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Re: [802.3BA] Discussion on 40G for => 10 km SMF



TF members,

I'm Kazuyuki Mori, Fujitsu Labs. I support 40G Serial and I basically agree with Takai-san regarding below points.

(1) Cost
My understanding is that, generally speaking, the final cost target for 40G optical transceiver should be 2 -3 times of 10G transceivers. In order to achieve this target , I again and again discussed the cost reduction approaches with TOSA/ROSA suppliers, IC suppliers, optical module suppliers and our laboratory experts. In case of CWDM, I haven't found any technical solution to achieve this target (<x4 cost of 10G transceiver), and there has been no presentations in IEEE to show this cost reduction approaches until now. On the other hand, 40G serial is feasible to achieve this target as shown in traverso_02_0708. I wonder that 40G transceiver cost will remain more than 4 times of 10G in future if once CWDM solution is authorized.

(2) Size
I think the size reduction is another big challenging target in CWDM as Chris already agreed in recent dialogues. Some people say that monolithic DFB array enables high density package solution, but CWDM option is almost impossible to be realized because the same active layer of LD cannot be applied. Also the hybrid integration using PLC with an integrated AWG MUX is sometimes picked up, but it is quite challenging due to high insertion loss of AWG caused by intrinsic Gaussian profile, and also due to AWG temperature dependence. In my perspective as a researcher, optical integration approach in 40G CWDM has some intrinsic problems and leads the cost increase. Please remember that this isn't the case of Vcsel array, but the case of DFBs and also with optical mux.

(3) Power
Steve pointed out that '40G SerDes are very power hungry', but this is not correct. Current SerDes is for 16:1 and 1:16, however 4:1 and 1:4 SerDes should be asuumed in We need to compare using 4:1 and 1:4 SerDes. In our estimation, 2W is possible by deleting unnecessary circuits from today's SerDes even when SiGe was used.

Kazuyuki Mori




----- Original Message ----- From: "Atsushi Takai" <atsushi.takai@xxxxxxxxxx>
To: <STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx>
Sent: Sunday, August 03, 2008 12:34 PM
Subject: Re: [802.3BA] Discussion on 40G for => 10 km SMF


Jeff

I do not know your background.
However I found, in your comment below, you misunderstood the optical
transmission technologies.
I do not want to argue line by line.

Just I would like to point one sentence:
"The biggest downside of 40G serial, seems to be the physics problem of
PMD.".
This is not true for 10km SMF.
The 40Gbit/s PMD was a technical challenge in several years ago but now it
is not downside.
Even, we are discussing 1310-nm devices while current module includes
1550-nm devices.
(We can neglect dispersion issue in case of 1310nm transmission)

The biggest cost in current serial module is silicon chip that is much more
volume sensitive.
I hope you know the accumulative shipment of 40Gbt/s client module is around
10K peaces or such range.
However IEEE confirmed market of 40GbE 10km serial enough for
standardization, you can expect much lower cost with higher volume.

Also investment for 40Gbit/s transmission networks started these years, thus
industry started invest for 40Gbit/s technologies.
You will find much activity in the industry.

All

I am very concerning during the meeting and e-mail discussion,
many of members may misunderstand the 40Gbit serial technology status and
activity in the industry,
and understand only the surface.
We, who has technology especially optical device technology, should be
responsible to let people understand the technology.
I will think about it.

=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=
Atsushi Takai
=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=
----- Original Message ----- From: "Jeff Meyer" <jmeyer@xxxxxxxxx>
To: <STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx>
Sent: Sunday, August 03, 2008 2:33 AM
Subject: Re: [802.3BA] Discussion on 40G for => 10 km SMF


Chris has a excellent point about

   _Other Aspects_

   It is no longer possible to simply increase Baud to match data rate,
   because of fundamental electrical and optical propagation limits.
   This was recognized during the 100G SMF PMD discussion, with Serial
   never a viable alternative for the 10km or 40km reach. In the
   future, all data rates beyond 100G will use some form of multi-lane
   technology. 40G is the inflection point where cost and difficulty of
   Serial rises dramatically compared to multi-lane alternatives.
   Optical communication has reached the point that all other forms of
   communication (wired or wireless) reached many years ago, where
   simple modulation format serial solutions are not practical.


The biggest downside of 40G serial, seems to be the physics problem of
PMD. However there are an increasing number of long haul equipment
providers who have solved this problem. There have been thousands of 40G
serial long haul installations deployed to date.

