JP2804355B2 - Control method for mode field diameter expansion of optical fiber - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber mode field diameter expansion control method for heating and expanding the mode field diameter of an optical fiber.

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

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 apparent from FIG. 2, the MFD can be enlarged by heating a predetermined area of the optical fiber for a desired time.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional method, as shown in FIG. 2, even if the heating time for the optical fiber is controlled, the size of the MFD varies, and the MFD is kept constant. There is a disadvantage that it is difficult to enlarge the size with good controllability.

The reason why the MFD varies is considered to be related to the surrounding environmental conditions and the original refractive index distribution of the core, but has not been quantified.

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

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

(Means for Solving the Problems) In order to achieve the above object, according to a first aspect of the present invention, there is provided an MFD expansion control method for an optical fiber in which an MFD is expanded by heating the optical fiber. The optical loss was measured while heating the connection portion of the optical fiber, and the heating of the optical fiber was stopped when the measured loss value reached a predetermined value.

In claim (2), in the method of claim (1), the heating of the optical fiber is stopped when the measured loss value decreases by a certain value from the initially measured value.

In claim (3), the optical fiber is heated to
In the MFD expansion control method for an optical fiber that expands the MFD, an optical fiber that has been fusion-spliced in advance is used, and the optical loss thereof is measured while heating the connection portion of the optical fiber, and the fusion splicing is performed based on the measured loss change characteristics. The minimum value of the loss value of the part was estimated, the time for stopping the heating was set from this minimum value, and the heating was stopped after the set time had elapsed.

(Operation) According to claim (1), the fusion spliced portion of the optical fiber that has been fusion spliced in advance is heated, and the optical loss is measured during the heating.

The measurement result of the optical loss is compared with a prescribed value specified in advance, and when the measured value reaches the prescribed value, the heating of the optical fiber is stopped.

According to claim (2), a comparison is made between the initially measured loss value and the subsequently measured loss value, and when the loss value is reduced by a certain value from the initial loss value, the loss of the optical fiber is reduced. Heating is stopped.

According to claim (3), the fusion spliced portion of the optical fiber which has been fusion spliced in advance is heated, and the optical loss is measured during this heating.

Next, the minimum value of the loss value of the fusion spliced portion is estimated from the measured change characteristic of the loss value. Subsequently, a time to stop heating is set from the estimated minimum value, and heating of the optical fiber is stopped after a lapse of the set time from the setting.

(Embodiment) FIG. 1 is an explanatory diagram of a first embodiment of a mode field diameter expansion control method for an optical fiber according to the present invention.

In FIG. 1, reference numerals 1a and 1b denote optical fibers whose one ends are fusion-spliced to each other. Reference numeral 11 denotes a fusion splicing portion, and reference numerals 2a and 2b denote gas burners as heating devices for heating the vicinity of the optical fibers 1a and 1b including the fusion splicing portion 11. 21a and 21b are flames of the gas burners 2a and 2b.

A control device 3 includes a light source 31, an optical power measurement unit 32, and a heating control unit 33.

The light source 31 is made of, for example, a semiconductor laser and has a connector 4a.
And the other end of the optical fiber 1a.

The optical power measuring unit 32 is connected to the optical fiber via the connector 4b.
The optical power of the light connected to the other end of 1b and emitted from the light source 31 after the propagation through the optical fibers 1a and 1b is measured.

The heating control unit 33 stops heating the fusion splicing unit 11 in the gas burners 2a and 2b by the following two methods.

That is, the input of the measurement signal MS based on the measurement result of the optical power measurement unit 32 causes the optical fibers 1a and 1b and the fusion splicing unit 1 to be connected.
Grasp the light loss change caused by propagating 1 and set the output time of the stop signal ST by the method described later, and output the stop signal ST to the gas burners 2a and 2b after the set time has elapsed from the setting time, and fusion splicing The heating of the part 11 is stopped.

Alternatively, the level of the measurement signal MS is compared with a preset reference value, and when the level of the measurement signal MS reaches the reference value level, the stop signal ST is output to the gas burners 2a and 2b to heat the fusion splicing section 11. To stop.

