EP1618685A1 - Module de correction de dispersion chromatique - Google Patents

Module de correction de dispersion chromatique

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Publication number
EP1618685A1
EP1618685A1 EP03776885A EP03776885A EP1618685A1 EP 1618685 A1 EP1618685 A1 EP 1618685A1 EP 03776885 A EP03776885 A EP 03776885A EP 03776885 A EP03776885 A EP 03776885A EP 1618685 A1 EP1618685 A1 EP 1618685A1
Authority
EP
European Patent Office
Prior art keywords
compensation optical
average
chromatic dispersion
optical fiber
compensation
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Withdrawn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
EP03776885A
Other languages
German (de)
English (en)
Inventor
Pierre Sillard
Bruno Dany
Alain Bertaina
Maxime Gorlier
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.)
Draka Comteq BV
Original Assignee
Draka Comteq BV
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Filing date
Publication date
Application filed by Draka Comteq BV filed Critical Draka Comteq BV
Publication of EP1618685A1 publication Critical patent/EP1618685A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02004—Optical fibres with cladding with or without a coating characterised by the core effective area or mode field radius
    • G02B6/02009—Large effective area or mode field radius, e.g. to reduce nonlinear effects in single mode fibres
    • G02B6/02014—Effective area greater than 60 square microns in the C band, i.e. 1530-1565 nm
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02004—Optical fibres with cladding with or without a coating characterised by the core effective area or mode field radius
    • G02B6/02009—Large effective area or mode field radius, e.g. to reduce nonlinear effects in single mode fibres
    • G02B6/02023—Based on higher order modes, i.e. propagating modes other than the LP01 or HE11 fundamental mode
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02214—Optical fibres with cladding with or without a coating tailored to obtain the desired dispersion, e.g. dispersion shifted, dispersion flattened
    • G02B6/02219—Characterised by the wavelength dispersion properties in the silica low loss window around 1550 nm, i.e. S, C, L and U bands from 1460-1675 nm
    • G02B6/02252—Negative dispersion fibres at 1550 nm
    • G02B6/02261—Dispersion compensating fibres, i.e. for compensating positive dispersion of other fibres
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02214—Optical fibres with cladding with or without a coating tailored to obtain the desired dispersion, e.g. dispersion shifted, dispersion flattened
    • G02B6/0228—Characterised by the wavelength dispersion slope properties around 1550 nm
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03661—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 4 layers only
    • G02B6/03672—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 4 layers only arranged - - + -
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03688—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 5 or more layers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29371—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion
    • G02B6/29374—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion in an optical light guide
    • G02B6/29376—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion in an optical light guide coupling light guides for controlling wavelength dispersion, e.g. by concatenation of two light guides having different dispersion properties
    • G02B6/29377—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion in an optical light guide coupling light guides for controlling wavelength dispersion, e.g. by concatenation of two light guides having different dispersion properties controlling dispersion around 1550 nm, i.e. S, C, L and U bands from 1460-1675 nm
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/29392—Controlling dispersion
    • G02B6/29394—Compensating wavelength dispersion

Definitions

  • the field of tne invention is chat of chromatic dispersion compensation modules
  • attenuation and attenuation coefficient are used interchangeably rfith regard to optical fibers
  • WDM wavelength division multiplexing
  • the bit rate is low, for example 2 5 gigabits per second (Gbit/s) per channel, it is not necessary to compensate the chromatic dispersion of the line optical fibers
  • Gbit/s gigabits per second
  • a line optical fiber generally has positive chromatic dispersion and positive dispersion slope Consequently, a chromatic dispersion compensating optical fiber will generally have negative chromatic dispersion and negative dispersion slope
  • the chromatic dispersion compensation optical fiber can be integrated into a chromatic dispersion compensation module
  • the spectral range within which chromatic dispersion is to be compensated can include one or more of bands C, L and S
  • the optical signal propagates m the chromatic dispersion
  • the two-stage amplifier system For the two-stage amplifier system to have a good optical signal-to-noise ratio and gain across the spectrum that is flat, the two-stage amplifier system presents a first amplifier with high gain, which yields high optical power at the output of the first amplifier, and it presents losses between the two amplifiers at a level that is fixed.
  • the chromatic dispersion compensation optical fiber integrated into the chromatic dispersion compensation module is a high-order mode (HOM) multimode optical fiber which has a very large effective area, for example of the order of 80 square micrometers ( ⁇ m 2 ) , which makes it much less sensitive to non-linear effects than a single-mode optical fiber; however, HOM multimode optical fibers nevertheless have some sensitivity to non-linear effects.
  • HOM multimode optical fibers To preserve good optical signal transmission quality it can be beneficial to limit the optical power input into an HOM multimode chromatic dispersion compensation optical fiber.
  • an attenuator can be placed between the first amplifier and the chromatic dispersion compensation module. The attenuator also controls the flatness of the gain across the spectrum.
  • the attenuator can be replaced by a wavelength routing component or by any other optical component that has losses and can therefore, like an attenuator, limit the optical power input into the chromatic dispersion compensation module.
  • the problem is to produce a chromatic dispersion compensation module offering the best possible quality.
  • the cost of a chromatic dispersion compensation module based on HOM multimode compensation optical fiber is relatively high because it includes the cost of the mode converters situated at the upstream and downstream ends of the HOM multimode compensation optical fibers .
  • this kind of compensation module can be more effective than a compensation module based on single-mode compensation optical fiber, because of the very highly negative values of the chromatic dispersion of the compensation optical fiber and because of the much greater ability of HOM multimode fibers with a very large effective area to withstand non-linear effects.
