Formation of a Spherical Lens at Optical Fiber Ends with a CO_2 Laser

A study was made of the use of a CO(2) laser for producing a hemispherical lens at the end of a fiber. When the fiber end is heated to the softening points of the material, it tends to become spherical in shape due to surface tension. A one-dimensional heat conduction model for the fiber can reasonably predict the required laser power for a given pulse length to produce lenses on fibers made of various kinds of materials. A He-Ne laser beam was coupled into a fiber to investigate the properties of the spherical lens. We also observed that such lens can couple light from a source into the fiber, can be used for imaging, and can focus enough laser intensity for machining various materials.