> 3.33 us per km Signals in fiber do not travel at c. They travel at lightspeed in glass. Light speed in a material is c/(the refractive index of the material)

> 3.33 us per km Signals in fiber do not travel at c. They travel at lightspeed in glass. Light speed in a material is c/(the refractive index of the material). For commercial glass fiber, 1.5 is a reasonable estimate for it's refractive index. So the actual time for 1 km is ~5 us.