RE: Patch cord for 1300 WWDM
Dave Dolfi,
I would like to address your concerns over launch conditions.
The launch requirement for the new 50 um fiber is presently specified as >=
85% encircled flux within a 16 um radius of the center of the fiber. This is
not much different than the launch requirement determined to be optimal for
enhanced 62.5 um fiber which is <= 25% encircled flux within 4.5 um radius
and >= 75% within 15 um radius of the center of the fiber. The main
difference is that the 62.5 um spec limits the amount of power allowed in
the very center of the fiber (within 4.5 um radius) while the 50 um spec has
no such limitation. But, the similarity of the outer radii specification
(85% within 16 um vs 75% within 15 um) permits solutions that meet both
requirements simultaneously. In short, the overall power concentration in
the center of the 50 um fiber is not required to be much different than that
for enhanced 62.5 fiber.
Further, the TIA FO2.2 data indicates launches that meet the above
requirements for enhanced 62.5 um fibers do not cause degradation of the
bandwidth below the OFL specification on installed-base 62.5 um fibers. In
fact, such launches usually cause bandwidth enhancement. By combining these
launches with 62.5 um fibers tested and determined to produce higher
restricted launch bandwidth, we can guarantee enhanced performance. Perhaps
even more to the point, the data collected by both the TIA and IEEE on this
subject has not shown any launch condition that caused the bandwidth to
collapse below the 160 MHz-km OFL spec for 62.5 um fiber. This includes
launches produced by single-transverse mode "CD" lasers as well as
multi-transverse mode VCSELs with various spot sizes and numerical
apertures. It also includes Radial Overfilled Launches that were developed
as a possible test launch condition by the IEEE MBI study group, which are
said to extract the "worst case" modal bandwidth for any laser launch. In
summary, there is no evidence of any launch condition that causes less than
160 MHz-km bandwidth from the installed base of 62.5 um fiber. The 100 m
capability of the 850 CWDM PMD is based on 160 MHz-km bandwidths.
Regards,
Paul Kolesar
----------
From: Dave Dolfi 3764 [SMTP:dolfi@xxxxxxxxxxxxxxxxxxxxxxxx]
Sent: Thursday, August 03, 2000 6:17 PM
To: stds-802-3-hssg@xxxxxxxx; billw@xxxxxxxxxxx
Cc: dave_dolfi@xxxxxxxxxxx
Subject: RE: Patch cord for 1300 WWDM
Dear Bill,
I'm happy that you agree with my summary of the patch cord
situation.
Unfortulately, I'm not sure that I agree with everything you seem
to be saying about 850 nm CWDM. Specifically, while I agree that
you could specify a VCSEL and a mux design which would achieve 100
meters on the installed 62.5 um MMF OR > 550 meters on the new
enhanced
bandwidth 50 um MMF, I'm not sure that a single design could achieve
both at the same time.
The 62.5 um conventional fiber requires a large spot at its input to
mitigate potential DMD problems if too much of the excitation is in
the central portion of the fiber, while the new fiber requires a
small spot centered at its input in order to satisfy the encircled
flux
requirement necessary to achieve the higher bandwidth. Can you
really
achieve both of these at the same time?
I think you need to prove that this is true before you can claim to
simultaneously achieve the bandwidths you are claiming over both
fiber
types.
Dave Dolfi
Agilent Technologies
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> Reply-To: <billw@xxxxxxxxxxx>
> From: "Bill Wiedemann" <billw@xxxxxxxxxxx>
> To: <stds-802-3-hssg@xxxxxxxx>
> Subject: RE: Patch cord for 1300 WWDM
> Date: Thu, 3 Aug 2000 10:38:21 -0700
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>
> Thank You.
> Everything you say is correct. 850CWDM has been designed to
directly meet
> the 100 meter objective over installed (DMD challenged) 62.5u MMF
and the
> 300m objective over MMF. In addition we can meet 300 meters over
existing
> 50 micron fiber and greater than 550 meters with the new high
bandwidth MMF.
>
> Finally experimental evidence has shown greater than 300 meter
performance
> over installed 62.5 micron fiber that is not DMD challenged.
>
> Bill Wiedemann
> Blaze
> 925-560-1610 x169
>
> At 02:11 PM 8/2/00 -0700, David W Dolfi wrote:
>
>
> >Everyone,
> >
> >
> >There seems to have been some confusion at the La Jolla
> >meeting over the necessity for an offset patch cord for
> >1300 nm WWDM. Because of this, and additional comments
> >made on the reflector since the meeting, I am writing
> >this email to clarify the situation.
> >
> >Fact 1. An offset patch cord is NOT required for 1300 nm
> >WWDM in order to meet the current MMF objectives of 802.3ae.
> >That is to say, it is NOT required in order to achieve a 100
> >meter link length on the installed base (this includes both
> >62.5 and 50 um standard MMF, which both have a 500 MHz-km OFL
> >bandwidth length product at 1300 nm), NOR is it requred to
> >achieve a 300 meter link length on the new enhanced BW
> >MMF, which also has a 500 MHz-km OFL bandwidth at 1300 nm.
> >
> >Needless to say (but I will for the sake of completeness)
> >1300 nm WWDM also supports single mode fiber up to 10 km,
> >again without a patch cord.
> >
> >
> >Fact 2. The ONLY time you need to use a patch cord with
> >1300 nm WWDM is if:
> >
> >1. You want to extend the link length of the MMF installed base
> >to 300 meters
> >
> >AND IN ADDITION TO THIS
> >
> >2. The fiber in question is "DMD challenged".
> >
> >
> >Please note that if you are in this particular situation, none
> >of the 850 nm based PMDs will satisfy your need, patch cord or
> >not (but see Note below). Your only alternative in this
situation,
> >with an 850 nm PMD, is to install new fiber, either the enhanced
BW
> >multimode fiber or single mode fiber. Therefore, the notion that
> >the patch cord is some sort of "penalty" you pay for using 1300
nm
> >WWDM is really the wrong way to think about it. Rather than a
> >shortcoming, it is actually a benefit, since it gives you the
(rel-
> >atively speaking) low cost option of using a patch cord in a sit-
> >uation where your only other alternative is to pull new fiber.
> >
> >Note: The 850 nm 4 channel CWDM PMD will allow you a 300 meter
link
> >length, without a patch cord, on the installed base of 50 um
fiber
> >ONLY. However, this is a small benefit, since the great majority
> >of the MMF installed base is 62.5 um fiber, on which 850 nm CWDM
> >will only support a 100 meter link length (due to the fact that
> >62.5 um fiber has an OFL bandwidth length product of only 160
> >MHz-km at 850 nm).
> >
> >
> >David Dolfi
> >Agilent Technologies
>
>