JPH0756048A - Optical fiber coupler and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Purpose] To provide an optical fiber coupler which has high mechanical strength, can be miniaturized, can endure use in a bad temperature environment, and has excellent temperature characteristics. [Structure] The cores 1a, 2a or the claddings 1b, 2b of the optical fibers f ₁ and f ₂ are doped with a dopant for controlling the refractive index in a predetermined concentration distribution. The optical coupling section of the optical fiber coupler 10 has the optical fibers f ₁ and f ₁ .
It is formed by fusing ₂ in parallel. Further, in this optical coupling portion, the dopant concentration distribution for controlling the refractive index is different from the dopant concentration distribution in the optical fiber portion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an optical fiber coupler used for optical communication, optical measurement, etc., and particularly, it is manufactured without melting and stretching, and has excellent mechanical strength and temperature characteristics. The present invention relates to an excellent optical fiber coupler and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, an optical fiber coupler has its optical coupling portion formed by melt drawing. That is, the conventional optical fiber coupler has a structure in which a plurality of optical fibers arranged in parallel to each other are stretched while being heated to narrow a core interval between adjacent optical fibers, thereby promoting optical coupling. It was

[0003]

However, the above-mentioned optical fiber coupler has a problem that the outer diameter of the optical coupling portion is thin and long, and the mechanical strength is small.

In addition, the conventional optical fiber coupler has a drawback that there is light leaking out from the clad due to the thin outer diameter of the optical coupling portion, resulting in excessive loss. In particular, in order to shorten the length of the optical coupling part, the clad of the adjacent optical fiber is thinned by etching etc. and then melt-stretched to form the optical coupling part, or the outer diameter of the optical coupling part by stretching. There is a strong tendency for excess loss to increase in optical fiber couplers that make the line extremely thin.

Further, the optical fiber coupler manufactured as described above is housed in the package by fixing the optical coupling part to the substrate by adhesion. However, the thermal coupling of the material of the optical coupling part and the package part accommodating the optical coupling part is performed. When there is a difference in expansion coefficient, tension is generated in the optical coupling portion when the ambient temperature changes. Due to the tension, the optical coupling portion extends, the length thereof increases, and the core interval between the adjacent optical fibers decreases. That is, the optical coupling coefficient of the optical fiber coupler changes. Specifically, the optical branching ratio changes. The smaller the outer diameter of the optical coupling portion, the greater the change due to the temperature, and the worse the temperature characteristics.

Therefore, in the conventional optical fiber coupler, the optical coupling portion is adhesively fixed to a protective substrate made of a material having a small difference in thermal expansion coefficient from that of the optical fiber, and the difference in thermal expansion coefficient from the optical fiber is small. The temperature characteristic was kept within a predetermined allowable range by storing it in a material package. However, the temperature range in which it can be used is limited, and it cannot withstand use in a bad temperature environment.

In view of such drawbacks, in order to provide an optical fiber coupler without fusion-stretching, an optical fiber having a large core diameter is used for an optical coupling portion, and a core portion of a normal fiber is fused at both ends thereof. Although a connection structure has been proposed, there is a problem that only a branching ratio of 50/50 is possible.

Therefore, an object of the present invention is to provide an optical fiber coupler which has a large mechanical strength, can be miniaturized, and can withstand use in a bad temperature environment, and is superior in temperature characteristics. It is also to provide a manufacturing method capable of manufacturing such an optical fiber with good reproducibility.

[0009]

The above object can be achieved by the optical fiber coupler and the manufacturing method thereof according to the present invention. In summary, the present invention provides an optical fiber coupler comprising a core or a clad, or a plurality of optical fibers in which a dopant for controlling the refractive index is added to the core and the clad in a predetermined concentration distribution. The optical coupling portion is formed by fusing adjacent optical fibers in parallel, and the concentration distribution of the dopant different from the predetermined concentration distribution is formed in the optical coupling portion. Is an optical fiber coupler.