As far as the Cost, Power, Size & Reliability I think this favors
serial. The cost saving of CWDM seems largely driven by the large number
of vendors providing 10G IC's and components. But let us ponder, if the
10GE fathers chose 4x 2.5G WDM to reduce risk in the late 1990's would
we be benefiting from the low costs and the large number of vendors? All
we need is multiple vendors of 40G serial components and the prices will
plummet. Lets face it the cost of SiGe is not that much higher than CMOS
unless you get to volumes greater than 100,000 parts. By then, CMOS
processes will catch up to SiGe in FT. I am a microwave guy and the 40G
packaging is not difficult these days ( there are many vendors that can
do LTCC fine line packages and they are "Open Tooled" so you can get a
reference design for the 40G electrical packages for no NRE ). If we
compare microwave packaging to flip chip mounting of lasers and optics,
I would imagine optics costs more, but I have no "hard data" to support
this.

The biggest reason why I favor serial over CWDM is the leadership for
the future. Lets take the risk like the 10G serial innovators did in the
late 90's. Once we get several manufacturers of 40G parts this prices
will plummet.

Schedule Risk. Albeit the risk for serial is higher but how much?

Let's keep technology moving forward for the future generations.



Jeff Meyer



Chris Cole wrote:

Takai-san痴 7/31/08 email discusses a number of points. Our arguments
concerning his first two points (Cost and Time to Market) are
unchanged from cole_04_0708, so are not repeated here. The remaining
points are addressed below.

_Power_

The long term power consumption of 40GE CWDM and 40GE Serial is
similar. Four 10G un-cooled DFBs and associated Laser Drivers use
about the same power as one cooled 40G EML and associated Modulator
Driver. The remaining ICs are also about the same if advanced process
nodes and new designs are assumed. As was pointed out by Joel Goergen
during the Q&A session in Denver, a 40GE Serial block diagram has
comparable circuitry to 40GE CWDM block diagram when drawn fairly to
permit apples to apples comparison.

There is no basis for a claim at this late stage in the debate that
Serial has a power advantage over CWDM, and that CWDM 菟ower reduction
plans are invisible.・In jewell_03_0508, p.9 and again in
traverso_02_0708 p. 12, ratios of power between an aggressive Serial
implementation and CWDM implementation are 0.96 and 0.97, i.e. clear
statements in pro-serial presentations that there is no advantage.

_Size_

For future generation products, CWDM has an advantage over Serial for
fitting into a smaller form factor like QSFP because similar to a
10GE-LR SFP+, the re-timing CDRs can be moved outside of the module.
Serial always has to have the 4:1 SerDes function in the module. Even
with aggressive projections about future component size and power,
Serial has a packaging and thermal management design challenge to fit
into QSFP.

What is required to fit 40GE CWDM into QSFP is optics integration.
This type of technology has been described in numerous presentations
to the HSSG and involves flip-chipping lasers onto a PLC with an
integrated AWG Mux. The CWDM grid prevents use of a monolithic DFB
array and requires flip-chipping discrete DFBs, but that is a yield
and cost issue not a feasibility or size issue. The time line for such
an advanced development program is lengthy, but is similar to
realistic PCB RF-interconnect 40GE Serial development schedules. The
investment required to bring this advanced technology to market is
high, again similar to one required for low cost 40GE Serial.

In contrast, no advanced technology development is required to quickly
bring to market first generation low cost CWDM products based on
discrete optics packaged in a larger form factor.

_Reliability_

There is no current 1310nm 10G DFB failure data that justifies
bringing up concerns about the reliability of a 4x10G CWDM PMD. 10G
1310nm PMDs ship in volume today with very high reliability. If there
is actual field failure data behind this concern, it would add
credibility to have it presented.

_Other Aspects_

It is no longer possible to simply increase Baud to match data rate,
because of fundamental electrical and optical propagation limits. This
was recognized during the 100G SMF PMD discussion, with Serial never a
viable alternative for the 10km or 40km reach. In the future, all data
rates beyond 100G will use some form of multi-lane technology. 40G is
the inflection point where cost and difficulty of Serial rises
dramatically compared to multi-lane alternatives. Optical
communication has reached the point that all other forms of
communication (wired or wireless) reached many years ago, where simple
modulation format serial solutions are not practical.

Chris