JP2002228858A - Lens added optical fiber and method for working the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make tapered parts and curved surfaces uniform in shape and to provide lens added optical fibers which ensure no unevenness in optical connection efficiency of manufactured articles and are excellent in yield. SOLUTION: In the lens added optical fiber 10 obtained by forming a tapered part 11 and a curved surface 13 adjacent to the part 11 at the front edge of an optical fiber, at least the core part 15 of the curved surface 13 is formed as a melt-transferred surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber with a lens used for optical coupling between a light emitting source used for optical communication and an optical fiber.

[0002]

2. Description of the Related Art As a light emitting source for optical communication, a laser diode (hereinafter referred to as an LD) or a light emitting diode is used. The pattern of the light emitted from the LD has an elliptical beam shape in which the light distribution is not a Gaussian distribution in a circular shape but is different in the vertical and horizontal directions. A typical LD having a wavelength of 980 nm has a pattern of emitted light having an aspect ratio of 2.5 to 4: 1. LD with such a large aspect ratio
Since the optical fiber with a lens used for coupling between the optical fiber and the optical fiber is an optical fiber with a wedge lens, the optical fiber with a wedge lens will be described below.

As a conventional optical fiber with a wedge-shaped lens, there is a two-stage wedge-shaped lens as shown in FIG. The optical fiber with lens 10 is symmetrical with respect to the core axis 12 of the optical fiber, and has a pair of tapered portions 11a that form a sharp ridge at the fiber tip. On the other hand, there is provided a lens comprising a pair of tapered portions 11b provided at a gentler angle than the tapered portion 11a (see Japanese Patent Application Laid-Open No. Hei 8-5865).

As shown in FIG. 7, a semi-cylindrical lens is formed by processing the tip of a wedge-shaped lens into a curved surface 13 for the purpose of efficiently condensing light similarly to the optical fiber with lens 10 shown in FIG. There is an optical fiber with lens 10. The optical fiber with lens 10 is provided with a pair of tapered portions 11 symmetrical with respect to a core axis 12 of the optical fiber to form a wedge shape, and has a semi-cylindrical curved surface 13 continuous with these tapered portions 11 (particularly). See Japanese Unexamined Patent Publication No. 8-86923).

[0005]

However, the conventional optical fiber with lens 10 described above has problems in optical coupling characteristics and processing accuracy.

A conventional optical fiber with a lens 10 shown in FIG.
In this method, the tip of the optical fiber is processed into a sharp ridge by polishing using a grindstone or the like, but it is very difficult to form the ridge because chipping or the like easily occurs at the ridge of the tip. Chipping at the tip of the optical fiber causes a loss, and significantly reduces optical coupling characteristics.

The optical fiber with lens 10 shown in FIG.
Must be polished while relatively rotating the tip of the optical fiber and the grindstone when processing the curved surface 13 by polishing,
It is difficult to polish at a constant curvature, and it is difficult to process a curved surface symmetrical with respect to the core axis 12 of the optical fiber. A lens which is asymmetrical with respect to the core axis 12 of the optical fiber significantly reduces the optical coupling characteristics.

Next, the above-mentioned conventional optical fiber with lens 10 has a problem in alignment accuracy with the LD.

The optical fiber with lens 10 shown in FIG. 6 has a lens effect only by wedge-shaped processing instead of curved surface processing, so that optimization for various LDs is limited.

In the same manner as described above, the optical fiber with lens 10 shown in FIG. 7 has a lens formed by only one pair of the tapered portion 11 and the semi-cylindrical curved surface 13. Limited to a part, optimization is limited for various LDs.

For this reason, in the optical fiber with lens 10 whose optimization is limited, the range in which high optical coupling efficiency can be obtained in alignment with the LD is extremely limited. Therefore, in assembling an LD module using the conventional optical fiber with lens 10, there has been a problem that high-precision alignment and fixing of the optical fiber are required, and the assembly cost is significantly increased.

