FABRICATION OF A CONCENTRIC-CIRCULAR FOCUSING GRATING COUPLER BY A CONIC-WAVE-FRONT INTERFERENCE METHOD AND LIGHT-CONVERGENCE EXPERIMENTS USING THE COUPLER

An interference method utilizing conic-wave-front light for the fabric ation of a concentric-circular and chirped grating is proposed. The de sign method and fabrication of an interference lens that generates con ic-wave-front light are also shown. A focusing element is constructed from a concentric-circular grating coupler with a 0.4-mm diameter and a concentric-circular focusing grating coupler with an annular apertur e of 2-mm focal length and 2.0-4.0-mm diameter. Light-convergence expe riments using the focusing element were able to obtain a focusing spot of 0.5 mu m x 0.7 mu m at half-intensity widths for a wavelength of 8 20 nm in combination with liquid-crystal polarization elements. (C) 19 95 Optical Society of America