JP5419935B2 - Multi-wavelength simultaneous OTDR and multi-wavelength simultaneous OTDR measurement method - Google Patents

Description

  The present invention relates to a multi-wavelength simultaneous measurement OTDR and a multi-wavelength simultaneous OTDR measurement method for simultaneously performing OTDR (Optical Time-Domain Reflectometer) measurement for a plurality of wavelengths.

  In an optical fiber laid to realize an optical network, when an optical fiber is introduced, OTDR measurement is performed with a plurality of wavelengths to grasp a construction completion state. By measuring at a plurality of wavelengths such as 1310 nm, 1550 nm, and 1625 nm, loss due to bending of the optical fiber can be grasped in more detail, and loss of the optical fiber at each wavelength can be accurately grasped.

On the other hand, an apparatus for performing OTDR measurement has been proposed (see, for example, Patent Documents 1 to 3). The OTDR of Patent Document 1 makes test light modulated with a correlation code incident on an optical fiber to be measured and receives backscattered light. At this time, by making the pulse width of the test light shorter than the gain saturation time of the transient response of the optical amplifier in the transmission line of the optical fiber to be measured, the signal light transmission characteristic is prevented from deteriorating.
In the OTDR of Patent Document 2, test light modulated with a pseudo-random code is incident on an optical fiber to be measured and the backscattered light is received.
In the OTDR of Patent Document 3, test light modulated using two types of Golay codes is incident on an optical fiber to be measured, and backscattered light is received.

Japanese Patent Laid-Open No. 2004-32420 Japanese Patent Laid-Open No. 9-26376 JP-A-4-54429

  To perform OTDR measurement for a plurality of wavelengths at the same time, it is necessary to provide a plurality of light sources, separate the signals of each wavelength with a wavelength filter, and receive backscattered light of each wavelength. Therefore, when performing the OTDR test for a plurality of wavelengths, the measurement is performed for each wavelength in order. When measurement is performed for each wavelength in order, if measurement time at a certain wavelength takes about 1 minute, it takes 3 minutes to measure three wavelengths.

  Although there is no problem when the number of cores is small, there are cases where it is necessary to perform OTDR measurement of an optical fiber with 1000 cores depending on the site, such as when measuring an optical fiber having a multi-core structure. In this case, there is a problem that 3000 minutes, that is, approximately about 2 days, must be spent for the OTDR measurement by simple calculation.

In Patent Document 1, there is a description that modulation is performed with a correlation code so that the signal-to-noise ratio is not deteriorated even if the power of the test light is lowered. However, in order to separate backscattered light from signal light having a different wavelength, A filter is used.
In Patent Document 2, there is a description that modulation is performed with a random code in order to find backscattered light even from within a noise level, but separation of backscattered light from light having a different wavelength is not considered.
In Patent Document 3, there is a description that modulation is performed using a Golay code in order to improve the dynamic range, but separation of backscattered light and light having different wavelengths is not considered.

  As described in Patent Documents 1 to 3, conventionally, a wavelength filter is used to separate signals having different wavelengths, and means for separating a plurality of wavelengths without using a wavelength filter has been proposed. Not. For this reason, even if the inventions described in Patent Documents 1 to 3 are combined, only an invention that separates a plurality of wavelengths using a wavelength filter can be configured. If it is going to separate a plurality of wavelengths using a wavelength filter, since it is necessary to mount a wavelength filter of each wavelength, there is a problem that the manufacturing cost of the device increases.

  Therefore, the present invention makes it possible to reduce the measurement time by separating the backscattered light of each wavelength without using a wavelength filter and simultaneously performing the optical pulse test of a plurality of wavelengths, thereby improving the efficiency of the construction. It aims to make possible.

  The multi-wavelength simultaneous measurement OTDR according to the present invention includes a random code generator (11) for generating two or more different random codes, and a random code from the random code generator, and a random code different for each wavelength. A plurality of light sources (13_1 to 13_N) having different wavelengths for outputting modulated test light, a combiner (21) for combining the test light from the plurality of light sources, and a combiner from the combiner. Wave light is output to the optical fiber to be measured, an optical coupler (14) to which backscattered light from the optical fiber to be measured is input, and the backscattered light input from the optical coupler is received and converted into an electrical signal A photoreceiver (16), a DC cut circuit (17) that cuts a DC component contained in an electrical signal from the photoreceiver, and an analog signal from the DC cut circuit is converted into a digital signal. Includes an AD conversion circuit (19) for the, a correlator (20) for performing a correlation operation between each random code from the digital signal and the random code generator from the AD conversion circuit.

