JP2010091406A - Method of correcting otdr nonlinearity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a method of correcting OTDR nonlinearity capable of performing more accurate measurement without being affected by nonlinearity possessed by an amplifier used for OTDR. <P>SOLUTION: OTDR characteristics F12 to output of rear scattered light are measured by applying test light from one end of a reference optical fiber; the straight line approximation data T are calculated; difference data ΔTa, ΔTb are calculated from the OTDR characteristics F12 and the straight line approximation data T; and the OTDR characteristics measured for the optical fiber to be measured are corrected by the difference data ΔTa, ΔTb. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  In the present invention, when measuring characteristics such as optical loss of an optical fiber and an optical fiber line with an optical pulse tester (hereinafter abbreviated as OTDR), the present invention is more accurate without being affected by the nonlinearity possessed by OTDR. The present invention relates to an OTDR non-linearity correction method for enabling accurate measurement.

Conventionally, a measurement method using an OTDR (abbreviation of Optical Time Domain Reflectometer) has been widely used as a method for measuring a failure point and a break point of a long-distance optical device such as an optical fiber transmission line with a resolution in units of meters.
Here, the OTDR enters a light pulse into the optical fiber under test, receives backscattered light from each part, and analyzes this to obtain a loss distribution and a loss value (loss value) on the optical fiber under test. ), Calculating the defect position.

  By the way, since the backscattered light from each part of the optical fiber under test has a very small power, the received backscattered light is converted into an electric signal in the OTDR and amplified by an amplifier (amplifier) ( For example, see Patent Documents 1 and 2).

JP-A-9-33389 JP-A-5-34239

  By the way, when one fiber is measured by a plurality of OTDRs, it is noticed that the linearity of the backscattered light intensity is different for each measuring instrument. Examining in detail, for example, the measuring device A has a measured value of a portion where backscattered light of −10 dBm is predicted, a reproducibility is −10.02 dBm, or a measured value of a portion where −20 dBm is expected. -19.70 dBm with good reproducibility. The direction and amount of this deviation are unique values for each measuring instrument. This value is caused by imperfect accuracy adjustment during amplification processing after a weak signal is received by the measuring instrument. Here, this phenomenon is referred to as nonlinearity of an amplifier that performs amplification processing. In the conventional OTDR, measurement is performed while ignoring the influence of such non-linearity. Therefore, the actually measured OTDR characteristic is different from the true value due to the influence of the non-linearity inherent to the measuring instrument, and the OTDR There has been a problem that the improvement of the measurement accuracy of characteristics is hindered.

  Furthermore, in recent years, with the improvement in performance of optical fibers, etc., it has been required to further improve the measurement accuracy of OTDR characteristics, and the measurement accuracy is required to be accurately measured to the order of, for example, 0.001 dB / km. However, in the conventional OTDR characteristic measurement in which the influence of the nonlinearity of the amplifier is ignored, there is a problem that it is difficult to meet the recent demand for improvement in measurement accuracy.

  An object of the present invention is to solve the above-described problem, and to provide an OTDR nonlinearity correction method that enables more accurate measurement without being affected by the nonlinearity of an amplifier used in OTDR. To do.

(1) In order to solve the above-described problem, an OTDR nonlinearity correction method according to the present invention includes:
Prepare a reference optical fiber,
Injecting test light from one or both ends of the reference optical fiber to measure OTDR characteristics, and calculating linear approximation data from the measured OTDR characteristics;
Calculating difference data from the OTDR characteristics and the linear approximation data;
An OTDR characteristic obtained by entering light from one end or both ends of an optical fiber to be measured is corrected by the difference data.

  (2) Further, in the OTDR nonlinearity correction method according to (1) above, when a plurality of the difference data exist for the same backscattered light output, an average value of the plurality of difference data is set as a new difference. It is good also as data.

  (3) Further, in the OTDR nonlinearity correction method according to (1) or (2), a plurality of reference optical fibers are prepared, each OTDR characteristic is measured, and an effective range thereof is determined. Difference data between the OTDR characteristics of the OTDR characteristics and the linear approximation data calculated from the OTDR characteristics, and when the effective ranges of the difference data calculated from the plurality of reference optical fibers overlap, the respective reference lights for the overlapping ranges The average value of the difference data calculated from the fiber is calculated, and the difference data calculated from each of the reference optical fibers is used for a range where the effective ranges of the difference data calculated from the plurality of reference optical fibers do not overlap. It is also possible to use new difference data.

