KR102146295B1 - Monitoring Apparatus for Optical Fiber Link in Wavelength Division Multiplexing Network - Google Patents

Abstract

According to the present invention, when the magnitude of light loss and reflection by the optical fiber are measured in the conventional OTDR system, the optical loss in the AWG is changed very sensitively to changes in a center wavelength of an optical pulse as shown in FIG. 3. In addition, even when the wavelength of an OTDR light source is controlled to a perfectly fixed value, since the center wavelength of the AWG is changed due to changes in external temperature or deteriorations over time because of characteristics of the AWG, the magnitude of the optical loss measured in the OTDR is changed. For the above reason, the dynamic range, which refers to a measurable loss range serveing as the most important performance parameter of the OTDR, is rapidly reduced, thereby reducing a measurement distance capable of measuring the loss of the optical communication line. The present invention presents a configuration that tunable laser or DFB LD is used as an OTDR light source in DWDM network to control the optical wavelength of the tunable laser or DFB LD in real time to enable, in real time, the output wavelength of the OTDR′s light source to match the center wavelength of the AWG changed by deterioration due to external temperature change and use, so that the loss of the optical path is accurately measured, and the dynamic range measurable with OTDR is maximized. By the above configuration, the optical pulse wavelength of OTDR is controlled to match the AWG center wavelength, so that the dynamic range of OTDR is increased.

Description

Optical fiber monitoring method using OTDR optical fiber link monitoring device in WDM network {Monitoring Apparatus for Optical Fiber Link in Wavelength Division Multiplexing Network}

The present invention relates to an optical path monitoring system in a WDM network. In particular, it relates to an optical path monitoring device in a high-density WDM network using a narrow-band single mode light source.

Prior art related to OTDR (Optical Time Domain Reflectometer) prior to the present invention will be described. The wavelength of a typical light source used in the OTDR device is shown in FIG. 4. The light source shown in FIG. 4 is a light emitting diode (LED) light source distributed in a wide wavelength band, a Fabry-Perot (FP) laser that generates light in a plurality of wavelength modes at regular intervals in a narrow optical wavelength band, and light of a single wavelength. It shows a DFB (Distributed Feed-Back) laser that occurs in a narrow wavelength band. Existing OTDR technology uses an OTDR as a light source for OTDR in a DWDM (Dense Wavelength Division Multiplexing) network with a significantly wider wavelength range than DFB LD (Laser Diode) as shown in FIG. There is a problem that a complicated coupling structure is required because it is connected to the optical path to be measured.

Another prior art is a technology in which OTDR using a single mode light source (DFB LD or tunable laser) is applied to a DWDM network. In the case of this technology, as shown in Fig. 3, the optical loss of AWG (Arrayed Waveguide Gratings) changes very sensitively to the wavelength change, so the loss of the optical path measured in the OTDR is measured inaccurately according to the minute change in the wavelength of the light source of the OTDR. there is a problem.

Registered Patent Publication 10-0928142 US Patent Publication US 7,042,559 Registered Patent Publication 10-1050954

In the present invention, in the conventional OTDR system, in measuring the magnitude of the optical loss and reflection due to the optical fiber, as shown in FIG. 3, the optical loss of the AWG changes very sensitively to the wavelength change, so that the wavelength of the light source of the OTDR There is a problem in that the loss of the optical path varies greatly depending on the minute change, and the measurement is caused. Even when the wavelength of the OTDR light source is controlled to a perfectly fixed value, the center of the AWG due to the change of external temperature or deterioration over time due to the characteristics of the AWG As the wavelength changes, there is a problem that the magnitude of the optical loss measured in the OTDR changes. Due to this reason, the dynamic range, which means the measurable loss range, which is the most important performance parameter of the OTDR, decreases rapidly, and there has been a problem that the measurement distance for measuring the loss of the optical communication line decreases.

There is a problem as described above, in the present invention

AWG that changes by deterioration due to external temperature change and use by using a variable wavelength laser or DFB LD as an OTDR light source in a DWDM (Dense Wavelength Division Multiplexing) network. By controlling in real time to match the center wavelength of, we want to measure the loss of an accurate optical path and maximize the dynamic range that can be measured with OTDR.

In addition, by accumulating and recording the change in the output wavelength of the OTDR light source, which is controlled in real time so that the output wavelength of the OTDR light source coincides with the center wavelength of the AWG that is changed by external temperature change and deterioration due to use, the change in the center wavelength of the AWG is recorded. By accumulating tracking, it detects in advance that the center wavelength of the AWG deviates from the allowable value and informs or generates an alarm to ensure the stability of the network.

