EP1338105A2

EP1338105A2 - Device and method for detecting distortions during optical information transmission

Info

Publication number: EP1338105A2
Application number: EP01989354A
Authority: EP
Inventors: Reinhold Noe
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2000-12-01
Filing date: 2001-11-28
Publication date: 2003-08-27
Also published as: WO2002045302A2; WO2002045302A3

Abstract

The invention relates to a device and to a corresponding method with which distortions of an optical signal (OS) are detected in an extreme value detector (DET1, DET2, DET3) by establishing a maximum signal and a minimum signal. The detected signal (ED), which is not differentiated at all, which is differentiated once or which is differentiated a number of times, is supplied as an alternating signal (SED1, SED2, SED3) to the extreme value detector (DET1, DET2, DET3). This enables, for example, the polarization mode dispersion of a higher order or the chromatic dispersion to be detected and, optionally, compensated for by means of a compensating element (C1, C2, TR).

Description

Arrangement and method for distortion detection in optical information transmission

The invention relates to an arrangement and an associated method for the distortion detection in optical information transmission according to the preamble of independent claims 1 and 9.

Polarization mode dispersion of optical fibers distorts the transmitted optical pulses in the optical information transmission. To detect these distortions, a number of electrical bandpass filters with subsequent power detectors are usually used on the receiver side, which spectrally analyze the detected signal. This is described in IEEE J. Lightwave Technology, 17 (1999) 9, pp. 1602-1616.

Low pass behavior of the spectrum indicates distortions due to polarization mode dispersion.

The disadvantage here is that, for example, distortions that can arise as a result of higher-order polarization mode dispersion are only weakly reflected in control signals obtained. This makes it difficult to compensate for such distortions. There are also distortions from other effects, e.g. can be chromatic dispersion, including those of a higher order, and nonlinear effects which cannot be detected with sufficient sensitivity according to the prior art.

The object of the invention is therefore to provide an arrangement and an associated method for the distortion detection in optical information transmission, which detect distortions differently and better than according to the prior art.

This object is achieved by an arrangement specified in claim 1 and by a method specified in claim 7. Advantageous further developments are specified in the subclaims.

The solution to the problem is that a maximum and / or a minimum of an alternating signal is determined and compared with one another. In the case of higher-order polarization mode dispersion, for example, the rising and falling signal edges have a gradient of different amounts when changing from zero to one or vice versa and sensitively indicate distortions caused by shear of the eye pattern. For the evaluation, the detected signal is preferably passed through a high-pass filter as a differentiator. Two oppositely polarized one-way rectifiers or one-way power detectors each indicate the maximum or minimum of the alternating signal thus formed. These are compared with each other. The same amounts indicate the same edge steepness of the detected signal and thus freedom from distortion. In extension of the inventive principle, other filters such as Multiple differentiators can be provided to form the alternating signal. The detected signal itself can also be used as an alternating signal without filtering. In this way, for example, the broadening or narrowing of return-to-zero pulses by means of dispersion or self-phase modulation can be detected.

The invention is explained in more detail using exemplary embodiments.

Show it

1 shows an optical data transmission link with an arrangement according to the invention for the distortion detection, FIG. 2 shows an eye pattern of the detected signal, FIG. 3 shows an eye pattern of an alternating signal, FIG. 4 shows a filter, FIG. 5 shows an extreme value detector, 6 shows another eye pattern of the detected signal, FIG. 7 shows an arrangement with an additional depolarizer and FIG. 8 shows a controller

The use of the arrangement according to the invention for the distortion detection is shown in an optical data transmission link according to FIG. An optical signal generating device TR, which is preferably designed as an optical transmitter, sends an optical signal OS via an optical waveguide LWL to an optical receiver RX. A first compensator C1 operating in the optical range can be provided between the receiver input IN and a photodetector PD for converting the optical signal OS into a detected signal ED designed as an electrical signal. The first compensator C1 is preferably an optical compensator of polarization mode dispersion or chromatic dispersion. The detected signal ED can be passed through a second compensator C2 operating in the electrical area. A downstream decision maker DFF outputs the transmitted data signal DS at decision maker output OD. The second compensator C2 is preferably an adaptive electrical transversal filter and / or a circuit for quantized feedback. In the latter case, the second compensator also receives the transmitted data signal DS. If the second compensator C2 also carries out quantized feedback, the transmitted data signal DS is fed to it.

