JP7603474B2 - Multi-core fiber light intensity distribution measuring device and multi-core fiber light intensity distribution measuring method - Google Patents

Description

The present invention relates to a device for measuring the light intensity distribution of a multicore fiber and a method for measuring the light intensity distribution of a multicore fiber.

Multicore fibers having multiple cores arranged in the cladding are known, and a device for measuring the characteristics of such multicore fibers is described in the following Patent Document 1. In this device for measuring the characteristics of a multicore fiber, light is incident on each core from one end of the multicore fiber, and the light exiting from the other end of the multicore fiber is imaged by an imaging device, and the characteristics of the multicore fiber are determined based on the image.

JP 2018-138910 A

The light image captured by the imaging device of Patent Document 1 is nothing but the light intensity distribution. Therefore, it can be understood that this imaging device measures the light intensity distribution. However, imaging devices have a dynamic range of light that can be captured, and light that exceeds this dynamic range tends to white out, while light that falls below this dynamic range tends to be unable to be captured or the S/N ratio tends to deteriorate beyond the acceptable range.

The characteristics of each core in a multicore fiber tend not to be uniform, and even when light is incident on each core under the same conditions, there is a tendency for the intensity of the light emitted from each core to vary. Therefore, in a core that emits light with a high intensity, the light near the center of the core may exceed the dynamic range of the imaging device, and in a core that emits light with a low intensity, the light near the periphery of the core may fall below the dynamic range of the imaging device. In these cases, even if the characteristics of the core are calculated based on the imaged data, there is a concern that the characteristics may be inaccurate. For this reason, there is a demand for more accurate measurement of the intensity distribution of the light emitted from each core.

The present invention aims to provide a multicore fiber light intensity distribution measuring device and a multicore fiber light intensity distribution measuring method that can more accurately measure the intensity distribution of light emitted from each core.

In order to achieve the above object, the light intensity distribution measuring device for a multicore fiber of the present invention comprises an input unit that inputs light of the same intensity simultaneously into one end of each core of the multicore fiber; an image data generating unit that captures the light exiting the other end of each of the cores with a camera and generates image data showing the light exiting each of the cores in a plurality of pixels; an extracted image data generating unit that extracts from the image data the pixels in which light of an intensity between the lower and upper limits of the dynamic range that the camera can capture is captured, and generates extracted image data; a converted image data generating unit that converts the light intensity of each of the pixels extracted by the extracted image data generating unit into the intensity per unit amount of light entering the core, and generates converted image data; and a synthetic image data generating unit that combines a plurality of the converted image data to generate synthetic image data showing the intensity distribution of the light exiting each of the cores. The incident unit changes the amount of light incident on the core so that the intensity of at least a portion of the light emitted from each of the cores falls within the range between the lower limit value and the upper limit value at least twice, and causes light to be incident on each of the cores multiple times; the image data generation unit generates the image data each time light is incident on each of the cores; the extracted image data generation unit generates the extracted image data for each of the image data; the converted image data generation unit generates the converted image data for each of the extracted image data; and the composite image data generation unit combines two or more of the converted image data for each of the cores to generate the composite image data.

In order to achieve the above object, the light intensity distribution measurement method of the multicore fiber of the present invention includes an incidence step of simultaneously injecting light of the same intensity into one end of each core of the multicore fiber; an image data generation step of capturing an image of the light exiting the other end of each of the cores with a camera and generating image data showing the light exiting each of the cores with a plurality of pixels; an extraction image data generation step of extracting from the image data the pixels in which light of an intensity between the lower and upper limits of the dynamic range that the camera can capture is captured, and generating extracted image data; a conversion image data generation step of converting the light intensity of each of the pixels extracted in the extraction image data generation step into the intensity per unit amount of light entering the core, and generating converted image data; and a synthetic image data generation step of synthesizing a plurality of the converted image data to generate synthetic image data showing the intensity distribution of the light exiting each of the cores. In the incidence step, the amount of light incident on the core is changed so that the intensity of at least a portion of the light emitted from each of the cores falls within the range between the lower limit value and the upper limit value at least twice, and light is incident on each of the cores multiple times; in the image data generation step, the image data is generated each time light is incident on each of the cores; in the extracted image data generation step, the extracted image data is generated for each of the image data; in the converted image data generation step, the converted image data is generated for each of the extracted image data; and in the composite image data generation step, two or more of the converted image data are combined for each of the cores to generate the composite image data.

When a certain amount of light is incident on each core and the light emitted from each core is captured by a camera, the light emitted from a certain core may be incident on a certain range of pixels within the dynamic range of the camera, and the light incident on the other pixels may be outside the dynamic range. In addition, if an amount of light different from this amount of light is incident on each core, the light emitted from this specific core may be incident on a range of pixels different from the above-mentioned certain range of pixels within the dynamic range of the camera. Therefore, in the above-mentioned multi-core fiber light intensity distribution measurement device and light intensity distribution measurement method, the amount of light incident on the core is changed so that the intensity of at least a part of the light emitted from each core falls within the dynamic range two or more times, and light is incident on each core multiple times. For this reason, the range of pixels extracted from the image data to become the extracted image data tends to be different each time light is incident on the core. By combining pixels with different ranges in this way, a wider range of pixels than one extracted image data will fall within the dynamic range of the camera. However, when the amount of light incident on the core is changed, the same pixel will show different light intensities in different image data. Therefore, by normalizing the light intensity of each pixel extracted in the extracted image data to the intensity per unit amount of light incident on the core, the same pixel in each converted image data will show approximately the same intensity of light. In this way, by synthesizing two or more converted image data obtained by normalizing the extracted image data for each core, the range of light captured within the dynamic range of the camera can be made larger than when the light emitted from each core is captured only once to generate image data showing the light intensity distribution. Therefore, the light intensity distribution measurement device and light intensity distribution measurement method for a multicore fiber can more accurately measure the intensity distribution of light emitted from each core.

