WO2001029596A1 - Dispositif de multiplexage optique en longueurs d'ondes et systeme de telecommunication optique mlo - Google Patents

Dispositif de multiplexage optique en longueurs d'ondes et systeme de telecommunication optique mlo Download PDF

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Publication number
WO2001029596A1
WO2001029596A1 PCT/EP2000/010428 EP0010428W WO0129596A1 WO 2001029596 A1 WO2001029596 A1 WO 2001029596A1 EP 0010428 W EP0010428 W EP 0010428W WO 0129596 A1 WO0129596 A1 WO 0129596A1
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WIPO (PCT)
Prior art keywords
optical
channels
couplers
multiplexing device
band
Prior art date
Application number
PCT/EP2000/010428
Other languages
English (en)
Inventor
Fausto Meli
Roberta Castagnetti
Stefano Piciaccia
Original Assignee
Corning O.T.I., Inc.
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Publication date
Application filed by Corning O.T.I., Inc. filed Critical Corning O.T.I., Inc.
Priority to JP2001532131A priority Critical patent/JP2003512795A/ja
Priority to EP00969536A priority patent/EP1224493A1/fr
Priority to KR1020027005071A priority patent/KR20020054333A/ko
Priority to AU79219/00A priority patent/AU7921900A/en
Priority to CA002385584A priority patent/CA2385584A1/fr
Publication of WO2001029596A1 publication Critical patent/WO2001029596A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0278—WDM optical network architectures
    • H04J14/0279—WDM point-to-point architectures
    • 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
    • H04J14/0201—Add-and-drop multiplexing
    • H04J14/0202—Arrangements therefor
    • H04J14/0208—Interleaved arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0201—Add-and-drop multiplexing
    • H04J14/0202—Arrangements therefor
    • H04J14/0209—Multi-stage arrangements, e.g. by cascading multiplexers or demultiplexers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0201—Add-and-drop multiplexing
    • H04J14/0202—Arrangements therefor
    • H04J14/0213—Groups of channels or wave bands arrangements
    • 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
    • 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
    • G02B6/29304—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 by diffraction, e.g. grating
    • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
    • G02B6/29317—Light guides of the optical fibre type
    • G02B6/29319—With a cascade of diffractive elements or of diffraction operations
    • G02B6/2932—With a cascade of diffractive elements or of diffraction operations comprising a directional router, e.g. directional coupler, circulator
    • 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
    • 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 an optical device for wavelength multiplexing a plurality of optical signals and a WDM (Wavelength Division Multiplexing) optical telecommunication system comprising it.
  • WDM Widelength Division Multiplexing
  • balanced optical coupler indicates an optical coupler that introduces substantially the same attenuation on the optical channels passing through it. That is, it indicates an optical coupler that has the same intrinsic loss for all the channels passing through it;
  • unbalanced optical coupler indicates an optical coupler which attenuates the optical channels passing through it differently from each other, depending on the input port through which they enter the coupler. That is, it indicates an optical coupler that has different intrinsic losses for the channels passing through it;
  • Nxl optical coupler indicates a coupler having N input ports (with N > 2) and one output port (or M output ports just one of which is used, with M > 2) .
  • a plurality of optical signal having predetermined wavelengths different from each other (channels) are sent over a same optical line by means of wavelength multiplexing devices.
  • the transmitted channels may be either digital or analog.
  • the wavelength multiplexing device most commonly used for wavelength multiplexing N channels in optical telecommunication systems is a Nxl passive balanced optical coupler (e.g. a conventional planar optical coupler or a fused optical fiber coupler) .
  • This optical coupler distributes the optical power of the optical channels entering the N input ports so that at the output port (or at each output port) there is a Nth fraction of power of each input channel (that is, it is a non wavelength selective optical coupler) . This is true also when the number of the input channels entering the optical coupler is less than the number of the input ports thereof.
  • this multiplexing device suffers the drawback of highly attenuating the transmitting power of each channel and, thus, of degrading the optical signal to noise ratio (SNR) at a receiving terminal.
  • SNR optical signal to noise ratio
  • optical SNR degradation becomes more and more important as the bit rates of the transmitted channels raise.
  • the required optical SNR level at the receiving terminal increases with the bit rate.
  • an optical wavelength multiplexing device other than the above mentioned passive optical coupler has been studied as, for example, a passive Arrayed Waveguide Grating (AWG) or a Mach Zehnder device as described in US 5 867 291.
  • AWG passive Arrayed Waveguide Grating
  • Mach Zehnder device as described in US 5 867 291.
  • EP 0 887 963 discloses optical multiplexing devices comprising multiple WDMs which are optically coupled to a common trunk line carrying multi -channel wavelength multiplexed light.
  • the multiple WDMs are cascaded in parallel or in series, or a combination of both, from the trunk line and multiplex different channels or wavelength sub-ranges.
  • the WDMs disclosed in this document are wavelength selective couplers and comprise an optical block carrying Fabry-Perot interference filters and other reflective elements to define a multi-bounce, zigzag expanded beam light path through the optical block.
  • the different optical channels accumulate imbalance in both the optical power and SNR owing to the fact that several optical components (optical fiber included) have nonuniform wavelength-dependent loss.
  • optical amplifiers such as erbium- doped fiber amplifiers, have nonuniform wavelength- dependent gain whereby each channel experiences a different optical gain.
  • the accumulated power and optical SNR imbalance can seriously limit system performance in three different ways.
  • BER Bit Error Rate
  • N. S. Bergano et al . discloses an experiment performed using a twenty wavelength transmitter and a 1260 Km gain flattened amplifier chain in a circulating loop. In such experiment, the odd and even wavelengths were multiplexed separately in a series of 4x1, 6x1 and 2x1 directional couplers. Furthermore, a 7dB of optical pre-emphasis was needed at the transmitter to equalize the received optical signal-to-noise ratios.
  • the pre-emphasis is, typically, achieved by optical attenuators adjusted for suitably attenuating the power of the channels at the transmitting terminal.
  • the optical transmitting power of the channels is further attenuated because of said adjustment of their reciprocal power.
  • the applicant aimed at providing an optical device capable of reducing the power losses at a transmitting terminal of a WDM optical telecommunication system having a high number of channels and a WDM optical telecommunication system having reduced losses at the transmitting terminal.
  • the multiplexing device of the invention suitably exploits the intrinsic losses of optical couplers to attenuate differently from each other at least two of said plurality M of optical channels while it multiplexes them.
  • a WDM optical telecommunication system allows to achieve a predetermined reciprocal attenuation of the power of the channels (e.g. for equalizing the optical power or SNR of the channels at the receiving terminal) without introducing significant additional losses on the channels besides those due to channels multiplexing.
  • the device of the invention reduces the need of using the aforementioned optical attenuators at the transmitting terminal of a WDM telecommunication system.
  • the difference in intrinsic loss among the couplers is at least equal to 2dB. More preferably, it is at least equal to 3dB. Even more preferably, it is at least equal to 3,5dB. Even more preferably, it is at least equal to 4dB. Further more preferably, it is at least equal to 4,5dB.
  • said tree topology has one input level having at least two optical couplers with intrinsic losses different from each other of at least 3 dB .
  • the difference in intrinsic losses between said at least two optical couplers is at least equal to 3.5 dB.
  • At least one of said at least three optical couplers is a non wavelength selective unbalanced optical coupler.
  • said tree topology typically has one input level and one output level.
  • said non wavelength selective unbalanced optical coupler is located at said output level of said tree topology.
  • At least one of said at least three optical couplers is a non wavelength selective optical coupler and at least one of said at least three optical couplers is a wavelength selective optical coupler.
  • said tree topology has one input level and one output level .
  • At said input level there are at least two optical couplers.
  • said at least two optical couplers are selected from the group comprising 2x1 and 4x1 optical couplers.
  • said at least two optical couplers have intrinsic losses different from each other.
  • said at least two couplers at the input of said tree topology are balanced. According to a variant, at least one of said at least two optical couplers is unbalanced.
