FR2838004A1 - Circulating amplifier signal optical signal transmission having intermediate amplifier connected first/second parts with pump module Raman broadcasting secondary order wave amplifier. - Google Patents

Abstract

The optical signal transmission installation has an optical signal transmission (2) with first (4) and second parts (5) connected by an intermediate amplification module. There is a pump module (11) delivering signals to a secondary signal by Raman broadcasting simulating secondary order forward waves from the intermediate amplifier module (6).

Description

encountered during the reception of said post-message.

  IMPROVED SIGNAL TRANSMISSION METHOD

  REMOTE CONTROLLED RELAY AMPLIFICATION OPTICS

  The invention relates to the field of optical signal transmission, and more particularly that of the amplification of circulating signals.

  in an optical transmission line.

  Some optical transmission lines, which connect remote transmitting and receiving stations, have two parts connected by an intermediate amplification module. This module generally comprises an amplification medium, such as a doped optical fiber, capable of amplifying received (primary) optical signals, in the presence of optical signals

(secondary) pump.

  When it is not possible to integrate the secondary pump signal generator in the intermediate module, the latter is installed in the transmitting station or in the receiving station. The secondary signals must therefore go up the first part of the line (co-propagative mode with respect to the primary signals) or the second part of the line (counter-propagative mode with respect to the primary signals), o to the intermediate module, which induces a loss of power by as much

  greater than the distance to be traveled is great.

  The power required by the intermediate module to amplify the primary signals being typically of the order of 10 mW (milliWatts), the maximum distance of the transmission line connecting the transmitting and receiving stations via the intermediate module will therefore depend directly of

  the power of the secondary signals delivered by this receiving station.

  Typically, for a starting power of 1 W (Watt), the maximum distance cannot exceed a value corresponding to a loss of approximately 20 dB for the part separating the intermediate and receiving stations, and o of approximately 15 dB for the part separating the intermediate and transmitting stations. If you want to increase this maximum distance, it is therefore imperative to use a higher starting power. However, in the commonly used transmission lines, such as a PSCF ", there is a power limit, typically 1.3 W. beyond which the transmission of the primary signals is irreparably degraded by oscillations.

  generated by Rayleigh reflections.

  In an attempt to remedy this drawback, it has been proposed to place filters on the transmission line. However, this solution can only be implemented in transmission lines specifically dedicated to

  transport of secondary pump signals, which is particularly costly.

  One of the aims of the invention is therefore to provide a solution

  alternative to the aforementioned drawback.

  It proposes for this purpose an optical signal transmission installation comprising i) at least one optical signal transmission line, formed of first and second parts connected by an intermediate module intended to amplify primary optical signals in the presence of an optical signal secondary pump, ii) at least one transmitting station capable of delivering primary optical signals in the first part, iii) at least one receiving station, connected to the second part for receiving primary optical signals from the station emission, and iv) at least one optical pumping module capable of delivering in one of the first and second parts, intended for the intermediate amplification module, at least one secondary optical pump signal and at least one tertiary optical signal from to amplify the power of the secondary signal by stimulated second order Raman scattering, before it

  reaches the intermediate amplification module.

  Since the secondary signals are amplified by the tertiary signal in a distributed manner over the entire length of the first or second part of the transmission line, the distance between the transmitting and receiving stations eVou the power of the secondary pump signals at o level of the intermediate amplification module can be significantly increased without the starting power of said secondary signals exceeding the

aforementioned limit.

  Furthermore, the intermediate amplification module may include amplification and guidance means comprising a material chosen from a group comprising glasses, glass derivatives, crystals and ceramics. This material is preferably doped with an ion or a rare earth complex, for example chosen from a group comprising thullum, erbium, nsodyme, praseodymium and dysprosium, or with a

  metal ion, such as chromium. But it can also include nano-

doped particles.

  The pumping module can be installed in the transmitting station

or at the receiving station.

  In the second situation, each receiving station may include a switching device, such as a circulator, connected to the pumping module, to a module for receiving primary signals and to the second part of the line, so as to transmit to the reception module the optical signals received and to inject into the second part of the line the

  secondary and tertiary signals delivered by the pumping module.

