JPS61155934A - Method and apparatus for measuring characteristic of optical fiber - Google Patents

Abstract

PURPOSE:To efficiently perform measurement by obtaining data necessary for succeeding measurement from the previous measurement and to perform synthetic judgement by the comparison of measured results, by successively performing the measurement of back scattering loss, the measurement of single wavelength loss and the measurement of a band. CONSTITUTION:The light from the light source 20 of a back scattering loss measuring apparatus 220 is incident to one terminal 11 of an optical fiber 50 to be measured through an optical directional coupler 19 and a measuring device photometric fiber 18 and the back scattering light from the optical fiber 50 is incident to a light detector 21 through the fiber 18 and the directional coupler 19. The length of the fiber is obtained from the detected results. Next, single wavelength loss is measured from the measured result by a single wavelength loss measuring apparatus 230 and the length of the fiber calculated by the apparatus 220. By utilizing the measured results of the length of the fiber and loss, a band is measured by a band measuring apparatus 240. By this method, because data necessary for the measurement of a succeeding item is obtained from the previous measurement, measurement is performed efficiently. Further, by the comparison of the measured result of each item, synthetic judgement can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method and apparatus for measuring the characteristics of an optical fiber. The present invention relates to a method and apparatus for measuring characteristics of optical fibers that can accurately measure characteristics.

Whether the conventional technology optical fiber has such characteristics as
This is important when actually using optical fibers. Therefore, when an optical fiber is manufactured, measurements are performed on various items such as backscattering loss, single wavelength loss also referred to as point loss, and band characteristics. For example, in the case of a graded index optical fiber, several measurements are performed such as backscattering loss measurement, single wavelength loss measurement, and band measurement.

Here, if we consider single wavelength loss measurement, light of a specific single wavelength is input into the optical fiber to be measured, and the level of the optical output is measured.

However, even if the characteristics of the optical fibers to be measured are the same and the same level of light is input to the optical fibers to be measured, if the optical fibers to be measured have different lengths, the output will naturally differ. Furthermore, the measured value also includes losses in the optical system of the measuring device other than the optical fiber to be measured. Therefore, it is necessary to correct the output value using the fiber length or the like. Therefore, single wavelength loss measurement requires data other than the measurement items, such as fiber length.

Furthermore, in the band measurement, the modulation frequency for the transmitted light is changed, and the output level at each modulation frequency is compared with the output level at each modulation frequency in the case of a reference fiber. In this case as well, the fiber length of the optical fiber to be measured is required, and the output level when not modulated must be made to match the output level when not modulated in the case of the reference fiber.

Problems to be Solved by the Invention As described above, in measuring the characteristics of an optical fiber to be measured, data other than the measurement items are required in order to obtain accurate measurement results for the measurement items. However, in the past, each item was measured separately, and the data necessary for the measurement was either measured or ignored each time. Therefore, the measurement results were often not reliable enough.

Furthermore, since the measurement of each item has conventionally been carried out separately, the evaluation of the measurement results has also been carried out independently of each other. However, it is difficult to evaluate completely independently whether the measurement results for each item are accurate or not.
Moreover, incorrect evaluations were often made.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method and apparatus for measuring characteristics of an optical fiber, which makes it possible to obtain data necessary for measuring each item in advance and to efficiently carry out accurate measurements.

Furthermore, it is an object of the present invention to provide an optical fiber characteristic measuring device that can comprehensively judge the results of measuring the characteristics of an optical fiber.

According to the present invention, a method for solving the problem is to perform backscattering loss measurement on the optical fiber to be measured, and then, using the fiber length obtained by the backscattering loss measurement, An optical fiber characteristic measuring method is provided, which is characterized in that a single wavelength loss measurement is performed on the same optical fiber to be measured.

In the above method, if necessary, a band measurement may be further performed using the fiber length and transmission loss obtained by the backscattering loss measurement and the single wavelength loss measurement.