  • said one optical coupler is a 2x1 optical coupler.
  • said one output optical coupler is an unbalanced optical coupler.
  • it is a balanced optical coupler.
  • said at least three optical couplers are selected from the group comprising conventional planar optical couplers and fused optical fiber couplers. This, makes the multiplexing device of the invention very simple to produce and at a low cost .
  • At least one of said at least three optical couplers is advantageously a wavelength selective optical coupler for coupling said at least two channels (or two groups of channels) .
  • said difference in wavelength is at least higher than 8nm. More preferably, it is at least higher than lOnm.
  • said wavelength selective optical coupler is a conventional interferential filter.
  • wavelength selective coupler typically has less losses than a conventional planar optical coupler or fused optical fiber coupler, it allows to reduce the losses of the multiplexing device.
  • fused optical coupler are intended to indicate a non wavelength selective optical coupler where otherwise not indicated.
  • said multiplexing device further comprises at least one attenuator having preselected loss.
  • said at least one attenuator is located at one of said at least N input ports of said multiplexing device.
  • Said attenuator can be, for example, an attenuating splice.
  • N is at least equal to 16. More preferably, N is at least equal to 32. Even more preferably, N is at least equal to 48. Even more preferably, N is at least equal to 64. Further more preferably, N is at least equal to 128.
  • N is a power of 2.
  • the multiplexing device of the invention has at least five optical couplers. More preferably, it has at least seven optical couplers. Even more preferably, it has at least eleven optical couplers. Further more preferably, it has at least fifteen optical couplers. Further more preferably, it has at least nineteen couplers.
  • said tree topology has one input level, one output level and at least one intermediate level .
  • two of said at least three optical couplers have intrinsic losses different from each other. More preferably, two of said at least three optical couplers have an intrinsic loss different from the intrinsic loss of a third of said at least three optical couplers. Even more preferably, said two optical couplers have an intrinsic loss lower than the intrinsic loss of said third optical coupler.
  • said at least three optical couplers are selected from the group comprising 2x1, 4x1, 8x1 and 16x1 optical couplers.
  • said at least three optical couplers are balanced.
  • At said at least one intermediate level there is at least one optical coupler.
  • said at least one optical coupler is a 2x1 optical coupler.
  • said at least one optical coupler is unbalanced.
  • said at least one optical coupler is advantageously a wavelength selective optical coupler for coupling said at least two groups of channels.
  • said difference in wavelength is at least higher than 8nm. More preferably, it is at least higher than lOnm.
  • said wavelength selective optical coupler is a conventional interferential filter.
  • said one optical coupler is a 2x1 optical coupler.
  • said one output optical coupler is a balanced optical coupler.
  • At least two groups of said optical channels are attenuated differently from each other.
  • two groups of said optical channels are attenuated differently from the remaining optical channels.
  • said optical channels are all differently attenuated to each other.
  • a transmitting terminal for supplying a plurality M of optical channels (with M>8) comprising a multiplexing unit for multiplexing said plurality M of optical channels, said multiplexing unit comprising a multiplexing device having N input ports (with N ⁇ M) and one output port and comprising at least three optical couplers having predetermined intrinsic losses and coupled together according to a tree topology, said tree topology having N inputs and one output corresponding to said N input ports and one output port; - an optical telecommunication line operatively coupled to said transmitting apparatus, for transmitting said plurality M of optical channels multiplexed by said multiplexing device; - a receiving terminal operatively coupled to said optical telecommunication line for receiving at least one part of the plurality M of optical channels; characterized in that a) the intrinsic loss of each of said at least three optical couplers is preselected; and b) said at least three optical couplers are arranged in said tree topology so that, passing through said multiplexing device, at least two of said plurality M
  • the difference in attenuation between said at least two channels is selected so as to equalize, at said receiving terminal, the optical power of said at least one part of the plurality M of optical channels.
  • the difference in attenuation between said at least two channels is selected so as to achieve, at said receiving terminal, a predetermined value of optical SNR for said at least one part of the plurality M of optical channels.
  • it is selected so as to equalize, at said receiving terminal, the optical SNR of said at least one part of the plurality M of optical channels.
  • said optical telecommunication line comprises at least one optical amplifying unit having a predetermined nonuniform wavelength dependent gain spectrum in a predetermined wavelength band.
  • the difference in attenuation between said at least two channels is typically selected depending on said gain spectrum.
  • the difference in attenuation between said at least two channels is selected so as to equalize the nonuniform gain spectrum of said at least one optical amplifying unit.
  • said plurality M of optical channels have wavelengths selected within said predetermined wavelength band of the gain spectrum.
  • the nonuniform gain spectrum of said at least one optical amplifying unit has a central substantially flat region and two opposite side inclined regions .
  • the number of the channels in the two opposite side inclined regions is lower than the number of the channels in the central substantially flat region.
  • said tree topology of the multiplexing device has an intermediate level comprising a wavelength selective optical coupler for coupling said two groups of optical channels having wavelengths within said two opposite side inclined regions of said gain spectrum.
  • said amplyfing unit comprises at least one erbium doped fiber amplifier.
  • said predetermined wavelength band wherein the amplifying unit has said predetermined nonuniform wavelength dependent gain spectrum comprises two sub-bands.
  • said nonuniform gain spectrum has a central substantially flat region and two opposite side inclined regions in each sub-band.
  • a first group of said plurality M of optical channels has wavelengths selected within a first of said two sub-bands and a second group of said plurality M of optical channels has wavelengths selected within the second of said two sub-bands.
  • the multiplexing unit further comprises a second multiplexing device, the first and the second multiplexing devices multiplexing the first and the second group of optical channels, respectively.
  • said amplifying unit has at least two erbium doped fiber amplifiers connected in parallel.
  • Fig. 1 is a schematic diagram of a WDM optical telecommunication system according to an embodiment of the present invention
  • Fig. 2 is a schematic diagram of a first terminal site of the system of Fig. 1 ;
  • Fig. 3 is a schematic diagram of a transmitter power amplifier section of the first terminal site of Fig. 2 ;
  • Fig. 4 is a schematic diagram of an optical line site of the system of Fig. 1 ;
  • Fig. 5 is a schematic diagram of a second terminal site of the system of Fig. 1 ;
  • Fig. 6 is a schematic diagram of a demultiplexing section of the second terminal site of Fig. 5;
  • Fig. 7 is a schematic diagram of a nonuniform gain spectrum, at the output of a receiver pre-amplifier section in the second terminal site of Fig. 5, of a chain of optical amplifiers cascaded in the optical telecommunication system 1 of Fig. 1;
  • Fig. 8 is a schematic diagram of an embodiment of a first multiplexing device, according to the invention, of the first terminal site of Fig. 2 ;
  • Fig. 9 is a schematic diagram of a step preemphasis curve (Fig. 9a) and a smoothened preemphasis curve (Fig. 9b) obtained in the system of Fig. 1 ;
  • Fig. 10 is a schematic diagram of a first embodiment of a second multiplexing device, according to the invention, of the first terminal site of Fig. 2;
  • Fig. 11 is a schematic diagram of a second embodiment of a second multiplexing device, according to the invention, of the first terminal site of Fig. 2.
  • the optical telecommunication system 1 hereinafter described with reference to Fig. 1 is unidirectional, that is signals travel from a terminal site to the other (in the present case from a first terminal site to a second terminal site) , but any consideration that follow is to be considered valid also for bi-directional systems, in which signals travel in both directions.
  • optical telecommunication system 1 is adapted to transmit up to one-hundred-twenty-eight (128) channels, from the hereinafter description it will be obvious that the number of channels is not a limiting feature for the scope and the spirit of the invention, and more than one-hundred-twenty-eight (128) channels can be used depending on the needs and requirements of the particular optical telecommunication system.
