title: Attenuation in waveguides on FR-4 boards due to periodic substrate undulations.
abstract: The guided-mode attenuation associated with optical-interconnect-polymer waveguides fabricated on FR-4 printed-circuit boards is quantified. The rigorous transmission-line network approach is used and the FR-4 substrate is treated as a long-period substrate grating. A quantitative metric for an appropriate matrix truncation is presented. The peaks of attenuation are shown to occur near the Bragg conditions that characterize the leaky-wave stop bands. For a typical 400 microm period FR-4 substrate with an 8 microm corrugation depth, a buffer layer thickness of about 40 microm is found to be needed to make the attenuation negligibly small.
authors.affiliation: School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA. yjchang@ece.gatech.edu
authors.forename: Yin-Jung
authors.initials: YJ
authors.lastname: Chang
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Gaylord
authors.forename: Gee-Kung
authors.initials: GK
authors.lastname: Chang