WO2000020907A1 - Amplificateur optique bidirectionnel a gain lineaire - Google Patents

Amplificateur optique bidirectionnel a gain lineaire Download PDF

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Publication number
WO2000020907A1
WO2000020907A1 PCT/US1998/020762 US9820762W WO0020907A1 WO 2000020907 A1 WO2000020907 A1 WO 2000020907A1 US 9820762 W US9820762 W US 9820762W WO 0020907 A1 WO0020907 A1 WO 0020907A1
Authority
WO
WIPO (PCT)
Prior art keywords
fiber
light
wavelengths
channeling
fibers
Prior art date
Application number
PCT/US1998/020762
Other languages
English (en)
Inventor
Salim N. Jabr
Gennady I. Farber
Edward A. Vetter
Sami T. Hendow
Original Assignee
Ditech Corporation
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
Priority to US08/896,930 priority Critical patent/US5887091A/en
Priority claimed from US08/896,930 external-priority patent/US5887091A/en
Application filed by Ditech Corporation filed Critical Ditech Corporation
Priority to PCT/US1998/020762 priority patent/WO2000020907A1/fr
Priority to AU97828/98A priority patent/AU9782898A/en
Publication of WO2000020907A1 publication Critical patent/WO2000020907A1/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
    • H04B10/293—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
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • 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
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/0675—Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06754—Fibre amplifiers
    • H01S3/06787—Bidirectional amplifier

