JPH07230018A - Coupler of optical fiber and preparation thereof - Google Patents

Abstract

PURPOSE: To provide the coupler for an optical fiber which is easily manufactured and low-priced, and its manufacturing method. CONSTITUTION: Cores 1, 5, 15, and 17 are provided with core expanding elements in the shape of a frustum of a truncated cone which propagate light respectively and a core expanding element common areas 20 where the respective adjacent core expanding elements are united at parts isolated from the end surfaces is formed. The core expanding elements and core expanding element common area 20 are formed in the shape of the frustum of the truncated cone and provided successively on the cover end surface by sinking one-end-surface sides of the cores 1, 5, 15, and 17 in a liquid photoreactive substance, making specific light solidifying and setting the photoreactive substance from the other-end- surface side, and emitting it from the one-end-surface side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coupler and its manufacturing method.

[0002]

BACKGROUND OF THE INVENTION Optical fibers are the most widely used medium for transmitting information by light. This optical fiber has a core in the center and a clad surrounding the core, so that most of the transmitted light is concentrated and propagated in the core. The cross-sectional diameter of the core is generally 0.01 mm or less in the case of a single mode fiber and 0.2 mm or less in the case of a multimode fiber. The small size of this core causes considerable technical difficulties in splicing optical fibers and mixing / distributing the transmitted light.

Very elaborate procedures are required to manufacture optical fiber couplers. The first multimode fiber couplers or optical mixers used in the early 1970s arranged two optical fibers in an orderly arrangement in a small, elongated, hollow box, and the light from one of the fibers was placed in this box. It is widely diffused through the inside so that the diffused light enters the other optical fiber. Such a coupler has been mainly used as a device having a role of uniformly distributing the light transmitted by one optical fiber to a large number of optical fibers. Therefore, as the length of this box is increased, the diffusion of the light is evenly widened, so that the effect of light distribution can be further obtained, and the structure is simple. However, the biggest drawback of this fiber coupler is that the end face of the box where the input and output are made is square, while the end face of the optical fiber is circular, which means that the light is widely diffused and is opposite. When the light is evenly radiated to the side, all the light that reaches the outside of the circle is lost. In addition, since the core diameter is very small relative to the optical fiber diameter, the core area occupies only a very small area of the entire optical fiber, and most of the light irradiated to the clad portion other than the core is also lost. turn into.

The so-called biconical fusion coupler (biconical fus) has been widely used from the early 1970s to the present.
ed coupler). This manufacturing method involves twisting a plurality of optical fibers so that they form a rope, and then pulling them from both sides while applying heat to stretch out the starch syrup. Is reduced to about 1/10, and light comes out from the core to the clad at the fused portion. Since the clads of the adjacent optical fibers are fused to each other, the light emitted from the core spreads to the optical fibers and is distributed / mixed.

In the early 1980s, single mode fibers overwhelmed multimode fibers in the optical fiber market. Many inventions have been made as biconical fusion couplers for single mode fibers have been put to practical use. For example, U.S. Pat.Nos. 4,798,438, 4,842,359 (Imoto, et.al.,), and U.S. Pat.
However, there are various problems involved, and especially when there are two or more sets of input or output fibers, there are still problems. Currently, for single-mode fiber couplers, some have 4 inputs and 4 outputs called 4x4, one have 1 input and 7 outputs called 1x7, and 2x The 2-coupler is not used at all because of the small number of channels. As a result, manufacturing a single mode fiber coupler as described above requires complicated steps and a long time,
The reality is that there is no possibility of being supplied at a low price.

As another optical coupler, there is one using a transparent body. As a typical example of this type, for example, US Pat.
4,566,753 (L. Manscheke), U.S. Patent 4,653,845 (Y. Trembl
ay and et.al.,), U.S. Pat. No. 4,904,042 (C. Dragone), U.S. Pat. No. 4,950,045 (T. Brichenno). This is to form a light transmission tube on the surface of a flat transparent body, and to spread the light transmission tube at a large number of branch points so as to play a role of distributing and mixing light. Despite being the most expensive, such methods are used almost exclusively for single-mode fiber couplers with a number of inputs and outputs greater than 4x4 or 1x7. This manufacturing process includes the steps of making a flat transparent body, cutting and polishing the end face of the fiber in order to make the connecting boundary surface into a state with no inclination or roughness, and 10 microns within an error of about 1 to 2 microns. Process of aligning the core of the core with a wave guide of several microns and abutting, bonding the fiber in a positioned state, and confirming that the fiber does not move more than 1-2 microns until the bonding is completed. . This cumbersome process makes the production of single mode couplers very expensive.