The incident section can change the amount of light incident on the core by changing the power of the light incident on the core or the period of time that the light is incident on the core.

In addition, when light of the same intensity is incident on each of the cores, the core from which the light with the lowest intensity is output is a dark core, the core from which the light with the highest intensity is output is a bright core, the amount of light incident on the dark core when the peak intensity of the light output from the dark core is the lower limit is the lower limit of the amount of light incident on each of the cores, and the amount of light incident on the bright core when the intensity of 1/ ^e2 of the peak intensity of the light output from the bright core is the upper limit is the upper limit of the amount of light incident on each of the cores. In this case, it is preferable that the incident unit causes light to be incident on each of the cores multiple times so that the amount of light incident on the core changes within a range between the lower limit and the upper limit. In addition, in the incident step, it is preferable that light is incident on each of the cores multiple times so that the amount of light incident on the core changes within a range between the lower limit and the upper limit.

In a typical multicore fiber, each core tends to exhibit roughly the same optical properties. Therefore, in a typical multicore fiber, by injecting light into each core multiple times so that the amount of light entering the core varies within a range between a lower limit value and an upper limit value as described above, multiple extracted image data can be generated based on the light exiting each core multiple times.

The light intensity distribution measuring device for the multicore fiber preferably includes a bright and dark core prediction unit that predicts the bright cores and the dark cores, and the light intensity distribution measuring method for the multicore fiber preferably includes a bright and dark core prediction step that predicts the bright and dark cores. In this case, the bright and dark core prediction unit and the bright and dark core prediction step perform the following processing. That is, when light of the same intensity is incident on each of the three cores arranged in a non-linear manner, one end of a straight line having a length proportional to the intensity of the light emitted from the three cores is arranged on the same plane so as to have the same arrangement as the three cores, and a slope passing through the other end of each of the straight lines is defined, the core of each of the cores of the multicore fiber whose slope is located on the side farthest from the plane is defined as the bright core, and the core whose slope is located on the side closest to the plane is defined as the dark core.

In a multicore fiber, due to its manufacturing method, a bright core is located at one end of a specific diameter of the cladding, and the intensity of the light emitted from the core gradually decreases from one end to the other end in the diameter direction, with a dark core tending to be located at the other end in the diameter direction. Therefore, as described above, it is possible to know the one end and the other end in the diameter direction based on the intensity of the light emitted from three cores positioned in a non-linear manner. Therefore, it is possible to easily predict the bright and dark cores without measuring the light emitted from all of the cores.

In addition, in the synthetic image data generating unit in the light intensity distribution measuring device for a multicore fiber, and in the synthetic image data generating step in the light intensity distribution measuring method for a multicore fiber, it is preferable that the average of the light intensities at the same pixel in each of the converted image data is set as the light intensity at that pixel in the synthetic image data.

When pixels are extracted multiple times as described above to generate multiple extracted images, some of the pixels extracted in each extracted image may be identical. In this case, by averaging and combining the light intensity at the same pixel as described above, it is possible to reduce measurement error compared to selecting one of the same pixels extracted multiple times.

In the extracted image data generating unit in the above-mentioned multicore fiber light intensity distribution measuring device and the extracted image data generating step in the multicore fiber light intensity distribution measuring method, it is preferable to not extract pixels in which light with an intensity lower than 1/ ^e2 of the peak intensity of the light emitted from each of the cores is captured.

In general, the characteristics of the mode field diameter of light propagating through an optical fiber are determined by the portion where the intensity is 1/ ^e2 of the peak intensity of the light at the outer edge of the light. Therefore, even if an intensity lower than 1/ ^e2 of the peak intensity of the light emitted from the core is within the dynamic range, by not extracting the light of that intensity, it is possible to remove light components that are not necessary for the general process of determining the characteristics of light, and this process can be made easier.

As described above, according to the present invention, a light intensity distribution measuring device for a multicore fiber and a light intensity distribution measuring method for a multicore fiber can be provided, which can more accurately measure the intensity distribution of light emitted from each core.

1 is a diagram showing an outline of a multicore fiber light intensity distribution measuring device according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a flowchart of steps of a method for measuring a light intensity distribution of a multicore fiber according to an embodiment of the present invention. FIG. 13 is a diagram illustrating a bright/dark core prediction step. FIG. 1 shows image data with an exposure time of 3 ms. FIG. 1 shows image data with an exposure time of 10 ms. FIG. 1 shows image data with an exposure time of 20 ms. FIG. 7 is a diagram showing the light intensity distribution of FIGS. 4 to 6. FIG. FIG. 13 is a diagram illustrating that composite image data can measure light intensity distribution more accurately than a single image data. 13A to 13C are diagrams illustrating a modified example of the extracted image data generating step.

Below, embodiments for carrying out the multicore fiber light intensity distribution measuring device and multicore fiber light intensity distribution measuring method according to the present invention are illustrated with the accompanying drawings. The embodiments illustrated below are intended to facilitate understanding of the present invention, and are not intended to limit the interpretation of the present invention. The present invention can be modified and improved from the following embodiments without departing from the spirit of the present invention. In addition, in this specification, the dimensions of each component may be exaggerated in some cases to facilitate understanding.

Figure 1 is a schematic diagram of a multicore fiber light intensity distribution measurement device according to an embodiment. A multicore fiber 10, whose light intensity distribution is measured in this embodiment, has multiple cores 11 and cladding 12 surrounding the outer circumferential surface of each core 11. Note that in this embodiment, a multicore fiber with four cores will be described as an example.

As shown in FIG. 1, the multicore fiber light intensity distribution measuring device 1 of this embodiment includes an input unit 20, an image data generating unit 30, a processor CP, a memory ME, and an intensity measuring unit 50.

The incident unit 20 simultaneously incidents light of the same intensity on one end of each core 11 of the multicore fiber 10. It is preferable that the wavelengths of the light incident on each core 11 are the same. The means for incident light on each core 11 is not particularly limited. For example, a core of a single-core fiber is connected to each core 11, and the incident unit 20 incidents light on each core 11 via the core of each single-core fiber. The incident unit 20 can change the amount of light incident on each core 11 by changing the power of the light incident on each core 11 or the period of incidence of the light incident on each core 11.

