FIBER FOR SIDE INJECTION OF LASER BEAM

PURPOSE:To reduce a high-order mode for transmitting beams along the peripheral part of a core, to suppress the expansion of projection beams to make the beams circular and concentrating the beam diameter into a small value by setting up the refractive index distribution constant of a core to a value smaller than a prescribed value. CONSTITUTION:Generally, the shape and size of projection beams depend upon the distribution of a transmission mode in the core radius direction. An inclined face 54 having 35 deg. inclined angle from the center axis is formed on the tip part of an optical fiber strand 53 consisting of a core 51 and a clad 52 and laser beams 55 transmitted on the center axis of the core 51 is fully reflected by the inclined face 54 and projected to the side of almost 60 deg. through the clad 52. Although the refractive index distribution constant alpha is 4, the shape of the projection beams shows almost an elliptical and widely expanded, but when the constant alpha is 3, the shape of the projection beams show a circle and the diameter of the beams is concentrated into a small value. Consequently it is preferable to set up the refractive index distribution constant alpha of the fiber strand to a value