WO2000014917A2 - Mise en oeuvre d'une liaison a multiplexage optique par repartition en longueur d'onde - Google Patents

Mise en oeuvre d'une liaison a multiplexage optique par repartition en longueur d'onde Download PDF

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Publication number
WO2000014917A2
WO2000014917A2 PCT/FI1999/000682 FI9900682W WO0014917A2 WO 2000014917 A2 WO2000014917 A2 WO 2000014917A2 FI 9900682 W FI9900682 W FI 9900682W WO 0014917 A2 WO0014917 A2 WO 0014917A2
Authority
WO
WIPO (PCT)
Prior art keywords
wavelengths
fiber
wavelength
phase conjugator
optical
Prior art date
Application number
PCT/FI1999/000682
Other languages
English (en)
Finnish (fi)
Other versions
WO2000014917A3 (fr
Inventor
Markku Oksanen
Original Assignee
Nokia Networks Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nokia Networks Oy filed Critical Nokia Networks Oy
Priority to AU53747/99A priority Critical patent/AU5374799A/en
Publication of WO2000014917A2 publication Critical patent/WO2000014917A2/fr
Publication of WO2000014917A3 publication Critical patent/WO2000014917A3/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/29—Repeaters
    • H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
    • H04B10/297—Bidirectional amplification
    • H04B10/2972—Each direction being amplified separately
    • 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
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2513—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion
    • H04B10/2531—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion using spectral inversion
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • 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

