Mode scrambler

Abstract

Provided is a low-loss mode scrambler in which a steady mode distribution can be obtained in a short distance and switch to an entire mode distribution state is easy even when incident light is smaller than a numerical aperture of a fiber to be measured in a multimode fiber having a core diameter exceeding several tens of m and a numerical aperture of 0.2 or more. One fiber 2 is wound around a plurality of bobbins 3a and 3b having a radius larger than a minimum bending radius of the fiber to form a bundle, and the fiber 2 is twisted by rotating the bobbins 3a and 3b to form a twisted portion 5, whereby it is possible to perform output of a steady mode from light incident on the fiber 2.

Claims

1. A mode scrambler comprising: a plurality of bobbins arranged in a radial direction thereof with an interval therebetween, and a fiber wound around the plurality of bobbins, and having a twisted portion formed by rotation of the plurality of bobbins about an arranged direction thereof as an axis to thereby bundle the plurality of bobbins with the fiber, wherein portions of the fiber are entangled to form the twisted portion to apply a torsional stress to the fiber.

2. The mode scrambler according to claim 1, wherein the fiber is wound around a core post provided between the bobbins at a time of rotating the bobbins.

3. The mode scrambler according to claim 1, wherein the plurality of bobbins includes two bobbins, and the fiber is a single fiber wound around the two bobbins, and includes a first portion wound around one of the two bobbins, a second portion wound around the other of the two bobbins, and the portions of the fiber extending between the two bobbins, which are twisted together to form the twisted portion of the fiber.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is an overall perspective view of a mode scrambler used in the most preferable embodiment of the present invention.

(2) FIG. 2 is an explanatory side view of the mode scrambler illustrated in FIG. 1.

(3) FIGS. 3(a) and 3(b) are side views according to another embodiment of the mode scrambler illustrated in FIG. 1.

DESCRIPTION OF EMBODIMENTS

(4) Hereinafter, embodiments of a mode scrambler according to the present invention will be described with reference to FIGS. 1, 2, 3(a) and 3(b). Incidentally, common reference numerals are given to those functioning as the same parts with respect to reference numerals illustrated in the drawings.

(5) FIGS. 1, 2, 3(a) and 3(b) illustrate an overall perspective view of a mode scrambler used in this embodiment, an explanatory side view of the mode scrambler, and a side view of another embodiment of the mode scrambler, respectively. Incidentally, a supporting structure of a bobbin and a fiber is not illustrated in the drawings.

(6) As understood from FIGS. 1 and 2, a mode scrambler 1 according to the present embodiment is provided with two bobbins 3a and 3b arranged in parallel in a radial direction, and is configured such that it is possible to wind the fiber 2 around these bobbins 3a and 3b. As illustrated in FIG. 1, for example, the single fiber 2 is wound around the bobbins 3a and 3b. Further, the bobbins 3a and 3b are configured such that it is possible to rotate the bobbins 3a and 3b coaxially in opposing directions opposite to each other, for example, the bobbin 3a in an R1 direction and the bobbin 3b in an R2 direction, using an axis R as a rotation axis thereof, in a state where the fiber 2 is wound therearound. Further, when the bobbins 3a and 3b are rotated in the opposing directions opposite to each other in this manner, the fiber 2, wound around these bobbins 3a and 3b, is twisted so that a twisted portion 5, twisted while a plurality of fibers is entangled with each other, is formed in the fiber 2.

(7) The twisted portion 5 is formed between the bobbins 3a and 3b so that the plurality of fibers 2 is twisted while being entangled with each other. The twisted portion 5 is oriented in a direction having a predetermined angle with respect to a longitudinal direction in which the fiber 2 is disposed, and is formed such that the fiber 2 is spirally wound around with respect to the other fiber 2. Since the twisted portion 5 is formed as the fiber 2 is twisted as described above, a higher-order mode distribution transmitted through the fiber 2 is attenuated at the twisted portion 5, and it is possible to obtain output light with a stable steady mode distribution.

