Mitsunori Saito

Ryukoku University, Otsu, Kumamoto Prefecture, Japan

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Publications (58)92.85 Total impact

  • Mitsunori Saito · Satoshi Ochiai
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    ABSTRACT: Nanoparticles that are dispersed in a solid matrix have no effect on co-dispersed molecules unless they happen to be located close to one another. A polymer with a high diffusion coefficient allows molecules to circulate in the matrix to find a particle that enhances their function. A polymer composite containing copper nanoparticles was created by a low-temperature, nonvacuum process. That is, laser ablation was conducted in polydimethylsiloxane oil for both anti-oxidation and efficient particle collection, and then this suspension was cured to create a metal-polymer composite. This composite enhanced optical functions of a photochromic dye owing to its high diffusivity.
    Optics Letters 09/2014; 39(18). DOI:10.1364/OL.39.005366 · 3.18 Impact Factor
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    ABSTRACT: We fabricated a deformable transmission grating with a silicone elastomer [poly(dimethylsiloxane)], and evaluated its optical characteristics during a compression process. This grating pattern was created on a silicone surface by a polymer mold that had been fabricated by photo-imprinting process with an SiC mold to realize a simple, low-cost fabrication process. We also measured the relationship between the grating period and compressive stress to the fabricated elements. The grating periods of the fabricated elements were evaluated from the measured diffraction angles. The grating periods of 3.02 and 410 nm were changed to 2.86 µm pitch and to 368 nm pitch, respectively, by compressing the fabricated element in one direction, perpendicular to the grooves.
    Japanese Journal of Applied Physics 05/2014; 53(6S):06JE03. DOI:10.7567/JJAP.53.06JE03 · 1.06 Impact Factor
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    ABSTRACT: An infrared wire-grid polarizer with an antireflection (AR) grating structure was fabricated using direct imprint lithography on both sides of a low toxicity chalcogenide glass (Sb-Ge-Sn-S system) simultaneously. The AR grating structure was designed using rigorous coupled-wave analysis theory. Silicon carbide with a grating period of 500 nm and glassy carbon with a grating period of 3 μm were employed as molds. After imprinting, a wire-grid polarizer was made by depositing Al obliquely on the grating. The transverse magnetic (TM) transmittance of the fabricated polarizer was over 70% at 8.5–10.5μm wavelength, although the transmittance of the glass substrate is 62–66%, and the extinction ratio was over 20 dB at 11μm wavelength. The polarizer has a high TM transmittance and is cheaper and simpler to fabricate as compared with conventional infrared polarizers.
    Infrared Physics & Technology 05/2014; 64. DOI:10.1016/j.infrared.2014.01.002 · 1.46 Impact Factor
  • Itsunari Yamada · Junji Nishii · Mitsunori Saito
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    ABSTRACT: A tunable transmission grating was fabricated by molding a silicone elastomer (polydimethylsiloxane). Its optical characteristics were then evaluated during compression. For fabrication, a glass plate with a photoimprinted polymer grating film was used as a mold. Both the grating period and diffraction transmittance of the molded elastomer were functions of the compressive stress. The grating period changed from 3.02 to 2.86 μm during compressing the elastomer in the direction perpendicular to the grooves.
    The Review of scientific instruments 01/2014; 85(1):013102. DOI:10.1063/1.4861198 · 1.58 Impact Factor
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    ABSTRACT: Infrared wire-grid polarizers were fabricated consisting of a 500-nm pitch Al grating on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) using the direct imprinting of subwavelength grating followed by a deposition of Al metal by thermal evaporation. To fabricate the subwavelength grating on a chalcogenide glass more easily, the sharp grating was formed on the mold surface. The fabricated polarizer with Al thickness of 130 nm exhibited a polarization function with a transverse magnetic transmittance greater than 60% in the 5–9-μm wavelength range, and an extinction ratio greater than 20 dB in the 4–11-μm wavelength range. The polarizer can be fabricated at lower costs and simpler fabrication processes compared to conventional infrared polarizers.
    SPIE Microtechnologies; 05/2013
  • Mitsunori Saito · Keisuke Hayashi