  According to the OTDR nonlinearity correction method according to the present invention, the difference data calculated from the OTDR characteristic obtained by the measurement processing for the reference optical fiber and its linear approximation data quantifies the nonlinearity of the amplifier used in the OTDR. By performing a correction process for subtracting the difference data from the OTDR characteristic obtained by the measurement process performed on the measurement target optical fiber, the influence of nonlinearity possessed by the amplifier in the OTDR is obtained. Therefore, more accurate OTDR characteristics can be measured, and the loss distribution and defect position can be more accurately evaluated from the corrected OTDR characteristics, which can be utilized for quality control of the optical fiber to be shipped.

Hereinafter, preferred embodiments of an OTDR nonlinearity correction method according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an embodiment of an OTDR that measures the characteristics of an optical fiber by an OTDR nonlinearity correction method according to the present invention, and FIG. 2 shows an OTDR nonlinearity correction method according to the present invention. FIG. 3 is an OTDR nonlinearity correction method according to the present invention, an explanatory diagram of an effective range on waveform data measured with respect to a reference optical fiber, and a flowchart showing a procedure for creating a difference data file for correcting the utility. 4 is an explanatory diagram of difference data calculated from the measured waveform data and its linear approximation data, FIG. 5 is an explanatory diagram showing a correction value for the backscattered light output, and FIG. 6 is an OTDR nonlinearity correction method according to the present invention. The procedure for correcting the OTDR characteristics measured for the optical fiber to be measured using the difference data is shown below. It is a flow chart.

  In the OTDR 100 shown in FIG. 1, the light source 5 such as a laser diode is excited by a pulse wave of a fixed period generated by the pulse generator 3, and an optical pulse is generated from the light source 5. The light pulse generated by the light source 5 passes through the directional coupler 7 and is incident on one end of an optical fiber 11 to be measured such as a reference optical fiber or an optical fiber to be measured connected via an optical connector 9. It propagates in the measurement optical fiber 11.

If there is a break point in the optical fiber 11 to be measured, the light pulse is generally totally reflected. In the OTDR measurement, the slope of the OTDR characteristic represents a loss value, and when there is a glass abnormality or winding disorder of the optical fiber, the waveform appears as a wave or a step, and the waveform also swells due to the influence of microbending.
By measuring the OTDR characteristics in this way, it is possible to detect abnormalities in the glass or winding state of the optical fiber.

The light pulse reflected in the measured optical fiber 11 returns to the directional coupler 7 as a backscattered light output, and is sent from the directional coupler 7 to the light receiving unit 13.
The light receiving unit 13 includes, for example, an avalanche photodiode (APD) and functions as a photoelectric converter that converts the received backscattered light output into an electric signal.

The electric signal converted in the light receiving unit 13 is amplified by an amplifier 15 and then sent to the signal processing device 17.
When the measured optical fiber 11 connected to the directional coupler 7 via the optical connector 9 is the reference optical fiber in the OTDR nonlinearity correction method of the present invention, the signal processing device 17 receives the received electrical fiber. Predetermined processing is performed on the signal to measure the OTDR characteristic with respect to the backscattered light output, while calculating the linear approximation data of the measured OTDR characteristic, and further, the difference data from the calculated OTDR characteristic and the calculated linear approximation data And the calculated difference data is stored in a predetermined storage device (not shown) together with the corresponding backscattered light output value.

  On the other hand, when the measured optical fiber 11 connected to the directional coupler 7 via the optical connector 9 is a measurement target optical fiber in the OTDR nonlinearity correction method of the present invention, the signal processing device 17 The OTDR characteristic obtained by injecting light from one or both ends of the optical fiber to be measured is measured, and the measured OTDR characteristic is corrected with the difference data stored in the storage device, thereby correcting the more accurate OTDR. Characteristics are calculated.

