EP1145056A3 - Fibre a polarisation circulaire pour circuits optiques - Google Patents

Fibre a polarisation circulaire pour circuits optiques

Info

Publication number
EP1145056A3
EP1145056A3 EP99948142A EP99948142A EP1145056A3 EP 1145056 A3 EP1145056 A3 EP 1145056A3 EP 99948142 A EP99948142 A EP 99948142A EP 99948142 A EP99948142 A EP 99948142A EP 1145056 A3 EP1145056 A3 EP 1145056A3
Authority
EP
European Patent Office
Prior art keywords
optical
circularly polarized
fiber
fibers
polarization
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99948142A
Other languages
German (de)
English (en)
Other versions
EP1145056A2 (fr
Inventor
Mohammed N. Islam
Daniel A. Nolan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Corning Inc
University of Michigan
Original Assignee
Corning Inc
University of Michigan
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 Corning Inc, University of Michigan filed Critical Corning Inc
Publication of EP1145056A2 publication Critical patent/EP1145056A2/fr
Publication of EP1145056A3 publication Critical patent/EP1145056A3/fr
Withdrawn legal-status Critical Current

Links

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
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2543—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to fibre non-linearities, e.g. Kerr effect
    • 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
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/105—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type having optical polarisation effects
    • 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
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/532—Polarisation modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/03—WDM arrangements
    • H04J14/0307—Multiplexers; Demultiplexers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/06—Polarisation multiplex systems

