Takuji Hatano

Surface-relief gratings with high spatial frequency fabricated using direct glass imprinting process

Surface-relief gratings with high spatial frequencies were first fabricated using a direct imprinting process with a glassy carbon mold at the softening temperature of phosphate glass. A grating with maximum height of 730 nm and 500 nm period was formed on the glass surface by the pressing at the softening temperature of glass under constant pressure of 0.4 kN/cm(2). Phase retardation of 0.1 lambda was observed between TE-polarized and TM-polarized light at 600 nm wavelength.

Glass Imprinting Process for Fabrication of Sub-Wavelength Periodic Structures

Using direct glass imprinting with glassy carbon molds, one-dimensional surface-relief gratings with 500 nm pitch were fabricated on phosphate glasses. The maximum grating height attained in this study was 730 nm, which was formed by pressing at the softening temperature of the glass at a constant pressure of 0.4 kN/cm2. A large area pattern 6 ×6 mm2 with a 350-nm groove depth was also fabricated. Phase retardation of 0.1 λ was attained between transverse electric (TE)- and transverse magnetic (TM)-polarized light in the visible wavelength region. Calculated retardation using a rigorous coupled wave analysis agreed well with the experimental results.

Bragg Grating Formation in Polyimide Waveguide by Ultraviolet Light Irradiation

The refractive index of polyimide can be changed by irradiation with ultraviolet light. The amount of change in refractive index is >10-3. The Kramers–Kronig model can explain the mechanism. Utilizing this phenomenon, Bragg gratings can be fabricated in a polyimide waveguide by irradiation with an ultraviolet laser beam. It has a possibility of application in tunable wavelength filters because polyimide has a birefringent characteristic and a large thermooptical constant.