  • One prior art compensation module is based on the use of an HOM multimode compensation optical fiber that does not have a very highly negative value for chromatic dispersion, in order to be able to achieve a chromatic dispersion to dispersion slope ratio that is sufficiently high to compensate not only the chromatic dispersion but also the dispersion slope of the line optical fiber.
  • a drawback of that first prior art is that it does not fully obtain the benefits of the very highly negative values of chromatic dispersion that HOM multimode optical fibers can achieve.
  • Another drawback of that first prior art is its poor multiple path interference (MPI) performance, although it has good performance in terms of insertion losses.
  • MPI multiple path interference
  • a second prior art compensation module is based on the use of a combination of an HOM multimode compensation optical fiber having a very highly negative value of chromatic dispersion together with a single-mode compensation optical fiber in order to obtain a chromatic dispersion to dispersion slope ratio that is sufficiently high for the compensation optical line to 'compensate not only the chromatic dispersion but also the dispersion slope of the line optical fiber.
  • One drawback of that prior art is its complex design and the resulting complexity of the process of fabricating the compensation module. Another drawback is that it does not provide compensation in a very wide spectral band.
  • a further drawback is that it loses to at least some degree an essential advantage of HOM multimode compensation optical fibers, namely their large effective area, as a result of associating them with a single-mode compensation optical fiber whose effective area is much smaller. Moreover, high losses occur at the connection between the HOM multimode compensation optical fiber and the single-mode compensation optical fiber, which further increases the already high insertion losses; indeed, the presence of a connector is unavoidable, which does not apply to the junction between two HOM multimode compensation optical fibers. In conclusion, improving the ability to withstand non-linear effects increases the complexity of the module and degrades insertion losses.
  • the object of the invention is to propose a high quality chromatic dispersion compensation module fully exploiting the benefits of HOM multimode optical fibers .
  • the compensation module of the invention does not contain any single-mode optical fiber.
  • Prior art methods of improving the quality of a compensation module are based on unilaterally improving a parameter that is partially representative of the quality of the compensation module. Unilaterally improving only one parameter that is partially representative of the quality of the compensation module, whether that parameter be insertion losses or non-linear phase, has two consequences. Firstly, it increases the cost of the compensation module. Secondly, it tends to degrade the other parameter that is partially representative of the quality of the compensation module, so the quality of the compensation module is improved less than desired, and possibly only little or not at all.
  • the method of the invention of improving the quality of a compensation module is completely different. Firstly, it creates a quality criterion which is globally representative of the quality of a compensation module and which integrates, with appropriate weighting, the contribution of the insertion losses and the contribution of the non-linear effects.
  • the contribution of the insertion losses corresponds to the conventional insertion losses except that it is related to full compensation of the line optical fiber, while the contribution of the non-linear effects is reflected in a non-linearity criterion related to but separate from the non-linear phase.
  • the non-linearity criterion is obtained by judicious simplification of the non-linear phase to take account of the constant nature of the losses between the two amplifiers of the two-stage amplification system.
  • Optimizing this novel quality criterion either significantly improves the insertion losses without excessively degrading ability to withstand non-linear effects, and thus globally improves the quality of the compensation module, or significantly improves ability to withstand non-linear effects without excessively degrading the insertion losses, and thus globally improves the quality of the compensation module.
  • the quality of the compensation module of the invention as measured by the novel quality criterion previously described is high.
  • the number of core segments in the core of the compensation optical fiber is preferably relatively high. In an application with relatively few channels in a spectral band, where linearity can be sacrificed to some degree, compensation optical fibers whose core comprises few core segments are acceptable.
  • the compensation module of the invention uses at least one compensation optical fiber whose core comprises a large number of core segments in order to be able to reconcile a very highly negative value of chromatic dispersion and a chromatic dispersion to dispersion slope ratio that is not only high but also has good linearity as a function of wavelength.
  • the core segments are preferably rectangular, as in the examples described hereinafter; the core segments can also nevertheless be triangular or " alpha-shaped; likewise, some core segments can have one particular shape and other core segments a different shape .
  • the first aspect of the invention therefore proposes a compensation module design method and two compensation modules, one suited to compensating a standard single-mode line optical fiber (SMF) and the other suited to compensating a non-zero dispersion shifted single-mode line optical fiber (NZ-DSF) .
  • the second aspect of the invention therefore proposes two compensation modules, one suited to compensating a standard single-mode line optical fiber and the other suited to compensating a nonzero dispersion shifted single-mode line optical fiber.
