JP2654755B2 - Low-reflection optical components with uneven mating connection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-reflection type optical component in which an optical fiber and a lens are connected by concave and convex fitting, and more particularly, to a lens having a conical convex portion formed on the end face of the optical fiber. The present invention relates to an optical component in which a conical concave portion is formed in a connection surface, and the two are directly fitted to each other and bonded and fixed. This technique can be applied to, for example, a pigtail-type fiber collimator that converts light propagating through an optical fiber into a parallel beam, or conversely, efficiently couples the parallel beam to the optical fiber.

[0002]

2. Description of the Related Art An optical component in which an optical fiber and a gradient index rod lens are integrated so that their optical axes are accurately aligned has been conventionally known. A fiber collimator, which is a typical example, has a function of converting light that has propagated through an optical fiber into a parallel beam, and coupling the parallel beam that has spatially propagated to the optical fiber. Therefore, by disposing various optical components in the parallel beam space formed by the fiber collimator, an optical splitter, an optical demultiplexer, an optical switch, and the like can be configured.

A conventional pigtail type fiber collimator has, for example, the following structure. The rod lens is inserted into a cylindrical lens holder and fixed with an adhesive or the like. On the other hand, the optical fiber cable is held by a cylindrical sleeve. The optical fiber exposed at the tip of the optical fiber cable is inserted into a pipe made of metal or glass, and further inserted and held in a ferrule. Then, the ferrule is inserted into the lens holder, the optical axis is adjusted, and a resin adhesive is filled between the ferrules to integrally fix the ferrule. Note that the sleeve is fitted into the lens holder. Here, the tip end of the optical fiber is opposed to (not in contact with) the end face of the rod lens at a constant interval, and the matching of the matching oil or the like is interposed between the gaps to adjust the optical axis or adjust the divergence angle. It is carried out.

In such a fiber collimator,
When the end surface of the rod lens is perpendicular to the optical axis, the amount of back reflection (the amount of reflected return) at the end surface increases. Therefore, when a light source or the like sensitive to return light is connected, the end face of the rod lens is processed obliquely so that the reflected light does not return to the optical fiber to reduce the amount of back reflection.

Meanwhile, as for an optical connector for coupling an optical fiber and a lens, a projection or a depression is automatically formed at a focal position of the lens, and a depression or a projection is formed at a core portion at the tip of the optical fiber to form an end face of the optical fiber. (Japanese Patent Application Laid-Open No. 5-333232) has been proposed.
No.). Here, the projection is formed on one surface of the flat microlens array by a photosensitive resin (for example, photosensitive polyimide resin).
Is applied, collimated light is incident from the lens surface on the opposite side to automatically expose at the focal position, and after curing, is formed by developing.

[0006]

In the fiber collimator having the conventional structure, when the rod lens end face is perpendicular to the optical axis, the amount of back reflection is large and is about -20 dB. If the rod lens end surface is an inclined surface, the amount of rear reflection is reduced (about -40 dB), but oblique processing of the rod lens end surface is required, and it is difficult to stably obtain high quality. Although there is a request from the user side for further reduction of the back reflection (specifically, -50 dB or less), it is difficult to cope with the demand. In any case, both ends of the rod lens must be precisely polished, resulting in a disadvantage that the number of processing steps increases and the cost increases. Furthermore,
The assembling work including precision alignment for aligning the optical axis position of the lens and the optical fiber requires skill, and the number of assembling steps is increased. Since high-precision parts such as ferrules are required, material costs are also high.

In this type of fiber collimator,
Although the loss fluctuation before and after the temperature cycle is guaranteed, in practice, the loss fluctuation during the temperature rise or the temperature fall often becomes a problem. Since there is a certain distance between the end surface of the optical fiber and the end surface of the rod lens, even if the periphery is fixed with a filled resin adhesive, the distance may be changed due to a difference in the coefficient of thermal expansion of the used member or the adhesive. The distance changes due to external stress applied to the optical fiber cable,
They lead to loss fluctuations. Also, if matching oil is placed in the gap, the expansion
Shrinkage causes characteristic fluctuations, which is a major problem.

In an optical connector in which a projection or a depression is automatically formed at a focal position of a lens and optically coupled to an end face of an optical fiber having a depression or a projection in a core without adjustment, precise alignment work is unnecessary. Meanwhile, while the lens material is glass, the projection material is resin or the like, and a difference in refractive index is inevitable. Since the reflection at the interface is caused by the difference in the refractive index, there is a limit in reducing the amount of back reflection, and it is difficult to achieve high performance.

