JP2007271993A - Optical fiber end part and its fixing structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a passive positioning means that has no physical impact onto an optical fiber end face and that uniquely decides a coordinate in the axial direction, in fixedly positioning an optical fiber end part. <P>SOLUTION: In the middle of the bare part 3 of an optical fiber end part, there is provided a fine diameter part 4 which is formed by etching the outer circumference of a clad. In a fixed substrate 10 on which the fine diameter part is to be fixed, there are installed a groove 11 in which the bare part 3 is housed and a projected part 12 which is formed inside the groove 11 so as to be fitted to the fine diameter part 4. The optical fiber end part is prevented from moving in either axial directions by being locked to the projected part 12 at two points, namely, at the near side and the far side with respect to the optical fiber end face of the fine diameter part 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for fixing an end portion of an optical fiber, and more particularly to an optical fiber end portion and an optical fiber end fixing structure capable of passive positioning in which the axial position of the optical fiber end portion is constrained to one point. About.

  Conventionally, in order to position and fix the end of the optical fiber in order to connect the optical fiber with another optical element or another optical fiber, a groove such as a V-shaped cross section or a rectangular cross section is formed on the surface of the substrate. By providing the optical fiber end portion on the groove, positioning in the in-plane direction perpendicular to the axis of the optical fiber end portion is often performed. An example in which the end portion of the optical fiber is fixed and connected to the optical waveguide by such a method is described in Patent Document 1. In such an optical fiber mounting groove, the end portion of the optical fiber is passively positioned in the in-plane direction perpendicular to the axis, but is passively positioned in the axial direction along the groove. In general, active positioning is often performed such as monitoring the amount of light that is actually transmitted through the optical fiber.

On the other hand, as a method of positioning the axial position of the end portion of the optical fiber in a passive manner, means for abutting the end face of the optical fiber against a wall surface formed on the substrate can be considered. Patent Document 2 describes an example of a module in which the end portion of the optical fiber is also positioned in the axial direction by such means so as to be coupled with the optical element. In addition to using the end face of the optical fiber, the end of the optical fiber is provided with a taper that decreases in diameter as it approaches the end face, and the tapered portion is abutted and locked to the opening of the through hole of the substrate. The means for determining the position of the optical fiber in the axial direction is described in Patent Document 3.
JP-A-5-188234 JP-A-9-61674 JP 2004-252274 A

Active positioning of the end of the optical fiber, such as actually passing light, is significantly disadvantageous in terms of man-hours and equipment compared to passive positioning, and the axial direction of the optical fiber is also possible if possible. Needless to say, it is desirable to provide passive positioning means.
However, in the method using the end face or tapered portion of the optical fiber for abutment as described in Patent Document 2 and Patent Document 3 described above, the wall surface and the opening of the optical fiber are related to the movement of the end portion of the optical fiber. Since there is still a degree of freedom in the axial movement in the direction away from the abutting means, it is impossible to passively complete positioning that ensures complete stability and reliability. In addition, in particular, in the method using the end face of the optical fiber for abutment, the end face of the optical fiber from which the signal light is emitted may be damaged by the abutment, and the deterioration of the optical characteristics due to this may become a further problem.

  These problems are particularly the case when the end face of the optical fiber is an oblique end face where the coupling optical axis is deflected, or when the optical fiber is a polarization-maintaining optical fiber and requires alignment of the polarization eigen axis. In positioning that requires alignment of the direction around the axis of the end of the optical fiber, it becomes extremely significant. That is, in these cases, in addition to the x, y and z3 direction coordinates of the end of the optical fiber (where z is the optical fiber axis direction), positioning of the θ component, which is the rotational azimuth around the z axis, is also required. After the three-way coordinates including the z direction are passively positioned using the substrate groove or through-hole and any butting means, the optical fiber end is rotated around the z-axis inside the groove or through-hole. Normally, θ is adjusted in an active manner. However, during this final θ adjustment, the conventional groove or through hole that constrains only the xy coordinates causes a slight deviation again in the z direction, which lacks a unique positioning hand. There is. Further, when z is readjusted after the θ adjustment, a slight shift is again caused in the adjusted θ in the process. In this way, the final positioning must end up with some inaccuracy, and the positioning accuracy is limited.