Definitions

  • This invention pertains to fiber communication systems and more particularly to the transmission and amplification of several multiplexed wavelengths on fiber carrying light simultaneously in two directions of propagation.
  • DWDM dense wavelength division multiplexing
  • BER is sensitive to several parameters of the transmission system such as the optical power at the receiver, the quality of the transmitter, but particularly to the ratio of signal power to noise power, known as the signal to noise ratio (SNR) at the receiver.
  • SNR signal to noise ratio
  • the SNR is determined by the addition of receiver thermal noise shot noise and noise added by optical amplifiers in the system.
  • optical amplifiers One of the most important parameters of optical amplifiers is the gain at the various wavelengths. For proper operation the receivers operating at the various wavelengths expect a common and substantially equal optical signal to noise ratio as well as substantially equal optical power. Since transmitters generally output substantially equal amounts of power at various wavelengths, the amplifiers in the system are expected to provide equal gain at the various channel wavelengths.
  • the material of the glass matrix containing the Erbium as well as dopants in that matrix affect the position and broadening of the atomic resonances in Erbium.
  • One of the known techniques for flattening the gain curve is the use of aluminum co-doping of Erbium doped fiber.
  • Another technique utilizes fluoride glass instead of silica glass as the fiber material.
  • Yet other techniques insert specially shaped spectral filters in line with the amplifiers to compensate for the difference in gain at different wavelengths.
  • U.S. Patent 5,050,949 by Di Giovanni and Giles describes the use of two stage fiber amplifiers to achieve flattened gain. The drawback of the two stage approach is that it still lacks enough suppression of the gain in the 1520 to 1535 nm spectral region to achieve the desired degree of flatness.
  • Circulators are optical devices with three or more fiber ports that channel the light from port I into port 1+1 , Bragg gratings are periodic index of refraction gratings imprinted into the fiber core by UV light and reflect fiber propagating light at specific wavelengths matching the periodicity of the gratings.
  • a generally useful device in fiber optics whose function is to transfer or channel light from one fiber to the next fiber in an ordered set of fibers is known as the circulator.
  • a circulator device will channel light from the first fiber in a set to the second fiber and from the second fiber to the third.
  • the point of connection between a fiber and the circulator is referred to as a port and generally the ports are numbered to indicate their ordering.
  • Circulators with three and four ports are commercially available from companies such as Etek of San Jose, California and The Kaifa Group of Sunnyvale, California.
  • light at frequencies f2 and f4 enters the first port P1 of the first circulator C1 and is channeled to the second port P2 where it enters a fiber with Bragg gratings G2 configured to reflect at f2 and f4 back into the circulator C1 and out to the third port P3 which is connected to the amplifier A1.
  • the output of the amplifier A1 is then fed to the fourth port P4 of a second circulator C2 and from there f2 and f4 exit through the first port P1 of the second circulator C2.
  • the wavelengths or frequencies f1 and f3 propagating in opposition to f2 and f4 are input through the first port P1 of the second circulator C2 and follow a similar if reverse path to f2 and f4.
  • Other types of bidirectional amplifiers have been described as in US patent 5,604,627 to Kohn where two wavelength division multiplexing devices (WDM) are utilized in place of the circulators to separate the counter-propagating light streams.
  • WDM wavelength division multiplexing devices
  • the drawback of the devices shown in the prior art is their failure to provide flat gain profiles especially in the 1533 nm spectral range as well as bidirectional operation.
  • Another objective of this invention is to simplify the construction of the amplifier and to reduce the cost of its manufacturing.
  • a third objective is to eliminate the use of attenuators and their temperature dependence in either unidirectional or bidirectional amplifiers.
  • a fourth objective is to reduce the number of circulators and circulator ports used.
  • a fifth objective is to eliminate the need for fiber couplers or wavelength routers required in the prior art to couple the pump and signal lights into the doped fiber.
  • a doped fiber amplifier comprising a four port circulator with a first fiber port connected to an input fiber a second port connected to an output fiber a third port connected to a first rare earth doped amplifying fiber the amplifying fiber having a multiplicity of fiber gratings written into its core to reflect specific light wavelengths, and a pump laser being connected to the end of the amplifying fiber to provide pump power to the rare earth dopant, a similar second amplifying fiber with a second set of gratings made to reflect at a second set of wavelengths is connected to the fourth port of the circulator.
  • Light at a first set of wavelengths enters the input fiber and is channeled to the gain fiber with the gratings arranged in such a manner that the wavelengths experiencing the most gain in the non uniform gain of the fiber, are reflected from the gratings nearest the circulator and thus travel a shorter distance in the gain fiber as they are reflected back to the circulator and channeled out to the output fiber. In this manner the gains or amplifications experienced by all wavelengths in the first set of wavelengths can be made equal.
  • the four port circulator can be made from two three port circulators properly interconnected.
  • Figure 1 is a description of a prior art bidirectional amplifier
  • Figure 2A is a schematic showing the preferred embodiment of the present invention
  • Figure 2B is a flow diagram showing the light paths of the counter-propagating light beams
  • Figure 4A is a schematic showing an alternative embodiment of the present invention.
  • Figure 4B is a flow diagram showing the light paths of the counter-propagating light beams
  • Figure 5 is a schematic showing a different implementation of the present invention.
  • Figure 6A is a schematic showing a third implementation of the present invention.
  • Figure 6B is a flow diagram showing the light paths of the counter-propagating light beams
  • Figure 7 is a schematic of a rare earth doped fiber amplifier with equal gain at multiple wavelengths.
  • FIG. 2A there is shown a schematic of the preferred embodiment of the present inventive fiber amplifier comprising an input fiber 10 connected to a first port P1 of a four port optical circulator 5, an output fiber 12 connected to the third port P3 of the circulator 5, a first amplifying fiber 6A the first end of the amplifying fiber 6 being connected to the second port P2 of the circulator 5 and the second end of the amplifying fiber 6 being connected to a pump laser 4A, a second amplifying fiber 6B the first end of this second amplifying fiber 6B being connected to the fourth port P4 of the circulator 5 and the second end of the second fiber 6B being connected to a second pump laser 4B.