  Still in this second situation, it is also possible to provide, in at least some of the reception stations, an auxiliary amplification device, such as an "EDFA" (Erblum Doped Fiber Amplifier), interposed between the routing device and the receiving module so as to amplify o the primary signals received before they are analyzed by said module

reception.

  In addition, the intermediate amplification module can be arranged so as to receive at least one other secondary optical pump signal for amplification of the primary signals. This other secondary signal can come either from the first or second part, or from another line of

  optical transmission connected to the intermediate module.

  The pumping module can also be arranged so as to deliver in the line, in the same direction as the secondary signals, to the

  minus another tertiary optical signal.

  The invention also relates to a method of optical amplification of signals on a transmission line comprising first and second parts connected by an intermediate amplification module, intended to amplify primary optical signals in the presence of a secondary optical signal pump, the first part receiving primary optical signals to be transmitted to the second part, and one of the first and second parts receiving jointly (preferably substantially simultaneously) i) the secondary optical pump signal, intended for the intermediate module of amplification, and ii) at least one tertiary optical signal capable of amplifying the power of the secondary signal by stimulated second Raman scattering

  order, before it reaches the intermediate amplification module.

  It is also possible to supply the intermediate module with at least one other secondary optical pump signal. It is also possible to deliver in the transmission line, in the same direction as said secondary signals,

  at least one other tertiary optical signal.

  The installation and the method according to the invention find a particularly interesting, although not exclusive, application in the field of telecommunications, and more particularly still in the field of transmission systems without signal regeneration device (such as

for example a repeater).

  Other characteristics and advantages of the invention will become apparent from

  examination of the detailed description below, and of the attached drawings, on

  which: o - Figure 1 schematically illustrates part of a primary signal transmission installation according to the invention, - Figure 2 schematically illustrates the amplification mechanism

optics according to the invention.

  The accompanying drawings are, for the most part, certain. Consequently, they may not only serve to complete the invention, but

  also contribute to its definition, if necessary.

  We first refer to Figure 1 to describe part of a

  installation for transmitting primary signals according to the invention.

  The installation shown here comprises a transmission station for: o data 1, connected, via an optical transmission line 2 (below

  called "the line>), at a remote data receiving station 3.

  The invention relates more particularly, although not exclusively, to transmission lines 2 which are not equipped with a signal regeneration device (or repeater). For example, the installation is intended for underwater or terrestrial transmissions without a repeater. However, it can also be intended for transmission lines fitted with repeaters on some of their portions only. Line 2 consists of a first part 4 and a second part 5, connected by an intermediate amplifier unit 6, hereinafter called intermediate amplifier. Each part 4, 5 being made up of an optical fiber, in what follows we will respectively call first and second

  fibers the first 4 and second 5 parts of line 2.

  The transmission station 1 is connected to the first fiber 4, and comprises a transmission module 7 capable of delivering data to be transmitted to the reception station 3, in the form of so-called primary optical signals, having at least a length of wave A1. For example, the

  wavelength of the primary signals is approximately 1555 nm (nanometers).

  In what follows, it will be considered that the primary signals have only one wavelength A1, but, of course, said signals

  primaries could be distributed over a range of wavelengths.

  Preferably, before being injected into the first fiber 4, the zo primary signals are the subject of an amplification, for example using a

  booster 8 amplifier.

  Once transmitted by the transmission module 7, the primary signals propagate in the first fiber 4 (arrow F1), in the direction of the intermediate box 6 where they must be the subject of a further amplification of

  so as to be able to reach the remote receiving station 3.

  The intermediate box 6 is a traditional amplifier, well known to those skilled in the art. It includes all the passive, and possibly active, optical elements necessary for amplification, except the pump light generator (secondary optical pump signals). It therefore includes optical coupling elements, such as eVou switches and isolators, and an amplification medium intended to amplify the primary signals.

  received, in the presence of secondary pump signals.

