Focusing Grating Coupler for Blue Laser Light

A focusing grating coupler (FGC) for use with a blue laser of 400-nm wavelength as a light source was fabricated for the first time. The FGC was designed to have a numerical aperture of 0.48 and a minimum period of 0.2 /spl mu/m when the focal length and the grating area were 900 /spl mu/m and 1/spl times/1 mm/sup 2/, respectively. Grating pattern of minimum line of 0.1 /spl mu/m was fabricated on a waveguide based on the boron phosphor-silicate glass material by electron-beam lithography process using the vector scan method. The spot size at the full width (1/e/sup 2/) was measured as 0.92 and 0.85/spl mu/m in x and y directions and was nearly the same as the diffraction limit.