In such an optical fiber coupler, (a) a plurality of optical fibers in which a dopant for controlling the refractive index is added to the core or the clad, or the core and the clad in a predetermined concentration distribution are prepared, Removing the coating of each optical fiber over a predetermined length to expose the cladding, (b) arranging the optical fibers parallel to each other with the exposed cladding in contact.
(C) heating and melting the contact portion of each optical fiber to form a fused portion; (d) heating and holding the fused portion at a predetermined temperature below the melting temperature of the fused portion for a predetermined time. It can be suitably manufactured by a manufacturing method characterized by

Further, the optical fiber coupler of the present invention is
(A) Prepare a plurality of optical fibers in which a dopant for controlling the refractive index is added to the core or the clad, or the core and the clad in a predetermined concentration distribution, and coat each optical fiber with a predetermined length. To expose the clad, and (b) heat and maintain a predetermined length of the exposed clad of each optical fiber at a predetermined temperature below the melting temperature of the clad for a predetermined time,
(C) arranging the optical fibers in parallel with each other such that the heated cladding contacts each other;
The clad portion in contact with each of the optical fibers may be heated and melted to form a fusion-bonded portion, which can be suitably manufactured.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical fiber coupler and a method for manufacturing the same according to the present invention will be described below in more detail with reference to the drawings.

FIG. 1 shows an optical fiber coupler 10 according to the present invention.
The cross section of the optical coupling part of is shown. Optical fiber coupler 1 of the present invention
Reference numeral 0 denotes an optical fiber coupler including at least two optical fibers, and the optical coupling portion is formed by fusing adjacent optical fibers in parallel. Further, what is important is that, as shown in FIGS. 3 (A) and 3 (B), each optical fiber f ₁ constituting the optical fiber coupler 10 of the present invention,
f ₂ is the core 1a, (2a) or the clad 1b (2
b), or both of the cores 1a, (2a) and the cladding are formed by adding a dopant in a predetermined concentration distribution to control the refractive index, and the optical coupling portion of FIG. ), A concentration distribution of the dopant different from the predetermined concentration distribution shown in FIG. 3 (A) is formed.

The characteristic construction of such an optical fiber coupler of the present invention will be better understood with reference to the manufacturing method which will now be described in connection with FIGS.

In the embodiments described below, the optical fiber coupler according to the present invention is a so-called 2 × 2 optical fiber in which two single mode optical fibers are fused to form an optical coupling portion. Although a coupler will be described, it should be understood that the fiber optic coupler of the present invention is not so limited.

Example 1 According to this example, first, as shown in FIG.
Two single mode optical fibers f ₁ (f ₂ ) having (2a) and the clad 1b (2b) are prepared by cutting them into a proper length. The optical fibers f ₁ and f ₂ have their outer coatings cut off over a predetermined length to form claddings 1 b and 2
b is exposed.

When the single mode optical fibers f ₁ and f ₂ used in the present invention are made of, for example, fused silica SiO ₂ as a matrix, the refractive index of the core or the clad is controlled as necessary. In order to do so, dopants such as Ge, P and B are added in a concentration distribution as shown in FIG.

Such optical fibers f ₁ and f ₂ are arranged parallel to the longitudinal direction so that their clad portions 1b and 2b are in contact with each other, and are attached to the fusion table (see FIG. 2A). )). Then, first, each optical fiber f ₁ , f
₂ to 1000-150 using, for example, a hydrogen oxygen burner
The cladding portions 1b and 2b are melted by heating to 0 ° C., and these portions are fused over a predetermined length. As a result, as shown in FIG. 2 (B), the gap between the cores 1a and 2a of both optical fibers f ₁ and f ₂ is narrowed, and the cores 1a and 2a are substantially circular because the clad portions 1b and 2b are fused and combined. The clad is deformed into the outer shape, i.e., it is located substantially at the center of the fused portion 12.

