KR100317809B1 - Apparatus for rejecting wime delay of gain-control channel of optical amplifier in Wavelength Division Multiplexed("WDM") networks - Google Patents

Abstract

The present invention provides a branch coupler for branching and outputting a plurality of information optical signals according to a set ratio in an optical amplifier of a wavelength division multiple network, and information which is currently being transmitted to the optical amplifier by detecting a part of the optical signal branched from the branch coupler. A control circuit for measuring an amount of change of the optical signal and outputting a compensation control optical signal according to the measured result, and a coupling coupler for coupling the compensation control optical signal output from the control circuit with the information optical signal transmitted to the optical amplifier; The present invention provides a device for removing time delay of a gain control channel of an optical amplifier in a wavelength division multiple network, which is connected between the branch coupler and the coupling coupler and delays an information optical signal transmitted to an optical amplifier for a predetermined time.

As described above, the present invention provides an optical fiber delay line and an optical branch / detector circuit in front of the optical amplifier of the WDM network to maintain the gain of the optical amplifier at the time of optical branch and optical coupling, thereby being transmitted by the optical fiber delay line. Since the electronic response speed of the control circuit is slower than the information light signal, the influence is minimized by the mutual gain modulation that is generated.

Description

Apparatus for rejecting wime delay of gain-control channel of optical amplifier in Wavelength Division Multiplexed ("WDM") networks}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing (WDM) communication network, and more particularly, to an apparatus for removing time delay of a gain control channel of an optical amplifier for removing cross gain modulation in channel branching / combining. It is about.

WDM networks are widely commercialized worldwide due to the advantages of maximizing data transmission capacity. The WDM network is an optical communication method that transmits optical signals of different colors through one optical fiber. WDM network includes optical multiplexer / demultiplexer and optical fiber amplifier. The line used here is an optical fiber. The optical multiplexing device is a transmitting device, and the demultiplexing device is a receiving device. The optical multiplexer does not multiplex an electrical signal, but multiplexes an optical signal from a laser diode (hereinafter, referred to as a channel) that emits different colors, and transmits the optical signal to a long-distance destination through an optical fiber. The received optical signals are separated into respective channels (i.e., their respective colors) through an optical filter. This is called a global multiplexing device. The optical fiber amplifier compensates for the losses incurred as optical signals are transmitted through the fiber. The amplifier amplifies several optical signals of different colors at the same time. For example, in a WDM network transmitting more than 600 km, about 8 units can be used in series.

The optical amplifier, like the electric amplifier, begins to decrease in inverse proportion to the input as the gain of the amplifier increases to some extent. This phenomenon is called gain saturation, and the input strength that starts saturation is called saturation input.

In a typical WDM network, the input to the amplifier is above the saturation input. That is, it operates in the region where the gain of the amplifier changes according to the change of the input. For this reason, the following phenomenon occurs.

When the input is A [dBm], the gain of the optical amplifier is Ga [dB]. When the input is reduced and B [dBm] (A> B), the gain of the optical amplifier is Gb [dB]. Because the amplifier operates in saturation, the gain of the amplifier is inversely proportional to the input. That is, Ga <Gb. It is easy to see how this phenomenon has a fatal effect on the WDM network. For example, consider the case where the optical signal Sega of each channel is C [dBm] and all 8 channels of signals enter the optical amplifier at the same time. In this case, the total input of the optical amplifier is C + 10 * log (8) = (C + 9) [dBm]. In this case, let the gain of the amplifier be Gc (the gain of each channel is also Gc). By accident, however, the gain of four channels will also increase. This means that one channel affects another channel that is irrelevant to itself. In WDM networks, this effect is called cross gain modulation, which generally has a bad effect on communication.

The mutual gain modulation phenomenon will be described with reference to FIG. In FIG. 1, the optical signals transmitted from the two channels are combined through the coupler 10 and transmitted to eight serially connected optical amplifiers OP # 1 to OP # 8. At this time, it is assumed that the first channel Ch1 is maintained (reference a), and the second channel Ch2 disappears from the WDM network at some point (ckawhb). Then, the output of the last eighth optical amplifier OP # 8 of the first channel Ch1 shows a large gain characteristic during the moment when the second channel disappears (see c). The output of the last eighth optical amplifier OP # 8 of the third channel Ch2 shows a transient gain characteristic for a while after the second channel disappears (see d). FIG. 2 is a variation diagram of the light output intensity of the surviving channel of the optical amplifier of FIG. 1 and shows that the gain characteristics are relatively large during the survival period 1 to 3 [㎳].

The conventional method for preventing the mutual gain modulation phenomenon as shown in FIG. 2 is to make the intensity of the signal input to the optical amplifier constant as shown in FIG. 3. For example, if four channels are lost in a WDM network, an additional optical signal corresponding to four channels is added to the optical amplifier. In this way, the input of one optical amplifier is always constant, and the gain of the optical amplifier is always constant, resulting in no influence on the channel where the lost channel remains. This method is called a control laser or control channel method.

