JPS5960411A - Connecting method of optical fiber - Google Patents

Abstract

PURPOSE:To connect polarized-wave conservative optical fibers together while their main axes are aligned to each other, and to propagate light while their planes of polarization are held, by pressing one of two main axes and a slanting end surface against each other and making the connection. CONSTITUTION:An elliptic core type polarized wave conservative optical fiber 1 has a core and an end surface 12. The end surface 12 has main axes 10 and 11 and is cut or polished slantingly to the main axis 10. When polarized wave conservative optical fibers 3 and 3' having slanting surfaces are connected together, the end surfaces are pressed against each other, and heated and welded by discharge arcs 5 and 5 of discharge electrodes 4 and 4'. Two axes of the fibers are aligned to each other by pressing the end surfaces against each other, so they are connectable at a connection point without disordering the planes of polarization. In addition, deterioration in S/N ratio is prevented by shifting two main axis positions at the connection point.

Description

[Detailed description of the invention] The present invention relates to a method for connecting polarization maintaining optical fibers.

As is well known, optical fibers have the following characteristics: light weight, small diameter, and excellent flexibility, but polarization-maintaining optical fibers propagate light while maintaining the plane of polarization in the direction of its principal axis. So even human world signal transmission is possible. However, in conventional optical fiber splicing technology, a method has been used in which the end face of the fiber is cut or polished perpendicular to the longitudinal direction of the fiber, and then the fiber is inserted and fixed into a fusion splice or a sleeve. Even if this technique is used for a holding optical fiber, it is impossible to make the two principal axes of the fiber coincide, and as a result, the plane of polarization is not maintained at the connection point, and the two principal axes of the fiber are misaligned. If the advantages of fiber were compromised, there were also disadvantages.

The present invention involves cutting or polishing the end faces of a pair of polarization-maintaining optical fibers to be connected so that they are inclined to one of the two main axes, and connecting both end faces of the pair of fibers after they are in contact with each other. Its purpose is to align the main axes of the pair of fibers to be connected and to maintain the plane of polarization at the connection point.

FIG. 1 (, ) is a perspective view of one embodiment of the present invention, and the first
Figure (b) is a cross-sectional view taken along line 5-A' in Figure 1 (a), where l is an elliptical core polarization-maintaining optical fiber, 2 is a core,
10.11 is the main axis, and 12 is the end face.

The end face is cut or polished so as to be inclined with respect to the main axis 10.

For connection, as shown in FIG. 2, polarization-maintaining optical fibers 8.3' with end faces formed in the same manner as described above are pressed so that their end faces are in contact with each other, and the discharge arc 5 of Group 1jL electrode 4.4' is connected. .5' to heat and fuse. By pressing the end faces together, the two main axes of the fibers coincide, so that the connection can be made without disturbing the plane of polarization at the connection point.

FIG. 8 is a perspective view of another embodiment of the present invention for a polarization-maintaining optical fiber in the form shown in FIG. 1, and FIG. 8(b)
8(a) is a cross-sectional view taken along line A-A' in FIG.
8' is a portion in which the cladding is doped with boron or the like in order to apply stress to the core, 10° 11 is the main axis, and 12 is the end face.

FIG. 4 is a diagram showing one method for finding the principal axis of a polarization-maintaining optical fiber. 18 is a light source, 14V1 polarizer, 15 is an analyzer, 16 is a rotatable original fiber grip, 17
．． 17' is a power meter.

As the analyzer, for example, a Wollaston prism whose main axis is known in advance can be used. Next, the work procedure will be explained.

First, the polarizer is properly positioned and the source is made to enter the polarization-maintaining optical fiber 8. Initially, the principal axis of the polarization-maintaining optical fiber 8 and the principal axis of the polarizer 14 do not coincide, so light propagates in two principal axis directions in the optical fiber.

At the output end, the output light is split into two directions by the Wollaston prism of the analyzer, and the power of the output light is measured by power meters 17, 17', respectively.

Next, the analyzer 15 is rotated, a position where the power ratio of the output light at the current position of the polarizer 14 is maximized is found, and the analyzer 15 is fixed. When the polarizer 14 is further rotated and the main axes of the polarizer 14 and the polarization maintaining optical fiber 8 coincide, the power ratio of the output light at the current position of the analyzer 15 becomes maximum. When the analyzer 15 is rotated again so that the principal axes of the analyzer 15 and the polarization-maintaining optical inlet 8 coincide, the power ratio of the output light becomes maximum. In this way, the position of the principal axis of the polarization-maintaining optical fiber 8 at the output end can be found. FIG. 5 is another method diagram for finding the principal axis of the polarization-maintaining optical fiber. - As an example, a method for finding the principal axis of a stressed polarization-maintaining optical fiber will be described.

After cutting or polishing the end face of the polarization-maintaining optical fiber 6 to a mirror-like state, a mixture of F, H, and O, or HF is used.

