CA2385046A1 - Hybrid fiber amplifier - Google Patents
Hybrid fiber amplifier Download PDFInfo
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- CA2385046A1 CA2385046A1 CA002385046A CA2385046A CA2385046A1 CA 2385046 A1 CA2385046 A1 CA 2385046A1 CA 002385046 A CA002385046 A CA 002385046A CA 2385046 A CA2385046 A CA 2385046A CA 2385046 A1 CA2385046 A1 CA 2385046A1
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- amplifier
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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
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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
- H04B10/2912—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form characterised by the medium used for amplification or processing
- H04B10/2916—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form characterised by the medium used for amplification or processing using Raman or Brillouin amplifiers
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- 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
-
- 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
- H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
- H01S3/16—Solid materials
- H01S3/1601—Solid materials characterised by an active (lasing) ion
- H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
- H01S3/1608—Solid materials characterised by an active (lasing) ion rare earth erbium
-
- 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
- H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
- H01S3/2375—Hybrid 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
- H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
- H01S3/2383—Parallel arrangements
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B2210/00—Indexing scheme relating to optical transmission systems
- H04B2210/25—Distortion or dispersion compensation
- H04B2210/258—Distortion or dispersion compensation treating each wavelength or wavelength band separately
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Lasers (AREA)
- Optical Communication System (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
A method and apparatus to amplify an optical signal is described. A first filter splits an optical signal into a first and second parts. A first Raman amplifier amplifies the first part. A second lumped amplifier amplifies the second part. A combiner combines the amplified first and second parts.
Description
METHOD AND APPARATUS TO PERFORM HYBRID OPTICAL
AMPLIFICATION
FIELD OF THE INVENTION
The invention relates to communications. More particularly, the invention relates to a method and apparatus to improve bandwidth of an optical amplifier by combining a distributed and lumped amplifier to form a hybrid optical amplifier for use with an optical communications system.
BACKGROUND OF THE INVENTION
Optical fiber amplifiers are fundamentally important to long-haul optical communications systems. Optical signals begin to attenuate as they travel over an optical fiber transmission medium due to a variety of factors such as fiber loss and dispersion. Optical amplifiers help compensate for such attenuation by providing additional power to the optical signal as it moves through the system. Because long-haul optical communications system typically carry signals over great distances (e.g., 600-10,000 kilometers or more), the system requires a relatively large number of optical amplifiers. Moreover, optical communications technology continues to move towards increasing the number of communications channels for a given set of wavelengths, ~ thereby increasing the requisite bandwidth of these amplifiers. Consequently, there is an ever-present need to increase the bandwidth of optical amplifiers, in order to decrease the number of amplifiers required by a .given system or increase the overall capacity of the system.
There are two general classes of optical amplifiers. The first class of optical amplifiers is referred to as lumped amplifiers. Lumped amplifiers linearly increase optical signal power of a supplied input signal via stimulated emission of fiber dopants such as erbium that is subject to an optical pump source. An 3o example of a lumped amplifier would be an Erbium Doped Fiber Amplifier (EDFA). The second class of optical amplifiers is referred to as distributed amplifiers. Distributed amplifiers increase optical signal power along the signal transmission path. An example of a distributed amplifier may be a Raman amplifier.
EDFAs are particular well-suited for providing optical gain in the medium to long wavelength ranges of the desired spectrum used by many optical communication systems. For example, EDFAs are used to provide optical gains between 1570 and 1610 nanometers (nm) (also referred to as the "L band"). They are also used to provide optical gain in the conventional wavelength range between to 1525 nm and 1565 nm (also referred to as the "C band"). C band EDFAs and L
band EDFAs, however, are limited in terms of their respective bandwidths. To overcome this limitation, a new type of lumped amplifier referred to as an "ultra wide band" EDFA was developed that combined the gain of the C band with the gain of the L band.
i5 Ultra wide band EDFAs provide a bandwidth of approximately 80 nm by essentially combining L band and C band amplifiers. Ultra wide band EDFAs use a circulator or filter to split (de-multiplex) the incoming optical channels into separate parallel sets of channels for amplification. The first set of channels comprises the L band wavelengths that are amplified by an L band amplifier.
The 2o second set of channels comprises the C band wavelengths that are amplified by a C
band amplifier. A circulator and Bragg grating combine (re-multiplex) the amplified signals to form the outgoing channels.
Raman amplifiers are well-suited for providing optical gain across the desired spectrum used by many optical communications systems, and in particular 25 the short to medium wavelength ranges of such spectrum. Raman amplification is accomplished by introducing the signal and ptunp energies along the same optical fiber. The pump and signal may be copropagating or counterpropagating with respect to one another. A Raman amplifier uses Stimulated Raman Scattering (SRS), which occurs in silica fibers when an intense pump beam propagates 30 through it. SRS is an inelastic scattering process in which an incident pump photon loses its energy to create another photon of reduced energy at a lower frequency. The remaining energy is absorbed by the fiber medium in the form of molecular vibrations (i.e., optical phonons). That is, pump energy of a given wavelength amplifies a signal at a longer wavelength.
