JPS6193419A - Optical coupling device - Google Patents

Abstract

PURPOSE:To eliminate substantially the reflection at the incident end face of an optical fiber by disposing a transparent plate to the incident end face of the optical fiber and filling the spacing with the optical fiber with a transparent material having a prescribed refractive index. CONSTITUTION:The incident end face 2 of the optical fiber made of glass or quartz and a glass or quartz plate 3 are adhered by epoxy 4. The refractive index of the glass or quartz is 1.4-1.5 and the refractive index of the epoxy is approximately 1.5 and therefore the reflectivity of light at the incident end face 2 of the optical fiber 1 is 0-0.12% and the quantity of the light returning to the oscillation region 6 of a semiconductor laser 5 is decreased by the reflection at the incident end face 2 of the optical fiber 1. The unstable phenomenon and characteristic change of the semiconductor laser are eliminated at all. The beam west of laser light 9 exists at the incident end face 2 of the optical fiber and the laser light 9 is made incident diagonally onto the incident face 7 of the glass plate 2 and therefore the reflected light 9' returns hardly to the oscillation region 6 of the laser 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical coupling device, and particularly to an optical coupling device between a semiconductor laser and an optical fiber.

When entering laser light emitted from a semiconductor laser into an optical fiber, there are many cases in which a microlens is used to narrow down the diverging laser light within the core diameter of the optical fiber (for example, 60 m diameter). The reality is that the tip of the optical fiber used for this purpose is not coated with anti-reflection coating. Therefore, the laser beam is reflected at the optical fiber entrance surface, and a portion of the laser beam returns to the semiconductor region via the microlens. As a result, the laser oscillation state becomes extremely unstable, and changes occur in both static and dynamic characteristics, such as an increase in noise and a change in current-light output characteristics.

In optical fiber communications, this characteristic change causes a fatal problem mainly due to deterioration of direct modulation characteristics.

A further disadvantage is that this phenomenon is more pronounced in optical coupling lens structures where the optical coupling loss to the optical fiber is smaller. This is because if the laser light from the semiconductor laser efficiently enters the source fiber, the light reflected at the input end face of the optical fiber will also efficiently return to the missed area of the semiconductor laser.

Therefore, although various highly efficient optical coupling lens structures have been reported, none of them have been put into practical use due to problems caused by reflected light at the input end face of the optical fiber. Therefore, until now,
The only way to avoid this reflection problem was to intentionally increase the optical coupling loss.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical coupling device that almost eliminates reflection at the input end face of an optical fiber when coupling light from a semiconductor laser to an optical fiber.

According to the present invention, in a device that focuses laser light from a semiconductor laser using a lens and couples it to an optical fiber, a transparent plate having a parallel principal surface that is not coated with an anti-reflection coating is attached to the input end surface of the optical fiber. The laser beam is arranged perpendicular to the optical axis, the space between the optical fiber and the transparent plate is filled with a transparent material having a refractive index, and the laser beam is focused by a lens so that the beam waist of the laser beam is located at the incident end face of the optical fiber. An optical coupling device characterized by this is obtained.

The present invention will be described below with reference to the drawings.

It is difficult to coat the input end face of an optical fiber with anti-reflection coating. In commonly used hard coats such as MgF, 5
Stable and strong coating cannot be achieved unless the temperature is raised to nearly 00℃. This causes a problem in that the nylon covering the core of the optical fiber melts. Therefore,
Instead of applying an anti-reflection coating to the input end face of an optical fiber, if the area near the input end face is made of a material with a refractive index similar to that of the optical fiber, and only the part used in front is coated with an anti-reflection coating in advance, reflections can be eliminated in practical equipment. I can do that.

