Multispan DWDM lines
Coherent systems on the basis of TS-100E and MS-100E-T10 transponders
Thanks to DP-QPSK modulation format and soft algorithm for forward error correction with 15% redundancy we have reached an extremely low required optical to signal noise ratio (OSNR required) for 100G transponders – 12.5 dB.
Dispersion compensation free coherent DWDM systems of 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). Absence of the dispersion compensators at the intermediate nodes leads to a significant spreading of signal pulses while there moving along fiber. Accumulation of nonlinear distortion in the compensation free DWDM line stems slowly. The OSNR margin in 4000 km DWDM line is equal to 5.7 dB.
At present T8 company develops new coherent 40G transponder, which will not require passive dispersion compensation as well as two coherent 100G transponders.
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. In these configurations it is 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.