JP2862091B2 - Optical fiber coupler manufacturing equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for manufacturing an optical fiber coupler that branches or combines light propagating in an optical fiber.

(Prior Art) In constructing an optical communication system, an optical data link network, or the like, an optical splitter that distributes an optical signal emitted from a light source at a desired ratio is important as a component. One of the optical branching devices is an optical fiber coupler, which is usually twisted or fused in parallel and then heated and melted using a heat source such as an acetylene burner. This is stretched under a constant tension to form a tapered portion.

As shown in FIG. 2, the heating by the burner, which is a heat source, is performed by clamping a plurality of optical fibers 21 with clampers 22 and 22 and fusing and stretching the burners 23 and 23 while reciprocating in the axial direction of the optical fibers. The way to do it is taken. In order to accurately extend a fine coupler, the reciprocating motion of the burner needs to be performed accurately, and the moving mechanism for that is required to be precise, and the manufacturing equipment of the optical fiber coupler becomes expensive, and the optical fiber coupler becomes expensive. Manufacturing costs are high.

Another problem caused by reciprocating the burner flame in the axial direction of the optical fiber is that even if the combustion gas and oxygen gas sent to the burner are accurately controlled, the flame fluctuates because the burner moves. That is, it is inevitable that the characteristics of the optical fiber coupler vary.

(Problems to be solved by the invention) The present invention has been made in view of the above-described problems,
It is an object of the present invention to provide an optical fiber coupler manufacturing apparatus capable of obtaining an optical fiber coupler with less variation in characteristics without requiring a burner moving mechanism.

(Means for Solving the Problems) The invention according to claim 1 is an apparatus for manufacturing an optical fiber coupler in which a plurality of optical fibers are heated, fused and drawn by a burner, wherein the optical fiber is used as the burner. Using a single burner having at least three or more nozzle holes linearly arranged along the longitudinal direction of the nozzle and having a diameter of the outer nozzle hole smaller than a diameter of the inner nozzle hole. It is characterized by the following.

According to a second aspect of the present invention, there is provided the optical fiber coupler manufacturing apparatus according to the first aspect, wherein the mixing ratio of the combustion gas and the oxygen gas supplied to the burner is kept constant, and the flow rate is controlled to control the drawing speed of the optical fiber. Characterized by having control means for controlling

(Operation) First, the heating temperature will be described.

Generally, when the hole diameter D at the tip of the nozzle of the burner increases, the gas flow rate q is proportional to D ² under a constant gas pressure p. In addition, the relationship between the gas flow rate q and the amount of heat generated by combustion (that is, the temperature T) when the mixture ratio of the combustion gas is constant is a proportional relationship. Therefore, when the gas pressure and the mixing ratio are constant, there is a fixed relationship between the nozzle hole diameter and the combustion temperature, and the temperature can be controlled by changing the burner hole diameter.

Next, a description will be given of a temperature distribution which is important in manufacturing a coupler.

Taking a step index type optical fiber as an example,
Light propagating in the optical fiber repeats total reflection at the interface between the core and the clad. In optical fiber couplers, the third
As shown in the figure, the angle θ at which light is totally reflected at the interface between the core and the cladding gradually increases in order to process the optical fiber into a tapered shape. Since the total reflection phenomenon occurs at an angle θc or less that is determined by the refractive index of the medium on both sides of the interface, if the distance in the propagation direction is Z and the core diameter is d, the light is totally reflected when Δd / ΔZ (taper angle) increases. Wet without waking. Therefore, Δd / ΔZ needs to be set to a certain value or less. According to experiments conducted by the inventors, excess loss was reduced to 0.
In order to make it 1 dB or less, it is necessary to make Δd / ΔZ 40 μm / mm or less. To achieve this, about 5m of optical fiber
A heating means for giving a gentle temperature gradient to a region near m is required. Therefore, it is a conventional method to move the burner by the moving means and control the movement to give a temperature gradient.

In the present invention, the burner has at least three or more nozzle holes linearly arranged along the longitudinal direction of the optical fiber, and the diameter of the outer nozzle hole is smaller than the diameter of the inner nozzle hole. By using the burner described above, a gentle temperature gradient can be given, and Δd / ΔZ can be reduced.

