JP2896947B2 - Optical fiber end structure and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an end structure of an optical fiber suitable for connecting to an optical waveguide or another optical fiber, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, connection loss occurs when an optical fiber is coupled to an optical waveguide or another optical fiber. The single biggest cause of the connection loss is a mismatch in the mode field diameter between the two in the case of a single mode fiber. Therefore, the most effective means for efficiently coupling the two is to make the mode field diameters of both the same, and the following three methods can be mentioned as a method for that. Here, a case where the optical fiber and the optical waveguide are coupled will be described.

A method of designing the structure of the coupling end of an optical waveguide device so that the mode field diameter of the optical waveguide matches the mode field diameter of the optical fiber.

For example, there is a method in which an end face of an optical waveguide is structured to have a lens effect, and a beam from an optical fiber that is wider than the optical waveguide is condensed and made incident on a core portion of the optical waveguide.

Further, an auxiliary waveguide is connected to the core of the optical waveguide, and all the incident light from the optical fiber is made incident on the auxiliary waveguide. There is also a method of transmitting the
2262, JP-A-60-172001, and JP-B-61-48695.

A method of designing the structure of the coupling end of an optical fiber so that the mode field diameter of the optical fiber matches the mode field diameter of the optical waveguide device.

For example, the tip of the optical fiber is made to be spherical, or the core shape near the end of the optical fiber is made thin or deformed (for example, elliptical), so that the core shape of the end of the optical fiber becomes the shape of the optical waveguide. A method of approaching the shape of the core portion and increasing the coupling efficiency of both (for example, JP-A-57-100409, JP-A-57-30811, and JP-A-60-88)
909).

In addition, a method of increasing the relative refractive index difference between the core and the clad at the end of the optical fiber to reduce the spot size and increase the coupling efficiency with the optical waveguide.

[0009] Between the optical fiber and the optical waveguide device,
A method in which a mode field conversion element having a mode field diameter matching each other is interposed (for example,
No. 4708).

On the other hand, other factors that cause connection loss include:
In addition to the single mode and the multimode, there is also a loss due to end face reflection caused by a difference in refractive index between the optical fiber and the optical waveguide.

As a means for preventing the reflection loss, a method of coating an end face of an optical fiber or an end face of an optical waveguide with an anti-reflection film (for example, Japanese Patent Application Laid-Open Nos. 57-10409, 60-1985). -164708).

[0012]

However, the above-mentioned prior art has the following problems. In the case of the above prior art, a fine processing technique on the optical waveguide substrate is required, and high precision is required.

For example, when an auxiliary waveguide is connected to an optical waveguide by distributed coupling, the rate at which the power of light incident on the auxiliary waveguide from the optical fiber shifts to the optical waveguide (coupling rate).
Changes periodically with respect to the connection distance between the optical waveguide and the auxiliary waveguide. For this reason, good coupling efficiency cannot be obtained unless the coupling length between the two is precisely set as designed.

In the case of the above-mentioned prior art, it is not easy to process an optical fiber with high accuracy. In addition, when fixing the spherical optical fiber to the end face of the optical waveguide,
The fixing method is not easy as compared with a normal fixing method of an optical fiber to an optical waveguide (a method of directly abutting and fixing with an adhesive).

In the case of the above-mentioned prior art, too, the precision of the design of the mode field conversion element itself is required, and if the precision is not precisely obtained, good coupling efficiency cannot be obtained. There are two locations between the devices and between the mode field conversion device and the optical waveguide, and locations where connection loss occurs increase.

On the other hand, when an anti-reflection film is used to prevent reflection loss, the cost is high, and the thickness of the anti-reflection film must be controlled with high precision.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned points, and it is an object of the present invention to provide an end portion of an optical fiber which can be easily processed and can be connected to other optical components stably and efficiently. It is to provide a structure and a manufacturing method thereof.

[0018]

According to the present invention, an end face of a core of an optical fiber is recessed from an end face of a cladding of the optical fiber, and an end face of the core is formed. The shape or the surface shape of the lens member 23 attached to the end face of the core 11 is formed to be a convex shape as long as it does not protrude from the end face of the clad 13.

Further, according to the present invention, the diameter of the core 31 at the end of the optical fiber 30 is increased, and the core 31 having the increased core diameter is provided.
The lens means 33 is directly attached to the end face of the lens.

