JP2945514B2 - Manufacturing method of optical fiber coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a coupler by stretching a part of a plurality of optical fibers while heating and fusing them.
The present invention relates to a method for manufacturing an optical fiber coupler by a so-called fusion drawing method.

[0002]

2. Description of the Related Art An optical fiber coupler is a device that branches and couples light between a desired plurality of optical fibers.
It is manufactured by stretching. In order to obtain an optical fiber coupler having a desired branching ratio, it is necessary to manufacture the optical fiber coupler while monitoring the branching ratio in the steps of melting and drawing.

[0003] As a method of monitoring the branching ratio, there are a transmission monitoring method generally used and a reflection monitoring method previously filed by the present applicant (Japanese Patent Application No. 1-275616).

FIG. 4 shows an apparatus for manufacturing an optical fiber coupler using this transmission monitoring method. As shown in FIG.
The two optical fibers 40a and 4 to be wound around 1
The optical fiber coupler 43 is formed by removing the coating of the portions corresponding to the respective coupler forming portions 42, bringing them into close contact with each other, heating, fusing, and stretching them with a burner or the like. To control this stretching, one of the optical fibers 40
a light source 44 is connected to one end of the
The photodetectors 46, 46 are connected to the other ends of the a, 40b via V-groove connectors 45, 45 for optical connection, respectively. The photodetectors 46 and 46 are connected to a computer 47, and the computer 47 is connected to a stretching control device 49 that controls a stretching jig 48.

Light that has entered the optical fibers 40a and 40b from the light source 44 passes through the coupler forming section 42 and is detected by both photodetectors 46 and 46. The detection result is input to the computer 47, and the computer 47 calculates the branching ratio based on the amounts of both transmitted lights. When the branching ratio reaches a desired value, the stretching control device 49
The stretching control device 49 stops the stretching of the stretching jig 48.

FIG. 5 shows an apparatus for manufacturing an optical fiber coupler using the reflection monitor method. In this apparatus, a photodetector 4 is provided at one end of each of the optical fibers 40a and 40b.
6, 46 are connected, and a light source 44 is connected to one of the optical fibers 40a via a measuring coupler 50 for splitting the reflected light. And the photodetector 4
6 and 46 are connected to a computer 47,
Is connected to a stretching control device 49 for controlling a stretching jig 48. On the other hand, the other ends of both optical fibers 40a and 40b are open. Reference numerals 51, 51 in the drawing denote refractive index matching oil for preventing reflection.

Light incident on the optical fiber 40a from the light source 44 via the measuring coupler 50 passes through the coupler forming section 42, is reflected at the open end of the optical fiber 40a, passes through the coupler forming section 42 again, and is branched. Then, both photodetectors 46,
Detected at 46. This detection result is input to the computer 47, and the computer 47 calculates the branching ratio based on the amounts of the two reflected lights. Then, when the branching ratio reaches a desired value, a control signal is output from the computer 47 to the stretching control device 49, whereby the stretching control device 49 stops the stretching of the stretching jig 48.

[0008]

In the former manufacturing method, however, the manufactured optical fiber coupler 45 must be disconnected at any time, so that either one of the end of the light source 44 or the photodetector 46 is required. Needs to be reconnected each time one optical fiber coupler 45 is manufactured. This connection work is time-consuming and requires skill, and if the proper connection is not made, it may affect the measurement error.

In the latter manufacturing method, there is no problem in connection work as in the transmission monitoring method, but the reflected light from the open end of the optical fiber 40a to be detected is weak Fresnel reflected light. Therefore, especially when the optical fiber 40a is long, the optical fiber 40a,
The influence of the Rayleigh scattered light within 40b appears remarkably, and this may cause a measurement error.

That is, when light enters the optical fiber, the light returning to the incident end includes Fresnel reflected light reflected from the far end of the optical fiber and Rayleigh scattering generated over the entire length of the optical fiber. There is light. Here, the Fresnel reflected light power is P _r , the Fresnel reflectivity is r, the transmittance of the optical fiber (output light power in transmission / incident light power in transmission) is α, and the incident light power is P ₀ . In this case, the Fresnel reflected light power is represented by P _r = P ₀ · α ² · r.

This means that when the optical fiber length becomes longer and the transmittance of the optical fiber becomes smaller, the Fresnel reflected light power becomes extremely small. On the other hand, as shown in FIG. 6, the Rayleigh scattered light power increases proportionally as the optical fiber length increases. Therefore, when a long optical fiber is used, the influence of Rayleigh scattered light appears remarkably. In this case, if only the Rayleigh scattered light power of the optical fiber can be measured in advance, only the Fresnel reflected light power among the reflected light powers including both can be calculated.

