WO2000049741A1 - Method and apparatus for providing optical amplification and gain equalization to an optical signal in an optical communication system - Google Patents

Method and apparatus for providing optical amplification and gain equalization to an optical signal in an optical communication system Download PDF

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Publication number
WO2000049741A1
WO2000049741A1 PCT/US2000/004141 US0004141W WO0049741A1 WO 2000049741 A1 WO2000049741 A1 WO 2000049741A1 US 0004141 W US0004141 W US 0004141W WO 0049741 A1 WO0049741 A1 WO 0049741A1
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Prior art keywords
optical
amplifiers
amplifier
gain
optical amplifier
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PCT/US2000/004141
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French (fr)
Inventor
Xiabing Ma
Morten Nissov
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Tyco Submarine Systems, Ltd.
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Publication date
Application filed by Tyco Submarine Systems, Ltd. filed Critical Tyco Submarine Systems, Ltd.
Priority to AU38589/00A priority Critical patent/AU3858900A/en
Publication of WO2000049741A1 publication Critical patent/WO2000049741A1/en

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    • 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
    • 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
    • H04B10/2933—Signal power control considering the whole optical path
    • H04B10/2935—Signal power control considering the whole optical path with a cascade of amplifiers

Definitions

  • the present invention relates generally to optical communication systems, and more particularly to a WDM optical communication system that employs rare-earth doped fiber amplifiers and gain equalization across the WDM signal bandwidth.
  • the lightwave systems use optical fibers to carry large amounts of multiplexed digital data over long distances from a transmit terminal to a receive terminal.
  • the maximum distance that the data can be transmitted in the fiber without amplification or regeneration is limited by the loss and dispersion associated with the optical fiber.
  • the lightwave systems may include a number of repeaters periodically located along the fiber route from the transmit terminal to the receive terminal. Each repeater boosts the weak received signal to compensate for the transmission losses which occurred from the last repeater.
  • Prior to the widespread availability of efficient optical amplifiers many systems converted the optical signals into electrical signals for amplification by conventional electrical amplifiers. The amplified electrical signals were then reconverted to the optical domain, for further distribution along the optical communication path. The advent of reliable and low cost optical amplifiers has obviated the need to convert signals into the electrical domain for amplification.
  • Optical amplifiers such as rare earth doped optical fiber amplifiers, require a source of pump energy.
  • a dedicated pump laser is coupled to the doped fiber for exciting the active medium (rare earth element) within the amplifier.
  • a communication signal is passed through the doped fiber.
  • the doped fiber exhibits gain at the wavelength of the communication signal, providing the desired amplification.
  • pump energy may be provided at a wavelength of 1485 nm or 980 nm, which coincide with the absorption peaks of erbium.
  • FIG. 1 shows the gain of a conventional EDFA as a function of wavelength over a spectral region of about 1525 nm to 1580 nm.
  • This spectral region is one in which the optical signals are often located.
  • the gain undergoes substantial variations over the spectral region. These variations are exacerbated when many different channels are used which extend over a wide 5 bandwidth.
  • Unequal gain distribution adversely effects the quality of the multiplexed optical signal, particularly in long-haul systems where insufficient gain leads to large signal-to-noise ratio degradations and too much gain can cause nonlinearity induced penalties.
  • Gain equalizers are therefore used in optical amplifier designs to ensure constant gain over the usable wavelength range.
  • optical transmission systems use a series of optical amplifiers that are substantially identical to one another. This simplifies design, manufacturing and deployment issue.
