JP2521526B2 - Optical cable - Google Patents

Description

TECHNICAL FIELD The present invention relates to an SZ slot type optical cable.

 Non-SZ conventional slotted optical cables are well known.

FIG. 6a is a conceptual diagram thereof, where 20 is the whole slot, 22 is its cylinder, and 24 is a groove. However, only one of the plurality of grooves 24 is shown as a single line having no width. In the following description, the groove 24 is also shown.

As shown in FIG. 6b, the optical fiber 10 or the optical fiber unit 12 is housed in the groove 24.

On the other hand, although the cross-sectional shape is the same, in order to facilitate the post-branch connection of the optical cable and to improve the productivity of the cable, as shown in FIG. 7a, the groove 24 is inverted right and left in the longitudinal direction. SZ cables are already known.

The present invention relates to an optical cable using the SZ slot.

[Prior Art] [1] Shape of Groove: FIG. 7b is a side view of the slot 20 shown in FIG. This is the case where the reversal angle is 2π (360 degrees), where 26 is the reversing part and 27 is the rotating part.

Further, the cylinder 22 of the slot 20 is connected to the reversing portion 26 by a bus bar.
FIG. 7c shows the shape of one cycle of the groove 24 when it is developed on a plane along the line 28 (FIGS. 7a and 7b).

This shape is usually a sine wave. The reason is that the groove is formed by the rotation of the die during slot extrusion, but when the rotation speed of the die is constant, the shape of the groove becomes a sine wave.

[2] When bent: In a normal slot type optical cable (non-SZ type, Fig. 6), when the cable is bent, the fiber in the groove moves.

That is, since there are not enough fibers on the inside of the bend and there is not enough fibers on the outside of the bend, the stress applied to the fibers is offset by moving the remaining fibers inside the bend to the outside of the bend.

[Problems to be Solved by the Invention] However, the normal SZ slot 20 (the groove shape in the developed view is a sine wave and the reversal angle is 2π) as described above is bent when bent as shown in FIG. The groove length inside (rotating part) is
Very short for the groove length on the outside of the bend (inversion).

That is, the fiber length inside the bend (rotating portion) is much shorter than the fiber length outside the bend (reversing portion).

This can be explained in more detail as follows.

For example, at the inverting section 26 shown by E in FIG. 7b,
If you bend it so that it is convex upward (so that the reversing part 26 is on the outside),
The lower side of the neutral surface 30 is the contraction side and the upper side is the extension side.

As shown on the right side of FIG. 7b, the surface of the cylinder 22 and the neutral surface 30
It intersects with π / 2 and 3π / 2 positions.

Therefore, in FIG. 7c, when the portion of π / 2 to π to 3π / 2 is hatched, this portion is on the contracted side below the neutral plane 30.

Here, the symbols A to I are added to the one pitch of the groove 24 in FIG. 7c as follows. That is, A and I on both sides of the pitch, E at the inversion part 26 (p / 2), B and H at the intersection of the π / 2 line, C and G at the intersection of the π line, and 3π / 2 line. Put D and F at the intersection of.

Looking at the range of A to E of the half cycle, the length BD of the groove 24 below the neutral surface 30 is shorter than the length (AB + DE) of the groove 24 above the neutral surface 30.

The reason is that while AB and DE are curved, BC and
This is because the CD is almost straight.

As described above, even if the excess fiber inside the bend moves to the outside, the fiber that is insufficient outside the bend cannot be offset.

Therefore, the fiber is pulled and pressed against the groove bottom and the groove wall, resulting in increased loss.

On the contrary, if the concave portion is bent upward at the reversal portion, the fiber becomes excessive and meanders in the groove. As a result, the loss is increased.

[Object of the Invention] In order to solve the above problems, a method for optimizing the trajectory of the slot groove in the longitudinal direction is proposed.

[Means for Solving the Problem] The length of the groove on the front half surface of the slot and the length of the groove on the back half surface are made equal (claim 1).

[Description] [1] Operation: When the length of the groove on the front half surface of the slot is equal to the length of the groove on the back half surface, when the cable is bent, the fiber on the neutral surface, the outer surface, and the inner surface is The stress applied to is offset by each inversion pitch, and no increase in loss occurs.

[2] Meaning of terms: The meanings of the front half and the back half of the slot are as follows.

That is, an arbitrary virtual plane including the central axis of the slot 20 has a front half surface on one side and a back half surface on the opposite side.

For example, in FIG. 7c, if the shaded portion is the back half surface, the other is the front half surface.

[3] Condition: The example of FIG. 7c is a case where the bending is performed so that the reversing part and the rotating part are separated.

However, in practice, the cable can be bent in all directions.

