ABSTRACT
Demands on communications are increasing rapidly worldwide, particularly in multimedia and Internet applications. This has led researchers to explore new possibilities of accessing a large fraction of the approximately 50 THz theoretical bandwidth of a single mode fiber. 1
Dense wavelength division multiplexing (DWDM) and optical amplification were utilized to get transmission capacity in the Terabit/second. 2-6 Systems with up to 128 wavelengths per fiber have been designed and are commercially available, although theoretically more than 1000 channels may be multiplexed in one fiber. 7 The use of wavelengths is not limited to increasing capacity; they can also be used to perform functions such as switching and routing. 8 Different enabling technologies have been employed to address various issues in deploying optical networks, which include routing in the optical domain, interoperability, scalability, and transparency. 9-12 Wavelength converters (WCs) add new dimension in this regard, as they enable conversion of data from one wavelength channel to another. This resolves wavelength contention, increases flexibility and capacity of the network, and enables distribution of control and management into smaller subnetworks. 11
Wavelength converters have many classifications, which depend on the mapping functions and the form of control signal, signal routing, or signal properties. 11 No matter what classification is chosen, important features that one should look for include: 9,13
• Bit rate transparency (up to 10Gb/s or more) • No extinction ratio degradation • High signal-to-noise ratio (SNR) (to ensure cascadability) • Moderate input power (~ 0 dBm) • Large wavelength span for input and output signals (at least for erbium doped fiber
amplifier [EDFA], 30 to 34 nm range) • Possibility of same input and output wavelengths (no conversion) to avail usage in
WDM switch blocks • Low chirp • Fast setup time of output wavelengths • Insensitive input signal polarization
• Good conversion efficiency • Cost issues
It may be difficult to find a wavelength converter that meets all the above features, but the choice will be system dependent.
