JP2007322628A - Method for splicing optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To splice single mode fibers having a different MFD without separately preparing a mechanism for converting the MFD, through reduced coupling loss. <P>SOLUTION: When the MFD of DCF1 and that of SMF2 are each w<SB>1</SB>and w<SB>2</SB>respectively, the MFD w<SB>3</SB>of a self-forming optical waveguide is set as w<SB>1</SB>>w<SB>3</SB>>w<SB>2</SB>if w<SB>1</SB>>w<SB>2</SB>is satisfied and as w<SB>1</SB><w<SB>3</SB><w<SB>2</SB>if w<SB>1</SB><w<SB>2</SB>is satisfied. For this purpose as necessary, between one end each of the DCF1 and SMF2, there is interposed a mixed solution 4 comprising a first photosetting resin for forming the core with a post-setting refractive index n<SB>core</SB>and a second photosetting resin for forming the clad with a post-setting refractive index n<SB>clad</SB>. The core 7 having a nearly uniform core diameter is formed by irradiating the other end of the DCF1 with a light beam having a wavelength for forming the core, while the clad 8 is formed by irradiating between one end each of the respective fibers with a light beam having a wavelength for forming the clad. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for connecting optical fibers, and more particularly to a method for connecting single mode fibers having different mode field diameters.

An optical fiber having a different mode field diameter (MFD), which is the diameter of the portion where the light intensity is 1 / e ² of the maximum value of the center of the core, for example, a dispersion compensating fiber (DCF) which is a kind of single mode fiber and a standard Although the outer diameter is the same as that of a typical single mode fiber (SMF), there is a difference of about twice as much with respect to MFD. When these are connected, a coupling loss shown in the following equation is generated in addition to a connection loss.

Coupling loss (dB) =-10 log Tw
Where Tw = [2 (w ₁ / w ₂ ) / {(w ₁ / w ₂ ) ² +1}] ² ,
w ₁ and w ₂ are optical fiber MFDs
Therefore, conventionally, in order to reduce the coupling loss due to these MFD mismatches, as shown in FIG. 1, between the DCF1 and the SMF2, the TEC (the MFD changes in a taper shape from one end to the other end). Thermally Expanded Core) The fiber 3 and the like were sandwiched (see Non-Patent Document 1).

  However, in the conventional connection method described above, a mechanism for converting the MFD, such as a TEC fiber, needs to be prepared separately, and the cost is increased by that amount. was there.

  On the other hand, self-forming optical waveguide technology has attracted attention as a supplement to an economical optical connection technology that is simpler and requires no alignment.

In the self-forming optical waveguide technology, the first and second photocurable resins having different refractive indexes after curing are filled between the ends of the fibers connecting these mixed solutions, and at least one of the optical fibers The light of the wavelength for the curing of the first photocurable resin is incident from the other end of the fiber to form the core portion, and then the wavelength for the curing of the second photocurable resin between the one ends of the fibers. The first photo-curing resin is formed from the other end of at least one of the optical fibers by forming a clad part by irradiating the first light, or filling the first photo-curing resin solution between the one ends of the fibers. The core portion is formed by injecting light having a curing wavelength, and then the first photocurable resin solution is removed from between the ends of each fiber and the second photocurable resin solution is removed. Filled and second photocurable resin between one end of each fiber By forming the cladding portion is irradiated with light of a wavelength for curing, and makes it possible a simple optical connection between the optical fiber (see Patent Document 1).
Japanese Patent No. 3444352 Kawakami, Shiraishi and Ohashi, “Optical Fibers and Fiber-Type Optical Devices”, Baifukan, 1996, pp. 201-225

  However, when the single-mode fibers having different MFDs are connected using the self-forming optical waveguide technology as described above, there is a problem that a coupling loss is generated together with a connection loss as described above.

  An object of the present invention is to connect single mode fibers having different MFDs by reducing the coupling loss by a self-forming optical waveguide technique without separately preparing a mechanism for converting the MFD.

