Method and arrangement for determining the dispersion of an optical transmission link
The invention relates to a method and an arrangement for determining the dispersion of an optical transmission link. By determining the signal quality, the bit error rate is measured for a modulated data signal depending on the modulation frequency of a noise signal (STS). The dispersion coefficient of the transmission link is calculated on the basis of the resulting discrete minima of the bit error rates. These measurements can take place advantageously during the operation of the data transmission. The method also provides additional information about the quality of the data transmission by determining the non-linear phase shift.
1 . A method for determining a dispersion of an optical transmission link, wherein a data signal is transmitted from a sender to a receiver, the method comprising:
modulating the data signal on the sending side using an adjustable noise signal having an adjustable frequency;
determining the signal quality of the received data signal on the receiving side;
changing the frequency of the noise signal and redetermining the signal quality, wherein this procedure is repeated until having an optimal frequency of the noise signal, wherein a maximal signal quality or a minimal interference of the noise signal is established; and
determining the dispersion from the optimal frequency of the noise signal.
2 . The method as claimed in claim 1 , wherein the signal quality is determined using bit errors of the received data signal or using an eye pattern of the received data signal or using a histogram of the received data signal.
3 . The method as claimed in claim 2 , wherein the signal quality is determined by recording a histogram of the received data signal.
4 . The method as claimed in claim 2 , wherein the data signal which is to be sent is protected by an error correction and/or error detection code, and wherein the bit error rate is determined on the receiving side with the aid of the error correction and/or error detection code.
5 . The method as claimed in claim 4 , wherein the amplitude of the noise signal and therefore the modulation index is only changed so far as the correcting capabilities of an error correction code which is used are not exceeded.
6 . The method as claimed in claim 1 , wherein the dispersion (assuming an absence of non-linearities) is calculated according to
π
λ
2
c
·
D
tot
·
f
STS
,
k
2
=
(
2
k
-
1
)
π
2
where
f STS,k is the frequency of the noise signal in [Hz],
c is the speed of light in a vacuum in [m/s],
λ is the wavelength of light in a vacuum [m] and
k=1, . . . , M, . . . n is the running index for the recorded minima of the bit error rate, wherein
D tot in [s/m] is the total dispersion of the optical transmission link.
7 . The method as claimed in claim 2 , wherein the dispersion (assuming an absence of non-linearities) is calculated according to
π
λ
2
c
·
D
tot
·
f
STS
,
k
2
=
(
2
k
-
1
)
π
2
where
f STS,k is the frequency of the noise signal in [Hz],
c is the speed of light in a vacuum in [m/s],
λ is the wavelength of light in a vacuum [m] and
k=1, . . . , M, . . . n is the running index for the recorded minima of the bit error rate, wherein
D tot in [s/m] is the total dispersion of the optical transmission link.
8 . The method as claimed in claim 4 , wherein the dispersion (assuming an absence of non-linearities) is calculated according to
π
λ
2
c
·
D
tot
·
f
STS
,
k
2
=
(
2
k
-
1
)
π
2
where
f STS,k is the frequency of the noise signal in [Hz]
c is the speed of light in a vacuum in [m/s],
λ is the wavelength of light in a vacuum [m] and
k=1, . . . ,M, . . . n is the running index for the recorded minima of the BER.
D tot in [s/m] is the total dispersion of the optical transmission link.
9 . The method as claimed in claim 5 , wherein the dispersion (assuming an absence of non-linearities) is calculated according to
π
λ
2
c
·
D
tot
·
f
STS
,
k
2
=
(
2
k
-
1
)
π
2
where
f STS,k is the frequency of the noise signal in [Hz],
c is the speed of light in a vacuum in [m/s],
λ is the wavelength of light in a vacuum [m] and
k=1, . . . ,M, . . . n is the running index for the recorded minima of the bit error rate, wherein
D tot in [s/m] is the total dispersion of the optical transmission link.
10 . The method as claimed in claim 2 , wherein a plurality of minima of the bit error rates are recorded, said bit error rates being dependent on the frequency of the noise signal, and wherein the non-linear phase shift in the optical transmission link is determined from a shift of these minima.
11 . The method as claimed in claim 3 , wherein a plurality of minima of the bit error rates are recorded, said bit error rates being dependent on the frequency of the noise signal, and wherein the non-linear phase shift in the optical transmission link is determined from a shift of these minima.
12 . The method as claimed in claim 4 , wherein a plurality of minima of the bit error rates are recorded, said bit error rates being dependent on the frequency of the noise signal, and wherein the non-linear phase shift in the optical transmission link is determined from a shift of these minima.
13 . The method as claimed in claim 1 , wherein the modulation of all output signals of a wavelength multiplexer is performed jointly in a modulator on the sending side.
14 . The method as claimed in claim 2 , wherein the modulation of all output signals of a wavelength multiplexer is performed jointly in a modulator on the sending side.
15 . The method as claimed in claim 1 , wherein the frequency and/or the amplitude of the noise signal is controlled by an evaluation unit on the receiving side via a service channel of the system control.
16 . The method as claimed in claim 2 , wherein the frequency and/or the amplitude of the noise signal is controlled by an evaluation unit on the receiving side via a service channel of the system control.
17 . A method for determining the dispersion of an optical transmission link,
in which a data signal is transmitted from a sender to a receiver,
wherein
the data signal is modulated on the sending side using an adjustable noise signal which has an adjustable frequency,
the signal quality of the received data signal is determined on the receiving side,
the frequency of the noise signal is varied and the signal quality is measured again,
this procedure is repeated until a maximal signal quality or a minimal interference of the noise signal is established in the case of an optimal frequency of the noise signal, and
the dispersion is calculated from the optimal frequency of the noise signal.
18 . An arrangement for determining a dispersion of an optical transmission link having a wavelength multiplexer on the sending side, the arrangement comprising:
a modulation unit for amplitude-modulating a data signal using a noise signal, wherein the modulation unit is arranged on the sending side, and wherein the modulation unit is configured in such a way that it can be adjusted in frequency and amplitude;
a measuring unit for capturing the signal quality of the data signal; and
an evaluation unit, wherein the measuring unit and the evaluation unit are arranged on the receiving side, and wherein the evaluation unit is connected to the modulation unit via a service channel of a system control for the purpose of controlling and adjusting the frequency and/or the amplitude of the noise signal.
19 . The arrangement as claimed in claim 18 , wherein the modulation unit is designed as a plug-in module arrangable at any position in front of or behind the multiplexer at the beginning of the optical transmission link.