KR100312375B1 - Wavelength Division Branch Multiplexer - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing multiplexing apparatus of a wavelength division multiplexing (WDM) system, comprising: a preamplifier for amplifying a wavelength division multiplexing (WDM) input optical signal; An optical demultiplexer for demultiplexing the WDM input optical signal amplified from the preamplifier for each channel; A plurality of optical switches receiving the signals output for each channel from the optical demultiplexer and combining and outputting the branched output to the branched channel and the external signal introduced to the combined channel by corresponding control signals; An optical multiplexer for multiplexing and outputting an optical signal output for each channel from the plurality of optical switches; A post amplifier for amplifying the output signal of the optical multiplexer; The channel equalization control means for monitoring the optical signal amplified and output from the post amplifier in real time, and controlling the output strength of the signal output for each channel to maintain a constant optical signal to noise ratio (OSNR) of each channel By reducing the system performance deterioration due to the difference between the received optical output and the OSNR difference between the channel at the conventional receiving end, and the WDM system management and operation by real-time monitoring of the wavelength, optical power intensity, OSNR of each channel There is an effect of facilitating.

Description

Wavelength Division Add-Drop Multiplexer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to apparatus for wavelength division multiplexing in wavelength division multiplexing (WDM) systems.

WDM is an optical communication method that transmits several different optical signals to one optical fiber and is widely used all over the world because of the advantage of maximizing data transmission capacity. In particular, wavelength division branched multiplexing apparatus of the WDM system is one of the important elements in combining and branching optical signal channels for a multiplexed transmission network such as, for example, Synchronous Digital Hierarchy (SDH).

The branch-coupled multiplexing apparatus 10 of the conventional WDM system includes a preamplifier 11, an optical demultiplexer 12, a plurality of optical switches 13-1 to 13-N, as shown in FIG. The optical multiplexer 14 and the post amplifier 15 are comprised.

The preamplifier 11 amplifies and applies the WDM optical signal applied from the optical fiber (0F) to the optical demultiplexer 12. The optical demultiplexer 12 separates the amplified WDM optical signal for each wavelength and applies the optical signal separated for each channel to the 2x2 optical switches 13-1 to 13-n, respectively.

Each 2x2 optical switch (13-1 to 13-N) receives a separate signal provided from each output port of the optical demultiplexer 12 and an optical signal (combined channel) to be combined for each channel from the outside. Perform 2x2 switching for. The 2x2 optical switches 13-1 to 13-N are controlled by a system processor and have two states of "BAR" state and "CROSS" state. For example, in the "BAR" state, the corresponding channel is not branched / coupled, and the separated optical signal from the optical demultiplexer 12 is passed as it is and transmitted to the optical multiplexer 14. In the "CROSS" state, the channel is branched / combined so that the optical signal separated from the optical demultiplexer 12 is outputted by branching (branch channel), and the signal to be newly combined at the node is combined and transmitted to the optical multiplexer 14. do.

The optical multiplexer 14 optically multiplexes each channel after branching / combining from each of the 2x2 optical switches 13-1 to 13-N, and the multiplexed signal is amplified by the post amplifier 15 to form an optical fiber ( OF: Optical Fiber).

In the branch / combining apparatus of the conventional WDM system as shown in FIG. As the process progresses, the difference between the light output intensities increases for each channel of the output stage.

The gain characteristics of the optical amplifiers as described above are not flat according to respective wavelengths, and the optical demultiplexer and the optical multiplexer have different insertion loss for each panel.

In addition, there is a problem that the insertion loss between each optical switch is different, and that the optical signal strength, that is, the level of the optical signal, of the newly combined channel at the corresponding node is different.

In addition, if the optical power intensity difference between the channels increases, each channel has different gains by the in-line amplifiers that pass through the transmission path, and thus, the number of inputs at the receiver of the receiver for each channel may be different. As the difference between the optical power intensity and the optical signal to noise ratio (OSNR) increases, there is a problem that causes a decrease in overall system performance.

The present invention has been made to solve the above problems of the prior art, and in real time by monitoring the output optical signal of the wavelength division branched multiplexing device under the control of the automatic control channel equalizer to maintain a constant OSNR between each channel It is an object of the present invention to provide a wavelength division branched multiplexing device.