One problem associated with both distributed and lumped amplifiers is that they are limited in terms of bandwidth. For example, ultra wide band amplifiers are limited to a bandwidth of approximately 80 nm. Similarly, conventional multi-pump Raman amplifiers are limited to approximately 80-100 nm. For separate reasons, it becomes difficult and cost prohibitive to increase each type of amplifier to beyond these limits. An optical amplifier providing greater bandwidth, however, would substantially improve the effectiveness of optical networks by providing extra capacity that can be used to carry more information, or reduce the number of optical amplifiers needed by the optical system and thus the overall cost and maintenance of the system.
In view of the foregoing, it can be appreciated that a substantial need exists for a method and apparatus to increase the bandwidth of an optical amplifier to solve the above-mentioned problems.
2o SUMMARY OF THE INVENTION
Embodiments of the present invention include a method and apparatus to perform optical amplification. In one embodiment of the present invention, an optical amplifier comprises both a lumped and distributed amplifier. The distributed amplifier amplifies a first part of an optical signal, while the lumped amplifier amplifies a second part of the optical signal.
With these and other advantages and features of the present invention that will become hereinafter apparent, the nature of the present invention may be more clearly understood by reference to the following detailed description, the appended 3o claims and to the several drawings attached herein.
AMPLIFICATION
FIELD OF THE INVENTION
The invention relates to communications. More particularly, the invention relates to a method and apparatus to improve bandwidth of an optical amplifier by combining a distributed and lumped amplifier to form a hybrid optical amplifier for use with an optical communications system.
BACKGROUND OF THE INVENTION
Optical fiber amplifiers are fundamentally important to long-haul optical communications systems. Optical signals begin to attenuate as they travel over an optical fiber transmission medium due to a variety of factors such as fiber loss and dispersion. Optical amplifiers help compensate for such attenuation by providing additional power to the optical signal as it moves through the system. Because long-haul optical communications system typically carry signals over great distances (e.g., 600-10,000 kilometers or more), the system requires a relatively large number of optical amplifiers. Moreover, optical communications technology continues to move towards increasing the number of communications channels for a given set of wavelengths, ~ thereby increasing the requisite bandwidth of these amplifiers. Consequently, there is an ever-present need to increase the bandwidth of optical amplifiers, in order to decrease the number of amplifiers required by a .given system or increase the overall capacity of the system.
There are two general classes of optical amplifiers. The first class of optical amplifiers is referred to as lumped amplifiers. Lumped amplifiers linearly increase optical signal power of a supplied input signal via stimulated emission of fiber dopants such as erbium that is subject to an optical pump source. An 3o example of a lumped amplifier would be an Erbium Doped Fiber Amplifier (EDFA). The second class of optical amplifiers is referred to as distributed amplifiers. Distributed amplifiers increase optical signal power along the signal transmission path. An example of a distributed amplifier may be a Raman amplifier.
EDFAs are particular well-suited for providing optical gain in the medium to long wavelength ranges of the desired spectrum used by many optical communication systems. For example, EDFAs are used to provide optical gains between 1570 and 1610 nanometers (nm) (also referred to as the "L band"). They are also used to provide optical gain in the conventional wavelength range between to 1525 nm and 1565 nm (also referred to as the "C band"). C band EDFAs and L
band EDFAs, however, are limited in terms of their respective bandwidths. To overcome this limitation, a new type of lumped amplifier referred to as an "ultra wide band" EDFA was developed that combined the gain of the C band with the gain of the L band.
i5 Ultra wide band EDFAs provide a bandwidth of approximately 80 nm by essentially combining L band and C band amplifiers. Ultra wide band EDFAs use a circulator or filter to split (de-multiplex) the incoming optical channels into separate parallel sets of channels for amplification. The first set of channels comprises the L band wavelengths that are amplified by an L band amplifier.
The 2o second set of channels comprises the C band wavelengths that are amplified by a C
band amplifier. A circulator and Bragg grating combine (re-multiplex) the amplified signals to form the outgoing channels.
Raman amplifiers are well-suited for providing optical gain across the desired spectrum used by many optical communications systems, and in particular 25 the short to medium wavelength ranges of such spectrum. Raman amplification is accomplished by introducing the signal and ptunp energies along the same optical fiber. The pump and signal may be copropagating or counterpropagating with respect to one another. A Raman amplifier uses Stimulated Raman Scattering (SRS), which occurs in silica fibers when an intense pump beam propagates 30 through it. SRS is an inelastic scattering process in which an incident pump photon loses its energy to create another photon of reduced energy at a lower frequency. The remaining energy is absorbed by the fiber medium in the form of molecular vibrations (i.e., optical phonons). That is, pump energy of a given wavelength amplifies a signal at a longer wavelength.
One problem associated with both distributed and lumped amplifiers is that they are limited in terms of bandwidth. For example, ultra wide band amplifiers are limited to a bandwidth of approximately 80 nm. Similarly, conventional multi-pump Raman amplifiers are limited to approximately 80-100 nm. For separate reasons, it becomes difficult and cost prohibitive to increase each type of amplifier to beyond these limits. An optical amplifier providing greater bandwidth, however, would substantially improve the effectiveness of optical networks by providing extra capacity that can be used to carry more information, or reduce the number of optical amplifiers needed by the optical system and thus the overall cost and maintenance of the system.
In view of the foregoing, it can be appreciated that a substantial need exists for a method and apparatus to increase the bandwidth of an optical amplifier to solve the above-mentioned problems.