Therefore, an optical fiber multi-port type coupler which does not require such a complicated process and is easily manufactured is
Especially in single-mode fibers, there is a great need.

In addition to the above-mentioned coupler, there is an optical fiber connector (hereinafter referred to as "connector") as an important component for optical fiber communication. However, for the end user of computer network communication, there is a price problem. Despite being an important issue, existing optical fiber connectors are expensive and are not easy to handle when attaching and detaching. Fiber optic connectors are expensive because the core is very thin. When the cores are abutted against each other, even if the cores are offset by 1 to 3 microns, the transmission loss of light becomes significantly large, so that extremely high accuracy is required.

In general, connecting fibers is relatively easy if the size of the light beam at the abutting surface can be increased. When the light beam is expanded, it is more affected by the angle (tilt of the axis) than the alignment (off-axis). For example, US patents
At 5,097,524, Wasserman and Gibolar show a connector incorporating ray expansion using a lens. Also, Moslehi et.al., in Optic Letters, Vol. 14, No. 23, page 1327, describes fiber connection based on ray expansion. And Hussey and Payne
Describes a method of expanding an optical fiber in Volume 24, page 1-14 of Electronic Letters. However, these ray expanding methods are not very useful for lowering the cost because of problems such as high precision required for alignment between the fiber and the ray expanding component.

Not only the connection between the optical fibers but also the connection between the optical fibers and the wave guide material (waveguide) is an important fiber optic technology. At present, the wave guide material is patterned on or near the surface of the transparent body by using optical transfer technology or advanced technology such as electric beam or laser beam. In most cases, the wave guide material is butted one-on-one with the optical fiber. For this connection, the end of the wave guide material is cut flat and at the right angle with respect to the wave guide surface, about 1
Polishing is performed with an assembly accuracy equal to or less than the wavelength of light so that the axis is not tilted within about 2 microns. Then, the end surface of the optical fiber is butted against the end portion of the wave guide material. The lateral alignment between the optical fiber core and the waveguide material must be done within a few microns. Then, a binding material (adhesive, matching agent) is applied to the abutting surfaces. However, due to a change in volume or the like, the positioning is misaligned during the curing of the binder, and connector loss is likely to occur. Even with perfect alignment, the geometrical differences between the round fiber core and the generally rectangular waveguide material cause transmission losses. In other words, fiber-waveguide channel splicing requires a very expensive work process, which is another reason why optical fibers have not penetrated the widespread consumer market, despite the potential for significant benefits. is there.

[0011]

SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to realize a novel optical interface capable of solving technical difficulties in manufacturing an optical fiber coupler and a connector such as highly accurate axis alignment. is there.

Another object of the present invention is to facilitate the connection of the optical fibers to make the compounding / connection between the optical fibers simple and inexpensive, and thereby to widely spread the optical communication. To do.

The basic feature of the invention is a core-extension that extends the core of an optical fiber. This core expansion element has the function of expanding and diverging the light transmitted through the core from the core into a larger cross-sectional area. This core expansion element has a cone shape (conical truncated cone shape very close to a cone), and the diameter of the portion of the optical fiber that closely adheres to the core is the same as that of the core. It is getting bigger. In particular,
When the function of mixing and distributing light is provided, it is essential and a feature that the diameter of the endmost portion (bottom diameter of the truncated cone) is larger than the entire diameter of the optical fiber. Furthermore, in order to prevent light that has entered the core expansion element at the correct angle from leaking as it spreads inside the core expansion element, that is, to ensure that light is propagated by repeating total internal reflection, refraction of the core expansion element is performed. The index is greater than the external index of refraction (ie, the index of refraction of the space surrounding the core expansion element).

