FR2777142A1 - OPTICAL AMPLIFIER FOR CONSTANTLY ADJUSTING THE OUTPUT POWER PER CHANNEL AND METHOD THEREOF - Google Patents

Abstract

Optical amplifier whose output power for each channel is controlled constantly, for amplifying a data channel optical signal when a control channel optical signal and a data channel optical signal including a plurality of channels are input together , the optical amplifier comprising a channel control unit (200), an amplification unit (230), an amplification control unit (240) and a wavelength coupling unit (280). The gain of the optical amplifier is controlled so that a target value of the amplified data channel optical signal corresponding to the number of channels actually becomes equal to a measured value. Thus, the output power for each channel can be controlled constantly.

Description

OPTICAL AMPLIFIER FOR CONSTANTLY ADJUSTING

  OUTPUT POWER PER CHANNEL AND METHOD FOR

THIS ONE

BACKGROUND OF THE INVENTION

  1. Field of the Invention The present invention relates to an optical amplifier for constantly adjusting the output power per channel and to a method thereof and, more particularly, an optical amplifier in a wavelength multiplexing system. , whose output power for each channel is constant, and

a process for it.

2. Description of the related art

  The development of an erbium-doped fiber amplifier as an optical fiber in the 1990s contributed to an evolution in the field of optical transmission. An erbium-doped fiber amplifier with wavelength multiplexing has also been developed with a wavelength multiplexing system which can transmit simultaneously 4

  with 16 channels, as well as a single channel.

  A flat gain optical amplifier used in a wavelength division multiplex transmission system has an amplification which varies according to a change in the number of channels or the intensity of an input signal. Such a variation in the amplification of the signal as a function of the wavelength degrades the flatness of the gain and generates errors in the system, thus harming long-distance transmission. In the wavelength-division multiplex transmission system adopting the erbium-doped fiber amplifier, it is important to control the output power per channel relative to the number of channels, since level transitions of Erbium-doped fiber amplifier output power occurs when the number of channels is changed due to the

  network reconfiguration or faults. That is

  say, since the wavelength division multiplexing erbium doped fiber amplifier must amplify the optical signals equally for a plurality of channels, the gain must be kept uniform for each wavelength. Also, the gain of the erbium doped fiber amplifier with wavelength multiplexing must be controlled so as to exhibit little variation as a function of

modification of the number of channels.

  An erbium doped fiber amplifier repeater with dynamic gain control for wavelength multiplex networks of C. Konish et al. presented in OFC'97 Technical Digest is used to allow an amplifier to output a constant intensity signal. FIG. 1 is a block diagram of a conventional erbium-doped fiber amplifier comprising an amplification unit 10, first and second couplers 12 and 14, a wavelength control unit 16 and a gain control 18. The first and second couplers 12 and 14 output part of the output signal from the amplification unit 10 to the wavelength control unit 16. The length control unit wave 16 receives and controls an amplified signal output from the second coupler 14. The gain control unit 18 controls the gain of the amplification unit 10 in accordance with the results of the control. The length control unit

  wave 16 includes an acoustically tunable filter

  optical, a photodiode, and a wavelength counter, and counts the number of channels of an optical signal amplified by the amplification unit. The gain control unit 18 controls the intensity of an output signal by adjusting the gain of the amplification unit using a photodiode or a

gain leveling device.

  However, the conventional structure is very complicated and large and uses many additional optical devices, so that it is difficult to use it in a real system. Also, the output port of the erbium-doped fiber amplifier directly splits an amplified optical signal, thus having a direct effect on the amplifier output.

with fiber doped with erbium.

SUMMARY OF THE INVENTION

  To solve the above problems, it is an object of the present invention to provide an optical amplifier in which the number of channels and the power of an optical signal are checked and the output power per channel is controlled constantly. by adjusting the gain of an erbium-doped fiber amplifier according to the number of channels

  and input power, and a method for this.

  Consequently, to achieve the above objective

  Above, an optical amplifier, whose output power for each channel is constantly controlled is provided, for amplifying an optical data channel signal when an optical control channel signal and an optical data channel signal comprising a a plurality of channels are inputted together, the optical amplifier comprising: a channel control unit for separating the optical control channel signal, for converting the optical control channel signal into an electrical signal, for extracting the number of channels included in the data channel of the converted signal, and to output the converted signal; an amplifier unit for amplifying the optical data channel signal using a predetermined control source; an amplification control unit for controlling the input of the control source, so that a target output power value of the amplification unit depending on the number of channels is really equal to a power value of measured output of the amplification unit; and a wavelength coupling unit for converting the output signal of the channel control unit into an optical signal and for coupling the optical signal to the optical data channel signal

amplified.