Therefore, no matter which direction the cable is bent, it is sufficient if the stress of the fiber can be offset between the outside and the inside of the neutral plane. That is, no matter which direction the cable is bent, the length of the groove must be the same on the outside and inside of the neutral plane.

 The requirements for that are described below.

First, the groove length is mathematically analyzed, and then a concrete example is described.

[Analysis of Shape of Slot Groove] (1) Calculation Model FIG. 4 shows one cycle of the groove 24 of the SZ slot 20.

 The coordinates are the opposite of x and y for simplicity.

The shaded portion represents one side of the slot 20 as described above. That is, the range of x to x + π is one side.

Here, only the main value is considered, and it is considered within the range of 0 ≦ y ≦ p / 2.

(2) Analysis The length l of the groove 24 in (x, x + π) of the function y = f (x) is It is expressed as

Since the length l of the groove 24 is constant regardless of the starting point x on one side, it is expressed by the following equation.

Here, if the indefinite integral is set to F (x), the equation (2) is That is, f ′ (x + π) = ± f ′ (x) Integrate, f (x + π) = ± f (x) + C Boundary condition f (0) = 0, f (π) = p / 4, f (2π) = From p / 2, the general solution f (x + π) = f (x) + p / 4 (3) is obtained.

(3) Consideration The above expression (3) shows that "function f (x) is the same function for each p / 4. ] Is shown.

That is, the ABC part (solid line) and the CDE part (broken line) in FIG. 5a may have the same function (same shape).

Therefore, the shape of one inversion pitch (= p / 2 minutes) is the same as the above-mentioned “function f (x) for every p / 4”. ”, The fiber stresses on the outside and inside of the bend will cancel out.

However, if only the above-mentioned requirements are satisfied, it is also possible to take as shown in FIG.

However, in the actual SZ slot as described above,
The inversion unit 26 needs to change smoothly, and it is natural to assume that f '(0) = ∞ and f' (2π) = ∞ as boundary conditions.

If equation (3) is satisfied, f (x) does not have to be specified, but as a special solution, in the case of a sine wave That is, when x and y are replaced and expressed, it becomes as follows.

The curve connected by arcs for each p / 8 satisfies Eq. (3) (see Fig. 1a).

In addition, there are infinite solutions, but there are methods to determine the curve from the viewpoint of manufacturing and methods to suppress it from the viewpoint of characteristics. The former is considered to be approximate, and the latter is approximate.

[Embodiment 1] [1] Shape of groove 24: (1) First, as shown in FIG. 1a, the positions of A to I on the vertical line that divides the distance between the dresses 0 to p into eight equal parts are shown in FIG. Determine as you would.

(2) Connect AB, BC, CD, and DE with arcs of the same shape so that the joints are smooth.

 The same applies between E and I.

[2] Its action: (1) As in the case of FIGS. 7b and 7c above, the bending neutral surface 3
It shall intersect with 0 and π / 2 and 3π / 2. The shaded area in Figure 1a is the inside of the bend.

However, in this case, since AB = BC = CD = DE, the lengths of the grooves 24 are equal both inside and outside the bend.

(2) When the neutral surface 30 passes an arbitrary position: For example, when passing the positions of t and t + π in FIG.
From Fig. 1c, it can be seen that the length of the groove 24 is equal both on the lower side (hatched portion) and the upper side of the bend (because JB = KD, BC = DE, CK = AJ).

(3) As in this case, if the locus is an arc,
Since the curvature becomes constant at an arbitrary place, it is advantageous in increasing the loss of the optical fiber.

[Embodiment 2] As shown in FIG. 2, ABC is connected by a partial curve of the sine wave (Equation (4) above), and CDE is connected by a partial curve of the same sine wave (Equation (5) above). tie.

Similarly, the curve of the groove 24 of A to I is formed between p / 2 and p on the right side.

In this way, if the locus of the groove 24 is a sine wave, there is an advantage that the position variation of the groove becomes smooth when manufacturing a slot or inserting an optical fiber into the groove, which is easy. .

[Embodiment 3] This is a method of actually determining the shape of the groove.

As described above, the slot groove is formed by the rotation of the die during extrusion. Further, if the rotational speed of the die is constant, the developed shape of the groove is a sine wave as shown in FIG. 3a. And (AB + DE)> (BC + CD).

Therefore, for one inversion pitch, as shown in FIG. 3b, the rotation speed of the die is reduced or temporarily stopped between the inversion parts A and E, for example, from the rotation part C to C '. Then, at C ', the speed is returned to the original speed.

In this way, the C'DE part of ABC is composed of a part of the same sinusoidal curve, but the CC 'part is
And the maximum amplitude Y is the same as that of C'DE, but is composed of part of a longer pitch sinusoidal curve (see FIGS. 3c and 3d).

