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WO2003030428A1 - Systeme pour ameliorer le rapport osnr d'un systeme de transmission dwdm - Google Patents

Systeme pour ameliorer le rapport osnr d'un systeme de transmission dwdm Download PDF

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Publication number
WO2003030428A1
WO2003030428A1 PCT/IN2001/000165 IN0100165W WO03030428A1 WO 2003030428 A1 WO2003030428 A1 WO 2003030428A1 IN 0100165 W IN0100165 W IN 0100165W WO 03030428 A1 WO03030428 A1 WO 03030428A1
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WO
WIPO (PCT)
Prior art keywords
dwdm
osnr
gain
signal
optical
Prior art date
Application number
PCT/IN2001/000165
Other languages
English (en)
Inventor
Parthasarathi Palai
Rajeev Roy
Original Assignee
Tejas Networks India Pvt. 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 Tejas Networks India Pvt. Ltd. filed Critical Tejas Networks India Pvt. Ltd.
Priority to PCT/IN2001/000165 priority Critical patent/WO2003030428A1/fr
Publication of WO2003030428A1 publication Critical patent/WO2003030428A1/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
    • H04B10/29—Repeaters
    • H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
    • H04B10/293—Signal power control
    • H04B10/294—Signal power control in a multiwavelength system, e.g. gain equalisation
    • H04B10/2941—Signal power control in a multiwavelength system, e.g. gain equalisation using an equalising unit, e.g. a filter
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/03—WDM arrangements
    • H04J14/0307—Multiplexers; Demultiplexers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0221—Power control, e.g. to keep the total optical power constant
    • H04J14/02216—Power control, e.g. to keep the total optical power constant by gain equalization
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B2210/00—Indexing scheme relating to optical transmission systems
    • H04B2210/25—Distortion or dispersion compensation
    • H04B2210/258—Distortion or dispersion compensation treating each wavelength or wavelength band separately

