Alcatel-Lucent 1675 LambdaUnite Installation And System Turn-Up Manual page 32

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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 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 so 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, IIa, IIIa, IIIb, 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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xxxii Alcatel-Lucent – Internal
Proprietary – Use pursuant to Company instruction
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, or 100,000 times
365-374-198R10.5.4
Issue 1 July 2009