And so that (AB + DE) = (BC + CC ′ + CD)
Determine the length of CC '.

The pitch p of the sinusoidal curve becomes longer and the inclination of the curve with respect to the horizontal axis becomes smaller as the rotational speed of the die is slowed. Then, when the rotation of the die is stopped, the pitch becomes infinite, and not a sinusoidal curve but a straight line parallel to the horizontal axis.

In the present invention, the expression “long pitch” includes the case where the pitch is infinite.

[Advantages of the Invention] (1) In the case of the invention according to claim 1, no matter which direction the cable is bent, the stress applied to the fiber at the neutral plane, the outside and the inside is offset at every one inversion pitch, Loss increase does not occur.

Further, the curvature of the groove is constant at any place, which is advantageous in that the loss of the optical fiber is increased.

(2) Also in the case of the invention according to claim 2, no matter which direction the cable is bent, the stress applied to the fiber on the neutral plane, the outer side, and the inner side is canceled for each inversion pitch, and the loss does not increase. .

Further, since a part of the sinusoidal curve is combined, there is an advantage that the position variation of the groove becomes smooth when manufacturing the slot or inserting the optical fiber into the groove, which is easy.

(3) Also in the case of the invention according to claim 3, no matter which direction the cable is bent, the stress applied to the fiber on the neutral surface, the outer side and the inner side is canceled for each one inversion pitch, and the loss does not increase. .

 In addition, the control of the die is easy, and the manufacturing is easy.

[Brief description of drawings]

FIGS. 1a to 3b relate to an embodiment of the present invention. FIG. 1a is an explanatory view of the shape of the groove in the first embodiment, and FIGS. 1b and 1c show the neutral surface 30 at an arbitrary position. FIG. 2 is an explanatory view of the shape of the groove in the second embodiment, FIGS. 3a and 3b are explanatory views of a fixed shape of the groove in the third embodiment, FIG. 3c and FIG. 3d is an explanatory diagram of the relationship between the sinusoidal curve and the pitch, FIG. 4 is an explanatory diagram of the shape analysis of the groove 24, FIG. 5a is an explanatory diagram of a general solution of the analysis, and FIG. 5b is a general analysis of the shape analysis. 6a is a conceptual diagram of a general non-SZ slot, FIG. 6b is an explanatory diagram of a cross section common to SZ slots and non-SZ slots, and FIG. 7a is a conventional diagram. Fig. 7b is a conceptual perspective view of the SZ slot, Fig. 7b is a conceptual side view of Fig. 7a seen from the side, Fig. 7c is its developed view, and Fig. 8 is a fiber transfer during cable bending. Model diagram. 10: Optical fiber, 12: Optical fiber unit 20: Slot, 22: Cylindrical 24: Groove, 26: Reversing part 27: Rotating part 28: Busbar, 30: Neutral surface 32: Curve, 34: Point 36: Pointed part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuyuki Sugawara 1440 Rokuzaki, Sakura City, Chiba Fujikura Electric Cable Co., Ltd. Sakura Factory (56) References JP-A-63-301911 (JP, A) JP-A 1- 169418 (JP, A)

Claims (3)

(57) [Claims] 1. Slot grooves are alternately inverted in the longitudinal direction,
In an SZ slot type optical cable in which optical fibers are housed and assembled in the groove, when the cylinder of the slot is cut into a plane along a generatrix in contact with the inversion part of the groove, the shape of one pitch of the groove is:
An optical cable in which the length of the groove on the front half surface of the slot is equal to the length of the groove on the back half surface by being connected by arcs having the same curvature and the same length for each 1/8 pitch. 2. The groove of the slot is alternately inverted in the longitudinal direction,
In an SZ slot type optical cable in which optical fibers are housed and gathered in the groove, when the cylinder of the slot is cut into a plane along a generatrix in contact with the inversion portion of the groove, the shape of one pitch of the groove is
An optical cable in which the length of the groove on the front half surface of the slot is equal to the length of the groove on the back half surface by being formed by a part of the sine wave curve having the same shape for each 1/4 pitch. 3. The groove of the slot is alternately inverted in the longitudinal direction,
An SZ slot type optical cable that stores and collects optical fibers in its groove, and when the slot cylinder is cut into a flat surface along a generatrix in contact with the inversion portion of the groove, the shape of the groove is a sine wave. In the form of a curve, the maximum amplitude does not change between adjacent inversion parts, and the part except for a part in the middle of both inversion parts is composed of a part of a sine wave curve of the same pitch. However, only a part of the middle part is constituted by a part of a sinusoidal curve having a pitch longer than that of the part excluding the middle part. An optical cable in which the length is equal to the length of the groove on the back half surface.