Fiber Optic Training

Section Two: What is Fiber Optics? pg.6

Singlemode Characteristics

Singlemode fiber uses focused laser light sources, which are much more powerful than the LED sources used in multimode.

Where light signals in a multimode can bounce within the core, causing “pulse spreading”, the core of singlemode is so small that the only light rays that can enter the core are those that enter perpendicular to the core. This virtually eliminates the “pulse spreading” problem.

Multimode fiber has relatively high loss (“attenuation”) over distance as the bouncing of the light signal within the core will cause the light rays to travel further, and lose energy in the bouncing process. Singlemode has very low loss over distance, because stronger laser light sources are used, and the small core eliminates energy loss from bouncing.

LESSON REVIEW

Key Points:

1. Laser light sources are used in singlemode.

2. Singlemode light rays travel straight through the core- a single path or “mode”.

3. This minimizes “pulse spreading” which occurs in multimode.

4. Singlemode has very low fiber span loss- .25 dB per kilometer @ 1550nm.

Pop Quiz:
True or False

LED light sources are used with singlemode fiber.