title: Monolithic integration and synchronous operation of germanium photodetectors and silicon variable optical attenuators.
abstract: We demonstrate the monolithic integration of germanium (Ge) p-i-n photodetector (PDs) with silicon (Si) variable optical attenuator (VOAs) based on submicrometer Si rib waveguide. A PD is connected to a VOA along the waveguide via a tap coupler. The PDs exhibit low dark current of ~60 nA and large responsivity of ~0.8 A/W at the reverse bias of 1 V at room temperature. These characteristics are uniform over the chip scale. The PDs generate photocurrents precisely with respect to DC optical power attenuated by the VOAs. Two devices work synchronously for modulated optical signals as well. 3-dB cut-off frequency of the VOA is ~100 MHz, while that of the PD is ~1 GHz. The synchronous response speed is limited by the VOA response speed. This is the first demonstration, to the best of our knowledge, of monolithic integration of Ge PDs with high-carrier-injection-based optical modulation devices based on Si.
authors.affiliation: NTT Microsystem Integration Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa, 243-0198, Japan. psbong@aecl.ntt.co.jp
authors.forename: Sungbong
authors.initials: S
authors.lastname: Park
authors.forename: Tai
authors.initials: T
authors.lastname: Tsuchizawa
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Shinojima
authors.forename: Hidetaka
authors.initials: H
authors.lastname: Nishi
authors.forename: Koji
authors.initials: K
authors.lastname: Yamada
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Ishikawa
authors.forename: Kazumi
authors.initials: K
authors.lastname: Wada
authors.forename: Seiichi
authors.initials: S
authors.lastname: Itabashi