Microlenses for coupling single-mode fibers to single-mode thin-film waveguides

A new method has been devised for producing microlenses on the ends of single-mode optical fibers. A lens is formed by dipping the fiber end into a negative photoresist while the fiber core carries greater, similar0.1 mW of He-Ne laser light. The photoresist lenses require no developing or rinsing. The lenses are shown to transform the near-Gaussian beam emitted by the fiber into another near-Gaussian beam with a reduced waist diameter. The size of the new waist can be selected by varying the number of times the fiber is dipped into the photoresist. The waist reduction is shown to increase coupling into single-mode optical waveguides.