3 is a block diagram of a control device for removing mutual gain modulation in a conventional WDM network, and includes two couplers C1 and C2, a control circuit 33, and an optical amplifier 35. The first coupler C1 combines two optical signals coming in the image table direction, and the second coupler C2 branches the input optical signal into two empty signals in the image table direction. At this time, the amount of separation can be adjusted. The control circuit 33 includes an optical detector PD for detecting the output of the second coupler C2 and an electronic circuit for generating a control signal for compensating for the change intensity of the optical signal according to the detection signal of the optical detector PD. And a laser diode LD driven according to the control signal and outputting a compensation control light signal. The optical amplifier 35 receives the compensation control optical signal 31 and the original signal 30 from the LD of the control circuit 33 and inputs them.

Referring to the operation of Figure 3 with time, it is assumed that when the time t = t0, the optical signal intensity input to the optical amplifier 35 is reduced. Then, a part of the optical signal is detected by the PD at t = t1 (t1> t0), thereby being known to the control circuit 33. The control circuit 33 drives the LD to output a compensation control light signal corresponding to the change in the intensity of the optical signal (t = t2). The compensation control optical signal 31 is combined with the original optical signal at the first coupler C1 and input to the optical amplifier 35. Of course, the distance between C1 and C2 is close to within 1m. On the other hand, for example, when a channel is added to the original signal, the intensity of the LD control optical signal becomes small, thereby making the input of the optical amplifier 35 constant.

In this manner, conventionally, the input of the optical amplifier is made constant. That is, conventionally, when a change in the intensity of the optical signal entering the optical amplifier occurs, the change is detected by the electric circuit, and then the LD is driven by the electronic circuit to generate a compensation control light signal. Originally, it consists of adding an optical signal and inputting it to an optical amplifier. Here, the electronic circuit must operate at a very high speed to completely compensate for the change in the reduced optical signal strength. This is because the electronic circuit operates relatively slowly compared to the speed of the optical signal. As shown in FIG. 3, the optical signal input to the optical amplifier 35 at t = t2 may not be completely compensated for, because the control circuit may go crazy to control the time domain. It is natural that the larger the time domain, the lower the performance of the WDM network.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and for the optical amplifier gain control of the WDM network, the delay of the time that the optical signal enters the optical amplifier by using the optical fiber delay line, thereby slowing down the electronic circuit driving the gain control channel. It is an object of the present invention to provide a time delay cancellation device of a gain control channel which minimizes the effect of response speed.

In order to achieve the above object, the present invention provides a branch coupler for branching and outputting a plurality of information optical signals according to a set ratio in an optical amplifier of a wavelength division multiple network, and detecting a part of an optical signal branched from the branch coupler. A control circuit for measuring the amount of change in the information optical signal currently being transmitted to the optical amplifier and outputting a compensation control optical signal according to the measured result, and an information light transmitted to the optical amplifier with the compensation control optical signal output from the control circuit. The time of the gain control channel of an optical amplifier in a wavelength division multiple network comprising a coupling coupler coupled to a signal and an optical fiber delay line connected between the branch coupler and the coupled coupler to delay a time of an information optical signal transmitted to an optical amplifier. Provide a delay elimination device.

1 is a view for explaining the mutual gain modulation phenomenon in the channel split / add (drop / drop) in the WDM network,

2 is a view illustrating a change in light output intensity of a survival channel of the optical amplifier of FIG. 1;

3 is a block diagram of a control device for removing mutual gain modulation in a conventional WDM network;

4 is a block diagram of a device for removing time delay of a gain control channel of an optical amplifier in a WDM network according to the present invention;

5 is a view illustrating a change in light intensity of a channel by the conventional removing device of FIG.

6 is a view illustrating a change in light intensity of a channel by the removal device of FIG. 4.

<Detailed Description of Codes>

400: optical amplifier C1, C2: optocoupler

430: control circuit PD1, PD2: optical detector

LD: AZr diode 450: fiber optic delay line

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

4 is a block diagram of an apparatus for removing mutual gain modulation in a WDM network according to the present invention. The apparatus includes an optical amplifier 400, a branch coupler C1, a control circuit 430, a coupling coupler C2, an optical fiber delay line 450 forming an information channel between the branch coupler C1 and the coupling coupler C2. ). The control circuit 430 includes a photo detector PD1 for detecting a change in the intensity of the optical signal, a laser diode LD for outputting a signal for compensating the change amount, and an electronic circuit for driving the LD.

The branch coupler C1 branches the information optical signal 41 inputted through the optical path 40 into an information signal for amplification and a control signal for measuring signal strength according to a specific ratio. The information signal is transmitted through the optical fiber delay line 450, and the control signal is applied to the photodetector PD1 of the control circuit 430 through the first intensity channel.

When the amount of change in the information light signal 41 is detected by measuring the control signal strength of the first control channel by PD1, the control circuit 430 drives the LD to provide a compensation control light signal for compensating for the amount of change. Output to coupling coupler (C2) through the control channel.

The coupling coupler C2 combines the information optical signal 41 transmitted through the optical fiber delay line 450 and the compensation control optical signal 42 of the second control channel to provide the optical amplifier 400.

