Abstract:
An optical amplifier for a 4-fiber system having two inputs and outputs is provided that makes use of a single amplifier rather than two separate amplifiers. The optical amplifier node makes use of an interleaver before and after the single amplifier to demultiplex and multiplex even and odd channel signals traveling in opposite directions. The optical amplifier node can be combined with other like amplifier nodes to provide more complex amplifier solutions at reduced costs due to the need for only half of the typical number of amplifiers. The optical amplifier node can also be combined with, e.g., variable optical attenuators, L/C filters, channel add/drop, and dispersion compensation modules to modify the optical signals as desired.

Description:
FIELD OF THE INVENTION 
     The invention relates to an optical amplifier, and more particularly relates to the use of a single optical amplifier to amplify signals traveling through a plurality of fibers. 
     BACKGROUND OF THE INVENTION 
     A conventional 4-fiber optical amplifier is illustrated in FIG.  1 . The optical amplifier node  10  has a first input fiber  12  that couples with a first variable optical attenuator  18  for attenuating optical signals carried over the first input fiber  12 . The variable optical attenuator  18  can be either before or after an amplifier  14 . In this instance, the optical signals leave the optical attenuator  18  and pass to the amplifier  14 . The resulting amplified optical signals exit the amplifier  14  and pass to a first output fiber  16 . A second input fiber  20  carries optical signals entering from a second direction opposite the direction of the signals in the first input fiber  12 . The second input fiber  20  couples to a second variable optical attenuator  26 . The attenuated optical signals pass to a second amplifier  22 . The amplified output from the second amplifier  22  passes to the second output fiber  24 . 
     In this conventional optical amplifier node, each signal path requires a separate optical amplifier. As optical amplifiers are costly, the use of multiple amplifiers poses a significant cost for constructing optical networks. 
     SUMMARY OF THE INVENTION 
     There is a need for an optical amplifier node that uses a single amplifier to amplify signals travelling in different directions. The present invention is directed toward further solutions. In accordance with aspects of the present invention, an optical amplifier node has a first and second input fiber in communication with a first interleaver. A first amplifier is also in communication with the first interleaver. A second interleaver is in communication with the first amplifier, and first and second output fibers are in communication with the second interleaver. The first and second input fibers, in accordance with one aspect of the present invention, each support signal traffic traveling in opposite directions. 
     The optical interleaver can take an optical signal and separate it into, e.g., odd and even channels when the optical signal passes through the interleaver in a first direction. A number of odd and even channels can also pass through the interleaver in a second direction, opposite to the first direction, and the interleaver will combine those odd and even signals into a combined signal. The interleaver can separate and combine other types of signals, and in different ways including by bit, byte, signal, channel, wavelength, band, and the like. 
     The optical amplifier node, in accordance with a further aspect of the present invention, has a first variable optical attenuator in communication with one of the first input fiber and the first output fiber. The optical amplifier node further has a second variable optical attenuator in communication with one of the second input fiber and the second output fiber. 
     In addition, the optical amplifier node can have a second amplifier in communication with an L/C splitter and L/C combiner. The function of the L/C splitter is to separate two wavelength bands spatially into two separate fibers. The C band is commonly defined as 1530 nm to 1565 nm, while the L band is commonly defined as 1570 nm to 1610 nm. The LIC combiner takes two separate C and L wavelength bands, and combines them accordingly. 
     Prior to a signal reaching the input of the optical amplifier node, the signal can travel through a multiplexor in communication with the first interleaver. A dispersion compensation module can be positioned on the communication path between the multiplexor and the first interleaver. A dispersion compensation module can also be positioned on the communication path between the first interleaver and the first amplifier to compensate for dispersion. Alternatively, the optical amplifier node can have a first amplifier that is a multistage access amplifier with an integrated dispersion compensation module. 
     The optical amplifier node, in accordance with other aspects of the present invention, includes a demultiplexor in communication with the second interleaver off of the output fiber. A dispersion compensation module can be positioned on the communication path between the demultiplexor and the second interleaver. 
     Aspects of the present invention further include a method of amplifying an optical signal. The method begins with routing signal traffic traveling originating from opposite directions through a first interleaver to interleave each of the opposing traveling signals into a combined signal. The method continues with routing the combined signal through a first amplifier to amplify that signal. The combined signal is then routed through a second interleaver to separate the combined signal into the distinct signals traveling in opposite directions. The method can further include the step of routing the signals originating from opposite directions through variable optical attenuators. Alternatively, the method can include the step of routing the combined signal through an L/C splitter, a second amplifier, and an L/C combiner. 
