JPH0498202A - Method for controlling expansion of mode field diameter of optical fiber - Google Patents

Abstract

PURPOSE:To uniformly obtain a required mode field diameter by making ultraviolet rays incident upon the core of an optical fiber during the heating of the fiber, monitoring the heating state by an image pickup means, and when a core diameter reaches a regulated value, aborting the heating of the fiber. CONSTITUTION:Both the sides of a required position of the optical fiber 1 in the axial direction are heated by gas burners 2a, 2b and ultraviolet rays (UV) are made incident from a light incident/projecting end face 13 upon the core part 11 by an ultraviolet irradiating device 4. When the UV is made incident, dopant in the core is excited, fluorescence is generated and a boundary between a core part 11 and a clad part 12 is cleared. Said status is photographed by a television camera 3 and its image data ID are inputted to a display part 5 and a control part 6. The display part 5 displays the image of a heating area. On the other hand, the control part 6 converts the input data into digital data DD by an A/D converter 61, calculates the measuring value of a core diameter by a core diameter calculating part 62 and outputs the calculated value to a comparator 63 as measuring value data RD. When the data RD reaches the level of a previously set threshold TH, the comparing part 63 generates a stop signal ST to stop the heating of the burners 2a, 2b.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a mode field diameter expansion control method for an optical fiber, which expands the mode field diameter of an optical fiber by heating it.

(Prior art) Conventionally, by heating an optical fiber with a burner, electric furnace, etc. for a certain period of time, the dopant in the core is diffused, the mode field diameter (hereinafter abbreviated as MFD) is expanded, and the loss at the connection point is reduced. There are known methods to reduce the size of

FIG. 2 is a graph showing the relationship between the heating time and the spread of the MFD when an optical fiber is heated with a heating width of 5 mm using a gas burner.

As is clear from FIG. 2, the MFD can be expanded by heating a predetermined region of the optical fiber for a desired period of time.

(Problems to be Solved by the Invention) However, as shown in FIG. 2, in the above conventional method, even if the heating time for the optical fiber is controlled, variations in the size of the MFD occur, and the MFD is kept at a constant level. The drawback is that it is difficult to enlarge the size with good controllability.

The reason for the variation in MFD is thought to be related to surrounding environmental conditions, the original refractive index distribution of the core, etc., but this has not been quantified.

As described above, if there is variation in the spread of the MFD for each core wire, the connection loss will increase due to MFD mismatch, so the conventional method has not been put into practical use at present.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a mode field diameter expansion control method for an optical fiber that can reliably obtain a desired mode field diameter without variation.

(Means for Solving the Problem) In order to achieve the above object, claim (1) provides an MF of an optical fiber that heats the optical fiber to expand its MFD.
In the expansion control method D, the core portion of the optical fiber is monitored by an imaging means while the optical fiber is being heated, and when the core diameter of the optical fiber based on the image data of the imaging means reaches a predetermined value. The heating of the optical fiber is now stopped.

Moreover, in claim (2), ultraviolet rays are made to enter the core of the optical fiber.

Moreover, in claim (3), ultraviolet rays are made to enter from the light input/output end face of the optical fiber.

Moreover, in claim (4), the optical fiber is bent, and the ultraviolet rays are incident from this bent portion.

Moreover, in claim (5), heating of the optical fiber is stopped when the maximum value of the core diameter of the optical fiber based on the image data reaches a specified value.

Further, in claim (6), the heating of the optical fiber is stopped when the average value of the core diameter of the optical fiber based on the image data of the heating area reaches a specified value. , heating of the optical fiber is stopped when an abnormality occurs in the shape of the optical fiber based on image data of the heating area.

Moreover, in claim (8), the optical fiber is monitored from a plurality of directions by the imaging means.

Moreover, in claim (9), when heating a plurality of optical fibers at once to enlarge the MFD of each optical fiber, all the optical fibers are monitored at once by the imaging means.

(Function) According to claim (1), a desired location of the optical fiber is heated by the heating device, and the core diameter of the heated region is gradually expanded. Further, during this heating, the core portion of the heated region of the optical fiber is photographed and monitored by an imaging means.

The core diameter of the optical fiber being expanded is calculated based on the image data of the imaging means, and heating of the optical fiber is stopped when the calculated value reaches a predetermined value.

Moreover, according to claim (2), ultraviolet rays are incident on the core of the optical fiber. As a result, the dopant in the core, mainly germanium, is excited, which generates fluorescence, causing the entire core to emit light. This makes the boundary between the core part and the cladding part clear.

Moreover, according to claim (3), ultraviolet rays are input from the light input/output end face of the optical fiber.