The present invention has been made based on such a principle, and it is an object of the present invention to provide a method of manufacturing an optical fiber coupler which minimizes the influence of Rayleigh scattered light when monitoring a branching ratio. .

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for heating and forming a coupler forming section of a plurality of optical fibers.
When forming a coupler by stretching while fusing, in a method of manufacturing an optical fiber coupler that detects the amount of light passing through the coupler forming portion and controls the stop of stretching based on the detected light amount, heating the coupler forming portion・ At least one prior to fusion
A first step of causing a certain amount of light to enter from one end of the optical fiber and detecting the amount of Rayleigh scattered light of the one optical fiber at one end of the one optical fiber; After the start of heating and fusion, a certain amount of light is made incident from one end side of one optical fiber, passes through the coupler forming section, is further reflected at the other end of the optical fiber, and is again formed in the coupler forming section. And the second step of detecting the amount of reflected light at one end of each of the plurality of optical fibers, the amount of light detected in the first step, and the amount of reflected light detected in the second step. A third step of correcting the light amounts of the respective lights and controlling the stop of the stretching based on the corrected light amount ratios of the respective lights.

In this case, it is preferable to detect the amount of Rayleigh scattered light by suppressing Fresnel reflection at the other end of one optical fiber. Further, in this case, it is preferable to suppress the Fresnel reflection by immersing the other end of one optical fiber in a refractive index matching agent.

[0015]

By detecting the amount of Rayleigh scattered light of one optical fiber at one end of one optical fiber prior to heating and fusion of the coupler forming portion, the Rayleigh scattered light generated in this optical fiber can be measured numerically. Can be grasped. Next, after heating, fusing and stretching of the coupler forming portion are started, a certain amount of light is incident from one end of one optical fiber, and the amount of reflected light is reduced by one of the plurality of optical fibers. , And subtracting the detected value of the Rayleigh scattered light from the detected value, the light amount of only the Fresnel reflected light during the coupler formation can be obtained. Then, if the branching ratio of the optical fiber coupler is calculated based on this light amount, an accurate branching ratio can be obtained.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an apparatus for manufacturing an optical fiber coupler for implementing the manufacturing method of the present invention will be described with reference to FIG. This manufacturing apparatus prepares two long single-mode optical fibers 1 wound around a bobbin 2 and unwinds them while unwinding the optical fiber coupler 3 having a 1: 1 branching ratio (50%).
Are continuously formed in large numbers. In this embodiment, 2
Although the same optical fiber 1 is used,
For the sake of simplicity, the description below will be described with the first optical fiber 1a at the top and the second optical fiber 1b at the bottom for convenience. Various devices for monitoring and controlling the branching ratio of the manufactured optical fiber coupler 3 are connected to one end of both optical fibers 1a and 1b, and the other end is a refractive index matching oil for preventing Fresnel reflection. 4a, 4b. In this case, however, the other end of the second optical fiber 1b is always inserted into the refractive index matching oil 4b, but the other end of the first optical fiber 1a is used in the manufacturing process described later.
There are cases where it is inserted into a and cases where it is taken out.
That is, there are a case where the Fresnel reflection is suppressed at the end of the first optical fiber 1a and a case where the reflection is actively performed. A coupler forming part 5 for both optical fibers 1a, 1b is formed on the refractive index matching oil 4a, 4b side of both optical fibers 1a, 1b. The coupler forming unit 5 includes the two optical fibers 1a and 1b.
After a part of the coating is removed, this part is heated and fused by a burner or the like in a close contact state, and further stretched to form the optical fiber coupler 3. Therefore, the coupler forming unit 5
Is attached to a stretching jig 8 having a burner 6 and a stretching table 7.

A light source 10 is connected to one end of the first optical fiber 1a via a measuring coupler 9.
Reference numeral 0 denotes a semiconductor laser or the like. A certain amount of light from the light source 10 is incident from one end of the first optical fiber 1a via the measuring coupler 9 having a branching ratio of 50%. First optical fiber 1a of measuring coupler 9
One of the side branches is connected to the first optical fiber 1a as described above, and the other is inserted into the refractive index matching oil 4c to prevent the influence of reflection from this portion. Conversely, one of the branches of the measuring coupler 9 on the monitor device side is connected to the light source 10 as described above, and the other is connected to the first photodetector 1.
1 connected. On the other hand, a second photodetector 12 is connected to one end of the second optical fiber 1b. First,
The second photodetectors 11 and 12 each include a light receiving element and the like, and further include a computer 1 for calculating a branching ratio.
3 is connected.

