Abstract:
The service disruptions that are caused when a high-power, multiple output amplifier is turned off to allow downstream sections of a fiber optic cable or optical equipment to be safely removed for repair or cleaning is substantially reduced by utilizing a number of switches that can pass a modulated light beam under normal conditions, or remove the light beam when maintenance is required.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a passive optical network (PON) and, more particularly, to a high-power, multiple output amplifier in a PON.  
         [0003]     2. Description of the Related Art  
         [0004]     A Fiber-To-The-Home (FTTH) passive optical network (PON) is a system that terminates a fiber optic cable in an optical network terminal (ONT) positioned at an interior or exterior location on a subscriber&#39;s premise. As a result, a substantial amount of bandwidth can be made available to the subscriber to provide a variety of services, such as plain old telephone service (POTS), Internet access service, and television service.  
         [0005]      FIG. 1  shows a circuit diagram that illustrates a portion of a prior-art FTTH PON  100 . As shown in  FIG. 1 , PON  100  includes a high-power, multiple output amplifier  110  that receives a modulated laser beam MLB either directly or indirectly from an optical line terminal (OLT), amplifies and splits the modulated laser beam MLB into a number of amplified modulated laser beams ALB 1 -ALBn, and outputs the amplified modulated laser beams ALB 1 -ALBn.  
         [0006]     As further shown in  FIG. 1 , amplifier  110  includes an erbium-doped fiber amplifier (EDFA)  112  that directly amplifies the modulated laser beam MLB. EDFA  112  utilizes a short length of optical fiber that has been doped with the rare-earth element erbium. When the modulated laser beam MLB passes through the short length of optical fiber, external energy is applied, such as at infrared (IR) wavelengths.  
         [0007]     The external energy excites the atoms in EDFA  112  which, in turn, increases the intensity of the modulated laser beam MLB to output an intensified modulated laser beam AMB. As a result, EDFA  112  maintains the modulation of the modulated laser beam MLB while at the same time increasing the brightness of the modulated laser beam MLB to output the intensified modulated laser beam AMB.  
         [0008]     In addition to EDFA  112 , amplifier  110  includes an optical splitter  114  that receives the intensified modulated laser beam AMB, and then splits the intensified modulated laser beam AMB to output the amplified modulated laser beams ALB 1 -ALBn. Thus, amplifier  110  amplifies the intensity of the modulated laser beam MLB, and then splits and outputs a number of laser beams.  
         [0009]     As further shown in  FIG. 1 , in addition to amplifier  110 , PON  100  also includes a corresponding number of optical fiber sections OF 1 -OFn that pass the amplified modulated laser beams ALB 1 -ALBn, and a corresponding number of local splitters SP 1 -SPn. The local splitters SP 1 -SPn receive the amplified modulated laser beams ALB 1 -ALBn from the optical fiber sections OF 1 -OFn, split the amplified modulated laser beams ALB 1 -ALBn to form a number of split laser beams SLB 1 -SLBm, and output the split laser beams SLB 1 -SLBm. For example, each local splitter SP can output up to 32 split laser beams SLB.  
         [0010]     PON  100  further includes a corresponding number of local fiber sections LF 1 -LFm that are connected to the local splitters SP 1 -SPn to carry the split laser beams SLB 1 -SLBm, and corresponding number of ONTs ONT 1 -ONTm that are connected to the local fiber sections LF 1 -LFm to receive the split laser beams SLB 1 -SLBm at the subscribers&#39; premises.  
         [0011]     One problem with amplifier  110  is the loss of service that occurs when maintenance must be performed to repair or clean one of the optical fiber sections OF 1 -OFn or the associated equipment. For example, when maintenance must be performed to optical fiber section OF 1 , a maintenance technician first turns off amplifier  110  to remove power (the laser beam) from optical fiber section OF 1 . Once power has been removed, optical fiber section OF 1  can be safely removed from amplifier  110 .  
         [0012]     However, when amplifier  110  is turned off to remove power from optical fiber section OF 1 , power is also removed from the remaining optical fiber sections OF 2 -OFn that are connected to amplifier  110 , thereby causing the loss of service to every subscriber whose signal passes through amplifier  110 .  
         [0013]     If maintenance is attempted without first removing power from amplifier  110 , inadvertent mishandling of the fiber or equipment can expose the technician&#39;s eyes to optical energy which can damage the technician&#39;s eyes. If the intensity of the optical energy is reduced to reduce the possibility of inadvertent eye damage, additional amplifiers must be added between the OLT and the subscribers&#39; premises which, in turn, significantly increases the cost to install and maintain the PON. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a circuit diagram illustrating a portion of a prior-art FTTH PON  100 .  
         [0015]      FIG. 2  is a circuit diagram illustrating an example of a portion of a FTTH PON  200  in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIG. 2  shows a circuit diagram that illustrates an example of a portion of a FTTH PON  200  in accordance with the present invention. PON  200  is similar to PON  100  and, as a result, utilizes the same reference numerals to designate the structures which are common to both passive optical networks.  
         [0017]     As shown in  FIG. 2 , PON  200  differs from PON  100  in that PON  200  utilizes a high-power, multiple output amplifier  210  in lieu of high-power, multiple output amplifier  110 . As with amplifier  110 , high-power multiple output amplifier  210  includes EDFA  112  and optical splitter  114 , both of which are configured in the same manner as with high-power, multiple output amplifier  110 .  
