JPS63305305A - Optical fiber coupler - Google Patents

Abstract

PURPOSE:To reduce the variation of coupling characteristics due to a temperature change or the like by setting up the area of the groove side face of a grooved base to a value smaller than the area of its opposite side face. CONSTITUTION:Two ground bases 5 each of which consists of a grooved base 14 obtained by embedding a ground optical fiber 5 forming a ground face 4 exposing the neighboring part of a core 3 on a part of the optical fiber by grinding and removing a clad part 2 in a groove 13 and fixing the fiber 5 so that the ground face 4 is turned upward are used and respective ground faces 4, 4 of these ground bases 15, 15 are brought into contact with each other to form a contact part 16. In the grooved base 14, the area of the face A forming the groove 13 for embedding the optical fiber is set up to a value smaller than the area of the face B opposed to the face A. Thereby, the contact area of respective ground bases 15, 15 can be reduced, and even if the accuracy of flatness on the groove side face is not sufficiently obtained, the variation of coupling characteristics due to temperature change or the like generated by the deflection or the like of a matching solution applied between respective groove side faces can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an optical fiber coupler that branches and combines light in optical communications, optical fiber sensors, and the like.

"Prior Art" Conventionally, as one of the optical fiber couplers used for the above-mentioned purpose, the one shown in FIG. 11 is known. The optical fiber coupler l shown in this figure consists of a polished optical fiber 5 formed by forming a polished surface 4 on a part of the optical fiber by polishing off the cladding part 2 to expose the vicinity of the core 3, and this polished optical fiber 5. The fiber 5 is buried in the groove 6 and the polished surface 4
A contact portion 9 is formed by using two polishing substrates 8 consisting of a grooved substrate 7 and a grooved substrate 7 fixed in a state facing upward, and by bringing the polishing surfaces 4.4 of each of these polishing substrates 8.8 into contact with each other. has been done. The polished optical fiber 5 is fixed within the groove 6 of the grooved substrate 7 by adhesive IO.

Furthermore, a matching liquid is interposed between each polishing surface 4.4, and when the optical power is combined between each polishing surface 4.4, the optical power is reflected by the polishing surface 4, etc. Reduces coupling loss.

This optical fiber coupler 1 connects each polished optical fiber 5.
At the contact portion 9 where the core 3.3 of the polished optical fiber 5 approaches, the optical power guided within the polished optical fiber 5 is branched and combined, and the optical power is combined.

This optical fiber coupler l is created as follows. First, a groove 6 for embedding an optical fiber is formed in a rectangular parallelepiped substrate made of a transparent material such as quartz glass, multicomponent glass, or fluoride glass. As shown in FIG. 12, this rectangular parallelepiped substrate has a thickness a1 width b1 length C such that a<b<c. Moreover, the groove 6 has the largest area (bX
c) is formed by grinding along the length C direction on one of the two surfaces (hereinafter referred to as A surface).

Through the above operations, the grooved substrate 7 shown in FIG. 12 is created. Next, an optical fiber is buried in the groove 6 of this grooved substrate 7, and an adhesive is filled in the groove 6 and then solidified. Next, the surface opposite to the surface A (hereinafter referred to as surface B) is fixed to a polishing holding jig, and the surface A with the groove 6 formed therein is
Polish the surface to a predetermined polishing amount. By this polishing, a part of the optical fiber fixed in the housing 6 is polished away to the vicinity of the core 3, and becomes a polished optical fiber 5. Further, the grooved substrate 7 holds the polished optical fiber 5 on its A side, and serves as a polished substrate 7 in which the polished surface 4 of the polished optical fiber 5 is exposed. Next, the two polished substrates 7 prepared as described above are stacked so that the polished surfaces 4.4 of each polished optical fiber are in contact with each other, and a matching liquid 11 is interposed between each A side. , bond using adhesive or the like. Through the above operations, the optical fiber coupler I is created.

``Problems to be Solved by the Invention'' By the way, in order to obtain good characteristics such as an accurate optical power coupling ratio and a small optical power coupling loss in an optical fiber coupler l having such a configuration, it is necessary to ,'fIt
Extremely precise flatness is required for the A side on the G side. Also,
For surface A, it is not enough to simply make the flatness accurate, but the amount of polishing, that is, the distance from the core 3 to surface A, must be accurately controlled, and polishing is performed so that both of these conditions are satisfied. It was quite difficult. For example, due to slight irregularities on the polishing machine during polishing, surface A and the polished surface 4 tend to become uneven as shown in FIGS. 3 and 4.
If the polished surface 4 is polished into an uneven shape, the matching liquid 11 interposed between the A surfaces will exist unevenly, optically affecting the refractive index, and geometrically causing expansion,
There was a problem in that the stress due to shrinkage was locally concentrated on the polished surface 4, and the optical power coupling characteristics changed significantly due to temperature changes, etc., and the environmental resistance of the optical fiber coupler deteriorated. .

