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re: missing MAS......


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.


J M Wincn
Cielo Communications, Inc.
325 Interlocken Pkwy, Bldg A
Broomfield, CO 80021-3497