  • a chromatic dispersion compensation module said module being adapted to comprise, an enclosure including an input terminal and an output terminal, a higher-order mode chromatic dispersion compensation optical line situated inside the enclosure and disposed between the input terminal and the output terminal, the line comprising one or more HOM multimode chromatic dispersion compensation optical fibers in series and not comprising any single-mode optical fiber, an input mode converter for converting the fundamental mode into said higher order mode, situated between the input terminal and the compensation optical line, an output mode converter for converting said higher order mode into the fundamental mode, situated between the compensation optical line and the output terminal, said module being adapted to be inserted by means of the input and output terminals into a transmission line comprising a single-mode line optical fiber adapted to transmit information in a spectral domain of use, the input terminal and the input mode converter together introducing into the transmission line an input loss Fi n expressed in dB, the output terminal and the output mode converter together introducing into the transmission line
  • D DCM represents the negative of the cumulative dispersion of the line optical fiber
  • said module being adapted to have a non-linearity criterion NLC representing the effects of the non-linear phase and expressed in 10 "6 kilometers per watt-decibel (km/W-dB) ,
  • a chromatic dispersion compensation module comprising, an enclosure including an input terminal and an output terminal, a higher-order mode chromatic dispersion compensation optical line situated inside the enclosure and disposed between the input terminal and the output terminal, the line comprising one or more HOM multimode chromatic dispersion compensation optical fibers in series and not comprising any single-mode optical fiber, an input mode converter for converting the fundamental mode into said higher order mode, situated between the input terminal and the compensation optical line, an output mode converter for converting said higher order mode into the fundamental mode, situated between the compensation optical line and the output terminal, the module being adapted to be inserted by means of the input and output terminals into a transmission line comprising a standard single-mode line optical fiber adapted to transmit information in a spectral domain of use, the input terminal and the input mode converter together introducing into the transmission line an input loss r ⁇ n expressed in dB, the output terminal and the output mode converter together
  • D DCM -1360 ps/nm
  • the module having a non-linearity criterion NLC representing the effects of the non- linear phase and expressed in 10 "6 km/W-dB, ⁇ x ⁇
  • the module having a quality criterion CQ expressed in dB, where CQ IL + lOlogNLC
  • the compensation optical fiber or the set of compensation optical fibers in series presenting: firstly, an average chromatic dispersion more negative than -200 ps/nm-km, secondly, an average chromatic dispersion to dispersion slope ratio in the range 240 nm to 400 nm, and thirdly, an average chromatic dispersion sufficiently negative for the quality criterion to be less than 9.5 dB .
  • a chromatic dispersion compensation module comprising, an enclosure including an input terminal (41) and an output terminal, a higher-order mode chromatic dispersion compensation optical line situated inside the enclosure and disposed between the input terminal and the output terminal, the line comprising one or more HOM multimode chromatic dispersion compensation optical fibers in series and not comprising any single-mode optical fiber, an input mode converter for converting the fundamental mode into said higher order mode, situated between the input terminal and the compensation optical line, an output mode converter for converting said higher order mode into the fundamental mode, situated between the compensation optical line and the output terminal, the module being adapted to be inserted by means of the input and output terminals into a transmission line comprising a single-mode non-zero (at 1550 nm) dispersion shifted line optical fiber adapted to transmit information in a spectral domain of use, the input terminal and the input mode converter together introducing
  • DDCM - 680 ps/nm
  • NLC non-linearity criterion
  • a eif - a DCF - XX the module having a quality criterion CQ expressed in dB, where CQ IL+ lOlogNLC , and the compensation optical fiber or the set of compensation optical fibers in series presenting: firstly, an average chromatic dispersion more negative than -250 ps/nm-km and, secondly, an average chromatic dispersion sufficiently negative for the quality criterion to be less than 5.5 dB .
  • the quality criterion remains valid and useful.
  • the invention is not restricted to a two-stage amplification and compensation system of the type described above.
  • the very low, and therefore very good, quality criterion values obtained with compensation modules of the invention make it possible to envisage using compensation modules of the invention in an amplification and compensation system including only one amplifier and no attenuator, in which case the compensation module of the invention would be situated downstream of the amplifier.
  • a chromatic dispersion compensation module comprising, an enclosure including an input terminal and an output terminal, a higher-order mode chromatic dispersion compensation optical line situated inside the enclosure and disposed between the input terminal and the output terminal, the line comprising one or more HOM multimode chromatic dispersion compensation optical fibers in series and not comprising any single-mode optical fiber, an input mode converter for converting the fundamental mode into said higher order mode, situated between the input terminal and the compensation optical line, an output mode converter for converting said higher order mode into the fundamental mode, situated between the compensation optical line and the output terminal, the module being adapted to be inserted by means of the input and output terminals into a transmission line comprising a standard single-mode line optical fiber adapted to transmit information in a spectral domain of use, and the compensation optical fiber or at least one of the compensation optical fibers in series having a core having at least five core segments, to which core cladding is added,
  • a chromatic dispersion compensation module comprising, an enclosure including an input terminal and an output terminal, a higher-order mode chromatic dispersion compensation optical line situated inside the enclosure and disposed between the input terminal and the output terminal, the line comprising one or more HOM multimode chromatic dispersion compensation optical fibers in series and not comprising any single-mode optical fiber, an input mode converter for converting the fundamental mode into said higher order mode, situated between the input terminal and the compensation optical line, an output mode converter for converting said higher order mode into the fundamental mode, situated between the compensation optical line and the output terminal, the module being adapted to be inserted by means of the input and output terminals into a transmission line comprising a single-mode non-zero (at 1550 nm) dispersion shifted line optical fiber adapted to transmit information in a spectral domain of use, and the compensation optical fiber or at least one of the compensation optical
  • - Figure 2 is a diagram showing an example of a compensation module of the invention
  • - Figure 3 is a table comparing the relative performance of prior art compensation modules and examples of compensation modules of the invention in the case of compensating a standard single-mode line optical fiber
  • - Figure 4 is a table comparing the relative performance of prior art compensation modules and examples of compensation modules of the invention in the case of compensating a non-zero dispersion shifted single-mode line optical fiber ;
  • FIG. 5 is a diagram showing a family of curves plotting the variation in the quality criterion as a function of the figure of merit of the compensation optical fiber at a chosen constant chromatic dispersion for the compensation optical fiber in the case of compensating a standard single-mode line optical fiber;
  • FIG. 6 is a table setting out absolute radius and maximum index difference values for a few examples of HOM multimode compensation optical fiber profiles used in a compensation module of the invention
  • FIG. 7 is a table setting out other properties of the HOM multimode compensation optical fiber profiles shown in Figure 6 ;
  • - Figure 8 is a diagram showing an example of a core profile with four core segments of an HOM multimode compensation optical fiber used in a compensation module of the invention
  • - Figure 9 is a diagram showing an example of a core profile with five core segments of an HOM multimode compensation optical fiber used in a compensation module of the invention.
