Why's the Fiber Industry so interested in Coherent Transponders?  According to Neal Bergano, it's the best way to increase capacity.  His paper examined the limits of coherent technology and what it can do for capacity.  Experiments he's done on Spectral Efficiency has produced real results.  The first generation of the system will increase capacity 10x.  In the future, he hopes to increase capacity further through new fiber structures with more linear fibers.