In addition, in the method in which the end face of the optical fiber is abutted against the wall surface, particularly in the process involving abutting means and friction with the rotation of the θ adjustment, an optical thin film is often provided and optically affected. There is a high risk of damaging the delicate end face.
In view of these circumstances, the present invention has no physical collision with the end face to which damage is to be avoided in the positioning and fixing of the optical fiber end for coupling with other optical elements, and the axial direction to the optical fiber. It is an object of the present invention to provide a passive positioning means that performs the function of uniquely determining and constraining the z-coordinate without requiring the application of pressure and tension, and enabling highly accurate positioning.

In order to achieve the above-mentioned object, the present invention is an optical fiber end portion in which the outer diameter of the clad is changed with respect to the axial direction of the optical fiber, and is formed by etching the outer circumference of the clad within a predetermined range in the axial direction. A narrow-diameter portion, and an original-diameter portion between the narrow-diameter portion and the end face of the optical fiber and having an original diameter as an outer diameter of the clad.
An optical fiber end fixing structure in which the optical fiber end is fixed to a fixed substrate, and a groove having a cross-sectional shape capable of fixing the original diameter portion of the optical fiber end to the fixed substrate, A convex portion that is formed inside the groove and fits into the small-diameter portion of the optical fiber end, and the optical fiber end fits the thin-diameter portion on the groove to the convex portion of the groove. The optical fiber end portion is positioned in the axial direction by locking to the convex portion at two points, a side close to the optical fiber end surface and a side far from the end surface of the optical fiber. And

According to the present invention, in positioning and fixing of an optical fiber end for coupling with another optical element, there is no physical contact with an end face that is not subject to damage, and axial pressing or tension on the optical fiber is not required. Therefore, a passive positioning means is provided that serves to uniquely determine and constrain the coordinates in the optical fiber axis direction and enables highly accurate positioning.
Further, as a specific form of use of the invention, when adjustment of the azimuth around the axis (θ adjustment) is required in positioning the optical fiber end, there is no friction of the abutting means against the end face, and x Thus, an operation that cannot be achieved by the conventional configuration, that is, rotation adjustment of the end portion of the optical fiber in a state in which complete positioning and fixing of the y, z3 coordinate components is secured can be realized.

In addition, when the θ adjustment is not required, the optical fiber end portion is passively and completely positioned with respect to the x, y, and z3 coordinate components. In that case, the fixing is practically achieved by press-fitting into the groove at the end of the optical fiber according to the invention.
In addition, in the case where the above-described θ adjustment is required or not required, a press plate similar to the conventional technology is added to this, and an adhesive is applied to complete the fixing. It is necessary to apply the agent not only to the holding plate but also to the gap between the optical fiber and the groove in order to fix the end of the optical fiber in the axial direction (z direction). There is no necessity, and the adhesive may be applied only between the press plate and the fixed substrate, for example. This form of use has the effect of reducing the amount of adhesive to be applied and preventing it from flowing out to unnecessary parts, and in particular eliminating the risk of wrapping around the end face of the optical fiber.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a single mode optical fiber is illustrated, but it can also be applied to multimode optical fibers having different core diameters.
Embodiment
FIGS. 1 and 2 show an optical fiber 1 (hereinafter referred to as “element wire”) 1 in which the covering material 2 at the end in the axial direction is peeled off, and the optical fiber is removed at the intermediate portion of the bare portion 3 thus peeled off. The structure of the end part of the optical fiber in which a part of the outer surface of the cladding is removed to form the narrow diameter part 4 is shown. That is, the strand 1 is covered with a coating material 2 (hereinafter referred to as UV coating) 2 made of, for example, an ultraviolet curable resin, on the outer side of the clad of the optical fiber. The bare portion 3 exposed by peeling off the UV coat 2 at the axial end portion of the strand 1 is formed with a small-diameter portion 4 in which a part of the outer layer thickness of the outer periphery of the cladding is removed by etching. In the bare part 3, between the narrow diameter part 4 and the end surface is an original diameter part in which the cladding diameter of the optical fiber is the original diameter. The removal depth of the small-diameter portion 4 is determined in accordance with the use conditions such as the degree of engagement with the mating member due to a step with the original diameter portion as described later within a range that does not affect the transmission of light. Moreover, the axial direction length of the small diameter part 4 is also decided by the said use conditions.