  To achieve the above objective, a method is proposed for constantly controlling the output power for each channel of an optical amplifier, comprising the steps of: (a) measuring the output power of the optical amplifier while changing the number of channels of an optical data channel signal, and memorizing the number of channels and the output power values as a function of the number of channels, when the power for each channel of the optical amplifier to amplify the optical data channel signal comprising a plurality of channels is constantly controlled; (b) interpreting a change in the number of channels of the optical data channel signal included in the input optical signal by measuring the power of the optical signal of input data channel, and extracting the number of channels of the optical signal from data channel; (c) establishing an output power value of the optical amplifier corresponding to the extracted number of channels, from among the output power values stored in step (a), as a target value; (d) measuring the output power for the input light signal amplified by the optical amplifier; and (e) adjusting the gain of the optical amplifier so that the measured value

  becomes really equal to the target value.

BRIEF DESCRIPTION OF THE DRAWINGS

  The above objectives and benefits of this

  invention will become more evident with description

  detailed of an embodiment thereof with reference to the accompanying drawings, in which: FIG. 1 is a functional diagram illustrating the configuration of a conventional optical amplifier; Figure 2 is a block diagram illustrating the configuration of an optical amplifier for constantly controlling the output power per channel, according to the present invention; Figure 3 is a flow diagram illustrating a method for constantly controlling the output power per channel of an optical amplifier, according to the present invention; Figs. 4A and 4B are graphs showing an output for each channel when a two-channel optical signal is input to an optical amplifier according to the present invention; and Figures 5A and 5B are graphs showing an output for each channel when a four-channel optical signal is input to an optical amplifier

according to the present invention.

  DESCRIPTION OF THE PREFERRED EMBODIMENT

  With reference to FIG. 2, an optical amplifier comprises a channel control unit 200, a first optical coupler 210, a first photodiode 211, a first isolator 220, an amplification unit 230, an amplification control unit 240 , a second isolator 250, a second optical coupler 260, a second photodiode 261, an external control unit 270 and a coupling unit

wavelengths 280.

  The channel control unit 200 decouples an optical control channel signal from which information regarding the number of channels is extracted, when an optical data channel signal and the optical control channel signal for controlling the data channels are coupled to each other and received as an input. The channel control unit 200 comprises a first selective wavelength coupler 201, an optical-electrical converter 202 and a system control unit 203. The first selective wavelength coupler 201 decouples the optical signal from

  control channel for optical input signals.

  The optical-electrical conversion unit converts the decoupled control channel optical signal into an electrical signal. The system controller 203 extracts information regarding the number of channels entered into the optical amplifier from the control channel electrical signal. Also, the system control unit 203 adds information regarding the amplification state of the amplification unit 230 output by the amplification control unit 240 to the electrical control channel signal. The amplifier unit 230 amplifies the optical data channel signal using a control source. The amplification unit 230 comprises a second selective wavelength coupler 231, an optical fiber doped with erbium 233, a third selective wavelength coupler 234 and first and second optical pumping sources 232 and 235 as amplification control sources for erbium-doped fiber 233. The second wavelength selective coupler 231 couples pump light from the first optical pump source 232 to the optical data channel signal , and the third selective wavelength coupler 234 outputs the pumping light from the second optical source of

  pumping 235 towards the fiber doped with erbium 233.

  Wavelength coupling unit 280 converts the electrical control channel signal output from the system control unit 203 into an optical signal, couples the converted optical signal to the optical data channel signal amplified by amplifier unit 230, and transmits the resulting signal to the next port. The wavelength coupling unit 280 comprises a fourth selective coupler in

  wavelengths 281 and an electrical converter-

  optical 282. The electrical-optical converter 282 converts an electrical signal of system control channel output from the system control unit 203 into an optical signal. The fourth wavelength selective coupler 281 couples the amplified data channel optical signal to the control channel optical signal. The operation of the optical amplifier having such a configuration will now be described. Channel control unit 200 separates a control channel wavelength using the first selective wavelength coupler 201 and converts the control channel optical signal to an electrical signal using the optical-electrical converter 202. System control unit 203 extracts information regarding the number of input channels from the current amplifier unit

  of the control channel electrical signal.