Next, the fused optical fibers f ₁ ,
f ₂ is removed from the fusion table, and the fusion portion 12 is fixedly arranged on a holding and fixing jig made of a high melting point metal, and the holding and fixing jig is heated, so that both optical fibers f ₁ , f _{The second} fused portion 12 is heated at a predetermined temperature equal to or lower than the melting temperature of the fused portion 12 for a predetermined time. This heating temperature is usually 80
0 to 1300 ° C., more preferably 900 to 110
The temperature is 0 ° C., and the heating time is 10 to 120 minutes.

If the heating temperature is lower than 800 ° C., the diffusion rate of the dopant becomes too slow, and if it exceeds 1300 ° C., the shape change due to softening becomes too large.

By this heating, the dopant added to control the refractive index is thermally diffused into a concentration distribution as shown in FIG. 3B, for example, to form a dopant diffusion region 20 (FIG. 2C). )). As a result, in the dopant diffusion region 20, the core diameter is substantially increased and the core
A decrease in the refractive index difference between the claddings occurs. That is, the electric field of light can be more widely distributed in the cladding portion 12.

Thus, the optical fiber coupler 1 of the present invention
At 0, a dopant diffusion region 20 having a refractive index smaller than the difference between the refractive indices of the core and the clad is formed between the cores of the optical coupling portion, and the optical coupling is mainly performed through this region. Occur.

According to the present embodiment, preferably, at the time of heating for diffusing the dopants in the optical fibers f ₁ and f ₂ , a predetermined wavelength is emitted from the LD light source to the input side of _one of the optical fibers, for example, the optical fiber f _1. of, for example, enters the monitoring beam of 1.55 .mu.m, the optical fibers f _1, an optical output detecting means to the output side of the f ₂ is connected, for example, a light receiving element such as a photodiode, the optical fibers f _1, f ₂ Monitor the output from. When the output from each of the optical fibers f ₁ and f ₂ reaches a desired value, for example, the optical fibers f ₁ and f 2
_It is preferred to stop heating when the outputs from ₂ are initially equal.

Embodiment 2 FIG. 4 shows a second embodiment of the method for manufacturing an optical fiber coupler according to the present invention. According to this embodiment, as shown in FIG. 4A, as in the first embodiment, two single mode optical fibers f ₁ and f ₂ having a core 1a (2a) and a clad 1b (2b) are provided. Prepared by cutting to a suitable length
Then, the outer coating is cut off over a predetermined length to expose the clad.

The single mode optical fibers f ₁ and f ₂ used in the present invention are made of, for example, fused silica SiO ₂ as a base material in the same manner as in the first embodiment. G to control the refractive index of the cladding
Dopants such as e, P and B are added in a concentration distribution as shown in FIG.

In each of the optical fibers f ₁ and f ₂ , the exposed lengths of the clads 1 b and 2 b are fixedly arranged on a holding jig for refractory metal, and the holding jig is heated. As a result, the exposed claddings 1b, 2b
Is heated at a predetermined temperature below the melting temperature of the clad for a predetermined time. The heating temperature is usually 800 to 1300 ° C., more preferably 900 to 1100 ° C., and the heating time is 10 to 120 minutes.

By this heating, each optical fiber f ₁ , f ₂
The dopant added to control the refractive index around the core thermally diffuses into the concentration distribution as shown in FIG. 3B as described above. In this dopant diffusion step, the heating temperature is limited to the extent that the outer shapes of the clads 1b and 2b are not deformed.

Then, the optical fibers f ₁ and f ₂ thus preliminarily subjected to the thermal diffusion are arranged in parallel with each other in the longitudinal direction, and the clad portions 1b and 2b thereof are arranged so as to be in contact with each other, and then are attached to the fusion table. Attach (Fig. 4 (B)). Then, the optical fibers f ₁ and f ₂ are heated to 1000 to 1500 ° C. by using, for example, a hydrogen oxygen burner, and the contacted clad portions 1 b and 2 b are fused over a predetermined length. As a result, as shown in FIG. 4C, both optical fibers f ₁ and f _{2 are}
The gap between the cores 1a and 2a of the
Is located in the clad where the clad portions 1b and 2b are melted and united and transformed into a substantially circular outer shape, that is, substantially in the center of the fused portion 12.

