KR100553572B1 - Apparatus for monitoring multi channel optical signal quality in wavelength division multiplexing system - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing system (WDM). In particular, the present invention relates to a wavelength division multiplexing system that monitors the performance of a multi-channel optical signal using a Mach-Zehnder optical interferometer. A multi-channel optical signal performance monitoring apparatus.

To this end, the present invention, by using a narrow bandwidth of the demultiplexing element such as a tunable filter or an arrayed waveguide diffraction grating (AWG) to extract the optical signal of a certain wavelength, and two outputs of the Mach-Zehnder interferometer It is configured to measure the performance of the optical signal, i.

Accordingly, the present invention has the effect of measuring the performance of the optical signal stably and reliably by implementing a simple circuit of low cost.

Description

Multi-channel optical signal performance monitoring device in wavelength division multiplexing system {APPARATUS FOR MONITORING MULTI CHANNEL OPTICAL SIGNAL QUALITY IN WAVELENGTH DIVISION MULTIPLEXING SYSTEM}

1 is a block diagram of a single channel optical signal monitoring apparatus using a Mach-Zehnder interferometer,

FIG. 2 is a graph showing transmission characteristics according to wavelengths of two output ports of the Mach-gender interferometer shown in FIG.

3 is a block diagram of a multi-channel optical signal performance monitoring apparatus in a wavelength division multiplexing system according to a first embodiment of the present invention;

4 is a block diagram of a multi-channel optical signal performance monitoring apparatus in a wavelength division multiplexing system according to a second preferred embodiment of the present invention;

5 is a graph showing the transmission characteristics according to the wavelength of the Mach-gender interferometer shown in FIG.

FIG. 6 is a block diagram of a multi-channel optical signal performance monitoring apparatus in a wavelength division multiplexing system according to a third preferred embodiment of the present invention.

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

300: variable wavelength filter 310, 610: Mach-gender interferometer

320, 330, 620: photodetector

340, 630: optical signal performance monitoring controller 600: wavelength demultiplexer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing system (WDM). In particular, the present invention relates to a wavelength division multiplexing system that monitors the performance of a multi-channel optical signal using a Mach-Zehnder interferometer. A channel optical signal performance monitoring apparatus.

In general, a wavelength division multiplexing (WDM) system is a very economical optical transmission method that can easily increase the transmission capacity because several different wavelengths are bundled and transmitted through a single optical fiber, and also various types of dependent signals It is very effective as a light transmission network for providing next generation multimedia service because it can accept.

In order to further increase the transmission capacity in the transmission scheme of such a WDM system, the transmission turbulence may be increased by increasing the number of channels. However, in this method, as the number of channels increases, the wavelength interval between the channels narrows, so the number of channels must be increased in consideration of the fiber loss bandwidth and the amplification bandwidth of the fiber amplifier.

In addition, as the wavelength spacing between the channels is narrowed, mutual influences between neighboring channels are increased. Therefore, monitoring of the performance of optical signals has become a more important problem in terms of system reliability.

Factors affecting the performance of the WDM system include the light intensity, wavelength, and optical signal to noise ratio (OSNR) of each channel. In particular, the wavelength change of the channel reduces the light intensity of the channel. In addition to causing performance degradation, it also affects adjacent channels, reducing the performance of the WDM system.

Therefore, as described above, by measuring the characteristics of the optical signal that affects the performance of the WDM system, that is, the light intensity, wavelength, and optical signal to noise ratio to determine whether there is an abnormal signal transmission, the transmission disturbance or performance degradation of the optical signal It should be checked and repaired quickly. Such optical signal performance monitoring device should be size that can be installed in WDM system, and be reliable and economical.

As described above, the multi-channel optical signal performance monitoring method includes the following methods.

The method using staggered transmission characteristics for a given wavelength in an arrayed waveguide grating (AWG) uses the two output ports of the AWG to monitor one channel, and thus the transmission characteristics of the two output ports according to the wavelength. As a staggered approach, for example, to monitor eight channels, an AWG of 16 output ports is needed, and each output port is not a wavelength for the channel, so it is only used for WDM channel monitoring.

However, the above-described method using the arrayed waveguide diffraction grating can monitor the wavelength of the optical signal performance, but it is difficult to monitor the light intensity.

