% for the glass coverslip. These results will be useful for nanophotonic device applications of nanodiamond NV centers in quantum information science and sensing. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.090110

Coupling of ultrathin tapered fibers with high-Q microsphere resonators at cryogenic temperatures and observation of phase-shift transition from undercoupling to overcoupling Reviewed

Masazumi Fujiwara, Tetsuya Noda, Akira Tanaka, Kiyota Toubaru, Hong-Quan Zhao, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 17 ) 19545 - 19553 2012.8

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

We cooled ultrathin tapered fibers to cryogenic temperatures and controllably coupled them with high-Q microsphere resonators at a wavelength close to the optical transition of diamond nitrogen vacancy centers. The 310-nm-diameter tapered fibers were stably nanopositioned close to the microspheres with a positioning stability of approximately 10 nm over a temperature range of 7-28 K. A cavity-induced phase shift was observed in this temperature range, demonstrating a discrete transition from undercoupling to overcoupling. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.019545

Coupling of ultrathin tapered fibers with high-Q microsphere resonators at cryogenic temperatures and observation of phase-shift transition from undercoupling to overcoupling Reviewed

Masazumi Fujiwara, Tetsuya Noda, Akira Tanaka, Kiyota Toubaru, Hong-Quan Zhao, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 17 ) 19545 - 19553 2012.8

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

We cooled ultrathin tapered fibers to cryogenic temperatures and controllably coupled them with high-Q microsphere resonators at a wavelength close to the optical transition of diamond nitrogen vacancy centers. The 310-nm-diameter tapered fibers were stably nanopositioned close to the microspheres with a positioning stability of approximately 10 nm over a temperature range of 7-28 K. A cavity-induced phase shift was observed in this temperature range, demonstrating a discrete transition from undercoupling to overcoupling. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.019545

Suppression of fluorescence phonon sideband from nitrogen vacancy centers in diamond nanocrystals by substrate effect Reviewed

Hong-Quan Zhao, Masazumi Fujiwara, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 14 ) 15628 - 15635 2012.7

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

Substrates effect is observed on the suppression of the phonon sideband from nitrogen vacancy (NV) centers in 50nm diamond nanocrystals at cryogenic temperatures. As a quantitative parameter of the population of phonon sidebands, the Debye-Waller factor is estimated from fluorescence spectra on glass, silicon, and silica-on-silicon substrates. Fluorescence spectra of negatively charged NV centers in nanodiamonds on silica-on-silicon substrates have average and maximum Debye-Waller factors of 12.7% (which is about six times greater than that of samples on glass substrates) and 19.3%, respectively. This effect is expected to be very important for future applications of NV centers in quantum information science and nanosensing. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.015628

Suppression of fluorescence phonon sideband from nitrogen vacancy centers in diamond nanocrystals by substrate effect Reviewed

Hong-Quan Zhao, Masazumi Fujiwara, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 14 ) 15628 - 15635 2012.7

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

Substrates effect is observed on the suppression of the phonon sideband from nitrogen vacancy (NV) centers in 50nm diamond nanocrystals at cryogenic temperatures. As a quantitative parameter of the population of phonon sidebands, the Debye-Waller factor is estimated from fluorescence spectra on glass, silicon, and silica-on-silicon substrates. Fluorescence spectra of negatively charged NV centers in nanodiamonds on silica-on-silicon substrates have average and maximum Debye-Waller factors of 12.7% (which is about six times greater than that of samples on glass substrates) and 19.3%, respectively. This effect is expected to be very important for future applications of NV centers in quantum information science and nanosensing. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.015628

A nanodiamond-tapered fiber system with high single-mode coupling efficiency Reviewed

Tim Schroeder, Masazumi Fujiwara, Tetsuya Noda, Hong-Quan Zhao, Oliver Benson, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 10 ) 10490 - 10497 2012.5

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

We present a fiber-coupled diamond-based single photon system. Single nanodiamonds containing nitrogen vacancy defect centers are deposited on a tapered fiber of 273 nanometer in diameter providing a record-high number of 689,000 single photons per second from a defect center in a single-mode fiber. The system can be cooled to cryogenic temperatures and coupled evanescently to other nanophotonic structures, such as microresonators. The system is suitable for integrated quantum transmission experiments, two-photon interference, quantum-random-number generation and nano-magnetometry. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.010490

