EP1550247A1 - Procede et systeme pour determiner des degradations du signal en presence de distorsions du signal - Google Patents

Procede et systeme pour determiner des degradations du signal en presence de distorsions du signal

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Publication number
EP1550247A1
EP1550247A1 EP03807733A EP03807733A EP1550247A1 EP 1550247 A1 EP1550247 A1 EP 1550247A1 EP 03807733 A EP03807733 A EP 03807733A EP 03807733 A EP03807733 A EP 03807733A EP 1550247 A1 EP1550247 A1 EP 1550247A1
Authority
EP
European Patent Office
Prior art keywords
signal
filter
optical
optical filter
adaptive
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03807733A
Other languages
German (de)
English (en)
Inventor
Marc Bohn
Richard Neuhauser
Marc-Steffen Wrage
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Original Assignee
Siemens AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP1550247A1 publication Critical patent/EP1550247A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion

Definitions

  • the invention relates to a method for determining signal degradations in the presence of signal distortions according to the preamble of claims 1 and 31 and two arrangements according to the preambles of claims 18 and 22.
  • WDM avelength division multiplex
  • the quality of individual channels of a transmitted WDM signal must be measured in order to control a so-called pre-emphasis or a tilt in the power level of the optical channels and thus to optimize the system performance.
  • occurring errors must be localized and their cause quickly determined.
  • the task of determining signal quality and the cause of errors is a central and as yet unsolved problem in the next generation of optical networks.
  • One method currently used to determine the signal quality is the measurement of the signal-to-noise ratios OSNR (Optical Signal-to-Noise Ratio) using an optical spectrum analyzer OSA (Optical Spectrum Analyzer).
  • OSNR Optical Signal-to-Noise Ratio
  • OSA Optical Spectrum Analyzer
  • the current measurement method of the signal-to-noise ratios OSNR by means of optical spectrum analysis also does not record any signal deteriorations which are caused by nonlinear effects such as stimulated Raman scattering SRS, four-wave mixing FWM, or by crosstalk or dispersion GVD. Effects such as Self-phase modulation SPM or cross-phase modulation XPM are incorrectly interpreted as OSNR deterioration.
  • An alternative method for determining the OSNR takes advantage of the different polarization properties of signal and amplifier noise (ASE). This method (“polarization nulling”) is based on the determination of the ratio between polarized signal and unpolarized noise.
  • the determination of the signal quality with the aid of a measured optical spectrum is no longer sufficient for optical data transmission systems for the reasons mentioned above.
  • Other methods are much more informative about the signal quality.
  • An example to be mentioned here would be the method of Q measurement, in which a second decision maker is shifted in his decision threshold against the decision threshold of the reference decision maker. If you apply the bit error rate above the detuned decision threshold, you can the optimal bit error rate is determined assuming Gaussian noise. If the bit sequence is known, the bit error rate can also be determined from the direct comparison of the transmitted and received bit pattern. In systems with "Forward Error Correction" FEC or "Enhanced Forward Error Correction” EFEC, the corrected bits can be used as a measure of the signal quality.
  • the power level of the optical signal or one of its channels is sampled synchronously with the help of a fast photodiode.
  • a variable delay line ensures that measurements can be made not only in the middle of the bit, but also to the left and right of it. In this way, the superimpositions of the power level profiles of many bits in a diagram are obtained.
  • EAS Electro Amplitude Sampling
  • the frequency distribution of the amplitude values of the received "zeros" and "ones” is measured and the signal quality is determined from this. In the synchronous case, this always happens at a fixed sampling time. This is usually in the middle of the bit.
  • Statements about the signal quality can be obtained from measured amplitude histograms from the width and position of the maxima or in the eye diagram from the eye opening.
  • the distributions of the "zeros" and the "ones" in the amplitude histogram widen and the free area in the eye diagram decreases. Signal deterioration caused by noise effects cannot be compensated for.
  • an arrangement is known in which adjustment of the transmission properties of an adaptive optical filter enables equalization of an optical signal in the case of dispersion GVD, self-phase modulation SPM and polarization mode dispersion PMD.