The present invention has been made to achieve the above object, a pre-amplifier for amplifying a wavelength division multiplex (WDM) input optical signal; An optical demultiplexer for demultiplexing the WDM input optical signal amplified from the preamplifier for each channel; A plurality of optical switches receiving the signals output for each channel from the optical demultiplexer and combining and outputting external signals flowing into the branched channel and the combined channel by the corresponding control signals; An optical multiplexer for multiplexing and outputting an optical signal output for each channel from the plurality of optical switches; A post amplifier for amplifying the output signal of the optical multiplexer; The channel equalization control means for monitoring the optical signal amplified and output from the post amplifier in real time, and controlling the output strength of the signal output for each channel to maintain a constant optical signal to noise ratio (OSNR) of each channel Characterized in that it is included.

1 is a block diagram of a wavelength division multiplexing apparatus of a conventional wavelength division multiplexing (WDM) system;

2 is a block diagram of a wavelength division branch coupled multiplexing apparatus employing a channel equalizer according to the present invention;

3 is a detailed block diagram of a channel equalizer of the present invention;

4 is a light spectrum distribution diagram obtained through the channel equalizer of the present invention.

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

21: Preamplifier 22: Optical Demultiplexer (ODMUX)

23-1 ~ 23-N: Optical switch 24: Optical multiplexer (OMUX)

25: post amplifier 27: tap coupler

28: channel equalizer 29: light output adjusting unit

29-1 ~ 29-N: Variable Optical Attenuator (VOA) 32: Wavelength Tunable Optical Bandpass Filter

33: photodetector 34: trans impedance circuit

35: A / D converter 36: microprocessor

Hereinafter, exemplary embodiments of a wavelength division branch defect multiplexing apparatus according to the present invention will be described with reference to the accompanying drawings.

2 is a block diagram of a wavelength division branch coupling multiplexing apparatus employing a channel equalizer according to the present invention, and FIG. 3 is a detailed block diagram of the channel equalizer of the present invention. 4 is a light spectrum distribution diagram through the channel equalizer of the present invention.

Referring to FIG. 2, the wavelength division branch multiplexing apparatus 200 according to the present invention includes a preamplifier 21, an optical demultiplexer 22, and a plurality, as can be seen in FIG. Optical switches 23-1 to 23-N, optical multiplexer 24 and post amplifier 25,

As a feedback control means for maintaining the signal output from the post amplifier 25, which is the final output stage, that is, OSNR between channels, the tap coupler 27, the channel equalizer 28, and a plurality of variable optical attenuators ( 29-1 to 29-N (Variable Optical Attenuator (VOA)) includes a light output adjusting unit 29.

The tap coupler 27 taps a portion of the output optical signal of the post amplifier 25 (a small amount that does not affect the transmission) to provide it to the channel equalizer 28.

Each of the variable light attenuators 29-1 to 29 -N of the light output adjusting unit 29 corresponds to each of the optical switches 23-1 to 23 -N according to the control signal C_S of the channel equalizer 28. After adjusting the intensity of the channel signal applied from the signal, the signal is provided to the optical multiplexer 24.

Referring to FIG. 3, the channel equalizer 28 according to the present invention includes a variable wavelength band pass filter 32, a photodetector 33, a transimpedance circuit 34, and an A / D converter 35. ) And microprocessor 36.

The wavelength variable optical band pass filter 32 may variably adjust the pass band, while sweeping a predetermined wavelength band that may be tunably adjusted to measure the optical spectrum of the optical signal applied from the tap coupler 27. The filtered signal is applied to the photodetector 33.

The photodetector 33 converts an input optical signal into an electrical signal, the transimpedance circuit 34 converts a voltage value proportional to a current value of the electrical signal, and the voltage value is the A / D converter. Converted to a digital signal through 35 is provided to the microprocessor 36.

The microprocessor 36 stores variable wavelength information of the wavelength variable optical band pass filter 32, and simultaneously processes the wavelength information and the digital signal from the A / D converter 35, Acquire optical spectrum information of the output optical signal. In addition, the wavelength variable optical band pass filter 32 is controlled according to the acquisition information, and the plurality of variable optical attenuators 29-1 to 29-N are controlled.