The degree of deterioration of the environmental resistance is proportional to the area of the uneven surface A in contact, and the larger the area, the worse the environmental resistance becomes. Furthermore, if the size of the unevenness on the polished surface is smaller than the wavelength order (about 1 μm), it will not have much effect on the environmental resistance, but if the unevenness is several times the wavelength order (about several μm) or more, , the environmental resistance deteriorates significantly. On the other hand, the 8 sides of the board are
A larger area is advantageous in terms of improving stability when holding the substrate on a holding jig and improving polishing accuracy.

The present invention aims to solve the above problems and provide an optical fiber coupler with excellent environmental resistance.

``Means for Solving the Problems'' This invention provides a polished optical fiber in which a polished surface is formed on a part of an optical fiber coupler by polishing off the cladding portion thereof to expose a portion near the core; Using two polished substrates consisting of a grooved substrate in which a polished optical fiber is buried in a groove and fixed with the polished surface facing upward, the polished surfaces of these polished substrates are brought into contact to form a contact portion. In an optical fiber coupler in which optical power is coupled at the contact portion, the grooved substrate has a surface area on the groove side smaller than that on the opposite side. And so.

"Function" The area of the groove side surface of the grooved substrate is made smaller than the area of the opposite side, so even if the flatness of the groove side surface of the grooved substrate is not sufficient, each groove can be Fluctuations in bonding characteristics due to temperature changes caused by uneven stress in the matching liquid interposed between the side surfaces can be reduced.

"Embodiment" FIG. 1 is a diagram showing an embodiment of the present invention, with reference numeral 1
2 is an optical fiber coupler. This optical fiber coupler 1
2 is a polished optical fiber 5 in which a polished surface 4 is formed on a part of the optical fiber by polishing off the cladding portion 2 to expose a portion near the core 3;
Using two polishing substrates 15, each consisting of a grooved substrate 14 that is embedded in the polishing substrate and fixed with its polishing surface 4 facing upward,
The polishing surfaces 4.4 of each of these polishing substrates 15.15 are brought into contact to form a contact portion 16.

As shown in FIGS. 2 to 4, the grooved substrate I4 is prepared by grinding away the periphery of the A side where the groove 13 for embedding the optical fiber is formed, and reducing the area of the A side to the eight opposite sides. It has a shape smaller than the area of . Further, as the material of the grooved substrate 14, a hard transparent material such as quartz glass, multi-component glass, or fluoride glass is used, and in particular, a material similar to the material constituting the polished optical fiber 5 is preferably used. .

This optical fiber coupler 12 connects two polished optical fibers 5
．． At the contact portion 16 where the cores 3.3 of 5 are close together, the optical power is branched or combined. For example, one polished optical fiber 5
When optical power is input into the core 3 on the input side of the optical fiber, part of this optical power is separated from the other polished optical fiber 5 side at the contact portion 9 and is input into the core 3, and as a result, the optical power on one side Optical power is obtained from the output side of the polished optical fiber 5 and the branched output side of the other polished optical fiber 5 with a predetermined coupling ratio.

The method for making this optical fiber coupler 12 is as follows. First, a substrate made of a transparent material such as quartz glass is appropriately ground, and the periphery of side A on which the groove 13 is to be formed is removed by grinding. Form [13]. Through this grinding operation,
A grooved base Fi, 14 having the structure shown in FIGS. 2 to 4 is created.

Next, an optical fiber is buried in the groove 13 of this grooved substrate 14, and an adhesive is filled in the groove 13 and then solidified. Next, the eight surfaces facing the A surface are fixed to a holding jig of a polishing device, and the A surface is polished until a predetermined amount of polishing is achieved. By this polishing operation, a part of the optical fiber fixed in 1lla is polished away to the vicinity of the core 3 to become a polished optical fiber 5, and the grooved substrate 14 is polished on the A side of the polished optical fiber 5. Polished substrate 1 with exposed surface 4
It becomes 5. Next, the two polished substrates 1 created as before
5 are placed one on top of the other with the polished surfaces 4 of each polished optical fiber 5 in contact with each other, and a matching liquid 11 is applied between each A surface.
After that, they are joined using an adhesive or the like. Through the above operations, the optical fiber coupler 12 is created.

