40 Gb/s optical modulation using monolithically chain integration of semiconductor optical amplifiers (SOA) and electroabsorption modulators (EAM)

Optoelectronic intergraded devices for 40 Gb/s optical modulation are important and have attracted a lots of interests in optical communication. Among the integrated optoelectronic devices of modulation, electroabsorption modulators (EAM) have been widely used in high-speed optical communication due to its high extinction ratio, low driving power, and the capability of integrating with other semiconductor devices [1]. However, based on 40 Gb/s modulation template, the high-speed electrical-to-optical (EO) based on EAMs is still limited on their waveguide properties, such as microwave properties and optical insertion loss [1-3]. Due to the highly loaded capacitance in EAM waveguide, devices suffer from high electrical reflection, high loss. Although such high-speed performance can be enhanced by fabricating small size of waveguide, the trade-off issue in optical insertion loss due to small waveguide still limits the overall performance. In the previous work, a cascaded integration of EAMs and semiconductor optical amplifiers (SOA) is demonstrated with not only the optical gain, but also the improved EO link by comparing the single EAM [4]. By periodically integrating EAMs with high impedance transmission line (HITL), the impedance can be increased to get lower electrical reflection, leading to a broadband EO response. In this work, using such integration technique, the cascaded integration of EAMs and SOAs is demonstrated with successful 40Gb/s digital transmission.