question about fiber and distances

[azev]

What is the maximum distances of a long haul single mode fiber without repeater ?

Did they use some sort of repeater to lay fiber across the ocean where the distance is well over thousands or miles ?

 

[spidey07]

Depends on what you're using it for. But distances from 50-100 km are common.

I believe optical amplifiers are used much more often than repeaters these days.

 

[azev]

how about one from oregon to hawaii for example... the distance is around 3000Miles. There has to be some equipment in between to amplify the light. If there is, what kind of equipment, and how did they get power in the middle of an ocean like that ??
I've always been curious on how did they do this ?

 

[jlazzaro]

they just put a device within the transmission path of the fiber. the most efficient fiber amplifiers are Erbium-Doped Fiber Amplifiers that operate in the 1550nm range...

the amplifier itself emits light energy in a signal wavelength (usually about 1540nm) using energy supplied to it by photons in a pump wavelength (usually 980nm) when stimulated by incoming photons in the signal - the signal which needs amplification. Just like in a laser, the emitted photons then stimulate other emissions, so there is an exponential growth of photons. Supporting the amplifier is a pump laser, which supplies the amplifier's energy, a coupler, which combines the pump laser beams and the signal laser beam and puts them on a single fiber, and an optical filter, which removes the remaining traces of the pump beam so that it doesn't interfere with reception of the signal.

amplifier diagram

source: http://www.thefoa.org/tech/fiberamp.htm

 

[azev]

so these Erbium-Doped Fiber Amplifiers doesnt require any other external power supply to do what its doing? Impressive.

Does anyone have any picture of the device ?

 

[jlazzaro]

google image search "EDFA". they look to just be a square device with 2 fiber ports and other misc buttons/switches.