In the present invention, the clad 55 at the end of the optical fiber 51 is removed to expose the core 53 by a predetermined length, and a desired refractive index smaller than the refractive index of the clad 55 is provided around the exposed core 53. Of the resin 57 is molded.

[0021]

The end face of the core 11 of the optical fiber 10 is recessed from the end face of the clad 13 of the optical fiber 10 and the core 11
In the optical fiber 10 in which the shape of the end face or the surface shape of the lens member 23 attached to the end face of the core 11 is formed in a convex shape, the spot of light emitted from the optical fiber 10 by the lens effect at the end of the optical fiber 10. The size can be reduced, and the coupling efficiency with other optical components can be improved. In addition, since the end face of the core 11 is located at a position recessed from the end face of the clad 13, the end face of the core 11 is not damaged, and a sufficient contact area with other optical components can be obtained. I can do it.

In the optical fiber 30 in which the diameter of the end of the core 31 is enlarged and the lens means 33 is directly attached to the end face of the core 31 having the enlarged core diameter, the effective opening diameter is increased by the enlarged core. In addition, the diameter of the entrance aperture to the optical fiber 30 can be made larger than the enlarged core diameter by the attached lens means 33. Therefore, the position adjustment when connecting this optical fiber 30 to another optical system is easy, and the coupling efficiency is high. Further, this optical fiber has a long focal length.

In the optical fiber 50 in which the core 53 is exposed by a predetermined length by removing the clad 55 at the end and the resin 57 is molded around the exposed core 53, the refractive index of the core 53 and the resin 57 are determined. Difference between core 53 and clad 55
Can be made larger than the difference in the refractive index. Therefore, the optical fiber 5
The spot size of the light emitted from 0 can be reduced.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[First Invention] FIG. 1 is a side sectional view showing an end structure of an optical fiber according to one embodiment of the present invention. As shown in the figure, the end face of the core 11 of the optical fiber 10 is
The end face of the clad 13 is not flush with the end face of the core 11.
Is concave more than the end surface of the clad. The end face of the core 11 is formed in a convex lens shape (spherical shape). In order to obtain such a structure, the end face of the optical fiber 10 may be etched.

With this configuration, the beam spot of the light emitted from the end face of the core 11 of the optical fiber 10 is narrowed and reduced.

FIG. 2 is a schematic side sectional view showing a connection structure when the end of the optical fiber 10 is connected to an optical waveguide core 17 provided on an optical waveguide substrate 15. As shown in the figure, the optical fiber 10 has a core 11 whose optical axis is the optical waveguide core 1.
7 is adhered and fixed by the adhesive 19 so as to coincide with the optical axis of the optical disk 7.

The light propagating through the core 11 of the optical fiber 10 is emitted from the end face of the core 11 so as to be condensed, and is incident on the optical waveguide core 11.

As described above, according to this embodiment, the core 1
Since the end face of the optical fiber 10 is formed in a convex lens shape, the coupling efficiency between the core 11 of the optical fiber 10 and the optical waveguide core 17 is improved.

Since the end face of the core 11 is recessed from the end face of the clad 13, when the optical fiber 10 is connected to the optical waveguide substrate 15 as shown in FIG. 2, only the end face of the clad 13 of the optical fiber 10 is formed. It comes into contact with the optical waveguide substrate 15. That is, the end face of the core 11 does not contact the optical waveguide core 17, and the end face is not damaged.

Further, the optical waveguide substrate 15 of the optical fiber 10
Since the contact surface is the entire end surface of the clad 13, the contact area can be sufficiently secured. Therefore, the connection can be securely fixed, and the connection can be performed by the ordinary bad joint method, so that the connection operation is simplified.

Heretofore, there has been a tip fiber having a lens effect at the tip of the optical fiber. However, the shape of the end face of this tip-shaped fiber is conical or tapered as a whole, so that when this end face is connected to the optical waveguide core, a contact area between the two cannot be obtained. For this purpose, a guide member or the like is separately required. Also, since the core end face of the spherical fiber may directly contact the optical waveguide core, care must be taken in handling the tip. On the other hand, in the case of the above embodiment, as described above, all such problems can be solved.

FIG. 3 is a side sectional view showing an end structure of an optical fiber according to another embodiment of the present invention. That is, FIG.
As in the embodiment shown in FIG. 1, each of the embodiments shown in FIGS. 1 to 3C is configured such that the end surface of the core 11 is recessed from the end surface of the clad 13 and the end surface of the core 11 is formed in a convex lens shape. I have.

