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

The authors have proposed, simulated, and experimentally demonstrated all-optical multiple logic gates using two parallel semiconductor optical amplifier (SOA)-Mach-Zehnder interferometer (MZI) structures that enable simultaneous operations of various logic functions of XOR, NOR, OR, and NAND. The proposed scheme, which is optimized by adjusting the optical gain and phase differences in SOA-MZI structures with creative and systematic method, has great merits to achieve the reshaped output pulses with high extinction ratio and enable the high-speed operation at over 10 Gb/s through performance enhancement of SOAs. Its validity is confirmed through simulation and experiments at 2.5 and 10 Gb/s, respectively

All-optical multiple logic gates with XOR, NOR, OR, and NAND functions using parallel SOA-MZI structures: theory and experiment

The novel design of an all-optical XOR gate by using cross-gain modulation of semiconductor optical amplifiers has been suggested and demonstrated successfully at 10 Gb/s. Boolean AB~ and A~B of the two input signals A and B have been obtained and combined to achieve the all-optical XOR gate. No additional input beam such as a clock signal or continuous wave light is used in this new design, which is required in other all-optical XOR gates.

All-optical XOR gate using semiconductor optical amplifiers without additional input beam

A detailed analytical traffic model for a photonic wavelength division multiplexing (WDM) packet switch block is presented and the requirements to the buffer size is analyzed. Three different switch architectures are considered, each of them representing different complexities in terms of component count and requirements to the components, it is shown that the number of fiber delay-lines, that form the optical buffer, can be substantially reduced by the use of tunable optical wavelength converters, thereby exploiting the wavelength domain to solve contention of optical packets. For a 16/spl times/16 switch with four wavelength channels per inlet, all at a load of 0.8, the number of delay-lines is reduced from 47 to 12 by use of tuneable optical wavelength converters. Apart from the number of delay-lines the physical buffer structure is analyzed with special attention to the possibilities offered by optics, i.e., the possibility of several outlets sharing the same physical buffer. For the three architectures presented here, a tradeoff in the buffer architectures is addressed: a buffer physically shared among an outlets requires many wavelengths internally in the switch block, whereas, architectures with buffers dedicated to each outlet require a smaller number of wavelengths.

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WDM packet switch architectures and analysis of the influence of tunable wavelength converters on the performance

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.

Limited-range wavelength translation in all-optical networks

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

Semiconductor optical amplifiers used for efficient wavelength conversion up to 4 Gb/s are discussed. The rise and fall times as well as extinction ratio are experimentally analyzed. System performance at 4 Gb/s is evaluated showing a penalty of only 1.5 dB for the converted signal for conversion over 17 nm. >

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4 Gb/s optical wavelength conversion using semiconductor optical amplifiers

Wavelength conversion over 18 nm is demonstrated at 2.5 Gb/s without change in BER performance. The converting element is a three-section distributed Bragg reflector (DBR) laser operating by gain saturation. Both IM-to-IM and IM-to-FM conversion schemes are investigated. For the latter scheme, a conversion gain of 10 dB is measured. >

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Optical wavelength conversion over 18 nm at 2.5 Gb/s by DBR-laser

Wavelength division multiplexing (WDM) is considered one of the most feasible ways to upgrade point-to-point transmission links and to meet the huge demand for transmission capacity. Next step in the rapid evolution is the introduction of WDM networks for efficient transport of information. As the network technology evolves we want the possibility of wavelength conversion or translation within the network or at its interfaces. The motivation is to achieve an optical layer providing dynamic transport reconfiguration, high level restoration and efficient use of the available fiber bandwidth the same way as the synchronous digital hierarchy (SDH) layer provides efficiency to the transport layer by time division multiplexing, time slot grooming and high speed protection. The aim of this paper is to briefly review the current state of optical wavelength conversion technology with emphasis on all-optical wavelength converters. Although WDM networks have the attractive feature that different signal formats can be transported in different wavelength layers, our focus will be on binary signal formats that are by far dominant for telecommunication traffic. The paper will start by giving a short motivation for wavelength converters in WDM networks in Sect. 2. The various types of wavelength converters are examined in Sect. 3, while Sect. 4 gives examples of new development areas for wavelength converters. Finally, a conclusion is given in Sect. 5.

Wavelength converter technology

High responsivity in a two-section semiconductor optical amplifier/detector, serving as a channel dropping mode is described. A simple receiver constructed using a 50 Omega amplifier with a sensitivity of -30.2 dBm at 140 Mb/s is demonstrated. >

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K.E. Stubkjaer

Papers

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

4 Gb/s optical wavelength conversion using semiconductor optical amplifiers

Optical wavelength conversion over 18 nm at 2.5 Gb/s by DBR-laser

Wavelength converter technology

Two-section semiconductor optical amplifier used as an efficient channel dropping node