# RE: Question? 1300nm WWDM channel width

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Jeff,

I agree with what you are saying.

Furthermore, the Typical spec for 1300nm DFBs and VCSELs are 0.085nm/*C.
The Maximum spec is 0.1nm/*C.  In determining the junction temperature range
that the lasers will see, there are several factors to consider.  The
tolerance of the temperature measuring equipment of the laser vendor can
introduce an error in the wavelength.  The amount of current being applied
to the laser directly effects the junction temperature and therefore the
wavelength of the laser.  I do not believe one can easily design a
transceiver for operation from 0 to 70*C with only a 10*C  margin. One
should at least have a 20*C margin.  A 30*C margin would be nice and safe.

Using only the typical numbers:
Temperature variation: 0.085nm/*C x (70*C+20*C) = 7.7nm
Laser tolerance at a particular temperature: 11.4nm - 7.7nm = 3.7nm

Therefore, the laser manufacutures have a +/- 1.8nm spec.  A spec of +/- 3nm
would significantly increase the yield and reduce the cost of the lasers.

If we are trying to make a specification that is conservative and not on the
edge, we should widen the channel width.  With a 14nm channel width, the
filter design and fabrication is still easy.  Why should we complicate the
overall design, reduce the yield of the laser manufacturing, and increase
the costs of the lasers, when we can increase the channel width now very
easily.

Regards,

Eric
*************************************************
Eric B. Grann, Ph.D.
Chief Technical Officer

Blaze Network Products Inc.
5180 Hacienda Drive
Dublin, CA 94568

phn: (925) 558-2100
fax:  (925) 558-2197
email: grann@xxxxxxxxxxx
website: http://www.blazenp.com
*************************************************

-----Original Message-----
From: Jeff Porter (rgbn10) [mailto:j.porter@xxxxxxxxxxxx]
Sent: Tuesday, October 31, 2000 5:57 PM
To: Eric Grann
Subject: Re: Question? 1300nm WWDM channel width

> In order to achieve a final transceiver temperature specification
> of 0-70*C, the lasers must have a slightly higher temperature range.  To
be
> safe, I would recommend a range of (-5) to 95*C.

I think Brian has you on the low end - don't really see a way
to be lower than ambient (for very long).

By claiming 80C range, is he claiming only 10C theta-J/A?  Or is he
counting on warming up to within 10C of final Tj "quickly enough",
so just adds 10C to minimum 70C range for slow time constants and
Tja variation (power variation, theta-variation?)

-----Original Message-----
From: brian_lemoff@xxxxxxxxxxx [mailto:brian_lemoff@xxxxxxxxxxx]
Sent: Tuesday, October 31, 2000 11:53 AM
To: stds-802-3-hssg@xxxxxxxx
Subject: RE: Question? 1300nm WWDM channel width

Eric,

Having surveyed the temperature dependence, not only of our lasers, but also
lasers from other vendors, a more reasonable number is 0.08 nm/degreeC,
rather then the 0.1 nm/degree number that you quoted.  In addition, with a 0
to 70 degree ambient temperature requirement, there is no reason why the
laser junction should see a 100 degree temperature range.  Of course this is
implementation dependent, but it is difficult to imagine much more than an
80 degree variation.  This would use up 6.4 nm of the 11.4 nm window,
leaving another 5 nm for tolerance.  Most laser vendors are comfortable with
a +/- 2.5 nm specification.

Best Regards,

Brian

***********************************************************************
Brian E. Lemoff, Ph.D.
Project Manager
LAN/MAN Optical Technologies
Agilent Laboratories
3500 Deer Creek Rd., MS 26M-9
Palo Alto, CA 94304-1392

phone:  (650) 485-8957
FAX:     (650) 485-3626
email:   brian_lemoff@xxxxxxxxxxx
***********************************************************************

> -----Original Message-----
> From: Eric Grann [mailto:grann@xxxxxxxxxxx]
> Sent: Tuesday, October 31, 2000 9:12 AM
> To: stds-802-3-hssg@xxxxxxxx
> Subject: Question? 1300nm WWDM channel width
>
>
>
> To all:
>
> I have been trying to get some feedback on the channel width
> of the 1300nm
> WWDM system.   As I currently understand the specifications,
> the bandwidth
> of an individual wavelength channel is 11.4nm (spec of *
> 5.7nm).  At these
> laser wavelengths, both DFBs and VCSELs have a temperature
> coefficient of
> 0.1nm/*C.  In order to achieve a final transceiver
> temperature specification
> of 0-70*C, the lasers must have a slightly higher temperature
> range.  To be
> safe, I would recommend a range of (-5) to 95*C.  With this range, the
> wavelength drift will account for 10nm of the channel
> bandwidth, leaving
> only 1.4nm for the tolerance of the laser fabrication.  The
> feedback I have
> received from several laser vendors is, this will be very difficult,
> resulting in low yields and increased costs for both DFBs and
> especially new
> 1300nm VCSELs.
>
> I would like to recommend that this specification be
> increased to at least
> 14nm (spec of * 7.0nm).  With a 24.5nm channel spacing, this
> will still
> provide plenty of room for a relatively simply filter.
>
> I would like to get some feedback and response to this recommendation.
>
> Eric Grann, Ph.D.
> Chief Technical Officer
> Blaze Network Products
>

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