While not an integrated system itself, looking for convenient information on the matter I stumbled upon https://arxiv.org/abs/2011.05313 . As for integrated electro-optical hardware that does coherent optics, I'd like to point at SFP optics; the ones that are sufficiently non-fancy with their electronics (up to 10km single-mode optics; no high-end-multimode optics; no exotic coherent optics) should not have a retimer on the RX side. Once you go to 1-Gbit/s transceivers you'll find ones with a linear RX stage; those should be suitable for rigging simple homodyne interferometry by just feeding a little TX back to the RX taking care to let the RX AGC run the RX path at high gain.