In the present invention, in order to solve the above-mentioned problem, the first mode curable resin for forming the core part and the second light for forming the clad part having different refractive indexes after curing are used for the single mode fibers having different MFDs. When forming and connecting a self-forming optical waveguide between them using a curable resin, the mode field diameter of the self-forming optical waveguide formed by curing the first and second photocurable resins is appropriately set, Specifically, when the mode field diameter of the single mode fiber to be connected is w ₁ , w ₂ (w ₁ ≠ w ₂ ), the mode field diameter w ₃ of the self-formed optical waveguide is set to w ₁ > w _2. If w ₁ > w ₃ > w ₂ , w ₁ <w ₂ , w ₁ <w ₃ <w ₂ is set.

Because the coupling loss when two optical fibers are connected by a self-forming optical waveguide is the coupling loss between one optical fiber and the self-forming optical waveguide, and the coupling loss between the self-forming optical waveguide and the other optical fiber. And w ₁ = w ₃ > w ₂ , w ₁ = w ₃ <w ₂ , w ₁ > w ₃ = w ₂ , w ₁ <w ₃ = w ₂ A coupling loss exactly the same as when two optical fibers are directly connected without forming a waveguide, and when w ₁ <w ₃ > w ₂ or w ₁ > w ₃ <w ₂ is satisfied, w ₁ This is because a coupling loss larger than the coupling loss based on the difference between w and w ₂ occurs.

At this time, the sum of the two coupling losses is the smallest when the geometric mean, that is, w ₃ = w ₁ (w ₂ / w ₁ ) ^1/2
When the mode field diameter w ₃ in the self-formed optical waveguide is set in this way, it is optimum.

The mode field diameter w ₃ in the self-forming optical waveguide is the relative refractive index difference Δ between the core portion and the cladding portion in the self-forming optical waveguide, in other words, the refraction after curing of the first photocurable resin for forming the core portion. It can be controlled by the refractive index n _clad after the curing of the refractive index n _core and the second photo-curing resin for forming the cladding part.

Specifically, when the radius of the core part of the self-forming optical waveguide is a and the wavelength of the communication light to be used is λ,
w ₃ /2a=0.65+1.619ν ^−1.5 + 2.879ν ⁻⁶
ν = a (2π / λ) n _core (2Δ) ^1/2
Δ = (n _core ² −n _clad ² ) / 2n _core ²
The refractive index n _core after curing of the first photocurable resin for forming the core portion and the refractive index n _clad after curing of the second photocurable resin for forming the cladding portion are set so as to satisfy It ’s fine.

Here, the refractive index n _core after curing of the first photocurable resin for forming the core part and the refractive index n _clad itself after curing of the second photocurable resin for forming the cladding part are mainly photocured. Can be set by selecting the material of the adhesive resin and adjusting the curing temperature.

  The single mode fiber referred to in the present invention includes the standard single mode fiber (SMF) and dispersion compensation fiber (DCF) described above, as well as a core such as a dispersion shifted fiber (DSF) and a polarization maintaining fiber (PMF). Refers to an optical fiber having only one mode of light propagating through.

According to the present invention, when a self-forming optical waveguide is formed and connected between single mode fibers having mode field diameters w ₁ and w ₂ (w ₁ ≠ w ₂ ), the mode field diameter w of the self-forming optical waveguide is set. the _3, w _1> w if _{2 w 1> w 3> w} 2, w 1 < by setting the w ₁ <w ₃ <w ₂ if w _2, a single-mode fiber between the MFD different Thus, the connection loss can be reduced, and a conventional mechanism for converting the MFD such as a TEC fiber becomes unnecessary, and the cost can be reduced accordingly.

<Preparation>
When connecting single mode fibers having different MFDs by the optical fiber connection method of the present invention, [1] setting (calculation) of MFD of self-forming optical waveguide, [2] after curing of photocurable resin It is necessary to set (calculate) the refractive index of the light and select a photocurable resin and a light source that satisfy these settings.

[1] Setting (calculation) of MFD of self-forming optical waveguide
When a self-forming optical waveguide is formed and connected between single-mode fibers having MFDs w ₁ and w ₂ (w ₁ ≠ w ₂ ), the mode field diameter w ₃ of the self-forming optical waveguide is set to w ₁ > w If it is ₂ , w ₁ > w ₃ > w ₂ , and if w ₁ <w ₂ , w ₁ <w ₃ <w ₂ is set.

