Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

RE: Connector Return Loss (1550 nm versus 850/1300 nm)

Paul and Goeff,

The Telecordia 40-dB return loss requirement may be intended for
1550-nanometer systems.  There was a discussion of these issues at the
Tampa 10GbE meeting in 2000, mostly revolving around what the receiver
return loss should be.  Basically, 850 and 1300 nanometer links are short
(1 Km or less) and are build by connecting randomly-chosen parts from bins,
while 1550 nanometer links are long (tens of Km) and are individually
engineered.  Use of optical isolators was discussed as well, but this is a
transmitter design issue, and thus should not be required.  The final
agreement was to leave the connector return loss specs as they were, but
for 1550 only tighten the receiver loss, and the RIN specs and measurement
would be how the transmitter was specified.  A tranmitter with an overly
sensitive laser might require an isolater, but this is not for the standard
to say.  If memory serves, the return loss spec was changed from 12 dB to
20 or 26 dB; the current draft should tell the story.

Anyway, we may wish to use Telecordia optical specs across the board for
1550 nanometer links, but 1300 and 850 nm links are a different issue.


At 10:24 AM 1/4/12, Kolesar, Paul F (Paul) wrote:
>Good point on passive splitter systems. Similar concerns exist for
>bi-directional transmission on the same fiber at the same wavelength. For
>EFM, both of these systems will probably be only on singlemode fiber and use
>singlemode connectors. While outside the scope of Structured Cabling
>Standards, the improved return loss performance that may be required for SM
>connectors is found elsewhere. For example, Telcordia now requires at least
>40 dB return loss for singlemode connectors. Fortunately, products exist
>that easily meet this performance level.
>        ----------
>        From:  Geoff Thompson [SMTP:gthompso@xxxxxxxxxxxxxxxxxx]
>        Sent:  Wednesday, April 11, 2001 6:22 PM
>        To:  Kolesar, Paul F (Paul)
>        Cc:  802.3ae; 'Doug.Coleman@xxxxxxxxxxx'
>        Subject:  RE: Connector Return Loss
>        Paul-
>        The only thing that I would add is that there is a 25 dB return loss
>        requirement for MM in 10BASE-F ( for 10BASE-FP (Passive
>Star). As
>        we start to consider both passive splitter systems and single fiber
>        in EFM return loss may again rear its ugly head.
>        Geoff
>        At 11:02 AM 4/11/01 -0400, Kolesar, Paul F (Paul) wrote:
>        >Doug,
>        >Here are my views:
>        >The 20 dB level for MM connectors is historical in that that has
>been the
>        >spec used by previous generations of application standards and is
>        >agreement with cabling standards.
>        >
>        >The 26 dB level for SM connectors initiated in Fibre Channel in the
>early to
>        >mid nineties. I believe this was at the request of 1300 nm
>        >vendors. It is also in agreement with cabling standards. It is
>        >to not that Telcordia (formerly Bellcore) used 27 dB in the past,
>which I
>        >believe was in concert with SONET equipment standards.
>        >
>        >The use of isolators in the transceiver is a design choice and not
>        >by IEEE 802.3. The receiver is specified with a minimum return loss
>        >the value of which has been the subject of debate.
>        >
>        >What type of testing are you referring to? Transceiver or cabling?
>        >
>        >Paul Kolesar
>        >Lucent Technologies
>        >
>        >         ----------
>        >         From:  Doug.Coleman@xxxxxxxxxxx
>        >         Sent:  Wednesday, April 11, 2001 9:23 AM
>        >         To:  802.3ae
>        >         Subject:  Connector Return Loss
>        >
>        >
>        >         Does anyone know the history behind the connector return
>        >numbers
>        >         proposed for 10 GbE?
>        >
>        >         The return loss for multimode connections shall be greater
>than 20
>        >dB.
>        >         The return loss for single mode connections shall be
>greater than 26
>        >dB.
>        >
>        >         Do the transceivers integrate isolators into them to
>address return
>        >loss?
>        >
>        >         Has any testing be done to demonstrate compatibility?
>        >
>        >         Thanks
>        >
>        >         Doug Coleman
>        >         Corning Cable Systems
>        >