KR20000034635A - Apparatus for monitoring channel of wavelength division multiplexing (wdm) system - Google Patents

Abstract

PURPOSE: An apparatus for monitoring channel of a wavelength division multiplexing (WDM) system is provided so that a management and operation of WDM system become easy by monitoring a wavelength, an output of light, and an optical signal to noise ratio (OSNR) at real time. CONSTITUTION: An apparatus for monitoring channel of a wavelength division multiplexing(WDM) system includes a measuring device, which measures an intensity of outputted light corresponding to the central wavelength of a tapping channel signal by using a wavelength variable light band pass filter(23) at a plurality of channel monitoring points positioned to the input and output terminal of the plurality of light amplifier. A microprocessor(27) processes the measured output light intensity signal as a digital signal and obtains information on a light spectrum of the corresponding light signal, simultaneously, controls the wavelength variable band pass filter(23) for making the wavelength band vary.

Description

Channel Monitoring apparatus for Wavelength Division Multiplexing ("WDM") system

The present invention relates to a channel monitoring apparatus for monitoring each channel of a multiplexed optical signal of a wavelength division multiplexing (WDM) system.

In a typical WDM system, a tone frequency is used as a method for monitoring a channel, which is complicated to implement a circuit for generating a tone frequency and a circuit for monitoring each channel. In addition, since the tone frequency should be a sufficient distance between the channels, there is a problem of limiting the channel capacity because it limits the number of channels in the WDM system.

In order to solve this problem, an apparatus for monitoring a channel using an arrayed wave-guide grating (AWG) is disclosed in Korean Patent Application No. 97-79470 filed by the inventor and filed December 30, 1997. The channel monitoring device supported by the specification of this patent application is a channel monitoring point between a plurality of amplifiers (post amplifiers, inline amplifiers, and preamplifiers) for compensating optical signal attenuation on the optical path between the optical multiplexer and the optical demultiplexer. Selectively switches the optical signal tapped by the tap coupler to the polymer optical switch, detects each wavelength by using the AWG module, converts it into a voltage value in a transimpedance circuit, and converts the signal selected through the channel multiplexer into an analog signal. Under the control of the switch, gain control and digital signals are converted by the op amp and A / D converter according to the corresponding channel monitoring point, and each channel is sequentially monitored by the microprocessor. This channel monitoring system calculates the OSNR (Optical Signal to Noise Ratio) by measuring the noise level of each optical amplifier by using AWG module that doubles the number of channels used in the WDM system and the wavelength interval is half. Monitor each channel.

However, since the apparatus uses an AWG module and a photodetector fixed at a specific wavelength to separate each wavelength to monitor each channel, only the optical power of the optical signal of each channel can be measured. In addition, in the case where the wavelength of each channel is shifted, the power of each channel becomes inaccurate, and the wavelength of each channel cannot be monitored. In addition, since each photodetector and transimpedance circuit is required for each channel, the hardware volume of the device is increased, the configuration is complicated, and the size of the device is considerably limited.

Accordingly, the present invention has been made to solve the above problems, the optical signal of each channel tapped at the channel monitoring point located at the input and output terminals of the plurality of optical amplifiers by using a variable wavelength optical bandpass filter for each channel The purpose of the present invention is to provide a channel monitoring apparatus of a WDM system for real-time monitoring of wavelength, optical power and OSNR of a corresponding channel by acquiring optical spectrum information.

The present invention for achieving the above object, in the WDM system including a plurality of optical amplifiers for compensating for the loss of the wavelength division multiplexing (WDM) optical signal on the transmission path, Means for measuring the output light intensity of the corresponding center wavelength by using the wavelength-varying optical band pass filter on the channel signals tapped at the two channel monitoring points; And microprocessor means for digitally processing the measured output light intensity signal to obtain optical spectrum information of the corresponding optical signal and controlling the wavelength variable optical band pass filter to vary the wavelength band. It is done.

1 is an overall configuration diagram of a WDM system according to an embodiment of the present invention;

2 is a detailed block diagram of a channel monitoring apparatus of the WDM system of FIG. 1;

3 is a light spectrum distribution diagram monitored by the channel monitoring apparatus of FIG. 1.

<Explanation of symbols for the main parts of the drawings>

20: channel monitoring device 21-1 to 21-n: tap coupler

22: polymer optical switch 23: wavelength variable optical bandpass filter

24: photodetector 25: transimpedance circuit

26: A / D converter 27: Microprocessor

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

1 is an overall configuration diagram of a WDM system according to an embodiment of the present invention, Figure 2 is a detailed block diagram of a channel monitoring apparatus of the WDM system of FIG.