The intensity measurement unit 50 includes a light receiving device such as a plurality of photodiodes, receives the light emitted from the other end of each core 11, and outputs a signal indicating the intensity of the light emitted from the other end of each core 11. The signal output from the intensity measurement unit 50 is input to the processor CP. The intensity measurement unit 50 is also configured to be movable on the optical path of the light emitted from the other end of each core 11 and off the optical path. Therefore, when the intensity measurement unit 50 measures the intensity of the light emitted from at least one of the cores 11, it is positioned on the optical path, but at other times it moves to a location off the optical path.

The image data generating unit 30 includes a camera 31 and a conversion unit 32. The camera 31 captures the light emitted from the other end of each core 11, and generates image data of the light emitted from each core 11. At this time, the intensity measuring unit 50 moves to a location other than on the optical path. The camera 31 is, for example, a CCD camera or the like, and has a plurality of light receiving elements arranged in a matrix, and each light emitted from the core 11 is received by each of the plurality of light receiving elements. Each light received by each light receiving element is output from the camera 31 as a pixel signal constituting an image. Therefore, each light emitted from the core 11 is represented by a plurality of pixels. The conversion unit 32 converts the signal of each pixel output from the camera 31 into a state that can be processed by the processor CP. For example, if the signal output from the camera 31 is an analog signal, the conversion unit 32 converts the signal into a digital signal, or assigns the address of the pixel to the signal of each pixel output from the camera 31. The signal including the image data generated by the image data generating unit 30 is input to the processor CP. The signal from each pixel contains information about the intensity of the light received by the light receiving element corresponding to that pixel in camera 31.

The processor CP may be, for example, an integrated circuit such as a microcontroller, an integrated circuit (IC), a large-scale integrated circuit (LSI), or an application specific integrated circuit (ASIC), or an NC (Numerical Control) device. When an NC device is used, the processor CP may or may not use a machine learning device. The processor CP includes a light/dark core prediction unit 41, an extracted image data generation unit 42, a converted image data generation unit 43, and a composite image data generation unit 44.

The processor CP is electrically connected to the memory ME, and the processor CP stores information in the memory ME and reads out information stored in the memory ME. The memory ME is, for example, a non-transitory recording medium, and is preferably a semiconductor recording medium such as a random access memory (RAM) or a read only memory (ROM), but may include any known type of recording medium, such as an optical recording medium or a magnetic recording medium. Note that "non-transitory" recording media includes all computer-readable recording media except for transient, propagating signals, and does not exclude volatile recording media.

When light of the same intensity is incident on each core 11 of the multicore fiber 10, the bright and dark core prediction unit 41 predicts the dark and bright cores when the core from which the light with the lowest intensity is output is the dark core and the core from which the light with the highest intensity is output is the bright core. Specifically, the bright and dark core prediction unit 41 inputs light of the same intensity from the input unit 20 to each of the three cores 11 arranged in a non-linear manner among the cores 11 of the multicore fiber 10. Then, using a signal input from the intensity measurement unit 50 to the processor CP, the bright and dark core prediction unit 41 arranges one end of a straight line having a length proportional to the intensity of each of the light output from the three cores 11 on the same plane so as to be arranged in the same manner as the arrangement of the three cores 11, and specifies a slope passing through the other end of each straight line. The bright and dark core prediction unit 41 then determines, of the cores 11 in the multicore fiber 10, the core 11 whose slope is located on the side farthest from the plane as a bright core, and the core 11 whose slope is located on the side closest to the plane as a dark core. The bright and dark core prediction unit 41 performs calculations to predict the bright and dark cores. Therefore, the above straight lines, planes, and slopes are imaginary and do not actually exist. The specific content of the bright and dark core prediction will be described later.

The extracted image data generating unit 42 extracts pixels in which light with an intensity between the lower limit and upper limit of the dynamic range that the camera 31 can capture is captured from the image data, and generates extracted image data. The extracted image data generating unit 42 uses information related to the light intensity of the signal of each pixel in the image data output by the image data generating unit 30 to compare the light intensity of each pixel with the range of the dynamic range of the camera 31 stored in the memory ME. The extracted image data generating unit 42 then extracts pixels whose light intensity is between the lower limit and upper limit of the dynamic range. The extracted image data generating unit 42 leaves the information of the extracted pixels as is, and replaces information related to the light intensity of pixels whose light intensity is not between the lower limit and upper limit of the dynamic range with zero, and converts the image data into extracted image data. Note that information related to the light intensity of pixels whose light intensity is not between the lower limit and upper limit of the dynamic range may be replaced with no information.

The converted image data generating unit 43 performs normalization to convert the light intensity of each pixel extracted by the extracted image data generating unit 42 into the intensity per unit amount of light incident on the core 11, and generates converted image data. For example, assume that light of a predetermined intensity is incident on each core 11 for 10 ms, and the image data generating unit 30 generates image data using that light. If the unit amount is the amount of light incident on the core 11 for 1 ms, and there is a linear relationship between the amount of light incident on the core 11 and the light intensity indicated by each pixel of the image data generated by the image data generating unit 30, then the converted image data generating unit 43 converts the information relating to the light intensity of each pixel extracted by the extracted image data generating unit 42 into information indicating 1/10 of the light intensity. However, there is generally no linear relationship between the amount of light incident on the core 11 and the light intensity indicated by each pixel of the image data generated by the image data generating unit 30. Therefore, the converted image data generating unit 43 uses a predetermined formula to calculate the light intensity of each extracted pixel so that it becomes the intensity per unit amount of light incident on the core 11. In this way, by normalizing each extracted pixel, even if different amounts of light are incident on each core 11 from the entrance portion 20, the converted image data generated by the converted image data generating unit 43 shows roughly the same light intensity for the same pixel.

