US-12625338-B2 - Fan-in/Fan-out device

US12625338B2US 12625338 B2US12625338 B2US 12625338B2US-12625338-B2

Abstract

The FIFO device includes an MCF, a first lens having a first optical axis parallel to a center axis of the MCF, a group of second lenses including the same number of second lenses having a second optical axis parallel to the first optical axis as cores of the MCF, and a group of single-core optical fibers including the same number of single-core optical fibers as the second lenses. An end face of each single-core optical fiber is obliquely polished so as to incline in a predetermined inclination direction with respect to a plane orthogonal to the center axis by a predetermined polishing angle. Oblique polishing directions of surrounding single-core optical fibers are set so that the corresponding second lenses are positioned closer to the first optical axis or to the first lens compared to their positions at the time when the surrounding single-core optical fibers are not obliquely polished.

Inventors

Tomoaki Kiriyama
Katsuhiro Iwasaki
Katsuya KITO

Assignees

KOHOKU KOGYO CO., LTD.

Dates

Publication Date: 20260512
Application Date: 20211222
Priority Date: 20201228

Claims (13)

1 . A Fan-in/Fan-out device, comprising: a multi-core optical fiber which has a pillar shape, and includes a plurality of first cores extending along an axial direction, and a common cladding surrounding the plurality of first cores; a first lens having a first optical axis parallel to a center axis of the multi-core optical fiber and being arranged so as to correspond to the multi-core optical fiber, and from which light beams which have been emitted from the respective first cores and whose principal rays are parallel to each other exit so that the principal rays incline in predetermined directions, respectively; a group of second lenses including a plurality of spatially separated second lenses each having a second optical axis parallel to the first optical axis, the group of second lenses being configured to converge each of the light beams exiting from the first lens, which have been emitted from the respective first cores with each of the corresponding second lenses; and a group of single-core optical fibers including the same number of single-core optical fibers as the number of the second lenses, each single-core optical fiber having a pillar shape, and including one second core extending along the center axis and a cladding surrounding the second core, end faces of the respective single-core optical fibers being arranged at positions at which the light beams exiting from the corresponding second lenses, which have been emitted from the respective first cores converge on the respective second cores, wherein, the end face of each of the single-core optical fibers is obliquely polished so as to incline in a first inclination direction with respect to a plane orthogonal to the center axis thereof by a first polishing angle, wherein, oblique polishing directions of surrounding single-core optical fibers of the single-core optical fibers, where center axes of the surrounding single-core optical fibers are positioned at positions separated away from the first optical axis, are set so that the corresponding second lenses are positioned closer to the first optical axis or closer to the first lens compared to non-obliquely polished positions of the corresponding second lenses at the time when the surrounding single-core optical fibers are not obliquely polished, and wherein, the end face of freely-selected one of the surrounding single-core optical fibers not parallel to at least one end surface of the surrounding single-core optical fiber except the freely-selected surrounding single-core optical fiber.
2 . The Fan-in/Fan-out device according to claim 1 , wherein the center axes of the respective single-core optical fibers are parallel to the second optical axes of the corresponding second lenses.
3 . The Fan-in/Fan-out device according to claim 1 , wherein when it is defined that, when end faces of the respective surrounding single-core optical fibers are viewed along the center axes thereof, line segments passing through centers of the respective end faces and are orthogonal to respective line segments connecting the first optical axis and the centers of the respective end faces are first orthogonal lines of the respective single-core optical fibers, and when it is defined that out of outer circumferences of the respective end faces, outer circumferences of portions on a side opposite to a side at which the first optical axis is positioned with respect to the respective first orthogonal lines are first outer circumferences, the respective oblique polishing directions are set so that proximal ends of respective oblique polishing reference axes are positioned on the respective first outer circumferences.
4 . The Fan-in/Fan-out device according to claim 3 , wherein the respective oblique polishing directions are set so that the proximal ends of the respective oblique polishing reference axes are positioned at middle points of the respective first outer circumferences.
5 . The Fan-in/Fan-out device according to claim 1 , wherein in a first case in which, when end faces of the respective surrounding single-core optical fibers are viewed along the center axes thereof, a reference line which is a straight line orthogonal to the first optical axis and extending in any direction does not pass through centers of the respective single-core optical fibers, when it is defined that line segments passing through centers of the end faces of the respective surrounding single-core optical fibers and are parallel to the reference line are parallel lines of the respective surrounding single-core optical fibers, and when it is defined that out of outer circumferences of the respective end faces, outer circumferences of portions on a side at which the first optical axis is positioned with respect to the respective parallel lines are second outer circumferences, the respective oblique polishing directions are set so that proximal ends of respective oblique polishing reference axes are positioned on the respective second outer circumferences, and wherein in a second case in which, when end faces of the respective surrounding single-core optical fibers are viewed along the center axes thereof, the reference line passes through centers of the respective surrounding single-core optical fibers, when it is defined that line segments passing through centers of the end faces of the respective surrounding single-core optical fibers and are orthogonal to the reference line are second orthogonal lines of the respective surrounding single-core optical fibers, and when it is defined that out of outer circumferences of the respective end faces, outer circumferences of portions on a side at which the first optical axis is positioned with respect to the respective second orthogonal lines are third outer circumferences, the respective oblique polishing directions are set so that the proximal ends of the respective oblique polishing reference axes are positioned on the respective third outer circumferences.