The light reflected at the other end of the first optical fiber 1a passes through the coupler forming section 5 and is branched, and each branched light is guided to both optical fibers 1a and 1b. The branched reflected light is further branched by the measuring coupler 9 on the first optical fiber 1a side and detected by the first photodetector 11, and the second photodetector 12 is detected on the second optical fiber 1b side.
Is to be detected. In this case, the other end of the first optical fiber 1a is inserted into the refractive index matching oil 4a to suppress the Fresnel reflection, and the first optical detector 11
In the case where only Rayleigh scattered light is detected by the above method, it is taken out from the refractive index matching oil 4a and Fresnel reflection is positively performed.
In some cases, reflected light composed of Rayleigh scattered light and Fresnel reflection is detected.

First photodetector 11 and second photodetector 12
Is detected by the computer 1 for calculating the branch ratio.
3, where the branching ratio is calculated by a calculation formula described later. When the calculated value reaches a desired branching ratio (50% in the case of the present embodiment), a control signal for stopping the stretching is output to the stretching control position 14 connected thereto.

The stretching control device 14 is connected to the stretching jig 8 and drives the stretching jig 8 based on a control signal from the computer 13. The stretching jig 8 is provided with a burner 6 for heating the coupler forming section 5 and a stretching table 7, whereby the coupler forming section 5 is heated, fused and stretched. When a control signal for stopping is input from the computer 13, the stretching control device 14 stops the stretching drive of the stretching jig 8 based on the stop signal.

Next, the principle of the monitoring method will be briefly described. First photodetector 11 before manufacturing optical fiber coupler
Assuming that the detected power (detected light amount) is P ₀ and the detected powers of the first and second photodetectors 11 and 12 during manufacture of the optical fiber coupler are P ₁ and P ₂ , respectively, the computer 13 calculates the power during manufacture. The branching ratio of the optical fiber coupler 3 (defined by the ratio of the branch-side optical power) is expressed by the following equation.

The branching ratio = (s / t + s) × 100 [%] where _{t = (P 1 / P 0} ) 1/2 s = (α 1 / α 2) S 0 (P 2 2 / P 0 P 1 ) ^1/2 Note, alpha _1, the 1 alpha _2, respectively, a second double optical fiber 1
a, 1b transmittance (output light power / incident light power), S
₀ is the main line side transmittance of the measuring coupler 9 (main line outgoing light power / main line incident light power). Based on the above formulas, the computer 13 performs an arithmetic process, and outputs a signal to stop stretching when the desired branching ratio is reached. Actually, P ₀ , P ₁ and P ₂ are described below. The value is a value that is subtracted and corrected by the detection value of the Rayleigh scattered light in the step of performing.

Here, a series of manufacturing steps will be described with reference to the flowchart of FIG. First, the coating of a part of the optical fiber 1 is removed to form the coupler forming section 5 (step 201). The coupler forming section 5 is fixed to the stretching tables 7, 7 of the stretching jig 8 on both sides (step 202). Then the first
After the other end of the optical fiber 1a is immersed in the refractive index matching oil 4a (step 203), the light source 10 is turned on (step 204), and the Rayleigh scattered light generated in the first optical fiber 1a is converted into the first light. Detect by the detector 11 (Step 20)
5). Then, the other end of the first optical fiber 1a is pulled out from the index matching oil 4a (step 206), the Fresnel reflection is ready to detect the reflected light P ₀ by the first optical detector 11 (Step 207). Thereafter, in this state, the coupler forming section 5 is heated by the burner 6, and this portion is fused (step 208) and further stretched (step 2).
09). During this stretching step, P ₁ and P ₂ are detected by the first photodetector 11 and the second photodetector 12, respectively (step 210). That is, these detected values are input to the computer 13, and the values of these optical powers (P ₀ , P
_The branching ratio is calculated by the computer 13 on the basis of the detected values of the Rayleigh scattered light for correcting these ( ₁ and P ₂ ) (step 211). And P in this stretching process
The detection of ₁ and P ₂ and the calculation of the branch ratio are repeated until the branch ratio becomes 50% (step 212), and the branch ratio becomes 50%.
When the value reaches%, the computer 13 outputs a stop signal to the stretching stop device 14. The stretching stop device 14 stops the stretching of the stretching jig 8 based on the stop signal (step 213). The optical fiber coupler 3 thus formed is finally molded or bonded to a protective member (not shown) such as a quartz case (step 21).
4).

By repeating the above steps as needed, two long optical fibers 1 wound on the bobbin 2 respectively.
A large number of optical fiber couplers 3 are sequentially formed from a and 1b. In this case, if the measuring coupler 9 and the second photodetector 12 are connected to the first and second optical fibers 1a and 1b, respectively, when the first optical fiber coupler 3 is manufactured, The connection work can be omitted from the manufacture of the optical fiber couplers 3 and thereafter.