Definitions

  • the present invention relates generally to systems that use optical fiber and optical fiber components, and particularly to such systems that include circularly polarized waveguide fiber.
  • the optical non-linearities that affect light wave transmission systems fall into two general categories.
  • the first category are stimulated scattering phenomena, such as stimulated Brillouin scattering and stimulated Raman scattering. These effects are interactions between an optical signal and a phonon in the transmission material. The frequency of the phonon determines the type of scattering that occurs.
  • the second category the nonlinear index of refraction gives rise to three effects, self phase modulation (SPM), cross phase modulation (XPM), and four wave mixing (4WM).
  • SPM self phase modulation
  • XPM cross phase modulation
  • 4WM four wave mixing
  • the nonlinear index which depends upon pulse intensity, leads to phase modulation of those pulses above a threshold intensity.
  • the threshold intensity depends upon the material used in the waveguide but is generally of the order of 10 mW.
  • One of the consequences of SPM is that the spectral width of signal pulses gradually increases as they propagate in the fiber. For operation near the zero dispersion wavelength of the waveguide, the spectral broadening of the signal will not degrade system performance. However, if there is sufficient group velocity dispersion, then the spectral broadening from SPM will result in temporal broadening of the pulses.
  • 4WM has a phase matching requirement.
  • the intensity modulation at the beat frequency of the waveguide modulates the refractive index, thus producing a phase modulation at the difference frequency of the two signals.
  • side-band frequencies are generated at the original frequencies plus and minus the difference frequencies (the lower frequency side band is called the Stokes frequency, and the higher frequency side band is called the anti-Stokes frequency).
  • the phase-matching requirement means that the index or speed at the two signal wavelengths must coincide with the index or speed of the Stokes and anti-Stokes waves. Therefore, 4WM depends strongly on total dispersion.
  • 4WM has two deleterious effects. First is the depletion of power from the signal wavelengths into the mixing products. Second, in systems that have equally spaced signal channels, the Stokes and anti-Stokes frequencies coincide with existing channels causing cross-talk. Also, the mixing products can interfere constructively or destructively with the existing channels, depending on the relative phases of the signals.
  • a quarter-wave retarder converts linearly polarized light into circularly polarized light and conversely.
  • the linearly polarized light is incident upon the QWR with its polarization axis at 45° to the right or left of the fast axis of the QWR.
  • a half-wave retarder rotates the polarization direction of linearly polarized light by 90 degrees.
  • the linearly polarized light is incident upon the HWR with its polarization axis at 45° to the right or left of the fast axis of the HWR.
  • a HWR converts right-hand circularly polarized light (RHC) into left- hand circularly polarized light (LHC) and conversely.
  • One aspect of the present invention is a circularly polarized single mode fiber (CPF).
  • the CPF has at least a slight birefringence and an axial twist that is substantially continuous along the CPF length.
  • the pitch of the axial twist is less than the beat length of the CPF so that circular polarization effects are large compared to linear polarization effects in the CPF.
  • Beat length is the fiber length between repeats of a given polarization state.
  • the CPF is so called because it preserves propagated circularly polarized light in a state of circular polarization, given that the launch orientation of the light matches a polarization mode of the fiber. The required launch is assumed throughout this application.
  • the CPF maintains the circular polarization of circularly polarized light (either right or left handed circularly polarized light) that is launched into the CPF.
  • the birefringence is ⁇ n about 10 "5 , where ⁇ n is the difference in refractive index of the two orthogonal polarization axes of the waveguide fiber.
  • the fiber can be made to have birefringence by any of several methods known in the art.
  • the core can be made elliptical in cross section or a non-uniform radially directed stress may be applied to the core.
  • the applied twist has a right handed pitch over a portion of the fiber length and left handed pitch over another portion.
  • the present invention includes an optical transmission link for high data rate, multiplexed systems.
  • the link makes use of CPF to suppress the non-linear effects that occur in systems using high power signals or make use of multiple wavelength channels.
  • the transmission link is formed from a plurality of CPF's optically coupled to each other.
  • the first CPF in the link is optically coupled to a multi-wavelength transmitter module and the last CPF in the link is optically coupled to a multi-wavelength receiver module.
  • Alternating the pitch from right to left handed polarized light for alternating channels effectively eliminates four wave mixing, the non-linear effect, which, in multiplexed systems, causes signal power loss an inter-channel cross talk.
  • one or more optical amplifiers are optically coupled into the link to maintain desired signal to noise ratio.
  • the transmission link may make use of local or distributed optical amplifiers, which can have any appropriate spacing. Embodiments of the invention which include desirable configurations of the transmitter or receiver module are discussed below.
  • particular optical switching or delaying circuits may be added to the transmission link.
  • These circuits provide capability for the transmission link to route or switch signals in several advantageous configurations.
  • NOLM non-linear optical loop mirrors
  • PCS polarization controlled systems
  • a feature of these circuits is that CPF is used at least over a portion of the circuit where the control signal and optical signal interact. The CPF enhances the cross phase modulation interaction between the two pulses so that lower control pulse power or shorter interaction lengths of fiber may be used.
