RE: Equalization
Gair:
For after thought. Try the impulse response and shake the fiber to observe
the response wave form changing. We will characterize more, when we have
opportunity to start designing the equalization circuit MM DMD fibers.
Regards,
Edward S. Chang
NetWorth Technologies, Inc.
EChang@xxxxxxxxxxxxxxxx
Tel: (610)292-2870
Fax: (610)292-2872
-----Original Message-----
From: Gair Brown [mailto:gdbrown@xxxxxxxxxxxxx]
Sent: Saturday, July 22, 2000 8:49 AM
Cc: edward.chang@xxxxxxxxxxxxxxxx; stds-802-3-hssg@xxxxxxxx
Subject: Re: Equalization
Ed,
I know of no data that illustrates this effect. Theoretically it might
be possible to observe this type of effect in a couple of cases that I
can think of
1) in the presence of large amounts of modal noise
2) in the presence of a highly unstable laser spatial/angular output
distribution
Modal noise does exist, but for the shortwave technologies 1) is
definitely not true. Previous modal noise measurement on shortwave
technology showed modal noise to be quite small. For longwave, I am not
sure.
There can be instabilities in laser spatial/angular output distribution,
but they are generally small compared to the types of deviations that
would be needed to greatly affect the DMD.
For most fibers that have been studied for DMD, the DMD slowly changes
with radial illumination location. In addition, neighboring areas (e.g.
core locations) have very similar DMD components, but with slightly
different power weightings. From a practical point of view, this
characterization is time invariant and quite stable. In order to create
time dependency in an "observed" DMD, the power distribution in the
fiber would have to become highly unstable. There does not appear to be
any justification to that assumption.
Gair
NetWorthTK@xxxxxxx wrote:
>
> IGair:
>
> I mean the frequency responce affected by DMD, the optical path will
change,
> and the DMD pattern will change to affect the resultant frequency
response.
>
> Regards,
> Ed Chang
> NetWorth Technologies, In.
>
> e
> <<
> Ed,
>
> I don't think so. Why should it?
>
> Gair
>
>
> Edward Chang wrote:
> >
> > Larry:
> >
> > When move the fiber, the DMD pattern changes
> >
> > Regards,
> >
> > Edward S. Chang
> > NetWorth Technologies, Inc.
> > EChang@xxxxxxxxxxxxxxxx
> > Tel: (610)292-2870
> > Fax: (610)292-2872
> >
> > -----Original Message-----
> > From: Larry Rennie [mailto:Larry.Rennie@xxxxxxx]
> > Sent: Friday, July 21, 2000 6:02 PM
> > To: Gair Brown; Edward Chang
> > Cc: HSSG
> > Subject: Re: Equalization
> >
> > I am also a bit confused regarding the time variance of the fiber
> > characteristics. What is their about the fiber that makes the
> > chracteristics time variant? Vipul, you too had an e-mail that said
the
> > fiber was time-variant.
> >
> > Regards,
> >
> > Larry Rennie
> >
> > ----- Original Message -----
> > From: Gair Brown <gdbrown@xxxxxxxxxxxxx>
> > To: Edward Chang <edward.chang@xxxxxxxxxxxxxxxx>
> > Cc: HSSG <stds-802-3-hssg@xxxxxxxx>
> > Sent: Friday, July 21, 2000 1:56 PM
> > Subject: Re: Equalization
> >
> > >
> > > Ed,
> > >
> > > You need to talk to some of the participants of the FO-2.2.1 round
> > > robins. I suspect that some of the participants do have data that
> > > contains phase information.
> > >
> > > On a different note. I believe that the fiber response is relatively
> > > invariant with respect to time. There is variation between different
> > > fibers, but for fibers selected using the RML requirements the
variation
> > > should be manageable.
> > >
> > > Gair
> > >
> > >
> > > Edward Chang wrote:
> > > >
> > > > Gare:
> > > >
> > > > The characterization done by Fo2.2.1 is are from optical property
point
> > of
> > > > view, which is very important of understanding the static optical
> > > > parameters.
> > > >
> > > > The equalization need different parameters, time domain frequency
> > response
> > > > with the information of amplitude, phase versus frequency, and the
> > dynamic
> > > > nature of the response and error correction rate relative to fiber
> > motions.