6 . The Fan-in/Fan-out device according to claim 5 , wherein in the first case, the respective oblique polishing directions are set so that the proximal ends of the respective oblique polishing reference axes are positioned at middle points of the respective second outer circumferences, and wherein in the second case, the respective oblique polishing directions are set so that the proximal ends of the respective oblique polishing reference axes are positioned at middle points of the respective third outer circumferences.
7 . The Fan-in/Fan-out device according to claim 1 , wherein when it is defined that, when end faces of the respective surrounding single-core optical fibers are viewed along the center axes thereof, line segments passing through centers of the respective end faces and are orthogonal to respective line segments connecting the first optical axis and the centers of the respective end faces are first orthogonal lines of the respective surrounding single-core optical fibers, and when it is defined that out of outer circumferences of the respective end faces, outer circumferences of portions on a side at which the first optical axis is positioned with respect to the respective first orthogonal lines are fourth outer circumferences, the respective oblique polishing directions are set so that proximal ends of respective oblique polishing reference axes are positioned on the respective fourth outer circumferences.
8 . The Fan-in/Fan-out device according to claim 7 , wherein the respective oblique polishing directions are set so that the proximal ends of the respective oblique polishing reference axes are positioned at middle points of the respective fourth outer circumferences.
9 . The Fan-in/Fan-out device according to claim 1 , wherein an end face of the multi-core optical fiber is obliquely polished so as to incline in a second inclination direction with respect to a plane orthogonal to a center axis thereof by a second polishing angle, and wherein when a straight line passing through a center of the end face and extending along an oblique polishing direction is defined as a reference axis in a case when the end face of the multi-core optical fiber is viewed along the center axis thereof, and when a direction directed from the reference axis toward one side with respect to the reference axis along an orthogonal axis orthogonal to the center axis and the reference axis is defined as a first orthogonal direction, and a direction directed from the reference axis toward another side with respect to the reference axis along the orthogonal axis is defined as a second orthogonal direction, the oblique polishing direction of the multi-core optical fiber is set so that, when the end face of the multi-core optical fiber is viewed along the center axis thereof, a separation distance is minimized, the separation distance being a sum of a distance from the reference axis to a first core that is most separated away from the reference axis in the first orthogonal direction and a distance from the reference axis to a first core that is most separated away from the reference axis in the second orthogonal direction.
10 . The Fan-in/Fan-out device according to claim 1 , wherein principal points of remaining second lenses of the second lenses in which at least one second lens is excluded are positioned on the same plane, respectively, and wherein a principal point of the at least one second lens is positioned closer to the first optical axis compared to the principal point of the at least one second lens obtained when assuming that principal points of all of the second lenses are positioned on the same plane.
11 . The Fan-in/Fan-out device according to claim 10 including 2n (n≥2) second lenses wherein, when the second lenses are viewed along the first optical axis, principal points of the second lenses are positioned at vertices of a regular polygon having the first optical axis as a center, respectively, n line segments each connecting principal points of a part of second lenses positioned on any one of diagonal lines of the regular polygon perpendicularly cross with the first optical axis at different positions on the first optical axis with each other, and lengths of the line segments are shorter than lengths of the line segments obtained when assuming that the n line segments perpendicularly cross with the first optical axis at the same position on the first optical axis with each other.
12 . The Fan-in/Fan-out device, comprising: the group of single-core optical fibers including the plurality of single-core optical fibers; the group of second lenses including the same number of the second lenses as the number of the single-core optical fibers; the first lens; and the multi-core optical fiber including the first cores whose number is at least more than or equal to the number of the single-core optical fibers, each being described in claim 1 , wherein light beams are propagated in a direction opposite to a direction in which light beams are propagated by the Fan-in/Fan-out device of claim 1 .
13 . The Fan-in/Fan-out device according to claim 1 , wherein the oblique polishing directions of the surrounding single-core optical fibers are set so as to satisfy at least one of a radially downsizing arrangement in which all of the corresponding second lenses are positioned closer to the first optical axis compared to the non-obliquely polished positions, and an optical-axis-direction downsizing arrangement in which all of the corresponding second lenses are positioned closer to the first lens compared to the non-obliquely polished positions.

