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RE: [802.3ae_Serial] 12 dB return loss for transmitter?

Hi all
 
My perception is, that this is an optical specification and as such it is the optical return loss (measured from the fiber side).
 
Just like SDH/SONET specifications, 10GE is an interface specification (at optical connections points S (=TP2) and R (=TP3)), and (optical) properties of the TX (jitter, rise/fall, eye mask etc.) and RX (sensitivity, tolerance etc.), ie. things that can be measured from the outside of the modules.
 
All 3 standards does not cover internal components specifications like the optical modulators S11 (electrical return loss) nor the MUX (driver) rise/fall time, output swing or S22.  These things are 'implementation specific' and as such it is unimportant, as long as the functionality and specifications are fulfilled at point S and R.
 
From a module vendors point of view, it will of course be nice to have some standard definitions for the interfaces at a component level, but I think it is out of scope for the 10GE standard.
 
XSBI/OIF/MSA interface (where instantiated) are covered in the same way.
 
 
 

Benny

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Benny Christensen, M.Sc.E.E, Ph.D.
Mileparken 22, DK-2740 Skovlunde, Denmark
Tel: +45 7010 1062, Fax: +45 7010 1063
e-mail: benny.christensen@intel.com, http://www.giga.dk
 

-----Original Message-----
From: Ron Miller [mailto:rmiller@brocade.com]
Sent: 8. februar 2002 06:44
To: 'Lindsay, Tom'; Ron Miller; Serial reflector 802.3ae (E-mail)
Subject: RE: [802.3ae_Serial] 12 dB return loss for transmitter?

Hi Tom
 
I believe that this is the electrical connection to the electro/optical module.
 
In the case of the optical transmitter(optical output) the same logic is appropriate.  However,
it is typically possible to get 30 or more db return loss.  also in the optical arena the source laser
can often be pulled in frequency by the reflected wave from the load, which may be a more important
source of degradation than the third pass signal combining with the incident signal at the receiver end.
 
Insertion loss S21 is from input  to output.  Return loss is reflected power and at the sending end is usually
referred to as S11, and at the receiving end S22.  All parameters are complex numbers.
 
Good luck
 
Ron
-----Original Message-----
From: Lindsay, Tom [mailto:tlindsay@stratoslightwave.com]
Sent: Thursday, February 07, 2002 4:04 PM
To: Ron Miller; Serial reflector 802.3ae (E-mail)
Subject: RE: [802.3ae_Serial] 12 dB return loss for transmitter?

Does everyone agree with Ron?
 
Ron, do you understand that this is an optical spec?
 
Thanks, Tom
-----Original Message-----
From: Ron Miller [mailto:rmiller@brocade.com]
Sent: Tuesday, February 05, 2002 10:40 PM
To: Lindsay, Tom; Serial reflector 802.3ae (E-mail)
Subject: RE: [802.3ae_Serial] 12 dB return loss for transmitter?

Tom
 
This is the return loss looking back into the transmitter.  Typically it is measured with the
drive circuit powered.  It is an AC measurement, and may vary according to the signal that
the transmitter is sending out.
 
The value of this measurement is in calculating or simulating the third pass signal, which is the
combination of the driving signal together with the reflection from the destination, coming back to the
source and reflecting again.  The total reflection from the source termination and the load termination
should be at least 20 db total for +/-10 percent ripple in the rails of the eye pattern.  So, 12 db at
each end would be 24 db or about +/ -6 percent ripple.  So, you normally want to do better.  20 db is
a very safe number at both ends resulting in 40 db or only about +/-1% ripple in the rails.
 
Ron miller
-----Original Message-----
From: Lindsay, Tom [mailto:tlindsay@stratoslightwave.com]
Sent: Tuesday, February 05, 2002 9:24 PM
To: Serial reflector 802.3ae (E-mail)
Subject: [802.3ae_Serial] 12 dB return loss for transmitter?

Dave Kabal, Dubravko and I were discussing the 12 dB return loss spec in Table 52-12.
 
What is it? Is this return loss looking back into the transmitter port from outside, or is it tolerance to return loss of the cable plant and receiver combination?
 
If the former, what is the technical reasoning? If the latter, it should at least be renamed or more preferably removed.

Thanks, Tom
Stratos NW
425/672-8035 x105