M.A. Summerfield

Limited-range wavelength translation in all-optical networks

This paper examines wavelength translation in all-optical wavelength-routed networks. Previous studies have shown that wavelength translation can improve the blocking performance of these networks. However, all the previous work has assumed that wavelength translators can translate from any input wavelength to any output wavelength. In contrast, all-optical wavelength translators demonstrated in the laboratory to date are, in general, only capable of limited translation. We assess, for the first time, the network performance improvements offered by realistic all-optical wavelength translators with a limited translation range. In particular, we consider all-optical wavelength translators based on four-wave mixing in semiconductor optical amplifiers. Using a simple model for their function, we consider the blocking performance of two-hop and multiple-hop paths, and unidirectional ring and mesh-torus networks. In all the cases we consider, significant improvement in the blocking performance of the network is obtained when limited-range wavelength translators with as little as one quarter of the full range an introduced. We also find that almost all of the network performance improvement observed by an ideal wavelength translator can be gained from a translator with only half of the full translation range.

Four-channel polarization-insensitive optically transparent wavelength converter

Multichannel wavelength converters may be important components in the cross-connects in future wavelength-division multiplexed (WDM) transport networks. We demonstrate a multichannel, polarization-insensitive, optically transparent wavelength converter, based on four-wave mixing in two semiconductor optical amplifiers in a polarization-diversity arrangement. Bit-error-rate (BER) measurements with four input 2.5-Gb/s WDM channels, spaced by 2 nm, show penalties for wavelength conversion less than 2.6 dB at 10/sup -9/ BER. Changes in the state of polarization of the input signals cause the output power to change by less than 1.2 dB, and the corresponding power penalties change by less than 0.9 dB.

Optimization of pump and signal powers for wavelength converters based on FWM in semiconductor optical amplifiers

We investigate the effect of input pump and signal powers on the noise performance and intersymbol interference (ISI) in a frequency-converter based on four-wave mixing (FWM) in a semiconductor optical amplifier. We demonstrate that there is an input pump power at which the noise figure of the frequency converter is a minimum, and a corresponding input signal power for which the output signal-to-noise ratio (SNR) is a maximum. We report bit-error-rate measurements which show that there is a trade-off between maximizing the output SNR, and minimizing intersymbol interference in the SOA. Consequently, the power penalty incurred in the frequency conversion can be minimized by careful selection of the input signal power. We show that power penalties of less than 1 dB are achievable.

WRAP: a medium access control protocol for wavelength-routed passive optical networks

We describe the WDM request/allocation protocol (WRAP), a media-access control protocol for wavelength-routed passive optical networks (WR-PONs) in which each node has a single fixed optical receiver and a single tunable optical transmitter. The protocol does not require a carrier sensing capability, a separate control channel, or any centralized control or scheduling. Access to transmission channels is regulated by allocations made at destination nodes in response to requests made by source nodes. Computer simulation is used to investigate three different allocation algorithms, one of which-the preferential/random algorithm-is shown to provide significantly better performance than the alternatives. Simulations are presented comparing the performance of WRAP to two previously proposed applicable protocols-the interleaved time division multiple access (I-TDMA) protocol, and the FatMAC protocol. WRAP is shown to provide fair and flexible access to the transmission capacity, enabling high network utilization to be achieved under a wide range of traffic conditions, while providing a guaranteed minimum bandwidth between each source-destination pair. We conclude that of the three protocols considered here, WRAP is the best-suited to general-purpose data communications applications such as local, campus, and metropolitan area networks.

Frequency-domain model of multiwave mixing in bulk semiconductor optical amplifiers

We present a new steady-state frequency-domain model of highly nondegenerate four-wave mixing in bulk semiconductor optical amplifiers (SOAs). The model can handle a large number of interacting optical fields and situations in which the nonlinear interactions are complex. It accounts for the longitudinal dependence of the population inversion in the SOA and the spectral dependence of the gain. Carrier population pulsations, spectral-hole burning, and carrier heating, which dominate the nonlinear response over bandwidths into the terahertz range, are included. The model also includes output amplified spontaneous emission noise and allows important system parameters such as signal-to-noise ratio and noise figure to be estimated. A number of applications of the model are presented in which good agreement between theoretical and experimental results is demonstrated.

Performance of networks using wavelength converters based on four-wave mixing in semiconductor optical amplifiers

In this paper, we examine the blocking performance of networks in which connections may be blocked due to either insufficient capacity or due to limitations in the transmission network. We use analytical expressions and network simulations to examine blocking in networks in which the quality of the received signal may be so poor that the connection is effectively blocked. In particular, we apply our analysis to networks which use wavelength converters based on four-wave mixing (FWM) in semiconductor optical amplifiers. We show that the performance improvements obtained using these wavelength converters can be significant, but this depends on whether the network uses fixed-frequency or tunable transmitters and receivers.

Optimum optical amplifier location in spectrum-sliced WDM passive optical networks for customer access

Summary form only given. Spectrum slicing is an attractive scheme for implementing wavelength-division multiplexing (WDM) passive optical networks (PONs) in the customer access environment. Amplification of signals from the filtered broadband incoherent sources that are typically used in spectrum-sliced PONs is dominated by noise processes to those found in systems using narrow-band laser sources. In this paper we examine the tradeoffs that determine the optimum location of the amplifier that maximizes the power budget for a spectrum-sliced WDM PON that uses incoherent sources.

Baseband optical carrier-sense multiple access - demonstration and sensitivity measurements

We demonstrate for the first time baseband optical carrier-sense multiple access with collision avoidance. We evaluate the performance of the baseband carrier-sense circuit with bit- and packet-error-rate measurements. The sensitivity of the carrier-sense circuit is -51.6 dBm.

Sensitivity evaluation of baseband carrier-sense circuit for optical CSMA/CA packet networks

The ability to detect the presence or absence of optical signals on specific channels is used to prevent packet collisions in networks implementing the optical carrier-sense multiple-access with collision avoidance (CSMA/CA) protocol. This optical carrier-sense capability can be provided by a baseband carrier-sense circuit (BCSC), which directly detects the envelope of optical packets propagating in the network. A fraction of the optical power of packets passing through a node is tapped off for detection at the BCSC. It is therefore desirable to minimize the amount of optical power required at the circuit to perform reliable packet detection such that the additional insertion loss encountered by the in-transit packets is minimal. However, the performance of the BCSC is limited at low levels of received optical power. For a given topology and size of a practical optical CSMA/CA packet network, knowledge of this sensitivity limit is essential for determining the power budget while ensuring that collision avoidance and minimal insertion loss are achieved. This paper identifies the factors that contribute to the sensitivity of the BCSC. A theoretical description of a practical implementation of the BCSC is derived and an efficient method to evaluate the sensitivity is presented. The theory is validated using experiments, with results showing that the model presented in this paper is a useful tool for the design and performance analysis of highly sensitive BCSCs in future optical CSMA/CA networks.

Performance analysis of baseband carrier-sense circuit in optical CSMA networks

In future shared medium optical packet networks, collision-free transmission may be achieved by detecting the presence or absence of optical packets on specific channels. Using a baseband carrier-sense circuit (BCSC), the direct detection of baseband optical signals can be employed to provide the carrier-sense capability required to avoid collisions in optical carrier-sense multiple access (CSMA) networks. In this work, we present a new theoretical model to analyze the performance of a BCSC in the presence of additive post-detection electrical noise. We validate the model using experiments and simulations. Our model provides a useful approach to BCSC design in future optical CSMA packet-switched networks.