DWDM Network Designs and Calculation

Engineering department of the company performs calculation of DWDM networks of any complexity in short terms. Our engineers calculate more than 200 projects every year, and dozens of them reach the practical implementation stage.
Based on initial data provided by customer (scheme of the network and distances between nodes, type and quantity of fibers on each span, plans of the network development) the engineering department solves the following tasks:

  • Development of a channelizing scheme and a principal scheme of the network;
  • Calculation of estimated quality of transmission in designed communication channels, and network reliability analysis;
  • Optimization of networks to decrease capital and operating expenses.

We have a profound experience in designing telecommunication systems based on new formats of modulation of the optical signal. We developed methods of optimization that make it possible to achieve optimal performance for combined networks where both coherent channels 100/200 Gbit/s and noncoherent channels 10 Gbit/s are transmitted simultaneously. Due to this our customers successfully put in operation 100G channels on an old infrastructure that was intended for 10G channels.

We use self-engineered specialized software for most effective design of DWDM networks. For calculation of networks of high complexity a working group is usually created with experts of R&D department of the company. R&D department performs theoretical analysis and numerical simulation of DWDM networks of complex topology, simulation of new components (optical amplifiers, transponders and other devices), simulation and analysis of linear and nonlinear effects using the OptSim™ software and other tools.


100G transponders in traditional DWDM line with passive dispersion compensators
In existed DWDM lines there are passive dispersion compensators, which were placed at intermediate amplification nodes. The most economical way of the bandwidth Increasing of such a lines is step-by-step substitution of “old” low speed channels on “new” higher speed channels. In this case for the long time period it is possible coexistence of channels of different speeds and different modulation formats like 10G NRZ, 40G DPSK, 100G DP-QPSK, 200G DP-16QAM. In these configurations there is a necessary to use periodical passive dispersion compensation. T8 engineers investigated functionality of the 100G transponders in DWDM line with periodical dispersion compensation. The OSNR margin in 1600 km DWDM line is equal
to 7.5 dB.

Coherent DWDM systems of a new generation
The use of coherent transponders makes it possible to build DWDM lines without passive dispersion compensators. Mathematical dispersion compensation takes place in the receiver’s DSP (digital signal processor).


Basic configurations
The most cost-efficient solutions used erbium doped fiber amplifiers (EDFA). The simultaneous use of a power amplifier and a preamplifier allows transmission of 16 optical channels for a distance up to 155 km and 80 channel for a distance up to 130 km. Simultaneous use of the transmission amplifier and preamplifier allows to organize 16x100 Gbps channels in lines up to 225 km or 80 channels in lines up to 205 km in length. Stock 3 dB was taken into account in the middle of the span.

Raman amplifiers
The use of counter Raman pumping of telecommunication fibers, simultaneously with EDFA amplifiers, allows organizing 16 channels of 100 Gbit/s in lines up to 260 km long, and 80 channels of 100 Gbit/s with a span of up to 235 km with a margin of 3 dB in the middle of the span. Adding a passing Raman pump makes the figures increase, respectively, to 275 km and 250 km.

ROPA (remote optical pumped amplifier) is remote pumping of fiber doped with erbium (EDF). The technology is used for very long sections of the DWDM line up to 475 km. Pumping is carried out on two fibers: signal and additional. Ultralow-loss fiber is used. The T8 laboratory successfully tested the transmission system of 10 * 100 Gbit/s channels in a very-long 500 km single-span fiber-optic DWDM line.