  • such systems may use either single stage or multiple stage erbium-doped fiber amplifiers (EDFAs).
  • EDFAs erbium-doped fiber amplifiers
  • Gain equalizers are often located immediately downstream from each optical amplifier or immediately downstream from every Nth optical amplifier, particularly for wide 1 5 band width applications.
  • the EDFA's that are used can be relatively complex multiple stage amplifiers.
  • complex multiple stage amplifiers require additional components such as additional pump sources and thus are more expensive and commensurately less reliable.
  • a WDM optical communication system includes a transmitter, a receiver and an optical fiber transmission path coupling the transmitter to the receiver. At least first and second optical amplifiers are disposed at intermediate points along the transmission path. One of the first and second optical amplifiers is more complex in design than the other of the first and second optical amplifiers.
  • the more complex optical amplifier includes a gain equalizer for providing substantially uniform gain across a WDM optical signal bandwidth. Moreover, the more complex amplifier generates more gain than the other optical amplifier. Accordingly, the more complex amplifier design is advantageously reserved for those situations where greater gain is required, whereas the remaining optical amplifiers may be simpler in design.
  • the more complex amplifier may be a multiple-stage amplifier, for example, while the more simply designed amplifier may be a single stage amplifier.
  • FIG. I shows the gain of a conventional EDFA as a function of wavelength over a spectral region of about 1525 nm to 1580 mm.
  • FIG. 2 shows a simplified schematic diagram of an optical communication system that employs optical amplifiers.
  • FIG. 3 shows a simplified diagram of one of the repeaters shown in FIG.
  • FIG. 4 shows an example of a two stage optical amplifier that may be employed in the present invention.
  • WDM wavelength division multiplexed
  • the system includes transmitter/receiver terminals 32 and 34 and optical transmission fiber paths 20 and 40 supporting bidirectional communication.
  • a plurality of optical amplifiers 22 and 42 are interposed in the fiber paths 20 and 40 between the transmitter/receiver terminals 34 and 32.
  • Optical amplifiers 22 and 42 contain a length of doped fiber that provides a gain medium, an energy source that pumps the fiber to provide gain, and a means of coupling the pump energy into the doped fiber without interfering with the signal being amplified. These components of the optical amplifiers are shown in greater detail in FIG. 3.
  • terminal 32 includes optical communication transmitters 200, 214 and 216 to transmit optical communications channels at wavelength ⁇ l, ⁇ 2 ... ⁇ N, respectively.
  • Multiplexer 210 multiplexes these signals together to form a multiplexed signal that is launched into optical fiber 20 for transmission to the receiving terminal 34.
  • demultiplexer 212 demultiplexes and routes ⁇ l, ⁇ 2 ... ⁇ N to receivers 208, 218 ... 220, respectively.
  • both terminals 32 and 34 serve as transmitters and receivers and hence, while not shown in FIG. I for purposes of clarity, each includes both transmitters and receivers.
  • each optical amplifier includes a rare-earth doped optical fiber 21, such as an erbium doped fiber (EDF), coupled to a source of optical pump energy 60 via a coupler 25 such as a wavelength division multiplexer (WDW).
  • An optical isolator 27 is typically located immediately downstream from each of the doped fibers. The isolator prevents amplified spontaneous emission from traveling back upstream and disrupting system stability by causing the amplifiers to oscillate.
  • a pair of such optical amplifiers supporting opposite -traveling signals is housed in a single unit 30 (see FIG. 1) known as a repeater.
  • the signals being transmitted from the terminals 32 and 34 are in optical form. There is no intermediate conversion to electrical form. While only three optical amplifier pairs are depicted in FIG. 2 for clarity of discussion, it should be understood by those skilled in the art that the present invention finds application in transmission paths of all lengths having many additional (or fewer) sets of such repeaters.
  • Pump unit 23 provides the optical pump energy for both transmission directions of the amplifier pair.
