JP2008020766A - Optical waveguide, optical waveguide module, and optical waveguide manufacturing method - Google Patents

Abstract

Even if a bent portion is formed, optical transmission loss due to the bending is small, the mode field diameter is large except for the bent portion, and the connection loss can be reduced without high-precision alignment, and the end surface is inclined at a small angle. Provided is an optical waveguide capable of obtaining a large return loss by a polishing process.
In an optical waveguide, a heating target portion of an optical waveguide having a core and a clad covering the core is heated to shift to a processing strain released state, and the heating target shifted to a processing strain released state. A bent portion 10 is formed by bending the portion 9 in a curved shape with a predetermined bending radius, and the bent portion 10 is shifted to a working strain state. The difference in refractive index and physical size between the core 2 and the clad 3 of the bent portion 10 are changed by heating the portion 9 to be heated.
[Selection] Figure 1

Description

  The present invention relates to an optical waveguide, an optical waveguide module, and an optical waveguide manufacturing method, and in particular, an optical waveguide, an optical waveguide module, and an optical waveguide capable of reducing a bending loss by a small bending portion of the optical waveguide and converting a light guiding direction. The present invention relates to an optical waveguide manufacturing method.

  At present, the operation speed of an electric circuit is approaching that of an optical transmission circuit. Therefore, in order to compensate a part of the high-speed operation of the electric circuit with an optical waveguide, the electric circuit and the optical transmission line are fused. ing. An optical fiber is used as an example of the optical waveguide.

  Specifically, a VCSEL (Vertical Cavity Surface Emitting Laser) is mounted on an electric circuit board, an optical signal emitted from the VCSEL is incident on an optical waveguide, propagated, and mounted on a PD (photograph) mounted on the electric circuit board. The light is received by a diode) and transmitted. It has been studied that this optical waveguide is embedded in the electric circuit board itself, or that the optical waveguide is disposed between a plurality of electric circuit boards and used instead of the electric cord. As the optical waveguide, for example, an organic waveguide sheet (a typical waveguide sheet is a polyimide waveguide sheet) and an optical fiber sheet having an optical fiber have been proposed.

  The VCSEL is a surface emitting laser, and the emission direction of the laser beam is perpendicular to the mounted electric circuit board. If the mounting direction of the VCSEL is perpendicular to the electric circuit board, the laser light emission direction will be parallel to the electric circuit board. Such laser mounting takes advantage of the high-density multiple mounting of the VCSEL. Therefore, the VCSEL mounting direction is usually not vertical.

The optical waveguide embedded in the electric circuit board guides light in a direction parallel to the electric circuit board. Therefore, in order to couple the laser light of the VCSEL to these optical waveguides, the optical waveguide of 90 degrees is used. A change of direction is required.
As such a 90-degree optical waveguide direction conversion method, the end face of the optical fiber is polished at 45 degrees, and the polished surface is subjected to metal deposition or the like to form a mirror, and the 90-degree optical waveguide direction conversion is performed. A method of converting the direction of the optical waveguide with a mirror having an angle of 45 degrees has been studied.

  Although the application area is different from the necessity for the 90-degree optical waveguide direction conversion as described above, for example, in FTTH (Fiber to the home data communication service: Fiber to the home) Although the fiber is wired, a general optical fiber cannot be bent with a bending radius of several centimeters or less due to problems of mechanical characteristics and optical characteristics. For this reason, it is necessary to secure a space to gently bend the optical fiber with a large bending radius at the corner portion of the room or the hole portion where the optical fiber is taken indoors from the outside. Damage. On the other hand, in recent years, optical fibers that can be bent mechanically and optically even when the minimum bending radius is 15 mm have been developed.

  Furthermore, as an application for converting the optical waveguide direction in an ultra-small size, a method of bending a desired portion of an optical fiber to a very fine diameter and bending it has been proposed and commercialized. In this method, the diameter of the optical fiber in the thinned portion is about several μm to 10 μm, and even if the optical fiber is bent at a bending radius of 1 mm, for example, the bending strain due to the bending is 1% or less, which is sufficient mechanically. It becomes possible to bend. In addition, optically, it is not a structure that confines light only with this thin fiber, but the core is an optical fiber and the cladding is the environment (air ), Equivalently functioning as a waveguide with an ultrahigh refractive index difference of several tens of percent, and even a small bending radius can be bent without loss of light.

  In the method in which the end face of the optical fiber or the optical waveguide described above is polished at 45 degrees, and metal polishing is performed on the polished surface to form a mirror, and the conversion is performed at 90 degrees, the optical fiber and the waveguide are accurately polished at 45 degrees. The work is not easy, and further processes such as metal vapor deposition require large-scale manufacturing facilities. Even when mounting, it is necessary to mount the 45-degree surface without being twisted directly above or below the electric circuit board, but such mounting is not easy. Also, in this method, light is guided through a medium other than the structure of the optical waveguide after being converted 90 degrees from the core of the optical fiber or the waveguide, so that the beam diameter is widened and good coupling is obtained. It ’s difficult.

  In addition, in the method of performing conversion with a mirror having an angle of 45 degrees, a minute mirror is required for miniaturization, and alignment with the minute mirror and the light beam propagates in the space up to the mirror part. In order to suppress the beam divergence caused by doing so, lens parts and the like must be added, the number of parts increases, and their alignment is not easy.

