Optical Networks - _3_8 Wavelength Converters_42

Optical Networks - _3_8 Wavelength Converters_42 - 3.8...

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3.8 Wavelength Converters 221 the interconnections are not difficult. However, practical considerations of power dissipation and board space dictate the necessity for having multiple printed circuit boards and perhaps multiple racks of equipment. The interconnects between these boards and racks need to operate at the line rate, which is typically 2.5 Gb/s or higher. High-quality electrical interconnects or optical interconnects can be used for this purpose. The drivers required for the electrical interconnects also dissipate a significant amount of power, and the distances possible are limited, typically to 5– 6 m. Optical interconnects make use of arrayed lasers and receivers along with fiber optic ribbon cables. These offer lower power dissipation and significantly longer reach between boards, typically to about 100 m or greater. 3.8 Wavelength Converters A wavelength converter is a device that converts data from one incoming wave- length to another outgoing wavelength. Wavelength converters are useful compo- nents in WDM networks for three major reasons. First, data may enter the network at a wavelength that is not suitable for use within the network. For example, the first-generation networks of Chapter 6 commonly transmit data in the 1310 nm wavelength window, using LEDs or Fabry-Perot lasers. Neither the wavelength nor the type of laser is compatible with WDM networks. So at the inputs and outputs of the network, data must be converted from these wavelengths to narrow-band WDM signals in the 1550 nm wavelength range. A wavelength converter used to perform this function is sometimes called a transponder. Second, wavelength converters may be needed within the network to improve the utilization of the available wavelengths on the network links. This topic is studied in detail in Chapter 10. Finally, wavelength converters may be needed at boundaries between different networks if the different networks are managed by different entities and these entities do not coordinate the allocation of wavelengths in their networks. Wavelength converters can be classified based on the range of wavelengths that they can handle at their inputs and outputs. A fixed-input, fixed-output device always takes in a fixed-input wavelength and converts it to a fixed-output wavelength. A variable-input, fixed-output device takes in a variety of wavelengths but always converts the input signal to a fixed-output wavelength. A fixed-input, variable-output device does the opposite function. Finally, a variable-input, variable-output device can convert any input wavelength to any output wavelength. In addition to the range of wavelengths at the input and output, we also need to consider the range of input optical powers that the converter can handle, whether the converter is transparent to the bit rate and modulation format of the input signals,
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222 Components and whether it introduces additional noise or phase jitter to the signal. We will see
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Optical Networks - _3_8 Wavelength Converters_42 - 3.8...

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