Optical transceiver question

Robert Jacobs rjacobs at pslightwave.com
Wed Sep 7 21:32:59 UTC 2016

Not buying fresh veggies here... All optics have about a 5 db range that the vendor will say it is good.  The better venders stamp the output power on the optics but not all do this... What he said is to achieve the 60 Km selling point you would have to have all the optic be on the high side of the db TX power... I have never heard of a 60 Km rated optics and it would seem they should be saying 40 to 60 not just 60.  It would be nice to say I only want the optics that have an output on the high side and will accept only a 1 db variance but have never seen that in reality.  Most are in the middle..

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-----Original Message-----
From: NANOG [mailto:nanog-bounces at nanog.org] On Behalf Of Eric Kuhnke
Sent: Wednesday, September 7, 2016 3:51 PM
To: nanog at nanog.org list <nanog at nanog.org>
Subject: Re: Optical transceiver question

What you're saying is if you purchase ten identical optics with the same SKU, and put them on a few hundred meters of coiled SC/UPC to SC/UPC simplex fiber and an optical power meter on the other end, they're showing varying real world Tx powers from between +0 to +5dBm?

That's not right at all, they're supposed to be sorted at the factory by their actual optical power output before they have labels put on them.

On Wed, Sep 7, 2016 at 1:23 PM, Frank Bulk <frnkblk at iname.com> wrote:

> We recently purchased some generic optics from a reputable reseller 
> that were marketed to reach 60 km.
> But what we found, based on the spec sheets, is that it could only 
> reach that distance if the optics were transmitting on the high side 
> of the transmit power range.
> For example, if the TX range was 0 to +5 dBm and minimum RX power was 
> -20 dB, the designed optical budget should be no more than 20 dB (0 - -20).
> Based on the wavelength the appropriate loss would be 0.4 dB/km and 
> results in only 50 km, not 60 km.  To get 60 km it would need 24 dB of 
> link margin, and that would only be attainable if it was transmitting 
> on the high side, at +4 dBm.
> Is it an industry practice to market distance based on the hot optics, 
> not on the worst case, which is minimum TX power?
> Frank

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