363-206-305
Issue 3, June 2000 Page 5 of 12
DDM-2000 F
IBER
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EACH
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IDEBAND
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Lightwave Safety Guidelines
General Laser Information
Lightwave/lightguide systems, their associated test sets, and similar operating systems use
semiconductor laser transmitters that emit 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-
infrared 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
Light energy emitted by laser and high-radiance LEDs in the 400-1400nm 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, magnifying the irradiance. The irradiance of energy that
reaches the retina is approximately 10
5
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 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 enough 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.
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