(8) Incidentally, the fiber 2 used in the present embodiment is an SI multimode fiber having a core diameter exceeding several tens m and a numerical aperture of 0.2 or more, and is incorporated in the mode scrambler 1 after being cut to have a length of 10 m or less. Further, the straight arrows in FIG. 1 indicate transmission paths of light in the fiber. Although the description is given using the example using SI multimode fiber in the present embodiment, a fiber other than this, such as a GI fiber, may be used as the fiber to be used, and is not limited to the above-described example.

(9) Further, the mode scrambler 1 can change the mode distribution to be output depending on the number of rotations of the bobbins 3a and 3b by using such a structure. That is, as understood from FIG. 1, torsional stresses in opposite directions to each other act on the fiber 2 in both propagation directions of travel c, which is a direction in which the incident light is incident on the twisted portion 5 for the first time, and return d, which is a direction in which in which light is incident from an opposing direction to the travel c toward the twisted portion 5, that is, the light having passed through the twisted portion 5 at least once is incident to the twisted portion 5 again, in the mode scrambler 1 according to the present embodiment. Accordingly, the mode scrambler 1 of the present embodiment can generate dispersion of the mode distribution in the twisted portion 5 which is the twisted part without reducing a bending radius of the fiber 2. Further, since the light does not leak to the outside regarding the light transmission in the fiber, it is possible to perform the transmission in the state of suppressing the loss caused by the light leaking out of the fiber.

(10) Further, the single fiber 2 is wound around the bobbins 3a and 3b, and the two bobbins 3a and 3b around which this fiber 2 has been wound are set to the state of being mutually rotated in the opposing directions opposite to each other, thereby generating the dispersion of the mode distribution in the fiber in the mode scrambler 1 of the present embodiment as understood from FIG. 2. Thus, it is possible to output the steady mode distribution corresponding to the characteristics of the fiber 2 by changing the number of rotations of the bobbins 3a and 3b. Further, the simplified structure, obtained only by winding the fiber 2 around the bobbins 3a and 3b and causing twist in the fiber 2 to form the twisted portion 5, is provided in the operation and configuration of the mode scrambler 1 of the present embodiment, thereby enabling the mode output, that is, the output of the steady mode distribution. Thus, the mode scrambler 1 as a whole can have an inexpensive configuration while improving practicality.

(11) Incidentally, from the same technical viewpoint as the number of times of twist as the number of times of twisting the fiber 2 in the twisted portion 5, even when it is configured such that the number of turns as the number of times of winding the fiber 2 around the two bobbins 3a and 3b is changed, it is possible to obtain various effects including the suppression of the loss caused by the light leaking out of the fiber as described above similarly to the case of changing the number of rotations as illustrated in FIG. 3(a). Further, the stress acting on the fiber 2 increases depending on a rotation angle of the bobbins 3a and 3b in this configuration, and thus, it is possible to output the steady mode distribution with a smaller torsional angle. Further, for a fiber having a hard fiber cover and having a small maximum diameter, represented by an outdoor fiber, it is possible to impart the same effects as the above-described structure illustrated in FIGS. 1 and 2 together with high general versatility by adopting the twisted structure using the core post 4 as illustrated in FIG. 3(b).

(12) In addition to these effects, for example, in the multimode fiber having the core diameter exceeding several tens m and the numerical aperture of 0.2 or more, it is possible to reproduce a mode distribution equivalent to the steady mode distribution when light is propagated over a long distance of the fiber 2 by making the numerical aperture of the incident light smaller than the numerical aperture of the fiber 2 even when the incident light is smaller than the numerical aperture of the fiber to be measured through the suppression of the loss caused by the light leaking out of the fiber in the invention described in the present application. Further, it is possible to perform output in not only the steady mode distribution but also the entire mode distribution including a higher-order mode distribution by using an adjustment mechanism based on the number of turns and the number of rotations.

(13) As described above, when the mode scrambler 1 according to the present invention is used, it is possible to provide the mode scrambler 1 in which the steady mode distribution can be obtained in a short distance, and switch to the entire mode distribution is easy. Incidentally, only one example of the mode scrambler according to the present invention has been described as above, and the configuration may be changed as appropriate without departing from a gist of the present invention.

REFERENCE SIGNS LIST

(14) 1 mode scrambler 2 fiber 3a, 3b bobbin 4 core post 5 twisted portion c, d light propagation direction in fiber R axis