  • FIR Finite Impulse Response
  • FSR Free Spectral Range
  • Signal distortions can also be detected by determining and evaluating the electrical spectrum of the digital data signals. Such evaluations are also used in laboratory experiments to control electrical equalizers and / or compensators for signal improvement. The evaluation of the electrical spectrum allows automated signal optimization, but mostly no distortion-specific statements. The electrical spectrum is strongly dependent on the transmitter and therefore not suitable for the detection of distortion in data transmission systems.
  • Some distortions can also be individually detected and examined. For example, chromatic dispersion can be measured using variable dispersion compensation and a downstream signal quality analyzer. Such solutions are technically complex and expensive. Furthermore, only the type of distortion to be examined is detected, but not a general signal distortion. For fast and comprehensive distortion detection, the approach of individual distortion detection is very complex and therefore not ideal.
  • the object of the invention is to provide a method and corresponding arrangements in which, for. B. statements about essential causes of signal degradation and the signal quality of a transmitted optical signal can be provided by means of an adaptive optical filter.
  • an adaptive optical filter e.g. B.
  • other components e.g. B. as an electrical or optical equalizer, an electrical or optical compensator, etc - used as the above-mentioned adaptive optical filter, a solution to achieve the above statement should also be given.
  • predefined transmission properties of the adaptive optical filter are set, each of which has an influence on one or more signal distortions.
  • One or more measurements of one or more quality parameters are carried out at the output of the adaptive optical filter. This makes it possible to make a statement as to which essential signal-influencing effects the measured signal is impaired.
  • the adaptive filter can only influence deterministic signal distortions, i. H. e.g. compensate for all distortions or just equalize dispersion.
  • compensation of the optical signal can be carried out through optimized settings of the adaptive optical filter. This aspect has already been explained in the prior art. Nevertheless, statements can be made about the noise-like disturbances using the exclusion principle. If e.g. If, for example, the signal-to-noise ratios OSNR are measured behind the adaptive optical filter (e.g. with polarization nulling or with an optical spectrum analyzer or with amplitude sampling), then various noise-like interferences (e.g. ASE, FWM, XPM, etc.) can also be be distinguished.
  • the selected quality parameter provides information about signal distortion or noise-like interference or both.
  • a spectral component is e.g. B. at a channel wavelength before feeding the signal into the isolated adaptive optical filter.
  • the adaptive optical filter is only followed by a fast photodiode with a downstream module for measuring the quality parameter.
  • the photodiode can also be integrated in the module for measuring the quality parameter.
  • several values of the quality parameter are stored and compared with the value of the quality parameter when the adaptive optical filter is fully transmitted. This gives a measure of the impairment of the optical signal with respect to signal interference.
  • the use of the adaptive filter in the optical domain is advantageous because the signal is influenced before the photodiode (and thus before the phase information is lost) and individual effects can be determined more easily.
  • Selected settings of the transmission properties of the adaptive optical filter can have a common influence on more than one signal distortion at the same time. For this reason, groups of measurements with different settings are also considered, so that clear statements about one or more signal distortions are provided.
  • an optical spectrum analyzer or another suitable quality measuring device can be connected to the adaptive optical filter.
  • one or more setting parameters of an electrical equalizer or a compensator are set depending on the shape of the distortion.
  • Can be used as an electrical equalizer can be implemented as FIR or IIR filters with several setting parameters, to which the optically-electrically converted signal is led and at whose output the determined eye diagram can be transformed accordingly by varying the setting parameters.
  • the adjustable equalizer or filter coefficients provided as setting parameters here are provided for the weighted sum of different phase or time-delayed signals of the distorted or filtered signal.
  • Different SignalVer achievements express themselves in different filter coefficient vectors, the z. B.
  • This method can also be used when using the previously mentioned optical adaptive filter or another optical compensator (e.g. dispersion compensator) with associated setting parameters.