For example, when w ₁ = 5 μm and w ₂ = 10 μm, a coupling loss of about 1.94 dB occurs when connected as they are. At this time, when a w ₁ = 5 μm fiber and a w ₂ = 10 μm fiber are connected by a w ₃ = 8 μm self-forming optical waveguide, a w ₁ = 5 μm fiber and a w ₃ = 8 μm self-forming optical waveguide are obtained. And the coupling loss between w ₃ = 8 μm self-forming optical waveguide and w ₂ = 10 μm fiber is 0.214 dB, so the total coupling loss is 0.926 dB + 0.214 dB = 1.140 dB, and the coupling loss can be greatly reduced as compared with the case where the connection is made as it is.

Furthermore, the sum of the two coupling losses is the smallest when the geometric mean, that is, w ₃ = w ₁ (w ₂ / w ₁ ) ^1/2
When the mode field diameter w ₃ of the self-formed optical waveguide is set in this way, it is optimum. In the example above,
w ₃ = w ₁ (w ₂ / w ₁ ) ^1/2
= 5 (10/5) ^1/2
= 7.07 ...
Therefore, the optimum w ₃ is about 7.07 μm.

In this case, the coupling loss between the w ₁ = 5 μm fiber and the w ₃ = 7.07 μm self-forming optical waveguide is 0.503 dB, and the w ₃ = 7.07 μm self-forming optical waveguide and w ₂ = 10 μm coupling loss is 0.503 dB, so the total coupling loss is 0.503 dB + 0.503 dB = 1.006 dB, which is the lowest coupling loss.
[2] Setting of refractive index after photocuring resin is cured (calculation)
The mode field diameter w ₃ in the self-forming optical waveguide described above is the relative refractive index difference Δ between the core portion and the cladding portion in the self-forming optical waveguide, in other words, after the first photocurable resin for forming the core portion is cured. The refractive index n _core and the refractive index n _clad after curing of the second photo-curing resin for forming the cladding part can be controlled.

Specifically, when the radius of the core part of the self-forming optical waveguide is a and the wavelength of the communication light to be used is λ,
w ₃ /2a=0.65+1.619ν ^−1.5 + 2.879ν ⁻⁶
ν = a (2π / λ) n core (2Δ) 1/2
Δ = (n _core ² −n _clad ² ) / 2n _core ²
The refractive index n _core after curing of the first photocurable resin for forming the core portion and the refractive index n _clad after curing of the second photocurable resin for forming the cladding portion are set so as to satisfy It ’s fine.

For example, when the above-described self-formed optical waveguide with w ₃ = 7.07 μm is realized with the core portion radius a = 2.6 μm and the communication wavelength λ = 1.31 μm, the first photocuring property for forming the core portion is used. When the refractive index n _core after the resin is cured is n _core = 1.453, the refractive index n _clad after the curing of the second photocurable resin for forming the cladding portion is 1.4326 from the above formula.

The radius “a” of the core portion of the self-forming optical waveguide is formed with a diameter similar to that of the MFD of the fiber that enters the light having the curing start wavelength of the first photocurable resin for forming the core portion. The light for forming the core part may be incident from either a fiber having a large MFD or a fiber having a small MFD. For the reasons described above, the light is incident from a fiber having a large MFD or a fiber having a small MFD. In this case, the set values (calculated values) of the refractive indexes after curing of the first and second photocurable resins are different. The refractive index n _core of the core portion by considering the Fresnel reflection, the core and comparable connection to the fiber is preferable.

<Embodiment 1>
FIG. 2 shows an example of the case of connecting using a mixed solution of first and second photocurable resins having different curing start wavelengths in Embodiment 1 of the optical fiber connecting method of the present invention. In the figure, 1 is a dispersion compensating fiber (DCF), 2 is a single mode fiber (SMF), 4 is a mixed solution of a photocurable resin, 5 is a light source for forming a core part, and 6 is a light source for forming a cladding part. .

  A mixed solution 4 of a photocurable resin includes two types of photocurable resins whose refractive index and curing start wavelength (reaction wavelength) after curing are adjusted, that is, a first photocurable resin for forming a core part, and a clad It is a mixed solution containing the second photocurable resin for forming the part, and is prepared in advance. Examples of resin materials for the first and second photocurable resins include acrylic, epoxy, oxetane, and vinyl ether.

