PDF of this tutorialIn the previous topic, we discussed the reasons for the variance of PMD over time. In addition to the time variance, PMD also varies over wavelengths. This variability over wavelength will be discussed again when we talk about PMD compensation, but here we will focus on the concept of second order PMD (SOPMD) (see Figure 5).
Figure 5. DGD Wavelength Spectrum
Figure 5 shows a typical variance of PMD over some select wavelengths from ω1 to ω2. This variance results in an optical dispersion that is a function of both the channel bandwidth and the value of DGD over that bandwidth.
The effects of this optical dispersion are evidenced in an optical pulse as a ragged edge of an optical eye.
SOPMD can also cause problems during the decoding of optical pulses at the receiver (see Figure 6).
Figure 6. Example of an Eye Pattern Distorted by Second-Order PMD
