JPH06174967A - Optical module - Google Patents

Abstract

PURPOSE:To suppress one mis-alignment or optical axes at the time of welding holders and to decrease connection loss so as to assure long-term reliability by forming grooves parallel along a laser welded part of the butt end faces of metallic holders mounted with optical parts to each other. CONSTITUTION:This optical module is formed by butting three pieces of blocks 10a to 10c mounted with the optical parts, such as optical fibers against each other and joining the joint parts thereof by laser welding. The central block 10a is constituted of a metallic holder 11a made of a metal having an approximately U shape in section and a coupler element 12 adhered and fixed to the inner side thereof and is so joined that the optical axes of the single mode optical fiber 14 and the coupler element 12 provided in the right and left blocks 10b, 10c align to each other. The parallel grooves 17a to 17h are, thereupon, formed along the laser welded part 19 at the end faces where the metallic molders butt against each other. Then, through-ports 18a to 18d are formed by these grooves at the time of joining the metallic holders to each other. The heat transmission path from the laser welded part 19 to the optical parts is thus extended and the heat is radiated from the through-ports.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to abutting metal holders mounted with optical parts such as optical fibers and optical waveguides.
The present invention relates to an optical module in which the joint portion is laser-welded.

[0002]

2. Description of the Related Art In the case of forming an optical module using optical parts such as an optical waveguide and an optical fiber, particularly when the optical fiber is a single mode, a highly accurate mounting technique is required to align these optical axes. . For example, the loss due to the optical axis shift that occurs when connecting the single mode optical fiber and the single mode optical waveguide is preferably 0.1 dB or less,
To keep the loss below this value, the optical axis deviation should be 1 μm.
Must be:

A method using an organic adhesive has been used for such a connection requiring high precision, but the organic adhesive is deteriorated due to a temperature change with time, and an optical axis shift occurs in the optical coupling system. However, there is a problem in that the coupling loss increases and the coupling loss increases.

Therefore, a fixing method by soldering, which is excellent in stability against a temperature change with time, has been used. However, in general, the melting point of the solder material is as low as around 183 ° C,
The creep phenomenon is likely to occur, and the residual stress during solidification is gradually released due to this creep phenomenon, causing a non-negligible optical axis shift, which makes it difficult to ensure long-term stability of the optical transmission system.

Therefore, recently, a fixing method has been developed which uses a welding technique which is stable with respect to temperature changes and which hardly causes a creep phenomenon.

However, when welding a metal material, shrinkage stress is generated in the joint due to shrinkage of the metal material during melting and solidification and cooling to room temperature, resulting in welding deformation.
To prevent this, in order to minimize the influence of heat on the welding material by minimizing the area of the weld, laser welding using a YAG laser with a high energy density and a small weld area is used as the welding heat source. Is being done.

FIG. 5 is an external perspective view of a conventional optical module.

As shown in the figure, the optical module is formed by joining three blocks 1a, 1b and 1c, to which optical components such as an optical fiber and an optical waveguide are fixedly bonded, by laser welding. Block 1a is made of quartz 1x
The 4-star coupler element 2 is bonded and fixed to a holder 3a made of stainless steel having a U-shaped cross section, and then both end surfaces are polished. The left block 1b has a single-mode precision V-groove block 4 on which a single-mode optical fiber 5 is fixed, and the single-core precision V-groove block 4 has a stainless steel holder 3b having the same cross section as the central block 1a. After being bonded and fixed to, the left end surface was polished. Block 1 on the right
In c, four single-mode optical fibers 8 are fixed on the 4-core precision V-shaped groove block 7, and the 4-core V-shaped groove block 7 is mounted on a stainless steel holder 3c having the same cross section as the central block 1b. After the adhesive fixing, the right end surface is polished.