Referring to FIG. 1, a WDM system includes a plurality of laser diodes (LD) 11-1 to 11 -N, an optical multiplexer (OMUX, 12), a post optical amplifier 13, and a plurality of inline optical amplifiers 14-1. 14-N), the pre-optical amplifier 15, the optical demultiplexer (ODMUX) 16, and the channel monitoring device 20.

The plurality of laser diodes 11-1 to 11-N generate an optical signal (channel) of each wavelength (λ1 to λN) used in the WDM system and apply it to the optical multiplexer 12. The optical multiplexer 12 applies the WDM optical signal obtained by optically multiplexing the optical signals to the post optical amplifier 13. The post optical amplifier 13 amplifies and transmits the WDM optical signal through a transmission path to compensate for the power damaged by the optical multiplexer 12.

The plurality of in-line optical amplifiers 14-1 to 14-N amplify the WDM optical signal and transmit the amplified WDM optical signal to the pre-optical amplifier 15 on the receiving side in order to compensate for the optical loss generated in each relay section on the transmission path.

The pre-optical amplifier 15 amplifies the received WDM optical signal and applies it to the optical demultiplexer 16. The optical demultiplexer 16 demultiplexes the amplified WDM optical signal for each wavelength (λ1 to λN) and is supplied to a lower dependent system (not shown).

The channel monitoring apparatus 20 includes a tap coupler TC at a channel monitoring point located at an input / output terminal of the post optical amplifier 13, the plurality of inline amplifiers 14-1 to 14 -N, and the pre optical amplifier 15. 21-1 ~ 21-n) processes the optical signal of each channel tapped and monitors in real time.

As shown in FIG. 2, the channel monitoring apparatus 20 includes a plurality of tap couplers 21-1 to 21-n, an nx1 polymer optical switch 22, a wavelength variable optical band pass filter 23, and a photodetector ( 24), transimpedance circuit 25, A / D converter 26 and microprocessor 27.

A plurality of tap couplers 21-1 to 21-n tap WDM optical signals at a predetermined percentage (a small amount that does not affect transmission) at each channel monitoring point, and a polymer optical switch 22 is configured to tap the plurality of tap couplers 21-1 to 21-n. Any one of the tapped optical signals from the tap coupler is selected and applied to the wavelength variable optical band pass filter 23.

The wavelength tunable optical band pass filter 23 can variably adjust the pass band, and repeatedly sweeps a predetermined wavelength band in order to measure the optical spectrum of each channel while constant wavelength of the optical signal selected from the optical switch 22. Filter by band and apply to the photodetector (24). The photodetector 24 converts the filtered optical signal into an electrical signal.

The transimpedance circuit 25 converts the voltage value in proportion to the current value of the electrical signal, and the A / D converter 26 converts the voltage value into a digital signal and provides it to the microprocessor.

The microprocessor 27 stores the variable wavelength information of the wavelength variable optical band pass filter 21 and simultaneously processes the wavelength information and the digital signal from the A / D converter 26 to monitor the corresponding channel. Obtain spectral information of the optical signal at the point. In addition, the polymer optical switch 22 is controlled to obtain a channel monitoring point, and the wavelength variable optical band pass filter 23 is controlled to change the wavelength band.

Hereinafter, the operation and effect of the present invention will be described with reference to FIGS.

Referring to FIG. 2, the optical signal tapped by the plurality of tap couplers 21 ˜ 1-21-n is applied to the polymer optical switch 22, and the polymer optical switch 22 is controlled by the microprocessor 27. In accordance with this, or sequentially switching the output of the desired tap coupler is applied to the wavelength variable optical band pass filter (23). The wavelength variable optical band pass filter 23 filters the input optical signal while repeatedly sweeping a predetermined wavelength band under the control of the microprocessor 27. The filtered optical signal is converted into an electrical signal via the photodetector 24, the trans impedance circuit 25, and the A / D converter 26, and then converted into an analog voltage value proportional to the optical output intensity. It is converted into a digital signal and provided to the microprocessor 27.

The microprocessor 27 processes the signal using the signal provided from the A / D converter 26. That is, the microprocessor 27 controls the center wavelength of the wavelength variable optical band pass filter 23 to sweep a predetermined band from the shortest wavelength side of the wavelength used in the system to the long wavelength side. At this time, the microprocessor 27 stores specific center wavelengths of the swept wavelength-variable optical bandpass filter 27 in a memory (not shown). Further, the microprocessor 27 matches the signal provided from the A / D converter 26 with the stored central wavelength information to obtain optical spectrum information at the corresponding channel monitoring point. Further, the spectral information obtained while repeatedly performing sweeping is updated.

