Performance monitoring based on optical autocorrelation
View Patent ↗An optical performance monitor (OPM) adapted to (i) sample an autocorrelation function corresponding to an optical signal transmitted in an optical network and (ii) based on the sampling, characterize two or more impairments concurrently present in the optical signal. In one embodiment, the OPM has an optical autocorrelator (OAC) coupled to a signal processor (SP). The OAC receives the optical signal from the network, generates two or more samples of its autocorrelation function, and applies said samples to the SP. The SP processes the samples and generates two or more signal metrics. Based on the signal metrics and reference data corresponding to the impairments, the SP then obtains a measure of each of the impairments.
1. Apparatus for performance monitoring in a communication system, the apparatus comprising:
(a) an optical autocorrelator (OAC) adapted to receive an optical signal from the communication system and to generate two or more samples of an autocorrelation function corresponding to the optical signal; and
(b) a signal processor (SP) coupled to the OAC and adapted to (i) characterize two or more impairments concurrently present in the optical signal based on the two or more samples, (ii) generate two or more signal metrics based on the two or more samples, and (iii) obtain values corresponding to the two or more impairments based on the two or more signal metrics and reference data corresponding to said impairments.
2. The invention of claim 1 , wherein the SP is further adapted to generate a feedback signal for the communication system based on the two or more impairments and the feedback signal is applied to the communication system to improve performance.
3. The invention of claim 1 , wherein the two or more impairments include at least one of dispersion, noise, and timing jitter.
4. The invention of claim 1 , wherein the reference data are obtained via computer simulation.
5. The invention of claim 1 , wherein the two or more samples comprise (i) a first sample corresponding to a substantially zero relative delay, (ii) a second sample corresponding to a relative delay of substantially one half bit period, (iii) a third sample corresponding to a relative delay of substantially one bit period, and (iv) a fourth sample corresponding to a relative delay of substantially one-and-a-half bit periods.
6. The invention of claim 5 , wherein: the two or more impairments are noise and dispersion; and the two or more signal metrics include metrics b ave and b h defined as follows:
b
ave
=
1
2
(
i
1
+
1
2
(
i
0.5
+
i
1.5
)
)
b
h
=
i
1
-
1
2
(
i
0.5
+
i
1.5
)
where i 0.5 is the second sample divided by the first sample; i 1 is the third sample divided by the first sample; and i 1.5 is the fourth sample divided by the first sample.
7. The invention of claim 6 , wherein the reference data represent two reference surfaces, one surface providing values of noise as a function of the metrics b ave and b h and the other surface providing values of dispersion as a function of the metrics b ave and b h .
8. The invention of claim 1 , wherein the OAC comprises:
a splitter adapted to direct four or more signal copies corresponding to the optical signal via four or more optical paths, wherein at least one of the optical paths is characterized by a time delay with respect to at least one other optical path; and
two or more detectors, each adapted to generate an electrical signal based on a superposition and mixing of two signal copies, wherein the samples are based on said electrical signals.
9. The invention of claim 8 , wherein the splitter is adapted to direct eight signal copies corresponding to the optical signal via eight optical paths, wherein:
first, second, fourth, sixths and eighth optical paths have a first time delay;
a third optical path has a delay greater than the first delay by substantially one half bit period;
a fifth optical path has a delay greater than the first delay by substantially one bit period; and
a seventh optical path has a delay greater than the first delay by substantially one-and-a-half bit periods.
10. The invention of claim 9 , wherein the two or more detectors comprise:
a first detector adapted to generate a first sample based on the copies received via the first and second optical paths;
a second detector adapted to generate a second sample based on the copies received via the third and fourth optical paths;
a third detector adapted to generate a third sample based on the copies received via the fifth and sixth optical paths; and
a fourth detector adapted to generate a fourth sample based the copies received via the seventh and eighth optical paths.
11. A method for monitoring performance in a communication system, the method comprising:
(A) generating two or more samples of an optical autocorrelation function corresponding to an optical signal of the communication system;
(B) characterizing two or more impairments concurrently present in the optical signal based on the two or more samples;
(C) generating two or more signal metrics based on the two or more samples; and
(D) obtaining values corresponding to the two or more impairments based on the two or more signal metrics and reference data corresponding to said impairments.
12. The invention of claim 11 , further comprising:
generating a feedback signal for the communication system based on the two or more impairments; and
applying the feedback signal to the communication system to improve performance.
13. The invention of claim 10 , wherein the two or more impairments include at least one of dispersion, noise, and timing jitter.
14. The invention of claim 12 , wherein the reference data are obtained via computer simulation.
15. The invention of claim 12 , wherein the two or more samples comprise (i) a first sample corresponding to a substantially zero relative delay, (ii) a second sample corresponding to a relative delay of substantially one half bit period, (iii) a third sample corresponding to a relative delay of substantially one bit period, and (iv) a fourth sample corresponding to a relative delay of substantially one-and-a-half bit periods.
16. The invention of claim 10 , wherein:
the two or more impairments are noise and dispersion; and
the two or more signal metrics include metrics b ave and b h defined as follows:
b
ave
=
1
2
(
i
1
+
1
2
(
i
0.5
+
i
1.5
)
)
b
h
=
i
1
-
1
2
(
i
0.5
+
i
1.5
)
where i 0.5 is the second sample divided by the first sample; i 1 is the third sample divided by the first sample; and i 1.5 is the fourth sample divided by the first sample.
17. The invention of claim 16 , wherein the reference data represent two reference surfaces, one surface providing values of noise as a function of the metrics b ave and b h and the other surface providing values of dispersion as a function of the metrics b ave and b h .
18. Apparatus for performance monitoring in a communication system, the apparatus comprising:
(A) means for generating two or more samples of an optical autocorrelation function corresponding to an optical signal of the communication system;
(B) means for characterizing two or more impairments concurrently present in the optical signal based on the two or more samples;
(C) means for generating two or more signal metrics based on the two or more samples; and
(D) means for obtaining values corresponding to the two or more impairments based on the two or more signal metrics and reference data corresponding to said impairments.
19. Apparatus for performance monitoring in a communication system, the apparatus comprising:
(a) an optical autocorrelator (OAC) adapted to receive an optical signal from the communication system and to generate two or more samples of an autocorrelation function corresponding to the optical signal; and
(b) a signal processor (SP) coupled to the OAC and adapted to characterize two or more impairments concurrently present in the optical signal based on the two or more samples, wherein the OAC comprises:
a splitter adapted to direct four or more signal copies corresponding to the optical signal via four or more optical paths, wherein at least one of the optical paths is characterized by a time delay with respect to at least one other optical path; and
two or more detectors, each adapted to generate an electrical signal based on a superposition and mixing of two signal copies, wherein the samples are based on said electrical signals.
20. The invention of claim 19 , wherein the splitter is adapted to direct eight signal copies corresponding to the optical signal via eight optical paths, wherein:
first, second, fourth, sixths and eighth optical paths have a first time delay;
a third optical path has a delay greater than the first delay by substantially one half bit period;
a fifth optical path has a delay greater than the first delay by substantially one bit period; and
a seventh optical path has a delay greater than the first delay by substantially one-and-a-half bit periods.
21. The invention of claim 20 , wherein the two or more detectors comprise:
a first detector adapted to generate a first sample based on the copies received via the first and second optical paths;
a second detector adapted to generate a second sample based on the copies received via the third and fourth optical paths;
a third detector adapted to generate a third sample based on the copies received via the fifth and sixth optical paths; and
a fourth detector adapted to generate a fourth sample based the copies received via the seventh and eighth optical paths.