Lucent DDM-2000 OC-3 User And Service Manual page 10

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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
Light energy emitted by laser and high-radiance LEDs in the 400-1400nm range my cause
eye damage if absorbed by the retina. When a beam of light enters the eye, the eye
magnifies and focuses the energy, magnifying the irradiance. The irradiance of energy that
reaches the retina is approximately 10
sufficiently intense, may cause a retinal burn.
The damage mechanism at the wavelengths used in telecommunications is thermal in
origin (that is, damage caused by heating). Therefore, a specific amount of energy is
required for a definite time to heat an area of retinal tissue. Damage is not instantaneous. It
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. Light energies above 1400
nm would cause surface and skin burns and do not affect the retinal area.
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 — Class I, II, IIa, IIIa, IIIb, or IV. Lasers are classified
according to the accessibly emission limits and their potential for causing injury. Lightwave
systems are generally classified as Class I, because, under normal operation conditions, all
energized laser transmitting circuit packs are terminated on optical fibers which enclose the
laser energy with fiber sheath, forming a protective housing. Also, covers are in place over
the circuit pack shelves.
Lightwave Safety Precautions
In its normal operating mode, a lightwave system is totally enclosed and presents no risk of
eye injury. It is a Class I system under the FDA/CDRH scheme.
The lightguide cables that interconnect various components of a lightwave system can
disconnect or break, and may expose people to lightwave emission. Also, certain
measures and maintenance procedures may expose the technician to emission from the
semiconductor laser during installation and servicing. Unlike more familiar laser devices,
such as solid-state and gas lasers, the emission pattern of a semiconductor laser results in
a highly divergent beam. In a divergent beam, the irradiance (power intensity) decreases
rapidly with distance. The greater the distance, the less energy will enter the eye, and the
less potential risk for eye injury.
Inadvertently viewing an unterminated fiber or damaged fiber with the unaided eye at
distances greater than 5 to 6 inches normally will not cause eye injury provided the power in
the fiber is less than a few mW at the shorter wavelengths and higher at the longer
5
or 100,000 times that at the cornea, and if
DDM-2000 OC-3 M
Issue 3, June 2001
ULTIPLEXER
363-206-285