The optical fiber delay line 450 is appropriately determined to have a sufficient delay time according to the response speed of the control circuit.

In a more preferred embodiment of the invention, the coupling coupler C2 employs two inputs: two outputs, and the control circuit 430 is a photodetector PD2 for measuring the output signal of the coupling coupler C2. It further includes. At this time, the PD2 configures the LD and the negative feedback circuit so that the light emission intensity of the LD can be feedback-controlled, thereby outputting a more precise compensation control light signal.

Hereinafter, the operation of this embodiment will be described in detail with reference to FIGS. 4 to 5.

Referring to FIG. 4, it is assumed that a change occurs in the intensity of a signal input to the optical amplifier 400 at t = t0. This change can occur when some channels fail in the WDM network or when operators remove some channels for some reason. The change in the input light intensity is detected through the PD1 of the control circuit 430, and the LD is driven by the electronic circuit to compensate for the lost light intensity by comparing the detected signal of the PD1 with a predetermined reference signal. Since this process is performed through the electronic circuit, some time is required for the PD1 to detect the amount of change in the optical signal intensity and output the actual compensation signal from the LD. Therefore, the incomplete signal which is in a state where the shortage of the optical signal is not filled is not input to the optical amplifier 400.

When the LD generates an actual compensation signal at t = t2, the WDM optical signal and the compensation control optical signal are combined by the coupling coupler CS and input to the optical amplifier 400. As a result, no change in the overall input light intensity of the optical amplifier 400 is detected, and there is no change in the gain of the optical amplifier. Here, the method of driving the LD by the PD1 may increase the accuracy by driving the LD by the negative feedback method.

5 is a light intensity variation diagram of the channel by the conventional control apparatus of FIG. 3, and FIG. 6 is a light intensity variation diagram of the channel by the control apparatus according to the present invention of FIG. 5 and 6 assume a two-channel WDM system, through which the performance of the present invention can be confirmed.

The construction conditions of the prior art and the present invention are set equally as follows. The control circuit is composed of mixed analog and digital circuits. The response speed of the analog circuit is 100 ms, and the delay time of the digital circuit is 70 ms. Eight optical amplifiers are connected in series. The input light intensity of each channel input to the optical amplifier is 50 Hz. Here, the optical signal strength of the remaining channel when one channel is lost and then restored again, for example, when two channels are present at the same time and one channel is removed at 1 ㎳ of the optical beam and then restored at 3 ㎳ again The change is compared through FIGS. 5 and 6.

Referring to FIG. 5, the maximum and minimum values of the light intensity of the first output (a), the third output (b), the fifth output (c), and the eighth output (d) of the remaining channel can be known. The difference between 8th output is 6㏈. This change is caused by another channel, and also due to the total response speed of the control circuit is 170 Hz.

On the other hand, referring to Figure 6, the maximum and minimum values of the light intensity of the first output (a), the third (b), the fifth output (c), the eighth output (d) of the remaining channel can be seen, The eighth output is 1.9kV. The optical fiber delay line length at this time was about 10 km.

As shown in the result of Fig. 6, when there is a change in the intensity of the input light entering the optical amplifier, the remaining channel is used by using an optical fiber delay line having a sufficient length to compensate for the electronic response speed of the control circuit driving the control channel. To compensate for the change in light intensity.

As described above, according to the present invention, an optical fiber delay line and an optical branch / detector circuit are installed in front of an optical amplifier of a WDM network to maintain a constant gain of the optical amplifier during optical branching and optical coupling. Since the electronic response speed of the control circuit is slower than the transmitted information light signal, there is an effect of minimizing the influence by the mutual gain modulation generated.

Claims (3)

In the optical amplifier of the wavelength division multiple network for amplifying an information optical signal, A branch coupler for branching and outputting the information light signal in plural numbers according to a set ratio; and detecting a part of the optical signal branched from the branch coupler to measure an amount of change of the information light signal currently being transmitted to the optical amplifier and measuring the result A control circuit for outputting a compensation control optical signal, a coupling coupler for coupling the compensation control optical signal output from the control circuit with an information optical signal transmitted to an optical amplifier, and coupled between the branch coupler and the coupling coupler. An apparatus for removing time delay of a gain control channel of an optical amplifier in a wavelength division multiple network, comprising: an optical fiber delay line for delaying an information optical signal transmitted to an amplifier for a predetermined time. The method of claim 1, wherein the control circuit is a first photodetector for detecting a change in the intensity of the optical signal by detecting the optical signal branched by the branch coupler, and the amount of change in the optical signal intensity detected by the first photodetector A laser diode for generating a compensation control optical signal according to the present invention, a second photo detector for detecting and measuring the intensity of the optical signal output from the coupling coupler, and a function of the first and second photo detectors. An apparatus for removing time delay of a gain control channel of an optical amplifier in a wavelength division multiple network, comprising: an electronic circuit for controlling generation of an optical signal. 3. The apparatus of claim 2, wherein the laser diode and the second photodetector comprise a negative feedback circuit.