Next, the two control methods applied to the control of the heating control unit 33 will be described in order with reference to FIGS.

FIG. 3 is a diagram showing a change in the loss of the connection portion and the spread of the MFD with the elapse of the heating time when the fusion spliced portion is heated. The curves shown represent changes in the mode field diameter.

As can be seen from FIG. 3, immediately after the start of the heating of the fusion spliced portion, after the splice loss suddenly decreases due to the self-centering effect due to the melting of the splice point, the loss change and the spread of the MFD are very small for a certain time ( A section).

Next, when the MFD spreads rapidly, the loss decreases parabolically (section B).

Further, the connection loss continues to increase parabolically following the lowest point D (section C). Again, MFD
Rapidly expands, but if the MFD in section C is too large, the boundary between the core and the cladding is not clear.

Therefore, heating until the connection loss is near the lowest point D
It is ideal to expand MFD.

The first control method applied to the heating control utilizes a connection loss characteristic that changes in a parabolic shape as shown in FIG.
In this method, an arbitrary point of a connection loss pattern that decreases in a parabolic manner in section B is set, and the MFD is enlarged to an arbitrary constant size.

That is, as shown in FIG. 5, since the minimum value of the connection loss can be estimated from the connection loss variation pattern, the heating time
From the connection loss values α ₁ , α ₂ , α ₃ … at t ₁ , t ₂ , t ₃ …, the connection loss α _{S at} which heating should be stopped is estimated, and the time T _S at which heating should be stopped since the estimation (for example, , T _S −t ₃ ), that is, a method of setting the output time of the stop signal ST.

In the vicinity of the lowest value of the connection loss (near the lowest point D),
Since the change in the connection loss value due to the heating time is not so large in the order of minutes, the setting error of the output time (heating stop time) T _S of the stop signal ST can be ignored.

The second control method applied to the heating control is the sixth control method.
As shown, set in advance a reference value alpha _S of connection loss, while keep monitoring the optical power sequentially by the measurement signal MS, stopped when the measured light power has reached the connection loss reference value alpha _S Output time of signal ST (heating stop time value)
This is how to determine T _S.

Further, since the loss improvement value due to the self-centering effect can be estimated from the initial connection loss, a method of stopping heating when the loss decreases by a certain value from the initial connection loss is also applicable.

 Next, the operation of the above configuration will be described.

The light emitted from the light source 31 of the control device 3 is an optical fiber
After propagating through 1a and passing through the fusion splicing section 11, it further propagates through the optical fiber 1b and enters the optical power measuring section 32.

In parallel with this, the optical fibers 1a and 1 including the fusion spliced portion 11
A predetermined portion b is heated by the gas burners 2a and 2b. With this heating, the MFD of the heated portion of the optical fibers 1a and 1b gradually expands.

The light power of the light incident on the optical power measurement unit 32 is measured, and the measurement result is used as the measurement signal MS as the heating control unit 33.
Is input to

In the heating control unit 33, for example, based on the input measurement signal MS, the connection loss values α ₁ , α ₂ , α at the heating times t ₁ , t ₂ , t ₃ .
_{3 ...} is grasped, the minimum value of the connection loss from connection loss variation pattern associated therewith, i.e., to stop the heating connection loss alpha _S is estimated.

Next, a time T _{S at} which heating should be stopped from the estimation time is set based on the estimation result, and a stop signal is output after the elapse of the time T _S.
ST is generated. The stop signal ST is output to the burners 2a and 2b, whereby the heating of the fusion splicing section 11 is stopped. As a result, an optical fiber having a desired MFD is obtained.

After the MFD is enlarged, by cutting the optical fiber in the vicinity of the fusion splicing section 11, an optical fiber having an arbitrary MFD at the tip can be obtained.

Further, since the heating width can be arbitrarily set by moving the gas burners 2a, 2b and the like at a constant width along the optical fiber axis, the length of the portion where the MFD is enlarged can be arbitrarily determined.

As described above, according to the present embodiment, the optical fiber
Heat the fusion spliced part 11 between 1a, 1b with gas burners 2a, 2b,
Since the fusion splice loss pattern at that time is obtained, and the heating is stopped by the heating control unit 33 at an optimum value based on the fusion splice loss pattern, a desired MFD can be reliably obtained without variation.