  • An advantage of using CPF in optical components which make use of XPM is that the XPM is not dependent upon relative polarization state, including circular or linear polarization, of the interacting signals.
  • the signal launch into the CPF should be an eigenmode supported by the CPF to achieve the benefit of polarization independence of XPM, in accordance with the launch condition disclosed above..
  • Fig. 1 is a schematic drawing of a multi-channel transmission link using CPF.
  • Figs. 2 and 3 are schematic drawings of alternative configurations of the transmitter module.
  • Figs. 4, 5, and 6 are schematic drawings of alternative configurations of the receiver module.
  • Fig. 7 is a schematic drawing of a NOLM switch using CPF.
  • Fig. 8 is a schematic drawing of a polarization coupled switch using CPF.
  • Fig. 9 is a schematic drawing of an experimental circuit used to test the NOLM switch using CPF.
  • Figs. 10 and 11 are charts of experimental results comparing twisted fiber (CPF) to non-twisted fiber.
  • Fig. 12 is a chart of polarization sensitivity versus the pitch of the twist in the CPF. Detailed Description of the Invention
  • a multi- wavelength transmitter module 2 launches wavelength division multiplexed (WDM) signal pulses into a first length of circularly polarized fiber 4.
  • WDM wavelength division multiplexed
  • Wavelengthm division multiplexer and demultiplexer devices currently suitable for WDM networks may be based on wavelength grating routers, littrow gratings, or Fabry-
  • the WDM pulses After traveling through this first CPF length 4, the WDM pulses are amplified by optional optical amplifier 6 and pass into a second length of CPF 8. The WDM pulses continue through alternating lengths of CPF 4 and CPF 8, which are optionally separated by optical amplifiers 6, until reaching the multi-wavelength receiver module 10 where WDM demultiplexing occurs and the signals are distributed to a target destination.
  • the optical circuit of Fig. 1 may comprise CPF having a zero dispersion wavelength, ⁇ 0 , near the signal wavelengths without incurring signal loss due to 4WM.
  • the use of CPF reduces the SPM dispersion.
  • the circuit may be operated in non-return-to-zero, return-to -zero, or soliton format.
  • the transmitter module contains a number N of lasers designated as 12 in Fig. 2.
  • the lasers launch linearly polarized light into the N ports of WDM device 14.
  • a HWR 18 is inserted into every other path 16 between a laser and the WDM 14 to change the direction of linear polarization by 90°.
  • the polarization is preserved through WDM 14 so that, upon passing through QWR 20, signals in adjacent channels are launched with opposite handed circular polarization into to the CPF and 4WM penalty is minimized.
  • there will be no 4WM between adjacent channels there may still be some 4WM between alternate channels.
  • the phase-matching and interaction length is made smaller because the wavelength because the spacing the interacting wavelength channels are farther apart. The density of channels can thus be traded off for less inter-channel interaction.
  • FIG. 3 An alternative transmitter module embodiment is shown in Fig. 3.
  • the N lasers 12 are connected to the ports of WDM 14 through QWR's 22, which convert the linearly polarized laser light into circularly polarized light.
  • the direction of circular polarization of signals in adjacent channels is opposite one from the other because the fast axis of every other QWR is rotated 90° compared to the QWR's adjacent.
  • the result is a multi-wavelength signal launch into the CPF link substantially identical to that illustrated in Fig. 2. If the wavelength range is wide, then there may be an advantage is using the Fig. 3 scheme over that of Fig. 2.
  • the QWR in Fig. 2 may not be broad band enough to launch all the wavelengths.
  • the QWR also provides isolation between the emitter (e.g., a laser diode) and reflections from the following optics.
  • the QWR's and HWR's may be bulk optical plates or other devices known in the art. However a preferred embodiment is one in which the QWR's and HWR's comprise optical fiber which is formed into loops which are rotated relative to one another. The fiber devices are easier to incorporate into the optical circuit and reflection and absorption losses are minimized.
  • Alternative embodiments of the receiver module are illustrated schematically in Figs. 4, 5, and 6. In the embodiment of Fig. 4, light enters the input port of WDM demultiplexer 14 from the last CPF 24 in the link. The demultiplexed signals are connected to band pass filters 26 through waveguides 16.
  • the filters deliver one of the N signals to each of the receivers 28 respectively.
  • the embodiment of Fig. 5 makes use of a polarization sensitive receiver 28 to further improve signal to noise ratio.
  • the circularly polarized light passes through QWR 20 before entering WDM demultiplexer 14.
  • the circularly polarized signals are thereby converted in linearly polarized signals.
  • a HWR 18 is placed in every other path between the filters 26 and polarization sensitive receivers 28. This HWR rotates the axis of polarization by 90° so that adjacent channels have orthogonal linear polarization.
  • the receiver module embodiment of Fig. 6 makes use of QWR's in the optical path between filter 26 and polarization sensitive receivers 28.
  • the fast axes of QWR's of adjacent paths are rotated 90° relative to each other.
  • channel cross talk between receivers is further limited because alternate receivers receive signals having opposite circular polarization.
  • the receiver module configurations of Figs. 5 and 6 have the added advantage of providing isolation between the transmission line and the receivers.
  • a switching component using a NOLM is illustrated in the schematic of Fig. 7.
  • the all fiber construction of the NOLM makes it particular compatible with the transmission link of Fig. 1.
  • the NOLM may be used to switch a selected wavelength at essentially any point along the transmission link.
  • the NOLM consists of a four-port directional coupler 30 in which two ports
  • the NOLM acts an interferometer having two arms which correspond to the two counter-propagating directions around the loop. This configuration is very stable because both arms involve exactly the same optical path.
  • the coupler divides the input signal 36 equally, the NOLM acts as a perfect mirror.
  • control signal 38 is coupled into the NOLM by coupler 38 and propagates only in one direction around the NOLM.