The most typical example is to place a flat glass 3 in front of the input end face 2 of the optical fiber 1, as shown in FIG. 1(a).
The structure is such that the space between them is bonded with epoxy 4. Glass or quartz has a refractive index of 1.4 to 1.5, and epoxy has a refractive index of approximately 1.5. Therefore, when the input end surface 2 of an optical fiber made of glass or quartz and the glass or quartz plate 8 are bonded with epoxy 4, the gap between them becomes epoxy instead of an air layer, so the reflectance of light at the input end surface 2 of the optical fiber is θ~0.1211C. On the other hand, in the conventional method, since the input end face of the optical fiber is in contact with air, the reflectance of light is 2.8 to 4. Therefore, the first
In the basic configuration shown in Figure (a), the input end face 2 of the optical fiber 1
The reflection of light at
Becomes 80 or less.

On the other hand, the incident surface of the glass plate 8? Now, the light is reflected. However, when optimal optical coupling to the optical fiber 1 is performed by the lens 8, the beam waist of the laser beam 9 is located at the incident end surface 2 of the optical fiber, and the laser beam 9 is obliquely incident on the incident surface 7 of the glass plate 8. Therefore, the reflected light 9' takes a trajectory different from that of the incident light 9, and therefore almost never returns to the oscillation region 6 of the semiconductor laser 5.

On the other hand, at the input end face 2 of the optical fiber at the beam waist position, the shape is close to normal incidence, so the trajectory of the reflected light matches the trajectory of the incident light, and most of the reflected light is from the semiconductor laser. Return to oscillation region 6.

Therefore, in the basic configuration of FIG. 1(a), if the thickness of the glass plate 8 is 0.5 m or more, there is almost no need to apply an anti-reflection coating to the incident surface 7 of the glass plate 8. However, if the laser beam 9 is almost perpendicularly incident on the incident surface 7 of the glass plate 80 as shown in FIG. is narrow, the spread angle of the laser beam is made small by a sideways cylindrical lens or semi-cylindrical lens 100, etc.)
In this case, it is desirable to apply a reflective coating 7' to the entrance surface 7. Anti-reflective coating of the glass plate 8 is an established technology and can be easily carried out at present.

In the present invention, there is no limit to the distance between the input end surface 2 of the optical fiber and the output surface 7'' of the glass plate 3 that opposes it. Regarding this, there are many adhesives other than epoxy, so any of them can be used.Also, as for the material of the glass plate, in addition to the various types of glass, quartz, sapphire, etc. can also be used to achieve the desired effect. In this book, we will use the general term "glass plate" to refer to the tora.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows an embodiment applied to a so-called pigtail with an optical fiber of 20 to 80 cm. laser crystal 1
Cap 1 of axially symmetrical package 11 centered on 0
The lens adapter 13 is bonded to Z with a screw, epoxy, or solder without any adjustment. The lens 14 is a cylindrical type SELFOC lens (for example, a diameter of 1.5 fi and a length of 8
, 8 cln) acts as a micro convex lens,
Laser light 10' with a large radiation angle from the semiconductor laser 10
Converge. The pigtail portion 15 is adapted to fit into this lens adapter 18.

The focused laser beam enters the incident end face 17 of the optical fiber 16.
After adjusting the position of the lens adapter 13 so that it fits to the maximum power, it is fixed with epoxy or solder. A transparent glass plate 18 is fixed in front of the input end face 17 of the optical fiber 16, and the space between the input end face 17 and the glass plate 18 is also fixed with epoxy 19. In production, optical fiber 1
Metal tube zO etc. that protects and fixes 6 is attached to the metal big till part 1.
Use the same epoxy to fix it in the center hole of 5. The shrink tube z1 is for protecting the optical fiber 16.

In detail, the nylon coating 23 is removed from the tip 22 of the optical fiber 16, and the tip 22 is replaced with a glass tube or metal tube z4.
is passing through. Additionally, there is a barbed tube 20 with a glass or metal 24 and an optical fiber nylon coating 28 passed inside. These are all fixed to each other with an adhesive such as epoxy. In this integrated state, the input end face 17 of the optical fiber is optically polished. metal tube zO
is fixed in the center hole, and a glass plate 18 having a thickness of 1 mm and optically polished on both sides is fixed in the hole 25 with epoxy. At this time, the gap between the input end face 17 of the optical fiber including the glass or metal tubes 24 and 20 and the glass plate 18 is also filled with epoxy 19.

