[time-nuts] 10 MHz over optical fiber?

[Bruce Griffiths]

w3kl at w3kl.com wrote:
> All:  Sorry for jumping in abruptly on this ongoing thread.  I have been meaning to chime in ever since the discussion got started.
>  
> I apologize in advance if I am dragging up an issue that has already been discussed and put to rest.
>  
> That being said, have you given consideration to the effects of chromatic dispersion in the fiber?
>  
> A good, telcom grade, dispersion shifted (designed for the 1550nm wavelength band, where absorption of the light by water is small), single mode fiber has a chromatic dispersion of approximately 1 to 10 ps/nm/km.  The concern therefore is changes in timing induced by changing wavelength content of the laser or LED used to drive the fiber - for example, due to temperature changes, etc.
>  
> If you've already considered this, then please ignore this.  Otherwise, it would be interesting to work through a "what if"?
>  
> jeff
>
> Jeffrey K. Okamitsu, PhD, MBA
> +1-609-638-5402
>
>   
Without compensation, the delay tempco of 34 km of fiber will be
somewhat more problematic unless the temperature of the entire run is
constant and/or expensive low delay tempco fiber is used.

Bruce