Performance optimization of dynamic all-optical networks

We explore and report on the temporal behavior of MEMS-based optical switching elements and optical amplifiers in multi-wavelength systems as may be utilized in next generation optical networks. The importance of this work is underscored by the growing use of dense wavelength division multiplexing (DWDM) in conjunction with dynamically controlled optically transparent network elements. Switching, using MEMS technology, has taken on an important role in supporting dynamic network reconfiguration. Such networks typically include optical amplifiers, and multiple wavelengths are amplified by a single network element The combination of MEMS switching with optical amplifiers and other active elements provides new challenges in overall system design, as the millisecond switching time of MEMS fabrics is comparable to the excited state lifetime in Erbium doped fiber amplifiers (EDFAs), thereby leading to potentially undesirable gain fluctuations and cross talk. Our observations of such transients show durations ranging upwards of 20 milliseconds and amplitudes of up to 2 dB, with transients affecting both switched and unswitched wavelengths. These effects can lead to degradation in end-to-end system performance, as measured by bit error rate (BER). This problem is particularly important for future optical networks where burst switching and packet switching, in addition to circuit switching will generate transients on finer time scales. We first examine and report on the temporal behavior of MEMS-based optical switching elements and optical amplifiers in multi-wavelength systems as may be utilized in next generation optical networks. Our experiments utilize commercially available MEMS switching fabrics and EDFAs, configured to emulate a realistic metro area network. We then use these experimental results to examine and compare several approaches to optimizing end-to-end performance. We explore a proactive approach, where routing and wavelength assignment decisions are based on algorithms that optimize the distribution of traffic, thereby minimizing the impacts of transients due to bursty traffic on unswitched traffic. We propose several algorithms for routing and wavelength assignment specifically designed for dynamic, all-optical networks, where wavelength conversion - is not available and quantify the reduction in performance impairments that can be achieved.