  In a system involving spatial propagation, the light exit end face to the space from the optical waveguide or optical fiber requires a non-reflective coating or oblique polishing in order to obtain a large return loss. However, a large-scale apparatus is required to perform the antireflection coating, and oblique polishing is more difficult to align with the 45-degree mirror because the radiation direction of the light beam deviates from the optical axis in the optical waveguide or optical fiber. There is a case.

  Next, even if the minimum bending radius of the optical fiber is 15 mm, an optical fiber that can be bent mechanically and optically is effective outdoors, but the bending radius that is allowed indoors and in a narrow space is even smaller. good. Such an optical fiber cannot be used when it is desired to make the bending radius of the bent portion of the optical fiber smaller than 15 mm.

As described above, the method of bending the desired portion of the optical fiber to have a very fine diameter causes a problem that the optical fiber is broken during handling because it has an extremely small diameter of about several μm. In this method, the reduction of the optical loss in the bent portion is basically that the external environment acts as a cladding, and is sensitive to changes in the external environment. That is, if moisture condensation occurs in this minute diameter portion due to environmental humidity and temperature fluctuations, light confinement at the minute bent portion will not function.

  In order to maintain the optical confinement function at the minute bending portion, it is necessary to perform hermetic sealing while the minute diameter portion is exposed to a gas such as air. That is, hermetic sealing with a minute diameter portion disposed in the cavity is required, but this is not easy. Moreover, even if the minute diameter portion is small, the structure portion that hermetically seals and protects the structure must be much larger than the minute diameter portion.

  Moreover, organic optical waveguide sheets and optical fiber sheets have been proposed as optical fibers and optical waveguides. First, the optical loss at the current technical level of organic optical waveguide sheets is as large as about 0.2 dB / cm. The optical power is reduced by 3 dB, that is, half or less, only by transmitting 15 cm in length. Considering the case where an optical signal is transmitted from the optoelectronic board to the backplane and further to the optoelectronic board, it is considered that the optical signal is transmitted over a distance of several tens of cm to 1 m. In this case, the connector portion Ignoring the connection loss, etc., only a transmission loss of the optical waveguide causes an optical loss of about 20 dB at the maximum.

  On the other hand, the optical fiber sheet is obtained by wiring a plurality of optical fibers between two flexible plastic films, and the characteristics are determined by the optical fiber. Compared with the transmission loss of the organic optical waveguide being 0.2 dB / cm, the transmission loss of the silica-based optical fiber is much smaller, about 0.2 dB / km. The transmission loss is small enough to be ignored at a distance of several meters at the maximum, such as transmission.

  In the case of a plastic optical fiber, there is an increase in transmission loss of several dB to several tens of dB / km. For example, even a loss of 500 dB / km is about 0.5 dB / m, which is 1/40 of that of an organic waveguide. The transmission loss is small at a distance of a few meters at the maximum, and there is no practical problem.

  However, since this optical fiber sheet is used to route light to a desired location through a plurality of optical fibers, the wired optical fibers intersect, and light loss occurs depending on the degree of this intersection. In order to avoid the light loss due to the intersection, it is conceivable to devise the wiring shape or to insert a buffer material in the intersection, but such a measure deteriorates the yield and further increases the cost. Further, the wiring on the sheet has a problem that the bending radius cannot be reduced due to the optical and mechanical strength of the optical fiber.

  In general, silica-based optical fibers are feared to have an increase in optical loss and mechanical destruction when the bending radius is 15 mm or less, and therefore, it is necessary to perform wiring with a radius larger than that, and it is difficult to reduce the optical fiber sheet. The wiring shape is also limited.

Therefore, the present inventors heat a desired portion of an optical waveguide having a core and a clad to shift the desired portion to a machining strain release state, and the desired portion that has shifted to the machining strain release state has a predetermined bending radius. Proposed to bend into a curved shape and shift to a working strain state. As a result, the refractive index difference between the core and the clad can be made larger than that of an optical fiber that is normally used, and it can be bent with a small bending radius without applying processing distortion by heating (see, for example, Patent Document 1).
JP 2005-292718 A

  However, the optical waveguide proposed by the present inventors described in Patent Document 1 has the following problems. Since the refractive index difference between the core and the clad is larger than that of a normal optical fiber, the optical field loss due to bending is small, but the mode field diameter (hereinafter abbreviated as MFD) is reduced.

  This MFD is small. Light is strongly confined in the core by a large refractive index difference, so that the optical transmission loss due to bending can be reduced, but at the same time, the optical electric field spread is small due to the strength of the confinement. This is a phenomenon that the MFD is small. The small MFD means that in order to connect low-loss optical fibers, it is necessary to align the optical fibers with very high accuracy.

For example, in the case of 10 μm, which is a typical MFD of a normal optical fiber, when a connection loss of 0.5 dB is allowed, the allowable displacement of the connection is about 1.7 μm. However, when the MFD is 5 μm, this allowable amount is about 0.85 μm.
For this reason, it was possible to increase the refractive index difference between the core and the clad of the optical fiber to make it resistant to bending and bend with low loss even with minute bending, but when connecting optical fibers with connectors etc. In this case, the connection loss of the connector is larger than that using a normal optical fiber, and in order to reduce the optical transmission loss due to this connection, a connector manufactured with higher accuracy than the normal accuracy is required.