In addition, in the conventional optical fiber with lens 10 having any shape, the tapered portion 11 and the curved surface 13 are greatly varied in shape because they are polished one by one. Even if the angle of curvature and the radius of curvature of the curved surface 13 can be obtained by simulation analysis or experiment, there is a problem that the variation in the shape of each manufactured product becomes large and the variation in the optical coupling efficiency also becomes large. Was.

[0013]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, the present invention relates to an optical fiber with a lens having a tapered portion and a curved surface continuous with the tapered portion at the tip of the optical fiber. Comprises a fusion transfer surface.

Further, in an optical fiber with a lens in which a tapered portion and a curved surface continuous with the tapered portion are formed at the distal end of the optical fiber, the tapered portion is preliminarily processed at the distal end of the optical fiber, and the predetermined curved surface and the tapered portion are formed. The distal end of the optical fiber is pressed against a molding die having a concave curved surface provided, and the distal end is melt-transfer-molded to form a curved surface.

Further, when the tip portion of the optical fiber is pressed against a molding die, a laser beam is irradiated to the molding die to generate heat and transfer by melting.

Further, when the tip of the optical fiber is pressed against the molding die, the molding die is preheated using an infrared heater.

Then, the tip of the optical fiber is pressed against a molding die in an atmosphere composed of an inert gas or a reducing gas.

[0018]

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

FIGS. 1A and 1B are a plan view and a side view showing an optical fiber with a lens according to an embodiment of the present invention. As is well known, the optical fiber includes a core section 15 having a circular cross section in which light is confined, and a cladding section 16 surrounding the core section 15 concentrically.

A wedge-shaped tapered portion 11 symmetrical to a core axis 12 of the optical fiber is formed at the tip of the optical fiber, and a semi-cylindrical curved surface 13 is provided continuously with the tapered portion 11. At least the core portion 15 of the curved surface 13 is formed by a fusion transfer surface, and the clad portion 16 of the tapered portion 11 is formed.
Is formed with a linear projection 14 parallel to the cylindrical direction of the curved surface 13.

The curved surface 13 side and the entire curved surface 13 from the convex portion 14 of the tapered portion 11 form a melt transfer surface, and the tapered portion 13 from the other convex portion 14 to the outer peripheral side of the optical fiber is a polished surface or an electric discharge machined surface.

Here, the polished surface refers to a surface polished with a diamond grindstone, diamond abrasive grains, or diamond abrasive paper, and has a myriad of fine scratches of about 1 μm or less. On the other hand, the molten surface softened the glass temporarily, and after cooling again, took advantage of the property of recovering the original physical properties of the glass, eliminating the damaged layer and polishing flaws generated during polishing, It is a smooth mirror surface that has been melted. For example, the surface on which electric discharge machining has been performed is a fused surface.

The method of distinguishing between the polished surface and the molten surface can be easily determined by observing the polished surface with a polishing flaw when observed with a metal microscope at a magnification of 1000 times, and since the fused surface is in a mirror surface state.

On the other hand, the fusion transfer surface of the present invention is formed by pressing the tip of an optical fiber against a heated molding die.
The surface on which the tip of the optical fiber is melted and the molding die is transferred. Therefore, unlike the molten surface formed by the above-mentioned electric discharge machining, traces of machining of the grindstone at the time of polishing applied to the molding die are also transferred. Here, the polished surface of the optical fiber and the polished surface of the molding die are the same polished surface, but since the polished material and the material to be polished are completely different, each polished surface is different, so that it is 200 times. The difference between the polished surface and the melt-transfer surface can be easily determined by using the above-described high-magnification metallographic microscope or the like.

For example, the polished surface of an optical fiber is a surface that has been scraped off by sharp particles at the tip of diamond or the like, so that the cross-section of the flaw has a sharp shape, whereas the fusion transfer surface is formed by melting the optical fiber. Since the shape of the molding die is the transferred surface, the cross section of the transferred scratch is more rounded than the polished surface.