  • a multiplicity of gratings 3A is written using methods well known in the art such as the exposure to two interfering beams of ultraviolet radiation.
  • a multiplicity of gratings 3B is written.
  • the spatial periods of gratings 3A are made such that each of the gratings 3A in the first amplifying fiber 6A reflects at a wavelength Wi from a first multiplicity of wavelengths.
  • the spatial periods of gratings 3B are made such that each of the gratings 3B in the second amplifying fiber 6B reflects at a wavelength Wj from a second distinct multiplicity of wavelengths.
  • the ordering of the gratings starting from the fiber end closest to the circulator, and the reflectivity of the gratings 3A and 3B is chosen in a specific manner described hereafter.
  • the fiber segment lengths between the individual gratings 3A and between the gratings 3B is also chosen in a specific manner. It is well known that the amplification experienced by light propagating in a pumped rare earth doped fiber varies depending on the wavelength. Let Gi be the gain experienced by light at wavelength Wi after propagating a length Di in the fiber starting at the circulator 5, being reflected by a grating with reflectivity Ri positioned at a fiber length Di from the circulator and propagating back to the circulator.
  • the length Di is chosen so that the product GiRi is the same for all wavelengths in the amplifier operating range. Taking the specific example of three wavelengths W1 , W2, W3 with corresponding gain coefficients per unit length g1 , g2, g3 such that g3 is larger than g2 and g2 larger than g1. It is clear that the lengths D1 , D2, D3 are to be chosen such that D3 is smaller than D2 and D2 smaller than D1 so that the gains G1 , G2, G3 come out equal. This result determines the ordering of the gratings 3 at wavelengths W1 , W2, W3.
  • FIG. 3 there is shown the schematic of a particular embodiment wherein the first port of circulator 106 and second port of circulator 105 are connected via fiber 14A.
  • the light at a first set of wavelengths enters the amplifier through the input fiber 10 and is channeled to the amplifying fiber 6A by the circulators 105 and 106 then reflected back, one wavelength from each corresponding grating 3A, into the circulator 106 then back out to fiber 12.
  • the light at a second set of wavelengths enters from the output fiber 12 in a direction counter-propagating to the first set of wavelengths, is channeled to the second amplifying fiber 6B by the circulators 106 and 105, reflected back to the circulator 105 by the set of gratings 3B and out to fiber 12.
  • Pump laser 4A is connected to the distal end of the amplifying fiber 6A as in the first embodiment.
  • Pump laser 4B is connected to the distal end of the amplifying fiber 6B as in the first embodiment.
  • the coupling of the pump light from the pump lasers 108 and 109 into the amplifying fiber 6B is done by utilizing wavelength sensitive couplers 9A and 9B thus enabling the choice of pumping the amplifier from either the proximal or the distal end relative to the circulator 107, or alternatively to pump simultaneously from both ends of the fiber 6B in order to increase the pump power available to the amplifier.
  • the couplers 9A and 9B available commercially from manufacturers such as Gould Inc. of New Jersey usually have three or four fiber ports. At least one of the ports of the couplers 9A and 9B may be utilized to monitor the light passing through the amplifying fiber 6B by means of a photodetector 15.
  • FIG. 4B there is shown in dashed lines the paths of two light beams at wavelengths W1 and W3 propagating in the right to left direction and two other light beams at wavelengths W2 and W4 propagating in the left to right direction
  • Figure 5 there is shown an embodiment of the oresent inventive device utilizing three port circulators 17A, 17B and 17C instead of four port circulators.
  • the light at a first set of wavelengths enters the device through the input fiber 10 to port P1 of circulator 17A and is channeled to port P2 and out to port P1 of the circulator 17C which in turn channels it to the amplifying fiber 6A and gratings 3A from whence it is reflected back to the circulator 17C which channels it to the circulator 17B and out to fiber 12.
  • Light at a second set of wavelengths propagating at the counter direction to the light at the first set of wavelengths enters the device through fiber 12 and is channeled by the circulator 17B to the amplifying assembly 20.
  • the amplifying assembly 20 comprises a wavelength sensitive coupler 9 which couples the input light and the pump light from laser 4 into the amplifying fiber 8.
  • the output of the amplifying fiber 8 goes to the third port P3 of the circulator 17A which channels the light to the fiber 10.
  • the amplifying assembly 20 is a more traditional amplifier assembly and has no gain flattening capability. This embodiment may be useful in cases where flattening is not required for both counter-propagating light waves.
  • FIG. 6A there is shown yet a different embodiment of the present inventive amplifier with a different arrangement of the gratings 303A and 303B.
  • Light at a first set of wavelengths enters the device through the input fiber 10 and is channeled to a first circulator 27A and through it to the gratings 303A which in this case are designed to pass the first set of wavelengths and reflect at a second set of wavelengths equal to the right to left propagating set of wavelengths.
  • the function of this first set of gratings 303A is to stop any light at the second set of wavelengths scattered back by the input fiber 10 or its continuation into the system transmission fiber.
  • the light at the first set of wavelengths continues through a traditional amplifier 20A to the second circulator 27B and out to fiber 12.
  • the amplifying assembly 20 is a more traditional amplifier assembly and has no gain flattening capability, however an additional set of gratings 23 is added to attenuate individual wavelengths by the appropriate amount so that all wavelengths emerge from the amplifiers 20A or 20B with equal powers.
  • FIG. 6B there is shown in dashed lines the paths of two light beams at wavelengths W1 and W3 propagating in the right to left direction and two other light beams at wavelengths W2 and W4 propagating in the left to right direction.
  • FIG 7 there is shown a schematic of a simpler optical amplifier with equal gain at multiple wavelengths.
  • the amplifier of figure 7 is designed for one- directional amplification and comprises an input fiber 10 connected to the first port of a three port circulator 55, an output fiber 12 connected to the third port of the circulator 55, a rare earth doped fiber 6 with a first end connected to the second port of circulator 55 and a second end connected to a pump laser 4, a set of fiber gratings 3 located in the doped fiber 6 at locations selected such that when light at a wavelength Wi propagates through the doped fiber 6, is reflected by the corresponding grating and propagates back to the circulator the light experiences an amplification independent of the wavelength Wi.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)
  • Lasers (AREA)