  Further, in this high refractive index difference fiber, the reflection of light at the end face, that is, the reflection attenuation amount is smaller than the value obtained by processing of a normal optical fiber, and there is a possibility that the system becomes unstable due to the reflected light. This is because the difference in refractive index increases and loss due to optical axis misalignment increases, but the connection loss due to angular misalignment is reduced, so the connector end face is usually taken as a measure against the return loss of the optical fiber. This is because even the oblique polishing such as polishing cannot provide a sufficient amount of reflection loss. For example, a normal optical fiber with an MFD of 10 μm by oblique polishing at 8 degrees has a high refractive index difference of 5 μm even when a return loss of about −50 dB is obtained with a reflectance of 4% at the fiber end face. In the case of an optical fiber, a return loss of only about -23 dB can be obtained even when the same angle of 8 degrees is applied.

  Therefore, in order to solve the above problems, the present invention reduces the loss of optical transmission due to the bending even if the bending portion is formed by bending with a small radius by heating, and the mode field diameter is large except for the bending portion, and high accuracy. An object of the present invention is to provide an optical waveguide, an optical waveguide module, and an optical waveguide manufacturing method capable of reducing connection loss even without proper alignment and obtaining a large amount of return loss by a small-angle end face oblique polishing process. .

  In order to solve the conventional problems, the present inventors have conducted intensive research. As a result, when the desired portion of the optical waveguide is heated to a predetermined temperature, the portion of the optical waveguide is released from the processing strain, and in that state, the predetermined bending is performed. When bending with a radius, we find that bending is performed without any strain. We find that releasing this strain also affects the refractive index difference of the fiber. At the same time as the formation of the part, the difference in the refractive index of the part to be heated is changed to reduce the loss of optical transmission due to bending. In addition, the core diameter is changed at the same time as the refractive index change, and the refractive index change at the heating target part and the parameter change due to the core diameter change ensure the optical transmission efficiency in the bent part and maintain the single mode optical fiber condition. It was decided to.

For this reason, in order to solve the above-mentioned problem, the optical waveguide of the present invention is heated to the part to be heated of the optical waveguide having the core and the clad covering the core, so that the processing strain is released. A bent portion is formed by bending the portion to be heated that has been shifted to a curved shape with a predetermined bending radius, and the bent portion is the optical waveguide that has been shifted to the processing strain state,
The difference in refractive index and physical size between the core and the clad of the bent part are changed by heating the part to be heated.
The optical waveguide of the present invention is preferably characterized in that the refractive index difference between the core and the clad in the bent portion of the optical waveguide is larger than that before heating, and the diameter of the core is reduced.

  The optical waveguide of the present invention preferably functions as a single mode optical fiber in which the refractive index difference between the core and the clad before heating the optical waveguide is 0.2% or more and 2% or less, and the heating of the optical waveguide is performed. By heating the target portion, the difference in refractive index between the core and the clad in the heating target portion becomes larger than that before heating, and the diameter of the core becomes smaller.

  In the optical waveguide according to the present invention, preferably, a difference in refractive index between the core and the clad in the bent portion of the optical waveguide is larger by 0.2% or more and 2% or less than before heating, The difference in refractive index between the core and the clad changes from 0.4% to 4%, and the diameter of the core changes small to maintain a single mode condition by the change in the refractive index difference. And

The optical waveguide of the present invention is preferably characterized in that the bending radius of the optical waveguide is 5.0 mm or less.
The optical waveguide module of the present invention is characterized in that a plurality of optical waveguides are arranged in an array, and at least a part of the plurality of optical waveguides is fixed by a fixing member having a positioning mechanism.
The optical waveguide module of the present invention is preferably characterized in that the optical waveguide is fixed in a state of being wired on one sheet.

The optical waveguide module of the present invention is preferably an optical waveguide module in which the optical waveguide is fixed in a state of being wired between at least two sheets.
The optical waveguide module of the present invention preferably includes a plurality of the optical waveguides, and the plurality of optical waveguides are fixed in a wired state.
In the optical waveguide module of the present invention, preferably, the material of the sheet is a flexible material.

The method of manufacturing an optical waveguide of the present invention heats a heating target portion of an optical waveguide having a core and a clad covering the core,
The heating target portion of the optical waveguide is shifted to a processing strain release state,
Bending part is formed by bending the part to be heated that has shifted to the processing strain release state in a curved shape with a predetermined bending radius,
The bent portion transitions to the processing strain state,
The difference in refractive index and physical size between the core and the clad of the bent part are changed by heating the part to be heated.

  According to the present invention, even if a bent portion is formed by bending with heating at a small radius, the loss of optical transmission due to the bending is small, and the mode field diameter is large except for the bent portion, even if there is no high-precision alignment. Connection loss can be reduced, and a large amount of return loss can be obtained by oblique polishing of the end surface at a small angle.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a preferred embodiment of the optical waveguide of the present invention. In FIG. 1, the optical waveguide 1 and the bending part manufacturing apparatus 200 of this optical waveguide 1 are shown.
An optical waveguide 1 shown in FIG. 1A is, for example, a quartz optical fiber, and has a constant refractive index difference Δ1 between the core and the clad over the entire length. The optical waveguide 1 is a single mode optical fiber having a core 2 and a clad 3 covering the core 2. The outer diameter D of the cladding 3 of the optical waveguide 1 is, for example, 125 μm.

