01-11-2018, 04:45 PM
Yes sir Scott. Spent a fair amount of time at Norfolk myself working with the Navy. Ships and planes run on fiber these days and have done so for some time now. Not up to date on how its done today but OTDRs used to either map and calculate attenuation in a fiber and/or actually tell you where a fault (break) was located. Fault location was done, in my day, using TOF (time of flight) techniques as opposed to phase. TOF is pretty straight forward when not much resolution is required. Generate a nanosecond pulse, start the clock, log the pulse reflection back in and stop the clock. If you know the speed of light and the index of refraction of the fiber you can locate the fault +/- a meter or so. Light travels about a foot per nanosecond in air so if you want to get high res with TOF then somebody has to invent a cheap picosecond clock (maybe they have for all I know) or do an interminable amount of averaging. Differential phase gave us about 1mm at 100mhz. I'd be surprised if they don't do better than that today.