I'm trying match the phase between different links(all the links has same devices with same parameters). As i know i have to place an exact same length of the fiber between all the links to perfectly match the phase between all the links. I'm unable perform exact calculations to match the phase to over wide bandwidth(around 10 MHz to 3000 MHz). I''m able to match at lower frequencies by cutting the fiber length approximately. Once i over but even by few mm length im going out of phase with the link. I need to have 6 degree phase difference between each link. Can some one give exact calculations to match the phase over wide band.?
Thanks
Surya
How long are your fibre links?
What fibre, and what optical wavelength are you using?
For Corning SMF 28e+ fibre, group refractive index is 1.4674 at 1310 nm, and 1.4679 at 1550 nm.
Group delay at 1550 nm is ng/c = 4.9 ns/m
6 degree phase difference at 3 GHz corresponds to a differential delay of 5.6 ps.
Length tolerance = Δt c / ng = 1.1 mm
If all fibres and all transmitters operate at the same wavelength, this is the accuracy you need to achieve.
Note that the refractive index of silica has a temperature coefficient of around 8.5·10-6 /K. https://arxiv.org/pdf/0805.0091, and a coefficient of linear expansion 0.5·10-6 K-1. http://www.kayelaby.npl.co.uk/general_physics/2_3/2_3_5.html
If your fibre length is L km, you will also need to control the temperature difference between fibres to better than 0.12/L °C. For 10 km fibre links, temperature tolerance is of order 0.01 °C.
Are you able to reduce the phase sensitivity of your radio over fibre application?
In addition to the previous comments, bearing in mind the length of the fiber links and the environmental factors, for fine tuning you can use commercially available devices.
See in the link:
https://www.ozoptics.com/ALLNEW_PDF/DTS0055.pdf
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