10 Frequently Asked Questions About Fiber Optics

Fiber optical technology typically presumes a service life of nearly 30 years. It is not a revolutionary or a new technology, in fact it is only about carrying light from one point to another. The questions that frequently asked around the industry are the art of mysticism, thus this post has collected questions made by professional during seminars, forum and projects. Solutions are also provided respectively to help readers to form the general understanding of this system.

Do signals really travel faster in fiber optics?

The speed here doesn’t refer to the the speed of signals in fiber optic cable, but the bandwidth potential of the fiber. Because you know that the speed of light in glass is about 2/3 C, but you might be surprised to know that signals in UTP (unshielded twisted pair) cables like Cat 5e travel at about the same speed (2/3 C). Coax, meanwhile, has a faster NVP (nominal velocity of propogation), about 0.9C, due to it's design.

What do I need for connecting Optic Fiber Cable to a Cat 5 Cable?

You need a media converter available from a number of companies for nearly $100-200.

Do you see any real serious problems in splicing together fiber cables from different manufacturers, as long as the cable is manufactured to the same specifications?

No, not as long as they are the same type and size, for example, multimode 62.5/125 or 50/125 and single mode should be normal (non-dispersion shifted) or dispersion shifted. Some single mode fibers are made for 1300 nm only, 1550 nm only or both, and they should not be mixed. Note that there are some other single mode fibers that have special coatings that cannot be mixed with others. Therefore you are supposed to ask your fiber vendors, splicer supplier or try it first before going into the field!

Will a single mode connector work on multi-mode cable?

The answer is maybe you can use SM connectors on MM but not the reverse. SM connectors are made to tighter tolerances—as is SM fiber—so the ferrule hole may be too small for some MM fibers. MM connectors have bigger holes for the fiber and will have high loss (>1dB) with SM. Also MM connectors may not be PC (physical contact) polish - terrible for return loss. MM fiber may not fit the smaller hole in SM connectors.

If you have a 50 micron fiber backbone, can you use 62.5 fiber jumpers on each end?

NO! On the receiver end it is OK, but on the transmitter end, the larger core of 62.5 into smaller 50 micron fiber will have fiber losses of 2-4 dB.

What is your view on using fiber optic connectors? Is it a better terminating method than fusion splice?

Of all the SFF (small form factor connectors), LC connector is the one that has become the most popular. In fact, it is the de facto standard connector for gigabit and 10 gigabit networks. Indeed the design is very well thought out. The smaller ferrule of a LC to LC fiber cable is easy to polish well and has excellent mating performance—which leads to low loss and back reflection. It is also easy to terminante and test.

What is the theoretical lifetime of optical fiber and optical fiber cables?

There is no “theoretical lifetime” of optical fibers. There is no industry accepted “wear out” mechanism for optical fiber. So there is no physical-chemical reach to test and accelerate in order to predict an eventual failure mechanism and corresponding failure reaction rate.

Can the same fiber-optic transceivers that are used with Om3 fiber, like SFP+ pluggable modules, be used with Om4 fiber or are there new transceiver types that need to be used?

Yes, you can use the same fiber optic transceivers for both Om3 and Om4 fibers because the two fiber types are basically the same except that Om4 fiber has higher bandwidth. The IEEE 10G Ethernet standard states that 300-meter Om3 and 400-meter Om4 link lengths are supported with 10GBase-S-compliant transceivers.

Which cabling media are typically used in data center/storage area network (SAN) environments?

There are a variety of different types of cabling media deployed in the data center. Multimode and single mode fiber, direct attach connection (DAC) cables, CX4 copper cables, and Category 6A twisted-pair all have a place.

The cabling type that is deployed is typically based on port type, cost, and distance. Distance is dictated by the architecture of the data center, which can be centralized/direct connect, distribution/top-of-rack switching, zoned distribution, or a combination of these.

Fiber is often deployed to connect top-of-rack switches to an aggregation switch at the end of the row or in another location, in centralized architectures for the "home runs," and in zoned distribution architectures. Multimode fiber supports all distances in the typical data center, such as connecting top-of-rack switches within rows back to an aggregation or core layer, or connecting servers to end-of-row switches. For larger data centers, where MM fiber patch cords may not suffice, single mode fiber can enable much longer distances. Single mode fiber can also be deployed within the row as a strategy for future applications that might use multiple-wavelength technologies. Another alternative to traditional cable and connector deployments for connectivity between servers and switches within the rack is to use direct attached cables connecting to SFP+ ports.

Is fiber more difficult to install than copper?

It depends on the comfort level and training of the technicians. Because fiber has been accepted as the standard choice for communications backbones for many years, today's installers are generally comfortable with the technology, but there is a learning curve for those just starting out. Of course, the same could be said of new generations of copper cabling. The new generation high-speed copper cables require more stringent and time-consuming installation techniques than were required in the past.

Compared to newer grades of copper cable, fewer regulations exist on the methods by which optical cable is pulled and terminated. In addition, there is no need to worry about the location of EMI/RFI sources during installation. Also, with fiber cables, there are no requirements for mitigating techniques when migrating to 10GbE and higher data rates as there are with UTP copper media.