JPH0372304A - Manufacture of optical coupler - Google Patents

Abstract

PURPOSE:To forming a large uniform fusion area which has a nearly ideal coupling efficiency and to miniaturize an optical coupler by controlling the quantity of heat given to an optical fiber in reciprocal motion by varying the quantity of heat of a heating source or the distance between the heating source and optical fiber. CONSTITUTION:A burner 12 is used as the heating source 12, which is put in the reciprocal motion in the direction of the optical fiber axis and so controlled that the gas flow rate of the burner is small in the center of the reciprocal motion to obtain the least quantity of heat generation and increased toward both ends of the reciprocal motion to obtain the larger quantity of heat generation, thereby making the quantity of heat given to optical fibers 13a and 13b substantially weak in the center of the reciprocal motion and larger toward both the ends. Both ends of the optical fibers 13a and 13b are applied with mutually equal constant drawing forces at all times. As the area which is thinned in diameter by drawing is expanded, the heated area becomes wide, so the amplitude of the reciprocal motion of the heat source 12 is increased gradually as the frequency of the reciprocal motion is increased. Consequently, the effect of thinning of the optical fiber diameter is prevented from being converged on the center, the area which is thinned in diameter relatively uniformly is formed large, and the coupler is nimiaturized.

Description

Detailed Description of the Invention "Field of Industrial Application" This invention is a method for manufacturing an optical coupler used in optical communications, optical fiber sensors, etc. The present invention relates to a method of manufacturing a fiber type optical coupler, and particularly aims to improve the optical characteristics and reduce the size of the fiber type optical coupler.

``Prior Art'' As shown in FIG. 4, the manufacturing equipment used for the fusion and stretching manufacturing method of fiber-type optical couplers includes a pair of stretching tables 11a and 11b that move smoothly on the same straight line, and Although not shown, the main components include a stretching force applying device that simultaneously applies force to the stretching tables 11a and 11b in the direction of increasing the distance from each other, and a heating FJ 12 such as a gas burner located between the stretching tables 11a and llb. The two optical fibers 13a and 13b with their coatings removed over an appropriate length are aligned and placed on the stretching tables 11a and llb so that the portions from which the coatings have been removed are in contact with each other, and placed in the fiber holder. 14a
, 14b are respectively gripped on the stretching table-1.

A photodetector 16a that inputs light from a light source 15 to one end of one optical fiber 13a and receives each output light from the other end of the optical fiber 13a and the end of the optical fiber 13b on the same side;
16b is provided to enable monitoring of the optical splitting ratio during the manufacture of the optical coupler.

As shown in FIG. 4, the heating source 12 is connected to an optical fiber 13a,
13b, the optical fibers 13a and 13b are fused together, and then, as shown in FIG. 5, while reciprocating the heating source 12 in the axial direction of the optical fibers, a force is simultaneously applied to the drawing tables 11a and llb in the direction of separating them from each other. In addition, it is stretched. Since the branching ratio of the optical coupler depends on the amount of stretching, stretching is performed while monitoring the optical branching ratio, and the stretching is completed when the desired optical branching ratio is obtained.

``Problems to be Solved by the Invention'' Fiber-type optical couplers manufactured using conventional manufacturing methods have a so-called piconic taper type in which the diameter is extremely thin at the center of the optical fiber fusion region and wide at both ends of the fusion region. The change in diameter was steep, and it was virtually impossible to arbitrarily control this.

In this case, the optical coupling efficiency (coupling coefficient) of both optical fiber waveguides varies according to the cross-sectional shape of each point along the optical fiber axis direction, and an inefficient structure is required to obtain the desired optical branching ratio as a whole. are doing. That is, since the above-mentioned tapered shape is forced, there are large portions where the coupling coefficient is extremely small over a large area in the axial direction.

This is a decisive obstacle when aiming at miniaturization of optical couplers.

Furthermore, as shown in Figure 6, the optical branching ratio depends on the wavelength of the incident light and increases or decreases according to the amount of stretching. As shown in Figure 2, there is a point where the optical branching ratio is 100% at λ1 and close to 0% at λ2, and this is often used to create a wavelength demultiplexer/multiplexer using a fiber type optical coupler. be exposed. In this case, the relationship between the coupling coefficient and wavelength determined for each cross section is not uniform, and as a result, the branching ratio for the two wavelengths is controlled by the characteristics of the manufacturing equipment, and the relationship between the two branching ratios cannot be controlled. Complete 100% as shown in Figure 6
, 0% could not be achieved.

Furthermore, when making an optical coupler using two optical fibers, one of the two fibers is pre-stretched before fusion splicing, or each of the two fibers is pre-stretched by a different amount and then the fibers are pre-stretched. By performing fusing and stretching, a so-called wide wavelength band optical coupler is manufactured. This utilizes the deformation of the branching ratio vs. wavelength characteristic due to the difference in propagation constant between two optical fibers, but at this time, the previously drawn optical fiber has a piconical taper shape, which is fused and Stretching becomes an extremely difficult task in practice. That is, when pre-drawn optical fibers are aligned and installed for fusion splicing, gaps are created between the optical fibers, making it difficult to achieve sufficient contact at the points to be fused. If a pre-drawn fiber with a diameter reduced in this way can be produced, the manufacturing yield of broadband optical couplers will be greatly improved.

