Copper plates can help dissipate heat by dispersing it towards the bottom of PCBs. This isn't 100% effective, as there are still hot spots to contend with. Very thin vapor chambers sandwiched between two c.
Co-packaged optics is an up-and-coming technology that addresses these challenges created by small form factor pluggable optical transceivers. With it, you can bring optics as close as possible to the s.