PDF of this tutorialThere are several technologies that can be utilized to compensate for the effects of PMD. These technologies have included the following:
- Mechanical devices that actually squeeze a portion of the fiber in order to realign the polarization pulses of the optical bit. In other words, a mechanical PMDC “counter-stresses” the fiber. The primary drawback of this method is that mechanical devices are more prone to failure over long durations; e.g., the original mechanical “step” switches of early voice networks, a technology of the early 20th century, demanded frequent maintenance and were prone to problems.
- Electronic devices that work after the receiver decoder, manipulating electrons in order to reduce bit errors. The primary drawback to this method is the difficulty in correcting an optical problem at the electronic layer.
The most reliable and efficient PMDC technology is the use of adaptive optics to realign and correct the pulses of dispersed optical bits. The high-level concept of adaptive optic technology is shown in Figure 11.
Figure 11. Graphical Representation of PMD Compensation on a Distorted Optical Pulse
The figure shows how dispersed optical bits from the fiber network are corrected by the PMDC. Before correction, the polarized pulses of the bits have been separated and dispersed by PMD. The PMDC realigns and reshapes the optical bits before they are decoded by the receiver (Rx). The adaptive optics of the PMDC are controlled by an intelligent algorithm that is driven by analysis of the optical bit.