Definitions

  • the present invention relates to a system for improving Optical Signal to Noise Ratio (OSNR) of a transmission system using non gain-flattened optical amplifiers.
  • the present invention also relates to an optically amplified Dense Wavelength Division Multiplexed (DWDM) transmission system that incorporates aforesaid system and has improved channel OSNR.
  • OSNR Optical Signal to Noise Ratio
  • optical amplifiers are an integral part.
  • EDFA erbium doped fiber amplifiers
  • the use of optical amplifiers results in the generation of noise. This generation is intrinsic to the amplification process.
  • the ratio of the optical signal power to the optical noise power is called the Optical Signal to Noise Ratio (OSNR) and is a measure of the quality of the signal transmission.
  • the intrinsic gain spectrum of an EDFA consists of several peaks and valleys. In a chain of cascaded amplifiers the signal near the peak of the gain will grow at the expense of other signals. Hence the optical signal to noise ratio (OSNR) for different channels will be different even if at the input to the link, they were same.
  • OSNR optical signal to noise ratio
  • OSNR of the system can be improved by demultiplexing the signal channels in the middle of the link and carrying out the spectral equalization by using separate amplifier for each channel and multiplexing them by an optical multiplexer for onward transmission.
  • a publication by L. Eskildsen et al., IEEE Photon. Tech. Lett 6,1321 (1994) gives a description of a similar scheme.
  • the drawback of such a scheme is that as the channel count increases the system will become expensive due to the use of separate optical amplifiers for each channel.
  • the main object of the present invention is to provide a system to improve the OSNR of channels of a transmission system.
  • Another object of the present invention is to provide a system which uses non gain- flattened EDFAs in a multichannel transmission system for reducing the relative variation in the OSNR across the channels.
  • Yet another object of the present invention is to provide a system for increasing the number of spans in a multichannel transmission system using non gain-flattened EDFAs.
  • Still another object of the present invention is to provide a system for alleviating the OSNR limitation on the link length in a multichannel transmission system using non gain- flattened EDFAs.
  • One more object of the present invention is to provide an optically amplified Dense
  • Wavelength Division Multiplexed (DWDM) transmission system that incorporates aforesaid system and has improved channel OSNR.
  • the present invention provides a system for improving Optical Signal to
  • OSNR Noise Ratio
  • the present invention also provides an optically amplified Dense Wavelength Division Multiplexed (DWDM) transmission system that incorporates aforesaid system and has improved channel OSNR.
  • DWDM Dense Wavelength Division Multiplexed
  • the present invention provides a system for improving Optical Signal to Noise Ratio (OSNR) of a transmission system using non gain-flattened optical amplifier, said system comprising a WDM Band Splitter (101) connected to plurality of Variable Optical Attenuators (NOAs) (102), outputs from all NOAs are connected to a WDM Band Combiner (103) and output of said WDM Band Combiner being passed through a non gain-flattened optical amplifier (104).
  • OSNR Optical Signal to Noise Ratio
  • the WDM Band splitter splits the incoming optical signal into plurality of multi-channel signal bands.
  • the WDM Band Splitter splits the incoming optical signal into two multi-channel signal bands.
  • the WDM Band Splitter splits the optical signal into two multi-channel signal bands, one having longer wavelengths and the other having shorter wavelengths.
  • spectral equalization is carried out on the two multi -channel signal bands.
  • spectral equalization of the multi-channel band is performed using individual non gain-flattened optical amplifiers.
  • the two multi-channel signal bands are separately transmitted through two Variable Optical Attenuators (102a) and (102b).
  • the two NOAs (102a and 102b) provide fine tuning required to obtain optimum link performance.
  • the attenuation provided by the two VOAs are set to provide equal lowest signal / channel powers in both bands.
  • the two multi-channel signal bands are combined by the WDM Band Combiner.
  • the combined multi-channel signal is passed through a non gain-flattened optical amplifier (104).
  • the non-gain flattened optical amplifier is an Erbium Doped Fiber Amplifier (EDFA).
  • EDFA Erbium Doped Fiber Amplifier
  • the EDFA is set for constant gain operation. In a further embodiment of the present invention, the EDFA is set to provide gain more than the insertion losses due to the WDM Band Splitter, VOAs and the WDM Band Combiner and also to provide the signals with additional power.
  • the system is optionally provided with one or more Optical Spectrum Analyzers (OSA) to view the spectra of the multi-channel signal bands.
  • OSA Optical Spectrum Analyzers
  • the present invention also provides an optically amplified Dense Wavelength Division Multiplexed (DWDM) transmission system having improved channel OSNR, said transmission system comprising an Array of Transmitters (201) whose output is multiplexed using a Multiplexer (202), the multiplexed signal is amplified using a Booster Amplifier (203) and launched into a number of spans, one or more systems as herein described before (208) connected in between the spans to improve the OSNR of the transmission system, the signal from the last span is given to a Demultiplexer (209) and the demultiplexed signal is detected using an array of receivers (210).
  • DWDM Dense Wavelength Division Multiplexed
  • the transmitter array consists of lOGbps externally modulated lasers (EML).
  • the transmitter array includes 16 channels from ITU- T grid no. 22 to 37.
  • the Booster Amplifier is a non gain- flattened EDFA operating under constant power configuration.
  • the transmission system comprises of twelve spans.
  • each span consists of 80 Km of ITU-T G. 652 compliant Single Mode Fibers (SMF) (206), a Dispersion Compensation Fiber (DCF) (204), two Inline Amplifiers ILA1 (207) and ILA2 (205).
  • SMF Single Mode Fibers
  • DCF Dispersion Compensation Fiber
  • ILA1 Inline Amplifiers
  • ILA2 ILA2
  • the DCF (204) compensates the accumulated dispersion of each span.
  • the Inline Amplifier (E A2) (205) makes up the nominal loss in the DCF.
  • the Inline Amplifier (ILA1) (207) makes up for the nominal loss in the SMF.
  • the Inline Amplifiers are non gain-flattened EDFAs.
  • ILAl and ELA2 are operated under constant gain conditions.
  • the system to improve the OSNR (208) is implemented after the fourth ' span.
  • the system (208) splits the 16 channel optical signal into 2 eight-channel signal bands, one having longer wavelengths and the other having shorter wavelengths.
  • the band having signals of longer wavelength comprises ITU-T grid Nos. 22 to 29.
  • the band having signals of shorter wavelength comprises ITU-T grid Nos. 30 to 37.
  • Figure 1 is a schematic configuration of the system, used to improve the OSNR.
  • Figure 2 is a schematic diagram of the DWDM transmission system employing the system of the present invention after the fourth span to improve the OSNR.
  • Figure 3 is the illustration of the spectrum of the signal after the Booster Amplifier
  • Figure 4 is the illustration of the spectrum of the signal at the end of the 5 th span, without any spectral reshaping.