The composite image data generating unit 44 synthesizes the multiple converted image data generated by the converted image data generating unit 43 to generate composite image data showing the intensity distribution of light emitted from each core 11. When two or more converted image data are created for each core 11 by multiple incidence of different amounts of light from the incident unit 20 to each core 11, the ranges of pixels extracted by the extracted image data generating unit 42 and converted by the converted image data generating unit 43 are different in the two or more converted image data. Therefore, the composite image data generating unit 44 combines pixels of different ranges to generate composite image data. Note that when two or more converted image data have data of the same pixel, it is preferable to set the average of the light intensity indicated by the same pixel in each converted image data as the light intensity of the pixel in the composite image data. By averaging and synthesizing the light intensity of the same pixel in this way, the measurement error can be reduced more than when selecting one of the same pixels extracted multiple times.

Next, we will explain a method for measuring the light intensity distribution of a multicore fiber 10 using the multicore fiber light intensity distribution measuring device 1.

Figure 2 is a diagram showing an example of a flowchart of the steps of the method for measuring the light intensity distribution of the multicore fiber 10 according to this embodiment. As shown in Figure 2, the method for measuring the light intensity distribution of this embodiment includes a bright and dark core prediction step S1 including a first incidence step S11, an intensity measurement step S12, and a calculation step S13, a second incidence step S2, an image data generation step S3, an extracted image data generation step S4, a converted image data generation step S5, and a composite image data generation step S6.

(First injection step S11)
In this step, three cores 11 arranged in a non-linear manner are selected from the cores 11 of the multicore fiber 10. Then, the bright/dark core prediction unit 41 of the processor CP controls the incidence unit 20 to cause light of the same intensity to be incident on one end of these three cores 11.

(Strength measurement step S12)
In this step, the intensity measuring unit 50 measures the intensity of the light emitted from the other end of each of the three cores 11 into which the light was incident in the first incident step S11. Therefore, the intensity measuring unit 50 is placed on the optical path of the light emitted from the other end of the three cores 11 so that the intensity of the light emitted from the other end of these cores 11 can be measured at least before this step. The intensity measuring unit 50 outputs a signal including information on each measured intensity to the processor CP. After that, the intensity measuring unit 50 moves to a location other than the optical path.

(Calculation step S13)
In this step, the bright and dark core prediction unit 41 predicts, by calculation, the dark core from which the light with the lowest intensity is output and the bright core from which the light with the highest intensity is output when light with the same intensity is input to each core 11 of the multi-core fiber 10 based on information input from the intensity measurement unit 50. FIG. 3 is a diagram for explaining this step. In FIG. 3, the multiple cores 11 of the multi-core fiber 10 are each referred to as cores 11a to 11d. As exemplified in the explanation of the bright and dark core prediction unit 41, in this step, the bright and dark core prediction unit 41 assumes three straight lines STa to STc whose lengths are proportional to the intensity of each of the lights output from the three cores 11a to 11c, using a signal input from the intensity measurement unit 50 to the processor CP. These straight lines STa to STc are virtual lines. Then, the bright and dark core prediction unit 41 arranges the straight lines STa to STc on one plane PL so that they are parallel to each other and one end of each of the straight lines STa to STc is arranged in the same arrangement as the three cores 11a to 11c. This plane PL is an imaginary plane. Next, the bright and dark core prediction unit 41 defines a slope SL passing through the other end of each of the straight lines STa to STc. This slope SL is a planar imaginary plane. The bright and dark core prediction unit 41 defines the core 11 of the multi-core fiber 10 whose slope SL is located on the side closest to the plane PL as the dark core, and defines the core 11 of the multi-core fiber 10 whose slope SL is located on the side farthest from the plane PL as the bright core. Note that in this step, it is sufficient to obtain a dark core and a bright core as a result, and when obtaining a dark core and a bright core, even if the slope SL is not defined, the gradient vector GR of the slope SL may be defined. In this case, the core 11 located closest to the gradient vector GR among the cores 11 is defined as a dark core, and the core 11 located closest to the gradient vector GR among the cores 11 is defined as a bright core. Even when the gradient vector is used to find the dark core and the bright core in this way, the dark core is ultimately the core located on the side of the cores 11 whose slope SL is closest to the plane PL, and the bright core is the core located on the side of the cores 11 whose slope SL is furthest from the plane PL.

Figure 3 shows an example in which light of the same intensity is incident on each of cores 11a to 11c, the intensity of the light emitted from core 11a is higher than the intensity of the light emitted from cores 11b and 11c, and the intensity of the light emitted from cores 11b and 11c is the same. In this example, core 11a is a bright core, and core 11d is a dark core. In this way, the dark cores and the bright cores are predicted.

The reason why the dark cores and the bright cores can be predicted in this way is as follows. That is, in multicore fibers, not limited to the multicore fiber 10 shown in this embodiment, due to the manufacturing method, the bright core is located at one end side of a specific diameter of the cladding, and the intensity of the light emitted from the core gradually decreases from the one end side to the other end side in the diameter direction, and the dark core tends to be located at the other end side in the diameter direction. Therefore, as described above, based on the intensity of the light emitted from the three cores 11a to 11c positioned in a non-linear manner, it is possible to know the one end side and the other end side in the diameter direction, and the core 11 located at one end side can be determined as a bright core, and the core 11 located at the other end side can be determined as a dark core. Therefore, the bright cores and dark cores can be easily predicted without measuring the light emitted from all the cores 11.

In the bright and dark core prediction step S1 of this embodiment, the dark cores and bright cores are obtained based on the intensity of light emitted from the three cores 11a to 11c as described above, so that the dark cores and bright cores can be obtained more easily than when light is incident on all the cores 11 to obtain the dark cores and bright cores. However, instead of the bright and dark core prediction step S1 of this embodiment, the dark cores and bright cores may be obtained by other methods. For example, light of the same intensity may be incident on all the cores 11, the intensity measurement unit 50 may measure the intensity of the light emitted from each core 11, and the processor CP may obtain the dark cores and bright cores based on the information on the intensity of the light emitted from each core 11 output from the intensity measurement unit 50. In this case, the dark cores and bright cores can be obtained more accurately than when the dark cores and bright cores are obtained by the example shown in FIG. 3.