     The signals traveling in opposite directions can travel through one of a multiplexor and a demultiplexor at points external to the amplifier. The method can further include the step of routing the combined signal through a dispersion compensation module, either as a stand alone module, or as a part of a mid-stage access amplifier having a dispersion compensation module built within. 
     The optical amplifier node, according to still another aspect of the present invention, can include a first and second input fiber in communication with a first interleaver. The optical amplifier node further includes a first amplifier in communication with the first interleaver. A second interleaver is in communication with the first amplifier. At least two dispersion compensation modules are in communication with the second interleaver. A third interleaver is in communication with at least two dispersion compensation modules. A second amplifier is in communication with the third interleaver. A fourth interleaver is in communication with the second amplifier, and a first and second output fiber are in communication with the fourth interleaver. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned features and advantages, and other features and aspects of the present invention, will become better understood with regard to the following description and accompanying drawings, wherein: 
     FIG. 1 is a diagrammatic illustration of a known optical amplifier node; 
     FIG. 2 is a diagrammatic illustration of an optical amplifier node according to a first embodiment of the present invention; 
     FIG. 3 is a diagrammatic illustration of an optical amplifier node according to a second embodiment of the present invention; 
     FIG. 4 is a diagrammatic illustration of an optical amplifier node according to a third embodiment of the present invention; 
     FIG. 5 is a diagrammatic illustration of an optical amplifier node according to a fourth embodiment of the present invention; 
     FIG. 6 is a diagrammatic illustration of an optical amplifier node according to a fifth embodiment of the present invention; 
     FIG. 7 is a diagrammatic illustration of an optical amplifier node according to a sixth embodiment of the present invention; and 
     FIG. 8 is a diagrammatic illustration of an optical amplifier node according to a seventh embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrative embodiments of the present invention generally relate to the use of a single amplifier to amplify signals from a 4-fiber system (two input fibers and two output fibers). Prior technology utilizes a single amplifier for each fiber, which results in two amplifiers forming an amplifier node for a 4-fiber system. The present invention utilizes an optical interleaver to multiplex an odd channel signal from a fiber containing signal traffic traveling in a first direction with an even channel signal from a fiber containing signal traffic traveling in a second direction, into a single optical fiber. The single optical fiber then passes through the optical amplifier. In the output portion of the optical amplifier, the single optical signal is demultiplexed with another interleaver. The four fibers into the system, the two inputs and two outputs, are then spatially directed to the correct routing. 
     FIGS. 2 through 8 wherein like parts are designated by like reference numerals throughout, illustrate example embodiments of an optical amplifier node according to the present invention. Although the present invention will be described with reference to the example embodiments illustrated in the figures, it should be understood that many alternative forms can embody the present invention. One of ordinary skill in the art will additionally appreciate different ways to alter the parameters of the embodiments disclosed, such as the size, shape, or type of elements or materials, in a manner still in keeping with the spirit and scope of the present invention. 
     FIG. 2 illustrates an optical amplifier node  30  according to one embodiment of the present invention. There is an even channel signal that travels through a first input fiber  32  into a first interleaver  36 . The even channel signal can be an odd channel signal, so long as the signal traveling through a second input fiber  34  is an even channel signal. 
     The even/odd channel separation is intended to indicate a signal being separated in an alternating fashion, e.g., every other sub-component of the signal is removed from the first signal to form two separate signals. The even/odd convention is utilized throughout this description for illustrative purposes only, and one of ordinary skill in the art will understand that the signals can be separated in any number of different manners, such as by bit, byte, wavelength, signal, band, and the like. The inventors anticipate that each of these different signal separation techniques are intended where appropriate in each illustrative instance of the even/odd channel separation technique as utilized throughout this description. 
     It should also be noted that each channel signal is associated with a separate wavelength, and a single fiber can carry a relatively large number of channels concurrently at different wavelengths. 
     A variable optical attenuator  38  is provided on the first input fiber  32  to attenuate the even channel signal as desired. If there is no need for attenuation, this optical attenuator  38  is not required as is understood by one of ordinary skill in the art. 