         [0018]     In accordance with the present invention, high-power, multiple output amplifier  210  additionally includes a corresponding number of 1:2 switches SW 1 -SWn that are connected to the outputs of optical splitter  114 . As shown, each of the switches SW 1 -SWn has a laser beam input LBI that receives one of the amplified modulated laser beams ALB 1 -ALBn.  
         [0019]     In addition, each of the switches SW 1 -SWn has a first laser beam output RB 1  that is connected to a corresponding optical fiber section OF 1 -OFn, and a second laser beam output RB 2 . Each of the switches SW 1 -SWn also has a control input CI that receives a control signal CS such that the switches SW 1 -SWn receive a corresponding number of control signal CS 1 -CSn.  
         [0020]     As further shown in  FIG. 2 , amplifier  210  includes a corresponding number of optical terminators OT 1 -OTn that are connected to the second laser beam outputs RB 2  of the switches SW 1 -SWn. In the present invention, an optical terminator OT is defined to be a device that absorbs all of the optical energy for a channel, allowing none to be reflected back to EDFA  112 .  
         [0021]     In operation, high-power, multiple output amplifier  210  receives the modulated laser beam MLB, and amplifies and splits the modulated laser beam into the amplified modulated laser beams ALB 1 -ALBn in the same manner as amplifier  110 . As a result, the laser beam input LBI of each of the switches SW 1 -SWn receives one of the amplified modulated laser beams ALB 1 -ALBn.  
         [0022]     The logic state of the control signal CS received by each of the switches SW 1 -SWn determines whether the amplified modulated laser beam ALB is passed to the first laser beam output RB 1  or the second laser beam output RB 2 . In normal operation, the logic states of the control signals CS 1 -CSn are set so that the switches SW 1 -SWn pass the received amplified modulated laser beams ALB 1 -ALBn to the corresponding optical fiber sections OF 1 -OFn.  
         [0023]     The logic states of the control signals CS 1 -CSn can be set, for example, by utilizing manually-operated, electrical or mechanical toggle switches or microprocessor control. Microprocessor control, in turn, can be provided, for example, via commands entered from a command line interface, or via commands entered from an Ethernet Telnet/HTTP interface.  
         [0024]     In accordance with the present invention, when maintenance is required to repair or clean fiber or equipment that lies downstream of an output of high-power, multiple output amplifier  210 , the logic state of the control signal CS that corresponds with the switch SW that passes a laser beam to the output is changed to pass the laser beam to an optical terminator.  
         [0025]     For example, if maintenance needs to be provided to fiber optic section OF 1 , the logic state of control signal CS 1  is changed so that switch SW 1  passes the amplified modulated laser beam ALB 1  to optical terminator OT 1 , which absorbs all of the optical energy of the amplified modulated laser beam ALB 1 , allowing none to be reflected back to EDFA  112 .  
         [0026]     Similarly, if maintenance needs to be provided to both the fiber optic section OF 2  and the local fiber LF 1  that is connected to splitter SP 1 , the logic states of the control signals CS 1  and CS 2  are changed so that switches SW 1  and SW 2  pass the amplified modulated laser beams ALB 1  and ALB 2 , respectively, to optical terminators OT 1  and OT 2 , respectively. Thus, multiple sections of the fiber can be disabled at the same time.  
         [0027]     In both of these examples, the logic states of the control signals CS that are connected to the remaining switches SW remain unchanged, allowing the amplified modulated laser beams ALB to continue to pass on to the subscribers. As a result, when maintenance needs to be provided, the present invention allows service to be cut to only those subscribers that receive a signal from amplifier  210  via the output that is associated with the maintenance.  
         [0028]     Once the logic state of a control signal CS has been changed and the corresponding optical terminator OT receives the amplified modulated laser beam ALB, the fiber or equipment requiring maintenance can be safely disconnected from the network (PON  200 ). When maintenance is complete, the fiber or equipment can then be reconnected to the network (PON  200 ).  
         [0029]     After being reconnected to the network, the logic state of the control signal CS is changed so that the amplified modulated laser beam ALB is again passed to the corresponding optical fiber section OF, thereby restoring the service to the subscribers that was lost during the maintenance period.  
         [0030]     Thus, one of the advantages of the present invention is that the vast majority of subscribers that receive a signal from high-power, multiple output amplifier  210  can continue to receive service during the maintenance period. As a result, the present invention significantly improves the quality of service that an operator can provide to their subscribers.  
         [0031]     In addition to improving the quality of service to the subscribers, another advantage of the present invention is that the present invention provides a method of easily removing power from a high power amplifier. Providing a method of easily removing power increases the likelihood that maintenance procedures will be followed, thereby improving safety by reducing the likelihood of inadvertent eye damage that can occur from working with a “live” fiber.  
         [0032]     It should be understood that the above descriptions are examples of the present invention, and that various alternatives of the invention described herein may be employed in practicing the invention. For example, although the  FIG. 2  example shows all of the optical fiber sections OF connected to the local splitters SP, one or more, including all, of the optical fiber sections OF 1 -OFn can alternately be connected directly to ONTs at the subscribers&#39; premises.  
         [0033]     Further, PON  200  can include a number of high-power, multiple output amplifier  210  that lie between the optical line terminal (OLT) and a subscriber&#39;s premise. Thus, it is intended that the following claims define the scope of the invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.