Here, the processing marks of the grindstone at the time of polishing applied to the molding die are also transferred to the melt transfer surface.
As will be described later, if the arithmetic average roughness (Ra) of the transfer surface of the molding die is set to 0.01 μm or less, the optical coupling efficiency is not affected. In the present invention, at least the core portion 15 of the curved surface 13 is formed as a fusion transfer surface, so that all the lens shapes are formed to be the same, and the optical coupling efficiency can be stabilized.

Next, the protruding portion 14 is used for the optical fiber 10 with a lens.
When the curved surface 13 and the tapered portion 11 are melt-transfer-molded at the end of the tapered portion, the tapered portion 11 is formed on a part of the tapered portion 11 which is separated from the molding die. That is, the surplus glass from the transfer surface of the molding die appears as the convex portion 14 as distortion.

The convex portion 14 is formed in a straight line parallel to the cylindrical direction of the curved surface 13. However, since the entrance of the transfer surface of the molding die is straight, the convex portion 14 is formed in this manner. However, by forming the entrance of the transfer surface of the molding die into a desired shape, it can be formed into various shapes.

Here, the size of the projection 14 is 0.02 μm or more.
The thickness is preferably 50 μm, and if it is less than 0.02 μm, it is difficult to confirm because of the measurement limit.
If the thickness exceeds 0 μm, the projections 13 protrude from the outer periphery of the optical fiber, and cannot be incorporated into a ferrule or a package.

The radius of curvature of the curved surface 13 is 1 μm to 20 μm.
m is desirable. Here, if the radius of curvature is less than 1 μm, the radius of curvature is too small for polishing, which is a pre-process of the melt transfer molding, and processing is impossible.
If the radius of curvature exceeds, the light emitted from the LD will not be sufficiently condensed by the lens portion, and will not enter the core portion 15 of the optical fiber satisfactorily, and the optical coupling efficiency will deteriorate.

The angle θ of the tapered portion 11 is an angle formed between the tapered portion 11 and a plane perpendicular to the core axis 12 of the optical fiber, and is preferably in the range of 10 ° <θ <70 °. This is because the optical coupling efficiency is extremely deteriorated when the angle θ is out of this range.

The radius of curvature of the curved surface 13 and the tapered portion 11
Is greatly affected by the characteristics of the LD used, and it is necessary to set a narrower tolerance within the above range depending on the type of LD.

Although a typical wedge-shaped lensed optical fiber has been described above, another embodiment of the present invention is shown in FIG.
As shown in (a) and (b), a tapered portion 11a having a large angle θ is formed in advance, and at least a core portion is melt-transfer-molded to obtain an optical fiber with a lens 10 on which a convex portion 14 is formed. Can also.

Conversely, as shown in FIG. 2C, a tapered portion 11b having a small angle θ is formed in advance, and at least a core portion is formed by melt transfer molding, and a convex portion 14 is formed. The optical fiber with lens 10 can also be used.

In any of the shapes shown in FIGS. 2 (a) to 2 (c), the tip can be made to be a fusion transfer surface, so that the shape can be manufactured stably without any variation. Coupling efficiency can be obtained.

Further, as shown in FIG.
Optical fiber with lens 10 in which two wedge shapes are formed in two stages
Alternatively, as shown in FIG. 3 (b), in the optical fiber with lens 10 in which the ridgeline of the curved surface 13 whose front end is viewed in plan is formed in a curved surface, the melt transfer surface may be formed at least in the core portion. .

Further, the present invention can be applied not only to the tapered portion 11 having a wedge shape but also to a tapered spherical shape having a conical tapered surface 17 as shown in FIG. That is, the optical fiber with lens 10 having the tapered portion 11 and the curved surface 13 continuous with the tapered portion 11 at the tip of the optical fiber can be applied irrespective of the shape.