(Second injection step S2)
In this step, the processor CP controls the incident unit 20 to cause the incident unit 20 to simultaneously incident light of the same intensity on one end of each of the cores 11 of the multicore fiber 10. It is preferable that the wavelength of the light incident from the incident unit 20 to each of the cores 11 is the same. The incident unit 20 changes the amount of light incident on the cores so that the intensity of at least a part of the light emitted from each of the cores 11 falls within the range between the lower limit value and the upper limit value of the dynamic range of the camera 31 two or more times, and causes the light to be incident on each of the cores 11 a plurality of times.

In this way, if light is made to enter each core 11 multiple times so that the intensity of at least a part of the light emitted from each core 11 falls within the range between the lower limit and the upper limit two or more times, the range in which the amount of light entering the core is changed is not particularly limited. However, if the amount of light entering the dark core when the peak intensity of the light emitted from the dark core is the lower limit of the dynamic range is set as the lower limit of the amount of light entering each core, and the amount of light entering the bright core when the intensity of 1/ ^e2 of the peak intensity of the light emitted from the bright core is the upper limit of the dynamic range is set as the upper limit of the amount of light entering each core, in this step, it is preferable to make light enter each core multiple times so that the amount of light entering each core 11 changes within the range between the lower limit and the upper limit. In general, each core of a multi-core fiber has roughly the same characteristics. Therefore, when light of the same intensity is entered into each core 11, the light exiting from each core 11 has an intensity distribution close to each other. Therefore, by varying the amount of light within this range and injecting light into each core 11 multiple times, in the case of a typical optical fiber, it is possible to generate two or more extracted image data, described below, for each core 11 based on the light exiting each core 11 multiple times.

(Image data generation step S3)
In this step, the image data generating unit 30 captures the light emitted from the other end of each core 11 with the camera 31, and generates image data showing the light emitted from each core 11 with multiple pixels. The camera 31 receives each light emitted from each core 11 with multiple light receiving elements, and a signal for each pixel is formed from the signal output from each light receiving element. Therefore, the image data captured by the camera 31 and output from the image data generating unit 30 via the conversion unit 32 includes data in which each light emitted from each core 11 is shown with multiple pixels.

In this step, the incident unit 20 changes the amount of light incident on the core 11, and generates image data each time light is incident on each core 11 multiple times. Each generated image data is input to the processor CP and stored in the memory ME. In the following description, the light emitted from one core 11 will be described. FIG. 4 is a diagram showing image data with an exposure time of 3 ms, FIG. 5 is a diagram showing image data with an exposure time of 10 ms, and FIG. 6 is a diagram showing image data with an exposure time of 20 ms. These image data are image data of light emitted from a specific core 11. The exposure time can be considered as the period of incidence of light incident on the core 11, and the intensity of light emitted from the incident unit 20 when capturing each image data is constant. Therefore, in this case, the exposure time is proportional to the amount of light incident on the core 11. As shown in FIGS. 4 to 6, it can be seen that as the amount of light incident on the core 11 increases, the apparent diameter of the light reflected in the image increases. This does not mean that the diameter of the light exiting core 11 increases as the amount of light entering core 11 increases; rather, near the outer edge of the light, the intensity of the light becomes smaller than the lower limit of the dynamic range of camera 31, so the smaller the amount of light entering core 11, the narrower the range of pixels that are exposed and appear as a light image.

(Extracted image data generating step S4)
In this step, the extracted image data generating unit 42 extracts pixels in which light with an intensity between the lower limit and upper limit of the dynamic range that the camera 31 can capture is captured from the image data, and generates extracted image data. In this step, the extracted image data generating unit 42 reads out each image data from the memory ME, and generates extracted image data for each image data. Thus, the extracted image data generating unit 42 generates extracted image data each time the incident unit 20 causes light to be incident on each core 11 multiple times. Each generated extracted image data is stored in the memory ME.

FIG. 7 is a diagram showing the light intensity distribution of FIG. 4 to FIG. 6. In this figure, the data in FIG. 4 where the exposure time is 3 ms is shown by a dotted line, the data in FIG. 5 where the exposure time is 10 ms is shown by a dashed line, and the data in FIG. 6 where the exposure time is 20 ms is shown by a dashed line. FIG. 7(A) is a diagram showing the image data in FIG. 4, FIG. 5, and FIG. 6. In FIG. 7(A), the solid line shows the outer periphery of light with a predetermined intensity that is an intensity of 1/ ^e2 or less of the peak intensity of the light. FIG. 7(B) shows the relationship between the light intensity distribution and the dynamic range of the camera 31. As shown in FIG. 7(A) and FIG. 7(B), when the exposure time is 3 ms, the light intensity of the pixel near the center of the light falls within the dynamic range of the camera 31, and the light intensity of the pixel other than the pixel near the center of the light is smaller than the lower limit of the dynamic range. In addition, when the exposure time is 10 ms, the light intensity of pixels near the center of the light is greater than the upper limit of the dynamic range, and the light intensity of pixels near the periphery of the light is less than the lower limit of the dynamic range. When the exposure time is 20 ms, the region where the light intensity falls within the dynamic range is closer to the periphery of the light than when the exposure time is 10 ms.

In this embodiment, pixels whose light intensity is between the lower and upper limits of the dynamic range of the camera 31, i.e., the pixels in the circular area surrounded by the dotted line in FIG. 7(A), the annular area surrounded by two dashed lines, and the annular area surrounded by two dashed and dotted lines, are extracted, and the light intensity of pixels whose light intensity is not between the lower and upper limits of the dynamic range is set to zero. Therefore, the extracted image data generated by the extracted image data generation unit 42 for each exposure time has the light intensity distribution shown in FIG. 7(C). Note that to avoid complicating the drawing, FIG. 7(C) does not show how the light intensity is set to zero.