At least a first, second or third alternating signal SED1, SED2, SED3 is formed from the detected signal ED, which is at least approximately proportional to the detected signal differentiated zero, once or twice. The direct component of the alternating signal SED1, SED2, SED3 is known and is preferably chosen to be zero. The first alternating signal SED1 is identical to the detected signal ED, the second alternating signal SED2 is the output signal of an at least approximately working as a differentiator. rt N rt Da 1 rt o to * ⁾ <FS to PJ to <iQ 0 tr M ü 10> ü Φ X ü FI) μ- tn tr FS 0 ^F rj F in rt

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N 0 0 0 lh ^ 3 rt H ¹ Φ MP ⁾ μ- FS XN 0 Φ NJ P ⁾ Φ ü IQ

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0 0 Φ rt Di Φ S 1 1 0 FS N Φ Φ rt - 1 ü Φ ö tn PJ 1 Φ Φ φ 10 rt 1 "φ 0 1 0 μ- IQ Φ) FS ω 1 1 μ- FS 1 1

I 1 1 0 tn 1

speak sent ones ONE or zeros ZERO of the optical signal OS. The horizontal axis is time t, the vertical axis is the detected signal ED. The course of time during a bit duration is shown. Although the eye opening is hardly closed, there are clear differences between the amount of steepness of the rising edges FI on the one hand and the amount of steepness of the falling edges F2 on the other hand.

FIG. 3 shows the second alternating signal SED2 that occurs in the case of a detected signal ED corresponding to FIG. 2. The course of time during a bit duration is shown. The second filter works approximately as a differentiator, which is achieved by a first-order high-pass filter with a low cut-off frequency compared to the bit clock frequency.

The horizontal axis is time t, the vertical axis is the second alternating signal SED2, and the time average of the second alternating signal SED2 is zero, which is characterized by the symbol 0. Extreme value signals SM1, SM2 are also shown. A first extreme value signal SM1 is a maximum signal SM1, a second extreme value signal SM2 is a minimum signal SM2. In this exemplary embodiment, the maximum signal SM1 and minimum signal SM2 differ by more than 10%, in spite of comparatively small distortions of the detected signal ED. The partially angular

Functional sequences can be traced back to a numerical differentiation carried out during the generation of FIG. 3 and do not occur in reality. In this exemplary embodiment, the controller regulates the invention, which relates to distortions caused by polarization mode dispersion, preferably the compensators C1, C2 and / or the optical signal generating device TR, in particular the transmission polarization of the optical signal OS or one in the optical signal generator - Compensation device TR contained compensator of polarization mode dispersion, so that the remaining distortions are minimal. This is then in this embodiment

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0 P 0 Mi - 0 0 FS p: rt 0 Ω FS μ- φ pα FS to 0 tr 0 Φ φ O Φ l_I. iq Φ

Pα 0 tn to 0: tq iQ W Φ 10 Φ tr o 3 tn Q ^ μ- p: 0 Φ 0 FS M g FS ^ Cd φ j W P

0 0 P g tr Cd to tn g in 0 μ- μ- rt (70 IQ to IQ Φ μ- Φ rt tr Pα <c] rt 0

0 to rt to FS tr g P IQ to P 0 £ 3 § ιq Φ p: Φ 10 μ- to 0 ⁽ Q 0 0 O Φ O ot O Pα tq g P μ- rt φ t μ- 0 Cd p: Frj 0 in tn 0 FS rt 0 X rt P 0 rt μ- FS Ω FS FS φ to 0 O 0 0 tn ⁽ Q iQ •? Tr to F- ¹ μ- μ- P Φ Φ φ ti 0 Di Φ 3 OP Mi tr IQ 10 P FS

