Most of the attention to fiber optic cable specifications is focused on the cable itself, not the fibers in it. But there are more choices today in fibers that require careful consideration. How well do you understand all the possible choices? Answers are on page 126. For explanations of the answers, visit

1. For almost 15 years, one fiber type was used for most premises applications. What was it?

A. 62.5/125 FDDI grade

B. 62.5/125 OM1

C. 50/125 OM2

D. 50/125 OM3

FDDI grade fiber was chosen in the late 1980s as the best choice for premises systems. OM1 fiber is a higher bandwidth version of that fiber.

2. Two fibers, 62.5/125 FDDI grade and 62.5/125 OM1, are actually the same fiber under different names.



OM1 fiber has higher bandwidth at 850 nm.

3. What specification distinguishes all four of the multimode fibers listed above and affects the choice between them.

A. Attenuation coefficient

B. Numerical aperture

C. Bandwidth

D. Loss

From top to bottom, the bandwidth of the fiber increases, making the choice easier for faster data speeds.

4. Which of these fibers was optimized for use with fast systems using 1,300 nm LED sources?

A. 62.5/125 FDDI grade or 62.5/125 OM1

B. 50/125 OM2

C. 50/125 OM3

FDDI-grade 62.5/125 fiber was chosen for a network called FDDI, which used 1,300 nm LED sources.

5. Which of these fibers was designed for equal performance with systems using either 850 nm or 1,300 nm sources?

A. 62.5/125 FDDI grade or 62.5/125 OM1

B. 50/125 OM2

C. 50/125 OM3

OM2 fiber has equal bandwidth at 850 and 1,300 nm. It was designed long ago when telcos still used multimode fiber on long distance links—about 15 km in those days—to support wavelength multiplexing at 850 and 1,300 nm.

6. Which of these fibers was optimized for use with 1 to 10 gigabit systems using 850 nm VCSEL sources?

A. 62.5/125 FDDI grade or 62.5/125 OM1

B. 50/125 OM2

C. 50/125 OM3

OM3 fiber has very high bandwidth at 850 nm for use with VCSELs.

7. All these fibers have about the same attenuation coefficients, so that is not a deciding issue in choosing one of them.



The attenuation of multimode fiber has been well developed to minimize loss on any fiber type.

8. Which specifications are important to the fiber manufacturer but are not necessary for users to call out in specifying fiber?

A. Numerical aperture

B. Core/cladding diameter

C. Core/cladding concentricity

D. All of the above

None of these specifications are important for users.

9. In choosing fibers today, match the fiber to the appropriate application:

A. 62.5/125 OM1  >  2. Compatibility with legacy cabling systems

The only reason to install 62.5/125 fiber is to match currently installed system fibers.

B. 50/125 OM2  >  3. Lowest cost fiber for general applications

OM2 50/125 is a low cost fiber for general applications but is probably not as good a choice as OM3.

C. 50/125 OM3  >  1. Highest bandwidth for backbones and future applications

OM3 fiber offers the best performance for today and the future.

HAYES is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at