In the two optical fibers f ₁ and f ₂ , the cladding portions 1b and 2b are fused to each other to narrow the core gap, and the dopant diffusion region 20 is also integrally connected.
An optical coupling part is formed. Optical coupling occurs in this dopant diffusion region 20. Thus, also in this embodiment, an optical fiber coupler similar to that of the first embodiment is manufactured.

Also in this embodiment, the optical fibers f ₁ , f
At the time of fusing ₂ , the monitor light of a predetermined wavelength, for example, 1.55 μm is made incident from the LD light source to the input side of _one of the optical fibers f ₁ , for example, each optical fiber f 1.
_1, the output side of the f ₂ connected optical output detecting means, for example, a light receiving element such as a photodiode, the optical fibers f _1,
The output from f ₂ is monitored and each optical fiber f
_When the output from ₁ and f ₂ reaches the desired value, for example,
It is preferred to stop heating when the outputs from optical fibers f ₁ and f ₂ are initially equal.

Example 3 According to the manufacturing method described in Example 1, a 2 × 2 optical fiber coupler was manufactured. According to this embodiment, the two single mode optical fibers f ₁ and f ₂ have a core diameter of 1
A quartz fiber having a diameter of 0 μm and a cladding outer diameter of 125 μm and made of fused silica SiO ₂ as a base material was used. In the core 1a (2a) and the clad 1b (2b), dopants Ge, P, B for controlling the refractive index,
It was added in a concentration distribution as shown in FIG.

The outer coating of each of the optical fibers f ₁ and f ₂ is 2c.
It was excised over a length of m and washed.

Both optical fibers f ₁ and f ₂ are arranged in parallel with each other in the longitudinal direction so that their cladding portions are in contact with each other, mounted on a fusion table, and heated to 1100 ° C. using a hydrogen oxygen burner. Then, they were fused over a length of 10 mm. As a result, as shown in FIG. 2B, the gap between the cores 1a and 2a of both optical fibers f ₁ and f ₂ was 90 μm, and the outer shape of the clad 12 was substantially circular with a diameter of 180 μm.

Next, the fused optical fibers f ₁ ,
f ₂ was removed from the fusing table, and the fusing part was fixedly arranged on a holding and fixing jig made of a high melting point metal. Then, the holding fixture was heated to about 1000 ° C. Incidentally, this at the time of heating for the dopant diffusion on the input side of the optical fiber f ₁ enters the monitor light 1.55μm from the LD light source, to connect the photodiode to the output side of the optical fibers f _1, f _2, The output from each optical fiber f ₁ and f ₂ was monitored.

When the heating time in the thermal diffusion step exceeds 30 minutes, optical coupling occurs, and when the heating time reaches 40 minutes,
An optical coupling portion having a branching ratio of 50/50 was formed at a wavelength of 1.55 μm.

The insertion loss of the optical fiber coupler 10 thus obtained was measured and found to be within 3.05 dB between any input end and output end. Excess loss was reduced as compared with the optical fiber coupler produced by drawing.

As for the temperature characteristics of the insertion loss, when the temperature is in the range of −55 ° C. to 125 ° C. when the ambient temperature is in the range of −55 ° C. to 125 ° C.
The fluctuation was within 0.1 dB. The upper limit temperature of 125 ° C. in the temperature range is the upper limit temperature at which the adhesive used for adhesion and fixing to the protective substrate can be used.