An object of the present invention is to eliminate the need for oblique processing or precision polishing on the lens connection surface side when connecting a lens to an optical fiber, and to easily perform automatic alignment without precision alignment work, and to provide a ferrule-like structure. It is an object of the present invention to provide a low-reflection optical component having a structure suitable for medium-volume and mass-production, which does not require any high-precision members, can be assembled with little need for a special technique by a skilled person.

[0010]

SUMMARY OF THE INVENTION The present invention is an optical component having a structure in which a lens is directly connected to the distal end face of an optical fiber by fitting concave and convex. That is, the present invention forms a convex portion in which the core portion of the optical fiber itself protrudes in a conical shape on the distal end surface of the optical fiber, forms a concave portion that fits with the convex portion on the lens connection surface, and This is a low-reflection type optical component that has a concave-convex fitting connection in which a portion and a concave portion are directly fitted and fixed with an optical adhesive near the fitted portion. As the lens used here, for example, a gradient index rod lens is preferable, and one end face is a precision polished face, the other end face is a cut face, and a conical indenter is hot pressed at the optical axis position of the cut face. A concave portion is formed by transfer. The optical fiber is a glass fiber, and the projection on the tip surface is formed by etching.

The combined body of the optical fiber and the lens, which is exposed from the jacket at the end of the optical fiber cable, is housed in a tubular jacket including a part of the jacket, and is held only in the vicinity of the end of the jacket. Adhesively integrated with the jacket. The tubular jacket includes, for example, a protective cover for holding a lens, and a cable holder for inserting an optical fiber cable at the center. With the combined optical fiber and lens in the protective cover, near the distal end of the jacket of the optical fiber cable so that most of the exposed optical fibers and the lens are free with respect to the protective cover. An adhesive is injected and fixed only between the portion and the protective cover portion. Thus, a pigtail-type optical component is formed. The jacket is
A structure in which two cylindrical bodies are joined back and forth may be used, or a structure in which half-cylindrical split molded products are combined.

[0012]

The convex portion of the optical fiber tip surface and the concave portion of the lens connection surface are fitted and physically in contact with each other, whereby the alignment is automatically performed. Moreover, both the convex portion and the concave portion are conical and oblique, and the convex portion is composed of the core portion of the optical fiber itself, so that there is no difference in the refractive index. -50 dB or less). The optical fiber and the lens are adhered and fixed in physical contact with each other, thereby improving the temperature characteristics and the impact resistance.

Since the lens has a clearance with respect to the protective cover, air in the protective cover is allowed to breathe in response to a change in temperature, and slight deformation of the optical fiber is allowed. Even though the lens and the lens are directly coupled to each other, excessive thermal stress is prevented from being applied to the optical fiber, and breakage of the optical fiber is prevented. In addition, loss fluctuation during heating and cooling can be minimized.

[0014]

FIG. 1 is an explanatory view showing one embodiment of an optical component according to the present invention, wherein A shows the entire configuration, and B shows an enlarged cross section of the concave / convex fitting connection portion. This optical component is an optical fiber 1
This is a structure in which the lens 12 is directly coupled to the front end of the lens. That is, a convex portion 16 whose core portion 14 protrudes in a conical shape is formed on the distal end surface of the optical fiber 10, and a conical concave portion 18 fitted with the convex portion 16 is formed on one end surface of the lens 12 ( Connection surface). Then, the convex portion 16 and the concave portion 18 are directly fitted to each other, and the optical adhesive 2 near the fitted portion.
0 is an adhesively fixed configuration.

The optical fiber 10 is a single mode glass fiber whose core is made of a material doped with germanium oxide, and the tip of the optical fiber 10 is made of hydrofluoric acid (H
F) and ammonium fluoride (NH ₄ F) by etching with a mixed solution, a bottom diameter of about 10 μm and a height of about 4 μm
Are formed. Therefore, the protrusion 16 is made of the same material as the core 14. Next, the lens 12 is a gradient index rod lens, which is made of cylindrical glass having both end faces perpendicular to the optical axis, and has a refractive index distribution in the radial direction from the central axis by ion diffusion. . One end face of the lens 12 is precisely polished, but the other end face may be a cut face, and a cone shape heated to about 210 to 400 ° C. (for example, a vertex angle of 120 °) is provided at the optical axis position of the cut face. ) Is pressed for about 5 seconds. By this hot pressing method, a conical concave portion 18 having a shape corresponding to the convex portion 16 can be formed. The concave portion 18 to be formed is transferred with the accuracy of the shape of the diamond indenter, so that the lens end surface can be either a cut surface (even if it is not a precision polished surface).
Sufficient surface accuracy can be obtained.