Further, as a current connection method between optical fibers, fusion splicing is mainly used, and techniques for improving connection loss, workability, and the like have reached a considerable level. However, in the future, with the introduction of subscriber optical fiber cables, the need for multiple pairs, connection replacement technology, and shortening of connection time are urgently needed, and connector connection is considered to be more effective than fusion splicing. .

In this case, the first problem is that the connection loss is large. However, according to the method of the present invention, a low-loss connector connection can be realized by connecting optical fibers in which the MFD is expanded uniformly without variation.

Also, in other connections such as mechanical splices, it is considered that the connection loss is reduced by using an optical fiber core wire in which the MFD is constantly expanded without variation, and this method can be used for connection of all optical fibers, There is an advantage that it helps to reduce connection loss.

At present, the connection loss of the connector connection of a normal optical fiber core is 0.35 dB on average, but the MFD can be reduced by the method of the present invention.
When using an optical fiber expanded 1.5 times, the connection loss becomes 0.1
It can be reduced to about dB.

In the present embodiment, the light source 31 is incorporated in the control device 3. However, the same effect as described above can be obtained even if the light source 31 is configured differently.

The same effect can be obtained even if the multi-core optical fiber is heated at once.

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

The difference between the second embodiment and the first embodiment is that instead of using the gas burner to heat the fusion spliced portion 11 of the optical fibers 1a and 1b using the flame thereof, discharge electrodes 5a and 5b are used.
Heating is performed by the discharge current 51.

Other configurations are the same as those of the first embodiment, and the obtained effects are the same as those of the first embodiment.

(Effects of the Invention) As described above, according to claims (1), (2) or (3), the fusion spliced portion between the optical fibers is heated, and based on the optical loss measured at that time. Since the heating is stopped at an optimum time, a desired MFD can be obtained without variation.

In addition, low-loss connector connection can be realized by interconnecting optical fibers in which the MFD is constantly expanded without variation.

Also, in connection with other splices such as mechanical splices, it is thought that the connection loss will be reduced by using an optical fiber core with an enlarged MFD without variation, and connection by this method is used for connection of all optical fibers. There is an advantage that it is possible to improve connection loss.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a first embodiment of a method for controlling the mode field diameter expansion of an optical fiber according to the present invention, FIG. 2 is a graph showing the relationship between the heating time and the expansion of the mode field diameter, and FIG. FIG. 4 is a diagram showing a change in loss of the connection portion and a spread of the MFD with the elapse of heating time when the fusion splicing portion is heated. FIG. FIG. 6 is an explanatory view of a second heating control method according to the present invention, and FIG. 6 is an explanatory view of a second embodiment of an optical fiber mode field diameter control method according to the present invention. In the figure, 1a, 1b: optical fiber, 11: fusion spliced part, 2a, 2b
... gas burners, 21a, 21b ... flame, 3 ... control device, 31
…… Light source, 32 …… Light power measurement unit, 33 …… Heating control unit,
5a, 5b: discharge electrode, 51: discharge current.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-117508 (JP, A) JP-A-56-4111 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 6/24

Claims (3)

(57) [Claims] 1. A method for controlling the mode field diameter of an optical fiber, comprising the steps of: heating an optical fiber to increase its mode field diameter; A method for controlling the mode field diameter expansion of an optical fiber, comprising measuring an optical loss and stopping the heating of the optical fiber when the measured loss value reaches a predetermined value. 2. The method for controlling the expansion of the mode field diameter of an optical fiber according to claim 1, wherein the heating of the optical fiber is stopped when the measured loss value decreases by a certain value from the initially measured value. 3. An optical fiber mode field diameter expansion control method for heating an optical fiber to expand its mode field diameter, comprising using an optical fiber that has been fusion-spliced in advance, and heating the connection portion of the optical fiber during heating. Measure the optical loss, estimate the minimum value of the loss value of the fusion spliced part from the measured loss change characteristics, set the time to stop heating from this minimum value, and stop heating after the set time has elapsed. Characteristic mode field diameter control method for optical fiber.