  • the module comprises a single compensation optical fiber, which fiber has parameters, or the module comprises a plurality of compensation optical fibers in series, constituting a set of fibers which has average parameters.
  • the compensation module is considered to comprise only one compensation optical fiber and the qualifier "average" in the definition of the parameters may be disregarded.
  • the compensation module comprises only one compensation optical fiber, the module has the great advantage that its design and fabrication are simplified.
  • the compensation module comprises a plurality of compensation optical fibers from the same family, i.e.
  • the fibers provide some properties that are defined with great accuracy, despite wider fabrication tolerances, for example more accurate compensation of the dispersion slope or the chromatic dispersion to dispersion slope ratio of the line optical fiber.
  • the compensation optical fibers of the same family are preferably connected together directly, but they could be connected together by means of connectors .
  • the compensation module has the advantages of simplicity of design and of improvement to some of its properties.
  • the compensation module comprises a plurality of separate compensation optical fibers that are matched and assembled together, they provide compensation over a very wide spectral band, i.e. over at least two of the spectral bands S, C and L.
  • the S, C and L spectral bands respectively range from approximately 1460 nanometers (nm) to approximately 1530 nm, from approximately 1530 nm to approximately 1565 nm, and from approximately 1565 nm to approximately 1615 nm.
  • the compensation module then has the drawback that it is difficult to design and produce.
  • This type of calculation of the average attenuation coefficient can be generalized to more than two compensation optical fibers in series. Only the average coefficient of attenuation, which is a special case of the optical fiber parameters, is calculated in this manner, and all the other average parameters are calculated in other ways.
  • the average chromatic dispersion to dispersion slope ratio is the ratio between the average chromatic dispersion and the average dispersion slope.
  • the average figure of merit is the negative of the ratio between the average chromatic dispersion and the average coefficient of attenuation.
  • optical fiber a and optical fiber b There is an exact non-linearity criterion formula in the case of two compensation optical fibers in series, referred to as optical fiber a and optical fiber b, for example.
  • the exponents a and b of the various parameters represent those parameters for the optical fibers a and b, respectively.
  • the chromatic dispersion compensation module comprises a chromatic dispersion compensation optical line and an enclosure having an input terminal and an output terminal.
  • the higher-order mode chromatic dispersion compensation optical line comprises one or more HOM multimode chromatic dispersion compensation optical fibers in series, does not comprise any single- mode optical fiber, is situated in the enclosure, and is disposed between the input terminal and the output terminal .
  • An input mode converter converts the fundamental mode into said higher order mode and is situated between the input terminal and the compensation optical line.
  • An output mode converter converts said higher order mode into the fundamental mode and is situated between the compensation optical line and the output terminal.
  • the module is intended to be connected, by means of the input and output terminals, into a transmission line comprising a single-mode line optical fiber adapted to transmit information in a spectral domain of use.
  • the input terminal and the input mode converter together introduce into the transmission line an input loss r ⁇ n expressed in dB.
  • the output terminal and the output mode converter together introduce into the transmission line an output loss F out expressed in dB .
  • the compensation line comprises a plurality of compensation optical fibers in series, additional connections between compensation optical fibers together introduce into the transmission line a connection loss Tinter expressed in dB .
  • the compensation optical fiber has average parameters at a wavelength of 1550 nm including an average coefficient of attenuation ⁇ D c F expressed in dB/km, an average chromatic dispersion D DCF expressed in ps/nm-km and that is negative, an average dispersion slope S DCF expressed in ps/nm 2 -km and that is negative, an average chromatic dispersion to dispersion slope ratio D DCF /S DCF expressed in nm, an average figure of merit FOM D C F expressed in ps/nm-dB and equal to -D DC F/C(.DCF (giving a value that is positive since D DCF s itself negative) , an average effective area e ff expressed in ⁇ m 2 , and an average second order refractive index coefficient as a function of intensity n 2 expressed in 10 "20 m 2 /W.
  • the average coefficient of attenuation in the case of a single compensation optical fiber is lumped with the corresponding coefficient of attenuation of the single compensation optical fiber, and in the case of a set of compensation optical fibers in series, the average coefficient of attenuation is equal to the sum of the corresponding attenuation coefficients of the various compensation optical fibers weighted by their respective contributions to the total series length of the compensation optical fibers plus the ratio of the connection loss divided by said total length
  • each of the other average parameters in the case of a single compensation optical fiber is lumped with the corresponding parameter of the single compensation optical fiber and each of the other average parameters in the case of a set of compensation optical fibers in series is equal to the arithmetic mean of the corresponding parameters of the compensation optical fibers when weighted by the respective lengths of the compensation optical fibers.
  • D DCM -1360 ps/n for compensating a standard single-mode line optical fiber
  • D DC M -1360 ps/n for compensating a standard single-mode line optical fiber
  • a standard segment of single-mode line optical fiber is approximately 80 kilometers (km) long, which gives an approximate cumulative chromatic dispersion of
  • the insertion losses are not the real insertion losses of the module, which could be relatively low if the module compensates only a portion of the cumulative dispersion, but rather the insertion losses that the module would have if it fully compensated the cumulative dispersion with a length of compensation optical fiber slightly longer than the length required to compensate only part of the cumulative dispersion.
