JP2005128449A - Optical fiber, its processing method and optical module using this optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber structure which converges light from an optical fiber and gives a beam smaller than a photoreceptor surface in a photoreceptor element. <P>SOLUTION: A top end part of an optical fiber 1 consisting of a core 1a and a clad 1b is formed obliquely for the optical axis 2 and at least the top end surface 3 of the core 1a is made curved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical fiber that provides a structure capable of obtaining sufficient coupling efficiency even with a light receiving element having a small light receiving diameter when the optical fiber and the light receiving element are coupled in optical communication.

  2. Description of the Related Art Conventionally, in the optical communication field, as a means for taking a coupling between an optical fiber and a light receiving element, as shown in FIG. 7, a tip surface of an optical fiber 21 comprising a central core 21a and a clad 21b formed on the outer periphery thereof is used. The inclined surface 23 is formed by polishing at an angle of about 45 ° with respect to the optical axis 22, and light is emitted from the side surface of the distal end portion of the optical fiber 21 as indicated by an arrow in the figure, and is applied to the light receiving surface 26 a of the light receiving element 26. The incident light is converted into an electrical signal.

  The tip surface of the optical fiber 21 is formed on the inclined surface 23 because the optical fiber 21 and the package (not shown) to which the light receiving element 26 is attached are parallel to the optical fiber 21, so that the optical fiber 21 and the light receiving surface 26a are parallel. It is necessary. The light that has passed through the core 21 a of the optical fiber 21 is reflected by the core 21 a portion in the inclined surface 23, spreads like a light beam as indicated by an arrow, and is applied to the light receiving surface 26 a of the light receiving element 26.

  However, as shown in FIG. 1 (d), in the optical fiber 21 in which the slope 21 is simply formed on the same surface of the core 21a and the clad 21b, the light begins to spread after the light is reflected by the slope 23, Since it has large beam diameters 24 and 25 of about 13.1 μm, it is an effective means for the light receiving element 26 having a large light receiving surface 26a. In this case, the light receiving surface 26a has a problem that it cannot be used when the light receiving surface 26a becomes small to satisfy the high speed.

  This is because, when a large light-receiving surface is provided, the parasitic capacitance of the light-receiving surface composed of a semiconductor increases, so that the CR time constant increases, and as a result, the signal delay time during light reception increases and high-speed communication is possible. This is because it disappears. When the diameter of the light receiving surface 26a corresponding to this high-speed communication becomes as small as 5 to 20 μm, the optical fiber 21 causes a reduction in coupling efficiency and is unacceptable as an optical fiber structure.

  As a method for solving this problem, as shown in FIG. 8, a method has been proposed in which the tip of an optical fiber 31 is processed into a spherical surface and a slope 33 is formed on a part of the spherical surface 35 (see Patent Document 1).

In this method, by forming the spherical surface 35 having the inclined surface 33, the refractive index difference between the core 31a and the clad 31b of the optical fiber 31 is eliminated, and in the spherical surface 35, the same characteristics as the coreless fiber are obtained. Accordingly, the emission point 32 of the optical fiber 31 is equivalent to that emitted from the virtual emission point 34, and is totally reflected by the inclined surface and focused by the condensing action of the spherical surface 35.
JP-A-1-62604

  However, in the conventional optical fiber 31 having the spherical surface 35 as shown in FIG. 8, although the beam diameter can be reduced, the spherical surface 35 is processed by polishing, and the spherical surface 35 is melted at the distal end of the optical fiber by discharge or the like. Therefore, it is difficult to obtain a spherical surface 35 having a diameter smaller than the diameter of the optical fiber 31 by polishing. Therefore, if the diameter of the spherical surface 35 at the tip is larger than the diameter of the optical fiber 31, the virtual emission point 34 cannot be lengthened and the focal point becomes long, so that it becomes difficult to focus on the near end. .

  For this reason, when an optical module incorporating an optical fiber 31 and a light receiving element is formed, the module itself becomes larger than an optical module having an optical fiber that is not spherically processed, and the optical module cannot be reduced in size. Have.