However, in the case of the embodiment shown in FIG.
The center of the end face of the first cladding 13 is located on the same plane as the end face of the clad 13. Even in this case, since the end face of the core 11 does not protrude from the end face of the clad 13,
The same operation and effect as those of the embodiment shown in FIG.

In the case of the embodiment shown in FIG. 3B, the shape of the end face of the core 11 is not spherical but aspheric.
With this configuration, the same operation and effect as those of the embodiment shown in FIG. 1 are produced. That is, in the present invention, the shape of the convex lens on the core end surface may be spherical or aspherical. In short, an appropriate shape for connection with the optical waveguide core or the like may be selected.

In the case of the embodiment shown in FIG. 3C, the resin 21 is filled in the recessed portion of the end face of the core 11 up to the end face of the clad 13. The material of the resin 21 needs to be transparent to the wavelength of light used.

In this embodiment, the beam diameter of the light emitted from the core 11 can be changed by appropriately selecting the refractive index of the resin 21. That is, in order to reduce the beam diameter, the refractive index of the resin
1, the refractive index of the resin 21 must be greater than the refractive index of the core 11 in order to increase the beam diameter.

FIG. 4 is a side sectional view showing an end structure of an optical fiber according to still another embodiment of the present invention. That is, in the case of the embodiment shown in FIGS. 6A and 6B, the end face of the core 11 is made flat and the lens members 23 and 25 are attached to the end face. The lens members 23 and 25 may be configured by adhering a hemispherical lens to the end face of the core 11 or by adhering and curing a resin on the end face of the core 11 so as to be hemispherical. Even in the case of this embodiment, the lens member 2
If the surfaces of the claddings 3 and 25 do not protrude from the end face of the clad 13, the same operation and effect as those of the embodiment shown in FIG.

FIG. 5 is a side sectional view showing an end structure of an optical fiber according to still another embodiment of the present invention. That is, in the case of the embodiment shown in FIGS. 3A and 3B, the shape of the end face of the core 11 is made concave, and lens members 27 and 29 made of resin are adhered to the end face of the core 11 and the surface of the core 11 is formed. The shape is a convex lens shape.

[Second Invention] FIG. 6 is a view showing an end structure of an optical fiber according to one embodiment of the present invention, and FIG.
Is a side sectional view, and FIG. 3B is a right side view. As shown in the drawing, in this embodiment, the core 3 of the optical fiber 30 is used.
The diameter of the optical fiber 30 is enlarged at its end (up to about 5 times the normal core diameter), and a lens means 33 composed of a grating having a lens function such as a Fresnel zone is attached to the end face of the optical fiber 30. doing. Thereby, the light propagating in the core 31 of the optical fiber 30 is narrowed down at the end face. In order to increase the efficiency of the narrowing, the grating may be blazed. Adjustment of the lens function such as the focal length can be performed by changing the grating pitch.

FIGS. 7A and 7B show another embodiment of the present invention. FIG. 7A is a side sectional view, and FIG. 7B is a right side view. 6, the diameter of the core 37 is enlarged at the end and the lens means 39 is attached to the end face of the optical fiber 35, as in the case of the embodiment shown in FIG. However, the lens means 3 in the case of this embodiment
9 is formed by attaching a resin made of a transmissive high refractive index material to the end face of the optical fiber 35. The adhered resin has a spherical surface due to its surface tension, thereby having a lens effect, and its radius of curvature is set by the viscosity and amount of the resin. In some cases, the surface of the resin may be polished.

FIGS. 8A and 8B show still another embodiment of the present invention. FIG. 8A is a side sectional view and FIG. 8B is a right side view. 6, the diameter of the core 43 is enlarged at its end and the lens means 4 is attached to the end face of the optical fiber 41, as in the embodiment shown in FIG.
5 is installed. However, in the case of this embodiment, a part of the end face of the optical fiber 41 (including at least the entire end face of the core 43) is etched into a spherical shape, and a resin made of a transparent high-refractive-index material is filled into the spherical surface. 4
5 is provided. The lens characteristics in this case are set by the etching amount of the core 43 and the curvature of the surface of the lens means 45.