  • the cumulative dispersion is chosen to be -1360 ps/nm or -680 ps/nm depending on the type of single-mode line optical fiber to be compensated, but the module can also be used to compensate other values of cumulative dispersion or even to compensate only a portion of the cumulative dispersion.
  • the insertion losses decrease as the figure of merit increases. The insertion losses remain constant for a constant figure of merit.
  • the compensation optical fiber or the set of compensation optical fibers in series has an average chromatic dispersion to dispersion slope ratio in the range 240 nm to 400 nm.
  • the compensation optical fiber or the set of compensation optical fibers in series preferably has an average chromatic dispersion to dispersion slope ratio in the range 270 nm to 370 nm.
  • the compensation optical fiber or the set of compensation optical fibers in series preferably has an average chromatic dispersion to dispersion slope ratio less than 200 n .
  • the module has a non-linearity criterion (NLC) representing non-linear effects, i.e. the effects of nonlinear phase, in the particular case of constant losses between the two amplifiers of the two-stage amplifier system,
  • NLC non-linearity criterion
  • CQ IL + lOlogNLC.
  • the two contributions, namely the insertion losses and the non-linearity criterion, are reduced to the same units and expressed in dB.
  • the quality criterion CQ is representative of the overall quality of a compensation module.
  • the quality criterion of the invention shows that it is beneficial to degrade slightly the insertion losses if the losses caused by non-linear effects and represented by the non- linearity criterion are improved proportionately more. For example, it is beneficial to increase the insertion losses by 1 dB if this reduces to 2 dB the contribution of the non-linearity criterion to the quality criterion.
  • reducing the quality criterion amounts to reducing the non-linearity criterion, as the insertion losses are constant at a constant figure of merit for the compensation optical fiber when the only parameters that vary are the parameters of the compensation optical fiber.
  • Reducing the non-linearity criterion at constant figure of merit amounts to increasing the product of the attenuation multiplied by the effective area and divided by the coefficient n 2 . Reducing n 2 and increasing the effective area seems fairly natural, whereas increasing the attenuation of the compensation optical fiber seems somewhat paradoxical .
  • FIG. 1 is a diagram showing an example of a transmission line integrating a compensation module of the invention.
  • the transmission line corresponds to a segment which, when periodically repeated and combined with send and receive devices, constitutes the communications system.
  • the transmission line comprises in succession, in the propagation direction of the optical signal, a line optical fiber 1 and an amplification and compensation system 6.
  • the amplification and compensation system 6 comprises in succession: an upstream amplifier 2, an attenuator 3, a compensation module 4 of the invention, and a downstream amplifier 5. Downstream from the downstream amplifier 5 there is the line optical fiber 1 of the next segment.
  • the optical signal After propagating along the line optical fiber 1, the optical signal is amplified by the upstream amplifier 2, attenuated by the attenuator 3, has its chromatic dispersion compensated by the compensation module 4, and is amplified again by the downstream amplifier 5, before entering the next segment, i.e. the next transmission line.
  • the attenuator 3 and the amplifier 5 are omitted.
  • FIG. 2 is a diagram showing an example of a compensation module of the invention.
  • the compensation module 4 comprises an enclosure 49 containing in succession: an input terminal 41, an upstream mode converter 46, a chromatic dispersion compensation optical line 40, a downstream mode converter 47, and an output terminal 42.
  • the compensation optical line 40 can comprise one or more optical fibers in series interconnected by connectors .
  • the upstream mode converter 46 converts most of the light energy propagating in the LP 0 ⁇ fundamental mode to a higher-order mode, for example LP 02 •
  • the downstream mode converter 47 converts most of the light energy propagating in the higher-order mode LP 02 to the fundamental mode LP 0 ⁇ .
  • the compensation optical line 40 comprises two compensation optical fibers 43 and 45 connected together by a connector 44.
  • the optical signal enters via the input terminal 41, is converted from the fundamental mode to a higher-order mode by the upstream converter 46, propagates in the compensation optical fiber 43, passes through the connector 44, propagates in the compensation optical fiber 45, is converted from said higher-order mode to the fundamental mode, and then exits via the downstream output terminal 42, i.e. at the input of the downstream amplifier 5.
  • Figure 3 is a table comparing the relative performance of prior art compensation modules and examples of compensation modules in accordance with the invention in the case of compensating a standard single- mode line optical fiber.
  • the first column gives the numbers of the compensation module examples.
  • the prior art compensation module examples are numbered Bl, B2 , B3.
  • Examples Bl, B2, B3 correspond to modules combining in series two compensation optical fibers, one of which is an HOM multimode fiber and the other of which is a single-mode fiber, all the optical fiber characteristics set out in the table corresponding to the characteristics of the HOM multimode compensation optical fiber.
  • the examples of compensation modules of the invention are numbered Al, A2 , A3, A4.
  • the next column gives the negative of the cumulative chromatic dispersion of the line optical fiber, which is the negative of the chromatic dispersion that would have to be compensated to compensate fully 80 km of the line optical fiber; it is denoted D D M and is expressed in ps/nm.
  • the next column gives the chromatic dispersion of the compensation optical fiber, which is denoted D DCF and is expressed in ps/nm-km.
  • the next column gives the dispersion slope of the compensation optical fiber, which is denoted S DCF and is expressed in ps/nm 2 -km.
  • the next column gives the average chromatic dispersion to dispersion slope ratio of the compensation optical fiber, which is denoted D DCF /S DCF and is expressed in nm.
  • the next column gives the coefficient of attenuation of the compensation optical fiber, which is denoted CC DCF and is expressed in dB/km.