  The optical fiber of the present invention is characterized in that the tip of the optical fiber composed of a core and a clad is formed obliquely with respect to the optical axis, and at least the tip of the core is curved.

  In addition, the tip of the core protrudes from the clad.

  Furthermore, the tip of the core is a curved surface having a curvature radius of 500 μm or less.

  In addition, a reflective film is formed at the tip of the core.

  Furthermore, after the tip of the optical fiber is polished and formed obliquely, the clad is preferentially eroded so that the tip of the core protrudes from the clad, and the tip of the core is processed into a curved shape by electric discharge machining. It is characterized by that.

  According to the optical fiber of the present invention, the tip of the optical fiber composed of the core and the clad is formed obliquely with respect to the optical axis, and at least the tip of the core is curved, so that the light is once condensed. By spreading backward, the beam diameter of the light emitted from the optical fiber can be reduced, and even when a light receiving element having a small light receiving surface is used, high coupling efficiency is possible.

  In addition, since the tip of the core has a curved surface with a radius of curvature of 500 μm or less, the beam diameter of the light emitted from the optical fiber is reduced so that the beam diameter is small at the condensing position and the coupling efficiency is maximized. It becomes possible.

  Furthermore, by forming a reflection film at the tip of the core, even if the light is not totally reflected only by the inclined surface of the tip of the optical fiber, all the light can be reflected by the reflection film, and the loss at this reflection part can be reduced. It can be eliminated and the coupling efficiency can be made higher.

  Furthermore, according to the optical fiber processing method of the present invention, the tip of the optical fiber is obliquely formed by polishing, and then the clad is preferentially eroded, so that the tip of the core protrudes from the clad. By processing the tip of the core into a curved surface by processing, it becomes possible to process a large amount of inexpensive products.

  According to the optical module using the optical fiber of the present invention, an inexpensive connection structure between the light receiving element and the optical fiber is possible, the speed of the light receiving module for optical communication is increased, and its spread is greatly promoted. It is.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1A to 1C are views showing an embodiment of an optical fiber of the present invention, where FIG. 1A is a front view, FIG. 1B is a partial cross-sectional view showing a tip portion, and FIG. It is a perspective view of figure (b).

  The optical fiber 1 of the present invention comprises a core 1a and a clad 1b formed on the outer periphery thereof, and is made of quartz, plastic or the like. For example, when made of quartz, the core 1a has a refractive index of about 1.4491. The clad 1b has a refractive index of about 1.4440.

  Here, as shown in FIGS. 1A to 1C, the optical fiber 1 of the present invention has its tip formed obliquely with a predetermined angle with respect to the optical axis 2, and at least the core 1a. The front end surface 3 of this is a curved surface.

  By using such a structure, when light is emitted from the optical fiber 1 as shown in FIGS. 1 (a) and 1 (b), the light confined in the core 1a is shown at the tip of the core 1a as indicated by an arrow. Reflected by the surface 3, passes through the cladding 1 b of the optical fiber 1, reaches the outer peripheral surface of the cladding 1 b, is emitted, and the distal end surface 3 of the core 1 a has a curved surface, so that the lens effect acts and the core 1 a The beam diameters 4 and 5 can be made smaller than when the tip surface 3 is a flat surface.

  Specifically, as shown in FIGS. 1A and 1B, light that has passed through the core 1a of the optical fiber 1 and reached the curved tip surface 3 is once reflected and collected by the lens effect. After being illuminated, the light reaches the outer peripheral surface of the cladding 1b and is emitted. At this time, due to the lens effect of the front end surface 3 of the core 1a, light is condensed between the front end surface 3 and the outer peripheral surface of the clad 1b, and the beam becomes smaller, so that the distance from the outer peripheral surface of the optical fiber 1 is short. 1A, the beam diameter 4 in the circumferential direction shown in FIG. 1A and the beam diameter 5 in the direction of the optical axis 2 shown in FIG. 1B correspond to the core 1a as shown in FIGS. The clad 1b can be made smaller than the beam diameters 24 and 25 in the conventional optical fiber 21 having the same planar inclined surface 23.