Another optical signal performance monitoring method is that the WDM optical signal is reflected from the optical fiber grating or optical grating, and then spatially distributed according to the wavelength. The multi-channel optical signal is obtained by using a device having 256 or 512 photodetectors. As a method of measuring at the same time, although the measurement time is shortened and the configuration is simple, there are problems of limitations in resolution and complexity of data processing operations.

Another optical signal performance reduction method is a method of measuring a WDM optical signal using a tunable filter.

Tunable filters include Fabry-Perot etalon filters and acousto-optic tunable filters (AOTFs), which are too expensive and less developed for AOTF. It is difficult to apply, and in the case of using a tunable Fabry-Perot etalon filter, it is difficult to set a reference wavelength because the transmission wavelength is easily changed according to the applied voltage.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to provide a multi-channel optical signal performance monitoring apparatus in a wavelength division multiplexing system capable of monitoring a stable and reliable multi-channel optical signal performance of a simple configuration and low cost. To provide.

The present invention for achieving the above object, in the multi-channel optical signal performance monitoring apparatus of the wavelength division multiplexing system for monitoring the optical signal performance of the input multi-wavelength, the wavelength of the optical signal by varying the light of a specific wavelength band A variable wavelength filter for extracting and providing a signal; A Mach-gender interferometer for providing an optical signal provided by the tunable filter through two output ports; A first photodetector for converting an optical signal provided from one port of the Mach-Gender interferometer into an electrical signal and providing the converted electrical signal; A second photodetector for converting and providing an optical signal provided from the other port of the Mach-Gender interferometer to an electrical signal; An optical signal performance monitoring controller which controls the filtering operation of the tunable filter and monitors optical signal performance by measuring optical intensity, wavelength, and optical signal-to-noise ratio of the optical signal from electrical signals provided by the first and second photodetectors. It is configured to include.

Hereinafter, with reference to the accompanying drawings will be described in detail the operation of the preferred embodiment according to the present invention.

FIG. 1 is a block diagram illustrating an apparatus for monitoring optical signal performance of a single channel in a wavelength division multiplexing system using a Mach-Gender interferometer. The Mach-Gender interferometer 100, the first and second photodetectors 110 and 120, The optical signal performance monitoring controller 130 is configured.

Referring to FIG. 1, the Mach-gender interferometer 100 includes a first optical coupler 10 and a second optical coupler 103, and a first optical coupler 101 and a second optical coupler 103. The path delay unit 130 is configured between the two paths, and will be described in detail with reference to the drawings shown in FIG. 2.

The path retarder 102 of the Mach-Gender interferometer 100 changes the length or refractive index between the first optical coupler 101 and the second optical coupler 102 when the output characteristics of the two ports cause optical signal interference. Delaying the path causes the output value to increase and decrease (or decrease and increase) depending on the wavelength as shown in FIG. 2.

The first photodetector 110 converts the intensity of the optical signal of one port output from the Mach-Zen interferometer 100 into an electrical signal and detects the converted electrical signal to the optical signal performance monitoring controller 130. to provide.

The second photodetector 120 converts and detects the intensity of the optical signal of the other output port of the Mach-gender interferometer 100 into an electrical signal, and provides the converted electrical signal to the optical signal performance monitoring controller 130. do.

The optical signal performance monitoring controller 130 controls the overall operation for monitoring the optical signal performance, and the optical signal characteristics, that is, the light intensity and the wavelength according to normal optical transmission are preset.

Therefore, the optical signal performance, that is, the light intensity and wavelength, etc. are measured from the output signals of the first photodetector 110 and the second photodetector 120, and if the measured value is out of the preset range, the operator is omitted. Print warning messages through the interface.

Referring to Figure 2, the process of measuring the light intensity and wavelength of the optical signal performance monitoring controller 130 will be described in detail.

For example, when an optical signal 200 having an arbitrary light intensity and wavelength represented by I _i (λ) enters port 1 of the Mach-Gender interferometer 100, the output signal 210 of one port 3 is The output signal 220 from the first photodetector 110 and the output signal 220 of the other port 4 are output to the second photodetector 120, and the expressions related to the wavelengths are represented by Equations 1 and 2, respectively.

