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Re: [HSSG] Regarding presentation "Implementation Considerations" by Roger Merel


My comments regarding the article were not in any way meant to slight the researchers whose work was reported, or their work, or to disagree with any of Jack's (Cunningham's) quotes.  I know Jack Cunningham from way back and respect him greatly.  The work they report only adds to the technological feasibility of 12x10G VCSEL arrays.  I apologize for any possible misunderstanding.

My discussion regarding the status of 12x3G and the technical feasibility of 12x10G VCSEL arrays mostly comprises defensable facts, followed by a reasonably-stated opinion.  "Well on the way" indicates that key capabilities have been demonstrated, in this case: 10G VCSEL speed, significant commercial volume at 1x10G and 12x3G, reliability at 1x10G  and 12x3G, and operation at 12x10G.  Of course challenges remain, but not so fundamental as those already demonstrated.  Yield and reliability are sure to be concerns for any multi-laser approach, especially if very high performance is required.   

You'll be hard-pressed to get any VCSEL vendors (or any other vendors!) to divulge the technical details of their recipes.  Instead I'll address concerns about array reliability and yield in a general and nonproprietary way.  Unless VCSELs are explicitly mentioned, these properties apply to ANY array of lasers, e.g. DFBs, FPs or VCSELs.  WEAROUT RELIABILITY: The wearout lifetime of a 12x array is usually NOT 12x shorter than that of a singlet.  It is only about 2x shorter in VCSEL experiments reported by both Infineon and AOC.  The fact that array wearout lifetime is shorter at all (for any array) is only due to variation among the elements.  If all elements aged identically, the wearout lifetime for a 12x array would be identical to that of a singlet.  Better uniformity results in better array lifetimes.  NON-WEAROUT RELIABILITY: Worst-possible-case early-failure rate is 12x higher for a 12x array compared to a singlet.  But again, the array penalty is often lessened by the!
  nature of the root cause.  For example, ESD is one culprit for early, non-wearout, failure.  If an ESD event kills a laser array for a multi-laser product (parallel or WDM), the effect is the same as if it kills a singlet in a serial product: it kills one module.  In this case there is no "array penalty," assuming the array is equally susceptible to ESD as the singlet.  VCSEL early-failure rates are already extremely low. [Any numbers here would lead down a rathole of definitions, conditions, exclusions, qualifications, etc.]  YIELD: Array yield behaves similarly to wearout reliability.  The better the uniformity, the closer the array yield approaches the singlet yield.

Since nearly all concepts discussed at HSSG involve multiple-laser sources of one kind or another, I hope the above is generally useful.



-----Original Message-----
From: Roger Merel [mailto:roger@xxxxxxxxxxx] 
Sent: Tuesday, September 26, 2006 9:05 AM
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [HSSG] Regarding presentation "Implementation Considerations" by Roger Merel

John (goes by "Jack") Cunningham is well versed in VCSELs.  The article is rather short and doesn't say very much.  They are specifically working on approaches for higher speed VCSELs.  So I'm sure the "experimental" is in the higher speeds.

Jack Jewell below would suggest that single VCSEL products at 10G + arrays products at 2.5/3.125G, and a demonstration with IBM in 2003 are together proof that 12x arrays at 10G not challenging... but by doing so in such a way specifically raises the exact red flags we are all concerned about... both yield and reliability for VCSELs scale inversely with direct modulation speed (tied in part to current density)... such that unless there is some new design and new material incorporated (rather than just improved manufacturing process control), one would have to be suspect that (10x or) 12x10G VCSEL arrays are and will continue to be "challenging".

With that all said, I am NOT suggesting that a 10x or 12x VCSELs should be precluded from a possible HS-Ethernet PMD.  HS-Ethernet is going to be challenging all-around.  The VCSEL array solutions are a viable avenue for some of the shorter distance applications.

It would be beneficial if Jack or other VCSEL vendors would explain what has changed in the technical basis of VCSELs to ameliorate the yield and reliability concerns especially tied to modulation rate and current density.  This could provide the SG with comfort for moving from Demos to Standards for (10x or) 12x 10G VCSELs.