  In the case of the OTDR 100 of the present embodiment, the OTDR characteristics, linear approximation data, difference data, and the like obtained by the processing of the signal processing device 17 are stored and stored in a storage device (not shown) and displayed on a liquid crystal display or the like. It is displayed on the device 19.

Next, the OTDR nonlinearity correction method of the present embodiment, which is performed using the OTDR 100 shown in FIG. 1, will be described. In addition, although the reference | standard optical fiber the state wound around the bobbin was used, it is not restricted to this, For example, it is also possible to use the fiber of a bundling state.
In the OTDR nonlinearity correction method of the present embodiment, first, a reference optical fiber having stable characteristics is prepared, and test light is incident from one or both ends of the reference optical fiber, and the backscattered light output is reduced. OTDR characteristics are measured, linear approximation data of the measured OTDR characteristics is calculated, difference data is further calculated from the measured OTDR characteristics and linear approximation data, and a difference data file in which the calculated difference data is arranged (correction) Create a data file and save it.
The difference data file creation process is performed according to the procedure shown in FIG.

Next, the difference data file creation process of FIG. 2 will be described in detail.
First, an optical fiber manufactured at an intermediate portion of a preform whose manufacturing conditions are stable is selected as a reference optical fiber (step S201). The reason for using an optical fiber whose manufacturing conditions are stable is that the stability of the manufacturing conditions leads to stabilization of each characteristic of the fiber, and the undulation in the OTDR measurement waveform represents only nonlinearity by the amplifier.
In the case of the present embodiment, as the reference optical fiber, an optical fiber that has stable characteristics (structure) in the length direction at the optical fiber preform stage before drawing and has no abnormality at the drawing stage is used.

Next, the optical fibers selected in step S201 are measured under actual measurement conditions.
In the case of the present embodiment, the test light is incident from one end (upper port) of the reference optical fiber to measure the OTDR characteristics, and the test light is incident from the other end (lower port) of the reference optical fiber. Then, the OTDR characteristic is measured, and as shown in FIG. 3, two waveforms, an upper-entrance incident waveform F1 and a lower-entrance incident waveform F2, are measured (step S202).

Next, an effective data range is determined from the measurement result obtained in step S202 (step S203). In this case, the effective range start position is after the portions F1b and F2b where the waveform is not stable due to the influence of Fresnel reflection near the incident, and the effective range end position is immediately before the portions F1a and F2a where the noise level is equal to or higher than the reference level. is there.
Specifically, the effective range of the upper opening incident waveform F1 is F1u shown in FIG. 3, and the effective range of the lower opening incident waveform F2 is F2u shown in FIG.

Next, waveform data F12 obtained by synthesizing the effective ranges of the upper entrance incident waveform F1 and the lower entrance incident waveform F2 is created (step S204).
Specifically, as shown in FIG. 3, in the area B12 where the effective ranges overlap in the upper-entrance incident waveform F1 and the lower-entrance incident waveform F2, waveform data that is the average of the respective waveform data is created, and the effective range is In the non-overlapping regions B1 and B2, waveform data using the respective waveform data F1 and F2 as they are is created.

Next, as shown in FIG. 4B, linear approximation (least square approximation) data T of the waveform data F12 in each of the regions B12, B1, and B2 is calculated, and the approximated data T and the original waveform data are calculated. The difference of F12 is obtained, and the obtained differences ΔTa and ΔTb are set as difference data (correction data) for each backscattered light output (step S205).
The OTDR waveform obtained by the measurement process for the reference optical fiber is a linear waveform if the amplification factor of the amplifier 15 of the OTDR 100 shows perfect linearity, but the actually measured OTDR waveform is not linear. 4 (a), the meandering waveform is as shown in FIG. 4 (b). As shown in FIG. 4 (b), the meandering portion of the waveform (the portion where the deviation from the straight line occurs) is the amplifier in the OTDR. Non-linearity possessed by.

Normally, the correction value for the backscattered light output varies depending on the magnitude of the backscattered light output as shown in FIG. FIG. 5 shows an example of the correction value for the backscattered light output, and is not directly related to the example of FIG. Since the correction value fluctuates in this way, a plurality of difference data having two or more values may be generated even in the case of the same backscattered light output.
Considering this, in the OTDR nonlinearity correction method of the present embodiment, when a plurality of difference data are generated, the average value of these difference data is handled as new difference data.