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Φ tr tr rt φ P FS to P 0 α S FS Da Pα 0 P IQ 0 Φ Da § - 10 P 10 0 10 0 tn Φ tr Φ FS tn Ω P Φ Φ 0 Φ μ- POX φ μ- P <! tQ ⁽ Q 0 "d Di iq - tn l_I. Φ FS Ωα Φ tr 0 to 3 0 in 10 F- ¹ F- ¹ α to μ- 0 iQ in φ μ- Ω P in Ω PP to

O rt φ X tn φ in rt p: Di tq tr X IQ rt - α o 3 IQ 0 Φ S ιq to 0 tr 0 to 0 φ

Da Φ X μ- Ω 0 tsi rt φ φ P Φ ω Pα - P to F- ¹ rt 10 g ⁽ Q 0 tq P 0 O tq μ- φ tr φ FS tr - X rt N IQ 0 F- ¹ FS X Φ H g α P ^ B φ Φ μ- μ- HP Pα 0 Da rt rt S Φ μ- μ- PX ot rt Φ rt tr H F- ¹ to F- ": 10 μ- FS ιq 0 Φ H μ- O 0 iq O Φ

0 F- ¹ Φ φ Fti 0 X φ P j3 to μ- Φ Φ Ui - to μ. μ- Ω in 0 μ- μ- IQ φ g SX φ α

Pi - in 0 CP 0 Φ FS 0 § μ- μ- 10 * "in 0 Pα ιq tr Ω P 3 Ω P Ω Φ XP φ • HH FS rt Da Φ IQ ιq φ rt μ- Pα 0 to Φ 0 Φ tr F- ¹ tr to φ g X tr FS p: g 0

FS XP μ- H Da Da Φ 0 rt 0 μ- rt P Da UJ 0 P μ- rj Φ g 0 to μ- 0- tr t φ 0 ü Ω to Φ Φ P ^ FS P iQ Φ N tn Ü ¹ Da F- ¹ öd φ in FS to 3 W Φ • g

Cd 0 in P tr 3 0 φ φ 0 <F- "S φ g X rt Φ φ α F- ¹ μ-. NP 0 0 rt P

X 0 in N - tn 0 0 o Φ rt 0 N μ- μ- FS S to rt ^• > ⁽ Q o 0 0 § H • - ö X rt Φ tr. FS 0 to μ- Φ X 0 FS P g FS μ- 0 o td μ. tq Pα N μ- μ-

FS i μ- <O Cd a Di 0 wg Ω 0 Pα Φ μ- Da tr <F- ¹ p: Ω α P μ- φ Φ tn J α Da φ 3

Φ φ 0 Φ tr • a μ- μ- P g F- ¹ tr μ- μ- 3 μ- Φ IQ tr N F- ¹ P 0 Ω 10 rt Ω μ- P c

3 FS φ FS Φ μ- φ Ω 0 φ P - φ to Φ rt 0 iq φ FS 0 φ Φ Pα Ω Φ 0 ^* φ cΛ Fd B

X 3 NS g Φ tr 0 XX μ- Φ 3 Φ FS tQ 0 »to Da tr p: tr X (- ^■ o Pα

Φ <Φ P FS tsi rt φ μ- to w ιq to S Φ F- ¹ α dg μ- φ rt rt 0: to Da M Φ

FS φ 0 FS öd X Φ • IQ μ- 3 g rt 0 &<μ- P FS Φ 0 o J w Φ μ- rt oo tn Fd μ- P rt rt FS α FS Φ μ- FS tti tr iQ F- ¹ co φ P tn Φ ιq Da μ- g 0 • H ω 0 10 FS 10 P φ FS Φ in IQ Φ 0 rt 3 • Φ Fiϊ IQ 3 μ- F- ¹ rt FS 0 Φ P Ω μ- Pα P 0 rt ^F d 0 10 P φ 0 μ- μ- FS 0 FS> tn. PN F- ¹ Ifl μ- NP 0 tr 0 FS α φ μ- iq φ 0 α rt rt ιq Φ IQ p: ü P rt φ φ Φ ^* Φ Φ H Da IQ φ μ- tfl μ- μ- iq α φ IQ 0 0 μ- p: O