  In the example shown in FIG. 1 and FIG. 2, the strand 1 has a UV coat 2 diameter of 250 μm, a bare portion 3 has a diameter of 125 μm, a length of 6 mm, and a narrow portion 4 has a diameter of 85 μm length is 2 mm, and the position is present in the central portion between the end face of the optical fiber of the strand 1 and the end of the UV coat 2. The bare part 3 from which the UV coat 2 is peeled off is made of glass or the like and is easily damaged. For this reason, in the example shown in FIG.1 and FIG.2, although the length of the bare part 3 exposed to the axial direction edge part of the strand 1 was 6 mm, depending on the use condition, the shorter bear part 3 may also exist.

  In forming such a small diameter portion 4 in such a short bare portion 3, a partial surface layer thickness of the outer periphery of the clad is removed by wet etching with a hydrofluoric acid solution with respect to the bare portion 3 of glass as follows. . That is, in this wet etching, first, a resist similar to that used in a semiconductor photolithography technique is applied to the bare portion 3 by a resist coating apparatus. Specifically, the resist is uniformly applied to the bare portion 3 of the strand 1 rotating at a constant speed by the spray coater nozzle 20 shown in FIG. Thereafter, pre-baking is performed in an oven, and the mask 21 on which a pattern having an opening width corresponding to the axial length of the small-diameter portion 4 is formed as shown in FIGS. For example, UV exposure is performed while rotating the bare portion 3 with an exposure apparatus, and the bare portion 9 is subjected to patterning corresponding to the axial length of the small diameter portion 4. Then, after developing with a developing solution, post-baking is performed in an oven. Next, the patterned part of the bare part 3 is immersed in a hydrofluoric acid solution for a predetermined time, and then the hydrofluoric acid solution is washed and dried. By adopting such a process, a narrow diameter portion 4 having round corners is formed in the bare portion 3 as shown in FIG. In this case, since the opposing wall surfaces 41 and 42 at both axial ends formed in the radial direction of the small diameter portion 4 are formed by isotropic wet etching, they approach each other as they approach the core of the axial center of the small diameter portion 4. It has a rounded curved surface. In the present embodiment, the two curved surfaces facing each other are engaged with a convex portion of a mating member described later. 3 and 4 is advantageous when a large number of strands 1 are processed simultaneously. In particular, the step of FIG. 4B is performed under one mask. Many strands 1 can be arranged in parallel and exposed while rotating simultaneously, which is advantageous in terms of cost.

  As for the etching depth of the small-diameter portion 4, the small-diameter portion 4 is engaged with a convex portion formed in a groove of a fixed substrate which is a fixing counterpart member described later. It is sufficient that the wire 1 is a recess having a depth enough to be fixed without moving in the axial direction in the groove. However, since the formation of the recess, that is, the narrow-diameter portion 4 reduces the thickness of the clad of the optical fiber, the depth is a range that leaves a sufficient thickness to stably confine the transmitted light in the core. Must. The etching depth of 20 μm illustrated in FIGS. 1 and 2 satisfies this usage condition in a single mode optical fiber having a core diameter of 10 μm and a cladding original diameter of 125 μm.