Further, the optical fiber coupler 10 of the present invention is
The polarization stability, that is, the fluctuation range of the branching ratio depending on the angle of the polarization plane when linearly polarized input light is used at the input end is 0.1
It was within%. This is because, according to the present invention, since the optical coupling portion is not formed by stretching, there is no stress strain remaining in the optical coupling portion due to the tension during stretching, and no polarization dependency occurs.

Furthermore, in the optical fiber coupler 10 of the present invention, the tension at which the optical coupling portion breaks is larger than the tension at which the optical fiber itself from which the coating is removed breaks, and the minimum value of the tension at which the optical coupling portion breaks is measured. It was impossible to do. With an optical fiber having a clad outer diameter of 125 μm, no breakage of the optical coupling portion was observed under a tension of at least 2000 g. This indicates that the mechanical strength of the optical fiber coupler of the present invention is significantly increased as compared with the case where the conventional optical fiber coupler is broken at 1000 g weight.

Further, in the conventional optical fiber coupler, the fusion splicing of 40 to 50 mm is required to form the optical coupling portion, whereas in the optical fiber coupler of the present invention, the optical coupling portion is about 10 mm. This is achieved by forming a fused portion of Therefore, according to the optical fiber coupler of the present invention, it is possible to greatly reduce the size.

[0041]

As described above, in the optical fiber coupler according to the present invention, the optical coupling portion is formed by fusing adjacent optical fibers in parallel, and furthermore, in this optical coupling portion, Since the dopant concentration distribution for controlling the refractive index is different from the dopant concentration distribution in the optical fiber part, it has high mechanical strength, can be miniaturized, and has poor temperature environment. It has the characteristics that it can be used under the temperature and has excellent temperature characteristics. Further, according to the manufacturing method of the present invention, such an optical fiber coupler having uniform optical characteristics can be manufactured with good reproducibility.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical coupling portion of an embodiment of an optical fiber coupler according to the present invention.

FIG. 2 is a process drawing for explaining an embodiment of a method for manufacturing an optical fiber coupler according to the present invention.

FIG. 3 is a diagram showing an optical fiber coupler according to the present invention and a dopant concentration distribution in an optical fiber for producing the coupler.

FIG. 4 is a process drawing for explaining another embodiment of the method for manufacturing an optical fiber coupler according to the present invention.

[Explanation of symbols]

 1a, 2a Core 1b, 2b Clad 10 Optical fiber coupler 12 Fusion part (clad) 20 Dopant diffusion region

Claims (3)

[Claims] 1. An optical fiber coupler comprising a core or a clad, or a plurality of optical fibers in which a dopant for controlling a refractive index is added to the core and the clad in a predetermined concentration distribution. The coupling portion is formed by fusing adjacent optical fibers in parallel, and further, in this optical coupling portion, a concentration distribution of the dopant different from the predetermined concentration distribution is formed. Optical fiber coupler. 2. (a) Prepare a plurality of optical fibers in which a dopant for controlling the refractive index is added to the core or the clad, or the core and the clad in a predetermined concentration distribution, and Removing the coating over a predetermined length to expose the cladding, (b) arranging the optical fibers in parallel with each other with the exposed cladding in contact, and (c) for each optical fiber. Heating and melting the contact portion to form a fused portion,
(D) A method for manufacturing an optical fiber coupler, wherein the fusion-bonded portion is heated and maintained at a predetermined temperature equal to or lower than the melting temperature of the fusion-bonded portion for a predetermined time. 3. A plurality of optical fibers in which (a) a core or a clad, or a dopant for controlling a refractive index is added to a core and a clad in a predetermined concentration distribution are prepared, and Removing the coating over a predetermined length to expose the clad; and (b) heating and maintaining the predetermined length of the exposed clad of each optical fiber at a predetermined temperature below the melting temperature of the clad for a predetermined time. And (c) arranging the optical fibers in parallel with each other so that the heated claddings come into contact with each other, and (d) heating and melting the clad portions of the optical fibers in contact with each other and fusing. Forming an optical fiber coupler.