WO2003052986A1 - Commande de filtres a longueur d'onde selectionnable dans reseaux optiques - Google Patents

Commande de filtres a longueur d'onde selectionnable dans reseaux optiques Download PDF

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Publication number
WO2003052986A1
WO2003052986A1 PCT/GB2002/005462 GB0205462W WO03052986A1 WO 2003052986 A1 WO2003052986 A1 WO 2003052986A1 GB 0205462 W GB0205462 W GB 0205462W WO 03052986 A1 WO03052986 A1 WO 03052986A1
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WO
WIPO (PCT)
Prior art keywords
filter
error rate
frequency
signal
optical
Prior art date
Application number
PCT/GB2002/005462
Other languages
English (en)
Inventor
Peter James Livermore
Martin Lomas
Peter Joseph Nicholls
Original Assignee
Marconi Uk Intellectual Property Ltd
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 Marconi Uk Intellectual Property Ltd filed Critical Marconi Uk Intellectual Property Ltd
Priority to AU2002350900A priority Critical patent/AU2002350900A1/en
Publication of WO2003052986A1 publication Critical patent/WO2003052986A1/fr

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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
    • H04B10/60—Receivers
    • H04B10/66—Non-coherent receivers, e.g. using direct detection
    • H04B10/67—Optical arrangements in the receiver
    • H04B10/671—Optical arrangements in the receiver for controlling the input optical signal
    • H04B10/675—Optical arrangements in the receiver for controlling the input optical signal for controlling the optical bandwidth of the input signal, e.g. spectral filtering
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems

Definitions

  • This invention relates to the control of tuneable filters in optical networks. It is particularly concerned with such filters used in Wave Division Multiplex (WDM) networks, especially, but not exclusively Dense WDM (DWDM) networks.
  • WDM Wave Division Multiplex
  • DWDM Dense WDM
  • the composite signal is dropped from the network and split in a 1:N splitter where N is the number of channels in the multiplex.
  • N is the number of channels in the multiplex.
  • Each of the N outputs of the splitter has an optical bandpass filter which is tuned to the frequency of a given channel so that only that channel is passed.
  • these filters are non-adjustable but it has been proposed to use tuneable wavelength selectable filters. If wavelength selectable filters are used, it is essential that they are precisely tuned to the centre frequency of the channel to be received. Failure to tune the filter sufficiently precisely will lead to an unacceptably high error rate in the received traffic. It is possible to use open loop control for the filter. However, this is disadvantageous as any variation in the filter centre frequency will lead to a degraded performance.
  • the invention overcomes the problems mentioned above by measuring the bit error rate of the data at a preset filter position and then dithering the filter frequency and measuring the error rate at each dithered frequency.
  • the filter can be set to the frequency at which the error rate is a minimum. As the signal is sent with forward error control data, the process is transparent to the user.
  • a method of tuning an adjustable optical filter which passes optical information from a DWDM optical network, the optical information being encoded using a forward error correction (FEC) code comprising setting the adjustable filter to a predetermined frequency and measuring the bit error rate in information passed by the filter; adjusting the filter tuning incrementally to further frequencies on each side of the predetermined frequency and measuring the bit error rate at each further frequency; and setting the filter to the frequency at which the bit error rate is a minimum.
  • FEC forward error correction
  • the invention further provides a tuneable optical filter system for use in an optical network in which optical information on the network is encoded with a forward error correction (FEC) code, comprising: a tuneable optical filter for receiving a DWDM signal from the network and for passing a selected band of the signal; a forward error correction decoder for decoding information passed by the filter and generating an error signal indicative of the error rate in the decoded information; and a controller for varying the tuning of the optical filter incrementally about a predetermined frequency, for comparing the error signal at each frequency to which the filter is tuned and for setting the filter at the frequency at which the error signal is indicative of the lowest error rate.
  • FEC forward error correction
  • Embodiments of the invention have the advantage that the exact optimum setting of the filter can be found in a manner that is transparent to the user.
  • embodiments of the invention use FEC bit error rate variations, the errors which are induced by dithering the tuning frequency are corrected by the FEC decoder and corrector before they reach the user.
  • the system can be operated at its maximum capacity so enhancing its usefulness.
  • Figure 1 is a schematic illustration of an optical ring network
  • Figure 2 is a schematic block diagram of an embodiment of the present invention.
  • Figure 3 is a flow chart illustrating operation of a method embodying the invention.
  • Figure 1 shows, schematically, a two fibre 10GHz optical network which carries a 32 channel DWDM signal.
  • a number of nodes 10 are arranged on the network. Traffic is sent on the network from a source node to a target node where it is dropped from the network.
  • Figure 2 shows a portion of one of the nodes 10 on the ring network.
  • the optical DWDM signal is split from the network by a signal splitter 12 to produce a dropped signal output 14.
  • the other output of the splitter is through traffic labelled T which remains on the network.
  • the dropped optical signal is passed to a 32:1 splitter 16 which outputs 32 signals, each of which comprises the 32 channel multiplex.
  • Figure 2 only shows how one of these channels is processed but it will be understood that similar processing is performed on each of the channels.
  • the output 18 from the signal splitter 16 is input to a tuneable filter 2Q.
  • the filter is an essentially mechanical component whose centre frequency is controlled by a servo motor.
  • the centre frequency can vary with time or with operating conditions such as temperature.
  • the output of the optical bandpass filter is a single wavelength signal which is passed to a receive side transponder 22 where the optical single wavelength signal is converted into an electrical signal. This electrical signal forms the input to a forward error control chip 24.
  • Forward error control is a well known method used in optical communications to enable a receiver to correct errors in the received data.
  • a degree of redundant coding is introduced into the data stream according to one of a number of coding algorithms.
  • One such algorithm is the Reed-Solomon algorithm which is a block based error correction code which encodes an array of k data symbols as in input and returns an array of n symbols.
  • a Reed Solomon encoder Operating in a 10GHz environment, a Reed Solomon encoder will convert a 9.9Gbps symbol stream into a 10.7Gbps stream.
  • the forward error correction encoding is introduced when traffic at 9.9Gbps is converted to the 10.7Gbps symbol stream when it is input into the optical network.
  • this 10.7Gbps stream passes through the tuneable filter 20 to the FEC chip 24.
  • the FEC chip 24 comprises a decoder 26 which decodes the electrical data symbols and a corrector 28 which operates under the control of correction data received from the decoder i to correct the decoded data.
  • the corrected data is then output to its intended destination as the 9.9Gbps stream.
  • the decoder 26 also calculates a bit error rate (BER) which is used as a control signal to control the tuning of the bandpass filter.
  • BER bit error rate
  • the signal controls the filter servo.
  • the bit error rate is a measure of the number of errors in the data stream and varies with the tuning of the filter. When the filter is in its optimum position, the bit error rate will be at a minimum.
  • the BER signal is fed to a microcontroller 30 which may typically be a microprocesser controlled device which generates a wavelength control signal to alter the tuning of the bandpass filter.
  • This signal is first converted to an analog signal by a digital to analog converter 32 and then applied to a control input of the filter. The manner in which the process operates will now be explained with reference to the flowchart of Figure 3.
  • the channel to which the bandpass filter is to pass is set, for example from a remote network manager.
  • channel 20 may be selected.
  • a value for the selected channel is retrieved from a look up table by the microcontroller 30 at step 42.
  • this may be an angle of 23°.
  • a control signal is output, converted to an analog signal and applied to the control input of the filter.
  • the bit error rate (BER) for this setting is retrieved from the FEC decoder.
  • the microcontroller determines whether there are any errors at step 46. If there are not, the filter is judged to be correctly positioned and the process loops back to step 40 with the BER being checked periodically.
  • the BER shows that there are errors the BER is stored and at step 48 the signal to the DAC 32 is incremented or decremented.
  • the signal change could represent +/-1E of filter position.
  • the signal is incremented by IE to an angle of 24°.
  • the error rate is then retrieved again at step 50 and the error rate at 24° compared with the error rate at 23° at step 52. If the error rate BER (T+ i) is not greater than the error rate BER ( ⁇ ) , then the sense of the adjustment of the filter is correct and is moving towards the optimum point. In that case, the process loops back and increments the filter angle by a further 1°.
  • the filter position is adjusted to a position 1° to the other side of the start position, that is 22°.
  • the BER is retrieved and stored (as BET( T+ D) at step 56.
  • the stored value is compared with the initial bit error rate. If the rate is falling a further decrement is made at step 54. If it is increasing the processing reverts back to step 44. Eventually a position will be established where BER is at a minimum. This position corresponds to the optimum filter position.
  • the filter can be tuned by deliberately introducing errors.
  • the FEC chip ensures that these errors are transparent to the user and that the user continues to receive error free data.
  • the use of dithering either side of the predetermined optimum point of the filter does not increase the error rate to such an extent that the FEC chip can no longer correct the errors.
  • the optimisation of the filter is performed gradually and continues while the system is running. If the centre frequency of the filter drifts, for example with time or temperature, the FEC error correction rate will measure a skew, showing that the degradation is greater in one direction than the other when the output is dithered. The filter can then be pulled back to its optimum operating point.
  • the system can be operated at full capacity.