As shown in FIG. 2, when the distal end surface of the optical fiber 10 is directed toward the connection surface of the lens 12 and is brought into contact therewith, the projection 1
By the fitting of the recess 6 with the recess 6, the positioning is automatically performed automatically. In order to adjust the very small gap that occurs at that time or to adjust the divergence angle of the output beam, if necessary,
A matching oil (not shown) may be interposed between the two. As the optical adhesive 20, from the viewpoint of workability,
For example, an ultraviolet curable adhesive is preferable. Thus, an optical component in which the optical fiber and the lens are integrally coupled is obtained.

Since such an optical component is connected by direct fitting of the conical convex portion 16 and the conical concave portion 18,
Even if the beam propagating through the optical fiber and traveling toward the lens is reflected at the connection portion, it is difficult for the beam to return in the optical axis direction, so that the reflected return light is greatly reduced. According to the experimental results, an optical component having a back reflection amount of −50 dB or less was easily obtained by the connection structure formed by the concave-convex fitting manufactured as described above.

In reality, the shapes of the convex portion of the optical fiber and the concave portion of the lens do not always completely match in terms of manufacturing accuracy. 3A shows that the concave portion 18 is deep and the convex portion 16
Is low. FIG. 3B shows a case where the concave portion 18 is shallow and the convex portion 16 is high. Although the drawings are drawn to be extremely extreme, the gaps (especially at the tip of the core portion 14) are very small. Even in such a state, the self-alignment is performed by fitting the convex portion 16 into the concave portion 18, and the optical fiber 10 and the lens 12 always come into physical contact with each other. If necessary, add matching oil 22 to the gap.
You just have to put Since the gap is extremely small as described above, even if the matching oil 22 is sandwiched, there is almost no effect on the temperature characteristics.

Such an optical component (a combination of an optical fiber and a lens) is usually incorporated and held in a tubular jacket. FIG. 4 shows an example of a pigtail type fiber collimator as one example. Fiber optic cable
This is a structure in which the optical fiber 10 is covered with a jacket 30. By cutting off the jacket at the distal end, the optical fiber 1 is covered only at the distal end.
0 is exposed. The jacket comprises a cylindrical protective cover portion 32 for holding the lens 12 and a cylindrical cable pressing portion 34 having an inner diameter at the center of which the optical fiber cable 30 can be inserted exactly. The step portion is configured to fit on the base end side of the protective cover portion 32. Such a jacket is made of plastics or metal (for example, brass).

The manufacturing order of the fiber collimator is as follows. First, the optical fiber cable 30 is inserted through the cable holding portion 34, and the tip of the optical fiber 10 and the connection surface of the lens 12 are fitted with the concave and convex as in the above-described embodiment and connected with the optical adhesive 20. Then, the lens 12 is inserted from the base end side of the protective cover part 32 to the step part 32a on the distal end side, and the cable pressing part 34 is fitted. With the combined body of the optical fiber 10 and the lens 12 thus arranged in the jacket, most of the exposed optical fiber 10 and the lens 12 are free with respect to the protective cover portion 32 ( The lens 12 has a certain clearance without being adhered to the protective cover 32), and the adhesive 38 is supplied from the adhesive inlet 36 only between the vicinity of the distal end portion of the optical fiber cable and the protective cover 32. Inject and fix. Reference numeral 40 denotes an air vent hole when the adhesive is injected.

The embodiment shown in FIG. 4 has a jacket structure in which the cylindrical protective cover 32 and the cable pressing portion 34 are fitted together. However, the protective cover and the cable pressing portion are formed into a semi-cylindrical integrated body. It is also possible to adopt a structure in which two molded products having such a split shape are combined as a molded product. In such a case, the combined body of the optical fiber and the lens is placed in one half-cylindrical molded product, covered with the other half-cylindrical molded product, and the vicinity of the tip of the jacket of the optical fiber cable. An adhesive is injected only between the jacket and fixed.

Generally, in such a pigtail type fiber collimator, since an optical fiber cable is long and heavy, an external stress such as a tensile force is likely to act. Adhesive 38
Fixation prevents the external stress from reaching the connection between the optical fiber 10 and the lens 12. Since the optical fiber 10 and the lens 12 are directly bonded to each other in a fitted state, the lens 12 is not bonded to the protective cover portion 32 without bonding, and a space is provided around the optical fiber 10. Can absorb the difference in thermal expansion between glass (lens) and plastic or metal (jacket).
Deformation so that 0 is slightly bent can also absorb the difference in thermal expansion. Further, by allowing the breathing of the air in the space formed around the optical fiber by the clearance between the lens 12 and the protective cover 32, the stress due to the thermal expansion and contraction of the air can be reduced. As a result, the temperature characteristics are improved, and there is no possibility that the optical fiber is broken.