This optical fiber coupler 12 is constructed using a polished substrate 14 in which the area of the A side in which the groove 13 is formed is set smaller than the area of the eight sides on the opposite side. Even if the area of the 8 surfaces is set large, the contact area of each polished substrate 15.15 can be made small, and even if the flatness accuracy of the A side is not sufficient, the matching interposed between each A side can be performed. Temperature 1 caused by unevenness of liquid 11, etc.
Fluctuations in coupling characteristics due to temperature changes, etc. can be reduced. Therefore, the environmental resistance of the optical fiber coupler 12 can be improved.

In addition, by setting the area of the A side small, it is possible to reduce variations in the coupling characteristics of the optical fiber coupler due to the flatness accuracy of the A side, thereby reducing the occurrence of polishing defects when polishing the A side. This makes it possible to easily manufacture optical fiber couplers.

FIG. 5 is a diagram showing another embodiment of the invention.

In the optical fiber coupler 12 according to the previous embodiment, as the grooved substrate 14, the periphery of the A side that forms the groove 13 for embedding the optical fiber is ground away, and the area of the A side is equal to the area of the eight opposite sides. It was constructed using something smaller than the
As shown in FIGS. 6 to 8, the optical fiber coupler 17 according to this embodiment has a substrate having a substantially T-shaped cross section in a direction perpendicular to the longitudinal direction.
The structure uses a grooved substrate 18 formed by forming a groove. As with the previous example, the grooved substrate 18 is made of a transparent hard material such as quartz glass, multi-component glass, or fluoride glass. A hole 20 for inserting the port 19 is formed in a corner of the grooved substrate 18.

This optical fiber coupler 17 is created as follows. First, an optical fiber is buried in the groove [3] of the grooved substrate 18 configured as described above, and an adhesive is further filled in the groove 13.
Fix the optical fiber within the groove. Next, this grooved substrate 18
The B side is fixed to a holding jig of a polishing device, and the A side is polished to a predetermined polishing amount. By this polishing, a polished substrate 21 with the polished optical fiber 5 fixed to the grooved substrate 18 is created. Next, the two polishing substrates 21 created as described above are attached to the polished surfaces 4 of each polished optical fiber 5.
are placed one on top of the other, and a matching liquid is interposed between each side A, and then bolts 19... are inserted into each hole 20...
Insert the nuts 22... into these bolts 19...
* is screwed to join the two polishing substrates 21. Through the above operations, the optical fiber coupler 17 is created.

This optical fiber coupler 17 can set the area ratio of the surface A, on which the groove 13 is formed, to the surface B, which is fixed to the holding jig, to be smaller than the optical fiber coupler 12 according to the previous example. The environmental resistance of the cover 18 can be further improved.

"Experiment example" ■, core diameter 50μm1 cladding diameter 125μm1 outer diameter 4
00 μm quartz-based multimode optical fiber
It was fixed to a grooved substrate made of quartz having the structure shown in FIGS. The dimensions of this grooved board are as follows.

Side A: 2 mm x 16 mm Side 8: 5 mm x 20 mm Thickness: 2III11~3 mm Groove width: 150 μm Place the B side of the grooved substrate with the optical fiber fixed onto the holding jig of the polishing device. It was fixed and the A side was polished to expose the area near the core. At this time, the amount of polishing from the core to the A side is 2~
It was set to 3 μm. The two polished substrates created in this way are
After overlapping the polished surfaces of the polished optical fibers and interposing a matching liquid between the A sides, the two polished substrates were joined using an adhesive to form an optical fiber coupler with a configuration similar to that shown in Figure 1. (hereinafter referred to as coupler A).

(2) An optical fiber similar to the above optical fiber was fixed to a grooved substrate made of quartz having the structure shown in FIGS. 6 to 8.

The dimensions of this grooved board are as follows.

A side...lll1m x 20m111B side = 5m
mX 20 mm Thickness: 3 mm to 4 mm Groove width: 150 μm The A-side of the grooved substrate to which the optical fiber was fixed was polished in the same manner as the coupler A described above to create a polished substrate. At this time, the amount of polishing from the core to the A side is 2 to 2, similar to coupler A.
It was set to 3 μm. After placing these two polished substrates together with the polished surfaces of the polished optical fibers and interposing a matching liquid between the A sides, insert a bolt into each bolt insertion hole, and screw a nut onto the bolt. The two polished substrates were then bonded together to create an optical fiber coupler having a configuration similar to that shown in FIG. 5 (hereinafter referred to as coupler B).