  • the next column gives the figure of merit of the compensation optical fiber, which is denoted FOM DCF and is expressed in ps/nm-dB.
  • the next three columns respectively give the input loss at the input terminal of the compensation module, the connection loss if any at the junction between the HOM multimode compensation optical fiber and the single-mode compensation optical fiber (for prior art modules of the second kind m which the output converter is m fact situated between the two compensation optical fibers) , and the output loss at the output terminal of the compensation module, which are respectively denoted r ⁇ n , F ⁇ nt er and F out , and which are expressed m dB .
  • the next column gives the insertion losses of the compensation module, which are denoted IL and are expressed m dB
  • the next column gives the effective area of the compensation optical fiber, which is denoted A eff and is expressed m ⁇ m 2 .
  • the next column gives the average second order coefficient of the refractive index of the compensation optical fiber as a function of the intensity of the optical signal that propagates therein, which is denoted n 2 and is expressed m 10 20 m 2 /W
  • n 2 the average second order coefficient of the refractive index of the compensation optical fiber as a function of the intensity of the optical signal that propagates therein
  • n 2 the average second order coefficient of the refractive index of the compensation optical fiber as a function of the intensity of the optical signal that propagates therein
  • n 2 the average second order coefficient of the refractive index of the compensation optical fiber as a function of the intensity of the optical signal that propagates therein
  • n 2 the average second order coefficient of the refractive index of the compensation optical fiber as a function of the intensity of the optical signal that propagates therein
  • m 10 20 m 2 /W
  • NLC non- linearity criterion of the compensation module
  • CO the quality criterion of the compensation module
  • Compensation modules m accordance with the first aspect of the invention do not use single-mode compensation optical fiber m the compensation module and either have a quality criterion that is lower, and therefore better, than the prior art modules or else, for an equivalent quality criterion, they use optical fibers that have a figure of merit that is much lower and which are therefore much less costly to produce.
  • the example Al is excluded from the first aspect of the invention because the quality criterion is too high and therefore too poor.
  • Compensation modules of the invention preferably have a very good quality criterion; to this end, the compensation optical fiber or the set of compensation optical fibers m series has an average chromatic dispersion that is sufficiently negative for the quality criterion to be less than 9 dB
  • Compensation modules of the invention preferably have an excellent quality criterion; to this end, the compensation optical fiber or the set of compensation optical fibers m series has an average chromatic dispersion that is sufficiently negative for the quality criterion to be less than 8.5 dB .
  • the insertion losses are preferably less than 5 dB , which is highly beneficial m the particular case of an amplification and compensation system using only one amplifier .
  • the compensation optical line preferably has a core having at least four core segments, to which core cladding is added.
  • At least one of the compensation optical fibers m the compensation optical line has a core having at least five core segments, to which core cladding is added
  • Figure 4 is a table comparing the relative performance of prior art compensation modules and examples of compensation modules m accordance with the invention m the case of compensating a non- zero dispersion shifted single-mode line optical fiber
  • the first column gives the numbers of the compensation module examples .
  • the prior art compensation module examples are numbered Bl, B2 , Cl, C2 , C3.
  • the examples of compensation modules m accordance with the invention are numbered A5 , A6, A7
  • Examples Bl and B2 correspond to modules combining m series two compensation optical fibers, one of which is an HOM multimode fiber and the other of which is a single-mode fiber, all the optical fiber characteristics set out m the table corresponding to the characteristics of the HOM multimode compensation optical fiber.
  • the next column gives the negative of the cumulative chromatic dispersion of the line optical fiber, which is the negative of the chromatic dispersion that would have to be compensated in order to fully compensate 80 km of the line optical fiber; it is denoted D DCM and is expressed in ps/nm.
  • the cumulative chromatic dispersion of a non-zero dispersion shifted single-mode line optical fiber is lower than the cumulative chromatic dispersion of a standard single-mode line optical fiber because its chromatic dispersion is lower.
  • the next column gives the chromatic dispersion of the compensation optical fiber, which is denoted D DCF and expressed in ps/nm-km.
  • the next column gives the dispersion slope of the compensation optical fiber, which is denoted S DCF and is expressed in ps/nm 2i km.
  • the next column gives the average chromatic dispersion to dispersion slope ratio of the compensation optical fiber, which is denoted D DCF /S DCF and is expressed in nm.
  • the next column gives the coefficient of attenuation of the compensation optical fiber, which is denoted (XD CF and is expressed in dB/km.
  • the next column gives the figure of merit of the compensation optical fiber, which is denoted FOM DCF and is expressed in ps/nm-dB.
  • the next three columns respectively give the input loss at the input terminal of the compensation module, the connection loss if any at the junction between the HOM multimode compensation optical fiber and the single-mode compensation optical fiber (for prior art modules of the second type in which the output converter is in fact situated between the two compensation optical fibers) , and the output loss at the output terminal of the compensation module, which are respectively denoted r ⁇ n , r ⁇ nte r and F ou t and which are expressed in dB .
  • the next column gives the insertion losses of the compensation module, which are denoted IL and are expressed in dB .
  • the next column gives the effective area of the compensation optical fiber, which is denoted A ef f and is expressed in ⁇ m 2 .
  • the next column gives the average second order coefficient of the refractive index of the compensation optical fiber as a function of the intensity of the optical signal that propagates in the fiber, which is denoted n 2 and is expressed in 10 ⁇ 20 m 2 /W.
  • the next column gives the non- linearity criterion of the compensation module, which is denoted NLC and is expressed in 10 " ⁇ km/W-dB.