The core portion of the optical fiber with a lens according to the present invention uses a so-called core-enlarged optical fiber whose core is preliminarily subjected to a core enlarging process, so that the optical coupling efficiency is further improved. An optical fiber can be obtained.

Next, a method for processing an optical fiber with a lens according to the present invention will be described with reference to FIG. In FIG. 5, on one surface of a molding die 31, a concave curved surface portion 31a having a curved surface and a tapered portion conforming to the end shape of the final optical fiber with a lens.
Are formed.

On the other hand, the distal end of the optical fiber with lens 10 is previously polished and formed into a tapered shape, and the radius of curvature and the inclination angle of the distal end are polished so as to approximate a desired shape. The optical fiber with lens 10 is moved along the core axis 12 and the tip of the optical fiber is pressed against the concave curved surface 31a of the molding die 31 with a weak pressing force. Simultaneously with this pressing, a laser beam 32a is emitted from the laser 32 from the opposite surface of the molding die 31a toward the concave curved surface portion 31a. Then, the concave curved surface portion 31a generates heat, and when the temperature becomes equal to or higher than the melting temperature of the optical fiber (1800 to 2000 ° C. in the case of quartz), the distal end portion of the optical fiber is melted and the convex curved surface corresponding to the concave curved surface shape is formed. It is transferred to a shape and molded.

For this reason, the convex portion 14 is formed in a portion of the optical fiber with lens 10 which is separated from the molding die 31.

If the volume of the irradiated portion is reduced by irradiating the molding die 31 with the laser beam 32a and heating it, the temperature of the concave curved surface portion 31a instantaneously reaches the desired temperature and the desired molding can be performed in a short time. When the irradiation of the laser beam 32a is stopped, the heat of the concave curved surface portion 31a is diffused throughout the molding die 31, and the temperature of the concave curved surface portion 31a rapidly decreases. This rate of temperature decrease is determined by the ratio of the heated partial volume of the molding die 31 to the non-heated partial volume. When the volume ratio is large, the temperature rise of the molding die 31 when the heat molding operation is repeated many times becomes small.

When a conventional resistance heating furnace or microwave heating furnace is used to heat the concave curved surface portion 31a of the molding die 31 to a desired temperature, the temperature of the entire molding die 31 rises. This causes a problem that convection occurs in the surrounding atmosphere or that the optical fiber is bent by heating the optical fiber close to the concave surface 31a by radiation.

Therefore, in the processing method of the present invention, the temperature of the concave curved surface portion 31a of the molding die 31 is selectively raised by a laser beam to form a molten transfer surface at least at the core portion of the optical fiber with lens. can do.

At this time, the amount of fusion at the tip of the optical fiber is extremely small, and since the curved surface is completed within a short time, the amount of generated molten scum is also extremely small, and it flows out onto the tapered peripheral surface. . Therefore, the formed optical fiber tip is kept clean. Since the amount of fusion of the optical fiber by the processing method of the present invention is very small and sufficient, the laser beam irradiation time required for the forming process is extremely short. Therefore, the concave curved surface portion of the forming die 31 is used. Heat generation in portions other than 31a is sufficiently suppressed.

When the optical fiber is made of quartz, its melting temperature is about 1800 to 2000 ° C., so that the molding die 31 can withstand a high temperature of 2000 ° C. or more and can be processed with high precision. It is preferable to be formed of a material having excellent oxidation resistance. As a material that meets these conditions, the maximum operating temperature is 2200 ° C.
Zirconia, silicon carbide having a maximum use temperature of 2300 ° C., and graphite having a maximum use temperature of 2500 ° C.

Although zirconia can be processed precisely,
Since the absorptance of laser light is low, a high heat resistant material having a high absorptivity of laser light needs to be bonded to the zirconia material in order to improve the heat generation efficiency of the laser. Therefore, it is more preferable to use silicon carbide or graphite, which is a material having a high laser light absorption rate and a high heat resistance.