Definitions

  • the invention relates generally to optical transmission systems us- ing wavelength division multiplexing. More specifically, the invention relates to the implementation of a bidirectional optical link using wavelength division multiplexing (WDM).
  • WDM wavelength division multiplexing
  • an optical signal is modulated with an outbound data stream, and the modulated optical signal is applied to optical fiber.
  • the bandwidth of the data stream can be increased or more wavelengths can be introduced, each of which is modulated with a discrete data stream.
  • the latter method is termed wavelength division multiplexing.
  • Wavelength division multiplexing is an efficient way of multiplying the capacity of optical fiber.
  • WDM Wavelength division multiplexing
  • FIGs 1a and 1b illustrate the principle of wavelength division multiplexing, using as an example a system having four parallel transmitter-receiver pairs.
  • Each of the four information sources (not shown in the figure) modulates one of four optical transmitters, each of which generates light at a different wavelength ( ⁇ .,... ⁇ 4 ).
  • the modulation bandwidth of each source is smaller than the distance between the wavelengths, and thus the spectra of the modulated signals do not overlap.
  • the signals generated by the transmitters are combined onto the same optical fiber OF in a WDM multiplexer WDM1 , which is a fully optical (and often passive) component.
  • WDM demultiplexer WDM2 which is also a fully optical (and often passive) component, separates the different spectral components of the com- bined signal from one another.
  • Each of these signals is detected at a discrete receiver. Hence, a narrow wavelength window is assigned for the use of each signal in a given wavelength range.
  • a typical practical example might be a system where the signals are in the 1550 nm wavelength range for example in such a way that the first signal is at wavelength 1544 nm, the second signal at wavelength 1548 nm, the third signal at wavelength 1552 nm and the fourth signal at wavelength 1556 nm.
  • the first signal is at wavelength 1544 nm
  • the second signal at wavelength 1548 nm
  • the third signal at wavelength 1552 nm
  • the fourth signal at wavelength 1556 nm a multiple of 100 GHz (approx. 0.8 nm) is becoming the de facto standard for the distance between wavelengths.
  • one of the primary goals is the cost- effectiveness of the network. It is essential in view of cost-effectiveness that all network resources can be utilized to the maximum. In order to achieve this, one should for example find (1) a way in which all possible components or network elements can be reused as efficiently as possible, and (2) a way in which the functionalities of the components can be utilized as well as possible for various purposes or in various applications.
  • the basic idea of the invention is to implement a bidirectional WDM link in such a way that the wavelengths transmitted from the opposite ends of the fiber are the same, and a bidirectional phase conjugator (or an equivalent device) performing the frequency shift in a known manner is provided on the fiber, the wavelengths received at the phase conjugator being folded relative to a given fold wavelength into outgoing wavelengths. In such a case, also the received frequencies are the same at both ends of the link.
  • the invention thus makes use of phase conjugation entailing such a frequency shift.
  • the transmitters are at mutually same wavelengths and also the receivers are at mutually same wavelengths. This allows precisely the same requirements to be set on the terminal equipment of the network, which will make the network more cost-effective than previously, since the same components can be used at both ends of the (bidirectional) links and no extra operations dependent on which link end is concerned are needed in the installation, commissioning or servicing phases.
  • the disper- sion created on the fiber link can simultaneously be effectively compensated for when the phase conjugator is located substantially halfway the link, and thus all wavelengths will have substantially the same transmission time across the link. This will be of significance particularly in the future when the transmission rates will be so high (in the order 100 Gbit/s) that accurate dispersion compensation is needed over the link.
  • the terminal equipment uses a bidirectional optical amplifier having a non-uniform gain spectrum, so that the received wavelengths fall on the "peak portion" of the useful wavelength range in the gain curve and the transmission wavelengths on the portion in which the gain curve is substantially flat.
  • Figures 1a and 1 b illustrate an optical transmission system using wavelength division multiplexing
  • FIG. 2 illustrates the principle of a WDM link in accordance with the invention
  • Figure 3 illustrates the configuration of terminal equipment used on the link of Figure 2
  • FIGS. 4a and 4b illustrate the gain curve of an optical amplifier in relation to the wavelengths used
  • Figure 5 illustrates the implementation of a bidirectional optical amplifier
  • Figure 6 illustrates the implementation of a bidirectional phase conjugator
  • FIG. 2 illustrates the principle of a transmission link in accordance with the invention.
  • Mutually similar terminals TE1 and TE2 are interconnected by an optical fiber link OL, comprising an optical fiber OF connecting the terminals and a bidirectional optical phase conjugator OPC, the preferred location of which is substantially in the middle of the link.
  • optical fiber link OL comprising an optical fiber OF connecting the terminals and a bidirectional optical phase conjugator OPC, the preferred location of which is substantially in the middle of the link.
  • four different wavelengths ⁇ ⁇ 1 , ⁇ T2 , ⁇ T3 and ⁇ T4 ) that are the same at the transmitters of both ends are transmitted from each terminal.
  • the phase conjugator OPC performs in a known manner a frequency shift on all wavelengths arriving therein by folding the incoming wavelength relative to a given fold wavelength.
  • both terminals receive at the same wavelengths, the values of which are dependent on the transmit wavelengths and the fold wavelength.
  • Figure 3 illustrates the general configuration of the terminal (TE1 or TE2) when the terminal is in accordance with a preferred embodiment of the invention (comprises a bidirectional amplifier of the kind to be described be- low).
  • the optical fiber is typically connected to an optical amplifier OFA, which in this case is a bidirectional amplifier, having a typical gain curve (amplification as a function of wavelength) of the type shown in Figures 4a and 4b.
  • OFA optical amplifier
  • the amplifier serves as a pre-amplifier ahead of the receiver and in the transmission direction as a booster amplifier subsequent to the transmitter.
  • the optical amplifier is not indispensable, however; separate amplifiers could also be dispensed with on shorter links. In general, however, such amplifiers are used.