  These secondary signals have at least one wavelength A2 (and therefore an energy) suitable for the transition of constituents of the amplification medium (such as for example erblum ions) towards certain energy levels, under conditions such as the stimulated emission becomes more important than the absorption and therefore the gain within the amplification medium becomes positive thus allowing amplification of the signals

primary received.

  The amplification medium is. for example, a glass, or a glass derivative, preferably doped with an ion or a rare earth complex, such as for example erblum, thulium, neodymium, praseodymium, or

  dysprosium, or with a metal ion, such as chromium.

  It is also possible to provide a co-dopant increasing the cross section

absorption, such as ytterblum.

  Among the glasses and glass derivatives which are particularly advantageous for accommodating d opants and co-opants, mention may be made of such lu rites glasses, phosphate-based glasses, silica-based glasses, glasses based on of bismuth, alumino-silicate glasses, borate glasses, alumina glasses, soda lime silica glasses or germanate glasses, optionally doped with chemical species such as alkali ions having in particular for

  effect of creating sites accepting rare earth ions.

  o As a variant, the glass may also contain nanoparticles

  amplification, preferably doped, in amorphous or crystalline phase.

  In the latter case, we then speak of nanocrystals or vitro-ceramics. These nanoparticles are dispersed in a host material (such as silica glass or one of the other materials presented above). Their characteristic dimensions are preferably less than one micron, and more

  preferably still less than ten nanometers.

  Similarly, instead of a glass or one of its derivatives, a polymer can be used, such as for example PMMA ("Poly-Methyl-Metacrylate>) or

  other organic materials well known to those skilled in the art.

  so But we can also consider using crystals (such as, for example, monocrystals, polycrystals or ceramics from YAG (Garnet Yttrium-Aluminum), WO4 (Yttrium Vanadate), CAS (Calclum AluminumSrontium), niobate from lithium, YSO, CNGG, YSGG,

Alumina or YAP).

  The erblum doped materials are particularly advantageous insofar as they offer a high amplification / loss ratio for a light whose wavelength is around 1555 nm, which is widely used in the field of optical communications. More precisely, in this wavelength range the amplifier is very insensitive to the polarization of light and has a wide gain range (typically 30

  nm) and low insertion losses.

  Once amplified by the intermediate box 6, under conditions to which we will return later, the primary signals are injected into the second fiber 5, where they flow to the receiving station 3 (arrow F'1

in Figure 1).

  The reception station 3 has a reception module 9 intended to analyze the primary signals received, preferably after amplification by an amplifier 10, such as an EDFA, with a view to their use or their

  relay to one or more other stations in the installation.

  The invention also provides a pumping module 11 comprising two sub-modules 12 and 13. In the example illustrated, this pumping module 11 is installed in the receiving station 3 (counter propagative mode), but o in a variant , it could be installed in transmission station 1 (co-propagative mode). The first sub-module 12 is arranged to deliver the so-called secondary "optical pump signals", having at least one wavelength A2 less than the wavelength (s) A1 of the primary signals, and necessary for amplification in the intermediate box 6

(arrow F4 in Figure 2).

  The second sub-module 13 is arranged to deliver so-called "tertiary" optical signals, having at least one wavelength A3 less than the wavelength (s) A1 of the primary signals and that (s) ) (A2) secondary signals, and intended to amplify the signals

  secondary inside the second fiber 5.

  The receiving station further comprises a switching device 14, such as an optical circulator, connected, firstly, to the second fiber, secondly, to the pumping module 11, and a third part, at

  reception module 9 or to amplifier 10 when the latter is present.

  When primary signals, coming from the intermediate box 6 via the second fiber 5, arrive at the reception station 3, the switcher 14 transmits them to the amplifier 10. Furthermore, the secondary and tertiary signals, delivered by the first 12 and second 13 submodules of the pumping module 11, are injected by the switcher 14 into the second fiber 5 o they flow, against the current of the primary signals, up to the bo ^ 'tier

intermediate 6.

  The wavelength A3 of the tertiary signals is chosen so as to optimize the coupling between the tertiary signals and the secondary signals

  A2 (arrow F3 in FIG. 2), during their propagation in the second fiber 5.