Δl is the distance at which the optical signal having the wavelength λ is delayed by the path retarder 102. Accordingly, by appropriately adjusting Δl, desired characteristics of the Mach-gender interferometer 100 can be obtained, and the light intensity of the input optical signal λ is represented by Equation 3 and the output of the first photodetector 110 and the second. It is expressed as the sum of the photodetector 120 outputs.

The wavelength of the input optical signal λ is expressed as a relative difference between the output of the first photodetector 110 and the output of the second photodetector 120 and is represented by Equation 4 below.

D (λ) = (light intensity at port 3 -_light intensity at port 4) / (light intensity at port 3 + light intensity at port 4)

= sin ² (π · Δl / λ)-cos ² (π · Δl / λ)

    =-cos (2 · π · Δl / λ)

At this time, in measuring the wavelength of the input optical signal (λ), although measured by the difference value between the output of the first photodetector 110 and the second photodetector 120, one of the Mach-gender interferometer 100 It can also be calculated using only the page output characteristics.

The measurement of the wavelength of the optical signal by the difference between the output of the first photodetector 110 and the output of the second photodetector 120 is performed so as to obtain a value that is not affected even if the optical intensity of the input optical signal is shaken. In addition, the optical signal performance monitoring controller 130 stores the difference value of the two outputs with respect to the wavelength of Equation 4, so that the information on the wavelength can be known from the relative difference between the two outputs.

3 is a block diagram of a multi-channel optical signal performance monitoring apparatus according to a first preferred embodiment of the present invention, including a tunable filter 300, a Mach-gender interferometer 310, a first photodetector 320, 2 includes a photodetector 330 and an optical signal performance monitoring controller 340.

The tunable filter 300 is a Fabry-Perot etalon filter, and the wavelength of the multi-channel optical signal input under the control of the optical signal performance monitoring controller 340 as can be seen in the following description. Is changed to select only a certain region of the wavelength and output to the Mach-gender interferometer (310).

The Mach-gender interferometer 310 outputs the transmission characteristics differently according to the wavelength output from the wavelength variable filter 300, and the first photodetector 320 connected to the Mach-gender interferometer 310 is a Mach-gender interferometer ( The intensity of the optical signal of one port output from 310 is converted into an electrical signal and detected, and the converted electrical signal is provided to the optical signal performance monitoring controller 340.

The second photodetector 330 converts and detects the intensity of the optical signal of the other output port of the Mach-gender interferometer 310 into an electrical signal, and provides the converted electrical signal to the optical signal performance monitoring controller 340. do.

The optical signal performance monitoring controller 340 controls to sequentially filter the region of the multichannel optical signal of the wavelength tunable filter 300, and the electrical signal output from the first photodetector 320 and the second photodetector 330. From the light intensity and wavelength is determined.

That is, the optical signal performance monitoring controller 340 calculates the transmittance according to the sum of the output of the first photodetector 320 and the output of the second photodetector 330 to measure the light intensity, and the first photodetector 320 The difference between the output of the second photodetector 330 and the output of the second photodetector 330 divided by the sum of the output of the first photodetector 320 and the output of the second photodetector 330, that is, the first photodetector 320 and the first photodetector 320. 2 The wavelength is measured from the relative difference between the photodetectors 330.

In addition, when the wavelength is calculated using only one output characteristic of the Mach-gender interferometer 310, the output of the first photodetector 320 (or the output of the second photodetector 330) may be converted into the first photodetector 320. It is calculated by the relative value of one output value divided by the sum of the output of the second photodetector 330 and the output of the second photodetector 330.

In addition, the optical signal performance monitoring controller 340 checks the existence of the channel when the light intensity is larger than the neighboring region, and obtains the ratio of the light intensity at this time to the light intensity in the neighboring region. Obtain

In this case, the optical signal performance of the optical signal performance monitoring controller 340, that is, the light intensity, wavelength, and optical signal-to-noise ratio calculation may be calculated by the onboard software or by individual microprocessors respectively mounted on the software. Those skilled in the art will readily understand.

4 is a block diagram illustrating a configuration of a multi-channel optical signal performance monitoring apparatus according to a second preferred embodiment of the present invention for improving the measurement wavelength band and accuracy of the multi-channel optical signal performance monitoring apparatus of FIG. 3. ), Optical splitter 410, first and second Mach-Gender interferometers 420 and 450, first to fourth photodetectors 430, 440, 460, 470, and optical signal performance monitoring controller 480. This will be described with reference to FIG. 5.

