re: missing MAS......
Pat:
At 20:50 29-12-1999 -0600, Patrick Gilliland wrote:
>-------------------------------------------------------
>[...]trivial case of
>a repeating 10101010101010101 sequence which has been
>filtered to remove all but the fundamental. A signal
>such as this would be of little use for transmission
>over multimode fiber. Therefore, to emphasize this
>"fundamental" frequency ignores the fundamentals of optical
>fiber transmission.
>-----------------------------------------------------------
sorry, this conclusion is misleading. if you will compare power spectra for both
2-PAM and 5-PAM, for 10e9 bits per second data transfer at equivalent BER,
using a suitably long PRBS, you will find that 5-PAM requires only half the
bandwidth. whether it is exactly 50% or slightly off in either direction, for coding
efficiency or other factor, isn't germane to the point of bandwidth efficiency.
[...]
>------------------------------------------
>[...]
>The advantages in processing of surface emitters
>are as you have named them. At present, their
>volumes are not sufficient to make them less costly
>than their edge emitting counterparts.
>---------------------------------------------------
i disagree, but even if your statement were true i predict this will not
be a problem for long.
>------------------------------------------------
>Yes. Everyone wants it cheap. Cost effective
>sounds so much better, though. One component
>which will meet your cost targets you might want
>to consider is a 1300nm VCSEL.
been there, seen that. a volume-manufacturable LW VCSEL has been a
kind of 'holy grail' for this industry, that pre-dates my involvement.
i don't know where things stand with external modulators now, but
'low cost' remains a primary goal.
> >my point is this: implementation of MAS, in whatever kind of line
> >code you like, does not depend on wavelength. therefore, if one can
> >implement (C or D)WDM at all, and if one can implement MAS at all,
> >then one can certainly consider implementing MAS on (C or D)WDM.
> >if one can think of any means to implement CDR for more than one
> >serial lane of data traffic on the copper side of a PHY, one can certainly
> >consider applying that method to the optic side, with MAS, through
> >(C or D)WDM. for what we know right now, choice of more than one
> >wavelength does not preclude consideration of one or another choice
> >of modulation for all.
>
>------------------------------------------------------
>I may have failed to express a point clearly.
>The difference between MAS and WDM lies in the
>need to skew compensate the individual WDM channels
>because of differential delays in the fiber due to
>chromatic dispersion, etc. After the skew is removed,
>only they may then be reassembled into a single channel.
[...]
yes, i'm aware of this. my point was to highlight the advantage that (for now,
anyway) MAS does not need WDM for it to succeed; at some point there
may be good reason to combine the two.
LaterAtion...
--
J M Wincn
Cielo Communications, Inc.
325 Interlocken Pkwy, Bldg A
Broomfield, CO 80021-3497
mwincn@xxxxxxxxxxxx