  The term “optimizing the coupling” here is understood to mean inducing an optimal amplification of the power of the secondary signals by Raman scattering.

  second order stimulated (or "second order SRS").

  The second-order amplification mechanism is notably described in the document by L. Labrunie et al "1.6 Tbits / s (160x10 Gbits / s) unrepeatered transmission over 321 km using second order pumping Raman amplification", post-deadline paper OM ' 01, and in the document by Rottwitt o et al "Transparent 80 km bi-directionnally pumped distributed Raman amplifier with second order pumping", ECOC 99, reqular paper Vol II,

proceedings, p.144-145.

  In fact, the secondary and tertiary signals propagating substantially simultaneously over the entire length of the second fiber 5, the secondary signals can be amplified in a substantially homogeneous manner

  over the entire length (this is called distributed amplification).

  Furthermore, the wavelengths A2 and A3 are chosen so as to

  do not disturb the circulation of primary signals in the second fiber 5.

  By way of nonlimiting example, when the wavelength A1 of the primary signals is equal to approximately 1555 nm and the amplification medium of the intermediate housing 6 is an erblum doped glass, signals can be chosen secondary signals having a wavelength A2 equal to approximately 1480 nm and tertiary signals presenting a wavelength A3 equal to

about 1390 nm.

  The invention also provides a method for optical amplification of signals on a transmission line 2 comprising first and second parts connected by an intermediate amplifier unit 6, intended to amplify primary optical signals (for example from 'a transmitting station 1 connected to the first part and intended for a receiving station connected to the second part), in the presence of at least one secondary optical signal from the pump going down or up the line 2 towards the box' ^ tier intermediary 6 (and for example from the transmitting station or the

o receiving station).

  This process can be implemented using the installation presented above. The main and optional functions and sub-functions provided by the steps of this process being substantially identical to those provided by the various means constituting the installation, only the steps implementing the main functions of the process will be summarized below.

according to the invention.

  This process consists in transmitting jointly (and preferably substantially simultaneously) in the first or second part 5 of line 2 (co-propagative or counter-propagative mode with respect to the primary o signals), on the one hand, the secondary optical signal pump, intended for the intermediate amplifier box 6, and on the other hand, at least one tertiary optical signal of a nature to amplify the power of the secondary signal by stimulated second order Raman scattering, before it reaches at

  intermediate amplification module.

  Thanks to the method and the installation according to the invention, it is in particular possible to use, in the second sub-module 13, a high power pump laser, to deliver the tertiary signals (A3) intended for amplification. second order, and in the first sub-module 12, a low power pump laser, for delivering the secondary signals (A2) o intended for the amplification of the primary signals in the intermediate box

am pl ificatio n 6.

  For example, it is possible to use secondary signals at 1480 nm and tertiary signals at 1390 nm whose respective starting powers are approximately 10 mW and 1.3 W. while obtaining an increase of approximately 1.5 dB in the power of said secondary signals at the level of the intermediate box 6, compared with the previous solutions. Of course, it is also possible to increase the starting power of the secondary signals and decrease that of the tertiary signals, so as to reduce the costs, in particular. The power of the tertiary signals can also be significantly increased to improve performance. In general, thanks to the invention, the respective starting powers of the secondary and tertiary signals can be optimized so as to obtain an incoming power (at the level of the box 6) chosen eVou as a function of the

  length that we want to give to the second fiber 5.

  The invention is not limited to the installation and method embodiments described above, only by way of example, but it encompasses all the variants that a person skilled in the art may envisage within the framework of

claims below.

  Thus, an installation and a method have been described in which the intermediate amplification module was only pumped by secondary signals having a single wavelength and coming from a single fbre (first or second part of the line of transmission). But the invention also applies to the case where the intermediate amplification module is pumped by secondary signals having different wavelengths (at least two) and coming from a single fiber (first or second part from the line of transm issiouj or from at least two distinct fibers (including said first or second part). In this case, it may be advantageous to also use several tertiary signals (at least two) having lengths d This situation is particularly suitable for cases where the primary signals are distributed in a wavelength interval, t, typically a few tens of nanometers. Of course, the amplification medium of the intermediate station

  so must be adapted to this situation.