According to the manufacturing method of the embodiment described above,
The optical fiber coupler 3 was actually manufactured, and the variation of the branching ratio was measured. In this manufacturing process, a superluminescent diode having a wavelength of 0.85 μm was used as the light source 10. Each of the first and second optical fibers 1a and 1b is a 0.85 μm band single mode fiber having a fiber length of 1 km, and the measuring coupler 9 is also a 0.85 μm band single mode coupler.

Under the above conditions, while monitoring the branching ratio, optical fiber couplers having various branching ratios were manufactured, and the branching ratios of the manufactured optical fiber couplers were measured by a transmission method. FIG. 3 shows the measurement results. The plots with black circles are optical fiber couplers manufactured by the reflection monitor method of the present embodiment, and the plots with white circles are manufactured by the conventional reflection monitor method shown in FIG. An optical fiber coupler. According to the measurement results, the reflection monitoring method and the transmission monitoring method of the present embodiment completely match, and according to the reflection monitoring method of the present embodiment, an optical fiber coupler with an accurate branching ratio was manufactured. You can see that. On the other hand, the conventional reflection monitoring method is different from the transmission monitoring method, and it can be confirmed that the branch ratio of the optical fiber coupler based on the conventional reflection monitoring method is somewhat inaccurate. Thus, it was confirmed that the reflection monitoring method of the present example was able to remove the influence of Rayleigh scattered light.

[0027]

As described above, according to the present invention, the Rayleigh scattered light generated in the optical fiber is detected in advance, and the monitor in the stretching operation of the coupler forming section is operated based on the detected value of the Rayleigh scattered light. Since the detection value of the reflected light is corrected, the influence of the Rayleigh scattered light can be eliminated as much as possible, and an optical fiber coupler with an accurate branching ratio can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an outline of an optical fiber coupler manufacturing apparatus that implements a manufacturing method of the present invention.

FIG. 2 is a flowchart showing a manufacturing process of the optical fiber coupler.

FIG. 3 is a diagram showing a comparison between an optical fiber coupler manufactured by a manufacturing method of the present invention and an optical fiber coupler manufactured by a conventional method.

FIG. 4 is an explanatory view showing an outline of an optical fiber coupler manufacturing apparatus which has performed a conventional manufacturing method.

FIG. 5 is an explanatory diagram illustrating an outline of an optical fiber coupler manufacturing apparatus that implements a conventional manufacturing method.

FIG. 6 is a diagram showing the relationship between the length of an optical fiber and the Rayleigh scattered light power.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical fiber 1a ... 1st optical fiber 1b ... 2nd optical fiber 3 ... Optical fiber coupler 4a ... Refractive index matching oil 5 ... Coupler forming part 10 ... Light source 11 ... 1st detector 12 ... 2nd detector 13 ... Computer 14 ... Stretching control device

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroaki Takimoto 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Hiroshi Suganuma 1st Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries Hiroshima Yokota (72) Inventor Hiroshi Yokota 1-chome, Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd.Yokohama Works (72) Kazuhiko Arimoto 7-31, Omorinishi 7-chome, Ota-ku, Tokyo (56) References JP-A-3-136008 (JP, A) JP-A-4-328505 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 6 / 28

Claims (3)

(57) [Claims] 1. A coupler forming section for a plurality of optical fibers,
When forming a coupler by stretching while heating and fusing, in the method of manufacturing an optical fiber coupler for detecting the amount of light passing through the coupler forming portion, and controlling the stop of the stretching based on this, Prior to heating and fusing of the coupler forming section, a certain amount of light is made incident from at least one end of the one optical fiber, and Rayleigh scattering of the one optical fiber is caused at one end side of the one optical fiber. A first step of detecting the amount of light, and after starting the heating and fusion of the coupler forming section, a certain amount of light is incident from one end side of the one optical fiber to form the coupler forming section. And further reflected at the other end of the optical fiber, again passed through the coupler forming section, and the amount of the reflected light is detected at one end side of the plurality of optical fibers, respectively. The step; A third step of correcting the light quantity of each light detected in the second step with the light quantity of the light detected in the step, and controlling the stop of the stretching based on the light quantity ratio of each corrected light; A method for manufacturing an optical fiber coupler, comprising: 2. The optical fiber coupler according to claim 1, wherein the detection of the amount of the Rayleigh scattered light is performed by suppressing Fresnel reflection at the other end of the one optical fiber. Method. 3. The method according to claim 2, wherein the suppression of the Fresnel reflection is performed by immersing the other end of the one optical fiber in a refractive index matching agent. .