(Embodiment) FIG. 1 is a configuration diagram of a main part of an embodiment of an optical fiber coupler manufacturing apparatus of the present invention. In the figure, 1 is an optical fiber, 2
Is a clamper and 3 is a burner. The optical fiber 1 is clamped by the clamper 2 after removing a part of the coating in the longitudinal direction. The clamper 2 is given tension in the direction of the arrow by a drawing stage (not shown), and draws the fused optical fiber. In this embodiment, the burner 3 has five nozzle holes as shown in FIG. 1 (B). The diameter of the central hole is h ₀ , the diameter of the two outer holes is h ₁ ,
Let h ₂ be the outer two holes, l ₁ be the distance between the center hole and the two outer holes, l ₂ be the distance between the outer two holes and the two outer holes, h ₀ = was _{0.8mm h 1 = 0.7mm h 2 =} 0.65mm l 1 = 1 2 = 1.7mm.

In this way, by making the nozzle hole larger at the center and symmetrically smaller at the outer side, it is possible to form a temperature distribution in which the center is higher and becomes lower toward the outer side. The spacing between the nozzles can be selected appropriately.

A coupler manufactured by the optical fiber manufacturing apparatus provided with the burner will be described. The manufactured coupler has a wavelength of 1.3μ.
Combining two m-mode single mode fibers (MFD 9.5 ± 1μm, cutoff wavelength 1.2 ± 1μm, cladding diameter 125μm)
An optical fiber coupler with a branching ratio of 50% at a wavelength of 1.3 μm was prototyped. Propane gas was used as the combustion gas. When using this burner, it is difficult to control the calorific value unless the mixing ratio of the combustion gas and the oxygen gas is constant. Therefore, using a mass flow controller for each gas, the mixing ratio of the propane gas and the oxygen gas is changed to the propane gas 1. On the other hand, oxygen gas 2
The control circuit was configured to have the ratio of At the time of fusion, the flow rate of propane gas was set to 45 cc / min, the distance between the burner and the fiber was reduced to 7 mm, heated for 120 seconds, and fused.
A tension of 3 g per side was applied to the stretching stage, the film was stretched, and the film was stretched until the branching ratio became 50%. In the case of stretching, the amount of stretching was controlled by lowering the gas flow rate while keeping the burner position.

FIG. 4 shows the cumulative distribution of the fifty optical fiber couplers prototyped above, wherein curve a represents the result according to the present invention. Curve b indicates that the burner of the above embodiment is perpendicular to the axial direction of the optical fiber, the moving speed is 3 mm / sec, and the moving width is 5.6 m.
This is the result of moving the burner by m. The movement was performed during the fusion, but the fusion time was 5 minutes and 10 seconds.

As is clear from this result, it is understood that the variation of the curve a is smaller.

(Effects of the Invention) As is clear from the above description, according to the present invention, the burner moving mechanism, which is indispensable for the conventional apparatus, is not required, and since the burner does not move, the fluctuation of the burner flame is small. In addition, variations in the characteristics of the manufactured optical fiber coupler can be reduced. Further, by increasing the burner structure and increasing the number of nozzle holes of the burner, it is possible to stably manufacture an optical fiber coupler capable of suppressing a change in the branching ratio with respect to the polarization direction incident on the coupler. There is an effect that can be done.

Furthermore, the mixing ratio of the combustion gas and the oxygen gas supplied to the burner is kept constant, and the drawing speed of the optical fiber is controlled by controlling the flow rate during drawing, thereby producing an optical fiber coupler having a precise branching ratio. There is.

[Brief description of the drawings]

FIG. 1 is a structural view of an essential part for explaining an optical fiber coupler manufacturing apparatus used in an embodiment of the manufacturing apparatus of the present invention, FIG. 2 is an explanatory view of a conventional manufacturing apparatus, and FIG. FIG. 4 is an explanatory diagram of the operation of the optical fiber coupler, and FIG. 4 is a graph for explaining data of a prototype. 1 ... optical fiber, 2 ... clamper, 3 ... burner.

Continuation of front page (72) Inventor Kazuhiko Arimoto 7-6-31 Omori Nishi, Ota-ku, Tokyo Sumiden Opcom Co., Ltd. (56) References JP-A-1-177002 (JP, A) JP-A-63 −205615 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G02B 6/28

Claims (2)

(57) [Claims] 1. An optical fiber coupler manufacturing apparatus in which a plurality of optical fibers are heated, fused and drawn by a burner, wherein the burners are linearly arranged along the longitudinal direction of the optical fibers. An apparatus for manufacturing an optical fiber coupler, wherein a single burner having at least three or more nozzle holes and having a diameter of an outer nozzle hole smaller than a diameter of an inner nozzle hole is used. 2. The apparatus according to claim 1, further comprising control means for controlling the flow rate of the optical fiber by controlling the flow rate while keeping the mixing ratio of the combustion gas and the oxygen gas supplied to the burner constant. Optical fiber coupler manufacturing equipment.