JPH01224709A - Fiber having rounded end and its production - Google Patents

Abstract

PURPOSE:To easily position a fiber having the rounded end and extend the distance between fibers having rounded ends by joining a transparent round bar-shaped member having a spherical front end face to the front end of the optical fiber and setting the distance from the junction surface to the front end face and the radius of curvature of the front end face so that the emitted light is parallel beams. CONSTITUTION:Since the round bar-shaped member is joined to the front end of a single mode optical fiber 1 and its front end face 2a is made spherical, a distance L and a radius R of curvature can be freely selected and a desired light beam state is obtained. When a multimode fiber 2 having the rounded and is used in a fiber type optical circuit after the distance L and the radius R of curvature are so set that the emitted light from the front end face 2a of the rounded end part is parallel beams, the coupling loss is kept very small even in case of the deviation of the position in the axial direction of the fiber 2 because the emitted light A is parallel beams. Thus, the fiber 2 having the rounded end is very easily positioned in the axial direction and the distance between fibers 2 having rouded ends is extended.

Description

[Detailed Description of the Invention] [Summary] Regarding a bulbous fiber that can be arranged together with an optical functional element to configure a fiber-type optical circuit, when producing a fiber-type optical circuit, it is necessary to In order to facilitate the alignment of the optical fibers and to increase the distance between the spherical fibers, a transparent round rod-shaped member with a spherical tip surface is bonded to the tip of the optical fiber, and the bonded surface is The distance from to the tip surface and the radius of curvature of the tip surface are configured so that the light emitted from the tip surface becomes a parallel beam.

[Industrial application field]

The present invention relates to a tipped fiber that can be arranged together with an optical functional element to configure a fiber-type optical circuit, and a method for manufacturing the same.

[Conventional technology]

Conventional spherical fibers are mainly used as a means for coupling light from semiconductor lasers or light emitting diodes into optical fibers with low loss. This type of spherical-tipped fiber includes (i) an optical fiber whose tip is melted and pulled out to form a spherical tip using surface tension, (ii) an optical fiber whose tip is melted to form a spherical tip, ( iii) Optical fiber whose tip is ground into a spherical shape with a cutting tool, etc.
Alternatively, (iv) one in which a spherical foreign material is attached to the tip of an optical fiber is known.

[Problem to be solved by the invention]

Recently, the inventors of the present invention have been conducting research on fiber-type optical circuits. In this fiber type optical circuit, for example, a groove is formed across the guide part on a support such as an optical fiber ferrule that has a guide part that can guide the optical fiber without a gap, and a groove is formed in this groove to allow light to pass through. By inserting a functional element and inserting a spherical fiber from both directions of the guide section, an optical circuit such as an optical isolator or a branching filter is constructed. According to this, the mutual positional relationship is almost certainly fixed simply by inserting the tipped fiber and the optical functional element into the predetermined guide portions and grooves of the support, which is extremely difficult to do with conventional optical circuits. The advantage is that alignment between the existing parts can be performed very easily, and therefore manufacturing costs can be significantly reduced.

However, as mentioned above, conventional bulbous fibers are manufactured mainly for the purpose of coupling light from semiconductor lasers and light emitting diodes, so when used in the above fiber-type optical circuit, the following problems occur: Problems like this arise.

That is, in the tipped fibers of (i) to (iii) above,
The length of the spherical tip (the distance from the core end surface of the optical fiber to the spherical surface of the spherical tip) cannot be set long, and the beam diameter at the output end inevitably becomes small, making it impossible to obtain a large lens effect. Furthermore, in the spherical fiber described in (iv) above, the length of the spherical tip and the lens curvature cannot be set independently, so the desired lens effect cannot be obtained. For these reasons, in any conventional spherical fiber, the emitted light tends to become a radiation beam, or even if it is a convergent beam, it tends to become a beam with a large divergence angle. Therefore, when such a spherical fiber is used in the above-mentioned fiber-type optical circuit, if the position of the spherical fiber, especially in the direction of the center axis, deviates even slightly from the optimum position, the coupling loss will increase. There was a problem in that alignment in the axial direction took time and effort. Further, for the same reason, it is impossible to increase the distance between the tip fibers, so there is also the problem that the thickness of the optical functional element that can be inserted between them is thin (limited).