Furthermore, according to the present invention, a backscattering loss measuring device;
A single wavelength loss measurement device and a band measurement device are arranged in series, and a measurement control device is further provided, and the measurement control device receives the fiber length of the optical fiber to be measured from the backscattering loss measurement device. an optical fiber that is configured to receive transmission loss from the single wavelength loss measuring device and output it to the single wavelength loss measuring device and the band measuring device, and to receive a transmission loss from the single wavelength loss measuring device and output it to the band measuring device. Characteristic measuring equipment will be provided.

In the method for measuring optical fiber characteristics according to the present invention as described above, backscattering loss measurement is performed prior to single wavelength loss measurement, so single wavelength loss measurement can be performed on the same optical fiber under test. In implementation, the fiber length obtained by backscattering loss measurements can be utilized. Therefore,
Accurate single wavelength loss characteristics can be obtained by correcting the output value with the fiber length.

Furthermore, if the band measurement is performed after the backscatter loss measurement and the single wavelength loss measurement, the fiber length and transmission loss obtained by the backscatter loss measurement and the single wavelength loss measurement are used in the band measurement, The unmodulated output level can be made to match the unmodulated output level of the reference fiber, and the measured value can also be corrected based on the fiber length, making it possible to obtain accurate band characteristics.

Further, in the optical fiber characteristic measuring apparatus according to the present invention described above, the method for measuring optical fiber characteristics according to the present invention described above can be efficiently carried out depending on the type of optical fiber to be measured.

Embodiments Hereinafter, embodiments of the optical fiber characteristic measuring method and apparatus according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing the configuration of an embodiment of an optical fiber characteristic measuring apparatus according to the present invention, which can carry out the optical fiber characteristic measuring method according to the present invention. Note that FIG. 1 shows a state in the middle of measurement.

In FIG. 1, reference numeral 10 indicates a bobbin of an optical fiber to be measured, which is placed on a moving table (not shown). Both ends 11 and 12 of the optical fiber to be measured wound around the bobbin 10 are held by a pair of optical fiber holders 13 and 14 provided on the moving stage 15. These optical fiber holders 13 and 14 to be measured can be composed of, for example, a groove block and a holding member having a complementary shape to the groove. Place the optical fiber to be measured at the bottom of the groove and place the holding member on top of it.
The optical fiber to be measured is
It can be held so that it does not move in two orthogonal directions.

The moving stage 15 is configured to be linearly movable in the direction of arrow X along a guide (not shown).

On the opposite side of the moving stage 15 from the optical fiber bobbin 10 to be measured, there is a measuring instrument side optical fiber holder 16.16A116.
B, 17A, and 17B are arranged in a straight line parallel to the moving direction of the moving stage 15. Those measuring instrument side optical fiber holders 16.16A, 16B and 17A117B
are respectively measuring instrument side optical fiber 18.18A118
B and one end of 19A and 19B is held. The other end of the measuring instrument side optical fiber 18 is connected to a light source 20 and a photodetector 21 via an optical directional coupler 19, and connects the light from the light source 20 to the measuring instrument side optical fiber 18. Light from the measuring instrument side optical fiber 18 is output to a photodetector 21. Measuring instrument side optical fibers 18A, 18B
The other ends are connected to the light sources 2OA and 20B, respectively, and the other ends of the measuring instrument side optical fibers 19A and 19B are connected to the photodetectors 21A and 21B. The distance between the light receiving side optical fiber holder and the light source side optical fiber holders 16A, 17A, 116B and 17B is the same as the distance between the light receiving side optical fiber holder and the light emitting side holder 13 on the moving stage 15.
and 14 intervals.

The light sources 20.2OA, 20B and the photodetector 21.
21A and 21B are connected to processing devices 22, 23, and 24 that process the measurements of the assigned measurement items, respectively. In the illustrated example, a backscattering loss measurement processing device 22, a single wavelength loss measurement processing device 23, and a band measurement processing device 24 are arranged from upstream in the moving direction X of the moving stage 15. Therefore, the backscattering loss measurement processing device 22, the single wavelength loss measurement processing device 23, and the band measurement processing device 24, together with their attached light sources, photodetectors, and measuring instrument side optical fibers, are connected to the measurement station A. ,B,C
It consists of

Further, the backscattering loss measurement processing device 22, the single wavelength loss measurement processing device 23, and the band measurement processing device 24 are connected to a measurement control device 25, and are controlled by the measurement control device 25. Note that the backscattering loss measurement processing device 22, the single wavelength loss measurement processing device 23, the band measurement processing device 24, and the measurement control device 25 can be configured with, for example, a microcomputer.