The optical fibers 30, shown in FIGS.
By connecting the light sources 35 and 41 to a light source such as a laser diode or a light emitting diode, or by using them in a connection system (shown in FIG. 9 described below) via an optical element, a highly efficient connection part can be formed. The reason is that first, the effective aperture diameter of the optical fibers 30, 35, 41 is increased by the core enlargement portion, and the diameter of the entrance aperture to the optical fiber is larger than the enlarged core diameter by the attached lens means. Because it is.

FIG. 9 is a schematic side view showing a specific example in which an optical element is inserted in the middle of a transmission system of an optical fiber by using the optical fiber 35 (other optical fibers 30 and 41) shown in FIG. FIG. That is, two optical fibers 35, 35 are provided on both sides of the optical element 47 (for example, an optical isolator).
Are arranged such that their end faces face each other, and the two optical fibers 35 and 35 and the optical element 47 are integrally fixed by a supporter 49. In the present invention, the optical fiber 3
Since the diameter of the core at the end of 5 is enlarged and the lens means 45 is provided, a long focal length can be obtained, and the optical element 47 can be easily installed between the two optical fibers 35.

In the embodiment shown in FIGS. 7 and 8, the lens means 3 is provided on the entire end faces of the optical fibers 35 and 41.
9 and 45 are attached, but the lens means need not be attached to the entire surface as long as the lens means is large enough to cover the core at the end face of the optical fiber.

As described above, the optical fibers 30, 35, and 41 shown in FIGS. 6, 7, and 8 can be configured simply by attaching lens means to the end surfaces of the optical fibers, so that the structure is simple and the manufacture is easy. is there. In each case, the diameter of the entrance aperture is large, the position can be easily adjusted when this is connected to another optical system, and the coupling efficiency is high. Further, as described above, since the optical fibers 30, 35, and 41 according to the present invention can have a long focal length, an optical element can be easily installed between the two optical fibers.

[Third Invention] FIGS. 10A and 10B are diagrams showing an end structure of an optical fiber according to one embodiment of the present invention. FIG. 10A is a side sectional view, and FIG. It is a figure which shows the refractive index distribution of the optical fiber shown to a).

This optical fiber 51 is
Is removed to expose the core 53 by a predetermined length, and the clad 55 is
Is formed by molding a resin 57 having a refractive index smaller than that of the core 53 and polishing the end face thereof together with the end face of the core 53.

FIG. 11 is a diagram showing a method of manufacturing the optical fiber 51. To manufacture the optical fiber 51, first, the optical fiber 51 shown in FIG. The core 53 of the optical fiber 51 is made of pure quartz, and the clad 55 is made by adding fluorine to quartz.
The material constitution of the core 53 and the clad 55 of the optical fiber 51 is not limited to this embodiment. That is, any material may be used as long as it has a material configuration in which the dopant amount of the clad 55 is larger than that of the core 53.

Next, the end of the optical fiber 51 is etched using a glass etching solution (for example, HF solution). Since a dopant for lowering the refractive index is added to the clad 55 of the optical fiber 51, the core 53 and the clad 55 have different etching rates, and the clad 55 is etched faster than the core 53. Therefore, as shown in FIG. 3B, the core 53 is exposed at the end of the optical fiber 51.

Next, as shown in FIG.
A resin 57 having a lower refractive index than that of the clad 55 is molded around the exposed portion.

Then, as shown in FIG. 5D, the end face of the core 53 is polished together with the resin 57 to adjust the shape of the end face. Thus, the optical fiber 51 has the structure shown in FIG.

FIG. 10 (b) shows the refractive index distribution of the core 53, the clad 55, and the resin 57 of the optical fiber 51. As shown in the figure, the portion where the resin 57 is molded has a large relative refractive index difference from the core 53. With this configuration, the light spot size at the end of the optical fiber 51 can be reduced.

That is, generally, the spot size ω _o of the optical fiber propagation light is Where A: core diameter a: core radius V: normalized frequency n ₁ : core refractive index n ₂ : cladding refractive index That is, as the difference between the core refractive index and the cladding refractive index increases, the light spot diameter decreases.

Therefore, when this optical fiber 51 is connected to, for example, an optical waveguide, the refractive index of the resin 57 used for the optical fiber 51 is selected so as to have a desired spot size according to the mode field diameter of the optical waveguide. Just do it. Thus, by selecting the refractive index of the resin 57 and adjusting the mode field diameter, a connection with high coupling efficiency can be performed.