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to facilitate the alignment of tip-shaped fibers in the central axis direction when manufacturing a fiber-type optical circuit, and to increase the distance between the tip-shaped fibers. shall be.

Another object of the present invention is to further improve the alignment accuracy in the perpendicular and rotational directions with respect to the central axis of the bulbous fiber when manufacturing a fiber-type optical circuit.

[Means to solve the problem]

A transparent round rod-shaped member with a spherical tip surface is bonded to the tip of an optical fiber, and the distance M from the bonded surface to the tip surface is
(L) and the radius of curvature (R) of the tip surface are set so that the light emitted from the tip surface becomes a parallel beam, thereby forming a spherical tip fiber.

A spherical fiber with such a configuration is manufactured by fusing a transparent round rod-like member with the same diameter to the tip of an optical fiber, then cutting this round rod-like member and processing the tip surface into a spherical surface. .

Further, a transparent round rod-shaped member having a spherical tip surface is bonded to the tip of an optical fiber, and the diameter of the round rod-shaped member including at least the vicinity of the bonded portion is f, [[l] larger than that of the optical fiber. By doing so, a tip fiber is constructed.

A spherical fiber with such a configuration is produced by fusing a transparent round rod-like member with the same diameter to the tip of the optical fiber, cutting this round rod-like member, and processing the tip surface into a spherical shape. It is manufactured by performing diameter reduction processing (for example, tapering, step formation, etc.) from the fiber to the tip surface.

[For production]

Generally, when designing a lens optical system, the distance from the object to the lens (in the case of a spherical fiber, the distance nL from the core end surface of the optical fiber to the tip surface of the spherical tip) and the lens curvature (in the case of a spherical fiber) is the radius of curvature R of the tip surface of the tip sphere
) are important, and the state of the light beam changes depending on their size.

In this regard, the spherical tip fiber of the present invention has a tip rod-like member joined to the tip of the optical fiber and its tip surface is made into a spherical shape. R can be freely selected, and thus a desired optical beam state (for example, a parallel beam system or a beam waist system with an arbitrary width) can be obtained.

Therefore, in the present invention, the distance and the radius of curvature R are set so that the light emitted from the tip surface of the spherical tip portion becomes a parallel beam. When a spherical fiber set in this way is used in a fiber-type optical circuit, the output light is a parallel beam, so even if the position of the spherical fiber in the central axis direction is shifted, the coupling loss remains extremely low. Ru. Therefore, alignment of the tip fiber in the central axis direction becomes very easy.

Furthermore, for the same reason, it is possible to increase the distance between the bulbous fibers, and it is possible to have a large degree of freedom in the thickness of the optical functional element that can be inserted between them.

In addition, if the diameter of the round rod-shaped member that is joined to the optical fiber and the vicinity of its joint is reduced, even if irregularities occur on the surface of the joint during the above-mentioned joining, the irregularities will be reduced in diameter. Cleanly removed during oxidation. Therefore, when a bulb-shaped fiber with a reduced diameter is used in a fiber-type optical circuit, there are no irregularities on the surface of the optical fiber, so the bulb-shaped fiber can be inserted into the guide part in close contact with the guide section. The positioning accuracy in the direction perpendicular to the central axis and in the rotational direction is further improved.

〔Example〕

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

FIG. 1 is a manufacturing process diagram of an embodiment of the present invention.