  • another optical compensator e.g. dispersion compensator
  • the invention therefore proposes to analyze one or more rows of set adjustment coefficients of an equalizer or a filter when the signal quality has arisen in order to obtain information about causes of signal distortion.
  • the adjustment coefficients must contain information about the equalized signal interference. If the equalizer or filter structure is known, the adjustment coefficients can be suitably analyzed. However, even without precise knowledge of the filter structure, the filter coefficients can be measured using targeted reference measurement solutions that provide information on how the filter coefficients are set, interpreted and analyzed for certain signal distortions.
  • the electrical equalizer or a compensator or the previously used optical adaptive filter do not necessarily have to be set to predefined values in this method.
  • the analysis of the signal quality is not carried out by deliberately influencing the optical or electrical signal by means of an optical or electrical adaptive filter and subsequent signal quality analysis. Rather, the adaptive filter is set once in such a way that the signal quality reaches an optimum in order to then determine from the analysis of the filter coefficients or their values at and / or up to the optimum signal interference.
  • the eye level, shape, size of the determined filtered or equalized eye diagram or the number of FEC corrected bits can be used.
  • the filter coefficients can be supplied or obtained directly from the electrical equalizer or compensators. Therefore, no additional electronic determination unit of the filter coefficients is required.
  • Electrical equalizers offer a very short response time and can, for example, within a few thousand bits, ie set or controlled in less than 1 ⁇ s at 10 Gb / s.
  • the method according to the invention therefore has a high speed.
  • optical compensators are largely independent of the data rate used and the modulation format of an optical signal. This aspect also applies to a limited extent to electrical equalizers that have a frequency tolerance of approx. 20-30% to the data rate.
  • These methods can be used at every measuring point of the transmission system, e.g. B. in an add-drop device by means of a decoupling device.
  • the delivered statements can e.g. B. be evaluated via the network management, so z. B. channel-selective changes to transmission properties can be made.
  • a simple portable computing unit such as a normal computer can also be used.
  • measurement and analysis of signal degradations can also be carried out by decoupling the signal or by using a monitoring channel at any measurement location.
  • a suitable arrangement with the optical adaptive filter is shown when a one- or two-stage amplifier is used to adapt the measured signal to the measurement dynamics.
  • Fig. 9 a characterization of the transmission function of the optical or electrical filter.
  • FIG. 1 A basic arrangement is described in FIG. 1, which enables a determination of signal degradations or distortions of an optical signal S transmitted in a transmission system.
  • a portion of the optical signal S is fed to an adaptive optical filter F and then according to a quality activity parameters measured from a measuring unit ME.
  • a measuring unit z. B an electrical spectrum analyzer or a power meter in a bandpass filter BPF connected upstream of the adaptive optical filter F for isolating an optical channel wavelength.
  • an optical-electrical converter O ⁇ W is interposed between the adaptive optical filter F and the measuring unit.
  • the optical-electrical converter OEW is often integrated in the ME measuring unit).
  • a fast photodiode is used here.
  • the use of the adaptive filter F in the optical domain is advantageous since the signal influence takes place before the photodiode OEW (and thus before the phase information is lost) and individual effects can thus be determined more easily.
  • the measurement unit ME is followed by a determination unit EE of the signal quality with at least one quality parameter such as OSNR, bit error rate, Q factor or a number of corrected bits in FEC / EFEC or for measuring polarization effects.
  • the selected quality parameter or the measuring unit EE provides information about signal distortions and also about residual noise-like disturbances such as OSNR.
  • the determination unit is integrated in a computer PC, which likewise controls the settings of the adaptive optical filter F by means of a control signal RS. The settings could also be controlled directly by a network management.
  • a first measurement MO of the quality parameter or parameters is carried out with a permeable setting of the adaptive optical filter F.
  • a bypass circuit can also be used for the full transmission of the signal.
  • Further measurements M1, M2, ... of the quality parameter are carried out by various settings of transmission properties of the adaptive optical filter F predefined in the computer PC, each of which has an influence on one of the signal distortions and from which an optimum of the quality parameter is determined.
