Mitsunori Saito

Ryukoku University, Otsu, Kumamoto Prefecture, Japan

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Publications (43)75.47 Total impact

  • [Show abstract] [Hide abstract]
    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. · 1.07 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; · 1.36 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. · 1.52 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
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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. · 1.69 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; · 1.36 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-. · 2.73 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-. · 2.73 Impact Factor
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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.
    Proc SPIE 05/2012;
  • [Show abstract] [Hide abstract]
    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-. · 1.07 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. · 3.39 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. · 2.21 Impact Factor
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    ABSTRACT: We fabricated a near-infrared wire-grid polarizer consisting of a 230-nm-pitch tungsten silicide (WSi) grating on a SiO2 substrate using two-beam interference lithography and dry etching. The transverse magnetic (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. We also measured the extinction coefficient kappa of WSi and verified that WSi is a suitable polarizing material in the near-infrared range.
    Japanese Journal of Applied Physics 01/2011; 50. · 1.07 Impact Factor
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    ABSTRACT: Self-controlled photonic switching was achieved by combining the photoconductivity of a semiconductor and the electrical tunability of a liquid crystal (LC). Pulse packets of 1.06 μm wavelength created free carriers in a silicon electrode of an LC cell, which triggered voltage application for LC reorientation. Consequently, polarization direction of the succeeding packets became perpendicular to that of the preceding packets, and they progressed in different directions after passing through a polarization beam splitter. The cascade LC cells divided a series of packets one by one in a self-controlled manner.
    Optics Letters 01/2011; 36(2):208-10. · 3.39 Impact Factor
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    ABSTRACT: Using two-beam interference lithography and dry etching, we fabricated a mid-IR wire-grid polarizer consisting of a 350 nm pitch WSi grating on an Y(2)O(3) ceramic substrate, which has wider transparency than sapphire. The transmittance of 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. The wire-grid polarizer with the Y(2)O(3) ceramic substrate provides high durability and good IR transparency.
    Optics Letters 09/2010; 35(18):3111-3. · 3.39 Impact Factor
  • Mitsunori Saito, Kentaro Koyama
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    ABSTRACT: Fluorescent droplet cavities were created in elastomer by using an ink-jet method. A solution for creating droplets was composed of fluorescent rhodamine, alcohol, and surfactant. Polysiloxane was used as a matrix, since its elasticity allowed droplet deformation that caused resonance-wavelength shift. The injected dye solution self-formed a sphere in the raw liquid of polysiloxane due to surface tension. The polysiloxane matrix solidified in 8 h after adding a curing agent. The droplet exhibited whispering-gallery-mode emission when it was excited by a frequency-doubled Nd:YAG laser pulse. The resonance peaks shifted to either short or long wavelengths as the droplet deformed by pressing the elastomer.
    Proc SPIE 04/2010;
  • Mitsunori Saito, Kentaro Koyama
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    ABSTRACT: A droplet-elastomer compound was fabricated by using an inkjet technique. Being emitted by a nozzle, a dye-doped surfactant self-formed a microsphere in a polysiloxane elastomer. Rapid vaporization during the droplet flight process was utilized advantageously to form a small sphere. The droplet volume was controlled between 1 and 103 pl, corresponding to a diameter range of 10-120 mum. When the droplet was excited by a 532 nm laser pulse, resonance peaks of whispering gallery modes appeared in the fluorescence spectrum. The peak wavelength was controlled by pressing the elastomer or deforming the droplet.
    Japanese Journal of Applied Physics 01/2010; 49. · 1.07 Impact Factor
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    ABSTRACT: An IR polarizer was fabricated by plating a Ni wire-grid on a Si substrate. The Si surface was processed by photolithography to create grooves with ˜200 nm width, ˜200 nm spacing, and ˜300 nm depth. After surface treatment, the Si plate was put in a plating bath for ˜5 min to fill the grooves with Ni. The excess Ni film that was deposited outside the grooves was removed by mechanical polishing. The fabricated wire-grid exhibited a polarization function with an extinction ratio of 15-20 dB in the 3-13 mum wavelength range.
    Japanese Journal of Applied Physics 01/2010; 49(5). · 1.07 Impact Factor
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    ABSTRACT: We fabricated a terahertz wire-grid polarizer consisting of a micrometer-pitch Al grating on a Si substrate by photolithography and wet etching. The ratio of TM and TE transmittances (extinction ratio) was over 35 dB at 0.5 THz. At the Brewster angle of the Si substrate, the polarization transmittance of a TM wave through the fabricated polarizer exceeded 95% and the extinction ratio was over 45 dB at approximately 1 THz. The fabricated polarizer has a higher extinction ratio than conventional free-standing terahertz wire-grid polarizers.
    Optics Letters 03/2009; 34(3):274-6. · 3.39 Impact Factor
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    ABSTRACT: We examined the effect of an antireflection (AR) coating to enhance the TM transmittance of the wire-grid polarizer. The polarization transmission spectra were calculated using the rigorous coupled-wave analysis. As a result, we verified that an AR film should be inserted between a wire-grid and a Si substrate as regards the TM transmittance and the polarization function. Based on the simulation results, we fabricated a tungsten silicide (WSi) wire-grid polarizer with SiO films on both sides of the Si substrate. The transmittance exceeded 80% at a 4-5 microm wavelength range, although the theoretical transmittance of Si substrate is 54% and the ratio of the TM and TE transmittances reached 24 dB at a 3 microm wavelength when the WSi grating has a 300 nm thickness, a 400 nm period, and a fill factor of 0.6. Wire-grid polarizers with higher transmittance and larger extinction ratio can be obtained by adjusting the AR film thickness, the fill factor, and the thickness of the WSi grating.
    Applied Optics 02/2009; 48(2):316-20. · 1.69 Impact Factor

Publication Stats

113 Citations
75.47 Total Impact Points

Institutions

  • 2003–2014
    • Ryukoku University
      • Department of Electronics and Informatics
      Otsu, Kumamoto Prefecture, Japan
  • 2013
    • Hokkaido University
      • Research Institute for Electronic Science
      Sapporo, Hokkaidō, Japan
  • 2010–2011
    • The University of Shiga Prefecture
      • Division of Electronic Systems Engineering
      Hikone, Shiga, Japan
  • 2008–2009
    • National Institute of Advanced Industrial Science and Technology
      Tsukuba, Ibaraki, Japan