The free-space implementation of White Rabbit remains to be done.
If you can modulate optical GE over your optical links, then it should
work out fairly well.
Actually, if you get that working, I'm sure they would enjoy seeing a
paper on that in EFTF.
Cheers,
Magnus
On 04/30/2016 08:06 AM, Bruce Griffiths wrote:
White Rabbit would be good in that a suitable TDC design with 1ns resolution
already exists for White Rabbit. This TDC is used in the Tunka valley (near
lake Baikal) Siberian Cherenkov telescope array. Note this TDC uses the SERDES
receiver in the FPGA to implement a serial to parallel converter with a 1GHz
clock synthesised from the 125MHz White Rabbit clock.
So far I haven't found an existing free space optical implementation of White
Rabbit.
Bruce
On Saturday, 30 April 2016 11:00 AM, Michael Wouters
<michaeljwout...@gmail.com> wrote:
So why not do White Rabbit free space ?
Cheers
Michael
On Sat, Apr 30, 2016 at 4:04 AM, Paul Boven <p.bo...@xs4all.nl> wrote:
Hi everyone,
On 04/29/2016 03:28 PM, Magnus Danielson wrote:
Phase/time transfer over fiber is shaping up, but White Rabbit is
starting to grow up and more reports for long distances is showing up.
ETFT is one of the placces to check for reports.
And the White Rabbit workshops, with the presentations online:
http://www.ohwr.org/projects/white-rabbit/wiki/Mar2016Meeting
I happen to be working on time transfer via White Rabbit. The White Rabbit
standard proscribes the use of 1000Base-Bx10 (10km reach bi-directional)
SFPs, but it turns out to work just fine with longer reach SFPs. However,
there are several effects that limit the accuracy that you can get on longer
links:
* Dispersion of the fiber (as the lasers change temperature, their
wavelength changes, and they experience a slightly different index of
refraction, hence propagation speed.
* Change in index of refraction in the fiber itself. The propagation speed
of both the uplink and downlink wavelength change, in absolute sense but
also their ratio changes. This is something the WR protocol can't
detect/correct for.
There are several people working on these issues, trying to improve both the
calibration and stability even further.
Regards, Paul Boven.
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