Abstract:
A wavelength division multiplexed optical amplifier controlling system and method. The wavelength division multiplexed optical amplifier controlling system includes an optical exchange system for generating and interpreting a supervision channel optical signal, multiplexing the supervision channel and data channels including optical signals having different wavelengths, and transmitting and receiving the multiplexed channels. Optical amplifying stages located in a transmission path are connected to the optical exchange system for amplification with uniform gain over a wavelength range including the data channel optical signals, according to information on the supervision channel optical signal. State information concerning amplification are inserted into the supervision channel when the optical exchange system requests the state information. An optical filter at each wavelength is used for supervision in a WDM-EDFA because a supervision channel having a predetermined wavelength is not necessary, so the structure of the WDM-EDFA becomes simpler.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system of controlling a wavelength division multiplexed optical amplifier and a method of its operation, and more particularly, to a system of controlling a wavelength division multiplexed optical amplifier for supervising the state of the optical multiplexer and controlling an amplification factor using a supervising channel and a control method for. 
     2. Description of the Related Art 
     With the development of the erbium doped fiber amplifier, a type of optical amplifier, enormous growth in the optical transmission field was achieved. Also, with the development of a wavelength division multiplexed system which can transmit four through sixteen channels at the same time as well as a single channel, came the development of a wavelength division multiplexed fiber amplifier (WDM-EDFA). 
     In general, in the WDM-EDFA, amplification gain must be uniformly maintained at each wavelength since more than four channels must be uniformly amplified at the same time, unlike the case of a single channel, the current of a pump laser diode must be controlled so that there is little change in the amplification gain according to changes in the number of channels (add/drop). 
     In a conventional optical amplifier control system, the amplification gain is controlled by optical filtering each wavelength or reading channel information sent from the supervising channel to a switching station or a relay station. However, the system structure becomes complicated in order to filter on each wavelength. Accordingly, costs inevitably increase and the volume of the WDM-EDFA increases. Also, there is a technical problem in that filtering should be correctly performed for an interchannel space of 0.8 nm. 
     To solve the above problem, the supervising channel multiplexed data channels are extracted at the same time by an optical divider. The supervising channel is optically filtered from the extracted 10% of the signal and then examined. However, in such a case, 10% signal loss occurs and it becomes very difficult to input information on the state of the WDM-EDFA to the supervising channel. Namely, synchronization between the WDM-EDFA and a switching system, a multiplexer (MUX), and a demultiplexer (DEMUX) becomes necessary. 
     SUMMARY OF THE INVENTION 
     To solve the above problem(s), it is an objective of the present invention to provide a wavelength division multiplexed optical amplifier control system by which it is possible to transfer the state of an optical amplifier to a switching station or a relaying station through a supervising channel and to control the amplification gain of each optical amplifier. 
     It is another objective of the present invention to provide a system of controlling a wavelength division multiplexed optical amplifier by which it is possible to perform remote supervision and remote control through a shorter path by linking adjacent optical amplifiers and a method control. 
     To achieve the first objective, there is provided a wavelength division multiplexed optical amplifier controlling system, comprising an optical exchange system for generating and interpreting a supervision channel optical signal, multiplexing the supervision channel and data channels comprised of a plurality of optical signals having different wavelengths, and transmitting and receiving the multiplexed channels and a plurality of optical amplifying portions located on a transmission path connected to the optical exchange system, for performing amplification so as to have even gain with respect to predetermined wavelength range which the data channel optical signal have according to the supervision channel optical signal information, and inserting the state information thereof into the supervision channel when the optical exchange system requests the state information thereof. 
     To achieve the second objective, there is provided a method for controlling and supervising the optical amplifying portion in the optical exchange system in an optical communication system in which the optical exchange system and the optical amplifying portion are connected to the optical transmission path, using a supervision channel, comprising the steps of (a) multiplexing the supervision channel optical signal having a predetermined form and a data channel optical signal comprised of optical signals having different wavelengths in the optical exchange system and transmitting the multiplexed optical signals, (b) separating the supervision channel from the optical signals multiplexed in the step (a) at the optical amplifier and amplifying the data channel optical signal according to predetermined control information included in the separated supervision channel, (c) converting the state information of the optical amplifying portion into an optical signal, loading the converted optical signal into the supervision channel, combining the supervision channel with the data channel amplified in the step (b), and transmitting the combination result, and (d) demultiplexing the optical signal at the optical exchange system, and checking the state of the optical amplifying portion by interpreting the supervision channel optical signal in the demultiplexed signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objectives and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: 
     FIG. 1 is a block diagram of a wavelength division multiplexed optical amplifier control system; 
     FIG. 2 is a block diagram of the wavelength division multiplexed optical amplifier of FlG.  1 ; 
     FIG. 3 is a flowchart of a method of controlling a wavelength division multiplexed optical amplifier according to the present invention; and 
     FIG. 4 is a protocol form for controlling the wavelength division multiplexed optical amplifier. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the present invention will be described in more detail with reference to the attached drawings. FIG. 1 is a block diagram of a wavelength division multiplexed optical amplifier control system according to the present invention. The control system shown in FIG. 1 includes a first optical exchange system  100 , first, second, third, and fourth WDM-EDFAs  110 ,  120 ,  130 , and  140 , and a second optical exchange system  150 . These elements are connected to each other by a bidirectional optical transmission line. 