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    ABSTRACT: An infrared Lyot filter was fabricated by integrating a polarization beam splitter and two retarders into a single device. A liquid crystal layer was constructed between two silicon pentaprisms that were designed suitably so that light was incident on this layer at 28°. At this angle, the liquid crystal transmitted p-polarized light (Brewster's angle) and reflected s-polarized light (total internal reflection). The p- or s-polarized light was directed to another liquid crystal layer (retarder) between the prism and a mirror, which induced a wavelength-dependent retardation in the reflection process. Consequently, the light that returned to the beam splitter was transmitted or reflected depending on wavelength.
    Optics Express 05/2013; 21(10):11984-93. DOI:10.1364/OE.21.011984 · 3.49 Impact Factor
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    ABSTRACT: We designed and fabricated an achromatic infrared wave plate. To examine its phase retardation characteristics, the birefringence was calculated using the effective medium theory. A wave plate with a subwavelength grating was fabricated by direct imprint lithography on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) based on calculated results. As a result of imprinting onto chalcogenide glass by a glassy carbon mold, a grating with 1.63 μm depth, a fill factor of 0.7, and a 3 μm period was obtained. The phase retardation of the elements reached around 30° in the 8.5-10.5 μm wavelength range. The fabrication of the infrared wave plate is less costly compared with conventional crystalline wave plates.
    Applied Optics 03/2013; 52(7):1377-82. DOI:10.1364/AO.52.001377 · 1.78 Impact Factor
  • Itsunari Yamada · Junji Nishii · Mitsunori Saito
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    ABSTRACT: The dependences of the incident angle and thermal durability of a tungsten silicide (WSi) wire-grid polarizer were examined. A WSi grating with a 0.5 fill factor, 260 nm depth, and 400 nm period was formed on a Si surface using two-beam interference and dry etching. The TM transmission spectrum of the fabricated element was greater than 60% at the incident angle of θ=40° (the angle between the incident direction and the perpendicular axis to the grating direction) in the 4−10 μm wavelength range. An extinction ratio of 22.2 dB was achieved at 2.5 μm wavelength. Additionally, results show that this polarizer has higher thermal resistance than that of commercial infrared polarizers. Therefore, this polarizer is effective for taking a polarized thermal image of high temperatures.
    Infrared Physics & Technology 01/2013; 63. DOI:10.1016/j.infrared.2013.12.009 · 1.46 Impact Factor
  • Mitsunori Saito · Shingo Nakamura
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    ABSTRACT: An optical system was designed and fabricated to achieve signal wavelength conversion. Although a rare-earth doped phosphor was useful to achieve the infrared-to-visible conversion, its long-lasting phosphorescence prevented high-frequency modulation. This problem was solved by using a time-space conversion method, in which a phosphorescent disk was rotated to attain the fast-response wavelength conversion. When an infrared pulse train with 500-ns duration and 1-MHz repetition rate was focused on the rotating disk, phosphorescent dots were created along the disk periphery. By detecting the phosphorescence at a downstream position of the dot trajectory, a visible signal of 1 MHz was observed.
    SPIE Optical Systems Design; 12/2012
  • Source
    Mitsunori Saito · Tatsuya Nishimura · Kohei Sakiyama · Sota Inagaki
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    ABSTRACT: Optical functions of organic dyes, e.g., fluorescence or photochromism, tend to degrade by light irradiation, which causes a short lifetime of photonic devices. Self-healing of optical functions is attainable by metabolizing bleached molecules with nonirradiated ones. A polydimethylsiloxane elastomer provides a useful matrix for dye molecules, since its flexible structure with nano-sized intermolecular spaces allows dye diffusion from a reservoir to an operation region. Swelling the elastomer with a suitable solvent promotes both dissolution and diffusion of dye molecules. This self-healing function was demonstrated by an experiment in which a photochromic elastomer exhibited improved durability against a repeated coloring-decoloring process.
    AIP Advances 10/2012; 2(4). DOI:10.1063/1.4764292 · 1.59 Impact Factor
  • Mitsunori Saito · Yoshihiro Nishimura
