Minutes of the LArg Front-end Optical Links Meeting

Present :

M-L.Andrieux - ISN
B.Dinkespiler - CPPM
J.Lundquist - KTH
R.McLaren - CERN     
M.Pearce - KTH
P.Schwemling - Paris   
R.Stroynowski - SMU

MINUTES 

o Report from CPPM - B.Dinkespiler

  Copper link  status.  
  Bernard reminded   us that 10 FEB  -> mini-ROD
  cables   have already been  installed  including the flat conversion
  cables running to  the mini-ROD's.  In addition,  4  copper link VME
  boards (P2  connectors) have been   built and tested  and another 10
  have been ordered. Bernard reiterated the need for careful planning
  and infrastructure (cable trays) if more copper links were to be
  installed reliably.
  
  MUX board.  
  A MUX board has been built to allow the 32 bits from the
  FEB to be fed into the 16 bit G-link input. This board has been sent
  to  Al Gara (together  with  optics) to be  tested   with a FEB  and
  mini-ROD. Initial results are very  encouraging and have been useful
  in understanding noise problems in the FEB -> mini-ROD system.

  Multi-channel BERT (bit error rate tester).  
  Work is starting in earnest  on this project now
  with a  student involved at CPPM.  It  is hoped to   be able to have
  results in time for the LEB Rome workshop.
   	
o Report from ISN - M-L. Andrieux

  Orleans Neutron Irradiation  Facility.
  The facility will replace  the
  SARA  irradiation facility in   Grenoble. It is  located  outside of
  Paris.        Full        information              from            :
  isnwww.in2p3.fr/atlas/andrieux/CERI.html. The facility can accommodate
  both cryogenic and room temperature irradiations.
  
  Amphenol Project.
  Marie-Laure reported on  the status of the Amphenol
  project. Many  of the  previous  problems have  now been  solved and
  Amphenol were  expected  to present a   prototype working link  at a
  meeting in their laboratories on July 9th. A second meeting is planned
  with Amphenol on July 29th at which time they must have produced
  two complete demonstrator links which fulfill the original specifications.

  New  personnel.
  Marie-Laure announced that  there  was a new  engineer
  working at ISN  on  the link project. His   first task would   be to
  investigate   the possibility of  driving  VCSEL's directly from the
  G-link output - thus removing the need for a laser driver.
     
o Report from KTH - M.Pearce

  Report from the ROD meeting.
  A number of points raised during the ROD
  meeting  (7th July,  CERN) are  relevant to the  FE-links  group : 
  o Location of ROD's (USA-15 or  surface) 
      - Cost  input from link group (underway MP) 
      - Check if 300m transmission is OK  (SMU have fibre) 
  o Optical splitting is an elegant  solution to trigger tower remapping
  o ROD demonstrator board  will have 2  links per board (one link per
    FEB) 
  o Final boards may have as many as 4 Gb/s links per board

  Fibre installation document.
  In  collaboration with R.McLaren's group
  at CERN, a  document   is under preparation  detailing  installation
  issues  for  LArg optical  fibres   and connectors (including serial
  control links).   The difference in cost of  housing ROD's in USA-15
  or on the surface is covered. At present price  quotes come from one
  company (Europtics) but a world-wide price survey is being launched.

  Fujikura fibre.
  Mark reported  that  the  SCT group have  approached
  Fujikura for a quote on approx. 15  km of radiation hard fibre. This
  fibre has   shown   negligible  radiation-induced  attenuation  for
  2*10**14 n/cm**2  and 240 kGy  (LArg  requires 2*10**13 n/cm**2, 800
  Gy). The fibre  has a 50/60/125 structure (pure silica core, fluorine
  doping)  and is step  index. Mark
  explained that if  a combined order were to  be placed with  the SCT
  group a decision was needed within a month. There are several issues
  to address : 
  o How  much fibre ?  
  o Can we use the same  ribbonisation (ie: 12-way) as the SCT ?  
  o Can this step index  fibre be joined to graded index fibre  (ie: 
    radiation hard step index fibre used  in the crack  region and coupled 
    to cheaper graded index fibre which runs to USA-15) ?  
  o Can the step index fibre support 1.6 Gb/s, ie: dispersion issues ?
  Mark showed that simple calculations together with simple dispersion
  measurements performed by the SCT group made it look unlikely that a
  fibre length over 20  metres would support  1.6  Gb/s data flow.  In
  order  to proceed Mark suggested  that a demonstrator link be tested
  with  the step index fibre  (40 m in  Stockholm) and  step to graded
  index coupling be investigated.