By applying this basic form of the core expansion element, a new light mixer can be designed. If multiple optical fibers are cut accurately (in a flat and non-tilted state), they are neatly bundled, and the above-mentioned core expansion elements are formed on the cut end faces, respectively, so that the cross-sectional areas of the core expansion elements gradually increase. At a position that becomes larger and is separated from the end face by a certain distance or more, these adjacent core expansion elements are made to be in contact with each other to form one body. The light is distributed / mixed in the core expansion element common region in which a plurality of core expansion elements are integrally coupled. It should be noted that tubes, rods, lenses, mirrors, and other optical elements may be further added to enhance the optical mixing function.

The simplest method for easily and inexpensively manufacturing the above-mentioned core expansion element is to precisely cut an optical fiber, and to light-curable or light-curable the end face of which is solidified or hardened when irradiated with ultraviolet rays. Light-polymerizable
izabule) photo-reactive materials (photo-reactive ma
terial) and then UV light is introduced into the optical fiber. The ultraviolet rays are radiated from the cut end face through the core of the optical fiber, and the light is gradually spread in the radiation process, so that the cross-sectional area is widened (conical shape or spread in a cone shape). The photoreactive material within the range where the ultraviolet rays spread is solidified by the ultraviolet rays, and as a result, a truncated cone-shaped core expansion element is continuously formed on the end face of the optical fiber. In this process, it is important to note that the diameter of the widest part at the end is larger than the entire diameter of the optical fiber in order to become the core expansion element of the coupler having the function of mixing and distributing light according to the present invention. We must meet the condition that it must be large.

[0016]

FIG. 1 shows an optical fiber having a core 1, a clad 2, an end face 3 and an end face 4, and a truncated cone-shaped core expansion element 9 provided on the end face 3. The core expansion element 9 of the present invention has the same diameter as the core 1 on the boundary with the end face 3, and expands as shown in the figure as it goes away from the end face 3. FIG. 2 is a side view of the embodiment shown in FIG. 1, and as shown, the maximum diameter of the core expansion element 9 is considerably larger than the cladding diameter. This is necessary for the combining or connecting function in the present invention and will be described in detail below.

The refractive index inside the core expansion element 9 is larger than that of the outside space, and thus the light is confined in the core expansion element 9. Core expansion element 9
As can be seen from the above, when the light travels in the direction in which the diameter of the truncated cone gradually decreases, the incident angle becomes smaller each time the light hits the surface (boundary surface) of the core expansion element 9. Therefore, if the divergence angle of the core expansion element of the optical fiber is too large or the taper length is too long,
Since the angle of incidence becomes small and the condition of total internal reflection cannot be satisfied in the middle part of the taper part, light may not be contained in the inside and leak, resulting in loss. There is. In order to eliminate such light loss, it is desirable to minimize the spread angle and shorten the taper length. When this divergence angle is sufficiently small, there is no light loss. Further, the thinner the cladding 6 of the optical fiber, the smaller the required maximum cross-sectional area of the core expansion element 9 (that is, the maximum diameter at the end) is required, and the loss of light can be reduced accordingly. Will be described in detail below. The spread angle described above is 3 to 4 in the case of a multimode fiber.
In the case of a single mode fiber, it is desirable to set it within 1 to 2 degrees.

FIG. 3 shows an embodiment of an optical fiber coupler according to the present invention having the function of an optical mixer. As described above, and as shown in FIG. 2, the maximum diameter of the core expansion element 9 is larger than the diameter of the clad 2. As a result, as shown in the figure, one core expansion element overlaps with an adjacent core expansion element, and light is mixed in the core expansion element common region 10 where the core expansion elements overlap. As shown in the figure,
Two fibers are juxtaposed side by side, each core expansion element being separated from each other in the vicinity of two independent end faces,
The core extension element common region 10 is formed by overlapping with each other at a position away from the end face. Therefore, the light 11 entering from the core 1 is emitted to the core expansion element common region 10 side.

It should be noted that, as shown in FIG. 3, when light enters from the core expansion element side, a light power divider.
There is also a function as. For example, when a laser beam or the like is put into the core expansion element common region 10, it can be divided into two cores 1 and 5.