0 μ- tr in iq to α 0 μ- Da μ- rt μ- φ Cd IQ FS P iQ FS 3 0 rt φ P P C φ iq P 0 o rt FS

P Ω Φ P Φ μ- Ω tj 0 0 Φ ⁽ Q μ- ö tn FS to 0 Φ tr p: rt in Ifl φ P Ω IQ pα Φ P tr μ- 0 tQ Φ tr 0 FS Φ K rt rt l- 0 g 0 Ml <§ rt rt μ- X to φ 0 tr 10 φ 0 0 φ Φ Pi N o 0 μ- rt Ω FS rt Φ Pα 0 t 0: o 10 FS Φ <g Φ FS tq

0 Φ P μ- g in e IQ

Φ Φ Fd P 0 Φ tr o <0 ffi P IQ tr FS μ- P D. tQ

0 μ- rt H φ 0 Φ FS Φ 3 0 in α FS 1 1 1 FS X IQ P rt Φ α Φ P o 1 μ- FS FS 1 1 Φ rt μ- Φ 1 Φ H F- ¹ FS 0 o 1 1 1 3 • 1 1 ^•> tQ

SMl, SM2 is replaced. The comparator CC can also be a quotient generator, since a certain quotient between the maximum signal SM1 and minimum signal SM2 can indicate freedom from distortion. In the case of the second extreme value detector DET2, the optimum quotient between maximum signal SM1 and minimum signal SM2 is at least approximately equal to 1.

In practice, the maximum detector Ml and minimum detector M2 designed as a one-way rectifier do not exactly detect the maximum or minimum of the alternating signal SED1, SED2, SED3 as the maximum signal SMl or minimum signal SM2, but rather to the mean value of the square of positive or negative components of the alternating signal SEDl, SED2 , SED3 proportional signals. However, this is not harmful, since such signals are also monotonous to the maximum or minimum of the alternating signal SED1, SED2, SED3 and are generally even better indicators of distortion, since they are less susceptible to noise.

The third filter FI3 is preferably designed as a double differentiator, which is done by double high-pass filtering in the second and first filters FI2, FI1. Triple and multiple differentiation is also possible. Instead of first-order high-pass filters, other high-pass filters or, if appropriate, band-pass filters or even low-pass filters can also be used. By using more than one distortion indication signal Ul, U2, U3 more than one distortion can be displayed.

FIG. 6 explains the function of the first extreme value detector DET1 in the case of an optical signal OS which is preferably designed as a return-to-zero signal. FIG. 6 shows a signal ED detected with the bit clock, which signal is simultaneously the first alternating signal SED1. It corresponds to an optical signal OS designed as a non-return-to-zero signal. Signal shapes of the detected signal ED and first alternating signal SED1 running above or below correspond to sent ones ONE or zeros NULL of the optical signal OS. The horizontal axis is time t, the vertical axis is the detected signal ED or first alternating signal SED1. Due to the low-pass filtering for noise suppression customary in optical receivers, the detected signal ED and the first alternating signal SED1 are a mixed form of return-to-zero and non-return-to-zero signal. The maximum signal SM1 and minimum signal SM2 differ significantly in this exemplary embodiment, not only in terms of their sign, namely the maximum signal SM1 corresponding to ones is greater in magnitude than the minimum signal corresponding to the transmitted zeros. The mean time value of the detected signal ED and the first alternating signal SED1 is equal to 0 and is identified by the symbol 0. A possible positive difference between the magnitude of the maximum signal SM1 minus the magnitude of the minimum signal SM2 or — according to the embodiment variant of the first extreme value detector DET1 according to FIG. 5 —a positive sum of positive signal maximum signal SM1 and negative signal minimum value SM2 indicates minimal pulse broadening. The controller MP can achieve this state by regulating the compensator C1, C2 by means of the first or second control signal VI, V2 or - since dispersion and self-phase modulation can at least partially compensate for each other - by regulating a level of the optical signal OS on the optical fiber LWL by the third control signal V3, which is fed to the optical signal generating device TR and, for example, controls the pumping power of an optical transmission amplifier or intermediate amplifier.