2o SUMMARY OF THE INVENTION
Embodiments of the present invention include a method and apparatus to perform optical amplification. In one embodiment of the present invention, an optical amplifier comprises both a lumped and distributed amplifier. The distributed amplifier amplifies a first part of an optical signal, while the lumped amplifier amplifies a second part of the optical signal.
With these and other advantages and features of the present invention that will become hereinafter apparent, the nature of the present invention may be more clearly understood by reference to the following detailed description, the appended 3o claims and to the several drawings attached herein.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an optical system in accordance with one embodiment of the present invention.
FIG. 2 is a block diagram of an optical amplifier in accordance with one embodiment of the present invention.
FIG. 3 is a block diagram of a Raman amplifier in accordance with one embodiment of the present invention.
FIG. 4 is a block diagram of a pump source for a Raman amplifier in accordance with one embodiment of the present invention.
to FIG. 5 is a block diagram of an ultra wide band EDFA amplifier in accordance with one embodiment of the present invention.
FIG. 6 is a block diagram of an optical amplifier in accordance with another embodiment of the present invention.
DETAILED DESCRIPTION
The embodiments of the present invention comprise a method and apparatus to amplify an optical signal over a greater bandwidth than conventional amplifiers. The greater bandwidth is achieved through the use of a hybrid optical 2o amplifier. The hybrid optical amplifier comprises both a lumped amplifier and a distributed amplifier. The gain of the lumped amplifier is combined with the gain of the distributed amplifier. For example, one embodiment of the present invention utilizes an ultra wide band EDFA amplifier having a bandwidth of approximately 80 nm, and a mufti-pump Raman amplifier having a bandwidth of approximately 100 nm. The overall bandwidth of the hybrid optical amplifier is the combination of both bandwidths, or approximately 180 nm minus some insertion loss associated with some of the additional components used to combine both amplifiers (e.g., band splitting filters, combiners andlor circulators).
The bandwidth of the hybrid optical amplifier directly correlates to the 3o bandwidth of the respective lumped and distributed amplifiers used in any one S
embodiment of the present invention. As the bandwidth of each respective type of amplifier increases, the overall bandwidth of the hybrid optical amplifier increases a given amount accordingly.
The combination of a lumped and distributed amplifier works well for a number of reasons. For example, the lumped amplifier can be used to amplify longer wavelengths while the distributed amplifier can be used to amplify shorter wavelengths. Therefore the distributed amplifier can still use the transmission media as the gain medium for amplification without interfering with those wavelengths to be amplified by the lumped amplifier. Similarly, the lumped to amplifier can be configured to pass the distributed amplified signals without significantly degrading those signals, Alternatively, a separate path could be set up if higher performance is desired.
It is worthy to note that any reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.
Referring now in detail to the drawings wherein like parts are designated by like reference numerals throughout, there is illustrated in FIG. 1 an optical system in accordance with one embodiment of the present invention. FIG. 1 discloses an optical communication system 100 that utilizes optical fiber amplifiers such as hybrid optical amplifiers. The system includes transmitter/receiver ("transceiver") terminals 102 and 104 and optical transmission fiber paths 110 and 112 supporting bi-directional communication. The signals being transmitted from terminals 102 and 104 are in optical form. There is no intermediate conversion to electrical form.
A plurality of optical amplifiers 106 and 108 are interposed in fiber paths 110 and 112 between terminals 102 and 104. The components of optical amplifiers 106 and 108 are shown in greater detail in FIG. 2. For clarity of discussion, fiber paths 110 and 112 are shown in FIG. 1 with only one optical amplifier each. It can be appreciated, however, that any number of optical amplifiers may be employed in each path and still fall within the scope of the present invention. In addition, such well-known parts of a communications system as drive electronics, detector electronics, splices, attenuators, couplers and so forth, are considered to be conventional and have been omitted in this and other figures.
FIG. 2 is a block diagram of an optical amplifier in accordance with one embodiment of the present invention. FIG. 2 illustrates a hybrid optical amplifier 200 that is representative of amplifiers 106 and 108, of FIG. 1. Amplifier 200 comprises a first amplifier 202, a bandsplitting filter 204, a first amplification path l0 214, a second amplification path 206, and an optical combiner 226. First amplification path 214 further comprises an optical isolator 216, a bandpass filter 218, a dispersion slope compensator 220, a coupler 222 and a power control line 224. An example of coupler 222 is a wavelength division multiplexer (WDM) coupler or a tap coupler. Second amplification path 206 further comprises an optical isolator 208, a lumped amplifier 210 and a bandpass filter 212.
Amplifier 200 operates to amplify one or more chamlels of an optical signal. Amplifier 200 receives an incoming optical signal. The incoming optical signal comprises a first part and a second part, with the first part representing those communication channels to be amplified using a distributed amplification scheme, and the second part representing those communication channels to be amplified using a lumped amplification scheme. In general, the wavelengths used by the communications channels of the first part are shorter than the wavelengths used by the communications channels of the second part.
Amplifier 202 receives both the first and second parts of the optical signals.
In this embodiment of the preferred invention, amplifier 202 is a Raman amplifier designed to amplify the shorter wavelengths of the first part. More particularly, the longer wavelengths of the second part are outside of the Raman gain region.
Consequently, amplifier 202 amplifies the communications channels of the first part but does not substantially affect the communications channels of the second part.