  • the first terminal site 10 is a transmitting terminal and preferably includes a multiplexing section (MUX) 11, a transmitter power amplifier section (TPA) 12 and a plurality of input channels 16.
  • the second terminal site 20 is a receiving terminal and preferably includes a receiver pre-amplifier (RPA) section 14, a demultiplexing section (DMUX) 15 and a plurality of output channels 17.
  • RPA receiver pre-amplifier
  • DMUX demultiplexing section
  • Each input channel 16 is received by multiplexing section 11.
  • Multiplexing section 11 that will be later described, multiplexes (or groups) input channels 16 preferably into three sub-bands, referred to as blue-band BB, first red- band RBI and second red-band RB2 , although multiplexing section 11 could alternatively group input channels 16 into a number of sub-bands greater or less than three.
  • the three sub-bands BB, RBI and RB2 are then received in succession by the TPA section 12, at least one line site 40 and the second terminal site 20.
  • Sections of optical fiber line 30 adjoin the at least one line site 40 with TPA section 12, RPA section 14, and possibly with others line sites 40 (not shown) .
  • TPA section 12, that will be later described with reference to Fig. 3 receives the separate sub-bands BB, RBI and RB2 from multiplexing section 11, amplifies and optimizes them, and then combines them into a single wide-band SWB for transmission on a first section of optical fiber line 30.
  • Line site 40 that will be later described with reference to Fig.
  • line site 40 receives the single wide-band SWB, re-divides the single wide-band SWB into the three sub-bands BB, RBI and RB2 , eventually adds and drops signals in each sub-band BB, RBI and RB2 , amplifies and optimizes the three sub-bands BB, RBI and RB2 and then recombines them into the single wide-band SWB.
  • line site 40 may be provided with Optical Add/Drop Multiplexers (OADM) of a known type .
  • OADM Optical Add/Drop Multiplexers
  • a second section of optical fiber line 30 couples the output of the line site 40 to either another line site 40 (not shown) or to RPA section 14 of second terminal site 20.
  • Demultiplexing section 15 receives the three sub-bands BB, RBI and RB2 from RPA section 14 and splits the three sub- bands BB, RBI and RB2 into the individual wavelengths of output channels 17.
  • the number of input channels 16 and output channels 17 may be unequal, owing to the fact that some channels can be dropped and/or added in line site (or line sites) 40.
  • Fig. 2 shows a more detailed diagram of the first terminal site 10 which includes, in addition to the multiplexing section 11 and the TPA section 12 an optical line terminal equipment (OLTE) 41 and a wavelength converter section (WCS) 42.
  • OLTE optical line terminal equipment
  • WCS wavelength converter section
  • OLTE 41 which may correspond to a standard line terminal equipment for use in a conventional SONET, ATM, IP or SDH system, includes transmitting/receiving (TX/RX) units (not shown) in a quantity that equals the number of channels in the first terminal site 10.
  • TX/RX transmitting/receiving
  • OLTE 41 may also comprise a collection of smaller separate OLTEs, such as three.
  • OLTE 41 has one-hundred-twenty- eight (128) TX/RX units for supplying 128 signals. Typically, said signals are at a generic wavelength.
  • OLTE 41 outputs a first group of sixteen (16) channels, a second group of forty-eight (48) channels and a third group of sixty- four (64) channels.
  • WCS 42 includes one-hundred-twenty-eight (128) wavelength converter modules WCM1-WCM128.
  • Units WCM1-WCM16 each receive a respective one of the first group of signals emitted from OLTE 41 to convert it from a generic wavelength into a selected wavelength comprised in the blue band BB; units WCM17-WCM64 each receive one of the second group of signals emitted from OLTE 41 to convert it from a generic wavelength into a selected wavelength comprised in the first red band RBI; and units WCM65-WCM128 each receive one of the third group of signals emitted from OLTE 41 to convert it from a generic wavelength into a selected wavelength comprised in the second red band RB2.
  • each WCM1-128 preferably comprises a module having a photodiode (not shown) for receiving an optical signal from OLTE 41 and converting it to an electrical signal, a laser or optical source (not shown) for generating a selected carrier wavelength, and an electro-optic modulator such as a Mach-Zehnder modulator
  • WCM1-128 may comprise a photodiode (not shown) together with a laser diode (not shown) that is directly modulated with the electrical signal to convert the received generic wavelength to the selected carrier wavelength of the laser diode.
  • Fig. 2 shows that the signals are provided and generated by the combination of OLTE 41 and WCM1-WCM128, each signal can also be directly provided and generated by an optical source suitable for supplying a signal with the selected wavelength.
  • the multiplexing section 11 includes three wavelength multiplexing devices (WM) 43, 44 and 45.
  • WM wavelength multiplexing devices
  • each selected wavelength signal output from units WCM1-WCM16 is received by WM 43
  • each selected wavelength signal output from WCM17-WCM64 is received by WM 44
  • each selected wavelength signal output from WCM65-WCM128 is received by WM 45.
  • WM 43, WM 44 and WM 45 combine the received signals of the three bands BB, RBI and RB2 into three respective wavelength division multiplexed signals.
  • WM 43 is a 16x1 wavelength multiplexing device
  • WM 44 is a 48x1 wavelength multiplexing device
  • WM 45 is a 64x1 wavelength multiplexing device.
  • the WM 43, 44, 45 will be later described.
  • the BB, RBI and RB2 multiplexed signals output from multiplexing section 11 are received by TPA section 12.
  • TPA section 12 includes three amplifier sections 51, 52,
  • Amplifier sections 51, 52 and 53 are preferably erbium-doped two-stages fiber amplifiers (although other rare-earth-doped fiber amplifiers or semiconductor amplifiers may be used) .
  • Each of the amplifiers 51, 52 and 53 is pumped by one or two laser diodes to provide optical gain to the signals it amplifies.
  • the characteristics of each amplifier, including its length and pump wavelength, are selected to optimize the performance of that amplifier for the particular sub- band that it amplifies.
  • the first stage of amplifier sections 51 and 52 may be pumped with a laser diode (not shown) operating at 980 nm (or 1480 nm) to amplify the BB band and the RBI band, respectively, in a linear or in a saturated regime.
  • a laser diode not shown
  • Appropriate laser diodes are available from the Applicant.
  • the laser diodes may be coupled to the optical path of the pre-amplifiers using 980/1550 (or 1480/1550) wavelength selective couplers (not shown) commonly available on the market, for example model SWDM0915SPR from E-TEK DYNAMICS, INC., 1885 Lundy Ave . , San Jose, CA (USA) .
  • the 980 nm pump provides a low noise figure for the amplifiers compared with other possible pump wavelengths.
  • the first stage of amplifier section 53 is preferably erbium-doped and amplifies the RB2 band with a 1480 nm (or 980 nm) pump (not shown) coupled to the optical path of the RB2 band using a 1480/1550 (or 980/1550) wavelength selective coupler (not shown) .
  • the second stage of each amplifier section 51-53 preferably operates in a saturated condition.
  • the second stage of amplifier section 51 is preferably erbium-doped and amplifies the BB band with another 980 nm (or 1480 nm) pump (not shown) coupled to the optical path of the BB band using a 980/1550 (or 1480/1550) wavelength selective coupler (not shown) described above.
  • the 980 nm pump provides better gain behavior and noise figure for signals in the low band region that covers 1529-35 nm.
  • the second stage of amplifier section 52 is preferably erbium-doped and amplifies the RBI band with a laser diode pump source operating at 1480 nm.
  • Such a laser diode is available on the market, such as model FOL1402PAX-1 supplied by JDS FITEL, INC., 570 Heston Drive, Nepean, Ontario (CA) .
  • the 1480 nm pump provides better saturated conversion efficiency behavior, which is needed in the RBI band for the greater number of channels in the region that covers 1542-1561 nm.
  • a higher power 980 nm pump laser or multiplexed 980 nm pump sources may be used.
  • the second stage of amplifier section 53 is preferably erbium- doped and amplifies the RB2 band with another 1480 nm pump (not shown) coupled to the optical path of the RB2 band using a WDM coupler (not shown) .
  • Filter 54 is a conventional band combining filter and may, for example, include two cascaded interferential filters with three port (not shown) , the first coupling the BB band with the RBI band and the second coupling the BB/RBl bands provided by the first filter with the RB2 band.
  • line site 40 receives and amplifies the channels within the single wideband SWB.
  • line site 40 includes several optical amplifiers (AMP) 64-69, three optical filters 70-72, an optical equalizing filter (EQ) 74 and three OADM devices 75-77.
  • AMP optical amplifiers
  • EQ optical equalizing filter
  • Filter 70 receives the single wide-band SWB and separates the RB2 band from the BB and the RBI bands.
  • Amplifier 64 receives and amplifies the BB and the RBI bands, whereas filter 71 receives the output from amplifier 64 and separates the BB band and the RBI band.
  • the gain spectrum in the BB band is first equalized in a conventional way by using a conventional equalizing filter 74, then the BB band is received by the first OADM 75 where predetermined signals are dropped and/or added, and further amplified by amplifier 65.