The moving stage 15 is moved in the direction indicated by arrow X by a conveyor device (not shown) or an operator, and the measuring instrument side optical fiber holders 16.
It is designed to be stopped every one step length corresponding to an interval of 6B. The conveyor device can be composed of, for example, a feed screw mechanism that feeds the moving stage along a guide and a reversible pulse motor that rotationally drives the feed screw. By appropriately selecting the number of driving pulses of such a pulse motor, the feed screw can be rotated by a predetermined amount to move the moving stage by a predetermined amount, that is, by one step. As the moving stage 15 moves,
The carriage carrying the bobbin 10 can also be advanced one step at a time in the direction indicated by arrow X by another conveyor device (not shown) or by an operator. It is preferable that the movement of the moving table on which the moving stage 15 and the mobi bobbin 10 are mounted is controlled by the measurement control device 25.

As seen in FIG. 1, the tip of the optical fiber to be measured is placed below the optical fiber holder 16 on the measuring instrument side, at the same distance as the distance between the pair of light output side holders and light input side holders 13 and 14. Optical sensors S1 and S2 for detection are arranged. These optical sensors S1 and S2 are connected to the measuring instrument side optical fibers 18 to 18B and 1 which are correctly set in the measuring instrument side optical fiber holders 16 to 16A and 17A-17B.
It is arranged so as to be located on a straight line connecting the ends of 9A to 19B.

Each of these optical sensors S1 and S2 is configured as follows, for example. In other words, a pair of optical fibers are arranged so as to be perpendicular to the extension line of the axis of the optical fiber to be measured and with the extension line of the axis of the optical fiber to be measured sandwiched between them, and light is emitted from one of them, and light is emitted from the other. It is configured to detect that the light beam incident on the optical fiber is partially or completely blocked by the optical fiber to be measured. The optical fiber used has a core diameter of several tens of μm. Since the diameter of the optical fiber to be measured when its coating is removed is 100 to 150 μm for a single mode optical fiber and 100 to 250 μm for a multimode optical fiber, the optical fiber to be measured has a diameter of 100 to 150 μm. The light beam emitted from the light emitting optical fiber and entering the light receiving optical fiber can be completely blocked.

The light emitted from the end face of the light-emitting optical fiber is diffused to some extent, and only the central portion of the light beam enters the light-receiving optical fiber. Therefore, even if the core diameter is several tens of μm,
By appropriately selecting the distance of the optical fiber of the photosensor, the diameter of the light beam used for photodetection can be substantially reduced. Furthermore, the output voltage from the light receiving element connected to the light receiving optical fiber of the photosensor is compared with an appropriate threshold level, and when the output voltage falls below the threshold level, it is determined that light has been blocked and the process is performed. Axial positioning is possible with micrometer accuracy.

Therefore, the moving stage 15 is positioned in front of the optical sensors S1 and S2, and the both end portions 11 and 12 of the optical fiber to be measured on the moving stage 15 are moved in the axial direction so that the tips thereof are connected to the optical sensors S1 and S2. The axial position of the optical fiber to be measured can be adjusted by adjusting the position where it is detected.

In this way, the optical fibers to be measured are correctly set in the optical fiber holders 13 and 14, and the measuring instrument side optical fibers 18 to 18B and 19 A-19B are correctly set in the measuring instrument side optical fiber holders 16 to 16B and 17 A-17B. If set, no matter which position the moving stage 15 is moved, the measuring instrument side optical fibers 18 to 18B and 1
The ends of the optical fibers to be measured can be located very close to the ends of the optical fibers 9A to 19B, for example, at a distance of 10 to 50 μm, respectively.

