Failure detection method integrated in optical amplifiers and remote optical transmitters for radio frequency on glass (RFOG) and distributed access architecture (DAA) cable television (CATV) networks

1 . An optical communication fiber link, comprising:

a monitoring system connected to an optical fiber communicating a signal, the monitoring system:

detecting a scattering of the signal from the optical fiber and detecting reference data from the signal, each separately provided from the optical fiber to the monitoring system;

monitoring the scattering for a change using a comparison to the reference data; and

determining, from the change, an absence or a presence of a fault in the optical fiber.

2 . The optical communication fiber link of claim 1 , wherein the monitoring system determines a temperature of the optical fiber from the scattering.

3 . The optical communication fiber link of claim 1 , wherein the monitoring system includes at least one of a circuit or a computer determining the absence or the presence of the fault by comparing the scattering to the reference data.

4 . The optical communication fiber link of claim 3 , wherein the reference data comprises at least one of:

an optical power of the signal transmitted by the optical fiber, or

a measurement of a backscattered optical power as a function of a distance along the optical fiber.

5 . The optical communication fiber link of claim 1 , wherein the monitoring system detects the scattering comprising noise and the monitoring system includes a computer or circuit executing a Kalman filter estimating an actual value for the scattering from the noise.

6 . The optical communication fiber link of claim 1 , wherein:

the optical communication fiber link includes:

a transmitter;

an amplifier; and

a receiver; wherein:

the optical fiber comprises a first segment transmitting the signal from the transmitter to the amplifier and a second segment transmitting the signal from the amplifier to the receiver, wherein the amplifier amplifies an intensity of the signal; and

the monitoring system includes a photodetector positioned to detect the scattering comprising a backscattering of the signal from one or more predetermined locations in the second segment or the first segment.

7 . The optical communication fiber link of claim 6 , wherein the transmitter further comprises:

a laser outputting the signal; and

a modulator modulating the laser such that the laser outputs the signal comprising a pilot signal and a communication distinct from the pilot signal, wherein the monitoring system detects the backscattering by demodulating the pilot signal from the backscattering.

8 . The optical communication fiber link of claim 7 , wherein the monitoring system further comprises:

a first photodetector positioned to detect the signal after an output from at least one of the transmitter or the amplifier and output a reference signal in response thereto;

the photodetector comprising a second photodetector positioned to detect the backscattering from the one or more predetermined locations and output a backscattering signal in response thereto;

a computer or circuit comparing the reference signal and the backscattering signal so as to determine the absence or the presence of the fault.

9 . The optical communication fiber link of claim 7 , wherein the monitoring system further comprises:

a first photodetector positioned to detect the signal after an output from at least one of the transmitter or the amplifier and output a reference signal in response thereto;

the photodetector comprising a second photodetector positioned to detect the backscattering from the one or more predetermined locations and output a backscattering signal in response thereto;

first circuitry determining, from the reference signal, at least one of a reference amplitude or a reference phase of the pilot signal in the reference signal;

second circuitry determining, from the backscattering signal, at least one of a backscattering amplitude or a backscattering phase of the pilot signal in the backscattering;

a computer or circuit determining the presence or absence of the fault using the reference phase, the reference amplitude, the backscattering phase, and the backscattering amplitude.

10 . The optical communication fiber link of claim 9 , wherein:

the pilot signal comprises a low frequency pilot tone;

the first circuitry comprises a first low pass filter extracting a first band of frequencies including the pilot tone, a first signal conditioner conditioning the first band of frequencies to form a first conditioned band of frequencies, and a de-modulator de-modulating the first conditioned band of frequencies to obtain the reference phase and the reference amplitude of the pilot signal; and

the second circuitry comprises a second low pass filter extracting a second band of frequencies including the pilot tone, a second signal conditioner conditioning the second band of frequencies to form a second conditioned band of frequencies, and the de-modulator de-modulating the second conditioned band of frequencies to obtain the backscattering phase and backscattering amplitude of the pilot signal.

11 . The optical communication fiber link of claim 10 , wherein the first photodetector, the second photodetector, the first circuitry, and the second circuitry are integrated with the transmitter or the amplifier.

12 . The optical communication fiber link of claim 10 , wherein:

the backscattering phase and backscattering amplitude comprise noise,

the computer or circuit executes a Kalman filter estimating, from the noise, actual values for the backscattering phase and the backscattering amplitude; and

the computer or circuit estimates the presence or absence of the fault by comparing the actual values estimated by the Kalman filter with reference data.

13 . The optical communication fiber link of claim 12 , wherein:

the reference data comprises:

a backscattering optical power as a function of a distance along the optical fiber;

transmitted power of the signal; and

the computer or circuit estimates a location of the fault as the distance associated with the actual value of the backscattering amplitude estimated by the Kalman filter taking into account the transmitted power of the signal.

14 . The optical communication fiber link of claim 12 , wherein the reference data includes a transmitted optical power of the signal and a distance to the fault is determined by correlating the actual value of the backscattering amplitude with the transmitted output power.

15 . The optical communication fiber link of claim 14 , further comprising a remote node including the monitoring system and at least one of the transmitter or the amplifier.

16 . The optical communication fiber link of claim 15 , wherein the transmitter comprises an analog transmitter.

17 . The optical communication fiber link of claim 1 , wherein the monitoring system further includes a telemetry interface transmitting, via telemetry, at least one of the scattering or a fault signal associated with the absence or the presence of a fault.

18 . The optical communication fiber link of claim 1 coupled to a cable television network, wherein the signal comprises one or more television signals used to view television.

19 . A method for on-line monitoring of an optical communication fiber link, comprising:

detecting a scattering of a signal and reference data in the signal from an optical fiber;

separating the scattering of the signal from the reference data; and

determining an absence or a presence of a fault in the optical fiber based upon a comparison of the reference data to the scattering of the signal.

20 . The method of claim 19 , wherein the monitoring comprises a computer or circuit determines the presence of absence of the fault by comparing the scattering to the reference data.

21 . The method of claim 19 , further comprising determining, from the scattering, a temperature of the optical fiber.