  • the RBI band is first amplified by amplifier 66, then received by the second OADM 76 where predetermined signals are dropped and/or added, and further amplified by amplifier 67.
  • the RB2 band is first amplified by amplifiers 68, then received by the third OADM 77 where predetermined signals are dropped and/or added, and further amplified by amplifier 69.
  • the amplified BB, RBI and RB2 bands are then recombined into the single wide-band SWB by filter 72.
  • Amplifier 64 which receives the BB and the RBI bands, preferably is an optical fiber amplifier that is operated in a linear regime. That is, amplifier 64 is operated in a condition where its output power is dependent on its input power. Depending on the actual implementation, amplifier 64 may alternatively be a single-stage or a multi-stage amplifier. By operating it in a linear condition, amplifier 64 helps to ensure relative power independence between the BB and RBI band channels. In other words, with amplifier 64 operating in a linear condition, the output power (and signal-to-noise ratio) of individual channels in the one of the two sub-bands BB, RBI does not vary significantly if channels in the other sub-band RBI, BB are added or removed.
  • first stage amplifier (such as amplifier 64) must be operated, in a line site 40, in an unsaturated regime, before extracting a portion of the channels for separate equalization and amplification.
  • amplifier 64 is an erbium-doped fiber amplifier, pumped in a co-propagating direction with a laser diode (not shown) operating at 980 nm pump to obtain a noise figure preferably less than 5.5 dB for each band.
  • Filter 71 may comprise, for example, a three-port device, preferably a conventional interferential filter, having a drop port that feeds the BB band into equalizing filter 74 and a reflection port that feeds the RBI band into amplifier 66.
  • Amplifier 66 is preferably an erbium-doped fiber amplifier that is operated in saturation, such that its output power is substantially independent from its input power. In this way, amplifier 66 serves to add a power booster to the channels in the RBI band compared with the channels in the BB band. Due to the greater number of channels in the RBI band compared with the BB band in the preferred embodiment, i.e. forty-eight (48) channels as opposed to sixteen (16), the RBI band channels typically will have had a lower gain when passing through amplifier 64. As a result, amplifier 66 helps to balance the power for the channels in the RBI band compared with the BB band. Of course, for other arrangements of channels between the BB and the RBI bands, amplifier 66 may not be required or may alternatively be required on the BB band side of line site 40.
  • amplifiers 64 and 66 may be viewed together as a two- stage amplifier with the first stage operated in a linear mode and the second stage operated in saturation.
  • amplifier 64 and 66 are preferably pumped with the same laser diode pump source.
  • line site 40 includes a wavelength selective coupler positioned between amplifier 64 and filter 71 that extracts 980 nm pump light that remains at the output of amplifier 64.
  • This wavelength selective coupler may be, for example, model number SWDMCPR3PS110 supplied by E-TEK DYNAMICS, INC., 1885 Lundy Ave .
  • the output from this wavelength selective coupler feeds into a second wavelength selective coupler (not shown) of the same type and positioned in the optical path after amplifier 66.
  • the two couplers are joined by an optical fiber 78 that transmits the residual 980 nm pump signal with relatively low loss.
  • the second wavelength selective coupler passes the residual 980 nm pump power into amplifier 66 in a counter-propagating direction.
  • RBI band signals are conveyed to OADM 76, for example an OADM of a known type.
  • OADM 76 RBI band signals are fed to amplifier 67.
  • amplifier 67 has a pump wavelength of, for example, 1480 nm from a laser diode source (not shown) having a pump power in excess of the laser (not shown) that drives amplifiers 64 and 66.
  • the 1480 nm wavelength provides good conversion efficiency for high output power output compared with other pump wavelengths for erbium-doped fibers.
  • a high power 980 nm pump source or a group of multiplexed pump sources could be used to drive amplifier 67.
  • Amplifier 67 preferably operates in saturation to provide the power boost to the signals within the RBI band, and if desired, may comprise a multi-stage amplifier.
  • the BB band After passing through amplifier 64 and filter 71, the BB band enters equalizing filter 74.
  • the gain characteristic for the erbium-doped fiber spectral emission range has a peak or hump in the BB band region, but remains fairly flat in the RBI band region. This is why, in order to provide a proper flattening of the gain characteristic for the channels, the spectrum of the channels is preferably splitted into a BB band and a RBI band and these bands are processed separately.
  • the equalizing filter 74 comprises a two-port device based on a conventional long period chirped Bragg grating technology that gives selected attenuation at different wavelengths.
  • equalizing filter 74 for the BB band may have a transfer function substantially equal to the inverse of the gain spectrum in the BB band region and an operating wavelength range of 1529 nm to 1536 nm, with a wavelength at the bottom of the valley at between 1530.3 nm and 1530.7 nm.
  • Equalizing filter 74 need not be used alone and may be combined in cascade with other filters (not shown) to provide an optimal filter shape, and thus, gain equalization for the particular amplifiers used in the WDM system 1.
  • Equalizing filter 74 may be manufactured by one skilled in the art, or may be obtained from numerous suppliers in the field. It is to be understood that the particular structure used for the equalizing filter 74 is within the realm of the skilled artisan and may include, for instance, a specialized Bragg grating like a long period grating, an interferential filter, or Mach-Zehnder type optical filters.
  • BB band signals are conveyed to OADM 75, which is, for example, of the same type of OADM 76, and then to amplifier 65.
  • amplifier 65 has a pump wavelength of 980 nm, provided by a laser diode source (not shown) and coupled via a wavelength selective coupler (not shown) to the optical path for pumping the amplifier 65 in a counter- propagating direction. Since the channels in the BB band pass through both amplifier 64 and amplifier 65, equalizing filter 74 may compensate for the gain disparities caused by both amplifiers. Thus, the decibel drop for equalizing filter 74 should be determined according to the overall amplification and line power requirements for the BB band.
  • the amplifier 65 preferably operates in saturation to provide a power boost to the signals in the BB band, and may be a multi-stage amplifier if desired.
  • the RB2 band is received from fiber amplifier 68, which is, preferably, an erbium doped fiber amplifier pumped with a 980 nm or a 1480 nm pump light, depending on the system requirements.
  • fiber amplifier 68 which is, preferably, an erbium doped fiber amplifier pumped with a 980 nm or a 1480 nm pump light, depending on the system requirements.
  • OADM 77 which is, for example, of the same type of OADMs 75 and 76, and then fed to amplifier 69.
  • Amplifier 69 is, as an example, an erbium doped amplifier adapted to amplify the RB2 band by means of a combination of one or more 1480 pump lasers.
  • filter 72 After passing through amplifiers 65, 67 and 69 respectively, the amplified BB, RBI and RB2 bands are then recombined by filter 72 into the single wide-band SWB.
  • filter 72 may, for example, include two cascaded interferential three port filter (not shown) , the first coupling the BB with the RBI bands and the second coupling the BB and RBI bands provided by the first filter with the RB2 band.
  • line site 40 may also include a dispersion compensating module (DCM) (not shown) for compensating for chromatic dispersion that may arise during transmission of the signals along the long-distance communication link.
  • DCM dispersion compensating module
  • the DCM (not shown) is preferably comprised of sub-units coupled upstream one or more of amplifiers 65, 67, 69 for compensating the dispersion of channels in the BB, RBI, RB2 bands, and may also have several forms.
  • the DCM may have an optical circulator with a first port connected to receive the channels in one or more than one of the three bands BB, RBI and RB2.
  • a chirped Bragg grating may be attached to a second port of the circulator.
  • the channels will exit the second port and be reflected in the chirped Bragg grating to compensate for chromatic dispersion.
  • the dispersion compensated signals will then exit a next port of the circulator for continued transmission in the WDM telecommunication system 1.
  • Other devices besides the chirped Bragg grating, such as a length of dispersion compensating fiber, may be used for compensating the chromatic dispersion.
  • the design and use of the DCM section are not limiting the present invention and the DCM section may be employed or omitted in the WDM system 1 depending on overall requirements for system implementation.
  • the combined single wide-band SWB signal passes through a length of long-distance optical transmission fiber of optical fiber line 30.