> > > > Furthermore, one has to define, how far we intend to deal with the
DMD
> > > > caused BW deficiency based on the installed MM fiber, then we can
setup
> > the
> > > > target specifications for equalization circuit to be designed.
> > > >
> > > > In all, the timing related parameters, and time domain frequency
> > responses
> > > > will be established.
> > > >
> > > > If we have time, eventually we will get some meaningful result.
This
> is
> > > > reason, I have proposed 5 PMDs to allow each PMD opportunity to be
> > improved
> > > > later.
> > > >
> > > > Regards,
> > > >
> > > > Edward S. Chang
> > > > NetWorth Technologies, Inc.
> > > > EChang@xxxxxxxxxxxxxxxx
> > > > Tel: (610)292-2870
> > > > Fax: (610)292-2872
> > > >
> > > > -----Original Message-----
> > > > From: Gair Brown [mailto:gdbrown@xxxxxxxxxxxxx]
> > > > Sent: Friday, July 21, 2000 2:15 PM
> > > > To: Edward Chang
> > > > Cc: HSSG
> > > > Subject: Re: Equalization
> > > >
> > > > Ed,
> > > >
> > > > The characterization has already been done by FO-2.2. I believe
Mike
> > > > Hackert's working group has a ton of data on the frequency response
of
> > > > RML compliant fibers.
> > > >
> > > > Gair
> > > >
> > > > Edward Chang wrote:
> > > > >
> > > > > Rohit:
> > > > >
> > > > > It is interesting. You ,may like to share your results with us?
> > > > >
> > > > > However, fiber dispersion and DMD is not exactly the same thing.
> > > > > The linear dispersion proportional to cable length is straight
> > forward,
> > > > the
> > > > > dispersion related to the non-linear DMD is different. We need
> > > > > characterization.
> > > > >
> > > > > Regards,
> > > > >
> > > > > Edward S. Chang
> > > > > NetWorth Technologies, Inc.
> > > > > EChang@xxxxxxxxxxxxxxxx
> > > > > Tel: (610)292-2870
> > > > > Fax: (610)292-2872
> > > > >
> > > > > -----Original Message-----
> > > > > From: owner-stds-802-3-hssg@xxxxxxxx
> > > > > [mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Rohit Sharma
> > > > > Sent: Thursday, July 20, 2000 9:21 PM
> > > > > To: HSSG
> > > > > Subject: RE: Equalization
> > > > >
> > > > > i believe DMD can be (has been) modelled as a Rayleigh multipath
> > fading
> > > > > channel and fast Decision Feedback Equalization (DFE) techniques
with
> > RLS
> > > > > (Recursive Least Squares) or LMS (least mean squares) algorithms
> > applied
> > > > for
> > > > > rapid convergence with a short training sequence (# of bits
roughly
> > equal
> > > > to
> > > > > the # of taps). J. Winters and cohorts in IEEE Transaction
(1990 -
> > will
> > > > dig
> > > > > out exact ref. tomorrow) and Stanford ISL with John Cioffi did a
> bunch
> > of
> > > > > work in this area in 1991-95 timeframe.
> > > > >
> > > > > part of my grad studies demonstrated an 11 (goes to 11!) tap
adaptive
> > > > > optoelectronic filter to equalize dispersion in mmf for 1 and 2.5
> Gbps
> > > > IMDD
> > > > > signals. Similar results were shown by other researdch groups
using
> > > > > electrical equalization with bipolar taps and DFE structures.
some
> > basic
> > > > > simulation results are available (and were published in Optics
> > Letters)
> > > > and
> > > > > if anyone is interested, send me email and that will prompt me to
dig
> > > > > through any relevant results i have...
> > > > >
> > > > > -rohit
> > > > >
> > > > > Rohit Sharma
> > > > > ONI Systems.
