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.

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

All-optical label swapping is a promising approach to ultra-high packet-rate routing and forwarding directly in the optical layer. In this paper, we review results of the DARPA Next Generation Internet program in all-optical label swapping at University of California at Santa Barbara (UCSB). We describe the overall network approach to encapsulate packets with optical labels and process forwarding and routing functions independent of packer bit rate and format. Various approaches to label coding using serial and subcarrier multiplexing addressing and the associated techniques for label erasure and rewriting, packet regeneration and packet-rate wavelength conversion are reviewed. These functions have been implemented using both fiber and semiconductor-based technologies and the ongoing effort at UCSB to integrate these functions is reported. We described experimental results for various components and label swapping functions and demonstration of 40 Gb/s optical label swapping. The advantages and disadvantages of using the various coding techniques and implementation technologies are discussed.

All-optical label swapping networks and technologies

Wavelength conversion has been proposed for use in wavelength-division multiplexed networks to improve efficiency. This study highlights systems challenges and performance issues which need to be addressed in order to incorporate wavelength conversion effectively. A review/survey of the enabling technologies, design methods, and analytical models used in wavelength-convertible networks is provided.

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Wavelength conversion in WDM networking

We present a 1 /spl times/ 2 all-optical packet switch. All the processing of the header information is carried out in the optical domain. The optical headers are recognized by employing the two-pulse correlation principle in a semiconductor laser amplifier in loop optical mirror (SLALOM) configuration. The processed header information is stored in an optical flip-flop memory that is based on a symmetric configuration of two coupled lasers. The optical flip-flop memory drives a wavelength routing switch that is based on cross-gain modulation in a semiconductor optical amplifier. We also present an alternative optical packet routing concept that can be used for all-optical buffering of data packets. In this case, an optical threshold function that is based on a asymmetric configuration of two coupled lasers is used to drive a wavelength routing switch. Experimental results are presented for both the 1 /spl times/ 2 optical packet switch and the optical buffer switch.

Optical packet switching and buffering by using all-optical signal processing methods

Dense WDM technologies make effective use of the vast fiber bandwidth and offer an added dimension to all-optical networks. Wavelength conversion at key network nodes is emerging as a fundamental functionality that can allow transparent interoperability, contention resolution, wavelength routing, and, in general, better utilization of the network resources under dynamic traffic patterns. We offer an overview of the enabling technologies and extend the treatment to the network application of these converters. Attention is given to semiconductor optical amplifiers and their use in wavelength converters. Converters based on four-wave mixing as well as those based on nonlinear optical loop mirrors are evaluated, paying special attention to signal integrity and architectural as well as performance issues. The use of wavelength converters in wavelength routing networks is explored together with the application of these devices in contention resolution and in the routing wavelength assignment problem. Future directions are outlined at the system as well as network levels.

All-optical wavelength conversion: technologies and applications in DWDM networks

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.

S. Lykke Danielsen

Papers

All-optical wavelength conversion by semiconductor optical amplifiers