  • the distance between the first and the second terminal site 10, 20 is sufficiently long to cause attenuation of the optical signals, i.e. 100 kilometers or more, one or more additional line sites 40 providing amplification may be used.
  • five spans of longdistance transmission fiber are used (each having a power loss of 0,22 dB/km and a length such as to provide a total span loss of approximately 25 dB) , separated by four amplifying line site 40.
  • RPA section 14 receives the single wide-band SWB from last line site 40 and prepares the signals of the single wide-band SWB for reception and detection at the end of the communication link.
  • RPA section 14 may include amplifiers (AMP) 81-85, filters 86 and 87, an equalizing filter 88 and, if necessary, three router modules 91-93.
  • AMP amplifiers
  • Filter 86 receives the single wide-band SWB and separates the RB2 band from the BB and RBI bands.
  • Amplifier 81 is preferably doped with erbium and amplifies the BB and RBI bands to help improve the signal-to-noise ratio for the channels in the BB and RBI bands.
  • Amplifier 81 is pumped, for example, with a 980 nm pump or with a pump at some other wavelength to provide a low noise figure for the amplifier.
  • the BB and RBI bands are in turn separated by filter 87.
  • amplifier 82 and 83 amplify the BB band and, respectively, the RBI band, with a 980 nm pumping.
  • amplifier 81 and 83 are preferably pumped with the same 980 nm laser diode pump source, by using a joining optical fiber 89 that transmits the residual 980 nm pump signal with relatively low loss.
  • amplifier 81 is associated with a wavelength selective coupler, positioned between amplifier 81 and filter 87, that extracts the 980 nm pump light that remains at the output of amplifier 81.
  • This wavelength selective coupler may be, for example, model number SWDMCPR3PS110 supplied by E-TEK DYNAMICS, INC., 1885 Lundy Ave . , San Jose, CA (USA) .
  • the output from this wavelength selective coupler feeds into a second wavelength selective coupler of the same type and positioned in the optical path after amplifier 83.
  • the two couplers are joined by an optical fiber 89 that transmits the residual 980 nm pump signal with relatively low loss.
  • the second wavelength selective coupler passes the residual 980 nm pump power into amplifier 83 in a counter-propagating direction.
  • amplifiers 81-83, filter 87 and equalizing filter 88 perform the same functions as amplifiers 64, 65 and 66, filter 71, and equalizing filter 74, respectively, of line site 40 and may comprise the same or equivalent parts depending on overall system requirements.
  • RPA section 14 may also include a dispersion compensating module (DCM) (not shown) for compensating for chromatic dispersion that may arise during transmission of the signals along the long-distance communication link.
  • DCM dispersion compensating module
  • the DCM (not shown) is preferably comprised of sub-units coupled upstream one or more of amplifiers 82, 83, 85 for compensating the dispersion of channels in the BB, RBI, RB2 bands, and may have the forms described with reference to TPA section 12.
  • Amplifier 84 is coupled to filter 86 to receive and amplify the RB2 band.
  • Amplifier 84 is, for example, an erbium- doped amplifier identical to the amplifier 68 of fig. 4.
  • RB2 band channels are then received by amplifier 85 that is, for example, an erbium-doped amplifier of a known type.
  • RPA section 14 further comprises a routing stage 90, which permits to adapt the channel spacing within the BB, RBI and RB2 bands to the channel separation capability of demultiplexing section 15.
  • RPA section 14 could include the routing stage 90 shown in Fig. 5.
  • Other structures may be added to RPA section 14 depending on the channel separation capability of demultiplexing section 15.
  • Routing stage 90 includes three router modules 91-93.
  • Each router module 91-93 separates the respective band into two sub-bands, each sub-band including half of the channels of the corresponding band. For example, if the BB band includes sixteen (16) channels ⁇ ⁇ - ⁇ 16 , each separated by 50 GHz, then router module 91 would split the BB band into a first sub-band BB' having channels ⁇ - L , ⁇ 3 , ... , ⁇ 15 separated by 100 GHz and a second sub-band BB' ' having channels ⁇ 2 , ⁇ 4 , ...., ⁇ 16 separated by 100 GHz and interleaved with the channels in the sub-band BB' . In a similar fashion, router modules 92 and 93 would split the RBI band and the RB2 band, respectively, into first sub-bands RBI' and RB2 ' and second sub-bands RBI'' and RB2 ' ' .
  • Each router module 91-93 may, for example, include an optical coupler (not shown) that has a first series of
  • Bragg gratings attached to a first port and a second series of gratings attached to a second port The Bragg gratings attached to the first port would have reflection wavelengths that correspond to every other channel (i.e. the even channels) , while the Bragg gratings attached to the second port would have reflection wavelengths that correspond to the remaining channels (i.e. the odd channels) .
  • This arrangement of gratings will also serve to split the single input path into two output paths with twice the channel -to-channel spacing.
  • each router module 91-93 separates the respective band into two or more serial sub-bands.
  • the BB band includes sixteen (16) channels ⁇ - ⁇ 16 , each separated by 50 GHz
  • router module 91 would split the BB band into a first sub-band BB' having channels ⁇ 1( ⁇ 2 , ..., ⁇ 8 and into a second sub-band BB' ' having channels ⁇ 9 , ⁇ 10 , .... , ⁇ 16 .
  • routers 91-93 may comprise interferential filters.
  • demultiplexing section 15 After passing through RPA section 14, the BB ' , BB ' ' , RBI 1 , RBI' 1 , RB2 ' and RB2 ' ' sub-bands are received by demultiplexing section 15.
  • demultiplexing section 15 includes six conventional wavelength demultiplexers (WDs) 95', 95'', 96', 96'', 97', 97'' which receive the respective sub-bands BB' , BB' ' , RBI', RBI'', RB2 ' and RB2 ' ' and provide the output channels 17.
  • Demultiplexing section 15 further includes receiving units Rxl-Rxl28 for receiving the output channels 17.
  • the wavelength demultiplexers preferably comprise arrayed waveguide grating (AWG) devices, but alternative structures for achieving the same or similar wavelength separation are contemplated. For instance, one may use interferential filters, Fabry-Perot filters, Mach Zehnder devices or in- fiber Bragg gratings in a conventional manner to demultiplex the channels within the sub-bands BB' , BB' ' , RBI ' , RBI ' ' , RB2 ' , RB2 ' ' .
  • AMG arrayed waveguide grating
  • demultiplexer section 15 combines interferential filter and AWG filter technology.
  • WDs 95', 95'' which are preferably eight channel demultiplexers with interferential filters, receive and demultiplex first sub-band BB' and second sub-band BB' ' , respectively.
  • WD 95' demultiplexes channels ⁇ ⁇ ⁇ 3 , ... , ⁇ 15
  • Both WD 95' and WD 95'' may be 1x8 type AWG 100 GHz demultiplexers.
  • WDs 96' and 96'' receive and demultiplex first sub-band RBI' and second sub-band RBI'', respectively, to produce channels ⁇ 17 - ⁇ 64
  • WDs 97' and 97'' receive and demultiplex first sub-band RB2 ' and second sub-band RB2 ' ' , respectively, to produce channels ⁇ 65 - ⁇ 128 .
  • Both WD 96' and WD 96'' may be lx 32 type AWG 100 GHz demultiplexers that are underequipped to use only twenty- four of the available demultiplexer ports and both WD 97' and WD 97'' may be lx 32 type AWG 100 GHz demultiplexers that uses all the available demultiplexer ports.
  • Output channels 17 are composed of the individual channels demultiplexed by WDs 95', 95'', 96', 96'', 97', 97'', and each channel of output channels 17 is received by one of receiving units Rxl-Rxl28.
  • Fig. 7 is a qualitative graph of the nonuniform gain spectrum at the end of the chain of optical amplifiers cascaded along the optical telecommunication system 1 (e.g. at the output of the RPA section 14) having five spans of long-distance transmission fiber (each having a length such as to provide a total span loss of approximately 25 dB) separated by four amplifying line site 40.
  • This graph does not show the tilt due to the known saturation phenomenon in the chain of optical amplifiers and approximately corresponds to the different gain for channels travelling through the telecommunication system and the different allocation of the three sub-bands BB, RBI and RB2.
  • the first sub-band BB preferably covers the range between 1529 nm and 1535 nm, corresponding to a first amplification wavelength range of erbium-doped fiber amplifiers, and allocates up to sixteen (16) channels;
  • the second sub-band RBI falls between 1541 nm and 1561 nm, corresponding to a second amplification wavelength range of erbium-doped fiber amplifiers, and allocates up to forty- eight (48) channels;
  • the third sub-band RB2 covers the range between 1575 nm and 1602 nm, corresponding to an amplification wavelength range of erbium-doped fiber amplifiers, and allocates up to sixty-four (64) channels.
  • the gain spectral graph of the erbium-doped fiber amplifiers is such that, although the 1575-1602 nm range offers the best performances in terms of amplification, channels can be advantageously allocated down to 1565 nm and up to 1620 nm.
  • Fig. 8 shows an embodiment of the 64x1 multiplexing device WM 45 operating in the RB2 band apted, according to the present invention, to be used in the optical telecommunication system 1.
  • the WM 45 comprises fifteen optical couplers arranged in a tree topology having 64 input ports and one output port.
  • Said tree topology has one input level, one output level and three intermediate levels.
