Microoptics for multichannel laser-to-waveguide coupling in optical cochlear implants

Optical cochlear implants are a novel approach to current electrical cochlear implants, which are medical devices for hearing restoration through stimulation of neurons in the inner ear. A higher frequency resolution of the generated sound perception is expected, when such stimulation is based on light instead of electric current. Optical waveguides are implemented to guide light from a laser light source into the cochlea. The divergent laser beam is focussed to the waveguide facet by an intermediate optical system based on microlenses to achieve high efficient laser-to-waveguide coupling. Multiple channels are necessary to cover a broad frequency spectrum, which leads to the application of arrays of lasers, lenses, and waveguides. A set of basic optical and geometrical conditions is derived for such multichannel coupling systems and four setups are proposed and evaluated for application in the optical cochlear implant. Various simulation methods are implemented to design and analyse the coupling setups. Measurements of a 9-channel coupling setup are conducted to validate the simulations and scrutinise the application of aspheric microlens surfaces. The results show a general practicability of microlens array based coupling setups that can achieve quasi-uniform, low-crosstalk coupling in a system with 100 µm lateral channel pitch. Manufacturing and assembly tolerances are discussed for the future fabrication of such coupling modules.