Here, adjustment of the refractive index after curing may be an arbitrary value for the refractive index before curing, but the refractive index n _core after curing of the first photocurable resin and the second photocurable resin. The first refractive index n _clad (where n _core > n _clad ) after curing is a value calculated in advance preparation, that is, a value that realizes an optimum mode field diameter w ₃ of the self-forming optical waveguide. And selecting a resin material of the second photocurable resin.

  Further, the adjustment of the curing start wavelength means that only the first curable resin starts the curing reaction by the light from the light source 5 for forming the core part, and the second curing is performed by the light from the light source 6 for forming the cladding part. This refers to selecting the resin materials of the first and second photocurable resins so that only the curable resin initiates the curing reaction. Unlike the refractive index after curing, the curing start wavelength itself may be an arbitrary value. Therefore, instead of selecting and adjusting the resin materials of the first and second photocurable resins, the light source for forming the core portion 5 and the wavelength of the light source 6 for forming the clad portion may be changed and adjusted.

  The light source 5 for forming the core part generates light having a wavelength at which only the first photocurable resin in the mixed solution 4 starts the curing reaction, and is either DCF1 or SMF2, for example, the other end of DCF1. Connected to.

In addition, the optical power of light emitted from one end of the fiber, which will be described later, into the mixed solution of the first and second photocurable resins or the first photocurable resin solution is in the first photocurable resin. If the optical power of the curing threshold is greatly exceeded, the core diameter of the formed core portion will not be uniform, and the mode field diameter w ₃ will be affected. Since the light power of the curing threshold varies depending on the type of the photocurable resin, the light source 5 is configured so that the optical power of the light emitted from one end of the fiber is the curing threshold in the first photocurable resin in the mixed solution 4. It is assumed that light of a power that does not greatly exceed the optical power of the light is generated. For example, when an acrylic resin is used as the first photocurable resin, 0.5 mW to 5 mW is preferable, and 1 mW is optimal.

  The light source 6 for forming the clad part generates light having a wavelength at which only the second photocurable resin in the mixed solution 4 starts the curing reaction, and is one end of each fiber (DCF1 and SMF2 here) described later. It arrange | positions so that between may be irradiated.

  FIG. 3 shows a connection process in the present embodiment. Hereinafter, the optical fiber connection method of the present invention will be described with reference to FIGS.

  First, as shown in FIG. 2 or FIG. 3 (a), DCF1 and SMF2 are arranged so that the ends to be connected are substantially opposed to each other with a predetermined gap therebetween, and the end faces of the ends of DCF1 and SMF2 are arranged. A photocurable resin mixed solution 4 is interposed therebetween.

  DCF1 and SMF2 are held by holding means (not shown), for example, holding means comprising a support base having a V-groove and a pressing plate for fixing the fiber to this base, and the above-described arrangement relationship is maintained until the end of the connection work. Shall. In addition, the relationship between the central axes of the fibers described above is only required to be maintained in the vicinity of one end to be connected, and it is needless to say that it is not necessary to have such a relationship in the entire length of each fiber. (This point is common to all the embodiments of the present invention).

  Further, as a specific method for interposing (filling) the mixed solution 4 between the end faces of the DCF 1 and the SMF 2, for example, the liquid is placed at a position where the ends of the DCF 1 and the SMF 2 of the support base constituting the holding means face each other. A reservoir depression is provided, and the mixed solution 4 may be dropped into the depression.

  Next, the core forming light source 5 connected to the other end of the DCF 1 is operated, and light having a wavelength for forming the core is incident from the other end. Then, light having a wavelength for forming the core part is emitted from one end of the DCF 1 into the mixed solution 4, whereby only the first photocurable resin in the mixed solution 4 reacts and cures, and FIG. 3 (b). As shown, a waveguide (core portion) 7 having a substantially uniform core diameter is formed between the end faces of the DCF 1 and the SMF 2.

  Next, after confirming that the core portion 7 is reliably formed between the end faces of the DCF 1 and the SMF 2, the light source 6 for forming the cladding portion is operated, and the gap between the ends of the DCF 1 and the SMF 2 is already formed. The waveguide portion is irradiated with light having a wavelength for forming a cladding portion. Then, only the second photocurable resin in the mixed solution 4 reacts and cures, and a clad portion 8 is formed around the core portion 7 as shown in FIG.