  The linear optical waveguide 1 shown in FIG. 1 (A) forms the bent portion 10 by heating as shown in FIG. 1 (B) using the bent portion manufacturing apparatus 200 shown in FIG. As illustrated in FIG. 1B, the bending portion manufacturing apparatus 200 includes two electrodes 4 and 5 and a control unit 6, and the control unit 6 energizes the electrodes 4 and 5 to provide electrodes 4 and 5. Arc discharge 7 is formed between the two. The arc discharge 7 is applied to the heating target portion 9 of the linear optical waveguide 1 to form a bent portion 10 as shown in FIG.

  When the desired portion 9 to be heated of the linear optical waveguide 1 is heated by the arc discharge 7, the portion 9 to be heated is heated at a temperature in the range from the bending point to the softening point, and the optical waveguide 1 is heated. The portion 9 shifts to a machining strain release state. And the part 9 to be heated that has shifted to the work strain release state is bent into a curved shape with a predetermined bending radius R shown in FIG. 2 to form a bent portion 10, and the bent portion 10 shifts to the work strain state. When the bent portion 10 is in a working strain state, the difference in refractive index between the core 2 and the clad 3 and the physical size of the bent portion 10 change due to the heating target portion 9 being heated. In this case, the difference in refractive index between the core 2 and the clad 3 in the bent portion 10 of the optical waveguide 1 becomes larger after heating than before heating, and the diameter S of the core 2 becomes smaller after heating than before heating. Yes.

  At this time, the bent portion 10 of the optical waveguide 1 is bent at a high temperature, and after being bent, the bent portion 10 is moved to a room temperature environment, so there is no distortion due to bending. That is, the bent portion 10 of the optical waveguide 1 is processed so that the bent state becomes the initial state. When the optical waveguide 1 is deformed from the processed state after processing, distortion occurs and breaks. However, when the bent portion 10 is processed, the used state does not cause distortion and does not break. However, when the bent portion 10 is returned to a linear shape, distortion occurs and breaks. Eventually, by selecting whether the initial strain release state is a straight state or a bent state, it is possible to avoid breakage due to strain when the optical waveguide 1 having a desired shape is formed.

In the optical waveguide 1 according to the embodiment of the present invention, the purpose is to reliably and easily convert the direction of the optical waveguide in a minute space. Therefore, the state for conversion is set in advance so that the initial strain release state is obtained. Breaking the optical waveguide 1 is avoided by processing the bent portion 10. The optical waveguide 1 according to the embodiment of the present invention can change the waveguide direction of light by 90 degrees by using a small bending portion 10 to reduce bending loss. The bending radius R of the optical waveguide 1 is preferably 5 0.0 mm or less. As described above, by setting the bending radius R to 5.0 mm or less, the optical waveguide 1 can be easily arranged indoors or in a narrow space where arrangement is limited.

  The diameter (outer diameter) D of the optical waveguide 1 is preferably 50 μm or more, and the bending radius R is preferably 5.0 mm or less. That is, it is physically impossible to simply bend the bending radius R at 50 μm with respect to the optical waveguide 1 having a diameter D of 50 μm. In addition, since it is not easy to handle an optical waveguide having a diameter D of less than 50 μm, the minimum diameter of the optical waveguide 1 is regulated to, for example, 50 μm to ensure ease of handling, and the numerical value of the bending radius R is In this structure, the bending is physically realized by setting the optical waveguide 1 to be 10 times the minimum diameter.

  In addition, as a preferable example, the diameter D of the optical waveguide 1 is 125 μm because the outer diameter is compatible with a typical optical waveguide that is generally used at present. The range can be greatly expanded. Further, by setting the bending radius R to 5.0 mm or less, the advantage of adopting the optical waveguide manufacturing method of the present invention is utilized. That is, when the bending radius R exceeds 5.0 mm, when a small-diameter optical fiber is used, the bending radius R does not lead to breaking strain, and processing strain relief processing in the embodiment of the present invention is not required. In some cases, if the bending radius R is 5.0 mm or less, even the optical waveguide 1 having a minimum diameter D of 50 μm that does not become difficult to handle requires processing strain relief processing.

Preferably, the optical waveguide 1 functions as a single mode optical fiber in which the refractive index difference between the core 2 and the clad 3 before heating the optical waveguide 1 is 0.2% or more and 2% or less, and the optical waveguide 1 is heated. By heating the portion 9, the difference in refractive index between the core 2 and the clad 3 of the heating target portion 9 becomes larger after heating than before heating, and the diameter S of the core 2 becomes smaller after heating than before heating. Here, if the refractive index difference between the core 2 and the clad 3 before heating the optical waveguide 1 is less than 0.2%, the optical confinement as the optical waveguide is weak, and light leaks due to slight bending or lateral pressure. This is not preferable because it tends to occur.
If the refractive index difference between the core 2 and the clad 3 before heating the optical waveguide 1 exceeds 2%, the optical confinement as the optical waveguide is strong and strong against bending and lateral pressure, but the mode field diameter is small. For example, in connection that requires positioning such as connector connection, high-accuracy positioning is required. If the accuracy is poor, a large connection loss is generated, which is not preferable.