Another embodiment of the invention is shown in FIG. 7. It is largely identical to that according to FIG. 1, but instead of the controller MP there is another controller MP2 and the optical signal generating device TR is followed by a depolarizer DEPOL, by means of which the optical signal OS is modulated with respect to its polarization. Depolarizers are made of electron, for example. Lett., Vol. 30 (1994) 18, pp. 1500-1501. The DEPOL depolarizer ensures that anisotropic distortions of the optical signal OS, which arise, for example, from polarization mode dispersion or due to the low polarization dependence of self-phase modulation, occur in the first to third distortion display signals U1, U2, U3 by first and third alternating components U1AC, U2AC , U3AC voice. It is also achieved that isotropic distortions of the optical signal OS, which arise, for example, from chromatic dispersion or the large polarization-independent portion of self-phase modulation, are expressed in the first to third distortion display signal U1, U2, U3 by first and third direct components U1DC, U2DC, U3DC.

According to FIG. 8, the further controller MP2 processes the distortion display signals U1, U2, U3 as required by the control of the compensating element Cl, C2, TR present in each case. In one exemplary embodiment, the further controller MP2 contains first to third AC component detectors DAC, D2AC, D3AC, which extract first to third AC component U1AC, U2AC, U3AC from the first to third distortion display signal U1, U2, U3. First to third alternating components UlAC, U2AC, U3AC are then fed to a controller core MPC, which controls a compensating element C1, C2, TR, which is preferably designed as a compensator of polarization mode dispersion. In a further exemplary embodiment, the further controller MP2 contains first to third DC component detectors D1DC, D2DC, D3DC, which extract first to third DC components U1DC, U2DC, U3DC from the first to third distortion display signal U1, U2, U3. First to third DC components U1DC, U2DC, U3DC are then fed to a controller core MPC, which controls a compensating element C1, C2, TR, which is preferably designed as a compensator of chromatic dispersion or influences the transmitting power of the optical signal OS. Reference character list

Cl, C2, TR compensating elements

Cl, C2 compensators

TR optical signal generating device

OS optical signal

Fiber optic cables

RX optical receiver

DS transmitted data signal

OD decision exit

VI, V2, V3 control signals

MP controller

PD photodetector

CG comparator

IN receiver input

DET1, DET2, DET3 extreme value detector

INI, IN2, IN3 Exte value detector input

OUTM1 maximum detector output

OUTM2 minimum detector output

0 value zero t time

DFF D flip-flop

ED detected signal

SEDl, SED2, SED3 alternating signal

FI1, FI2, FI3 filter

SMl, SM2 extreme value signals

SMl maximum signal

SM2 minimum signal

Gl, G2 DC component

ADD adder

Ml maximum detector

M2 minimum detector

Ul, U2, U3 distortion display signal

R series resistance

L parallel inductance

Rl, R2 resistors

Cl, C2 capacitors Dl, D2 diodes

UU1, UU2 voltage sources

ONE ones

ZERO zeros

D1AC, D2AC, D3AC AC component detectors

D1DC, D2DC, D3DC DC component detectors

DEPOL depolarizer

UlAC, U2AC, U3AC alternating shares

U1DC, U2DC, U3DC DC components

MPC controller core

Claims

claims

1. Arrangement for a distortion detection in optical information transmission with an optical signal (OS) and an optical receiver (RX), in which a detected signal (ED) occurs, characterized in that an extreme value detector (DET1, DET2, DET3) is provided which at least approximately determines an extreme value signal (SM1, SM2) of an alternating signal (SED1, SED2, SED3) derived from the detected signal (ED).