  The first optical coupler 210 separates approximately 1% of the optical data channel signal which is passed through the first selective wavelength coupler 201. The first photodiode 211 converts the optical data channel signal into an electrical signal and outputs the electrical signal to the amplification control unit 240. The second optical coupler 260 separates approximately 1% of the optical data channel signal which is amplified by the amplification unit 230 and which is passed through the second isolator 250. Second photodiode 261 converts the separate data channel optical signal into an electrical signal and outputs the electrical signal

  to the 240 amplifier control unit.

  The amplification control unit 240 monitors the power of a data channel optical signal input to the amplification unit 230 from the amplitude of an electrical signal received from the first photodiode 211 and determines whether data channels are added or removed. The gain of the amplification unit 230 is controlled by the results of the control of the amplification power. The amplification control unit 240 informs the system control unit 203 of the amplification state of

amplification unit 230.

  The external control unit 270 is connected to the amplification control unit 240, via an RS-232C cable, and allows a user to control the state of the amplification unit 230 from the outside and to control the amplification characteristics of the amplification unit 230 by adjusting the parameters

of the amplification unit 230.

  In the amplification unit 230, the gain is controlled by the pumping power of the first and second optical pumping sources 232 and 235 which are

  controlled by the amplification control unit 240.

  The amplification unit 230 amplifies an optical data channel signal by the degree of amplification controlled. The amplification is carried out as follows. When pump light, having a central wavelength of 380 nm, from the first and second pump sources 232 and 235 is applied to the erbium-doped fiber 233, the implanted pump light excites the ions erbium of a basic state in the fiber doped with erbium 233, the fiber doped with erbium being an amplification medium doped with a rare earth metal such as erbium. The optical data channel signal is amplified by the stimulated emission of

excited erbium.

  The first and second isolators 220 and 250 improve the gain and noise characteristics of an amplified signal by blocking the spontaneous amplified emission forward and backward generated by the fiber doped with erbium and the beams reflected by an optical device connected to each of the isolators 220

and 250.

  Wavelength coupling unit 280 converts the control channel electrical signal, in which the amplification state data of the amplification unit 230 is contained, into an optical signal using the electrical converter -optics 282, couples the amplified data channel optical signal and the control channel optical signals using the fourth wavelength selective coupler 281 and transmits the resulting signal to the next amplification port or reception port. Figure 3 is a flowchart illustrating a method for constantly controlling the output power per channel of an optical amplifier, according to the present invention. The operation of the present invention will now be described with

reference to figure 3.

  First, the output of each channel of the amplification unit 230 is controlled constantly, the output values of the second photodiode 261 which are a function of the number of input channels are measured by varying the number of channels between the maximum number and the minimum number of channels that the erbium 233-doped fiber is capable of amplifying. The output values of the second photodiode 261 as a function of the number of channels are stored as data in a storage unit (not shown) installed in the amplification control unit 240, in step 300. Alternatively, the power output for each channel is determined as a plurality of values and the output value of the second photodiode 261 to be measured with respect to each of the determined output values is stored as data in the storage unit installed in the the amplifier control unit 240. A user can select a desired output value for each channel from the values stored in the amplifier control unit 240 using the external control unit 270. The control unit external control 270 is connected to the control unit

  240 amplifier via the RS-232 cable.

  The first selective wavelength coupler 201 decouples the optical signal from the control channel

  optical input signals. The optical converter

  electrical 202 converts the decoupled control channel optical signal to an electrical signal and stores the electrical signal in the system control unit 203. The system control unit 203 extracts the number of channels from the optical channel signal

data from a control channel.

  Amplification control unit 240 monitors the power of an input optical signal received from the first photodiode 211, interprets a change in the number of channels and reads the number of extracted channels

  of the system control unit 203.

  The amplification control unit 240 reads a target output value from the second photodiode 261 as a function of the number of channels extracted from the data stored in the system control unit 203, in step 302. The control unit amplifier 240 measures the output power of an optical data channel signal amplified by the amplifier unit 230 by measuring the output value of the second photodiode 261, in step 304. The control unit amplifier 240 compares the target value of the step

  302 to the measured value of step 304, in step 306.