In this embodiment, first, as shown in FIG. 1(a), for example, the core diameter a+=9. czm, cladding diameter b I= 126
For example, at the tip of a μm single mode fiber 1, the core diameter a2 = 80 μm1 and the cladding diameter b2 = 126 μm
The multimode fibers 2 are fused using arc discharge or the like. At this time, since the materials of the two fibers 1゜2 are almost the same, they can be easily fused together, and the joining surface (
Almost no reflected light is generated at the core end surface (1a) of the fiber 1. Furthermore, since the two fibers 1.2 have the same diameter, they self-align so that their central axes coincide due to surface tension, and the fusion is completed in the most desirable state.

Thereafter, the multimode fiber 2 is cut at an appropriate position, and its tip end surface 2a is processed into a spherical surface using a melting method, a grinding method, or the like. However, at this time, the direction from the bonding surface 1a to the tip surface 2 is such that the emitted light A from the tip surface 2a becomes a parallel beam.
The distance MuL to a and the radius of curvature R of the tip surface 2a are set. For this setting, let the distance from the tip surface 2a to the convergence point of the emitted light A be l, and this distance! How 11tE changes depending on the lens shape (ie, the above-mentioned radius and radius) was calculated by a ray tracing method. The results are shown in FIG. Then, as is clear from the figure, L is 1.7 of R.
It was found that when the number of times (L=1.7R) is 2J=■, the emitted light A becomes a parallel beam.

From this, set L and R so that L = 1.7R (for example, L = 170 μm, R - 100 μm).
.

Subsequently, as shown in FIG. 1(e), the single mode fiber 1 is tapered from the vicinity of the bonding surface 1a to the distal end surface 2a of the multimode fiber 2. Due to this tapering, even if irregularities occur on the surface of the bonding surface 1a during the fusion process shown in FIG. 1(a), these irregularities can be neatly removed.

Next, FIG. 4 shows a cross-sectional configuration of an optical isolator as an example of a fiber-type optical circuit configured using two bulb-shaped fibers 10 of this example obtained as described above. This optical isolator consists of the two tipped fibers 10.10
(However, these are assumed to have been subjected to single polarization processing in advance), a Faraday rotator 11 with a rotation angle of 45° made of YIG components, etc., and an external support 12 that supports them. ing. As shown in FIG. 5, the external support body 12 is fixed, for example, so as to cross a guide portion 12a for guiding the optical fiber that penetrates in the axial direction of the cylindrical ferrule for the optical fiber. Width groove 12b
was formed. In FIG. 4, the Faraday rotator 11 is inserted into the groove 12b of the external support 12, and the two spherical fibers 10. 12 guide portions 12a from both directions.

This allows only light in one direction (light in the direction of arrow B) to pass through and blocks light in the opposite direction (light in the direction of arrow C), similar to the principle of a normal optical isolator.

When the spherical fiber 10.10 of this embodiment is used in an optical isolator as described above, since the output beam is a parallel beam as shown in FIG. 1(b), the spherical fiber 10.
The 0.10 crimp plane is in the direction of the central axis (in the direction of arrow B or C)
Even if there is a deviation, there will be no coupling loss. Therefore, when manufacturing an optical isolator, alignment of the tip fiber 10.10 in the central axis direction becomes very easy. moreover,
For the same reason, it is possible to increase the distance between the spherical fibers 10 and 10, and it is possible to have a large degree of freedom in the thickness of the optical functional element (Faraday rotator 11) that can be inserted between them.

Furthermore, since the unevenness on the surface of the joint surface 1a of the spherical fiber 10.10 has been removed by tapering as shown in FIG.
This allows it to be inserted in close contact with a. Therefore, the alignment accuracy in the direction perpendicular to the central axis of the tip fiber 10.10 and in the rotational direction (direction of arrow θ) can be further improved.

Note that instead of tapering as shown in FIG. 1fc), a step may be formed from the single mode fiber 1 side of the bonding surface 1a as shown in FIG. In addition, even if other than these, single mode fiber 1
If diameter reduction processing is performed from the tip surface 2a,
The same effects as in the above embodiment can be obtained.

