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DWDM Active Systems with Optical Amplifiers

DWDM systems with amplifiers are used when building long-distance backbone networks and metropolitan area networks or metro networks.


In a longer line, EDFA optical amplifiers, which ensure recovery of the signal weakened by the optical fiber, are installed at specified distances. EDFA amplifiers are able to amplify the signal of any format and, at the same time, to restore a large number of independent WDM channels. However, EDFA, providing the power amplification of the transmitted optical signal, accumulates distortions, which occur in various parts of the DWDM network. Such distortions lead to the lower OSNR (Optical Signal-to-Noise Ratio) at the receiving side of the system.


At the network design stage, such source noise margin is envisaged for each channel that would provide the required signal noise immunity at the end of the line.


When creating long-haul DWDM networks, several EDFA amplifiers are installed sequentially in the line. The number of amplifiers in one section is limited and depends on the optical cable type, channel count, data transmission rate of each channel, and permissible OSNR value.


DWDM amplifiers


The possible length of lines when using active DWDM system is determined not only with installed optical amplifiers and the OSNR value, but also with the influence of chromatic dispersion — the distortion of transmitted signal impulses — on transmitted signals.

At the design stage of the DWDM network project, permissible values of chromatic dispersion for the transceivers are taken into account, and, if necessary, chromatic dispersion compensation modules (DCM) are included in the line. DCM introduces additional attenuation into the line, which leads to a reduction of the amplified section length.


Solution for a Single Optical Fiber


DWDM active systems are typically based on the dual-fiber signal transmission. This occurs due to the fact that EDFAs amplify one-directional signals only. Such harsh conditions are not always feasible within the real data transmission network.


Prointech specialists have developed a solution, which implements the DWDM active system on the single fiber basis. This scheme differs from the standard dual-fiber system by the presence of two additional optical filters. These Red/Blue filters divide the C-band used when transmitting DWDM signals into two sub-bands: Red one (1547.72 – 1564.68 nm), and Blue one (1528.77 – 1543.73 nm). Thus, two spectrally separated transmission media are generated within a single fiber.


DWDM 1 fiber



Solutions based on DWDM systems are not trivial tasks and require precise calculations of chromatic DCM installation sites and settings of EDFA optical amplifiers depending on the source data and the desired network length.


System Capabilities:


  • joint transmission of up to 40 duplex communication channels;
  • support of all transmission protocols;
  • transmission of any kind of traffic: data, voice, multimedia.


Transmission Medium Features:


  • single/dual optical fibers;
  • maximum route length of up to 200 km (depending on fiber-inserted attenuations);
  • maximum value of fiber-inserted attenuations of about 40 dB.