  • the next column gives the quality criterion of the compensation module, which is denoted CQ and is expressed in dB .
  • Compensation modules of the invention have a quality criterion which is much lower than and therefore much better than the prior art modules: there is a difference of approximately 1 dB between the worst compensation module obtained by the method of the invention and the best compensation module obtained in the prior art. An improvement of 1 dB is already considerable.
  • the invention preferably relates to compensation modules having a very good quality criterion; to this end, the compensation optical fiber or the set of compensation optical fibers in series has average chromatic dispersion that is sufficiently negative for the quality criterion to be less than 5 dB .
  • the invention preferably relates to compensation modules having an excellent quality criterion; to this end, the compensation optical fiber or the set of compensation optical fibers in series has average chromatic dispersion that is sufficiently negative for the quality criterion to be less than 4.5 dB .
  • the insertion losses are preferably less than 4 dB, which is highly beneficial in the particular case of an amplification and compensation system using only one amplifier.
  • At least one of the compensation optical fibers in the compensation optical line has a core having at least four core segments, to which core cladding is added.
  • At least one of the compensation optical fibers in the compensation optical line has a core having at least five core segments, to which core cladding is added.
  • Figure 5 is a diagram showing a family of curves plotting the variation in the quality criterion as a function of the figure of merit of the compensation optical fiber at a chosen constant chromatic dispersion for the compensation optical fiber and in the case of compensating a standard single-mode line optical fiber.
  • the general trends of the curves shown in Figure 5 apply equally to compensating a non- zero dispersion shifted line optical fiber.
  • the quality criterion CQ expressed in dB is plotted up the ordinate axis.
  • the figure of merit FOM DCF expressed in ps/nm-dB is plotted along the abscissa axis.
  • the curve CA corresponds to a chromatic dispersion of -300 ps/nm-km.
  • the curve CB corresponds to a chromatic dispersion of -350 ps/nm-km.
  • the curve CC corresponds to a chromatic dispersion of -400 ps/nm-km.
  • the curves CA, CB, CC show that in order to reduce the quality criterion, and thus improve it, it is more effective to reduce the chromatic dispersion of the compensation optical fiber at constant figure of merit than to increase the figure of merit of the compensation optical fiber at constant chromatic dispersion. This is all the more true if the figure of merit is high and in particular greater than a value of approximately 300 ps/nm-dB.
  • the compensation optical line preferably comprises a single optical fiber connecting the input terminal to the output terminal . A plurality of compensation optical fibers in series provides better compensation of the dispersion slope of the line optical fiber, at the cost of some complexity.
  • the signal amplification and chromatic dispersion compensation system preferably comprises in succession a first signal amplifier, a signal attenuator, a chromatic dispersion compensation module of the invention, and a second signal amplifier.
  • the signal amplification and chromatic dispersion compensation system comprises a single signal amplifier followed by a chromatic dispersion compensation module of the invention.
  • compensation modules of the invention which are better than those of the prior art, and much better than those of compensation modules based only on single-mode compensation optical fibers, it is possible to use a compensation module with only one amplifier.
  • the transmission line preferably comprises in succession a single-mode line optical fiber for transmitting information in a spectral range of use and a signal amplification and chromatic dispersion compensation system of the invention.
  • Figure 6 is a table of absolute maximum index difference and radius values for a few examples of profiles of HOM multimode compensation optical fibers used in a compensation module of the invention.
  • the left-hand column identifies the profiles Al to A7.
  • the numbers Al to A7 are the same as in Figures 3 and 4 : two numbers that are the same correspond to the same compensation optical fiber.
  • the second column indicates the number of core segments in the core index profile of the example concerned.
  • the next six columns give the radii in ⁇ m of the varying core index profile.
  • the last six columns give one thousand times the index difference relative to the constant index of the cladding (no units) . Not all the boxes of the table are filled in, as not all the profiles have the same number of core segments. Negative index differences indicate buried core segments.
  • Figure 7 is a table of other properties of profiles of the HOM multimode compensation optical fibers shown in Figure 6.
  • the boxes of this table that contain no figure but only a dash correspond to properties that are so bad that they render the optical fiber unusable at the wavelength concerned or in the operating spectral range concerned.
  • the left-hand column identifies the profiles, as already explained hereinabove.
  • the next column gives the number of core segments in each profile. For each profile, the other columns give properties of the optical fiber corresponding to the profile concerned.
  • the next column gives the effective area A eff expressed in ⁇ m 2 at a wavelength of 1550 nm.
  • the next column gives the chromatic dispersion expressed in ps/nm-km at a wavelength of 1550 nm.
  • the next seven columns give the dispersion slopes expressed in ps/nm 2 -km at the wavelengths of 1530 nm, 1550 nm, 1565 nm, 1570 nm, 1580 nm, 1590 nm, 1605 nm, respectively.
  • the next column gives the minimum chromatic dispersion wavelength expressed in nm.
  • the last three columns give the maximum relative slope variations expressed as a percentage for respective operating spectral ranges in the range 1530 nm to 1565 nm, in the range 1530 nm to 1580 nm, and in the range 1530 nm to 1605 nm.
  • the relative variation in the dispersion slope over an operating spectral range corresponds to the quotient obtained by dividing the difference between the maximum dispersion slope over said operating spectral range and the minimum dispersion slope over said operating spectral range by the average dispersion slope over said operating spectral range.
  • the poor results in the last column correspond to maximum relative variations of slope that are much higher than those in the other columns, and can be explained in particular by minimum chromatic dispersion wavelengths that are too close to the upper limit of the operating spectral range concerned.