Bandsplitting filter 204 receives the amplified first part and the unamplified second part. Bandsplitting filter 204 operates to split (de-multiplex) the amplified first part from the second part. First amplification path 214 receives the amplified first part and passes the signals through to combiner 226. Second amplification path 206 receives the unamplified second part and amplifies the same.
First amplification path 214 passes the signals through to combiner 222.
Optical isolator 216 receives the amplified first part. Optical isolator 216 operates to prevent transmission of back reflections from other elements and Raleigh back-scattered signals. Bandpass filter 218 receives the amplified first part and ensures 1o that only those wavelengths used for the communications channels of the first part are passed through. Dispersion slope compensator 220 receives the amplified first part and is designed to ensure that the accumulated dispersion of the amplified first part is as close as possible for a desired number (e.g., zero). Coupler 222 receives the amplified first part and sends a power control signal via power control line 224 is to amplifier 202. A gain flattening filter (GFF) 223 receives the amplified first part and flattens or equalizes the gain for the amplified first part as desired.
Combiner 226 receives the amplified first part and combines the amplified first part with the amplified second part as described below.
Second amplification path 206 amplifies the second part of the incoming 20 optical signal. Optical isolator 208 receives the second part of the optical signal.
Optical isolator operates to prevent transmission of back reflections from amplifier 210. Amplifier 210 receives the second part of the optical signal. In this embodiment of the present invention, amplifier 210 is a lumped amplifier designed to amplify the longer wavelengths of the communications channels of the second 25 part. Bandpass filter 212 receives the amplified second part and ensures that only those wavelengths used for the communications channels of the second part are passed through. A dispersion slope compensator (not shown) may also be utilized in this path as necessary for the amplified second part. Combiner 226 receives the amplified second part and combines the amplified second part with the amplified 3o first part as described above.
FIG. 3 is a block diagram of a Raman amplifier in accordance with one embodiment of the present invention. FIG. 3 illustrates a Raman amplifier 300 that is representative of amplifier 202, as discussed with reference to FIG. 2.
Raman amplifier 300 includes a gain medium referred to as optical fiber portion 306 of the transmission path in which Raman gain is to be generated. This portion 306 of fiber may vary in size and may be limited, for example, to a small section of the transmission path. Alternatively, fiber portion 306 in which Raman gain is generated may have a length encompassing the entire transmission path. Fiber portion 306 is coupled to a source of optical pump energy 302 via a coupler such as a WDM coupler. Pump source 302 receives the power control signal from coupler 222 discussed with reference to FIG. 2.
The given performance of each individual Raman amplifier is design dependent. Design considerations include length of the gain medium (e.g., fiber portion 306), effective cross-section of the gain medium, dispersion characteristics of the fiber, power from the pump source (e.g, pump source 302), choice of Bragg grating or optical filter to recycle pump power, and various other factors.
With respect to dispersion, dispersion slope compensator 220 should be configured to provide an average dispersion as close to zero as possible. This can be accomplished by, for example, combining positive and negative dispersion fibers 2o resulting in an accumulated dispersion as close to a desired number as possible for a desired application (e.g., near zero dispersion slope). The dispersion compensation function performed by amplifiers discussed herein obviates the need to use individual dispersion compensators for the system.
FIG. 4 is a block diagram of a pump source for a Raman amplifier in accordance with one embodiment of the present invention. FIG. 4 illustrates a pump source 400 that is representative of pump source 302, as discussed with reference to FIG. 3. Pump source 400 comprises a first optical pump 404 and a second optical pump 406. An optical coupler 408 combines the energy from pumps 404 and 406 and directs the resulting beam to WDM coupler 304. Pumps 404 and 406 generate pump energy at different wavelengths selected to maximize the amplifier bandwidth. For example, pump 404 may provide pump energy at 1455 nm and pump 406 may provide pump energy at 1495 nm to amplify a WDM
signal ranging from 1530-1610 nm. Although only two pumps are described with reference to pump source 400, it can be appreciated that any number of pumps can be used and still fall within the scope of the present invention.
A power control unit 410 is connected to pumps 404 and 406. Power control unit 410 operates to actively control the power evolution of amplifier 202.
Power control unit 410 receives a power control signal from coupler 222 via power control line 224. Power control unit 410 compensates the gain provided by pump to source 302 to the first part of the optical signal in accordance with the power control signal so that the desired signal level power level is maintained.
FIG. 5 is a block diagram of an ultra wide band EDFA amplifier in accordance with one embodiment of the present invention. FIG. 5 illustrates an ultra wide band EDFA 500 that is representative of a lumped amplif er 210, as discussed with reference to FIG. 2. Ultra wide band EDFA 500 comprises a bandsplitting filter 502. Bandsplitting filter 502 receives the second part and separates the second part into C band and L band signals. As discussed previously the C band extends between approximately about 1525 nm to 1565 nm while the L
band covers between about 1570 and 1610 nm. The C band signals pass through a dispersion slope compensator 504. A C band EDFA amplifier 506 receives and amplifies the C band signals. The L band signals pass through a dispersion slope compensator 508. An L band EDFA amplifier 510 receives and amplifies the L
band signals. Combiner 512 receives and combines the amplified C and L band signals into a single amplified second part. It is worthy to note that a skilled person would understand the need to add other components in ultra wide band EDFA 500, such as isolators to prevent transmission of back reflections from amplifier 506 or amplifier 510, as necessary for a particular system.