  • the control signal 38 phase shifts the input signal 36 traveling in that direction by means of the non-linear XPM.
  • FIG. 1 is illustrated in Fig. 8.
  • a linearly polarized signal pulse 36 is circularly polarized by QWR 20 before launch into CPF 4.
  • the CPF preserves the polarization so that the second QWR 20 converts the pulse 38 into a linearly polarized pulse before entering polarization sensitive coupler 46.
  • Coupler 46 passes the linearly polarized signal pulse 36 and couples one polarization component from control pulse 38. Both pulses are converted into circularly polarized pulses by the QWR 20 located in the optical path downstream of coupler 46.
  • the signal and control pulses interact through XPM in the CPF lengths 4 downstream of coupler 46.
  • the direction of circular polarization of the signal and control pulses can be selected to be opposite in direction so that at the QWR just ahead of the polarization sensitive filter 48 the two signals are converted to linearly polarized pulses whose axes of polarization are orthogonal. Then the polarization sensitive filter 48 is selected to pass the signal pulse and reflect the control pulse.
  • the effect of the XPM interaction is illustrated by the side figure of Fig. 8 which shows the output signal pulse 50 on a time axis 52. The XPM interaction can be sufficient to move the signal pulse 50 out of a particular clock window thereby changing a 1 bit to a 0 bit in a digital system.
  • the CPF waveguide can be made by any of several methods known in the art.
  • an appropriate reference is U.S. application number 09/117,280, Hawk, which is herein in its entirety incorporated by reference.
  • the reference sets forth a method of making CPF by starting with a preform designed to produce a fiber which has a moderate birefringence.
  • a twist is impressed upon the fiber by twisting either the preform or the fiber itself.
  • the fiber may be twisted by spinning the drawing tractors back and forth about the long axis of the fiber, introducing a sinusoidal twist of the fiber axes.
  • the twist pitch must be shorter than the beat length of the fiber.
  • This level of birefringence is readily induced, for example, by making the core slightly elliptical or by implanting in the fiber a non-uniform radial stress.
  • the predicted efficiency of CPF in optical communications circuits and devices was tested using the NOLM switch shown schematically in Fig. 9.
  • the signal pulse 38 at 1535 nm is launched through the 50/50 coupler to counter- propagate around the loop mirror.
  • the control pulse was polarized and launched into the loop by means of polarization sensitive coupler 40 and extracted by downstream polarization sensitive coupler 40. This extraction method is most useful because the relative polarization states of the signal and control pulses does not affect the XPM interaction.
  • the control and signal pulses interacted through XPM in the top sector of the loop including waveguide fiber length 54.
  • the efficiency of the switching was measured by measuring the intensity of the 1535 nm output pulse switched through the NOLM.
  • the folded fiber polarization controller 56 similar to 33 in Fig.7 discussed above, was adjusted to maximize signal output.
  • Curve 58 shows the variation of output signal intensity as a function of polarization of the input signal 38 for the case in which fiber length 54 is twisted.
  • the curve 58 shows the switch is substantially polarization independent when twisted fiber is used. An intensity variation of only 0.6 dB was observed over a polarization change from 0 to 200 degrees.
  • the chart shown in Fig. 11 gives the percent non-linear transmission through twisted and non-twisted fiber for changes in polarization state of the input signal.
  • the polarization states are indicated at the top and bottom of the chart as up or down arrows for linearly polarized signals and right and left hand loops for the two types of circular polarization.
  • a CPF having a twist of 8 turns/m shows in curve 62 about 0.05 % variation in non-linear signal transmission for all of the polarization states.
  • a variation of about 0.3 %, curve 64 in Fig.11 was measured for the untwisted fiber for the same changes in input signal polarization state.
  • the CPF provides an order of magnitude improvement in polarization insensitivity as compared to the untwisted fiber.
  • Experimental chart 12 shows in date points 66 that polarization insensitivity does depend upon the number of axial twists per meter. In general, good results may be expected for twist rates greater than about 6/meter.
  • a polarization maintaining transmission line can be comprised of various sections of CPF without any need for orienting the fibers at splices.
  • CPF in transmission links and associated optical components.
  • the general problem of signals at two wavelengths of light interacting through the nonlinear index of refraction, where one wave imparts a phase shift on the other wave is best solved using CPF.
  • This nonlinear interaction is independent of the input state of polarization of the waves because the XPM is the same when the two waves are parallel or identical in polarization (XPM ) as when the input state of polarization of the waves are perpendicular or orthogonal (XPM ⁇ ).
  • the two beams through each arm of the interferometer must end at the same state of polarization for there to be complete interference at the output coupler or beam splitter.
  • PC polarization controller
  • CPF circularly polarized waveguide fiber
  • CPF CPF
  • XPM linearly birefringent fiber
  • the enhancement in XPM which is valuable in switching devices, but can lead to cross talk in WDM transmission links.
  • the deleterious XPM in such links can be minimized by proper spacing of the channels, i.e., by arranging for the channels to completely walk through each other due to XPM dispersion.
  • switches which can be made more efficient by use of CPF are nonlinear optical loop mirrors or soliton-dragging and soliton-trapping logic gates.
  • the use of CPF in these devices provides switching at half the switching energy or half of the waveguide fiber length as compared to the same devices implemented using linearly polarized fibers.
  • the CPF can be one of the key enabling technologies toward reaching the sub-pico-joule switching energy that will be required for all-optical switches in high performance systems.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)
  • Optical Integrated Circuits (AREA)