Hereinafter, with reference to the accompanying drawings 2 to 4 of the wavelength division branched multiplexing device according to the present invention having the above configuration, the operation and effect according to an embodiment will be described in detail.

Referring to FIG. 2, the WDM input optical signal 20 transmitted through the optical fiber is amplified by the preamplifier 21, and then separated into wavelengths λ1 to λN through the optical demultiplexer 22. do. Here, 1-N is a channel input / output port index. Each channel optical signal separated for each wavelength is applied to the 2x2 optical switches 23-1 to 23-N.

Each 2x2 optical switch 23-1 to 23-N receives a separate signal applied from each output port of the optical demultiplexer 22 and a corresponding optical signal (combined channel) to be combined for each channel. Branch or combine signals by 2x2 switching.

At this time, each 2x2 optical switch 23-1 to 23-N is controlled by the system processor and has two states of "BAR" state and "CROSS" state. For example, the branch / combination of the corresponding channel is not performed in the “BAR” state, and the separated optical signal from the optical demultiplexer 22 is passed through to each of the variable optical attenuators 29-1 to 29-N. Is sent.

In the " CROSS " state, the corresponding channel is branched / combined so that the optical signal separated from the optical demultiplexer 22 is branched and outputted as a branched optical signal (branch channel). The signals are combined and transmitted to each of the variable optical attenuators 29-1 to 29-N.

Each of the variable optical attenuators 29-1 to 29-N is controlled by the microprocessor 36 (see Fig. 3) based on the information of the output optical signal 26 processed by the channel equalizer 28. do. That is, the optical output intensity of each channel of the optical switches 23-1 to 23-N is determined by the user or design in each of the variable optical attenuators 29-1 to 29-N according to the control signal of the microprocessor 36. It is adjusted to correspond to the predetermined level set by the.

The optical multiplexer 24 optically multiplexes each channel signal output from the variable optical attenuators 29-1 to 29 -N, and the multiplexed signal is amplified by the post amplifier 25. .

A small amount of the optical signal 26 output from the post amplifier 25, that is, a portion of the signal T_S is tapped by the tap coupler 27 to be provided to the channel equalizer 28, and the remaining signal is It is transmitted through the optical fiber (OF).

Referring to FIG. 3, the channel equalizing unit 28 is described. The optical signal T_S tapped by the tap coupler 27 is applied to the wavelength variable optical band pass filter 32.

The wavelength variable optical band pass filter 32 filters a signal having a corresponding wavelength among the input optical signals T_S while repeatedly sweeping the wavelength band according to a predetermined period under the control of the microprocessor 36. To print.

The sweeped filtered optical signal is converted into an electrical signal via the photodetector 33, the transimpedance circuit 34, and the A / D converter 35, and has an analog form proportional to the optical output intensity. It is converted into a voltage value and then converted into a digital signal and provided to the microprocessor 36.

The microprocessor 36 processes the signal using the signal provided from the A / D converter 35. That is, the microprocessor 36 controls the center wavelength of the wavelength variable optical band pass filter 32 to sweep a predetermined band from the shortest wavelength to the longest wavelength among the wavelengths used in the system.

At this time, the microprocessor 36 stores specific center wavelengths of the swept wavelength-variable optical bandpass filter 32 in a memory (not shown). In addition, the microprocessor 36 obtains optical spectrum information of the corresponding output optical signal 26 (see FIG. 2) by matching the signal output from the A / D converter 35 with the stored signal, and also performs sweeping. The obtained spectral information is updated while performing repeatedly.

4 is an optical spectrum distribution diagram obtained through the channel equalization process by the channel equalizer 28 of FIG. 2, and shows the light output intensity for the wavelength of each channel. Reference numeral 40 is a noise level for Amplified Spontaneous Emission (ASE).

