Optical filter device

An optical filter device, comprising:

• a first 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 an optical axis positioned on a center axis of the first multi-core optical fiber, the first lens being configured to collimate a light beam diverging after being emitted from each of the plurality of first cores, and to collect the collimated light beams which have been emitted from the plurality of first cores, respectively;
• an optical filter having a first surface which light beams exiting from the first lens enter and on which a light collecting point of emission light exiting from the first lens is positioned, and a second surface which is opposed to the first surface, and from which the light beams passing through the optical filter exit, the optical filter being configured to allow a light beam in a specific wavelength band to pass therethrough at any transmission intensity, the optical filter being rotated by a predetermined rotation angle about a rotation axis extending in a specific direction perpendicular to the optical axis of the first lens at said light collecting point at which the light beams are collected on the first surface, from a position at which the first surface is parallel to a plane orthogonal to the optical axis;
• a second lens configured to converge each of the light beams exiting from the optical filter, which have been emitted from the plurality of first cores, respectively;
• and
• a second optical fiber extending along the axial direction, said second optical fiber having a pillar shape, and including cores which all of the light beams exiting from the second lens, which have been emitted from the plurality of first cores, respectively, enter,
• wherein, when a direction directed from a reference axis which passes through the optical axis and is parallel to the rotation axis toward one side with respect to the reference axis along an orthogonal axis orthogonal to the optical 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,
• a circumferential orientation of the first multi-core optical fiber is set so that, when an end face of the first multi-core optical fiber is viewed along the center axis of the first multi-core optical fiber, 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.