In addition, about the formation position of this small diameter part 4, since the position of the end surface of the strand 1 is fixed correctly, it can be said that it is preferable that it is a position close | similar to the end surface fundamentally. Here, the end face of the strand 1 may exist in the groove of the fixed substrate, or may protrude from the groove.
FIG. 6 illustrates an embodiment in which the grooves are formed in an array for a fixed substrate 10 that is a positioning and fixing counterpart member in which a groove 11 in which the end portion of the optical fiber of the strand 1 is positioned and fixed is formed. The fixed substrate 10 is used as a part of an optical module (not shown) for coupling a light source element, a light receiving element, an optical waveguide element or an arrangement thereof to an optical fiber (element wire 1), or another optical fiber or its The groove 11 is configured as a part of an optical connector module (not shown) for coupling with an array or the like, and the groove 11 is configured so that the end surface of the strand 1 accommodated in the groove 11 appropriately opposes these coupling partner elements. Formed on the fixed substrate 10. The groove 11 has a rectangular cross section, has a width that accommodates the original diameter portion of the bare portion 3 of the strand 1 at the end of the fixed substrate 10, and the depth thereof is the same as the original diameter portion of the bare portion 3 or It is formed to have a slightly shallow dimension. A convex portion 12 is formed in the groove 11 separated from the end face of the fixed substrate 10 so as to correspond to the small diameter portion 4 formed in the bare portion 3 of the strand 1. The convex portion 12 is formed in the groove 11 that contacts the position of the small diameter portion 4 in a state where the bare portion 3 of the strand 1 is positioned with respect to the fixed substrate 10, and has substantially the same length as the small diameter portion 4. It has the thickness which the dent of the thin diameter part 4 fits. That is, the groove 11 is formed to have a narrow width so that the narrow diameter portion 4 of the bear portion 3 is accommodated in the groove 11 and locked by the convex portion 12. In forming the grooves 11 and the protrusions 12, for example, the groove 11 having a rectangular cross section and the rectangular cross section are preferably formed by a deep trench technique using anisotropic dry etching (reactive ion etching) on the fixed substrate 10 made of silicon. The convex portion 12 is formed. Although three grooves 11 shown in FIG. 6 are arranged, the number of grooves 11 can be appropriately changed according to the number of strands 1.

  The description so far has been made on the premise of the wire structure shown in FIGS. 1 and 2, but at the end of the optical fiber in which the lens portion 5 is provided at the tip of the bare portion 3 as shown in FIG. 7. On the other hand, the end surfaces of the optical fibers having an optical thin film such as an antireflection film formed on the end surfaces thereof, or the end surfaces thereof are obliquely polished as in the example shown in FIG. The present invention can be applied to the end portion of the optical fiber without change. In particular, when an optical thin film is formed on the end face, the use of the present invention is advantageous because it is averse to abutting means and damage due to friction in the prior art. Further, even when the end face is obliquely polished, the use of the present invention is extremely useful since adjustment of the azimuth around the optical fiber end (axis adjustment) is usually required as will be described later.

  FIG. 8 shows a state in which three grooves 11 are formed in an array in the fixed substrate 10 and the optical fiber ends of the three strands 1 are arranged in the array in the grooves 11. 11 shows a state in which the narrow diameter portion 4 of the bear portion 3 is inserted into the 11 convex portions 12. As is apparent from the plane of FIG. 8A and the cross section of FIG. 8B, the convex portion 12 contacts the above-described two curved surfaces facing each other of the small-diameter portion 4 at the end of the optical fiber. The positioning in the axial direction is uniquely determined, and the wire 1 does not move in any axial direction. In order to accommodate the optical fiber end of the strand 1 in the groove 11 as described above, the optical fiber end of the strand 1 is placed on the groove 11 of the fixed substrate and adjusted appropriately from above with the holding plate. Just press fit.

FIG. 10 shows a cross-sectional view of the state where the pressing plate 30 is bonded and fixed and finally fixed. Conventionally, it is necessary to apply the adhesive not only to the pressing plate but also between the optical fiber and the groove for fixing the end of the optical fiber in the axial direction (z direction). However, since this is not necessary in the present invention, the adhesive may be applied only between the pressing plate and the fixed substrate as shown.
FIG. 9 illustrates a case where the orientation around the axis of the end portion of the optical fiber of the strand 1 is rotationally adjusted (θ adjustment). Here, a rod lens 5 is provided at an end portion via a spacer 6, and an end portion of an optical fiber having a structure having the rod lens 5 as an oblique end surface is positioned. In this case, the spacer 6 is provided in order to increase the degree of freedom in designing the outgoing light profile of the rod lens, and the oblique end surface of the rod lens 5 is for preventing reflected return light at the end surface. From such an oblique end surface, light is deflected with a deflection angle with respect to the axis and enters and exits. Therefore, the positioning of the optical fiber end also requires adjustment of the azimuth around the axis (θ). However, when the present invention is applied, as shown in the embodiment shown in FIG. 9, the narrow-diameter portion 4 at the end of the optical fiber and the convex portion 12 of the groove 11 are respectively the curved surface of the opposing wall surfaces 41 and 42 and the convex portion. It will be locked in line contact with the wall surfaces at both corners in the axial direction. Therefore, in the axial direction, the small diameter portion 4 and the convex portion 12 are positioned and fixed, but in the axial direction. Can be easily rotated.