     In a general optical communications system, the first optical exchange system  100  is separated from the second optical exchange system  150  by a distance of about 200 km. The first and second optical exchange systems multiplex or demultiplex eight data channels having different wavelengths and a supervising channel, generate a supervising channel signal to be multiplexed, and interpret a divided supervising channel signal. The plurality of first, second, third, and fourth WDM-EDFAs  110 ,  120 ,  130 , and  140  handle signal transmission bidirectionally between the first and second optical exchange systems  100  and  150  and control the amount of amplification with reference to the data of the supervising channel. Also, when there is a request from the first optical exchange system  100  or the second optical exchange system  150 , the WDM-EDFAs construct and transfer the supervising channel signals thereof. At this time, since the first and third WDM-EDFAs  110  and  130  and the second and fourth WDM-EDFAs  120  and  140  are linked to each other in order to shorten the signal path, one optical exchange system can bidirectionally supervise and control all the amplifying portions. 
     The first and second optical exchange systems  100  and  150  include supervising and controlling portions  102  and  152 , multiplexers (MUX)  104  and  154 , and demultiplexers (DEMUX)  106  and  156 , respectively. 
     The multiplexers (MUX)  104  and  154  multiplex data channels having eight different wavelengths and a supervising channel having a wavelength that is shorter than those of the data channels. The demultiplexers (DEMUX)  106  and  156  demultiplex the multiplexed optical signals. The supervising and controlling portions  102  and  152  supervise the respective WDM-EDFAs connected to the supervising channels of the MUXs  104  and  154  and the DEMUXs  106  and  156  or construct the supervising channels in order to control the amplification gains of the respective WDM-EDFAs. 
     FIG. 2 is a block diagram of the WDM-EDFAs  110 ,  120 ,  130 , and  140 . Each WDM-EDFA according to FIG. 2 includes an optical filter  200 , an erbium doped fiber (EDF)  210  as an optical amplifier, first and second pump light sources  220  and  230  as driving portions our the EDF  210 , a micro processor unit (MPU) controller  240 , and an optical coupler  250 . 
     The optical filter  200  extracts the supervising channel from the multiplexed optical signal and transmits the optical signals of the remaining data channels. The EDF  210  amplifies the transmitted optical signals of the remaining data channels. The first and second pump light sources  220  and  230  generate pump light for amplifying the data channel optical signal at the EDF  210 . The MPU controller  240  converts the supervising channel optical signal extracted by the optical filter  200  into an electrical signal and obtains data required for amplification by the EDF  210 . Current is provided to the first and second pump light sources  220  and  230  according to the data and various kinds of state information with respect to the EDF  210  are converted into the optical signals and are output. The optical coupler  250  combines the data channel optical signals amplified by the EDF  210  with the supervising channel optical signal of the MPU controller  240  and transmits the combination result. 
     The MPU controller  240  is comprises a photoelectric converter  242  such as a photo diode, an MPU  244 , and an electrooptic converter  246  such as a distributed feedback laser diode. 
     The photoelectric converter  242  converts the supervising channel optical signal into an electrical signal. The MPU  244  interprets the supervising channel signal converted into the electrical signal, controls the bias current of the first and second pump light sources  220  and  230  or constructs various kinds of state information of the first and second pump light sources  220  and  230  as the supervising channel data. The electrooptic converter  246  converts the supervising channel data of the MPU  244  into an optical signal and outputs the conversion result. 
     The operation will be described with reference to FIGS. 3 and 4. FIG. 3 is a flow chart illustrating a method of controlling the wavelength division multiplexed optical amplifier according to the present invention. FIG. 4 is a protocol form for controlling the WDM-EDFAs. 
     IDs are given to the first and second optical exchange systems  100  and  150  and the respective WDM-EDFAs  110 ,  120 ,  130 , and  140 . The supervising channel data having the protocol shown in FIG. 4 is generated in the MUX  104  or  154  of a transmission part of the first and second optical exchange systems  100  and  150  (step  300 ). The protocol has a form of a receiver port ID  400  of eight bits a transmitter port ID of eight bits an external control flag of one bit, a channel add/drop checking field of eight bits  406 , an external supervision request flag of one bit, first pump light source bias current  410 , second pump light source bias current of eight bits  412 , the temperature  414  of the first pump light source of eight bits, the temperature  416  of the second pump light source of eight bits, and a WDM-EDFA alarm field of six bits. 
