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Laser Safety Guidelines
365-575-925R1.5
Lucent Technologies
x i x
Issue 1, April 2002
L
ASER
S
AFETY
G
UIDELINES
General Laser Information
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
5
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 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 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, 2, 3A, 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