Etch with a mixture of NH, FI HsO. 8 mol of Go is contained in the core 7 of the polarization-maintaining optical fiber 6.
%, the stress-applying portion 8.8' is doped with Go and B in a 12 mat ratio, so the etching rate differs due to the difference in composition, resulting in unevenness on the fiber end face.

Figure 5 (2L) is a 7-eyeper 6 that has been etched with a mixture of HF, H, and O. FIG. 5(b) shows a fiber 6 that has been etched with a mixed solution of HII', NHF, and H2O, and the stress-applying parts 8 and 8' are concave. Giving part 8
．． An example in which 8' is convex is shown. As is well known, the positions of the two main axes of the fiber are determined by the positional relationship between the stress applying part 8° 8' and the core 7, so the positions of the main axes can be found by looking at the shape of the end face after etching. . Once the main shaft is found, the fiber or fiber grip is marked and then cut or polished.

FIG. 6 is a schematic diagram of another embodiment of the invention, 8.8'
1 is a polarization-maintaining optical fiber having an end face formed thereon, and 18 is a sleeve. The sleeve 18 has an inner diameter equal to the outer diameter of the optical fiber 8.8', so that the fiber 8.8' can be inserted into the sleeve 18! As shown in FIG. 6(a), after inserting the fibers 8.8' into the sleeve 18, the fibers 8.8'
．． When 8' is rotated and pushed in, both fibers are brought together with their main axes naturally aligned, as shown in FIG. 6(b). Thereafter, the fiber 8.8 is attached using adhesive (not shown).
' and sleeve 18 are fixed, the connection is completed.

FIG. 7 is a schematic view of another embodiment of the present invention, in which 8 is a polarization-maintaining optical fiber, 19 is a sleeve for the core, and 20 is a sleeve for fixing the core. As is well known, optical fibers made of glass are easily damaged and broken, so extreme care must be taken when forming the end face. Therefore, as shown in FIG. 7(a), the polarization-maintaining optical fiber 8 is inserted into the sleeve 19 for the pressure core before forming the end face, and after being fixed with an adhesive (not shown), the fiber is tilted to the main axis of the end face. Let it form. The other fiber 8 also forms an end face in the same manner.

Next, as shown in Fig. 7(b), insert the core pieces into the sleeve 2.
When they meet within 0, the main axes of the fibers coincide. Thereafter, the connection is completed by fixing the polarization maintaining optical fiber 8.3' with an adhesive or the like (not shown).

FIG. 8 is a perspective view of another embodiment of the present invention, 8.8
' are polarization-maintaining fibers, 10, 11 . 10'.

11' is the main axis, and 12.12' is the end face. As shown in FIG. 8, the end face 12 of one polarization-maintaining optical fiber 3 is
The end face 12' of the other polarization-maintaining optical fiber/<8' is formed at an angle with the main axis 11'. Circular polarization maintaining optical fiber, <8
, 87 in the above-described manner, the main axes lO and ll
', 11 and 1 (1' match (7 is connected).

The 91st chapter shows the influence that differences in the coupling of the principal axes have on the output waveform. (Figure 9(a) shows the case where the principal axes lO and 1()' coincide, and Fig. 1(b) shows the case where the principal axes lO and 11' coincide.) As is well-known, for example, stress applying type In a polarization-maintaining optical fiber, the speed of light whose polarization plane coincides with the principal axis 10 is faster than the velocity of light whose polarization plane coincides with the other principal axis 11. Furthermore, the input light in the direction of the main axis 10 slightly oozes out in the direction of the main axis 11, and the waveform is distorted due to the difference in light speed. For example, the delay time in the main axis lO and the 11 direction due to passing through the fiber is τp7.
. .

The lengths of the two fibers to be connected are l□.

J, km, the delay time of the pulse in the direction of the two principal axes is ts:=l at the connection point and 1 at the output point.
0==(I!□+12)τ. Let the bit width of the input pulse be t, and if ti (t.), then 4 is extremely low.

On the other hand, as shown in FIG. 9(b), when the main axes 10 and 11' are aligned and connected, the pulse delay time at the connection point is
ti”'1τ, but the main axis reverses after passing the connection point, so the delay time at the output point is t0= (1
□-1!2) τ, and - deterioration can be prevented.

FIG. 10 shows another embodiment of the present invention, in which 8.8' is a polarization maintaining optical fiber, 21.21' is an interface between the core and Clarad, and 22 is a connection surface between the cores. Polarization maintaining optical fiber 8
The light that has propagated through the connection surface undergoes Fresnel reflection. The relationship is as follows, where α is the inclination angle of the end face, θ=9+l o
, −(χ.

Here, if the critical angle at which the reflected light escapes to the cladding is θ, then nl is the refractive index of the core θ), and n2 is the refractive index of the cladding.

