Velocity-Matching Enhancement in Cascaded Integration of EAMs and SOAs Using Bypass High Impedance Transmission Lines

Velocity-matching effect in cascaded integration (CI) of electroabsorption modulators (EAMs) and semiconductor optical amplifiers (SOAs) utilizing bypass high impedance transmission lines (HITLs) is analyzed and demonstrated in this work. By experimentally and theoretically comparing different types of CI structures, the retarded phase in slower microwave waveguide of EAMs can be compensated from the fast waveguide of HITL to match the optical wave in EAM and SOA waveguides, improving high-speed electrooptical (EO) conversion. It thereby suggests high-frequency EO response of CI structure can be beneficial from not only the impedance-matching, but also further phase-matching condition. A 1.3-mm-long SOA-integrated EAM with phase retardation of less than 0.2 radii at 40 GHz and impedance matching has been demonstrated, leading to a -3-dB EO bandwidth of 46 GHz. It suggests that a controllable phase delay through HITL can be used for releasing the design burden of the long-integrated optoelectronic devices for high-speed high-efficient performance.