The difference in refractive index between the core 2 and the clad 3 of the bent portion 10 of the optical waveguide 1 becomes larger by 0.2% or more and 2% or less after heating than before heating. The refractive index difference of the clad 3 changes from 0.4% to 4%, and the diameter S of the core 2 changes small enough to maintain the single mode condition by changing the refractive index difference. Here, if the refractive index difference between the core 2 and the clad 3 of the bent portion 10 is less than 0.4%, it is difficult to cope with the bending radius at R = 5.0 mm or less, and a large bending loss is generated. Absent.
Further, if the refractive index difference between the core 2 and the clad 3 of the bent portion 10 exceeds 4%, it is necessary to make the core diameter as small as several μm or less in order to maintain the single mode condition. Exceeding% results in a multimode condition, which is also undesirable because it causes a large bending loss and loss due to mode mismatch.

As an example, the refractive index of the portion 9 to be heated that has shifted to the processing strain release state is 0.7% before heating, but is changed to 1.7% by heating. The core diameter S was about 7 μm before heating, but was reduced to about 4 μm after heating.
FIG. 3 shows how the refractive index changes before and after heating the portion 9 to be heated and the diameter S of the core 2. In FIG. 3, the vertical axis indicates the change Δn in the refractive index of the heating object 9, and the horizontal axis indicates the diameter S of the core 2.

Further, the single mode condition is maintained in the bent portion 10 and the remaining portion of the optical waveguide 1 excluding the bent portion 10, and the optical waveguide 1 includes the bent portion 10 corresponding to the heating target portion 9 and the bent portion 10. In combination with the non-heated target part, optical transmission in a single mode is possible.
In this embodiment, the bending radius R is larger than 5.0 mm, for example, about 1.0 mm, and the optical transmission loss accompanying bending is about 0.2 dB. As a comparative example of the present invention, if the refractive index difference of the heating target portion 9 and the diameter S of the core 2 are not changed by heating of the heating target portion 9, the optical transmission loss due to the bending of the bending portion 10 is It is several tens dB or more and cannot be used as an optical transmission line.

The return loss is about −37 dB when the end face of the optical waveguide 1 is polished by 8 degrees. If all the non-heated portions of the optical waveguide 1 other than the heating target portion 9 have the same refractive index difference and the diameter S of the core 2 as those after the heating, the return loss is reduced even if the 8 degree polishing process is performed. Only about -24dB can be obtained.
In this embodiment, the refractive index profile of the core 2 and the clad 3 is a step index type, and the core 2 is made of pure SiO 2 that is not doped with anything. The refractive index is lower than. This fluorine-doped region is a portion having a diameter of about 100 μm, and the outside thereof is made of pure SiO 2 up to a diameter of 125 μm, and the portion up to the diameter of 100 μm functions as the cladding 2.

  In the optical waveguide 1 according to another embodiment of the present invention, the diameter D of the optical waveguide 1 is 80 μm, and the internal refractive index difference, the change in the refractive index difference after heating, and the change in the core diameter are equivalent. It is. However, in the optical waveguide 1 having a diameter D of 125 μm, the outer side from the core 2 was a fluorine-doped region up to a diameter of 100 μm and the outer side was pure SiO 2. In the optical waveguide 1 having a diameter D of 80 μm, the outer side from the core 2 was outside. All of them have a fluorine-doped cladding 3 up to a diameter of 80 μm. The optical waveguide 1 having a diameter D of 80 μm is characterized in that since the outer diameter is smaller than that of the optical waveguide 1 having a diameter D of 125 μm, mechanical distortion with respect to bending is small and it is difficult to break.

4 and 5 show an embodiment of the optical waveguide of the present invention.
Since these optical waveguides are formed by connecting a plurality of types of optical waveguides having different refractive index differences, they can also be called optical waveguide modules.
The optical waveguide (optical waveguide module 70) 1 of FIGS. 4 and 5 is different from the optical waveguide 1 shown in FIG. 2 in that a plurality of types of optical waveguides 1 having different refractive index differences are connected in series by the fusion splicing portion 50. This is an example of connection.

The optical waveguide module 70 in FIG. 4 is configured by connecting one first optical waveguide 1-1 and one second optical waveguide 1-2 in series. In the first optical waveguide 1-1, for example, the refractive index difference Δ1 between the core and the cladding is in the range of 0.8% to 3.5%, preferably the refractive index difference Δ1 is 1.0% to 3.0%. Is within the range. In the second optical waveguide 1-2, for example, the refractive index difference Δ2 between the core and the clad is 0.2% or more. The first optical waveguide 1-1 and the second optical waveguide 1-2 are fused and connected using a fusion splicing portion 50.
The fusion spliced portion 50 is heated to reduce the mismatch between the refractive index differences Δ1 and Δ2 between the core and the clad and the mismatch of the mode field diameter, and the heated portion 9 of the optical waveguide 1-1 is heated to be a bent portion. 10 is formed.

  In the optical waveguide module 70 of FIG. 4, since the optical waveguides 1-1 and 1-2 having a high refractive index difference are used, the equivalent refractive index of the core or cladding is equal to the equivalent refractive index of the core or cladding of a general optical waveguide. Is different. Further, since the refractive index difference Δ is also different, there is a difference between the mode field diameter of a general optical waveguide and the mode field diameter of the optical waveguide used in the optical waveguide direction changing portion of the present invention. When objects having different refractive indexes are brought into contact with each other and an optical signal is passed through that portion, light is reflected at the boundary portion of the refractive index. This is a phenomenon that must be avoided in optical communication. Generally, the return loss is required to be 50 dB or more.