Therefore, for example, by observing the oblique end surface with a microscope from above the fixed substrate 10 or performing active alignment for monitoring the amount of light coupled to the coupling partner through light, there is no axial misalignment. Only the components can be adjusted.
The description so far has been made on the case where the groove 11 of the fixed substrate 10 is formed in a rectangular cross section, but it is also possible to form the cross section in a V shape as shown in FIG. That is, as shown in FIGS. 11A and 11B, the fixed substrate 10 made of a silicon single crystal substrate can be configured as a V-shaped cross section formed by anisotropic wet etching. In this case, the convex portion is produced as a portion of the V-shaped groove having a relatively small width and depth. That is, in the wet etching with crystal anisotropy, the depth is also uniquely determined according to the width of the opening of the mask. If a narrower cross-sectional V-shaped groove is formed, the portion becomes a shallow groove, and a convex portion 12 as shown in the figure can be obtained. The method of use is not different from the case of the above-described rectangular groove.

It is an edge part front view of an optical fiber strand. It is an edge part perspective view of an optical fiber strand. It is explanatory drawing which shows a resist application process. It is explanatory drawing which shows an exposure process. It is a detailed block diagram of an example of a thin diameter part. It is a perspective view of an example of a fiber groove. It is an edge part front view of the optical fiber strand provided with the lens part. It is an arrangement | sequence state figure of an optical fiber strand. It is (theta) adjustment state figure of an optical fiber strand. It is a fixed state figure of an optical fiber strand. It is a block diagram of the other example of a fiber groove.

Claims (6)

An optical fiber end portion in which the outer diameter of the cladding is changed with respect to the axial direction of the optical fiber,
A narrow-diameter portion formed by etching the outer periphery of the clad within a predetermined range in the axial direction, and a raw-diameter portion between the narrow-diameter portion and the end face of the optical fiber and having an original outer diameter of the clad And at least an optical fiber end portion. An optical fiber end fixing structure formed by fixing the optical fiber end described in claim 1 to a fixed substrate,
The fixed substrate is provided with a groove having a cross-sectional shape that can fix the original diameter portion of the optical fiber end portion, and a convex portion that is formed inside the groove and fits into the small diameter portion of the optical fiber end portion. The end portion of the optical fiber is fixed on the groove by fitting the narrow diameter portion to the convex portion of the groove, and the optical fiber end portion is at the two points of the narrow diameter portion near the optical fiber end face and the far side. An optical fiber end fixing structure in which the optical fiber end is positioned in the axial direction by locking to a convex portion. An arrayed optical fiber end fixing structure formed by fixing a plurality of optical fiber end portions according to claim 2 to a fixed substrate in an array,
A plurality of array-shaped grooves each having a cross-sectional shape capable of fixing the original diameter portion of each of the optical fiber ends to a fixed substrate, and the small diameter of each end of each optical fiber formed inside each of the grooves. And a plurality of the optical fiber end portions are respectively fixed on the respective grooves by fitting the small diameter portions to the convex portions of the respective grooves. An array shape in which each optical fiber end portion is positioned in the axial direction by engagement with the convex portion at two points, a side closer to the optical fiber end face and a side far from the end face of each small diameter portion. Fixed structure of the optical fiber end. An optical fiber end fixing structure according to any one of claims 2 and 3,
The optical fiber end fixing structure, wherein the groove provided on the fixed substrate is a rectangular cross-sectional groove, and the convex portion is formed by a change in a groove width of the rectangular cross-sectional groove. An optical fiber end fixing structure according to any one of claims 2 and 3,
The groove provided in the fixed substrate has a V-shaped cross section, and the convex portion is formed by changing the groove width and depth of the V-shaped cross section. . An optical module in which an optical fiber and another optical element or an optical fiber are coupled by using the optical fiber end fixing structure according to any one of claims 2 to 5.

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