The core expansion element according to the present invention is provided on the end faces 3 and 7 of the fiber core. Most desirable in this manufacturing method is to make a core expansion element from a liquid photoreactive substance, but when such a substance is irradiated with light,
Some physicochemical properties change, and some solidify or harden. In order to make a core expansion element using this, after the end faces 3 and 7 of the optical fiber are immersed in the substance, light is diverged in a conical shape from the end faces 3 and 7. This light enters the input side end faces 4 and 8 of the optical fiber and is emitted from the output side end faces 3 and 7, but since the emitted light spreads in a conical shape, as shown in FIG.
When two optical fibers are arranged adjacent to each other, they merge with an adjacent core expansion element to form a core expansion element common region 10.

In order to fabricate a complete optical fiber coupler, the basic features shown in FIG. 3 are joined face to face to form the configuration shown in FIG. In this case, core 1,
The light rays incident on 5, 15, and 17 are mixed or distributed through the core expansion element common region 20. When the core expansion element common region 20 is sufficiently long, the light is sufficiently mixed, and the distribution amount of the light in the output side optical fiber is almost the same. This distribution amount of light is independent of the wavelength of light. The core expansion element 9 and the core expansion element common regions 10 and 20 may be surrounded by air or liquid or solid, but the material is transparent and has a lower refractive index than the core expansion element. There must be.

In FIG. 4, the optical fibers are arranged in parallel completely in parallel, but the invention is not limited to this, and the core expansion element common region 20 may be increased by arranging the optical fibers slightly inward. In the above and below, the optical fibers are arranged and arranged in parallel, but they may all be tilted slightly inward.

FIG. 4 shows two in / outputs (2 × 2), but as shown in FIG. 5, 6 × 6.
May be For example, this number is 8x8, 16x16,
A combination of 8 × 16, 1 × 16, etc. can also be used.

FIG. 5 shows the optical fibers 33 to 44 on one plane.
That is, although the one-dimensional arrangement is shown, this may be arranged two-dimensionally. FIG. 6 shows a sectional view taken along line XX ′ of FIG. 5, and FIG. 7 shows a sectional view taken along line YY ′. As shown in FIG. 6, the cores 21 to 26 in which light is contained are all separated from each other, but in FIG. 7, they overlap as the core expansion element common region 50. 8 shows a cross section of the optical fiber portion when the optical fibers 33 to 44 are two-dimensionally arranged, and FIG. 9 shows a cross section of the core expansion element common region 50 portion.

Modifications of the coupler shown in FIG. 4 are shown in FIGS.
4 shows. FIG. 10 shows an example in which a hollow tube 51 is extrapolated to a coupler having a basic shape. Tube 51 and tube 5
As described above, the inside of 1 must have a refractive index lower than that of the core expansion element common region 20. The diameter of the tube 51 is smaller than the maximum diameter of the core expansion element common region 20 of FIG. 4, but by doing so, the side surface of the core expansion element common region 20 is included therein. (That is, the inner peripheral surface of the tube 51 also serves as part of the peripheral boundary surface of the core expansion element common region 20). The cross-sectional shape of the pipe 51 is circular, triangular, rectangular,
Any other shape may be used.

In FIG. 11, in order to increase the coupler length,
An example is shown in which a transparent medium 52 that propagates light is inserted in the middle of the core expansion element common region 20.

FIG. 12 shows an example in which a lens 53 for converging light rays is inserted in the middle of the core expansion element common area 20 in order to increase the overlap of the light rays.

Core expansion element common area 1 of the example in FIG.
It is also possible to provide a reflecting surface at the end of 0 and mix the light entering either the core 1 or 5 in the core expansion element common region 10 and then reflect the light back to both cores 1 and 5.

The core expansion element mentioned above can also be manufactured by precision molding. The fiber placement may be verified and a suitable mold used to position between the fiber end face and the separate input port of the core expansion element. This molding is particularly useful in mass production, and the cost of manufacturing the initial parts is high, but the unit price thereafter is low.

According to the coupler manufacturing method of the present invention described below, it is possible to perform perfect axis alignment between the core end surface of the optical fiber and each core expansion element. 1 in a single-mode fiber to reduce light loss
Alignment accuracy of ˜2 microns is required, but the alignment method of the present invention is most effective for use in single mode fiber couplers, which account for over 90% of the coupler market. This is a very simple and inexpensive method of manufacturing a single mode fiber coupler, which can be achieved with a small initial investment and is described below.

