Could you do this with fibers that are also in use for communications? It makes sense that if you tune your transmitter/receiver to squeeze absolutely as much

Could you do this with fibers that are also in use for communications? It makes sense that if you tune your transmitter/receiver to squeeze absolutely as much data as you can through a fiber, the results will be very sensitive to the conditions along that fiber. So, monitoring the error rate should give you precise information about the fiber's characteristics.