The positions of the holders 3a, 3b, 3c are adjusted while the end faces are abutted to find the position where the light loss is the smallest, and the laser beams are simultaneously radiated from both sides of the abutting faces to instantly weld and fix them. There are usually two or more welding points 9 to improve the connection strength. This welding operation is performed on the two joining surfaces on the single-core fiber 5 side and the 4-core fiber 8 side.

[0010]

However, there is a problem that when the holders are welded and fixed to each other by laser, the loss due to the optical axis shift increases. The causes of the optical axis shift are considered to be 1) the impact of laser light irradiation, and 2) the non-uniformity of the amount of heat shrinkage between the two holders in the direction orthogonal to the optical axis during the cooling process after solidification of the weld.

For 1), the holders are pressed in the optical axis direction to generate a static frictional force against the laser shock at the abutting end faces in the laser emission direction, or each holder is firmly clamped. There is a method. Further, JP-A-2-298904 discloses that a cutout portion is provided in the vicinity of the abutting end portion in order to suppress the output of laser light.

For 2), it is possible to irradiate the center of the joint with laser light so as to equalize the amount of heat conduction to both holders.

However, in any case, this is a very difficult technique in practice.

Further, since metal parts for YAG laser welding are generally plated with gold, cracks are likely to occur at the welded portion, and optical coupling loss due to optical axis shift due to welding deformation increases. It is difficult to secure long-term reliability of the optical coupling part due to cracks. Since the reflectance of the YAG laser light on the gold-plated layer of the welded part is high, the energy required for welding becomes large, and there is a problem that the optical axis shifts due to the impact force of this laser light.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide an optical module capable of suppressing the optical axis deviation during holder welding, reducing the connection loss and ensuring long-term reliability.

[0016]

In order to achieve the above object, the present invention is directed to an optical module in which metal holders mounted with optical components are butted to each other and the joints thereof are laser-welded to each other. Parallel grooves are formed along the laser welded portion on the matching end faces.

Further, according to the present invention, in the optical module in which the side faces are gold-plated and the metal holders on which the optical parts are mounted are butted to each other and the joints thereof are laser-welded, the gold-plated portions of the laser-welded portions are previously removed and laser-welded. It is a thing.

[0018]

According to the above construction, since parallel grooves are formed along the laser welded portion on the end faces where the metal holders abut each other, when the two metal holders are joined, a through hole is formed by these grooves. The heat conduction path from the laser welded part to the optical component is extended, and heat is dissipated through this through-hole, reducing the amount of heat conduction to the optical component and making the optical axis after welding solidification. The deviation is reduced.

Further, after the gold plating of the laser-welded portion of the gold plating applied to the holder is removed in advance, the holder is laser-welded, so that the amount of laser light reflected from the holder is reduced. Therefore, laser welding can be performed with low energy, the laser impact force is reduced, and the optical axis shift is reduced.

[0020]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is an external perspective view of an embodiment of the optical module of the present invention.

As shown in the figure, the optical module comprises three blocks 1 on which optical components such as optical fibers and optical waveguides are mounted.
0a, 10b, and 10c are abutted against each other, and their joints (both left and right side surfaces) are joined by laser welding.

The central block 10a of the optical module is
The holder 11a is made of metal (for example, stainless steel) and has a substantially U-shaped cross section, and the quartz 1 × 4 star coupler element 12 is fixedly adhered to the inside of the holder 11a.

The block 10b on the left side is a holder 11b made of stainless steel having the same cross section as the block 10a at the center.
And a single-mode precision V-groove block 13 fixed in the holder 11b and a single-mode optical fiber 14 fixed on the single-core precision V-groove block 13. The optical axis of the fiber 14 and the optical axis of the 1 × 4 star coupler element 12 made of quartz are joined so as to coincide with each other.

The right block 10c is also the central block 1
0a stainless steel holder 11c with the same cross section
And a four-core precision V-groove block 15 fixed in the holder 11c and four single-mode optical fibers 16 fixed on the four-core precision V-groove block 15, respectively. Optical axes of four single mode optical fibers 16 and a 1 × 4 star coupler element 12 made of quartz
Are joined so that their optical axes coincide with each other.

