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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. · 1.41 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. · 3.40 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. · 3.40 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. · 3.40 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. · 3.40 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. · 1.41 Impact Factor
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ABSTRACT: We designed and fabricated a tungsten silicide wire-grid polarizer. To examine its polarization characteristics, the transmission spectra of the polarizer were simulated using the effective medium theory. The polarizer was fabricated based on the simulation results. The transverse magnetic (TM) polarization transmittance of the fabricated polarizer was greater than 50% over the 5 mum wavelength, and the ratio of TM and transverse electric transmittance was greater than 100 (20 dB) in the infrared range. This fabricated polarizer has higher durability and better compatibility with microfabrication processes than conventional infrared polarizers.
Applied Optics 10/2008; 47(26):4735-8. · 1.41 Impact Factor
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ABSTRACT: A fluorescent microdroplet was formed in elastomer to facilitate handling and wavelength tuning. A methanol solution of rhodamine 6G was put into a solidifying polysiloxane resin with a needle. Addition of surfactant was effective to stabilize the droplet. Being excited by a laser pulse (532 nm, > 50 microJ/mm(2), 5 ns), the droplet exhibited a whispering gallery mode emission in the 570-610 nm wavelength range. The resonance peaks shifted as the droplet diameter expanded by elastomer deformation.
Optics Express 09/2008; 16(16):11915-9. · 3.59 Impact Factor
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ABSTRACT: An IR laser of 940 nm wavelength induced photochromic reaction in acrylate that contained both spirobenzopyran and rare-earth doped oxide (Gd(2)O(2)S:YbEr). The rare-earth elements were excited by two 940 nm photons and emitted a 550 nm photon, which caused photochromic isomerization of spirobenzopyran. This acrylate turned to its original orange color by either thermal relaxation or ultraviolet irradiation, and was bleached again by IR laser irradiation.
Optics Letters 09/2008; 33(15):1687-9. · 3.40 Impact Factor
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ABSTRACT: An infrared (IR) polarizer with tungsten silicide (WSi) wire grid was fabricated by two-beam interference exposure and reactive ion etching. To enhance TM transmittance, silicon monoxide was deposited between the WSi wire grid (400 nm period) and a Si substrate. The transmittance was over 80% in the 4-5 microm wavelength range. The ratio of TM and TE transmittances was over 100 (20 dB) in the 2.5-6 microm wavelength range. The fabricated polarizer has higher durability and better compatibility with microfabrication processes compared with conventional IR polarizers.
Optics Letters 03/2008; 33(3):258-60. · 3.40 Impact Factor
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ABSTRACT: A nonlinear input-output characteristic was observed when neodymium doped yttrium aluminum garnet laser passed through a silicon cell containing a twisted-nematic liquid crystal. The laser beam excited free carriers in the silicon plate, which triggered electrical reorientation of the liquid crystal. Consequently, the polarization direction of the laser beam changed, and the output beam passing through a polarizer became weaker as the input power increased. This function was utilized for self-branching of an optical pulse train.
Applied Physics Letters 10/2007; 91(14):141110-141110-3. · 3.84 Impact Factor
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ABSTRACT: Photosensitive solid-liquid compounds were fabricated by filling nanoholes of alumina or polymer films with dye solution. Although these compounds can be handled as solid in device fabrication processes, the liquid phase inside 50–200 nm holes provides a sufficient free volume for photochromic dye to change molecular structure. Nanoholes also prevent the solution to flow disturbing an optically written image. A function of the rewritable grating was demonstrated by bleaching a polycarbonate-based compound with various interference fringes of green laser.
Applied Physics Letters 09/2007; · 3.84 Impact Factor
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ABSTRACT: Time-resolved spectrometry was conducted in the mid-infrared region (2.8-4.6 microm). A galvano-mirror causes a spectrally dispersed beam to repeatedly sweep up and down a PtSi focal plane array so that each element of the array is struck by the beam only once at some point within a time frame. Transient spectra of flowing gases (hydrocarbon and carbon dioxide) were measured at 80 micros intervals.
Optics Letters 07/2007; 32(12):1656-8. · 3.40 Impact Factor
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ABSTRACT: A notable change in the photochromic characteristics was observed when the benzene solution of spirobenzopyran was put in nanoholes of anodic alumina. The absorption peak that appeared in the ultraviolet irradiation process shifted to a shorter wavelength, and the decay time of the decoloration process became approximately 200 times longer than that of the original solution. After a preservation period of several days, however, both the absorption wavelength and the decay time recovered to those of the original solution. These experimental results suggest that the photochromic isomerization in the alumina nanoholes is affected by the large surface area of the matrix rather than the limited free volume.
Applied Optics 12/2006; 45(31):8019-25. · 1.41 Impact Factor
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ABSTRACT: Crystalline 20- to 40- nm - diam Ge nanoparticles were precipitated periodically in Ge – B – SiO <sub>2</sub> thin glass films fabricated by the plasma-enhanced chemical vapor deposition method. Such a periodic structure was created by exposure to an interference pattern with a KrF excimer laser ( 248 nm wavelength) and successive annealing at 600° C . Nanoparticles were precipitated predominantly in the unirradiated region after photoinduced refractive index change was erased completely after annealing up to 500° C .
Applied Physics Letters 11/2004; · 3.84 Impact Factor
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ABSTRACT: Thermally stabilized photo-induced channel waveguides with Bragg gratings were fabricated in Ge-B-SiO2 thin glass films by exposure with KrF excimer laser and successive annealing at 600 degrees C. The annealing reversed the photo-induced refractive index pattern and also enhanced its thermal stability. The stabilized channel waveguide with a Bragg grating showed diffraction efficiency of 18.0 dB and 18.7 dB for TE- and TM-like modes, respectively. The diffraction efficiencies and wavelengths for both modes never changed after heat treatment at 500 degrees C, whereas the conventional photo-induced grating decayed even at 200 degrees C.
Optics Express 10/2004; 12(19):4589-95. · 3.59 Impact Factor
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ABSTRACT: We fabricated an emergency illumination panel by stacking two translucent pictures, one of which was painted with ink and the other with phosphors. When the panel was illuminated by backlight or room light, only the ink-printed picture was visible to the human eye and only the phosphorescent picture was visible in darkness. A two-way mirror was inserted between the two pictures both to prevent super-imposition of the two images and to enhance phosphorescence. This phosphorescent emergency sign acted as an illuminator independently of electric power sources and provided sufficient brightness for reading newspaper headlines.
Applied Optics 07/2004; 43(18):3608-13. · 1.41 Impact Factor
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ABSTRACT: The ordinary and extraordinary complex refractive indices, n(o) - j kappa(o) and n(e) - j kappa(e), of a nematic liquid crystal were measured in the infrared region at 3.0-11.5-microm wavelength. The complex refractive indices were evaluated in terms of the angular dependence of the reflectance. Semicylindrical CsI prisms and a goniometer were used for measurement of the reflectance in a wide incident-angle range and throughout the wide infrared spectral region. Refractive indices n(o) and n(e) changed notably near the absorption wavelength. Negative birefringence, i.e., n(e) < n(o), was observed in the vicinity of 6.6 microm, where n(e) changed more than did n(o).
Applied Optics 05/2003; 42(13):2366-71. · 1.41 Impact Factor