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Jonathan Thatcher
> > > > > > [mailto:Jonathan.Thatcher@xxxxxxxxxxxxxxxxxxxx]
> > > > > > Sent: Thursday, July 20, 2000 4:07 PM
> > > > > > To: 'vipul.bhatt@xxxxxxxxxxx'; HSSG
> > > > > > Subject: RE: Equalization
> > > > > >
> > > > > >
> > > > > >
> > > > > > Vipul,
> > > > > >
> > > > > > You have really caught my attention on this one. What exactly
is a
> "
> > > > > > time-variant impulse?"
> > > > > >
> > > > > > jonathan
> > > > > >
> > > > > > >-----Original Message-----
> > > > > > >From: Vipul Bhatt [mailto:vipul.bhatt@xxxxxxxxxxx]
> > > > > > >Sent: Thursday, July 20, 2000 1:46 PM
> > > > > > >To: HSSG
> > > > > > >Subject: RE: Equalization
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >Rich,
> > > > > > >
> > > > > > >I was skeptical, like you, about the ability of equalization
to
> > > > > > >overcome DMD. I still am. But what made me more open minded is
my
> > > > > > >willingness to examine two key propositions: DMD behavior can
be
> > > > > > >approximated as that of a fading multipath channel. And
> > equalization
> > > > > > >can overcome the effect of a fading multipath channel.
> > > > > > >
> > > > > > >Why fading multipath? Consider this. A multimode fiber with
DMD is
> > > > > > >seen by an optical signal as a channel that propagates various
> > > > > > >portions of its energy (modes) through a refractive index
profile
> > > > > > >that is sharply different (at places) than intended. The
> > propagation
> > > > > > >velocity of a mode depends on refractive index. Over distance,
on
> > > > > > >average, some modes will have a cumulative average of a low
(lower
> > > > > > >than intended) refractive index path, thereby abnormally
> decreasing
> > > > > > >their path delay, while others may not. In some bad cases, a
bit
> > > > > > >arriving at the receiver is almost split in two or three
replicas.
> > > > > > >And the amplitude of each replica is changing dynamically.
Guess
> > > > > > >what, that is not far from the behavior of a fading multipath
> > > > > > >channel. Equalizers that deal with this phenomenon are used in
TV
> > > > > > >de-ghosting circuits and digital radio.
> > > > > > >
> > > > > > >To an equalization expert, DMD may not look so challenging -
it's
> > > > > > >just another channel with randomly time-variant impulse
> > > > > > >response...:-)
> > > > > > >
> > > > > > >But then, we both are putting the cart before the horse. Let's
> wait
> > > > > > >to hear some presentations from equalization experts. Even if
it
> > can
> > > > > > >be done, I will want to know whether it can be done
> > cost-effectively
> > > > > > >and on time. Our discussion should serve as a guide to them
about
> > > > > > >what we would like to hear.
> > > > > > >
> > > > > > >Thanks,
> > > > > > >Vipul
> > > > > > >
> > > > > >
> > > >
> > > > --
> > > > Naval Surface Warfare Center
> > > > browngd@xxxxxxxxxxxxx
> > > > Code B35 PH:
> 540-653-1579
> > > > 17320 Dahlgren Road FAX:
> 540-653-8673
> > > > Building 1500 Room 110A
> > > > Dahlgren, VA 22448-5100
> > >
> > > --
> > > Naval Surface Warfare Center
> > > browngd@xxxxxxxxxxxxx
> > > Code B35 PH:
540-653-1579
> > > 17320 Dahlgren Road FAX:
540-653-8673
> > > Building 1500 Room 110A
> > > Dahlgren, VA 22448-5100
> > >
> > >
>
> --
> Naval Surface Warfare Center
> browngd@xxxxxxxxxxxxx
> Code B35 PH: 540-653-1579
> 17320 Dahlgren Road FAX: 540-653-8673
> Building 1500 Room 110A
> Dahlgren, VA 22448-5100
>
>
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> Date: Fri, 21 Jul 2000 18:24:17 -0400
> From: Gair Brown <.gdbrown@xxxxxxxxxxxxx>
> Organization: Naval Surface Warfare Center
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> Subject: Re: Equalization
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--
Naval Surface Warfare Center
browngd@xxxxxxxxxxxxx
Code B35 PH: 540-653-1579
17320 Dahlgren Road FAX: 540-653-8673
Building 1500 Room 110A
Dahlgren, VA 22448-5100