Fault locator for long haul transmission system

1. A system comprising:

a first device to:

generate a first optical signal at a first wavelength,

generate a second optical signal at a second wavelength,

combine the first optical signal and the second optical signal to form a first combined signal, and

transmit the first combined signal on a first fiber optic link in a first direction; and

a second device to:

receive, from the first device, the first combined signal,

extract, from the first combined signal, the first optical signal at the first wavelength and the second optical signal at the second wavelength,

transmit the extracted first optical signal toward a target,

receive a reflection of the transmitted first optical signal, from the target, as a reflected first optical signal,

combine the reflected first optical signal and the extracted second optical signal to form a second combined signal, and

transmit the second combined signal to the first device, on a second fiber optic link in a second direction opposite the first direction,

where the first device is further to:

receive, from the second device, the second combined signal; and

split the second combined signal to separate the reflected first optical signal at the first wavelength and the second optical signal at the second wavelength,

where the first device and the second device operate in a fiber optic network that includes multiple optical amplifiers along the first fiber optic link and the second fiber optic link, and

where the second optical signal prevents automatic laser shutdown of at least one of the multiple optical amplifiers.

2. The system of claim 1 , where the target is a fault in a fiber optic link in the fiber optic network.

3. The system of claim 2 , where first device is further to determine a location of the fault based on the reflected first optical signal.

4. The system of claim 1 , where the second device includes an optical circulator for transmitting the first optical signal and the reflected first optical signal.

5. The system of claim 1 , where the second device includes a power coupler for transmitting the first optical signal and the reflected first optical signal.

6. The system of claim 1 , where the second device includes a wavelength coupler and a wavelength decoupler for combining and splitting at least one of:

the first optical signal and the second optical signal; or

the reflected first optical signal and the second optical signal.

7. A method comprising:

generating an optical signal;

transmitting the optical signal on a first fiber path in a first direction through at least one optical amplifier;

receiving a reflection of the optical signal on the first fiber path in a second direction opposite the first direction;

transmitting the reflected optical signal on a second fiber path in the second direction, where the second fiber path differs from the first fiber path;

transmitting a second optical signal, where the second optical signal is transmitted on either:

the first fiber path in the first direction through the at least one optical amplifier, or

the second fiber path in the second direction through the at least one optical amplifier,

where the second optical signal prevents an automatic laser shutdown of the at least one optical amplifier; and

determining a location of a fault on the first fiber path based on the reflected optical signal.

8. A method comprising:

generating an optical signal;

transmitting the optical signal on a first fiber path in a first direction through at least one optical amplifier;

receiving a reflection of the optical signal on the first fiber path in a second direction opposite the first direction;

transmitting the reflected optical signal on a second fiber path in the second direction, where the second fiber path differs from the first fiber path;

generating a second optical signal;

transmitting the second optical signal on the second fiber path in the second direction through the at least one other optical amplifier;

switching the second optical signal to the first fiber path in the second direction;

receiving a reflection of the second optical signal on the first fiber path in the first direction;

transmitting the reflected second optical signal on the first fiber path in the first direction; and

determining a location of a fault on the first fiber path based on the reflected optical signal and the reflected second optical signal.

9. The method of claim 8 , where the reflected first optical signal is transmitted one the second fiber path by an optical circulator.

10. The method of claim 8 , where the reflected first optical signal is transmitted on the second fiber path by a power coupler.

11. The method of claim 8 , further comprising:

combining at least one of the first optical signal and the second optical signal, or the reflected first optical signal and the reflected second optical signal, to form a combined signal;

amplifying the combined signal; and

splitting the amplified combined signal to form at least one of:

an amplified first optical signal and an amplified second optical signal, or

an amplified reflected first optical signal and an amplified second optical signal.

12. A system comprising:

a fiber network including a first fiber path and a second fiber path, where the first fiber path includes at least one first amplifier, and where the second-fiber path includes at least one second amplifier;

means for generating an optical signal;

means for transmitting the optical signal on the first fiber path in a first direction through the at least one first amplifier;

means for receiving, from the first fiber path in a second direction opposite the first direction, a reflection of the optical signal through the at least one second amplifier;

means for transmitting the reflection of the optical signal along the second fiber path in the second direction;

means for generating a second optical signal;

means for transmitting the second signal on the second fiber path in the second direction through the at least one second amplifier,

where the second optical signal prevents an automatic laser shutdown of the at least one first amplifier or the at least one second amplifier; and

means for determining a location of a fault on the first fiber path based on the reflected optical signal.

13. The system of claim 12 , further comprising:

means for switching the second optical signal from the first fiber path in the first direction to the second fiber path in the second direction.

14. The system of claim 12 , where the means for generating the second optical signal includes a laser.

15. The system of claim 12 , where the means for transmitting the reflection of the optical signal include at least one of:

an optical circulator, or

a power coupler.

16. The system of claim 12 , further comprising:

means for forming a combined signal by combining at least one of:

the first optical signal and the second optical signal; or

the reflection of first optical signal and the second optical signal; and

means for receiving the combined signal and splitting the combined signal to obtain at least one of:

the first optical signal and the second optical signal, or

the reflection of first optical signal and the second optical signal.

17. A system comprising:

means for generating an optical signal associated with a fiber network that includes a first fiber path and a second fiber path, where the first fiber path includes at least one first amplifier, and where the second-fiber path includes at least one second amplifier;

means for transmitting the optical signal on the first fiber path in a first direction through the at least one first amplifier;

means for receiving, from the first fiber path in a second direction opposite the first direction, a reflection of the optical signal through the at least one second amplifier;

means for transmitting the reflection of the optical signal along the second fiber path in the second direction;

means for generating a second optical signal;

means for transmitting the second optical signal on the second fiber path in the second direction;

means for switching the second optical signal from the second fiber path, in the second direction, to the first fiber path in the second direction;

means for transmitting a reflection of the second optical signal on the first fiber path in the first direction; and

means for determining the location of a fault on the first fiber path based on the reflected optical signal and the reflected second optical domain reflectrometry signal.

18. The system of claim 17 , further comprising:

means for switching the second optical signal from the first fiber path in the first direction to the second fiber path in the second direction.

19. The system of claim 17 , where:

the means for generating the first optical signal includes a first laser,

the means for generating the second optical signal includes a second laser, and

where the first laser and the second laser generate the first optical signal and the second optical signals at respective different wavelengths.

20. The system of claim 17 , where the means for transmitting the reflection of the optical signal includes at least one of:

an optical circulator, or

a power coupler.