Waveguide-Based Optical Modules for Cochlear Implant Applications

Cochlear implants (CIs) enable open speech comprehension in otherwise deaf patients. Potential improvements affect the limited spatial resolution of the electric stimulus. Optogenetic activation promises a better spatial resolution due to high-precision activation with micro-scaled light emitters. Here, we discuss the development of passive optical modules with integrated micro-optics and laser diode arrays. Remote red-emitting laser diodes are placed outside the cochlea and coupled to polymer-based waveguides with lens-based systems. The waveguides, which are directing the light towards and into the cochlea need to be highly flexible to enable precise placement in the scala tympani with a bending radius of down to 2.5 mm for the human cochlea. Ridge waveguide laser diodes are used due to their available power of several tens of milliwatts. Multibeam applications are enabled by emitter chips with a multitude of parallel aligned laser ridges with a lateral spacing in the 100 µm range. The astigmatic emission profiles of the ridge laser diodes has to be addressed in the optics design, as well as the integration of a transparent sapphire window into the beam path. We evaluate different optical systems on the path towards a human optical cochlear implant prototype, including macroscopic aspherical lenses, which enable medium-scaled optics with beam path length in the range of 15 mm. Further miniaturization of the beam path length to less than 2 mm can be achieved via a micro-lens-based approach. Here, we discuss the different optical systems in terms of channel scalability and waveguide coupling.