(Converted image data generating step S5)
In this step, the converted image data generating unit 43 converts the light intensity of each pixel extracted in the extracted image data generating step S4 into the intensity per unit amount of light incident on the core 11 to generate converted image data. The converted image data generating unit 43 reads each piece of extracted image data from the memory ME and generates converted image data for each piece of extracted image data. Thus, the converted image data generating unit 43 generates converted image data each time the incident unit 20 causes light to be incident on each of the cores 11 multiple times. Each piece of generated converted image data is stored in the memory ME.

As described above, generally, there is no linear relationship between the amount of light incident on the core 11 and the light intensity of each pixel of the image data generated by the image data generation unit 30. Therefore, the converted image data generation unit 43 uses a predetermined formula to calculate the light intensity of each extracted pixel to be the intensity per unit amount of light incident on the core 11, and generates the converted image data. The converted image data in which each pixel is converted in this way has a light intensity distribution in which the light intensity distribution shown in FIG. 7(C) is compressed in the light intensity direction, as shown in FIG. 7(D). Note that in order to avoid complicating the diagram, the scale of the light intensity direction is different between FIG. 7(C) and FIG. 7(D). In this way, by performing normalization to convert the light intensity of each extracted pixel in the extracted image data into the intensity per unit amount of light incident on the core 11, the same pixel in each converted image data will show approximately the same intensity of light. In FIG. 7(D), in order to distinguish between the lines, the curves showing the converted image data with an exposure time of 3 ms, the curves showing the converted image data with an exposure time of 10 ms, and the curves showing the converted image data with an exposure time of 20 ms are drawn slightly offset from one another.

(Synthetic image data generating step S6)
In this step, the composite image data generating unit 44 generates composite image data by combining two or more converted image data for each core 11. In this step, each converted image data is read from the memory ME, and the same pixels of each converted image data are combined. The converted image data of 3 ms shown by the dotted line, the converted image data of 10 ms shown by the dashed line, and the converted image data of 20 ms shown by the dashed line in FIG. 7(D) are combined. In this example, some pixels of the converted image data with an exposure time of 3 ms overlap with pixels of the converted image data with an exposure time of 10 ms, and other pixels indicating the area near the center of the light do not overlap with pixels of any of the converted image data. In addition, some pixels of the converted image data with an exposure time of 20 ms overlap with pixels of the converted image data with an exposure time of 10 ms, and other pixels indicating the area near the periphery of the light do not overlap with pixels of any of the converted image data. In this example, if there is only one data indicating the intensity of light for the same pixel of multiple converted image data, the data is used as the data indicating the intensity of light of the pixel in the composite image data. On the other hand, when the data indicating the light intensity for the same pixel in the multiple converted image data is two or more, as described above, the average of the light intensities indicated by the pixel in each converted image data is used as the data indicating the light intensity of the pixel in the composite image data. However, when the data indicating the light intensity for the same pixel in the multiple converted image data is two or more, the pixel in any of the converted image data may be used as the pixel in the composite image data. In this way, the composite image data having the light intensity distribution shown in FIG. 7(D) is generated.

Figure 8 shows a composite image obtained when light of the same intensity is incident on each core 11 from the incident portion 20 multiple times with exposure times of 3 ms, 5 ms, 8 ms, 10 ms, 15 ms, 20 ms, 30 ms, 50 ms, 100 ms, 300 ms, and 500 ms. In this example, the composite image was visually roughly the same as the image obtained with an exposure time of 5 ms.

As described above, the light intensity distribution measuring device 1 of the multi-core fiber of this embodiment includes an input unit 20 that simultaneously inputs light of the same intensity into one end of each core 11 of the multi-core fiber 10, an image data generating unit 30 that captures the light exiting the other end of each core 11 with a camera 31 and generates image data showing the light exiting each core 11 in multiple pixels, an extracted image data generating unit 42 that extracts from the image data pixels where light of an intensity between the lower and upper limits of the dynamic range that can be captured by the camera 31 is captured and generates extracted image data, a converted image data generating unit 43 that converts the light intensity of each pixel extracted by the extracted image data generating unit 42 into the intensity per unit amount of light entering the core 11 and generates converted image data, and a synthetic image data generating unit 44 that combines the multiple converted image data to generate synthetic image data showing the intensity distribution of the light exiting each of the cores. The incident unit 20 changes the amount of light incident on the core 11 so that the intensity of at least a portion of the light emitted from each core 11 falls within the range between the lower and upper limits of the dynamic range at least twice, and causes light to be incident on each core 11 multiple times; the image data generation unit 30 generates image data each time light is incident on each core 11; the extracted image data generation unit 42 generates extracted image data for each image data; the converted image data generation unit 43 generates converted image data for each extracted image data; and the composite image data generation unit 44 combines two or more converted image data for each core 11 to generate composite image data.

In addition, the light intensity distribution measurement method of the multi-core fiber of this embodiment includes a second incidence step S2, which is an incidence step in which light of the same intensity is simultaneously incident on one end of each core 11 of the multi-core fiber 10; an image data generation step S3 in which the light exiting the other end of each core 11 is captured by the camera 31 to generate image data showing the light exiting each core 11 with a plurality of pixels; an extracted image data generation step S4 in which pixels in which light of an intensity between the lower and upper limits of the dynamic range that the camera 31 can capture is captured are extracted from the image data to generate extracted image data; a converted image data generation step S5 in which the light intensity of each pixel extracted in the extracted image data generation step S4 is converted into the intensity per unit amount of light incident on the core 11 to generate converted image data; and a composite image data generation step S6 in which the plurality of converted image data are combined to generate composite image data showing the intensity distribution of the light exiting each core 11. In the second incidence step S2, the amount of light incident on the core 11 is changed so that the intensity of at least a portion of the light emitted from each core 11 falls within the range between the lower and upper limits of the dynamic range at least twice, and light is incident on each core 11 multiple times; in the image data generation step S3, image data is generated each time light is incident on each core 11; in the extracted image data generation step S4, extracted image data is generated for each image data; in the converted image data generation step S5, converted image data is generated for each extracted image data; and in the composite image data generation step S6, two or more converted image data are combined for each core 11 to generate composite image data.