This method, as shown in FIGS.
A method of using a photo-reactive substance 55 sensitive to light, in particular, ultraviolet light. When light 56 is incident on the core 1 of the optical fiber and is emitted from the end face 3 as shown in the figure, within the emission range. At, the properties of the photoreactive substance change. Figure 1
As shown in FIG. 3, a core expansion element is formed within the radiation range 9. (That is, the joint portion between the core expansion element and the core 1 has a perfectly matched shape, and the joint portion is perfectly aligned.) The photoreactive substance is exposed to the ultraviolet ray 56. It may be a polymer that changes from a liquid to a solid, and a substance that dissolves when immersed in a developing solution when exposed to ultraviolet rays, or conversely, a substance that remains only around the part that is exposed to ultraviolet light and remains intact. Various photoreactive substances can be mentioned, such as resists and special glass raw materials that solidify only when exposed to light. When using a substance that does not dissolve in the developer, it becomes easier to obtain the desired refractive index relationship by filling the empty space with another substance, and the core expansion element has a higher refractive index than the outside surroundings. Can be adjusted.

In the case of manufacturing as shown in FIG. 13, when irradiating light, especially the ultraviolet ray 56, its intensity and time are made sufficiently long, and the wavelength of the light is selected so that the core expansion element 9 of The length and spread can be made sufficient, and the above-mentioned functions can be provided. Also, it has been stated that the smaller the divergence angle of the core expansion element 9, the less the light loss. However, in order to reduce the divergence angle, the light 56 incident on the core 1 of the optical fiber is selected,
If the optical fiber is made to enter at an angle substantially parallel to the optical fiber, the truncated cone-shaped core expansion element 9 also becomes narrow and sharp.
The end face 3 does not need to be flat, and the core expansion element 9
It may be concave, convex, or any other shape in order to specify the angle or shape of the.

FIG. 14 shows that a method similar to the above can be used when there is more than one optical fiber. The only difference is that when the ultraviolet rays 56 are radiated through the two cores 1 and 5, the emitted light overlaps with each other to form one core expansion element common region 10. As described above, the closer the cores 1 and 5 are to each other, the easier it is to overlap them. Therefore, if necessary, the claddings 2 and 6 of the optical fiber are made as thin as possible to reduce the overall diameter of the optical fiber. Is desirable.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical fiber and a core expansion element provided on an end surface of the core.

FIG. 2 is a plan view of FIG.

FIG. 3 is a plan view showing a state in which core expansion elements respectively provided in the cores of two optical fibers overlap each other at a certain position to form a core expansion element common region.

FIG. 4 is a plan view showing a state in which the example of FIG. 3 is face-to-face.

5 is a plan view showing a modified example of the example of FIG.

6 is a cross-sectional view taken along the line XX ′ in FIG.

FIG. 7 is a cross-sectional view taken along line YY ′ of FIG.

FIG. 8 is a sectional view of an optical fiber portion when the optical fibers are two-dimensionally arranged.

FIG. 9 is a cross-sectional view of a core expansion element common region portion when optical fibers are two-dimensionally arranged.

FIG. 10 is a plan view showing a modified example in which a tube is externally inserted in the core expansion element common region.

FIG. 11 is a plan view showing a modified example in which a transparent medium object is inserted between core expansion elements.

FIG. 12 is a plan view showing a modified example in which a lens is inserted between core expansion elements.

FIG. 13 is a diagram illustrating a method of manufacturing a coupler according to the present invention.

FIG. 14 is a diagram illustrating a method of manufacturing a coupler according to the present invention.

