WDM networks make a very effective utilization of the fiber bandwidth and offer flexible interconnections based on wavelength routing. In high capacity, dynamic WDM networks, blocking due to wavelength contention can he reduced by wavelength conversion. Wavelength conversion addresses a number of key issues in WDM networks including transparency, interoperability, and network capacity. Strictly transparent networks offer seamless interconnections with full reconfigurability and interoperability. Wavelength conversion may be the first obstacle in realizing a transparent WDM network. Among numerous wavelength conversion techniques reported to date, only a few techniques offer strict transparency. Optoelectronic conversion (O/E-E/O) techniques achieve limited transparency, yet their mature technologies allow deployment in the near future. The majority of all-optical wavelength conversion techniques also offer limited transparency but they have a potential advantage over the optoelectronic counterpart in realizing lower packaging costs and crosstalk when multiple wavelength array configurations are considered. Wavelength conversion by difference-frequency generation offers a full range of transparency while adding no excess noise to the signal. Recent experiments showed promising results including a spectral inversion and a 90 nm conversion bandwidth. This paper reviews various wavelength conversion techniques, discusses the advantages and shortcomings of each technique, and addresses their implications for transparent networks.

Wavelength conversion technologies for WDM network applications

Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber.

All-optical wavelength conversion by semiconductor optical amplifiers

Semiconductor optical amplifiers are useful building blocks for all-optical gates as wavelength converters and OTDM demultiplexers. The paper reviews the progress from simple gates using cross-gain modulation and four-wave mixing to the integrated interferometric gates using cross-phase modulation. These gates are very efficient for high-speed signal processing and open up interesting new areas, such as all-optical regeneration and high-speed all-optical logic functions.

/pdf/semiconductor-optical-amplifier-based-all-optical-gates-for-4wdu6yc0vj.pdf

Semiconductor optical amplifier-based all-optical gates for high-speed optical processing

This paper reviews the work carried out under the European ACTS KEOPS (KEys to Optical Packet Switching) project, centering on the definition, development and assessment of optical packet switching and routing networks capable of providing transparency to the payload bit rate. The adopted approach uses optical packets of fixed duration with low bit rate headers to facilitate processing at the network/node interfaces. The paper concentrates on the networking concepts developed in the KEOPS project through a description of the implementation issues pertinent to optical packet switching nodes and network/node interfacing blocks, and consideration of the network functionalities provided within the optical packet layer. The implementation, from necessity, relies on advanced optoelectronic components specifically developed within the project, which are also briefly described.

Transparent optical packet switching: the European ACTS KEOPS project approach

Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is an important tool for frequency conversion and fast optical switching in all-optical communication networks. We review the main applications of SOAs as nonlinear optical components. Concentrating on FWM, we define general parameters that are of relevance for signal processing applications. We show, how basic experiments and general simulation procedures can be used to determine optimum operating conditions for the intended applications. Besides a comprehensive investigation of FWM among continuous waves, we present new experimental results on FWM with picosecond optical pulses. A comparison of both reveals a different behavior and demonstrates that new optimization criteria and advanced theoretical models have to be applied for the case of short optical pulses. Moreover, we discuss the possibility to extract the dynamical SOA parameters from our experiments.

Four-wave mixing in semiconductor optical amplifiers for frequency conversion and fast optical switching

Semiconductor optical amplifiers have been monolithic integrated in a passive symmetric Mach-Zehnder interferometer to form a compact polarization insensitive all-optical wavelength converter operating at up to 10 Gb/s. A simple method for reducing the impact of input power variations is proposed that increases the input power dynamic range from 4-8 dB.

/pdf/wavelength-conversion-by-optimized-monolithic-integrated-n4p10jmb2c.pdf

Wavelength conversion by optimized monolithic integrated Mach-Zehnder interferometer

An all-optical wavelength-converter based on monolithic integration of a Mach-Zehnder interferometer and integrated semiconductor optical amplifiers was demonstrated. This device exhibited high stability, penalty-free conversion at 5 Gbit/s (at a BER of 10/sup 9/), no-excess penalty after a transmission over 60 km on standard fiber, and low signal-polarization dependency. The device operated in a 26-nm-wide optical window. >

An all-optical wavelength-converter with semiconductor optical amplifiers monolithically integrated in an asymmetric passive Mach-Zehnder interferometer

Wavelength division multiplexed (WDM) networks are currently subject to an immense interest because of the extra capacity and flexibility they provide together with the possibilities for graceful system upgrades. For full network flexibility it is very attractive to be able to translate the channel wavelengths in an easy way and preferably without opto-electronic conversion. Here, we will first briefly look at advantages of employing optical wavelength converters in WDM networks and next review the optical wavelength conversion devices with emphasis on recent developments.

/pdf/wavelength-conversion-devices-and-techniques-2vwp7o9vfe.pdf

Wavelength conversion devices and techniques

A passive phase-section is integrated in one arm of an interferometric all-optical wavelength converter. The passive phase-section is demonstrated to increase the extinction ratio regeneration capabilities of the converter by 10 dB and to improve the receiver sensitivity by 3.9 dB, for the converted signal at 2.5 Gbit/s.

Regeneration improvement in all-optical wavelength converter, based on a Mach-Zehnder interferometer, by means of phase-shifter section

A 1.55 mu m GaInAsP/InP optical amplifier integrated with access waveguides provides 0 dB fibre to fibre gain at only 47 mA bias current and a 5 dB saturation gain already high enough to design 0 dB integrated complex circuits. Polarisation gain dependence and gain ripple are less than 0.5 dB and 0.7 dB, respectively. >

G. Glastre

Papers

Wavelength conversion by optimized monolithic integrated Mach-Zehnder interferometer

An all-optical wavelength-converter with semiconductor optical amplifiers monolithically integrated in an asymmetric passive Mach-Zehnder interferometer

Wavelength conversion devices and techniques

Regeneration improvement in all-optical wavelength converter, based on a Mach-Zehnder interferometer, by means of phase-shifter section

Polarisation insensitive 1.55 μm semiconductor integrated optical amplifier with access waveguides grown by LP-MOCVD