When a certain amount of light is incident on each core 11 and the light emitted from each core 11 is captured by the camera 31, the light emitted from a certain core 11 may be incident on a certain range of pixels within the dynamic range of the camera 31, and the light incident on the other pixels may be outside the dynamic range. In addition, if an amount of light different from this amount of light is incident on each core 11, the light emitted from this specific core 11 may be incident on a range of pixels different from the above-mentioned certain range of pixels within the dynamic range of the camera 31. Therefore, in the above-mentioned light intensity distribution measurement device 1 and light intensity distribution measurement method for a multi-core fiber, the amount of light incident on the core 11 is changed so that the intensity of at least a part of the light emitted from each core 11 falls within the dynamic range two or more times, and light is incident on each core 11 multiple times. For this reason, the range of pixels extracted from the image data to become the extracted image data tends to be a different range each time light is incident on the core 11. By combining pixels of different ranges in this way, a wider range of pixels than one extracted image data will be dynamically captured by the camera 31. However, if the amount of light incident on the core 11 is changed, the same pixel will show a different amount of light. Therefore, by normalizing the light intensity of each pixel extracted in the extracted image data to the intensity per unit amount of light incident on the core 11, the same pixel in each converted image data will show approximately the same intensity of light. In this way, by synthesizing two or more converted image data obtained by normalizing the extracted image data for each core 11, the range of light captured within the dynamic range of the camera can be made larger than when the light emitted from each core 11 is captured only once to generate image data showing the light intensity distribution. Therefore, according to the light intensity distribution measuring device 1 and the light intensity distribution measuring method for the multi-core fiber 10, the intensity distribution of light emitted from each core 11 can be measured more accurately.

Figure 9 is a diagram showing that the composite image data can measure the light intensity distribution more accurately than a single image data. In Figure 9, the solid line shows the light intensity distribution when the exposure time is 5 ms, and the dashed line shows the light intensity distribution by the composite image shown in Figure 11. As described above, the composite image shown in Figure 8 looks almost the same as the image when the exposure time is 5 ms. However, it was found that the light intensity distribution when the exposure time is 5 ms has distortion in the curve outside about 9 μm from the center of the light, and cannot be evaluated correctly due to poor S/N. In contrast, the light intensity distribution of the composite image is a curve with less distortion at least from the center of the light to about 12 μm, resulting in a good S/N ratio. Therefore, as described above, according to the light intensity distribution measuring device 1 and light intensity distribution measuring method of the multi-core fiber 10 of this embodiment, the intensity distribution of the light emitted from each core 11 can be measured more accurately.

Although the present invention has been described above using the above embodiment as an example, the present invention is not limited to the above embodiment.

In the above embodiment, a multicore fiber with four cores is exemplified, but the number of cores is not limited to four as long as it is multiple.

In the above embodiment, bright cores and dark cores are predicted. However, if the amount of light incident on the core 11 is changed so that the intensity of at least a portion of the light emitted from the core 11 falls within the range between the lower limit and the upper limit of the dynamic range at least twice, and light is incident on each core multiple times, it is not necessary to predict bright cores and dark cores. In this case, the intensity measurement unit 50 and the bright and dark core prediction unit 41 are not required. In this case, the amount of light may be changed in multiple stages, for example, from a sufficiently small amount of light that causes the light emitted from all cores to be lower than the lower limit of the dynamic range, to a sufficiently large amount of light that causes the light emitted from all cores to be higher than the upper limit of the dynamic range.

Also, the extraction image data generating step S4 may be modified as follows. FIG. 10 is a diagram for explaining this modification. In this diagram, a state in which the peak intensity of light is lower than the upper limit of the dynamic range of the camera 31 is shown. The curve consisting of the solid line and the dashed line in FIG. 10 indicates the light intensity distribution in the image data. In this modification, even if the pixel has a light intensity within the dynamic range of the camera 31, a pixel in which light with an intensity lower than 1/ ^e2 of the peak intensity of the light emitted from each core 11 is not extracted. Therefore, the pixel in the region shown by the dotted line in FIG. 10 that was extracted in the above embodiment is not extracted, the light intensity is set to zero, and the extraction image data having the light intensity shown by the solid line is generated.

In general, the characteristics of the mode field diameter of light propagating through an optical fiber are determined by the portion where the intensity is 1/ ^e2 of the peak intensity of the light at the outer edge of the light. Therefore, even if an intensity lower than 1/ ^e2 of the peak intensity of the light emitted from the core is within the dynamic range, by not extracting the light of that intensity, it is possible to remove light components that are not necessary for the general process of determining the characteristics of light, and this process can be made easier.

In the multicore fiber 10, crosstalk may occur between the cores 11. However, if the light intensity of this crosstalk is equal to or less than 1/ ^e2 of the peak intensity of the light, the influence of the crosstalk can be eliminated by implementing the above modified example.

The present invention provides a multicore fiber light intensity distribution measurement device and a multicore fiber light intensity distribution measurement method that can more accurately measure the intensity distribution of light emitted from each core, and can be used in fields such as optical communications.

