Alcatel-Lucent 1643 AMS User's Operation Manual page 29

About this information product
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 105, or 100,000 times
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 long enough 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
International Electro-technical Commission is an international standards body that
writes laser safety standards under IEC-60825. Classification schemes are similar with
Classes divided into Classes 1, 1M, 2, 2M, 3R, 3B, and 4. Lasers are classified
according to the accessible emission limits and their potential for causing injury.
Optical fiber telecommunication systems are generally classified as Class I/1 because,
under normal operating conditions, all energized laser transmitting circuit packs are
terminated on optical fibers which enclose the laser energy with the fiber sheath
forming a protective housing. Also, a protective housing/access panel is typically
installed in front of the laser circuit pack shelves The circuit packs themselves,
however, may be FDA/CDRH Class I, IIIb, or IV or IEC Class 1, 1M, 3R, 3B, or 4.
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365-312-807R7.2
Issue 4, May 2007
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Alcatel-Lucent - Proprietary
See notice on first page
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