Information Technology Reference
In-Depth Information
Laser Safety and Classes of Operation
Many optical transceivers that are used in optical networking use laser diodes for
their light sources. The wavelengths of light that are used are in the infrared range,
which is beyond the range of human sight. However, light in these wavelengths
could still be harmful if sufficiently intense. All of the optical sources that are rec-
ommended for fiber LAN operation are operated at Class 1, at power levels below
that considered hazardous. However, other classes of laser operation exist and you
should be aware of their relative dangers.
In the United States, ANSI Z136.2 defines four classes of operation for lasers
(Table 11.6). Classes 1, 2, and 3 may be used in optical communications systems.
Class 4 lasers have power levels that are very high and are primarily used in med-
ical and industrial applications. They also include some types of military applica-
tions. The optical power increases with the class.
Class 1 laser sources are generally considered inherently safe, as they have
power levels that are very low. Class 2 low-power sources use visible light radiation,
and should never be viewed directly. Class 3 are medium-power sources such as
optical amplifiers and pump lasers. They may be visible wavelengths or not, but
they should never be viewed directly, and they require eye protection. Laser diodes
are quite capable of producing Class 3 intensity.
Laser safety goggles are available that tune out specific wavelength ranges,
while allowing enough other visible light through that you can see to work. You
must choose protective goggles or glasses with a sufficient amount of attenuation at
the laser's wavelength. These glasses are rated in decibels of attenuation at a partic-
ular wavelength. Be careful, as the common optical density ratings, such as OD-1 or
OD-2 indicate orders of magnitude, referenced to 10 dB, so an OD of 1 would be
10 dB and an OD of 2 would be 100 dB—quite a difference.
TABLE 11.6
Laser Safety Classes of Operation*
Class
Relative power
Typical source
Safety characteristics
1
Low
LED and VCSEL
Safe—when operated normally
2
Low—visible
Laser diodes and
Caution—do not view directly without eye
ultrabright LEDs
protection
3
Medium
High-power laser
Danger—eye diodes, optical protection
required amplifiers, and pump lasers
4
High
Medical and
Extreme danger—eye
industrial lasers
protection and physical protection required
*Classes of operation defined in ANSI Z136.2.