FIG. 6 is a block diagram of an optical amplifier in accordance with another embodiment of the present invention. FIG. 6 illustrates an optical 3o amplifier 600. Optical amplifier 600 comprises a distributed amplifier 602 and a lumped amplifier 604. An example of distributed amplifier 602 is a multi-pump Raman amplifier, such as amplifier 300 as described with FIG. 3. An example of lumped amplifier 604 is an ultra wide band EDFA amplifier, such as amplifier as described with FIG. 5.
FIG. 1 is a block diagram of an optical system in accordance with one embodiment of the present invention.
FIG. 2 is a block diagram of an optical amplifier in accordance with one embodiment of the present invention.
FIG. 3 is a block diagram of a Raman amplifier in accordance with one embodiment of the present invention.
FIG. 4 is a block diagram of a pump source for a Raman amplifier in accordance with one embodiment of the present invention.
to FIG. 5 is a block diagram of an ultra wide band EDFA amplifier in accordance with one embodiment of the present invention.
FIG. 6 is a block diagram of an optical amplifier in accordance with another embodiment of the present invention.
DETAILED DESCRIPTION
The embodiments of the present invention comprise a method and apparatus to amplify an optical signal over a greater bandwidth than conventional amplifiers. The greater bandwidth is achieved through the use of a hybrid optical 2o amplifier. The hybrid optical amplifier comprises both a lumped amplifier and a distributed amplifier. The gain of the lumped amplifier is combined with the gain of the distributed amplifier. For example, one embodiment of the present invention utilizes an ultra wide band EDFA amplifier having a bandwidth of approximately 80 nm, and a mufti-pump Raman amplifier having a bandwidth of approximately 100 nm. The overall bandwidth of the hybrid optical amplifier is the combination of both bandwidths, or approximately 180 nm minus some insertion loss associated with some of the additional components used to combine both amplifiers (e.g., band splitting filters, combiners andlor circulators).
The bandwidth of the hybrid optical amplifier directly correlates to the 3o bandwidth of the respective lumped and distributed amplifiers used in any one S
embodiment of the present invention. As the bandwidth of each respective type of amplifier increases, the overall bandwidth of the hybrid optical amplifier increases a given amount accordingly.
The combination of a lumped and distributed amplifier works well for a number of reasons. For example, the lumped amplifier can be used to amplify longer wavelengths while the distributed amplifier can be used to amplify shorter wavelengths. Therefore the distributed amplifier can still use the transmission media as the gain medium for amplification without interfering with those wavelengths to be amplified by the lumped amplifier. Similarly, the lumped to amplifier can be configured to pass the distributed amplified signals without significantly degrading those signals, Alternatively, a separate path could be set up if higher performance is desired.
It is worthy to note that any reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.
Referring now in detail to the drawings wherein like parts are designated by like reference numerals throughout, there is illustrated in FIG. 1 an optical system in accordance with one embodiment of the present invention. FIG. 1 discloses an optical communication system 100 that utilizes optical fiber amplifiers such as hybrid optical amplifiers. The system includes transmitter/receiver ("transceiver") terminals 102 and 104 and optical transmission fiber paths 110 and 112 supporting bi-directional communication. The signals being transmitted from terminals 102 and 104 are in optical form. There is no intermediate conversion to electrical form.
A plurality of optical amplifiers 106 and 108 are interposed in fiber paths 110 and 112 between terminals 102 and 104. The components of optical amplifiers 106 and 108 are shown in greater detail in FIG. 2. For clarity of discussion, fiber paths 110 and 112 are shown in FIG. 1 with only one optical amplifier each. It can be appreciated, however, that any number of optical amplifiers may be employed in each path and still fall within the scope of the present invention. In addition, such well-known parts of a communications system as drive electronics, detector electronics, splices, attenuators, couplers and so forth, are considered to be conventional and have been omitted in this and other figures.
FIG. 2 is a block diagram of an optical amplifier in accordance with one embodiment of the present invention. FIG. 2 illustrates a hybrid optical amplifier 200 that is representative of amplifiers 106 and 108, of FIG. 1. Amplifier 200 comprises a first amplifier 202, a bandsplitting filter 204, a first amplification path l0 214, a second amplification path 206, and an optical combiner 226. First amplification path 214 further comprises an optical isolator 216, a bandpass filter 218, a dispersion slope compensator 220, a coupler 222 and a power control line 224. An example of coupler 222 is a wavelength division multiplexer (WDM) coupler or a tap coupler. Second amplification path 206 further comprises an optical isolator 208, a lumped amplifier 210 and a bandpass filter 212.
Amplifier 200 operates to amplify one or more chamlels of an optical signal. Amplifier 200 receives an incoming optical signal. The incoming optical signal comprises a first part and a second part, with the first part representing those communication channels to be amplified using a distributed amplification scheme, and the second part representing those communication channels to be amplified using a lumped amplification scheme. In general, the wavelengths used by the communications channels of the first part are shorter than the wavelengths used by the communications channels of the second part.
Amplifier 202 receives both the first and second parts of the optical signals.
In this embodiment of the preferred invention, amplifier 202 is a Raman amplifier designed to amplify the shorter wavelengths of the first part. More particularly, the longer wavelengths of the second part are outside of the Raman gain region.