  As described above, a separate mechanism for converting the MFD is prepared by forming a self-forming optical waveguide having the optimum MFD in the connection between single mode fibers having different MFDs that will cause coupling loss if they are connected as they are. Therefore, it is possible to reduce the coupling loss and connect.

<Embodiment 2>
FIG. 4 shows a second embodiment of an optical fiber connecting method according to the present invention, in which a connection is made using a mixed solution of first and second photocurable resins having different curing times in place of the curing start wavelength. In the figure, the same components as those of the first embodiment are denoted by the same reference numerals. That is, 1 is a dispersion compensating fiber (DCF), 2 is a single mode fiber (SMF), 9 is a mixed solution of a photocurable resin, and 10a and 10b are light sources.

  The photo-curable resin mixed solution 9 includes two types of photo-curing resins in which the refractive index after curing and the time required for curing are adjusted, that is, the first photo-curing resin for forming the core and the clad-forming It is a mixed solution containing the second photocurable resin, and is prepared in advance.

Here, adjustment of the refractive index after curing may be an arbitrary value for the refractive index before curing, but the refractive index n _core after curing of the first photocurable resin and the second photocurable resin. The first refractive index n _clad (where n _core > n _clad ) after curing is a value calculated in advance preparation, that is, a value that realizes an optimum mode field diameter w ₃ of the self-forming optical waveguide. And selecting a resin material of the second photocurable resin.

In addition, the adjustment of the time required for curing is the time t1 from the start of curing by starting light irradiation from the light source in the first curable resin to the end of curing and the light irradiation from the light source in the second curable resin. The time t2 from the start of curing to the end of curing is
t1 <t2
The selection of the resin material of the first and second photo-curing resins so as to satisfy the above condition.

  The curing start wavelength is adjusted so that the curing reaction is started by light from the light sources 10a and 10b having the same wavelength in both the first and second photocurable resins.

  Both the light sources 10a and 10b generate light having a wavelength at which the first and second photocurable resins in the mixed solution 9 start a curing reaction. The light source 10a is either DCF1 or SMF2, for example, DCF1. The light source 10b is disposed so as to irradiate between one end of each fiber (DCF1 and SMF2 here) described later.

  As in the case of the first embodiment, the light source 10a is such that the optical power of the light emitted from one end of the fiber does not greatly exceed the optical power of the curing threshold value in the first photocurable resin in the mixed solution 9. It is assumed that light of such power is generated.

  FIG. 5 shows a connection process in the present embodiment. Hereinafter, the optical fiber connection method of the present invention will be described with reference to FIGS. 4 and 5.

  First, as shown in FIG. 4 or FIG. 5 (a), DCF1 and SMF2 are arranged so that one end to be connected to each other is substantially opposed with a predetermined gap therebetween, and the end faces of one end of DCF1 and SMF2 are arranged. A mixed solution 9 of a photocurable resin is interposed therebetween.

  Next, the light source 10a connected to the other end of the DCF 1 is operated, and light is incident from the other end. Then, light is emitted from one end of the DCF 1 into the mixed solution 9, thereby reacting and curing with the first and second photocurable resins in the mixed solution 9, but the first light in the mixed solution 9. The time required for curing is different between the curable resin and the second photocurable resin, and the time t1 required for curing the first photocurable resin is longer than the time t2 required for curing the second photocurable resin. Since it is shorter, the first photo-curable resin reacts more and cures, and as shown in FIG. 5B, the waveguide (core portion) has a substantially uniform core diameter between the end faces of the DCF1 and the SMF2. ) 11 is formed.

  Next, after confirming that the core portion 11 is reliably formed between the end faces of the DCF1 and SMF2, the light source 10b is operated, and the waveguide portion between the ends of the DCF1 and SMF2 is formed. Irradiate light. Then, similarly to the above, the first and second photo-curing resins in the mixed solution 9 also react and harden, and as shown in FIG. 5C, the hardened portion is the clad portion 12 between the DCF1 and the SMF2. However, since the molar concentration of the first photocurable resin is low due to the formation of the core portion 11 described above, a difference in refractive index is produced between the core portion 11 and the core portion 11 as a result.