Next, an embodiment of the optical fiber characteristic measuring method according to the present invention using the above-mentioned optical fiber characteristic measuring apparatus will be described in the case of measuring the characteristics of a graded index optical fiber. Before measuring the optical fiber to be measured, 1.
A reference fiber of about 2 m is measured, and the measured values of the reference fiber are used to calculate each measured value of the optical fiber to be measured. However, since the measurement of the reference fiber and the measurement of the optical fiber to be measured are substantially the same, only the measurement of the optical fiber to be measured will be described below.

First, the moving stage 15 is positioned in front of the optical sensors S1 and S2, and both ends of the optical fiber 10 to be measured are set in the holders 13 and 14.
They are positioned at predetermined intervals and in mutually orthogonal X and Y directions perpendicular to the axis of the optical fiber.

At that time, the distance between the optical fiber holder pair to be measured and the distance between the optical sensor S1 and the pair of optical sensors 82 are the same, so the optical fibers to be measured held in the holders 13 and 14 are connected to the optical sensors S1 and 82. Position it so that the extension line passes through it.

In this state, both end portions of the optical fibers to be measured set in the holders 13 and 14 are displaced in the axial direction, and stopped at positions where their tips are detected by the optical sensors S1 and S2. As a result, both ends of the optical fiber under test are
When the moving stage 15 is located at each measurement station, it can be located very close to the tip of the measuring instrument side optical fiber.

Next, the moving stage 15 is moved one step, that is, in the direction of the inter-step distance arrow X, and both ends of the optical fiber to be measured held by the boulders 13 and 14 are positioned at the backscattering loss measurement station A. At this time, the tip of one end 11 of the optical fiber to be measured is located in a light transmission relationship with the tip of the measuring instrument side optical fiber 18. Figure 1 shows
The state at this time is illustrated.

In this state, the measurement control device 25 outputs a command to the backscattering loss measurement processing device 22 to perform backscattering loss measurement on the optical fiber 10 to be measured.

That is, the backscattering loss measurement processing device 22 uses the light source 20
A light pulse is generated, and the light pulse is input to one end of the optical fiber 10 to be measured via the directional coupler 19.

As a result, backscattered light reflected at various points in the longitudinal direction of the optical fiber returns due to Rayleigh scattering in the optical fiber 10 to be measured.

The backscattered light from the input end of the optical fiber 10 to be measured is received by the photodetector 21 via the directional coupler 19. Then, the backscattering loss measurement processing device 22 observes changes in the output level of the photodetector 19, that is, the reflected light signal level, on the time axis.

An example of the reflected light signal level in backscattering measurement is shown in FIG. 2. The curve of the reflected light signal level, that is, the BS curve, initially shows the Fresnel reflection R1 at the input end.
appears, and then, in the normal case, a gradient section S in which the level gradually decreases continues, and finally, a Fresnel reflection R2 appears at the output end, ending with a backscattering section E at the output end. If there is an abnormality, a step or the like will be formed in the slope section S. Second
As can be seen from the figure, from this backscattering loss measurement, the fiber length of the optical fiber 10 to be measured can be determined, and also breakages and the like can be determined. Furthermore, since the slope of the slope section S indicates twice the transmission loss per unit length, the transmission loss per unit length (dB/
Km). When the above measurements are completed,
The measurement data is output to the measurement control device 25.

Therefore, the measurement control device 25 instructs the moving stage 15 to move. As a result, the moving stage 15 moves one step, that is, one step in the direction of the distance arrow position correctly.

That is, the tips of both ends 11 and 12 of the optical fiber to be measured are located in an optical coupling relationship with the tips of the measuring instrument side optical fibers 18A and 19A. In this state, the measurement control device 25
It supports the next single wavelength loss measurement processing device 23 to start the measurement and also supplies the fiber length obtained by backscattering loss measurement.

