title: Design and performance of thin cylindrical diffusers created in Ge-doped multimode optical fibers.
abstract: Cylindrical fiber diffusers have become common tools for various medical therapies. However, their large outer diameters and short lengths restrict their clinical application in some newly developed light therapies. Here, a 250-microm outer-diameter diffuser with an active length that exceeds 5 cm is presented. Diffusers are created in photosensitive optical fibers with outer cladding diameters of 140 microm by use of a structured beam from an excimer laser. Predetermined emission profiles can be achieved. Photometric characteristics, including longitudinal, polar, and azimuthal emission diagrams, were determined by use of a goniometer to assess the light-emission performance of the diffuser. Longitudinal isotropy of better than +/- 10% was achieved. Polar and azimuthal emissions were within +/- 15% of those of an ideal linear Lambertian emitter. Polar uniformity could be improved by an insignificant increase in the outer diameter by use of a diffusing recoating compound. The residual leakage of light at the distal end of the diffuser can be as little as 1%. Other physical parameters tested include minimal bending radius after recoating (< 5 mm) and maximum power handling (> 1.0W cm(-1)). All materials employed were biocompatible.
authors.affiliation: Walsh Medical Devices, Inc., 1200 South Service Road, West Unit 3, Oakville, Ontario L6L 5T7, Canada.
authors.forename: Leonid
authors.initials: L
authors.lastname: Vesselov
authors.forename: William
authors.initials: W
authors.lastname: Whittington
authors.forename: Lothar
authors.initials: L
authors.lastname: Lilge