Macrobending losses of glass fibers for optical cochlear stimulation

Laser stimulation of the cochlea could be a potential alternative to conventional electric cochlea implants in treatment of sensorineural hearing loss. An optical hearing aid requires means of delivery to stimulate different areas inside the cochlea such as glass fibers. The necessary fiber bending inside the inner ear can lead to losses and thereby reduction of the stimulation volume. In order to assess those effects, measurements of attenuation and breakage due to fiber bending were performed. Energy losses of fibers with different diameters, numerical apertures (NA), wavelengths and bending radii were measured. Measurements of the NA at fiber tip with different radii as well as a computer simulation of the experiments were performed. Based on dimensions of a segmented cochlea, the position of expected failure of the fiber due to breakage and energy losses can be demonstrated. None of the used fibers could be inserted into the apex. Fibers with smaller diameters can withstand smaller bend radii. Energy losses could be reduced with smaller core diameters and higher NA. In conclusion, the results provide a basis for further studies regarding the optical stimulation of the cochlea.