Toshihiko Einishi

Fabrication of a mid-IR wire-grid polarizer by direct imprinting on chalcogenide glass

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.

Fabrication of Achromatic Infrared Wave Plate by Direct Imprinting Process on Chalcogenide Glass

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-?m depth, a fill factor of 0.7, and 3-?m 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 ?m wavelengths, and the transmittance exceeded that of a flat substrate over 8 ?m wavelength. Fabrication of the mid-infrared wave plate is thereby less expensive than that of conventional crystalline wave plates.

Optical Waveguides Fabricated by Classical Staining Process

Optical waveguides were prepared by the incorporation of silver or copper ions into soda-lime silicate and borosilicate glass substrates using a classical staining process. The waveguides were colorless and optically clear, indicating that silver and copper metal nanoparticles and Cu2O nanoparticles that cause coloration of glasses were not formed. The increase in the refractive index at 633 nm reached 4×10-2 and 1×10-2 for the silver-doped and copper-doped waveguide layers, respectively. The ion distribution measured by energy dispersion X-ray analysis showed that the silver and copper ions reached depths of 5 and 20 µm, respectively, in the substrates. Single-mode propagations at 633 nm and 1.54 µm were observed for both silver-doped and copper-doped waveguides.

Design and fabrication of an achromatic infrared wave plate with Sb–Ge–Sn–S system chalcogenide glass

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.

Infrared Polarizer Fabrication by Imprinting on Sb--Ge--Sn--S Chalcogenide Glass

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.

Direct imprinting on chalcogenide glass and fabrication of infrared wire-grid polarizer

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.

Optical waveguide fabricated by ion-exchange using stain method

Optical waveguides were prepared by the incorporation of silver or copper ions using the classical staining. We used commercially available soda-lime silicate and borosilicate glasses as substrates. Silver or copper stain was applied on a side of the glass substrates. The substrates were heat-treated at elevated temperature for various times. The treated glasses were optically clear and almost colorless except for a few samples stained for longer time. This indicates that silver and copper metal nanoparticles and Cu2O nanoparticles causing coloration of glasses were not formed in the glass substrates. The ion-incorporation process was approximately controlled by the diffusion of ions. We observed the propagation of 633 nm laser radiation by a prism coupling method showing that the glass surface region plays a role of waveguide. Refractive index change more than 0.01 at 633 nm was achieved in the waveguide layers.