  In addition, when devices having different mode field diameters are connected to each other, a connection loss due to a diameter difference occurs at the connection portion. Although the mode field diameter of a general optical waveguide varies depending on the wavelength used, it is about 10 μm, and the mode field diameter of the optical waveguide 1-1 used for the bent portion 10 which is an optical waveguide direction changing portion is about 3 μm. If the connection is made with this diameter difference, the connection loss is 5 dB or more. In order to facilitate connection with an external device or a laser generator, it is effective to connect a general optical fiber and an external device, and then connect to an optical waveguide module. Therefore, in order to reduce these reflection attenuation and connection loss, the refractive index difference Δ1 between the core and the clad is in the range of 0.8% to 3.5%, preferably 1.0% to 3.0%. The first optical waveguide 1-1 within the range and the second optical waveguide 1-2 in which the refractive index difference Δ2 between the core and the clad is 0.2% or more are fusion spliced to form a fusion spliced portion. 50 is heated to reduce the mismatch of the refractive index difference Δ between the core and the clad and the mismatch of the mode field diameter. This increases the return loss and suppresses connection loss. By this method, the return loss was 50 dB or more, and the connection loss was about 0.2 dB.

  In the embodiment of FIG. 4, an optical fiber having a single-mode optical waveguide mode with a refractive index difference Δ1 of 2.5% and a refractive index difference Δ1 of 2.5% when the diameter D is 80 μm and the bending radius R is 1 mm is 90 °. In this case, one side of the optical fiber is fused and connected to an optical fiber having a diameter D of 80 μm, a refractive index difference Δ2 of 0.35%, and an optical waveguide mode depending on the used wavelength, and a single mode is used. Heating with a burner reduced the refractive index difference Δ mismatch and mode field diameter mismatch. The wavelength used is 1.3 μm. According to the measurement results, the return loss was 50 dB or more, and the connection loss was 0.2 dB.

  In another embodiment of FIG. 5, the optical waveguide module 71 is configured by connecting one first optical waveguide 1-3 and two second optical waveguides 1-4 in series. In the first optical waveguide 1-3, for example, the refractive index difference Δ1 between the core and the clad is in the range of 0.8% to 3.5%, preferably in the range of 1.0% to 3.0%. . In the second optical waveguide 1-4, for example, the refractive index difference Δ2 between the core and the clad is 0.2% or more. The first optical waveguide 1-3 and the second optical waveguide 1-4 are fusion spliced, the fusion spliced portion 50 is heated, the mismatch of the refractive index difference Δ between the core and the clad, and the mode field diameter The bending portion 10 is formed by reducing the mismatch and heating the heating target portion 9 of the optical waveguide.

In the optical waveguide module 70 of FIG. 4, an optical waveguide compatible with the characteristics of a general optical waveguide is fused and connected only to one side of the optical waveguide direction changing portion, and the fusion-bonded portion 50 is heated to thereby change the refractive index difference Δ1. , Δ2 mismatch and mode field diameter mismatch. On the other hand, in the embodiment of FIG. 5, a second optical waveguide 1-4 compatible with the characteristics of a general optical waveguide is fused and connected to both ends of the first optical waveguide 1-3. By heating the fusion splicing portion 50 at the place, the mismatch of the refractive index differences Δ1, Δ2 and the mismatch of the mode field diameter are reduced. This facilitates connection with an external device on either side of the optical waveguide direction changer.

Embodiments in 80μm diameter D is in Fig 5, to the bending radius R is bent 90 degrees at 1 mm, ₁ 2.5% difference in refractive index delta, using an optical fiber optical waveguide mode by using wavelength is single mode Then, an optical fiber having a diameter D of 80 μm, a refractive index difference Δ ₂ of 0.35%, and an optical waveguide mode depending on the wavelength used is a single mode on both sides, and the fusion splicing portion 50 is formed with a gas burner. By heating, the mismatch of the refractive index differences Δ1, Δ2 and the mismatch of the mode field diameter were reduced. The wavelength used is 1.3 μm. According to the measurement results, the return loss was 50 dB or more, and the connection loss was about 0.4 dB.

6 and 7 are views showing a preferred embodiment of the optical waveguide module of the present invention.
The optical waveguide module 100 shown in FIGS. 6 and 7 is formed by arraying a plurality of optical waveguides 1 and fixing them with a fixing member 120. Thereby, the plurality of optical waveguides 1 can collectively convert the optical waveguide direction by 90 degrees. Since the input / output portion of the optical waveguide module 100 is an optical waveguide whose characteristics are compatible with those of a general optical waveguide, it is possible to connect the external device with good characteristics.
In this embodiment, for example, the fixing means 120 has the positioning mechanism 130 so that the optical waveguide 1 having a diameter of 125 μm and a refractive index difference Δ ₁ of 2.5% is parallel. The positioning mechanism 130 includes a plurality of positioning holes 131. In each optical waveguide 1, the optical waveguide direction is converted by 90 degrees from the input side end portion to the output side end portion. The fixing means 120 is a rectangular parallelepiped block, and has a hole 150 formed therein. Each hole 150 is inserted with a pin 140 for mechanically fixing to other members. Both the input-side end face and the output-side end face, which are polishing end faces of each optical waveguide 1, are polished at an angle of 4 degrees with respect to the 90-degree plane.