Therefore, the condition for the end face inclination angle for the reflected light to escape to the cladding is Il.

If the end face inclination angle satisfies this condition, it is possible to prevent problems such as fluctuations in the oscillation frequency of the laser diode of the light source and fluctuations in the output power caused by reflected light in coherent transmission.

As explained above, the method for connecting optical fibers according to the present invention is to connect the end faces of the polarization-maintaining optical fiber so that they are inclined to one of the two main axes, and then connect the end faces of the fibers so that they are in contact with each other. By pressing and connecting a pair of fibers, it is possible to connect the fibers with their main axes aligned, so there is an advantage that light can be propagated while maintaining the plane of polarization.

Another feature is that deterioration of S/N can be prevented by changing the positions of the two main shafts at the connection point.

As explained in Kira, if the end face inclination angle is set above a certain angle, all Fresnel-reflected light can be emitted to the cladding, and in coherent transmission, the reflected light can cause fluctuations in the laser diode's oscillation frequency and increase the output power. It has the advantage of being able to solve problems such as fluctuations.

In particular, since the end face is formed in advance to match the main axis, when connecting using a sleeve, push the fiber in while rotating, and when the fiber stops moving,
It has the advantage of excellent workability in that the main axes naturally align.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of an embodiment of the present invention;
The figure is a perspective view of another embodiment of the present invention, FIG. 4 is a diagram of one method for finding the principal axis of a polarization-maintaining optical fiber, and FIG. 5 is another method for finding the principal axis of a polarization-maintaining optical fiber. Figure, 6th
The figure shows a schematic diagram of an embodiment of the present invention, and is a sectional view in the case of connection using a sleeve. Figure 7 shows an outline of another embodiment of the present invention, and Figure 7 0) shows a sleeve for a core. Fig. 7(b) is a perspective view of the case where the core is connected using a sleeve for fixing the core.
Id sectional view, FIG. 8 is a perspective view of another embodiment of the present invention, FIGS. Showing another example of
FIG. 4 is an explanatory diagram of a method for determining an end face angle for removing Fresnel reflection from an end face. 1.1'... Elliptical core polarization maintaining optical fiber, z, 2
'...Core, 8.8'...Polarization maintaining optical fiber4.
4'...discharge electrode, 5.5'...arc, 6...
Stressed thick polarization maintaining optical fiber? ... Core, 8.8
'... Boron-doped cladding part, 10.
10'...Main axis of polarization-maintaining fiber, 11.11'
...The other main axis of the polarization-maintaining optical fiber, 12.12'
... end face, 18 ... light source, 14 ... polarizer,
15... Analyzer, 1G... Optical fiber grip part,
17.1? '...Power meter, 18...Sleeve, 19.19'...Sleeve for core, 2o...S, Lee, B for fixing core, 21.21'...D and cladding boundary surface, 22... core connection surface. Patent applicant H book 1MJ bond Arashizume public corporation

Claims (1)

[Claims] 1. When a pair of polarization-maintaining optical fibers having two principal axes (10, 11) are to be connected, the end face (12) of the pair of fibers is connected to the principal axis (10, 10) of one polarization plane. )
1. A method for splicing optical fibers, which comprises cutting or polishing the fibers so as to be inclined with respect to the fibers, pressing the fibers so that their end surfaces are in contact with each other, and then fusion splicing the fibers. λ When connecting a pair of polarization-maintaining optical fibers having two principal axes (10, 11), the end face (12) of the pair of fibers is connected to the principal axis (10) of one polarization plane.
After cutting or polishing at an angle to the fiber pair, the fiber pair is placed in a sleeve (
1g) A method for connecting optical fibers, which comprises: inserting the fibers into the fiber B, pressing the fibers so that their end faces come into contact with each other, and then fixing the fibers B. & A pair of polarization-maintaining optical fibers P to be connected, each having an inner diameter equivalent to the outer diameter of the fiber (19
), the end faces of the pair of fibers are cut or polished so as to be inclined with respect to the main axis of one polarization plane, and a sleeve 7' (20 3. The method of connecting optical fibers according to claim 2, further comprising inserting the fibers into the fibers and pressing the fibers so that their end surfaces are in contact with each other, and then fixing the fibers. 4. In a pair of polarization maintaining optical fibers to be connected,
The end face of one fiber is located at the main axis of the two polarization planes (10,
The end face of the other fiber is cut or polished so as to be inclined with respect to one of the fibers (11) (10), and the end face of the other fiber is
2) The optical fiber connecting method according to claim 1, 2, or 8, characterized in that the optical fiber is cut or polished at an angle with respect to (2). (5) The inclination angle α of the end face of the seven eyeglasses makes the refractive index of the core n□
, when the refractive index of the cladding is e ng. 5. The optical fiber connection method according to claim 1, wherein