Years ago when I was learning the basics of fiber-optic transmission we applied a laser to each end of the 1 mile long spool, at the same frequency, and measured the output of the ends. There was a drop of about 67% of the optical power. When a single laser was used it emitted 94% of the input optical power.
When we used a higher transmission power on one end, the lower transmission power dropped by 83% while the higher power dropped by 51%. using 1.3 and 1.9 lasers (offset wave lengths) resulted in the same losses. (the experiment was deigned to show that bi-directional communications in fiber will not function)
Either the photons collided and caused scattering attenuation or there is still a very low understanding of photon energy process. Given that the QAM transmission was totally destroyed, for either end, its a good bet that it is a collision related event.
QM theory shown extremely questionable by observable experiment. Even if all matter radiates in all directions the temperature (power-output) of the matter, matters. The energy of a colder object reaching the other hotter object is also very questionable.
Photons don't interact with each other. Photons do interact with matter.
Fiber optics do constrain light by internal reflection, although not perfectly. There is obviously a chance that two photons hitting the fiber optic matter simultaneously will result in a different outcome than simple reflection.
Someone here posted up an interesting experiment showing two laser beams coming off a surface as one reasonably coherent stream of light that was a different colour than the original two lasers.
Weird stuff happens when you play with light, so what? General principles are seldom seen in reality without confounding factors obscuring them..