  If the two values are really identical, the information concerning the current amplification unit 230, for example the number of channels, the value of current controlled from an optical pumping source, etc., is output to the system control unit 203 or to the external control unit 270. The system control unit 203 adds the amplification state data of the current amplification unit 230 outputs of the control unit amplifier 240 to the control channel data and outputs the result to the electrical-optical converter 282. The electrical-optical converter 282 converts an electrical control channel signal input from the system controller 203 into a optical signal. The fourth wavelength selective coupler 281 couples the control channel optical signal to the data channel optical signal amplified by the amplification unit 230 and transmits the coupled signal to the next amplification port or

reception, at step 310.

  If the target value of step 302 is really not equal to the measured value of step 304, the amplification control unit 240 really equalizes the two values by controlling the input current of the first and second optical pumping sources 232 and 235 as a function of the difference between the target value and the measured value, in step 308. If the output value for each channel is incorrectly selected by the user or if the number of channels is modified , the output value of a new standard of the second photodiode 261 becomes a target value and the output for each channel is thus maintained. That is, as described above, when the channel output is selected, the gain is controlled by the amplification control unit 240 even when the intensity of an input signal for each channel or the number of channels is changed, so that the output per channel is maintained constantly. In particular, when the number of channels has been modified according to whether the channels are coupled or divided, a transient overshoot of each channel power is suppressed, in this way, the output is maintained by

consistently.

  Figs. 4A and 4B are graphs showing an output for each channel when optical signals from two channels having, respectively, 1542 nm and 1560 nm wavelengths are input to an optical amplifier according to the present invention. Figure 4A refers to the case in

  which the input power for each channel is -

  15 dBm and Figure 4B refers to the case in

  which the input power for each channel is -

  dBm, each showing a constant output of +5 dBm regardless of the intensity of the input. Here, a dotted line indicates an input waveform and a solid line indicates an output waveform. Figures 5A and 5B are graphs showing an output for each channel when optical signals from four channels having, respectively, wavelengths of 1542 nm, 1548 nm, 1554 nm and 1560 nm are input to an optical amplifier according to the present invention. Figure 5A refers to the case where the input power for each channel is -15 dBm and Figure 5B refers to the case in

  which the input power for each channel is -

  dBm, each showing a constant output of +5 dBm independent of the intensity of the input. Here, a dotted line indicates the input waveform and a

  solid line indicates the output waveform.

  According to the present invention, when an optical input signal having a plurality of data channels is amplified, the output power for each channel can be maintained steadily by controlling the degree of amplification of an amplification unit to make the target value of the output value for each channel really identical to an actual measured value. In particular, the output for each channel can be kept constant even when the intensity of an input signal or the number of channels is changed, so that an optical amplifier according to the present invention can be used

  in a channel coupling / division system.

  Also, many additional optical devices are not required and the optical amplifier has a simple structure, so it is easy to apply the optical amplifier to

  a real optical communication system.

  In addition, the output power for each channel is represented as data with respect to the optical signals of a plurality of channels, the output power for each channel can be selected from the data values by a user. Thus, the output power for each channel required, differently depending on the structure of a transmission system, can be selected. Of course, the invention is not limited to the exemplary embodiments described and shown above, from which other modes and other embodiments can be provided, without

  however, depart from the scope of the invention.

Claims (12)