The molding die 31 can be made of titanium carbide (TiC) as a different material from the above. In this case, it can be used at a high temperature of 2400 ° C. or more in an oxidizing atmosphere. The laser light absorption of this titanium carbide is higher than that of zirconia but lower than that of graphite. That is, titanium carbide has an advantage that it can be used in an oxidizing atmosphere, but has a disadvantage that the efficiency of instantaneous heating by laser beam irradiation is low.

Such a material is made of an inert gas (for example, N
₂ gas) or an atmosphere composed of a reducing gas (for example, H ₂ gas). In such a case,
It is preferable that an inert gas or a reducing gas be fed into the space surrounding the heated portion of the molding die 31 to protect it.

Here, the molding die 31 of the present invention is formed with high precision by a micromachining apparatus, and at least the concave curved surface portion 31a has an arithmetic average roughness (Ra) of 0.1.
It must be polished to a mirror surface of 01 μm or less. This is because the surface roughness of the concave curved surface portion 31a is transferred to the curved surface 13 of the optical fiber with lens 10 as it is. This is because the coupling efficiency is deteriorated.

Next, as the heating laser 32, a carbon dioxide gas laser, a YAG laser, an excimer laser or the like can be used, but a carbon dioxide gas laser is preferably used. The carbon dioxide laser has a wavelength of 10.6 μm,
This is because the graphite is absorbed by the graphite at an absorption rate of 100%, and therefore, there is an advantage that the heat generation efficiency is extremely high with respect to the molding die 31 made of graphite.

The laser 32 has a good focusing property and can be locally heated.
It is desirable that the spot diameter is about 0.6 to 1.0 mm and the irradiation time is about 2 seconds.

The laser processing condition is that the workpiece is an optical fiber made of quartz glass, and if the laser beam 32a of high output is directly irradiated, a crack may occur due to a heat shock. To prevent the temperature of the optical fiber from rising rapidly by irradiating the laser light before or after the irradiation of the laser beam 32a, further weakening the output before and after, or to reduce the heat shock by using an infrared heating device 33 or the like. Irradiation with the laser beam 32a may be performed in a state where the molding die 31 is heated in advance by the heating means.

The infrared lamp 33a of the infrared heating device 33 as the heating means is, for example, a halogen lamp.
The infrared rays are focused by the quartz rod lens 33b. The rod lens 33b has a diameter of about 5 to 8 mm, and is arranged so that the tip end surface is close to the molding die 31.

In this case, the infrared heating device 33 is set at 200 ° C.
By preheating to the extent, cracks in the optical fiber due to heat shock during laser heating can be prevented. The coating of the optical fiber and the molding die 31 and the infrared heating device 33 are separated from each other by using a shielding plate 34 so that the coating of the optical fiber is not melted. It is because.

When H ₂ is used as the reducing gas when the infrared heating device 33 is used, it is very dangerous. Therefore, it is better to use N ₂ which is an inert gas.

The optical fiber with lens 10 of the present invention is mainly applied to a single mode optical fiber, but can also be applied to a multimode optical fiber. The present invention can also be applied to a plurality of parallel processing optical fibers. In this case, a desired number of concave curved surface portions 31a are formed in the molding die 31, the laser beam 32a is divided into a desired number of beams, and this is irradiated on the molding die 31, and What is necessary is just to heat the curved surface part 31a.

[0058]

EXAMPLE Here, an experiment was conducted by the following method. An optical fiber with a lens 10 in which the tip of the optical fiber of the present invention shown in FIG. 1 is melt-processed using a molding die 31 to form a fusion transfer surface at least on a core portion 15 and a convex portion 14 is formed on a tapered portion 11. As a comparative example, ten optical fibers 10 each having a lens whose curved surface 13 at the tip of the conventional optical fiber shown in FIG. 7 was finished by polishing were prototyped, and the optical coupling efficiency was measured.

