Carbon dioxide lasers plastically bend larger-diameter sapphire fibers

Single-crystal sapphire fibers have excellent physical and chemical properties that facilitate their use in infrared sensing and power-delivery applications. The crystals are extremely difficult to bend, however, which has often limited applications to smaller-diameter, less-efficient fibers. Using two 80-W carbon dioxide (CO₂ ) lasers, researchers at Zhejiang University (Hangzhou, China) have plastically bent 325-850-µm-diameter sapphire fibers with typical bending radii as small as 2.8 mm—much smaller than their minimum elastic bending radii. During the experiments, one laser directly irradiated each fiber to its softening temperature, the other, expanded by a zinc selenide lens, was used as an auxiliary heater to control the temperature distribution along the fiber and help adjust the bending radius.

Original losses of test fibers ranged from 2.1 to 2.8 dB/m at a wavelength of 900 nm. Additional optical losses caused by the bending process were less than 0.1 dB at 900 nm. The average strength reduction of bent fibers was roughly 10%, still high enough that fibers could resist mechanical vibrations as strong as 10 g. The damage threshold of bent fibers was higher than 150 MW/cm² when a 1064-nm Nd:YAG laser pulse was used, which makes fibers applicable in medical applications. Contact Limin Tong at [email protected].