1: Light intensity distribution measuring device 10: Multi-core fiber 11: Core 20: Incident section 30: Image data generating section 41: Bright and dark core prediction section 42: Extracted image data generating section 43: Converted image data generating section 44: Synthetic image data generating section 50: Intensity measuring section CP: Processor ME: Memory S1: Bright and dark core prediction step S2: Second incident step (incident step)
S3: Image data generation step S4: Extracted image data generation step S5: Converted image data generation step S6: Composite image data generation step

Claims (10)

an input section for simultaneously inputting light of the same intensity into one end of each of the cores of the multi-core fiber;
an image data generating unit that captures an image of the light emitted from the other end of each of the cores with a camera and generates image data that shows the light emitted from each of the cores using a plurality of pixels;
an extracted image data generating unit that generates extracted image data by extracting from the image data the pixels at which light with an intensity between a lower limit value and an upper limit value of a dynamic range that can be captured by the camera is captured;
a converted image data generating unit that converts the light intensity of each of the pixels extracted by the extracted image data generating unit into an intensity per unit amount of light incident on the core, to generate converted image data;
a composite image data generating unit that combines a plurality of the converted image data to generate composite image data indicating an intensity distribution of light emitted from each of the cores;
Equipped with
the incidence unit changes the amount of light incident on the cores so that an intensity of at least a portion of the light emitted from each of the cores falls within a range between the lower limit value and the upper limit value two or more times, thereby causing light to be incident on each of the cores a plurality of times;
the image data generation unit generates the image data each time light is incident on each of the cores,
the extracted image data generating unit generates the extracted image data for each of the image data;
the converted image data generating unit generates the converted image data for each of the extracted image data;
the composite image data generation unit generates the composite image data by combining two or more of the converted image data for each of the cores. 2. The device for measuring light intensity distribution of a multicore fiber according to claim 1, wherein, when light of the same intensity is incident on each of the cores, the core from which light with the lowest intensity is output is a dark core, the core from which light with the highest intensity is output is a bright core, an amount of light incident on the dark core when the peak intensity of the light output from the dark core is the lower limit amount is a lower limit amount of the amount of light incident on each of the cores, and an amount of light incident on the bright core when an intensity of 1/e2 ^of the peak intensity of the light output from the bright core is the upper limit amount is an upper limit amount of the amount of light incident on each of the cores, a bright and dark core prediction unit that predicts the bright cores and the dark cores,
3. The device for measuring light intensity distribution of a multi-core fiber according to claim 2, wherein the bright/dark core prediction unit causes light of the same intensity to be incident on each of the three cores arranged in a non-linear manner, arranges one end of a straight line having a length proportional to the intensity of light output from the three cores on the same plane so as to have the same arrangement as the three cores, and defines a slope passing through the other end of each of the straight lines, wherein the core of each of the multi-core fiber whose slope is furthest from the plane is determined as the bright core, and the core whose slope is closest to the plane is determined as the dark core. 4. The multicore fiber light intensity distribution measuring device according to claim 1, wherein the synthetic image data generating unit sets an average of light intensities at the same pixel of each of the converted image data as the light intensity at that pixel of the synthetic image data. 5. The device for measuring light intensity distribution of a multicore fiber according to claim 1 , wherein the extracted image data generation unit does not extract the pixels in which light with an intensity lower than 1/ ^e2 of a peak intensity of the light emitted from each of the cores is captured. an input step of simultaneously inputting light of the same intensity into one end of each core of the multicore fiber;
an image data generating step of capturing an image of light emitted from the other end of each of the cores with a camera and generating image data showing the light emitted from each of the cores with a plurality of pixels;
an extracted image data generating step of generating extracted image data by extracting from the image data the pixels at which light with an intensity between a lower limit value and an upper limit value of a dynamic range that can be captured by the camera is captured;
a converted image data generating step of converting the light intensity of each of the pixels extracted in the extracted image data generating step into an intensity per unit amount of light incident on the core to generate converted image data;
a synthetic image data generating step of synthesizing a plurality of the converted image data to generate synthetic image data indicating an intensity distribution of light emitted from each of the cores;
Equipped with
In the incidence step, the amount of light incident on each of the cores is changed so that the intensity of at least a portion of the light emitted from each of the cores falls within the range between the lower limit value and the upper limit value two or more times, and light is incident on each of the cores a plurality of times;
In the image data generating step, the image data is generated every time light is incident on each of the cores,
In the extraction image data generating step, the extraction image data is generated for each of the image data;
In the converted image data generating step, the converted image data is generated for each of the extracted image data;
a light intensity distribution measuring method for a multicore fiber, the light intensity distribution measuring method being characterized in that, in the synthetic image data generating step, two or more of the converted image data are combined for each of the cores to generate the synthetic image data. 7. The method for measuring a light intensity distribution of a multicore fiber according to claim 6, wherein, when light of the same intensity is incident on each of the cores, the core from which light with the lowest intensity is output is a dark core, the core from which light with the highest intensity is output is a bright core, an amount of light incident on the dark core when a peak intensity of light output from the dark core is the lower limit amount is a lower limit amount of the amount of light incident on each of the cores, and an amount of light incident on the bright core when an intensity of 1/ ^e2 of the peak intensity of light output from the bright core is the upper limit amount is an upper limit amount of the amount of light incident on each of the cores, in the inputting step, light is input to each of the cores a plurality of times such that the amount of light incident on the core changes in a range between the lower limit amount and the upper limit amount. A bright and dark core prediction step of predicting the bright core and the dark core,
8. The method for measuring a light intensity distribution of a multi-core fiber according to claim 7, wherein, in the bright and dark core prediction step, when light of the same intensity is incident on each of the three cores arranged in a non-linear manner, one end of a straight line having a length proportional to the intensities of the light output from the three cores is arranged on the same plane so as to be arranged in the same manner as the arrangement of the three cores, and a slope passing through the other end of each of the straight lines is defined, the core of each of the multi-core fiber whose slope is located on a side farthest from the plane is defined as the bright core, and the core whose slope is located closest to the plane is defined as the dark core. 9. The method for measuring a light intensity distribution of a multicore fiber according to claim 6, wherein in the synthetic image data generating step, an average of light intensities at the same pixel of each of the converted image data is set as the light intensity at that pixel of the synthetic image data. 10. The method for measuring a light intensity distribution of a multicore fiber according to claim 6, wherein, in the extracted image data generating step, a pixel in which light with an intensity lower than 1/ ^e2 of a peak intensity of light emitted from each of the cores is captured is not extracted.

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