  However, at a position away from the outer peripheral surface of the optical fiber 1, the beam diameters 4 and 5 are conversely larger than those of the optical fiber 21 having the inclined surface 23 at the tip as in the conventional case. Therefore, although depending on the material of the optical fiber 1 and the type of light passing therethrough, the beam diameters 4 and 5 are reduced when the light receiving element is located within the range of about 60 μm or less from the outer peripheral surface of the optical fiber 1. Therefore, when used as an optical module, the size can be sufficiently reduced.

  Moreover, when the distance from the outer peripheral surface of the optical fiber 1 is long, it is preferable to use a method as shown in FIG.

  When the light receiving element cannot be disposed near the optical fiber 1, a lens 7 is provided between the optical fiber 1 and the light receiving element 6 as shown in FIG. By condensing with the above, smaller beam diameters 8 and 9 can be obtained. In this case, contrary to the case of FIG. 1, the beam diameters 24 and 25 of the conventional optical fiber 21 are smaller at the position where the distance from the outer peripheral surface of the optical fiber 1 is shorter, but the outer periphery of the optical fiber 1 is smaller. It is smaller than the beam diameters 24 and 25 in the conventional optical fiber 21 at a position away from the surface. Therefore, this is effective when the light receiving element 6 cannot be installed close to the optical fiber 1.

  Furthermore, in the optical fiber 1 of the present invention, it is preferable that the tip of the core 1a protrudes from the cladding 1b. Thereby, the front end surface 3 of the core 1a can be processed into a smaller radius of curvature.

  The tip surface 3 of the core 1a can have a curvature radius of 500 μm or less, and the collected light can have a smaller beam diameter 4 and 5 by the tip surface 3 having a small curvature radius.

When the curvature radius exceeds 500 μm, the light condensing effect by the tip surface 3 of the core 1a is reduced, and the beam diameter cannot be effectively reduced. Furthermore, the radius of curvature is more preferably 50 to 150 μm.

  For example, when the radius of curvature of the tip surface 3 of the core 1a is 500 μm and the diameter of the core 1a is 10 μm, the protruding amount is about 50 μm.

  The tip surface 3 of the core 1a may be curved as shown in the partial cross-sectional view shown in FIG. 3, and the core 1a and the clad 1b may be formed on the same surface. In this case, the radius of curvature is preferably 500 μm or less as in the case where the core 1a is protruded from the clad 1b.

  Further, in the optical fiber 1 of the present invention, as shown in the partial cross-sectional view shown in FIG. 4, it is preferable to form a reflective film 10 at the tip of the core 1 a, and light is not totally reflected by the slope of the tip of the optical fiber 1. Even in this case, it is possible to reflect all the light, and there is no loss at the reflection portion, and as a result, the coupling efficiency to the light receiving element is increased.

The reflective film is made of Au, Ag, Al or the like for a metal, and SiO ₂ , TiO ₂ , Ta ₂ O ₅ or the like for a dielectric. The thickness of the metal film is 0.05 to 10 μm. 1 to 4 layers are formed so as to form a reflection film, and these are formed on the entire front end surfaces of the core 1a and the clad 1b of the optical fiber 1 by vapor deposition or sputtering.

  Further, the inclined surface formed at the tip of the optical fiber 1 preferably has an angle between the normal of the inclined surface and the optical axis 2 of 35 to 45 °. When this angle exceeds 45 °, although depending on the refractive indexes of the core 1a and the clad 1b of the optical fiber 1, there is a case where the light is not totally reflected on the inclined surface, and the light that is not reflected is lost. On the other hand, when the angle is less than 35 °, light is incident on the light receiving surface of the light receiving element at an angle, and reflection on the light receiving surface increases, thereby increasing loss.

  Here, the processing method of the optical fiber of this invention is demonstrated based on FIG.

