Pilot tones for optical signal wavelength identification and power measurement
View Patent ↗A method of optical communication includes providing a plurality of optical signals each associated with a distinct channel of a composite optical signal. A unique pilot tone signature is superimposed on each channel. The spectral composition of each signature includes a plurality of frequencies. In one embodiment, binary frequency shift keying at a frequency f m is used to shift between instantaneous frequencies f 1 and f 2 wherein f 2 +Δf=f 1 −Δf=f c . Choosing Δ f f m ≈ 1.1602 produces a spectrum having a plurality of dominant components at least some of which have substantially the same amplitude. A method of detecting the presence of a selected pilot tone signature having a plurality n of dominant spectral components F 1 . . . F n includes generating a power spectrum P 0 (f). S k (f) is calculated as a product of a plurality of frequency shifted versions of P 0 (f), where kε{1 . . . n}. The existence of a dominant spectral component at F k indicates the presence of the selected pilot tone signature.
1. A method of communicating an optical signal, comprising:
a) superimposing a pilot tone signature on a selected channel of an optical signal having a plurality of channels, wherein the pilot tone signature is distinct from that associated with any other channel of the plurality of channels, wherein the pilot tone signature comprises a plurality (n) of tones;
b) maintaining a pre-determined ratio of a power of the pilot tone signature to a power of the selected channel;
c) computing S k (f) as a product of a plurality of frequency shifted versions of a power spectrum P 0 (f) of the optical signal; and
d) thresholding S k (f) to identify a dominant peak indicative of the presence of the pilot tone signature to identify the selected channel.
2. The method of claim 1 wherein the plurality of tones is generated substantially simultaneously.
3. The method of claim 1 wherein the plurality of tones is generated sequentially, one at a time.
4. The method of claim 1 wherein a) further comprises frequency shift keying a pilot tone source at a modulation frequency f m to produce a plurality of distinct instantaneous frequencies including a first instantaneous frequency f 1 and a second instantaneous frequency f 2 , wherein f 1 >f 2 .
5. The method of claim 4 wherein f 1 and f 2 deviate from a center frequency
f
c
=
f
1
+
f
2
2
by a deviation frequency Δf such that
f
2
+
Δ
f
=
f
c
=
f
1
-
Δ
f
,
wherein
β
=
Δ
f
f
m
≈
1.1602
.
6. The method of claim 1 wherein a) further comprises one of a frequency shift keying and a phase shift keying of a pilot tone source.
7. The method of claim 1 wherein n is odd.
8. The method of claim 1 wherein n is even.
9. The method of claim 1 wherein the dominant spectral components associated with the pilot tone signature have substantially a same amplitude.
10. The method of claim 1 wherein an amplitude of the dominant spectral components associated with the pilot tone signature varies.
11. The method of claim 1 wherein n≦5.
12. The method of claim 1 further comprising:
e) determining an optical power of the pilot tone signature; and
f) estimating an optical power of the selected channel from the determined optical power of the pilot tone signature and the pre-determined ratio.
13. The method of claim 12 wherein a proper subset of the dominant spectral components associated with the pilot tone signature is used to determine the optical power of the pilot tone signature.
14. The method of claim 1 wherein c) includes computing
S
k
(
f
)
=
∏
i
=
1
n
P
0
(
f
-
(
F
k
-
F
i
)
)
,
where
k
∈
{
1
…
n
}
.
15. The method of claim 1 wherein c) includes the step of computing
S
=
∏
l
M
P
i
,
wherein each P i is a frequency shifted copy of P 0 , wherein each copy is shifted from P 0 by an integer multiple of a pre-determined displacement frequency ΔF.
16. A method of communicating an optical signal, comprising:
a) providing a plurality of optical signals, each associated with a distinct channel of a composite optical signal;
b) superimposing a distinct pilot tone signature on each channel, wherein each pilot tone signature comprises a plurality (n) of tones;
c) maintaining a pre-determined ratio of a power of each pilot tone signature to a power of the associated channel;
d) computing S k (f) as a product of a plurality of frequency shifted versions of a power spectrum P 0 (f) of the composite optical signal; and
e) thresholding S k (f) to identify a dominant peak indicative of the presence of a selected pilot tone signature.
17. The method of claim 16 wherein n is odd.
18. The method of claim 16 wherein n is even.
19. The method of claim 16 wherein the plurality of tones is generated substantially simultaneously.
20. The method of claim 16 wherein the plurality of tones is generated sequentially, one at a time.