Abstract

L'invention concerne une fibre guide d'onde monomode à polarisation circulaire et des systèmes de transmission multiplexés haut débit utilisant ladite fibre. La fibre à polarisation circulaire atténue les effets non linéaires présents dans ces voies de transmission rapides. En particulier, elle atténue de plus de 30 % l'automodulation de phase et supprime sensiblement le mélange à quatre ondes. Ce dernier phénomène est dû au fait que ledit mélange ne peut se produire dans une voie multiplexée constituée d'une pluralité de fibres à polarisation circulaire disposées de façon que les fibres adjacentes aient une polarisation circulaire opposée. La fibre atténue l'effet non linéaire de la modulation de phase croisée, caractéristique qui peut être utilisée dans les composants de commutation optique associés à la voie de transmission. En outre, l'importance de la modulation de phase croisée dans les fibres à polarisation circulaire est indépendante des états de polarisation relative du signal et des impulsions de commande.
EP99948142A 1998-09-17 1999-09-07 Fibre a polarisation circulaire pour circuits optiques Withdrawn EP1145056A3 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US10075798P 1998-09-17 1998-09-17
US100757P 1998-09-17
PCT/US1999/020473 WO2000016139A2 (fr) 1998-09-17 1999-09-07 Fibre a polarisation circulaire pour circuits optiques

Publications (2)

Publication Number Publication Date
EP1145056A2 EP1145056A2 (fr) 2001-10-17
EP1145056A3 true EP1145056A3 (fr) 2002-09-11

Family

ID=22281379

Family Applications (1)

Application Number Title Priority Date Filing Date
EP99948142A Withdrawn EP1145056A3 (fr) 1998-09-17 1999-09-07 Fibre a polarisation circulaire pour circuits optiques

Country Status (7)

Country Link
EP (1) EP1145056A3 (fr)
JP (1) JP2002525647A (fr)
CN (1) CN1406342A (fr)
AU (1) AU6137899A (fr)
CA (1) CA2344682A1 (fr)
TW (1) TW459148B (fr)
WO (1) WO2000016139A2 (fr)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BRPI0116585B1 (pt) * 2000-12-28 2015-08-04 Prysmian Cavi Sistemi Energia Cabo óptico para telecomunicações, fibra óptica adequada para uso em um cabo óptico, e, método para confeccionar a mesma
EP1463966A4 (fr) * 2001-12-06 2005-08-10 Chiral Photonics Inc Procede et appareil de polarisation reglable a fibre chirale integree
JP2005173530A (ja) 2003-11-17 2005-06-30 Osaka Industrial Promotion Organization 光信号処理方法及び装置、非線形光ループミラーとその設計方法並びに光信号変換方法
WO2005100274A1 (fr) * 2004-04-07 2005-10-27 Fujikura Ltd. Processus de production de fibre optique et fibre optique
US8111957B2 (en) * 2008-07-10 2012-02-07 Corning Incorporated +cylindrical polarization beams
CN106169950B (zh) * 2016-07-21 2023-08-18 西南大学 基于全光纤的长距离激光混沌同步装置
WO2020133325A1 (fr) * 2018-12-29 2020-07-02 华为技术有限公司 Dispositif et procédé de transmission optique
US20220155538A1 (en) * 2020-11-13 2022-05-19 Ayar Labs, Inc. Mitigation of Polarization Impairments in Optical Fiber Link

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2515693B1 (fr) * 1981-11-03 1985-10-11 Thomson Csf Procede de fabrication d'un objet a structure chiralique issu a partir d'une source de matiere formable et dispositif mettant en oeuvre ce procede
US4515436A (en) * 1983-02-04 1985-05-07 At&T Bell Laboratories Single-mode single-polarization optical fiber
US5298047A (en) * 1992-08-03 1994-03-29 At&T Bell Laboratories Method of making a fiber having low polarization mode dispersion due to a permanent spin
EP0635739B1 (fr) * 1993-07-21 2000-03-22 AT&T Corp. Boucle de fibre rétroréfléchissante améliorée pour le démultiplexage temporel
US5452394A (en) * 1994-02-24 1995-09-19 Huang; Hung-Chia Practical circular-polarization maintaining optical fiber
US5587791A (en) * 1994-09-27 1996-12-24 Citeq Optical interferometric current sensor and method using a single mode birefringent waveguide and a pseudo-depolarizer for measuring electrical current

Also Published As

Publication number Publication date
CA2344682A1 (fr) 2000-03-23
AU6137899A (en) 2000-04-03
EP1145056A2 (fr) 2001-10-17
WO2000016139A3 (fr) 2001-11-22
TW459148B (en) 2001-10-11
JP2002525647A (ja) 2002-08-13
WO2000016139A2 (fr) 2000-03-23
CN1406342A (zh) 2003-03-26

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