An optical fiber coupler having the same structure as the conventional optical fiber coupler shown in FIG. 11 was prepared and compared with the performance of couplers A and B. This optical fiber coupler uses the same optical fibers as those used in the previous two couplers, and has the structure shown in FIG.

It was fixed to a wooden grooved substrate. The dimensions of this grooved board are as follows:
The symbol a shown in Figure 2 is 2.5 mm, b is 5 mm, and c is 20
It was from 11II11. After the optical fiber was fixed in the groove of this grooved substrate, the A side was polished to obtain a polished substrate. At this time, polishing 1 was performed to a distance of 2 to 3 μm from the core to the A side, as in the previous two couplers. Next, the two polished substrates are placed on top of each other with the polished surfaces of the polished optical fibers placed on top of each other, and A
After interposing a matching liquid between the surfaces, they were joined using an adhesive to form an optical fiber coupler (hereinafter referred to as coupler C).

In the three couplers produced as described above, the degree of variation in coupling ratio with respect to temperature change and the change in coupling loss with respect to temperature change were measured. Figures 9 and 10 are diagrams showing the results of these measurements, with Figure 9 showing the degree of variation in the coupling ratio of the three couplers with respect to temperature changes, and Figure 10 showing the degree of variation in the coupling ratio of the three couplers with respect to temperature changes. It is a graph showing changes in loss. Note that the graph in FIG. 1O shows the change in coupling loss with respect to temperature change, assuming that the coupling loss at 20° C. of each coupler is zero.

As is clear from these graphs, coupler A and coupler B, which are optical fiber couplers according to the present invention, have smaller fluctuations in coupling ratio and coupling loss with respect to temperature changes than coupler C with a conventional configuration, and are less susceptible to temperature changes. It was confirmed that the environmental resistance of the optical fiber coupler was worse than that of conventional optical fiber couplers.

"Effects of the Invention" As explained above, the optical fiber coupler according to the present invention is constructed using a grooved substrate in which the area of the surface on which the grooves are formed is smaller than the area of the opposite side. By setting the surface area of the side fixed to the holding jig large, the contact area of each polished substrate can be reduced, and even if the flatness of the groove side surface is not sufficient, the surface area of each groove side can be reduced. Fluctuations in bonding characteristics due to temperature changes caused by unevenness of the matching liquid interposed between the surfaces can be reduced. Therefore, the environmental resistance of the optical fiber coupler can be improved.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an optical fiber coupler showing an embodiment of the present invention, and FIGS. 2 to 4 are diagrams showing a grooved substrate used in the optical fiber coupler of FIG. 2 is a plan view of the grooved substrate, FIG. 3 is a front view thereof, FIG. 4 is a side view thereof, and FIG. 5 is a diagram showing another embodiment of the present invention, in which an optical fiber coupler is shown. , and FIGS. 6 to 8 are diagrams showing a grooved substrate used in the optical fiber coupler shown in FIG. 5, FIG. 6 is a plan view of the grooved substrate, and FIG. FIG. 8 is a front view of the same, FIG. 8 is a side view of the same, and FIGS. 9 and 10 are graphs showing the results of comparing the degree of variation in coupling characteristics with respect to temperature changes of the optical fiber coupler according to the present invention with a conventional optical fiber coupler. The figure is a side sectional view showing a conventional optical fiber coupler, and FIG. 12 is a perspective view showing a grooved substrate used in the optical fiber coupler shown in FIG. 11.
FIGS. 13 and 14 are diagrams for explaining the unevenness of the matching liquid in a conventional optical fiber coupler. 2... Clad part, 3... Core, 4... Polished surface,
5... Polished optical fiber, 12.17... Optical fiber converter, 13... Groove, 14.18... Grooved substrate, 1
5.21... Polished substrate.

Claims (1)

[Claims] A polished optical fiber formed by polishing off a cladding portion of a part of an optical fiber to form a polished surface exposing a portion near the core, and embedding this polished optical fiber in a groove, A grooved substrate is fixed with the polished surface facing upward, and a contact portion is formed by bringing the polished surfaces of these polishing substrates into contact with each other, and the optical power is generated at this contact portion. The optical fiber coupler is characterized in that the grooved substrate has a surface area on the groove side smaller than an area of the surface on the opposite side.