This low reflection type optical component is useful as a fiber collimator. If a lens system is selected so that incident light from the optical axis center position of one lens end surface becomes parallel light at the other lens end surface, the light propagated through the optical fiber is converted into a light beam with good parallelism by the lens. Is converted. Conversely, when a parallel beam enters the lens, it can be efficiently coupled to the optical fiber. Therefore, if optical components are arranged in the parallel beam space formed by such a fiber collimator, an optical splitter, an optical splitter, an optical switch, and the like can be configured. Depending on the selection of the lens, an optical component that does not emit the collimated light but gives a desired divergence angle to the beam emitted from the lens end face can also be configured. In the above embodiment, a gradient index rod lens is used as a lens, but a spherical lens may be used.

[0024]

As described above, the present invention has a structure in which a protruding portion that protrudes in a conical shape is formed on the tip end surface of an optical fiber and is directly fitted into the concave portion of the lens connection surface and is adhesively fixed. There is no need to perform oblique processing on the lens to reduce the amount, the lens connection surface may be a cut surface (no need to be a precision polished surface), the processing steps are shortened, and an inexpensive lens can be used. In the present invention, since the alignment is automatically performed by the fitting of the convex portion and the concave portion, precision alignment work requiring skill is not required, the manufacturing apparatus can be simplified, and a high-precision expensive member such as a ferrule is used. Is also unnecessary, and medium- and high-volume production is possible, so that the manufacturing cost is greatly reduced.

According to the present invention, since the core portion of the optical fiber itself has a structure in which the convex portion protruding in a conical shape and the conical concave portion of the lens connecting surface are directly fitted, the beam propagated through the optical fiber. Is hardly returned to the optical fiber even if it is reflected at the connection part, so that the amount of back reflection can be greatly reduced (−5).
0 dB or less). Further, since the concave and convex fitting portions are in physical contact, the temperature characteristics are improved, and the shock resistance and the vibration resistance are also improved. As a result, a high-quality low-reflection optical component that exhibits good characteristics and is stable against changes in the surrounding environment can be obtained.

According to the present invention, a combined body of an optical fiber and a lens is housed in a cylindrical jacket including a part of a jacket,
Adhesive integrated with the jacket only near the end of the jacket,
The structure is extremely simple, and the cost can be significantly reduced due to effects such as reduction in the number of members, simplification of each member, cost reduction, and ease of assembly. And the optical fiber cable has a structure in which the optical fiber is covered with a jacket,
Although it is long and heavy, when the combined body of the optical fiber and the lens is held by the jacket, the jacket and the jacket are mainly fixed with an adhesive, and the lens and the jacket are not bonded and are free from each other. Since the surroundings are also mostly spaces, it is possible to absorb the difference in thermal expansion of each member and prevent the optical fiber from being subjected to excessive stress in the jacket.
There is no possibility that the optical fiber will be damaged.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of an optical component according to the present invention.

FIG. 2 is an explanatory view of the assembly.

FIG. 3 is an explanatory view showing an example of an uneven fitting connection portion.

FIG. 4 is an explanatory view showing an example of an optical component according to the present invention incorporated in a jacket.

DESCRIPTION OF SYMBOLS 10 Optical fiber 12 Lens 14 Core part 16 Convex part 18 Concave part 20 Optical adhesive 30 Optical fiber cable 32 Protective cover part 34 Cable holding part

Claims (4)

(57) [Claims] 1. An optical component comprising an optical fiber and a lens, wherein a core portion of the optical fiber is formed on a tip end surface of the optical fiber by etching so as to protrude in a conical shape.
Provided with a convex portion was, forms a conical to mate with the convex portion
The concave portion formed by the transfer of the conical indenter is provided on the connection surface of the lens as described above , and the convex portion and the concave portion are directly fitted,
A low-reflection type optical component having a concave / convex fitting connection, wherein the optical component is fixed by an optical adhesive near the fitting portion. 2. The lens is a gradient index rod lens, one end surface of which is a precision polished surface and the other end surface of which is a cut surface, and a concave portion formed by transferring a conical indenter at an optical axis position of the cut surface. The optical component according to claim 1, wherein: 3. A combined body of an optical fiber and a lens, which is exposed from a jacket at the tip of an optical fiber cable, is housed in a cylindrical jacket including a part of the jacket, and only in the vicinity of the end of the jacket. The optical component according to claim 1, wherein the optical component is bonded and integrated with the jacket. 4. A tubular jacket includes a protective cover for holding a lens, and a cable pressing portion through which an optical fiber cable is inserted. A combined body of the optical fiber and the lens is housed in the protective cover. In this state, inject the adhesive only between the protective cover and the vicinity of the tip of the jacket of the optical fiber cable so that most of the exposed optical fiber and the lens are free with respect to the protective cover. 4. The optical component according to claim 3, wherein the optical component is fixed.