  • Figure 5 is the illustration of the spectrum of the signals just after implementing the system of the present invention at the end of the 4 th Span.
  • Figure 6 is the illustration of the spectrum of the signals after the 5 th span after implementing the system of the present invention at the end of the 4 th span.
  • Figure 7 is the illustration of the OSNR map of an ordinary DWDM system (without implementing the system of the present invention).
  • Figure 8 is the illustration of the OSNR map when the system of the present invention is implemented.
  • Table 1 provides a list of parameters used to simulate the DWDM link, as detailed in figure 2, using VPItransmissionmakerTM WDM software.
  • Table 2 provides the numbers corresponding to the graphical representation of the OSNR ⁇ of all channels from spans 1 through 12 and at the output of the system 208 as illustrated by Figure 8.
  • Table 3 provides the data showing the improvement in the OSNR in each of the individual channels over the entire span, once the system 208 is implemented after the fourth span.
  • a system through which the OSNR improvement is achieved.
  • the signal is transmitted to a WDM Band Splitter 101.
  • the function of the band splitter is to split the incoming signals into two bands.
  • One band consists of the longer wavelengths and the other band consists of the shorter wavelengths. While the figure specifically refers to two bands, this can be generalized to having more bands.
  • the spectra of the two bands may be viewed in an Optical Spectrum Analyzer (OSA).
  • OSA Optical Spectrum Analyzer
  • Each of the bands has peaks and valleys of signals.
  • the bands are separately transmitted through two separate Variable Optical Attenuators 102a and 102b.
  • the VOAs are set such that the minimum signal or channel powers in the two bands are more or less equal.
  • the VOAs 102a and 102b are subsequently fine-tuned for optimum link performance when the scheme is implemented in a DWDM transmission system.
  • the bands are subsequently combined using a WDM band combiner 103.
  • the combined signals are passed through a non gain-flattened EDFA 104.
  • the EDFA is set for constant gain operation.
  • the EDFA 104 is used to overcome the insertion losses due to the WDM Band Splitter, VOAs and the WDM Band Combiner and also to provide the signals with additional power.
  • FIG. 2 is illustrating the use of the scheme to improve the OSNR in a multi-span optically amplified DWDM transmission system.
  • the output of a Transmitter Array 201 is multiplexed using a Multiplexer 202.
  • the signal is then boosted by a non gain-flattened Booster Amplifier 203 and launched into the first span.
  • span number one, four, five and twelve are illustrated.
  • the Dispersion Compensating Fibers (DCF) in span numbers one, four, five and twelve are denoted by 204a, 204b, 204c, and 204d, respectively.
  • DCF Dispersion Compensating Fibers
  • the ITU-T G.652 compliant Single Mode Fiber (SMF) in span numbers one, four, five and twelve are denoted by 206a, 206b, 206c, and 206d respectively.
  • SMF Single Mode Fiber
  • ILAl The non gain-flattened Inline Amplifiers used to make up for the nominal loss in the SMF is denoted by ILAl and are represented in the figure in span number one, four, five and twelve by 207a, 207b, 207c and 207d, respectively.
  • the non gain-flattened Inline Amplifiers used to make up for the nominal loss in the DCF is denoted by ILA2 and are represented in the figure in span number one, four, five and twelve by 205a, 205b, 205c and 205d, respectively.
  • the scheme to improve the OSNR 208 is implemented after the fourth span. The detailed working of the same has been explained earlier with reference to Figure 1.
  • the signal coming out of the multiplexer is introduced to the next span, namely the fifth span and it gets transmitted to the subsequent spans.
  • the signal is demultiplexed using the Demultiplexer 209.
  • the demultiplexed signals are detected by an array of receivers 210.
  • the simulation parameters used to simulate the link using VPItransmissionmakerTM WDM are provided in Table 1.
  • the transmitter array includes 16 Channels from ITU-T grid no. 22 to 37 consisting of lOGbps externally modulated lasers (EML).
  • EML externally modulated lasers
  • the signals are multiplexed using a multiplexer and thereafter boosted by a non gain-flattened booster EDFA operated under a constant power configuration.
  • Each span consists of 80 km of ITU-T G.652 compliant fibers.
  • Link loss is compensated by a non-gain flattened EDFA operating under constant gain condition.
  • the accumulated dispersion of each span is compensated by a Dispersion Compensating Fiber (DCF) and the loss incurred in the DCF length is compensated by another non-gain flattened EDFA operating under constant gain condition.
  • DCF Dispersion Compensating Fiber
  • the scheme to improve the OSNR as has been detailed in Figure 1 has been implemented after the fourth span.
  • the two bands that are split consist of ITU-T grid 22-29 in the first band and ITU-T grid 30-37 in the second band.
  • Figure 3 illustrates the spectrum after the Booster Amplifier. In the 1530 nm region, the gap in the spectrum is attributed to the amplified spontaneous emission (ASE) rejection filter used with each amplifier in order to prevent the saturation of subsequent amplifiers in the link by ASE noise. It can be observed from the figure that the spectrum of the transmitters is more or less flat after the booster amplifier.
  • ASE amplified spontaneous emission
  • Figure 4 illustrates the spectrum after the fifth span wherein the scheme to improve the OSNR is not implemented. It can be observed that there are peaks and valleys of the amplifier in the signal band. The valleys degrade the OSNR considerably.
  • Figure 5 illustrates the spectrum after the implementation of the scheme to improve the OSNR.
  • the spectrum is noted at the point where the signal is launched into the fifth span.
  • VOAs 103a and 103b are used to fine-tune the settings to get optimum link performance.
  • Figure 6 illustrates the spectrum at the end of the fifth span where the scheme to improve the OSNR is carried out at the end of the fourth span. As had been mentioned earlier with reference to figure 5 the spectral reshaping done at the end of the fourth span can be observed.
  • the OSNR map when channels are transmitted across all twelve spans without the implementation of the scheme to improve the OSNR, is illustrated in Figure 7.
  • the improvement in the OSNR after the implementation of the scheme can be seen in Figure 8.
  • the corresponding data is tabulated in Table 2.
  • the data showing the improvement in the OSNR in each of the individual channels over the entire span, once the system 208 is implemented after the fourth span is shown in Table 3.
  • the implementation of the scheme to improve the OSNR results in all channels having a Bit Error Rate (BER) of less than 1 in 10 15 even at the end of the eighth span.
  • Table 1 List of parameters used to simulate the DWDM link, as detailed in Figure 2, using VPItransmissionmakerTM WDM software.
  • Table 2 The numbers corresponding to the graphical representation of the OSNR of all channels from spans 1 through 12 and at the output of the system 208 as illustrated by Figure 8 are given in the table below.
  • Table 3 The improvement in the OSNR in the various spans, once the system 208 is implemented after the fourth span, over a link where system 208 is not implemented, is given in the table below.