  • the pump unit 23 includes pump laser 60, pump controller 64 and
  • Pump laser 60 generates an optical pump beam at a suitable wavelength for producing amplification in EDF 21.
  • the pump controller 64 comprises a comparator and feedback circuit for powering and controlling the pump laser 60.
  • the SCR circuit 65 receives a portion of the optical signal tapped by couplers 29.
  • the pump controller 64 responsive to signals from the SCR processor 65, applies current to pump laser 60 to adjust the total output power generated by the pump laser 60
  • the optical amplifier shown in FIG. 3 is a single stage optical amplifier.
  • multiple stage optical amplifiers are sometimes used in, which the gain medium comprises two or more segments of doped fiber, e.g., doped with erbium, separated by an opticalisolator.
  • Gain equalizers are often used in connection with multiple stage amplifiers for a variety of reasons. Primarily, however, this is because the process of gain equalization requires the elimination_of excess gain at select wavelengths to provide a constant gain across the usable bandwidth. Since they employ more segments of fiber that act as a gain medium, multiple stage amplifiers can provide greater gain than a single stage amplifier, thus making them more amenable to gain equalization.
  • the gain equalizers employed in the present invention may be any suitable component known to those of ordinary skill in the art.
  • suitable gain equalizers include, but are not limited to, long period gratings, short period gratings, and dielectric thin film filters.
  • FIG. 4 shows an example of a two stage optical amplifier having two doped fiber segments 33 and 35. While for purposes of clarity FIG. 4 shows only a single transmission path, one of ordinary skill in the art will recognize that a two (or more) stage amplifier may be readily employed in a repeater supporting bidirectional communication, such as shown in FIG. 3. Moreover, FIG. 4 shows only the optical paths through the amplifier and not the associated control circuitry such as shown in FIG. 3. Pumps 37 and 38 provide pump power to doped fibers 33 and 35, respectively, via couplers 30 and 3 1. Gain equalization is accomplished by inserting a gain equalizer 36 in the transmission path. As well known to those of ordinary skill in the art, the location of the gain equalizer 36 requires a trade-off between the total amplifier output power and the amplifier noise figure.
  • the location of the gain equalizer 36 is determined by properly balancing these competing amplifier characteristics. For example, if the gain equalizer 36 is inserted between the doped fiber segments 33 and 35, the output power of the amplifier will be optimized at the expense of an increase in the noise figure. Alternatively, if the gain equalizer 36 is inserted downstream from both doped fiber segments 33 and 35 (at the position denoted by reference numeral 36A in FIG. 4), the noise figure will be minimized at the expense of a reduction in total output power.
  • the present inventors have recognized that if gain equalization is only required in select ones of the optical amplifiers along the transmission path, then only these select optical amplifiers need to be more complex in design.
  • the remaining optical amplifiers that do not employ gain equalization may be more simply designed amplifiers such as single stage amplifiers.
  • the more complex optical amplifiers may be multiple stage optical amplifiers. That is, in accordance with the present invention, the transmission system employs more than one optical amplifier design. Relatively simple and inexpensive amplifiers such as single stage amplifiers are used when gain equalizers are not provided. More complex amplifiers such as multiple stage amplifiers are thus reserved for those situations where additional gain is needed to compensate for the provision of gain equalization.
  • the more complex amplifiers used in connection with gain equalizers are not limited to multiple stage amplifiers. Rather, they may be more complex in others respects in order to provide additional gain. For example, while both the more complex and the simpler amplifiers may have the same number of stages, the more complex amplifiers may employ stronger pump sources than the simpler amplifiers.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
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  • Optical Communication System (AREA)