  • the adaptive optical filter F z. B. can be set to different dispersion values. The signal quality as a function of the dispersion is measured and the optimal dispersion compensation setting and the signal quality with optimal dispersion compensation are obtained.
  • the actual signal quality can be determined at any point in the optical transmission system, regardless of the accumulated dispersion.
  • the dispersion tolerance can also be determined at this point, which is a measure of how exactly the residual dispersion must be set in order to achieve a certain bit error rate.
  • the signal quality is optimized by means of the adaptive optical filter F.
  • all distortion effects are influenced or compensated for regardless of their cause.
  • the best possible signal quality is obtained after equalizing the signal.
  • Only noise-like interference such. B. amplifier noise, FWM or SRS now lead to a signal deterioration.
  • targeted distortions can only be caused by e.g. B. SPM can be compensated. This provides information about which interference effect affects the signal and in what way.
  • the determination of the signal quality with optimal dispersion compensation allows a reliable statement about the signal quality at the measuring location and about the status of the dispersion compensation.
  • the influence of different filter settings on the results of the different measurement methods for signal quality analysis can be determined and used as a criterion for information.
  • additional signal Measured signal-to-noise ratios OSNR a distinction from noise-like effects is made possible as already mentioned above.
  • One or more quality parameters can also provide information about polarization effects (e.g. PDL polarization dependent loss, PMD polarization mode dispersion, DGD differential group delay, DOP degree of polarization, etc.).
  • the actual signal quality can be measured on each network element of an optical transmission link, regardless of the accumulated dispersion of the transmission link.
  • the dispersion leads to signal distortions, which can in principle be reversed by DCF (Dispersion Compensating Fiber) or other compensation methods.
  • the signal quality in the channel can be measured as a function of different filter parameters and enables signal and error analysis.
  • the signal quality analysis can include different methods and also several methods at the same time. Different signal disturbances such as dispersion, SPM or noise-like disturbances (amplifier noise, FWM, SRS, etc.) can be detected and differentiated.
  • FIG. 2 shows an arrangement for determining signal degradations of an optical broadband signal S transmitted via a transmission system, from which at least one spectral and / or amplitude-related component S1 is coupled out by means of a coupler KO and fed to an adaptive optical filter F.
  • the spectral component of the signal S is selected by means of a bandpass filter BPFO connected downstream of a broadband coupler KO.
  • the adaptive optical filter F is a measuring unit ME and ne determination unit EE downstream to determine one or more quality parameters.
  • a control unit SE is connected to the adaptive optical filter F at least for switching through and / or influencing signal distortions up to the equalization of the optical signal S by setting predefined transmission properties of the adaptive optical filter F.
  • a bandpass filter BPFO is connected downstream of the coupler KO. This will e.g. with multiplex signal S, a channel of signal S is isolated and transmitted further.
  • the bandpass filter BPFO is followed by an amplifier VI with a further bandpass filter BPF1 connected downstream.
  • the amplifier VI adjusts the amplified signal to the measurement dynamics of an optical-electrical converter according to FIG. 1.
  • the bandpass filter BPF1 also ensures that noise components are largely suppressed from ASE (Amplified Spontaneous Emission).
  • An amplifier V0 is optionally interposed between the coupler KO and the bandpass filter BPFO as a booster of the signal component S1.
  • a control unit SE connected to the adaptive optical filter is used to control a module for influencing the phase and / or amplitude response of the optical signal, which is integrated in the adaptive optical filter F.
  • the signal S2 filtered at the output of the adaptive optical filter F is fed to the measuring unit ME.
  • the quality measurement according to FIG. 1 then takes place by means of the determination unit EE.
  • a communication means KM is used between the control unit SE and the determination unit EE or the measurement unit ME, on the one hand to provide a status of the setting of the adaptive optical filter F on the determination unit or a further control unit, and on the other hand to regulate the adaptive optical filter F from the determination unit EE. Therefore the communication medium KM is best intended directionally.