     The variable optical attenuators illustrated throughout FIGS. 2-8 are shown prior to the interleaver and amplifier combinations, and after the interleaver and amplifier combinations. The applicants intend for the variable optical attenuators to be placed in either or both locations in all illustrated embodiments (although the variable optical attenuators are typically illustrated in one or the other locations herein), or alternatively in intermediate locations between interleavers, as required by the particular implementations. 
     An odd channel signal enters the optical amplifier node  30  through the second input fiber  34 . The odd channel signal travels in the opposite direction to the even channel signal. The odd channel signal enters the first interleaver  36  after passing through a variable optical attenuator  40 . Again, this optical attenuator  40  is only required if attenuation of the signal is necessary. 
     A first interleaver  36  combines each of the even and odd channel signals into a combined signal, which then exits the first interleaver  36  through a connecting fiber  42 . The connecting fiber  42  routes the combined signal to a first amplifier  44 , which amplifies the signal. 
     The single amplified signal then leaves the amplifier  44  and travels through the connecting fiber  46  to a second interleaver  48 . The second interleaver  48  splits the amplified signal into the respective even and odd channel signals. The even channel signal propogates in the same direction as it entered the optical amplifier node  30  by exiting through the first output fiber  50 . The odd channel signal, likewise, propagates in its original direction by exiting the second interleaver  48  through the second output fiber  52 . 
     FIG. 3 illustrates another embodiment of an optical amplifier node  54 . The illustrated embodiment combines two of the arrangements shown in FIG.  2 . The embodiment shown in FIG. 3 has a first input fiber  32  through which the even channel signal enters and the second input fiber  34  through which the odd channel signal enters. Again, these even and odd designations can be reversed as understood by one of ordinary skill in the art. 
     The signals combined in the first interleaver  36  travel through the connecting fiber  42  to the amplifier  44 . The amplified combined signals exit the amplifier  44  and travel along the connecting fiber  46  to the second interleaver  48 , where the signals are separated. At this point, the even channel signal travels through a first dispersion compensation module  56 , while the odd channel signal travels through a second dispersion compensation module  58 . Both signals are then combined in a third interleaver  37 . The combined signals travel along a connecting fiber  43 , through a second amplifier  45 , along a connecting fiber  47 , to a fourth interleaver  49 . Upon exiting the fourth interleaver  49 , the even channel signal passes through a variable optical attenuator  38  placed on the output fiber  50 , while the odd channel signal passes through a variable optical attenuator  40  and passes through the second output fiber  52 . 
     The optical attenuators  38  and  40  of FIG. 3 can be placed and attenuate the optical signals prior to entry into the amplifier or amplifiers, on either side of the dispersion compensation modules  56  and  58 , or the optical signals can pass through the optical attenuators  38  and  40  subsequent to exiting the amplifier or amplifiers. 
     FIG. 4 illustrates still another embodiment of an optical amplifier node  60  according to aspects of the present invention. An even channel signal enters through the first input fiber  32  into the first interleaver  36 , while the odd channel signal enters through the second input fiber  34  into the first interleaver  36 . It should be noted that the even and odd channel designations are merely for illustrative purposes as being split signals that can be combined and split by the interleavers  36 ,  37 ,  48 , and  49 . 
     The combined signal propagates through the connecting fiber  42 , the amplifier  44 , the connecting fiber  46 , and the second interleaver  48 . The second interleaver  48  splits the combined signal into the respective even channel and odd channel signals. The even channel signals proceed through a first dispersion compensation module  56 , and then passes through a channel drop  62  and a channel add  64 . Meanwhile, the odd channel signal passes through a dispersion compensation module  58  and a separate channel drop  62  and channel add  64 . The even and odd signals once again combine in the third interleaver  37  after passing through the channel drops  62  and channel adds  64 . 
     The channel drop  64  enables the amplifier node  60  to remove predetermine channel signals from a stream of signals passing through the node  60 . The channel add  64 , likewise enables the amplifier node  60  to add predetermined channel signals to a stream of signals passing through the node  60 . 
     The combined signals exit the third interleaver  37  along the connecting fiber  43  to the amplifier  45 . The amplifier  45  amplifies the combined signal, and the amplified combined signal exits along the connecting fiber  47  to the fourth interleaver  49 , where the combined signal is once again split into the even and odd channel signals. The even channel signal exits the interleaver  49 , passes through the variable optical attenuator  38  and propagates along the first output fiber  50 . The even channel signal exits the interleaver  49 , passes through the variable optical attenuator  40 , and propagates along the second output fiber  52 . 