According to claim (4), the optical fiber is bent, and the ultraviolet rays are incident from this bent portion.

According to claim (5), heating of the optical fiber is stopped when the maximum value of the core diameter of the optical fiber calculated based on the image data reaches a specified value.

Further, according to claim (6), the average value of the core diameter of the optical fiber calculated based on the image of the heating area is obtained, and when this average value reaches a specified value, the heating of the optical fiber is started. Canceled.

According to claim (7), when an abnormality occurs in the shape of the optical fiber based on the image of the heated region, heating of the optical fiber is immediately stopped.

Moreover, according to claim (8), the optical fiber is monitored not only from one direction but from a plurality of directions by the imaging means.

Moreover, in claim (9), when heating a plurality of optical fibers at once to enlarge the MFD of each optical fiber, all the optical fibers are monitored at once by the imaging means.

(Embodiment) FIG. 1 is an explanatory diagram of a first embodiment of the mode field diameter expansion control method for an optical fiber according to the present invention, in which (a) in the figure is a conceptual diagram, and (a) in the figure is a conceptual diagram; b) is an overall block configuration diagram including the control system.

In FIG. 1, 1 is an optical fiber that expands the MFD, 1
1 is the core portion of the optical fiber 1, 12 is the cladding portion of the optical fiber 1, 13 is the negative light input/output end surface (cut surface) of the optical fiber 1, and 2a and 2b are gas burners as heating devices. A predetermined location in the axial direction is heated from both sides over a predetermined length. 21a and 21b are gas burners 2a and 2
A flame b is used, and a television camera 3 is used to photograph the state transition due to heating of the heating region of the optical fiber 1. Reference numeral 4 denotes an ultraviolet irradiation device, which is disposed opposite the light input/output end face 1'3 of the optical fiber 1, and irradiates ultraviolet rays UV into the core portion 11 of the optical fiber 1.

Reference numeral 5 denotes a display section, which inputs the pig ID of the image taken by the television camera 3 and displays the television image.

6 is a control unit including an A/D converter 61 that performs analog-to-digital conversion of image data ID from the television camera 3;
A core diameter calculation unit 62 that calculates an actual value of the core diameter based on the digital data DD from the A/D converter 61 and a pre-input reference value, and outputs the actual measurement value RD, and an actual measurement value by the core diameter calculation unit 62. The data RD is compared with the preset threshold value TH, and the actual measured value R
The comparison unit 63 outputs a stop signal ST to the burners 2a and 2b to stop combustion when D reaches a threshold value TH.

Next, the operations of the core diameter calculation section 62 and the comparison section 63 will be explained in more detail with reference to FIG.

FIG. 3 shows an image taken by the television camera 3 of the display section 5 in FIG. 1, and is a diagram showing how the diameter A of the core section 11 expands to the diameter B at the heated portion.

The threshold value TH is an initial setting value, and is set to the desired core diameter to be expanded, and the comparison unit 63 determines whether the level of the actual measurement value pig RD by the core diameter calculation unit 62 is the level of the threshold value TH, as described above. When the stop signal ST is reached, a stop signal ST is generated.

The method of outputting the actual value data RD of the core diameter calculation unit 62 includes a method of outputting the maximum value of the actual value of the heated area as the actual value data RD, and a method of outputting the average value of the core diameter of the heated area as the actual value data RD. There is a method of calculating and outputting it as actual measurement value data RD.

In these cases, as shown in FIG.
A method in which the portion (L) of 1 is larger than the core diameter A before heating, and a method in which the portion (Ll) is taken as a wafer-like enlargement are appropriately selected and applied.

Next, the operation according to the configuration described in "2" will be explained.

A desired position in the axial direction of the optical fiber 1 is heated from both sides thereof by gas burners 2a and 2b. In parallel with this,
Ultraviolet light UV is incident on the core portion 11 of the optical fiber 1 from the light input/output end face 13 using the ultraviolet irradiation device 4 .

In this way, when ultraviolet rays are incident on the core portion 11, the dopants in the core, mainly germanium, are excited,
This generates fluorescence, causing the entire core to emit light. This makes the boundary between the core portion 11 and the rad portion 12 clear.

The optical fiber 1 in the heating area in such a state is photographed by the television camera 3, and this image pig ID is input to the display section 5 and the control section 6.

As this image data ID is input to the display unit 5, the current image of the heating area of the optical fiber 1 is displayed.

On the other hand, the image data ID that entered the control unit 6 is first
The analog data is converted into digital data DD by the /D converter 61, and then input to the core diameter calculation section 62.