Description

TECHNICAL FIELD The present invention relates to a Fan-in/Fan-out device. Specifically, the present invention relates to a spatially coupled Fan-in/Fan-out device that includes a multi-core optical fiber and a plurality of single-core optical fibers, and optically couples them. BACKGROUND ART Internet communication traffic demands are increasing year by year, and optical communication has been desired to achieve higher speed and larger capacity. Hitherto, in order to respond to those demands, a wavelength division multiplexing (WDM) technology, a digital coherent technology, and other technologies have been used to promote an increase in transmission capacity. In recent years, as a new multiplexing technology, a space division multiplexing (SDM) technology using a multi-core optical fiber is gathering attention. It is said that the SDM technology allows further higher speed and further larger capacity to be achieved. Along with the progress of research and development of the SDM technology, demands for a Fan-in/Fan-out device (hereinafter also referred to as “FIFO”) have been increased. A FIFO device is an optical device that includes a multi-core optical fiber and a plurality of single-core optical fibers, and optically couples them. As examples of FIFO devices, spatially coupled, fiber bundle, and fusion-drawn devices can be mentioned, for example. A spatially coupled FIFO device is characterized by optically coupling a multi-core optical fiber and a single-core optical fiber using a lens (including a glass block, and the like). Although the size of components in the spatially coupled FIFO device becomes larger compared to that in the fiber bundle device or the fusion-drawn FIFO device, there is an advantage of reducing insertion loss. Patent Literature 1 discloses a spatially coupled FIFO device arranged along a certain axis. This FIFO device optically couples each core of a multi-core optical fiber with (cores) of the same number of single-core optical fibers as the cores of the multi-core optical fiber. The FIFO device includes a first optical system and a second optical system. The first optical system is composed of a GRIN (Gradient Index) lens and a glass block, and the second optical system is composed of a lens array. The lens array has the same number of lenses as the single-core optical fibers. The first optical system is positioned on a multi-core optical fiber side along the axis, and the second optical system is positioned on a single-core optical fiber side along the axis. The first optical system is configured to collimate (make parallel) and deflect light beams emitted from respective cores of the multi-core optical fiber. The second optical system is configured to deflect each of the light beams exiting from the first optical system, which have been emitted from the respective cores with each of the lenses corresponding to the respective cores (of the multi-core optical fiber), and converge each of the light beams onto an end face of each of the single-core optical filters corresponding to the respective lenses. CITATION LIST Patent Literature [PTL 1] JP 6554891 B2 SUMMARY OF INVENTION Technical Problem When each single-core optical fiber is formed so that the end face thereof is orthogonal to the axis, there is a possibility that each light beam exiting from the second optical system through the first optical system is reflected by the end face of each single-core optical fiber, and a reflected light enters each core of the multi-core optical fiber via the FIFO device. Such reflected light is generally referred to as “reflected return light.” The reflected return light has a possibility of entering a transmission-side communication device via the multi-core optical fiber or being reflected multiple times so that an optical characteristic of signal light is reduced. In view of the above, hitherto, suppressing entry of the reflected return light into each core of the multi-core optical fiber (i.e., reduction of the reflected return light) has been performed by polishing the end faces of the single-core optical fibers so as to be tilted with respect to a plane orthogonal to the axis. Hereinafter, an action of polishing an end face of an optical fiber so as to be inclined with respect to a plane orthogonal to the axis is referred to as “obliquely polishing.” In the FIFO device of Patent Literature 1, each end face of a plurality of single-core optical fibers is collectively obliquely polished under a state in which the plurality of single-core optical fibers are being bundled, thereby reducing the reflected return light. However, according to the technique of Patent Literature 1, there is a problem that the size of a coupling portion (a portion of the FIFO device that optically couples the multi-core optical fiber and the single-core optical fibers) of the FIFO device further increases. That is, when an end face of an optical fiber is obliquely polished, it is generally necessary to deflect