Design of aspherical-lensed Si surface optical coupler for coupling with standard single-mode optical fibers

Abstract

A vertically curved Si surface optical coupler for coupling with 10 μm mode-field-diameter single-mode optical fibers was designed. By introducing a sharpened aspherical SiO2 coupler top with a strong optical focusing effect compared with a conventional hemispherical top, we succeeded in shortening the Si inverse taper which acted as an optical beam expander. In numerical simulations, the designed coupler exhibited coupling losses of 0.6 dB and 0.8 dB for TE and TM polarizations, respectively, and a 0.5-dB-loss-increment bandwidth of 250 nm. Furthermore, its optical alignment sensitivity and return loss were analyzed. Consequently, this device showed a small return loss of about −34 dB without applying an anti-reflection coating.