The core diameter calculation unit 62 calculates the actual value of the core diameter of the heating area based on the digital data DD from the A/D converter 61 and the reference data input in advance, and calculates, for example, the average value based on this. Actual measurement data RD
It is output to the comparator 63 as .

The comparison unit 63 compares the actual measurement value data RD by the core diameter calculation unit 62 with a preset threshold value TH, and if the level of the actual measurement value data RD reaches the level of the threshold value TH, that is, , a stop signal ST is generated when the core diameter is expanded to a desired value by heating.

This stop signal ST is output to the burners 2a and 2b, thereby stopping the heating of the optical fiber 1.

As explained above, according to this embodiment, the optical fiber 1
While heating the desired position of the core with gas bars 2a and 2b, the state of the heating area is monitored by the television camera 3, and the actual value of the core diameter is determined in real time based on the image data ID of the television camera 3. Since the heating of the optical fiber 1 is stopped when the preset threshold value TH is reached, the desired MFD can be reliably obtained without variation.

In addition, fusion splicing is currently the mainstream method for connecting optical fibers, and techniques for improving splice loss, workability, etc. have reached a considerable level. However, from now on,
With the introduction of subscriber optical fiber cables, there is an urgent need for multiple pairs, connection switching technology, and shortening of connection time, and connector connection is considered to be more effective than fusion splicing.

In that case, the biggest problem is that the connection loss is large, but by the method of the present invention, a low-loss connector connection can be realized by connecting optical fibers whose MFDs are constantly expanded without variation.

In addition, for other connections such as mechanical splices, it is thought that splice loss will be reduced by using optical fiber cores with uniformly expanded MFD, and splices using this method can be used for all types of optical fiber connections. This has the advantage of helping to improve connection loss.

Currently, the average splice loss of normal optical fiber connector connections is 0.35 dB, but with the method of the present invention, MF
If an optical fiber with D expanded by about 1.5 times is used, the connection loss can be reduced to about 0.1 dB.

In addition, in this embodiment, when monitoring with the television camera 3, the boundary between the core part 11 and the cladding part 12 is clearly defined by making the core part 11 of the optical fiber 1 incident on ultraviolet rays to generate fluorescence. Therefore, it is possible to obtain a highly accurate actual measured value of the core diameter with little error, and it is possible to control the MFD with high accuracy.

In this embodiment, the television camera 3 monitors in one direction, but is not limited to this, and may have a plurality of monitoring directions, thereby improving accuracy.

In addition, in this embodiment, explanation was given using a single optical fiber as an example, but if there are multiple optical fibers to be heated, it is necessary to make sure that the incidence of ultraviolet rays and the monitoring with a television camera can be performed on multiple fibers at once. is desirable.

Furthermore, it is of course possible to configure the heating of the optical fiber to be immediately stopped when an abnormality occurs in the shape of the optical fiber based on the image data of the heated region.

FIG. 4 is an explanatory diagram of a second embodiment of the method for controlling mode field diameter expansion of an optical fiber according to the present invention.

The second embodiment differs from the first embodiment in that instead of using a gas burner to heat the tip fiber 1 with its flame, discharge electrodes 7a and 7b are used and the discharging current 71 is used to heat the tip fiber 1. It's what I did.

Other structures, functions, and effects are the same as those of the first embodiment.

FIG. 5 is an explanatory diagram of a third embodiment of the method for controlling mode field diameter expansion of an optical fiber according to the present invention.

The third embodiment differs from the first embodiment in that instead of inputting ultraviolet rays from the light input/output end surface (cut surface) 13 of the optical fiber 1, the optical fiber 1 is bent. The reason is that the light is made to enter from the bent portion 14.

According to the third embodiment, ultraviolet rays can be input from any location on the optical fiber 1.

Other structures, functions, and effects are the same as those of the first embodiment.

FIG. 6 is an explanatory diagram of a fourth embodiment of the method for controlling mode field diameter expansion of an optical fiber according to the present invention.

The fourth embodiment differs from the first embodiment in that a light 8 for illuminating the heating area of the optical fiber 1 is placed at a position facing the television camera 3 across the heating area.

This has the advantage that the heating area can be photographed more clearly by the television camera 3.

Other structures, functions, and effects are the same as those of the first embodiment.

FIG. 7 is an explanatory diagram of a fifth embodiment of the method for controlling mode field diameter expansion of an optical fiber according to the present invention.

The difference between the fifth embodiment and the second embodiment is that, like the fourth embodiment, the heating area is illuminated at a position facing the television camera 3 across the heating area of the optical fiber 1. This is due to the placement of light 8.

Also according to the fifth embodiment, the television camera 3 in the heating area
This has the advantage that the images taken by the camera become clearer.