FIG. 3 is a light spectrum distribution chart monitored by the channel monitoring apparatus of FIG. 1, showing light output intensity for wavelengths of each channel. FIG. 30 is the noise level for Amplified Spontaneous Emission (ASE).

Referring to FIG. 3, the deviation of the center wavelength of each channel λ ₁ to λ ₅ can be monitored, and the optical output of each channel is monitored by measuring the vertices S1 to S5 in the spectrum of each channel. can do. In addition, the OSNR of each channel can be monitored by measuring the ASE noise levels N1 to N4 of the optical amplifiers for each channel and calculating them with the optical output of each channel.

For example, for channel 1 λ ₁ , the original center wavelength is 1549.3 nm. However, the actual measured wavelength is 1549.2 nm. This means that it has shifted towards the shorter wavelength by 0.1 nm from the original center. In addition, if the vertex value of channel 1 (λ ₁ ) is 5 μm (this value is the value mapped to the output value of A / D converter 26 to μm, which is an optical output unit), then channel ₁ (λ _1). ), The light output is 5㏈m. In this case, channel # 1 (λ ₁₎ the wavelength (1549.3㎚) and channel 2 (λ ₂₎ the light output level of a wavelength in 1550.1㎚ the middle of the wavelength (1550.9㎚) of the channel is time 1 (λ ₁ Since the value is -15 dBm, the OSNR is 20 dB for channel 1. The OSNR can be calculated in the same manner as the above in the remaining 2 to N-1 channels (λ ₂ to λ _N-1 ).

By the optical spectrum analysis as shown in Fig. 3, the microprocessor 27 (see Fig. 2) is characterized in that the wavelength of each channel deviates from the center wavelength, the light output intensity of each channel, and the light at the intermediate wavelength between each channel. OSNR of each channel is calculated by measuring the output strength and estimating the noise level of each channel from the obtained information.

As described above, the WDM system using the channel monitoring apparatus of the present invention can monitor the wavelength, the light output strength, and the OSNR of each channel in real time, thereby facilitating the management and operation of the WDM system. In addition, the output of the preamplifier of the receiving end transmits OSNR information for each channel to the transmitting end through DCC (Data Communication Channels), so that the optical power can be adjusted for the corresponding channel using a variable optical attenuator for each channel, thus preemphasis of the WDM system. (pre-emphasis) can be controlled in real time.

Claims (5)

A WDM system including a plurality of optical amplifiers for compensating for loss of wavelength division multiplexing (WDM) optical signals on a transmission path, Means for measuring an output light intensity of a corresponding center wavelength of the channel signal tapped at the plurality of channel monitoring points located at the input / output ends of the plurality of optical amplifiers using a wavelength variable optical band pass filter; And And digital processor processing the measured output light intensity signal to obtain optical spectrum information of the corresponding optical signal and controlling the wavelength variable optical band pass filter to vary the wavelength band. Channel monitoring device of the WDM system. The method of claim 1, wherein the measuring means A plurality of tap couplers tapping the WDM optical signal by a predetermined percentage at each channel monitoring point; An optical switch for selecting one of the optical signals of the plurality of tap couplers; A wavelength tunable optical bandpass filter for filtering the selected tapped optical signal into a predetermined wavelength band while repeatedly sweeping a predetermined wavelength band under the control of the microprocessor means; A photo detector converting the filtered optical signal into an electrical signal; A transimpedance circuit for converting a voltage value proportional to a current value of the electrical signal; And an A / D converter converting the voltage value into a digital signal and providing the converted voltage to the microprocessor means. The channel monitoring apparatus of claim 2, wherein the optical switch selects a specific channel monitoring point under the control of the microprocessor means. The channel monitoring apparatus of claim 2, wherein the optical switch sequentially switches a plurality of channel monitoring points. The method of claim 1, wherein the microprocessor means, Control the center wavelength of the wavelength variable optical band pass filter to be swept to a predetermined band, store a specific center wavelength at the time of sweeping, match the stored value with the signal value applied from the measuring means, and then output the corresponding channel monitoring light signal. Obtaining spectral information for, and measuring the wavelength information, light output and noise of each channel from the spectral information, the channel monitoring apparatus of the WDM system.