Also, instead of the multimode fiber 2 described above, core diameter a 2-50 p rns cladding diameter b 2-126
A μm Gl multimode fiber may be fused. In this way, the lens effect can be expanded even inside the fiber, so the overall lens effect can be further enhanced.

However, when using a multimode fiber or a Gl multimode fiber in this way, one should be selected that has a core diameter a2 that is sufficiently larger than the core diameter al of the other single mode fiber 1. In addition to such a combination of a single mode fiber and a multimode fiber, a combination of a normal optical fiber and a transparent glass rod having the same diameter may be used.

Furthermore, although FIG. 4 shows an example of the configuration of an optical isolator,
The bulbous fiber of the present invention can also be applied to other fiber-type optical circuits (for example, demultiplexers, polarization beam splitters, optical couplers, etc.), and the same effects as described above can be obtained.

〔Effect of the invention〕

According to the bulb-shaped fiber of the present invention, the alignment of the bulb-shaped fiber in the central axis direction can be facilitated when producing a fiber-type optical circuit, especially by making the emitted light a parallel beam. Furthermore, since the distance between the spherical fibers can be increased, the thickness of the optical functional element that can be inserted between the fibers can have a large degree of freedom.

In addition, by reducing the diameter of the round rod-shaped member joined to the optical fiber, it can be inserted closely into the guide part when fabricating a fiber-type optical circuit, so that it can be inserted in the vertical direction and rotational direction with respect to the central axis of the tipped fiber. The alignment accuracy can be further improved.

Furthermore, according to the method for manufacturing a spherical fiber of the present invention, the optical fiber and the round rod-like member having the same diameter are self-aligned so that their central axes coincide with each other due to surface tension, and the fusion is completed in the most desirable state. .

Furthermore, parallel beam systems and beam waist systems can be manufactured with good design efficiency.

[Brief explanation of the drawing]

Figures 1 (a) to [C] are manufacturing process diagrams of one embodiment of the present invention, Figure 2 is a configuration diagram of another embodiment of the present invention, and Figure 3 shows changes depending on the lens shape (L, R). Figure 4 is a cross-sectional configuration diagram of an optical isolator using a spherical fiber according to an embodiment of the present invention, and Figure 5 is a diagram showing the results of calculating the distance l by the ray tracing method. 3 is a perspective view of the body 12. FIG. DESCRIPTION OF SYMBOLS 1...Single mode fiber, 1a...Joining surface, 2...Multimode fiber, 2a...Tip surface. Patent Applicant Fujitsu Limited (b) The Great Arashi Ij of the Present Development Figure 1 Implementation of the 4 Packs of the Present Invention 4G1] Figure 2

Claims (1)

[Claims] 1) A transparent round bar-shaped member (2) having a spherical tip surface (2a) is bonded to the tip of an optical fiber (1), and the distance from the bonding surface (1a) to the tip surface is 1. A spherical-tipped fiber characterized in that the distance and the radius of curvature of the tip surface are set so that light emitted from the tip surface becomes a parallel beam. 2) A transparent round rod-shaped member (2) having a spherical tip surface (2a) is bonded to the tip of the optical fiber (1), and the round rod-shaped member including at least the vicinity of the bonded portion is larger than the optical fiber. A tipped fiber characterized by its small diameter. 3) After fusing a transparent round bar-shaped member (2) with the same diameter as the optical fiber to the tip of the optical fiber (1), cutting the round bar-shaped member and processing the tip surface (2a) into a spherical shape. A method for manufacturing a bulbous fiber, comprising producing the bulbous fiber according to claim 1. 4) After fusing a transparent round rod-like member (2) with the same diameter as the optical fiber to the tip of the optical fiber (1), cutting the round rod-like member and processing its end surface (2a) into a spherical surface. 3. A method for manufacturing a bulb-shaped fiber according to claim 2, wherein the bulb-shaped fiber according to claim 2 is manufactured by performing a diameter-reducing process from the optical fiber to the distal end surface.