  Laser  driver news.
  A replacement  (cheaper !) laser driver and VCSEL
  combination has been    made at   KTH  to   replace the   commercial
  transceiver units used to date. The circuit is  still under test and
  results will  be available in a  few weeks. The  laser driver uses a
  sub-micron BiCMOS process and its radiation hardness will need to be
  evaluated (total dose and SEE).
 
  Mitel News.
  Prototype VCSEL and PIN (4-way) arrays have been received
  from  Mitel. The devices are  based around the MT-ferrule. The PIN's
  are being evaluated  by the  Oxford SCT  group. The VCSEL's  will be
  tested electrically by Oxford  and  at Gb/s  speeds (with the  laser
  driver) by KTH.  Mitel are happy to accept input on future packaging
  ideas.

  Irradiation    facilities in Sweden.
  Mark  briefly  reported on two
  neutron  facilities  near to  Stockholm. One  is   based on a reactor
  source  and  the other on  an  ion beam  and target. Both facilities
  offer the possibility  of quick and easy  evaluation of devices such
  as the  laser  driver being developed  at KTH  and  will be  visited
  during August with a view to arranging access times etc.

  A  32  bit ATLAS   data  generator  (Presented by J.  Lundqvist). 
  Johan explained the current progress with using an Analog devices SHARC
  DSP to  generator 32 wide ATLAS data  words to be fed into Bernard's
  BERT.  The  device  could send  a pre-generated   list of data words
  stored in memory (32 K) but would need a faster DSP to realise truly
  pseudo-random word generation at 40 MHz.

o Report from SMU - R.Stroynowski

  Transceiver autopsies. 
  Richard summarised results from the dissection
  of   the Gb/s transceivers irradiated during  the  March neutron tests at
  SARA.  In all transceivers (Honeywell, HP, Methode) the  VCSEL's  survived 
  the total dose (10 yrs  LHC).  In the    Honeywell transceiver, the CMOS 
  driver   chips died.  The most  promising transceiver from  Methode  was 
  full  of a potting compound   which  proved   hard to   dissolve    for 
  further investigations.

  Alcoa-Fujikura fibre. 
  Richard  reported  that a  second  batch of the
  Alcoa-Fujikura  fibre had been  purchased.  This fibre is completely
  standard and meant for interconnects between Gb ethernet transceivers. 
  Previous tests 
  (http://www.cern.ch/Atlas/GROUPS/FRONTEND/links/minutes/may15_fibre.html)
  showed  that the fibre was  remarkably radiation tolerant. A further
  gamma test on this new batch has reproduced  earlier results. The same
  fibre   will also be neutron   irradiated  at SARA.  There was  some
  discussion over the results  and in particular  how to determine why
  the fibre was so radiation resistant even though it was not designed
  to be so.  In particular, it was suggested  that the dopants in  the
  fibre could be deduced using an appropriate spectrometry technique.

  Optical splitters. 
  Richard  showed samples of optical splitters  from
  various  manufacturers.    The   insertions losses    measured  were
  compatible with those  in the  data-sheets.  Tests of the  splitters
  within a  Gb/s  link were planned in   the near  future  (during the
  forthcoming SARA irradiation test of 15/16 July ?). As mentioned above
  optical splitters are an elegant and highly cost effective way of
  realising trigger tower remapping between FEB's and ROD's.

o A.O.B.

  Robert described a new type of low-profile connector called an MT-RJ
  which could be  useful  where a  fibre fibre density  is needed, ie:
  patch panels, ROD etc. (http://www.hp.com/HP-COMP/sff/)