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    ABSTRACT: Polyethylene-glycol (PEG) exhibited bistable transmission characteristics (transparent or opaque) in heating (melting) and cooling (freezing) processes. The bistable temperature range depended on the molecular weight and extended when different types of PEGs were mixed. For example, when PEGs with molecular weights of 300 and 2000 were mixed, the bistability took place in the 2-38 °C range. This phenomenon was used to fabricate a bistable optical fiber switch in which the mixed PEG was put in the gap between the ends of two polymer fibers. The bistable transmission property was demonstrated by controlling the device temperature with a Peltier element.
    Proceedings of SPIE - The International Society for Optical Engineering 10/2012; DOI:10.1117/12.928337 · 0.20 Impact Factor
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    ABSTRACT: Polydimethylsiloxane (PDMS) contains a large, flexible free space between weakly-bonded molecules, which allows notable molecular diffusion. A toluene solution of diarylethene (photochromic dye) was mixed with a PDMS oil, and then the mixture was cured in a glass vessel by adding a curing agent. Violet laser (405 nm wavelength) irradiation induced an absorption band at around 530 nm, and consequently, the irradiated portion exhibited a red color. The colored portion gradually expanded to the entire sample because of diffusion of the dye molecules. This diffusion characteristic was used for improving an organic dye durability against a photo-induced degradation.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2012; DOI:10.1117/12.928339 · 0.20 Impact Factor
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    ABSTRACT: We fabricated infrared wire-grid polarizers with an antireflection (AR) grating structure by the simultaneous imprinting on both sides of a low-toxicity chalcogenide glass (Sb--Ge--Sn--S system). Silicon carbide and glassy carbon plates were used as molds for the direct glass imprinting. A wire-grid polarizer of 100-nm-thick was produced by depositing Al obliquely on the grating. Although the transmittance of the chalcogenide glass substrate was 62--66% in the 8.5--10.5 μm wavelength range, the transverse magnetic (TM) transmittance of the fabricated element became higher than 70% owing to the AR structure. The extinction ratio was larger than 20 dB at 11 μm wavelength.
    Applied Physics Express 08/2012; 5(8):2502-. DOI:10.1143/APEX.5.082502 · 2.57 Impact Factor
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    ABSTRACT: An achromatic infrared wave plate was fabricated by forming a subwavelength grating on the chalcogenide glass using direct imprint lithography. A low toxic chalcogenide glass (Sb--Ge--Sn--S system) substrate was imprinted with a grating of 1.63-μm depth, a fill factor of 0.7, and 3-μm period using glassy carbon as a mold at 253 °C and 3.8 MPa. Phase retardation of the element reached around 30° at 8.5--10.5 μm wavelengths, and the transmittance exceeded that of a flat substrate over 8 μm wavelength. Fabrication of the mid-infrared wave plate is thereby less expensive than that of conventional crystalline wave plates.
    Applied Physics Express 07/2012; 5(7):2601-. DOI:10.1143/APEX.5.072601 · 2.57 Impact Factor
  • Itsunari Yamada · Kohei Fukumi · Junji Nishii · Mitsunori Saito
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    ABSTRACT: We fabricated a subwavelength-grating structure on the Y2O3 ceramic substrate, which has higher transparency than silicon in the mid-infrared range. After coating a photoresist on this substrate, we formed a grating pattern of 350-nm pitch by the two-beam interference of the He-Cd laser (325-nm wavelength). By using this photoresist grating as a mask, WSi was etched with reactive SF6 ions. The transmittance of the transverse magnetic (TM) polarization was greater than 70% in the 3-7-μm wavelength range without antireflection films and the extinction ratio was over 20 dB in the 2.5-5-μm wavelength range. In addition, we also fabricated near-infrared wire-grid polarizer consisting of a 230-nm pitch WSi grating on a SiO2 substrate. The TM polarization transmittance of the fabricated polarizer exceeded 80% in the 1000-1600-nm wavelength range. The extinction ratio was higher than 20 dB in the 650-1500-nm wavelength range.
    Proceedings of SPIE - The International Society for Optical Engineering 05/2012; DOI:10.1117/12.919758 · 0.20 Impact Factor