-----Original Message-----
From: Jack Jewell [mailto:Jack.Jewell@xxxxxxxxxxxxx]
Sent: Tuesday, September 26, 2006 7:19 AM
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [HSSG] Regarding presentation "Implementation Considerations" by Roger Merel

The tone of the article misleadingly suggests that the implementation of VCSEL arrays is "still at rather experimental stage."  Suffice it to say that there are well over 100,000 12-channel parallel VCSEL-array link products operating in the field at present.  Significant volumes began several years ago and keep rising.  Manufacturers and users of these parallel optical interconnections are represented at 802.3 and the present HSSG.  There is no need to discuss the technological details of monitoring (the subject of the article) here; it is handled by various means.  The parallel optical interconnect products have undergone rigorous qualification by customers with the highest standards of quality and reliability.  VCSEL-array based parallel links are real, and this email is surely traveling through some of them.

The present links typically operate at a lane rate (channel rate) of 2.7-3.3Gbps.  Customer-driven initiatives are already underway to increase the lane rate to 10Gbps.  IBM (with Picolight) demonstrated a 12x10Gbps link operating over 300m of MMF at OFC 2003.  It used "SNAP-12" modules, i.e. the same modules used today.  Since then, 10Gbps VCSEL technology has matured significantly, driven by 10GBASE-SR sales.

Parallel optical links using VCSEL arrays, detector arrays, and MM parallel fibers are well on the way to showing "technically feasible" at speeds up to 120Gbps.


-----Original Message-----
From: Hajduczenia, Marek [mailto:marek.hajduczenia@xxxxxxxxxxx]
Sent: Tuesday, September 26, 2006 2:36 AM
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: [HSSG] Regarding presentation "Implementation Considerations" by Roger Merel

Dear all,
If I recall it correctly, Roger expressed his concerns for the wavelength selection plan on slide number 8 of his presentation and pointed out that most likely the VCSEL arrays with 10 or more integrated sources can be technologically challenging. I would only like to point out that perhaps we should investigate his proposal to use integrated VCSEL arrays operating at 10+ Gbit/s -> here is why: The arrays seems to be still at rather experimental stage though this is not the first piece of evidence that such devices can be achieved and may be a much cheaper solution than standard WDM systems ... 
Looking forward to receiving any feedback ...
Best wishes

Marek Hajduczenia
Rua Irmãos Siemens, 1
Ed. 1, Piso 1
2720-093 Amadora
* Marek.Hajduczenia@xxxxxxxxxxx
*+351.21.416.7472  *+351.21.424.2082


-----Original Message-----
From: Andy Moorwood [mailto:amoorwood@xxxxxxxxxxxxxxxxxxx]
Sent: segunda-feira, 25 de Setembro de 2006 18:36
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: [HSSG] Reach Ad Hoc, call for participation and conference call announce ment

Dear HSSG Members,
thank you to those who have already replied with their intent to join this activity, let me echo John's request for participation.  I want to schedule a conference call for Thursday October 5th at 11 am to 12:30 Pacific with the following objectives:
1. Identify what media and reach information is already available to the group for the nominated applications: "HPCC, Data Center, Metro, others"
2. Identify what media reach questions are of particular interest to the group.  For example, the 10 gigabit LR specification has a link budget capable of supporting a reach of 10km in many installations. Are end users actually using this budget? considerably less ? or they could use more ?
3. Define a schedule for future conference calls To facilitate data sharing/viewing  at the meeting we need to use some kind of collaborative environment in addition to voice conferencing.  Extreme uses "Conference Place" by Intercall and I will host this kick off meeting (If other members care to donate resources for future meetings this would be appreciated).  Live data sharing does however impose some restrictions in that a member needs to be invited to the meeting place.  
Consequently I need a minimum of 24 hours notice prior to the meeting if a member intends to participate.
If  a member wants to present at the meeting I need a minimum of 48 hours notice  and the slides (PDF or PPT) format Any requests not meeting these timelines will be supported on a best efforts basis.  If it is possible to support audio only participation on a "drop in basis" I will forward this to the reflector just prior to the meeting.
Thanks for your support !