Consequently, amplifier 202 amplifies the communications channels of the first part but does not substantially affect the communications channels of the second part.
Bandsplitting filter 204 receives the amplified first part and the unamplified second part. Bandsplitting filter 204 operates to split (de-multiplex) the amplified first part from the second part. First amplification path 214 receives the amplified first part and passes the signals through to combiner 226. Second amplification path 206 receives the unamplified second part and amplifies the same.
First amplification path 214 passes the signals through to combiner 222.
Optical isolator 216 receives the amplified first part. Optical isolator 216 operates to prevent transmission of back reflections from other elements and Raleigh back-scattered signals. Bandpass filter 218 receives the amplified first part and ensures 1o that only those wavelengths used for the communications channels of the first part are passed through. Dispersion slope compensator 220 receives the amplified first part and is designed to ensure that the accumulated dispersion of the amplified first part is as close as possible for a desired number (e.g., zero). Coupler 222 receives the amplified first part and sends a power control signal via power control line 224 is to amplifier 202. A gain flattening filter (GFF) 223 receives the amplified first part and flattens or equalizes the gain for the amplified first part as desired.
Combiner 226 receives the amplified first part and combines the amplified first part with the amplified second part as described below.
Second amplification path 206 amplifies the second part of the incoming 20 optical signal. Optical isolator 208 receives the second part of the optical signal.
Optical isolator operates to prevent transmission of back reflections from amplifier 210. Amplifier 210 receives the second part of the optical signal. In this embodiment of the present invention, amplifier 210 is a lumped amplifier designed to amplify the longer wavelengths of the communications channels of the second 25 part. Bandpass filter 212 receives the amplified second part and ensures that only those wavelengths used for the communications channels of the second part are passed through. A dispersion slope compensator (not shown) may also be utilized in this path as necessary for the amplified second part. Combiner 226 receives the amplified second part and combines the amplified second part with the amplified 3o first part as described above.
FIG. 3 is a block diagram of a Raman amplifier in accordance with one embodiment of the present invention. FIG. 3 illustrates a Raman amplifier 300 that is representative of amplifier 202, as discussed with reference to FIG. 2.
Raman amplifier 300 includes a gain medium referred to as optical fiber portion 306 of the transmission path in which Raman gain is to be generated. This portion 306 of fiber may vary in size and may be limited, for example, to a small section of the transmission path. Alternatively, fiber portion 306 in which Raman gain is generated may have a length encompassing the entire transmission path. Fiber portion 306 is coupled to a source of optical pump energy 302 via a coupler such as a WDM coupler. Pump source 302 receives the power control signal from coupler 222 discussed with reference to FIG. 2.
The given performance of each individual Raman amplifier is design dependent. Design considerations include length of the gain medium (e.g., fiber portion 306), effective cross-section of the gain medium, dispersion characteristics of the fiber, power from the pump source (e.g, pump source 302), choice of Bragg grating or optical filter to recycle pump power, and various other factors.
With respect to dispersion, dispersion slope compensator 220 should be configured to provide an average dispersion as close to zero as possible. This can be accomplished by, for example, combining positive and negative dispersion fibers 2o resulting in an accumulated dispersion as close to a desired number as possible for a desired application (e.g., near zero dispersion slope). The dispersion compensation function performed by amplifiers discussed herein obviates the need to use individual dispersion compensators for the system.
FIG. 4 is a block diagram of a pump source for a Raman amplifier in accordance with one embodiment of the present invention. FIG. 4 illustrates a pump source 400 that is representative of pump source 302, as discussed with reference to FIG. 3. Pump source 400 comprises a first optical pump 404 and a second optical pump 406. An optical coupler 408 combines the energy from pumps 404 and 406 and directs the resulting beam to WDM coupler 304. Pumps 404 and 406 generate pump energy at different wavelengths selected to maximize the amplifier bandwidth. For example, pump 404 may provide pump energy at 1455 nm and pump 406 may provide pump energy at 1495 nm to amplify a WDM
signal ranging from 1530-1610 nm. Although only two pumps are described with reference to pump source 400, it can be appreciated that any number of pumps can be used and still fall within the scope of the present invention.
A power control unit 410 is connected to pumps 404 and 406. Power control unit 410 operates to actively control the power evolution of amplifier 202.
Power control unit 410 receives a power control signal from coupler 222 via power control line 224. Power control unit 410 compensates the gain provided by pump to source 302 to the first part of the optical signal in accordance with the power control signal so that the desired signal level power level is maintained.
FIG. 5 is a block diagram of an ultra wide band EDFA amplifier in accordance with one embodiment of the present invention. FIG. 5 illustrates an ultra wide band EDFA 500 that is representative of a lumped amplif er 210, as discussed with reference to FIG. 2. Ultra wide band EDFA 500 comprises a bandsplitting filter 502. Bandsplitting filter 502 receives the second part and separates the second part into C band and L band signals. As discussed previously the C band extends between approximately about 1525 nm to 1565 nm while the L
band covers between about 1570 and 1610 nm. The C band signals pass through a dispersion slope compensator 504. A C band EDFA amplifier 506 receives and amplifies the C band signals. The L band signals pass through a dispersion slope compensator 508. An L band EDFA amplifier 510 receives and amplifies the L
band signals. Combiner 512 receives and combines the amplified C and L band signals into a single amplified second part. It is worthy to note that a skilled person would understand the need to add other components in ultra wide band EDFA 500, such as isolators to prevent transmission of back reflections from amplifier 506 or amplifier 510, as necessary for a particular system.