The light source has a wavelength of 980 nm, the intensity distribution (mode field) pattern of the emitted light has an elliptical shape having an aspect ratio of 4: 1, and the optical fiber is a circularly symmetric single mode optical fiber having a mode field diameter of 6.0 μm. Using.

The angle θ between the tapered portion 11 and a plane perpendicular to the core axis 12 of the optical fiber was 50 °, and the radius of curvature of the curved surface 13 at the tip was 4 μm.

A carbon dioxide laser was used as the laser 32, a halogen lamp was used as the infrared heating device 33, and a molding die 31 was made of silicon carbide. Also, the concave curved surface portion 31
a was an inert gas of N ₂ .

The results are shown in Table 1.

As can be seen from Table 1, the optical coupling efficiency of the optical fiber with lens 10 having the tip portion formed by the conventional polishing is 75.94% and 6.49% in average value and variation.
On the other hand, the tip of the present invention is
The optical coupling efficiency of the optical fiber with lens 10 melt-transfer-molded by the laser 32 using
The results are 2.73% and 1.87%, which indicates that the optical fiber with a lens 10 of the present invention has significantly improved optical coupling efficiency.

[0064]

[Table 1]

[0065]

According to the present invention, in an optical fiber with a lens in which a tapered portion and a curved surface continuous with the tapered portion are formed at the tip of the optical fiber, at least the core portion of the curved surface is formed as a fusion transfer surface, so that the tapered portion is formed. In addition, it is possible to provide an optical fiber with a lens which is excellent in the yield and has no variation in the shape of the curved surface and no variation in the optical coupling efficiency of each manufactured product.

[Brief description of the drawings]

FIG. 1A is a plan view showing a fiber with a lens of the present invention, and FIG. 1B is a side view of the same.

FIGS. 2A to 2C are side views showing another embodiment of the present invention.

FIG. 3A is a side view showing another embodiment of the present invention, and FIG. 3B is a plan view of the same.

FIG. 4 is a side view showing another embodiment of the present invention.

FIG. 5 is a diagram illustrating a method for processing an optical fiber with a lens according to the present invention.

FIG. 6 is a side view showing a conventional optical fiber with a lens.

FIG. 7 is a side view showing a conventional optical fiber with a lens.

[Explanation of symbols]

 Reference Signs List 10 optical fiber with lens 11 taper portion 11a taper portion 11b taper portion 12 core shaft 13 curved surface 14 convex portion 15 core portion 16 clad portion 17 conical taper portion surface 31 molding die 31a concave curved surface portion 32 laser 32a laser beam 33 infrared heating Device 33a Infrared lamp 33b Rod lens 34 Shielding plate θ Angle

Claims (5)

[Claims] 1. An optical fiber with a lens, wherein a tapered portion and a curved surface continuous with the tapered portion are formed at the tip of the optical fiber, wherein at least a core portion of the curved surface is a fusion transfer surface. 2. In an optical fiber with a lens having a tapered portion and a curved surface continuous with the tapered portion at the distal end of the optical fiber, the tapered portion is preliminarily processed at the distal end of the optical fiber, and the predetermined curved surface and the tapered portion are formed. A method for processing an optical fiber with a lens, characterized in that the tip of the optical fiber is pressed against a molding die having a concave curved surface provided, and the tip is melt-transfer-molded to form a curved surface. 3. The method according to claim 2, wherein when the tip of the optical fiber is pressed against the molding die, a laser beam is applied to the molding die to generate heat and transfer by fusion. Processing method of optical fiber with lens. 4. The lens-equipped lens as set forth in claim 3, wherein when the tip of the optical fiber is pressed against the molding die, the molding die is preheated using an infrared heating device. Optical fiber processing method. 5. The method for processing an optical fiber with a lens according to claim 2, wherein the tip of the optical fiber is pressed against a molding die in an atmosphere composed of an inert gas or a reducing gas.