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Germanium photodetectors have been considered to be mature components in the silicon photonics systems, especially for applications in the near infrared communication band. In order to avoid the restriction between quantum efficiency and carrier transit time, attentions should be payed to integrated waveguide photodetectors, which control the light transmission and the transmission of carriers in two perpendicular directions. Integrated waveguide coupling mainly include end-coupling and evanescent coupling. Compared with end-coupling, evanescent coupling is more easily realized though its coupling efficiency is lower than that of end-coupling. This paper reports an integrated waveguide photodetector exploiting evanescent coupling with some design that the center of silicon rib waveguide would be halfsurrounded by the germanium region. And light could be coupled from the top and both sides of the silicon rib waveguide into the germanium region. Simulations were carried out to compare our design with the conventional evanescent coupling configuration by finite difference time domain (FDTD) algorithm on the same condition such as the incident light power and the size of the light absorbing region. Compared with the conventional evanescent coupling configuration, the half-surrounded configuration could contribute a more substantial light absorption efficiency and responsivity.
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