     In still another embodiment of the invention, as illustrated in FIG. 5, another optical amplifier node  66  is provided. An even channel signal enters through the first input fiber  32  into the first interleaver  36 . An odd channel signal enters through the second input fiber  34  into the first interleaver  36 . Again, the even and odd channel designations are intended merely to illustrate a split signal that can be combined and split by the particular interleaver technology employed as previously detailed. 
     The first interleaver  36  combines the even and odd channel signals into a combined signal, which exits along the connecting path  42 . The combined signal then enters an L/C splitter  70 , whereupon the signal splits and a first portion of the signal travels along connecting fiber  72  to a second amplifier  68  while a second portion of the signal propagates along the connecting fiber  42  to the first amplifier  44 . The first and second signal portions recombine at an L/C combiner  76  and enter the second interleaver  48  as a combined signal. The second interleaver  48  once again separates the combined signal into the respective even and odd channels, which exit the second interleaver  48  along the first output fiber  50  and the second output fiber  52 . 
     FIG. 6 illustrates still another optical amplifier node  78 . In this optical amplifier node  78 , e.g., the even channel signal first passes through a multiplexor  80  prior to passing through a dispersion compensation module  82  on the first input fiber  32 , which leads to the first interleaver  36 . The, e.g., odd channel signal enters directly through the second input fiber  34  into the first interleaver  36 . The first interleaver  36  combines the even and odd channel signals into a combined signal and the combined signal exits the first interleaver  36  along the connecting fiber  42 . The amplifier  44  amplifies the combined signal and the amplified combined signal travels along the connecting fiber  46  to the second interleaver  48 . The second interleaver  48  separates the combined signal into even and odd channel signals. The even channel signal exits along the first output fiber  50 , while the odd channel signal exits along the second output fiber  52 , through a dispersion compensation module  84 , and into a demultiplexor  86 . 
     In an alternative arrangement to that of FIG. 6, an additional optical amplifier node  88  is illustrated in FIG.  7 . The, e.g., even channel signal passes through the multiplexor  80  and enters the first interleaver  36  along the first input fiber  32 . The, e.g., odd channel signal enters along the second input fiber  34  into the first interleaver  36 . The first interleaver  36  combines the even and odd channel signals, and the combined signal exits along the connecting fiber  42  and through the dispersion compensation module  90 . The combined signal is then amplified in the first amplifier  44 , travels through the connecting fiber  46 , and enters the second interleaver  48 . The second interleaver  48  separates the signals into even and odd channels. The even channel exits on the first output fiber  50 , while the odd channel exits through the second output fiber  52  and into the demultiplexor  86 . 
     FIG. 8 illustrates still another embodiment of the present invention. An optical amplifier node  92  has an, e.g., even channel signal entering through the multiplexor  80 , along the first input fiber  32 , and into the first interleaver  36 . The, e.g., odd channel signal enters the first interleaver  36  through the second input fiber  34 . The first interleaver  36  combines the even and odd channels into a combined signal, which travels along the connecting fiber  42  to a mid-stage access amplifier  94  with a dispersion compensation module  96  built within. The amplified combined signal exits along the connecting fiber  46  and enters the second interleaver  48 . The second interleaver  48  separates the even and odd channels, and the even channel exits along the first output fiber  50 . The odd channel signal exits through the second output fiber  52 , and enters the demultiplexor  86 . 
     There are many features and advantages associated with aspects of the present invention. Embodiments of the present invention provide amplification of optical signals traveling in opposite directions using a single amplifier, thereby reducing the required number of amplifiers to perform signal amplification. The signals entering the amplifier node of the present invention must contain one collection of signals, e.g., odd channels, traveling in one direction and another collection of signals, e.g., even channels traveling in the other direction. The channel signals can be traveling on for example, 200 GHz or 100 GHz channel spacing. There is only one gain available for the traffic traveling in both directions because there is only one amplifier. The introduction of a variable optical attenuator either before or after the amplifier enables two different effective gains. The optical performance of the amplifier node of the present invention has the same functionality as an amplifier node having two individual non-multiplexed amplifiers, one on each fiber, although the present invention requires only half the number of amplifiers, thus substantially reducing costs associated with forming the networked structures. 
     Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode for carrying out the invention. Details of the structure may vary substantially without departing from the spirit of the invention, and exclusive use of all modifications that come within the scope of the appended claims is reserved. It is intended that the invention be limited only to the extent required by the appended claims and the applicable rules of law.