How Much Do You Know About PM Patch Cables?

When talking about fiber optic patch cables, you may know LC fiber patch cables or MTP/MPO fiber cables. Besides these cables, there are some special fiber patch cables, such as mode conditioning patch cables, which has been introduced in the previous article. Today we will introduce another special fiber patch cable—polarization maintaining (PM) fiber patch cables.

Definition of PM Patch Cables

 

At the very first beginning, let’s check the basic definition about the PM patch cables. PM patch cords are based on a high precision butt-style connection technique. The PM axis orientation is maintained by using male connectors with a positioning key and a bulkhead female receptacle with a tightly toleranced keyway, ensuring good repeatability in extinction ratios and insertion losses.

 

Why Need PM Patch Cables?

 

When a normal fiber is bent or twisted, stresses are induced in the fiber and the stresses will change the polarization state of light traveling through the fiber. If the fiber is subjected to any external perturbations, say changes in the fiber’s position or temperature, then the final output polarization will vary with the time. This is true for even short lengths of fiber, and is undesirable in many applications that require a constant output polarization from the fiber.

To solve this problem, PM fibers are developed. These fibers work by inducing a difference in the speed of light for two perpendicular polarizations traveling through the fiber. This birefringence creates two principal transmission axes within the fiber, known respectively as the fast and slow axes of the fiber. Provided the input light into a PM fiber is linearly polarized and orientated along one of these two axis, then the output light from the fiber will remain linearly polarized and aligned with that axis, even when subjected to external stresses. A one meter long connectorized patch cord constructed with PM fiber can typically maintain polarization to at least 30dB at 1550 nm when properly used. Naturally, how well a PM fiber maintains polarization depends on the input launch conditions into the fiber. Perhaps the most important factor is the alignment between the polarization axis of the light with the slow axis of the fiber.

Connectors of PM Patch Cables

 

Given the importance of the alignment of the PM axis across a connection, the choice of connector is especially important. The most common type of PM connector is FC connector which has a positioning key to preserve the angular orientation of the fiber. The industry standard is to align the slow axis of the fiber with the connector key. The tolerances between the key and keyway on standard FC connectors are too loose to accurately maintain angular alignment, so manufacturers have tightened the key dimension tolerances on PM connectors. The key dimensions being used are based on FC angle polished connector (APC) standards. Unfortunately, two APC standards are currently on the market, a narrow, or reduced key design, and a wide key design. The two dimensions are incompatible with one another, so it is important to know beforehand which design you are using. Besides the FC connectors, PM patch cables using other connector types are also available, such as SC connectors. In all cases, there must be a key or similar structure to act as a reference, and tight tolerances must be kept to ensure that the ferrules cannot rotate.

Conclusion

 

PM patch cables are widely used in polarization sensitive fiber optic systems for transmission of light that requires the PM state to be maintained. FS.COM provides polarization maintaining (PM) patch cables with various connector types. For the details, welcome to visit www.fs.com.

Originally published: www.fiberopticshare.com/much-know-pm-patch-cables.html

Mode Conditioning Patch Cables Overview

Fiber optic patch cables play an important role in fiber optic connection. There are numbers of fiber patch cables on the market, ranging from the standard fiber patch cables to special fiber patch cables, such as mode conditioning patch cables, bend insensitive patch cables, traceable fiber patch cables, etc. This article will not introduce all of these fiber jumpers, only focus on the mode conditioning patch cables.

 

Why Need Mode Conditioning Cables?

 

Transceiver optics used in Gigabit Ethernet (1000BASE-LX) launch only single-mode long wave signals (1310 nm). This poses a problem if an existing fiber network utilizes multimode cables. When a single-mode signal is launched into a multimode fiber, the phenomenon known as DMD (differential mode delay) can create multiple signals within the multimode fiber. This effect can confuse the receiver and produce errors. Mode conditioning cables utilize an offset between the single-mode fiber and multimode fiber to eliminate DMD and the resulting multiple signals allowing use of 1000BASE-LX over existing multimode fiber cable system.

What Are Mode Conditioning Fiber Patch Cables?

 

Mode conditioning patch cables are required when Gigabit 1000BASE-LX routers and switches are installed into existing multimode cable plants. They are used to adapt the single-mode output of Gigabit Ethernet (1000BASE-LX) transceivers to a multimode cable network. They are fully compliant with IEEE 802.3z application standards.

 

The conditioned channel of mode conditioning patch cables consists of a single-mode fiber which has been fusion spliced to a multimode fiber in an offset manner, with a precise core alignment and angle. The non-conditioned channel of mode conditioning patch cables consists of one length of multimode cable. Light is launched on to the multimode fiber of the conditioned channel at a specific angle, giving the patch cord its mode conditioning properties. The fusion splice is protected by a black over-wrap. The other side has both a multimode and single-mode cable end. This side of the cable connects to the Gigabit transceiver equipment with the single-mode leg connecting to the transmit side. The side has two multimode cable ends connecting to the cable plant.

Things You Should Know When Using Mode Conditioning Patch Cables

 

Use mode conditioning patch cables in pairs. It means that you will need a mode conditioning patch cable at each end to connect the equipment to the cable plant. So then these cables are usually ordered in even numbers. The only reason to order an odd number of mode conditioning cables is to have a spare on hand. Mode conditioning patch cables can only convert single-mode to multimode. If you want to convert multimode to single-mode, then a media converter will be required.

If your Gigabit LX switch is equipped with SC or LC connectors, please be sure to connect the yellow leg (single-mode) of the cable to the transmit side, and the orange leg (multimode) to the receive side of the equipment. It is imperative that this configuration be maintained on both ends. The swap of transmit and receive can only be done at the cable plant side.

 

If some customers remain reluctant to deploy MCP cables, and for customers using OM3 or OM4 cables, please measure the power level before plugging the fiber into the adjacent receiver. When the received power is measured above -3dBm (in 1000BASE-LX links), a 5-dB attenuator for 1300 nm should be used and plugged at the transmitter source of the optical module on each side of the link. Actually, OM3/OM4 MCP can also work in this event. While whether all multimode fiber types require mode conditioning, you can contact the manufacturer of your installed cable for the answer.

Summary

 

Mode conditioning patch cables are duplex multimode cords that have a small length of single-mode fiber at the start of the transmission leg. The basic principle behind the cords is that you launch your laser into the small section of single-mode fiber. The other end of the single-mode fiber is coupled to multimode section of the cable with the core offset from the center of the multimode fiber. FS.COM provides various types of mode conditioning patch cables with different connectors. All these mode conditioning patch cables are in high quality and low price. For more details, welcome to visit www.fs.com or contact us over sales@fs.com.

Originally published: www.fiberopticshare.com/mode-conditioning-patch-cables-overview.html