Design and fabrication of a waveguide photodiode for 1.55-/spl mu/m band access receivers

A waveguide photodiode that can be used in 1.55-/spl mu/m-band access receivers was designed and fabricated. We simulated the optical coupling characteristics, focusing especially on the external quantum efficiency and coupling tolerance for different input spot sizes and for different waveguide-layer structures. The results clearly showed that both high efficiency and high tolerance can be obtained in an optimized symmetric structure for a hemispherically ended fiber. The fabricated device, optimized in the basis of the simulation, showed excellent characteristics such as an external quantum efficiency of more than 95% and a coupling tolerance of 6.5 /spl mu/m in the vertical direction.