Polarization Mode Dispersion of Installed Fibers

Polarization mode dispersion (PMD), a potentially limiting impairment in high-speed long-distance fiber-optic communication systems, refers to the distortion of propagating optical pulses due to random birefringences in an optical system. Because these perturbations (which can be introduced through manufacturing imperfections, cabling stresses, installation procedures, and environmental sensitivities of fiber and other in-line components) are unknowable and continually changing, PMD is unique among optical impairments. This makes PMD both a fascinating research subject and potentially one of the most challenging technical obstacles for future optoelectronic transmission. Mitigation and compensation techniques, proper emulation, and accurate prediction of PMD-induced outage probabilities critically depend on the understanding and modeling of the statistics of PMD in installed links. Using extensive data on buried fibers used in long-haul high-speed links, the authors discuss the proposition that most of the temporal PMD changes that are observed in installed routes arise primarily from a relatively small number of "hot spots" along the route that are exposed to the ambient environment, whereas the buried shielded sections remain largely stable for month-long time periods. It follows that the temporal variations of the differential group delay for any given channel constitute a distinct statistical distribution with its own channel-specific mean value. The impact of these observations on outage statistics is analyzed, and the implications for future optoelectronic fiber-based transmission are discussed     

High-capacity packet-switched optical ring network

We propose a novel architecture with MAC and admission control protocols for a high-capacity packet-switched optical ring network. In this network the link capacity significantly exceeds the node bit rate. Nodes transmit and receive packets on multiple wavelengths in parallel by using novel optical techniques. Network control is simple since the load is balanced over wavelengths at the physical layer. The MAC protocol is based on credits, and the derived admission control protocol has similar complexity as in a single channel network. Consequently, the network can follow fast traffic changes which are typical in data networks     

Monitoring PMD-induced penalty and other system performance metrics via a high-speed spectral polarimeter

We developed and tested a nonintrusive technique for estimating polarization-mode-dispersion-induced system penalties based on spectral polarization measurements. Other system characteristics such as power fluctuations and carrier-frequency drift could also be monitored simultaneously. Our spectral polarimeter works in milliseconds, and can be scaled to monitor all channels in the C-band.     

Comparison of system penalties from first- and multiorder polarization-mode dispersion

We experimentally investigate the polarization-mode dispersion (PMD)-induced system penalty arising from first-order and all-order PMD. We use a measurable quantity, "string" length, to parameterize the penalty, find a deterministic correction to the accepted first-order PMD-induced system penalty approximation, and discuss the implications for system outages. Further, we show that higher orders of PMD introduce an additional penalty scatter that is nearly independent of "string" length, and correlated to the magnitude of the second-order PMD vector.     

Experimental demonstration of composite-packet-switched WDM network

We propose and demonstrate experimentally a novel technique for packet switching on a ring network. We use the wavelength dimension to increase the transmission line rate and a novel packet-stacking technique to add/drop packets. Packet stacking is used for transport rate multiplication and for equal loading of wavelengths on the physical layer. Packet stacking, switching, and unstacking have been successfully demonstrated on a four-node hubbed ring network serving five source-destination pairs on four wavelengths. Each wavelength was running at 1-Gb/s bit rate.     

Broad-band PMD mitigation with a single polarization controller

We analyze the performance of a broad-band polarization-mode-dispersion (PMD) mitigation technique for wavelength-division-multiplexing systems based on a single polarization rotator placed in various positions along the span. We show that the PMD-induced penalty can be significantly reduced.     

Impact of cumulative polarization-dependent gain on SOA-based optical packet switching networks

The physical layer scalability of multistage interconnection networks is determined by the maximum number of internal switching nodes that packets can traverse error-free. We show that for nodes based on commercial semiconductor optical amplifier switches with polarization-dependent gain of less than 0.35 dB, the maximum number of cascaded nodes could vary by as much as 20 nodes, depending both on the packet wavelength and its state of polarization. We explain such a dramatic effect by optical signal-to-noise ratio degradation due to accumulated amplified spontaneous emission noise with the number of nodes.     

The effect of the frequency dependence of PMD on the performance of optical communications systems

The authors study numerically the importance of the frequency dependence of the polarization-mode dispersion (PMD) vector to the operation of optical systems and evaluate the validity of the second-order PMD approximation. They show that there is no relevant range of parameters in which the second-order PMD approximation is useful and question the validity of considering discrete high-orders of PMD.     

First-order PMD outage for the hinge model

System outage due to first-order polarization-mode dispersion of links obeying the hinge model is analyzed using outage maps. We find that some fraction of the wavelength-division-multiplexed fiber capacity does not meet any outage specification.     

Polarization-Dependent Gain in SOA-Based Optical Multistage Interconnection Networks

The small polarization dependence (< 1 dB) of optical components becomes significant in optical multistage interconnection networks. The cumulative effect can ultimately limit physical layer scalability by changing the maximum number of internal nodes that optical packets can traverse error free. It is shown that for nodes based on commercial semiconductor optical amplifier (SOA) switches with polarization-dependent gains of less than 0.35 dB, the maximum number of cascaded nodes changes by as much as 20 nodes, depending on both the packet wavelength and its state of polarization. This deviation in the number of nodes could correspond to a 100-fold decrease in the number of interconnected ports of an optical interconnection network such as the data vortex. This dramatic effect is explained in terms of optical signal-to-noise ratio degradation due to accumulated amplified spontaneous emission noise originating from the SOA device in the node