"Means for Solving the Problem" According to the present invention, in the optical fiber stretching process performed before optical fiber fusion, or in the optical fiber fusion area stretching process performed after fusion, the optical fiber is While heating the optical fiber, the heating source is reciprocated relative to the optical fiber in its axial direction, and the amount of heating given to the optical fiber during the reciprocating movement is called the calorific value of the heating source, or the amount of heat generated by the heating source and the light source. It is controlled by changing the distance to the fiber, and the amount of heating is made relatively small at the center of the reciprocating motion, and gradually varied so that it becomes relatively large as it approaches both ends.

Alternatively, the stretching force applied to both ends of the optical fiber is reversely controlled on the forward and backward paths of the reciprocating motion so that a substantial stretching force is applied only to the end of the optical fiber on the opposite side to the moving direction of the heating source.

This makes it possible to create a drawn fiber with a uniform diameter, making it easy to create a wide wavelength band optical coupler, and forming a large fused area with near-ideal coupling efficiency. By omitting the small part of the optical coupler, the optical coupler can be made smaller.

Furthermore, the fiber fusion region cross section is shaped as desired for the relationship between the coupling efficiency and the wavelength, and each part creates a coupling region of that cross section, thereby controlling the relationship between the optical branching ratio of the optical coupler and the wavelength. A more accurate wavelength demultiplexer/multiplexer can be created.

"Example" FIG. 1 shows a stretching process in an example of the present invention, and parts corresponding to those in FIG. 4 are given the same reference numerals. A burner is used as the heating source 12, and the heating source 12 is reciprocated in the optical fiber axis direction.At the center of the reciprocating movement, the gas flow rate of the burner is small and the calorific value is the weakest, and as it goes to both ends of the reciprocating movement, the gas The flow rate is controlled to be large and the amount of heat generated is strong, and the amount of heating substantially given to the optical fibers 13a, 13b is weak at the center of the reciprocating motion and becomes stronger toward both ends. A constant and equal stretching force is always applied to both ends of the optical fibers 13a and 13b.

Furthermore, in order to widen the heating area as the area reduced in diameter by stretching widens, the amplitude of the reciprocating motion of the heating source 12 is gradually increased in accordance with the number of reciprocating movements. This prevents the effect of reducing the diameter of the optical fiber from being concentrated in the center, and makes it possible to form a large area where the diameter is reduced in a relatively uniform manner.

FIG. 2 shows another embodiment of the present invention, in which a burner is used as the heating source I2, its gas flow rate, that is, the calorific value, is kept constant, and the reciprocating movement of the heating source 12 is accompanied by a light beam at its center. The heating source 12 is moved away from the optical fibers 13a, 13b and closer to the optical fibers 13a, 13b at both ends, with a motion component perpendicular to the optical fiber axis. The distance between the optical fibers 13a, 13b and the heating source 12 is controlled during the reciprocating motion, and the temperature is weak at the center of the reciprocating motion.
Strong heating is performed on the optical fibers 13a, 13b at both ends. Note that the optical fiber 13a with figure 8 motion
, 13b, there is little heating applied to the optical fibers 13a, 13b.

Furthermore, the heating source 12 is located on the right side of the figure 8 movement in the figure, on the stretching table 1.
During the time on the 1b side, the right stretching table 11b is fixed,
During the time when only the left stretching table 11a is applied with a stretching force and the heating source 12 is on the left side of the figure 8 movement, the left side stretching table 11a is fixed and only the right side stretching table 11b is applied with a stretching force. When the heating HI3 is on the right side of the optical fiber, the right stretching table 11b is fixed and the stretching force is applied only to the left stretching table 11a, so the part of the optical fiber that has been heated and stretched to be thinner moves to the left side. , on the other hand, since the heating B12 moves to the right, it heats the part of the optical fiber that has not been reduced in diameter, and that part is reduced in diameter by stretching and moves to the left. is made smaller in diameter. Conversely, if the heating source 12 is on the right side of the figure 8 movement, the left stretching table 11a is fixed and the right stretching table 11b is
When a stretching force is applied to only the optical fiber, the portion of the optical fiber whose diameter has been reduced by heating and drawing moves to the right, and the heating source 12 also moves to the right due to the movement, but part of the portion whose diameter has been reduced also moves to the right. As it is heated, that part becomes thinner and thinner (-4
It is difficult to reduce the diameter by 1.

In the previous explanation, the stretching table that fixes one half of the figure-8 movement and the other half and the stretching table that applies the stretching force are reversed, but as can be understood from the previous explanation, the light of the heating source 12 fiber 13
It is sufficient to fix the stretching table on the side in the moving direction along the axial direction of a and 13b, and apply a stretching force to the stretching table on the opposite side to the moving direction.
Further, in the above description, one of the stretching tables is fixed, but a weak stretching force may be applied to the fixed stretching table, and substantial stretching may be performed by the stretching force applied to the other stretching table.