  • the optical amplifier OFA is connected to a prior art multiplexer/demultiplexer unit WDM, which serves in the transmission direction as an optical multiplexer combining the signals arriving from separate input waveguides IWG (from transmitters) onto a combined input and output waveguide IOWG, and in the receiving direction as an optical demultiplexer dividing the signals arriving from the combined input and output waveguide IOWG onto separate output waveguides (to receivers).
  • WDM prior art multiplexer/demultiplexer unit WDM, which serves in the transmission direction as an optical multiplexer combining the signals arriving from separate input waveguides IWG (from transmitters) onto a combined input and output waveguide IOWG, and in the receiving direction as an optical demultiplexer dividing the signals arriving from the combined input and output waveguide IOWG onto separate output waveguides (to receivers).
  • a transmitter unit is connected to each input waveguide and a receiver unit is connected to each output waveguide.
  • the transmitter units are denoted with the common reference TXU and the receiver units with the common
  • the non-uniform gain curve of the optical amplifier OFA is typically of the kind shown in Figures 4a and 4b: in the useful area of the gain curve, certain wavelengths located in that region (FR) of said area where the gain is substantially even experience a proportionately smaller gain than certain shorter wavelengths that are located at the peak PK of the gain curve.
  • the shape of the gain curve is also dependent on the optical power: the lower the power, the larger the "peak portion" PK appearing at shorter wavelengths, that is, the greater the gain difference experienced by short and long wavelengths.
  • the figures also illustrate the location of the wavelengths used on the transmission link in accordance with the invention relative to a gain curve of this kind by representing the gain curve for each transmission direction and incorporating into the curve of the receiving direction (Figure 4b) the set of received wavelengths Rx (4 wavelengths) and into the curve of the transmission direction ( Figure 4a) the set of wavelengths Tx of the transmis- sion direction.
  • the fold wavelength of the phase conjugator OPC is denoted with reference ⁇ c .
  • the bidirectional phase conjugator changes the set of wavelengths Tx transmitted from each end into wavelength set Rx which is received at each terminal.
  • the above procedure affords maximum gain for the preamplifier of the receiving direction. Since it is known that the noise characteristics of the entire receiving branch are determined on the basis of the noise figure and gain of the first amplifier in the chain, the characteristics of the receiving branch can be improved by increasing the gain of said amplifier. This is achieved in the system in accordance with the invention simply by leaving the gain curve unflattened, i.e., by using a simpler amplifier than usual.
  • the same amplifier which is simpler than normal can be used in the network both as a booster amplifier and a preamplifier.
  • the bidirectionality of the optical amplifier OFA is achieved for example by using two unidirectional amplifiers OFA1 and two circulators C1 and C2 as shown in Figure 5.
  • a signal arriving from the left enters the lower branch through ports 1 and 2 of circulator C1 , experiences amplification in amplifier OFA2, and proceeds through ports 3 and 1 of circulator C2 further to the fiber on the right in the figure.
  • a signal arriving from the right in the figure enters the uppermost branch through ports 1 and 2 of circulator C2, experiences amplification in amplifier OFA1 , and proceeds through ports 3 and 1 of circulator C1 further to the fiber on the left in the figure.
  • the circulator is a(n optical) device known per se, which directs a signal received at a given port to the next port in succession.
  • each unidirectional amplifier can be for example a con- ventional erbium-doped fiber amplifier EDFA.
  • EDFA con- ventional erbium-doped fiber amplifier
  • Such amplifiers are not suitable for implementing conventional WDM links, since their uneven gain curve (cf. Figures 4a and 4b) places restrictions on the selection of wavelengths. For this reason, amplifiers with a flattened gain curve are used on WDM links.
  • the two most common ways of flattening the gain curve are either (1 ) to incorporate into the EDFA a filter evening out the gain differences, or (2) to exchange the active fiber in the amplifier for fiber having a flatter gain curve.
  • Such fiber is for example erbium-doped fluoride fiber, for which reason said amplifiers are called erbium-doped fluoride fiber amplifiers, EDFFA.
  • EDFFA erbium-doped fluoride fiber amplifiers
  • the useful range of the gain curve of EDFA is approximately 1525 nm...1570 nm, and the (unsmoothed) gain curve has a peak at about 1532 nm, in which event the wavelengths on the receiving side can be in the range 1530 nm and the transmission wavelengths for example in the 1540 nm or 1550 nm range.
  • a system of four wavelengths could be for example such that the reception wavelengths are 1528, 1530, 1532 and 1534 nm and the transmission wavelengths for example 1548, 1550, 1552 and 1554 nm, the fold wavelength being 1541 nm.
  • FIG. 6 illustrates in detail the implementation of a bidirectional phase conjugator OPC.
  • the phase conjugator is based on two unidirectional components which are made into one bidirectional component by means of circulators (C1' and C2'), as was the case with the amplifier.
  • C1' and C2' circulators
  • Both unidirectional phase conjugators OPC1 and OPC2 are implemented in a known manner.
  • an unidirectional phase conjugator has previously been used for compensation of dispersion.
  • a unidirectional phase conjugator comprises a non-linear optical element NLE, a pump laser PL, a WDM coupler CO coupling the actual signal and the signal arriving from the pump to the non-linear element, and a filter F at the output of the nonlinear element.
  • NLE non-linear optical element
  • WDM coupler CO coupling the actual signal and the signal arriving from the pump to the non-linear element
  • filter F at the output of the nonlinear element.
  • the operation of the phase conjugator is based on four-wave mixing taking place optically in the non-linear material. If the actual signal has a fre- quency f1 and the pump laser operates at a frequency f3, different mixing results are obtained at the output of the non-linear element, e.g. the frequency 2 ⁇ f3-f1 , which is at the desired frequency. The unwanted frequencies are filtered out by means of filters (F1 and F2).
  • the non-linear element can be for example a strip of single-mode fiber or a semiconductor piece serving as a single-mode waveguide. It is also possible to use a semiconductor laser amplifier serving simultaneously as a pump laser and a non-linear element.
  • phase conjugator Since the folding of the wavelengths is an essential functional feature from the point of view of the invention, the phase conjugator can in principle be replaced by any device folding the incoming wavelengths relative a fold wavelength. In this context, therefore, the phase conjugator is to be construed generally as a device carrying out such an operation.

