Jonathan P. R. Lacey

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.

Blocking in multiwavelength TDM networks

This paper examines the relative importance of wavelength conversion and time‐slot interchange in improving the performance of multiwavelength time‐division multiplexed networks. It is shown that, in networks with a small number of wavelengths, each carrying a large number of time‐division multiplexed channels, significant performance improvements are achieved by the introduction of time‐slot interchange alone, without wavelength conversion. However, some performance improvements are also achieved by the introduction of wavelength conversion alone.

All-optical 1300-nm to 1550-nm wavelength conversion using cross-phase modulation in a semiconductor optical amplifier

All-optical 1300-nm to 1550-nm wavelength converters may be important components in lightwave networks which use both the 1300-nm and the 1550-nm low-loss transmission windows of silica optical fiber. We describe a new all-optical 1300-nm to 1550-nm wavelength converter, based on cross-phase modulation in a 1300-nm semiconductor optical amplifier. We demonstrate operation of the wavelength converter at 1.25 Gb/s, and present bit-error rate measurements. The wavelength converter demonstrated here potentially operates at high speed, with low input power and low polarization-sensitivity.

Widely tunable four-wave mixing in semiconductor optical amplifiers with constant conversion efficiency

The conversion efficiency and output signal-to-noise ratio (SNR) of single-pump four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is strongly dependent on frequency shift. We examine a scheme for FWM in SOAs that uses two orthogonally polarized pumps. We compare experimentally and theoretically the conversion efficiency and SNR of the orthogonal-pump scheme with single-pump FWM. The orthogonal-pump scheme has nearly constant conversion efficiency and SNR over the 4.5-THz range of frequency shifts measured. Experimental and theoretical results for the conversion efficiency and SNR of the orthogonal-pump scheme agree to within 3.5 dB.

Performance of WDM ring and bus networks in the presence of homodyne crosstalk

This paper examines the effects of coherent and incoherent homodyne crosstalk in wavelength division multiplexed (WDM) ring and bus networks using reconfigurable optical add-drop multiplexers (OADMs). It is widely understood that incoherent homodyne crosstalk causes power penalties at the receivers in these networks. We show that coherent homodyne crosstalk causes a range of possible received powers, and that coherent and incoherent crosstalk together lead to a range of possible power penalties. A Monte Carlo simulation is used to examine the probability distribution of power penalties due to homodyne crosstalk under various conditions. We find that increasing the switch and multiplexer crosstalk within each OADM, and increasing the number of WDM channels, all produce increased probabilities of large power penalties. However, the number of nodes through which a signal is transmitted does not affect the power penalty distribution.

Multiwavelength cross-connects for optical transport networks

Multiwavelength cross-connects (M-XCs) will play a key role in future optical multiwavelength transport networks. In this paper, we propose a class of optical wavelength interchange devices that can be used as basic building-blocks for multiwavelength optical cross-connects. We describe three different multiwavelength cross-connect structures that can be constructed using these building blocks. We investigate their blocking performance and examine issues such as complexity, modularity, and wavelength channel spacing associated with the proposed cross-connect structures.

Homodyne crosstalk in WDM ring and bus networks

We examine the combined effects of coherent and incoherent crosstalk in wavelength-division multiplexed (WDM) ring and bus networks which use add-drop multiplexers. It is widely understood that incoherent crosstalk in these networks causes a fixed bit-error-rate (BER) door at the receiver. We show that coherent crosstalk causes a range of possible received powers. In combination with incoherent crosstalk, this leads to a range of possible BER floor positions. We use a Monte Carlo simulation to show that when both coherent and incoherent crosstalk are considered, BER floors are likely to be higher than previously appreciated. Satisfactory network performance can be ensured by careful network management, or by reducing component leakage.

All-optical wavelength translation over 80 nm at 2.5 Gb/s using four-wave mixing in a semiconductor optical amplifier

Wavelength conversion using conventional single pump four-wave mixing in semiconductor optical amplifiers is limited to wavelength shifts of a few tens of nanometers due to the decrease of signal-to-noise ratio with wavelength shift. In this letter, we demonstrate an 80-mn wavelength shift with four-wave mixing (FWRW) using two orthogonally polarized pumps. The power penalty at a 10/sup -9/ bit-error rate for a 2.5-Gb/s signal is less than 1.0 dB. This result demonstrates the large wavelength shift capacity of this (FWM) technique.

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.