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

Re: Equalization


I agree with many of the points you are making with respect to the
difficulty of characterizing the frequency response of a
laser/multi-mode fiber optical link in order to equalize for the effects
of multi-mode dispersion.

However, I don't believe that such characterization is impossible, it's
just very difficult. As a level set and in light of the objective of
this equalization thread: to extend multimode cable plant distances
using laser sources at a given data rate, I would personally instead
chose to go to multilevel signaling first. It's likely to be easier,
lower power, applicable to a broader base of fibers, etc. Please don't
misunderstand me, I'm not trying to bring back multi-level signaling at
the moment. I'm just commenting about the difficulty of this
equalization effort. As Oscar Agazzi and I have presented and explained
to the Task Force, equalization and multi-mode signaling are orthogonal
and both can be employed separately or in combination to enable extended
link distances.

The real purpose of this note is to properly frame the level of
difficulty of this equalization effort. You stated that the design of
the equalizer would include: "intergap inserting bits, error check,
speed correction".  This is not true and should not be used as an
argument against investigating equalization techniques. These other
required 10 GbE link functions are completely orthogonal to equalization
have associated with them accepted proposals and are based on proven
technology. Let's not obfuscate the equalization task ahead of us if we
seriously plan to invest any effort in it.
Best Regards,

Edward Chang wrote:
> Gair:
> I basically agree with you.
> However, to design a equalizer to meet 10 Gigabit per second with all these
> timing critical requirements, intergap inserting bits, error check, speed
> correction.......and to assure BER of 10^-12 are complex, and will need a
> lot of detail work, which is beyond our conceptual discussion on the
> reflector for last several days.
> As an engineering practice, define and characterize the problem first, then
> chose the most optimum tool to resolve the problem.  Otherwise, develop a
> new tool to resolve the problem, if it is necessary.  Design of equalization
> with MM fiber is no exception to this common practice.
> Walter is giving us more understandable signals for a possibility of 5 PMDs.
> Let us seize the opportunity to get to work this project.
> Regards,
> Edward S. Chang
> NetWorth Technologies, Inc.
> Tel: (610)292-2870
> Fax: (610)292-287
Richard Taborek Sr.                 Phone: 408-845-6102       
Chief Technology Officer             Cell: 408-832-3957
nSerial Corporation                   Fax: 408-845-6114
2500-5 Augustine Dr.
Santa Clara, CA 95054