The present invention is to solve the above problem,

In an OTDR having an optical pulse wavelength controller, an optical splitter (or optical circulator), and an optical receiver (photodiode), the optical pulse signal generated by the optical pulse wavelength controller is transmitted to an optical fiber with the optical splitter (or optical circulator). The optical signal that has passed through the AWG is received and analyzed through the optical receiver from among the signals incident through and backscattered of the incident light,

By controlling the center wavelength of the optical pulse wavelength controller of the OTDR, the dynamic range of the OTDR is increased by controlling the backscatter signal passing through the AWG to increase.It provides an optical path monitoring device in a WDM network.

In addition, in an OTDR having an optical pulse wavelength controller, an optical splitter (or optical circulator) and an optical receiver (photodiode), the optical pulse signal generated by the optical pulse wavelength controller is transmitted to the optical fiber by the optical splitter (or optical circulator). Optical circulator), and by controlling the center wavelength of the optical pulse wavelength controller of the OTDR by receiving and analyzing the optical signal that has passed through the AWG among the backscattered signals of the incident light, Light rays in a WDM network, characterized in that by controlling the backscattering signal passing through the AWG to increase, measuring the difference from the initial optical center wavelength of the AWG, and measuring and displaying the degree of light quality due to the change in the center wavelength of the AWG. To provide a monitoring device.

In addition, there is provided an optical path monitoring apparatus in a WDM network, characterized in that, when the level of light quality exceeds a set range, a notification or an alarm is operated.

In addition, by accumulating and storing the light quality level with weather information of the area where the AWG is installed in a storage device inside or outside the OTDR, and storing light quality information by time, season, and cumulative use time after installation of the AWG, It provides an optical path monitoring device in a WDM network, characterized in that it has a quality prediction function for predicting degradation and operating a notification or alarm.

In addition, the central wavelength of the AWG is measured from the central wavelength set by the optical pulse wavelength controller, and the optical pulse wavelength controller sets the central wavelength by controlling the temperature of the light source using a thermoelectric element. Provides an optical path monitoring device in

The present invention aims to accurately measure optical loss and reflection information of an optical path regardless of a change in a wavelength of an optical pulse of an OTDR or a change in a center wavelength of a multiplexer/demultiplexer.

In addition, regardless of the change in the wavelength of the optical pulse of the OTDR or the change in the center wavelength of the multiplexer/demultiplexer, the length of monitoring the optical path that can be measured with the OTDR does not decrease. When the optical pulse wavelength of the OTDR is accurately controlled, the optical pulse By recording and analyzing the OTDR waveform according to the wavelength of the multiplexer/demultiplexer by tracking and managing the change in the center wavelength of the multiplexer/demultiplexer, it is a means to stably maintain the optical path quality by generating a notification or alarm before the center wavelength exceeds the threshold. Provides.

In general, the optical filter used as a multiplexer/demultiplexer uses AWG, and since the center wavelength changes to the same extent for all channels, the change information of the center wavelength of the data channel is estimated by observing the change of the wavelength connected to the OTDR. It is possible. In particular, in the case of a demultiplexer installed outdoors, a change in the center wavelength occurs frequently because the external environment changes severely, which is a major cause of deteriorating the quality of the data optical signal.

The present invention has the effect of increasing the dynamic range by solving the above problem by accurately controlling the optical pulse wavelength of the OTDR.

1 is a configuration diagram of an existing OTDR system.
2 is a block diagram of a WDM communication network that communicates using multiple wavelengths.
3 shows the AWG loss characteristics at 100 GHz channel intervals.
4 is a graph of emission wavelength characteristics of LED, FP LASER, and DFB LASER.
5 is a block diagram of a DFB LASER used in the OTDR of the present invention.
6 is a WDM network in which the OTDR of the present invention is installed.
7 is a comparison of a dynamic range between an existing OTDR and an OTDR system of the present invention.
8 is a schematic diagram for measuring backscattering by the OTDR system of the present invention.

Communication related terms used in the present invention are to be defined and used as follows.

A. OTDR: Optical Time Domain Reflectometer

B. WDM: Wavelength Division Multiplexing

C. DWDM: Dense Wavelength Division Multiplexing

D. AWG: Arrayed Waveguide Gratings

E. DFB LD: Distributed Feed-Back Laser Diode

F. Optical Splitter: Optical Splitter

G. Optical Circulator

H. TEC: Thermo Electric Cooler

I. Single mode light source: DFB LD or tunable laser

The basic configuration of the OTDR system to be improved in the present invention is shown in Fig. 1. The function of the OTDR is a device that monitors the state of an optical path composed of optical fibers that form the basis of the Internet and communication networks. In other words, it is a device that measures the optical loss according to the distance of the optical fiber path and the magnitude of light reflection at the optical connection point.