The tunable filter 400 varies the wavelength of the input optical signal under the control of the optical signal performance monitoring controller 480 and selects a certain region of the wavelength, that is, an optical signal of a specific wavelength band, and outputs the optical signal to the optical splitter 410. do.

The optical splitter 410 distributes a predetermined region of the wavelength output from the wavelength tunable filter 400 and outputs it to the first Mach-gender interferometer 420 and the second Mach-gender interferometer 430.

In this case, the first Mach-gender interferometer 420 alternates the transmission characteristics according to the wavelengths output from the optical splitter 410, that is, the transmission characteristics 510 and 520 according to the wavelengths as shown in FIG. 5A. The second photoelectric detector 430 and the second photodetector 440, and the second Mach-gender interferometer 420 alternates transmission characteristics according to wavelengths output from the optical splitter 410. As shown in FIG. 5B, the light beams may have transmission characteristics 530 and 540 according to wavelengths, and are output to the third photodetector 460 and the fourth photodetector 470.

The first and second photodetectors 430 and 440 convert the intensity of the optical signal output from each of the two ports of the first Mach-gender interferometer 420 into electrical signals and provide them to the optical signal performance monitoring controller 480. The third and fourth photodetectors 460 and 470 convert the intensity of the optical signal output from each of the two ports output from the second Mach-gender interferometer 450 into electrical signals to convert the optical signal into an electrical signal. 480).

FIG. 5C illustrates a relative difference between the first photodetector 430, the second photodetector 440, the third photodetector 460, and the fourth photodetector 470 illustrated in FIGS. 5A and 5B, respectively. As shown, the solid line represents the relative difference between the first photodetector 430 and the second photodetector 440, and the dotted line represents the relative difference between the third photodetector 460 and the fourth photodetector 470.

In addition, 5d represents the sum and difference of the relative difference of the transmission characteristics according to the wavelengths of the first and second Mach-gender interferometers 420 and 450 of FIG. 5C, and the solid line represents the first and second Mach-gender interferometers ( The relative difference of the transmission characteristics according to the wavelengths of 420 and 450 is shown, and the dotted line represents the sum of the transmission characteristics according to the wavelengths of the first and second Mach-gender interferometers 420 and 450.

In addition, since the first and second Mach-gender interferometers 420 and 450 may use the linear transmission characteristics of the Mach-gender interferometer, accuracy may be degraded when optical signals of too few transmittances or wavelength bands are input. It increases the accuracy.

Areas 'A', 'B', 'C', and 'D' in FIGS. 5C and 5D are determined by FIG. 5D. That is, looking at 5d, the area 'A' is the area where the solid line is larger than 0 and the dotted line is smaller than 0, 'B' is the area where both the solid line and the dotted line are smaller than 0, and 'C' is the dotted line is greater than 0 and the solid line is 0. It is a smaller area, and 'D' indicates an area larger than 0 for both solid and dashed lines.

Accordingly, if the wavelength of the optical signal is at the point 'A' of FIGS. 5C and D, the first Mach-gender interferometer 420 corresponding to the solid line of FIG. 5C is used. If the wavelength of the optical signal is at the point B, the dotted line of FIG. 5C is used. Using the corresponding second Mach-Gender interferometer 450, if it is at point 'C', then using the first Mach-Gender interferometer 420 corresponding to the solid line of Fig. 5C, and if it is at point 'D', A second Mach-gender interferometer 450 corresponding to the dotted line is used.

This area classification and use are all oversized in the optical signal performance monitoring controller 480.

FIG. 6 is a block diagram illustrating a multi-channel optical signal performance monitoring apparatus according to a third exemplary embodiment of the present invention. The wavelength demultiplexer 600 extracts only an optical signal having a desired wavelength band by demultiplexing an input optical signal. In response to each of the two output ports of the N Mach-gender interferometer 610 and the N Mach-gender interferometer 610 that output differently the transmission characteristics of the multi-channel optical signal output from the wavelength demultiplexer 600 By measuring the light intensity, wavelength, and optical signal to noise ratio from the output signals of the 2N photodetectors 620 and 2N photodetectors 620 connected to convert the output signal of the Mach-gender interferometer 610 into an electrical signal It consists of an optical signal performance monitoring controller 630 for monitoring the performance of the optical signal.