  • a table for registering the signal-influencing effects can be generated according to corresponding settings of the transmission properties of the adaptive optical filter F when the transmission properties are newly set. The registration enables an analysis or a separation of the signal-influencing effects depending on the setting of the transmission properties of the adaptive optical filter F.
  • the transmission properties of the adaptive optical filter F can be regulated from an analysis of one of the determined quality parameters with respect to one or a group of signal degradations.
  • a predefined variation of the transmission properties of the adaptive optical filter F makes it possible to analyze and / or separate the signal quality with regard to various signal-influencing effects.
  • the signal can be optimized with regard to one or more quality parameters by means of suitable setting parameters of the adaptive optical filter F, and conclusions can be drawn about the signal degradations from the setting parameters.
  • FIG. 3 shows an arrangement for measuring signal degradations of an optical broadband signal S transmitted via a transmission system which is cost-effective as in FIG. 2 and whose at least one amplitude-related component S1 is coupled out by means of a coupler KO and fed to an adaptive optical filter F.
  • a first circulator C1, a bandpass filter BPFO and then a second circulator C2 are interposed between the coupler KO and the adaptive optical filter F.
  • An optical signal feedback FB for transmitting the filtered signal S2 to the second circulator C2 is connected at the output of the adaptive optical filter F.
  • the filtered signal S2 is output to a measuring unit ME of a signal quality according to FIG. 2 via the circulator C2, the bandpass filter BPFO and the first circulator C1.
  • the adaptive optical filter F is one Control unit SE is connected at least for switching through and / or for influencing signal distortions until the optical signal S is equalized.
  • An amplifier VI is interposed between the bandpass filter BPFO and the second circulator C2.
  • the amplifier VI can also be arranged as desired in the optical signal feedback FB, ie it can be connected upstream or downstream of the adaptive optical filter F.
  • the coupler KO and the first circulator C1 are optionally connected with an amplifier V0 as a booster, as in FIG. 2.
  • the main advantage of the arrangement shown in FIG. 3 is that one of the two bandpass filters BPFO, BPF1 according to FIG. 2 is saved and thus leads to a reduction in costs.
  • an optical-electrical converter is connected upstream of the measuring unit ME.
  • Both arrangements can also at the end of a transmission path or z. B. connected to the output of an add-drop module. As a result, the coupler KO and the amplifier V0 are no longer required.
  • bandpass filters BPO, BPF1 and BPFO used as channel selectors are provided in the previously explained exemplary embodiments as variable wavelength filters for the selective transmission of an optical channel in a wavelength division multiplex technique.
  • the method according to the invention can be used for different multiplexing techniques (polarization multiplex, time division multiplex, etc.).
  • FIG. 4 now shows a further arrangement for determining signal degradations in the presence of signal distortions.
  • nes branched from a transmission system optical WDM signal S in which after the passage of the WDM signal S through a wavelength-selective filter BPF, the outgoing signal is fed to an optical-electrical converter OEW with a downstream electrical equalizer EQ.
  • the equalizer EQ provided as FIR or IIR filter
  • different filter coefficients provided as setting parameters are set according to the invention, and an eye diagram z. B. determined by means of an oscilloscope.
  • the filter coefficients can be selected in various ways.
  • the signal quality can be changed by one or more changes in the filter coefficients e.g. B.
  • the filter coefficients can be optimized with respect to the size of the eye and the resulting deviations of the filter coefficients can be analyzed in terms of signal distortion.
  • the filter coefficients can also be changed from predefined values as test vectors, and on the basis of eye-specific requirements or properties.
  • the filter coefficients can also be set based on other signal quality parameters, such as bit error rate, Q value or the electrical spectrum.
  • the aim of changing and analyzing the filter coefficients is to achieve the fastest possible and automatic determination of different distortions such as dispersion, phase mode dispersion, self-phase modulation, etc.
  • a computer or a microprocessor can be used as a control unit, an analysis unit of the equalized signal in conjunction with a series of filter coefficients providing information about the signal distortions determined.