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

Abstract

Cette invention se rapporte à un système servant à améliorer le rapport signal optique/bruit (OSNR) d'un système de transmission en utilisant des amplificateurs optiques à gain aplati (104), ainsi qu'à un système de transmission multiplexé en longueur d'onde dense (DWDM) optiquement amplifié, qui intègre le système faisant l'objet de cette invention et qui possède un rapport OSNR de canal amélioré.
PCT/IN2001/000165 2001-10-03 2001-10-03 Systeme pour ameliorer le rapport osnr d'un systeme de transmission dwdm WO2003030428A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/IN2001/000165 WO2003030428A1 (fr) 2001-10-03 2001-10-03 Systeme pour ameliorer le rapport osnr d'un systeme de transmission dwdm

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IN2001/000165 WO2003030428A1 (fr) 2001-10-03 2001-10-03 Systeme pour ameliorer le rapport osnr d'un systeme de transmission dwdm

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Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5361319A (en) * 1992-02-04 1994-11-01 Corning Incorporated Dispersion compensating devices and systems
US5712717A (en) * 1995-03-03 1998-01-27 France Telecom High isolation, optical add-drop multiplexer
US6069718A (en) * 1997-09-19 2000-05-30 Nortel Networks Corporation Distortion penalty measurement procedure in optical systems using noise loading
US6115157A (en) * 1997-12-24 2000-09-05 Nortel Networks Corporation Methods for equalizing WDM systems
US6141130A (en) * 1998-01-14 2000-10-31 Jds Fitel Inc. Spectral equalizer for multiplexed channels
US6236499B1 (en) * 1999-04-15 2001-05-22 Nortel Networks Limited Highly scalable modular optical amplifier based subsystem
US6275313B1 (en) * 1998-02-03 2001-08-14 Lucent Technologies Inc. Raman gain tilt equalization in optical fiber communication systems
US20020015201A1 (en) * 2000-07-21 2002-02-07 Sycamore Networks, Inc. Method and apparatus for extending fiber transmission distance with multiple pre-emphases in optically amplified DWDM system

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5361319A (en) * 1992-02-04 1994-11-01 Corning Incorporated Dispersion compensating devices and systems
US5712717A (en) * 1995-03-03 1998-01-27 France Telecom High isolation, optical add-drop multiplexer
US6069718A (en) * 1997-09-19 2000-05-30 Nortel Networks Corporation Distortion penalty measurement procedure in optical systems using noise loading
US6115157A (en) * 1997-12-24 2000-09-05 Nortel Networks Corporation Methods for equalizing WDM systems
US6141130A (en) * 1998-01-14 2000-10-31 Jds Fitel Inc. Spectral equalizer for multiplexed channels
US6275313B1 (en) * 1998-02-03 2001-08-14 Lucent Technologies Inc. Raman gain tilt equalization in optical fiber communication systems
US6236499B1 (en) * 1999-04-15 2001-05-22 Nortel Networks Limited Highly scalable modular optical amplifier based subsystem
US20020015201A1 (en) * 2000-07-21 2002-02-07 Sycamore Networks, Inc. Method and apparatus for extending fiber transmission distance with multiple pre-emphases in optically amplified DWDM system

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