A nanodiamond-tapered fiber system with high single-mode coupling efficiency Reviewed

Tim Schroeder, Masazumi Fujiwara, Tetsuya Noda, Hong-Quan Zhao, Oliver Benson, Shigeki Takeuchi

OPTICS EXPRESS 20 ( 10 ) 10490 - 10497 2012.5

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

We present a fiber-coupled diamond-based single photon system. Single nanodiamonds containing nitrogen vacancy defect centers are deposited on a tapered fiber of 273 nanometer in diameter providing a record-high number of 689,000 single photons per second from a defect center in a single-mode fiber. The system can be cooled to cryogenic temperatures and coupled evanescently to other nanophotonic structures, such as microresonators. The system is suitable for integrated quantum transmission experiments, two-photon interference, quantum-random-number generation and nano-magnetometry. (C) 2012 Optical Society of America

DOI： 10.1364/OE.20.010490

Near-field coupling of a single NV center to a tapered fiber Reviewed

Tim Schroeder, Masazumi Fujiwara, Tetsuya Noda, Hong-Quan Zhao, Andreas W. Schell, Guenter Kewes, Oliver Benson, Shigeki Takeuchi

ADVANCES IN PHOTONICS OF QUANTUM COMPUTING, MEMORY, AND COMMUNICATION V 8272 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPIE-INT SOC OPTICAL ENGINEERING

Furhter miniaturization of funcionalized quantum optical systems down to nm-dimensions and their integration into fibre optical networks is a major challange for future implementations of quantum information, quantum communication and quantum processing applications. Furthermore, scalability, long-term stability and room-as well as liquid helium temperature operation are benchmarking properties of such systems.
In this paper, we present the realizations of fiber-coupled diamond-based single photon systems. First, an alignment free, mu m-scale single photon source consisting of a single nitrogen vacancy center facet coupled to an optical fiber operating at room temperature is presented. Near-field coupling of the single nitrogen vacancy center is realized by placing a pre-selected nanodiamond directly on the fiber facet in a bottom-up approach. Its photon collection efficiency is comparable to a far-field collection via an air objective with a numerical aperture of 0.82. As the system can be simultaneously excited and its photons be recollected through the fiber, it can be used as a fiber-connected single quantum sensor that allows optical near-field probing on the quantum level. Secondly single nanodiamonds that contain nitrogen vacancy defect centers, are nearfield coupled to a tapered fiber of 300 nanometer in diameter. This system provides a record-high number of 97 kcps single photons from a single defect center into a single mode optical fiber. The entire system can be cooled to liquid Helium temperatures and reheated without breaking. Furhtermore, the system can be evanescently coupled to various nanophotonic structures, e. g. microresonators. The system can also be applied for integrated quantum transmission experiments and the realization of two-photon interference. It can be used as a quantum-random-number generator as well as a probe for nano-magnetometry.

DOI： 10.1117/12.907961

Suppression of Phonon Sidebands in the Spectrum of Nitrogen Vacancy Centers in Diamond Nano-Crystals Reviewed

Hong-Quan Zhao, Masazumi Fujiwara, Shigeki Takeuchi

ADVANCES IN PHOTONICS OF QUANTUM COMPUTING, MEMORY, AND COMMUNICATION V 8272 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPIE-INT SOC OPTICAL ENGINEERING

We report the substrate effects on the zero-phonon transitions and suppression of phonon side bands in the NV center spectrum. Fluorescence spectra of NV centers in cryogenic temperatures were measured by depositing diamond nanocrystals on different substrates including glass slides, undoped Si, and silica (1 similar to 2um) on undoped Si (SiO2/Si). We found that SiO2/Si substrate was an effective substrate to suppress the phonon side band from spectra of NV-centers. Temperature dependence of NV-zero-phonon line Debye-Waller factor on Si and SiO2/Si were measured, from 2.5K to 230K, Debye-Waller factor decreased linearly on both of the two substrates.

