Fan-in/fan-out device

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 face the multi-core optical fiber;
• a group of second lenses including a plurality of second lenses each having a second optical axis parallel to the first optical axis;
• 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 a center axis parallel to the second optical axis and a cladding surrounding the second core,
• and being configured to propagate light beam in either one direction of a first progress direction and a second progress direction, the first progress direction being a progress direction of light beams which are emitted from the respective first cores of the multi-core optical fiber, pass through the first lens and the second lenses corresponding to the respective first cores, and converge on the respective second cores of the single-core optical fibers corresponding to the second lenses, and the second progress direction a being a progress direction of light beams which are emitted from the respective second cores, pass through the corresponding second lenses and the first lens, and converge on the respective first cores corresponding to the second lenses,
• wherein, when defining a beam waist diameter of each of the light beams exited from the first lens as a first beam waist diameter, and defining a distance from the first lens to a beam waist position in a progress direction of a principal ray of each of the light beams as a first beam waist distance based on an assumption that the light beams propagate in the first progress direction, defining a beam waist diameter of each of the light beams exited from the respective second lenses as a second beam waist diameter, and defining a distance from the second lenses to a beam waist position in a progress direction of a principal ray of each of the light beams as a second beam waist distance based on an assumption that the light beams propagate in the second progress direction, and defining a maximum value of a beam waist distance sum at a time when an inter-lens distance is equal to the beam waist distance sum as a distance sum maximum value, the inter-lens distance being a distance between the first lens and the respective second lenses in a progress direction of a principal ray of each of the light beams, and the beam waist distance sum being a sum of the first beam waist distance and the second beam waist distance at a time when the first beam waist diameter matches the second beam waist diameter,
• an end face of the multi-core optical fiber is obliquely polished so as to incline in a predetermined inclination direction with respect to a plane orthogonal to a center axis thereof by a predetermined polishing angle, and thereby occurring n types of variations in a distance between the respective first cores and the first lens in a progress direction of a principal ray of each light beam, and occurring n types of variations in the first beam waist diameter of each of the light beams emitted from the respective first cores,
• each of the single-core optical fibers is arranged with respect to the corresponding second lens such that the second beam waist diameter of the light beam corresponding to each of the single-core optical fiber matches the corresponding first beam waist diameter,
• further, when defining the first and the second beam waist diameters at the time when the beam waist distance sum is the distance sum maximum value as a beam-waist-diameter-at-maximum-distance, and defining a maximum value and a minimum value of n types of the first and the second beam waist diameters as a beam waist maximum diameter and a beam waist minimum diameter, respectively,
• the multi-core optical fiber is arranged with respect to the first lens at such a position that the beam waist maximum diameter is greater than the beam-waist-diameter-at-maximum-distance, and the beam waist minimum diameter is smaller than the beam-waist-diameter-at-maximum-distance.