Patent ID: 7313301

Claim:
An optical fiber device comprising: a first multi-mode optical fiber; a second multi-mode optical fiber having a core radius rc and a numerical aperture NA which are substantially the same as those of the first multi-mode optical fiber; and a first condenser lens and a second condenser lens which have substantially the same focal length; wherein the first multi-mode optical fiber and the second multi-mode optical fiber are optically coupled to each other at their end faces through the first condenser lens and the second condenser lens; the first condenser lens and the second condenser lens are arranged such that they are spaced apart from each other by four times the focal length and their optical center axes are substantially put into coincidence with each other; the first multi-mode optical fiber is arranged such that it is spaced apart from the first condenser lens by a distance larger than the focal length and the center axis of light emitted from the first multi-mode optical fiber is substantially put into coincidence with the optical center axis of the first condenser lens; the second multi-mode optical fiber is arranged such that it is spaced apart from the second condenser lens by a distance larger than the focal length and the center axis of light emitted from the second multi-mode optical fiber is substantially put into coincidence with the optical center axis of the second condenser lens; the first multi-mode optical fiber is arranged with respect to the first condenser lens such that a light ray proceeding from the outermost perimeter of the core of the first multi-mode optical fiber toward the optical center axis of the first multi-mode optical fiber and having a largest tilt angle with respect to the optical center axis of the first multi-mode optical fiber substantially passes through the position of the focal point of the first condenser lens between the first multi-mode optical fiber and the first condenser lens; and the second multi-mode optical fiber is arranged with respect to the second condenser lens such that a light ray proceeding or traveling from the outermost perimeter of the core of the second multi-mode optical fiber toward the optical center axis of the second multi-mode optical fiber and having a largest tilt angle with respect to the optical center axis of the second multi-mode optical fiber substantially passes through the position of the focal point of the second condenser lens between the second multi-mode optical fiber and the second condenser lens.