Other structures, functions, and effects are the same as those of the second embodiment.

(Effects of the Invention) As explained above, according to claim (1), (5) or (6), the state of the heating region is monitored by the imaging means while heating a desired position of the optical fiber, and the imaging means The actual value of the core diameter is determined in real time based on the image data of the device, and heating of the optical fiber is stopped when this actual value reaches a preset value, so the desired MFD can be produced without any variation. You can definitely get it.

In addition, low-loss connector connection can be realized by connecting optical fibers with uniformly expanded mode field diameters.

In addition, in other connections such as mechanical splices, it is thought that splice loss can be reduced by using optical fiber cores with uniformly expanded MFD, and this method can be used to connect all optical fibers. , which has the advantage of helping to improve connection loss.

Further, according to claim (2), (3) or (4), since the boundary between the core part and the cladding part of the optical fiber can be made clear, a highly accurate core diameter with little error can be obtained, Highly accurate control of the MFD is possible.

Further, according to claim (7), heating of the optical fiber is stopped when an abnormality occurs in the shape of the optical fiber based on the image of the heating area, so it is possible to prevent the occurrence of defective products. .

Moreover, according to claim (8), there is an advantage that the accuracy can be further improved by controlling the enlargement of the MFD.

Further, according to claim (9), when there are a plurality of optical fibers to be heated, the incidence of ultraviolet rays and the monitoring by the imaging means can be performed on the plurality of fibers at the same time, thereby increasing the efficiency of the work.
Accuracy can be improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a first embodiment of the mode field diameter expansion control method of an optical fiber according to the present invention, in which (a) is a conceptual diagram and (b) is a control system. 2 is a graph showing the relationship between heating time and the spread of mode field diameter, FIG. 3 is a diagram showing a television image when heating an optical fiber, and FIG. 4 is a diagram showing the optical fiber according to the present invention. FIG. 5 is an explanatory diagram of a second embodiment of the method for controlling the motofield diameter expansion of an optical fiber according to the present invention, and FIG. FIG. 7 is an explanatory diagram of a fourth embodiment of the method for controlling mode field diameter expansion of an optical fiber according to the present invention, and FIG. 7 is an explanatory diagram of a fifth embodiment of the method for controlling mode field diameter expansion of an optical fiber according to the present invention. . In the figure, 1... optical fiber, 11... core part, 12...
...Clad part, 13...Light input/output end face, 2a, 2b
...Gas burner, 21a, 21b...Flame, 3...
Television camera, 4... Ultraviolet irradiation device, 5... Display section, 6... Control section, 7a, 7b... Discharge electrode, 71
...discharge current, 8...light. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (9)

[Claims] (1) In an optical fiber mode field diameter expansion control method in which the optical fiber is heated to expand its mode field diameter, the core portion of the optical fiber is monitored by an imaging means while the optical fiber is being heated; A method for controlling mode field diameter expansion of an optical fiber, characterized in that heating of the optical fiber is stopped when the core diameter of the optical fiber reaches a predetermined value based on image data. (2) The method for controlling mode field diameter expansion of an optical fiber according to claim (1), wherein ultraviolet rays are incident on the core of the optical fiber. (3) The method for controlling mode field diameter expansion of an optical fiber according to (2), wherein the ultraviolet rays are incident on the light input/output end face of the optical fiber. (4) The method for controlling mode field diameter expansion of an optical fiber according to (2), wherein the optical fiber is bent and the ultraviolet rays are incident from the bent portion. (5) The light according to claim (1), (2), (3), or (4), wherein heating of the optical fiber is stopped when the maximum value of the core diameter of the optical fiber based on the image data reaches a specified value. Method for controlling fiber mode field diameter expansion. (6) Claim (1), (2), (3) or (4), wherein the heating of the optical fiber is stopped when the average value of the core diameter of the optical fiber based on the image data of the heating area reaches a specified value. The mode field diameter expansion control method of the optical fiber described. (7) The mode of the optical fiber according to claim (1), (2), (3) or (4), wherein heating of the optical fiber is stopped when an abnormality occurs in the shape of the optical fiber based on image data of the heated region. Field diameter expansion control method. (8) Claims (1), (2), (3), (4), (5), (6) in which the optical fiber is monitored from multiple directions by the imaging means.
) or (7), the mode field diameter expansion control method of an optical fiber. (9) Claims (1) and (2) in which, when heating a plurality of optical fibers at once to expand the mode field diameter of each optical fiber, all optical fibers are monitored at once by an imaging means.
), (3), (4), (5), (6), (7) or (
8) Method for controlling mode field diameter expansion of an optical fiber.