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

Abstract

Un filtre optique accordable est utilisé pour la sélection d'une voie donnée de données dans un multiplex DWDM (multiplexage par répartition en longueur d'onde). Les données sont codées sur la voie par correction d'erreur sans circuit de retour. Le filtre est réglé sur une position prémémorisée pour la voie sélectionnée et le taux d'erreur sur les bits est mesuré au niveau de cette position. L'accord est ensuite assuré par tremblotement autour de la position originale et le taux d'erreur est mesuré à chaque réglage. Le filtre est réglé sur la position au niveau de laquelle le taux d'erreur sur les bits est minimum, de sorte que l'accord soit optimisé.
PCT/GB2002/005462 2001-12-19 2002-12-04 Commande de filtres a longueur d'onde selectionnable dans reseaux optiques WO2003052986A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002350900A AU2002350900A1 (en) 2001-12-19 2002-12-04 Control of wavelength selectable filters in optical networks

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0130346.0 2001-12-19
GBGB0130346.0A GB0130346D0 (en) 2001-12-19 2001-12-19 Control of wavelength selectable filters in optical networks

Publications (1)

Publication Number Publication Date
WO2003052986A1 true WO2003052986A1 (fr) 2003-06-26

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Family Applications (1)

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PCT/GB2002/005462 WO2003052986A1 (fr) 2001-12-19 2002-12-04 Commande de filtres a longueur d'onde selectionnable dans reseaux optiques

Country Status (3)

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AU (1) AU2002350900A1 (fr)
GB (1) GB0130346D0 (fr)
WO (1) WO2003052986A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113196693A (zh) * 2019-02-25 2021-07-30 华为技术有限公司 用于控制光网络中的光信号的方法和装置

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5552919A (en) * 1992-06-27 1996-09-03 Canon Kabushiki Kaisha Tunable-filter control method, tunable-filter control apparatus and optical communication system using the same
US6043922A (en) * 1996-06-03 2000-03-28 Nec Corporation Optical receiver board, optical wavelength-tuning filter module used for optical receiver board, and actuator for optical wavelength-tuning filter module
EP1011216A1 (fr) * 1998-12-14 2000-06-21 Alcatel Système de transmission à fibre optique comprenant un filtre de réception de largeur variable
US20010019436A1 (en) * 2000-03-03 2001-09-06 Isao Nakajima System and method for equalizing transmission characteristics in wavelength division multiplexing optical communication system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5552919A (en) * 1992-06-27 1996-09-03 Canon Kabushiki Kaisha Tunable-filter control method, tunable-filter control apparatus and optical communication system using the same
US6043922A (en) * 1996-06-03 2000-03-28 Nec Corporation Optical receiver board, optical wavelength-tuning filter module used for optical receiver board, and actuator for optical wavelength-tuning filter module
EP1011216A1 (fr) * 1998-12-14 2000-06-21 Alcatel Système de transmission à fibre optique comprenant un filtre de réception de largeur variable
US20010019436A1 (en) * 2000-03-03 2001-09-06 Isao Nakajima System and method for equalizing transmission characteristics in wavelength division multiplexing optical communication system

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
TOMIZAWA M ET AL: "FORWARD ERROR CORRECTING CODES IN SYNCHRONOUS FIBER OPTIC TRANSMISSION SYSTEMS", JOURNAL OF LIGHTWAVE TECHNOLOGY, IEEE. NEW YORK, US, vol. 15, no. 1, 1997, pages 43 - 51, XP000642276, ISSN: 0733-8724 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113196693A (zh) * 2019-02-25 2021-07-30 华为技术有限公司 用于控制光网络中的光信号的方法和装置
CN113196693B (zh) * 2019-02-25 2023-03-03 华为技术有限公司 用于控制光网络中的光信号的方法和装置

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Publication number Publication date
GB0130346D0 (en) 2002-02-06
AU2002350900A1 (en) 2003-06-30

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