[time-nuts] Fw: Optical transfer of time and frequency

Michael Wouters michaeljwouters at gmail.com
Mon May 2 05:14:30 EDT 2016


One other possibility occurs to me that might be doable with surplus
gear and sticks to the  budget. Instead of using WR, give up on
getting time of day and just send a 1 kHz pulse stream in each
direction. Each station then measures against its own GPSDO clock
using a standard/homebrew TIC and records the difference. This is
ambiguous modulo 1 ms but this is trivially resolved using GPS. You
also probably know the distance between the stations to much better
than 1 ms = 300 km :-) . You then post-process but this can be done
with very little latency if you're keen.

Cheers
Michael

On Mon, May 2, 2016 at 1:44 AM, Tom Van Baak <tvb at leapsecond.com> wrote:
>> Has anybody experienced with free-space optical gigabit Ethernet
>> links? I am curious about whether the transceivers have a fixed
>> latency or at least a latency one can easily quantify online. This is
>> the trickiest part for adding WR support on top of a given physical
>> layer.
>
> Hi Javier,
>
> When searching this topic I ran across a commercial laser solution:
>
> http://www.laseroptronics.com/products.cfm/product/27-0-0.htm
> http://www.laseroptronics.com/index.cfm/id/57-66.htm
> http://www.laseroptronics.com/index.cfm/id/57-69.htm
> etc.
>
> But, according to /57-67.htm it "starts" at $15k per node. Plus there's the cost of all the WR pieces, assuming the two are even compatible. So this is vastly above the ~$2k budget mentioned by OP. I also assume OP is not ready to embark on a one-off, multi-man-year R&D project.
>
> This particular issue -- how to synchronize (or, at least phase compare) multiple oscillators by a two-way laser link over a few km to within 500 ps -- is really quite interesting. It would, for example, allow me to do live monitoring of 5071A Cs time dilation on my next mountain-valley relativity experiment.
>
> /tvb
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