I assume you mean the speed of light in copper, or silicon instead of a vacuum? If so, may i warp your assumptions by the suggestion of using silicon photonics, and

[1] https://en.wikipedia.org/wiki/Photonic-crystal_fiber

theryby gaining 30% more speed?

Some article from 2013:

[2] https://www.extremetech.com/extreme/161687-darpa-creates-hol...

Some company from now:

[3] https://www.nktphotonics.com/lasers-fibers/product-category/...