Thin cylindrical diffusers in multimode Ge-doped silica fibers.

Background and Objectives: Cylindrical fiber diffusers are common tools in photodynamic therapy (PDT). However, large outer diameter and short length limit the indications to which they can be applied. Here a diffuser with an outer diameter of 250 pm and an active length exceeding 5 cm was developed. Study Design/Materials and Methods: Diffusers based on photosensitive quartz optical fibers with a cladding diameter of 140 pm were developed using a structured beam from an excimer laser. A complete set of photometric characteristics, including longitudinal, polar, and azimuth radiance emission diagrams were collected. Results and Conclusions: The longitudinal radiance emission is homogenous to within +/-10%. The ability to create custom designed longitudinal emission profiles was demonstrated. The variations of the polar and azimuth radiance emission diagrams were within +/-15% from an ideal Lambertian emitter. The polar uniformity can be improved with a slight increase of the outer diameter using a diffusing recoating compound. The residual light leakage at the distal end of the fiber diffuser was suppressed to 2%. The minimal bending radius after recoating is similar to 5 mm. Maximum power distribution is >0.5 W cm(-1).