Abstract

A WDM optical communication system is provided that includes a transmitter, a receiver and an optical fiber transmission path coupling the transmitter to the receiver. At least first and second optical amplifiers are disposed at intermediate points along the transmission path. One of the first and second optical amplifiers is more complex in design than the other of the first and second optical amplifiers. The more complex optical amplifier may include a gain equalizer for providing substantially uniform gain across a WDM optical signal bandwidth. Moreover, the more complex amplifier generates more gain than the other optical amplifier. Accordingly, the more complex amplifier design is reserved for those situations where greater gain is required, whereas the remaining optical amplifiers may be simpler in design. The more complex amplifier may be a multiple-stage amplifier, for example, while the more simply designed amplifier may be a single stage amplifier.

Description

METHOD AND APPARATUS FOR PROVIDING AMPLIFICATION
AND GAIN EQUALIZATION TO AN OPTICAL SIGNAL IN AN
OPTICAL COMMUNICATION SYSTEM
Field of the Invention
The present invention relates generally to optical communication systems, and more particularly to a WDM optical communication system that employs rare-earth doped fiber amplifiers and gain equalization across the WDM signal bandwidth.
Background of the Invention
Commercial lightwave systems use optical fibers to carry large amounts of multiplexed digital data over long distances from a transmit terminal to a receive terminal. The maximum distance that the data can be transmitted in the fiber without amplification or regeneration is limited by the loss and dispersion associated with the optical fiber. To transmit optical signals over long distances, the lightwave systems may include a number of repeaters periodically located along the fiber route from the transmit terminal to the receive terminal. Each repeater boosts the weak received signal to compensate for the transmission losses which occurred from the last repeater. Prior to the widespread availability of efficient optical amplifiers, many systems converted the optical signals into electrical signals for amplification by conventional electrical amplifiers. The amplified electrical signals were then reconverted to the optical domain, for further distribution along the optical communication path. The advent of reliable and low cost optical amplifiers has obviated the need to convert signals into the electrical domain for amplification.
Optical amplifiers, such as rare earth doped optical fiber amplifiers, require a source of pump energy. In a rare earth doped optical fiber amplifier, for example, a dedicated pump laser is coupled to the doped fiber for exciting the active medium (rare earth element) within the amplifier. At the same time, a communication signal is passed through the doped fiber. The doped fiber exhibits gain at the wavelength of the communication signal, providing the desired amplification. If the doped optical fiber is doped with erbium., for example, pump energy may be provided at a wavelength of 1485 nm or 980 nm, which coincide with the absorption peaks of erbium.
FIG. 1 shows the gain of a conventional EDFA as a function of wavelength over a spectral region of about 1525 nm to 1580 nm. This spectral region is one in which the optical signals are often located. Clearly, the gain undergoes substantial variations over the spectral region. These variations are exacerbated when many different channels are used which extend over a wide 5 bandwidth. Unequal gain distribution adversely effects the quality of the multiplexed optical signal, particularly in long-haul systems where insufficient gain leads to large signal-to-noise ratio degradations and too much gain can cause nonlinearity induced penalties. Gain equalizers are therefore used in optical amplifier designs to ensure constant gain over the usable wavelength range.
In general, optical transmission systems use a series of optical amplifiers that are substantially identical to one another. This simplifies design, manufacturing and deployment issue. For example, such systems may use either single stage or multiple stage erbium-doped fiber amplifiers (EDFAs). Gain equalizers are often located immediately downstream from each optical amplifier or immediately downstream from every Nth optical amplifier, particularly for wide 1 5 band width applications. When gain equalizers are required, the EDFA's that are used can be relatively complex multiple stage amplifiers. Unfortunately, complex multiple stage amplifiers require additional components such as additional pump sources and thus are more expensive and commensurately less reliable.