2. Arrangement according to claim 1, characterized in that the extreme value detector (DET1, DET2, DET3) has a maximum detector (Ml) and / or a minimum detector (M2) which is an extreme value signal designed as a maximum signal (SM1) or minimum signal (SM2) (SMl, SM2) determined.

3. Arrangement according to claim 1 or 2, characterized in that a first alternating signal (SEDl) is at least approximately proportional to the detected signal (ED).

4. Arrangement according to one of claims 1 to 3, characterized in that a second or third filter (FI2, FI3), which is preferably designed as a high-pass filter of first or second degree, is provided, which has a second or third alternating signal (SED2, SED3) is derived from the detected signal (ED).

5. Arrangement according to one of claims 1 to 4, characterized in that the extreme value detector (DETl, DET2, DET3) has a comparator (CC) which has the maximum signal (SMl) and the

Minimum signal (SM2) compares and thereby generates a distortion display signal (Ul, U2, U3).

6. Arrangement according to one of claims 1 to 5, characterized in that a compensating element (Cl, C2, TR) is provided which a control signal (VI, V2, V3) derived from a distortion display signal (Ul, U2, U3) receives.

7. Arrangement according to one of claims 1 to 6, characterized in that a DC component detector (DlDC, D2DC, D3DC) is provided which extracts its DC component (U1DC, U2DC, U3DC) from a distortion display signal (Ul, U2, U3) that the compensating element (C1, C2, TR) is preferably designed as a compensator for chromatic dispersion or influencing the transmission power of the optical signal OS.

8. Arrangement according to claim 7, characterized in that a depolarizer (DEPOL) is provided on the transmission side, through which there is an anisotropic distortion of the optical

Signals (OS) in an alternating component (UlAC, U2AC, U3AC) of a distortion display signal (Ul, U2, U3).

9. A method for a distortion detection in optical information transmission with an optical signal (OS) and an optical receiver (RX), in which a detected signal (ED) occurs, characterized in that at least one extreme value signal (SM1, SM2) is one of the detected signal (ED) derived alternating signal (SEDl,

SED2, SED3) is determined at least approximately.

10. The method according to claim 9, characterized in that an extreme value signal (SM1, SM2) designed as a maximum signal (SM1) or minimum signal (SM2) is determined.

11. The method according to claim 9 or 8, characterized in that a first, second or third alternating signal (SED1, SED2, SED3) is derived from the detected signal (ED) at least approximately by zero-fold, single or double differentiation ,

12. The method according to any one of claims 9 to 11, characterized in that the maximum signal (SMl) and minimum signal (SM2) for generating a distortion display signal (Ul, U2, U3) are compared.

13. The method according to any one of claims 9 to 12, characterized in that a control signal (VI, V2, V3) derived from a distortion display signal (U1, U2, U3) is fed to a compensating element (Cl, C2, TR).

14. Arrangement according to one of claims 9 to 13, characterized in that the DC component (U1DC, U2DC, U3DC) is extracted from a distortion display signal (Ul, U2, U3) that the compensating element (Cl, C2, TR) preferably as Compensator of chromatic dispersion or the transmission power of the optical signal OS is formed.

15. The arrangement according to claim 14, characterized in that the optical signal (OS) is depolarized on the transmission side, so that an anisotropic distortion of the optical signal (OS) in an alternating component (UlAC, U2AC, U3AC) of a distortion display signal (Ul, U2, U3) affects.