  First, the tip of the optical fiber 1 having the core 1a and the clad 1b is polished by bringing it into contact with the rotating polishing sheet so as to form a predetermined angle, and the tip surface is 35 to 45 as shown in FIG. Process to about °.

  Next, the cladding 1b of the optical fiber 1 is obliquely immersed in ammonium fluoride or the like to selectively melt the cladding 1b, and the tip of the core 1a is protruded as shown in FIG.

  In addition, since the outer peripheral part of the clad 1b is also melted, only the polished surface is immersed as much as possible.

  Furthermore, the tip end surface 3 of the core 1a can be processed into a curved surface as shown in FIG. 5C by applying local heat to the tip portion by electric discharge or the like to melt the periphery of the core 1a.

  The radius of curvature of the tip surface 3 of the core 1a can be adjusted by controlling the time of immersion in ammonium fluoride or the like. When the amount of protrusion increases, the radius of curvature of the core 1a decreases and when the amount of protrusion decreases. The radius of curvature increases.

  Further, in the above-described processing method, the entire surface of the core 1a and the cladding 1b may be processed into a curved shape by applying local heat such as electric discharge to the tip without performing the step of selectively melting the cladding 1b. Is possible. This method is suitable when the radius of curvature is large.

  The optical fiber 1 thus obtained can be suitably used as a light receiving optical module as shown in FIG. 6, and a V-groove 12 is provided in a Si platform 11 where a light receiving element 6 is placed. The optical fiber 1 of the present invention as described above is placed in the V groove 12. Then, the direction of the light beam is changed at the distal end surface 3, and after once condensed, light is emitted from the outer peripheral surface of the optical fiber 1 and is incident on the light receiving surface 6 a of the light receiving element 6. In this case, since the beam diameter of the light emitted from the optical fiber 1 is small, the light receiving element 6 can be placed close to the optical fiber 1, and in particular, a light receiving element having a small light receiving surface used for high-speed communication. It can use suitably for the optical module to be used. In this case, it can be particularly preferably used when the diameter of the light receiving surface 6a of the light receiving element 6 is 20 μm or less.

(Example 1)
Next, examples of the optical fiber of the present invention will be described.

  As an example of the optical fiber of the present invention, an optical fiber 1 as shown in FIG. 1 was produced. The specifications of the optical fiber used are as follows.

Outer diameter (clad outer diameter): 125 μm
Refractive index of clad: 1.4440
Core diameter: 10 μm
Refractive index of the core: 1.4490
Beam diameter in optical fiber: 10 μm
The tip of the optical fiber is formed obliquely at 45 ° with respect to the optical axis, the tip surface of the core 1a is an ellipsoidal curved surface, the radius of curvature in the major axis direction is 500 μm, and the minor axis direction is The curvature radius was 250 μm.

  As a comparative example, a conventional optical fiber 21 as shown in FIGS. 1D and 1E was manufactured. The specifications of the optical fiber are the same as described above except that the tip of the core is flat.

Then, using these two types of optical fibers, an optical fiber on the side where the end face is not processed is connected to a light source having a wavelength of 1.55 μm, and a magnifying lens is provided for measuring the beam diameter of light emitted from the optical fiber. The imaging tube was arranged in accordance with the optical axis of the emitted light, and the position of the imaging tube was moved in the optical axis direction to measure the beam diameter. The beam diameter is indicated by 1 / e ² width.

FIG. 9A shows the beam diameter in the circumferential direction and the beam diameter in the axial direction of the optical fiber of the present invention and the conventional optical fiber as a comparative example, respectively.

  As is clear from FIG. 9A, in the range where the distance from the side surface of the optical fiber is close to 0 to 60 μm, both the beam diameter in the circumferential direction and the beam diameter in the axial direction are smaller than those in the conventional optical fiber. I understand that. Therefore, it is possible to obtain an optical fiber with high coupling efficiency and low loss for a light receiving element having a small light receiving surface with a diameter of 20 μm or less used for high speed communication. Further, the coupling efficiency can be further increased by arranging the light receiving surface at such a distance that the beam diameter is smaller than the diameter of 20 μm of the light receiving surface.