It would therefore be desirable to use in an optical transmission system the simplest optical amplifier arrangement possible while also employing gain equalization wherever necessary along the transmission path.
Summary of the Invention
In accordance with the present invention, a WDM optical communication system is provided that includes a transmitter, a receiver and an optical fiber transmission path coupling the transmitter to the receiver. At least first and second optical amplifiers are disposed at intermediate points along the transmission path. One of the first and second optical amplifiers is more complex in design than the other of the first and second optical amplifiers.
In one embodiment of the invention, the more complex optical amplifier includes a gain equalizer for providing substantially uniform gain across a WDM optical signal bandwidth. Moreover, the more complex amplifier generates more gain than the other optical amplifier. Accordingly, the more complex amplifier design is advantageously reserved for those situations where greater gain is required, whereas the remaining optical amplifiers may be simpler in design. The more complex amplifier may be a multiple-stage amplifier, for example, while the more simply designed amplifier may be a single stage amplifier.
Brief Description of the Drawings
FIG. I shows the gain of a conventional EDFA as a function of wavelength over a spectral region of about 1525 nm to 1580 mm. FIG. 2 shows a simplified schematic diagram of an optical communication system that employs optical amplifiers.
FIG. 3 shows a simplified diagram of one of the repeaters shown in FIG.
FIG. 4 shows an example of a two stage optical amplifier that may be employed in the present invention.
Detailed Description
Referring to FIG. 2, there is disclosed a wavelength division multiplexed (WDM) optical communication system which utilizes optical fiber amplifiers. The system includes transmitter/receiver terminals 32 and 34 and optical transmission fiber paths 20 and 40 supporting bidirectional communication. A plurality of optical amplifiers 22 and 42 are interposed in the fiber paths 20 and 40 between the transmitter/receiver terminals 34 and 32. Optical amplifiers 22 and 42 contain a length of doped fiber that provides a gain medium, an energy source that pumps the fiber to provide gain, and a means of coupling the pump energy into the doped fiber without interfering with the signal being amplified. These components of the optical amplifiers are shown in greater detail in FIG. 3.
As shown, terminal 32 includes optical communication transmitters 200, 214 and 216 to transmit optical communications channels at wavelength λl, λ2 ... λN, respectively. Multiplexer 210 multiplexes these signals together to form a multiplexed signal that is launched into optical fiber 20 for transmission to the receiving terminal 34. At the receiving terminal 215, demultiplexer 212 demultiplexes and routes λl, λ2 ... λN to receivers 208, 218 ... 220, respectively. Of course, in a bidirectional communication system such as shown in FIG. 1 , both terminals 32 and 34 serve as transmitters and receivers and hence, while not shown in FIG. I for purposes of clarity, each includes both transmitters and receivers.
Referring to FIG. 3, each optical amplifier includes a rare-earth doped optical fiber 21, such as an erbium doped fiber (EDF), coupled to a source of optical pump energy 60 via a coupler 25 such as a wavelength division multiplexer (WDW). An optical isolator 27 is typically located immediately downstream from each of the doped fibers. The isolator prevents amplified spontaneous emission from traveling back upstream and disrupting system stability by causing the amplifiers to oscillate. In undersea communication systems a pair of such optical amplifiers supporting opposite -traveling signals is housed in a single unit 30 (see FIG. 1) known as a repeater. The signals being transmitted from the terminals 32 and 34 are in optical form. There is no intermediate conversion to electrical form. While only three optical amplifier pairs are depicted in FIG. 2 for clarity of discussion, it should be understood by those skilled in the art that the present invention finds application in transmission paths of all lengths having many additional (or fewer) sets of such repeaters.
Pump unit 23 provides the optical pump energy for both transmission directions of the amplifier pair. The pump unit 23 includes pump laser 60, pump controller 64 and
20 supervisory /command response (SCR) processor 65. Pump laser 60 generates an optical pump beam at a suitable wavelength for producing amplification in EDF 21. For erbium doped fibers, pump wavelengths in the neighborhood of 1485 nm or 980 nm are suitable. The pump controller 64 comprises a comparator and feedback circuit for powering and controlling the pump laser 60. The SCR circuit 65 receives a portion of the optical signal tapped by couplers 29. The pump controller 64, responsive to signals from the SCR processor 65, applies current to pump laser 60 to adjust the total output power generated by the pump laser 60