In this way, an almost reflection-free optical fiber entrance end face 17 that complies with the principle shown in FIG. 1 is obtained.

As a result, the instability phenomenon and characteristic change of the semiconductor laser caused by reflection at the input end face of the optical fiber are completely eliminated.

Incidentally, in FIG. 2, various configurations are realized in the vicinity of the tip 28 of the optical fiber, and the example described here is only one example.

In the example shown in FIG. 2, the optical coupling loss is 8 to 6 dB, and the laser beam is obliquely incident on the incident surface 18' of the glass plate 180 at a considerable angle. For this purpose, the glass plate 18 is 062~0.8
There is almost no need to apply non-reflective coach ink to the entrance surface 18' of the glass plate 18 unless it is as thin as a mirror.

Further, optical polishing of the input end surface 17 of the optical fiber and the output surface 18# of the glass plate 18 facing the optical fiber is not necessarily required if the refractive index of the epoxy 19 is appropriately selected. Furthermore, from the viewpoint of the structure of the big till, the lens may be included in the package of the semiconductor laser, or conversely, it may be fixed within the big till.

FIG. 8 shows an embodiment applied to one-way connector type optical coupling. A semiconductor laser in the same package 11 as in Figure @2 is placed inside the jack 80 of the optical fiber connector.

A SELFOC lens (product name 11) is fixed to the tip of the lens, and the laser beam from the laser crystal 10 is transmitted to the optical fiber tip incident surface 8 of the plug 82 of the optical fiber connector.
The beam waist is adjusted to position 8.

Inside the plug 8z of the optical fiber connector, a glass plate 34 is closely fixed to the input end surface 88 of the optical fiber 85 with epoxy 86 in the same manner as shown in FIG. In this case as well, the instability phenomenon and characteristic change of the semiconductor laser due to reflection at the input end face 8'8 of the optical fiber are completely eliminated. Incidentally, the lens 31 may be placed inside the plug 82 of the optical fiber connector.

The embodiments described above are merely examples, and can be applied to many optical fiber coupling systems. In the above embodiments, it is clear that the type of laser package, the shape and type of the lens for converging the seven-eye laser beam, the pigtail shape, etc. are not limited to those described above.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are device configuration diagrams for explaining the present invention in detail. FIG. 2 is a sectional view of the device configuration for explaining an embodiment in which the present invention is applied to the Big Till system. be. v! , 8 is a cross-sectional view of a device configuration for explaining an embodiment in which the present invention is applied to a single type of optical fiber connector. 1 , 16 , 85 - - - Light 7 fiber - 12, 17
゜88・・・Incidence end face of optical fiber, 13.1
8゜84...Glass plate, 4.19.86...
... Epoxy, 5.10 ... Semiconductor laser,
6... Semiconductor laser oscillation region, 7'... Group...
Non-reflective coating clear, 8...lens, 1oo
......Cylindrical lens, 11...Semiconductor laser package, 1!2...Cap, 18...
... Lens adapter, 14.81 ... Selfoc lens (product name), 15 ... Pigtil part, 20 ... Metal tube, 21 ... Contraction Tube, 2B... Surface optical fiber non-nylon coating 924
...Glass or metal tube, 25 ... Glass plate insertion hole, 80 ... Optical fiber connector jack, 82 ... Optical fiber connector plug. (υJ

Claims (1)

[Claims] In a device that converges laser light from a semiconductor laser with a lens and couples it to an optical fiber, a transparent plate having a parallel principal surface that is not coated with an anti-reflection coating is provided on the incident end surface of the optical fiber, and the principal surface is perpendicular to the optical axis of the optical fiber. The space between the optical fiber and the transparent plate is filled with a transparent material having a refractive index substantially equal to the refractive index of the optical fiber and the transparent plate, and the beam waist of the laser beam is located at the incident end face of the optical fiber. An optical coupling device characterized in that a laser beam is converged by the lens.