Optical fiber output coupler for a power laser

Claim 1

Output coupling apparatus for a power laser beam transmitting optical fiber, comprising: first lens means for collimating as a first collimated beam portion the power laser beam emitted from an output end of the fiber; second lens means for expanding the first collimated beam portion into a second collimating beam portion having a larger diameter than the first collimated beam portion; third lens means for focussing, onto a surface, the second collimating beam portion as a focussed spot having a predetermined diameter; means for mounting said first, second and third lens means and the fiber output end in alignment so that the power laser beam emitted from the fiber output end is collimated by said first lens means, expanded by said second lens means and focussed to the focussed spot by said third lens means; said first lens means comprising a first p1ano-convex lens having a focal length f 1 and being mounted a distance f 1 from the fiber output end; said second lens means comprising a second and a third p1ano-convex lens, said second p1ano-convex lens being mounted to intercept the first collimating beam portion and provide an expanding beam portion beyond a focal point of said second p1ano-convex lens, said third p1ano-convex lens being mounted to intercept the expanding beam portion and provide the second collimated beam portion, said second and third p1ano-convex lenses having respective focal lengths f 3 and f 4 being spaced from one another by a distance that is the sum of f 3 and f 4 ; and said third lens means comprising a fourth p1ano-convex lens having a focal length f 2 , the focussed spot being a distance f 2 from said fourth p1ano-convex lens.