Referring to FIG. 4, the deviation of the center wavelength of each channel λ1 to λ5 can be monitored, and the corresponding light output is monitored for each channel 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, in the case of channel 1, the center wavelength is 1549.3 nm. However, the actual measured wavelength is 1549.2 nm. This means that the transition from the center to the short wavelength by 0.1 nm also means that the vertex value of channel 1 (λ1) is 5 dBm (this value maps the output value of the A / D converter 35 to dBm, the light output unit). In this case, the optical output of the first channel (λ1) is 5dBm. At this time, the corresponding optical output level at 1550.1 nm, which is a wavelength between the wavelength of the first channel λ1 (1549.3 nm) and the second channel λ2 (1550.9 nm), is the noise of the first channel λ1. Since this value is approximated to level N1, if this value is -15dBm, 0SNR for channel 1 becomes 20dB. OSNR can be calculated in the same manner as the above in the remaining 2 to 5 channels (λ2 to λ5).

By the optical spectrum analysis as shown in FIG. 4, the microprocessor 36 (refer to FIG. 3) is characterized in that the wavelength of each channel deviates from the center wavelength, the light output intensity of each channel, and the intermediate by each channel. The OSNR of each channel is calculated by measuring the light output intensity at the wavelength and estimating the noise level of each channel from the information thus obtained. The microprocessor 36 controls the degree of light attenuation of each of the variable optical attenuators 29-1 to 23 -N by comparing the OSNR of each channel so that all channels have the same OSNR.

As described above, the present invention measures the OSNR of each channel by optical spectrum analysis by real-time monitoring the output optical signal of the wavelength division branch coupled multiplexing device, and the OSNR between the channels by automatic control is constant using this information. There is an effect that can be maintained.

In addition, the present invention has the effect of reducing the system performance degradation due to the difference in the received optical output between the channel and the OSNR difference in the conventional receiver.

In addition, since the wavelength, light output strength, OSNR of each channel can be monitored in real time, the WDM system can be easily managed and operated.

Claims (4)

A preamplifier for amplifying a wavelength division multiplex (WDM) input optical signal; An optical demultiplexer for demultiplexing the WDM input optical signal amplified from the preamplifier for each channel; A plurality of optical switches receiving the signals output for each channel from the optical demultiplexer and combining and outputting the branched output to the branched channel and the external signal introduced to the combined channel by corresponding control signals; An optical multiplexer for multiplexing and outputting an optical signal output for each channel from the plurality of optical switches; A post amplifier for amplifying the output signal of the optical multiplexer; The channel equalization control means for monitoring the optical signal amplified and output from the post amplifier in real time, and controlling the output strength of the signal output for each channel to maintain a constant optical signal to noise ratio (OSNR) of each channel Wavelength division branch coupling multiplexing apparatus, characterized in that the configuration is included. 2. The apparatus of claim 1, wherein the channel equalization control means comprises: a tap coupler for tapping a portion of an optical signal output from the post amplifier; A channel equalizer which outputs a corresponding signal controlling the intensity of the optical signal branched / combined for each channel by an optical spectrum analyzed by processing the optical signal tapped from the tap coupler; And a plurality of variable optical attenuators configured to control the optical signal intensity output from the optical switch for each channel according to the control signal of the channel equalizer to a predetermined level and output the optical signal to the optical multiplexer. Combined Multiplexing Device. 3. The apparatus of claim 2, wherein the channel equalizer comprises: a wavelength variable optical band pass filter configured to receive an optical signal output from the tap coupler and filter the optical signal for each channel by filtering a band having a predetermined wavelength; An optical detector that receives an optical signal filtered by the channel from the wavelength variable optical band pass filter and outputs the converted optical signal; A transimpedance circuit for converting a current value of a signal output from the photodetector into a corresponding voltage value and outputting the converted voltage value; An A / D converter converting the voltage value output from the transimpedance circuit into a digital signal and outputting the digital signal; A wavelength division branch combining multiplexing comprising a microprocessor for processing the digital signal output from the A / D converter to analyze the intensity of the optical signal for each channel and outputting the control signal of the variable optical attenuator. Device. 4. The microprocessor of claim 3, wherein the microprocessor controls the center wavelength of the wavelength tunable optical bandpass filter to be swept to a predetermined band, records the corresponding center wavelength of the sweep, and records the recorded center wavelength and the A / D converter. And spectral information of the channel is obtained by comparing the digital signals input from the digital signal, and the wavelength information, light output, and noise of the channel are measured from the spectrum information.