The signal processing processor shown in Fig. 1 generates a single pulse. The pulses generated by the signal processing processor are driven by a light source made of a laser diode through a pulse driver to generate optical pulses from the light source. The generated optical pulse is incident on the optical fiber for optical communication through an optical circulator or an optical splitter.

As the optical pulse incident on the optical communication optical fiber passes through the optical communication optical fiber, Rayleigh back scattering occurs continuously, and this signal is a photodiode connected to the optical splitter (or optical circulator). It is incident on the OTDR light receiving unit composed of and measures the size together with the time after the light pulse is generated.

That is, the OTDR measurement system enters the optical pulse generated from one side into an optical fiber constituting an optical communication line through an optical splitter (or optical circulator), and the backscatter generated from the optical fiber from the incident is detected by the optical splitter (or optical circulator). Light loss and light reflection according to the distance of the optical fiber constituting the optical communication network by continuously measuring the size of the backscatter by continuously measuring it with a photodiode provided on one side of the device and converting it to an analog digital converter (A/D converter). Interpretation is possible.

After all, if an OTDR is installed on one side of an optical communication line, the optical loss and reflection magnitude of the optical fiber can be measured according to the distance. FIG. 2 is a configuration of an OTDR serving as the above function on a WDM (Wavelength Division Multiplexing) network. In the WDM network, the WDM system combines and transmits signals using a multiplexer at the transmitter, and the receiver's demultiplexer divides and receives them. In general, since an optical material has no directionality to an optical signal due to its optical characteristics, it is possible to have a device to do both at the same time, and to function as an optical add-drop multiplexer. In DWDM optical network, since the interval between channels is very narrow and accommodates many wavelengths at the same time, it is generally implemented using AWG based on PLC (Planar Lightwave Circuit) rather than thin film filter. The main characteristic of this AWG is that all channels have the same wavelength change.

Unlike a laser light source, the optical receiver has stable light reception characteristics in a wide wavelength range of several hundred nm or more, not a specific wavelength. Therefore, the demultiplexer (demultiplexer in Fig. 2) must provide the wavelength selectivity of the receiver of the WDM system.

In summary, the WDM network combines multi-wavelength laser light sources used as transmitters through a multiplexer and transmits them through a single optical fiber, and at the receiving end, diverges into each wavelength through a demultiplexer to each optical receiver. It consists of a network that distributes to. In a typical DWDM network, the wavelength interval between channels is 100GHz (~0.8nm) or 50GHz (~0.4nm). The multiplexer and demultiplexer generally use AWG, and the optical loss characteristics according to the wavelength of the AWG are shown in FIG. 3. That is, the multi-wavelength laser signal transmitted through the optical fiber passes through the AWG, is decomposed into specific wavelengths, and is connected to an optical receiver for each wavelength band to complete a communication line.

For stable communication of such a WDM network, the function of the AWG is important. The OTDR technology that monitors the entire optical fiber communication line including the AWG function is as follows.

The DFB LD light source used in the OTDR of the present invention is a single mode laser, and the output wavelength is determined according to the wavelength of the Bragg grating integrated in the light source. Bragg grating's wavelength characteristics change according to temperature, and generally has a rate of change of 0.1nm/℃.

Therefore, in order to keep the light output wavelength constant, the temperature of the DFB LD light source module must be controlled with an accuracy of 0.1 °C or less. As shown in Fig. 5, precise temperature control is performed by integrating TEC (Thermo Electric Cooler) into the light source, but for precise temperature control, contact between thermistor and TEC, contact with LD (laser diode) and TEC, and temperature in the light source according to external temperature. Many variables such as distribution and the problem of changes due to deterioration of the module over time should also be considered. In general, it is not easy to control ±0.05nm wavelength during the life cycle with DFB LD, which causes more than 1dB of optical loss change by passing through AWG.

In the case of a tunable laser used as another light source technology, a tunable filter for wavelength tunability is built into the light source, and for precise wavelength control, an expensive wavelength locker that does not change wavelength characteristics depending on the operating environment is built in. It is not used as an instrument and can only be used as a measuring instrument.

