Mode Conditioning Patch Cord

What is a Mode Conditioning Patch Cord? A mode conditioning patch cord is a duplex multimode cord that has a small length of singlemode fiber at the start of the transmission leg. The basic principle behind the cord is that you launch your laser into the small section of single mode fiber. The other end of the singlemode fiber is coupled to multimode section of the cable with the core offset from the center of the multimode fiber. The laser light thus misses the “dip” and this new launch condition more closely mimics a standard LED launch. The bonus is that you still retain the speed advantages of using a laser.

A Mode Conditioning Patchcord (MCP) creates an offset in the launch from the laser into the multimode fiber, avoiding the index dip in the center of the fiber and allowing the signal to propagate properly through the fiber.   Newer “Laser Enhanced” multimode fibers do not exhibit this phenomenon due to the engineering of the fiber without an index dip in the core.

In legacy fiber optic systems, multimode fibers were not designed to properly transmit a SM laser source without the creation of dispersion problems, where the original signal becomes spread out over distance (>300m in most systems) and pulses can combine with each other creating an unreadable signal at the receiving end.   This was caused by a small dip in the Index of Refraction profile of the fiber in the center of the core in which the laser transmission becomes “mode locked”.

First thing I have to mention here is “BE CAREFUL!” optical equipment can be very expensive and not knowing what you are doing can lead to damage and or a hefty bill if replacement parts are needed. Second, know what you’re dealing with. In most cases you will end up needed to use a fiber optic attenuator, but read up on it, or call the Manufacturer for specifications and technical support. Other than possible damage to your equipment you could cause noise within the signal, and that will will not allow you to produce the best signal possible.

The solution is to test and know your signal strength, and use a fiber optic attenuator to adjust the signal strength. Here is how you do it. Simply measure the power of the signal being received, then subtract the maximum input power of the active equipment from the measured power of the signal. This formula will let you determine the amount of attenuation needed.

When it comes to getting a fiber optic attenuator you have several options. Before you go shopping for one be sure you know at what level you want to attenuate your signal and then choose what type will work best for you. Attenuators are available in either fixed or variable levels of attenuation, and as pigtailed devices, bulkhead adapters, or male-to-female hybrids. Taking the time to choose the right one cans save you big time.

Generally speaking there are two obvious attributes to identify singlemode from multimode fiber optic connectors. Remember it is important for you to keep your connectors in the original packaging from the manufacturer, doing this will eliminate any further investigation and save you some time that could have been better used on something else. If for some reason you are working with loose connectors the first thing you should do is look at the connector boot This can be an obvious indication of the connector type. The second thing you should do in examine the ferrule of the connector.

In most cases you will find standard boots on the connectors. That being said, when examining the connector boots know that singlemode boots are generally blue or white in color. Multimode connector boots are usually beige or black. Looking at the boot color can be the first indication to you of that particular fiber optic connector mode type. You can save yourself further investigation time if you look for these obvious color differences in the boot. Be aware that, fiber optic connector boots can be custom ordered and there is a small chance you could be looking at a special ordered boot and this could throw off your investigation.

The main difference between singlemode and multimode fiber optic connectors is the ferrule of the connector. Singlemode connectors will almost always have a Zirconia (ceramic) ferrule while multimode connectors can be made of stainless steel (Nickel-Silver), composite (plastic), or Zirconia. identifying the material in which these ferrules are made of can also sale you time in investigating your connector types. Lastly, the size of the hole in the center of the ferrule will be the end all determining factor to identify the correct fiber type that the connector is designed for. A standard singlemode Zirconia ferrule will usually have a ferrule hole of about 126 microns, while standard multimode ferrules will be closer to 127-128 microns. The difference is very small, but can make a large impact on insertion loss if the larger multimode ferrule is used on singlemode fiber. We are talking about microns here so it could be hard to accurately identify the diameters of these holes with the naked eye.

If you find yourself faced with the task of identifying fiber optic mode types be sure to follow these steps and it might save you a bunch of time calling around for support or researching for information on the web. Always remember the best way to tell the two connectors apart is to keep them in their original packaging until ready for use.