     The transmitting and receiving ports IDs  400  and  402  show calling or called IDs. The external control flag  404  is set to 1 by the optical exchange system when the amplification gain of an arbitrary WDM-EDFA is to be controlled. The channel add/drop checking field  406  indicates the respective channel presences among eight data channels. The external supervision request flag  408  shows whether there is a supervision request from the optical exchange system. When there is a supervision request, the external supervision request flag is set to 1. The first and second pump light source bias currents  401  and  412  show the bias current values of the first and second pump light sources set from the outside in order to control the amplification gain of the WDM-EDFA. The temperatures of the first and second pump light sources show the temperatures of the first and second pump light sources which the WDM-EDFA receives in order to supervise whether the WDM-EDFA is amplified from the outside. The WDM-EDFA alarm field  418  shows whether there is an input or output power supply error in the WDM-EDFA, current supply errors of the first and second pump light sources, and temperature sensing errors of the first and second pump light sources. 
     The supervision channels generated in the respective WDM-EDFAs are multiplexed with eight data channels through the MUX  104  or  154  and are transferred at a high speed (step  302 ). In the respective WDM-EDFAs  110 ,  120 ,  130 , and  140  on an optical transmission path, the optical filter  200  extracts the supervision channel optical signal from the multiplexed optical signals. The photoelectric converter  242  converts the supervision channel optical signal into an electrical signal (step  304 ). At this time, when an alarm (not shown) is connected to the output terminal of the photoelectric converter  242  as a supervisor of the optical transmission path, giving an alarm when the output power of the photoelectric converter  242  is not less than a threshold value to, it is possible to sense whether the optical transmission path normally operates. 
     The MPU  244  checks each field of the protocol from the electrical signal converted in the step  304 . The check is performed as follows. When the external control flag  404  is 1 (step  306 ) and the receiver ID  400  is the same as the ID of the WDM-EDFA (step  308 ) which the MPU  244  associate with the bias current fields  410  and  412  of the first and second pump light sources, those current bias are provided is to the first and second pump light sources  220  and  230  (step  310 ). When the external control flag  404  is 0 or the receiver ID  400  is different from the ID of its WDM-EDFA, the current value determined in the MPU  244  is supplied to the bias current value of the first and second pump light sources  220  and  230  (step  312 ). The first and second pump light sources  220  and  230  generate pumping light according to the supplied bias current. The EDF  210  amplifies the data channel optical signal which has passed through the optical filter  200  so as to have an even gain with respect to each wavelength by the pumping light. 
     After the amplification, the external supervision request flag of the protocol is checked (step  313 ). When the external supervision request flag  408  is  1  and the receiver ID  400  is the same as the ID of the WDM-EDFA which the MPU  244  check (step  314 ), the state information of that WDM-EDFA, i.e., the values of the temperature fields  414  and  416  of the first and second pump light sources and the WDM-EDFA alarm field  418  are set and the ID of the location requesting external supervision and the ID of that WDM-EDFA are respectively input to the receiver ID field  400  and the transmitter ID field  402  (step  316 ). The electrooptic converter  246  converts the set supervision channel data into the optical signal. When the external supervision flag  408  is 0 or the receiver ID  400  is different from the ID of that WDM-EDFA, the above-mentioned protocol data is converted into the optical signal through the electrooptic converter  246  without change. 
     The optical coupler  250  combines the supervision channel converted into the optical signal with the data channel optical signal amplified by the EDF  210 . When there are more WDM-EDFAs on the optical transmission path, the above-mentioned processes are repeated. The data channel optical signal is amplified and the supervision channel optical signal is added to the data channel optical signal, which reaches the optical exchange system  100  or  150 . 
     The DEMUX  106  or  156  in the optical exchange system  100  or  150  demultiplexes the multiplexed data channel optical signal and the supervision channel optical signal. The supervision controlling portion  102  or  152  connected to the supervision channel interprets the supervision channel optical signal and supervises the state of each WDM-EDFA (step  320 ). 
     According to the present invention, the structure of the WDM-EDFA becomes simpler by using the supervision channel since an optical filter per each wavelength for supervision in the WDM-EDFA is not necessary. Therefore, it is possible to lower costs and there is no loss in the optical signal which occurs when using a conventional optical demultiplexer. Also, since amplification is not necessary in a supervision channel band due to separating only the supervision channel, processing the supervision channel, converting the supervision channel into the optical signal, and combining the converted optical signal into the optical transmission path, it is possible to ease the burden of flattening the amplification gain of the supervision channel band as, the well as data channel band in the WDM-EDFA and to easily combine the state information of the WDM-EDFA into the optical transmission path. Accordingly, remote supervision and remote control can be achieved. Also, since gain control is performed by sending channel add/drop information to the supervision channel, it is possible to compensate for the time error of the gain control according to the change of channels by the optical exchange system. Accordingly, it is easier to supervise, maintain, and repair IN-LlNE WDM-EDFA in an optical communications system.