  • the input level comprises eight balanced optical couplers: two couplers 16x1 202, 202', two couplers 8x1 206, 206' and four 4x1 couplers 205, 205', 207, 207'.
  • the first intermediate level comprises two 2x1 wavelength selective optical couplers 213, 213'.
  • the second intermediate level level comprises two 2x1 unbalanced couplers 217, 217'.
  • the third intermediate level comprises two 2x1 balanced couplers 225, 225 ' .
  • the output level comprises one 2x1 balanced coupler 231.
  • unbalanced coupler are intended to indicate a non wavelength selective optical coupler where otherwise not indicated.
  • said 16x1 optical couplers 202, 202' are located in corresponding multiplexing units 240, 240', said couplers 205, 206, 207, 213, 217 and 205', 206', 207', 213', 217' are located in multiplexing units 204 and 204', respectively; and couplers 225, 225' and 231 are located in a multiplexing unit 224.
  • the two 16x1 optical couplers 202, 202' have 16 input fibers 208 and 208', respectively, and are each able to combine 16 entering optical channels along a single corresponding output port 203 and 203'.
  • the optical coupler 205, 205', 206, 206', 207, 207' have input optical fibers 208, 208' and optical output fibers 209, 209', 210, 210', 211, 211', respectively.
  • the output fiber 209 of the optical coupler 205 is connected to a first input 212 of the wavelength selective optical coupler 213 and the output fiber 211 of the optical coupler 207 is connected to a second input 214 of said coupler 213.
  • An output fiber 215 of the coupler 213 is connected to an input port 216 of the unbalanced optical coupler 217.
  • the wavelength selective optical coupler 213 is able to combine channels entering port 212 and 214 along a single port 215.
  • the output fiber 210 of the optical coupler 206 is connected to an input port 218 of the unbalanced optical coupler 217.
  • the unbalanced optical coupler 217 is able to combine the optical channels entering at input ports 218 and 216 along the output fiber 219.
  • the unbalanced optical coupler 217 is of the type 40:60: i.e., 40% of the optical power at the input port 218 is sent at the output fiber 219 and 60% of the optical power at the input port 216 is sent at the output fiber 219.
  • the optical fibers 219 and 219' are respectively connected to the output ports 221 and 221' of the multiplexing units 204 and 204' .
  • the output port 221 of the multiplexing unit 204 and the output port 203 of the multiplexing unit 240 are respectively optically connected to input ports 222 and 223 of the multiplexing unit 224.
  • the output port 221' of the multiplexing unit 204' and the output port 203' of the multiplexing unit 240' are respectively optically connected to input ports 222' and 223' of the multiplexing unit 224.
  • the two optical couplers 225 and 225' of the multiplexing unit 224 have respectively input ports 226, 227 and 226' and 227' optically connected respectively to the input ports 222, 223 and 222', 223'.
  • the optical couplers 225 and 225' are able to combine optical channels entering the input fibers along the output fibers 228 and 228' .
  • the output fibers 228 and 228' are connected to ports 229, and 230 of the 2x1 optical coupler 231 that is able to combine the entering optical channels along one output fiber 232.
  • This output fiber 232 is connected to an output port 233 of the WM 45.
  • the multiplexing device WM 45 combines 64 channels entering from fibers 208 and 208' in a single output port 233.
  • the optical couplers in the WM 45 are conventional planar optical couplers or fused fiber optical couplers. This makes the wavelength multiplexing device WM 45 very simple to produce and at low cost.
  • E-TEK makes fiber fused and planar optical coupler suitable for using in the WM 45 above described, e.g., the 2x2 optical coupler 217 can be an E-TEK coupler, Model SWBC2PS0PRL19 and the 16x1 optical coupler 202 can be an E- TEK coupler, Model SWTCYE30RPRL10 having operating band of 1574-1603 nm.
  • optical couplers 213 and 213' are wavelength selective optical coupler. More particularly, they are conventional band combining interferential filters. However, they can also be planar optical couplers or fused fiber optical couplers.
  • Interferential filters are preferred because they have less intrinsic losses than the planar or fused fiber optical couplers.
  • Band combining interferential filters suitable for using in the WM 45 of the invention are made by E-TEK.
  • each input fiber 208, 208' is provided of attenuating splices 100, 100' selected so as to have a predetermined value of loss, as it will be later described.
  • these attenuating splices 100, 100' are of the conventional type for which a pre-established attenuation is obtained by a suitable misalignment of the optical axes of the fibers that are connected therein.
  • the WM 45 there are eight different optical paths for eight different groups of channels.
  • these eight optical paths are the following :
  • Each optical path has a loss that depends on the intrinsic losses of the optical couplers comprised therein.
  • a conventional Nxl optical coupler comprises N optical waveguides, as planar waveguides or optical fibers, optically coupled and the coupling occurring between adjacent waveguides introduces a loss. As already described above, this loss is related to the number of optical waveguides optically coupled, independently on the number of the effectively used input ports.
  • an additional loss, "excess loss”, due to production process has also to be considered.
  • the excess loss rises as the number of input ports of the coupler increases.
  • the real intrinsic loss of a coupler is generally the sum of the ideal intrinsic loss and the excess loss.
  • optical couplers of the described embodiment of the invention have substantially the following real intrinsic losses, IL:
  • IL 1 dB.
  • the 64 channels belonging to the RB2 band have wavelengths "•i , " ⁇ l' ⁇ 2, 2 i - 3 ⁇ ⁇ , 3, ... 32 _ A 32 .
  • a first sub-band RB2 ' comprises thirty-two channels (32) having wavelengths ⁇ 1 - ⁇ 32 and a second sub-band RB2 " comprises 32 channels having wavelengths ⁇ 1 - ⁇ 32 .
  • each sub-band the channels have a spacing of 100 GHz while the distance between a channel ⁇ n of the first sub- band and a channel ⁇ ' n of the second sub-band is of 50 GHz.
  • the four (4) wavelengths ⁇ 1( ⁇ 2 ⁇ 3# ⁇ 4 and the four (4) wavelengths ⁇ ' 1# ⁇ 2 ⁇ ' 3j ⁇ ' 4 lie in a inclined side region C x of the gain spectrum in the RB2 band.
  • the four (4) wavelengths ⁇ 29; ⁇ 30 ⁇ 31 _ ⁇ 32 and the four (4) wavelengths ⁇ ' 29, ⁇ ' 30 ⁇ ' 31 _ ⁇ ' 32 lie in the inclined side region C 2 of the gain spectrum in the RB2 band.
  • the twenty- four (24) wavelengths ⁇ 5 , ⁇ 6 , ... ⁇ 27 , ⁇ 28 and the wavelengths ⁇ ' 5 ⁇ ⁇ ' 6 , ... ⁇ ' 27 , ⁇ ' 28 lie in a substantially flat central region of the gain spectrum in the RB2 band.
  • the eight wavelengths ⁇ 5 ,. administrat, ⁇ 12 correspond to a region A and the sixteen wavelengths ⁇ 13 ,..., ⁇ 28 ( ⁇ ' 13 ,..., ⁇ ' 28 ) correspond to a region B of the gain spectrum in the RB2 band.
  • the channels having wavelengths ⁇ X ⁇ ⁇ 2 ⁇ 3/ ⁇ 4 , ⁇ ' lr ⁇ 2 ⁇ ' 3 ⁇ ⁇ ' 4 (region C x ) and the channels having wavelengths ⁇ 29; ⁇ 30 ⁇ 31f ⁇ 32 , ⁇ ' 29 ⁇ ' 30 ⁇ ' 3 . 1, ⁇ ' 32 (region C 2 ) are less amplified than the channels having wavelengths ⁇ 5j ⁇ 6 , ... ⁇ 27 , ⁇ 28 , ⁇ ' 5# ⁇ ' 6 , ... ⁇ ' 27 , ⁇ ' 28 (regions A, B) . More particularly, the maximum gain difference ⁇ between the side regions C l t C 2 and the central regions A,B is equal to 4 dB.
  • the real intrinsic losses of the couplers of the multiplexing device WD 45 and their arrangement in the tree topology are selected so as to attenuate the channels having wavelengths in regions A and B more than the channels having wavelengths in regions C and C 2 of a quantity equal to about ⁇ (4dB) .
  • a suitable optical SNR for the optical channels 17 in the RB2 band can be achieved.
  • the difference in attenuation among the channels having wavelengths in regions A and B and those having wavelengths in regions C- L and C 2 can be selected so as to meet predetermined system requirements as, for example, the equalization of the optical power or SNR of the optical channels 17 at the second terminal site 20.
  • the channels having wavelengths ⁇ 5 ,. chorus, ⁇ 12 (corresponding to the region A of the amplifier gain spectrum) pass through the above defined optical path a and undergo substantially the following losses:
  • the total loss IL aT is equal to about 22.4 dB, wherein the index "T" indicates the Total loss.
  • the total loss IL aT is equal to about 23 dB .
  • the total loss IL bT IL ⁇ . T is equal to about 22.1 dB.
  • T is equal to about 22.6 dB.
  • the total loss IL C 1 2 ⁇ IL C , 2 2 ⁇ is equal to about 18.3 dB .
  • the total loss IL c ⁇ ,2 ⁇ IL C' ⁇ ,2 T i s equal to about 18.8 dB .
  • the channels having wavelengths corresponding to the regions A, B of the gain spectrum undergo a total loss greater of about 4 dB than the total loss suffered by the channels having wavelengths corresponding to the regions
  • Fig. 9a shows a schematic graph of the preemphasis "step" undergone by the channels passing through the optical paths described above.
  • the system 1 of the invention carries out the preemphasis and multiplexing operations at the transmitting terminal site 10 with reduced losses.
  • the preemphasis and multiplexing operations are performed by optical attenuators (adjusted so as to have a preemphasis value of 4dB) and a conventional 64x1 optical passive balanced coupler, respectively. Therefore, at the transmitting terminal of a conventional system the maximum total loss is equal to about 27 dB (4dB of preemphasis, 18 dB of ideal intrinsic loss of the conventional 64x1 optical coupler, about 4 dB of excess loss and 1 dB for the connection at the output port of the coupler) .
