Not all fiber optic systems are the same, and one big difference is the wavelength used for transmission. The wavelength affects performance, testing and the choice of components, so let’s see how well you understand it. Correct answers and explanations are in red.

1. The wavelength of light is basically a measure of the “color” of the light.
True
False

We specify the color of light by the wavelength of the light.

2. The wavelength of light used in glass optical fiber is in a region of spectrum called _________.
A. Ultraviolet
B. Visible
C. Infrared
D. Green

Fiber optic systems with glass fiber use infrared light. Visible light is in the region of 500–700nm. Infrared light is ~800nm or higher.

3. What wavelength sources are used with multimode glass optical fibers?
A. 650 nm
B. 850 nm
C. 1,300 nm
D. 1,550 nm

Multimode fiber uses light sources at 850 and 1300 nm, mostly LEDs or 850nm VCSELs (lasers).

4. What wavelength sources are used with single-mode glass optical fibers?
A. 650 nm
B. 850 nm
C. 1,310 nm
D. 1,550 nm

Single-mode fibers are designed for longer wavelength sources, lasers in the range of 1310 and 1550 nm, with some wavelength division multiplexing systems using the entire spectral range.

5. What wavelength sources are used with plastic optical fibers?
A. 650 nm
B. 850 nm
C. 1,300 nm
D. 1,550 nm

Plastic optical fiber has its lowest attenuation at 650 nm.

6. What type of optical fiber uses a wavelength of light that is easily visible to the human eye?
A. Plastic optical fiber
B. Multimode fiber
C. Single-mode fiber

Plastic optical fiber uses sources at 650 nm, a wavelength we see as bright red. The sensitivity of the human eye decreases fast after this red wavelength.

7. As the wavelength of light gets _________, the attenuation of the optical fiber _________.
A. Shorter, decreases
B. Longer, decreases
C. Longer, increases
D. Longer, stays the same

The attenuation of optical fiber is mainly caused by scattering which decreases fast at longer wavelengths.

8. As the wavelength of light gets _________, the sensitivity of the optical fiber to stress _________.
A. Shorter, decreases
B. Longer, decreases
C. Longer, increases
D. Longer, stays the same

At longer wavelengths, the fiber becomes more sensitive to stress losses (e.g. kinks or stress caused during pulling the cable).

9. Connector and splice losses are generally _________ at _________ wavelengths.
A. Lower, longer
B. Higher, longer
C. The same, all

Connector and splice losses are not generally sensitive to the wavelength of the light.

10. When measuring optical power from a transmitter or at a receiver, the optical power meter does not need to be calibrated at the actual wavelength of the system transmitter.
True
False

The detectors used in optical power meters vary greatly with wavelength, so the meter must be calibrated at the wavelength being tested. For fiber optics, meters are calibrated at 650 and 850 nm if they have silicon detectors or 850, 1300/1310 and 1550 nm for germanium or InGaAs detectors.

HAYES is a VDV writer and educator and the president of The Fiber Optic Association. Find him at www.JimHayes.com.