Angled Polish Connectors and DWDM

dear peoples of NANOG,

I've always held the -- possibly completely false -- notion that
angled connectors (APC) were not idea for fiber spans carrying
multiple dense/DWDM wavelengths. However, after copious amounts of
googling and duckduckgo'ing I cannot find an opinion or tech note one
way or the other. Are there situations when angled connectors are not
to be used? Are they 'safe' or even recommended for any kind of DWDM
application? I know they're not meant for mating directly with optics,
but for panels, x-conns, and distribution frames...?

I have this sinking feeling I've been misunderstanding angled
connectors all these years. cluebats are appreciated. please be


Hi Aaron,

Are there situations when angled connectors are not
to be used? Are they 'safe' or even recommended for any kind of DWDM

To my knowledge APC is always better than PC connectors. APC are used
to eliminate back reflections. Due to the angled connector reflections
are sent mostly towards the cladding and not the core and therefore.

The effecs of back reflections are great. Read this

I can not see why APC connectors are not to be used, even with DWDM.
The only problem with APC is that there are different kinds of angles
(8 degrees and 9 degrees) and polishments of the tip. When using the
wrong connectors (for example a 8 degrees against a 9 degrees in a
coupler) you will introduce more loss. This would be the reasons why
some people fear to use APC.

regards, Igor

I've been told this is very important in HFC solutions (hybrid fibre coax).

Operationally though, having APC is a hassle. I know of companies who mandated APC for a few years for all installations, but then reverted back to UPC due to operational problems (people putting UPC cables into APC ODFs etc).

So while APC might be technically superior when properly installed, it's not always better when looking at the whole "system".

Indeed. I have always held the idea that APC connectors induced
greater chromatic and/or polarization mode dispersion -- yet can't
find any resources that claim so, nor does that fit in with my working
mental model of how light propagates. Just something I picked up
during the hellish days of trying to deploy 10GbE before it was cool;
now I'd like to know if it is grounded in any science (-:


Just tossing this in here. I don't claim to know either way.

On the current project I'm working on all of the panels are LC-APC. This seems to have not been a problem for our DWDM vendor, who we have been working very closely with, and I assume know about our use of APC.
So far our PMD testing has come back clear.

How have you done the PMD testing?

For verifying PMD and CD through an actual wavelength (not per-fiber, but through all the ADMs etc), I haven't really been able to find a good solution. Suggestions welcome.

All tests done per span on dark fiber.

CDs via a Nettest FD440: 1520nm to 1640nm
PMD via a PerkinElmer* device: Just at 1550nm.


Couldn't find a model number in the test results. Just a reference to PerkinElmer.

We have been using APC connectors on our DWDM deployments now for about 5
years and have had no issues with it at all.

Additionally, last year we engaged several DWDM system providers and one
of the questions we asked them was, did they know of any issues with APC
connectors especially with regard to dual polarization systems. All vendors
came back with having no issues with APC connectors.