  The multi-wavelength simultaneous measurement OTDR according to the present invention includes a plurality of light sources (13_1 to 13_N), a multiplexer (21), an optical coupler (14), a light receiver (16), and an AD converter circuit (19). Therefore, an optical pulse test with a plurality of wavelengths can be performed. The multi-wavelength simultaneous measurement OTDR according to the present invention further includes a random code generator (11), a DC cut circuit (17), and a correlator (20). The backscattered light intensity can be observed. For this reason, the multi-wavelength simultaneous measurement OTDR according to the present invention makes it possible to reduce the measurement time by separating the backscattered light of each wavelength without using a wavelength filter and simultaneously performing the optical pulse test of a plurality of wavelengths. It is possible to improve the efficiency of construction.

In the multi-wavelength simultaneous measurement OTDR according to the present invention, the multiplexer may be a WDM (Wavelength Division Multiplexers).
According to the present invention, the coupling loss in the multiplexer can be reduced.

  In the multi-wavelength simultaneous OTDR measurement method according to the present invention, a random code generation procedure for generating two or more different random codes and a random code generated by the random code generation procedure are input, and a plurality of lights having different wavelengths are input. Test light output procedure for outputting test light modulated with different random codes, multiplexing procedure for combining test light output in the test light output procedure, and multiplexed light combined in the multiplexing procedure A light receiving procedure for outputting to the optical fiber to be measured, receiving backscattered light from the optical fiber to be measured and converting it into an electrical signal, and a DC cut procedure for cutting a DC component included in the electrical signal converted by the light receiving procedure And an AD conversion procedure for converting an AC component after cutting a DC component by the DC cut procedure into a digital signal, and a digital signal converted by the AD conversion procedure, A serial correlation procedure performing correlation operation between each random code which is generated by the random code generator steps, in this order.

  Since the multi-wavelength simultaneous OTDR measurement method according to the present invention includes a test light output procedure, a multiplexing procedure, a light receiving procedure, and an AD conversion procedure, a multi-wavelength optical pulse test can be performed. Since the multi-wavelength simultaneous OTDR measurement method according to the present invention further includes a random code generation procedure, a direct current cut procedure, and a correlation processing procedure, the backscattered light intensity of each wavelength is observed without using a wavelength filter. be able to. For this reason, the multi-wavelength simultaneous OTDR measurement method according to the present invention can reduce the measurement time by separating the backscattered light of each wavelength without using a wavelength filter and simultaneously performing the optical pulse test of multiple wavelengths. It is possible to improve the efficiency of construction.

  According to the present invention, it is possible to reduce the measurement time by separating the backscattered light of each wavelength without using a wavelength filter and simultaneously performing the optical pulse test of a plurality of wavelengths, thereby improving the efficiency of construction. Can do.

An example of the multi-wavelength simultaneous measurement OTDR according to the present embodiment is shown. An example of test light modulated with a random code is shown. An example of the characteristics of the optical fiber to be measured is shown. An example of the electrical signal output from the light receiver 16 is shown. An example of an output waveform from the correlator 20 that performs correlation calculation of a code among the random codes C_1 to C_N is shown. An example of usage of the multi-wavelength simultaneous measurement OTDR according to the present embodiment is shown.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

  FIG. 1 shows an example of the multi-wavelength simultaneous measurement OTDR according to the present embodiment. The multi-wavelength simultaneous measurement OTDR includes a random code generator 11, modulators 12_1 to 12_N, light sources 13_1 to 13_N, a multiplexer 21, an optical coupler 14, a port 15, a light receiver 16, and a DC cut circuit. 17, an amplifier 18, an AD conversion circuit 19, and a correlator 20.

  The multi-wavelength simultaneous OTDR measurement method according to the present embodiment includes a random code generation procedure, a test light output procedure, a multiplexing procedure, a light receiving procedure, a DC cut procedure, an AD conversion procedure, and a correlation processing procedure. Have in order.

  In the random code generation procedure, the random code generator 11 simultaneously generates two or more different random codes C_1 to C_N for each wavelength of the test light. The random codes C_1 to C_N are M-sequence codes, for example.

The test light output procedure, multiwavelength simultaneous measurement OTDR outputs a test light _{L T _1~L} T _N simultaneously. For example, the modulators 12_1 to 12_N are current control circuits, for example, and simultaneously modulate the output light from the light sources 13_1 to 13_N according to the random codes C_1 to C_N from the random code generator 11. The light sources 13_1 to 13_N are, for example, LDs (Laser Diodes), and the wavelengths of the light sources 13_1 to 13_N are different. Source 13_1~13_N a random code C_1～C_N, and outputs the modulated test light _{L T _1~L} T _N random code C_1～C_N. FIG. 3 shows an example of test light modulated with a random code.

The combined procedure, multiplexer 21 multiplexes the test light _{L T _1~L} T _N from the light source 13_1 to 13_n. The multiplexer 21 is preferably a WDM (Wavelength Division Multiplexers). Thereby, the coupling loss in the multiplexer 21 can be reduced. The optical coupler 14 guides the combined light to the port 15. The port 15 can be connected to the optical fiber 93 to be measured, and outputs the combined light from the optical coupler 14 to the optical fiber 93 to be measured. Thus, the multiplexed light L _M is incident on the measured optical fiber 93.

  Here, in the test light output procedure, the light sources 13_1 to 13_N continuously output the test light for a predetermined time that is longer than the time required for light to propagate through the optical fiber 93 to be measured.

In this case, the random code generator 11 has a random code having a code length over the predetermined time. For example, the code length N of the random code is expressed by the following equation using the pulse width Pw, the measured optical fiber length L _fiber, and the propagation velocity v of light in the optical fiber.
N> (2 / v) · (L _fiber / Pw)
However, N satisfies 2 ⁿ −1.
Therefore, in this embodiment, when the optical fiber length L _fiber to be measured is 500 m and the 1-bit pulse width Pw of the random code is 10 nsec, the code length N is 511 bits or more.

  In this embodiment, the random code generator 11 continuously generates a random code having a code length over the predetermined time four times, and the light sources 13_1 to 13_N continuously test over four times the predetermined time. Output light.

In the light receiving procedure, the multi-wavelength simultaneous measurement OTDR operates as follows.
Port 15, is back-scattered light L _B from the measured optical fiber 93 is inputted. The optical coupler 14 guides the backscattered light _{L B} from the port 15 to the light receiver 16. Light receiver 16 is converted into an electric signal by receiving backscattered light L _B inputted from the optical coupler 14.

Here, the optical fiber to be measured, backscattering light _{L B} corresponding to the random code C_1~C_N is received by the photodetector 16. Backscattered light modulated by random code L _B becomes level center modulated signal with. When the measured optical fiber 93 has optical fiber characteristics as shown in FIG. 3, the electrical signal output from the light receiver 16 is as shown in FIG.

  In the DC cut procedure, the DC cut circuit 17 cuts the DC component included in the electrical signal from the light receiver 16. The DC cut circuit 17 is a capacitor, for example, and AC-couples the electrical signal from the light receiver 16.

  In the AD conversion procedure, the AD conversion circuit 19 converts the analog signal from the DC cut circuit 17 into a digital signal.

In the correlation processing procedure, the correlator 20 performs a correlation operation between the digital signal from the AD conversion circuit 19 and each random code from the random code generator 11. Backscattered light L _B of a plurality of wavelengths modulated with random code is converted into a digital signal by the AD converter 19. However, by acquiring the correlation between the digital signal and the random codes C_1 to C_N in the correlation processing procedure, each backscattered light modulated by each random code C_1 to C_N can be extracted. Therefore, even in an environment where the backscattered light is entered with a plurality of wavelengths to observe the back scattered light generated by the test light L _T _1~L _{T _N} of each wavelength, be made OTDR measurements at each wavelength It becomes possible.

  FIG. 5 shows an example of an output waveform from the correlator 20 that performs correlation calculation of a certain code among the random codes C_1 to C_N. The characteristics of the optical fiber to be measured shown in FIG. 3 can be reproduced in two times except for the first and last of the four consecutive generations of random codes. As described above, by using the test light in which the random code is continuously generated three times or more, signal amplification is performed after AC coupling even when optical pulses having a plurality of wavelengths are simultaneously incident on the optical fiber 93 to be measured. Therefore, a multiple wavelength OTDR test can be performed without using a wavelength filter.

FIG. 6 shows an example of a usage pattern of the multi-wavelength simultaneous measurement OTDR according to the present embodiment. In the present embodiment, an example is shown in which a multi-wavelength simultaneous measurement OTDR is connected to a PON. In the PON, one optical line 91 is branched by an optical coupler 92 into a plurality of optical lines 93_1 to 93_N. Thereby, communication is performed between the OLT 96 and the plurality of ONUs 97_1 to 97_N. Wavelength filter 94_1~94_N and wavelength filter 95 is arranged at an end portion of the optical path 91 and optical lines 93_1～93_N, by passing the signal light _{S C} transmitted by the PON reflects the signal light _{S C} other light .