FIG. 6 shows a WDM network in which the OTDR of the present invention is used and a structure in which the OTDR of the present invention is combined. An OTDR having a single mode light source is connected to a set input terminal of the wavelength multiplexer, and the internal structure of the OTDR is as shown in the bottom of FIG. 6. The signal processing processor sets the tunable filter through the wavelength control unit (in the case of DFB LD, it is the temperature of the TEC, and the physical variable controlled according to the type of other tunable tunable filter may vary). After setting the wavelength in this way, a single pulse is generated from the signal processing processor. The single mode light source laser diode is driven by using a pulse driver with the generated single pulse signal. The pulsed light source thus generated is incident on the multiplexer through an optical splitter (or optical circulator). In this way, the variable wavelength optical pulse signal incident to the multiplexer is transmitted to the demultiplexer installed on the opposite side of the communication line composed of the optical fiber, and in the process of being transmitted, it continuously generates backscatter inside the optical fiber, and to one side of the optical splitter (or optical circulator). The signal is converted into an electric signal through a photodiode constituting the OTDR light receiving unit and transmitted to the OTDR signal processing process through an A/D converter.

That is, the magnitude of the electrical signal over time measured by the photodiode is interpreted as the optical loss level over the distance, and the magnitude and position of the optical loss and reflection of the optical path for the corresponding wavelength are accurately determined as the magnitude of the optical loss level. Will be measured.

As shown in Fig. 7, if both the multiplexer (the position of the distance L1 from the OTDR) and the demultiplexer (the position of the distance L2 from the OTDR) have a central wavelength at λn, and the wavelength of the OTDR optical pulse is also generated at λn, the multiplexer and the demultiplexer In FIG. 7, the corresponding wavelength has the minimum optical loss, and an OTDR waveform such as blue in FIG. 7 is obtained, so that the measurable distance of the OTDR is greater than L3 in FIG. 7.

However, when the optical pulse wavelength of the OTDR is changed to λ _LD , the loss of the optical signal by the size of ΔP1 and ΔP2 for the corresponding wavelength in the multiplexer and the demultiplexer increases, and accordingly, the red OTDR waveform of FIG. 7 is obtained.

That is, the optical loss in the multiplexer and demultiplexer increases by ΔP1 and ΔP2, respectively, so that the loss is measured, and the length of the measurable optical path is also reduced to L3. This is the same problem that occurs even when the center wavelength of the multiplexer/demultiplexer changes. In the present invention, by actively controlling the optical pulse wavelength of the OTDR, accurate optical path information is measured, and a measurable distance is maintained constant to provide a technology for stably monitoring the state of the optical path.

In other words, the existing OTDR technology sets the optical center wavelength of a single mode light source to the center wavelength of the AWG regardless of changes in the external temperature or changes due to deterioration of the AWG. As a result, the dynamic range decreases and the length of the measurable optical line decreases.

In addition, there is a problem that the quality of the optical communication line cannot be deteriorated due to the change in the center wavelength of the AWG.

The wavelength control unit according to the optical path state, which is the core of the present invention, is a configuration that cannot be found in the existing OTDR. In the conventional OTDR, since the light center wavelength is kept constant when the single mode light source is used, There is a wavelength control unit that operates independently, but a wavelength control unit according to the state of the optical path is unnecessary. However, the wavelength control unit of the present invention analyzes the back light scattering signal measured by the light receiving unit provided in the OTDR, and uses the center wavelength of the single mode light source as a feedback signal to increase the size of the light. It is characterized in that the center wavelength of the optimal single mode light source is set by changing the center wavelength of the pulse and scanning the back light scattering signal in real time.

To further explain,

A reference measurement step of measuring the size of the light-scattering signal returned through the AWG among the back light-scattering signals received starting at a basic setting wavelength by the light receiving unit and making this a comparison standard; And a wavelength change and measurement step of setting a center wavelength by increasing as much as a set wavelength from the basic setting wavelength and measuring a back light scattering signal. And a center wavelength comparison step of comparing the signal measured in the reference measurement step with the signal measured in the wavelength conversion and measurement step. And when the signal measured in the comparison step is larger than the signal measured in the reference measurement step, the measurement direction is increased by a set wavelength to set the center wavelength, and the measurement and comparison are repeated, and the signal measured in the comparison step is measured as a reference. A center wavelength search step of setting a center wavelength by reducing the measurement direction by a set wavelength, updating the default wavelength to the most recently measured wavelength, and repeating the measurement and comparison; And a data storage step of storing a center wavelength, a measurement time, and a magnitude value of the backscatter when the center wavelength from which the maximum backscatter signal appears in the center wavelength search step is searched. And when the maximum backscatter measurement value of the OTDR comes out, when a size difference between the maximum backscatter measurement value and a preset threshold value occurs, the current center wavelength is set as a default setting wavelength and the reference measurement is performed. It provides an ODTR characterized by repeating the process of setting the center wavelength from step.

The present invention provides an OTDR having the following configuration to solve this problem.