  • the connections among a corresponding high number of transmitting units - each comprising, for example, one OLTE and one wavelength conversion modules WCM - and the input ports of the multiplexing device are very complicated and take up a lot of room.
  • the arrangement of the devices comprised in terminal or line sites of an optical telecommunication system is regulated by standardizing rules as the ones fixed by the American National Standard Institute (ANSI) or the European Standard Telecommunication Institute (ETSI) .
  • ANSI American National Standard Institute
  • ETSI European Standard Telecommunication Institute
  • a sub-rack may houses eight or multiple of eight transmitting units in suitable slots.
  • the ETSI standard establishes that a single sub-rack may houses six or multiple of six transmitting units.
  • each sub- rack typically, eight or sixteen transmitting units in each sub- rack, for ANSI standard, and six or twelve transmitting units in each sub-rack, for ETSI standard, are employed.
  • one multiplexing device can be connected at most to two sub-rack.
  • the multiplexing device of the invention thanks to the flexibility of its stucture, simplifies the connections to external devices (e.g. transmitting units) and can be easly designed from time to time so as to meet a required standard (e.g. ANSI or ETSI) simply by grouping its optical couplers in predetermined multiplexing units.
  • ANSI ANSI or ETSI
  • the multiplexing device WM 45 shown in Fig. 8, comprising four multiplexing units 240, 240', 204 and 204' with 16 inputs, can advantageously be used to multiplexe 64 channels outcoming from four sub-racks, each comprising 16 transmitting units according the ANSI standard.
  • each multiplexing unit 240, 240', 204, 204' of WM 45 can be housed in separated sub-racks and can be placed near the sub-rack containing the corresponding 16 transmitting units so as to facilitate the connections among transmitting units and the multiplexing device.
  • the multiplexing device WM 45 of the invention has the same modularity of the sub-rack designed according to the ANSI standard, it can extremely simplify the connections among OLTE 41 and WCM 42 units and multiplexing unit 11.
  • multiplexing devices that are particularly suitable for the ETSI standard can be easly designed by a person skilled in the art on the basis of the present description and without departing from the spirit of the invention.
  • the WM 45 described before and depicted in Fig. 8 can be modified by eliminating the optical paths a', £>', c ' .
  • Fig. 10 shows an embodiment of the 48x1 multiplexing device WM 44 operating in the RBI band apted, according to the present invention, to be used in the optical telecommunication system 1.
  • the WM 44 comprises eleven optical couplers arranged in a tree topology having 48 input ports and one output port.
  • Said tree topology has one input level, one output level and two intermediate levels.
  • the input level comprises six balanced optical couplers: two couplers 16x1 202, 202' and four 4x1 couplers 205, 205 ' , 207, 207' .
  • the first intermediate level comprises two 2x1 wavelength selective optical couplers 213, 213'.
  • the second intermediate level level comprises two 2x1 unbalanced couplers 217, 217'.
  • the output level comprises one 2x1 balanced coupler 231.
  • couplers 202, 205, 207, 213, 217 and 202', 205', 207', 213', 217' are located in multiplexing units 250 and 250', respectively; and coupler 231 is located in a multiplexing unit 270.
  • the two multiplexing units 250, 250' have input fibers 208 and 208' and have output ports 251 and 251'. Both ports 251 and 251' are optically connected to the input ports 253 and 253' of the multiplexing unit 270.
  • the multiplexing unit 270 has an output port 254.
  • the output ports of the optical couplers 205 and 207 are optically connected to the input ports of the optical coupler 213 (213').
  • the output ports of the optical couplers 202 (202') and the optical coupler 213 (213') are connected to the input ports of the unbalanced optical coupler 217 (217') .
  • the output fiber 219 (219') of the unbalanced optical coupler 217 (217') is connected to the output port 251 (251') of multiplexing unit 250 (250').
  • Each input fiber 208, 208' is provided of attenuating splices 100, 100' able to be adjusted at a suitable value of loss .
  • the devices employed in the WM 44 are of the same type of the ones described with reference to WM 45 and thus are indicated with the same reference numbers.
  • Suitable devices employed in the WM 44 for the RBI band are made by E-TEK.
  • the 48 channels belonging to the RBI band have wavelengths ⁇ lf ⁇ '- L , ⁇ 2; ⁇ ' 2 , ⁇ 3# ⁇ ' 3 , ... ⁇ 24/ ⁇ ' 24 .
  • a first group of channels comprises thirty-two (24) channels having respectively wavelengths ⁇ 2 - ⁇ 24
  • a second group of channels comprises channels having wavelength ⁇ 2 - ⁇ 24 .
  • the wavelengths ⁇ 1# ⁇ 2 ⁇ 3 ⁇ ⁇ 4 , and the wavelengths ⁇ ' 1# ⁇ 2 ⁇ ' 3 _ ⁇ ' 4 lie in a side inclined region E 2 of the gain spectrum in the RBI band.
  • the wavelengths ⁇ 21 _ ⁇ 22 ⁇ 23; ⁇ 24 and the wavelengths ⁇ ' 21j ⁇ ' 22 ⁇ ' 23, ⁇ ' 24 lie in a side inclined region E 2 of the gain spectrum in the RBI band.
  • the wavelengths ⁇ 5; ⁇ 6 ,..., ⁇ 19# ⁇ 20 and the wavelengths ⁇ ' 5j ⁇ ' 6 ,..., ⁇ ' 19r ⁇ ' 20 lie in a central substantially flat region D of the gain spectrum in the RBI band.
  • the maximum gain difference ⁇ between the side regions E 2 , E 2 and the central D is of about 4 dB .
  • the real intrinsic losses of the couplers of the multiplexing device WD 44 and their arrangement in the tree topology are selected so as to attenuate the channels having wavelengths in the central region D more than the channels having wavelengths in regions E 2 and E 2 of a quantity equal to ⁇
  • the channels having wavelengths corresponding to the regions D of the optical amplifier gain undergo a total loss greater of about 4 dB than the total loss suffered by the channels having wavelengths corresponding to the regions E 2 , E 2 .
  • Fig. 9a is a graph of the preemphasis step undergone by the channels passing through the above mentioned optical paths of the WM 44.
  • a suitable adjustment of the attenuating splices 100, 100' for any channels allows a smoothening of the curve of Fig. 9a as shown in Fig. 9b.
  • the multiplexing unit 250' and the optical coupler 231 can be eliminated and the port 251 of multiplexing unit 250 can be used as output port of the multiplexing device.
  • the WM 44 has the advantage of reducing the losses at the transmitting terminal site 10 of the telecommunication system 1 and of improving the connections to the transmitting units.
  • the WM 44 of Fig. 10 have a modularity suitable for the connection to three sub-racks each comprising 16 transmitting units, according to the ANSI standard.
  • the sixteen input ports of the optical coupler 202 and the ones of optical coupler 202 ' can be connected to corresponding transmitting units of a first and second sub-rack while the eight input ports of the optical couplers 205, 207 and the ones of optical couplers 205', 207' can be connected to a first and a second group of eight transmitting units of the third sub-rack, respectively.
  • FIG. 11 A second embodiment of the 48 channels WM 44 operating in the RBI band made in accordance with the invention is shown in Fig. 11.
  • the optical couplers of this second embodiment of WM 44 are grouped differently, in order to satisfy a different modularity requirement .
  • this embodiment having modularity 8 and 16, is suitable for the connection to 6 sub-racks each comprising 8 transmitting units or to 2 sub-racks, each comprising 8 re ⁇
  • transmitting units and 2 sub-racks, each comprising 16 transmitting units.
  • the two 16x1 optical couplers 202 and 202' are arranged in two multiplexing units 280, 280'; the four couplers 205, 207, 205', 207' are arranged in multiplexing units 260, 260' and the three couplers 217, 217', 231 are arranged in multiplexing unit 270.
  • the output ports 203 and 203' of the multiplexing units 280, 280' are connected to input ports 263 and 263', respectively, of the multiplexing unit 270.
  • output ports 261 and 261' of the two multiplexing units 260 and 260' are connected to input ports 262, 262', respectively, of the multiplexing unit 270.
  • the balanced optical couplers, the unbalanced optical couplers and the wavelength selective optical couplers provide the same losses before listed.
  • the gain equalization in the BB band is performed by means of the above mentioned equalization filters 74 and 88 and the wavelength multiplexing device WM 43 is a conventional passive optical balanced coupler.
  • the wavelength multiplexing device WM 43 is a conventional passive optical balanced coupler.
  • it is a planar or fused fibers coupler.
  • Fig. 7 schematically shows the curve corresponding to the gain spectrum in the BB band at the end of the chain of optical amplifiers cascaded in the telecommunication system 1 (unbroken line) and the corresponding equalized gain curve (dashed line) .
  • the gain equalization in the BB band can also be carried out by means of a multiplexing device of the invention suitably designed according to principles that will be clear to the skilled in the art on the basis of the present description and without departing from the spirit of the invention.