FIG. 6 is a block diagram of an optical amplifier in accordance with another embodiment of the present invention. FIG. 6 illustrates an optical 3o amplifier 600. Optical amplifier 600 comprises a distributed amplifier 602 and a lumped amplifier 604. An example of distributed amplifier 602 is a multi-pump Raman amplifier, such as amplifier 300 as described with FIG. 3. An example of lumped amplifier 604 is an ultra wide band EDFA amplifier, such as amplifier as described with FIG. 5.
5 Optical amplifier 600 operates to amplify optical signals for an optical communications system. Optical amplifier 600 receives an incoming optical signal. The incoming optical signal comprises a first part and a second part, with the first part representing those communication channels to be amplified using a distributed amplification scheme, and the second part representing those to communication channels to be amplified using a lumped amplification scheme.
In general, the wavelengths used by the communications channels of the first part are shorter than the wavelengths used by the communications channels of the second part.
Amplifier 602 receives both the first and second parts of the optical signals.
In this embodiment of the present invention, amplifier 602 is a Raman amplifier designed to amplify the shorter wavelengths of the first part. More particularly, the longer wavelengths of the second part are outside the Raman gain region.
Consequently, amplifier 602 amplifies the communications channels of the first part but does not substantially affect the communications channels of the second 2o part.
Amplifier 604 receives the amplified first part and the unamplified second part. In this embodiment of the present invention, amplifier 604 is an ultra wide band EDFA designed to amplify the longer wavelengths of the second part. More particularly, the shorter wavelengths of the first part are outside of the EDFA gain region. Consequently, amplifier 604 amplifies the communications channels of the second part but does not substantially affect the communications channels of the first part. This can be accomplished by selecting a combination of doping levels and host material that minimizes the absorption of EDFA in the Raman amplifier spectral region.
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 present invention. For example, the embodiments were described using a communication network. A communication network, however, can utilize an infinite number of network devices configured in an infinite number of ways.
The communication network described herein is merely used by way of example, and is not meant to limit the scope of the present invention.
In general, the wavelengths used by the communications channels of the first part are shorter than the wavelengths used by the communications channels of the second part.
Amplifier 602 receives both the first and second parts of the optical signals.
In this embodiment of the present invention, amplifier 602 is a Raman amplifier designed to amplify the shorter wavelengths of the first part. More particularly, the longer wavelengths of the second part are outside the Raman gain region.
Consequently, amplifier 602 amplifies the communications channels of the first part but does not substantially affect the communications channels of the second 2o part.
Amplifier 604 receives the amplified first part and the unamplified second part. In this embodiment of the present invention, amplifier 604 is an ultra wide band EDFA designed to amplify the longer wavelengths of the second part. More particularly, the shorter wavelengths of the first part are outside of the EDFA gain region. Consequently, amplifier 604 amplifies the communications channels of the second part but does not substantially affect the communications channels of the first part. This can be accomplished by selecting a combination of doping levels and host material that minimizes the absorption of EDFA in the Raman amplifier spectral region.
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 present invention. For example, the embodiments were described using a communication network. A communication network, however, can utilize an infinite number of network devices configured in an infinite number of ways.
The communication network described herein is merely used by way of example, and is not meant to limit the scope of the present invention.
Claims (21)
1. An optical amplifier, comprising:
a distributed amplifier to amplify a first part of an optical signal; and a lumped amplifier to amplify a second part of said optical signal.
a distributed amplifier to amplify a first part of an optical signal; and a lumped amplifier to amplify a second part of said optical signal.
2. The optical amplifier of claim 1, wherein said distributed amplifier is a Raman amplifier, and said lumped amplifier is an erbium-doped fiber amplifier (EDFA).
3. The optical amplifier of claim 2, further comprising:
a first filter between said distributed and lumped amplifier, said first filter to separate said amplified first part from said second part prior to amplifying said second part; and a combiner to combine said amplified first and second parts.
a first filter between said distributed and lumped amplifier, said first filter to separate said amplified first part from said second part prior to amplifying said second part; and a combiner to combine said amplified first and second parts.
4. The optical amplifier of claim 2, wherein said EDFA is to pass said amplified first part.
5. The optical amplifier of claim 4, wherein said EDFA is to amplify wavelengths in a C band and an L band.
6. The optical amplifier of claim 5, wherein said Raman amplifier is to amplify wavelengths below said C and L bands.
7. The optical amplifier of claim 6, wherein said EDFA comprises:
a filter to separate a first set of wavelengths in said C band from a second set of wavelengths in said L band;
a first EDFA to amplify said first set of wavelengths;
a second EDFA to amplify said second set of wavelengths; and a combiner to combine said amplified first and second sets of wavelengths.
a filter to separate a first set of wavelengths in said C band from a second set of wavelengths in said L band;
a first EDFA to amplify said first set of wavelengths;
a second EDFA to amplify said second set of wavelengths; and a combiner to combine said amplified first and second sets of wavelengths.
