An almost aberration-free focusing grating coupler with a grating area of 1 × 1 mm2 and a 2-mm focal length was made by using an electron beam writing system with accurately calibrated electron beam deflection and an accurate parameter setting of the effective refractive index of the waveguide. The smallest focused spot size achieved was 1.2 µm (FWHM), which is 1.06 times the value of the diffraction-limited spot size.
© 1990 Optical Society of America
Fumihiro Sogawa, Yoshikazu Hori, and Makoto Kato, "Fabrication of aberration-free focusing grating couplers," Appl. Opt. 29, 5103-5105 (1990)