FIG. 8 shows another preferred embodiment of the optical waveguide module of the present invention.
When the optical waveguide module 300 is manufactured, two optical waveguides 1 and two sheets 350 are used as an example. Two optical waveguides 1 are arranged in two sheets 350. The refractive index difference Δ1 between the core and the clad of each optical waveguide 1 arranged in the two sheets 350 is set within a range of 0.8% to 3.5%, for example.
In the embodiment of FIG. 8, an optical fiber having a general outer diameter of 125 μm for the outer diameter of the glass portion and 250 μm for the outer diameter of the coating is used, but the refractive index difference Δ ₁ between the core and the clad is 2.5%. An optical waveguide having a very large refractive index difference Δ1 is used, which is different from about 0.3% which is the refractive index difference Δ1 of a typical single mode optical fiber.

  In order to bend mechanically small, the diameter D of the glass portion may be made smaller, but if the diameter D is made too small, the light trapped in the core will escape because the cladding is too thin, Causes optical transmission loss. Therefore, the transmission loss can be suppressed by setting the cladding diameter, that is, the outer diameter of the optical fiber to at least 10 times the mode field diameter.

In the embodiment of FIG. 9, the optical waveguide 1 is fixed by using one sheet 350 instead of using two sheets 350.
The material of the sheet 350 shown in FIG. 8 and FIG. 9 is a flexible material, such as polyimide, polyethylene terephthalate, low density or high density polyethylene, polypropylene, polyester, nylon 6, nylon 66, Films such as ethylene-tetrafluoroethylene copolymer, poly-4-methylpentene, polyvinylidene chloride, plasticized polyvinyl chloride, polyether ester copolymer, ethylene-vinyl acetate copolymer, and flexible polyurethane are used.

FIG. 10 shows yet another preferred optical waveguide module 400 of the present invention.
FIG. 10 shows an example in which a plurality of optical waveguides 1 are wired along the wall portions 802 and 803 using the fixing means 120 in the corner portion 801 of the room of the building 800. Thus, when the optical waveguide 1 is wired in the corner portion 801 of the room, it is necessary to secure several cm as the minimum bending radius of the optical waveguide 1, but the optical waveguide module 400 according to the embodiment of the present invention is used. By using this, the size of the fixing means 100 of the optical waveguide module 400 can be 1 cm or less, and the wiring for optical transmission at the corner portion 801 can be bent by 90 degrees.

FIG. 11 shows yet another preferred optical waveguide module 300 of the present invention.
FIG. 11 is also referred to as an electric / optical fusion board, and has an optical waveguide module 300 sandwiched between two electric circuit boards 501 and 501, for example. The optical waveguide module 300 enables the electric circuit boards 501 and 501 to transmit light.
In the optical waveguide 1 according to the embodiment of the present invention, the heating target portion 9 of the optical waveguide 1 having the core 2 and the clad 3 covering the core 2 is heated to shift to the processing strain released state, and then to the processing strain released state. A bent portion 10 is formed by bending the portion 9 to be heated in a curved shape with a predetermined bending radius, and the bent portion 10 is shifted to a working strain state. The difference in refractive index and physical size between the core 2 and the clad 3 of the bent portion 10 are changed by heating the portion 9 to be heated.

  In the embodiment of the present invention, the refractive index difference between the core 2 and the clad 3 in the bent portion of the optical waveguide 1 becomes larger than before heating, and the diameter of the core 2 becomes smaller. As a result, even if the bent portion 10 is formed by bending with a small bending radius R, the loss of optical transmission by the bent portion 10 is small, and the mode field diameter is large except for the bent portion 10, and high-precision alignment is achieved. Connection loss can be reduced even if there is no gap, and a large amount of return loss can be obtained by oblique polishing of the end face at a small angle.

  In the embodiment of the present invention, the optical waveguide 1 functions as a single mode optical fiber in which the refractive index difference between the core 2 and the clad 3 before heating is 0.2% or more and 2% or less. By heating, the difference in refractive index between the core 2 and the clad 3 in the portion to be heated becomes larger than before heating, and the diameter of the core 2 becomes smaller. As a result, the optical waveguide 1 has a small optical transmission loss due to bending, a large mode field diameter other than the bent portion, and can reduce the connection loss even without high-precision alignment. It can be used as a single mode optical fiber capable of obtaining a large return loss.

  In the embodiment of the present invention, the refractive index difference between the core 2 and the clad 3 of the bent portion 10 of the optical waveguide 1 becomes larger by 0.2% or more and 2% or less than before heating, so that the core 2 of the bent portion 10 is increased. The refractive index difference between the clad 3 and the clad 3 changes from 0.4% to 4%, and the diameter of the core 2 changes small enough to maintain the single mode condition due to the change in the refractive index difference. As a result, the loss of optical transmission due to bending is small, the mode field diameter is large except for the bent part, and connection loss can be reduced even without high-accuracy alignment. Can definitely get

In an embodiment of the present invention, the bending radius of the optical waveguide is 5.0 mm or less. Thereby, an optical waveguide can be arranged even in a small space or corner.
In the optical waveguide module of the embodiment of the present invention, a plurality of optical waveguides 1 are arranged in an array, and at least a part of the plurality of optical waveguides 1 is fixed by a fixing member 120 having a positioning mechanism. As a result, even if a bent part is formed by bending with a small radius, the loss of optical transmission due to the bending is small, and the mode field diameter is large except for the bent part, and the connection loss is reduced even without accurate alignment. Can be reduced, and a large amount of return loss can be obtained by obliquely polishing the end surface at a small angle.