Abstract

L'invention concerne un amplificateur à fibres optiques dopées aux terres rares amplifiant de manière bidirectionnelle et ayant un gain équilibré sur de multiples longueurs d'ondes. Cet amplificateur trouve différentes applications dans la transmission par fibre bidirectionnelle multiplexée en longueur d'onde dense. Selon une première variante, un circulateur (5) à quatre ports (P1, P2, P3, P4) est utilisé avec deux fibres d'amplification (6A, 6B), chacune dans une direction de propagation, et avec une multitude de réseaux de diffraction (3A, 3B) configurés de manière à équilibrer le gain sur des longueurs d'ondes différentes. L'invention concerne aussi d'autres variantes utilisant des circulateurs à trois ports et quatre ports et un dispositif amplificateur plus général ayant un gain égal sur de multiples longueurs d'ondes.
PCT/US1998/020762 1997-07-18 1998-10-02 Amplificateur optique bidirectionnel a gain lineaire WO2000020907A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US08/896,930 US5887091A (en) 1997-07-18 1997-07-18 Bidirectional optical amplifier having flat gain
PCT/US1998/020762 WO2000020907A1 (fr) 1997-07-18 1998-10-02 Amplificateur optique bidirectionnel a gain lineaire
AU97828/98A AU9782898A (en) 1997-07-18 1998-10-02 Bidirectional optical amplifier having flat gain

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US08/896,930 US5887091A (en) 1997-07-18 1997-07-18 Bidirectional optical amplifier having flat gain
PCT/US1998/020762 WO2000020907A1 (fr) 1997-07-18 1998-10-02 Amplificateur optique bidirectionnel a gain lineaire

Publications (1)

Publication Number Publication Date
WO2000020907A1 true WO2000020907A1 (fr) 2000-04-13

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AU (1) AU9782898A (fr)
WO (1) WO2000020907A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001097413A1 (fr) * 2000-06-15 2001-12-20 Agilent Technologies, Inc. Reflecteur a composants optiques non reciproques
GB2379327A (en) * 2001-08-30 2003-03-05 Marconi Caswell Ltd Amplifier

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5039199A (en) * 1989-12-29 1991-08-13 At&T Bell Laboratories Lightwave transmission system having remotely pumped quasi-distributed amplifying fibers
US5050949A (en) * 1990-06-22 1991-09-24 At&T Bell Laboratories Multi-stage optical fiber amplifier
US5557442A (en) * 1993-06-04 1996-09-17 Ciena Corporation Optical amplifiers with flattened gain curves
US5563733A (en) * 1994-08-25 1996-10-08 Matsushita Electric Industrial Co., Ltd. Optical fiber amplifier and optical fiber transmission system
US5604627A (en) * 1995-05-18 1997-02-18 Robert Bosch Gmbh Optical amplifier device
US5633741A (en) * 1995-02-23 1997-05-27 Lucent Technologies Inc. Multichannel optical fiber communications

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5039199A (en) * 1989-12-29 1991-08-13 At&T Bell Laboratories Lightwave transmission system having remotely pumped quasi-distributed amplifying fibers
US5050949A (en) * 1990-06-22 1991-09-24 At&T Bell Laboratories Multi-stage optical fiber amplifier
US5557442A (en) * 1993-06-04 1996-09-17 Ciena Corporation Optical amplifiers with flattened gain curves
US5563733A (en) * 1994-08-25 1996-10-08 Matsushita Electric Industrial Co., Ltd. Optical fiber amplifier and optical fiber transmission system
US5633741A (en) * 1995-02-23 1997-05-27 Lucent Technologies Inc. Multichannel optical fiber communications
US5604627A (en) * 1995-05-18 1997-02-18 Robert Bosch Gmbh Optical amplifier device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001097413A1 (fr) * 2000-06-15 2001-12-20 Agilent Technologies, Inc. Reflecteur a composants optiques non reciproques
GB2379327A (en) * 2001-08-30 2003-03-05 Marconi Caswell Ltd Amplifier

Also Published As

Publication number Publication date
AU9782898A (en) 2000-04-26

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