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    ABSTRACT: We fabricated infrared wire-grid polarizers consisting of a 500-nm pitch Al grating on a low toxic chalcogenide glass (Sb--Ge--Sn--S system) using the direct imprinting of subwavelength grating followed by a deposition of Al metal by thermal evaporation. To fabricate the subwavelength grating on a chalcogenide glass more easily, the sharp grating was formed on the mold surface. The fabricated polarizer with Al thickness of 130 nm exhibited a polarization function with a transverse magnetic transmittance greater than 60% in the 5--9 μm wavelength range, and an extinction ratio greater than 20 dB in 3.5--11 μm wavelength range. The extinction ratio of the element with Al wires of 180-nm thickness reached 27 dB at 5.4-μm wavelength. The polarizer can be fabricated at lower costs and simpler fabrication processes compared to conventional infrared polarizers.
    Japanese Journal of Applied Physics 01/2012; 51(1):2201-. DOI:10.1143/JJAP.51.012201 · 1.06 Impact Factor
  • Mitsunori Saito · Shingo Nakamura · Teppei Kita
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    ABSTRACT: Lanthanide-doped phosphors achieve signal wavelength conversion between visible and infrared communication systems. A long lifetime of their excited states is advantageous for inducing two-photon absorption that realizes upconversion. The long lifetime, however, restricts the conversion rate to ∼500 bit/s because of the afterglow. This contradiction was solved by embedding a phosphor (YbEr:Gd2O2S) in a rotating disk. When an infrared (940 nm) pulse train of 1 Mbit/s (time domain) was focused on the disk, a fluorescent dot array (space domain) was created and moved with the disk rotation. Consequently, a visible (∼550 nm) pulse train was detected on the dot trajectory.
    Applied Physics Letters 11/2011; 99(19). DOI:10.1063/1.3660262 · 3.52 Impact Factor
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    ABSTRACT: A mid-IR wire-grid polarizer with a 500 nm pitch was fabricated on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) by the thermal imprinting of periodic grating followed by the thermal evaporation of Al metal. After imprinting, deposition of Al on the grating at an oblique angle produced a wire-grid polarizer. The fabricated polarizer showed polarization with TM transmittance greater than 60% at 5-9 μm wavelengths and an extinction ratio greater than 20 dB at 3.5-11 μm wavelengths. This polarizer with a high extinction ratio can be fabricated more simply and less expensively than conventional IR polarizers.
    Optics Letters 10/2011; 36(19):3882-4. DOI:10.1364/OL.36.003882 · 3.18 Impact Factor
  • Mitsunori Saito · Keisuke Hayashi
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    ABSTRACT: A polarization beam splitter and tunable retarders were combined into a single element by using Si pentaprisms and liquid crystal (LC). An LC layer that was sandwiched between the two pentaprisms acted as a polarization beam splitter that reflected s-polarized light and transmitted p-polarized light. The other two LC layers that were attached to the outer surfaces of the pentaprisms acted as tunable retarders; i.e., they changed the polarization states of the reflected and transmitted light beams. When these beams were reflected back to the former LC layer (the beam splitter), wavelength selection took place owing to the wavelength dependence of the polarization state. This performance was confirmed by optical experiments in the infrared region.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2011; DOI:10.1117/12.891996 · 0.20 Impact Factor
  • Mitsunori Saito · Yoku Hirose
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    ABSTRACT: Infrared transmission characteristics of magnetic fluids were measured in the 4 – 10 μm wavelength range by using suspensions of kerosene and magnetite nanoparticles. The optical density of the magnetic fluid increased gradually toward short wavelengths, which indicated that scattering was a principal origin of the optical loss. When a magnetic field of 900 G was applied in the direction perpendicular to the optical path, the optical density increased or decreased depending on whether the polarization direction of the probe beam was parallel or perpendicular to the magnetic field. By contrast, an axial magnetic field reduced the optical density for both polarizations.
    Journal of the Optical Society of America B 06/2011; 28(7):1645-1649. DOI:10.1364/JOSAB.28.001645 · 1.81 Impact Factor

Publication Stats

277 Citations
92.85 Total Impact Points

Institutions

  • 2000–2014
    • Ryukoku University
      • Department of Electronics and Informatics
      Otsu, Kumamoto Prefecture, Japan
  • 2013
    • Hokkaido University
      • Research Institute for Electronic Science
      Sapporo, Hokkaidō, Japan
  • 2003
    • Osaka University
      • Graduate School of Engineering
      Suika, Ōsaka, Japan