Claims (19)

  1. Installation for transmitting optical signals, comprising at least one line for transmitting optical signals (2), comprising first (4) and second (5) parts connected by an intermediate amplification module (6), suitable for amplifying primary optical signals (A1) in the presence of a secondary optical pump signal (A2), at least one transmitting station (1), capable of delivering in said first part (4) primary optical o signals (A1) , at least one receiving station (3), connected to said second part (5) for receiving said primary optical signals, and at least one optical pumping module (11) arranged to deliver one of the first (4) and second (5) parts, intended for said intermediate amplification module (6), said secondary optical pump signal (A2), characterized in that each pumping module (11) is arranged to deliver in one first (4) and second (5) parts, in the same sen s that said secondary signal (A2), at least one tertiary optical signal (A3) capable of amplifying the power of said secondary signal (A2) by stimulated second order Raman scattering, before it reaches said audit   intermediate amplification module (6).   2. Installation according to claim 1, characterized in that said intermediate amplification module (6) comprises amplification and guidance means comprising a material chosen from a group comprising the   glasses, glass derivatives, crystals and ceramics.   3. Installation according to claim 2, characterized in that said   material is doped with a rare earth ion or complex.   4. Installation according to claim 3, characterized in that the ion or the rare earth complex is chosen from a group comprising thullum,   Erbium, neodymium, praseodymium and dysprosium.   o 5. Installation according to claim 2, characterized in that said   material is doped with a metal ion, especially chromium.   6. Installation according to claim 2, characterized in that said   material includes doped nanoparticles. !   7. Installation according to one of claims 1 to 6, characterized in that   that said pumping module (11) is installed in the transmitting station (1).   8. Installation according to one of claims 1 to 6, characterized in that   that said pumping module (11) is installed in the receiving station (3) 9. Installation according to claim 8, characterized in that each reception station (3) comprises a module for receiving primary signals (9) and a switching device (14) connected to said pumping (11) and reception modules. (9) and to said second part of the line (5) so as to transmit to said reception module (9) the primary signals (A1) received and to inject into said second part of the line (5) said signals   secondary (A2) and tertiary (A3) delivered by said pumping module (11).   10. Installation according to claim 9 characterized in that it comprises an auxiliary amplification device (10) interposed between said   referral device (14) and said receiving module (9).   11. Installation according to one of claims 1 to 10, characterized in that   that said intermediate module (6) is arranged to receive at least one other secondary optical signal.   12. Installation according to claim 11, characterized in that said zo pumping module (11) is arranged to deliver said other signal secondary in said line (2).   13. Installation according to claim 11, characterized in that it comprises another optical transmission line connected to said module   intermediate (6) and in which said other secondary signal circulates.   14. Installation according to one of claims 1 to 13, characterized in that   that said pumping module (11) is arranged to deliver in line (2), in the same direction as said secondary signals, at least one other signal tertiary optics.   15. Method for optical amplification of signals on a transmission line (2) comprising first (4) and second (5) parts connected by an intermediate amplification module (6), suitable for amplifying primary optical signals (A1 ) in the presence of a secondary optical pump signal (A2), said first part (4) receiving primary optical signals (A1) intended for the second part (5), and one of said first (4) and second ( 5) parts receiving said secondary optical pump signal (A2) intended for said intermediate amplification module (6), characterized in that one polishes in one of the first (4) and second (5) parts, in the same direction as said secondary signal (A2), and jointly, at least one tertiary optical signal (A3) capable of amplifying the power of said secondary signal (A2) by stimulated second order Raman scattering, before   that it does not reach said intermediate amplification module (6).   16. Method according to claim 15, characterized in that said intermediate module (6) is supplied with at least one other optical signal secondary pump.   17. Method according to one of claims 15 and 16, characterized in that   that at least one other tertiary optical signal is delivered in said line (2),   in the same sense as said secondary signals.   s 18. Application of the installation and process according to one of the   previous claims to Raman amplification in the field of   telecommunications. 19. Application according to claim 18, characterized in that the field of telecommunications is that of transmission systems