Eye protection in DWDM systems -- what threshold?

Kevin Hodle kevin.hodle at gmail.com
Tue Jun 9 06:16:53 UTC 2009

Hi Deepak,

   Most modern DWDM transponders with 160km network side optics will
be launching anywhere from -2dBm to +2dBm depending on how warm the
laser is, assuming a +2 dBm launch you are looking at around 1.6mW -
not something you want to be exposing your eyes too. If you've also
deployed EDFA's in your optical topology potentially adding another
+20 dBm or so, its a good idea to start documenting expected optical
power levels at each point in your topology for times when splice work
or other maintenance work needs to be performed. To be on the safe
side, the best policy is to simply shut down any light contributing
lasers on a given  strand when performing any kind of maintenance on
that strand (design your optical topology with redundancy in mind, so
you can seamlessly take light off a given path if need be). Modern
gear usually comes equipped with a feature called ALS (Auto Laser
Shutdown), where if an LOS condition is detected the laser is
automatically shutdown. If your gear supports this, enable it. It
could potentially save an ignorant tech's eyesight :).

Kevin Hodle

On Mon, Jun 8, 2009 at 11:42 PM, Deepak Jain<deepak at ai.net> wrote:
> At what power level do DWDM systems become dangerous to work near (i.e. not staring into any optics, using light meters, etc)? I never see technicians on inside DWDM systems using eye protection, but I see power levels of amps going higher and higher. On a recent meter I saw almost .6mW...
> Any pointers to a document saying 1550nm becomes dangerous at xxxx dbM?
> Thanks in advance,
> DJ

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