That is, the multi-channel optical signal performance monitoring apparatus according to the third embodiment uses the narrow bandwidth of the demultiplexing element such as AWG instead of the tunable filters in the first and second embodiments to respectively input channels of the optical signal. By separating and monitoring the performance of the optical signal, the operator can monitor for each wavelength band desired.

As described above, in the wavelength division multiplexing system according to the present invention, the multi-channel optical signal performance monitoring apparatus extracts an optical signal having a predetermined band wavelength using a wavelength tunable filter or an arrayed waveguide diffraction grating. By extracting the optical signal using the difference in the transmission characteristics according to the wavelength to measure the performance of the optical signal, it is possible to ensure the stability and reliability of the wavelength division multiplexing system, and to reduce the cost of the wavelength division multiplexing system. have.

Claims (7)

In the multi-channel optical signal performance monitoring device of the wavelength division multiplexing system for monitoring the input optical signal performance of multiple wavelengths, A variable wavelength filter for varying the wavelength of the optical signal to extract and provide an optical signal of a specific wavelength band; A Mach-gender interferometer for providing an optical signal provided by the tunable filter through two output ports; A first photodetector for converting an optical signal provided from one port of the Mach-Gender interferometer into an electrical signal and providing the converted electrical signal; A second photodetector for converting and providing an optical signal provided from the other port of the Mach-Gender interferometer to an electrical signal; An optical signal performance monitoring controller which controls the filtering operation of the tunable filter and monitors optical signal performance by measuring optical intensity, wavelength, and optical signal-to-noise ratio of the optical signal from electrical signals provided by the first and second photodetectors. In the wavelength division multiplexing system comprising a multi-channel optical signal performance monitoring device. The optical splitter of claim 1, further comprising: an optical splitter configured to distribute an optical signal of a specific wavelength band provided by the variable wavelength filter; A second Mach-gender interferometer for providing optical signals distributed at the optical splitter through two output ports; A third photodetector for converting an optical signal provided from one port of the second Mach-gender interferometer into an electrical signal and providing the optical signal to the optical signal performance monitoring controller; The multi-channel optical signal performance of the wavelength division multiplexing system further comprises a fourth optical detector for converting the optical signal provided from the other port of the second Mach-gender interferometer to an electrical signal to provide to the optical signal performance monitoring controller monitor. The wavelength division multiplexing system of claim 1, wherein the optical signal performance monitoring controller measures the light intensity by calculating a transmittance according to the sum of the first photodetector output and the second photodetector output. In multi-channel optical signal performance monitoring device. The optical signal performance monitoring controller of claim 1, wherein the optical signal performance monitoring controller is configured to divide the difference between the first photodetector output and the second photodetector output by a sum of the output of the first photodetector and the second photodetector output. A multi-channel optical signal performance monitoring apparatus in a wavelength division multiplexing system, characterized in that for measuring the wavelength. 5. The optical signal performance monitoring controller of claim 4, wherein the optical signal performance monitoring controller measures the wavelength from a first photodetector output (or a second photodetector output divided by the sum of the first photodetector output and the second photodetector output). A multi-channel optical signal performance monitoring apparatus in a wavelength division multiplexing system. [4] The wavelength division multiplexing system of claim 1 or 3, wherein the optical signal performance monitoring controller measures the optical signal to noise ratio by obtaining a ratio of the light intensity to the light intensity in a neighboring region. Channel optical signal performance monitoring device. In the multi-channel optical signal performance monitoring device of the wavelength division multiplexing system for monitoring the input optical signal performance of multiple wavelengths, A wavelength demultiplexer for demultiplexing the optical signal and extracting and providing an optical signal having a specific wavelength band; N Mach-gender interferometers providing optical signals provided by the wavelength demultiplexer through two output ports; 2N photodetectors connected to the two output ports of the N Mach-gender interferometers to convert the output signals of the Mach-gender interferometers into electrical signals and output the electrical signals; And an optical signal performance monitoring controller for monitoring the performance of the optical signal from the output signals of the 2N photodetectors.

Images