  In addition, in order to obtain the relative refractive index difference as described above, the clad considering the molar concentration of the first photocurable resin for forming the core portion remaining in the mixed solution 9 at the end of the formation of the core portion 11 is taken into account. It is necessary to adjust the refractive index after curing of the second photocurable resin for forming the part.

  As described above, the same effect as in the first embodiment can be exhibited even in connection using a light source of one kind of wavelength.

<Embodiment 3>
FIG. 6 shows an example of the case where the optical fiber connection method of the present invention is used in Embodiment 3, where the first photocurable resin and the second photocurable resin are used separately, In the figure, the same components as those in the first and second embodiments are denoted by the same reference numerals. That is, 1 is a dispersion compensating fiber (DCF), 2 is a single mode fiber (SMF), 10a and 10b are light sources, and 13 and 14 are photocurable resin solutions.

  The photocurable resin solution 13 is a solution containing the first photocurable resin for forming the core portion, and the photocurable resin solution 14 is the second photocurable resin for forming the cladding portion. Each solution is prepared in advance.

Here, as in the first and second embodiments, the refractive index before curing may be any value, but the refractive index n _core after curing of the first photocurable resin and the second photocurable resin. The refractive index n _clad after curing (where n _core > n _clad ) is the value calculated in advance preparation, that is, the value that realizes the optimum mode field diameter w ₃ of the self-formed optical waveguide. The resin material of the 1st and 2nd photocurable resin shall be selected and adjusted.

  In this case, the curing start wavelength is adjusted so that both the first and second photocurable resins start the curing reaction by light from the light sources 10a and 10b having the same wavelength. It is not necessary to adjust the time required for this.

  The light sources 10a and 10b both emit light having a wavelength at which the first photocurable resin in the photocurable resin solution 13 and the second photocurable resin in the photocurable resin solution 14 start a curing reaction. The light source 10a is connected to either DCF1 or SMF2, for example, the other end of DCF1, and the light source 10b irradiates between one end of each fiber (DCF1 and SMF2 here) described later. Are arranged as follows.

  Similarly to the first and second embodiments, the light source 10a is configured such that the optical power of light emitted from one end of the fiber is equal to the curing threshold value in the first photocurable resin in the photocurable resin solution 13. It is assumed that light having a power that does not greatly exceed the optical power is generated.

  In practice, the solutions 13 and 14 are not simultaneously filled between the ends of each fiber, but both solutions are shown in FIG. 6 for convenience.

  FIG. 7 shows a connection process in the present embodiment. Hereinafter, the optical fiber connection method of the present invention will be described with reference to FIGS.

  First, as shown in FIG. 7 (a), DCF1 and SMF2 are arranged so that one ends to be connected are substantially opposed to each other with a predetermined gap therebetween, and light is transmitted between the end faces of one end of DCF1 and SMF2. The light source 10a connected to the other end of the DCF 1 is operated by interposing the curable resin solution 13, and light is incident from the other end. Then, light is emitted from one end of the DCF 1 into the solution 13, whereby the first photocurable resin in the solution 13 reacts and cures, and the waveguide has a substantially uniform core diameter between the end surfaces of the DCF 1 and the SMF 2. (Core part) 15 is formed.

  Next, after confirming that the core portion 15 is reliably formed between the end faces of the DCF1 and the SMF2, as shown in FIG. 7B, a photocurable resin is formed between the end faces of the one end of the DCF1 and the SMF2. The solution 13 is removed, and the light curable resin solution 14 is interposed instead, and the light source 10b is operated to irradiate light to the already formed waveguide portion between the ends of the DCF1 and the SMF2. . Then, the second photocurable resin in the solution 14 reacts and cures, and the clad portion 16 is formed around the core portion 15.

  As described above, the same effects as those of the first and second embodiments can be exhibited in the connection using the photocurable resin for forming the core part and the photocurable resin for forming the clad separately.

  In the present embodiment, the curing start wavelengths of the first and second photocurable resins may be different from each other. In this case, the wavelength of the light source 10a is set to cure the first photocurable resin. The resin material of the first and second photocurable resins is selected so as to match the start wavelength and the wavelength of the light source 10b matches the cure start wavelength of the second photocurable resin, or the light source 10a and The wavelength of 10b shall be adjusted.