(Example 2)
Next, as shown in FIG. 2, the evaluation was performed by an optical system using a lens between the optical fiber and the light receiving element.

  The specifications of the optical fiber and the wavelength of light were the same as in Example 1, and the tip of the core was an ellipsoid having a major axis radius of 208 μm and a minor axis radius of 104 μm.

  As a lens, a ball lens having a refractive index of 1.50 and a diameter of 100 μm was used.

  Further, as a comparative example, an optical fiber as shown in FIGS. 1D and 1E was used in the same manner as the optical fiber used in Example 1.

  And each beam diameter was measured like Example 1. FIG.

  FIG. 9B shows the beam diameter 8 in the circumferential direction and the beam diameter 9 in the axial direction after being emitted from the optical fiber 1 processed at the tip and transmitted through the ball lens.

  In addition, the horizontal axis of FIG.9 (b) has shown the distance from an optical fiber side surface to a ball lens.

  From FIG. 9 (b), the beam diameter in the circumferential direction is smaller for the conventional optical fiber when the distance between the side surface of the optical fiber and the lens is 70 μm or less, but for the optical fiber of the present invention when the distance is 70 μm or more. It can be seen that the beam diameter is small.

  Therefore, when the light receiving element cannot be installed close to the optical fiber, the beam diameter is smaller than that of the conventional one, so that the loss to the light receiving surface of the light receiving element is reduced, and as a result, high coupling efficiency is obtained.

  As described above, when the light receiving element is close to the optical fiber, the structure shown in FIG. 1 is used. When the light receiving element is separated from the optical fiber, the structure shown in FIG. 2 is used.

(A), (b), (c) shows one Embodiment of the optical fiber of this invention, respectively, The front view of a front-end | tip part, a fragmentary sectional view, and a fragmentary perspective view, (d), (e) is conventional The optical fiber of these is shown, and it is a front view and a partial sectional view, respectively. (A), (b) is a figure explaining the beam diameter at the time of receiving the emitted light from the optical fiber of this invention using a lens. It is a fragmentary sectional view showing other embodiments of the optical fiber of the present invention. It is a fragmentary sectional view showing other embodiments of the optical fiber of the present invention. (A)-(c) is a fragmentary sectional view explaining the manufacturing method of the optical fiber of this invention. It is a perspective view which shows the optical module of this invention. It is a fragmentary sectional view which shows the front-end | tip part of the conventional optical fiber. It is a fragmentary sectional view which shows the front-end | tip part of the conventional optical fiber. (A), (b) is a graph which shows the measurement result of the beam diameter of an optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 31 Optical fiber 1a, 21a, 31a Core 1b, 21b, 31b Clad 2, 22 Optical axis 3 Core tip surface 4 Beam diameter in the circumferential direction 5 Beam diameter in the axial direction 6, 26 Light receiving element 6a, 26a Light receiving surface 7 Lens 8 Beam diameter in circumferential direction 9 Beam diameter in axial direction 10 Reflective film 11 Si platform 12 V groove 14 Emission light 23, 33 Slope 32 Emission point 34 Virtual emission point 35 Spherical surface

Claims (6)

An optical fiber comprising: an optical fiber having a core and a clad formed with a tip portion inclined with respect to the optical axis, and at least the tip portion of the core having a curved surface. The optical fiber according to claim 1, wherein a tip of the core protrudes from the clad. The optical fiber according to claim 1 or 2, wherein the tip of the core has a curved shape with a radius of curvature of 500 µm or less. The optical fiber according to any one of claims 1 to 3, wherein a reflection film is formed at a tip of the core. 5. The optical fiber processing method according to claim 1, wherein the tip of the core protrudes from the clad by preferentially eroding the clad after forming the tip of the optical fiber obliquely by polishing. And processing the tip of the core into a curved surface by electric discharge machining. An optical module comprising the optical fiber according to claim 1.

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