As shown in the figure, four through-holes 18a-18d each having an elongated hole in cross section are formed at the joints of the respective holders 11a, 11b, 11c of this optical module.

FIG. 2 is a partially enlarged view of the central block of the optical module shown in FIG.

In the figure, the holder 1 of the block 10a
Two parallel grooves 17b and 17d along the side surface of the holder 11a are formed on the left end surface of the la 1a. Both grooves 17b, 17d are formed, for example, about 1 mm from the outside and inside with a length of about 5 mm, a width of about 1 mm, and a depth of about 2 mm, and have a substantially U-shaped cross section. Grooves 17e and 17g having a similar shape are also formed on the right end surface (see FIG. 1) of the holder 11a.

On the end surface of the holder 11b used for the block 10b on the left side of the optical module on the side facing the central block 10a, a groove 17a having a shape as shown in the figure is provided at a position facing the grooves 17b and 17d. , 17c are formed. On the end surface of the holder 11c used for the right block 10c of the optical module on the side facing the central block 10a, at a position facing the grooves 17e and 17g,
Grooves 17f and 17h having a shape as shown in the figure are formed.

Therefore, when the block 10a and the block 10b are butted and joined to each other, the groove 17a and the groove 17b form a through hole 18a having a long hole in cross section, and the grooves 17c and 17d form a similar through hole 18b. It Similarly, when the block 10a and the block 10c are butted and joined to each other, the groove 17e and the groove 17f form the through hole 18c, and the grooves 17g and 17h form the through hole 18d.
Although the grooves 17a to 17h have a U-shaped cross section in the drawing, the present invention is not limited to this, and if a parallel through hole is formed along the joint, it may have a V-shaped or U-shaped shape. Other shapes such as a square shape may be used. Incidentally, each block 10a
It goes without saying that the end faces of 10c are mirror-finished.

Here, a method of manufacturing this optical module will be described.

Other holders 11b, 11 of the holder 11a
Grooves 17a to 17h that are parallel to the side surfaces of the holders 11a to 11c are formed on the end faces that face c, and the optical components are bonded and fixed and then mirror-finished. Each of these holders 11a to 11c,
The position where the light loss is the smallest is found by adjusting the positions while abutting the end faces, and the YAG laser light is simultaneously irradiated from both sides of the abutting faces in the direction of arrow S to instantly weld 1
By fixing 9 the optical module is formed. In addition, the number of welds is usually two or more to improve the connection strength. This work is for the single-core fiber 14 side, 4-core fiber 1
It is carried out at two joining surfaces on the 6 side.

Next, the operation of the embodiment will be described.

Since parallel grooves 17a to 17h are formed along the laser welded portion 19 on the end faces where the holders 11a to 11c used for the blocks 10a to 10c abut each other,
When joining the holders 11b and 11c to both sides of the holder 11a to form an optical module, these grooves 17a to 17h are formed.
Thus, the through holes 18a to 18d are formed. Therefore, the laser light extends the heat conduction path from the welded portion 19 to the optical components inside each of the holders 11a to 11c, and at the same time, the through holes 1 are formed.
Heat is radiated to the outside through 8a to 18d, the amount of heat conduction to the optical component is reduced, and the optical axis shift of the optical component after welding and solidification is reduced.

FIG. 3 is a graph showing the relationship between the number of times laser light is emitted when the optical module shown in FIG. 1 is formed and the amount of increase in cumulative loss due to optical axis shift. Indicates the cumulative loss increase due to the optical axis shift. Black circles show conventional examples, and white circles show examples (the number of samples is 10).

