Not OP, so I'm guessing purely on my knowledge of how most of the industry works, but there's likely some sort of FPGA with custom IP at the center, connected to a powerful optical transmitter/receiver.

Associated reading can be found here: https://www.esa.int/Enabling_Support/Space_Engineering_Techn...

https://ntrs.nasa.gov/api/citations/20150009433/downloads/20...

https://www.fierceelectronics.com/electronics/fpga-enables-h...

The main paper seems to be behind a paywall (rolleyes), but I did find this synopsis that covers the basic approach and hardware: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=4...

It sounds like this test payload was part of a larger CubeSet built by NASA, but the actual datacom components seem pretty much off the shelf (besides the optics). 100Gbps transceivers, an optical mux, and an EDFA - all common in terrestrial telecom - and some IR optics to collimate the beam.