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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)
  • Lasers (AREA)

Abstract

L'invention concerne un dispositif (44; 45) de multiplexage optique, permettant le multiplexage en longueurs d'ondes d'une pluralité (M) de canaux (16) optiques, M étant ≥ 8. Ce dispositif (44; 45) de multiplexage comprend N points (208, 208') d'entrée, N étant $me(G)M, et un point (233; 254) de sortie, et au moins trois coupleurs (202, 202', 205, 205', 207, 207', 206, 206', 213, 213', 217, 217', 225, 225', 231) optiques présentant des atténuations intrinsèques prédéterminées et reliés les uns aux autres selon une topologie arborescente, cette topologie comprenant N entrées et une sortie correspondant audits N points (208, 208') d'entrée et un point (233; 254) de sortie. Ce dispositif est caractérisé en ce que a) l'atténuation intrinsèque de chacun des coupleurs (202, 202', 205, 205', 207, 207', 206, 206', 213, 213', 217, 217', 225, 225', 231) optiques est présélectionné, et b) ces coupleurs (202, 202', 205, 205', 207, 207', 206, 206', 213, 213', 217, 217', 225, 225', 231) optiques sont disposés selon ladite topologie arborescente de telle manière qu'en passant à travers le dispositif (44; 45) de multiplexage, au moins deux de la pluralité M de canaux (16) optiques présentent une atténuation différente l'un de l'autre. Lorsque le dispositif est intégré à un système de transmission MLO, p. ex. un système utilisant des amplificateurs de fibre en ligne, ces différences d'atténuation des canaux de la ligne de transmission peuvent être égalisées.
PCT/EP2000/010428 1999-10-21 2000-10-20 Dispositif de multiplexage optique en longueurs d'ondes et systeme de telecommunication optique mlo WO2001029596A1 (fr)

Priority Applications (5)

Application Number Priority Date Filing Date Title
JP2001532131A JP2003512795A (ja) 1999-10-21 2000-10-20 光波長多重化デバイスおよびｗｄｍ光遠隔通信システム
EP00969536A EP1224493A1 (fr) 1999-10-21 2000-10-20 Dispositif de multiplexage optique en longueurs d'ondes et systeme de telecommunication optique mlo
KR1020027005071A KR20020054333A (ko) 1999-10-21 2000-10-20 광학적 파장 멀티플렉싱 디바이스와 ｗｄｍ 광통신 시스템
AU79219/00A AU7921900A (en) 1999-10-21 2000-10-20 Optical wavelength multiplexing device and wdm optical telecommunication system
CA002385584A CA2385584A1 (fr) 1999-10-21 2000-10-20 Dispositif de multiplexage optique en longueurs d'ondes et systeme de telecommunication optique mlo

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
EP99203458.7 1999-10-21
EP99203458 1999-10-21
US16137399P 1999-10-26 1999-10-26
US60/161,373 1999-10-26

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Publication number Priority date Publication date Assignee Title
WO2011119107A1 (fr) 2010-03-24 2011-09-29 Nitto Denko Corporation Système optique

Families Citing this family (1)

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JP4757938B2 (ja) * 2009-09-24 2011-08-24 富士通株式会社 プリエンファシス方法、光通信システム、および、制御装置

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Publication number Priority date Publication date Assignee Title
EP0660142A1 (fr) * 1993-12-22 1995-06-28 Siemens Aktiengesellschaft Module de couplage optique
US5809190A (en) * 1996-11-13 1998-09-15 Applied Fiber Optics, Inc. Apparatus and method of making a fused dense wavelength-division multiplexer
EP0887963A2 (fr) * 1997-06-26 1998-12-30 Corning Incorporated Dispositives optiques en cascade à multiplexage optique
WO1999007096A1 (fr) * 1997-08-01 1999-02-11 Pirelli Cavi E Sistemi S.P.A Systeme d'amplification multibande pour multiplexage de division de longueur d'onde dense

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Publication number Priority date Publication date Assignee Title
EP0660142A1 (fr) * 1993-12-22 1995-06-28 Siemens Aktiengesellschaft Module de couplage optique
US5809190A (en) * 1996-11-13 1998-09-15 Applied Fiber Optics, Inc. Apparatus and method of making a fused dense wavelength-division multiplexer
EP0887963A2 (fr) * 1997-06-26 1998-12-30 Corning Incorporated Dispositives optiques en cascade à multiplexage optique
WO1999007096A1 (fr) * 1997-08-01 1999-02-11 Pirelli Cavi E Sistemi S.P.A Systeme d'amplification multibande pour multiplexage de division de longueur d'onde dense

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Title
ORAZI R J ET AL: "CASCADED NARROW CHANNEL FUSED FIBRE WAVELENGTH DIVISION MULTIPLEXERS", ELECTRONICS LETTERS,GB,IEE STEVENAGE, vol. 32, no. 4, 15 February 1996 (1996-02-15), pages 368 - 370, XP000558159, ISSN: 0013-5194 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2011119107A1 (fr) 2010-03-24 2011-09-29 Nitto Denko Corporation Système optique
WO2011119106A1 (fr) 2010-03-24 2011-09-29 Nitto Denko Corporation Structure multicouche et son procédé de formation

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JP2003512795A (ja) 2003-04-02
CA2385584A1 (fr) 2001-04-26
EP1224493A1 (fr) 2002-07-24

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