As described above, according to the present invention, the spot size at the end of the optical fiber can be easily adjusted without complicated steps such as fine processing.

FIG. 12 is a view showing another embodiment of the present invention. FIG. 12 (a) is a side sectional view, and FIG. 12 (b) shows a refractive index distribution of the optical fiber shown in FIG. 12 (a). FIG. This optical fiber 61 is different from the optical fiber 51 shown in FIG. 10 only in that the exposed length of the core 63 is long and the mold length of the resin 67 is accordingly long. Other points are the same as those of the optical fiber 51 shown in FIG.

[0058]

As described above in detail, the end structure of the optical fiber according to the present invention has the following excellent effects. In an optical fiber in which the end face of the core of the optical fiber is recessed from the end face of the clad of the optical fiber and the shape of the core end face or the surface shape of a lens member attached to the core end face is formed in a convex shape, The spot size of the light emitted from the fiber can be reduced, and the coupling efficiency with other optical components can be improved.

Further, despite the structure in which the core end has a lens effect, the core end is located at a position recessed from the clad end, so that the core end is not damaged.
In addition, since a sufficient contact area with other optical components can be obtained, stable connection and fixing can be performed.

An optical fiber having a structure in which the core diameter at the end of the optical fiber is enlarged and the lens means is directly attached to the end face of the core having the enlarged core diameter has a simple structure and is easy to manufacture. . Further, the position adjustment when connecting this optical fiber to another optical system is easy, and the coupling efficiency is high. Furthermore, since this optical fiber has a long focal length,
An optical element can be easily installed between two optical fibers.

In an optical fiber in which the clad at the end of the optical fiber is removed to expose the core by a predetermined length and a resin having a desired refractive index smaller than that of the clad is molded around the exposed core. The spot size of the light emitted from the optical fiber can be easily adjusted. In addition, complicated processes such as microfabrication are not required for manufacturing the optical fiber.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an end structure of an optical fiber according to an embodiment of the first invention.

FIG. 2 is a schematic side sectional view showing a connection structure when an end of the optical fiber 10 is connected to an optical waveguide core 17;

FIG. 3 is a side sectional view showing an end structure of an optical fiber according to another embodiment of the present invention.

FIG. 4 is a side sectional view showing an end structure of an optical fiber according to still another embodiment of the present invention.

FIG. 5 is a side sectional view showing an end structure of an optical fiber according to still another embodiment of the present invention.

FIG. 6 is a diagram showing an end structure of an optical fiber according to one embodiment of the second invention.

FIG. 7 is a diagram showing another embodiment of the present invention.

FIG. 8 is a diagram showing still another embodiment of the present invention.

9 is a schematic side view showing a specific example when an optical element is inserted in the middle of a transmission system of an optical fiber using the optical fiber 35 shown in FIG.

FIG. 10 is a view showing an end structure of an optical fiber according to an example of the third invention.

FIG. 11 is a diagram illustrating a method of manufacturing the optical fiber 51.

FIG. 12 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 optical fiber 11 core 13 clad 23, 25, 27, 29 lens member 30, 35, 41 optical fiber 31, 37, 43 core 33, 39, 45 lens means 51, 61 optical fiber 53, 63 core 55, 65 clad 57 , 67 resin

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Claims (4)

(57) [Claims] 1. An end face of a core of an optical fiber connected to another optical component is recessed from an end face of a clad of the optical fiber, and a shape of the end face of the core or a lens member attached to the end face of the core. An end structure of an optical fiber, wherein a surface shape is formed in a convex shape so as not to protrude from an end surface of the clad. 2. An optical fiber according to claim 1, wherein the diameter of the core at the end of the optical fiber connected to another optical component is increased, and lens means is directly attached to the end face of the core having the increased core diameter. End structure. 3. An optical fiber to be connected to another optical component, a clad at an end of the optical fiber is removed to expose a core by a predetermined length,
An end structure of an optical fiber, wherein a resin having a desired refractive index smaller than the refractive index of the clad is molded around the exposed core. 4. A step of removing a clad at an end of an optical fiber to be connected to another optical component by etching to expose the core by a predetermined length; A method of manufacturing an end of an optical fiber, comprising: a step of molding a resin having a small desired refractive index; and a step of polishing an end face of a core together with the resin.