Free Space Optics: A Viable Last Mile Alternative

摘要

This paper explores Free Space Optics (FSO) as an access technology in the "last mile" of metropolitan area networks (MANs). These networks are based in part on fiber-optic telecommunications infrastructure, including network architectures of Synchronous Optical Network (commonly referred to as SONET), the North American standard for synchronous data transmission; and Synchronous Digital Hierarchy (commonly referred to as SDH), the international standard and equivalent of SONET. Several converging forces have moved FSO beyond a "niche" technology for use only in local area networks (LANs) as a bridge connecting two facilities. FSO now allows service providers to cost effectively provide optical bandwidth for access networks and accelerate the extension of metro optical networks bridging what has been termed by industry experts as the "optical dead zone." The "optical dead zone" refers to both the slowdown in capital investment in the short-term future and the actual connectivity gap that exists today between core metro optical networks and the access optical networks. Service providers have built extensive core and minimal metro networks but have not yet provided optical bandwidth to the access market largely due to the non-compelling economics to bridge the dead zone with fiber. Historically, such infrastructure build-out slowdowns have been blamed on a combination of economics, time-to-market constraints and limited technology options. However, new technology developments and market acceptance of FSO give service providers a new cost-effective alternative to provide high-bandwidth services with optical bandwidth in the access networks. Merrill Lynch predicts FSO will grow into a $2 billion market by 2005. "The drivers for this market are a mere 5%-6% penetration of fiber to business buildings; cost effective solution versus RF or fiber; and significant capacity which can only be matched by a physical fiber link," Merrill Lynch reports. This paper will describe FSO technology, its capabilities and its limitations. The paper will investigate how FSO technology has evolved to its current stage for deployment in MANs, LANs, wireless backhaul and metropolitan network extensions ― applications that fall within the category of "last mile." The paper will address the market, drivers and the adoption of FSO, plus provide a projection of future FSO technology, based on today's product roadmaps. The paper concludes with a summary of findings and recommendations.