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

Abstract

L'invention se rapporte à un procédé de mise en oeuvre d'une liaison de transmission optique et à un système de transmission optique de données. Un premier ensemble de signaux optiques ayant des longueurs d'onde différentes les unes par rapport aux autres est émis à partir d'une première extrémité de la fibre optique et un second ensemble de signaux optiques ayant des longueurs d'onde différentes les unes par rapport aux autres est émis à partir de l'autre extrémité de la fibre optique. De manière à améliorer le rapport coût-efficacité du réseau, on utilise les mêmes longueurs d'onde pour le premier ensemble et le second ensemble de signaux, et en outre, on met en oeuvre un conjugateur de phase bidirectionnel (OPC) sur la fibre, qui transforme chaque longueur d'onde d'entrée une longueur d'onde donnée de sortie par repliement de la longueur d'onde en entrée par rapport à une longueur d'onde de repliement préétablie, ce qui rend possible la réception de signaux au niveau des deux extrémités de la fibre à des longueurs d'onde identiques qui sont les longueurs d'onde en sortie du conjugateur de phase.
PCT/FI1999/000682 1998-09-04 1999-08-17 Mise en oeuvre d'une liaison a multiplexage optique par repartition en longueur d'onde WO2000014917A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU53747/99A AU5374799A (en) 1998-09-04 1999-08-17 Implementing an optical wdm connection

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI981895 1998-09-04
FI981895A FI105628B (fi) 1998-09-04 1998-09-04 Optisen WDM-yhteyden toteutus

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WO2000014917A2 true WO2000014917A2 (fr) 2000-03-16
WO2000014917A3 WO2000014917A3 (fr) 2000-06-02

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006058830A1 (fr) * 2004-12-02 2006-06-08 Siemens Aktiengesellschaft Procede de compensation de la diaphonie entre reel et reel fonction de la sequence des bits du a une diffusion raman stimulee, systeme de transmission longueur d'onde optique-multiplex et convertisseur de longueur d'onde optique
US7187868B2 (en) 2001-07-30 2007-03-06 Pirelli Cavi E Sistemi S.P.A., Wavelength division multiplexing optical transmission system using a spectral inversion device
EP2077631A1 (fr) * 2008-01-03 2009-07-08 Dowslake Microsystems Corporation Amplificateur d'émetteur/récepteur optique

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0776103A2 (fr) * 1995-11-22 1997-05-28 Fujitsu Limited Système de communication utilisant la conjugation de phase optique
US5777770A (en) * 1995-03-20 1998-07-07 Fujitsu Limited Optical phase conjugator and optical reception apparatus and optical transmission apparatus for use with optical communication system employing the optical phase conjugator

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5777770A (en) * 1995-03-20 1998-07-07 Fujitsu Limited Optical phase conjugator and optical reception apparatus and optical transmission apparatus for use with optical communication system employing the optical phase conjugator
EP0776103A2 (fr) * 1995-11-22 1997-05-28 Fujitsu Limited Système de communication utilisant la conjugation de phase optique

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7187868B2 (en) 2001-07-30 2007-03-06 Pirelli Cavi E Sistemi S.P.A., Wavelength division multiplexing optical transmission system using a spectral inversion device
WO2006058830A1 (fr) * 2004-12-02 2006-06-08 Siemens Aktiengesellschaft Procede de compensation de la diaphonie entre reel et reel fonction de la sequence des bits du a une diffusion raman stimulee, systeme de transmission longueur d'onde optique-multiplex et convertisseur de longueur d'onde optique
EP2077631A1 (fr) * 2008-01-03 2009-07-08 Dowslake Microsystems Corporation Amplificateur d'émetteur/récepteur optique

Also Published As

Publication number Publication date
FI981895A (fi) 2000-03-05
FI981895A0 (fi) 1998-09-04
AU5374799A (en) 2000-03-27
WO2000014917A3 (fr) 2000-06-02
FI105628B (fi) 2000-09-15

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