  1. An optical amplifier, the output power of which for each channel is constantly controlled, for amplifying an optical data channel signal when an optical control channel signal and an optical data channel signal comprising a plurality of channels are entered together, the optical amplifier being characterized in that it comprises: a channel control unit (200) for separating the optical control channel signal, for converting the optical control channel signal into an electrical signal, for extracting the number of channels included in the data channel from the converted signal, and for outputting the converted signal; an amplifier unit (230) for amplifying the optical data channel signal using a predetermined control source; an amplification control unit (240) for controlling the input of the control source so that a target output power value of the amplification unit (230) depending on the number of channels is really equal to a measured output power value of the amplification unit (230); and a wavelength coupling unit (280) for converting the output signal of the channel control unit (200) into an optical signal and for coupling the optical signal to the optical channel signal amplified data.   2. Optical amplifier, the output power of which for each channel is constantly controlled according to claim 1, characterized in that   that it further includes an optical converter-   electrical (202) interposed between the channel control unit (200) and the amplification control unit (240) to convert a portion of the optical data channel signal to an electrical signal, so that the unit Amplification Control (240) can interpret a change in the number of channels from the power of the data channel optical signal. 3. An optical amplifier whose output power for each channel is constantly controlled according to claim 1, characterized in that the amplification control unit (240) comprises a storage unit for storing the number of channels and the measured output values of the amplifier unit (230) as a function of the number of channels when the output of the amplifier unit (230) for   each channel is constantly controlled.   4. An optical amplifier whose output power for each channel is constantly controlled according to claim 1, characterized in that the amplification control unit (240) comprises a storage unit for storing the output values of l amplifier unit (230) measured as a function of the number of channels with respect to a determined output for each channel when an output for each channel is determined to be a plurality of values.   5. An optical amplifier whose output power for each channel is controlled constantly according to claim 1, characterized in that the channel control unit (200) adds the amplification state data of the unit d amplification (230), received from the amplification control unit (240), to the control channel data, and outputs the resulting control channel data to the wavelength coupling unit ( 280). 6. An optical amplifier, the output power of which for each channel is constantly controlled according to claim 5, characterized in that the wavelength coupling unit (280) converts the control channel data, in which the amplification state data of the amplification unit (230) is contained, from the control channel unit, into an optical signal, and couples the optical control channel signal to the   amplified data channel optical signal.   7. An optical amplifier whose output power for each channel is constantly controlled according to claim 1, characterized in that the channel control unit (200) comprises: a wavelength selective coupler for decoupling the signal control channel optics of optical input signals; an optical-electrical converter (202) for converting the decoupled control channel optical signal to an electrical signal; and a system controller (203) for extracting information about the number of channels from the electrical signal, for transmitting the information to the boost control unit (240), and for outputting the control channel data to which the amplification state data of   the amplifier unit (230) are contained.   8. An optical amplifier whose output power for each channel is constantly controlled according to claim 1, characterized in that the amplification unit (230) comprises: a control source whose input value is adjusted by the amplification control unit (240); a wavelength selective coupler for coupling the output of the control source to the optical data channel signal; and an erbium-doped optical fiber (233) whose gain is controlled by the output of the control source to amplify the optical data channel signal. 9. An optical amplifier whose output power for each channel is constantly controlled according to claim 8, characterized in that it further comprises: a first isolator (220) interposed between the amplification unit (230) and the channel control unit (200) to prevent an amplified spontaneous emission behind the amplification unit (230) from being reflected by the channel control unit (200) and entering the unit amplification (230); and a second isolator (250) interposed between the amplification unit (230) and the wavelength coupling unit (280) to prevent spontaneous emission amplified in front of the amplification unit ( 230) is reflected by the wavelength coupling unit (280) and enters the unit amplification (230).   10. An optical amplifier whose output power for each channel is constantly controlled according to claim 1, characterized in that the amplification control unit (240) further comprises an external control unit (270) connected to a serial cable, so that a user can select the target output power value to from the outside.   11. A method for constantly controlling the output power for each channel of an optical amplifier, characterized in that it comprises the steps consisting in: (a) measuring the output power of the optical amplifier while modifying the number of channels of a data channel optical signal, and store the number of channels and the output power values as a function of the number of channels, when the power for each channel of the optical amplifier to amplify the optical signal of data channel comprising a plurality of channels is constantly controlled; (b) interpreting a change in the number of channels of the optical data channel signal included in the input optical signal by measuring the power of the optical signal of input data channel, and extracting the number of channels of the optical signal from data channel; (c) setting an output power value of the optical amplifier corresponding to the extracted number of channels, from among the output power values stored in step (a), as a target value; (d) measuring the output power of the input light signal amplified by the optical amplifier; and (e) adjusting the gain of the optical amplifier so that the measured value becomes truly equal to the target value.   12. A method for constantly controlling the output power for each channel of an optical amplifier, characterized in that it comprises the steps consisting in: (a) measuring the output power of the optical amplifier while modifying the number of channels of a data channel optical signal, and storing the number of channels and the output power values as a function of the number of channels, when the power per channel of the optical amplifier is determined to be a plurality of values; (b) interpreting a change in the number of channels of the optical data channel signal included in the input optical signal by measuring the power of the optical signal of input data channel, and extracting the number of channels of the optical signal from data channel; (c) setting an output power value of the optical amplifier corresponding to the extracted number of channels, from among the output power values stored in step (a), as a target value; (d) measuring the output power of the input light signal amplified by the optical amplifier; and (e) adjusting the gain of the optical amplifier, so that the measured value becomes truly equal to the target value.