Shaped fiber tips for medical and industrial applications

Abstract

Shaped fiber tips are machined or sculpted fiber ends which are formed using the glass from the fiber with no additional glass material. The tips are fabricated through either mechanical or laser machining processes. The tips are very useful in medical and industrial applications which require high power laser delivery (material or tissue cutting), even light distribution over a broad area (tissue ablation or photodynamic therapy), modified beam divergence or spot size (materials processing and communications links), or optical power redirection from the axis of the fiber in areas with small space restrictions (tissue ablation or perforations inside the human body). Descriptions of various shaped tips are provided, with concentration on tapered tips. The tapered tip is the most commonly used. The primary objective of this study was to measure the optical loss of such tapers vs. taper length, input (launch) numerical aperture (NA), and fiber diameter. The tapers fabricated and analyzed were 2:1 tapers using 0.22 NA fibers with 200, 400, and 500 um cores. The optical loss at 633nm for fibers with a 0.22 NA was measured to be 5.9dB (25% transmission) for a fully filled input NA and 0.8 dB (83% transmission) for a 0.12 input NA. The taper loss was found to depend strongly on input NA, but be relatively independent of taper length and fiber diameter. An optical modeling ray trace program was used to analyze the taper performance and validate the actual measurements. The modeling analysis will be a useful tool in design of tapers as well as other shaped fiber tips.