The single wavelength loss measurement processing device 23 operates the light source 2OA in response to instructions from the measurement control device 25 to couple light of a specific wavelength to the input end 11 of the optical fiber 10 to be measured. Then, the light propagated through the optical fiber 10 to be measured is received by the photodetector 21A from the output end 12 of the optical fiber 10 to be measured, and the level P out of the light is detected. The measured value P. uL and reference value P1. ．． The difference between the total loss and the fiber length of the optical fiber 10 to be measured is used to calculate the Km conversion loss from the total loss and the fiber length of the optical fiber 10 to be measured.

When the above single wavelength loss measurement is completed and the single wavelength loss measurement processing device 23 outputs the measurement data to the measurement control device 25, the measurement control device 25 instructs the movement of the moving stage 15, and 15 by one step in the direction of arrow X, and both ends of the optical fibers to be measured held in holders 13 and 14 are positioned with respect to band measurement station C. Thereafter, the measurement control device 25 instructs the next band measurement device 24 to start measurement, and also outputs the fiber length obtained by the backscattering loss measurement and the total loss (Pout- P, , ) are supplied.

Bandwidth measurement can be performed more easily and with better measurement accuracy by matching the output level of the optical fiber under test when no modulation is performed with the output level of the reference fiber when no modulation is performed. Therefore, the band measurement device 24 couples the unmodulated light from the light source 20B to the input end 11 of the optical fiber 10 under test using the total loss obtained in the single wavelength loss measurement. The light level P detected by the photodetector 21A coupled to the output end 12 of. For example, the attenuation amount of an attenuator attached to the light source 20B is adjusted so that uL matches the optical level p in in the case of the reference fiber. In this state, the output of the photodetector 21B is detected while changing the modulation frequency of the light from the light source 20B.

An example of the optical signal output level obtained by the band measurement is shown in FIG. Then, the optical signal output level at each modulation frequency is
By subtracting the optical signal output level at each modulation frequency for the reference fiber as shown in Figure 4 and converting it into m, a band characteristic curve as shown in Figure 5 is obtained, and the measurement results are as follows. is output to the measurement control device 25. In the graph of FIG. 5, the frequency at which the regression line drawn along the slope of the curve intersects with the 6 dB level is usually called the bandwidth.

Figure 6 shows the output level P of the optical fiber under test when no modulation is performed.
. Output level at uL reference fiber p in
FIG. 7 is a graph of band characteristics when band measurement is performed without making adjustments to match the output level P of the optical fiber under test when no modulation is performed. , t are adjusted to match the output level P in of the reference fiber and band measurement is performed. As can be seen from both graphs, the bandwidth is approximately 800 MHz in the example of FIG. 6, and approximately 700 MHz in the example of FIG.
z, and unless adjustment is made to match P out and Pln, an erroneous measurement result will be obtained that is 15% wider than the actual band characteristic.

Thus, the backscattering loss measurement, single wavelength loss measurement, and band measurement for the graded index optical fiber are completed. The optical fiber to be measured 10 is mounted on a moving stage 1
5 is removed.

The measurement control device 25 that receives the measurement results can also determine the reliability of the measurement from the data obtained by measuring each item. The table below shows the Km obtained from backscatter loss measurements.
The conversion loss and the Km conversion loss obtained from the single wavelength loss measurement are listed.

Nagi:From the comparison of the measurement results above, for Samples 4 and 7, the Km-equivalent loss by single wavelength loss measurement is larger than the Km-equivalent loss by backscatter loss measurement, and alignment, or axis alignment, in single wavelength loss measurement. It can be determined that it was defective.

In addition, sample 5 has a large loss both by backscattering loss measurement and by single wavelength loss measurement, and it can be evaluated that the loss of the optical fiber itself to be measured is large.

Therefore, in this embodiment, the measurement control device 25 compares the Km-equivalent loss obtained by backscattering loss measurement and the Km-equivalent loss obtained from single wavelength loss measurement, and if the difference between the two is equal to or greater than a predetermined level, the measurement control device 25 determines that the measurement is defective. When the difference between the two is below the predetermined level and both are higher than the reference value, it is displayed that the optical fiber to be measured is defective.