  Subsequently, the backscattered light output and the difference data corresponding to the backscattered light output are sorted and stored in the descending order of the backscattered light output, thereby creating a difference data file (corrected data file) and storing it in the OTDR 100. The data is stored in a storage device (not shown) that is equipped (step S206).

In the OTDR nonlinearity correction method of the present embodiment, when measuring the OTDR characteristic by entering light from one or both ends of the measurement target optical fiber, the OTDR characteristic of the measurement target optical fiber is measured as shown in FIG. On the other hand, a correction process for correcting with the difference data obtained in the process of FIG. 2 is performed.
The procedure of the correction process in FIG. 6 will be described below.

First, the measurement of the OTDR characteristic is performed on the measurement target optical fiber under the same measurement conditions as those when collecting the difference data by the reference optical fiber shown in FIG. 2 (step S301).
Next, difference data that matches the backscattered light output of the OTDR characteristic obtained by measurement with respect to the measurement target optical fiber is selected from the difference data file created in the process of FIG. 2 (step S302).
Next, the difference data selected from the difference data file is subtracted from the actual OTDR characteristic data obtained by the measurement for the measurement target optical fiber, and the resulting OTDR characteristic data is used as the OTDR characteristic data of the measurement target optical fiber. (Step S303).

  In the OTDR nonlinearity correction method of the present embodiment described above, a reference optical fiber is prepared, test light is incident from one or both ends of the reference optical fiber, and the OTDR characteristic with respect to the backscattered light output is measured. After calculating the linear approximation data of the measured OTDR characteristics and calculating difference data from the OTDR characteristics and the linear approximation data as shown in FIG. 4B, light is transmitted from one or both ends of the optical fiber to be measured. The OTDR characteristic obtained by incidence is corrected with the difference data obtained with the reference optical fiber.

  Here, since the difference data calculated from the OTDR characteristic obtained by the measurement processing for the reference optical fiber and the linear approximation data thereof is data obtained by quantifying the nonlinearity of the amplifier 15 used in the OTDR 100, the measurement target By performing a correction that subtracts the difference data from the OTDR characteristics obtained by the measurement process performed on the optical fiber, the OTDR is more accurate without being affected by the nonlinearity of the amplifier in the OTDR. The characteristics can be measured, and the loss distribution and the defect position can be more accurately evaluated from the corrected OTDR characteristics, which can be used for quality control of the optical fiber to be shipped.

  Furthermore, in the OTDR nonlinearity correction method according to the present embodiment, as a reference optical fiber for measuring the OTDR characteristic for calculating difference data, the characteristic (structure) in the length direction at the optical fiber preform stage before drawing is provided. Since an optical fiber that is stable and has no abnormality at the stage of drawing is used, the reliability of differential data as non-linearity quantification data of the amplifier 15 can be improved.

Further, in the OTDR nonlinearity correction method of the present embodiment, when there are a plurality of difference data with respect to the backscattered light output data as shown in FIG. 5, an average value of the plurality of difference data is newly set. The difference data.
By doing in this way, one difference data respond | corresponds with respect to one backscattered light output data, and a correction | amendment process can be performed.

In the present embodiment, as described above, OTDR characteristics from both ends of the reference optical fiber are measured, and difference data for the backscattered light output data is calculated from the calculated linear approximation data. For example, as shown in FIG. 3, the measurement result on the emission end side when entering from the opposite end side is used as the difference data for the incident end side where a large fluctuation is likely to occur in the measurement waveform.
In this way, it is possible to eliminate the specific influence at the incident end and the influence due to the state (winding state) in the longitudinal direction of the optical fiber, so that improvement in measurement accuracy can be expected.

  More specifically, an optical fiber that is likely to cause a large shake on the measurement waveform by calculating effective differential data for each part in the longitudinal direction of the optical fiber based on the measurement results measured from both ends. The correctness of the measurement waveform can also be corrected for the incident end side of the optical fiber, and accurate measurement can be performed for a wider longitudinal range along the longitudinal direction of the optical fiber.

