MEMS: THE PATH TO LARGE OPTICAL CROSSCONNECTS

MEMS: THE PATH TO LARGE OPTICAL CROSSCONNECTS

ABSTRACT:

Continuous growth in demand for optical network capacity and the sudden maturation of WDM(wave length division multiplexing) technologies have fueled the development of optical network systems that transport tens to hundreds of wavelengths per fiber, with each wavelength modulated at 10 Gb/s or more. Micro-electromechanical systems devices are recognized to be the enabling technologies to build the next-generation cost-effective and reliable high-capacity optical cross connect. While the promises of automatically reconfigurable networks and bit-rate-independent photonic switching are bright, the endeavor to develop a high-port-count MEMS based OXC involves overcoming challenges in MEMS design and fabrication, optical packaging, and mirror control. Due to the interdependence of many design parameters, manufacturing tolerances, and performance requirements, careful trade-offs must be made in MEMS device design as well as system design. This paper emphasizes various design trade-offs, and multidisciplinary system considerations for building reliable and manufacturability large MEMS-based OXCs.

INTRODUCTION:

To meet the growing demand for high data bandwidth, service providers are building optical networks around the globe using the latest wavelength-division multiplexed (WDM) technologies with mesh network architecture .Light paths between access points in a network are created using fiber links containing many wavelength channels in each fiber, where each channel or port can have a data rate of up to 2.5 or 10 Gb/s. At the edge of the networks are the clients (IP/ATM routers, optical add-drop multiplexers, etc.) that use these light paths as high-capacity pipes for data/voice traffic. Data rate per port is expected to continue to increase (40 Gb/s in the very near future). The number of wavelength channels (or ports) per fiber will also continue to rise as WDM technologies mature.

For long-haul core networks, core switching is needed for two main purposes: network provisioning and restoration. Provisioning occurs when new data routes have to be established or existing routes modified. A network switch should carry out reconfiguration requests over time intervals on the order of a few minutes. However, in many core networks today, provisioning for high-capacity data pipes (OC-48 -2.5 Gb/s and OC-192 -10Gb/s) requires a slow manual process, taking several weeks or longer. High-capacity reconfigurable switches that can respond automatically and quickly to service requests can increase network flexibility, and thus bandwidth hand profitability. On the other hand, restoration must take place in events of network failures (e.g., an accidental cable cut). A network switch needs to reroute traffic automatically in a time interval on the order of 100 ms, thus restoring operation of the network. Traditionally, network restoration is performed primarily by digital electronic cross-connects and synchronous optical network (SONET) add-drop multiplexers, operating at a data rate of about 45–155 Mb/s. For switches in a core network handling hundreds of gigabits per second of traffic, restoration at a coarser granularity is desirable in terms of both cost and manageability. Provisioning and restoration at coarse granularities also makes sense in light of the development of high-speed service-layer equipment such as IP routers with 10Gb/s interface and Gigabit Ethernet. These provisioning and restoration requirements of next-generation optical networks demand innovations in switching technologies.


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