Process diagram showing an example of a conventional method for connecting optical fibers having different MFDs The block diagram which shows Embodiment 1 of the connection method of the optical fiber of this invention Process drawing which shows Embodiment 1 of the optical fiber connection method of this invention The block diagram which shows Embodiment 2 of the connection method of the optical fiber of this invention Process drawing which shows Embodiment 2 of the connection method of the optical fiber of this invention The block diagram which shows Embodiment 3 of the connection method of the optical fiber of this invention Process drawing which shows Embodiment 3 of the optical fiber connection method of this invention

Explanation of symbols

  1: dispersion compensation fiber (DCF), 2: single mode fiber (SMF), 3: TEC fiber, 4, 9: mixed solution of photocurable resin, 5: light source for forming core part, 6: for forming cladding part 7, 11, 15: Waveguide (core part), 8, 12, 16: Clad part, 10a, 10b: Light source, 13, 14: Photocurable resin solution.

Claims (6)

Single mode fibers having different mode field diameters are bonded to each other using a first photocurable resin for forming a core part and a second photocurable resin for forming a clad part, which have different refractive indexes after curing. A method of forming and connecting a formed optical waveguide,
When the mode field diameters of the single mode fibers to be connected are w ₁ and w ₂ , the first photocurable resin for forming the core part and the second photocurable resin for forming the clad part are cured. the mode field diameter w ₃ of the self-forming optical waveguide to be formed is set to w _1> if _{w 2 w 1> w 3>} w 2, w 1 < if _{w 2 w 1 <w 3 <} w 2 An optical fiber connection method. The mode field diameter w ₃ of the self-forming optical waveguide is
w ₃ = w ₁ (w ₂ / w ₁ ) ^1/2
The optical fiber connection method according to claim 1, wherein: When the radius of the core portion of the self-forming optical waveguide is a and the wavelength of communication light to be used is λ, the refractive index after curing of the first photocurable resin for forming the core portion satisfies the following formula: The refractive index n _clad after curing of the second photo-curing resin for forming the n _core and the clad part is set. w ₃ /2a=0.65+1.619ν ^−1.5 + 2.879ν ⁻⁶
ν = a (2π / λ) n _core (2Δ) ^1/2
Δ = (n _core ² −n _clad ² ) / 2n _core ²
The optical fiber connection method according to claim 1 or 2. Using a first photocurable resin for forming a core part and a second photocurable resin for forming a clad part, wherein at least one of the curing start wavelength or the time required for curing is different,
Each single mode fiber is arranged so that one end of each single mode fiber is substantially opposed with a predetermined gap therebetween,
Interposing a mixed solution of the first and second photocurable resins between one end of each fiber;
Light from a light source having a wavelength corresponding to the curing start wavelength of the first photocurable resin is incident from the other end of one of the single mode fibers to cure the first photocurable resin to form the core portion. And
Forming a clad portion by irradiating light from a light source having a wavelength corresponding to the curing start wavelength of the second photocurable resin between one end of each fiber to cure the second photocurable resin. The optical fiber connection method according to any one of claims 1 to 3. Each single mode fiber is arranged so that one end of each single mode fiber is substantially opposed with a predetermined gap therebetween,
Interposing a solution of the first photocurable resin between one end of each fiber;
Light from a light source having a wavelength corresponding to the curing start wavelength of the first photocurable resin is incident from the other end of one of the single mode fibers to cure the first photocurable resin to form the core portion. And
Removing the first photocurable resin solution from between the ends of each fiber and interposing the second photocurable resin solution between the ends of each fiber;
Forming a clad portion by irradiating light from a light source having a wavelength corresponding to the curing start wavelength of the second photocurable resin between one end of each fiber to cure the second photocurable resin. The optical fiber connection method according to any one of claims 1 to 3. As a light source having a wavelength corresponding to the curing start wavelength of the first photocurable resin, the light is emitted from one end of the fiber into a mixed solution of the first and second photocurable resins or a solution of the first photocurable resin. The light source according to claim 4 or 5, wherein a light source that generates light having an optical power that does not greatly exceed an optical power of a curing threshold in the first photocurable resin is used. Fiber connection method.

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