You may learn about LC fiber patch cables or MTP/MPO fiber cables while talking about fiber optic patch cables. Apart from these cables, there are some special fiber patch cables, such as polarization maintaining patch cable and mode conditioning patch cables that have been introduced in the previous article.
PM Patch Cables
At first, let me check the basic definition of the PM patch cables. On a high precision, the butt-style connection technique is polarization-maintaining the isolator is based. By using male connectors with a positioning key and a bulkhead female receptacle with a tight tolerance keyway the PM axis orientation is maintained, and hence ensures good repeatability in extinction ratios and insertion losses.
Need of PM Patch Cables
Stresses are induced in the fiber when a normal fiber is bent or twisted and the polarization state of light will be changed by the stresses traveling through the fiber. The final output polarization varies with the change in temperature or position of the fiber.
Polarization maintaining circulator is developed to solve this problem. For two perpendicular polarizations traveling through the fiber, inducing a difference in the speed of light will make these fibers perform. Within the fiber, this birefringence creates two principal transmission axes which are known as the fast and slow axes of the fiber.
Provided the input light into a PM fiber is linearly polarized and orientated along with one of these two axes, then from the fiber, the output light will remain linearly polarized and aligned with that axis, even when it is subjected to external stresses. To maintain polarization to at least 30dB at 1550 nm a one-meter-long connector’s patch cord constructed with PM fiber should be properly used. How well a PM fiber maintains polarization will depend on the input launch conditions into the fiber. The alignment between the polarization axes of the light with the slow axis of the fiber is the most important factor.
Conclusion
For transmission of light needing the PM state to be maintained, in polarization-sensitive fiber optic systems PM patch cables are used widely. With various connector types, many companies provide polarization-maintaining patch cables.
