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Today, multimode fiber optic systems are lagging behind singlemode systems in terms of growth. In addition to supporting high data throughput, singlemode systems are attractive because they are easy to upgrade and help to "future proof" installations. Nonetheless, multimode fiber still gets plenty of coverage in any fiber optic cable guide. Why? Because multimode is still the fiber of choice for many applications.
For example, multimode fiber optic cable is well suited for systems that have short fiber optic links, such as Local Area Networks (LANs) and Storage Area Networks (SANs).
Multimode Advantages
Multimode fiber optic cable and components are less expensive and easier to work with than their singlemode counterparts. This is due largely to the fact that the multimode fiber core is larger, and alignment tolerances are much less critical than they are for singlemode fiber.
Like singlemode, multimode fiber provides high bandwidth at high speeds, but transmission is limited to shorter distances than singlemode. (In longer cable runs, the multiple paths of light in a multimode fiber tend to create signal distortion).
Standard multimode cable is made of glass fibers, usually 50-to-100 micron in diameter (most common is 62.5). Multimode cable is also available as low-cost Plastic Optical Fiber (POF), which offers performance similar to glass cable for very short runs.
Singlemode Advantages
Generally, singlemode cable provides less signal attenuation, higher transmissions speeds, and up to 50 times greater transmission distance than multimode cable. Singlemode cable can transmit data at terabits per second over 100km without requiring re-amplification of the signal.
Singlemode fiber typically has a diameter of only 8.3 to 10 microns, which is much narrower than multimode fiber which is usually 50 to 100 microns in diameter. The small core of a singlemode fiber allows for the propagation of only one light wave, so there is no possibility of distortion due to overlapping light pulses. Also, singlemode is more stable than multimode for systems that have branching devices, such as couplers.
Which to Choose?
When deciding whether to use multimode or singlemode fiber, a lot depends on a system's current and future bandwidth requirements. As a general guide, think of multimode bit rate as being limited to 100Mbps over distances up to 40km, with shorter links allowing for bit rates up to 10Gbps.
If your system is comprised of relatively short fiber links and bandwidth requirements are not expected to exceed multimode capacity over the system's lifetime, then multimode may be the logical choice. It is less expensive to purchase, install and maintain.
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