From the figure, the average value of the loss increase amount due to the deviation of the optical axis of the optical component is reduced to less than half as compared with the conventional example, and the variation is also reduced. As a result, welding with YAG laser
It was possible to obtain an optical module in which the optical axis deviation during fixing was greatly reduced, the connection loss was low, and the stability was high.

FIG. 4 is an external perspective view of another embodiment of the optical module of the present invention. However, the metal holder has a box shape that shields optical components.

The difference from the embodiment shown in FIG. 1 is that the gold plating of the laser welded portion is removed in advance and the laser welding is performed.

As shown in the figure, an optical module is formed by joining three blocks 20a to 20c containing optical components, and optical fibers are connected to both ends. A holder 21a used for the central block 20a and holders 21b, 21c used for both left and right blocks 20b, 20c.
Is gold-plated in the vicinity of the laser welded portion 22, that is, except for the joint portion 23.

When this joining portion 23 is irradiated with YAG laser light and welded, the amount of laser light reflected from each of the holders 21a to 21c is reduced as compared with the case where gold plating is applied, so that laser light of low energy is used. It becomes possible to weld with, laser impact force is reduced, and optical axis shift is reduced.
Therefore, the optical axis shift at the time of welding / fixing with the YAG laser is significantly reduced, and an optical module with low connection loss can be obtained.

In the present embodiment, the joining portion 23 of the metal holder is used.
However, the gold plating of the entire metal holder may be removed. Moreover, 42Ni, Kovar, Invar, or the like is used for the metal holder.

Further, a low melting point solder such as a eutectic solder may be plated in advance on a portion (the portion to be welded) which is not plated with gold. In this case, since the energy required for welding the YAG laser can be reduced, the impact force during welding can be reduced and the loss of the optical coupling system can be reduced.

Further, Ni plating may be applied in order to prevent rust and the like of the material of the portion not subjected to gold plating (since Ni plating does not cause cracks in the welded portion during YAG laser welding).

As described above, according to the present embodiment, parallel grooves are formed along the laser welded portion on the end faces where the metal holders abut each other, or the side faces are plated with gold and the metal on which the optical component is mounted is mounted. In an optical module in which holders made of metal are abutted against each other and the joints are laser-welded, the gold plating on the laser-welded portion is removed in advance and laser-welded, so optical axis deviation during holder welding is suppressed, connection loss is reduced, and long-term reliability is ensured. It is possible to realize an optical module that can secure the property.

[0045]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) Since the amount of heat generated when the holder of the optical module is welded and fixed by the YAG laser is reduced to the optical component, the optical axis shift is greatly reduced.

(2) Since the gold plating on the welded portion is removed, laser welding can be performed at low energy, cracks and welding deformation are less likely to occur, and the optical axis shift is greatly reduced.

(3) By plating the portion to be welded with a low melting point solder such as eutectic solder, the energy required for welding the YAG laser can be reduced and the optical axis shift can be reduced.

[Brief description of drawings]

FIG. 1 is an external perspective view of an embodiment of an optical module of the present invention.

FIG. 2 is a partially enlarged view of a central block of the optical module shown in FIG.

FIG. 3 is a graph showing the relationship between the number of times laser light is emitted and the cumulative loss increase amount due to optical axis deviation when forming the optical module shown in FIG.

FIG. 4 is an external perspective view of another embodiment of the optical module of the present invention.

FIG. 5 is an external perspective view of a conventional optical module.

[Explanation of symbols]

 11a-11c (Metal) Holder 17a-17h Groove 19 Laser welding part

Claims (2)

[Claims] 1. An optical module in which metal holders mounted with optical parts are butted against each other and the joint portion thereof is laser-welded, and a groove parallel to the laser-welded portion is formed on an end face where the both metal holders are butted against each other. An optical module characterized by being formed. 2. An optical module in which metal holders having side surfaces plated with gold and optical components mounted on each other are butted to each other and the joints thereof are laser-welded, the gold-plating of the laser-welded portion is previously removed and laser-welded. Optical module.