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

[Ron Miller <rmiller@brocade.com>]

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