Actually it has already been discussed in some pretty good detail on this forum. As I recall there was even a really good demonstration video showing the test setup that was posted here. It is an impressive effort to say the least by academics on a shoestring budget. As it says it is silicon photonics. The laser is external with a rather leaky optical connection where the chip is shaved for optical connection on one side with bump bonds on the other side for flip chip. Some older tech whispering gallery modulator in silicon with transimpedance amplifier and heater circuit along with enough transistors to perform modulation and error control. You might be able to find some of the discussions from this forum going back two years ago.