Further, while controlling the heating amount shown in FIG. 1, while the heating B12 is moving in the direction of the drawing table 11b,
1b is fixed, a stretching force is applied to the stretching table 11a, and heating is performed.
1. When 12 is moving in the direction of the stretching table 11a, the stretching table 11a
may be fixed, and a stretching force may be applied to the stretching table llb. Furthermore, as can be understood from the above explanation, the amount of heating to the optical fiber is not controlled, but is kept constant, the drawing table on the side of the moving direction of the heating source is fixed during the reciprocating motion of the heating source 12, and the drawing table on the side of the moving direction of the heating source is fixed, and Even if a stretching force is applied to the side stretching table and the stretching table is reversely controlled in the forward and return directions of the reciprocating motion, -
Extended portions of various diameters can be obtained.

In the above description, the present invention has been applied to the process of drawing a fused region of two optical fibers, but the present invention can also be applied to a process of drawing a fused region of three or more optical fibers. Further, the present invention can also be applied to an optical fiber stretching process performed before the optical fibers are fused together.

"Effect of the Invention J As described above, according to the present invention, during the reciprocating movement of the heating source in the drawing process, the amount of heating of the optical fiber is controlled so that it is weak in the center of the reciprocating movement and becomes strong at both ends, or The stretching force at both ends of the optical fiber is reversely controlled depending on the direction of movement of the heating source so that a substantial stretching force is applied only to the end of the optical fiber on the opposite side to the direction of movement of the heating source, or By performing both of these controls at the same time, the diameter reduction effect is distributed instead of being concentrated in the center, and this control is applied to the preliminary stretching before fusion and the stretching after fusion to create a cross-sectional structure close to the ideal. According to the present invention, a small optical coupler can be obtained in which a coupling region having a shape of -, so by setting this cross section to the desired wavelength relationship of coupling efficiency, the branching ratio is 100% for wavelength C, as shown by the broken line in Figure 3. The branching ratio is 0% for
It is possible to create a high-precision wavelength demultiplexer/multiplexer. Furthermore, by applying the preliminary drawing step, an optical fiber with a small diameter portion such as - is obtained, so it is necessary to align the pre-drawn optical fiber with an undrawn optical fiber or an optical fiber with a different amount of drawing. Installation can be performed easily, and a wide wavelength band optical coupler can be manufactured with high yield.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the invention, FIG. 2 is a diagram showing another embodiment of the invention, and FIG. 3 is an example of the relationship between the light branching ratio and the amount of stretching obtained by applying the invention. Figure 4 shows the fusion process in the conventional manufacturing method, Figure 5 shows the stretching process in the conventional manufacturing method, and Figure 6 shows the light branching ratio and stretching obtained by the conventional manufacturing method. FIG.

Claims (7)

[Claims] (1) In a method of manufacturing a fiber-type optical coupler by heating and fusing and stretching at least two optical fibers, an optical fiber drawing process is performed before fusing the optical fibers, or after fusing the optical fibers. In the drawing process of the optical fiber fusion region, the heating source performs a relative reciprocating motion with an axial component with respect to the optical fiber while heating the optical fiber, and during the reciprocating motion, the heating source is substantially applied to the optical fiber. A method for manufacturing an optical coupler, characterized in that the amount of heating is controlled so that the amount of heating is weak at the center of the reciprocating motion and strong at both ends. (2) The reciprocating motion is a linear reciprocating motion, and the heating amount is controlled by controlling the amount of heat generated by the heating source to be small at the center of the reciprocating motion and large at both ends. 2. The method of manufacturing an optical coupler according to claim 1. (3) The method of manufacturing an optical coupler according to claim 2, wherein the heat source is a gas burner, and the amount of heat generated is controlled by controlling the gas flow rate of the burner. (4) The amount of heating is controlled by giving the reciprocating motion a component perpendicular to the optical fiber axis such that the reciprocating motion moves away from the optical fiber at the center and approaches the optical fiber at both ends. A method for manufacturing an optical coupler according to claim 1. (5) The method for manufacturing an optical coupler according to claim 1, wherein the amplitude of the reciprocating motion is increased as the number of repetitions of the reciprocating motion increases. (6) In a method for manufacturing a fiber-type optical coupler by heating and fusing and stretching at least two optical fibers, an optical fiber drawing step is performed before fusing the optical fibers, or is carried out after fusing the optical fibers. In the process of stretching the optical fiber fusion region, the heating source performs a relative reciprocating motion with an axial component to the optical fiber while heating the optical fiber, and the heating source moves the optical fiber on the opposite side to the moving direction of the heating source. A method for manufacturing an optical coupler, characterized in that the stretching force applied to both ends of the optical fiber is independently controlled on the forward and backward paths of the reciprocating motion so that a substantial stretching force is applied only to one end. (7) The optical coupler according to claim 6, characterized in that the amount of heating substantially applied to the optical fiber during the reciprocating motion is controlled so that it is weak at the center of the reciprocating motion and becomes strong at both ends. Production method.