Effective electro-optical modulation with high extinction ratio by a graphene-silicon microring resonator

Graphene opens up for novel optoelectronic applications thanks to its high carrier mobility, ultra-large absorption bandwidth, and extremely fast material response. In particular, the opportunity to control optoelectronic properties through tuning of Fermi level enables electro-optical modulation, optical-optical switching, and other optoelectronics applications. However, achieving a high modulation depth remains a challenge because of the modest graphene-light interaction in the graphene-silicon devices, typically, utilizing only a monolayer or few layers of graphene. Here, we comprehensively study the interaction between graphene and a microring resonator, and its influence on the optical modulation depth. We demonstrate graphene-silicon microring devices showing a high modulation depth of 12.5 dB with a relatively low bias voltage of 8.8 V. On-off electro-optical switching with an extinction ratio of 3.8 dB is successfully demonstrated by applying a square-waveform with a 4 V peak-to-peak voltage.Comment: 12 pages, including 7 figure

Teraflows over Gigabit WANs with UDT

The TCP transport protocol is currently ine#cient for high speed data transfers over long distance networks with high bandwidth delay products. The challenge is to develop a protocol which is fast over networks with high bandwidth delay products, fair to other high volume data streams, and friendly to TCP-based flows. We describe here a UDP based application level transport protocol named UDT (UDP based Data Transfer) with these properties and which is designed to support distributed data intensive computing applications. UDT can utilize high bandwidth e#ciently over wide area networks with high bandwidth delay products. Unlike TCP, UDT is fair to flows independently of their round trip times. In addition, UDT is friendly to concurrent TCP flows, which means it can be deployed not only on experimental research networks but also on production networks. To ensure these properties, UDT employs a novel congestion control approach that combines rate based and window based control mechanisms. In this paper, we describe the congestion control algorithms used by UDT and provide some experimental results demonstrating that UDT is fast, fair and friendly