The optical amplifier shown in FIG. 3 is a single stage optical amplifier. As previously mentioned, multiple stage optical amplifiers are sometimes used in, which the gain medium comprises two or more segments of doped fiber, e.g., doped with erbium, separated by an opticalisolator. Gain equalizers are often used in connection with multiple stage amplifiers for a variety of reasons. Primarily, however, this is because the process of gain equalization requires the elimination_of excess gain at select wavelengths to provide a constant gain across the usable bandwidth. Since they employ more segments of fiber that act as a gain medium, multiple stage amplifiers can provide greater gain than a single stage amplifier, thus making them more amenable to gain equalization.
The gain equalizers employed in the present invention may be any suitable component known to those of ordinary skill in the art. For example, suitable gain equalizers include, but are not limited to, long period gratings, short period gratings, and dielectric thin film filters.
FIG. 4 shows an example of a two stage optical amplifier having two doped fiber segments 33 and 35. While for purposes of clarity FIG. 4 shows only a single transmission path, one of ordinary skill in the art will recognize that a two (or more) stage amplifier may be readily employed in a repeater supporting bidirectional communication, such as shown in FIG. 3. Moreover, FIG. 4 shows only the optical paths through the amplifier and not the associated control circuitry such as shown in FIG. 3. Pumps 37 and 38 provide pump power to doped fibers 33 and 35, respectively, via couplers 30 and 3 1. Gain equalization is accomplished by inserting a gain equalizer 36 in the transmission path. As well known to those of ordinary skill in the art, the location of the gain equalizer 36 requires a trade-off between the total amplifier output power and the amplifier noise figure. Thus, the location of the gain equalizer 36 is determined by properly balancing these competing amplifier characteristics. For example, if the gain equalizer 36 is inserted between the doped fiber segments 33 and 35, the output power of the amplifier will be optimized at the expense of an increase in the noise figure. Alternatively, if the gain equalizer 36 is inserted downstream from both doped fiber segments 33 and 35 (at the position denoted by reference numeral 36A in FIG. 4), the noise figure will be minimized at the expense of a reduction in total output power.
The present inventors have recognized that if gain equalization is only required in select ones of the optical amplifiers along the transmission path, then only these select optical amplifiers need to be more complex in design. The remaining optical amplifiers that do not employ gain equalization may be more simply designed amplifiers such as single stage amplifiers. In contrast the more complex optical amplifiers may be multiple stage optical amplifiers. That is, in accordance with the present invention, the transmission system employs more than one optical amplifier design. Relatively simple and inexpensive amplifiers such as single stage amplifiers are used when gain equalizers are not provided. More complex amplifiers such as multiple stage amplifiers are thus reserved for those situations where additional gain is needed to compensate for the provision of gain equalization.
The more complex amplifiers used in connection with gain equalizers are not limited to multiple stage amplifiers. Rather, they may be more complex in others respects in order to provide additional gain. For example, while both the more complex and the simpler amplifiers may have the same number of stages, the more complex amplifiers may employ stronger pump sources than the simpler amplifiers.
Although various embodiments are specifically illustrated and described herein, it will be appreciated that modifications and variations of the present invention are covered by the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention. For example, the invention is equally applicable to unidirectional transmission systems as well as bidirectional transmission systems. In the former case only one of the transmission paths 20 or 40 shown in FIG. 4 would be employed. Further, although the present invention has been discussed in terms of an erbium-doped fiber amplifier, the invention contemplates the use of other optical amplifier arrangements. For example, Raman amplifiers may be employed in which the more complex amplifier, for instance, uses stronger pump sources than the simpler amplifier.

