Speaker: Stu Milner
Affiliation: University of Maryland, College Park, Dept. of Civil and Environmental Engineering
Topic: "Lightwave Wireless Communications at 100s THz for Sensor Networks"

Abstract
Wireless lightwave communications have the highest available bandwidth of all wireless communication technologies because of their carrier frequencies of hundreds of terahertz. Examples include 1.55 micrometer infrared systems (194 THz), and 980 nm Free Space Optical (FSO) systems (~300 THz). FSO-based sensor networks using direct line of light (LOS) laser links are spatially efficient and physically secure. Their data rates can range from b/s to Gb/s with the complete optical transceiver system consuming power in the tens of mW. These features are advantageous for low-power communication networks over short distances in environments where LOS is available, and where radio frequency connectivity must be avoided because of interference or security problems. The range of links in FSO networks is limited by power requirements and angular coverage. Recent interest in THz carriers has focused on RF systems. In this presentation, we discuss how such carriers can be used in FSO-based systems with implications for THz and directional wireless RF networks.

In order for FSO directional networks to provide viable short-range connectivity, the networks must provide signal coverage over a wide field of view and operate with efficient media access protocols to minimize random access times for the independent transmitting nodes within the network. In this talk, the system design, prototyping and experimental results of an FSO sensor network using a 300 THz carrier is presented. The system includes a network of small, low power (mW), integrated systems, or "motes," that transmit data optically to a central "cluster head," which controls the network traffic of all the motes and can relay data to another cluster head in a series of multi-hops to achieve data communication over longer distances. To provide wide field of view signal coverage, each cluster head is equipped with multiple vertical cavity surface emitting lasers oriented in different directions and controlled to diverge at 10 degrees. To implement the media access controls in this directional wireless network, a master-slave architecture is implemented.