Alcatel-Lucent 1643 AMS Installation Manual page 36

Safety
Laser safety
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Overview
Optical fiber telecommunication systems, their associated test sets, and similar
operating systems use semiconductor laser transmitters that emit infrared (IR) light at
wavelengths between approximately 800 nanometers and 1600 nanometers. The emitted
light is above the red end of the visible spectrum, which is normally not visible to the
human eye. Although radiant energy at near-IR wavelengths is officially designated
invisible, some people can see the shorter wavelength energy even at power levels
several orders of magnitude below any that have been shown to cause injury to the
eye.
Conventional lasers can produce an intense beam of monochromatic light. The term
monochromaticity means a single wavelength output of pure color that may be visible
or invisible to the eye. A conventional laser produces a small-size beam of light, and
because the beam size is small the power density (also called irradiance) is very high.
Consequently, lasers and laser products are subject to federal and applicable state
regulations as well as international standards for their safe operation.
A conventional laser beam expands very little over distance, or is said to be very well
collimated. Thus, conventional laser irradiance remains relatively constant over
distance. However, lasers used in lightwave systems have a large beam divergence,
typically 10 to 20 degrees. Here, irradiance obeys the inverse square law (doubling the
distance reduces the irradiance by a factor of 4) and rapidly decreases over distance.
Lasers and eye damage
The optical energy emitted by laser and high-radiance LEDs in the 400-1400 nm range
may cause eye damage if absorbed by the retina. When a beam of light enters the eye,
the eye magnifies and focuses the energy on the retina magnifying the irradiance. The
irradiance of the energy that reaches the retina is approximately 10
more than at the cornea and, if sufficiently intense, may cause a retinal burn.
The damage mechanism at the wavelengths used in an optical fiber telecommunications
is thermal in origin i.e., damage caused by heating. Therefore, a specific amount of
energy is required for a definite time to heat an area of retinal tissue. Damage to the
retina occurs only when one looks at the light sufficiently long that the product of the
retinal irradiance and the viewing time exceeds the damage threshold. Optical energies
above 1400 nm cause corneal and skin burns but do not affect the retina. The
thresholds for injury at wavelengths greater than 1400 nm are significantly higher than
for wavelengths in the retinal hazard region.
Classification of lasers
Manufacturers of lasers and laser products in the U.S. are regulated by the Food and
Drug Administration's Center for Devices and Radiological Health (FDA/CDRH) under
21 CFR 1040. These regulations require manufacturers to certify each laser or laser
product as belonging to one of four major Classes I, II, lla, IlIa, lllb, or IV. The
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