In an OTDR having an optical pulse wavelength controller, an optical splitter (or optical circulator), and an optical receiver (photodiode), the optical pulse signal generated by the optical pulse wavelength controller is transmitted to an optical fiber with the optical splitter (or optical circulator). The optical signal that has passed through the AWG is received and analyzed through the optical receiver from among the signals incident through and backscattered of the incident light,

By controlling the central wavelength of the optical pulse wavelength controller of the OTDR, the dynamic range of the OTDR is increased by controlling the AWG backscatter signal to increase.

In addition, in an OTDR having an optical pulse wavelength controller, an optical splitter (or optical circulator) and an optical receiver (photodiode), the optical pulse signal generated by the optical pulse wavelength controller is transmitted to the optical fiber by the optical splitter (or optical circulator). Optical circulator), and receives and analyzes the optical signal passing through the AWG among the backscattered signals of the incident light through the optical receiver,

By controlling the center wavelength of the optical pulse wavelength controller of the OTDR, by controlling the AWG backscatter signal to increase, the difference from the initial optical center wavelength of the AWG is measured to measure the degree of optical quality due to the change in the center wavelength of the AWG. It provides an optical path monitoring device in a WDM network, characterized in that the display.

In addition, there is provided an optical path monitoring apparatus in a WDM network, characterized in that, when the level of light quality exceeds a set range, a notification or an alarm is operated.

In addition, by accumulating and storing the light quality level with weather information of the area where the AWG is installed in a storage device inside or outside the OTDR, and storing light quality information by time, season, and cumulative use time after installation of the AWG, It provides an optical path monitoring device in a WDM network, characterized in that it has a quality prediction function for predicting degradation and operating a notification or alarm.

100: light source (DFB-LD)
200: temperature measurement unit (Thermistor)
300: Thermoelectric device (TEC)
400: Heat Sink

Claims (4)

DFB LASER light source; And
A wavelength control unit capable of varying the wavelength of the DFB LASER light source; And
The wavelength control unit controls a wavelength of 0.1 nm as the temperature of the TEC changes by 1 degree through temperature control of the TEC coupled with the DFB LASER light source,
An optical splitter that connects the light of the light source to a multiplexer of the WDM network, and connects the backscatter of the optical path generated by the disconnection of the repeater or line on the WDM network so that the photodiode can measure it; And a signal processing processor,
The wavelength control unit changes the center wavelength of the optical pulse by using the center wavelength of the single mode light source as a feedback signal so that the size of the signal can be increased by analyzing the back light scattering signal measured by the light receiving unit provided in the OTDR. Then, by scanning the backscattering signal in real time, the central wavelength of the optimal single mode light source is set, and the wavelength of the DFB LASER light source is controlled so that the backscattering signal measured by the photodiode increases,
When the level of light quality measured by the photodiode exceeds a set range, a notification or alarm is activated,
In a WDM network that has a temperature control unit for preventing a change in a center frequency due to the ambient temperature of the AWG (Arrayed Waveguide Gratings) provided in the multiplexer, and combines the AWG to the temperature control unit to maintain the AWG at a set temperature. In the optical path monitoring method using an optical time domain reflectometer (OTDR) type optical path monitoring device,
A reference measurement step of measuring the size of the light-scattering signal returned through the AWG among the received back light-scattering signals starting at a basic setting wavelength, and making this a comparison standard; And
A wavelength change and measurement step of setting a center wavelength by increasing as much as a set wavelength from the basic setting wavelength and measuring a back light scattering signal; And
A center wavelength comparison step of comparing the signal measured in the reference measurement step with the signal measured in the wavelength change and measurement step; And
If the signal measured in the comparison step is larger than the signal measured in the reference measurement step, the measurement direction is increased by a set wavelength to set the center wavelength, and the measurement and comparison are repeated, and the signal measured in the comparison step is the reference measurement step. A center wavelength search step of setting a center wavelength by reducing the measurement direction by a set wavelength, updating the default wavelength to the most recently measured wavelength, and repeating the measurement and comparison; And
A data storage step of storing a center wavelength, a measurement time, and a magnitude value of the backscatter when the center wavelength from which the maximum backscatter signal appears in the center wavelength search step is searched; And
When the maximum backscatter measurement value of the OTDR comes out, when a difference in magnitude between the maximum backscatter measurement value and a preset threshold value occurs, the current center wavelength is set as the default setting wavelength from the reference measurement step. An optical path monitoring method using an optical time domain reflectometer (OTDR) type optical path monitoring device in a WDM network, characterized in that the central wavelength setting process is repeated. delete delete delete

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