  In addition, since the measurement result of the intermediate part is relatively stable on the measurement waveform of the measurement result from each of the one end and the other end, this stable part will be described with reference to FIG. 3 in the above embodiment. As described above, the average value of the difference data calculated for the measurement results from the respective ends may be used as the true difference data. Thereby, it is possible to improve measurement accuracy while suppressing an increase in arithmetic processing.

Furthermore, in the OTDR nonlinearity correction method according to the present invention, in the difference data file creation process shown in FIG. 2, a plurality of reference optical fibers are prepared, and the difference data calculated from the respective OTDR characteristics and linear approximation data. It is preferable to use the average value of the difference data as new difference data.
By doing so, the dispersion of difference data due to individual differences of the used reference optical fibers is averaged, and the versatility when used as correction data is improved.

Further, in the OTDR nonlinearity correction method of the present embodiment, when creating difference data, the measurement of the OTDR characteristic for the reference optical fiber was performed from both ends, but the measurement of the OTDR characteristic for the reference optical fiber was It is also conceivable to implement only from one end of the mouth or lower mouth.
However, differential data with higher versatility (reliability) can be obtained by performing measurement from both ends as in the above embodiment.

  Further, in the OTDR nonlinearity correction method of the present embodiment, when there are OTDR data of a plurality of reference optical fibers, a plurality of difference data is created and averaged to obtain new difference data. However, OTDR data itself of a plurality of reference optical fibers may be averaged, and linear approximation data may be calculated from the OTDR data obtained by averaging to obtain difference data.

  Table 1 below shows an example of the backscattered light output value actually measured by the procedure based on the present invention and the correction value obtained for the output value.

It is a block diagram which shows the structure of one Embodiment of OTDR which measures the characteristic of an optical fiber with the OTDR nonlinearity correction method which concerns on this invention. It is a flowchart which shows the preparation procedure of the difference data for correct | amending the non-linearity of OTDR with the OTDR non-linearity correction method which concerns on this invention. It is explanatory drawing of the effective range on the waveform data measured with respect to the reference | standard optical fiber with the OTDR nonlinearity correction method which concerns on this invention. It is explanatory drawing of the difference data calculated from the measured waveform data and its linear approximation data. It is explanatory drawing which shows the correction value with respect to backscattered light output. It is a flowchart which shows the process sequence which correct | amends the OTDR characteristic measured with respect to the measuring object optical fiber with difference data with the OTDR nonlinearity correction method which concerns on this invention.

Explanation of symbols

3 Pulse generator 5 Light source (laser diode)
7 Directional coupler 9 Optical connector 13 Light receiving part (photoelectric converter)
15 Amplifier
17 Signal Processing Device 19 Display Device 100 OTDR (Optical Pulse Tester)
F1 Upper entrance incident waveform (OTDR characteristic waveform)
F2 Lower entrance incident waveform (OTDR characteristic waveform)
F12 Effective range composite waveform data T Linear approximation data ΔTa, ΔTb Difference data (correction data)

Claims (3)

Prepare a reference optical fiber,
Injecting test light from one or both ends of the reference optical fiber to measure OTDR characteristics, and calculating linear approximation data from the measured OTDR characteristics;
Calculating difference data from the OTDR characteristics and the linear approximation data;
An OTDR nonlinearity correction method, wherein an OTDR characteristic obtained by making light incident from one end or both ends of an optical fiber to be measured is corrected by the difference data.   2. The OTDR nonlinearity correction method according to claim 1, wherein when a plurality of the difference data exist for the same backscattered light output, an average value of the plurality of difference data is used as new difference data. . Preparing a plurality of reference optical fibers, measuring each OTDR characteristic and determining its effective range, calculating difference data between the OTDR characteristic of the effective range and linear approximation data calculated from the OTDR characteristic, When the effective ranges of the difference data calculated from a plurality of reference optical fibers overlap, an average value of the difference data calculated from the respective reference optical fibers is calculated for the overlapped range, and is calculated from the plurality of reference optical fibers. 3. The OTDR nonlinearity according to claim 1, wherein a difference data calculated from each of the reference optical fibers is used as a new difference data for a range in which the effective ranges of the difference data do not overlap. 4. Correction method.

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