  • FIG. 5 shows an alternative arrangement according to FIG. 4 with an optical compensator OK instead of the optical-electrical converter OEW and the electrical equalizer EQ.
  • the same setting is carried out and the coefficients of the optical compensator OK are analyzed as in Fig. 4.
  • This also applies to an optical adaptive filter instead of the optical compensator.
  • FIG. 6 shows a representation of a setting space of filter coefficients, in which the resulting filter coefficients can be interpreted for further analysis, for example, as components P1, P2, P3 of a vector.
  • This vector is classified in terms of its position, length and direction in the parameter space of the filter coefficients.
  • One of the distortions e.g. B. dispersion, polarization mode dispersion PMD or self-phase modulation SPM, thus has adjacent coefficient vectors in an environment of the parameter space.
  • different signal distortions are equalized by setting different actuating vectors, different distortions and eye shapes are located in mutually separate environments in the parameter space.
  • FIG. 7 shows a first set of settings of here complex amplitude components of the seven filter coefficients of a 6th order FIR filter used as an equalizer with different signal distortions.
  • FIG. 8 shows a second set of settings for amounts of the complex amplitude components of the seven filter coefficients of a 6th order FIR filter used as an equalizer with different signal distortions according to FIG. 7.
  • the advantage of FIG. 7 is half the number of coefficients to be considered for the determination of the distortions, but at the expense or risk that the determination may not be accurate enough.
  • Fig. 9 shows a further possible application of the invention, which consists in the adjustment coefficients, which are suitable for an equalization z. B. have set by means of a compensator provided as a filter to calculate the transfer function of the transmission path of the optical signal S and to characterize it.
  • a compensator provided as a filter to calculate the transfer function of the transmission path of the optical signal S and to characterize it.
  • GD the transfer function of the 6th order optical FIR filter used here - and since the transfer function of this filter can ideally be inverse to the transfer function of the transmission path of the optical signal by precise analysis the transfer function of the filter can be used to determine the causes of interference in the optical signal on the transmission link.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Optical Communication System (AREA)

Abstract

L'invention concerne un procédé et plusieurs systèmes servant à déterminer des dégradations d'un signal optique transmis dans un système de transmission en présence de distorsions du signal. Selon l'invention, au moins une fraction du signal optique est transmise, au niveau d'un point de mesure du système de transmission, à un filtre adaptatif électrique ou optique, puis est mesurée selon un ou plusieurs paramètres de qualité. Une première mesure du paramètre de qualité est effectuée avec un réglage passant du filtre adaptatif et les mesures suivantes du paramètre de qualité sont exécutées avec des propriétés d'état passant prédéfinies du filtre optique adaptatif qui ont respectivement une influence sur une des distorsions du signal. Cela permet une analyse ou une séparation d'effets ou de groupes d'effets influant sur le signal. Selon un autre mode de réalisation de l'invention, les paramètres de filtre réglés d'une structure de correcteur ou de filtre optique/électrique sont analysés après optimisation de la qualité du signal.
EP03807733A 2002-10-08 2003-09-04 Procede et systeme pour determiner des degradations du signal en presence de distorsions du signal Withdrawn EP1550247A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE10246723A DE10246723A1 (de) 2002-10-08 2002-10-08 Verfahren und Anordnung zur Ermittlung von Signaldegradationen in Anwesenheit von Signalverzerrungen
DE10246723 2002-10-08
PCT/DE2003/002941 WO2004034611A1 (fr) 2002-10-08 2003-09-04 Procede et systeme pour determiner des degradations du signal en presence de distorsions du signal

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EP (1) EP1550247A1 (fr)
CN (1) CN1689255A (fr)
CA (1) CA2501372A1 (fr)
DE (1) DE10246723A1 (fr)
WO (1) WO2004034611A1 (fr)

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US20050201757A1 (en) 2005-09-15
DE10246723A1 (de) 2004-05-13
CA2501372A1 (fr) 2004-04-22
WO2004034611A1 (fr) 2004-04-22
US20060088318A1 (en) 2006-04-27

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