  • Examples A2 and A6 are excluded from the second aspect of the invention because the linearity of the dispersion slope as a function of wavelength is relatively poor, as is the linearity of the chromatic dispersion to dispersion slope ratio. These examples have only three core segments .
  • Example Al is excluded from the second aspect of the invention because the negative chromatic dispersion is not sufficiently negative.
  • This example has only four core segments.
  • Figure 8 is a diagram showing an example of a core profile with four core segments of an HOM multimode compensation optical fiber used in a compensation module of the invention.
  • the radii expressed in ⁇ m are plotted along the abscissa axis. One thousand times the index differences is plotted up the ordinate axis (no units) .
  • the first core segment also known as the central core segment, has a maximum index difference ⁇ nl with respect to the constant index of the cladding and an outside radius rl .
  • the maximum index difference ⁇ nl is positive.
  • the index is preferably constant between a zero radius and the radius rl .
  • the second core segment also known as the first peripheral core segment, has an absolute maximum index difference value ⁇ n2 with respective to the constant index of the cladding and an outside radius r2.
  • the absolute maximum index difference value ⁇ n2 can be positive or negative.
  • the index is preferably constant between the radius rl and the radius r2.
  • the third core segment also known as the second peripheral core segment, has an absolute maximum index difference value ⁇ n3 with respect to the constant index of the cladding and an outside radius r3.
  • the absolute maximum index difference value ⁇ n3 can be positive or negative.
  • the index is preferably constant between the radius r2 and the radius r3.
  • the fourth core segment also known as the third peripheral core segment, has an absolute maximum index difference value ⁇ n4 with respect to the constant index of the cladding and an outside radius r4.
  • the absolute maximum index difference value ⁇ n4 can be positive or negative.
  • the index is preferably constant between the radius r3 and the radius r4. Beyond the radius r4 is the constant index cladding.
  • Figure 9 shows diagrammatically one example of a core profile with five core segments of an HOM multimode compensation optical fiber used in a compensation module of the invention.
  • the radii expressed in ⁇ m are plotted along the abscissa axis. One thousand times the index differences is plotted up the ordinate axis (no units) .
  • the first core segment also known as the central core segment, has an absolute maximum index difference value ⁇ nl with respect to the constant index of the cladding and an outside radius rl .
  • the maximum index difference ⁇ nl is positive.
  • the index is preferably constant between a zero radius and the radius rl .
  • the second core segment also known as the first peripheral core segment, has an absolute maximum index difference value ⁇ n2 with respective to the constant index of the cladding and an outside radius r2.
  • the absolute maximum index difference value ⁇ n2 can be positive or negative.
  • the index is preferably constant between the radius rl and the radius r2.
  • the third core segment also known as the second peripheral core segment, has an absolute maximum index difference value ⁇ n3 with respect to the constant index of the cladding and an outside radius r3.
  • the absolute maximum index difference value ⁇ n3 can be positive or negative.
  • the index is preferably constant between the radius r2 and the radius r3.
  • the fourth core segment also known as the third peripheral core segment, has an absolute maximum index difference value ⁇ n4 with respect to the constant index of the cladding and an outside radius r4.
  • the absolute maximum index difference value ⁇ n4 can be positive or negative.
  • the index is preferably constant between the radius r3 and the radius r4.
  • the fifth core segment also known as the fourth peripheral core segment, has an absolute maximum index difference value ⁇ n5 with respect to the constant index of the cladding and an outside radius r5.
  • the absolute maximum index difference value ⁇ n5 can be positive or negative.
  • the index is preferably constant between the radius r4 and the radius r5. Beyond the radius r5 is the constant index cladding.

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)

Abstract

L'invention concerne des modules de correction de dispersion chromatique et des procédés de conception desdits modules. Le procédé de conception consiste à optimiser par réduction d'un critère de qualité original. La fibre optique de correction du module possède une dispersion chromatique inférieure à un premier seuil et une dispersion chromatique suffisamment négative pour que le critère de qualité soit inférieur à un second seuil.
EP03776885A 2003-04-29 2003-09-19 Module de correction de dispersion chromatique Withdrawn EP1618685A1 (fr)

Applications Claiming Priority (2)

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FR0305224A FR2854517B1 (fr) 2003-04-29 2003-04-29 Module de compensation de dispersion chromatique
PCT/EP2003/012397 WO2004098101A1 (fr) 2003-04-29 2003-09-19 Module de correction de dispersion chromatique

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EP1618685A1 true EP1618685A1 (fr) 2006-01-25

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US5261016A (en) * 1991-09-26 1993-11-09 At&T Bell Laboratories Chromatic dispersion compensated optical fiber communication system
JPH1188260A (ja) * 1997-09-09 1999-03-30 Fujitsu Ltd 光伝送路の分散補償装置
JP2000031900A (ja) * 1998-07-08 2000-01-28 Fujitsu Ltd 光ファイバ通信のための方法並びに該方法の実施に使用する端局装置及びシステム
JP3471271B2 (ja) * 1999-08-12 2003-12-02 株式会社フジクラ 光ファイバおよび光伝送システム
US20020118934A1 (en) * 2001-02-23 2002-08-29 Yochay Danziger Method and system for dispersion management with Raman amplification
US20030026533A1 (en) * 2001-08-03 2003-02-06 Yochay Danziger Configurable dispersion management device
US6650814B2 (en) * 2001-12-11 2003-11-18 Corning Incorporated Single mode dispersion compensating optical fiber

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FR2854517A1 (fr) 2004-11-05
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FR2854517B1 (fr) 2005-08-05
CN1778057A (zh) 2006-05-24

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