Design of tapered optical fibers to achieve high spatial selectivity during infrared neural stimulation (Conference Presentation)

Abstract

Purpose: Optical stimulation methods in development aim to provide high spatial selectivity of target tissue, overcoming a critical limitation of contemporary neural prostheses. The purpose of this study is to determine if tapered fibers are capable of delivering the minimum necessary power density 1W/mm2 within a 0.050mm spot size to induce focused infrared neural stimulation (INS). Materials: A numerical simulation program based on equations derived from Snell’s law was developed in MATLAB to predict the energy emitted from a tapered fiber coupled to a Capella laser (λ=1863nm, Lockheed Martin Aculight). Energy predictions were compared to emittance from a tapered fiber (core diameter = 200µm, tapered output face = 50µm, NA=0.22) to determine its accuracy. Energy measurements were made at 17.8, 41.6, 65.4, 89.3, and 113.1µJ output energy and at distances between 0-2 mm from the fiber-tip with a Coherent FieldMax Energy meter coupled to a detector with a 2.1 mm aperture. Results: Mean difference between the predicted and measured energy ranged from 4.3±1.9µJ (17.8µJ) to 16.3±11.3 µJ (113.1µJ). Minimum required power density within a 0.05 mm spot size was predicted to be achieved at 0 mm for all energies, at 2 mm for 41.6µJ, and at distances ≥ 1.0 mm for 17.8 µJ. Conclusion: A numerical simulation program was developed that accurately predicts within minimal error the emittance from a tapered fiber. The predicted results indicate feasibility of tapered optical fibers to provide a more efficient and selective means of delivering the minimum power density necessary to achieve INS.