In the optical waveguide module of the embodiment of the present invention, the optical waveguide 1 is fixed in a state of being wired on one sheet 350. Thereby, the optical waveguide 1 can produce an optical waveguide module reliably using one sheet.
In the optical waveguide module according to the embodiment of the present invention, the optical waveguide 1 is fixed in a state of being wired between at least two sheets. Thereby, the optical waveguide 1 can produce an optical waveguide module reliably using two sheets.

The optical waveguide module according to the embodiment of the present invention has a plurality of optical waveguides, and the plurality of optical waveguides are fixed in a wired state. Thereby, a plurality of optical transmission lines can be obtained with certainty.
In the optical waveguide module according to the embodiment of the present invention, the material of the sheet 350 is a flexible material. Thereby, the flexibility of the optical waveguide module can be ensured, and the optical waveguide module can be reliably arranged according to the state of the part where the optical waveguide module is set.

By the way, this invention is not limited to the said embodiment, A various modified example is employable.
For example, when the bent portion manufacturing apparatus 200 in FIG. 1 forms the bent portion 10 in the optical waveguide 1, in order to heat the desired heating target portion 9 of the optical waveguide 1, heating is performed by arc discharge. Yes. However, the bending portion manufacturing apparatus 200 is not limited to this, and various means such as heating by a burner and heating by a furnace can be adopted.
In the illustrated optical waveguide 1, the light changing direction is 90 degrees, but the angle is not limited to 90 degrees, and an arbitrary angle can be selected.
In the illustrated embodiment, the refractive index difference is also referred to as an equivalent refractive index difference.

It is a perspective view which shows preferable embodiment of the optical waveguide of this invention. It is a figure which shows the example of a shape of the optical waveguide which has a bending part. It is a figure which shows the mode of this refractive index change before a heating object part is heated, and after a heating, and the mode of a change of the diameter of a core. It is a figure which shows preferable embodiment of the optical waveguide module of this invention. It is a figure which shows preferable embodiment of the optical waveguide module of this invention. It is a figure which shows preferable embodiment of the optical waveguide module of this invention. It is a figure which shows preferable embodiment of the optical waveguide module of this invention. It is a figure which shows preferable embodiment of the optical waveguide module of this invention. It is a figure which shows preferable embodiment of the optical waveguide module of this invention. It is a figure which shows preferable embodiment of the optical waveguide module of this invention. It is a figure which shows preferable embodiment of the optical waveguide module of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical waveguide 4,5 Electrode 6 Control part 9 Heating target part 10 Bending part 70,71 Optical waveguide module 100 Optical waveguide module 200 Bending part manufacturing apparatus 200 of the optical waveguide 1
300 optical waveguide module 301 optical waveguide module

Claims (11)

A heating target portion of an optical waveguide having a core and a clad covering the core is heated to shift to a processing strain release state, and the heating target portion transferred to the processing strain release state is bent in a curved shape with a predetermined bending radius. A bent portion is formed, and the bent portion is the optical waveguide that is shifted to the processing strain state,
An optical waveguide, wherein a difference in refractive index and a physical size between the core and the clad of the bent portion are changed by heating the portion to be heated. The optical waveguide according to claim 1, wherein a difference in refractive index between the core and the clad in the bent portion of the optical waveguide is larger than that before heating, and the diameter of the core is reduced. The refractive index difference between the core and the clad before heating the optical waveguide functions as a single mode optical fiber of 0.2% or more and 2% or less, and heating the heating target portion of the optical waveguide, The optical waveguide according to claim 2, wherein a difference in refractive index between the core and the clad in the heating target portion is larger than that before heating, and the diameter of the core is reduced. The difference in refractive index between the core and the clad in the bent portion of the optical waveguide is larger by 0.2% or more and 2% or less than before heating, so that the refractive index difference between the core and the clad in the bent portion is increased. 3. The light guide according to claim 2, wherein the light diameter changes from 0.4% to 4%, and the diameter of the core changes small to a size that maintains a single mode condition by the change in the refractive index difference. Waveguide. The optical waveguide according to any one of claims 1 to 4, wherein the bending radius of the optical waveguide is 5.0 mm or less. A plurality of the optical waveguides according to any one of claims 1 to 5 are arranged in an array, and at least a part of the plurality of optical waveguides is fixed by a fixing member having a positioning mechanism. A featured optical waveguide module. 6. An optical waveguide module, wherein the optical waveguide according to claim 1 is fixed in a state of being wired on a single sheet. 6. An optical waveguide module, wherein the optical waveguide according to claim 1 is fixed in a state of being wired between at least two sheets. 9. The optical waveguide module according to claim 7, comprising a plurality of the optical waveguides, wherein the plurality of the optical waveguides are fixed in a wired state. The optical waveguide module according to any one of claims 7 to 9, wherein a material of the sheet is a material having flexibility. Heating a heating target portion of an optical waveguide having a core and a clad covering the core;
The heating target portion of the optical waveguide is shifted to a processing strain release state,
Bending part is formed by bending the part to be heated that has shifted to the processing strain release state in a curved shape with a predetermined bending radius,
The bent portion transitions to the processing strain state,
A method of manufacturing an optical waveguide, wherein a difference in refractive index and a physical size between the core and the clad in the bent portion are changed by heating the portion to be heated.

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