DOI： 10.1117/12.906638

Highly Efficient Coupling of Photons from Nanoemitters into Single-Mode Optical Fibers Reviewed

Masazumi Fujiwara, Kiyota Toubaru, Tetsuya Noda, Hong-Quan Zhao, Shigeki Takeuchi

NANO LETTERS 11 ( 10 ) 4362 - 4365 2011.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Highly efficient coupling of photons from nanoemitters into single-mode optical fibers is demonstrated using tapered fibers. A percentage (7.4 +/- 1.2%) of the total emitted photons from single CdSe/ZnS nanocrystals were coupled into a 300 nm diameter tapered fiber. The dependence of the coupling efficiency on the taper diameter was investigated and the coupling efficiency was found to increase exponentially with decreasing diameter. This method is very promising for nanoparticle sensing and single-photon sources.

DOI： 10.1021/nl2024867

Development of microfabricated TiO2 channel waveguides Reviewed

Masayuki Furuhashi, Masazumi Fujiwara, Takahito Ohshiro, Makusu Tsutsui, Kazuki Matsubara, Masateru Taniguchi, Shigeki Takeuchi, Tomoji Kawai

AIP ADVANCES 1 ( 3 ) 2011.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

An optical channel waveguide is a key solution to overcome signal propagation delay. For the benefits of miniaturization, development of microfabrication process for waveguides is demanded. TiO2 is one of the suitable candidates for the microfabricated waveguide because of the high refractive index and the transparency. In the present study, conventional microfabrication processes manufactured TiO2 channel waveguides with 1-20 mu m width on oxidized Si substrates and the propagation loss was measured. The prepared channels successfully guided light of 632.8 nm along linear and Y-branched patterns. The propagation loss for the linear waveguide was 9.7 dB/cm. Copyright 2011 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [doi:10.1063/1.3615716]

DOI： 10.1063/1.3615716

Development of microfabricated TiO2 channel waveguides Reviewed

Masayuki Furuhashi, Masazumi Fujiwara, Takahito Ohshiro, Makusu Tsutsui, Kazuki Matsubara, Masateru Taniguchi, Shigeki Takeuchi, Tomoji Kawai

AIP ADVANCES 1 ( 3 ) 2011.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

An optical channel waveguide is a key solution to overcome signal propagation delay. For the benefits of miniaturization, development of microfabrication process for waveguides is demanded. TiO2 is one of the suitable candidates for the microfabricated waveguide because of the high refractive index and the transparency. In the present study, conventional microfabrication processes manufactured TiO2 channel waveguides with 1-20 mu m width on oxidized Si substrates and the propagation loss was measured. The prepared channels successfully guided light of 632.8 nm along linear and Y-branched patterns. The propagation loss for the linear waveguide was 9.7 dB/cm. Copyright 2011 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [doi:10.1063/1.3615716]

DOI： 10.1063/1.3615716

Optical transmittance degradation in tapered fibers Reviewed

Masazumi Fujiwara, Kiyota Toubaru, Shigeki Takeuchi

OPTICS EXPRESS 19 ( 9 ) 8596 - 8601 2011.4

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

We investigated the cause of optical transmittance degradation in tapered fibers. Degradation commences immediately after fabrication and it eventually reduces the transmittance to almost zero. It is a major problem that limits applications of tapered fibers. We systematically investigated the effect of the dust-particle density and the humidity on the degradation dynamics. The results clearly show that the degradation is mostly due to dust particles and that it is not related to the humidity. In a dust free environment it is possible to preserve the transmittance with a degradation of less than the noise (+/- 0.02) over 1 week. (C) 2011 Optical Society of America

DOI： 10.1364/OE.19.008596

Optical transmittance degradation in tapered fibers Reviewed

Masazumi Fujiwara, Kiyota Toubaru, Shigeki Takeuchi

OPTICS EXPRESS 19 ( 9 ) 8596 - 8601 2011.4

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

We investigated the cause of optical transmittance degradation in tapered fibers. Degradation commences immediately after fabrication and it eventually reduces the transmittance to almost zero. It is a major problem that limits applications of tapered fibers. We systematically investigated the effect of the dust-particle density and the humidity on the degradation dynamics. The results clearly show that the degradation is mostly due to dust particles and that it is not related to the humidity. In a dust free environment it is possible to preserve the transmittance with a degradation of less than the noise (+/- 0.02) over 1 week. (C) 2011 Optical Society of America

DOI： 10.1364/OE.19.008596

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