8. The optical amplifier of claim 7, further comprising:
a first dispersion slope compensator between said filter and said first EDFA; and a second dispersion slope compensator between said filter and said second EDFA.
a first dispersion slope compensator between said filter and said first EDFA; and a second dispersion slope compensator between said filter and said second EDFA.
9. The optical amplifier of claim 2, wherein said Raman amplifier is a multi-pump Raman amplifier.
10. The optical amplifier of claim 3, further comprising:
an optical isolator connected to said first filter to isolate said amplified first part;
a second filter connected to said optical isolator to filter said amplified first part; and a dispersion slope compensator connected to said second filter to perform dispersion slope compensation for said amplified first part.
an optical isolator connected to said first filter to isolate said amplified first part;
a second filter connected to said optical isolator to filter said amplified first part; and a dispersion slope compensator connected to said second filter to perform dispersion slope compensation for said amplified first part.
11. The optical amplifier of claim 9, wherein said first filter is a band splitting filter, and said second filter is a band pass filter.
12. The optical amplifier of claim 2, wherein said Raman amplifier comprises:
a gain medium to amplify said first part using Raman gain;
a pump source to provide energy to said gain medium; and a coupler to couple said energy to said gain medium.
a gain medium to amplify said first part using Raman gain;
a pump source to provide energy to said gain medium; and a coupler to couple said energy to said gain medium.
13. The optical amplifier of claim 12, wherein said pump source comprises a plurality of pumps operating at different wavelengths.
14. The optical amplifier of claim 13, wherein said coupler is a wavelength division multiplexer.
15. The optical amplifier of claim 2, wherein said EDFA amplifier comprises:
an erbium-doped gain medium to amplify said second part;
a pump source to provide energy to said gain medium; and a coupler to couple said energy to said gain medium.
an erbium-doped gain medium to amplify said second part;
a pump source to provide energy to said gain medium; and a coupler to couple said energy to said gain medium.
16. The optical amplifier of claim 15, wherein said coupler is a wavelength division multiplexer.
17. A method to perform optical amplification, comprising:
amplifying a first part of an optical signal using a distributed amplifier;
and amplifying a second part of said optical signal using a lumped amplifier.
amplifying a first part of an optical signal using a distributed amplifier;
and amplifying a second part of said optical signal using a lumped amplifier.
18. The method of claim 17, wherein said distributed amplifier is a Raman amplifier, and said lumped amplifier is an erbium-doped fiber amplifier (EDFA).
19. The method of claim 18, further comprising:
filtering said amplified first part from said second part prior to amplifying said second part;
combining said amplified first part and said second part after said second part has been amplified.
filtering said amplified first part from said second part prior to amplifying said second part;
combining said amplified first part and said second part after said second part has been amplified.
20. The method of claim 18, further comprising passing said amplified first part through said EDFA.
21. An optical system, comprising:
an optical transceiver to send an optical signal;
an optical amplifier comprising a distributed amplifier and a lumped amplifier, with said distributed amplifier to amplify a first part of said optical signal, and said lumped amplifier to amplify a second part of said optical signal; and an optical transceiver to receive said amplified optical signal.
an optical transceiver to send an optical signal;
an optical amplifier comprising a distributed amplifier and a lumped amplifier, with said distributed amplifier to amplify a first part of said optical signal, and said lumped amplifier to amplify a second part of said optical signal; and an optical transceiver to receive said amplified optical signal.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US61645100A | 2000-07-14 | 2000-07-14 | |
| US09/616,451 | 2000-07-14 | ||
| PCT/US2001/022230 WO2002007270A2 (en) | 2000-07-14 | 2001-07-13 | Hybrid fiber amplifier |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2385046A1 true CA2385046A1 (en) | 2002-01-24 |
Family
ID=24469520
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002385046A Abandoned CA2385046A1 (en) | 2000-07-14 | 2001-07-13 | Hybrid fiber amplifier |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU2001280556A1 (en) |
| CA (1) | CA2385046A1 (en) |
| WO (1) | WO2002007270A2 (en) |
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| AR049379A1 (en) | 2004-04-30 | 2006-07-26 | Irm Llc | COMPOUNDS AND COMPOSITIONS AS INHIBITORS OF KATEPSINS |
| CN104821481B (en) * | 2015-05-15 | 2017-08-25 | 中国电子科技集团公司第八研究所 | A kind of mixing discrete highly nonlinear optical fiber amplifier based on double feedback arrangements |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5905838A (en) * | 1998-02-18 | 1999-05-18 | Lucent Technologies Inc. | Dual window WDM optical fiber communication |
| US6356384B1 (en) * | 1998-03-24 | 2002-03-12 | Xtera Communications Inc. | Broadband amplifier and communication system |
| EP1088375B1 (en) * | 1998-06-16 | 2010-11-10 | Xtera Communications, Inc. | Dispersion compensating and amplifying optical element |
-
2001
- 2001-07-13 WO PCT/US2001/022230 patent/WO2002007270A2/en active Application Filing
- 2001-07-13 AU AU2001280556A patent/AU2001280556A1/en not_active Abandoned
- 2001-07-13 CA CA002385046A patent/CA2385046A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO2002007270A3 (en) | 2002-04-18 |
| AU2001280556A1 (en) | 2002-01-30 |
| WO2002007270A2 (en) | 2002-01-24 |
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