The characterization done by Fo2.2.1 is are from optical property point of
view, which is very important of understanding the static optical
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
Edward S. Chang
NetWorth Technologies, Inc.
From: Gair Brown [mailto:firstname.lastname@example.org]
Sent: Friday, July 21, 2000 2:15 PM
To: Edward Chang
Subject: Re: Equalization
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.
Edward Chang wrote:
> 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,
> dispersion related to the non-linear DMD is different. We need
> Edward S. Chang
> NetWorth Technologies, Inc.
> Tel: (610)292-2870
> Fax: (610)292-2872
> -----Original Message-----
> From: email@example.com
> [mailto:firstname.lastname@example.org]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
> rapid convergence with a short training sequence (# of bits roughly equal
> the # of taps). J. Winters and cohorts in IEEE Transaction (1990 - will
> 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
> 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)
> if anyone is interested, send me email and that will prompt me to dig
> through any relevant results i have...
> Rohit Sharma
> ONI Systems.
> > -----Original Message-----
> > From: Jonathan Thatcher
> > [mailto:Jonathan.Thatcher@worldwidepackets.com]
> > Sent: Thursday, July 20, 2000 4:07 PM
> > To: 'email@example.com'; 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:firstname.lastname@example.org]
> > >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
Code B35 PH: 540-653-1579
17320 Dahlgren Road FAX: 540-653-8673
Building 1500 Room 110A
Dahlgren, VA 22448-5100