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

[David Kabal <David.Kabal@picolight.com>]

Mike (et al):

 

We missed you at the last meetings. I hope all is well with you and that you will "meet me in St. Louis".

 

We had a very interesting discussion about return loss at the last meeting (Santa Rosa), although no attempt was made to change the specifications, only to rename them.

 

There appear to be four parameters of interest in a link, all confusingly named and specified, IMHO. My attempt to rename these parameters more descriptively and call them out explicitly by these new names met with enough resistance that it didn't get approved, although everyone appeared to think it was a "good" idea. Some present felt it was too much change and that it would invite comments to rename these parameters, but due to the amount of churn already present in the clause, let me try again:

 

• Optical Return Loss Tolerance (ORLT): Looking out of the transmitter, the maximum reflectance it can tolerate during operation.
• Transmitter Reflectance (TR): Looking into the transmitter, the maximum reflectance observed.
• Receiver Reflectance (RR): Looking into the receiver, the maximum reflectance observed.
• Maximum Discrete Reflectance (MDR): Looking into the fiber plant, the maximum reflectance of any point along that optical fiber (usually a connector).

 

I won't play around with the sign of the numbers right now, but here's how I think these are specified currently for each link type:

 

                        ORLT   TR        RR        MDR

10GBASE-S:     12         -           -12        -20

10GBASE-L:     12         -12        -12        -26

10GBASE-E:     21         -26        -27        -26

 

-          indicates not specified

 

Comments? Suggestions? I really want to make this as clear as possible, so I am going to recommend that: ORLT, TR be listed in each PMD's transmit parameters explicitly, and RR in each PMD's receive parameters, and that MDR be listed explicitly as such where it is now. In addition, if it is appropriate, we can include a measurement technique referencing appropriate other standards for any specifications we deem appropriate.

 

Cheers,
Dave

------

David Kabal

Sr. Technology Planner

Picolight

 

e-mail: david.kabal@picolight.com

Main: 303-530-3189 x7498

Direct: 303-527-7498

Fax: 303-527-4961

 

-----Original Message-----
From: owner-stds-802-3-hssg-serialpmd@majordomo.ieee.org [mailto:owner-stds-802-3-hssg-serialpmd@majordomo.ieee.org] On Behalf Of Mike Dudek
Sent: Monday, February 25, 2002 7:17 PM
To: Christensen, Benny
Cc: Serial PMD Ad Hoc Reflector (E-mail) (E-mail)
Subject: Re: FW: [802.3ae_Serial] 12 dB return loss for transmitter?

 

This is all good information, however returning to the original question.  The 12dB return loss for the transmitter is as Ron said a specification on the transmitter, not the cable plant.  It is measured by injecting an optical signal into the Tx and measuring how much light is reflected back.  It was included to keep Interferometric noise to a low level.  This noise is generated when there is a triple path (ie reflection from the Rx which then gets reflected back by the Tx with a single mode source.).  It would be nice to remove the specification, but a significant amount of work was done in the serial Ad Hoc to show that the specification is needed unless the return loss on the Rx is tightened.