The OTDR 101 is disposed at either one of the optical line 91 and the ends of the optical lines 93_1 to 93_N, and enters test light obtained by modulating the light having the reflected wavelengths of the wavelength filters 94_1 to 94_N and 95 with a random code toward the optical coupler 92. To do. Then, the test light wavelength filter 94_1～94_N, reflected or scattered backward scattered light _{L B} at 95 or optical line 91,93_1～93_N, performs the correlation process with the random code and receives without passing through the wavelength filter .

  For example, the OTDR 101 is connected to the optical line 93_3. In this case, in the test light output procedure, the light sources 13_1 to 13_N continuously output the test light for a predetermined time longer than the time required for light to propagate through the optical fiber 93 to be measured. The end of the optical line 91 may be a wavelength filter 95, and the end of the optical line 93_3 may be a wavelength filter 94_3.

  Although the background light is modulated by the communication signal, the bit rate is very high compared to the modulation frequency of the light sources 13_1 to 13_N. Therefore, when the light is converted into an electric signal by the light receiver 16, it is limited to the OTDR reception band. It will be. Further, the low frequency background light is cut by the DC cut circuit 17.

Some of the modulated background light is converted into a digital signal by the AD conversion circuit 19 with the modulated backscattered light L _B by random code. However, since the background light has no correlation with the random codes C_1 to C_N, only the backscattered light characteristic having the correlation is extracted. Therefore, even in an environment containing the background light in addition to the backscattered light of a plurality of wavelengths to observe the back scattered light generated by the test light L _T _1~L _{T _N} of each wavelength, the influence of the background light OTDR measurement can be performed without any problem.

  In this embodiment, the example in which the test light is incident from the ONU side toward the OLT side has been described. However, the test light may be incident from the OLT side to the ONU side. In this case, the OTDR 101 is inserted between the optical coupler 92 and the wavelength filter 95.

  The present invention can be applied to the information communication industry.

11: random code generators 12_1 to 12_N: modulators 13_1 to 13_N: light sources 14, 92: optical coupler 15: port 16: light receiver 17: DC cut circuit 18: amplifier 19: AD conversion circuit 20: correlator 21: combination Wavers 91, 93_1 to 93_N: optical line 93: optical fibers to be measured 94_1 to 94_N, 95: wavelength filter 96: OLT
97_1 to 97_N: ONU
101: OTDR

Claims (3)

A random code generator (11) for generating two or more different random codes;
A plurality of light sources (13_1 to 13_N) having different wavelengths, which receive a random code from the random code generator and output test light modulated with a different random code for each wavelength;
A multiplexer (21) for multiplexing the test light from the plurality of light sources;
An optical coupler (14) for outputting the combined light from the multiplexer to the optical fiber to be measured and receiving backscattered light from the optical fiber to be measured;
A light receiver (16) that receives the backscattered light input from the optical coupler and converts it into an electrical signal;
A DC cut circuit (17) for cutting a DC component contained in the electrical signal from the light receiver;
An AD conversion circuit (19) for converting an analog signal from the DC cut circuit into a digital signal;
A correlator (20) for performing a correlation operation between the digital signal from the AD conversion circuit and each random code from the random code generator;
Multi-wavelength simultaneous measurement OTDR (Optical Time-Domain Reflectometer).   2. The multi-wavelength simultaneous measurement OTDR according to claim 1, wherein the multiplexer is a WDM (Wavelength Division Multiplexers). A random code generation procedure for generating two or more different random codes;
A test light output procedure in which a random code generated in the random code generation procedure is input and a plurality of lights having different wavelengths are modulated with different random codes,
A multiplexing procedure for multiplexing the test light output in the test light output procedure;
A light receiving procedure for outputting the combined light combined in the multiplexing procedure to the optical fiber to be measured, receiving backscattered light from the optical fiber to be measured and converting it into an electrical signal;
A DC cut procedure for cutting a DC component contained in the electrical signal converted by the light receiving procedure;
An AD conversion procedure for converting an AC component after cutting the DC component in the DC cut procedure into a digital signal;
A correlation processing procedure for performing a correlation operation between the digital signal converted by the AD conversion procedure and each random code generated by the random code generation procedure;
Multi-wavelength simultaneous OTDR measurement method having

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