Lasers And Eye Damage; Classification Of Lasers; Lightwave Safety Precautions For Optical Fiber Telecommunication Systems - Lucent Technologies 300584935 Manual De Uso

Lasers and Eye Damage

Classification of Lasers

Lightwave Safety Precautions for Optical Fiber Telecommunication Systems

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PacketStar PSAX Multiservice Media Gateways
Safety Guidelines
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.
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 magnify-
ing the irradiance. The irradiance of the energy that reaches the retina is approx-
5
imately 10 or 100,000 times that at the cornea and, if sufficiently intense, may
cause a retinal burn.
The damage mechanism at the wavelengths used in telecommunications is ther-
mal 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 prod-
uct 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.
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 Electrotechnical Commission is an interna-
tional standards body that writes laser safety standards. Classification schemes are
similar with Classes divided into Classes 1, 2, 3A, 3B, and 4. Lasers are classified
according to the accessible emission limits and their potential for causing injury.
Lightwave 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, covers are typically in place over the circuit pack
shelves. The circuit packs themselves, however, may be FDA/CDRH Class I or IIIb
or IEC Class 1 or 3B.
In its normal operating mode, a lightwave system is totally enclosed and presents
no risk of eye injury. It is a Class I/1 system under the FDA and IEC classifica-
tions.
The lightguide cables that interconnect various components of a lightwave sys-
tem 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 pat-
tern of a semiconductor laser results in a highly divergent beam. In a divergent
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