Claims

CLAIMS.:
1. A WDM optical communication system, comprising: a transmitter and a receiver-, an optical fiber transmission path coupling said transmitter to said receiver; at least first and second optical amplifiers disposed at intermediate points along said transmission path, wherein at least one of said optical amplifiers is a single stage amplifier and the other of said optical amplifiers is a multi-stage optical amplifier.
2. The system of claim 1 wherein said multi-stage optical amplifier includes a gain equalizer for providing substantially uniform gain across a WDM optical signal bandwidth.
3. The system of claim 1 further comprising a first plurality of single stage amplifiers and a second plurality of multi-stage amplifiers, wherein each of the second plurality of multi-stage amplifiers includes a gain equalizer for providing substantially uniform gain across a WDM optical signal bandwidth.
4. The system of claim 1 wherein said first and second amplifiers are rare-earth doped optical amplifiers.
5 . The system of claim 3 wherein the first and second plurality of amplifiers are rare-earth doped optical amplifiers.
6. A method for transmitting an optical signal through a WDM optical communication system, comprising: transmitting the optical signal into an optical fiber transmission path-, amplifying the optical signal with a single stage optical amplifier at one point along the transmission path; amplifying the optical signal with a multi-stage optical amplifier at another point along the transmission path;
equalizing gain imparted across the bandwidth of the optical signal with a gain equalizer associated with the multi-stage optical amplifier.
7. The method of claim 6 wherein said single stage and multistage amplifiers are rare-earth doped optical amplifiers.
8 . A WDM optical communication system, comprising: a transmitter and a receiver; an optical fiber transmission path coupling said transmitter to said receiver; at least first and second optical amplifiers disposed at intermediate points along said transmission path, wherein at least one of said optical amplifiers is more complex in design than the other of said optical amplifiers.
9. The system of claim 8 wherein the more complex optical amplifier is a multi-stage optical amplifier and the other optical amplifier has at least one less stage than the more complex optical amplifier.
10. The system of claim 9 wherein the other optical amplifier is a single-stage optical amplifier
11. The system of claim 8 wherein the more complex optical amplifier employs a stronger pump source than the other optical amplifier.
12. The system of claim 9 wherein said multi-stage optical amplifier includes a gain equalizer for providing substantially uniform gain across a WDM optical signal bandwidth.
13. The system of claim 8 further comprising a first plurality of the more complex amplifiers and a second plurality of the other amplifiers, wherein each of the first plurality of the more complex amplifiers includes a gain equalizer for providing substantially uniform gain across a WDM optical signal bandwidth.
14. The system of claim 8 wherein said first and second amplifiers are rare-earth doped optical amplifiers.
15. The system of claim 13 wherein said first and second plurality of amplifiers are rare-earth doped optical amplifiers.
16. The system of claim 8 wherein said first and second amplifiers are Raman optical amplifiers.
17. The system of claim 13 wherein said first and second plurality of amplifiers are Raman optical amplifiers
18. The system of claim 1 wherein said first and second amplifiers are Raman optical amplifiers.
19. The system of claim 3 wherein said first and second plurality of amplifiers are
Raman optical amplifiers.
20. A method for transmitting an optical signal through a WDM optical communication system, comprising: transmitting the optical signal into an optical fiber transmission path; amplifying the optical signal with an optical amplifier of a first type at one point along the transmission path; amplifying the optical signal with an optical amplifier of a second type at another point along the transmission path; equalizing gain imparted across the bandwidth of the optical signal with a gain equalizer associated with the optical amplifier of the second type.
21. The method of claim 20 wherein the optical amplifier of the second type is more complex in design than the optical amplifier of the first type.
22. The method of claim 20 wherein the optical amplifier of the first type is a single stage amplifier and the optical amplifier of the second type is a multi-stage amplifier.
23. The method of claim 21 wherein the optical amplifier of the second type employs a stronger pump source than the optical amplifier of the first type.
24. The method of claim 20 wherein the optical amplifier of the second type generates more gain than the optical amplifier of the first type.
25. The system of claim 8 wherein the more complex optical amplifier generates more gain than the other optical amplifier.
PCT/US2000/004141 1999-02-16 2000-02-16 Method and apparatus for providing optical amplification and gain equalization to an optical signal in an optical communication system WO2000049741A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1274185A1 (en) * 2001-07-05 2003-01-08 Alcatel Optical transmission system with stimulated Raman scattering amplification and gain equalization

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0139081A2 (en) * 1983-09-28 1985-05-02 Polaroid Corporation Optical communications system using raman repeaters and components therefor
US5748364A (en) * 1994-04-14 1998-05-05 Pirelli Cavi S.P.A. Amplified telecommunication system for wavelength-division multiplexing transmissions

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0139081A2 (en) * 1983-09-28 1985-05-02 Polaroid Corporation Optical communications system using raman repeaters and components therefor
US5748364A (en) * 1994-04-14 1998-05-05 Pirelli Cavi S.P.A. Amplified telecommunication system for wavelength-division multiplexing transmissions

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1274185A1 (en) * 2001-07-05 2003-01-08 Alcatel Optical transmission system with stimulated Raman scattering amplification and gain equalization
FR2827099A1 (en) * 2001-07-05 2003-01-10 Cit Alcatel STIMULATED RAMAN DIFFUSION AMPLIFICATION OPTICAL FIBER TRANSMISSION SYSTEM

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