Investigation of tapered silver / silver halide coated hollow glass waveguides for the transmission of CO 2 laser radiation Carlos M. Bledt *a , Daniel V. Kopp a , and James A. Harrington a a Dept. of Material Science & Engineering, Rutgers University, Piscataway, NJ 08855 Saiko Kino b and Yuji Matsuura b b Graduate School of Biomedical Engineering, Tohoku University, Sendai 980-8579, Japan Jason M. Kriesel c c Opto-Knowledge Systems, Inc., 19805 Hamilton Ave., Torrance, CA 90502-1341 ABSTRACT The present study focuses on the theoretical and practical infrared radiation propagation properties of tapered silver / silver iodide coated Hollow Glass Waveguides (HGWs). Tapered HGWs with inner diameters ranging from 300 µm to 650 µm with a linear taper increasing at an approximate rate of 1.5 µm/cm were fabricated and optimized for low-loss transmission of CO 2 laser radiation at of 10.6 µm. The theoretical losses in these tapered silver / silver iodide coated HGWs are calculated for light transmitted from the big to the small and vice versa. Theoretical calculations used in this study are based on ray-optics. Experimental loss measurements are likewise presented, along with the calculated and measured output beam divergence. The experimental bending losses of the tapered HGWs are studied and compared with those measured and for those for non-tapered, straight bore sizes from 300 to 700 µm. Experimental losses for tapered Ag/AgI HGWs ranged from 0.732 – 1.340 dB/m depending on configuration and bending radius. Keywords: Infrared fiber optics, hollow waveguides, tapered waveguides, ray tracing analysis, geometrical optics. 1. INTRODUCTION Silver (Ag) / silver iodide (AgI) coated HGWs have been successfully used for the low loss delivery of infrared radiation ranging from Ȝ = 2 – 14 µm. Applications include laser surgery, photothermal imaging, and spectroscopy. The basic Ag / AgI HGW structure consists of a reflective Ag plus a dielectric AgI thin film deposited on the inner surface of a fused silica capillary all using a liquid-phase chemistry approach. The vast majority of Ag / AgI HGWs consist of silica capillary tubing whose bore diameter is constant along the entire length with bore sizes ranging from 200 – 1,000 µm. The ability to fabricate constant diameter low-loss Ag / AgI HGWs have led to their commercialization, particularly for medical systems requiring the delivery of high power CO 2 laser radiation for surgical applications. In the past, Ag / AgI HGWs with different geometries have also been fabricated, most notably rectangular and square waveguides which maintain the polarization. Another Ag / AgI HGW structure involves a tapered design in which the bore diameter of the silica capillary varies along the HGW length. Both short and long tapered Ag / AgI HGWs have been shown to have interesting properties differing from those with a constant bore HGWs. [1] For comparison, the various geometries of various Ag / AgI HGWs which have been successfully fabricated to date are presented in Figure 1. * cmbledt@eden.rutgers.edu ; Phone 862-485-9289; irfibers.rutgers.edu Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XII, edited by Israel Gannot, Proc. of SPIE Vol. 8218, 821802 · © 2012 SPIE CCC code: 1605-7422/12/$18 · doi: 10.1117/12.912201 Proc. of SPIE Vol. 8218 821802-1 Downloaded from SPIE Digital Library on 02 Jul 2012 to 128.6.227.171. Terms of Use: http://spiedl.org/terms