However, unless we compare the Km-equivalent loss obtained by backscattering loss measurement with the Km-equivalent loss obtained from single-wavelength loss measurement as in the past, it was determined that samples 4 and 7 had large losses in the optical fibers themselves. This results in incorrect evaluations being made.

In the above optical fiber characteristic measuring device, once the optical fiber to be measured is set, the
Continuous measurements can be made while using data from previous measurements. Therefore, the operator can continuously measure the characteristics of the optical fiber over many items simply by sequentially setting the optical fiber to be measured on the moving stage.

Furthermore, by comparing the data obtained by measuring each item with each other, it is possible to perform a more accurate evaluation of the measurement results.

Although an example of measuring the characteristics of a graded index optical fiber has been described above, the method according to the present invention can also be applied to measuring the characteristics of a single mode optical fiber. In that case, by performing the backscatter loss measurement and the single wavelength loss measurement in that order, the data obtained in the backscatter loss measurement can be used for the single wavelength loss measurement. Therefore, the above-mentioned measuring device can also measure the above-mentioned two characteristics of a single mode optical fiber.

Effects of the Invention As is clear from the above description, in the optical fiber characteristic measuring method according to the present invention, the data necessary for measuring each item can be manually prepared in advance, and the measurement can be performed efficiently and accurately.

According to the optical fiber characteristic measuring device according to the present invention, the above-described optical fiber characteristic measuring method according to the present invention can be efficiently carried out.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an optical fiber characteristic measuring apparatus according to the present invention, which is capable of implementing an optical fiber characteristic measuring method. FIG. 2 is a graph showing an example of the results of backscattering loss measurement. FIG. 3 is a graph showing an example of the output optical signal level of the optical fiber to be measured in band measurement. FIG. 4 is a graph showing an example of the output optical signal level in band measurement for the reference fiber. FIG. 5 is a graph showing an example of the output optical signal level of the optical fiber under test corrected based on the band characteristics of the reference fiber. FIG. 6 is a graph showing an example of the output optical signal level of the optical fiber under test when the output level in the non-modulated state is not corrected. FIG. 7 is a graph showing an example of the output optical signal level of the optical fiber under test when the output level in the non-modulated state is corrected. [Main reference numbers] 10. Bobbin of the optical fiber to be measured, 11.12. Each end of the optical fiber to be measured, 13.14.
- Optical fiber holder to be measured, 15...Movement stage, 16. 16A, 16B, 17A, 17B... Measuring instrument side optical fiber holder, 18. 18A, 18B, 19A, 19B... Measuring instrument side optical fiber, 19.・Optical directional coupler, 20.2OA, 20B...Light source, 21.2LA, 21B...Photodetector, 22...Backscattering loss measurement processing device 23...Single wavelength loss measurement processing device 24...Band Measurement processing device 25...Measurement control device

Claims (5)

[Claims] (1) Perform backscattering loss measurement on the optical fiber under test, and then use the fiber length obtained by the backscattering loss measurement to measure single wavelength loss on the same optical fiber under test. A method for measuring characteristics of an optical fiber, characterized by carrying out the following. (2) The optical fiber to be measured is a graded index optical fiber, and band measurement is performed using the fiber length and transmission loss obtained by the backscatter loss measurement and single wavelength loss measurement. A method for measuring characteristics of an optical fiber according to claim (1), characterized in that: (3) The optical fiber according to claim 1 or 2, wherein the measurement results of each item on the same optical fiber to be measured are compared and the quality is further determined. Characteristic measurement method. (4) A backscattering loss measurement device, a single wavelength loss measurement device, and a band measurement device are arranged in succession, and a measurement control device is further provided, and the measurement control device controls the backscattering loss measurement device. receives the fiber length of the optical fiber to be measured and outputs it to the single wavelength loss measuring device and the band measuring device, and receives the transmission loss from the single wavelength loss measuring device and outputs it to the band measuring device. An optical fiber characteristic measuring device characterized by: (5) The measurement control device is configured to receive measurement data for the same optical fiber to be measured from each measurement device, collate the measurement results for the optical fiber to be measured, and further determine pass/fail. An optical fiber characteristic measuring device according to claim (4), characterized in that: