Tunable wavelength filter with a subwavelength resonant grating

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A guided-mode resonant grating acts as a narrow-band optical reflection filter. A tunable wavelength filter with the guided-mode resonant grating with electro-optical effect was proposed. The resonant grating consists of comb-shaped electrodes, which also act as a diffraction grating, and slab waveguide with the quadratic electro-optic effect on a low refractive-index substrate. The waveguide layer is a transparent ceramic of lead lanthanum zirconate titanate (PLZT : Pb_<1-x>La_x(Zr_yTi_<1-y>)_<1 x/4>O_3, n=2.54) on a sapphire substrate. The comb-shaped grating of indium thin oxide (ITO) or indium titanium oxide (ITiO) is made on the PLZT layer with lithography techniques.A new numerical simulation program based on the finite difference time domain (FDTD) method was developed for calculating the light behavior in a non-uniform anisotropic optical medium. The simulation results showed that the resonant wavelength with 1nm bandwidth was shifted by a few nanometers for 5V applied voltage.The designed resonant grating was fabricated. Before making the comb-shaped grating, the process condition for depositing a transparent PLZT layer with the sol-gel method were founded. After pattering the comb-shaped electrodes on an electron-beam resist layer, the electrode was made by InTiO sputtering and the lift-off technique. The fabricated resonant grating had a reflection peak at 1030nm light wavelength with 3nm bandwidth. However, the resonant wavelength was not shifted by applying voltage to the electrodes. The electrodes were short-circuited by tiny flakes of the InTiO which was stuck in the electrode grating grooves, so that the electric field was not impressed on the PLZT waveguide layer.To control the resonant wavelength with Kerr medium was also discussed with numerical simulations. Such the nonlinear optical resonator will be an all-optical switch.