An optical backplane for high performance switches

We have demonstrated an optical backplane which provides high speed bit-synchronous digital data interconnection for a variety of applications, including high performance time division switching and packet switching. In addition to discussing architectures and technologies for optical backplanes, we will describe a prototype digital time division switch and its optical backplane to aid in understanding these new technologies and their implications on switching. Our optical backplane is an optical fiber-based design in which all components are targeted for high speed over very short (10s of meters maximum) distances at the lowest possible cost. The new components developed include specialty fibers, high performance short wavelength active devices, low-cost molded plastic optical backplane connectors, and a new low-cost polymeric resin-filled optical coupler technology for splitting and combining optical signals. The passive components are designed to support a large range of interconnection speeds so that only active devices need be changed to optimize cost/performance for a particular application. The optical bus architecture resembles an electrical passive bus in which circuit boards can be inserted and removed without interrupting the bus or causing bus errors. The resulting optical backplane can be used to provide inherently electromagnetic interference free backplane communication which does not depend on costly shielding and grounding techniques. Other advantages include equipment size reduction, reduced requirements for quality of power, and inherent lightning and power-cross protection. Our prototype optical backplane-based switch demonstrates that optical technology can provide cost reduction of conventional telephony switching equipment and provides the opportunity to design much higher bandwidth busses than can be implemented with conventional electrical technology. When such optical bussing technologies are applied to a telephony switch, higher port densities and wider distribution options are possible. Optical busses can extend busses not only between shelves within a cabinet but may also be used between cabinets. Our prototype switch uses high numerical aperture, large diameter, step-index optical waveguides which have a smaller bandwidth-distance product than fibers typically used for tele-communications. These waveguides were used to give us a much broader spectrum of optical component design choices, while still maintaining relatively high bandwidths over the limited distances required for interconnecting circuit packs within switching equipment.