[Explanation of symbols]

 1, 5 core 2, 6 clad 3, 7 end face 4, 8 end face 9 core expansion element 10, 20, 50 core expansion element common region 11 light 55 photoreactive substance 56 ultraviolet light

Claims (18)

[Claims] 1. A core having an end surface substantially perpendicular to the optical axis, a clad surrounding the core, and a core expansion element provided on the end surface of the core. The core expansion element emits light from the end surface of the core. An optical fiber characterized in that it has a truncated cone shape whose diameter gradually expands as it moves away from the end face at the same divergence angle as that of time, and its refractive index is larger than the external refractive index due to light propagation by total internal reflection. Coupler. 2. The optical fiber coupler according to claim 1, wherein the maximum diameter of the core expansion element is larger than the outer diameter of the optical fiber. 3. The optical fiber coupler according to claim 1, wherein the cladding is thin near the end face. 4. The optical fiber coupler according to claim 1, wherein the core expansion element is made of a photoreactive material whose physical properties are changed by exposure. 5. A plurality of cores each having an end face substantially perpendicular to the optical axis and arranged side by side substantially parallel to each other, a clad surrounding each core, and a light provided beyond the end face provided on each end face of each core. The core expansion element is a truncated cone shape whose diameter gradually expands with increasing distance from the end surface at the same divergence angle as when light is emitted from the end surface of the core. In areas where the distance between cores is greater than each other, they form a common area for core expansion elements for mixing and distributing light together, and the refractive index for external light propagation due to total internal reflection. Fiber optic coupler characterized by greater than rate. 6. The optical fiber coupler according to claim 5, wherein the cores are arranged in parallel on a plane. 7. The optical fiber coupler according to claim 5, wherein the cores are two-dimensionally arranged substantially in parallel. 8. A transparent tube externally inserted in the common region of the core expansion element, wherein a part of an inner peripheral surface of the tube constitutes a peripheral boundary surface of the common region of the core expansion element, and a refractive index of the tube. The optical fiber coupler according to claim 5, wherein is smaller than the refractive index of the core expansion element. 9. The optical fiber coupler according to claim 5, wherein each core expansion element and the core expansion element common region are formed by molding. 10. The optical fiber coupler according to claim 5, wherein each core expansion element and the core expansion element common region are made of a photoreactive material whose physical properties are changed by exposure. 11. The optical fiber coupler according to claim 10, wherein the photoreactive substance is a polymer which is solidified by ultraviolet rays. 12. The optical fiber coupler according to claim 10, wherein the photoreactive material is a photoresist. 13. A coupler for an optical fiber according to claim 10, wherein the photoreactive substance is a special glass whose substance characteristic changes depending on the exposure intensity. 14. A plurality of cores each having an end face substantially perpendicular to the optical axis and arranged side by side in substantially parallel to each other, a clad surrounding each core, and a light provided beyond the end face provided on each end face of each core. The core expansion element is a truncated cone shape whose diameter gradually expands with increasing distance from the end surface at the same divergence angle as when light is emitted from the end surface of the core. In areas where the distance between cores is greater than each other, they form a common area for core expansion elements for mixing and distributing light together, and the refractive index for external light propagation due to total internal reflection. A plurality of cores having end faces that are substantially perpendicular to the optical axis and arranged side by side substantially parallel to each other, and a clad surrounding each core,
The core expansion element is provided on each end surface of each core and propagates light across the end surface.The core expansion elements are separated from the end surface at the same spread angle as when the light is emitted from the end surface of the core. It is a truncated cone shape whose diameter gradually expands, and the portion where the diameter is larger than the distance between the cores forms a common area for mixing and distributing light together, and the light by total reflection The second coupler group has a refractive index higher than that of the outside for propagation, and the core expansion element common region of the first coupler group and the core expansion element common region of the second coupler group face each other. An optical fiber coupler characterized by being arranged together. 15. A fiber optic coupler according to claim 14, wherein a transparent medium for propagating light is inserted in the common region of the core expansion element. 16. The transparent object is a lens.
5. An optical fiber coupler according to item 5. 17. The method for producing a coupler according to claim 1, wherein one end surface of the core is immersed in a photoreactive substance whose physical properties are changed by exposure, and then the photoreactive substance A method for manufacturing an optical fiber coupler, characterized in that a desired core expansion element shape is obtained by irradiating the other end surface of the core with light whose property is changed and radiating the light from the one end surface at a specific spread angle. 18. The divergence angle of light from one end face of the core is
18. The method of manufacturing an optical fiber coupler according to claim 17, wherein the optical fiber coupler is made smaller by selecting only light rays having a small spread angle.