Presentation for 40 GBPS DWDM Optical System Coding

Today, 40 GBPS DWDM technology has break through the various difficulties, and began to enter the commercial field. The key technology of 40 GBPS DWDM is the more advanced coding method, and the dispersion compensation.

Currently 40 GBPS DWDM coding type is various, different coding have different various physical indicators,after decades of development fiber optic network has formed a complicated system, in the G.652 and G.655 represented the mainstream of the optical fiber can also be subdivided, their effects on 40 GBPS DWDM systems are different. How to choose the appropriate coding technology and optical fiber type, 40 GBPS DWDM network construction has important reference value.

In ordinary NRZ coding optical signals, for example, 40 GBPS signals faster than 10 GBPS rate, spectral broadening 4 times, so the dispersion tolerance is only about 1/16 of the 10 GBPS signal, PMD tolerance only a quarter; Four times the rate of increase will lead to a 6 db OSNR margin improvement. In addition, 40 GBPS signal between the belt and belt nonlinear effect is more serious.

For 40 GBPS wavelength division system, the chromatic dispersion of the fiber can be made rough compensation through the DCF model, then through TDCM for accurate compensation of each channel, so as to achieve the system dispersion capacity limit, and the automatic single channel dispersion compensation technology has been underway for practical application, therefore has not key point affect 40 GBPS DWDM optical systems.

Depends on adding single-wave into the fiber optical power can improve the MPI- SM OSNR values effectively, but high fiber optical power will lead to obvious nonlinear effect, when the system is all channel with, the nonlinear effect will be more and more outstanding. Optical fiber nonlinear effects difficult to compensate and control, only to avoid as far as possible, and avoiding the means mainly to reduce the fiber optical power and avoid the zero dispersion wavelengths.

40 GBPSDWDMoptical system coding

P-40 GBPS DPSK encoding is the most competitive coding technology. Compared with the NRZ coding, can support 50 GHZ interval DWDM optical system. Besides P - DPSK encoding is very suitable for 40 GBPS channel and 10 GBPS channel mixed in the same system, under the condition of the OSNR and PMD standard optical fiber links, can be loaded directly on 10 GBPS DWDM systems 40 GBPS OTU, can be a smooth upgrade to 40 GBPS DWDM optical systems.

RZ DQPSK - coding of PMD further improve dispersion tolerance, optical signal spectrum bandwidth is small, high spectrum efficiency, but similar to DP - QPSK, the coding technique is also more complex, the cost is high, and the system nonlinear effect and different rate of channel mixing ability needs further validation.
　　　
Different fiber optic network in 40 GBPS DWDM optical system

40 GBPS DWDM system depends not only on the performance of coding technology, optical fiber type selection is very important, unsuitable optical fiber selection may even affect the opening of the system.

40 GBPS coding type, there is no certain corresponding requirements, in theory can be used liberally. 40 GBPS coding all have their own different types of performance indicators and application scenarios, different types of optical fiber also has its own characteristics, no absolute advantages and disadvantages. Only in a specific environment through different point of view of comprehensive consideration, can pick out the most suitable coding and fiber type.

40 GBPS DWDM optical systems will still face limited OSNR, dispersion, PMD, dispersion, nonlinear effects, and affected by the PMD and nonlinear effect is more apparent, but no matter what kind of optical fiber, 40 GBPS OSNR of DWDM optical system, dispersion, PMD tolerance index don't have changes, so when comparing the influence of different types on 40 GBPS DWDM optical system, take the dispersion slope, PMD, dispersion coefficient and attenuation coefficient into consideration.