How can the Trilogy frames be interconnected over fibre?

If the system is a Gemini, matrices can be connected over standards based IP,  you would need to convert the IP to fibre infrastructure but that is straightforward. The electric interface on Gemini is RJ45. This would give you at best 7.5 KHz audio using G722 with other codecs available if there is less bandwidth.
If you are extending the HSL (High Speed Link) which carries audio at full 20 Hz-20 KHz bandwidth but it is not IP.  It is delivered on a pair of RJ45s. Trilogy has a bespoke fibre interface to convert the HSL to single mode fibre.  If this fibre is then multiplexed distance is not an issue, if it isn't the maximum is 10 kilometers. You will also need the IP connection carried over the fibre for switching data etc.
If the matrix system is Mercury then it only has the IP connection for both data and audio delivered on an RJ45 as per the Gemini above.

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